CME

Obstructive sleep apnea (OSA) is an independent risk factor for ischemic stroke and may also, infrequently, be a consequence of stroke. It is significantly underdiagnosed in the general population and is highly prevalent in patients who have had a stroke. Many patients likely had their stroke because of this chronic untreated condition.

This review focuses on OSA and its prevalence, consequences, and treatment in patients after a stroke.

DEFINING AND QUANTIFYING OSA

OSA is the most common type of sleep-disordered breathing.^1,2 It involves repeated narrowing or complete collapse of the upper airway despite ongoing respiratory effort.^3,4 Apneic episodes are terminated by arousals from hypoxemia or efforts to breathe.⁵ In contrast, central sleep apnea is characterized by a patent airway but lack of airflow due to absent respiratory effort.⁵

In OSA, the number of episodes of apnea (absent airflow) and hypopnea (reduced airflow) are added together and divided by hours of sleep to calculate the apnea-hypopnea index (AHI). OSA is diagnosed by either of the following^3,4:

• AHI of 5 or higher, with clinical symptoms related to OSA (described below)
• AHI of 15 or higher, regardless of symptoms.

The AHI also defines OSA severity, as follows³:

• Mild: AHI 5 to 15
• Moderate: AHI 15 to 30
• Severe: AHI greater than 30.

Diagnostic criteria (eg, definition of hypopnea, testing methods, and AHI thresholds) have varied over time, an important consideration when reviewing the literature.

OSA IS MORE COMMON THAN EXPECTED AFTER STROKE

In the most methodologically sound and generalizable study of this topic to date, the Wisconsin Sleep Cohort Study⁶ reported in 2013 that about 14% of men and 5% of women ages 30 to 70 have an AHI greater than 5 (using 4% desaturation to score hypopneic episodes) with daytime sleepiness. Other studies suggest that 80% to 90% of people with OSA are undiagnosed and untreated.^1,7

The prevalence of OSA in patients who have had a stroke is much higher, ranging from 30% to 96% depending on the study methods and population.^1,8–12 A 2010 meta-analysis¹¹ of 29 studies reported that 72% of patients who had a stroke had an AHI greater than 5, and 29% had severe OSA. In this analysis, 7% of those with sleep-disordered breathing had central sleep apnea; still, these data indicate that the prevalence of OSA in these patients is about 5 times higher than in the general population.

RISK FACTORS MAY DIFFER IN STROKE POPULATION

Several risk factors for OSA have been identified.

Obesity is one of the strongest risk factors, with increasing body mass index (BMI) associated with increased OSA prevalence.^4,6,13 However, obesity appears to be a less significant risk factor in patients who have had a stroke than in the general population. In the 2010 meta-analysis¹¹ of OSA after stroke, the average BMI was only 26.4 kg/m² (with obesity defined as a BMI > 30.0 kg/m²), and increasing BMI was not associated with increasing AHI.

Male sex and advanced age are also OSA risk factors.^4,5 They remain significant in patients after a stroke; about 65% of poststroke patients who have OSA are men, and the older the patient, the more likely the AHI is greater than 10.¹¹

Ethnicity and genetics may also play important roles in OSA risk, with roughly 25% of OSA prevalence estimated to have a genetic basis.^14,15 Some risk factors for OSA such as craniofacial shape, upper airway anatomy, upper airway muscle dysfunction, increased respiratory chemosensitivity, and poor arousal threshold during sleep are likely determined by genetics and ethnicity.^14,15 Compared with people of European origin, Asians have a similar prevalence of OSA, but at a much lower average BMI, suggesting that other factors are significant.¹⁴ Possible genetically determined anatomic risk factors have not been specifically studied in the poststroke population, but it can be assumed they remain relevant.

Several studies have tried to find an association between OSA and type, location, etiology, or pattern of stroke.^{10,11,16–19} Although some suggest links between cardioembolic stroke and OSA,^16,20 or thrombolysis and OSA,¹⁰ most have found no association between OSA and stroke features.^11,12,21,22

HOW DOES OSA INCREASE STROKE RISK?

Untreated severe OSA is associated with increased cardiovascular mortality,^21,22 and OSA is an independent risk factor for incident stroke.²³ A number of mechanisms may explain these relationships.

Intermittent hypoxemia and recurrent sympathetic arousals resulting from OSA are thought to lead to many of the comorbid conditions with which it is associated: hypertension, coronary artery disease, heart failure, arrhythmias, pulmonary hypertension, and stroke. Repetitive decreases in ventilation lead to oxygen desaturations that result in cycles of increased sympathetic outflow and eventual sustained nocturnal hypertension and daytime chronic hypertension.^1,5,9,13 Also implicated are various changes in vasodilator and vasoconstrictor substances due to endothelial dysfunction and inflammation, which are thought to play a role in the atherogenic and prothrombotic states induced by OSA.^1,5,13

Cerebral circulation is altered primarily by the changes in partial pressure of carbon dioxide (Pco₂). During apnea, the Pco₂ rises, causing vasodilation and increased blood flow. After the apnea resolves, there is hyperpnea with resultant decreased Pco₂, and vasoconstriction. In a patient who already has vascular disease, the enhanced vasoconstriction could lead to ischemia.^1,5

Changes in intrathoracic pressure result in distortion of cardiac architecture. When the patient tries to breathe against an occluded airway, the intrathoracic pressure becomes more and more negative, increasing preload and afterload. When this happens repeatedly every night for years, it leads to remodeling of the heart such as left and right ventricular hypertrophy, with reduced stroke volume, myocardial ischemia, and increased risk of arrhythmia.^1,5,13

Untreated OSA is believed to predispose patients to develop atrial fibrillation through sympathetic overactivity, vascular inflammation, heart rate variability, and cardiac remodeling.²⁴ As atrial fibrillation is a major risk factor for stroke, particularly cardioembolic stroke, it may be another pathway of increased stroke risk in OSA.^16,20,25

 

 

CLINICAL MANIFESTATIONS OF OSA NOT OBVIOUS AFTER STROKE

OSA typically causes both daytime symptoms (excessive sleepiness, poor concentration, morning headache, depressive symptoms) and nighttime signs and symptoms (snoring, choking, gasping, night sweats, insomnia, nocturia, witnessed episodes of apnea).^3,4,26 Unfortunately, because these are nonspecific, OSA is often underdiagnosed.^4,26

Identifying OSA after a stroke may be a particular challenge, as patients often do not report classic symptoms, and the typical picture of OSA may have less predictive validity in these patients.^1,27,28 Within the first 24 hours after a stroke, hypersomnia, snoring history, and age are not predictive of OSA.¹ Patients found to have OSA after a stroke frequently do not have the traditional symptoms (sleepiness, snoring) seen in usual OSA patients. And they have higher rates of OSA at a younger age than the usual OSA patients, so age is not a predictive risk factor. In addition, daytime sleepiness and obesity are often absent or less prominent.^1,9,27,28  Finally, typical OSA signs and symptoms may be attributed to the stroke itself or to comorbidities affecting the patient, lowering suspicion for OSA.

OSA MAY HINDER STROKE RECOVERY, WORSEN OUTCOMES

OSA, particularly when moderate to severe, is linked to pathophysiologic changes that can hinder recovery from a stroke.

Intermittent hypoxemia during sleep can worsen vascular damage of at-risk tissue: nocturnal hypoxemia correlates with white matter hyperintensities on magnetic resonance imaging, a marker of ischemic demyelination.²⁹ Oxidative stress and release of inflammatory mediators associated with intermittent hypoxemia may impair vascular blood flow to brain tissue attempting to repair itself.³⁰ In addition, sympathetic overactivity and Pco₂ fluctuations associated with OSA may impede cerebral circulation.

Taken together, such ongoing nocturnal insults can lead to clinical consequences during this vulnerable period.

A 1996 study³¹ of patients recovering from a stroke found that an oxygen desaturation index (number of times that the blood oxygen level drops below a certain threshold, as measured by overnight oximetry) of more than 10 per hour was associated with worse functional recovery at discharge and at 3 and 12 months after discharge. This study also noted an association between time spent with oxygen saturations below 90% and the rate of death at 1 year.

A 2003 study³² reported that patients with an AHI greater than 10 by polysomnography spent an average of 13 days longer on the rehabilitation service and had worse functional and cognitive status on discharge, even after controlling for multiple confounders. Several subsequent studies have confirmed these and similar findings.^8,33,34

OSA has also been linked to depression,³⁵ which is common after stroke and may worsen outcomes.³⁶ The interaction between OSA, depression, and poststroke outcomes warrants further study.

In the general population, OSA has been independently associated with increased risk of stroke or death from any cause.^21,22,37 These associations have also been reported in the poststroke population: a 2014 meta-analysis found that OSA increased the risk of a repeat stroke (relative risk [RR] 1.8, 95% confidence interval [CI] 1.2–2.6) and all-cause mortality (RR 1.69, 95% CI 1.4–2.1).³⁸

TESTING FOR OSA AFTER STROKE

Because of the high prevalence of OSA in patients who have had a stroke and the potential for worse outcomes associated with untreated OSA, there should be a low threshold for evaluating for OSA soon after stroke. Objective testing is required to qualify for therapy,  and the gold standard for diagnosis of OSA is formal polysomnography conducted in a sleep laboratory.^2–4 Unfortunately, polysomnography may be unacceptable to some patients, is costly, and is resource-intensive, particularly in an inpatient or rehabilitation setting.²⁸ Ideally, to optimize testing efficiency, patients should be screened for the likelihood of OSA before polysomnography is ordered.

Questionnaires can help determine the need for further testing

Questionnaires developed to assess OSA risk³⁹ include the following:

The Berlin questionnaire, developed in 1999, has 10 questions assessing daytime and nighttime signs and symptoms and presence of hypertension.

The STOP questionnaire, developed in 2008, assesses snoring, tiredness, observed apneic episodes, and elevated blood pressure.

The STOP-BANG questionnaire, published in 2010, includes the STOP questions plus BMI over 35 kg/m², age over 50, neck circumference over 41 cm, and male gender.

A 2017 meta-analysis³⁹ of 108 studies with nearly 50,000 people found that the STOP-BANG questionnaire performed best with regard to sensitivity and diagnostic odds ratio, but with poor specificity.

These screening tools and modified versions of them have also been evaluated in patients who have had a stroke.

In 2015, Boulos et al²⁸ found that the STOP-BAG (a version of STOP-BANG that excludes neck circumference) and the 4-variable (4V) questionnaire (sex, BMI, blood pressure, snoring) had moderate predictive value for OSA within 6 months after sroke.

In 2016, Katzan et al⁴⁰ found that the STOP-BAG2 (STOP-BAG criteria plus continuous variables for BMI and age) had a high sensitivity for polysomnographically diagnosed OSA within the first year after a stroke. The specificity was significantly better than the STOP-BANG or the STOP-BAG questionnaire, although it remained suboptimal at 60.5%.

In 2017, Sico et al⁴¹ developed and assessed the SLEEP Inventory (sex, left heart failure, Epworth Sleepiness Scale, enlarged neck, weight in pounds, insulin resistance or diabetes, and National Institutes of Health Stroke Scale) and found that it outperformed the Berlin and STOP-BANG questionnaires in the poststroke setting. The SLEEP Inventory had the best specificity and negative predictive value, and a slightly better ability to correctly classify patients as having OSA or not, classifying 80% of patients correctly.

These newer screening tools (eg, STOP-BAG, STOP-BAG2, SLEEP) can be used to identify with reasonable accuracy which patients need definitive testing after stroke.

Pulse oximetry is another possible screening tool          

Overnight pulse oximetry may also help screen for sleep apnea and stratify risk after a stroke. A 2012 study⁴² of overnight oximetry to screen patients before surgery found that the oxygen desaturation index was significantly associated with the AHI measured by polysomnography. However, oximetry testing cannot distinguish between OSA and central sleep apnea, so it is insufficient to diagnose OSA or qualify patients for therapy. Further study is needed to examine the ability of overnight pulse oximetry to screen or to stratify risk for OSA after stroke.

Polysomnography vs home testing

Polysomnography is the gold standard for diagnosing OSA. Benefits include technical support and trouble-shooting, determining relationships between OSA, body position, and sleep stage, and the ability to intervene with treatment.² However, polysomnography can be cumbersome, costly, and resource-intensive.

A home sleep apnea test, ie, an unattended, limited-channel sleep study, may be an acceptable alternative.^2–4,43,44 Home testing does not require a sleep technologist to be present during testing, uses fewer sensors, and is less expensive than overnight polysomnography, but its utility can be limited: it fails to accurately discriminate between episodes of OSA and central sleep apnea, there is potential for false-negative results, and it can underestimate sleep apnea burden because it does not measure sleep.²

Institutional resources and logistics may influence the choice of diagnostic modality. No data exist on outcomes from different diagnostic testing methods in poststroke patients. Further research is needed.

 

 

POSITIVE AIRWAY PRESSURE THERAPY: BENEFITS, CHALLENGES, ALTERNATIVES

The first-line treatment for OSA is positive airway pressure (PAP).³ For most patients, this is continuous PAP (CPAP) or autoadjusting PAP (APAP). In some instances, particularly for those who cannot tolerate CPAP or who have comorbid hypoventilation, bilevel PAP (BPAP) may be indicated. More advanced PAP therapies are unlikely to be used after stroke.

PAP therapy is associated with reduced daytime sleepiness, improved mood, normalization of sleep architecture, improved systemic and pulmonary artery blood pressure, reduced rates of atrial fibrillation after ablation, and improved insulin sensitivity.^45–49 Whether it reduces the risk of cardiovascular events, including stroke, remains controversial; most data suggest that it does not.^50,51 However, when adherence to PAP therapy is considered rather than intention to treat, treatment has been found to lead to improved cardiovascular outcomes.⁵²

Mixed evidence of benefits after stroke

Observational studies provide evidence that CPAP may help patients with OSA after stroke, although results are mixed.^53–58 The studies ranged in size from 14 to 105 patients, enrolled patients with mostly moderate to severe OSA, and followed patients from 10 days to 7 years. Adherence to therapy was generally good in the short term (50%–70%), but only  15% to 30% of patients remained adherent at 5 to 7 years. Variable outcomes were reported, with some studies finding improved symptoms in the near term and mixed evidence of cardiovascular benefit in the longer ones. However, as these studies lacked randomization, drawing definitive conclusions on CPAP efficacy is difficult.

Several short-term randomized controlled trials of CPAP have been performed in patients after stroke. A 2018 meta-analysis⁵⁹ included 10 such trials with a total of 564 patients (range 30–140 patients), with most having 1 to 3 months of follow-up (range 1 week to over 5 years). Eight of the 10 studies are summarized in Table 1 (1 study was omitted because many of the patients had central sleep apnea, and 1 was primarily a feasibility study).^60–67

Patients were enrolled in the index admission or when starting a rehabilitation service—generally 2 to 3 weeks after their stroke. No clear association was found between the timing of initiating PAP therapy and outcomes. All patients had ischemic strokes, but few details were provided regarding stroke location, size, and severity. Exclusion criteria included severe underlying cardiopulmonary disease, confusion, severe stroke with marked impairment, and inability to cooperate. Almost all patients had moderate to severe OSA, and patients with central sleep apnea were excluded.

The major outcomes examined were drop-out rates, PAP adherence, and neurologic improvement based on neurologic functional scales (National Institutes of Health Stroke Scale and Canadian Neurologic Scale). As expected, dropout rates were higher in patients randomized to CPAP (OR 1.83, 95% CI 1.05–3.21, P = .03), although overall adherence was better than anticipated, with mean CPAP use across trials of 4.5 hours per night (95% CI 3.97–5.08) and with about 50% to 60% of patients adhering to therapy for at least 4 hours nightly.

Improvement in neurologic outcomes favored CPAP (standard mean difference 0.54, 95% CI 0.026–1.05), although considerable heterogeneity was seen. Improved sleepiness outcomes were inconsistent. Major cardiovascular outcomes were reported in only 2 studies (using the same data set) and showed delayed time to the next cardiovascular event for those treated with CPAP but no difference in cardiovascular event-free survival.

PAP poses more challenges after stroke

The primary limitation to PAP therapy is poor acceptance and adherence to therapy.⁵⁹ High rates of refusal of therapy and difficulty complying with treatment have been noted in the poststroke population, although recent studies have reported better adherence rates. How rates of adherence play out in real-world settings, outside of the controlled environment of a research study, has yet to be determined.

In general, CPAP adherence is affected by claustrophobia, difficulty tolerating a mask, problems with pressure intolerance, irritating air leaks, nasal congestion, and naso-oral dryness. Many such barriers can be overcome with use of a properly fitted mask, an appropriate pressure setting, heated humidification, nasal sprays (eg, saline, inhaled steroids), and education, encouragement, and reassurance.

After a stroke, additional obstacles may impede the ability to use PAP therapy.⁶⁸ Facial paresis (hemi- or bifacial) may make fitting of the mask problematic. Paralysis or weakness of the extremities may limit the ability to adjust or remove a mask. Aphasia can impair communication and understanding of the need to use PAP therapy, and upper-airway problems related to stroke, including dysphagia, may lead to pressure intolerance or risk of aspiration. Finally, a lack of perceived benefit, particularly if the patient does not have daytime sleepiness, may limit motivation.

Consider alternatives

For patients unlikely to succeed with PAP therapy, there are alternatives. Surgery and oral appliances are not usually realistic options in the setting of recent stroke, but positional therapy, including the use of body positioners to prevent supine sleep, as well as elevating the head of the bed, may be of some benefit.^69,70 A nasopharyngeal airway stenting device (nasal trumpet) may also be tolerated by some patients.

Avoiding or minimizing sedating medications that may worsen OSA, such as benzodiazepines and opioids, should be considered.³ Oxygen therapy, while helping to maintain oxygen saturation during sleep, does not prevent airway collapse, and its role for treating OSA in patients after stroke is unclear.

A proposed algorithm for screening, diagnosing, and treating OSA in patients after stroke is presented in Figure 1.

Obstructive sleep apnea (OSA) is an independent risk factor for ischemic stroke and may also, infrequently, be a consequence of stroke. It is significantly underdiagnosed in the general population and is highly prevalent in patients who have had a stroke. Many patients likely had their stroke because of this chronic untreated condition.

This review focuses on OSA and its prevalence, consequences, and treatment in patients after a stroke.

DEFINING AND QUANTIFYING OSA

OSA is the most common type of sleep-disordered breathing.^1,2 It involves repeated narrowing or complete collapse of the upper airway despite ongoing respiratory effort.^3,4 Apneic episodes are terminated by arousals from hypoxemia or efforts to breathe.⁵ In contrast, central sleep apnea is characterized by a patent airway but lack of airflow due to absent respiratory effort.⁵

In OSA, the number of episodes of apnea (absent airflow) and hypopnea (reduced airflow) are added together and divided by hours of sleep to calculate the apnea-hypopnea index (AHI). OSA is diagnosed by either of the following^3,4:

• AHI of 5 or higher, with clinical symptoms related to OSA (described below)
• AHI of 15 or higher, regardless of symptoms.

The AHI also defines OSA severity, as follows³:

• Mild: AHI 5 to 15
• Moderate: AHI 15 to 30
• Severe: AHI greater than 30.

Diagnostic criteria (eg, definition of hypopnea, testing methods, and AHI thresholds) have varied over time, an important consideration when reviewing the literature.

OSA IS MORE COMMON THAN EXPECTED AFTER STROKE

In the most methodologically sound and generalizable study of this topic to date, the Wisconsin Sleep Cohort Study⁶ reported in 2013 that about 14% of men and 5% of women ages 30 to 70 have an AHI greater than 5 (using 4% desaturation to score hypopneic episodes) with daytime sleepiness. Other studies suggest that 80% to 90% of people with OSA are undiagnosed and untreated.^1,7

The prevalence of OSA in patients who have had a stroke is much higher, ranging from 30% to 96% depending on the study methods and population.^1,8–12 A 2010 meta-analysis¹¹ of 29 studies reported that 72% of patients who had a stroke had an AHI greater than 5, and 29% had severe OSA. In this analysis, 7% of those with sleep-disordered breathing had central sleep apnea; still, these data indicate that the prevalence of OSA in these patients is about 5 times higher than in the general population.

RISK FACTORS MAY DIFFER IN STROKE POPULATION

Several risk factors for OSA have been identified.

Obesity is one of the strongest risk factors, with increasing body mass index (BMI) associated with increased OSA prevalence.^4,6,13 However, obesity appears to be a less significant risk factor in patients who have had a stroke than in the general population. In the 2010 meta-analysis¹¹ of OSA after stroke, the average BMI was only 26.4 kg/m² (with obesity defined as a BMI > 30.0 kg/m²), and increasing BMI was not associated with increasing AHI.

Male sex and advanced age are also OSA risk factors.^4,5 They remain significant in patients after a stroke; about 65% of poststroke patients who have OSA are men, and the older the patient, the more likely the AHI is greater than 10.¹¹

Ethnicity and genetics may also play important roles in OSA risk, with roughly 25% of OSA prevalence estimated to have a genetic basis.^14,15 Some risk factors for OSA such as craniofacial shape, upper airway anatomy, upper airway muscle dysfunction, increased respiratory chemosensitivity, and poor arousal threshold during sleep are likely determined by genetics and ethnicity.^14,15 Compared with people of European origin, Asians have a similar prevalence of OSA, but at a much lower average BMI, suggesting that other factors are significant.¹⁴ Possible genetically determined anatomic risk factors have not been specifically studied in the poststroke population, but it can be assumed they remain relevant.

Several studies have tried to find an association between OSA and type, location, etiology, or pattern of stroke.^{10,11,16–19} Although some suggest links between cardioembolic stroke and OSA,^16,20 or thrombolysis and OSA,¹⁰ most have found no association between OSA and stroke features.^11,12,21,22

HOW DOES OSA INCREASE STROKE RISK?

Untreated severe OSA is associated with increased cardiovascular mortality,^21,22 and OSA is an independent risk factor for incident stroke.²³ A number of mechanisms may explain these relationships.

Intermittent hypoxemia and recurrent sympathetic arousals resulting from OSA are thought to lead to many of the comorbid conditions with which it is associated: hypertension, coronary artery disease, heart failure, arrhythmias, pulmonary hypertension, and stroke. Repetitive decreases in ventilation lead to oxygen desaturations that result in cycles of increased sympathetic outflow and eventual sustained nocturnal hypertension and daytime chronic hypertension.^1,5,9,13 Also implicated are various changes in vasodilator and vasoconstrictor substances due to endothelial dysfunction and inflammation, which are thought to play a role in the atherogenic and prothrombotic states induced by OSA.^1,5,13

Cerebral circulation is altered primarily by the changes in partial pressure of carbon dioxide (Pco₂). During apnea, the Pco₂ rises, causing vasodilation and increased blood flow. After the apnea resolves, there is hyperpnea with resultant decreased Pco₂, and vasoconstriction. In a patient who already has vascular disease, the enhanced vasoconstriction could lead to ischemia.^1,5

Changes in intrathoracic pressure result in distortion of cardiac architecture. When the patient tries to breathe against an occluded airway, the intrathoracic pressure becomes more and more negative, increasing preload and afterload. When this happens repeatedly every night for years, it leads to remodeling of the heart such as left and right ventricular hypertrophy, with reduced stroke volume, myocardial ischemia, and increased risk of arrhythmia.^1,5,13

Untreated OSA is believed to predispose patients to develop atrial fibrillation through sympathetic overactivity, vascular inflammation, heart rate variability, and cardiac remodeling.²⁴ As atrial fibrillation is a major risk factor for stroke, particularly cardioembolic stroke, it may be another pathway of increased stroke risk in OSA.^16,20,25

 

 

CLINICAL MANIFESTATIONS OF OSA NOT OBVIOUS AFTER STROKE

OSA typically causes both daytime symptoms (excessive sleepiness, poor concentration, morning headache, depressive symptoms) and nighttime signs and symptoms (snoring, choking, gasping, night sweats, insomnia, nocturia, witnessed episodes of apnea).^3,4,26 Unfortunately, because these are nonspecific, OSA is often underdiagnosed.^4,26

Identifying OSA after a stroke may be a particular challenge, as patients often do not report classic symptoms, and the typical picture of OSA may have less predictive validity in these patients.^1,27,28 Within the first 24 hours after a stroke, hypersomnia, snoring history, and age are not predictive of OSA.¹ Patients found to have OSA after a stroke frequently do not have the traditional symptoms (sleepiness, snoring) seen in usual OSA patients. And they have higher rates of OSA at a younger age than the usual OSA patients, so age is not a predictive risk factor. In addition, daytime sleepiness and obesity are often absent or less prominent.^1,9,27,28  Finally, typical OSA signs and symptoms may be attributed to the stroke itself or to comorbidities affecting the patient, lowering suspicion for OSA.

OSA MAY HINDER STROKE RECOVERY, WORSEN OUTCOMES

OSA, particularly when moderate to severe, is linked to pathophysiologic changes that can hinder recovery from a stroke.

Intermittent hypoxemia during sleep can worsen vascular damage of at-risk tissue: nocturnal hypoxemia correlates with white matter hyperintensities on magnetic resonance imaging, a marker of ischemic demyelination.²⁹ Oxidative stress and release of inflammatory mediators associated with intermittent hypoxemia may impair vascular blood flow to brain tissue attempting to repair itself.³⁰ In addition, sympathetic overactivity and Pco₂ fluctuations associated with OSA may impede cerebral circulation.

Taken together, such ongoing nocturnal insults can lead to clinical consequences during this vulnerable period.

A 1996 study³¹ of patients recovering from a stroke found that an oxygen desaturation index (number of times that the blood oxygen level drops below a certain threshold, as measured by overnight oximetry) of more than 10 per hour was associated with worse functional recovery at discharge and at 3 and 12 months after discharge. This study also noted an association between time spent with oxygen saturations below 90% and the rate of death at 1 year.

A 2003 study³² reported that patients with an AHI greater than 10 by polysomnography spent an average of 13 days longer on the rehabilitation service and had worse functional and cognitive status on discharge, even after controlling for multiple confounders. Several subsequent studies have confirmed these and similar findings.^8,33,34

OSA has also been linked to depression,³⁵ which is common after stroke and may worsen outcomes.³⁶ The interaction between OSA, depression, and poststroke outcomes warrants further study.

In the general population, OSA has been independently associated with increased risk of stroke or death from any cause.^21,22,37 These associations have also been reported in the poststroke population: a 2014 meta-analysis found that OSA increased the risk of a repeat stroke (relative risk [RR] 1.8, 95% confidence interval [CI] 1.2–2.6) and all-cause mortality (RR 1.69, 95% CI 1.4–2.1).³⁸

TESTING FOR OSA AFTER STROKE

Because of the high prevalence of OSA in patients who have had a stroke and the potential for worse outcomes associated with untreated OSA, there should be a low threshold for evaluating for OSA soon after stroke. Objective testing is required to qualify for therapy,  and the gold standard for diagnosis of OSA is formal polysomnography conducted in a sleep laboratory.^2–4 Unfortunately, polysomnography may be unacceptable to some patients, is costly, and is resource-intensive, particularly in an inpatient or rehabilitation setting.²⁸ Ideally, to optimize testing efficiency, patients should be screened for the likelihood of OSA before polysomnography is ordered.

Questionnaires can help determine the need for further testing

Questionnaires developed to assess OSA risk³⁹ include the following:

The Berlin questionnaire, developed in 1999, has 10 questions assessing daytime and nighttime signs and symptoms and presence of hypertension.

The STOP questionnaire, developed in 2008, assesses snoring, tiredness, observed apneic episodes, and elevated blood pressure.

The STOP-BANG questionnaire, published in 2010, includes the STOP questions plus BMI over 35 kg/m², age over 50, neck circumference over 41 cm, and male gender.

A 2017 meta-analysis³⁹ of 108 studies with nearly 50,000 people found that the STOP-BANG questionnaire performed best with regard to sensitivity and diagnostic odds ratio, but with poor specificity.

These screening tools and modified versions of them have also been evaluated in patients who have had a stroke.

In 2015, Boulos et al²⁸ found that the STOP-BAG (a version of STOP-BANG that excludes neck circumference) and the 4-variable (4V) questionnaire (sex, BMI, blood pressure, snoring) had moderate predictive value for OSA within 6 months after sroke.

In 2016, Katzan et al⁴⁰ found that the STOP-BAG2 (STOP-BAG criteria plus continuous variables for BMI and age) had a high sensitivity for polysomnographically diagnosed OSA within the first year after a stroke. The specificity was significantly better than the STOP-BANG or the STOP-BAG questionnaire, although it remained suboptimal at 60.5%.

In 2017, Sico et al⁴¹ developed and assessed the SLEEP Inventory (sex, left heart failure, Epworth Sleepiness Scale, enlarged neck, weight in pounds, insulin resistance or diabetes, and National Institutes of Health Stroke Scale) and found that it outperformed the Berlin and STOP-BANG questionnaires in the poststroke setting. The SLEEP Inventory had the best specificity and negative predictive value, and a slightly better ability to correctly classify patients as having OSA or not, classifying 80% of patients correctly.

These newer screening tools (eg, STOP-BAG, STOP-BAG2, SLEEP) can be used to identify with reasonable accuracy which patients need definitive testing after stroke.

Pulse oximetry is another possible screening tool          

Overnight pulse oximetry may also help screen for sleep apnea and stratify risk after a stroke. A 2012 study⁴² of overnight oximetry to screen patients before surgery found that the oxygen desaturation index was significantly associated with the AHI measured by polysomnography. However, oximetry testing cannot distinguish between OSA and central sleep apnea, so it is insufficient to diagnose OSA or qualify patients for therapy. Further study is needed to examine the ability of overnight pulse oximetry to screen or to stratify risk for OSA after stroke.

Polysomnography vs home testing

Polysomnography is the gold standard for diagnosing OSA. Benefits include technical support and trouble-shooting, determining relationships between OSA, body position, and sleep stage, and the ability to intervene with treatment.² However, polysomnography can be cumbersome, costly, and resource-intensive.

A home sleep apnea test, ie, an unattended, limited-channel sleep study, may be an acceptable alternative.^2–4,43,44 Home testing does not require a sleep technologist to be present during testing, uses fewer sensors, and is less expensive than overnight polysomnography, but its utility can be limited: it fails to accurately discriminate between episodes of OSA and central sleep apnea, there is potential for false-negative results, and it can underestimate sleep apnea burden because it does not measure sleep.²

Institutional resources and logistics may influence the choice of diagnostic modality. No data exist on outcomes from different diagnostic testing methods in poststroke patients. Further research is needed.

 

 

POSITIVE AIRWAY PRESSURE THERAPY: BENEFITS, CHALLENGES, ALTERNATIVES

The first-line treatment for OSA is positive airway pressure (PAP).³ For most patients, this is continuous PAP (CPAP) or autoadjusting PAP (APAP). In some instances, particularly for those who cannot tolerate CPAP or who have comorbid hypoventilation, bilevel PAP (BPAP) may be indicated. More advanced PAP therapies are unlikely to be used after stroke.

PAP therapy is associated with reduced daytime sleepiness, improved mood, normalization of sleep architecture, improved systemic and pulmonary artery blood pressure, reduced rates of atrial fibrillation after ablation, and improved insulin sensitivity.^45–49 Whether it reduces the risk of cardiovascular events, including stroke, remains controversial; most data suggest that it does not.^50,51 However, when adherence to PAP therapy is considered rather than intention to treat, treatment has been found to lead to improved cardiovascular outcomes.⁵²

Mixed evidence of benefits after stroke

Observational studies provide evidence that CPAP may help patients with OSA after stroke, although results are mixed.^53–58 The studies ranged in size from 14 to 105 patients, enrolled patients with mostly moderate to severe OSA, and followed patients from 10 days to 7 years. Adherence to therapy was generally good in the short term (50%–70%), but only  15% to 30% of patients remained adherent at 5 to 7 years. Variable outcomes were reported, with some studies finding improved symptoms in the near term and mixed evidence of cardiovascular benefit in the longer ones. However, as these studies lacked randomization, drawing definitive conclusions on CPAP efficacy is difficult.

Several short-term randomized controlled trials of CPAP have been performed in patients after stroke. A 2018 meta-analysis⁵⁹ included 10 such trials with a total of 564 patients (range 30–140 patients), with most having 1 to 3 months of follow-up (range 1 week to over 5 years). Eight of the 10 studies are summarized in Table 1 (1 study was omitted because many of the patients had central sleep apnea, and 1 was primarily a feasibility study).^60–67

Patients were enrolled in the index admission or when starting a rehabilitation service—generally 2 to 3 weeks after their stroke. No clear association was found between the timing of initiating PAP therapy and outcomes. All patients had ischemic strokes, but few details were provided regarding stroke location, size, and severity. Exclusion criteria included severe underlying cardiopulmonary disease, confusion, severe stroke with marked impairment, and inability to cooperate. Almost all patients had moderate to severe OSA, and patients with central sleep apnea were excluded.

The major outcomes examined were drop-out rates, PAP adherence, and neurologic improvement based on neurologic functional scales (National Institutes of Health Stroke Scale and Canadian Neurologic Scale). As expected, dropout rates were higher in patients randomized to CPAP (OR 1.83, 95% CI 1.05–3.21, P = .03), although overall adherence was better than anticipated, with mean CPAP use across trials of 4.5 hours per night (95% CI 3.97–5.08) and with about 50% to 60% of patients adhering to therapy for at least 4 hours nightly.

Improvement in neurologic outcomes favored CPAP (standard mean difference 0.54, 95% CI 0.026–1.05), although considerable heterogeneity was seen. Improved sleepiness outcomes were inconsistent. Major cardiovascular outcomes were reported in only 2 studies (using the same data set) and showed delayed time to the next cardiovascular event for those treated with CPAP but no difference in cardiovascular event-free survival.

PAP poses more challenges after stroke

The primary limitation to PAP therapy is poor acceptance and adherence to therapy.⁵⁹ High rates of refusal of therapy and difficulty complying with treatment have been noted in the poststroke population, although recent studies have reported better adherence rates. How rates of adherence play out in real-world settings, outside of the controlled environment of a research study, has yet to be determined.

In general, CPAP adherence is affected by claustrophobia, difficulty tolerating a mask, problems with pressure intolerance, irritating air leaks, nasal congestion, and naso-oral dryness. Many such barriers can be overcome with use of a properly fitted mask, an appropriate pressure setting, heated humidification, nasal sprays (eg, saline, inhaled steroids), and education, encouragement, and reassurance.

After a stroke, additional obstacles may impede the ability to use PAP therapy.⁶⁸ Facial paresis (hemi- or bifacial) may make fitting of the mask problematic. Paralysis or weakness of the extremities may limit the ability to adjust or remove a mask. Aphasia can impair communication and understanding of the need to use PAP therapy, and upper-airway problems related to stroke, including dysphagia, may lead to pressure intolerance or risk of aspiration. Finally, a lack of perceived benefit, particularly if the patient does not have daytime sleepiness, may limit motivation.

Consider alternatives

For patients unlikely to succeed with PAP therapy, there are alternatives. Surgery and oral appliances are not usually realistic options in the setting of recent stroke, but positional therapy, including the use of body positioners to prevent supine sleep, as well as elevating the head of the bed, may be of some benefit.^69,70 A nasopharyngeal airway stenting device (nasal trumpet) may also be tolerated by some patients.

Avoiding or minimizing sedating medications that may worsen OSA, such as benzodiazepines and opioids, should be considered.³ Oxygen therapy, while helping to maintain oxygen saturation during sleep, does not prevent airway collapse, and its role for treating OSA in patients after stroke is unclear.

A proposed algorithm for screening, diagnosing, and treating OSA in patients after stroke is presented in Figure 1.

Obstructive sleep apnea (OSA) is an independent risk factor for ischemic stroke and may also, infrequently, be a consequence of stroke. It is significantly underdiagnosed in the general population and is highly prevalent in patients who have had a stroke. Many patients likely had their stroke because of this chronic untreated condition.

This review focuses on OSA and its prevalence, consequences, and treatment in patients after a stroke.

DEFINING AND QUANTIFYING OSA

OSA is the most common type of sleep-disordered breathing.^1,2 It involves repeated narrowing or complete collapse of the upper airway despite ongoing respiratory effort.^3,4 Apneic episodes are terminated by arousals from hypoxemia or efforts to breathe.⁵ In contrast, central sleep apnea is characterized by a patent airway but lack of airflow due to absent respiratory effort.⁵

In OSA, the number of episodes of apnea (absent airflow) and hypopnea (reduced airflow) are added together and divided by hours of sleep to calculate the apnea-hypopnea index (AHI). OSA is diagnosed by either of the following^3,4:

• AHI of 5 or higher, with clinical symptoms related to OSA (described below)
• AHI of 15 or higher, regardless of symptoms.

The AHI also defines OSA severity, as follows³:

• Mild: AHI 5 to 15
• Moderate: AHI 15 to 30
• Severe: AHI greater than 30.

Diagnostic criteria (eg, definition of hypopnea, testing methods, and AHI thresholds) have varied over time, an important consideration when reviewing the literature.

OSA IS MORE COMMON THAN EXPECTED AFTER STROKE

In the most methodologically sound and generalizable study of this topic to date, the Wisconsin Sleep Cohort Study⁶ reported in 2013 that about 14% of men and 5% of women ages 30 to 70 have an AHI greater than 5 (using 4% desaturation to score hypopneic episodes) with daytime sleepiness. Other studies suggest that 80% to 90% of people with OSA are undiagnosed and untreated.^1,7

The prevalence of OSA in patients who have had a stroke is much higher, ranging from 30% to 96% depending on the study methods and population.^1,8–12 A 2010 meta-analysis¹¹ of 29 studies reported that 72% of patients who had a stroke had an AHI greater than 5, and 29% had severe OSA. In this analysis, 7% of those with sleep-disordered breathing had central sleep apnea; still, these data indicate that the prevalence of OSA in these patients is about 5 times higher than in the general population.

RISK FACTORS MAY DIFFER IN STROKE POPULATION

Several risk factors for OSA have been identified.

Obesity is one of the strongest risk factors, with increasing body mass index (BMI) associated with increased OSA prevalence.^4,6,13 However, obesity appears to be a less significant risk factor in patients who have had a stroke than in the general population. In the 2010 meta-analysis¹¹ of OSA after stroke, the average BMI was only 26.4 kg/m² (with obesity defined as a BMI > 30.0 kg/m²), and increasing BMI was not associated with increasing AHI.

Male sex and advanced age are also OSA risk factors.^4,5 They remain significant in patients after a stroke; about 65% of poststroke patients who have OSA are men, and the older the patient, the more likely the AHI is greater than 10.¹¹

Ethnicity and genetics may also play important roles in OSA risk, with roughly 25% of OSA prevalence estimated to have a genetic basis.^14,15 Some risk factors for OSA such as craniofacial shape, upper airway anatomy, upper airway muscle dysfunction, increased respiratory chemosensitivity, and poor arousal threshold during sleep are likely determined by genetics and ethnicity.^14,15 Compared with people of European origin, Asians have a similar prevalence of OSA, but at a much lower average BMI, suggesting that other factors are significant.¹⁴ Possible genetically determined anatomic risk factors have not been specifically studied in the poststroke population, but it can be assumed they remain relevant.

Several studies have tried to find an association between OSA and type, location, etiology, or pattern of stroke.^{10,11,16–19} Although some suggest links between cardioembolic stroke and OSA,^16,20 or thrombolysis and OSA,¹⁰ most have found no association between OSA and stroke features.^11,12,21,22

HOW DOES OSA INCREASE STROKE RISK?

Untreated severe OSA is associated with increased cardiovascular mortality,^21,22 and OSA is an independent risk factor for incident stroke.²³ A number of mechanisms may explain these relationships.

Intermittent hypoxemia and recurrent sympathetic arousals resulting from OSA are thought to lead to many of the comorbid conditions with which it is associated: hypertension, coronary artery disease, heart failure, arrhythmias, pulmonary hypertension, and stroke. Repetitive decreases in ventilation lead to oxygen desaturations that result in cycles of increased sympathetic outflow and eventual sustained nocturnal hypertension and daytime chronic hypertension.^1,5,9,13 Also implicated are various changes in vasodilator and vasoconstrictor substances due to endothelial dysfunction and inflammation, which are thought to play a role in the atherogenic and prothrombotic states induced by OSA.^1,5,13

Cerebral circulation is altered primarily by the changes in partial pressure of carbon dioxide (Pco₂). During apnea, the Pco₂ rises, causing vasodilation and increased blood flow. After the apnea resolves, there is hyperpnea with resultant decreased Pco₂, and vasoconstriction. In a patient who already has vascular disease, the enhanced vasoconstriction could lead to ischemia.^1,5

Changes in intrathoracic pressure result in distortion of cardiac architecture. When the patient tries to breathe against an occluded airway, the intrathoracic pressure becomes more and more negative, increasing preload and afterload. When this happens repeatedly every night for years, it leads to remodeling of the heart such as left and right ventricular hypertrophy, with reduced stroke volume, myocardial ischemia, and increased risk of arrhythmia.^1,5,13

Untreated OSA is believed to predispose patients to develop atrial fibrillation through sympathetic overactivity, vascular inflammation, heart rate variability, and cardiac remodeling.²⁴ As atrial fibrillation is a major risk factor for stroke, particularly cardioembolic stroke, it may be another pathway of increased stroke risk in OSA.^16,20,25

 

 

CLINICAL MANIFESTATIONS OF OSA NOT OBVIOUS AFTER STROKE

OSA typically causes both daytime symptoms (excessive sleepiness, poor concentration, morning headache, depressive symptoms) and nighttime signs and symptoms (snoring, choking, gasping, night sweats, insomnia, nocturia, witnessed episodes of apnea).^3,4,26 Unfortunately, because these are nonspecific, OSA is often underdiagnosed.^4,26

Identifying OSA after a stroke may be a particular challenge, as patients often do not report classic symptoms, and the typical picture of OSA may have less predictive validity in these patients.^1,27,28 Within the first 24 hours after a stroke, hypersomnia, snoring history, and age are not predictive of OSA.¹ Patients found to have OSA after a stroke frequently do not have the traditional symptoms (sleepiness, snoring) seen in usual OSA patients. And they have higher rates of OSA at a younger age than the usual OSA patients, so age is not a predictive risk factor. In addition, daytime sleepiness and obesity are often absent or less prominent.^1,9,27,28  Finally, typical OSA signs and symptoms may be attributed to the stroke itself or to comorbidities affecting the patient, lowering suspicion for OSA.

OSA MAY HINDER STROKE RECOVERY, WORSEN OUTCOMES

OSA, particularly when moderate to severe, is linked to pathophysiologic changes that can hinder recovery from a stroke.

Intermittent hypoxemia during sleep can worsen vascular damage of at-risk tissue: nocturnal hypoxemia correlates with white matter hyperintensities on magnetic resonance imaging, a marker of ischemic demyelination.²⁹ Oxidative stress and release of inflammatory mediators associated with intermittent hypoxemia may impair vascular blood flow to brain tissue attempting to repair itself.³⁰ In addition, sympathetic overactivity and Pco₂ fluctuations associated with OSA may impede cerebral circulation.

Taken together, such ongoing nocturnal insults can lead to clinical consequences during this vulnerable period.

A 1996 study³¹ of patients recovering from a stroke found that an oxygen desaturation index (number of times that the blood oxygen level drops below a certain threshold, as measured by overnight oximetry) of more than 10 per hour was associated with worse functional recovery at discharge and at 3 and 12 months after discharge. This study also noted an association between time spent with oxygen saturations below 90% and the rate of death at 1 year.

A 2003 study³² reported that patients with an AHI greater than 10 by polysomnography spent an average of 13 days longer on the rehabilitation service and had worse functional and cognitive status on discharge, even after controlling for multiple confounders. Several subsequent studies have confirmed these and similar findings.^8,33,34

OSA has also been linked to depression,³⁵ which is common after stroke and may worsen outcomes.³⁶ The interaction between OSA, depression, and poststroke outcomes warrants further study.

In the general population, OSA has been independently associated with increased risk of stroke or death from any cause.^21,22,37 These associations have also been reported in the poststroke population: a 2014 meta-analysis found that OSA increased the risk of a repeat stroke (relative risk [RR] 1.8, 95% confidence interval [CI] 1.2–2.6) and all-cause mortality (RR 1.69, 95% CI 1.4–2.1).³⁸

TESTING FOR OSA AFTER STROKE

Because of the high prevalence of OSA in patients who have had a stroke and the potential for worse outcomes associated with untreated OSA, there should be a low threshold for evaluating for OSA soon after stroke. Objective testing is required to qualify for therapy,  and the gold standard for diagnosis of OSA is formal polysomnography conducted in a sleep laboratory.^2–4 Unfortunately, polysomnography may be unacceptable to some patients, is costly, and is resource-intensive, particularly in an inpatient or rehabilitation setting.²⁸ Ideally, to optimize testing efficiency, patients should be screened for the likelihood of OSA before polysomnography is ordered.

Questionnaires can help determine the need for further testing

Questionnaires developed to assess OSA risk³⁹ include the following:

The Berlin questionnaire, developed in 1999, has 10 questions assessing daytime and nighttime signs and symptoms and presence of hypertension.

The STOP questionnaire, developed in 2008, assesses snoring, tiredness, observed apneic episodes, and elevated blood pressure.

The STOP-BANG questionnaire, published in 2010, includes the STOP questions plus BMI over 35 kg/m², age over 50, neck circumference over 41 cm, and male gender.

A 2017 meta-analysis³⁹ of 108 studies with nearly 50,000 people found that the STOP-BANG questionnaire performed best with regard to sensitivity and diagnostic odds ratio, but with poor specificity.

These screening tools and modified versions of them have also been evaluated in patients who have had a stroke.

In 2015, Boulos et al²⁸ found that the STOP-BAG (a version of STOP-BANG that excludes neck circumference) and the 4-variable (4V) questionnaire (sex, BMI, blood pressure, snoring) had moderate predictive value for OSA within 6 months after sroke.

In 2016, Katzan et al⁴⁰ found that the STOP-BAG2 (STOP-BAG criteria plus continuous variables for BMI and age) had a high sensitivity for polysomnographically diagnosed OSA within the first year after a stroke. The specificity was significantly better than the STOP-BANG or the STOP-BAG questionnaire, although it remained suboptimal at 60.5%.

In 2017, Sico et al⁴¹ developed and assessed the SLEEP Inventory (sex, left heart failure, Epworth Sleepiness Scale, enlarged neck, weight in pounds, insulin resistance or diabetes, and National Institutes of Health Stroke Scale) and found that it outperformed the Berlin and STOP-BANG questionnaires in the poststroke setting. The SLEEP Inventory had the best specificity and negative predictive value, and a slightly better ability to correctly classify patients as having OSA or not, classifying 80% of patients correctly.

These newer screening tools (eg, STOP-BAG, STOP-BAG2, SLEEP) can be used to identify with reasonable accuracy which patients need definitive testing after stroke.

Pulse oximetry is another possible screening tool          

Overnight pulse oximetry may also help screen for sleep apnea and stratify risk after a stroke. A 2012 study⁴² of overnight oximetry to screen patients before surgery found that the oxygen desaturation index was significantly associated with the AHI measured by polysomnography. However, oximetry testing cannot distinguish between OSA and central sleep apnea, so it is insufficient to diagnose OSA or qualify patients for therapy. Further study is needed to examine the ability of overnight pulse oximetry to screen or to stratify risk for OSA after stroke.

Polysomnography vs home testing

Polysomnography is the gold standard for diagnosing OSA. Benefits include technical support and trouble-shooting, determining relationships between OSA, body position, and sleep stage, and the ability to intervene with treatment.² However, polysomnography can be cumbersome, costly, and resource-intensive.

A home sleep apnea test, ie, an unattended, limited-channel sleep study, may be an acceptable alternative.^2–4,43,44 Home testing does not require a sleep technologist to be present during testing, uses fewer sensors, and is less expensive than overnight polysomnography, but its utility can be limited: it fails to accurately discriminate between episodes of OSA and central sleep apnea, there is potential for false-negative results, and it can underestimate sleep apnea burden because it does not measure sleep.²

Institutional resources and logistics may influence the choice of diagnostic modality. No data exist on outcomes from different diagnostic testing methods in poststroke patients. Further research is needed.

 

 

POSITIVE AIRWAY PRESSURE THERAPY: BENEFITS, CHALLENGES, ALTERNATIVES

The first-line treatment for OSA is positive airway pressure (PAP).³ For most patients, this is continuous PAP (CPAP) or autoadjusting PAP (APAP). In some instances, particularly for those who cannot tolerate CPAP or who have comorbid hypoventilation, bilevel PAP (BPAP) may be indicated. More advanced PAP therapies are unlikely to be used after stroke.

PAP therapy is associated with reduced daytime sleepiness, improved mood, normalization of sleep architecture, improved systemic and pulmonary artery blood pressure, reduced rates of atrial fibrillation after ablation, and improved insulin sensitivity.^45–49 Whether it reduces the risk of cardiovascular events, including stroke, remains controversial; most data suggest that it does not.^50,51 However, when adherence to PAP therapy is considered rather than intention to treat, treatment has been found to lead to improved cardiovascular outcomes.⁵²

Mixed evidence of benefits after stroke

Observational studies provide evidence that CPAP may help patients with OSA after stroke, although results are mixed.^53–58 The studies ranged in size from 14 to 105 patients, enrolled patients with mostly moderate to severe OSA, and followed patients from 10 days to 7 years. Adherence to therapy was generally good in the short term (50%–70%), but only  15% to 30% of patients remained adherent at 5 to 7 years. Variable outcomes were reported, with some studies finding improved symptoms in the near term and mixed evidence of cardiovascular benefit in the longer ones. However, as these studies lacked randomization, drawing definitive conclusions on CPAP efficacy is difficult.

Several short-term randomized controlled trials of CPAP have been performed in patients after stroke. A 2018 meta-analysis⁵⁹ included 10 such trials with a total of 564 patients (range 30–140 patients), with most having 1 to 3 months of follow-up (range 1 week to over 5 years). Eight of the 10 studies are summarized in Table 1 (1 study was omitted because many of the patients had central sleep apnea, and 1 was primarily a feasibility study).^60–67

Patients were enrolled in the index admission or when starting a rehabilitation service—generally 2 to 3 weeks after their stroke. No clear association was found between the timing of initiating PAP therapy and outcomes. All patients had ischemic strokes, but few details were provided regarding stroke location, size, and severity. Exclusion criteria included severe underlying cardiopulmonary disease, confusion, severe stroke with marked impairment, and inability to cooperate. Almost all patients had moderate to severe OSA, and patients with central sleep apnea were excluded.

The major outcomes examined were drop-out rates, PAP adherence, and neurologic improvement based on neurologic functional scales (National Institutes of Health Stroke Scale and Canadian Neurologic Scale). As expected, dropout rates were higher in patients randomized to CPAP (OR 1.83, 95% CI 1.05–3.21, P = .03), although overall adherence was better than anticipated, with mean CPAP use across trials of 4.5 hours per night (95% CI 3.97–5.08) and with about 50% to 60% of patients adhering to therapy for at least 4 hours nightly.

Improvement in neurologic outcomes favored CPAP (standard mean difference 0.54, 95% CI 0.026–1.05), although considerable heterogeneity was seen. Improved sleepiness outcomes were inconsistent. Major cardiovascular outcomes were reported in only 2 studies (using the same data set) and showed delayed time to the next cardiovascular event for those treated with CPAP but no difference in cardiovascular event-free survival.

PAP poses more challenges after stroke

The primary limitation to PAP therapy is poor acceptance and adherence to therapy.⁵⁹ High rates of refusal of therapy and difficulty complying with treatment have been noted in the poststroke population, although recent studies have reported better adherence rates. How rates of adherence play out in real-world settings, outside of the controlled environment of a research study, has yet to be determined.

In general, CPAP adherence is affected by claustrophobia, difficulty tolerating a mask, problems with pressure intolerance, irritating air leaks, nasal congestion, and naso-oral dryness. Many such barriers can be overcome with use of a properly fitted mask, an appropriate pressure setting, heated humidification, nasal sprays (eg, saline, inhaled steroids), and education, encouragement, and reassurance.

After a stroke, additional obstacles may impede the ability to use PAP therapy.⁶⁸ Facial paresis (hemi- or bifacial) may make fitting of the mask problematic. Paralysis or weakness of the extremities may limit the ability to adjust or remove a mask. Aphasia can impair communication and understanding of the need to use PAP therapy, and upper-airway problems related to stroke, including dysphagia, may lead to pressure intolerance or risk of aspiration. Finally, a lack of perceived benefit, particularly if the patient does not have daytime sleepiness, may limit motivation.

Consider alternatives

For patients unlikely to succeed with PAP therapy, there are alternatives. Surgery and oral appliances are not usually realistic options in the setting of recent stroke, but positional therapy, including the use of body positioners to prevent supine sleep, as well as elevating the head of the bed, may be of some benefit.^69,70 A nasopharyngeal airway stenting device (nasal trumpet) may also be tolerated by some patients.

Avoiding or minimizing sedating medications that may worsen OSA, such as benzodiazepines and opioids, should be considered.³ Oxygen therapy, while helping to maintain oxygen saturation during sleep, does not prevent airway collapse, and its role for treating OSA in patients after stroke is unclear.

A proposed algorithm for screening, diagnosing, and treating OSA in patients after stroke is presented in Figure 1.

Should clinicians abandon the activated partial thromboplastin time (aPTT) for monitoring heparin therapy in favor of tests that measure the activity of the patient’s plasma against activated factor X (anti-Xa assays)?

Although other anticoagulants are now available for preventing and treating arterial and venous thromboembolism, unfractionated heparin—which requires laboratory monitoring of therapy—is still widely used. And this monitoring can be challenging. Despite its wide use, the aPTT lacks standardization, and the role of alternative monitoring assays such as the anti-Xa assay is not well defined.

This article reviews the advantages, limitations, and clinical applicability of anti-Xa assays for monitoring therapy with unfractionated heparin and other anticoagulants.

UNFRACTIONATED HEPARIN AND WARFARIN ARE STILL WIDELY USED

Until the mid-1990s, unfractionated heparin and oral vitamin K antagonists (eg, warfarin) were the only anticoagulants widely available for clinical use. These agents have complex pharmacokinetic and pharmacodynamic properties, resulting in highly variable dosing requirements (both between patients and in individual patients) and narrow therapeutic windows, making frequent laboratory monitoring and dose adjustments mandatory.

Over the past 3 decades, other anticoagulants have been approved, including low-molecular-weight heparins, fondaparinux, parenteral direct thrombin inhibitors, and direct oral anticoagulants. While these agents have expanded the options for preventing and treating thromboembolism, unfractionated heparin and warfarin are still the most appropriate choices for many patients, eg, those with stage 4 chronic kidney disease and end-stage renal disease on dialysis, and those with mechanical heart valves.

In addition, unfractionated heparin remains the anticoagulant of choice during procedures such as hemodialysis, percutaneous transluminal angioplasty, and cardiopulmonary bypass, as well as in hospitalized and critically ill patients, who often have acute kidney injury or require frequent interruptions of therapy for invasive procedures. In these scenarios, unfractionated heparin is typically preferred because of its short plasma half-life, complete reversibility by protamine, safety regardless of renal function, and low cost compared with parenteral direct thrombin inhibitors.

As long as unfractionated heparin and warfarin remain important therapies, the need for their laboratory monitoring continues. For warfarin monitoring, the prothrombin time and international normalized ratio are validated and widely reproducible methods. But monitoring unfractionated heparin therapy remains a challenge.

UNFRACTIONATED HEPARIN’S EFFECT IS UNPREDICTABLE

Unfractionated heparin, a negatively charged mucopolysaccharide, inhibits coagulation by binding to antithrombin through the high-affinity pentasaccharide sequence.^1–6 Such binding induces a conformational change in the antithrombin molecule, converting it to a rapid inhibitor of several coagulation proteins, especially factors IIa and Xa.^2–4

Unfractionated heparin inhibits factors IIa and Xa in a 1:1 ratio, but low-molecular-weight heparins inhibit factor Xa more than factor IIa, with IIa-Xa inhibition ratios ranging from 1:2 to 1:4, owing to their smaller molecular size.⁷

One of the most important reasons for the unpredictable and highly variable individual responses to unfractionated heparin is that, infused into the blood, the large and negatively charged unfractionated heparin molecules bind nonspecifically to positively charged plasma proteins.⁷ In patients who are critically ill, have acute infections or inflammatory states, or have undergone major surgery, unfractionated heparin binds to acute-phase proteins that are elevated, particularly factor VIII. This results in fewer free heparin molecules and a variable anticoagulant effect.⁸

In contrast, low-molecular-weight heparins have longer half-lives and bind less to plasma proteins, resulting in more predictable plasma levels following subcutaneous injection.⁹

 

 

MONITORING UNFRACTIONATED HEPARIN IMPROVES OUTCOMES

In 1960, Barritt and Jordan¹⁰ conducted a small but landmark trial that established the clinical importance of unfractionated heparin for treating venous thromboembolism. None of the patients who received unfractionated heparin for acute pulmonary embolism developed a recurrence during the subsequent 2 weeks, while 50% of those who did not receive it had recurrent pulmonary embolism, fatal in half of the cases.

The importance of achieving a specific aPTT therapeutic target was not demonstrated until a 1972 study by Basu et al,¹¹ in which 162 patients with venous thromboembolism were treated with heparin with a target aPTT of 1.5 to 2.5 times the control value. Patients who suffered recurrent events had subtherapeutic aPTT values on 71% of treatment days, while the rest of the patients, with no recurrences, had subtherapeutic aPTT values only 28% of treatment days. The different outcomes could not be explained by the average daily dose of unfractionated heparin, which was similar in the patients regardless of recurrence.

Subsequent studies showed that the best outcomes occur when unfractionated heparin is given in doses high enough to rapidly achieve a therapeutic prolongation of the aPTT,^12–14 and that the total daily dose is also important in preventing recurrences.^15,16 Failure to achieve a target aPTT within 24 hours of starting unfractionated heparin is associated with increased risk of recurrent venous thromboembolism.^13,17

Raschke et al¹⁷ found that patients prospectively randomized to weight-based doses of intravenous unfractionated heparin (bolus plus infusion) achieved significantly higher rates of therapeutic aPTT within 6 hours and 24 hours after starting the infusion, and had significantly lower rates of recurrent venous thromboembolism than those randomized to a fixed unfractionated heparin protocol, without an increase in major bleeding.

Smith et al,¹⁸ in a study of 400 consecutive patients with acute pulmonary embolism treated with unfractionated heparin, found that patients who achieved a therapeutic aPTT within 24 hours had lower in-hospital and 30-day mortality rates than those who did not achieve the first therapeutic aPTT until more than 24 hours after starting unfractionated heparin infusion.

Such data lend support to the widely accepted practice and current guideline recommendation⁸ of using laboratory assays to adjust the dose of unfractionated heparin to achieve and maintain a therapeutic target. The use of dosing nomograms significantly reduces the time to achieve a therapeutic aPTT while minimizing subtherapeutic and supratherapeutic unfractionated heparin levels.^19,20

THE aPTT REFLECTS THROMBIN INHIBITION

The aPTT has a log-linear relationship with plasma concentrations of unfractionated heparin,²¹ but it was not developed specifically for monitoring unfractionated heparin therapy. Originally described in 1953 as a screening tool for hemophilia,^22–24 the aPTT is prolonged in the setting of factor deficiencies (typically with levels < 45%, except for factors VII and XIII), as well as lupus anticoagulants and therapy with parenteral direct thrombin inhibitors.^8,25,26

Because thrombin (factor IIa) is 10 times more sensitive than factor Xa to inhibition by the heparin-antithrombin complex,^4,7 thrombin inhibition appears to be the most likely mechanism by which unfractionated heparin prolongs the aPTT. In contrast, aPTT is minimally or not at all prolonged by low-molecular-weight heparins, which are predominantly factor Xa inhibitors.⁷

HEPARIN ASSAYS MEASURE UNFRACTIONATED HEPARIN ACTIVITY

While the aPTT is a surrogate marker of unfractionated heparin activity in plasma, unfractionated heparin activity can be measured more precisely by so-called heparin assays, which are typically not direct measures of the plasma concentration of heparins, but rather functional assays that provide indirect estimates. They include protamine sulfate titration assays and anti-Xa assays.

Protamine sulfate titration assays measure the amount of protamine sulfate required to neutralize heparin: the more protamine required, the greater the estimated concentration of unfractionated heparin in plasma.^8,27–29 Protamine titration assays are technically demanding, so they are rarely used clinically.

Anti-Xa assays provide a measure of the functional level of heparins in plasma.^29–33 Chromogenic anti-Xa assays are available on automated analyzers with standardized kits^29,33,34 and may be faster to perform than the aPTT.³⁵

Experiments in rabbits show that unfractionated heparin inhibits thrombus formation and extension at concentrations of 0.2 to 0.4 U/mL as measured by the protamine titration assay,²⁷ which correlated with an anti-Xa activity of 0.35 to 0.67 U/mL in a randomized controlled trial.³²

Assays that directly measure the plasma concentration of heparin exist but are not clinically relevant because they also measure heparin molecules lacking the pentasaccharide sequence, which have no anticoagulant activity.³⁶

 

 

ANTI-Xa ASSAY VS THE aPTT

Anti-Xa assays are more expensive than the aPTT and are not available in all hospitals. For these reasons, the aPTT remains the most commonly used laboratory assay for monitoring unfractionated heparin therapy.

However, the aPTT correlates poorly with the activity level of unfractionated heparin in plasma. In one study, an anti-Xa level of 0.3 U/mL corresponded to aPTT results ranging from 47 to 108 seconds.³¹ Furthermore, in studies that used a heparin therapeutic target based on an aPTT ratio 1.5 to 2.5 times the control aPTT value, the lower end of that target range was often associated with subtherapeutic plasma unfractionated heparin activity measured by anti-Xa and protamine titration assays.^28,31

Because of these limitations, individual laboratories should determine their own aPTT therapeutic target ranges for unfractionated heparin based on the response curves obtained with the reagent and coagulometer used. The optimal therapeutic aPTT range for treating acute venous thromboembolism should be defined as the aPTT range (in seconds) that correlates with a plasma activity level of unfractionated heparin of 0.3 to 0.7 U/mL based on a chromogenic anti-Xa assay, or 0.2 to 0.4 U/mL based on a protamine titration assay.^32,34–36

Nevertheless, the anticoagulant effect of unfractionated heparin as measured by the aPTT can be unpredictable and can vary widely among individuals and in the same patient.⁷ This wide variability can be explained by a number of technical and biologic variables. Different commercial aPTT reagents, different lots of the same reagent, and different reagent and instrument combinations have different sensitivities to unfractionated heparin, which can lead to variable aPTT results.³⁷ Moreover, high plasma levels of acute-phase proteins, low plasma antithrombin levels, consumptive coagulopathies, liver failure, and lupus anticoagulants may also affect the aPTT.^{7,25,32,36–41} These variables account for the poor correlation—ranging from 25% to 66%—reported between aPTT and anti-Xa assays.^32,42–48

Such discrepancies may have serious clinical implications: if a patient’s aPTT is low (subtherapeutic) or high (supratherapeutic) but the anti-Xa assay result is within the therapeutic range (0.3–0.7 units/mL), changing the dose of unfractionated heparin (guided by an aPTT nomogram) may increase the risk of bleeding or of recurrent thromboembolism.

CLINICAL APPLICABILITY OF THE ANTI-Xa ASSAY

Neither anti-Xa nor protamine titration assays are standardized across reference laboratories, but chromogenic anti-Xa assays have better interlaboratory correlation than the aPTT^49,50 and can be calibrated specifically for unfractionated or low-molecular-weight heparins.^29,33

Although reagent costs are higher for chromogenic anti-Xa assays than for the aPTT, some technical variables (described below) may partially offset the cost difference.^29,33,41 In addition, unlike the aPTT, anti-Xa assays do not need local calibration; the therapeutic range for unfractionated heparin is the same (0.3–0.7 U/mL) regardless of instrument or reagent.^33,41

Most important, studies have found that patients monitored by anti-Xa assay achieve significantly higher rates of therapeutic anticoagulation within 24 and 48 hours after starting unfractionated heparin infusion than those monitored by the aPTT. Fewer dose adjustments and repeat tests are required, which may also result in lower cost.^32,51–55

While these studies found chromogenic anti-Xa assays better for achieving laboratory end points, data regarding relevant clinical outcomes are more limited. In a retrospective, observational cohort study,⁵¹ the rate of venous thromboembolism or bleeding-related death was 2% in patients receiving unfractionated heparin therapy monitored by anti-Xa assay and 6% in patients monitored by aPTT (P = .62). Rates of major hemorrhage were also not significantly different.

In a randomized controlled trial³² in 131 patients with acute venous thromboembolism and heparin resistance, rates of recurrent venous thromboembolism were 4.6% and 6.1% in the groups randomized to anti-Xa and aPTT monitoring, respectively, whereas overall bleeding rates were 1.5% and 6.1%, respectively. Again, the differences were not statistically significant.

Though some have suggested that the anti-Xa should be the preferred monitoring assay for intravenous unfractionated heparin therapy,^29,41 the ideal assay has not been established by large-scale randomized controlled trials correlating different assays with meaningful clinical outcomes.^8,33 Nevertheless, anti-Xa assays are considered the most accurate method of monitoring unfractionated heparin in cases of heparin resistance or lupus anticoagulant, and in other clinical circumstances (Table 1).^56–58

Heparin resistance. Some patients require unusually high doses of unfractionated heparin to achieve a therapeutic aPTT: typically, more than 35,000 U over 24 hours,^7,8,32 or total daily doses that exceed their estimated weight-based requirements. Heparin resistance has been observed in various clinical settings.^{7,8,32,37–40,59–61} Patients with heparin resistance monitored by anti-Xa had similar rates of recurrent venous thromboembolism while receiving significantly lower doses of unfractionated heparin than those monitored by the aPTT.³²

Lupus anticoagulant. Patients with the specific antiphospholipid antibody known as lupus anticoagulant frequently have a prolonged baseline aPTT,²⁵ making it an unreliable marker of anticoagulant effect for intravenous unfractionated heparin therapy.

Critically ill infants and children. Arachchillage et al³⁵ found that infants (< 1 year old) treated with intravenous unfractionated heparin in an intensive care department had only a 32.4% correlation between aPTT and anti-Xa levels, which was lower than that found in children ages 1 to 15 (66%) and adults (52%). In two-thirds of cases of discordant aPTT and anti-Xa levels, the aPTT was elevated (supratherapeutic) while the anti-Xa assay was within the therapeutic range (0.3–0.7 U/mL). Despite the lack of data on clinical outcomes (eg, rates of thrombosis and bleeding) with the use of an anti-Xa assay, it has been considered the method of choice for unfractionated heparin monitoring in critically ill children, and especially in those under age 1.^{41,44,62–64}

While anti-Xa assays may also be better for unfractionated heparin monitoring in critically ill adults, the lack of clinical outcome data from large-scale randomized trials has precluded evidence-based recommendations favoring them over the aPTT.^8,34

 

 

LIMITATIONS OF ANTI-Xa ASSAYS

Anti-Xa assays are hampered by some technical limitations:

Samples must be processed within 1 hour to avoid heparin neutralization.³⁴

Samples must be clear. Hemolyzed or opaque samples (eg, due to bilirubin levels > 6.6 mg/dL or triglyceride levels > 360 mg/dL) cannot be processed, as they can cause falsely low levels.

Exposure to other anticoagulants can interfere with the results. The anti-Xa assay may be unreliable for unfractionated heparin monitoring in patients who are transitioned from low-molecular-weight heparins, fondaparinux, or an oral factor Xa inhibitor (apixaban, betrixaban, edoxaban, rivaroxaban) to intravenous unfractionated heparin, eg, due to hospitalization or acute kidney injury.^65,66 Different reports have found that anti-Xa assays may be elevated for as long as 63 to 96 hours after the last dose of oral Xa inhibitors,^67–69 potentially resulting in underdosing of unfractionated heparin. In such settings, unfractionated heparin therapy should be monitored by the aPTT.

ANTI-Xa ASSAYS AND LOW-MOLECULAR-WEIGHT HEPARINS

Most patients receiving low-molecular-weight heparins do not need laboratory monitoring.⁸ Alhenc-Gelas et al⁷⁰ randomized patients to receive dalteparin in doses either based on weight or guided by anti-Xa assay results, and found that dose adjustments were rare and lacked clinical benefit.

However, the use of low-molecular-weight heparin-specific anti-Xa assays should be considered for certain patients (Table 2).⁸

The suggested therapeutic anti-Xa levels for low-molecular-weight heparins are:

• 0.5–1.2 U/mL for twice-daily enoxaparin
• 1.0–2.0 U/mL for once-daily enoxaparin or dalteparin.

Levels should be measured at peak plasma level (ie, 3–4 hours after subcutaneous injection, except during pregnancy, when it is 4–6 hours), and only after at least 3 doses of low-molecular-weight heparin.^8,71 Unlike the anti-Xa therapeutic range recommended for unfractionated heparin therapy, these ranges are not based on prospective data, and if the assay result is outside the suggested therapeutic target range, current guidelines offer no advice on safely adjusting the dose.^8,71

Measuring anti-Xa activity is particularly important for pregnant women with a mechanical prosthetic heart valve who are treated with low-molecular-weight heparins. In this setting, valve thrombosis and cardioembolic events have been reported in patients with peak low-molecular-weight heparin anti-Xa assay levels below or even at the lower end of the therapeutic range, and increased bleeding risk has been reported with elevated anti-Xa levels.^71–74 Measuring trough low-molecular-weight heparin anti-Xa levels has been suggested to guide dose adjustments during pregnancy.⁷⁵

Clearance of low-molecular-weight heparins as measured by the anti-Xa assay is highly correlated with creatinine clearance.^76,77 A strong linear correlation has been demonstrated between creatine clearance and anti-Xa levels of enoxaparin after multiple therapeutic doses, and low-molecular-weight heparins accumulate in the plasma, especially in patients with creatine clearance less than 30 mL/min.⁷⁸ The risk of major bleeding is significantly increased in patients with severe renal insufficiency (creatinine clearance < 30 mL/min) not on dialysis who are treated with either prophylactic or therapeutic doses of low-molecular-weight heparin.^79–81 In a meta-analysis, the risk of bleeding with therapeutic-intensity doses of enoxaparin was 4 times higher than with prophylactic-intensity doses.⁷⁹ Although bleeding risk appears to be reduced when the enoxaparin dose is reduced by 50%,⁸ the efficacy and safety of this strategy has not been determined by prospective trials.

ANTI-Xa ASSAYS IN PATIENTS RECEIVING DIRECT ORAL ANTICOAGULANTS

Direct oral factor Xa inhibitors cannot be measured accurately by heparin anti-Xa assays. Nevertheless, such assays may be useful to assess whether clinically relevant plasma levels are present in cases of major bleeding, suspected anticoagulant failure, or patient noncompliance.⁸²

Intense research has focused on developing drug-specific chromogenic anti-Xa assays using calibrators and standards for apixaban, edoxaban, and rivaroxaban,^82,83 and good linear correlation has been shown with some assays.^82,84 In patients treated with oral factor Xa inhibitors who need to undergo an urgent invasive procedure associated with high bleeding risk, use of a specific reversal agent may be considered with drug concentrations more than 30 ng/mL measured by a drug-specific anti-Xa assay. A similar suggestion has been made for drug concentrations more than 50 ng/mL in the setting of major bleeding.⁸⁵ Unfortunately, such assays are not widely available at this time.^82,86

While drug-specific anti-Xa assays could become clinically important to guide reversal strategies, their relevance for drug monitoring remains uncertain. This is because no therapeutic target ranges have been established for any of the direct oral anticoagulants, which were approved on the basis of favorable clinical trial outcomes that neither measured nor were correlated with specific drug levels in plasma. Therefore, a specific anti-Xa level cannot yet be used as a marker of clinical efficacy for any specific oral direct Xa inhibitor.

Should clinicians abandon the activated partial thromboplastin time (aPTT) for monitoring heparin therapy in favor of tests that measure the activity of the patient’s plasma against activated factor X (anti-Xa assays)?

Although other anticoagulants are now available for preventing and treating arterial and venous thromboembolism, unfractionated heparin—which requires laboratory monitoring of therapy—is still widely used. And this monitoring can be challenging. Despite its wide use, the aPTT lacks standardization, and the role of alternative monitoring assays such as the anti-Xa assay is not well defined.

This article reviews the advantages, limitations, and clinical applicability of anti-Xa assays for monitoring therapy with unfractionated heparin and other anticoagulants.

UNFRACTIONATED HEPARIN AND WARFARIN ARE STILL WIDELY USED

Until the mid-1990s, unfractionated heparin and oral vitamin K antagonists (eg, warfarin) were the only anticoagulants widely available for clinical use. These agents have complex pharmacokinetic and pharmacodynamic properties, resulting in highly variable dosing requirements (both between patients and in individual patients) and narrow therapeutic windows, making frequent laboratory monitoring and dose adjustments mandatory.

Over the past 3 decades, other anticoagulants have been approved, including low-molecular-weight heparins, fondaparinux, parenteral direct thrombin inhibitors, and direct oral anticoagulants. While these agents have expanded the options for preventing and treating thromboembolism, unfractionated heparin and warfarin are still the most appropriate choices for many patients, eg, those with stage 4 chronic kidney disease and end-stage renal disease on dialysis, and those with mechanical heart valves.

In addition, unfractionated heparin remains the anticoagulant of choice during procedures such as hemodialysis, percutaneous transluminal angioplasty, and cardiopulmonary bypass, as well as in hospitalized and critically ill patients, who often have acute kidney injury or require frequent interruptions of therapy for invasive procedures. In these scenarios, unfractionated heparin is typically preferred because of its short plasma half-life, complete reversibility by protamine, safety regardless of renal function, and low cost compared with parenteral direct thrombin inhibitors.

As long as unfractionated heparin and warfarin remain important therapies, the need for their laboratory monitoring continues. For warfarin monitoring, the prothrombin time and international normalized ratio are validated and widely reproducible methods. But monitoring unfractionated heparin therapy remains a challenge.

UNFRACTIONATED HEPARIN’S EFFECT IS UNPREDICTABLE

Unfractionated heparin, a negatively charged mucopolysaccharide, inhibits coagulation by binding to antithrombin through the high-affinity pentasaccharide sequence.^1–6 Such binding induces a conformational change in the antithrombin molecule, converting it to a rapid inhibitor of several coagulation proteins, especially factors IIa and Xa.^2–4

Unfractionated heparin inhibits factors IIa and Xa in a 1:1 ratio, but low-molecular-weight heparins inhibit factor Xa more than factor IIa, with IIa-Xa inhibition ratios ranging from 1:2 to 1:4, owing to their smaller molecular size.⁷

One of the most important reasons for the unpredictable and highly variable individual responses to unfractionated heparin is that, infused into the blood, the large and negatively charged unfractionated heparin molecules bind nonspecifically to positively charged plasma proteins.⁷ In patients who are critically ill, have acute infections or inflammatory states, or have undergone major surgery, unfractionated heparin binds to acute-phase proteins that are elevated, particularly factor VIII. This results in fewer free heparin molecules and a variable anticoagulant effect.⁸

In contrast, low-molecular-weight heparins have longer half-lives and bind less to plasma proteins, resulting in more predictable plasma levels following subcutaneous injection.⁹

 

 

MONITORING UNFRACTIONATED HEPARIN IMPROVES OUTCOMES

In 1960, Barritt and Jordan¹⁰ conducted a small but landmark trial that established the clinical importance of unfractionated heparin for treating venous thromboembolism. None of the patients who received unfractionated heparin for acute pulmonary embolism developed a recurrence during the subsequent 2 weeks, while 50% of those who did not receive it had recurrent pulmonary embolism, fatal in half of the cases.

The importance of achieving a specific aPTT therapeutic target was not demonstrated until a 1972 study by Basu et al,¹¹ in which 162 patients with venous thromboembolism were treated with heparin with a target aPTT of 1.5 to 2.5 times the control value. Patients who suffered recurrent events had subtherapeutic aPTT values on 71% of treatment days, while the rest of the patients, with no recurrences, had subtherapeutic aPTT values only 28% of treatment days. The different outcomes could not be explained by the average daily dose of unfractionated heparin, which was similar in the patients regardless of recurrence.

Subsequent studies showed that the best outcomes occur when unfractionated heparin is given in doses high enough to rapidly achieve a therapeutic prolongation of the aPTT,^12–14 and that the total daily dose is also important in preventing recurrences.^15,16 Failure to achieve a target aPTT within 24 hours of starting unfractionated heparin is associated with increased risk of recurrent venous thromboembolism.^13,17

Raschke et al¹⁷ found that patients prospectively randomized to weight-based doses of intravenous unfractionated heparin (bolus plus infusion) achieved significantly higher rates of therapeutic aPTT within 6 hours and 24 hours after starting the infusion, and had significantly lower rates of recurrent venous thromboembolism than those randomized to a fixed unfractionated heparin protocol, without an increase in major bleeding.

Smith et al,¹⁸ in a study of 400 consecutive patients with acute pulmonary embolism treated with unfractionated heparin, found that patients who achieved a therapeutic aPTT within 24 hours had lower in-hospital and 30-day mortality rates than those who did not achieve the first therapeutic aPTT until more than 24 hours after starting unfractionated heparin infusion.

Such data lend support to the widely accepted practice and current guideline recommendation⁸ of using laboratory assays to adjust the dose of unfractionated heparin to achieve and maintain a therapeutic target. The use of dosing nomograms significantly reduces the time to achieve a therapeutic aPTT while minimizing subtherapeutic and supratherapeutic unfractionated heparin levels.^19,20

THE aPTT REFLECTS THROMBIN INHIBITION

The aPTT has a log-linear relationship with plasma concentrations of unfractionated heparin,²¹ but it was not developed specifically for monitoring unfractionated heparin therapy. Originally described in 1953 as a screening tool for hemophilia,^22–24 the aPTT is prolonged in the setting of factor deficiencies (typically with levels < 45%, except for factors VII and XIII), as well as lupus anticoagulants and therapy with parenteral direct thrombin inhibitors.^8,25,26

Because thrombin (factor IIa) is 10 times more sensitive than factor Xa to inhibition by the heparin-antithrombin complex,^4,7 thrombin inhibition appears to be the most likely mechanism by which unfractionated heparin prolongs the aPTT. In contrast, aPTT is minimally or not at all prolonged by low-molecular-weight heparins, which are predominantly factor Xa inhibitors.⁷

HEPARIN ASSAYS MEASURE UNFRACTIONATED HEPARIN ACTIVITY

While the aPTT is a surrogate marker of unfractionated heparin activity in plasma, unfractionated heparin activity can be measured more precisely by so-called heparin assays, which are typically not direct measures of the plasma concentration of heparins, but rather functional assays that provide indirect estimates. They include protamine sulfate titration assays and anti-Xa assays.

Protamine sulfate titration assays measure the amount of protamine sulfate required to neutralize heparin: the more protamine required, the greater the estimated concentration of unfractionated heparin in plasma.^8,27–29 Protamine titration assays are technically demanding, so they are rarely used clinically.

Anti-Xa assays provide a measure of the functional level of heparins in plasma.^29–33 Chromogenic anti-Xa assays are available on automated analyzers with standardized kits^29,33,34 and may be faster to perform than the aPTT.³⁵

Experiments in rabbits show that unfractionated heparin inhibits thrombus formation and extension at concentrations of 0.2 to 0.4 U/mL as measured by the protamine titration assay,²⁷ which correlated with an anti-Xa activity of 0.35 to 0.67 U/mL in a randomized controlled trial.³²

Assays that directly measure the plasma concentration of heparin exist but are not clinically relevant because they also measure heparin molecules lacking the pentasaccharide sequence, which have no anticoagulant activity.³⁶

 

 

ANTI-Xa ASSAY VS THE aPTT

Anti-Xa assays are more expensive than the aPTT and are not available in all hospitals. For these reasons, the aPTT remains the most commonly used laboratory assay for monitoring unfractionated heparin therapy.

However, the aPTT correlates poorly with the activity level of unfractionated heparin in plasma. In one study, an anti-Xa level of 0.3 U/mL corresponded to aPTT results ranging from 47 to 108 seconds.³¹ Furthermore, in studies that used a heparin therapeutic target based on an aPTT ratio 1.5 to 2.5 times the control aPTT value, the lower end of that target range was often associated with subtherapeutic plasma unfractionated heparin activity measured by anti-Xa and protamine titration assays.^28,31

Because of these limitations, individual laboratories should determine their own aPTT therapeutic target ranges for unfractionated heparin based on the response curves obtained with the reagent and coagulometer used. The optimal therapeutic aPTT range for treating acute venous thromboembolism should be defined as the aPTT range (in seconds) that correlates with a plasma activity level of unfractionated heparin of 0.3 to 0.7 U/mL based on a chromogenic anti-Xa assay, or 0.2 to 0.4 U/mL based on a protamine titration assay.^32,34–36

Nevertheless, the anticoagulant effect of unfractionated heparin as measured by the aPTT can be unpredictable and can vary widely among individuals and in the same patient.⁷ This wide variability can be explained by a number of technical and biologic variables. Different commercial aPTT reagents, different lots of the same reagent, and different reagent and instrument combinations have different sensitivities to unfractionated heparin, which can lead to variable aPTT results.³⁷ Moreover, high plasma levels of acute-phase proteins, low plasma antithrombin levels, consumptive coagulopathies, liver failure, and lupus anticoagulants may also affect the aPTT.^{7,25,32,36–41} These variables account for the poor correlation—ranging from 25% to 66%—reported between aPTT and anti-Xa assays.^32,42–48

Such discrepancies may have serious clinical implications: if a patient’s aPTT is low (subtherapeutic) or high (supratherapeutic) but the anti-Xa assay result is within the therapeutic range (0.3–0.7 units/mL), changing the dose of unfractionated heparin (guided by an aPTT nomogram) may increase the risk of bleeding or of recurrent thromboembolism.

CLINICAL APPLICABILITY OF THE ANTI-Xa ASSAY

Neither anti-Xa nor protamine titration assays are standardized across reference laboratories, but chromogenic anti-Xa assays have better interlaboratory correlation than the aPTT^49,50 and can be calibrated specifically for unfractionated or low-molecular-weight heparins.^29,33

Although reagent costs are higher for chromogenic anti-Xa assays than for the aPTT, some technical variables (described below) may partially offset the cost difference.^29,33,41 In addition, unlike the aPTT, anti-Xa assays do not need local calibration; the therapeutic range for unfractionated heparin is the same (0.3–0.7 U/mL) regardless of instrument or reagent.^33,41

Most important, studies have found that patients monitored by anti-Xa assay achieve significantly higher rates of therapeutic anticoagulation within 24 and 48 hours after starting unfractionated heparin infusion than those monitored by the aPTT. Fewer dose adjustments and repeat tests are required, which may also result in lower cost.^32,51–55

While these studies found chromogenic anti-Xa assays better for achieving laboratory end points, data regarding relevant clinical outcomes are more limited. In a retrospective, observational cohort study,⁵¹ the rate of venous thromboembolism or bleeding-related death was 2% in patients receiving unfractionated heparin therapy monitored by anti-Xa assay and 6% in patients monitored by aPTT (P = .62). Rates of major hemorrhage were also not significantly different.

In a randomized controlled trial³² in 131 patients with acute venous thromboembolism and heparin resistance, rates of recurrent venous thromboembolism were 4.6% and 6.1% in the groups randomized to anti-Xa and aPTT monitoring, respectively, whereas overall bleeding rates were 1.5% and 6.1%, respectively. Again, the differences were not statistically significant.

Though some have suggested that the anti-Xa should be the preferred monitoring assay for intravenous unfractionated heparin therapy,^29,41 the ideal assay has not been established by large-scale randomized controlled trials correlating different assays with meaningful clinical outcomes.^8,33 Nevertheless, anti-Xa assays are considered the most accurate method of monitoring unfractionated heparin in cases of heparin resistance or lupus anticoagulant, and in other clinical circumstances (Table 1).^56–58

Heparin resistance. Some patients require unusually high doses of unfractionated heparin to achieve a therapeutic aPTT: typically, more than 35,000 U over 24 hours,^7,8,32 or total daily doses that exceed their estimated weight-based requirements. Heparin resistance has been observed in various clinical settings.^{7,8,32,37–40,59–61} Patients with heparin resistance monitored by anti-Xa had similar rates of recurrent venous thromboembolism while receiving significantly lower doses of unfractionated heparin than those monitored by the aPTT.³²

Lupus anticoagulant. Patients with the specific antiphospholipid antibody known as lupus anticoagulant frequently have a prolonged baseline aPTT,²⁵ making it an unreliable marker of anticoagulant effect for intravenous unfractionated heparin therapy.

Critically ill infants and children. Arachchillage et al³⁵ found that infants (< 1 year old) treated with intravenous unfractionated heparin in an intensive care department had only a 32.4% correlation between aPTT and anti-Xa levels, which was lower than that found in children ages 1 to 15 (66%) and adults (52%). In two-thirds of cases of discordant aPTT and anti-Xa levels, the aPTT was elevated (supratherapeutic) while the anti-Xa assay was within the therapeutic range (0.3–0.7 U/mL). Despite the lack of data on clinical outcomes (eg, rates of thrombosis and bleeding) with the use of an anti-Xa assay, it has been considered the method of choice for unfractionated heparin monitoring in critically ill children, and especially in those under age 1.^{41,44,62–64}

While anti-Xa assays may also be better for unfractionated heparin monitoring in critically ill adults, the lack of clinical outcome data from large-scale randomized trials has precluded evidence-based recommendations favoring them over the aPTT.^8,34

 

 

LIMITATIONS OF ANTI-Xa ASSAYS

Anti-Xa assays are hampered by some technical limitations:

Samples must be processed within 1 hour to avoid heparin neutralization.³⁴

Samples must be clear. Hemolyzed or opaque samples (eg, due to bilirubin levels > 6.6 mg/dL or triglyceride levels > 360 mg/dL) cannot be processed, as they can cause falsely low levels.

Exposure to other anticoagulants can interfere with the results. The anti-Xa assay may be unreliable for unfractionated heparin monitoring in patients who are transitioned from low-molecular-weight heparins, fondaparinux, or an oral factor Xa inhibitor (apixaban, betrixaban, edoxaban, rivaroxaban) to intravenous unfractionated heparin, eg, due to hospitalization or acute kidney injury.^65,66 Different reports have found that anti-Xa assays may be elevated for as long as 63 to 96 hours after the last dose of oral Xa inhibitors,^67–69 potentially resulting in underdosing of unfractionated heparin. In such settings, unfractionated heparin therapy should be monitored by the aPTT.

ANTI-Xa ASSAYS AND LOW-MOLECULAR-WEIGHT HEPARINS

Most patients receiving low-molecular-weight heparins do not need laboratory monitoring.⁸ Alhenc-Gelas et al⁷⁰ randomized patients to receive dalteparin in doses either based on weight or guided by anti-Xa assay results, and found that dose adjustments were rare and lacked clinical benefit.

However, the use of low-molecular-weight heparin-specific anti-Xa assays should be considered for certain patients (Table 2).⁸

The suggested therapeutic anti-Xa levels for low-molecular-weight heparins are:

• 0.5–1.2 U/mL for twice-daily enoxaparin
• 1.0–2.0 U/mL for once-daily enoxaparin or dalteparin.

Levels should be measured at peak plasma level (ie, 3–4 hours after subcutaneous injection, except during pregnancy, when it is 4–6 hours), and only after at least 3 doses of low-molecular-weight heparin.^8,71 Unlike the anti-Xa therapeutic range recommended for unfractionated heparin therapy, these ranges are not based on prospective data, and if the assay result is outside the suggested therapeutic target range, current guidelines offer no advice on safely adjusting the dose.^8,71

Measuring anti-Xa activity is particularly important for pregnant women with a mechanical prosthetic heart valve who are treated with low-molecular-weight heparins. In this setting, valve thrombosis and cardioembolic events have been reported in patients with peak low-molecular-weight heparin anti-Xa assay levels below or even at the lower end of the therapeutic range, and increased bleeding risk has been reported with elevated anti-Xa levels.^71–74 Measuring trough low-molecular-weight heparin anti-Xa levels has been suggested to guide dose adjustments during pregnancy.⁷⁵

Clearance of low-molecular-weight heparins as measured by the anti-Xa assay is highly correlated with creatinine clearance.^76,77 A strong linear correlation has been demonstrated between creatine clearance and anti-Xa levels of enoxaparin after multiple therapeutic doses, and low-molecular-weight heparins accumulate in the plasma, especially in patients with creatine clearance less than 30 mL/min.⁷⁸ The risk of major bleeding is significantly increased in patients with severe renal insufficiency (creatinine clearance < 30 mL/min) not on dialysis who are treated with either prophylactic or therapeutic doses of low-molecular-weight heparin.^79–81 In a meta-analysis, the risk of bleeding with therapeutic-intensity doses of enoxaparin was 4 times higher than with prophylactic-intensity doses.⁷⁹ Although bleeding risk appears to be reduced when the enoxaparin dose is reduced by 50%,⁸ the efficacy and safety of this strategy has not been determined by prospective trials.

ANTI-Xa ASSAYS IN PATIENTS RECEIVING DIRECT ORAL ANTICOAGULANTS

Direct oral factor Xa inhibitors cannot be measured accurately by heparin anti-Xa assays. Nevertheless, such assays may be useful to assess whether clinically relevant plasma levels are present in cases of major bleeding, suspected anticoagulant failure, or patient noncompliance.⁸²

Intense research has focused on developing drug-specific chromogenic anti-Xa assays using calibrators and standards for apixaban, edoxaban, and rivaroxaban,^82,83 and good linear correlation has been shown with some assays.^82,84 In patients treated with oral factor Xa inhibitors who need to undergo an urgent invasive procedure associated with high bleeding risk, use of a specific reversal agent may be considered with drug concentrations more than 30 ng/mL measured by a drug-specific anti-Xa assay. A similar suggestion has been made for drug concentrations more than 50 ng/mL in the setting of major bleeding.⁸⁵ Unfortunately, such assays are not widely available at this time.^82,86

While drug-specific anti-Xa assays could become clinically important to guide reversal strategies, their relevance for drug monitoring remains uncertain. This is because no therapeutic target ranges have been established for any of the direct oral anticoagulants, which were approved on the basis of favorable clinical trial outcomes that neither measured nor were correlated with specific drug levels in plasma. Therefore, a specific anti-Xa level cannot yet be used as a marker of clinical efficacy for any specific oral direct Xa inhibitor.

Should clinicians abandon the activated partial thromboplastin time (aPTT) for monitoring heparin therapy in favor of tests that measure the activity of the patient’s plasma against activated factor X (anti-Xa assays)?

Although other anticoagulants are now available for preventing and treating arterial and venous thromboembolism, unfractionated heparin—which requires laboratory monitoring of therapy—is still widely used. And this monitoring can be challenging. Despite its wide use, the aPTT lacks standardization, and the role of alternative monitoring assays such as the anti-Xa assay is not well defined.

This article reviews the advantages, limitations, and clinical applicability of anti-Xa assays for monitoring therapy with unfractionated heparin and other anticoagulants.

UNFRACTIONATED HEPARIN AND WARFARIN ARE STILL WIDELY USED

Until the mid-1990s, unfractionated heparin and oral vitamin K antagonists (eg, warfarin) were the only anticoagulants widely available for clinical use. These agents have complex pharmacokinetic and pharmacodynamic properties, resulting in highly variable dosing requirements (both between patients and in individual patients) and narrow therapeutic windows, making frequent laboratory monitoring and dose adjustments mandatory.

Over the past 3 decades, other anticoagulants have been approved, including low-molecular-weight heparins, fondaparinux, parenteral direct thrombin inhibitors, and direct oral anticoagulants. While these agents have expanded the options for preventing and treating thromboembolism, unfractionated heparin and warfarin are still the most appropriate choices for many patients, eg, those with stage 4 chronic kidney disease and end-stage renal disease on dialysis, and those with mechanical heart valves.

In addition, unfractionated heparin remains the anticoagulant of choice during procedures such as hemodialysis, percutaneous transluminal angioplasty, and cardiopulmonary bypass, as well as in hospitalized and critically ill patients, who often have acute kidney injury or require frequent interruptions of therapy for invasive procedures. In these scenarios, unfractionated heparin is typically preferred because of its short plasma half-life, complete reversibility by protamine, safety regardless of renal function, and low cost compared with parenteral direct thrombin inhibitors.

As long as unfractionated heparin and warfarin remain important therapies, the need for their laboratory monitoring continues. For warfarin monitoring, the prothrombin time and international normalized ratio are validated and widely reproducible methods. But monitoring unfractionated heparin therapy remains a challenge.

UNFRACTIONATED HEPARIN’S EFFECT IS UNPREDICTABLE

Unfractionated heparin, a negatively charged mucopolysaccharide, inhibits coagulation by binding to antithrombin through the high-affinity pentasaccharide sequence.^1–6 Such binding induces a conformational change in the antithrombin molecule, converting it to a rapid inhibitor of several coagulation proteins, especially factors IIa and Xa.^2–4

Unfractionated heparin inhibits factors IIa and Xa in a 1:1 ratio, but low-molecular-weight heparins inhibit factor Xa more than factor IIa, with IIa-Xa inhibition ratios ranging from 1:2 to 1:4, owing to their smaller molecular size.⁷

One of the most important reasons for the unpredictable and highly variable individual responses to unfractionated heparin is that, infused into the blood, the large and negatively charged unfractionated heparin molecules bind nonspecifically to positively charged plasma proteins.⁷ In patients who are critically ill, have acute infections or inflammatory states, or have undergone major surgery, unfractionated heparin binds to acute-phase proteins that are elevated, particularly factor VIII. This results in fewer free heparin molecules and a variable anticoagulant effect.⁸

In contrast, low-molecular-weight heparins have longer half-lives and bind less to plasma proteins, resulting in more predictable plasma levels following subcutaneous injection.⁹

 

 

MONITORING UNFRACTIONATED HEPARIN IMPROVES OUTCOMES

In 1960, Barritt and Jordan¹⁰ conducted a small but landmark trial that established the clinical importance of unfractionated heparin for treating venous thromboembolism. None of the patients who received unfractionated heparin for acute pulmonary embolism developed a recurrence during the subsequent 2 weeks, while 50% of those who did not receive it had recurrent pulmonary embolism, fatal in half of the cases.

The importance of achieving a specific aPTT therapeutic target was not demonstrated until a 1972 study by Basu et al,¹¹ in which 162 patients with venous thromboembolism were treated with heparin with a target aPTT of 1.5 to 2.5 times the control value. Patients who suffered recurrent events had subtherapeutic aPTT values on 71% of treatment days, while the rest of the patients, with no recurrences, had subtherapeutic aPTT values only 28% of treatment days. The different outcomes could not be explained by the average daily dose of unfractionated heparin, which was similar in the patients regardless of recurrence.

Subsequent studies showed that the best outcomes occur when unfractionated heparin is given in doses high enough to rapidly achieve a therapeutic prolongation of the aPTT,^12–14 and that the total daily dose is also important in preventing recurrences.^15,16 Failure to achieve a target aPTT within 24 hours of starting unfractionated heparin is associated with increased risk of recurrent venous thromboembolism.^13,17

Raschke et al¹⁷ found that patients prospectively randomized to weight-based doses of intravenous unfractionated heparin (bolus plus infusion) achieved significantly higher rates of therapeutic aPTT within 6 hours and 24 hours after starting the infusion, and had significantly lower rates of recurrent venous thromboembolism than those randomized to a fixed unfractionated heparin protocol, without an increase in major bleeding.

Smith et al,¹⁸ in a study of 400 consecutive patients with acute pulmonary embolism treated with unfractionated heparin, found that patients who achieved a therapeutic aPTT within 24 hours had lower in-hospital and 30-day mortality rates than those who did not achieve the first therapeutic aPTT until more than 24 hours after starting unfractionated heparin infusion.

Such data lend support to the widely accepted practice and current guideline recommendation⁸ of using laboratory assays to adjust the dose of unfractionated heparin to achieve and maintain a therapeutic target. The use of dosing nomograms significantly reduces the time to achieve a therapeutic aPTT while minimizing subtherapeutic and supratherapeutic unfractionated heparin levels.^19,20

THE aPTT REFLECTS THROMBIN INHIBITION

The aPTT has a log-linear relationship with plasma concentrations of unfractionated heparin,²¹ but it was not developed specifically for monitoring unfractionated heparin therapy. Originally described in 1953 as a screening tool for hemophilia,^22–24 the aPTT is prolonged in the setting of factor deficiencies (typically with levels < 45%, except for factors VII and XIII), as well as lupus anticoagulants and therapy with parenteral direct thrombin inhibitors.^8,25,26

Because thrombin (factor IIa) is 10 times more sensitive than factor Xa to inhibition by the heparin-antithrombin complex,^4,7 thrombin inhibition appears to be the most likely mechanism by which unfractionated heparin prolongs the aPTT. In contrast, aPTT is minimally or not at all prolonged by low-molecular-weight heparins, which are predominantly factor Xa inhibitors.⁷

HEPARIN ASSAYS MEASURE UNFRACTIONATED HEPARIN ACTIVITY

While the aPTT is a surrogate marker of unfractionated heparin activity in plasma, unfractionated heparin activity can be measured more precisely by so-called heparin assays, which are typically not direct measures of the plasma concentration of heparins, but rather functional assays that provide indirect estimates. They include protamine sulfate titration assays and anti-Xa assays.

Protamine sulfate titration assays measure the amount of protamine sulfate required to neutralize heparin: the more protamine required, the greater the estimated concentration of unfractionated heparin in plasma.^8,27–29 Protamine titration assays are technically demanding, so they are rarely used clinically.

Anti-Xa assays provide a measure of the functional level of heparins in plasma.^29–33 Chromogenic anti-Xa assays are available on automated analyzers with standardized kits^29,33,34 and may be faster to perform than the aPTT.³⁵

Experiments in rabbits show that unfractionated heparin inhibits thrombus formation and extension at concentrations of 0.2 to 0.4 U/mL as measured by the protamine titration assay,²⁷ which correlated with an anti-Xa activity of 0.35 to 0.67 U/mL in a randomized controlled trial.³²

Assays that directly measure the plasma concentration of heparin exist but are not clinically relevant because they also measure heparin molecules lacking the pentasaccharide sequence, which have no anticoagulant activity.³⁶

 

 

ANTI-Xa ASSAY VS THE aPTT

Anti-Xa assays are more expensive than the aPTT and are not available in all hospitals. For these reasons, the aPTT remains the most commonly used laboratory assay for monitoring unfractionated heparin therapy.

However, the aPTT correlates poorly with the activity level of unfractionated heparin in plasma. In one study, an anti-Xa level of 0.3 U/mL corresponded to aPTT results ranging from 47 to 108 seconds.³¹ Furthermore, in studies that used a heparin therapeutic target based on an aPTT ratio 1.5 to 2.5 times the control aPTT value, the lower end of that target range was often associated with subtherapeutic plasma unfractionated heparin activity measured by anti-Xa and protamine titration assays.^28,31

Because of these limitations, individual laboratories should determine their own aPTT therapeutic target ranges for unfractionated heparin based on the response curves obtained with the reagent and coagulometer used. The optimal therapeutic aPTT range for treating acute venous thromboembolism should be defined as the aPTT range (in seconds) that correlates with a plasma activity level of unfractionated heparin of 0.3 to 0.7 U/mL based on a chromogenic anti-Xa assay, or 0.2 to 0.4 U/mL based on a protamine titration assay.^32,34–36

Nevertheless, the anticoagulant effect of unfractionated heparin as measured by the aPTT can be unpredictable and can vary widely among individuals and in the same patient.⁷ This wide variability can be explained by a number of technical and biologic variables. Different commercial aPTT reagents, different lots of the same reagent, and different reagent and instrument combinations have different sensitivities to unfractionated heparin, which can lead to variable aPTT results.³⁷ Moreover, high plasma levels of acute-phase proteins, low plasma antithrombin levels, consumptive coagulopathies, liver failure, and lupus anticoagulants may also affect the aPTT.^{7,25,32,36–41} These variables account for the poor correlation—ranging from 25% to 66%—reported between aPTT and anti-Xa assays.^32,42–48

Such discrepancies may have serious clinical implications: if a patient’s aPTT is low (subtherapeutic) or high (supratherapeutic) but the anti-Xa assay result is within the therapeutic range (0.3–0.7 units/mL), changing the dose of unfractionated heparin (guided by an aPTT nomogram) may increase the risk of bleeding or of recurrent thromboembolism.

CLINICAL APPLICABILITY OF THE ANTI-Xa ASSAY

Neither anti-Xa nor protamine titration assays are standardized across reference laboratories, but chromogenic anti-Xa assays have better interlaboratory correlation than the aPTT^49,50 and can be calibrated specifically for unfractionated or low-molecular-weight heparins.^29,33

Although reagent costs are higher for chromogenic anti-Xa assays than for the aPTT, some technical variables (described below) may partially offset the cost difference.^29,33,41 In addition, unlike the aPTT, anti-Xa assays do not need local calibration; the therapeutic range for unfractionated heparin is the same (0.3–0.7 U/mL) regardless of instrument or reagent.^33,41

Most important, studies have found that patients monitored by anti-Xa assay achieve significantly higher rates of therapeutic anticoagulation within 24 and 48 hours after starting unfractionated heparin infusion than those monitored by the aPTT. Fewer dose adjustments and repeat tests are required, which may also result in lower cost.^32,51–55

While these studies found chromogenic anti-Xa assays better for achieving laboratory end points, data regarding relevant clinical outcomes are more limited. In a retrospective, observational cohort study,⁵¹ the rate of venous thromboembolism or bleeding-related death was 2% in patients receiving unfractionated heparin therapy monitored by anti-Xa assay and 6% in patients monitored by aPTT (P = .62). Rates of major hemorrhage were also not significantly different.

In a randomized controlled trial³² in 131 patients with acute venous thromboembolism and heparin resistance, rates of recurrent venous thromboembolism were 4.6% and 6.1% in the groups randomized to anti-Xa and aPTT monitoring, respectively, whereas overall bleeding rates were 1.5% and 6.1%, respectively. Again, the differences were not statistically significant.

Though some have suggested that the anti-Xa should be the preferred monitoring assay for intravenous unfractionated heparin therapy,^29,41 the ideal assay has not been established by large-scale randomized controlled trials correlating different assays with meaningful clinical outcomes.^8,33 Nevertheless, anti-Xa assays are considered the most accurate method of monitoring unfractionated heparin in cases of heparin resistance or lupus anticoagulant, and in other clinical circumstances (Table 1).^56–58

Heparin resistance. Some patients require unusually high doses of unfractionated heparin to achieve a therapeutic aPTT: typically, more than 35,000 U over 24 hours,^7,8,32 or total daily doses that exceed their estimated weight-based requirements. Heparin resistance has been observed in various clinical settings.^{7,8,32,37–40,59–61} Patients with heparin resistance monitored by anti-Xa had similar rates of recurrent venous thromboembolism while receiving significantly lower doses of unfractionated heparin than those monitored by the aPTT.³²

Lupus anticoagulant. Patients with the specific antiphospholipid antibody known as lupus anticoagulant frequently have a prolonged baseline aPTT,²⁵ making it an unreliable marker of anticoagulant effect for intravenous unfractionated heparin therapy.

Critically ill infants and children. Arachchillage et al³⁵ found that infants (< 1 year old) treated with intravenous unfractionated heparin in an intensive care department had only a 32.4% correlation between aPTT and anti-Xa levels, which was lower than that found in children ages 1 to 15 (66%) and adults (52%). In two-thirds of cases of discordant aPTT and anti-Xa levels, the aPTT was elevated (supratherapeutic) while the anti-Xa assay was within the therapeutic range (0.3–0.7 U/mL). Despite the lack of data on clinical outcomes (eg, rates of thrombosis and bleeding) with the use of an anti-Xa assay, it has been considered the method of choice for unfractionated heparin monitoring in critically ill children, and especially in those under age 1.^{41,44,62–64}

While anti-Xa assays may also be better for unfractionated heparin monitoring in critically ill adults, the lack of clinical outcome data from large-scale randomized trials has precluded evidence-based recommendations favoring them over the aPTT.^8,34

 

 

LIMITATIONS OF ANTI-Xa ASSAYS

Anti-Xa assays are hampered by some technical limitations:

Samples must be processed within 1 hour to avoid heparin neutralization.³⁴

Samples must be clear. Hemolyzed or opaque samples (eg, due to bilirubin levels > 6.6 mg/dL or triglyceride levels > 360 mg/dL) cannot be processed, as they can cause falsely low levels.

Exposure to other anticoagulants can interfere with the results. The anti-Xa assay may be unreliable for unfractionated heparin monitoring in patients who are transitioned from low-molecular-weight heparins, fondaparinux, or an oral factor Xa inhibitor (apixaban, betrixaban, edoxaban, rivaroxaban) to intravenous unfractionated heparin, eg, due to hospitalization or acute kidney injury.^65,66 Different reports have found that anti-Xa assays may be elevated for as long as 63 to 96 hours after the last dose of oral Xa inhibitors,^67–69 potentially resulting in underdosing of unfractionated heparin. In such settings, unfractionated heparin therapy should be monitored by the aPTT.

ANTI-Xa ASSAYS AND LOW-MOLECULAR-WEIGHT HEPARINS

Most patients receiving low-molecular-weight heparins do not need laboratory monitoring.⁸ Alhenc-Gelas et al⁷⁰ randomized patients to receive dalteparin in doses either based on weight or guided by anti-Xa assay results, and found that dose adjustments were rare and lacked clinical benefit.

However, the use of low-molecular-weight heparin-specific anti-Xa assays should be considered for certain patients (Table 2).⁸

The suggested therapeutic anti-Xa levels for low-molecular-weight heparins are:

• 0.5–1.2 U/mL for twice-daily enoxaparin
• 1.0–2.0 U/mL for once-daily enoxaparin or dalteparin.

Levels should be measured at peak plasma level (ie, 3–4 hours after subcutaneous injection, except during pregnancy, when it is 4–6 hours), and only after at least 3 doses of low-molecular-weight heparin.^8,71 Unlike the anti-Xa therapeutic range recommended for unfractionated heparin therapy, these ranges are not based on prospective data, and if the assay result is outside the suggested therapeutic target range, current guidelines offer no advice on safely adjusting the dose.^8,71

Measuring anti-Xa activity is particularly important for pregnant women with a mechanical prosthetic heart valve who are treated with low-molecular-weight heparins. In this setting, valve thrombosis and cardioembolic events have been reported in patients with peak low-molecular-weight heparin anti-Xa assay levels below or even at the lower end of the therapeutic range, and increased bleeding risk has been reported with elevated anti-Xa levels.^71–74 Measuring trough low-molecular-weight heparin anti-Xa levels has been suggested to guide dose adjustments during pregnancy.⁷⁵

Clearance of low-molecular-weight heparins as measured by the anti-Xa assay is highly correlated with creatinine clearance.^76,77 A strong linear correlation has been demonstrated between creatine clearance and anti-Xa levels of enoxaparin after multiple therapeutic doses, and low-molecular-weight heparins accumulate in the plasma, especially in patients with creatine clearance less than 30 mL/min.⁷⁸ The risk of major bleeding is significantly increased in patients with severe renal insufficiency (creatinine clearance < 30 mL/min) not on dialysis who are treated with either prophylactic or therapeutic doses of low-molecular-weight heparin.^79–81 In a meta-analysis, the risk of bleeding with therapeutic-intensity doses of enoxaparin was 4 times higher than with prophylactic-intensity doses.⁷⁹ Although bleeding risk appears to be reduced when the enoxaparin dose is reduced by 50%,⁸ the efficacy and safety of this strategy has not been determined by prospective trials.

ANTI-Xa ASSAYS IN PATIENTS RECEIVING DIRECT ORAL ANTICOAGULANTS

Direct oral factor Xa inhibitors cannot be measured accurately by heparin anti-Xa assays. Nevertheless, such assays may be useful to assess whether clinically relevant plasma levels are present in cases of major bleeding, suspected anticoagulant failure, or patient noncompliance.⁸²

Intense research has focused on developing drug-specific chromogenic anti-Xa assays using calibrators and standards for apixaban, edoxaban, and rivaroxaban,^82,83 and good linear correlation has been shown with some assays.^82,84 In patients treated with oral factor Xa inhibitors who need to undergo an urgent invasive procedure associated with high bleeding risk, use of a specific reversal agent may be considered with drug concentrations more than 30 ng/mL measured by a drug-specific anti-Xa assay. A similar suggestion has been made for drug concentrations more than 50 ng/mL in the setting of major bleeding.⁸⁵ Unfortunately, such assays are not widely available at this time.^82,86

While drug-specific anti-Xa assays could become clinically important to guide reversal strategies, their relevance for drug monitoring remains uncertain. This is because no therapeutic target ranges have been established for any of the direct oral anticoagulants, which were approved on the basis of favorable clinical trial outcomes that neither measured nor were correlated with specific drug levels in plasma. Therefore, a specific anti-Xa level cannot yet be used as a marker of clinical efficacy for any specific oral direct Xa inhibitor.

A 48-year-old man presents to his primary care physician because of progressively decreasing energy and gradual decline in both libido and erectile function for the past 18 months. He has noticed decreased morning erections as well. He rates his libido at 3 to 4 on a scale of 10 for the past 6 months. He also reports poor motivation, depressed mood, impaired concentration, and sleep disturbances. He reports no hair loss, headache, or dizziness, and no decrease in shaving frequency. Review of his systems is otherwise unremarkable.

He has had dyslipidemia for 3 years and is not known to have hypertension or diabetes. His medications include atorvastatin, vitamin E, and multivitamins.

He is married with 3 children and does not wish to have more. He works as a software engineer and leads a sedentary lifestyle. He is a nonsmoker and occasionally drinks alcohol on the weekends.

On physical examination, he is alert and oriented and appears well. His height is 5 feet 10 inches (178 cm), weight 230 lb (104 kg), and body mass index (BMI) 32.8 kg/m². His blood pressure is 115/83 mm Hg and pulse rate is 82 beats per minute and regular. Findings on cardiovascular and pulmonary examination are normal. He has large fatty breasts but without palpable glandular tissue.

Abdominal examination reveals central obesity—waist circumference 48 inches (122 cm)—without tenderness or organomegaly. There are no striae.

Genitourinary examination reveals normal hair distribution, a normal-sized penis, and slightly soft testes with testicular volume of 18–20 mL bilaterally.

His primary care physician suspects that he has low testosterone and orders some basic laboratory tests; the results are normal except for a low total testosterone level (Table 1).

FURTHER TESTING

1. Which of the following tests should his physician order next?

• Repeat total testosterone measurement
• Free testosterone measurement by commercial assay
• Calculated free testosterone
• Bioavailable testosterone measurement
• Serum inhibin B measurement

This patient presents with several nonspecific symptoms. But collectively they suggest testosterone deficiency (hypogonadism).

Symptoms and signs of low testosterone vary according to age of onset. Prepubertal onset is associated with incomplete or delayed puberty, no development of secondary sexual characteristics, eunuchoid features, and small penis and testes. Postpubertal onset is associated with a wide array of symptoms (Table 2). Most manifestations of low testosterone are nonspecific, such as fatigue, impaired concentration, and sleep disturbance.¹

Together, erectile dysfunction, low libido, and decreased morning erections strongly suggest hypogonadism.² Loss of body hair and decreased shaving frequency are specific symptoms of hypogonadism; however, they require years to develop.³ Gynecomastia can also occur due to loss of the inhibitory action of testosterone on breast growth and a relative increase in estradiol. This occurs more in primary hypogonadism, due to the increase in luteinizing hormone (LH), which stimulates the remaining Leydig cells to secrete estradiol rather than testosterone.⁴

Screening for hypogonadism in men may be warranted in several conditions, even without clinical manifestations of low testosterone (Table 3).^5–10

To diagnose hypogonadism in men and to start treatment for it, current guidelines recommend that the patient should have clinical features as well as laboratory evidence of low testosterone.^5,6

Measuring testosterone: Total, free, bound, and bioavailable

Testosterone, a steroid hormone, circulates in the serum either as free testosterone or bound to several plasma proteins, mainly sex-hormone binding globulin (SHBG) and albumin.

Total testosterone includes both the free and bound fractions, whereas bioavailable testosterone includes both free and the portion bound to albumin, which has low affinity and can dissociate and be used at the tissue level.¹¹

Low levels of total testosterone do not necessarily reflect a hypogonadal state, as a man with altered SHBG levels or binding capabilities can have low total but normal free testosterone levels and no manifestations.¹² Several conditions can alter the levels of SHBG, including obesity, diabetes, aging, thyroid dysfunction, and others.^5,13

Because our patient is obese, his total testosterone level is not a reliable indicator of hypogonadism, and repeating its measurement will not add diagnostic value.

Therefore, an alternative measurement should be used to accurately reflect the testosterone levels. From a physiologic point of view, bioavailable testosterone is the active form of testosterone and is the most accurate to be measured in a patient with hypogonadism. Nevertheless, because of technical difficulties in its measurement and lack of evidence correlating bioavailable testosterone with the clinical picture of hypogonadism, it is recommended that the level of free testosterone be used.⁵

The gold standard for direct measurement of serum free testosterone is equilibrium dialysis, but this is expensive and time-consuming.¹⁴ Commercial assays for free testosterone exist but have been deemed unreliable.^14,15 It is recommended that free testosterone be measured by equilibrium dialysis or calculated using equations based on total testosterone, SHBG, and albumin levels.⁵ These equations are reliable and give results very close to the values obtained by equilibrium dialysis.¹⁵ Therefore, in our patient, it would be suitable to calculate the free testosterone level next.

Serum levels of free testosterone vary according to several factors. Diurnal variation of testosterone has been established: levels are highest in the morning and decline throughout the day.¹⁶ Food decreases testosterone levels.¹⁷ In addition, there is considerable day-to-day variation.¹8 Therefore, at least 2 readings of fasting morning testosterone on 2 separate days are recommended for the diagnosis of hypogonadism.⁵

Inhibin B is a hormone produced by Sertoli cells in the testes in response to follicle-stimulating hormone (FSH) stimulation. In turn, it acts as negative feedback, together with testosterone, to inhibit FSH release from the pituitary. Inhibin B has been shown to reflect spermatogenesis in the testes and therefore fertility.¹⁹ Inhibin B levels were found to be low in patients with central hypogonadism, due to less FSH release; however, they did not correlate with testosterone levels.²⁰

 

 

CASE RESUMED: CHARACTERIZING HIS HYPOGONADISM

The patient’s physician orders morning fasting total testosterone, SHBG, and albumin testing and calculates the free testosterone level, which yields a value of 3 ng/dL (reference range 4.5–17). This is confirmed by a repeat measurement, which yields a value of 2.9 ng/dL. Laboratory test results combined with his clinical presentation are consistent with hypogonadism.

2. What is the most appropriate next step?

• Measurement of serum LH and FSH
• Measurement of serum prolactin
• Scrotal ultrasonography
• Gonadotropin-releasing hormone (GnRH) stimulation test
• Semen analysis

After hypogonadism is diagnosed, it is important to distinguish if it is primary or central. This is achieved by measuring serum LH and FSH.⁵ All biotin supplements should be stopped at least 72 hours before measuring LH and FSH, as biotin can interfere with the assays, yielding false values.²¹

Secretion of FSH and LH from the anterior pituitary is under the influence of pulsatile release of GnRH from the hypothalamus. LH acts on Leydig cells in the testes to produce testosterone, whereas FSH acts on Sertoli cells, together with testosterone, to bring about spermatogenesis in the seminiferous tubules. Testosterone acts centrally as negative feedback to decrease the release of LH and FSH.

Primary hypogonadism occurs due to testicular failure, ie, the testes themselves fail to produce testosterone, leading to hypogonadism. The decrease in testosterone levels, together with inhibin B if Sertoli cells are damaged, lead to loss of negative feedback on the hypothalamus and pituitary, and therefore increased levels of LH and FSH. This is termed hypergonadotropic hypogonadism. Testicular failure may also result in impaired spermatogenesis and infertility due to destruction of testicular structures, in which case fertility cannot be restored.

Central hypogonadism occurs when the pituitary fails to produce LH and FSH (secondary hypogonadism) or when the hypothalamus fails to produce GnRH and subsequently the lack of secretion of LH and FSH from the pituitary (tertiary hypogonadism). The lack of LH will result in no stimulation of Leydig cells to produce testosterone, and therefore its deficiency. Serum hormone levels in central hypogonadism will reveal low testosterone, with either low or inappropriately normal gonadotropins (LH and FSH). This is termed hypogonadotropic hypogonadism. The lack of FSH, together with testosterone deficiency will also result in decreased spermatogenesis and therefore infertility. Testicular structures are preserved, however, and fertility can be restored with appropriate therapy, as discussed below.

Prolactin should be measured only if the patient has central hypogonadism. Its measurement is not warranted at this point in the patient’s workup. The implications of prolactin and its relationship to hypogonadism will be discussed later.

Although, this stepwise approach is not convenient for many patients, some physicians follow it because it is cost-effective, especially in those who are not insured. However, other physicians order FSH, LH, and sometimes prolactin with the confirmatory low testosterone measurement. Laboratories can also be instructed to wait to measure the pituitary hormones and to do so only if low testosterone is confirmed.

Varicocele, a possible cause of male infertility, can also impair Leydig cell function and cause low testosterone. In fact, surgical repair of varicocele has been demonstrated to increase serum testosterone.²² Scrotal ultrasonography is used to diagnose varicocele, but this also should be ordered at a later stage in the workup if primary hypogonadism is diagnosed.

The GnRH stimulation test is important for the diagnosis and evaluation of precocious or delayed puberty in children. In boys with delayed puberty, a poorer response to GnRH stimulation indicates central hypogonadism rather than constitutional delay.²³ It has no role in the evaluation of postpubertal or adult-onset hypogonadism.

Semen analysis is important to evaluate fertility if the patient is interested in further procreation.⁵ Low testosterone levels may result in impaired spermatogenesis and therefore infertility. On the other hand, treatment with exogenous testosterone will also result in infertility, by feedback inhibition of LH and FSH and therefore inhibition of spermatogenesis. If the patient wishes to preserve fertility, treatment options other than testosterone should be considered; examples include clomiphene citrate, human menopausal gonadotropin, and human chorionic gonadotropin.^23,24

Our patient has no desire to expand his family; therefore, a semen analysis and attempts to preserve spermatogenesis are not indicated.

 

 

CASE RESUMED: SEARCHING FOR CAUSES

His physician orders testing of serum LH and FSH, yielding the following values:

• LH 1.6 mIU/mL (reference range 1.8–12)
• FSH 1.9 mIU/mL (reference range 1.5–12.5).

The diagnosis of central hypogonadism is established.

3. Which investigation is the least appropriate in the further evaluation of this patient?

• 
  Serum free thyroxine (T₄) and morning cortisol measurement
• Serum prolactin measurement
• Serum ferritin measurement
• Pituitary magnetic resonance imaging (MRI)
• Chromosomal karyotyping

The diagnosis of central hypogonadism warrants evaluation for possible causes. These are summarized in Table 4.

Serum free thyroxine and morning cortisol

Since this patient’s LH and FSH values are abnormal, it is important to evaluate the status of other anterior pituitary hormones. In patients with pituitary abnormalities, serum free T₄ is a more reliable test for assessing thyroid function than thyroid-stimulating hormone (TSH), because of loss of the negative feedback of thyroid hormones on the diseased pituitary. In contrast, serum TSH is considered the best single thyroid test to assess primary thyroid dysfunction.

Other measurements include prolactin and morning cortisol (reflecting adrenocorticotropic hormone status).

Prolactin measurement

Prolactin measurement is important to evaluate for hyperprolactinemia, as this will lead to hypogonadism by inhibition of GnRH secretion.²⁵ Different pathologic, pharmacologic, and physiologic conditions can result in hyperprolactinemia, including prolactinomas, other pituitary and hypothalamic lesions, primary hypothyroidism, and medications such as antipsychotics.²⁵ Dopamine agonists are the mainstay treatment for hyperprolactinemia.

Ferritin measurement

Ferritin measurement is indicated to diagnose iron overload conditions such as hemochromatosis, which can result in primary hypogonadism via testicular damage or in secondary hypogonadism via pituitary damage.²⁶

Pituitary MRI with contrast

Pituitary MRI with contrast is used to diagnose structural lesions of the pituitary or hypothalamus. This diagnostic modality is indicated for patients with pituitary dysfunction, including central hypogonadism, manifestations of a mass effect (headache, visual field defects), persistent hyperprolactinemia, and panhypopituitarism, among others. To improve the diagnostic yield of pituitary MRI, the Endocrine Society guidelines recommend it for men with serum total testosterone levels below 150 ng/dL.⁵ However, some clinicians have a lower threshold for ordering pituitary MRI for patients with central hypogonadism. Physician judgment and expertise should be exercised and the decision made on an individual basis.

Chromosomal karyotyping

Chromosomal karyotyping is not indicated in our patient. It is reserved for those with primary hypogonadism to diagnose Klinefelter syndrome, which has a karyotype of 47,XXY.

CASE RESUMED: MOSH SYNDROME

Our patient’s prolactin, free T₄, morning cortisol, and ferritin levels are measured, yielding normal values. No abnormalities are seen on pituitary MRI. A clinical reevaluation is conducted, revealing no history of head trauma or head and neck radiation. The lack of an obvious cause in our patient’s clinical presentation and workup, together with his obesity (BMI 32.8 kg/m²) supports the diagnosis of obesity as the cause of his hypogonadism.

Obesity can be a cause of secondary hypogonadism, which has led to the term “MOSH” (male obesity-associated secondary hypogonadism) syndrome. In fact, a cross-sectional study has demonstrated that 40% of nondiabetic obese (BMI ≥ 30 kg/m²) men over age 45 have low serum free testosterone levels, compared with 26% for lean (BMI < 25 kg/m²) men.²⁷ Moreover, obesity has been found to be a strong predictor of testosterone replacement therapy.²⁸ Other studies have also found an inverse relationship between BMI and testosterone levels.²⁹

Several mechanisms interact in the pathogenesis of MOSH syndrome. Adipose tissue possesses aromatase activity, which converts androgens into estrogens.³⁰ Peripheral estrogen production can in turn exert feedback inhibition on pituitary gonadotropin secretion.³¹ In obese men, increased adipose tissue leads to increased aromatase activity and more estrogen, so more feedback inhibition on the pituitary and subsequently secondary hypogonadism. 


Leptin, a hormone produced by adipocytes, is also increased in obesity, and was found to be inversely correlated with serum testosterone.³² Studies have demonstrated that leptin has an inhibitory effect on the enzymatic pathway that synthesizes testosterone in Leydig cells.³³

Proinflammatory cytokines have also been implicated, as central obesity is associated with an increase in these cytokines, which in turn act negatively on the hypothalamus and impair GnRH release leading to lower testosterone.^34,35

Treating obesity-related hypogonadism

In a pilot study,³⁶ lifestyle attempts to reduce obesity were shown to improve hormonal levels. Bariatric surgery has also been demonstrated to be successful.³⁷

Clomiphene citrate, a selective estrogen receptor modulator, increases endogenous testosterone secretion by inhibiting the negative feedback of estrogen on the hypothalamus and pituitary and thus increasing LH and FSH. It also preserves endogenous testosterone production, since it does not suppress the hypothalamic-pituitary-testicular axis.³⁸ This made clomiphene citrate a potential treatment for men with central hypogonadism including those with MOSH.³⁹

Nevertheless, there are no randomized trials to prove its safety and efficacy in the management of central hypogonadism.⁵ Regarding its use in men wishing to preserve fertility, most studies did not show improvement. However, a meta-analysis demonstrated statistically significant increased pregnancy rates in partners of men with idiopathic infertility if the men used 50 mg of clomiphene citrate daily.⁴⁰

Testosterone deficiency can be a marker of metabolic syndrome, which needs to be managed more urgently than hypogonadism. A cross-sectional study found not only an association between metabolic syndrome and low serum testosterone, but also with each individual component of metabolic syndrome on its own, all of which need to be addressed.¹⁰

 

 

CASE CONTINUED: BEGINNING TREATMENT

The physician counsels the patient regarding the implications, potential adverse outcomes, and available treatments for his obesity, including lifestyle modification and bariatric surgery. The patient declines surgery and wishes to adopt a weight-reducing diet and exercise program, for which he is referred to a dietitian.

In addition, in view of the patient’s clinically and biochemically proven hypogonadism, his physician offers testosterone replacement therapy. He orders a serum prostate-specific antigen (PSA) level, which is 1.3 ng/dL (reference range < 4 ng/dL). The patient is prescribed 5 g of 1% testosterone gel daily.

TESTOSTERONE REPLACEMENT THERAPY

4. Which is the most common adverse effect of testosterone replacement therapy?

• Cardiovascular events
• Erythrocytosis
• Prostate cancer
• Infertility
• Obstructive sleep apnea

Testosterone is indicated for men with an established diagnosis of hypogonadism. The benefits of testosterone replacement are summarized in Table 5.^5,6

Clinicians should be very cautious in initiating testosterone replacement therapy in any patient with an unstable medical condition.

There are several formulations of testosterone replacement therapy, including intramuscular injections, transdermal gels or patches, buccal tablets, an intranasal gel, and oral tablets. Of note, there are 2 different forms of oral testosterone preparations: testosterone undecanoate and 17-alpha alkylated testosterone. The former is unavailable in the United States and the latter is not recommended for use due to its proven hepatic toxicity.⁴¹

Testosterone and erythrocytosis

Meta-analyses have concluded that the most frequent adverse event of testosterone replacement therapy is a significant rise in hematocrit.⁴² This rise was found to be dose-dependent and was more marked in older men.⁴³ Although all preparations can cause erythrocytosis, parenteral forms have been observed to raise it the most, particularly short-term injectables.^44,45

The mechanism behind this increase is attributed to increased erythropoietin levels and improved usage of iron for red blood cell synthesis.⁴⁶ In fact, testosterone replacement therapy has been shown to improve hemoglobin levels in patients with anemia.⁴⁷ On the other hand, increasing hematocrit levels may lead to thrombotic and vasoocclusive events.⁴⁴

It is strongly recommended that baseline hematocrit levels be measured before initiating testosterone replacement therapy.^5,6 The hematocrit level should also be monitored 3 to 6 months into treatment and yearly thereafter while on testosterone.⁵Figure 1 summarizes the appropriate steps to undertake regarding hematocrit levels, according to the American Urological Association.⁶

Testosterone and prostate cancer

The relationship between testosterone treatment and prostate cancer has long been studied. Historically, testosterone replacement therapy was believed to increase the risk of prostate cancer; however, recent studies and meta-analyses have shown that this is not the case.^42,48 Nevertheless, clinical guidelines still recommend prostate monitoring for men on testosterone replacement therapy.^5,6

Furthermore, the clinician should make sure the patient does not have prostate cancer before initiating testosterone replacement therapy. Since there is a significant incidence of prostate cancer in men with serum PSA of 2.5–4.0 ng/mL, a patient with hypogonadism and a serum PSA in that range or higher should have appropriate evaluation before initiating testosterone replacement therapy.⁴⁹ The Endocrine Society recommendations for prostate monitoring are summarized in Table 6.⁵

Testosterone and cardiovascular risk

The evidence regarding this issue has been contradictory and inconsistent. Meta-analyses have demonstrated that low testosterone is associated with higher risk of major adverse cardiovascular events.⁵⁰ These studies argue for the use of testosterone replacement therapy in hypogonadal men to decrease the risk. However, other studies and meta-analyses have found that testosterone replacement therapy is associated with increased cardiovascular risk and have concluded that major adverse cardiac events are in fact a risk of testosterone replacement therapy.⁵¹

Current recommendations advocate against the use of testosterone replacement therapy in men with uncontrolled heart failure or with cardiovascular events in the past 3 to 6 months.^5,6 Cardiovascular risk factors should be addressed and corrected, and patients should be educated on cardiovascular symptoms and the need to report them if they occur.

Testosterone and infertility

As described earlier, testosterone replacement therapy increases negative feedback on the pituitary and decreases LH and FSH production, leading to less spermatogenesis. Other treatment options should be sought for hypogonadal men wishing to preserve fertility.

Other adverse effects

Other adverse effects of testosterone replacement therapy include acne, oily skin, obstructive sleep apnea, gynecomastia, and balding.

Given all the adverse events that can be associated with testosterone replacement therapy, the risks and benefits of treating hypogonadism in each patient should be taken into consideration, and an individualized approach is required.

 

 

CASE RESUMED: FOLLOW-UP

The patient presents 3 months later for follow-up. He reports significant improvement in his presenting symptoms including energy, libido, and erectile function. He also reports some improvement in his mood and concentration. He has lost 12 lb (5.4 kg) and is still trying to improve his diet and exercise program. He is compliant with his testosterone gel therapy.

His serum calculated free testosterone level is 7.8 ng/dL (4.5–17), and his hematocrit is 46%. The patient is instructed to continue his treatment and to return after 9 months for further follow-up.

TAKE-HOME POINTS

• Men with hypogonadism usually present with nonspecific manifestations, so clinicians should keep a high index of suspicion.
• Both clinical and biochemical evidence of hypogonadism should be present to diagnose and start treatment for it.
• Low levels of serum total testosterone do not necessarily reflect hypogonadism.
• The hormonal profile of central hypogonadism reveals low serum testosterone with low or inappropriately normal serum LH and FSH levels.

Obesity can cause central hypogonadism and should be suspected after pituitary and other systemic causes are excluded.

A 48-year-old man presents to his primary care physician because of progressively decreasing energy and gradual decline in both libido and erectile function for the past 18 months. He has noticed decreased morning erections as well. He rates his libido at 3 to 4 on a scale of 10 for the past 6 months. He also reports poor motivation, depressed mood, impaired concentration, and sleep disturbances. He reports no hair loss, headache, or dizziness, and no decrease in shaving frequency. Review of his systems is otherwise unremarkable.

He has had dyslipidemia for 3 years and is not known to have hypertension or diabetes. His medications include atorvastatin, vitamin E, and multivitamins.

He is married with 3 children and does not wish to have more. He works as a software engineer and leads a sedentary lifestyle. He is a nonsmoker and occasionally drinks alcohol on the weekends.

On physical examination, he is alert and oriented and appears well. His height is 5 feet 10 inches (178 cm), weight 230 lb (104 kg), and body mass index (BMI) 32.8 kg/m². His blood pressure is 115/83 mm Hg and pulse rate is 82 beats per minute and regular. Findings on cardiovascular and pulmonary examination are normal. He has large fatty breasts but without palpable glandular tissue.

Abdominal examination reveals central obesity—waist circumference 48 inches (122 cm)—without tenderness or organomegaly. There are no striae.

Genitourinary examination reveals normal hair distribution, a normal-sized penis, and slightly soft testes with testicular volume of 18–20 mL bilaterally.

His primary care physician suspects that he has low testosterone and orders some basic laboratory tests; the results are normal except for a low total testosterone level (Table 1).

FURTHER TESTING

1. Which of the following tests should his physician order next?

• Repeat total testosterone measurement
• Free testosterone measurement by commercial assay
• Calculated free testosterone
• Bioavailable testosterone measurement
• Serum inhibin B measurement

This patient presents with several nonspecific symptoms. But collectively they suggest testosterone deficiency (hypogonadism).

Symptoms and signs of low testosterone vary according to age of onset. Prepubertal onset is associated with incomplete or delayed puberty, no development of secondary sexual characteristics, eunuchoid features, and small penis and testes. Postpubertal onset is associated with a wide array of symptoms (Table 2). Most manifestations of low testosterone are nonspecific, such as fatigue, impaired concentration, and sleep disturbance.¹

Together, erectile dysfunction, low libido, and decreased morning erections strongly suggest hypogonadism.² Loss of body hair and decreased shaving frequency are specific symptoms of hypogonadism; however, they require years to develop.³ Gynecomastia can also occur due to loss of the inhibitory action of testosterone on breast growth and a relative increase in estradiol. This occurs more in primary hypogonadism, due to the increase in luteinizing hormone (LH), which stimulates the remaining Leydig cells to secrete estradiol rather than testosterone.⁴

Screening for hypogonadism in men may be warranted in several conditions, even without clinical manifestations of low testosterone (Table 3).^5–10

To diagnose hypogonadism in men and to start treatment for it, current guidelines recommend that the patient should have clinical features as well as laboratory evidence of low testosterone.^5,6

Measuring testosterone: Total, free, bound, and bioavailable

Testosterone, a steroid hormone, circulates in the serum either as free testosterone or bound to several plasma proteins, mainly sex-hormone binding globulin (SHBG) and albumin.

Total testosterone includes both the free and bound fractions, whereas bioavailable testosterone includes both free and the portion bound to albumin, which has low affinity and can dissociate and be used at the tissue level.¹¹

Low levels of total testosterone do not necessarily reflect a hypogonadal state, as a man with altered SHBG levels or binding capabilities can have low total but normal free testosterone levels and no manifestations.¹² Several conditions can alter the levels of SHBG, including obesity, diabetes, aging, thyroid dysfunction, and others.^5,13

Because our patient is obese, his total testosterone level is not a reliable indicator of hypogonadism, and repeating its measurement will not add diagnostic value.

Therefore, an alternative measurement should be used to accurately reflect the testosterone levels. From a physiologic point of view, bioavailable testosterone is the active form of testosterone and is the most accurate to be measured in a patient with hypogonadism. Nevertheless, because of technical difficulties in its measurement and lack of evidence correlating bioavailable testosterone with the clinical picture of hypogonadism, it is recommended that the level of free testosterone be used.⁵

The gold standard for direct measurement of serum free testosterone is equilibrium dialysis, but this is expensive and time-consuming.¹⁴ Commercial assays for free testosterone exist but have been deemed unreliable.^14,15 It is recommended that free testosterone be measured by equilibrium dialysis or calculated using equations based on total testosterone, SHBG, and albumin levels.⁵ These equations are reliable and give results very close to the values obtained by equilibrium dialysis.¹⁵ Therefore, in our patient, it would be suitable to calculate the free testosterone level next.

Serum levels of free testosterone vary according to several factors. Diurnal variation of testosterone has been established: levels are highest in the morning and decline throughout the day.¹⁶ Food decreases testosterone levels.¹⁷ In addition, there is considerable day-to-day variation.¹8 Therefore, at least 2 readings of fasting morning testosterone on 2 separate days are recommended for the diagnosis of hypogonadism.⁵

Inhibin B is a hormone produced by Sertoli cells in the testes in response to follicle-stimulating hormone (FSH) stimulation. In turn, it acts as negative feedback, together with testosterone, to inhibit FSH release from the pituitary. Inhibin B has been shown to reflect spermatogenesis in the testes and therefore fertility.¹⁹ Inhibin B levels were found to be low in patients with central hypogonadism, due to less FSH release; however, they did not correlate with testosterone levels.²⁰

 

 

CASE RESUMED: CHARACTERIZING HIS HYPOGONADISM

The patient’s physician orders morning fasting total testosterone, SHBG, and albumin testing and calculates the free testosterone level, which yields a value of 3 ng/dL (reference range 4.5–17). This is confirmed by a repeat measurement, which yields a value of 2.9 ng/dL. Laboratory test results combined with his clinical presentation are consistent with hypogonadism.

2. What is the most appropriate next step?

• Measurement of serum LH and FSH
• Measurement of serum prolactin
• Scrotal ultrasonography
• Gonadotropin-releasing hormone (GnRH) stimulation test
• Semen analysis

After hypogonadism is diagnosed, it is important to distinguish if it is primary or central. This is achieved by measuring serum LH and FSH.⁵ All biotin supplements should be stopped at least 72 hours before measuring LH and FSH, as biotin can interfere with the assays, yielding false values.²¹

Secretion of FSH and LH from the anterior pituitary is under the influence of pulsatile release of GnRH from the hypothalamus. LH acts on Leydig cells in the testes to produce testosterone, whereas FSH acts on Sertoli cells, together with testosterone, to bring about spermatogenesis in the seminiferous tubules. Testosterone acts centrally as negative feedback to decrease the release of LH and FSH.

Primary hypogonadism occurs due to testicular failure, ie, the testes themselves fail to produce testosterone, leading to hypogonadism. The decrease in testosterone levels, together with inhibin B if Sertoli cells are damaged, lead to loss of negative feedback on the hypothalamus and pituitary, and therefore increased levels of LH and FSH. This is termed hypergonadotropic hypogonadism. Testicular failure may also result in impaired spermatogenesis and infertility due to destruction of testicular structures, in which case fertility cannot be restored.

Central hypogonadism occurs when the pituitary fails to produce LH and FSH (secondary hypogonadism) or when the hypothalamus fails to produce GnRH and subsequently the lack of secretion of LH and FSH from the pituitary (tertiary hypogonadism). The lack of LH will result in no stimulation of Leydig cells to produce testosterone, and therefore its deficiency. Serum hormone levels in central hypogonadism will reveal low testosterone, with either low or inappropriately normal gonadotropins (LH and FSH). This is termed hypogonadotropic hypogonadism. The lack of FSH, together with testosterone deficiency will also result in decreased spermatogenesis and therefore infertility. Testicular structures are preserved, however, and fertility can be restored with appropriate therapy, as discussed below.

Prolactin should be measured only if the patient has central hypogonadism. Its measurement is not warranted at this point in the patient’s workup. The implications of prolactin and its relationship to hypogonadism will be discussed later.

Although, this stepwise approach is not convenient for many patients, some physicians follow it because it is cost-effective, especially in those who are not insured. However, other physicians order FSH, LH, and sometimes prolactin with the confirmatory low testosterone measurement. Laboratories can also be instructed to wait to measure the pituitary hormones and to do so only if low testosterone is confirmed.

Varicocele, a possible cause of male infertility, can also impair Leydig cell function and cause low testosterone. In fact, surgical repair of varicocele has been demonstrated to increase serum testosterone.²² Scrotal ultrasonography is used to diagnose varicocele, but this also should be ordered at a later stage in the workup if primary hypogonadism is diagnosed.

The GnRH stimulation test is important for the diagnosis and evaluation of precocious or delayed puberty in children. In boys with delayed puberty, a poorer response to GnRH stimulation indicates central hypogonadism rather than constitutional delay.²³ It has no role in the evaluation of postpubertal or adult-onset hypogonadism.

Semen analysis is important to evaluate fertility if the patient is interested in further procreation.⁵ Low testosterone levels may result in impaired spermatogenesis and therefore infertility. On the other hand, treatment with exogenous testosterone will also result in infertility, by feedback inhibition of LH and FSH and therefore inhibition of spermatogenesis. If the patient wishes to preserve fertility, treatment options other than testosterone should be considered; examples include clomiphene citrate, human menopausal gonadotropin, and human chorionic gonadotropin.^23,24

Our patient has no desire to expand his family; therefore, a semen analysis and attempts to preserve spermatogenesis are not indicated.

 

 

CASE RESUMED: SEARCHING FOR CAUSES

His physician orders testing of serum LH and FSH, yielding the following values:

• LH 1.6 mIU/mL (reference range 1.8–12)
• FSH 1.9 mIU/mL (reference range 1.5–12.5).

The diagnosis of central hypogonadism is established.

3. Which investigation is the least appropriate in the further evaluation of this patient?

• 
  Serum free thyroxine (T₄) and morning cortisol measurement
• Serum prolactin measurement
• Serum ferritin measurement
• Pituitary magnetic resonance imaging (MRI)
• Chromosomal karyotyping

The diagnosis of central hypogonadism warrants evaluation for possible causes. These are summarized in Table 4.

Serum free thyroxine and morning cortisol

Since this patient’s LH and FSH values are abnormal, it is important to evaluate the status of other anterior pituitary hormones. In patients with pituitary abnormalities, serum free T₄ is a more reliable test for assessing thyroid function than thyroid-stimulating hormone (TSH), because of loss of the negative feedback of thyroid hormones on the diseased pituitary. In contrast, serum TSH is considered the best single thyroid test to assess primary thyroid dysfunction.

Other measurements include prolactin and morning cortisol (reflecting adrenocorticotropic hormone status).

Prolactin measurement

Prolactin measurement is important to evaluate for hyperprolactinemia, as this will lead to hypogonadism by inhibition of GnRH secretion.²⁵ Different pathologic, pharmacologic, and physiologic conditions can result in hyperprolactinemia, including prolactinomas, other pituitary and hypothalamic lesions, primary hypothyroidism, and medications such as antipsychotics.²⁵ Dopamine agonists are the mainstay treatment for hyperprolactinemia.

Ferritin measurement

Ferritin measurement is indicated to diagnose iron overload conditions such as hemochromatosis, which can result in primary hypogonadism via testicular damage or in secondary hypogonadism via pituitary damage.²⁶

Pituitary MRI with contrast

Pituitary MRI with contrast is used to diagnose structural lesions of the pituitary or hypothalamus. This diagnostic modality is indicated for patients with pituitary dysfunction, including central hypogonadism, manifestations of a mass effect (headache, visual field defects), persistent hyperprolactinemia, and panhypopituitarism, among others. To improve the diagnostic yield of pituitary MRI, the Endocrine Society guidelines recommend it for men with serum total testosterone levels below 150 ng/dL.⁵ However, some clinicians have a lower threshold for ordering pituitary MRI for patients with central hypogonadism. Physician judgment and expertise should be exercised and the decision made on an individual basis.

Chromosomal karyotyping

Chromosomal karyotyping is not indicated in our patient. It is reserved for those with primary hypogonadism to diagnose Klinefelter syndrome, which has a karyotype of 47,XXY.

CASE RESUMED: MOSH SYNDROME

Our patient’s prolactin, free T₄, morning cortisol, and ferritin levels are measured, yielding normal values. No abnormalities are seen on pituitary MRI. A clinical reevaluation is conducted, revealing no history of head trauma or head and neck radiation. The lack of an obvious cause in our patient’s clinical presentation and workup, together with his obesity (BMI 32.8 kg/m²) supports the diagnosis of obesity as the cause of his hypogonadism.

Obesity can be a cause of secondary hypogonadism, which has led to the term “MOSH” (male obesity-associated secondary hypogonadism) syndrome. In fact, a cross-sectional study has demonstrated that 40% of nondiabetic obese (BMI ≥ 30 kg/m²) men over age 45 have low serum free testosterone levels, compared with 26% for lean (BMI < 25 kg/m²) men.²⁷ Moreover, obesity has been found to be a strong predictor of testosterone replacement therapy.²⁸ Other studies have also found an inverse relationship between BMI and testosterone levels.²⁹

Several mechanisms interact in the pathogenesis of MOSH syndrome. Adipose tissue possesses aromatase activity, which converts androgens into estrogens.³⁰ Peripheral estrogen production can in turn exert feedback inhibition on pituitary gonadotropin secretion.³¹ In obese men, increased adipose tissue leads to increased aromatase activity and more estrogen, so more feedback inhibition on the pituitary and subsequently secondary hypogonadism. 


Leptin, a hormone produced by adipocytes, is also increased in obesity, and was found to be inversely correlated with serum testosterone.³² Studies have demonstrated that leptin has an inhibitory effect on the enzymatic pathway that synthesizes testosterone in Leydig cells.³³

Proinflammatory cytokines have also been implicated, as central obesity is associated with an increase in these cytokines, which in turn act negatively on the hypothalamus and impair GnRH release leading to lower testosterone.^34,35

Treating obesity-related hypogonadism

In a pilot study,³⁶ lifestyle attempts to reduce obesity were shown to improve hormonal levels. Bariatric surgery has also been demonstrated to be successful.³⁷

Clomiphene citrate, a selective estrogen receptor modulator, increases endogenous testosterone secretion by inhibiting the negative feedback of estrogen on the hypothalamus and pituitary and thus increasing LH and FSH. It also preserves endogenous testosterone production, since it does not suppress the hypothalamic-pituitary-testicular axis.³⁸ This made clomiphene citrate a potential treatment for men with central hypogonadism including those with MOSH.³⁹

Nevertheless, there are no randomized trials to prove its safety and efficacy in the management of central hypogonadism.⁵ Regarding its use in men wishing to preserve fertility, most studies did not show improvement. However, a meta-analysis demonstrated statistically significant increased pregnancy rates in partners of men with idiopathic infertility if the men used 50 mg of clomiphene citrate daily.⁴⁰

Testosterone deficiency can be a marker of metabolic syndrome, which needs to be managed more urgently than hypogonadism. A cross-sectional study found not only an association between metabolic syndrome and low serum testosterone, but also with each individual component of metabolic syndrome on its own, all of which need to be addressed.¹⁰

 

 

CASE CONTINUED: BEGINNING TREATMENT

The physician counsels the patient regarding the implications, potential adverse outcomes, and available treatments for his obesity, including lifestyle modification and bariatric surgery. The patient declines surgery and wishes to adopt a weight-reducing diet and exercise program, for which he is referred to a dietitian.

In addition, in view of the patient’s clinically and biochemically proven hypogonadism, his physician offers testosterone replacement therapy. He orders a serum prostate-specific antigen (PSA) level, which is 1.3 ng/dL (reference range < 4 ng/dL). The patient is prescribed 5 g of 1% testosterone gel daily.

TESTOSTERONE REPLACEMENT THERAPY

4. Which is the most common adverse effect of testosterone replacement therapy?

• Cardiovascular events
• Erythrocytosis
• Prostate cancer
• Infertility
• Obstructive sleep apnea

Testosterone is indicated for men with an established diagnosis of hypogonadism. The benefits of testosterone replacement are summarized in Table 5.^5,6

Clinicians should be very cautious in initiating testosterone replacement therapy in any patient with an unstable medical condition.

There are several formulations of testosterone replacement therapy, including intramuscular injections, transdermal gels or patches, buccal tablets, an intranasal gel, and oral tablets. Of note, there are 2 different forms of oral testosterone preparations: testosterone undecanoate and 17-alpha alkylated testosterone. The former is unavailable in the United States and the latter is not recommended for use due to its proven hepatic toxicity.⁴¹

Testosterone and erythrocytosis

Meta-analyses have concluded that the most frequent adverse event of testosterone replacement therapy is a significant rise in hematocrit.⁴² This rise was found to be dose-dependent and was more marked in older men.⁴³ Although all preparations can cause erythrocytosis, parenteral forms have been observed to raise it the most, particularly short-term injectables.^44,45

The mechanism behind this increase is attributed to increased erythropoietin levels and improved usage of iron for red blood cell synthesis.⁴⁶ In fact, testosterone replacement therapy has been shown to improve hemoglobin levels in patients with anemia.⁴⁷ On the other hand, increasing hematocrit levels may lead to thrombotic and vasoocclusive events.⁴⁴

It is strongly recommended that baseline hematocrit levels be measured before initiating testosterone replacement therapy.^5,6 The hematocrit level should also be monitored 3 to 6 months into treatment and yearly thereafter while on testosterone.⁵Figure 1 summarizes the appropriate steps to undertake regarding hematocrit levels, according to the American Urological Association.⁶

Testosterone and prostate cancer

The relationship between testosterone treatment and prostate cancer has long been studied. Historically, testosterone replacement therapy was believed to increase the risk of prostate cancer; however, recent studies and meta-analyses have shown that this is not the case.^42,48 Nevertheless, clinical guidelines still recommend prostate monitoring for men on testosterone replacement therapy.^5,6

Furthermore, the clinician should make sure the patient does not have prostate cancer before initiating testosterone replacement therapy. Since there is a significant incidence of prostate cancer in men with serum PSA of 2.5–4.0 ng/mL, a patient with hypogonadism and a serum PSA in that range or higher should have appropriate evaluation before initiating testosterone replacement therapy.⁴⁹ The Endocrine Society recommendations for prostate monitoring are summarized in Table 6.⁵

Testosterone and cardiovascular risk

The evidence regarding this issue has been contradictory and inconsistent. Meta-analyses have demonstrated that low testosterone is associated with higher risk of major adverse cardiovascular events.⁵⁰ These studies argue for the use of testosterone replacement therapy in hypogonadal men to decrease the risk. However, other studies and meta-analyses have found that testosterone replacement therapy is associated with increased cardiovascular risk and have concluded that major adverse cardiac events are in fact a risk of testosterone replacement therapy.⁵¹

Current recommendations advocate against the use of testosterone replacement therapy in men with uncontrolled heart failure or with cardiovascular events in the past 3 to 6 months.^5,6 Cardiovascular risk factors should be addressed and corrected, and patients should be educated on cardiovascular symptoms and the need to report them if they occur.

Testosterone and infertility

As described earlier, testosterone replacement therapy increases negative feedback on the pituitary and decreases LH and FSH production, leading to less spermatogenesis. Other treatment options should be sought for hypogonadal men wishing to preserve fertility.

Other adverse effects

Other adverse effects of testosterone replacement therapy include acne, oily skin, obstructive sleep apnea, gynecomastia, and balding.

Given all the adverse events that can be associated with testosterone replacement therapy, the risks and benefits of treating hypogonadism in each patient should be taken into consideration, and an individualized approach is required.

 

 

CASE RESUMED: FOLLOW-UP

The patient presents 3 months later for follow-up. He reports significant improvement in his presenting symptoms including energy, libido, and erectile function. He also reports some improvement in his mood and concentration. He has lost 12 lb (5.4 kg) and is still trying to improve his diet and exercise program. He is compliant with his testosterone gel therapy.

His serum calculated free testosterone level is 7.8 ng/dL (4.5–17), and his hematocrit is 46%. The patient is instructed to continue his treatment and to return after 9 months for further follow-up.

TAKE-HOME POINTS

• Men with hypogonadism usually present with nonspecific manifestations, so clinicians should keep a high index of suspicion.
• Both clinical and biochemical evidence of hypogonadism should be present to diagnose and start treatment for it.
• Low levels of serum total testosterone do not necessarily reflect hypogonadism.
• The hormonal profile of central hypogonadism reveals low serum testosterone with low or inappropriately normal serum LH and FSH levels.

Obesity can cause central hypogonadism and should be suspected after pituitary and other systemic causes are excluded.

A 48-year-old man presents to his primary care physician because of progressively decreasing energy and gradual decline in both libido and erectile function for the past 18 months. He has noticed decreased morning erections as well. He rates his libido at 3 to 4 on a scale of 10 for the past 6 months. He also reports poor motivation, depressed mood, impaired concentration, and sleep disturbances. He reports no hair loss, headache, or dizziness, and no decrease in shaving frequency. Review of his systems is otherwise unremarkable.

He has had dyslipidemia for 3 years and is not known to have hypertension or diabetes. His medications include atorvastatin, vitamin E, and multivitamins.

He is married with 3 children and does not wish to have more. He works as a software engineer and leads a sedentary lifestyle. He is a nonsmoker and occasionally drinks alcohol on the weekends.

On physical examination, he is alert and oriented and appears well. His height is 5 feet 10 inches (178 cm), weight 230 lb (104 kg), and body mass index (BMI) 32.8 kg/m². His blood pressure is 115/83 mm Hg and pulse rate is 82 beats per minute and regular. Findings on cardiovascular and pulmonary examination are normal. He has large fatty breasts but without palpable glandular tissue.

Abdominal examination reveals central obesity—waist circumference 48 inches (122 cm)—without tenderness or organomegaly. There are no striae.

Genitourinary examination reveals normal hair distribution, a normal-sized penis, and slightly soft testes with testicular volume of 18–20 mL bilaterally.

His primary care physician suspects that he has low testosterone and orders some basic laboratory tests; the results are normal except for a low total testosterone level (Table 1).

FURTHER TESTING

1. Which of the following tests should his physician order next?

• Repeat total testosterone measurement
• Free testosterone measurement by commercial assay
• Calculated free testosterone
• Bioavailable testosterone measurement
• Serum inhibin B measurement

This patient presents with several nonspecific symptoms. But collectively they suggest testosterone deficiency (hypogonadism).

Symptoms and signs of low testosterone vary according to age of onset. Prepubertal onset is associated with incomplete or delayed puberty, no development of secondary sexual characteristics, eunuchoid features, and small penis and testes. Postpubertal onset is associated with a wide array of symptoms (Table 2). Most manifestations of low testosterone are nonspecific, such as fatigue, impaired concentration, and sleep disturbance.¹

Together, erectile dysfunction, low libido, and decreased morning erections strongly suggest hypogonadism.² Loss of body hair and decreased shaving frequency are specific symptoms of hypogonadism; however, they require years to develop.³ Gynecomastia can also occur due to loss of the inhibitory action of testosterone on breast growth and a relative increase in estradiol. This occurs more in primary hypogonadism, due to the increase in luteinizing hormone (LH), which stimulates the remaining Leydig cells to secrete estradiol rather than testosterone.⁴

Screening for hypogonadism in men may be warranted in several conditions, even without clinical manifestations of low testosterone (Table 3).^5–10

To diagnose hypogonadism in men and to start treatment for it, current guidelines recommend that the patient should have clinical features as well as laboratory evidence of low testosterone.^5,6

Measuring testosterone: Total, free, bound, and bioavailable

Testosterone, a steroid hormone, circulates in the serum either as free testosterone or bound to several plasma proteins, mainly sex-hormone binding globulin (SHBG) and albumin.

Total testosterone includes both the free and bound fractions, whereas bioavailable testosterone includes both free and the portion bound to albumin, which has low affinity and can dissociate and be used at the tissue level.¹¹

Low levels of total testosterone do not necessarily reflect a hypogonadal state, as a man with altered SHBG levels or binding capabilities can have low total but normal free testosterone levels and no manifestations.¹² Several conditions can alter the levels of SHBG, including obesity, diabetes, aging, thyroid dysfunction, and others.^5,13

Because our patient is obese, his total testosterone level is not a reliable indicator of hypogonadism, and repeating its measurement will not add diagnostic value.

Therefore, an alternative measurement should be used to accurately reflect the testosterone levels. From a physiologic point of view, bioavailable testosterone is the active form of testosterone and is the most accurate to be measured in a patient with hypogonadism. Nevertheless, because of technical difficulties in its measurement and lack of evidence correlating bioavailable testosterone with the clinical picture of hypogonadism, it is recommended that the level of free testosterone be used.⁵

The gold standard for direct measurement of serum free testosterone is equilibrium dialysis, but this is expensive and time-consuming.¹⁴ Commercial assays for free testosterone exist but have been deemed unreliable.^14,15 It is recommended that free testosterone be measured by equilibrium dialysis or calculated using equations based on total testosterone, SHBG, and albumin levels.⁵ These equations are reliable and give results very close to the values obtained by equilibrium dialysis.¹⁵ Therefore, in our patient, it would be suitable to calculate the free testosterone level next.

Serum levels of free testosterone vary according to several factors. Diurnal variation of testosterone has been established: levels are highest in the morning and decline throughout the day.¹⁶ Food decreases testosterone levels.¹⁷ In addition, there is considerable day-to-day variation.¹8 Therefore, at least 2 readings of fasting morning testosterone on 2 separate days are recommended for the diagnosis of hypogonadism.⁵

Inhibin B is a hormone produced by Sertoli cells in the testes in response to follicle-stimulating hormone (FSH) stimulation. In turn, it acts as negative feedback, together with testosterone, to inhibit FSH release from the pituitary. Inhibin B has been shown to reflect spermatogenesis in the testes and therefore fertility.¹⁹ Inhibin B levels were found to be low in patients with central hypogonadism, due to less FSH release; however, they did not correlate with testosterone levels.²⁰

 

 

CASE RESUMED: CHARACTERIZING HIS HYPOGONADISM

The patient’s physician orders morning fasting total testosterone, SHBG, and albumin testing and calculates the free testosterone level, which yields a value of 3 ng/dL (reference range 4.5–17). This is confirmed by a repeat measurement, which yields a value of 2.9 ng/dL. Laboratory test results combined with his clinical presentation are consistent with hypogonadism.

2. What is the most appropriate next step?

• Measurement of serum LH and FSH
• Measurement of serum prolactin
• Scrotal ultrasonography
• Gonadotropin-releasing hormone (GnRH) stimulation test
• Semen analysis

After hypogonadism is diagnosed, it is important to distinguish if it is primary or central. This is achieved by measuring serum LH and FSH.⁵ All biotin supplements should be stopped at least 72 hours before measuring LH and FSH, as biotin can interfere with the assays, yielding false values.²¹

Secretion of FSH and LH from the anterior pituitary is under the influence of pulsatile release of GnRH from the hypothalamus. LH acts on Leydig cells in the testes to produce testosterone, whereas FSH acts on Sertoli cells, together with testosterone, to bring about spermatogenesis in the seminiferous tubules. Testosterone acts centrally as negative feedback to decrease the release of LH and FSH.

Primary hypogonadism occurs due to testicular failure, ie, the testes themselves fail to produce testosterone, leading to hypogonadism. The decrease in testosterone levels, together with inhibin B if Sertoli cells are damaged, lead to loss of negative feedback on the hypothalamus and pituitary, and therefore increased levels of LH and FSH. This is termed hypergonadotropic hypogonadism. Testicular failure may also result in impaired spermatogenesis and infertility due to destruction of testicular structures, in which case fertility cannot be restored.

Central hypogonadism occurs when the pituitary fails to produce LH and FSH (secondary hypogonadism) or when the hypothalamus fails to produce GnRH and subsequently the lack of secretion of LH and FSH from the pituitary (tertiary hypogonadism). The lack of LH will result in no stimulation of Leydig cells to produce testosterone, and therefore its deficiency. Serum hormone levels in central hypogonadism will reveal low testosterone, with either low or inappropriately normal gonadotropins (LH and FSH). This is termed hypogonadotropic hypogonadism. The lack of FSH, together with testosterone deficiency will also result in decreased spermatogenesis and therefore infertility. Testicular structures are preserved, however, and fertility can be restored with appropriate therapy, as discussed below.

Prolactin should be measured only if the patient has central hypogonadism. Its measurement is not warranted at this point in the patient’s workup. The implications of prolactin and its relationship to hypogonadism will be discussed later.

Although, this stepwise approach is not convenient for many patients, some physicians follow it because it is cost-effective, especially in those who are not insured. However, other physicians order FSH, LH, and sometimes prolactin with the confirmatory low testosterone measurement. Laboratories can also be instructed to wait to measure the pituitary hormones and to do so only if low testosterone is confirmed.

Varicocele, a possible cause of male infertility, can also impair Leydig cell function and cause low testosterone. In fact, surgical repair of varicocele has been demonstrated to increase serum testosterone.²² Scrotal ultrasonography is used to diagnose varicocele, but this also should be ordered at a later stage in the workup if primary hypogonadism is diagnosed.

The GnRH stimulation test is important for the diagnosis and evaluation of precocious or delayed puberty in children. In boys with delayed puberty, a poorer response to GnRH stimulation indicates central hypogonadism rather than constitutional delay.²³ It has no role in the evaluation of postpubertal or adult-onset hypogonadism.

Semen analysis is important to evaluate fertility if the patient is interested in further procreation.⁵ Low testosterone levels may result in impaired spermatogenesis and therefore infertility. On the other hand, treatment with exogenous testosterone will also result in infertility, by feedback inhibition of LH and FSH and therefore inhibition of spermatogenesis. If the patient wishes to preserve fertility, treatment options other than testosterone should be considered; examples include clomiphene citrate, human menopausal gonadotropin, and human chorionic gonadotropin.^23,24

Our patient has no desire to expand his family; therefore, a semen analysis and attempts to preserve spermatogenesis are not indicated.

 

 

CASE RESUMED: SEARCHING FOR CAUSES

His physician orders testing of serum LH and FSH, yielding the following values:

• LH 1.6 mIU/mL (reference range 1.8–12)
• FSH 1.9 mIU/mL (reference range 1.5–12.5).

The diagnosis of central hypogonadism is established.

3. Which investigation is the least appropriate in the further evaluation of this patient?

• 
  Serum free thyroxine (T₄) and morning cortisol measurement
• Serum prolactin measurement
• Serum ferritin measurement
• Pituitary magnetic resonance imaging (MRI)
• Chromosomal karyotyping

The diagnosis of central hypogonadism warrants evaluation for possible causes. These are summarized in Table 4.

Serum free thyroxine and morning cortisol

Since this patient’s LH and FSH values are abnormal, it is important to evaluate the status of other anterior pituitary hormones. In patients with pituitary abnormalities, serum free T₄ is a more reliable test for assessing thyroid function than thyroid-stimulating hormone (TSH), because of loss of the negative feedback of thyroid hormones on the diseased pituitary. In contrast, serum TSH is considered the best single thyroid test to assess primary thyroid dysfunction.

Other measurements include prolactin and morning cortisol (reflecting adrenocorticotropic hormone status).

Prolactin measurement

Prolactin measurement is important to evaluate for hyperprolactinemia, as this will lead to hypogonadism by inhibition of GnRH secretion.²⁵ Different pathologic, pharmacologic, and physiologic conditions can result in hyperprolactinemia, including prolactinomas, other pituitary and hypothalamic lesions, primary hypothyroidism, and medications such as antipsychotics.²⁵ Dopamine agonists are the mainstay treatment for hyperprolactinemia.

Ferritin measurement

Ferritin measurement is indicated to diagnose iron overload conditions such as hemochromatosis, which can result in primary hypogonadism via testicular damage or in secondary hypogonadism via pituitary damage.²⁶

Pituitary MRI with contrast

Pituitary MRI with contrast is used to diagnose structural lesions of the pituitary or hypothalamus. This diagnostic modality is indicated for patients with pituitary dysfunction, including central hypogonadism, manifestations of a mass effect (headache, visual field defects), persistent hyperprolactinemia, and panhypopituitarism, among others. To improve the diagnostic yield of pituitary MRI, the Endocrine Society guidelines recommend it for men with serum total testosterone levels below 150 ng/dL.⁵ However, some clinicians have a lower threshold for ordering pituitary MRI for patients with central hypogonadism. Physician judgment and expertise should be exercised and the decision made on an individual basis.

Chromosomal karyotyping

Chromosomal karyotyping is not indicated in our patient. It is reserved for those with primary hypogonadism to diagnose Klinefelter syndrome, which has a karyotype of 47,XXY.

CASE RESUMED: MOSH SYNDROME

Our patient’s prolactin, free T₄, morning cortisol, and ferritin levels are measured, yielding normal values. No abnormalities are seen on pituitary MRI. A clinical reevaluation is conducted, revealing no history of head trauma or head and neck radiation. The lack of an obvious cause in our patient’s clinical presentation and workup, together with his obesity (BMI 32.8 kg/m²) supports the diagnosis of obesity as the cause of his hypogonadism.

Obesity can be a cause of secondary hypogonadism, which has led to the term “MOSH” (male obesity-associated secondary hypogonadism) syndrome. In fact, a cross-sectional study has demonstrated that 40% of nondiabetic obese (BMI ≥ 30 kg/m²) men over age 45 have low serum free testosterone levels, compared with 26% for lean (BMI < 25 kg/m²) men.²⁷ Moreover, obesity has been found to be a strong predictor of testosterone replacement therapy.²⁸ Other studies have also found an inverse relationship between BMI and testosterone levels.²⁹

Several mechanisms interact in the pathogenesis of MOSH syndrome. Adipose tissue possesses aromatase activity, which converts androgens into estrogens.³⁰ Peripheral estrogen production can in turn exert feedback inhibition on pituitary gonadotropin secretion.³¹ In obese men, increased adipose tissue leads to increased aromatase activity and more estrogen, so more feedback inhibition on the pituitary and subsequently secondary hypogonadism. 


Leptin, a hormone produced by adipocytes, is also increased in obesity, and was found to be inversely correlated with serum testosterone.³² Studies have demonstrated that leptin has an inhibitory effect on the enzymatic pathway that synthesizes testosterone in Leydig cells.³³

Proinflammatory cytokines have also been implicated, as central obesity is associated with an increase in these cytokines, which in turn act negatively on the hypothalamus and impair GnRH release leading to lower testosterone.^34,35

Treating obesity-related hypogonadism

In a pilot study,³⁶ lifestyle attempts to reduce obesity were shown to improve hormonal levels. Bariatric surgery has also been demonstrated to be successful.³⁷

Clomiphene citrate, a selective estrogen receptor modulator, increases endogenous testosterone secretion by inhibiting the negative feedback of estrogen on the hypothalamus and pituitary and thus increasing LH and FSH. It also preserves endogenous testosterone production, since it does not suppress the hypothalamic-pituitary-testicular axis.³⁸ This made clomiphene citrate a potential treatment for men with central hypogonadism including those with MOSH.³⁹

Nevertheless, there are no randomized trials to prove its safety and efficacy in the management of central hypogonadism.⁵ Regarding its use in men wishing to preserve fertility, most studies did not show improvement. However, a meta-analysis demonstrated statistically significant increased pregnancy rates in partners of men with idiopathic infertility if the men used 50 mg of clomiphene citrate daily.⁴⁰

Testosterone deficiency can be a marker of metabolic syndrome, which needs to be managed more urgently than hypogonadism. A cross-sectional study found not only an association between metabolic syndrome and low serum testosterone, but also with each individual component of metabolic syndrome on its own, all of which need to be addressed.¹⁰

 

 

CASE CONTINUED: BEGINNING TREATMENT

The physician counsels the patient regarding the implications, potential adverse outcomes, and available treatments for his obesity, including lifestyle modification and bariatric surgery. The patient declines surgery and wishes to adopt a weight-reducing diet and exercise program, for which he is referred to a dietitian.

In addition, in view of the patient’s clinically and biochemically proven hypogonadism, his physician offers testosterone replacement therapy. He orders a serum prostate-specific antigen (PSA) level, which is 1.3 ng/dL (reference range < 4 ng/dL). The patient is prescribed 5 g of 1% testosterone gel daily.

TESTOSTERONE REPLACEMENT THERAPY

4. Which is the most common adverse effect of testosterone replacement therapy?

• Cardiovascular events
• Erythrocytosis
• Prostate cancer
• Infertility
• Obstructive sleep apnea

Testosterone is indicated for men with an established diagnosis of hypogonadism. The benefits of testosterone replacement are summarized in Table 5.^5,6

Clinicians should be very cautious in initiating testosterone replacement therapy in any patient with an unstable medical condition.

There are several formulations of testosterone replacement therapy, including intramuscular injections, transdermal gels or patches, buccal tablets, an intranasal gel, and oral tablets. Of note, there are 2 different forms of oral testosterone preparations: testosterone undecanoate and 17-alpha alkylated testosterone. The former is unavailable in the United States and the latter is not recommended for use due to its proven hepatic toxicity.⁴¹

Testosterone and erythrocytosis

Meta-analyses have concluded that the most frequent adverse event of testosterone replacement therapy is a significant rise in hematocrit.⁴² This rise was found to be dose-dependent and was more marked in older men.⁴³ Although all preparations can cause erythrocytosis, parenteral forms have been observed to raise it the most, particularly short-term injectables.^44,45

The mechanism behind this increase is attributed to increased erythropoietin levels and improved usage of iron for red blood cell synthesis.⁴⁶ In fact, testosterone replacement therapy has been shown to improve hemoglobin levels in patients with anemia.⁴⁷ On the other hand, increasing hematocrit levels may lead to thrombotic and vasoocclusive events.⁴⁴

It is strongly recommended that baseline hematocrit levels be measured before initiating testosterone replacement therapy.^5,6 The hematocrit level should also be monitored 3 to 6 months into treatment and yearly thereafter while on testosterone.⁵Figure 1 summarizes the appropriate steps to undertake regarding hematocrit levels, according to the American Urological Association.⁶

Testosterone and prostate cancer

The relationship between testosterone treatment and prostate cancer has long been studied. Historically, testosterone replacement therapy was believed to increase the risk of prostate cancer; however, recent studies and meta-analyses have shown that this is not the case.^42,48 Nevertheless, clinical guidelines still recommend prostate monitoring for men on testosterone replacement therapy.^5,6

Furthermore, the clinician should make sure the patient does not have prostate cancer before initiating testosterone replacement therapy. Since there is a significant incidence of prostate cancer in men with serum PSA of 2.5–4.0 ng/mL, a patient with hypogonadism and a serum PSA in that range or higher should have appropriate evaluation before initiating testosterone replacement therapy.⁴⁹ The Endocrine Society recommendations for prostate monitoring are summarized in Table 6.⁵

Testosterone and cardiovascular risk

The evidence regarding this issue has been contradictory and inconsistent. Meta-analyses have demonstrated that low testosterone is associated with higher risk of major adverse cardiovascular events.⁵⁰ These studies argue for the use of testosterone replacement therapy in hypogonadal men to decrease the risk. However, other studies and meta-analyses have found that testosterone replacement therapy is associated with increased cardiovascular risk and have concluded that major adverse cardiac events are in fact a risk of testosterone replacement therapy.⁵¹

Current recommendations advocate against the use of testosterone replacement therapy in men with uncontrolled heart failure or with cardiovascular events in the past 3 to 6 months.^5,6 Cardiovascular risk factors should be addressed and corrected, and patients should be educated on cardiovascular symptoms and the need to report them if they occur.

Testosterone and infertility

As described earlier, testosterone replacement therapy increases negative feedback on the pituitary and decreases LH and FSH production, leading to less spermatogenesis. Other treatment options should be sought for hypogonadal men wishing to preserve fertility.

Other adverse effects

Other adverse effects of testosterone replacement therapy include acne, oily skin, obstructive sleep apnea, gynecomastia, and balding.

Given all the adverse events that can be associated with testosterone replacement therapy, the risks and benefits of treating hypogonadism in each patient should be taken into consideration, and an individualized approach is required.

 

 

CASE RESUMED: FOLLOW-UP

The patient presents 3 months later for follow-up. He reports significant improvement in his presenting symptoms including energy, libido, and erectile function. He also reports some improvement in his mood and concentration. He has lost 12 lb (5.4 kg) and is still trying to improve his diet and exercise program. He is compliant with his testosterone gel therapy.

His serum calculated free testosterone level is 7.8 ng/dL (4.5–17), and his hematocrit is 46%. The patient is instructed to continue his treatment and to return after 9 months for further follow-up.

TAKE-HOME POINTS

• Men with hypogonadism usually present with nonspecific manifestations, so clinicians should keep a high index of suspicion.
• Both clinical and biochemical evidence of hypogonadism should be present to diagnose and start treatment for it.
• Low levels of serum total testosterone do not necessarily reflect hypogonadism.
• The hormonal profile of central hypogonadism reveals low serum testosterone with low or inappropriately normal serum LH and FSH levels.

Obesity can cause central hypogonadism and should be suspected after pituitary and other systemic causes are excluded.

Some people, most of them relatively young women, experience lightheadedness, a racing heart, and other symptoms (but not hypotension) when they stand up, in a condition known as postural tachycardia syndrome (POTS).¹ Although not known to shorten life,¹ it can be physically and mentally debilitating.^2,3 Therapy rarely cures it, but a multifaceted approach can substantially improve quality of life.

This review outlines the evaluation and diagnosis of POTS and provides guidance for a therapy regimen.

HOW IS POTS DEFINED?

POTS is a multifactorial syndrome rather than a specific disease. It is characterized by all of the following^1,4–6:

• An increase in heart rate of ≥ 30 bpm, or ≥ 40 bpm for those under age 19, within 10 minutes of standing from a supine position
• Sustained tachycardia (> 30 seconds) 
• Absence of orthostatic hypotension (a fall in blood pressure of ≥ 20/10 mm Hg)
• Frequent and chronic duration (≥ 6 months).

These features are critical to diagnosis. Hemodynamic criteria in isolation may describe postural tachycardia but are not sufficient to diagnose POTS.

The prevalence of POTS is estimated to be between 0.2% and 1.0%,⁷ affecting up to 3 million people in the United States. Most cases arise between ages 13 and 50, with a female-to-male ratio of 5:1.⁸

MANY NAMES, SAME CONDITION

In 1871, Da Costa⁹ described a condition he called “irritable heart syndrome” that had characteristics similar to those of POTS, including extreme fatigue and exercise intolerance. Decades later, Lewis¹⁰ and Wood¹¹ provided more detailed descriptions of the disorder, renaming it “soldier’s heart” or “Da Costa syndrome.” As other cases were documented, more terms arose, including “effort syndrome” and “mitral valve prolapse syndrome.”

In 1982, Rosen and Cryer¹² were the first to use the term “postural tachycardia syndrome” for patients with disabling tachycardia upon standing without orthostatic hypotension. In 1986, Fouad et al¹³ described patients with postural tachycardia, orthostatic intolerance, and a small degree of hypotension as having “idiopathic hypovolemia.”

In 1993, Schondorf and Low¹⁴ established the current definition of POTS, leading to increased awareness and research efforts to understand its pathophysiology.

MULTIFACTORIAL PATHOPHYSIOLOGY

During the last 2 decades, several often-overlapping forms of POTS have been recognized, all of which share a final common pathway of sustained orthostatic tachycardia.^15–19 In addition, a number of common comorbidities were identified through review of large clinic populations of POTS.^20,21

Hypovolemic POTS

Up to 70% of patients with POTS have hypovolemia. The average plasma volume deficit is about 13%, which typically causes only insignificant changes in heart rate and norepinephrine levels while a patient is supine. However, blood pooling associated with upright posture further compromises cardiac output and consequently increases sympathetic nerve activity. Abnormalities in the renin-angiotensin-aldosterone volume regulation system are also suspected to impair sodium retention, contributing to hypovolemia.^1,22

Neuropathic POTS

About half of patients with POTS have partial sympathetic denervation (particularly in the lower limbs) and inadequate vasoconstriction upon standing, leading to reduced venous return and stroke volume.^17,23 A compensatory increase in sympathetic tone results in tachycardia to maintain cardiac output and blood pressure.

Hyperadrenergic POTS

Up to 50% of patients with POTS have high norepinephrine levels (≥ 600 pg/mL) when upright. This subtype, hyperadrenergic POTS, is characterized by an increase in systolic blood pressure of at least 10 mm Hg within 10 minutes of standing, with concomitant tachycardia that can be similar to or greater than that seen in nonhyperadrenergic POTS. Patients with hyperadrenergic POTS tend to report more prominent symptoms of sympathetic activation, such as palpitations, anxiety, and tremulousness.^24,25

Norepinephrine transporter deficiency

The norepinephrine transporter (NET) is on the presynaptic cleft of sympathetic neurons and serves to clear synaptic norepinephrine. NET deficiency leads to a hyperadrenergic state and elevated sympathetic nerve activation.¹⁸ NET deficiency may be induced by common antidepressants (eg, tricyclic antidepressants and serotonin-norepinephrine reuptake inhibitors) and attention-deficit disorder medications.⁴

Mast cell activation syndrome

The relationship between mast cell activation syndrome and POTS is poorly understood.^4,26 Mast cell activation syndrome has been described in a subset of patients with POTS who have sinus tachycardia accompanied by severe episodic flushing. Patients with this subtype have a hyperadrenergic response to postural change and elevated urine methylhistamine during flushing episodes.

Patients with mast cell activation syndrome tend to have strong allergic symptoms and may also have severe gastrointestinal problems, food sensitivities, dermatographism, and neuropathy. Diagnosis can be difficult, as the condition is associated with numerous markers with varying sensitivity and specificity.

Autoimmune origin

A significant minority of patients report a viral-like illness before the onset of POTS symptoms, suggesting a possible autoimmune-mediated or inflammatory cause. Also, some autoimmune disorders (eg, Sjögren syndrome) can present with a POTS-like manifestation.

Research into the role of autoantibodies in the pathophysiology of POTS offers the potential to develop novel therapeutic targets. Auto­antibodies that have been reported in POTS include those against M1 to M3 muscarinic receptors (present in over 87% of patients with POTS),²⁷ cardiac lipid raft-associated proteins,²⁸ adrenergic G-protein coupled receptors, alpha-1-adrenergic receptors, and beta-1- and beta-2-adrenergic receptors.²⁹ Although commercial enzyme-linked immunosorbent assays can assess for these antibody fragments, it is not known whether targeting the antibodies improves outcomes. At this time, antibody testing for POTS should be confined to the research setting.

LINKS TO OTHER SYNDROMES

POTS is often associated with other conditions whose symptoms cannot be explained by postural intolerance or tachycardia.

Ehlers-Danlos syndromes are a group of inherited heterogeneous disorders involving joint hypermobility, skin hyperextensibility, and tissue fragility.³⁰ The hypermobile subtype is most commonly associated with POTS, with patients often having symptoms of autonomic dysregulation and autonomic test abnormalities.^31–33 Patients with POTS may have a history of joint subluxations, joint pain, cervical instability, and spontaneous epidural leaks. The reason for the overlap between the two syndromes is not clear.

Chronic fatigue syndrome is characterized by persistent fatigue that does not resolve with rest and is not necessarily associated with orthostatic changes. More than 75% of patients with POTS report general fatigue as a major complaint, and up to 23% meet the full criteria for chronic fatigue syndrome.³⁴

 

 

DIAGNOSTIC STRATEGY

A patient presenting with symptoms suggestive of POTS should first undergo a detailed history and physical examination. Other causes of sinus tachycardia should be considered. 

Detailed history, symptom review

The history should focus on determining symptom burden, including tachycardia onset, frequency, severity, and triggers; the presence of syncope; and the impact of symptoms on daily function and quality of life.

POTS-associated orthostatic intolerance manifests with cardiac and noncardiac symptoms (Table 1).

Presyncope and its associated symptoms occur in less than one-third of patients with POTS, and syncope is not a principal feature.⁴ If syncope is the predominant complaint, alternative causes should be investigated. The usual cause of syncope in the general population is thought to be vasovagal.

In addition to orthostatic intolerance, gastrointestinal disturbances are common in POTS, presenting as abdominal pain, heartburn, irregular bowel movements, diarrhea, or constipation. Symptoms of gastroparesis are less common. Gastrointestinal symptoms tend to be prolonged, lasting hours and occurring multiple times a week. They tend not to improve in the supine position.³⁵ 

POTS-associated symptoms may develop insidiously, but patients often report onset after an acute stressor such as pregnancy, major surgery, or a presumed viral illness.⁴ Whether these putative triggers are causative or coincidental is unknown. Symptoms of orthostatic intolerance tend to be exacerbated by dehydration, heat, alcohol, exercise, and menstruation.^36,37

Consider the family history: 1 in 8 patients with POTS reports familial orthostatic intolerance,³⁸ suggesting a genetic role in some patients. Inquire about symptoms or a previous diagnosis of Ehlers-Danlos syndrome and mast cell activation syndrome.

Consider other conditions

Other causes of orthostatic tachycardia are listed in Table 2.^39–41 Most can be diagnosed with a careful history, physical examination, and laboratory tests. Two of the more challenging diagnoses are described below. 

Pheochromocytoma causes hyperadrenergic symptoms (eg, palpitations, lightheadedness) like those in POTS, but patients with pheochromocytoma typically have these symptoms while supine. Pheochromocytoma is also characterized by plasma norepinephrine levels much higher than in POTS.⁴ Plasma metanephrine testing helps diagnose or rule out pheochromocytoma.⁵

Inappropriate sinus tachycardia, like pheochromocytoma, also has clinical features similar to those of POTS, as well as tachycardia present when supine. It involves higher sympathetic tone and lower parasympathetic tone compared with POTS; patients commonly have a daytime resting heart rate of at least 100 bpm or a 24-hour mean heart rate of at least 90 bpm.^1,42 While the intrinsic heart rate is heightened in inappropriate sinus tachycardia, it is not different between POTS patients and healthy individuals.^42,43 Distinguishing POTS from inappropriate sinus tachycardia is further complicated by the broad inclusion criteria of most studies of inappropriate sinus tachycardia, which failed to exclude patients with POTS.⁴⁴ The Heart Rhythm Society recently adopted distinct definitions for the 2 conditions.¹

Physical examination: Focus on vital signs

The most critical component of the physical examination is thorough measurement of orthostatic vital signs (Figure 1). Blood pressure and heart rate should be measured while the patient has been supine for at least 5 minutes, and again after being upright for 1, 3, 5, and 10 minutes. These measurements determine if orthostatic hypotension is present and whether the patient meets the heart rate criteria for POTS. Patients with POTS tend to experience greater orthostatic tachycardia in the morning, so evaluation early in the day optimizes diagnostic sensitivity.⁵

Dependent acrocyanosis—dark red-blue discoloration of the lower legs that is cold to the touch—occurs in about half of patients with POTS upon standing.⁴ Dependent acrocyanosis is associated with joint hypermobility and Ehlers-Danlos syndrome, so these conditions should also be considered if findings are positive.

Laboratory testing for other causes

Laboratory testing is used mainly to detect primary causes of sinus tachycardia. Tests should include:

• Complete blood cell count with hematocrit (for severe anemia)
• Thyroid-stimulating hormone level (for hyperthyroidism)
• Electrolyte panel (for significant electrolyte disturbances).

Evidence is insufficient to support routinely measuring the vitamin B₁₂ level, iron indices, and serum markers for celiac disease, although these may be done if the history or physical examination suggests related problems.⁴ Sicca symptoms (severe dry eye or dry mouth) should trigger evaluation for Sjögren syndrome.

Electrocardiography needed

Electrocardiography should be performed to investigate for cardiac conduction abnormalities as well as for resting markers of a supraventricular tachyarrhythmia. Extended ambulatory (Holter) monitoring may be useful to evaluate for a transient reentrant tachyarrhythmia⁴; however, it does not record body position, so it can be difficult to determine if detected episodes of tachycardia are related to posture.

Additional testing for select cases

Further investigation is usually not needed to diagnose POTS but should be considered in some cases. Advanced tests are typically performed at a tertiary care referral center and include: 


• Quantitative sensory testing to evaluate for small-fiber neuropathy (ie, Quantitative Sudomotor Axon Reflex Test, or QSART), which occurs in the neuropathic POTS subtype
• Formal autonomic function testing to characterize neurovascular responsiveness  
• Supine and standing plasma norepinephrine levels (fractionated catecholamines) to characterize the net activation of the sympathetic nervous system
• Blood volume assessments to assess hypovolemia 
• Formal exercise testing to objectively quantify exercise capacity.

 

 

GRADED MANAGEMENT

No single universal gold-standard therapy exists for POTS, and management should be individually determined with the primary goals of treating symptoms and restoring function. A graded approach should be used, starting with conservative nonpharmacologic therapies and adding medications as needed.

While the disease course varies substantially from patient to patient, proper management is strongly associated with eventual symptom improvement.¹

NONPHARMACOLOGIC STEPS FIRST

A multipronged nonpharmacologic approach should be used for all patients before resorting to medications (Table 3). In an observational study, most patients reported that such interventions were more helpful than medications.⁴⁵ The following elements are recommended:

Education

Patients should be informed of the nature of their condition and referred to appropriate healthcare personnel. POTS is a chronic illness requiring individualized coping strategies, intensive physician interaction, and support of a multidisciplinary team. Patients and family members can be reassured that most symptoms improve over time with appropriate diagnosis and treatment.¹ Patients should be advised to avoid aggravating triggers and activities.

Exercise

Exercise programs are encouraged but should be introduced gradually, as physical activity can exacerbate symptoms, especially at the outset. Several studies have reported benefits from a short-term (3-month) program, in which the patient gradually progresses from non-upright exercise (eg, rowing machine, recumbent cycle, swimming) to upright endurance exercises. At the end of these programs, significant cardiac remodeling, improved quality of life, and reduced heart rate responses to standing have been reported, and benefits have been reported to persist in patients who continued exercising after the 3-month study period.^46,47

Despite the benefits of exercise interventions, compliance is low.^46,47 To prevent early discouragement, patients should be advised that it can take 4 to 6 weeks of continued exercise before benefits appear. Patients are encouraged to exercise every other day for 30 minutes or more. Regimens should primarily focus on aerobic conditioning, but resistance training, concentrating on thigh muscles, can also help. Exercise is a treatment and not a cure, and benefits can rapidly disappear if regular activity (at least 3 times per week) is stopped.⁴⁸

Compression stockings

Compression stockings help reduce peripheral venous pooling and enhance venous return to the heart. Waist-high stockings with compression of at least 30 to 40 mm Hg offer the best results. 

Diet

Increased fluid and salt intake is advisable for patients with suspected hypovolemia. At least 2 to 3 L of water accompanied by 10 to 12 g of daily sodium intake is recommended.¹ This can usually be accomplished with diet and salt added to food, but salt tablets can be used if the patient prefers. The resultant plasma volume expansion may help reduce the reflex tachycardia upon standing.⁴⁹

Check medications

The clinician should review—and perhaps discontinue—medications the patient is already taking that may exacerbate tachycardia or related symptoms (Table 4).⁵⁰ Venodilators decrease preload, thereby reducing cardiac output and blood pressure, which triggers compensatory tachycardia. Diuretics can reduce effective blood volume and lower preload, leading to worsened symptoms mediated by hypovolemia.

Rescue therapy with saline infusion

Intravenous saline infusion can augment blood volume in patients who are clinically decompensated and present with severe symptoms.¹ Intermittent infusion of 1 L of normal saline has been found to significantly reduce orthostatic tachycardia and related symptoms in patients with POTS, contributing to improved quality of life.^51,52

Chronic saline infusions are not recommended for long-term care because of the risk of access complications and infection.¹ Moak et al⁵³ reported a high rate of bacteremia in a cohort of children with POTS with regular saline infusions, most of whom had a central line. On the other hand, Ruzieh et al⁵⁴ reported significantly improved symptoms with regular saline infusions without a high rate of complications, but patients in this study received infusions for only a few months and through a peripheral intravenous catheter.

 

 

DRUG THERAPY

Drug therapy for POTS should be used only if nonpharmacologic interventions do not adequately relieve symptoms. Given the heterogeneity of POTS, treatment should be tailored to the patient’s underlying pathophysiology, key clinical features, and comorbidities. These considerations should guide the initial selection of medications, with adjustments as needed to alleviate adverse effects (Table 5).

No medications are approved by the US Food and Drug Administration (FDA) or Health Canada specifically for treating POTS, making all pharmacologic recommendations off-label. Although the drugs discussed below have been evaluated for POTS in controlled laboratory settings, they have yet to be tested in robust clinical trials.

Blood volume expansion

Several drugs expand blood volume, which may reduce orthostatic tachycardia.

Fludrocortisone is a synthetic aldosterone analogue that enhances sodium and water retention. Although one observational study found that it normalizes hemodynamic changes in response to orthostatic stress, no high-level evidence exists for its effectiveness for POTS.⁵⁵ It is generally well tolerated, although possible adverse effects include hyperkalemia, hypertension, fatigue, nausea, headache, and edema.^5,56

Desmopressin is a synthetic version of a natural antidiuretic hormone that increases kidney-mediated free-water reabsorption without sodium retention. It significantly reduces upright heart rate in patients with POTS and improves symptom burden. Although potential adverse effects include edema and headache, hyponatremia is the primary concern with daily use, especially with the increased water intake advised for POTS.⁵⁷ Patients should be advised to use desmopressin no more than once a week for the acute improvement of symptoms. Intermittent monitoring of serum sodium levels is recommended for safety.

Erythropoietin replacement has been suggested for treating POTS to address the significant deficit in red blood cell volume. Although erythropoietin therapy has a direct vasoconstrictive effect and largely improves red blood cell volume in patients with POTS, it does not expand plasma volume, so orthostatic tachycardia is not itself reduced.²² Nevertheless, it may significantly improve POTS symptoms refractory to more common methods of treatment, and it should be reserved for such cases. In addition to the lack of effect on orthostatic tachycardia, drawbacks to using erythropoietin include its high cost, the need for subcutaneous administration, and the risk of life-threatening complications such as myocardial infarction and stroke.^58,59

Heart rate-lowering agents

Propranolol, a nonselective beta-adrenergic antagonist, can significantly reduce standing heart rate and improve symptoms at low dosages (10–20 mg). Higher dosages can further restrain orthostatic tachycardia but are not as well tolerated, mainly due to hypotension and worsening of existing symptoms such as fatigue.⁶⁰ Regular-acting propranolol works for about 4 to 5 hours per dose, so full-day coverage often requires dosing 4 times per day.

Ivabradine is a selective blocker of the  “funny” (I_f) channel that reduces the sinus node firing rate without affecting blood pressure, so it slows heart rate without causing supine hypertension or orthostatic hypotension.

A retrospective case series found that 60% of patients with POTS treated with ivabradine reported symptomatic improvement, and all patients experienced reduced tachycardia with continued use.⁶¹ Ivabradine has not been compared with placebo or propranolol in a randomized controlled trial, and it has not been well studied in pregnancy and so should be avoided because of potential teratogenic effects.

When prescribing ivabradine for women of childbearing age, a negative pregnancy test may be documented prior to initiation of therapy, and the use of highly effective methods of contraception is recommended. Ivabradine should be avoided in women contemplating pregnancy. Insurance coverage can limit access to ivabradine in the United States.

Central nervous system sympatholytics

Patients with prominent hyperadrenergic features may benefit from central sympatholytic agents. However, these drugs may not be well tolerated in patients with neuropathic POTS because of the effects of reduced systemic vascular resistance⁵ and the possible exacerbation of drowsiness, fatigue, and mental clouding.⁴ Patients can be extremely sensitive to these medications, so they should initially be prescribed at the lowest dose, then gradually increased as tolerated.

Clonidine, an alpha-2-adrenergic agonist, decreases central sympathetic tone. In hyperadrenergic patients, clonidine can stabilize heart rate and blood pressure, thereby reducing orthostatic symptoms.⁶²

Methyldopa has effects similar to those of clonidine but is easier to titrate owing to its longer half-life.⁶³ Methyldopa is typically started at 125 mg at bedtime and increased to 125 mg twice daily, if tolerated.             

 

 

Other agents

Midodrine is a prodrug. The active form, an alpha-1-adrenergic agonist, constricts peripheral veins and arteries to increase vascular resistance and venous return, thereby reducing orthostatic tachycardia.⁵² It is most useful in patients with impaired peripheral vasoconstriction (eg, neuropathic POTS) and may be less effective in those with hyperadrenergic POTS.⁶⁴ Major limitations of midodrine include worsening supine hypertension and possible urinary retention.³⁹

Because of midodrine’s short half-life, frequent dosing is required during daytime hours (eg, 8 AM, noon, and 4 PM), but it should not be taken within 4 to 5 hours of sleep because of the risk of supine hypertension. Midodrine is typically started at 2.5 to 5 mg per dose and can be titrated up to 15 mg per dose.

Midodrine is an FDA pregnancy category  C drug (adverse effects in pregnancy seen in animal models, but evidence lacking in humans). While ideally it should be avoided, we have used it safely in pregnant women with disabling POTS symptoms.

Pyridostigmine, an acetylcholinesterase inhibitor, increases cardiovagal tone and possibly sympathetic tone. It has been reported to significantly reduce standing heart rate and improve symptom burden in patients with POTS.⁶⁵ However, pyridostigmine increases gastrointestinal mobility, leading to severe adverse effects in over 20% of patients, including abdominal cramps, nausea, and diarrhea.⁶⁶

Droxidopa, a synthetic amino acid precursor of norepinephrine, improves dizziness and fatigue in POTS with minimal effects on blood pressure.⁶⁷

Modafinil, a psychostimulant, may improve POTS-associated cognitive symptoms.⁴ It also raises upright blood pressure without significantly worsening standing heart rate or acute orthostatic symptoms.⁶⁸

EFFECTS OF COMORBID DISORDERS ON MANAGEMENT

Ehlers-Danlos syndrome

Pharmacologic approaches to POTS should not be altered based on the presence of Ehlers-Danlos syndrome, but because many of these patients are prone to joint dislocation, exercise prescriptions may need adjusting.

A medical genetics consult is recommended for patients with Ehlers-Danlos syndrome. Although the hypermobile type (the form most commonly associated with POTS) is not associated with aortopathy, it can be confused with classical and vascular Ehlers-Danlos syndromes, which require serial aortic screening.³⁰

Mast cell activation syndrome

Consultation with an allergist or immunologist may help patients with severe symptoms.

Autoantibodies and autoimmunity

Treatment of the underlying disorder is recommended and can result in significantly improved POTS symptoms.

SPECIALTY CARE REFERRAL

POTS can be challenging to manage. Given the range of physiologic, emotional, and functional distress patients experience, it often requires significant physician time and multidisciplinary care. Patients with continued severe or debilitating symptoms may benefit from referral to a tertiary-care center with experience in autonomic nervous system disorders.

PROGNOSIS

Limited data are available on the long-term prognosis of POTS, and more studies are needed in pediatric and adult populations. No deaths have been reported in the handful of published cases of POTS in patients older than 50.¹ Some pediatric studies suggest that some teenagers “outgrow” their POTS. However, these data are not robust, and an alternative explanation is that as they get older, they see adult physicians for their POTS symptoms and so are lost to study follow-up.^6,44,69 

We have not often seen POTS simply resolve without ongoing treatment. However, in our experience, most patients have improved symptoms and function with multimodal treatment (ie, exercise, salt, water, stockings, and some medications) and time.

Some people, most of them relatively young women, experience lightheadedness, a racing heart, and other symptoms (but not hypotension) when they stand up, in a condition known as postural tachycardia syndrome (POTS).¹ Although not known to shorten life,¹ it can be physically and mentally debilitating.^2,3 Therapy rarely cures it, but a multifaceted approach can substantially improve quality of life.

This review outlines the evaluation and diagnosis of POTS and provides guidance for a therapy regimen.

HOW IS POTS DEFINED?

POTS is a multifactorial syndrome rather than a specific disease. It is characterized by all of the following^1,4–6:

• An increase in heart rate of ≥ 30 bpm, or ≥ 40 bpm for those under age 19, within 10 minutes of standing from a supine position
• Sustained tachycardia (> 30 seconds) 
• Absence of orthostatic hypotension (a fall in blood pressure of ≥ 20/10 mm Hg)
• Frequent and chronic duration (≥ 6 months).

These features are critical to diagnosis. Hemodynamic criteria in isolation may describe postural tachycardia but are not sufficient to diagnose POTS.

The prevalence of POTS is estimated to be between 0.2% and 1.0%,⁷ affecting up to 3 million people in the United States. Most cases arise between ages 13 and 50, with a female-to-male ratio of 5:1.⁸

MANY NAMES, SAME CONDITION

In 1871, Da Costa⁹ described a condition he called “irritable heart syndrome” that had characteristics similar to those of POTS, including extreme fatigue and exercise intolerance. Decades later, Lewis¹⁰ and Wood¹¹ provided more detailed descriptions of the disorder, renaming it “soldier’s heart” or “Da Costa syndrome.” As other cases were documented, more terms arose, including “effort syndrome” and “mitral valve prolapse syndrome.”

In 1982, Rosen and Cryer¹² were the first to use the term “postural tachycardia syndrome” for patients with disabling tachycardia upon standing without orthostatic hypotension. In 1986, Fouad et al¹³ described patients with postural tachycardia, orthostatic intolerance, and a small degree of hypotension as having “idiopathic hypovolemia.”

In 1993, Schondorf and Low¹⁴ established the current definition of POTS, leading to increased awareness and research efforts to understand its pathophysiology.

MULTIFACTORIAL PATHOPHYSIOLOGY

During the last 2 decades, several often-overlapping forms of POTS have been recognized, all of which share a final common pathway of sustained orthostatic tachycardia.^15–19 In addition, a number of common comorbidities were identified through review of large clinic populations of POTS.^20,21

Hypovolemic POTS

Up to 70% of patients with POTS have hypovolemia. The average plasma volume deficit is about 13%, which typically causes only insignificant changes in heart rate and norepinephrine levels while a patient is supine. However, blood pooling associated with upright posture further compromises cardiac output and consequently increases sympathetic nerve activity. Abnormalities in the renin-angiotensin-aldosterone volume regulation system are also suspected to impair sodium retention, contributing to hypovolemia.^1,22

Neuropathic POTS

About half of patients with POTS have partial sympathetic denervation (particularly in the lower limbs) and inadequate vasoconstriction upon standing, leading to reduced venous return and stroke volume.^17,23 A compensatory increase in sympathetic tone results in tachycardia to maintain cardiac output and blood pressure.

Hyperadrenergic POTS

Up to 50% of patients with POTS have high norepinephrine levels (≥ 600 pg/mL) when upright. This subtype, hyperadrenergic POTS, is characterized by an increase in systolic blood pressure of at least 10 mm Hg within 10 minutes of standing, with concomitant tachycardia that can be similar to or greater than that seen in nonhyperadrenergic POTS. Patients with hyperadrenergic POTS tend to report more prominent symptoms of sympathetic activation, such as palpitations, anxiety, and tremulousness.^24,25

Norepinephrine transporter deficiency

The norepinephrine transporter (NET) is on the presynaptic cleft of sympathetic neurons and serves to clear synaptic norepinephrine. NET deficiency leads to a hyperadrenergic state and elevated sympathetic nerve activation.¹⁸ NET deficiency may be induced by common antidepressants (eg, tricyclic antidepressants and serotonin-norepinephrine reuptake inhibitors) and attention-deficit disorder medications.⁴

Mast cell activation syndrome

The relationship between mast cell activation syndrome and POTS is poorly understood.^4,26 Mast cell activation syndrome has been described in a subset of patients with POTS who have sinus tachycardia accompanied by severe episodic flushing. Patients with this subtype have a hyperadrenergic response to postural change and elevated urine methylhistamine during flushing episodes.

Patients with mast cell activation syndrome tend to have strong allergic symptoms and may also have severe gastrointestinal problems, food sensitivities, dermatographism, and neuropathy. Diagnosis can be difficult, as the condition is associated with numerous markers with varying sensitivity and specificity.

Autoimmune origin

A significant minority of patients report a viral-like illness before the onset of POTS symptoms, suggesting a possible autoimmune-mediated or inflammatory cause. Also, some autoimmune disorders (eg, Sjögren syndrome) can present with a POTS-like manifestation.

Research into the role of autoantibodies in the pathophysiology of POTS offers the potential to develop novel therapeutic targets. Auto­antibodies that have been reported in POTS include those against M1 to M3 muscarinic receptors (present in over 87% of patients with POTS),²⁷ cardiac lipid raft-associated proteins,²⁸ adrenergic G-protein coupled receptors, alpha-1-adrenergic receptors, and beta-1- and beta-2-adrenergic receptors.²⁹ Although commercial enzyme-linked immunosorbent assays can assess for these antibody fragments, it is not known whether targeting the antibodies improves outcomes. At this time, antibody testing for POTS should be confined to the research setting.

LINKS TO OTHER SYNDROMES

POTS is often associated with other conditions whose symptoms cannot be explained by postural intolerance or tachycardia.

Ehlers-Danlos syndromes are a group of inherited heterogeneous disorders involving joint hypermobility, skin hyperextensibility, and tissue fragility.³⁰ The hypermobile subtype is most commonly associated with POTS, with patients often having symptoms of autonomic dysregulation and autonomic test abnormalities.^31–33 Patients with POTS may have a history of joint subluxations, joint pain, cervical instability, and spontaneous epidural leaks. The reason for the overlap between the two syndromes is not clear.

Chronic fatigue syndrome is characterized by persistent fatigue that does not resolve with rest and is not necessarily associated with orthostatic changes. More than 75% of patients with POTS report general fatigue as a major complaint, and up to 23% meet the full criteria for chronic fatigue syndrome.³⁴

 

 

DIAGNOSTIC STRATEGY

A patient presenting with symptoms suggestive of POTS should first undergo a detailed history and physical examination. Other causes of sinus tachycardia should be considered. 

Detailed history, symptom review

The history should focus on determining symptom burden, including tachycardia onset, frequency, severity, and triggers; the presence of syncope; and the impact of symptoms on daily function and quality of life.

POTS-associated orthostatic intolerance manifests with cardiac and noncardiac symptoms (Table 1).

Presyncope and its associated symptoms occur in less than one-third of patients with POTS, and syncope is not a principal feature.⁴ If syncope is the predominant complaint, alternative causes should be investigated. The usual cause of syncope in the general population is thought to be vasovagal.

In addition to orthostatic intolerance, gastrointestinal disturbances are common in POTS, presenting as abdominal pain, heartburn, irregular bowel movements, diarrhea, or constipation. Symptoms of gastroparesis are less common. Gastrointestinal symptoms tend to be prolonged, lasting hours and occurring multiple times a week. They tend not to improve in the supine position.³⁵ 

POTS-associated symptoms may develop insidiously, but patients often report onset after an acute stressor such as pregnancy, major surgery, or a presumed viral illness.⁴ Whether these putative triggers are causative or coincidental is unknown. Symptoms of orthostatic intolerance tend to be exacerbated by dehydration, heat, alcohol, exercise, and menstruation.^36,37

Consider the family history: 1 in 8 patients with POTS reports familial orthostatic intolerance,³⁸ suggesting a genetic role in some patients. Inquire about symptoms or a previous diagnosis of Ehlers-Danlos syndrome and mast cell activation syndrome.

Consider other conditions

Other causes of orthostatic tachycardia are listed in Table 2.^39–41 Most can be diagnosed with a careful history, physical examination, and laboratory tests. Two of the more challenging diagnoses are described below. 

Pheochromocytoma causes hyperadrenergic symptoms (eg, palpitations, lightheadedness) like those in POTS, but patients with pheochromocytoma typically have these symptoms while supine. Pheochromocytoma is also characterized by plasma norepinephrine levels much higher than in POTS.⁴ Plasma metanephrine testing helps diagnose or rule out pheochromocytoma.⁵

Inappropriate sinus tachycardia, like pheochromocytoma, also has clinical features similar to those of POTS, as well as tachycardia present when supine. It involves higher sympathetic tone and lower parasympathetic tone compared with POTS; patients commonly have a daytime resting heart rate of at least 100 bpm or a 24-hour mean heart rate of at least 90 bpm.^1,42 While the intrinsic heart rate is heightened in inappropriate sinus tachycardia, it is not different between POTS patients and healthy individuals.^42,43 Distinguishing POTS from inappropriate sinus tachycardia is further complicated by the broad inclusion criteria of most studies of inappropriate sinus tachycardia, which failed to exclude patients with POTS.⁴⁴ The Heart Rhythm Society recently adopted distinct definitions for the 2 conditions.¹

Physical examination: Focus on vital signs

The most critical component of the physical examination is thorough measurement of orthostatic vital signs (Figure 1). Blood pressure and heart rate should be measured while the patient has been supine for at least 5 minutes, and again after being upright for 1, 3, 5, and 10 minutes. These measurements determine if orthostatic hypotension is present and whether the patient meets the heart rate criteria for POTS. Patients with POTS tend to experience greater orthostatic tachycardia in the morning, so evaluation early in the day optimizes diagnostic sensitivity.⁵

Dependent acrocyanosis—dark red-blue discoloration of the lower legs that is cold to the touch—occurs in about half of patients with POTS upon standing.⁴ Dependent acrocyanosis is associated with joint hypermobility and Ehlers-Danlos syndrome, so these conditions should also be considered if findings are positive.

Laboratory testing for other causes

Laboratory testing is used mainly to detect primary causes of sinus tachycardia. Tests should include:

• Complete blood cell count with hematocrit (for severe anemia)
• Thyroid-stimulating hormone level (for hyperthyroidism)
• Electrolyte panel (for significant electrolyte disturbances).

Evidence is insufficient to support routinely measuring the vitamin B₁₂ level, iron indices, and serum markers for celiac disease, although these may be done if the history or physical examination suggests related problems.⁴ Sicca symptoms (severe dry eye or dry mouth) should trigger evaluation for Sjögren syndrome.

Electrocardiography needed

Electrocardiography should be performed to investigate for cardiac conduction abnormalities as well as for resting markers of a supraventricular tachyarrhythmia. Extended ambulatory (Holter) monitoring may be useful to evaluate for a transient reentrant tachyarrhythmia⁴; however, it does not record body position, so it can be difficult to determine if detected episodes of tachycardia are related to posture.

Additional testing for select cases

Further investigation is usually not needed to diagnose POTS but should be considered in some cases. Advanced tests are typically performed at a tertiary care referral center and include: 


• Quantitative sensory testing to evaluate for small-fiber neuropathy (ie, Quantitative Sudomotor Axon Reflex Test, or QSART), which occurs in the neuropathic POTS subtype
• Formal autonomic function testing to characterize neurovascular responsiveness  
• Supine and standing plasma norepinephrine levels (fractionated catecholamines) to characterize the net activation of the sympathetic nervous system
• Blood volume assessments to assess hypovolemia 
• Formal exercise testing to objectively quantify exercise capacity.

 

 

GRADED MANAGEMENT

No single universal gold-standard therapy exists for POTS, and management should be individually determined with the primary goals of treating symptoms and restoring function. A graded approach should be used, starting with conservative nonpharmacologic therapies and adding medications as needed.

While the disease course varies substantially from patient to patient, proper management is strongly associated with eventual symptom improvement.¹

NONPHARMACOLOGIC STEPS FIRST

A multipronged nonpharmacologic approach should be used for all patients before resorting to medications (Table 3). In an observational study, most patients reported that such interventions were more helpful than medications.⁴⁵ The following elements are recommended:

Education

Patients should be informed of the nature of their condition and referred to appropriate healthcare personnel. POTS is a chronic illness requiring individualized coping strategies, intensive physician interaction, and support of a multidisciplinary team. Patients and family members can be reassured that most symptoms improve over time with appropriate diagnosis and treatment.¹ Patients should be advised to avoid aggravating triggers and activities.

Exercise

Exercise programs are encouraged but should be introduced gradually, as physical activity can exacerbate symptoms, especially at the outset. Several studies have reported benefits from a short-term (3-month) program, in which the patient gradually progresses from non-upright exercise (eg, rowing machine, recumbent cycle, swimming) to upright endurance exercises. At the end of these programs, significant cardiac remodeling, improved quality of life, and reduced heart rate responses to standing have been reported, and benefits have been reported to persist in patients who continued exercising after the 3-month study period.^46,47

Despite the benefits of exercise interventions, compliance is low.^46,47 To prevent early discouragement, patients should be advised that it can take 4 to 6 weeks of continued exercise before benefits appear. Patients are encouraged to exercise every other day for 30 minutes or more. Regimens should primarily focus on aerobic conditioning, but resistance training, concentrating on thigh muscles, can also help. Exercise is a treatment and not a cure, and benefits can rapidly disappear if regular activity (at least 3 times per week) is stopped.⁴⁸

Compression stockings

Compression stockings help reduce peripheral venous pooling and enhance venous return to the heart. Waist-high stockings with compression of at least 30 to 40 mm Hg offer the best results. 

Diet

Increased fluid and salt intake is advisable for patients with suspected hypovolemia. At least 2 to 3 L of water accompanied by 10 to 12 g of daily sodium intake is recommended.¹ This can usually be accomplished with diet and salt added to food, but salt tablets can be used if the patient prefers. The resultant plasma volume expansion may help reduce the reflex tachycardia upon standing.⁴⁹

Check medications

The clinician should review—and perhaps discontinue—medications the patient is already taking that may exacerbate tachycardia or related symptoms (Table 4).⁵⁰ Venodilators decrease preload, thereby reducing cardiac output and blood pressure, which triggers compensatory tachycardia. Diuretics can reduce effective blood volume and lower preload, leading to worsened symptoms mediated by hypovolemia.

Rescue therapy with saline infusion

Intravenous saline infusion can augment blood volume in patients who are clinically decompensated and present with severe symptoms.¹ Intermittent infusion of 1 L of normal saline has been found to significantly reduce orthostatic tachycardia and related symptoms in patients with POTS, contributing to improved quality of life.^51,52

Chronic saline infusions are not recommended for long-term care because of the risk of access complications and infection.¹ Moak et al⁵³ reported a high rate of bacteremia in a cohort of children with POTS with regular saline infusions, most of whom had a central line. On the other hand, Ruzieh et al⁵⁴ reported significantly improved symptoms with regular saline infusions without a high rate of complications, but patients in this study received infusions for only a few months and through a peripheral intravenous catheter.

 

 

DRUG THERAPY

Drug therapy for POTS should be used only if nonpharmacologic interventions do not adequately relieve symptoms. Given the heterogeneity of POTS, treatment should be tailored to the patient’s underlying pathophysiology, key clinical features, and comorbidities. These considerations should guide the initial selection of medications, with adjustments as needed to alleviate adverse effects (Table 5).

No medications are approved by the US Food and Drug Administration (FDA) or Health Canada specifically for treating POTS, making all pharmacologic recommendations off-label. Although the drugs discussed below have been evaluated for POTS in controlled laboratory settings, they have yet to be tested in robust clinical trials.

Blood volume expansion

Several drugs expand blood volume, which may reduce orthostatic tachycardia.

Fludrocortisone is a synthetic aldosterone analogue that enhances sodium and water retention. Although one observational study found that it normalizes hemodynamic changes in response to orthostatic stress, no high-level evidence exists for its effectiveness for POTS.⁵⁵ It is generally well tolerated, although possible adverse effects include hyperkalemia, hypertension, fatigue, nausea, headache, and edema.^5,56

Desmopressin is a synthetic version of a natural antidiuretic hormone that increases kidney-mediated free-water reabsorption without sodium retention. It significantly reduces upright heart rate in patients with POTS and improves symptom burden. Although potential adverse effects include edema and headache, hyponatremia is the primary concern with daily use, especially with the increased water intake advised for POTS.⁵⁷ Patients should be advised to use desmopressin no more than once a week for the acute improvement of symptoms. Intermittent monitoring of serum sodium levels is recommended for safety.

Erythropoietin replacement has been suggested for treating POTS to address the significant deficit in red blood cell volume. Although erythropoietin therapy has a direct vasoconstrictive effect and largely improves red blood cell volume in patients with POTS, it does not expand plasma volume, so orthostatic tachycardia is not itself reduced.²² Nevertheless, it may significantly improve POTS symptoms refractory to more common methods of treatment, and it should be reserved for such cases. In addition to the lack of effect on orthostatic tachycardia, drawbacks to using erythropoietin include its high cost, the need for subcutaneous administration, and the risk of life-threatening complications such as myocardial infarction and stroke.^58,59

Heart rate-lowering agents

Propranolol, a nonselective beta-adrenergic antagonist, can significantly reduce standing heart rate and improve symptoms at low dosages (10–20 mg). Higher dosages can further restrain orthostatic tachycardia but are not as well tolerated, mainly due to hypotension and worsening of existing symptoms such as fatigue.⁶⁰ Regular-acting propranolol works for about 4 to 5 hours per dose, so full-day coverage often requires dosing 4 times per day.

Ivabradine is a selective blocker of the  “funny” (I_f) channel that reduces the sinus node firing rate without affecting blood pressure, so it slows heart rate without causing supine hypertension or orthostatic hypotension.

A retrospective case series found that 60% of patients with POTS treated with ivabradine reported symptomatic improvement, and all patients experienced reduced tachycardia with continued use.⁶¹ Ivabradine has not been compared with placebo or propranolol in a randomized controlled trial, and it has not been well studied in pregnancy and so should be avoided because of potential teratogenic effects.

When prescribing ivabradine for women of childbearing age, a negative pregnancy test may be documented prior to initiation of therapy, and the use of highly effective methods of contraception is recommended. Ivabradine should be avoided in women contemplating pregnancy. Insurance coverage can limit access to ivabradine in the United States.

Central nervous system sympatholytics

Patients with prominent hyperadrenergic features may benefit from central sympatholytic agents. However, these drugs may not be well tolerated in patients with neuropathic POTS because of the effects of reduced systemic vascular resistance⁵ and the possible exacerbation of drowsiness, fatigue, and mental clouding.⁴ Patients can be extremely sensitive to these medications, so they should initially be prescribed at the lowest dose, then gradually increased as tolerated.

Clonidine, an alpha-2-adrenergic agonist, decreases central sympathetic tone. In hyperadrenergic patients, clonidine can stabilize heart rate and blood pressure, thereby reducing orthostatic symptoms.⁶²

Methyldopa has effects similar to those of clonidine but is easier to titrate owing to its longer half-life.⁶³ Methyldopa is typically started at 125 mg at bedtime and increased to 125 mg twice daily, if tolerated.             

 

 

Other agents

Midodrine is a prodrug. The active form, an alpha-1-adrenergic agonist, constricts peripheral veins and arteries to increase vascular resistance and venous return, thereby reducing orthostatic tachycardia.⁵² It is most useful in patients with impaired peripheral vasoconstriction (eg, neuropathic POTS) and may be less effective in those with hyperadrenergic POTS.⁶⁴ Major limitations of midodrine include worsening supine hypertension and possible urinary retention.³⁹

Because of midodrine’s short half-life, frequent dosing is required during daytime hours (eg, 8 AM, noon, and 4 PM), but it should not be taken within 4 to 5 hours of sleep because of the risk of supine hypertension. Midodrine is typically started at 2.5 to 5 mg per dose and can be titrated up to 15 mg per dose.

Midodrine is an FDA pregnancy category  C drug (adverse effects in pregnancy seen in animal models, but evidence lacking in humans). While ideally it should be avoided, we have used it safely in pregnant women with disabling POTS symptoms.

Pyridostigmine, an acetylcholinesterase inhibitor, increases cardiovagal tone and possibly sympathetic tone. It has been reported to significantly reduce standing heart rate and improve symptom burden in patients with POTS.⁶⁵ However, pyridostigmine increases gastrointestinal mobility, leading to severe adverse effects in over 20% of patients, including abdominal cramps, nausea, and diarrhea.⁶⁶

Droxidopa, a synthetic amino acid precursor of norepinephrine, improves dizziness and fatigue in POTS with minimal effects on blood pressure.⁶⁷

Modafinil, a psychostimulant, may improve POTS-associated cognitive symptoms.⁴ It also raises upright blood pressure without significantly worsening standing heart rate or acute orthostatic symptoms.⁶⁸

EFFECTS OF COMORBID DISORDERS ON MANAGEMENT

Ehlers-Danlos syndrome

Pharmacologic approaches to POTS should not be altered based on the presence of Ehlers-Danlos syndrome, but because many of these patients are prone to joint dislocation, exercise prescriptions may need adjusting.

A medical genetics consult is recommended for patients with Ehlers-Danlos syndrome. Although the hypermobile type (the form most commonly associated with POTS) is not associated with aortopathy, it can be confused with classical and vascular Ehlers-Danlos syndromes, which require serial aortic screening.³⁰

Mast cell activation syndrome

Consultation with an allergist or immunologist may help patients with severe symptoms.

Autoantibodies and autoimmunity

Treatment of the underlying disorder is recommended and can result in significantly improved POTS symptoms.

SPECIALTY CARE REFERRAL

POTS can be challenging to manage. Given the range of physiologic, emotional, and functional distress patients experience, it often requires significant physician time and multidisciplinary care. Patients with continued severe or debilitating symptoms may benefit from referral to a tertiary-care center with experience in autonomic nervous system disorders.

PROGNOSIS

Limited data are available on the long-term prognosis of POTS, and more studies are needed in pediatric and adult populations. No deaths have been reported in the handful of published cases of POTS in patients older than 50.¹ Some pediatric studies suggest that some teenagers “outgrow” their POTS. However, these data are not robust, and an alternative explanation is that as they get older, they see adult physicians for their POTS symptoms and so are lost to study follow-up.^6,44,69 

We have not often seen POTS simply resolve without ongoing treatment. However, in our experience, most patients have improved symptoms and function with multimodal treatment (ie, exercise, salt, water, stockings, and some medications) and time.

Some people, most of them relatively young women, experience lightheadedness, a racing heart, and other symptoms (but not hypotension) when they stand up, in a condition known as postural tachycardia syndrome (POTS).¹ Although not known to shorten life,¹ it can be physically and mentally debilitating.^2,3 Therapy rarely cures it, but a multifaceted approach can substantially improve quality of life.

This review outlines the evaluation and diagnosis of POTS and provides guidance for a therapy regimen.

HOW IS POTS DEFINED?

POTS is a multifactorial syndrome rather than a specific disease. It is characterized by all of the following^1,4–6:

• An increase in heart rate of ≥ 30 bpm, or ≥ 40 bpm for those under age 19, within 10 minutes of standing from a supine position
• Sustained tachycardia (> 30 seconds) 
• Absence of orthostatic hypotension (a fall in blood pressure of ≥ 20/10 mm Hg)
• Frequent and chronic duration (≥ 6 months).

These features are critical to diagnosis. Hemodynamic criteria in isolation may describe postural tachycardia but are not sufficient to diagnose POTS.

The prevalence of POTS is estimated to be between 0.2% and 1.0%,⁷ affecting up to 3 million people in the United States. Most cases arise between ages 13 and 50, with a female-to-male ratio of 5:1.⁸

MANY NAMES, SAME CONDITION

In 1871, Da Costa⁹ described a condition he called “irritable heart syndrome” that had characteristics similar to those of POTS, including extreme fatigue and exercise intolerance. Decades later, Lewis¹⁰ and Wood¹¹ provided more detailed descriptions of the disorder, renaming it “soldier’s heart” or “Da Costa syndrome.” As other cases were documented, more terms arose, including “effort syndrome” and “mitral valve prolapse syndrome.”

In 1982, Rosen and Cryer¹² were the first to use the term “postural tachycardia syndrome” for patients with disabling tachycardia upon standing without orthostatic hypotension. In 1986, Fouad et al¹³ described patients with postural tachycardia, orthostatic intolerance, and a small degree of hypotension as having “idiopathic hypovolemia.”

In 1993, Schondorf and Low¹⁴ established the current definition of POTS, leading to increased awareness and research efforts to understand its pathophysiology.

MULTIFACTORIAL PATHOPHYSIOLOGY

During the last 2 decades, several often-overlapping forms of POTS have been recognized, all of which share a final common pathway of sustained orthostatic tachycardia.^15–19 In addition, a number of common comorbidities were identified through review of large clinic populations of POTS.^20,21

Hypovolemic POTS

Up to 70% of patients with POTS have hypovolemia. The average plasma volume deficit is about 13%, which typically causes only insignificant changes in heart rate and norepinephrine levels while a patient is supine. However, blood pooling associated with upright posture further compromises cardiac output and consequently increases sympathetic nerve activity. Abnormalities in the renin-angiotensin-aldosterone volume regulation system are also suspected to impair sodium retention, contributing to hypovolemia.^1,22

Neuropathic POTS

About half of patients with POTS have partial sympathetic denervation (particularly in the lower limbs) and inadequate vasoconstriction upon standing, leading to reduced venous return and stroke volume.^17,23 A compensatory increase in sympathetic tone results in tachycardia to maintain cardiac output and blood pressure.

Hyperadrenergic POTS

Up to 50% of patients with POTS have high norepinephrine levels (≥ 600 pg/mL) when upright. This subtype, hyperadrenergic POTS, is characterized by an increase in systolic blood pressure of at least 10 mm Hg within 10 minutes of standing, with concomitant tachycardia that can be similar to or greater than that seen in nonhyperadrenergic POTS. Patients with hyperadrenergic POTS tend to report more prominent symptoms of sympathetic activation, such as palpitations, anxiety, and tremulousness.^24,25

Norepinephrine transporter deficiency

The norepinephrine transporter (NET) is on the presynaptic cleft of sympathetic neurons and serves to clear synaptic norepinephrine. NET deficiency leads to a hyperadrenergic state and elevated sympathetic nerve activation.¹⁸ NET deficiency may be induced by common antidepressants (eg, tricyclic antidepressants and serotonin-norepinephrine reuptake inhibitors) and attention-deficit disorder medications.⁴

Mast cell activation syndrome

The relationship between mast cell activation syndrome and POTS is poorly understood.^4,26 Mast cell activation syndrome has been described in a subset of patients with POTS who have sinus tachycardia accompanied by severe episodic flushing. Patients with this subtype have a hyperadrenergic response to postural change and elevated urine methylhistamine during flushing episodes.

Patients with mast cell activation syndrome tend to have strong allergic symptoms and may also have severe gastrointestinal problems, food sensitivities, dermatographism, and neuropathy. Diagnosis can be difficult, as the condition is associated with numerous markers with varying sensitivity and specificity.

Autoimmune origin

A significant minority of patients report a viral-like illness before the onset of POTS symptoms, suggesting a possible autoimmune-mediated or inflammatory cause. Also, some autoimmune disorders (eg, Sjögren syndrome) can present with a POTS-like manifestation.

Research into the role of autoantibodies in the pathophysiology of POTS offers the potential to develop novel therapeutic targets. Auto­antibodies that have been reported in POTS include those against M1 to M3 muscarinic receptors (present in over 87% of patients with POTS),²⁷ cardiac lipid raft-associated proteins,²⁸ adrenergic G-protein coupled receptors, alpha-1-adrenergic receptors, and beta-1- and beta-2-adrenergic receptors.²⁹ Although commercial enzyme-linked immunosorbent assays can assess for these antibody fragments, it is not known whether targeting the antibodies improves outcomes. At this time, antibody testing for POTS should be confined to the research setting.

LINKS TO OTHER SYNDROMES

POTS is often associated with other conditions whose symptoms cannot be explained by postural intolerance or tachycardia.

Ehlers-Danlos syndromes are a group of inherited heterogeneous disorders involving joint hypermobility, skin hyperextensibility, and tissue fragility.³⁰ The hypermobile subtype is most commonly associated with POTS, with patients often having symptoms of autonomic dysregulation and autonomic test abnormalities.^31–33 Patients with POTS may have a history of joint subluxations, joint pain, cervical instability, and spontaneous epidural leaks. The reason for the overlap between the two syndromes is not clear.

Chronic fatigue syndrome is characterized by persistent fatigue that does not resolve with rest and is not necessarily associated with orthostatic changes. More than 75% of patients with POTS report general fatigue as a major complaint, and up to 23% meet the full criteria for chronic fatigue syndrome.³⁴

 

 

DIAGNOSTIC STRATEGY

A patient presenting with symptoms suggestive of POTS should first undergo a detailed history and physical examination. Other causes of sinus tachycardia should be considered. 

Detailed history, symptom review

The history should focus on determining symptom burden, including tachycardia onset, frequency, severity, and triggers; the presence of syncope; and the impact of symptoms on daily function and quality of life.

POTS-associated orthostatic intolerance manifests with cardiac and noncardiac symptoms (Table 1).

Presyncope and its associated symptoms occur in less than one-third of patients with POTS, and syncope is not a principal feature.⁴ If syncope is the predominant complaint, alternative causes should be investigated. The usual cause of syncope in the general population is thought to be vasovagal.

In addition to orthostatic intolerance, gastrointestinal disturbances are common in POTS, presenting as abdominal pain, heartburn, irregular bowel movements, diarrhea, or constipation. Symptoms of gastroparesis are less common. Gastrointestinal symptoms tend to be prolonged, lasting hours and occurring multiple times a week. They tend not to improve in the supine position.³⁵ 

POTS-associated symptoms may develop insidiously, but patients often report onset after an acute stressor such as pregnancy, major surgery, or a presumed viral illness.⁴ Whether these putative triggers are causative or coincidental is unknown. Symptoms of orthostatic intolerance tend to be exacerbated by dehydration, heat, alcohol, exercise, and menstruation.^36,37

Consider the family history: 1 in 8 patients with POTS reports familial orthostatic intolerance,³⁸ suggesting a genetic role in some patients. Inquire about symptoms or a previous diagnosis of Ehlers-Danlos syndrome and mast cell activation syndrome.

Consider other conditions

Other causes of orthostatic tachycardia are listed in Table 2.^39–41 Most can be diagnosed with a careful history, physical examination, and laboratory tests. Two of the more challenging diagnoses are described below. 

Pheochromocytoma causes hyperadrenergic symptoms (eg, palpitations, lightheadedness) like those in POTS, but patients with pheochromocytoma typically have these symptoms while supine. Pheochromocytoma is also characterized by plasma norepinephrine levels much higher than in POTS.⁴ Plasma metanephrine testing helps diagnose or rule out pheochromocytoma.⁵

Inappropriate sinus tachycardia, like pheochromocytoma, also has clinical features similar to those of POTS, as well as tachycardia present when supine. It involves higher sympathetic tone and lower parasympathetic tone compared with POTS; patients commonly have a daytime resting heart rate of at least 100 bpm or a 24-hour mean heart rate of at least 90 bpm.^1,42 While the intrinsic heart rate is heightened in inappropriate sinus tachycardia, it is not different between POTS patients and healthy individuals.^42,43 Distinguishing POTS from inappropriate sinus tachycardia is further complicated by the broad inclusion criteria of most studies of inappropriate sinus tachycardia, which failed to exclude patients with POTS.⁴⁴ The Heart Rhythm Society recently adopted distinct definitions for the 2 conditions.¹

Physical examination: Focus on vital signs

The most critical component of the physical examination is thorough measurement of orthostatic vital signs (Figure 1). Blood pressure and heart rate should be measured while the patient has been supine for at least 5 minutes, and again after being upright for 1, 3, 5, and 10 minutes. These measurements determine if orthostatic hypotension is present and whether the patient meets the heart rate criteria for POTS. Patients with POTS tend to experience greater orthostatic tachycardia in the morning, so evaluation early in the day optimizes diagnostic sensitivity.⁵

Dependent acrocyanosis—dark red-blue discoloration of the lower legs that is cold to the touch—occurs in about half of patients with POTS upon standing.⁴ Dependent acrocyanosis is associated with joint hypermobility and Ehlers-Danlos syndrome, so these conditions should also be considered if findings are positive.

Laboratory testing for other causes

Laboratory testing is used mainly to detect primary causes of sinus tachycardia. Tests should include:

• Complete blood cell count with hematocrit (for severe anemia)
• Thyroid-stimulating hormone level (for hyperthyroidism)
• Electrolyte panel (for significant electrolyte disturbances).

Evidence is insufficient to support routinely measuring the vitamin B₁₂ level, iron indices, and serum markers for celiac disease, although these may be done if the history or physical examination suggests related problems.⁴ Sicca symptoms (severe dry eye or dry mouth) should trigger evaluation for Sjögren syndrome.

Electrocardiography needed

Electrocardiography should be performed to investigate for cardiac conduction abnormalities as well as for resting markers of a supraventricular tachyarrhythmia. Extended ambulatory (Holter) monitoring may be useful to evaluate for a transient reentrant tachyarrhythmia⁴; however, it does not record body position, so it can be difficult to determine if detected episodes of tachycardia are related to posture.

Additional testing for select cases

Further investigation is usually not needed to diagnose POTS but should be considered in some cases. Advanced tests are typically performed at a tertiary care referral center and include: 


• Quantitative sensory testing to evaluate for small-fiber neuropathy (ie, Quantitative Sudomotor Axon Reflex Test, or QSART), which occurs in the neuropathic POTS subtype
• Formal autonomic function testing to characterize neurovascular responsiveness  
• Supine and standing plasma norepinephrine levels (fractionated catecholamines) to characterize the net activation of the sympathetic nervous system
• Blood volume assessments to assess hypovolemia 
• Formal exercise testing to objectively quantify exercise capacity.

 

 

GRADED MANAGEMENT

No single universal gold-standard therapy exists for POTS, and management should be individually determined with the primary goals of treating symptoms and restoring function. A graded approach should be used, starting with conservative nonpharmacologic therapies and adding medications as needed.

While the disease course varies substantially from patient to patient, proper management is strongly associated with eventual symptom improvement.¹

NONPHARMACOLOGIC STEPS FIRST

A multipronged nonpharmacologic approach should be used for all patients before resorting to medications (Table 3). In an observational study, most patients reported that such interventions were more helpful than medications.⁴⁵ The following elements are recommended:

Education

Patients should be informed of the nature of their condition and referred to appropriate healthcare personnel. POTS is a chronic illness requiring individualized coping strategies, intensive physician interaction, and support of a multidisciplinary team. Patients and family members can be reassured that most symptoms improve over time with appropriate diagnosis and treatment.¹ Patients should be advised to avoid aggravating triggers and activities.

Exercise

Exercise programs are encouraged but should be introduced gradually, as physical activity can exacerbate symptoms, especially at the outset. Several studies have reported benefits from a short-term (3-month) program, in which the patient gradually progresses from non-upright exercise (eg, rowing machine, recumbent cycle, swimming) to upright endurance exercises. At the end of these programs, significant cardiac remodeling, improved quality of life, and reduced heart rate responses to standing have been reported, and benefits have been reported to persist in patients who continued exercising after the 3-month study period.^46,47

Despite the benefits of exercise interventions, compliance is low.^46,47 To prevent early discouragement, patients should be advised that it can take 4 to 6 weeks of continued exercise before benefits appear. Patients are encouraged to exercise every other day for 30 minutes or more. Regimens should primarily focus on aerobic conditioning, but resistance training, concentrating on thigh muscles, can also help. Exercise is a treatment and not a cure, and benefits can rapidly disappear if regular activity (at least 3 times per week) is stopped.⁴⁸

Compression stockings

Compression stockings help reduce peripheral venous pooling and enhance venous return to the heart. Waist-high stockings with compression of at least 30 to 40 mm Hg offer the best results. 

Diet

Increased fluid and salt intake is advisable for patients with suspected hypovolemia. At least 2 to 3 L of water accompanied by 10 to 12 g of daily sodium intake is recommended.¹ This can usually be accomplished with diet and salt added to food, but salt tablets can be used if the patient prefers. The resultant plasma volume expansion may help reduce the reflex tachycardia upon standing.⁴⁹

Check medications

The clinician should review—and perhaps discontinue—medications the patient is already taking that may exacerbate tachycardia or related symptoms (Table 4).⁵⁰ Venodilators decrease preload, thereby reducing cardiac output and blood pressure, which triggers compensatory tachycardia. Diuretics can reduce effective blood volume and lower preload, leading to worsened symptoms mediated by hypovolemia.

Rescue therapy with saline infusion

Intravenous saline infusion can augment blood volume in patients who are clinically decompensated and present with severe symptoms.¹ Intermittent infusion of 1 L of normal saline has been found to significantly reduce orthostatic tachycardia and related symptoms in patients with POTS, contributing to improved quality of life.^51,52

Chronic saline infusions are not recommended for long-term care because of the risk of access complications and infection.¹ Moak et al⁵³ reported a high rate of bacteremia in a cohort of children with POTS with regular saline infusions, most of whom had a central line. On the other hand, Ruzieh et al⁵⁴ reported significantly improved symptoms with regular saline infusions without a high rate of complications, but patients in this study received infusions for only a few months and through a peripheral intravenous catheter.

 

 

DRUG THERAPY

Drug therapy for POTS should be used only if nonpharmacologic interventions do not adequately relieve symptoms. Given the heterogeneity of POTS, treatment should be tailored to the patient’s underlying pathophysiology, key clinical features, and comorbidities. These considerations should guide the initial selection of medications, with adjustments as needed to alleviate adverse effects (Table 5).

No medications are approved by the US Food and Drug Administration (FDA) or Health Canada specifically for treating POTS, making all pharmacologic recommendations off-label. Although the drugs discussed below have been evaluated for POTS in controlled laboratory settings, they have yet to be tested in robust clinical trials.

Blood volume expansion

Several drugs expand blood volume, which may reduce orthostatic tachycardia.

Fludrocortisone is a synthetic aldosterone analogue that enhances sodium and water retention. Although one observational study found that it normalizes hemodynamic changes in response to orthostatic stress, no high-level evidence exists for its effectiveness for POTS.⁵⁵ It is generally well tolerated, although possible adverse effects include hyperkalemia, hypertension, fatigue, nausea, headache, and edema.^5,56

Desmopressin is a synthetic version of a natural antidiuretic hormone that increases kidney-mediated free-water reabsorption without sodium retention. It significantly reduces upright heart rate in patients with POTS and improves symptom burden. Although potential adverse effects include edema and headache, hyponatremia is the primary concern with daily use, especially with the increased water intake advised for POTS.⁵⁷ Patients should be advised to use desmopressin no more than once a week for the acute improvement of symptoms. Intermittent monitoring of serum sodium levels is recommended for safety.

Erythropoietin replacement has been suggested for treating POTS to address the significant deficit in red blood cell volume. Although erythropoietin therapy has a direct vasoconstrictive effect and largely improves red blood cell volume in patients with POTS, it does not expand plasma volume, so orthostatic tachycardia is not itself reduced.²² Nevertheless, it may significantly improve POTS symptoms refractory to more common methods of treatment, and it should be reserved for such cases. In addition to the lack of effect on orthostatic tachycardia, drawbacks to using erythropoietin include its high cost, the need for subcutaneous administration, and the risk of life-threatening complications such as myocardial infarction and stroke.^58,59

Heart rate-lowering agents

Propranolol, a nonselective beta-adrenergic antagonist, can significantly reduce standing heart rate and improve symptoms at low dosages (10–20 mg). Higher dosages can further restrain orthostatic tachycardia but are not as well tolerated, mainly due to hypotension and worsening of existing symptoms such as fatigue.⁶⁰ Regular-acting propranolol works for about 4 to 5 hours per dose, so full-day coverage often requires dosing 4 times per day.

Ivabradine is a selective blocker of the  “funny” (I_f) channel that reduces the sinus node firing rate without affecting blood pressure, so it slows heart rate without causing supine hypertension or orthostatic hypotension.

A retrospective case series found that 60% of patients with POTS treated with ivabradine reported symptomatic improvement, and all patients experienced reduced tachycardia with continued use.⁶¹ Ivabradine has not been compared with placebo or propranolol in a randomized controlled trial, and it has not been well studied in pregnancy and so should be avoided because of potential teratogenic effects.

When prescribing ivabradine for women of childbearing age, a negative pregnancy test may be documented prior to initiation of therapy, and the use of highly effective methods of contraception is recommended. Ivabradine should be avoided in women contemplating pregnancy. Insurance coverage can limit access to ivabradine in the United States.

Central nervous system sympatholytics

Patients with prominent hyperadrenergic features may benefit from central sympatholytic agents. However, these drugs may not be well tolerated in patients with neuropathic POTS because of the effects of reduced systemic vascular resistance⁵ and the possible exacerbation of drowsiness, fatigue, and mental clouding.⁴ Patients can be extremely sensitive to these medications, so they should initially be prescribed at the lowest dose, then gradually increased as tolerated.

Clonidine, an alpha-2-adrenergic agonist, decreases central sympathetic tone. In hyperadrenergic patients, clonidine can stabilize heart rate and blood pressure, thereby reducing orthostatic symptoms.⁶²

Methyldopa has effects similar to those of clonidine but is easier to titrate owing to its longer half-life.⁶³ Methyldopa is typically started at 125 mg at bedtime and increased to 125 mg twice daily, if tolerated.             

 

 

Other agents

Midodrine is a prodrug. The active form, an alpha-1-adrenergic agonist, constricts peripheral veins and arteries to increase vascular resistance and venous return, thereby reducing orthostatic tachycardia.⁵² It is most useful in patients with impaired peripheral vasoconstriction (eg, neuropathic POTS) and may be less effective in those with hyperadrenergic POTS.⁶⁴ Major limitations of midodrine include worsening supine hypertension and possible urinary retention.³⁹

Because of midodrine’s short half-life, frequent dosing is required during daytime hours (eg, 8 AM, noon, and 4 PM), but it should not be taken within 4 to 5 hours of sleep because of the risk of supine hypertension. Midodrine is typically started at 2.5 to 5 mg per dose and can be titrated up to 15 mg per dose.

Midodrine is an FDA pregnancy category  C drug (adverse effects in pregnancy seen in animal models, but evidence lacking in humans). While ideally it should be avoided, we have used it safely in pregnant women with disabling POTS symptoms.

Pyridostigmine, an acetylcholinesterase inhibitor, increases cardiovagal tone and possibly sympathetic tone. It has been reported to significantly reduce standing heart rate and improve symptom burden in patients with POTS.⁶⁵ However, pyridostigmine increases gastrointestinal mobility, leading to severe adverse effects in over 20% of patients, including abdominal cramps, nausea, and diarrhea.⁶⁶

Droxidopa, a synthetic amino acid precursor of norepinephrine, improves dizziness and fatigue in POTS with minimal effects on blood pressure.⁶⁷

Modafinil, a psychostimulant, may improve POTS-associated cognitive symptoms.⁴ It also raises upright blood pressure without significantly worsening standing heart rate or acute orthostatic symptoms.⁶⁸

EFFECTS OF COMORBID DISORDERS ON MANAGEMENT

Ehlers-Danlos syndrome

Pharmacologic approaches to POTS should not be altered based on the presence of Ehlers-Danlos syndrome, but because many of these patients are prone to joint dislocation, exercise prescriptions may need adjusting.

A medical genetics consult is recommended for patients with Ehlers-Danlos syndrome. Although the hypermobile type (the form most commonly associated with POTS) is not associated with aortopathy, it can be confused with classical and vascular Ehlers-Danlos syndromes, which require serial aortic screening.³⁰

Mast cell activation syndrome

Consultation with an allergist or immunologist may help patients with severe symptoms.

Autoantibodies and autoimmunity

Treatment of the underlying disorder is recommended and can result in significantly improved POTS symptoms.

SPECIALTY CARE REFERRAL

POTS can be challenging to manage. Given the range of physiologic, emotional, and functional distress patients experience, it often requires significant physician time and multidisciplinary care. Patients with continued severe or debilitating symptoms may benefit from referral to a tertiary-care center with experience in autonomic nervous system disorders.

PROGNOSIS

Limited data are available on the long-term prognosis of POTS, and more studies are needed in pediatric and adult populations. No deaths have been reported in the handful of published cases of POTS in patients older than 50.¹ Some pediatric studies suggest that some teenagers “outgrow” their POTS. However, these data are not robust, and an alternative explanation is that as they get older, they see adult physicians for their POTS symptoms and so are lost to study follow-up.^6,44,69 

We have not often seen POTS simply resolve without ongoing treatment. However, in our experience, most patients have improved symptoms and function with multimodal treatment (ie, exercise, salt, water, stockings, and some medications) and time.

A 72-year-old woman presents to the emergency department with progressive nausea and vomiting. One week earlier, she developed early satiety and nausea with vomiting after eating solid food. Three days later her symptoms progressed, and she became unable to take anything by mouth. The patient also experienced a 40-lb weight loss in the previous 3 months. She denies symptoms of abdominal pain, hematemesis, or melena. Her medical history includes cholecystectomy and type 2 diabetes mellitus, diagnosed 1 year ago. She has no family history of gastrointestinal malignancy. She says she smoked 1 pack a day in her 20s. She does not consume alcohol.

On physical examination, she is normotensive with a heart rate of 105 beats per minute. The oral mucosa is dry, and the abdomen is mildly distended and tender to palpation in the epigastrium. Laboratory evaluation reveals hypokalemia and metabolic alkalosis.

Computed tomography (CT) reveals a mass 3 cm by 4 cm in the pancreatic head. The mass has invaded the medial wall of the duodenum, with obstruction of the pancreatic and common bile ducts and extension into and occlusion of the superior mesenteric vein, with soft-tissue expansion around the superior mesenteric artery. CT also reveals retained stomach contents and an air-fluid level consistent with gastric outlet obstruction.

INTRINSIC OR EXTRINSIC BLOCKAGE

Gastric outlet obstruction, also called pyloric obstruction, is caused by intrinsic or extrinsic mechanical blockage of gastric emptying, generally in the distal stomach, pyloric channel, or duodenum, with associated symptoms of nausea, vomiting, abdominal pain, and early satiety. It is encountered in both the clinic and the hospital.

Here, we review the causes, diagnosis, and management of this disorder.

BENIGN AND MALIGNANT CAUSES

Causes of obstruction are classified as either benign or malignant (Table 1). However, all cases of gastric outlet obstruction should be assumed to be due to underlying malignancy unless proven otherwise.¹

In a retrospective study of 76 patients hospitalized with gastric outlet obstruction between 2006 and 2015 at our institution,² 29 cases (38%) were due to malignancy and 47 (62%) were due to benign causes. Pancreatic adenocarcinoma accounted for 13 cases (17%), while gastric adenocarcinoma accounted for 5 cases (7%); less common malignant causes were cholangiocarcinoma, cancer of the ampulla of Vater, duodenal adenocarcinoma, hepatocellular carcinoma, and metastatic disease. Of the benign causes, the most common were peptic ulcer disease (13 cases, 17%) and postoperative strictures or adhesions (11 cases, 14%).

These numbers reflect general trends around the world.

Less gastric cancer, more pancreatic cancer

The last several decades have seen a trend toward more cases due to cancer and fewer due to benign causes.^3–14

In earlier studies in both developed and developing countries, gastric adenocarcinoma was the most common malignant cause of gastric outlet obstruction. Since then, it has become less common in Western countries, although it remains more common in Asia and Africa.^7–14 This trend likely reflects environmental factors, including decreased prevalence of Helicobacter pylori infection, a major risk factor for gastric cancer, in Western countries.^15–17

At the same time, pancreatic cancer is on the rise,¹⁶ and up to 20% of patients with pancreatic cancer develop gastric outlet obstruction.¹⁸ In a prospective observational study of 108 patients with malignant gastric outlet obstruction undergoing endoscopic stenting, pancreatic cancer was by far the most common malignancy, occurring in 54% of patients, followed by gastric cancer in 13%.¹⁹

Less peptic ulcer disease, but still common

Peptic ulcer disease used to account for up to 90% of cases of gastric outlet obstruction, and it is still the most common benign cause.

In 1990, gastric outlet obstruction was estimated to occur in 5% to 10% of all hospital admissions for ulcer-related complications, accounting for 2,000 operations annually.^20,21 Gastric outlet obstruction now occurs in fewer than 5% of patients with duodenal ulcer disease and fewer than 2% of patients with gastric ulcer disease.²²

Peptic ulcer disease remains an important cause of obstruction in countries with poor access to acid-suppressing drugs.²³

Gastric outlet obstruction occurs in both acute and chronic peptic ulcer disease. In acute peptic ulcer disease, tissue inflammation and edema result in mechanical obstruction. Chronic peptic ulcer disease results in tissue scarring and fibrosis with strictures.²⁰

Environmental factors, including improved diet, hygiene, physical activity, and the decreased prevalence of H pylori infection, also contribute to the decreased prevalence of peptic ulcer disease and its complications, including gastric outlet obstruction.³ The continued occurrence of peptic ulcer disease is associated with widespread use of low-dose aspirin and nonsteroidal anti-inflammatory drugs (NSAIDs), the most common causes of peptic ulcer disease in Western countries.^24,25

Other nonmalignant causes of gastric outlet obstruction are diverse and less common. They include caustic ingestion, postsurgical strictures, benign tumors of the gastrointestinal tract, Crohn disease, and pancreatic disorders including acute pancreatitis, pancreatic pseudocyst, chronic pancreatitis, and annular pancreas. Intramural duodenal hematoma may cause obstruction after blunt abdominal trauma, endoscopic biopsy, or gastrostomy tube migration, especially in the setting of a bleeding disorder or anticoagulation.²⁶

Tuberculosis should be suspected in countries in which it is common.⁷ In a prospective study of 64 patients with benign gastric outlet obstruction in India,²⁷ 16 (25%) had corrosive injury, 16 (25%) had tuberculosis, and 15 (23%) had peptic ulcer disease. Compared with patients with corrosive injury and peptic ulcer disease, patients with gastroduodenal tuberculosis had the best outcomes with appropriate treatment.

Other reported causes include Bouveret syndrome (an impacted gallstone in the proximal duodenum), phytobezoar, diaphragmatic hernia, gastric volvulus, and Ladd bands (peritoneal bands associated with intestinal malrotation).^7,28,29

 

 

PRESENTING SYMPTOMS

Symptoms of gastric outlet obstruction include nausea, nonbilious vomiting, epigastric pain, early satiety, abdominal distention, and weight loss.

In our patients, the most common presenting symptoms were nausea and vomiting (80%), followed by abdominal pain (72%); weight loss (15%), abdominal distention (15%), and early satiety (9%) were less common.²

Patients with gastric outlet obstruction secondary to malignancy generally present with a shorter duration of symptoms than those with peptic ulcer disease and are more likely to be older.^8,13 Other conditions with an acute onset of symptoms include gastric polyp prolapse, percutaneous endoscopic gastrostomy tube migration, gastric volvulus, and gallstone impaction.

Patients with gastric outlet obstruction associated with peptic ulcer disease generally have a long-standing history of symptoms, including dyspepsia and weight loss over several years.⁴

SIGNS ON EXAMINATION

On examination, look for signs of chronic gastric obstruction and its consequences, such as malnutrition, cachexia, volume depletion, and dental erosions.

A succussion splash may suggest gastric outlet obstruction. This is elicited by rocking the patient back and forth by the hips or abdomen while listening over the stomach for a splash, which may be heard without a stethoscope. The test is considered positive if present 3 or more hours after drinking fluids and suggests retention of gastric materials.^30,31

In thin individuals, chronic gastric outlet obstruction makes the stomach dilate and hypertrophy, which may be evident by a palpably thickened stomach with visible gastric peristalsis.⁴

Other notable findings on physical examination may include a palpable abdominal mass, epigastric pain, or an abnormality suggestive of metastatic gastric cancer, such as an enlarged left supraclavicular lymph node (Virchow node) or periumbilical lymph node (Sister Mary Joseph nodule). The Virchow node is at the junction of the thoracic duct and the left subclavian vein where the lymphatic circulation from the body drains into the systemic circulation, and it may be the first sign of gastric cancer.³² Sister Mary Joseph nodule (named after a surgical assistant to Dr. William James Mayo) refers to a palpable mass at the umbilicus, generally resulting from metastasis of an abdominal malignancy.³³

SIGNS ON FURTHER STUDIES

Laboratory evaluation may show signs of poor oral intake and electrolyte abnormalities secondary to chronic nausea, vomiting, and dehydration, including hypochloremic metabolic alkalosis and hypokalemia.

The underlying cause of gastric outlet obstruction has major implications for treatment and prognosis and cannot be differentiated by clinical presentation alone.^1,9 Diagnosis is based on clinical features and radiologic or endoscopic evaluation consistent with gastric outlet obstruction.

Plain radiography may reveal an enlarged gastric bubble, and contrast studies may be useful to determine whether the obstruction is partial or complete, depending on whether the contrast passes into the small bowel.

CT or magnetic resonance imaging may show gastric distention with retained stomach contents, suggesting a gastric, pyloric, duodenal, or pancreatic mass (Figure 1).

Upper endoscopy is often needed to establish the diagnosis and cause. Emptying the stomach with a nasogastric tube is recommended before endoscopy to minimize the risk of aspiration during the procedure, and endotracheal intubation should be considered for airway protection.³⁴ Findings of gastric outlet obstruction on upper endoscopy include retained food and liquid. Endoscopic biopsy is important to differentiate between benign and malignant causes. For patients with malignancy, endoscopic ultrasonography is useful for diagnosis via tissue sampling with fine-needle aspiration and locoregional staging.³⁵

A strategy. Most patients whose clinical presentation suggests gastric outlet obstruction require cross-sectional radiologic imaging, upper endoscopy, or both.³⁶ CT is the preferred imaging study to evaluate for intestinal obstruction.^36,37 Patients with suspected complete obstruction or perforation should undergo CT before upper endoscopy. Oral contrast may interfere with endoscopy and should be avoided if endoscopy is planned. Additionally, giving oral contrast may worsen patient discomfort and increase the risk of nausea, vomiting, and aspiration.^36,37

Following radiographic evaluation, upper endoscopy can be performed after gastric decompression to identify the location and extent of the obstruction and to potentially provide a definitive diagnosis with biopsy.³⁶

DIFFERENTIATE FROM GASTROPARESIS

Gastroparesis is a chronic neuromuscular disorder characterized by delayed gastric emptying without mechanical obstruction.³⁸ The most common causes are diabetes, surgery, and idiopathy. Other causes include viral infection, connective tissue diseases, ischemia, infiltrative disorders, radiation, neurologic disorders, and paraneoplastic syndromes.^39,40

Gastric outlet obstruction and gastroparesis share clinical symptoms including nausea, vomiting, abdominal pain, early satiety, and weight loss and are important to differentiate.^36,38 Although abdominal pain may be present in both gastric outlet obstruction and gastroparesis, in gastroparesis it tends not to be the dominant symptom.⁴⁰

Gastric scintigraphy is most commonly used to objectively quantify delayed gastric emptying.³⁹ Upper endoscopy is imperative to exclude mechanical obstruction.³⁹

 

 

MANAGEMENT

Initially, patients with signs and symptoms of gastric outlet obstruction should be given:

• Nothing by mouth (NPO)
• Intravenous fluids to correct volume depletion and electrolyte abnormalities
• A nasogastric tube for gastric decompression and symptom relief if symptoms persist despite being NPO
• A parenteral proton pump inhibitor, regardless of the cause of obstruction, to decrease gastric secretions⁴¹
• Medications for pain and nausea, if needed.

Definitive treatment of gastric outlet obstruction depends on the underlying cause, whether benign or malignant.

Management of benign gastric outlet obstruction

Symptoms of gastric outlet obstruction resolve spontaneously in about half of cases caused by acute peptic ulcer disease, as acute inflammation resolves.^9,22

Endoscopic dilation is an important option in patients with benign gastric outlet obstruction, including peptic ulcer disease. Peptic ulcer disease-induced gastric outlet obstruction can be safely treated with endoscopic balloon dilation. This treatment almost always relieves symptoms immediately; however, the long-term response has varied from 16% to 100%, and patients may require more than 1 dilation procedure.^25,42,43 The need for 2 or more dilation procedures may predict need for surgery.⁴⁴ Gastric outlet obstruction after caustic ingestion or endoscopic submucosal dissection may also respond to endoscopic balloon dilation.³⁶

Eradication of H pylori may be effective and lead to complete resolution of symptoms in patients with gastric outlet obstruction due to this infection.^45–47

NSAIDs should be discontinued in patients with peptic ulcer disease and gastric outlet obstruction. These drugs damage the gastrointestinal mucosa by inhibiting cyclo-oxygenase (COX) enzymes and decreasing synthesis of prostaglandins, which are important for mucosal defense.⁴⁸ Patients may be unaware of NSAIDs contained in over-the-counter medications and may have difficulty discontinuing NSAIDs taken for pain.⁴⁹

These drugs are an important cause of refractory peptic ulcer disease and can be detected by platelet COX activity testing, although this test is not widely available. In a study of patients with peptic ulcer disease without definite NSAID use or H pylori infection, up to one-third had evidence of surreptitious NSAID use as detected by platelet COX activity testing.⁵⁰ In another study,⁵¹ platelet COX activity testing discovered over 20% more aspirin users than clinical history alone.

Surgery for patients with benign gastric outlet obstruction is used only when medical management and endoscopic dilation fail. Ideally, surgery should relieve the obstruction and target the underlying cause, such as peptic ulcer disease. Laparoscopic surgery is generally preferred to open surgery because patients can resume oral intake sooner, have a shorter hospital stay, and have less intraoperative blood loss.⁵² The simplest surgical procedure to relieve obstruction is laparoscopic gastrojejunostomy.

Patients with gastric outlet obstruction and peptic ulcer disease warrant laparoscopic vagotomy and antrectomy or distal gastrectomy. This removes the obstruction and the stimulus for gastric secretion.⁵³ An alternative is vagotomy with a drainage procedure (pyloroplasty or gastrojejunostomy), which has a similar postoperative course and reduction in gastric acid secretion compared with antrectomy or distal gastrectomy.^53,54

Daily proton pump inhibitors can be used for patients with benign gastric outlet obstruction not associated with peptic ulcer disease or risk factors; for such cases, vagotomy is not required.

Management of malignant gastric outlet obstruction

Patients with malignant gastric outlet obstruction may have intractable nausea and abdominal pain secondary to retention of gastric contents. The major goal of therapy is to improve symptoms and restore tolerance of an oral diet. The short-term prognosis of malignant gastric outlet obstruction is poor, with a median survival of 3 to 4 months, as these patients often have unresectable disease.⁵⁵

Surgical bypass used to be the standard of care for palliation of malignant gastric obstruction, but that was before endoscopic stenting was developed.

Endoscopic stenting allows patients to resume oral intake and get out of the hospital sooner with fewer complications than with open surgical bypass. It may be a more appropriate option for palliation of symptoms in patients with malignant obstruction who have a poor prognosis and prefer a less invasive intervention.^55,56

Endoscopic duodenal stenting of malignant gastric outlet obstruction has a success rate of greater than 90%, and most patients can tolerate a mechanical soft diet afterward.³⁴ The procedure is usually performed with a 9-cm or 12-cm self-expanding duodenal stent, 22 mm in diameter, placed over a guide wire under endoscopic and fluoroscopic guidance (Figure 2). The stent is placed by removing the outer catheter, with distal-to-proximal stent deployment.

Patients who also have biliary obstruction may require biliary stent placement, which is generally performed before duodenal stenting. For patients with an endoscopic stent who develop biliary obstruction, endoscopic retrograde cholangiopancreatography can be attempted with placement of a biliary stent; however, these patients may require biliary drain placement by percutaneous transhepatic cholangiography or by endoscopic ultrasonographically guided transduodenal or transgastric biliary drainage.

From 20% to 30% of patients require repeated endoscopic stent placement, although most patients die within several months after stenting.³⁴ Surgical options for patients who do not respond to endoscopic stenting include open or laparoscopic gastrojejunostomy.⁵⁵

Laparoscopic gastrojejunostomy may provide better long-term outcomes than duodenal stenting for patients with malignant gastric outlet obstruction and a life expectancy longer than a few months.

A 2017 retrospective study of 155 patients with gastric outlet obstruction secondary to unresectable gastric cancer suggested that those who underwent laparoscopic gastrojejunostomy had better oral intake, better tolerance of chemotherapy, and longer overall survival than those who underwent duodenal stenting. Postsurgical complications were more common in the laparoscopic gastrojejunostomy group (16%) than in the duodenal stenting group (0%).⁵⁷

In most of the studies comparing endoscopic stenting with surgery, the surgery was open gastrojejunostomy; there are limited data directly comparing stenting with laparoscopic gastrojejunostomy.⁵⁵ Endoscopic stenting is estimated to be significantly less costly than surgery, with a median cost of $12,000 less than gastrojejunostomy.⁵⁸ As an alternative to enteral stenting and surgical gastrojejunostomy, ultrasonography-guided endoscopic gastrojejunostomy or gastroenterostomy with placement of a lumen-apposing metal stent is emerging as a third treatment option and is under active investigation.⁵⁹

Patients with malignancy that is potentially curable by resection should undergo surgical evaluation before consideration of endoscopic stenting. For patients who are not candidates for surgery or endoscopic stenting, a percutaneous gastrostomy tube can be considered for gastric decompression and symptom relief.

CASE CONCLUDED

The patient underwent esophagogastroduodenoscopy with endoscopic ultrasonography for evaluation of her pancreatic mass. Before the procedure, she was intubated to minimize the risk of aspiration due to persistent nausea and retained gastric contents. A large submucosal mass was found in the duodenal bulb. Endoscopic ultrasonography showed a mass within the pancreatic head with pancreatic duct obstruction. Fine-needle aspiration biopsy was performed, and pathology study revealed pancreatic adenocarcinoma. The patient underwent stenting with a 22-mm by 12-cm WallFlex stent (Boston Scientific), which led to resolution of nausea and advancement to a mechanical soft diet on hospital discharge.

She was scheduled for follow-up in the outpatient clinic for treatment of pancreatic cancer.

A 72-year-old woman presents to the emergency department with progressive nausea and vomiting. One week earlier, she developed early satiety and nausea with vomiting after eating solid food. Three days later her symptoms progressed, and she became unable to take anything by mouth. The patient also experienced a 40-lb weight loss in the previous 3 months. She denies symptoms of abdominal pain, hematemesis, or melena. Her medical history includes cholecystectomy and type 2 diabetes mellitus, diagnosed 1 year ago. She has no family history of gastrointestinal malignancy. She says she smoked 1 pack a day in her 20s. She does not consume alcohol.

On physical examination, she is normotensive with a heart rate of 105 beats per minute. The oral mucosa is dry, and the abdomen is mildly distended and tender to palpation in the epigastrium. Laboratory evaluation reveals hypokalemia and metabolic alkalosis.

Computed tomography (CT) reveals a mass 3 cm by 4 cm in the pancreatic head. The mass has invaded the medial wall of the duodenum, with obstruction of the pancreatic and common bile ducts and extension into and occlusion of the superior mesenteric vein, with soft-tissue expansion around the superior mesenteric artery. CT also reveals retained stomach contents and an air-fluid level consistent with gastric outlet obstruction.

INTRINSIC OR EXTRINSIC BLOCKAGE

Gastric outlet obstruction, also called pyloric obstruction, is caused by intrinsic or extrinsic mechanical blockage of gastric emptying, generally in the distal stomach, pyloric channel, or duodenum, with associated symptoms of nausea, vomiting, abdominal pain, and early satiety. It is encountered in both the clinic and the hospital.

Here, we review the causes, diagnosis, and management of this disorder.

BENIGN AND MALIGNANT CAUSES

Causes of obstruction are classified as either benign or malignant (Table 1). However, all cases of gastric outlet obstruction should be assumed to be due to underlying malignancy unless proven otherwise.¹

In a retrospective study of 76 patients hospitalized with gastric outlet obstruction between 2006 and 2015 at our institution,² 29 cases (38%) were due to malignancy and 47 (62%) were due to benign causes. Pancreatic adenocarcinoma accounted for 13 cases (17%), while gastric adenocarcinoma accounted for 5 cases (7%); less common malignant causes were cholangiocarcinoma, cancer of the ampulla of Vater, duodenal adenocarcinoma, hepatocellular carcinoma, and metastatic disease. Of the benign causes, the most common were peptic ulcer disease (13 cases, 17%) and postoperative strictures or adhesions (11 cases, 14%).

These numbers reflect general trends around the world.

Less gastric cancer, more pancreatic cancer

The last several decades have seen a trend toward more cases due to cancer and fewer due to benign causes.^3–14

In earlier studies in both developed and developing countries, gastric adenocarcinoma was the most common malignant cause of gastric outlet obstruction. Since then, it has become less common in Western countries, although it remains more common in Asia and Africa.^7–14 This trend likely reflects environmental factors, including decreased prevalence of Helicobacter pylori infection, a major risk factor for gastric cancer, in Western countries.^15–17

At the same time, pancreatic cancer is on the rise,¹⁶ and up to 20% of patients with pancreatic cancer develop gastric outlet obstruction.¹⁸ In a prospective observational study of 108 patients with malignant gastric outlet obstruction undergoing endoscopic stenting, pancreatic cancer was by far the most common malignancy, occurring in 54% of patients, followed by gastric cancer in 13%.¹⁹

Less peptic ulcer disease, but still common

Peptic ulcer disease used to account for up to 90% of cases of gastric outlet obstruction, and it is still the most common benign cause.

In 1990, gastric outlet obstruction was estimated to occur in 5% to 10% of all hospital admissions for ulcer-related complications, accounting for 2,000 operations annually.^20,21 Gastric outlet obstruction now occurs in fewer than 5% of patients with duodenal ulcer disease and fewer than 2% of patients with gastric ulcer disease.²²

Peptic ulcer disease remains an important cause of obstruction in countries with poor access to acid-suppressing drugs.²³

Gastric outlet obstruction occurs in both acute and chronic peptic ulcer disease. In acute peptic ulcer disease, tissue inflammation and edema result in mechanical obstruction. Chronic peptic ulcer disease results in tissue scarring and fibrosis with strictures.²⁰

Environmental factors, including improved diet, hygiene, physical activity, and the decreased prevalence of H pylori infection, also contribute to the decreased prevalence of peptic ulcer disease and its complications, including gastric outlet obstruction.³ The continued occurrence of peptic ulcer disease is associated with widespread use of low-dose aspirin and nonsteroidal anti-inflammatory drugs (NSAIDs), the most common causes of peptic ulcer disease in Western countries.^24,25

Other nonmalignant causes of gastric outlet obstruction are diverse and less common. They include caustic ingestion, postsurgical strictures, benign tumors of the gastrointestinal tract, Crohn disease, and pancreatic disorders including acute pancreatitis, pancreatic pseudocyst, chronic pancreatitis, and annular pancreas. Intramural duodenal hematoma may cause obstruction after blunt abdominal trauma, endoscopic biopsy, or gastrostomy tube migration, especially in the setting of a bleeding disorder or anticoagulation.²⁶

Tuberculosis should be suspected in countries in which it is common.⁷ In a prospective study of 64 patients with benign gastric outlet obstruction in India,²⁷ 16 (25%) had corrosive injury, 16 (25%) had tuberculosis, and 15 (23%) had peptic ulcer disease. Compared with patients with corrosive injury and peptic ulcer disease, patients with gastroduodenal tuberculosis had the best outcomes with appropriate treatment.

Other reported causes include Bouveret syndrome (an impacted gallstone in the proximal duodenum), phytobezoar, diaphragmatic hernia, gastric volvulus, and Ladd bands (peritoneal bands associated with intestinal malrotation).^7,28,29

 

 

PRESENTING SYMPTOMS

Symptoms of gastric outlet obstruction include nausea, nonbilious vomiting, epigastric pain, early satiety, abdominal distention, and weight loss.

In our patients, the most common presenting symptoms were nausea and vomiting (80%), followed by abdominal pain (72%); weight loss (15%), abdominal distention (15%), and early satiety (9%) were less common.²

Patients with gastric outlet obstruction secondary to malignancy generally present with a shorter duration of symptoms than those with peptic ulcer disease and are more likely to be older.^8,13 Other conditions with an acute onset of symptoms include gastric polyp prolapse, percutaneous endoscopic gastrostomy tube migration, gastric volvulus, and gallstone impaction.

Patients with gastric outlet obstruction associated with peptic ulcer disease generally have a long-standing history of symptoms, including dyspepsia and weight loss over several years.⁴

SIGNS ON EXAMINATION

On examination, look for signs of chronic gastric obstruction and its consequences, such as malnutrition, cachexia, volume depletion, and dental erosions.

A succussion splash may suggest gastric outlet obstruction. This is elicited by rocking the patient back and forth by the hips or abdomen while listening over the stomach for a splash, which may be heard without a stethoscope. The test is considered positive if present 3 or more hours after drinking fluids and suggests retention of gastric materials.^30,31

In thin individuals, chronic gastric outlet obstruction makes the stomach dilate and hypertrophy, which may be evident by a palpably thickened stomach with visible gastric peristalsis.⁴

Other notable findings on physical examination may include a palpable abdominal mass, epigastric pain, or an abnormality suggestive of metastatic gastric cancer, such as an enlarged left supraclavicular lymph node (Virchow node) or periumbilical lymph node (Sister Mary Joseph nodule). The Virchow node is at the junction of the thoracic duct and the left subclavian vein where the lymphatic circulation from the body drains into the systemic circulation, and it may be the first sign of gastric cancer.³² Sister Mary Joseph nodule (named after a surgical assistant to Dr. William James Mayo) refers to a palpable mass at the umbilicus, generally resulting from metastasis of an abdominal malignancy.³³

SIGNS ON FURTHER STUDIES

Laboratory evaluation may show signs of poor oral intake and electrolyte abnormalities secondary to chronic nausea, vomiting, and dehydration, including hypochloremic metabolic alkalosis and hypokalemia.

The underlying cause of gastric outlet obstruction has major implications for treatment and prognosis and cannot be differentiated by clinical presentation alone.^1,9 Diagnosis is based on clinical features and radiologic or endoscopic evaluation consistent with gastric outlet obstruction.

Plain radiography may reveal an enlarged gastric bubble, and contrast studies may be useful to determine whether the obstruction is partial or complete, depending on whether the contrast passes into the small bowel.

CT or magnetic resonance imaging may show gastric distention with retained stomach contents, suggesting a gastric, pyloric, duodenal, or pancreatic mass (Figure 1).

Upper endoscopy is often needed to establish the diagnosis and cause. Emptying the stomach with a nasogastric tube is recommended before endoscopy to minimize the risk of aspiration during the procedure, and endotracheal intubation should be considered for airway protection.³⁴ Findings of gastric outlet obstruction on upper endoscopy include retained food and liquid. Endoscopic biopsy is important to differentiate between benign and malignant causes. For patients with malignancy, endoscopic ultrasonography is useful for diagnosis via tissue sampling with fine-needle aspiration and locoregional staging.³⁵

A strategy. Most patients whose clinical presentation suggests gastric outlet obstruction require cross-sectional radiologic imaging, upper endoscopy, or both.³⁶ CT is the preferred imaging study to evaluate for intestinal obstruction.^36,37 Patients with suspected complete obstruction or perforation should undergo CT before upper endoscopy. Oral contrast may interfere with endoscopy and should be avoided if endoscopy is planned. Additionally, giving oral contrast may worsen patient discomfort and increase the risk of nausea, vomiting, and aspiration.^36,37

Following radiographic evaluation, upper endoscopy can be performed after gastric decompression to identify the location and extent of the obstruction and to potentially provide a definitive diagnosis with biopsy.³⁶

DIFFERENTIATE FROM GASTROPARESIS

Gastroparesis is a chronic neuromuscular disorder characterized by delayed gastric emptying without mechanical obstruction.³⁸ The most common causes are diabetes, surgery, and idiopathy. Other causes include viral infection, connective tissue diseases, ischemia, infiltrative disorders, radiation, neurologic disorders, and paraneoplastic syndromes.^39,40

Gastric outlet obstruction and gastroparesis share clinical symptoms including nausea, vomiting, abdominal pain, early satiety, and weight loss and are important to differentiate.^36,38 Although abdominal pain may be present in both gastric outlet obstruction and gastroparesis, in gastroparesis it tends not to be the dominant symptom.⁴⁰

Gastric scintigraphy is most commonly used to objectively quantify delayed gastric emptying.³⁹ Upper endoscopy is imperative to exclude mechanical obstruction.³⁹

 

 

MANAGEMENT

Initially, patients with signs and symptoms of gastric outlet obstruction should be given:

• Nothing by mouth (NPO)
• Intravenous fluids to correct volume depletion and electrolyte abnormalities
• A nasogastric tube for gastric decompression and symptom relief if symptoms persist despite being NPO
• A parenteral proton pump inhibitor, regardless of the cause of obstruction, to decrease gastric secretions⁴¹
• Medications for pain and nausea, if needed.

Definitive treatment of gastric outlet obstruction depends on the underlying cause, whether benign or malignant.

Management of benign gastric outlet obstruction

Symptoms of gastric outlet obstruction resolve spontaneously in about half of cases caused by acute peptic ulcer disease, as acute inflammation resolves.^9,22

Endoscopic dilation is an important option in patients with benign gastric outlet obstruction, including peptic ulcer disease. Peptic ulcer disease-induced gastric outlet obstruction can be safely treated with endoscopic balloon dilation. This treatment almost always relieves symptoms immediately; however, the long-term response has varied from 16% to 100%, and patients may require more than 1 dilation procedure.^25,42,43 The need for 2 or more dilation procedures may predict need for surgery.⁴⁴ Gastric outlet obstruction after caustic ingestion or endoscopic submucosal dissection may also respond to endoscopic balloon dilation.³⁶

Eradication of H pylori may be effective and lead to complete resolution of symptoms in patients with gastric outlet obstruction due to this infection.^45–47

NSAIDs should be discontinued in patients with peptic ulcer disease and gastric outlet obstruction. These drugs damage the gastrointestinal mucosa by inhibiting cyclo-oxygenase (COX) enzymes and decreasing synthesis of prostaglandins, which are important for mucosal defense.⁴⁸ Patients may be unaware of NSAIDs contained in over-the-counter medications and may have difficulty discontinuing NSAIDs taken for pain.⁴⁹

These drugs are an important cause of refractory peptic ulcer disease and can be detected by platelet COX activity testing, although this test is not widely available. In a study of patients with peptic ulcer disease without definite NSAID use or H pylori infection, up to one-third had evidence of surreptitious NSAID use as detected by platelet COX activity testing.⁵⁰ In another study,⁵¹ platelet COX activity testing discovered over 20% more aspirin users than clinical history alone.

Surgery for patients with benign gastric outlet obstruction is used only when medical management and endoscopic dilation fail. Ideally, surgery should relieve the obstruction and target the underlying cause, such as peptic ulcer disease. Laparoscopic surgery is generally preferred to open surgery because patients can resume oral intake sooner, have a shorter hospital stay, and have less intraoperative blood loss.⁵² The simplest surgical procedure to relieve obstruction is laparoscopic gastrojejunostomy.

Patients with gastric outlet obstruction and peptic ulcer disease warrant laparoscopic vagotomy and antrectomy or distal gastrectomy. This removes the obstruction and the stimulus for gastric secretion.⁵³ An alternative is vagotomy with a drainage procedure (pyloroplasty or gastrojejunostomy), which has a similar postoperative course and reduction in gastric acid secretion compared with antrectomy or distal gastrectomy.^53,54

Daily proton pump inhibitors can be used for patients with benign gastric outlet obstruction not associated with peptic ulcer disease or risk factors; for such cases, vagotomy is not required.

Management of malignant gastric outlet obstruction

Patients with malignant gastric outlet obstruction may have intractable nausea and abdominal pain secondary to retention of gastric contents. The major goal of therapy is to improve symptoms and restore tolerance of an oral diet. The short-term prognosis of malignant gastric outlet obstruction is poor, with a median survival of 3 to 4 months, as these patients often have unresectable disease.⁵⁵

Surgical bypass used to be the standard of care for palliation of malignant gastric obstruction, but that was before endoscopic stenting was developed.

Endoscopic stenting allows patients to resume oral intake and get out of the hospital sooner with fewer complications than with open surgical bypass. It may be a more appropriate option for palliation of symptoms in patients with malignant obstruction who have a poor prognosis and prefer a less invasive intervention.^55,56

Endoscopic duodenal stenting of malignant gastric outlet obstruction has a success rate of greater than 90%, and most patients can tolerate a mechanical soft diet afterward.³⁴ The procedure is usually performed with a 9-cm or 12-cm self-expanding duodenal stent, 22 mm in diameter, placed over a guide wire under endoscopic and fluoroscopic guidance (Figure 2). The stent is placed by removing the outer catheter, with distal-to-proximal stent deployment.

Patients who also have biliary obstruction may require biliary stent placement, which is generally performed before duodenal stenting. For patients with an endoscopic stent who develop biliary obstruction, endoscopic retrograde cholangiopancreatography can be attempted with placement of a biliary stent; however, these patients may require biliary drain placement by percutaneous transhepatic cholangiography or by endoscopic ultrasonographically guided transduodenal or transgastric biliary drainage.

From 20% to 30% of patients require repeated endoscopic stent placement, although most patients die within several months after stenting.³⁴ Surgical options for patients who do not respond to endoscopic stenting include open or laparoscopic gastrojejunostomy.⁵⁵

Laparoscopic gastrojejunostomy may provide better long-term outcomes than duodenal stenting for patients with malignant gastric outlet obstruction and a life expectancy longer than a few months.

A 2017 retrospective study of 155 patients with gastric outlet obstruction secondary to unresectable gastric cancer suggested that those who underwent laparoscopic gastrojejunostomy had better oral intake, better tolerance of chemotherapy, and longer overall survival than those who underwent duodenal stenting. Postsurgical complications were more common in the laparoscopic gastrojejunostomy group (16%) than in the duodenal stenting group (0%).⁵⁷

In most of the studies comparing endoscopic stenting with surgery, the surgery was open gastrojejunostomy; there are limited data directly comparing stenting with laparoscopic gastrojejunostomy.⁵⁵ Endoscopic stenting is estimated to be significantly less costly than surgery, with a median cost of $12,000 less than gastrojejunostomy.⁵⁸ As an alternative to enteral stenting and surgical gastrojejunostomy, ultrasonography-guided endoscopic gastrojejunostomy or gastroenterostomy with placement of a lumen-apposing metal stent is emerging as a third treatment option and is under active investigation.⁵⁹

Patients with malignancy that is potentially curable by resection should undergo surgical evaluation before consideration of endoscopic stenting. For patients who are not candidates for surgery or endoscopic stenting, a percutaneous gastrostomy tube can be considered for gastric decompression and symptom relief.

CASE CONCLUDED

The patient underwent esophagogastroduodenoscopy with endoscopic ultrasonography for evaluation of her pancreatic mass. Before the procedure, she was intubated to minimize the risk of aspiration due to persistent nausea and retained gastric contents. A large submucosal mass was found in the duodenal bulb. Endoscopic ultrasonography showed a mass within the pancreatic head with pancreatic duct obstruction. Fine-needle aspiration biopsy was performed, and pathology study revealed pancreatic adenocarcinoma. The patient underwent stenting with a 22-mm by 12-cm WallFlex stent (Boston Scientific), which led to resolution of nausea and advancement to a mechanical soft diet on hospital discharge.

She was scheduled for follow-up in the outpatient clinic for treatment of pancreatic cancer.

A 72-year-old woman presents to the emergency department with progressive nausea and vomiting. One week earlier, she developed early satiety and nausea with vomiting after eating solid food. Three days later her symptoms progressed, and she became unable to take anything by mouth. The patient also experienced a 40-lb weight loss in the previous 3 months. She denies symptoms of abdominal pain, hematemesis, or melena. Her medical history includes cholecystectomy and type 2 diabetes mellitus, diagnosed 1 year ago. She has no family history of gastrointestinal malignancy. She says she smoked 1 pack a day in her 20s. She does not consume alcohol.

On physical examination, she is normotensive with a heart rate of 105 beats per minute. The oral mucosa is dry, and the abdomen is mildly distended and tender to palpation in the epigastrium. Laboratory evaluation reveals hypokalemia and metabolic alkalosis.

Computed tomography (CT) reveals a mass 3 cm by 4 cm in the pancreatic head. The mass has invaded the medial wall of the duodenum, with obstruction of the pancreatic and common bile ducts and extension into and occlusion of the superior mesenteric vein, with soft-tissue expansion around the superior mesenteric artery. CT also reveals retained stomach contents and an air-fluid level consistent with gastric outlet obstruction.

INTRINSIC OR EXTRINSIC BLOCKAGE

Gastric outlet obstruction, also called pyloric obstruction, is caused by intrinsic or extrinsic mechanical blockage of gastric emptying, generally in the distal stomach, pyloric channel, or duodenum, with associated symptoms of nausea, vomiting, abdominal pain, and early satiety. It is encountered in both the clinic and the hospital.

Here, we review the causes, diagnosis, and management of this disorder.

BENIGN AND MALIGNANT CAUSES

Causes of obstruction are classified as either benign or malignant (Table 1). However, all cases of gastric outlet obstruction should be assumed to be due to underlying malignancy unless proven otherwise.¹

In a retrospective study of 76 patients hospitalized with gastric outlet obstruction between 2006 and 2015 at our institution,² 29 cases (38%) were due to malignancy and 47 (62%) were due to benign causes. Pancreatic adenocarcinoma accounted for 13 cases (17%), while gastric adenocarcinoma accounted for 5 cases (7%); less common malignant causes were cholangiocarcinoma, cancer of the ampulla of Vater, duodenal adenocarcinoma, hepatocellular carcinoma, and metastatic disease. Of the benign causes, the most common were peptic ulcer disease (13 cases, 17%) and postoperative strictures or adhesions (11 cases, 14%).

These numbers reflect general trends around the world.

Less gastric cancer, more pancreatic cancer

The last several decades have seen a trend toward more cases due to cancer and fewer due to benign causes.^3–14

In earlier studies in both developed and developing countries, gastric adenocarcinoma was the most common malignant cause of gastric outlet obstruction. Since then, it has become less common in Western countries, although it remains more common in Asia and Africa.^7–14 This trend likely reflects environmental factors, including decreased prevalence of Helicobacter pylori infection, a major risk factor for gastric cancer, in Western countries.^15–17

At the same time, pancreatic cancer is on the rise,¹⁶ and up to 20% of patients with pancreatic cancer develop gastric outlet obstruction.¹⁸ In a prospective observational study of 108 patients with malignant gastric outlet obstruction undergoing endoscopic stenting, pancreatic cancer was by far the most common malignancy, occurring in 54% of patients, followed by gastric cancer in 13%.¹⁹

Less peptic ulcer disease, but still common

Peptic ulcer disease used to account for up to 90% of cases of gastric outlet obstruction, and it is still the most common benign cause.

In 1990, gastric outlet obstruction was estimated to occur in 5% to 10% of all hospital admissions for ulcer-related complications, accounting for 2,000 operations annually.^20,21 Gastric outlet obstruction now occurs in fewer than 5% of patients with duodenal ulcer disease and fewer than 2% of patients with gastric ulcer disease.²²

Peptic ulcer disease remains an important cause of obstruction in countries with poor access to acid-suppressing drugs.²³

Gastric outlet obstruction occurs in both acute and chronic peptic ulcer disease. In acute peptic ulcer disease, tissue inflammation and edema result in mechanical obstruction. Chronic peptic ulcer disease results in tissue scarring and fibrosis with strictures.²⁰

Environmental factors, including improved diet, hygiene, physical activity, and the decreased prevalence of H pylori infection, also contribute to the decreased prevalence of peptic ulcer disease and its complications, including gastric outlet obstruction.³ The continued occurrence of peptic ulcer disease is associated with widespread use of low-dose aspirin and nonsteroidal anti-inflammatory drugs (NSAIDs), the most common causes of peptic ulcer disease in Western countries.^24,25

Other nonmalignant causes of gastric outlet obstruction are diverse and less common. They include caustic ingestion, postsurgical strictures, benign tumors of the gastrointestinal tract, Crohn disease, and pancreatic disorders including acute pancreatitis, pancreatic pseudocyst, chronic pancreatitis, and annular pancreas. Intramural duodenal hematoma may cause obstruction after blunt abdominal trauma, endoscopic biopsy, or gastrostomy tube migration, especially in the setting of a bleeding disorder or anticoagulation.²⁶

Tuberculosis should be suspected in countries in which it is common.⁷ In a prospective study of 64 patients with benign gastric outlet obstruction in India,²⁷ 16 (25%) had corrosive injury, 16 (25%) had tuberculosis, and 15 (23%) had peptic ulcer disease. Compared with patients with corrosive injury and peptic ulcer disease, patients with gastroduodenal tuberculosis had the best outcomes with appropriate treatment.

Other reported causes include Bouveret syndrome (an impacted gallstone in the proximal duodenum), phytobezoar, diaphragmatic hernia, gastric volvulus, and Ladd bands (peritoneal bands associated with intestinal malrotation).^7,28,29

 

 

PRESENTING SYMPTOMS

Symptoms of gastric outlet obstruction include nausea, nonbilious vomiting, epigastric pain, early satiety, abdominal distention, and weight loss.

In our patients, the most common presenting symptoms were nausea and vomiting (80%), followed by abdominal pain (72%); weight loss (15%), abdominal distention (15%), and early satiety (9%) were less common.²

Patients with gastric outlet obstruction secondary to malignancy generally present with a shorter duration of symptoms than those with peptic ulcer disease and are more likely to be older.^8,13 Other conditions with an acute onset of symptoms include gastric polyp prolapse, percutaneous endoscopic gastrostomy tube migration, gastric volvulus, and gallstone impaction.

Patients with gastric outlet obstruction associated with peptic ulcer disease generally have a long-standing history of symptoms, including dyspepsia and weight loss over several years.⁴

SIGNS ON EXAMINATION

On examination, look for signs of chronic gastric obstruction and its consequences, such as malnutrition, cachexia, volume depletion, and dental erosions.

A succussion splash may suggest gastric outlet obstruction. This is elicited by rocking the patient back and forth by the hips or abdomen while listening over the stomach for a splash, which may be heard without a stethoscope. The test is considered positive if present 3 or more hours after drinking fluids and suggests retention of gastric materials.^30,31

In thin individuals, chronic gastric outlet obstruction makes the stomach dilate and hypertrophy, which may be evident by a palpably thickened stomach with visible gastric peristalsis.⁴

Other notable findings on physical examination may include a palpable abdominal mass, epigastric pain, or an abnormality suggestive of metastatic gastric cancer, such as an enlarged left supraclavicular lymph node (Virchow node) or periumbilical lymph node (Sister Mary Joseph nodule). The Virchow node is at the junction of the thoracic duct and the left subclavian vein where the lymphatic circulation from the body drains into the systemic circulation, and it may be the first sign of gastric cancer.³² Sister Mary Joseph nodule (named after a surgical assistant to Dr. William James Mayo) refers to a palpable mass at the umbilicus, generally resulting from metastasis of an abdominal malignancy.³³

SIGNS ON FURTHER STUDIES

Laboratory evaluation may show signs of poor oral intake and electrolyte abnormalities secondary to chronic nausea, vomiting, and dehydration, including hypochloremic metabolic alkalosis and hypokalemia.

The underlying cause of gastric outlet obstruction has major implications for treatment and prognosis and cannot be differentiated by clinical presentation alone.^1,9 Diagnosis is based on clinical features and radiologic or endoscopic evaluation consistent with gastric outlet obstruction.

Plain radiography may reveal an enlarged gastric bubble, and contrast studies may be useful to determine whether the obstruction is partial or complete, depending on whether the contrast passes into the small bowel.

CT or magnetic resonance imaging may show gastric distention with retained stomach contents, suggesting a gastric, pyloric, duodenal, or pancreatic mass (Figure 1).

Upper endoscopy is often needed to establish the diagnosis and cause. Emptying the stomach with a nasogastric tube is recommended before endoscopy to minimize the risk of aspiration during the procedure, and endotracheal intubation should be considered for airway protection.³⁴ Findings of gastric outlet obstruction on upper endoscopy include retained food and liquid. Endoscopic biopsy is important to differentiate between benign and malignant causes. For patients with malignancy, endoscopic ultrasonography is useful for diagnosis via tissue sampling with fine-needle aspiration and locoregional staging.³⁵

A strategy. Most patients whose clinical presentation suggests gastric outlet obstruction require cross-sectional radiologic imaging, upper endoscopy, or both.³⁶ CT is the preferred imaging study to evaluate for intestinal obstruction.^36,37 Patients with suspected complete obstruction or perforation should undergo CT before upper endoscopy. Oral contrast may interfere with endoscopy and should be avoided if endoscopy is planned. Additionally, giving oral contrast may worsen patient discomfort and increase the risk of nausea, vomiting, and aspiration.^36,37

Following radiographic evaluation, upper endoscopy can be performed after gastric decompression to identify the location and extent of the obstruction and to potentially provide a definitive diagnosis with biopsy.³⁶

DIFFERENTIATE FROM GASTROPARESIS

Gastroparesis is a chronic neuromuscular disorder characterized by delayed gastric emptying without mechanical obstruction.³⁸ The most common causes are diabetes, surgery, and idiopathy. Other causes include viral infection, connective tissue diseases, ischemia, infiltrative disorders, radiation, neurologic disorders, and paraneoplastic syndromes.^39,40

Gastric outlet obstruction and gastroparesis share clinical symptoms including nausea, vomiting, abdominal pain, early satiety, and weight loss and are important to differentiate.^36,38 Although abdominal pain may be present in both gastric outlet obstruction and gastroparesis, in gastroparesis it tends not to be the dominant symptom.⁴⁰

Gastric scintigraphy is most commonly used to objectively quantify delayed gastric emptying.³⁹ Upper endoscopy is imperative to exclude mechanical obstruction.³⁹

 

 

MANAGEMENT

Initially, patients with signs and symptoms of gastric outlet obstruction should be given:

• Nothing by mouth (NPO)
• Intravenous fluids to correct volume depletion and electrolyte abnormalities
• A nasogastric tube for gastric decompression and symptom relief if symptoms persist despite being NPO
• A parenteral proton pump inhibitor, regardless of the cause of obstruction, to decrease gastric secretions⁴¹
• Medications for pain and nausea, if needed.

Definitive treatment of gastric outlet obstruction depends on the underlying cause, whether benign or malignant.

Management of benign gastric outlet obstruction

Symptoms of gastric outlet obstruction resolve spontaneously in about half of cases caused by acute peptic ulcer disease, as acute inflammation resolves.^9,22

Endoscopic dilation is an important option in patients with benign gastric outlet obstruction, including peptic ulcer disease. Peptic ulcer disease-induced gastric outlet obstruction can be safely treated with endoscopic balloon dilation. This treatment almost always relieves symptoms immediately; however, the long-term response has varied from 16% to 100%, and patients may require more than 1 dilation procedure.^25,42,43 The need for 2 or more dilation procedures may predict need for surgery.⁴⁴ Gastric outlet obstruction after caustic ingestion or endoscopic submucosal dissection may also respond to endoscopic balloon dilation.³⁶

Eradication of H pylori may be effective and lead to complete resolution of symptoms in patients with gastric outlet obstruction due to this infection.^45–47

NSAIDs should be discontinued in patients with peptic ulcer disease and gastric outlet obstruction. These drugs damage the gastrointestinal mucosa by inhibiting cyclo-oxygenase (COX) enzymes and decreasing synthesis of prostaglandins, which are important for mucosal defense.⁴⁸ Patients may be unaware of NSAIDs contained in over-the-counter medications and may have difficulty discontinuing NSAIDs taken for pain.⁴⁹

These drugs are an important cause of refractory peptic ulcer disease and can be detected by platelet COX activity testing, although this test is not widely available. In a study of patients with peptic ulcer disease without definite NSAID use or H pylori infection, up to one-third had evidence of surreptitious NSAID use as detected by platelet COX activity testing.⁵⁰ In another study,⁵¹ platelet COX activity testing discovered over 20% more aspirin users than clinical history alone.

Surgery for patients with benign gastric outlet obstruction is used only when medical management and endoscopic dilation fail. Ideally, surgery should relieve the obstruction and target the underlying cause, such as peptic ulcer disease. Laparoscopic surgery is generally preferred to open surgery because patients can resume oral intake sooner, have a shorter hospital stay, and have less intraoperative blood loss.⁵² The simplest surgical procedure to relieve obstruction is laparoscopic gastrojejunostomy.

Patients with gastric outlet obstruction and peptic ulcer disease warrant laparoscopic vagotomy and antrectomy or distal gastrectomy. This removes the obstruction and the stimulus for gastric secretion.⁵³ An alternative is vagotomy with a drainage procedure (pyloroplasty or gastrojejunostomy), which has a similar postoperative course and reduction in gastric acid secretion compared with antrectomy or distal gastrectomy.^53,54

Daily proton pump inhibitors can be used for patients with benign gastric outlet obstruction not associated with peptic ulcer disease or risk factors; for such cases, vagotomy is not required.

Management of malignant gastric outlet obstruction

Patients with malignant gastric outlet obstruction may have intractable nausea and abdominal pain secondary to retention of gastric contents. The major goal of therapy is to improve symptoms and restore tolerance of an oral diet. The short-term prognosis of malignant gastric outlet obstruction is poor, with a median survival of 3 to 4 months, as these patients often have unresectable disease.⁵⁵

Surgical bypass used to be the standard of care for palliation of malignant gastric obstruction, but that was before endoscopic stenting was developed.

Endoscopic stenting allows patients to resume oral intake and get out of the hospital sooner with fewer complications than with open surgical bypass. It may be a more appropriate option for palliation of symptoms in patients with malignant obstruction who have a poor prognosis and prefer a less invasive intervention.^55,56

Endoscopic duodenal stenting of malignant gastric outlet obstruction has a success rate of greater than 90%, and most patients can tolerate a mechanical soft diet afterward.³⁴ The procedure is usually performed with a 9-cm or 12-cm self-expanding duodenal stent, 22 mm in diameter, placed over a guide wire under endoscopic and fluoroscopic guidance (Figure 2). The stent is placed by removing the outer catheter, with distal-to-proximal stent deployment.

Patients who also have biliary obstruction may require biliary stent placement, which is generally performed before duodenal stenting. For patients with an endoscopic stent who develop biliary obstruction, endoscopic retrograde cholangiopancreatography can be attempted with placement of a biliary stent; however, these patients may require biliary drain placement by percutaneous transhepatic cholangiography or by endoscopic ultrasonographically guided transduodenal or transgastric biliary drainage.

From 20% to 30% of patients require repeated endoscopic stent placement, although most patients die within several months after stenting.³⁴ Surgical options for patients who do not respond to endoscopic stenting include open or laparoscopic gastrojejunostomy.⁵⁵

Laparoscopic gastrojejunostomy may provide better long-term outcomes than duodenal stenting for patients with malignant gastric outlet obstruction and a life expectancy longer than a few months.

A 2017 retrospective study of 155 patients with gastric outlet obstruction secondary to unresectable gastric cancer suggested that those who underwent laparoscopic gastrojejunostomy had better oral intake, better tolerance of chemotherapy, and longer overall survival than those who underwent duodenal stenting. Postsurgical complications were more common in the laparoscopic gastrojejunostomy group (16%) than in the duodenal stenting group (0%).⁵⁷

In most of the studies comparing endoscopic stenting with surgery, the surgery was open gastrojejunostomy; there are limited data directly comparing stenting with laparoscopic gastrojejunostomy.⁵⁵ Endoscopic stenting is estimated to be significantly less costly than surgery, with a median cost of $12,000 less than gastrojejunostomy.⁵⁸ As an alternative to enteral stenting and surgical gastrojejunostomy, ultrasonography-guided endoscopic gastrojejunostomy or gastroenterostomy with placement of a lumen-apposing metal stent is emerging as a third treatment option and is under active investigation.⁵⁹

Patients with malignancy that is potentially curable by resection should undergo surgical evaluation before consideration of endoscopic stenting. For patients who are not candidates for surgery or endoscopic stenting, a percutaneous gastrostomy tube can be considered for gastric decompression and symptom relief.

CASE CONCLUDED

The patient underwent esophagogastroduodenoscopy with endoscopic ultrasonography for evaluation of her pancreatic mass. Before the procedure, she was intubated to minimize the risk of aspiration due to persistent nausea and retained gastric contents. A large submucosal mass was found in the duodenal bulb. Endoscopic ultrasonography showed a mass within the pancreatic head with pancreatic duct obstruction. Fine-needle aspiration biopsy was performed, and pathology study revealed pancreatic adenocarcinoma. The patient underwent stenting with a 22-mm by 12-cm WallFlex stent (Boston Scientific), which led to resolution of nausea and advancement to a mechanical soft diet on hospital discharge.

She was scheduled for follow-up in the outpatient clinic for treatment of pancreatic cancer.

Total hip or knee replacement (also called total joint arthroplasty) is highly successful at relieving pain and restoring function, but at the risk of acute kidney injury, which is a sudden loss of renal function. Various factors have been associated with this risk, some of which are potentially modifiable, notably, the use of nephrotoxic antibiotics and other drugs.

This review examines the incidence of acute kidney injury using current criteria in total joint arthroplasty of the hip or knee in general, and in the setting of revision surgery for prosthetic joint infection in particular, in which the risk is higher. We identify risk factors for acute kidney injury and propose ways to lower the risk.

MILLIONS OF PROCEDURES ANNUALLY

Total replacement of the hip^1,2 or knee³ is being done more and more. Kurtz et al⁴ estimate that by the year 2030, we will see approximately 3.5 million primary total knee and 500,000 primary total hip replacements every year. In addition, revision total knee procedures are expected to exceed 250,000 per year, and revision total hip procedures are expected to exceed 90,000 per year.⁴

Chronic infection may complicate up to 2% of these procedures and is associated with significant morbidity, death, and financial costs. Currently, it may be the reason for 25% of total joint arthroplasty revisions,⁵ but by the year 2030, it is projected to account for 66% of revision total knee arthroplasties and 48% of revision total hip arthroplasties.⁶

PRIMARY TOTAL JOINT ARTHROPLASTY AND ACUTE KIDNEY INJURY

We searched Ovid MEDLINE for articles on acute kidney injury and either arthroplasty or antibiotic-loaded cement spacers. We found 22 studies, with a total of 72,850 patients, that assessed the incidence of acute kidney injury after primary or revision total joint arthroplasty of the hip or knee, or both, using current criteria^7–28 (Table 1), and 3 additional studies that used discharge diagnosis coding.^29–31

Study designs, findings varied widely

The incidence of acute kidney injury varied markedly among the studies of primary total joint arthroplasty or revision for aseptic reasons. Numerous factors explain this heterogeneity.

Designs ranged from single-center studies with relatively small numbers of patients to large regional and national samples based on administrative data.

The definition of acute kidney injury also varied, although many used current criteria, specifically the RIFLE (risk, injury, failure, loss, end-stage renal disease),³² AKIN (Acute Kidney Injury Network),³³ and KDIGO (Kidney Disease Improving Global Outcomes)³⁴ creatinine criteria (Table 2). Some studies considered only higher stages of acute kidney injury (equivalent to KDIGO stage 2 or 3), ignoring the most common stage, ie, stage 1. No study considered urine output criteria.

Almost all of the studies were retrospective. We are not aware of any randomized controlled trials.

Discharge diagnosis may miss many cases

Several studies based the diagnosis of acute kidney injury on International Classification of Diseases, Ninth Revision (ICD-9) coding from hospital discharge summaries.

Nadkarni et al,²⁹ in the largest study published to date, used the nationwide inpatient sample database of more than 7 million total joint arthroplasties and found an incidence of acute kidney injury based on ICD-9 coding of 1.3% over the years 2002 to 2012, although this increased to 1.8% to 1.9% from 2010 to 2012.

Lopez-de-Andres et al,³⁰ in a similar study using the Spanish national hospital discharge database, evaluated 20,188 patients who underwent revision total hip or knee arthroplasty and found an overall incidence of acute kidney injury of 0.94%, also using ICD-9 coding.

Gharaibeh et al³¹ used similar methods to diagnose acute kidney injury in a single-center study of 8,949 patients and found an incidence of 1.1%.

Although these 3 studies suggest that the incidence of acute kidney injury is relatively low, Grams et al³⁵ found the sensitivity of ICD-9 coding from hospital records for the diagnosis of acute kidney injury to be only 11.7% compared with KDIGO serum creatinine and urine output criteria. This suggests that the true incidence in these studies may be many times higher, possibly near 10%.

Do all stages of kidney injury count?

Jafari et al,⁷ in a large series from a single medical center, used only the “I” (injury) and “F” (failure) levels of the RIFLE criteria (corresponding to stages 2 and 3 of the KDIGO criteria) and found an incidence of 0.55% in more than 17,000 total joint arthroplasties.

Jamsa et al⁸ used the same criteria for acute kidney injury (only “I” and “F”) and found 58 cases in 5,609 patients in whom postoperative serum creatinine was measured, for an incidence of 1%; the remaining 14,966 patients in their cohort did not have serum creatinine measured, and it was assumed they did not have acute kidney injury. Neither of these studies included the most common “R” (risk) stage of acute kidney injury.

Parr et al³⁶ recently studied a nationwide sample of 657,840 hospitalized veterans and found that of 90,614 who developed acute kidney injury based on KDIGO creatinine criteria, 84% reached only stage R. This suggests that if all stages were considered, the true incidence of acute kidney injury would have been higher—possibly 4% in the Jafari series and possibly 7% in the Jamsa series.

Smaller studies had higher rates

Smaller, single-center series reported much higher incidences of acute kidney injury.

Kimmel et al¹¹ found an incidence of 14.8% in 425 total joint arthroplasties using RIFLE creatinine criteria.

Johansson et al²⁵ found an incidence of 19.9% in 136 total joint arthroplasties using KDIGO creatinine criteria.

Sehgal et al⁹ found an incidence of 21.9% in 659 total joint arthroplasties using AKIN creatinine criteria.

Challagundla et al²⁴ found an incidence of 23.7% in 198 procedures using RIFLE creatinine criteria.

Weingarten et al,¹⁰ in a single-center series of 7,463 total joint arthroplasties, found an incidence of acute kidney injury of only 2.2% using AKIN criteria, although 12% of the patients with acute kidney injury did not return to their baseline serum creatinine levels by 3 months.

Our estimate: Nearly 10%

In total, in the 20 studies in Table 1 that included all stages of acute kidney injury, there were 1,909 cases of acute kidney injury in 34,337 patients, for an incidence of 5.6%. Considering that all studies but one were retrospective and none considered urine output criteria for acute kidney injury, we believe that using current KDIGO criteria, the true incidence of acute kidney injury complicating primary lower-extremity total joint arthroplasties is really closer to 10%.

 

 

RISK FACTORS FOR ACUTE KIDNEY INJURY

Various factors have been associated with development of acute kidney injury by multivariate analysis in these studies. Some are modifiable, while others are not, at least in the short term.

Nonmodifiable risk factors

Older age is often significant in studies assessing primary total joint arthroplasty or revision total joint arthroplasty not specifically for infection.^{11,12,16,17,26,28}

Obesity is also a major factor in the development of acute kidney injury,^{7,10–12,17,18} and, along with age, is a major factor contributing to the need for joint replacement in the first place.

Male sex may increase risk.²⁹

Diabetes mellitus was identified as a risk factor in several studies,^10,12,17,20 and hypertension in a few.^7,10,24

Other comorbidities and factors such as cardiovascular disease,^7,10 liver disease,⁷ pulmonary disease,⁷ high American Society of Anesthesiology score,^8,19 and benign heart murmurs preoperatively by routine physical examination have also been linked to acute kidney injury after joint arthroplasty.²⁸

Chronic kidney disease as a risk factor

Chronic kidney disease at baseline was associated with acute kidney injury in several of these series.^{7,11–13,15,19,29}

Warth et al¹² studied 1,038 patients and found an incidence of acute kidney injury of 11% in the 135 with chronic kidney disease (defined as serum creatinine > 1.2 mg/dL) and who received acetaminophen or narcotics for pain control, compared with 4.8% in the remaining 903 patients without chronic kidney disease, who received ketorolac or celecoxib.

Perregaard et al¹³ studied 3,410 patients who underwent total hip arthroplasty and found an incidence of acute kidney injury (per KDIGO creatinine criteria) of 2.2% overall, but 7% in the 134 patients with chronic kidney disease based on KDIGO creatinine criteria.

Nowicka et al¹⁵ found an incidence of acute kidney injury of 16.7% in the 48 patients with chronic kidney disease (defined as a glomerular filtration rate estimated by the Cockroft-Gault formula of less than 60 mL/min/1.73 m²), compared with 4.5% in the remaining 289.

Modifiable risk factors

Modifiable risk factors that should be considered in high-risk cases include anemia, perioperative blood transfusion, perioperative use of renin-angiotensin-aldosterone system inhibitors such as angiotensin-converting enzyme (ACE) inhibitors and angiotensin II receptor blockers (ARBs), particular antibiotics used for prophylaxis, and nonsteroidal anti-inflammatory drugs used postoperatively.

Anemia and blood transfusion

Preoperative anemia has been associated with postoperative acute kidney injury in various surgical settings such as cardiac surgery.^37,38 Perioperative red blood cell transfusions have also been associated with acute kidney injury in cardiac surgery; similar results may apply to total joint arthroplasty.

Choi et al,¹⁷ in 2,467 patients undergoing hip replacement, found a significant risk for acute kidney injury if postoperative hemoglobin was consistently below 10 g/dL compared with consistently above this level, with an inverse probability-of-treatment weighted odds ratio of 1.817 (P = .011).

Others have found a significant association of perioperative blood transfusion with acute kidney injury in total joint arthroplasty.^10,29

Nadkarni et al,²⁹ for example, used the nationwide inpatient sample database and found by multivariate analysis that perioperative blood transfusion was strongly associated with acute kidney injury, with an adjusted odds ratio of 2.28 (95% confidence interval [CI] 2.15–2.42, P < .0001).

Comment. A higher incidence of acute kidney injury may represent confounding by indication bias, as sicker patients or complicated surgeries may require transfusion, and this risk may not be completely accounted for by multivariate analysis. It is also possible, however, that transfusions per se may contribute to acute kidney injury. Possible direct or indirect mechanisms mediating acute kidney injury include hemolytic reactions, circulatory overload, acute lung injury, and immunomodulatory effects.³⁹

Preoperative transfusion in anemic patients undergoing cardiac surgery may also reduce the incidence of postoperative acute kidney injury both by correcting the anemia and by limiting the need for perioperative transfusions.⁴⁰ It remains to be determined whether elective preoperative transfusion to correct anemia would reduce postoperative development of acute kidney injury in total joint arthroplasty. As an aside, perioperative transfusion has also been linked to development of periprosthetic joint infection.⁴¹

Renin-angiotensin-aldosterone system inhibitors

Several studies found perioperative use of renin-angiotensin-aldosterone system inhibitors to be a risk factor for acute kidney injury.

Kimmel et al¹¹ reported adjusted odds ratios of 2.70 (95% CI 1.12–6.48) for ACE inhibitor use and 2.64 (95% CI 1.18–5.93) for ARB use in a study of 425 primary total joint arthroplasties.

Challagundla et al²⁴ found an odds ratio of 3.07 (95% CI 1.40–6.74) with ACE inhibitor or ARB use by multivariate analysis in 198 total joint arthroplasties.

Nielson et al¹⁸ studied 798 patients who underwent total joint arthroplasty and found that preoperative use of renin-angiotensin system inhibitors was associated with a significantly higher rate of postoperative acute kidney injury (8.3% vs 1.7% without inhibition), which was statistically significant by multivariate analysis (odds ratio 2.6, 95% CI 1.04–6.51).

We recommend holding renin-angiotensin-aldosterone system inhibitors 7 days before surgery through the postoperative period in high-risk cases.

Aminoglycoside use as a risk factor

Prophylactic administration of systemic antibiotics is the standard of care. In a systematic review of 26 studies and meta-analysis of 7 studies (3,065 patients), prophylactic antibiotics reduced the relative risk of wound infection by 81% with an absolute risk reduction of 8%.⁴²

A modifiable risk factor for acute kidney injury is the specific antibiotic used for prophylaxis. Multiple studies assessed the risk of acute kidney injury comparing regimens containing an aminoglycoside (typically gentamicin) with regimens lacking these agents.^20–26 In general, these studies found a significantly higher risk of acute kidney injury when gentamicin was used.

Challagundla et al²⁴ found an incidence of acute kidney injury of 52% using RIFLE creatinine criteria in 52 patients receiving 8 g total of flucloxacillin plus 160 mg of gentamicin (120 mg if they weighed less than 60 kg) compared with 8% in 48 patients given cefuroxime (3 g total) and 14% in an additional 52 patients also given cefuroxime.

Johansson et al²⁵ found an incidence of KDIGO creatinine-based acute kidney injury of 13% in 70 patients given dicloxacillin alone prophylactically compared with 27% given dicloxacillin and gentamicin, with a relative risk of 3.

Bell et al,²¹ in a large registry-based analysis from Scotland involving 7,666 elective orthopedic procedures, found that use of flucloxacillin 2 g plus a single dose of gentamicin 4 mg/kg was significantly associated with a 94% higher risk of acute kidney injury (KDIGO creatinine criteria) compared with a cefuroxime-based regimen, with absolute rates increasing from 6.2% to 10.8%.

Dubrovskaya et al²⁰ and Ferguson et al,²⁶ in contrast, found no increased risk with addition of gentamicin.

We recommend avoiding aminoglycosides for prophylaxis in primary lower-extremity total joint arthroplasty in patients at higher risk unless required for specific microbiologic reasons.

Vancomycin may also increase risk

Courtney et al¹⁹ assessed the risk of adding vancomycin to cefazolin for routine prophylaxis in a retrospective series of 1,828 total hip or knee arthroplasties and found a significantly higher rate of acute kidney injury, using AKIN criteria (13% vs 8%, odds ratio by multivariate analysis 1.82, P = .002).¹⁹

Other agents shown to be effective in treating periprosthetic joint infections or complicated skin and soft-tissue infections with resistant organisms include daptomycin⁴³ and linezolid.⁴⁴ These nonnephrotoxic alternatives to vancomycin may be a consideration if prophylaxis for methicillin-resistant Staphylococcus aureus is deemed necessary in patients at risk for acute kidney injury.

 

 

PROSTHETIC JOINT INFECTIONS AND ANTIBIOTIC-LOADED CEMENT

Deep infection may complicate nearly 1% of total hip⁴⁵ and 2% of total knee arthroplasties.⁴⁶ Kurtz et al^4,6 have projected that by 2030, infection will be the cause of two-thirds of the estimated 268,000 revision total knee arthroplasties and about half of the estimated 96,700 revision total hip arthroplasties.

The most common method of treating a chronically infected replacement joint is a 2-stage procedure.⁵ First, the prosthesis is removed, all infected bone and soft tissue is debrided, and an antibiotic-loaded cement spacer is implanted. Systemic antibiotics are given concurrently, typically for about 6 weeks. After the infection is brought under control, perhaps 2 to 3 months later, the spacer is removed and a new joint is implanted with antibiotic-loaded cement. A 1-stage procedure may be an option in selected cases and would obviate the need for an antibiotic-loaded cement spacer.^47,48

Of obvious relevance to development of acute kidney injury is the choice and amount of antibiotics embedded in the cement used for spacers and in implantation. Very high antibiotic levels are achieved within the joint space, usually with little systemic absorption, although significant systemic exposure has been documented in some cases.

The polymethylmethacrylate cement used for these purposes comes in 40-g bags. Multiple bags are typically required per joint, perhaps 2 to 4.⁴⁹

The rate of elution of antibiotics is determined by several factors, including surface area, porosity, and the number of antibiotics. In general, elution is greatest early on, with exponential decline lasting perhaps 1 week,  followed by slow, sustained release over weeks to months.⁵⁰ However, several in vitro studies have indicated that only about 5%^50,51 of the total antibiotic actually elutes over time.

Initially, multiple antibiotic-laden cement beads were used to fill the joint space, but this significantly limited function and mobility.⁵² Now, cement spacers are used, and they can be nonarticulating or articulating for maximal joint mobility.⁵³ Although much greater antibiotic elution occurs from beads due to their high surface area-to-volume ratio, spacers still provide an adequate dose.

ANTIBIOTIC-LOADED CEMENT: DOSAGE AND ELUTION CHARACTERISTICS

Antibiotic-loaded cement can be either low-dose or high-dose.

Low-dose cement

Low-dose cement typically consists of 0.5 to 1.0 g of antibiotic per 40-g bag of cement, usually an aminoglycoside (gentamicin or tobramycin) or vancomycin, and can be purchased premixed by the manufacturer. Such cement is only used prophylactically with primary total joint arthroplasty or revision for aseptic reasons, a practice common in Europe but less so in the United States. Some American authors propose antibiotic-loaded cement prophylaxis for patients at high risk, eg, those with immunosuppression, inflammatory cause of arthritis, or diabetes.⁵⁴

Vrabec et al,⁵⁵ in a study of low-dose tobramycin-loaded cement used for primary total knee arthroplasty, found a peak median intra-articular tobramycin concentration of 32 mg/L at 6 hours, declining to 6 mg/L at 48 hours with all serum levels 0.3 mg/L or less (unmeasureable) at similar time points.

Sterling et al,⁵⁶ studying primary total hip arthroplasties with low-dose tobramycin-loaded cement, found mean levels in drainage fluid of 103 mg/L at 6 hours, declining to 15 mg/L at 48 hours. Serum levels peaked at 0.94 mg/L at 3 hours, declining to 0.2 mg/L by 48 hours.

Although most of the antibiotic elution occurs early (within the first week), antibiotic can be found in joint aspirates up to 20 years later.⁵⁷ We are unaware of any well-documented cases of acute kidney injury ascribable to low-dose antibiotic-loaded cement used prophylactically. One case report making this assertion did not determine serum levels of aminoglycoside.⁵⁸

High-dose cement

High-dose antibiotic-loaded cement typically contains about 4 to 8 g of antibiotic per 40-g bag of cement and is used in the treatment of prosthetic joint infection to form the spacers. The antibiotic must be mixed into the cement powder by the surgeon in the operating room.

There is no standard combination or dosage. The choice of antibiotic can be tailored to the infecting organism if known. Otherwise, gram-positive organisms are most common, and vancomycin and aminoglycosides are often used together. This particular combination will enhance the elution of both antibiotics when studied in vitro, a process termed “passive opportunism.”⁵⁹ Other antibiotics in use include aztreonam, piperacillin, teicoplanin, fluoroquinolones, cephalosporins, and daptomycin, among others.

About 8 g of antibiotic total per 40-g bag is the maximum to allow easy molding.⁵² As an example, this may include 4 g of vancomycin and 3.6 g of tobramycin per 40 g. Given that 3 to 4 such bags are often used per joint, there is significant risk of systemic exposure.

Kalil et al⁶⁰ studied 8 patients who received high-dose tobramycin-loaded cement to treat periprosthetic joint infections of the hip or knee and found that 7 had detectable serum levels (mean 0.84 mg/L, highest 2.0 mg/L), including 1 with a level of 0.9 mg/L on day 38; 4 of these 8 developed acute kidney injury by AKIN criteria, although other risk factors for acute kidney injury existed. Nearly all had concomitant vancomycin (3 to 8 g) added to the cement as well.

Hsieh et al⁶¹ studied 46 patients with infected total hip arthroplasties treated with high-dose antibiotic-loaded cement spacers (vancomycin 4 g and aztreonam 4 g per 40-g bag) and found vancomycin levels in joint drainage higher than 1,500 mg/L on day 1, decreasing to 571 mg/L on day 7; serum levels were low (range 0.1–1.6 mg/L at 24 hours), falling to undetectable by 72 hours.

 

 

ANTIBIOTIC-LOADED CEMENT SPACERS AND ACUTE KIDNEY INJURY

Case reports have associated high-dose antibiotic-loaded cement spacers with acute kidney injury.

Curtis et al⁶² described an 85-year-old patient with stage 3 chronic kidney disease who was treated for an infected total knee arthroplasty with an antibiotic-loaded cement spacer (containing 3.6 g of tobramycin and 3 g of cefazolin per 40-g bag, 3 bags total) and developed stage 3 acute kidney injury. After 16 days and 3 hemodialysis sessions, the patient’s serum tobramycin level was still 2 mg/L despite receiving no systemic tobramycin.

Wu et al⁶³ reported a case of acute kidney injury that required dialysis after implantation of a tobramycin- and vancomycin-loaded spacer, with persistent serum tobramycin levels despite repeated hemodialysis sessions until the spacer was removed.

Chalmers et al⁶⁴ described 2 patients with acute kidney injury and persistently elevated serum tobramycin levels (3.9 mg/L on day 39 in 1 patient and 2.0 mg/L on day 24 in the other patient) despite no systemic administration.

In these and other case reports,^65–67 dialysis and spacer explantation were usually required. 


Comment. It is intuitive that acute kidney injury would more likely complicate revision total joint arthroplasties for infection than for primary total joint arthroplasties or revisions for aseptic reasons, given the systemic effects of infection and exposure to nephrotoxic or allergenic antibiotics. And the available data suggest that the risk of acute kidney injury is higher with revision for prosthetic joint infection than with revision for aseptic reasons. However, many of the studies were retrospective, relatively small, single-center series and used different definitions of acute kidney injury.

We are aware of 17 studies specifically addressing acute kidney injury or postoperative complications in general that may have included acute kidney injury.^{50,52,61,68–81} Ten of these studies found at least 1 case of acute kidney injury (Table 3). Of note, 7 studies totaling 219 patients reported no cases of acute kidney injury, although acute kidney injury per se was not mentioned and no definition of it was provided.^{50,61,76,77,79,80,82}

Luu et al⁸³ performed a systematic review of studies published between January 1989 and June 2012 reporting systemic complications (including acute kidney injury) of 2-stage revision arthroplasties including placement of an antibiotic-loaded cement spacer for treatment of periprosthetic joint infection. Overall, 10 studies were identified with 544 total patients. Five of these studies, with 409 patients, reported at least 1 case of acute kidney injury for a total of 27 patients, giving an incidence of 6.6% in these studies.^68–71 The remaining 5 studies, totaling 135 patients, did not report any cases of acute kidney injury,^{50,61,76–78} although that was not the primary focus of any of those trials.

Most notable from this systematic review, the study of Menge et al⁶⁹ retrospectively determined the incidence of acute kidney injury (defined as a 50% rise in serum creatinine to > 1.4 mg/dL within 90 days of surgery) to be 17% in 84 patients with infected total knee arthroplasties treated with antibiotic-loaded cement spacers. A mean of 3.5 bags of cement per spacer were used in the 35 articulating spacers, compared with 2.9 per nonarticulating spacer. These spacers contained vancomycin in 82% (median 4.0 g, range 1–16 g) and tobramycin in 94% (median 4.8 g, range 1–12 g), among others in small percentages. The dose of tobramycin in the spacer considered either as a dichotomous variable (> 4.8 g, OR 5.87) or linearly (OR 1.24 per 1-g increase) was significantly associated with acute kidney injury, although systemic administration of aminoglycosides or vancomycin was not.

Additional single-center series that were published subsequent to this review have generally used more current diagnostic criteria.

Noto et al⁷² found that 10 of 46 patients treated with antibiotic-loaded cement spacers had a greater than 50% rise in serum creatinine (average increase 260%). All spacers contained tobramycin (mean dose 8.2 g), and 9 of 10 also contained vancomycin (mean 7.6 g). All of the 9 patients with acute kidney injury with follow-up data recovered renal function.

Reed et al⁷⁵ found 26 cases of acute kidney injury (based on RIFLE creatinine criteria) in 306 patients with antibiotic-loaded cement spacers treating various periprosthetic joint infections (including hips, knees, shoulders, and digits) and compared them with 74 controls who did not develop acute kidney injury. By multivariable analysis, receipt of an ACE inhibitor within 7 days of surgery and receipt of piperacillin-tazobactam within 7 days after surgery were both significantly more common in cases with acute kidney injury than in controls without acute kidney injury.

Aeng et al⁷³ prospectively studied 50 consecutive patients receiving antibiotic-loaded spacers containing tobramycin (with or without vancomycin) for treatment of infected hip or knee replacements. Using RIFLE creatinine criteria, they found an incidence of acute kidney injury of 20% (10 of 50). Factors significantly associated with acute kidney injury included cement premixed by the manufacturer with gentamicin (0.5 g per 40-g bag) in addition to the tobramycin they added, intraoperative blood transfusions, and postoperative use of nonsteroidal anti-inflammatory drugs.

Geller et al,⁷⁴ in a multicenter retrospective study of 247 patients with prosthetic joint infections (156 knees and 91 hips) undergoing antibiotic-loaded cement spacer placement, found an incidence of acute kidney injury of 26% based on KDIGO creatinine criteria. Significant risk factors included higher body mass index, lower preoperative hemoglobin level, drop in hemoglobin after surgery, and comorbidity (hypertension, diabetes, chronic kidney disease, or cardiovascular disease). Most of the spacers contained a combination of vancomycin and either tobramycin (81%) or gentamicin (13%). The spacers contained an average of 5.3 g (range 0.6–18 g) of vancomycin (average 2.65 g per 40-g bag) and an average of 5.2 g (range 0.5–16.4 g) of tobramycin (average 2.6 g per bag).

As in Menge et al,⁶⁹ this study illustrates the wide range of antibiotic dosages in use and the lack of standardization. In contrast to the study by Menge et al, however, development of acute kidney injury was not related to the amount of vancomycin or tobramycin contained in the spacers. Eventual clearance of infection (at 1 and 2 years) was significantly related to increasing amounts of vancomycin. Multiple different systemic antibiotics were used, most commonly vancomycin (44%), and systemic vancomycin was not associated with acute kidney injury.

Yadav et al,⁸¹ in a study of 3,129 consecutive revision procedures of the knee or hip, found an incidence of acute kidney injury by RIFLE creatinine criteria of 29% in the 197 patients who received antibiotic-loaded cement spacers for periprosthetic joint infection compared with 3.4% in the 2,848 who underwent revision for aseptic reasons. In 84 patients with prosthetic joint infection having various surgeries not including placement of a spacer, the acute kidney injury rate at some point in their course was an alarmingly high 82%. In the group that received spacers, only age and comorbidity as assessed by Charlson comorbidity index were independently associated with acute kidney injury by multivariate analysis. Surprisingly, modest renal impairment was protective, possibly because physicians of patients with chronic kidney disease were more vigilant and took appropriate measures to prevent acute kidney injury.

Overall, the risk of acute kidney injury appears to be much higher during treatment of prosthetic joint infection with a 2-stage procedure using an antibiotic-loaded cement spacer than after primary total joint arthroplasty or revision for aseptic reasons, and may complicate up to one-third of cases.

 

 

REDUCING RISK DURING TREATMENT OF INFECTED REPLACEMENT JOINTS

Due to lack of appropriate data, how best to mitigate the risk of acute kidney injury is uncertain. In our opinion, however, the following measures should be considered (Table 4).

As in primary total joint arthroplasty in general, higher-risk cases should be identified based on age, body mass index, chronic kidney disease, comorbidities (hypertension, diabetes, established cardiovascular disease), and anemia.

Preoperative transfusion can be considered case by case depending on degree of anemia and associated risk factors.

All renin-angiotensin-aldosterone system inhibitors should be withheld starting 1 week before surgery.

Both nonselective and cyclooxygenase-2 selective nonsteroidal anti-inflammatory drugs should be avoided, if possible.

Strict attention should be paid to adequate intraoperative and postoperative fluid resuscitation.

Kidney function should be monitored closely in the early postoperative period, including urine output and daily creatinine for at least 72 hours.

Systemic administration of potentially nephrotoxic antibiotics should be minimized, especially the combination of vancomycin with piperacillin-tazobactam.⁸⁴ Daptomycin is a consideration.⁴³

If acute kidney injury should develop, serum levels of vancomycin or aminoglycosides should be measured if the spacer contains these antibiotics. The spacer may need to be removed if toxic serum levels persist.

TAKE-HOME POINTS

Acute kidney injury may complicate up to 10% of primary lower-extremity total joint arthroplasties and up to 25% of periprosthetic joint infections treated with a 2-stage procedure including placement of an antibiotic-loaded cement spacer in the first stage.

Risk factors for acute kidney injury include older age, obesity, chronic kidney disease, and overall comorbidity. Potentially modifiable risk factors include anemia, perioperative transfusions, aminoglycoside prophylaxis, perioperative renin-angiotensin system blockade, and postoperative nonsteroidal anti-inflammatory drugs. These should be mitigated when possible.

In patients with periprosthetic joint infection who receive antibiotic-loaded cement spacers, especially patients  with additional risk factors for acute kidney injury, strict attention should be paid to the dose of antibiotic in the spacer, with levels checked postoperatively if necessary. Nonnephrotoxic antibiotics should be chosen for systemic administration when possible.

Prospective randomized controlled trials are needed to guide therapy after total joint arthroplasty, and to verify the adverse long-term outcomes of acute kidney injury in this setting.

Total hip or knee replacement (also called total joint arthroplasty) is highly successful at relieving pain and restoring function, but at the risk of acute kidney injury, which is a sudden loss of renal function. Various factors have been associated with this risk, some of which are potentially modifiable, notably, the use of nephrotoxic antibiotics and other drugs.

This review examines the incidence of acute kidney injury using current criteria in total joint arthroplasty of the hip or knee in general, and in the setting of revision surgery for prosthetic joint infection in particular, in which the risk is higher. We identify risk factors for acute kidney injury and propose ways to lower the risk.

MILLIONS OF PROCEDURES ANNUALLY

Total replacement of the hip^1,2 or knee³ is being done more and more. Kurtz et al⁴ estimate that by the year 2030, we will see approximately 3.5 million primary total knee and 500,000 primary total hip replacements every year. In addition, revision total knee procedures are expected to exceed 250,000 per year, and revision total hip procedures are expected to exceed 90,000 per year.⁴

Chronic infection may complicate up to 2% of these procedures and is associated with significant morbidity, death, and financial costs. Currently, it may be the reason for 25% of total joint arthroplasty revisions,⁵ but by the year 2030, it is projected to account for 66% of revision total knee arthroplasties and 48% of revision total hip arthroplasties.⁶

PRIMARY TOTAL JOINT ARTHROPLASTY AND ACUTE KIDNEY INJURY

We searched Ovid MEDLINE for articles on acute kidney injury and either arthroplasty or antibiotic-loaded cement spacers. We found 22 studies, with a total of 72,850 patients, that assessed the incidence of acute kidney injury after primary or revision total joint arthroplasty of the hip or knee, or both, using current criteria^7–28 (Table 1), and 3 additional studies that used discharge diagnosis coding.^29–31

Study designs, findings varied widely

The incidence of acute kidney injury varied markedly among the studies of primary total joint arthroplasty or revision for aseptic reasons. Numerous factors explain this heterogeneity.

Designs ranged from single-center studies with relatively small numbers of patients to large regional and national samples based on administrative data.

The definition of acute kidney injury also varied, although many used current criteria, specifically the RIFLE (risk, injury, failure, loss, end-stage renal disease),³² AKIN (Acute Kidney Injury Network),³³ and KDIGO (Kidney Disease Improving Global Outcomes)³⁴ creatinine criteria (Table 2). Some studies considered only higher stages of acute kidney injury (equivalent to KDIGO stage 2 or 3), ignoring the most common stage, ie, stage 1. No study considered urine output criteria.

Almost all of the studies were retrospective. We are not aware of any randomized controlled trials.

Discharge diagnosis may miss many cases

Several studies based the diagnosis of acute kidney injury on International Classification of Diseases, Ninth Revision (ICD-9) coding from hospital discharge summaries.

Nadkarni et al,²⁹ in the largest study published to date, used the nationwide inpatient sample database of more than 7 million total joint arthroplasties and found an incidence of acute kidney injury based on ICD-9 coding of 1.3% over the years 2002 to 2012, although this increased to 1.8% to 1.9% from 2010 to 2012.

Lopez-de-Andres et al,³⁰ in a similar study using the Spanish national hospital discharge database, evaluated 20,188 patients who underwent revision total hip or knee arthroplasty and found an overall incidence of acute kidney injury of 0.94%, also using ICD-9 coding.

Gharaibeh et al³¹ used similar methods to diagnose acute kidney injury in a single-center study of 8,949 patients and found an incidence of 1.1%.

Although these 3 studies suggest that the incidence of acute kidney injury is relatively low, Grams et al³⁵ found the sensitivity of ICD-9 coding from hospital records for the diagnosis of acute kidney injury to be only 11.7% compared with KDIGO serum creatinine and urine output criteria. This suggests that the true incidence in these studies may be many times higher, possibly near 10%.

Do all stages of kidney injury count?

Jafari et al,⁷ in a large series from a single medical center, used only the “I” (injury) and “F” (failure) levels of the RIFLE criteria (corresponding to stages 2 and 3 of the KDIGO criteria) and found an incidence of 0.55% in more than 17,000 total joint arthroplasties.

Jamsa et al⁸ used the same criteria for acute kidney injury (only “I” and “F”) and found 58 cases in 5,609 patients in whom postoperative serum creatinine was measured, for an incidence of 1%; the remaining 14,966 patients in their cohort did not have serum creatinine measured, and it was assumed they did not have acute kidney injury. Neither of these studies included the most common “R” (risk) stage of acute kidney injury.

Parr et al³⁶ recently studied a nationwide sample of 657,840 hospitalized veterans and found that of 90,614 who developed acute kidney injury based on KDIGO creatinine criteria, 84% reached only stage R. This suggests that if all stages were considered, the true incidence of acute kidney injury would have been higher—possibly 4% in the Jafari series and possibly 7% in the Jamsa series.

Smaller studies had higher rates

Smaller, single-center series reported much higher incidences of acute kidney injury.

Kimmel et al¹¹ found an incidence of 14.8% in 425 total joint arthroplasties using RIFLE creatinine criteria.

Johansson et al²⁵ found an incidence of 19.9% in 136 total joint arthroplasties using KDIGO creatinine criteria.

Sehgal et al⁹ found an incidence of 21.9% in 659 total joint arthroplasties using AKIN creatinine criteria.

Challagundla et al²⁴ found an incidence of 23.7% in 198 procedures using RIFLE creatinine criteria.

Weingarten et al,¹⁰ in a single-center series of 7,463 total joint arthroplasties, found an incidence of acute kidney injury of only 2.2% using AKIN criteria, although 12% of the patients with acute kidney injury did not return to their baseline serum creatinine levels by 3 months.

Our estimate: Nearly 10%

In total, in the 20 studies in Table 1 that included all stages of acute kidney injury, there were 1,909 cases of acute kidney injury in 34,337 patients, for an incidence of 5.6%. Considering that all studies but one were retrospective and none considered urine output criteria for acute kidney injury, we believe that using current KDIGO criteria, the true incidence of acute kidney injury complicating primary lower-extremity total joint arthroplasties is really closer to 10%.

 

 

RISK FACTORS FOR ACUTE KIDNEY INJURY

Various factors have been associated with development of acute kidney injury by multivariate analysis in these studies. Some are modifiable, while others are not, at least in the short term.

Nonmodifiable risk factors

Older age is often significant in studies assessing primary total joint arthroplasty or revision total joint arthroplasty not specifically for infection.^{11,12,16,17,26,28}

Obesity is also a major factor in the development of acute kidney injury,^{7,10–12,17,18} and, along with age, is a major factor contributing to the need for joint replacement in the first place.

Male sex may increase risk.²⁹

Diabetes mellitus was identified as a risk factor in several studies,^10,12,17,20 and hypertension in a few.^7,10,24

Other comorbidities and factors such as cardiovascular disease,^7,10 liver disease,⁷ pulmonary disease,⁷ high American Society of Anesthesiology score,^8,19 and benign heart murmurs preoperatively by routine physical examination have also been linked to acute kidney injury after joint arthroplasty.²⁸

Chronic kidney disease as a risk factor

Chronic kidney disease at baseline was associated with acute kidney injury in several of these series.^{7,11–13,15,19,29}

Warth et al¹² studied 1,038 patients and found an incidence of acute kidney injury of 11% in the 135 with chronic kidney disease (defined as serum creatinine > 1.2 mg/dL) and who received acetaminophen or narcotics for pain control, compared with 4.8% in the remaining 903 patients without chronic kidney disease, who received ketorolac or celecoxib.

Perregaard et al¹³ studied 3,410 patients who underwent total hip arthroplasty and found an incidence of acute kidney injury (per KDIGO creatinine criteria) of 2.2% overall, but 7% in the 134 patients with chronic kidney disease based on KDIGO creatinine criteria.

Nowicka et al¹⁵ found an incidence of acute kidney injury of 16.7% in the 48 patients with chronic kidney disease (defined as a glomerular filtration rate estimated by the Cockroft-Gault formula of less than 60 mL/min/1.73 m²), compared with 4.5% in the remaining 289.

Modifiable risk factors

Modifiable risk factors that should be considered in high-risk cases include anemia, perioperative blood transfusion, perioperative use of renin-angiotensin-aldosterone system inhibitors such as angiotensin-converting enzyme (ACE) inhibitors and angiotensin II receptor blockers (ARBs), particular antibiotics used for prophylaxis, and nonsteroidal anti-inflammatory drugs used postoperatively.

Anemia and blood transfusion

Preoperative anemia has been associated with postoperative acute kidney injury in various surgical settings such as cardiac surgery.^37,38 Perioperative red blood cell transfusions have also been associated with acute kidney injury in cardiac surgery; similar results may apply to total joint arthroplasty.

Choi et al,¹⁷ in 2,467 patients undergoing hip replacement, found a significant risk for acute kidney injury if postoperative hemoglobin was consistently below 10 g/dL compared with consistently above this level, with an inverse probability-of-treatment weighted odds ratio of 1.817 (P = .011).

Others have found a significant association of perioperative blood transfusion with acute kidney injury in total joint arthroplasty.^10,29

Nadkarni et al,²⁹ for example, used the nationwide inpatient sample database and found by multivariate analysis that perioperative blood transfusion was strongly associated with acute kidney injury, with an adjusted odds ratio of 2.28 (95% confidence interval [CI] 2.15–2.42, P < .0001).

Comment. A higher incidence of acute kidney injury may represent confounding by indication bias, as sicker patients or complicated surgeries may require transfusion, and this risk may not be completely accounted for by multivariate analysis. It is also possible, however, that transfusions per se may contribute to acute kidney injury. Possible direct or indirect mechanisms mediating acute kidney injury include hemolytic reactions, circulatory overload, acute lung injury, and immunomodulatory effects.³⁹

Preoperative transfusion in anemic patients undergoing cardiac surgery may also reduce the incidence of postoperative acute kidney injury both by correcting the anemia and by limiting the need for perioperative transfusions.⁴⁰ It remains to be determined whether elective preoperative transfusion to correct anemia would reduce postoperative development of acute kidney injury in total joint arthroplasty. As an aside, perioperative transfusion has also been linked to development of periprosthetic joint infection.⁴¹

Renin-angiotensin-aldosterone system inhibitors

Several studies found perioperative use of renin-angiotensin-aldosterone system inhibitors to be a risk factor for acute kidney injury.

Kimmel et al¹¹ reported adjusted odds ratios of 2.70 (95% CI 1.12–6.48) for ACE inhibitor use and 2.64 (95% CI 1.18–5.93) for ARB use in a study of 425 primary total joint arthroplasties.

Challagundla et al²⁴ found an odds ratio of 3.07 (95% CI 1.40–6.74) with ACE inhibitor or ARB use by multivariate analysis in 198 total joint arthroplasties.

Nielson et al¹⁸ studied 798 patients who underwent total joint arthroplasty and found that preoperative use of renin-angiotensin system inhibitors was associated with a significantly higher rate of postoperative acute kidney injury (8.3% vs 1.7% without inhibition), which was statistically significant by multivariate analysis (odds ratio 2.6, 95% CI 1.04–6.51).

We recommend holding renin-angiotensin-aldosterone system inhibitors 7 days before surgery through the postoperative period in high-risk cases.

Aminoglycoside use as a risk factor

Prophylactic administration of systemic antibiotics is the standard of care. In a systematic review of 26 studies and meta-analysis of 7 studies (3,065 patients), prophylactic antibiotics reduced the relative risk of wound infection by 81% with an absolute risk reduction of 8%.⁴²

A modifiable risk factor for acute kidney injury is the specific antibiotic used for prophylaxis. Multiple studies assessed the risk of acute kidney injury comparing regimens containing an aminoglycoside (typically gentamicin) with regimens lacking these agents.^20–26 In general, these studies found a significantly higher risk of acute kidney injury when gentamicin was used.

Challagundla et al²⁴ found an incidence of acute kidney injury of 52% using RIFLE creatinine criteria in 52 patients receiving 8 g total of flucloxacillin plus 160 mg of gentamicin (120 mg if they weighed less than 60 kg) compared with 8% in 48 patients given cefuroxime (3 g total) and 14% in an additional 52 patients also given cefuroxime.

Johansson et al²⁵ found an incidence of KDIGO creatinine-based acute kidney injury of 13% in 70 patients given dicloxacillin alone prophylactically compared with 27% given dicloxacillin and gentamicin, with a relative risk of 3.

Bell et al,²¹ in a large registry-based analysis from Scotland involving 7,666 elective orthopedic procedures, found that use of flucloxacillin 2 g plus a single dose of gentamicin 4 mg/kg was significantly associated with a 94% higher risk of acute kidney injury (KDIGO creatinine criteria) compared with a cefuroxime-based regimen, with absolute rates increasing from 6.2% to 10.8%.

Dubrovskaya et al²⁰ and Ferguson et al,²⁶ in contrast, found no increased risk with addition of gentamicin.

We recommend avoiding aminoglycosides for prophylaxis in primary lower-extremity total joint arthroplasty in patients at higher risk unless required for specific microbiologic reasons.

Vancomycin may also increase risk

Courtney et al¹⁹ assessed the risk of adding vancomycin to cefazolin for routine prophylaxis in a retrospective series of 1,828 total hip or knee arthroplasties and found a significantly higher rate of acute kidney injury, using AKIN criteria (13% vs 8%, odds ratio by multivariate analysis 1.82, P = .002).¹⁹

Other agents shown to be effective in treating periprosthetic joint infections or complicated skin and soft-tissue infections with resistant organisms include daptomycin⁴³ and linezolid.⁴⁴ These nonnephrotoxic alternatives to vancomycin may be a consideration if prophylaxis for methicillin-resistant Staphylococcus aureus is deemed necessary in patients at risk for acute kidney injury.

 

 

PROSTHETIC JOINT INFECTIONS AND ANTIBIOTIC-LOADED CEMENT

Deep infection may complicate nearly 1% of total hip⁴⁵ and 2% of total knee arthroplasties.⁴⁶ Kurtz et al^4,6 have projected that by 2030, infection will be the cause of two-thirds of the estimated 268,000 revision total knee arthroplasties and about half of the estimated 96,700 revision total hip arthroplasties.

The most common method of treating a chronically infected replacement joint is a 2-stage procedure.⁵ First, the prosthesis is removed, all infected bone and soft tissue is debrided, and an antibiotic-loaded cement spacer is implanted. Systemic antibiotics are given concurrently, typically for about 6 weeks. After the infection is brought under control, perhaps 2 to 3 months later, the spacer is removed and a new joint is implanted with antibiotic-loaded cement. A 1-stage procedure may be an option in selected cases and would obviate the need for an antibiotic-loaded cement spacer.^47,48

Of obvious relevance to development of acute kidney injury is the choice and amount of antibiotics embedded in the cement used for spacers and in implantation. Very high antibiotic levels are achieved within the joint space, usually with little systemic absorption, although significant systemic exposure has been documented in some cases.

The polymethylmethacrylate cement used for these purposes comes in 40-g bags. Multiple bags are typically required per joint, perhaps 2 to 4.⁴⁹

The rate of elution of antibiotics is determined by several factors, including surface area, porosity, and the number of antibiotics. In general, elution is greatest early on, with exponential decline lasting perhaps 1 week,  followed by slow, sustained release over weeks to months.⁵⁰ However, several in vitro studies have indicated that only about 5%^50,51 of the total antibiotic actually elutes over time.

Initially, multiple antibiotic-laden cement beads were used to fill the joint space, but this significantly limited function and mobility.⁵² Now, cement spacers are used, and they can be nonarticulating or articulating for maximal joint mobility.⁵³ Although much greater antibiotic elution occurs from beads due to their high surface area-to-volume ratio, spacers still provide an adequate dose.

ANTIBIOTIC-LOADED CEMENT: DOSAGE AND ELUTION CHARACTERISTICS

Antibiotic-loaded cement can be either low-dose or high-dose.

Low-dose cement

Low-dose cement typically consists of 0.5 to 1.0 g of antibiotic per 40-g bag of cement, usually an aminoglycoside (gentamicin or tobramycin) or vancomycin, and can be purchased premixed by the manufacturer. Such cement is only used prophylactically with primary total joint arthroplasty or revision for aseptic reasons, a practice common in Europe but less so in the United States. Some American authors propose antibiotic-loaded cement prophylaxis for patients at high risk, eg, those with immunosuppression, inflammatory cause of arthritis, or diabetes.⁵⁴

Vrabec et al,⁵⁵ in a study of low-dose tobramycin-loaded cement used for primary total knee arthroplasty, found a peak median intra-articular tobramycin concentration of 32 mg/L at 6 hours, declining to 6 mg/L at 48 hours with all serum levels 0.3 mg/L or less (unmeasureable) at similar time points.

Sterling et al,⁵⁶ studying primary total hip arthroplasties with low-dose tobramycin-loaded cement, found mean levels in drainage fluid of 103 mg/L at 6 hours, declining to 15 mg/L at 48 hours. Serum levels peaked at 0.94 mg/L at 3 hours, declining to 0.2 mg/L by 48 hours.

Although most of the antibiotic elution occurs early (within the first week), antibiotic can be found in joint aspirates up to 20 years later.⁵⁷ We are unaware of any well-documented cases of acute kidney injury ascribable to low-dose antibiotic-loaded cement used prophylactically. One case report making this assertion did not determine serum levels of aminoglycoside.⁵⁸

High-dose cement

High-dose antibiotic-loaded cement typically contains about 4 to 8 g of antibiotic per 40-g bag of cement and is used in the treatment of prosthetic joint infection to form the spacers. The antibiotic must be mixed into the cement powder by the surgeon in the operating room.

There is no standard combination or dosage. The choice of antibiotic can be tailored to the infecting organism if known. Otherwise, gram-positive organisms are most common, and vancomycin and aminoglycosides are often used together. This particular combination will enhance the elution of both antibiotics when studied in vitro, a process termed “passive opportunism.”⁵⁹ Other antibiotics in use include aztreonam, piperacillin, teicoplanin, fluoroquinolones, cephalosporins, and daptomycin, among others.

About 8 g of antibiotic total per 40-g bag is the maximum to allow easy molding.⁵² As an example, this may include 4 g of vancomycin and 3.6 g of tobramycin per 40 g. Given that 3 to 4 such bags are often used per joint, there is significant risk of systemic exposure.

Kalil et al⁶⁰ studied 8 patients who received high-dose tobramycin-loaded cement to treat periprosthetic joint infections of the hip or knee and found that 7 had detectable serum levels (mean 0.84 mg/L, highest 2.0 mg/L), including 1 with a level of 0.9 mg/L on day 38; 4 of these 8 developed acute kidney injury by AKIN criteria, although other risk factors for acute kidney injury existed. Nearly all had concomitant vancomycin (3 to 8 g) added to the cement as well.

Hsieh et al⁶¹ studied 46 patients with infected total hip arthroplasties treated with high-dose antibiotic-loaded cement spacers (vancomycin 4 g and aztreonam 4 g per 40-g bag) and found vancomycin levels in joint drainage higher than 1,500 mg/L on day 1, decreasing to 571 mg/L on day 7; serum levels were low (range 0.1–1.6 mg/L at 24 hours), falling to undetectable by 72 hours.

 

 

ANTIBIOTIC-LOADED CEMENT SPACERS AND ACUTE KIDNEY INJURY

Case reports have associated high-dose antibiotic-loaded cement spacers with acute kidney injury.

Curtis et al⁶² described an 85-year-old patient with stage 3 chronic kidney disease who was treated for an infected total knee arthroplasty with an antibiotic-loaded cement spacer (containing 3.6 g of tobramycin and 3 g of cefazolin per 40-g bag, 3 bags total) and developed stage 3 acute kidney injury. After 16 days and 3 hemodialysis sessions, the patient’s serum tobramycin level was still 2 mg/L despite receiving no systemic tobramycin.

Wu et al⁶³ reported a case of acute kidney injury that required dialysis after implantation of a tobramycin- and vancomycin-loaded spacer, with persistent serum tobramycin levels despite repeated hemodialysis sessions until the spacer was removed.

Chalmers et al⁶⁴ described 2 patients with acute kidney injury and persistently elevated serum tobramycin levels (3.9 mg/L on day 39 in 1 patient and 2.0 mg/L on day 24 in the other patient) despite no systemic administration.

In these and other case reports,^65–67 dialysis and spacer explantation were usually required. 


Comment. It is intuitive that acute kidney injury would more likely complicate revision total joint arthroplasties for infection than for primary total joint arthroplasties or revisions for aseptic reasons, given the systemic effects of infection and exposure to nephrotoxic or allergenic antibiotics. And the available data suggest that the risk of acute kidney injury is higher with revision for prosthetic joint infection than with revision for aseptic reasons. However, many of the studies were retrospective, relatively small, single-center series and used different definitions of acute kidney injury.

We are aware of 17 studies specifically addressing acute kidney injury or postoperative complications in general that may have included acute kidney injury.^{50,52,61,68–81} Ten of these studies found at least 1 case of acute kidney injury (Table 3). Of note, 7 studies totaling 219 patients reported no cases of acute kidney injury, although acute kidney injury per se was not mentioned and no definition of it was provided.^{50,61,76,77,79,80,82}

Luu et al⁸³ performed a systematic review of studies published between January 1989 and June 2012 reporting systemic complications (including acute kidney injury) of 2-stage revision arthroplasties including placement of an antibiotic-loaded cement spacer for treatment of periprosthetic joint infection. Overall, 10 studies were identified with 544 total patients. Five of these studies, with 409 patients, reported at least 1 case of acute kidney injury for a total of 27 patients, giving an incidence of 6.6% in these studies.^68–71 The remaining 5 studies, totaling 135 patients, did not report any cases of acute kidney injury,^{50,61,76–78} although that was not the primary focus of any of those trials.

Most notable from this systematic review, the study of Menge et al⁶⁹ retrospectively determined the incidence of acute kidney injury (defined as a 50% rise in serum creatinine to > 1.4 mg/dL within 90 days of surgery) to be 17% in 84 patients with infected total knee arthroplasties treated with antibiotic-loaded cement spacers. A mean of 3.5 bags of cement per spacer were used in the 35 articulating spacers, compared with 2.9 per nonarticulating spacer. These spacers contained vancomycin in 82% (median 4.0 g, range 1–16 g) and tobramycin in 94% (median 4.8 g, range 1–12 g), among others in small percentages. The dose of tobramycin in the spacer considered either as a dichotomous variable (> 4.8 g, OR 5.87) or linearly (OR 1.24 per 1-g increase) was significantly associated with acute kidney injury, although systemic administration of aminoglycosides or vancomycin was not.

Additional single-center series that were published subsequent to this review have generally used more current diagnostic criteria.

Noto et al⁷² found that 10 of 46 patients treated with antibiotic-loaded cement spacers had a greater than 50% rise in serum creatinine (average increase 260%). All spacers contained tobramycin (mean dose 8.2 g), and 9 of 10 also contained vancomycin (mean 7.6 g). All of the 9 patients with acute kidney injury with follow-up data recovered renal function.

Reed et al⁷⁵ found 26 cases of acute kidney injury (based on RIFLE creatinine criteria) in 306 patients with antibiotic-loaded cement spacers treating various periprosthetic joint infections (including hips, knees, shoulders, and digits) and compared them with 74 controls who did not develop acute kidney injury. By multivariable analysis, receipt of an ACE inhibitor within 7 days of surgery and receipt of piperacillin-tazobactam within 7 days after surgery were both significantly more common in cases with acute kidney injury than in controls without acute kidney injury.

Aeng et al⁷³ prospectively studied 50 consecutive patients receiving antibiotic-loaded spacers containing tobramycin (with or without vancomycin) for treatment of infected hip or knee replacements. Using RIFLE creatinine criteria, they found an incidence of acute kidney injury of 20% (10 of 50). Factors significantly associated with acute kidney injury included cement premixed by the manufacturer with gentamicin (0.5 g per 40-g bag) in addition to the tobramycin they added, intraoperative blood transfusions, and postoperative use of nonsteroidal anti-inflammatory drugs.

Geller et al,⁷⁴ in a multicenter retrospective study of 247 patients with prosthetic joint infections (156 knees and 91 hips) undergoing antibiotic-loaded cement spacer placement, found an incidence of acute kidney injury of 26% based on KDIGO creatinine criteria. Significant risk factors included higher body mass index, lower preoperative hemoglobin level, drop in hemoglobin after surgery, and comorbidity (hypertension, diabetes, chronic kidney disease, or cardiovascular disease). Most of the spacers contained a combination of vancomycin and either tobramycin (81%) or gentamicin (13%). The spacers contained an average of 5.3 g (range 0.6–18 g) of vancomycin (average 2.65 g per 40-g bag) and an average of 5.2 g (range 0.5–16.4 g) of tobramycin (average 2.6 g per bag).

As in Menge et al,⁶⁹ this study illustrates the wide range of antibiotic dosages in use and the lack of standardization. In contrast to the study by Menge et al, however, development of acute kidney injury was not related to the amount of vancomycin or tobramycin contained in the spacers. Eventual clearance of infection (at 1 and 2 years) was significantly related to increasing amounts of vancomycin. Multiple different systemic antibiotics were used, most commonly vancomycin (44%), and systemic vancomycin was not associated with acute kidney injury.

Yadav et al,⁸¹ in a study of 3,129 consecutive revision procedures of the knee or hip, found an incidence of acute kidney injury by RIFLE creatinine criteria of 29% in the 197 patients who received antibiotic-loaded cement spacers for periprosthetic joint infection compared with 3.4% in the 2,848 who underwent revision for aseptic reasons. In 84 patients with prosthetic joint infection having various surgeries not including placement of a spacer, the acute kidney injury rate at some point in their course was an alarmingly high 82%. In the group that received spacers, only age and comorbidity as assessed by Charlson comorbidity index were independently associated with acute kidney injury by multivariate analysis. Surprisingly, modest renal impairment was protective, possibly because physicians of patients with chronic kidney disease were more vigilant and took appropriate measures to prevent acute kidney injury.

Overall, the risk of acute kidney injury appears to be much higher during treatment of prosthetic joint infection with a 2-stage procedure using an antibiotic-loaded cement spacer than after primary total joint arthroplasty or revision for aseptic reasons, and may complicate up to one-third of cases.

 

 

REDUCING RISK DURING TREATMENT OF INFECTED REPLACEMENT JOINTS

Due to lack of appropriate data, how best to mitigate the risk of acute kidney injury is uncertain. In our opinion, however, the following measures should be considered (Table 4).

As in primary total joint arthroplasty in general, higher-risk cases should be identified based on age, body mass index, chronic kidney disease, comorbidities (hypertension, diabetes, established cardiovascular disease), and anemia.

Preoperative transfusion can be considered case by case depending on degree of anemia and associated risk factors.

All renin-angiotensin-aldosterone system inhibitors should be withheld starting 1 week before surgery.

Both nonselective and cyclooxygenase-2 selective nonsteroidal anti-inflammatory drugs should be avoided, if possible.

Strict attention should be paid to adequate intraoperative and postoperative fluid resuscitation.

Kidney function should be monitored closely in the early postoperative period, including urine output and daily creatinine for at least 72 hours.

Systemic administration of potentially nephrotoxic antibiotics should be minimized, especially the combination of vancomycin with piperacillin-tazobactam.⁸⁴ Daptomycin is a consideration.⁴³

If acute kidney injury should develop, serum levels of vancomycin or aminoglycosides should be measured if the spacer contains these antibiotics. The spacer may need to be removed if toxic serum levels persist.

TAKE-HOME POINTS

Acute kidney injury may complicate up to 10% of primary lower-extremity total joint arthroplasties and up to 25% of periprosthetic joint infections treated with a 2-stage procedure including placement of an antibiotic-loaded cement spacer in the first stage.

Risk factors for acute kidney injury include older age, obesity, chronic kidney disease, and overall comorbidity. Potentially modifiable risk factors include anemia, perioperative transfusions, aminoglycoside prophylaxis, perioperative renin-angiotensin system blockade, and postoperative nonsteroidal anti-inflammatory drugs. These should be mitigated when possible.

In patients with periprosthetic joint infection who receive antibiotic-loaded cement spacers, especially patients  with additional risk factors for acute kidney injury, strict attention should be paid to the dose of antibiotic in the spacer, with levels checked postoperatively if necessary. Nonnephrotoxic antibiotics should be chosen for systemic administration when possible.

Prospective randomized controlled trials are needed to guide therapy after total joint arthroplasty, and to verify the adverse long-term outcomes of acute kidney injury in this setting.

Total hip or knee replacement (also called total joint arthroplasty) is highly successful at relieving pain and restoring function, but at the risk of acute kidney injury, which is a sudden loss of renal function. Various factors have been associated with this risk, some of which are potentially modifiable, notably, the use of nephrotoxic antibiotics and other drugs.

This review examines the incidence of acute kidney injury using current criteria in total joint arthroplasty of the hip or knee in general, and in the setting of revision surgery for prosthetic joint infection in particular, in which the risk is higher. We identify risk factors for acute kidney injury and propose ways to lower the risk.

MILLIONS OF PROCEDURES ANNUALLY

Total replacement of the hip^1,2 or knee³ is being done more and more. Kurtz et al⁴ estimate that by the year 2030, we will see approximately 3.5 million primary total knee and 500,000 primary total hip replacements every year. In addition, revision total knee procedures are expected to exceed 250,000 per year, and revision total hip procedures are expected to exceed 90,000 per year.⁴

Chronic infection may complicate up to 2% of these procedures and is associated with significant morbidity, death, and financial costs. Currently, it may be the reason for 25% of total joint arthroplasty revisions,⁵ but by the year 2030, it is projected to account for 66% of revision total knee arthroplasties and 48% of revision total hip arthroplasties.⁶

PRIMARY TOTAL JOINT ARTHROPLASTY AND ACUTE KIDNEY INJURY

We searched Ovid MEDLINE for articles on acute kidney injury and either arthroplasty or antibiotic-loaded cement spacers. We found 22 studies, with a total of 72,850 patients, that assessed the incidence of acute kidney injury after primary or revision total joint arthroplasty of the hip or knee, or both, using current criteria^7–28 (Table 1), and 3 additional studies that used discharge diagnosis coding.^29–31

Study designs, findings varied widely

The incidence of acute kidney injury varied markedly among the studies of primary total joint arthroplasty or revision for aseptic reasons. Numerous factors explain this heterogeneity.

Designs ranged from single-center studies with relatively small numbers of patients to large regional and national samples based on administrative data.

The definition of acute kidney injury also varied, although many used current criteria, specifically the RIFLE (risk, injury, failure, loss, end-stage renal disease),³² AKIN (Acute Kidney Injury Network),³³ and KDIGO (Kidney Disease Improving Global Outcomes)³⁴ creatinine criteria (Table 2). Some studies considered only higher stages of acute kidney injury (equivalent to KDIGO stage 2 or 3), ignoring the most common stage, ie, stage 1. No study considered urine output criteria.

Almost all of the studies were retrospective. We are not aware of any randomized controlled trials.

Discharge diagnosis may miss many cases

Several studies based the diagnosis of acute kidney injury on International Classification of Diseases, Ninth Revision (ICD-9) coding from hospital discharge summaries.

Nadkarni et al,²⁹ in the largest study published to date, used the nationwide inpatient sample database of more than 7 million total joint arthroplasties and found an incidence of acute kidney injury based on ICD-9 coding of 1.3% over the years 2002 to 2012, although this increased to 1.8% to 1.9% from 2010 to 2012.

Lopez-de-Andres et al,³⁰ in a similar study using the Spanish national hospital discharge database, evaluated 20,188 patients who underwent revision total hip or knee arthroplasty and found an overall incidence of acute kidney injury of 0.94%, also using ICD-9 coding.

Gharaibeh et al³¹ used similar methods to diagnose acute kidney injury in a single-center study of 8,949 patients and found an incidence of 1.1%.

Although these 3 studies suggest that the incidence of acute kidney injury is relatively low, Grams et al³⁵ found the sensitivity of ICD-9 coding from hospital records for the diagnosis of acute kidney injury to be only 11.7% compared with KDIGO serum creatinine and urine output criteria. This suggests that the true incidence in these studies may be many times higher, possibly near 10%.

Do all stages of kidney injury count?

Jafari et al,⁷ in a large series from a single medical center, used only the “I” (injury) and “F” (failure) levels of the RIFLE criteria (corresponding to stages 2 and 3 of the KDIGO criteria) and found an incidence of 0.55% in more than 17,000 total joint arthroplasties.

Jamsa et al⁸ used the same criteria for acute kidney injury (only “I” and “F”) and found 58 cases in 5,609 patients in whom postoperative serum creatinine was measured, for an incidence of 1%; the remaining 14,966 patients in their cohort did not have serum creatinine measured, and it was assumed they did not have acute kidney injury. Neither of these studies included the most common “R” (risk) stage of acute kidney injury.

Parr et al³⁶ recently studied a nationwide sample of 657,840 hospitalized veterans and found that of 90,614 who developed acute kidney injury based on KDIGO creatinine criteria, 84% reached only stage R. This suggests that if all stages were considered, the true incidence of acute kidney injury would have been higher—possibly 4% in the Jafari series and possibly 7% in the Jamsa series.

Smaller studies had higher rates

Smaller, single-center series reported much higher incidences of acute kidney injury.

Kimmel et al¹¹ found an incidence of 14.8% in 425 total joint arthroplasties using RIFLE creatinine criteria.

Johansson et al²⁵ found an incidence of 19.9% in 136 total joint arthroplasties using KDIGO creatinine criteria.

Sehgal et al⁹ found an incidence of 21.9% in 659 total joint arthroplasties using AKIN creatinine criteria.

Challagundla et al²⁴ found an incidence of 23.7% in 198 procedures using RIFLE creatinine criteria.

Weingarten et al,¹⁰ in a single-center series of 7,463 total joint arthroplasties, found an incidence of acute kidney injury of only 2.2% using AKIN criteria, although 12% of the patients with acute kidney injury did not return to their baseline serum creatinine levels by 3 months.

Our estimate: Nearly 10%

In total, in the 20 studies in Table 1 that included all stages of acute kidney injury, there were 1,909 cases of acute kidney injury in 34,337 patients, for an incidence of 5.6%. Considering that all studies but one were retrospective and none considered urine output criteria for acute kidney injury, we believe that using current KDIGO criteria, the true incidence of acute kidney injury complicating primary lower-extremity total joint arthroplasties is really closer to 10%.

 

 

RISK FACTORS FOR ACUTE KIDNEY INJURY

Various factors have been associated with development of acute kidney injury by multivariate analysis in these studies. Some are modifiable, while others are not, at least in the short term.

Nonmodifiable risk factors

Older age is often significant in studies assessing primary total joint arthroplasty or revision total joint arthroplasty not specifically for infection.^{11,12,16,17,26,28}

Obesity is also a major factor in the development of acute kidney injury,^{7,10–12,17,18} and, along with age, is a major factor contributing to the need for joint replacement in the first place.

Male sex may increase risk.²⁹

Diabetes mellitus was identified as a risk factor in several studies,^10,12,17,20 and hypertension in a few.^7,10,24

Other comorbidities and factors such as cardiovascular disease,^7,10 liver disease,⁷ pulmonary disease,⁷ high American Society of Anesthesiology score,^8,19 and benign heart murmurs preoperatively by routine physical examination have also been linked to acute kidney injury after joint arthroplasty.²⁸

Chronic kidney disease as a risk factor

Chronic kidney disease at baseline was associated with acute kidney injury in several of these series.^{7,11–13,15,19,29}

Warth et al¹² studied 1,038 patients and found an incidence of acute kidney injury of 11% in the 135 with chronic kidney disease (defined as serum creatinine > 1.2 mg/dL) and who received acetaminophen or narcotics for pain control, compared with 4.8% in the remaining 903 patients without chronic kidney disease, who received ketorolac or celecoxib.

Perregaard et al¹³ studied 3,410 patients who underwent total hip arthroplasty and found an incidence of acute kidney injury (per KDIGO creatinine criteria) of 2.2% overall, but 7% in the 134 patients with chronic kidney disease based on KDIGO creatinine criteria.

Nowicka et al¹⁵ found an incidence of acute kidney injury of 16.7% in the 48 patients with chronic kidney disease (defined as a glomerular filtration rate estimated by the Cockroft-Gault formula of less than 60 mL/min/1.73 m²), compared with 4.5% in the remaining 289.

Modifiable risk factors

Modifiable risk factors that should be considered in high-risk cases include anemia, perioperative blood transfusion, perioperative use of renin-angiotensin-aldosterone system inhibitors such as angiotensin-converting enzyme (ACE) inhibitors and angiotensin II receptor blockers (ARBs), particular antibiotics used for prophylaxis, and nonsteroidal anti-inflammatory drugs used postoperatively.

Anemia and blood transfusion

Preoperative anemia has been associated with postoperative acute kidney injury in various surgical settings such as cardiac surgery.^37,38 Perioperative red blood cell transfusions have also been associated with acute kidney injury in cardiac surgery; similar results may apply to total joint arthroplasty.

Choi et al,¹⁷ in 2,467 patients undergoing hip replacement, found a significant risk for acute kidney injury if postoperative hemoglobin was consistently below 10 g/dL compared with consistently above this level, with an inverse probability-of-treatment weighted odds ratio of 1.817 (P = .011).

Others have found a significant association of perioperative blood transfusion with acute kidney injury in total joint arthroplasty.^10,29

Nadkarni et al,²⁹ for example, used the nationwide inpatient sample database and found by multivariate analysis that perioperative blood transfusion was strongly associated with acute kidney injury, with an adjusted odds ratio of 2.28 (95% confidence interval [CI] 2.15–2.42, P < .0001).

Comment. A higher incidence of acute kidney injury may represent confounding by indication bias, as sicker patients or complicated surgeries may require transfusion, and this risk may not be completely accounted for by multivariate analysis. It is also possible, however, that transfusions per se may contribute to acute kidney injury. Possible direct or indirect mechanisms mediating acute kidney injury include hemolytic reactions, circulatory overload, acute lung injury, and immunomodulatory effects.³⁹

Preoperative transfusion in anemic patients undergoing cardiac surgery may also reduce the incidence of postoperative acute kidney injury both by correcting the anemia and by limiting the need for perioperative transfusions.⁴⁰ It remains to be determined whether elective preoperative transfusion to correct anemia would reduce postoperative development of acute kidney injury in total joint arthroplasty. As an aside, perioperative transfusion has also been linked to development of periprosthetic joint infection.⁴¹

Renin-angiotensin-aldosterone system inhibitors

Several studies found perioperative use of renin-angiotensin-aldosterone system inhibitors to be a risk factor for acute kidney injury.

Kimmel et al¹¹ reported adjusted odds ratios of 2.70 (95% CI 1.12–6.48) for ACE inhibitor use and 2.64 (95% CI 1.18–5.93) for ARB use in a study of 425 primary total joint arthroplasties.

Challagundla et al²⁴ found an odds ratio of 3.07 (95% CI 1.40–6.74) with ACE inhibitor or ARB use by multivariate analysis in 198 total joint arthroplasties.

Nielson et al¹⁸ studied 798 patients who underwent total joint arthroplasty and found that preoperative use of renin-angiotensin system inhibitors was associated with a significantly higher rate of postoperative acute kidney injury (8.3% vs 1.7% without inhibition), which was statistically significant by multivariate analysis (odds ratio 2.6, 95% CI 1.04–6.51).

We recommend holding renin-angiotensin-aldosterone system inhibitors 7 days before surgery through the postoperative period in high-risk cases.

Aminoglycoside use as a risk factor

Prophylactic administration of systemic antibiotics is the standard of care. In a systematic review of 26 studies and meta-analysis of 7 studies (3,065 patients), prophylactic antibiotics reduced the relative risk of wound infection by 81% with an absolute risk reduction of 8%.⁴²

A modifiable risk factor for acute kidney injury is the specific antibiotic used for prophylaxis. Multiple studies assessed the risk of acute kidney injury comparing regimens containing an aminoglycoside (typically gentamicin) with regimens lacking these agents.^20–26 In general, these studies found a significantly higher risk of acute kidney injury when gentamicin was used.

Challagundla et al²⁴ found an incidence of acute kidney injury of 52% using RIFLE creatinine criteria in 52 patients receiving 8 g total of flucloxacillin plus 160 mg of gentamicin (120 mg if they weighed less than 60 kg) compared with 8% in 48 patients given cefuroxime (3 g total) and 14% in an additional 52 patients also given cefuroxime.

Johansson et al²⁵ found an incidence of KDIGO creatinine-based acute kidney injury of 13% in 70 patients given dicloxacillin alone prophylactically compared with 27% given dicloxacillin and gentamicin, with a relative risk of 3.

Bell et al,²¹ in a large registry-based analysis from Scotland involving 7,666 elective orthopedic procedures, found that use of flucloxacillin 2 g plus a single dose of gentamicin 4 mg/kg was significantly associated with a 94% higher risk of acute kidney injury (KDIGO creatinine criteria) compared with a cefuroxime-based regimen, with absolute rates increasing from 6.2% to 10.8%.

Dubrovskaya et al²⁰ and Ferguson et al,²⁶ in contrast, found no increased risk with addition of gentamicin.

We recommend avoiding aminoglycosides for prophylaxis in primary lower-extremity total joint arthroplasty in patients at higher risk unless required for specific microbiologic reasons.

Vancomycin may also increase risk

Courtney et al¹⁹ assessed the risk of adding vancomycin to cefazolin for routine prophylaxis in a retrospective series of 1,828 total hip or knee arthroplasties and found a significantly higher rate of acute kidney injury, using AKIN criteria (13% vs 8%, odds ratio by multivariate analysis 1.82, P = .002).¹⁹

Other agents shown to be effective in treating periprosthetic joint infections or complicated skin and soft-tissue infections with resistant organisms include daptomycin⁴³ and linezolid.⁴⁴ These nonnephrotoxic alternatives to vancomycin may be a consideration if prophylaxis for methicillin-resistant Staphylococcus aureus is deemed necessary in patients at risk for acute kidney injury.

 

 

PROSTHETIC JOINT INFECTIONS AND ANTIBIOTIC-LOADED CEMENT

Deep infection may complicate nearly 1% of total hip⁴⁵ and 2% of total knee arthroplasties.⁴⁶ Kurtz et al^4,6 have projected that by 2030, infection will be the cause of two-thirds of the estimated 268,000 revision total knee arthroplasties and about half of the estimated 96,700 revision total hip arthroplasties.

The most common method of treating a chronically infected replacement joint is a 2-stage procedure.⁵ First, the prosthesis is removed, all infected bone and soft tissue is debrided, and an antibiotic-loaded cement spacer is implanted. Systemic antibiotics are given concurrently, typically for about 6 weeks. After the infection is brought under control, perhaps 2 to 3 months later, the spacer is removed and a new joint is implanted with antibiotic-loaded cement. A 1-stage procedure may be an option in selected cases and would obviate the need for an antibiotic-loaded cement spacer.^47,48

Of obvious relevance to development of acute kidney injury is the choice and amount of antibiotics embedded in the cement used for spacers and in implantation. Very high antibiotic levels are achieved within the joint space, usually with little systemic absorption, although significant systemic exposure has been documented in some cases.

The polymethylmethacrylate cement used for these purposes comes in 40-g bags. Multiple bags are typically required per joint, perhaps 2 to 4.⁴⁹

The rate of elution of antibiotics is determined by several factors, including surface area, porosity, and the number of antibiotics. In general, elution is greatest early on, with exponential decline lasting perhaps 1 week,  followed by slow, sustained release over weeks to months.⁵⁰ However, several in vitro studies have indicated that only about 5%^50,51 of the total antibiotic actually elutes over time.

Initially, multiple antibiotic-laden cement beads were used to fill the joint space, but this significantly limited function and mobility.⁵² Now, cement spacers are used, and they can be nonarticulating or articulating for maximal joint mobility.⁵³ Although much greater antibiotic elution occurs from beads due to their high surface area-to-volume ratio, spacers still provide an adequate dose.

ANTIBIOTIC-LOADED CEMENT: DOSAGE AND ELUTION CHARACTERISTICS

Antibiotic-loaded cement can be either low-dose or high-dose.

Low-dose cement

Low-dose cement typically consists of 0.5 to 1.0 g of antibiotic per 40-g bag of cement, usually an aminoglycoside (gentamicin or tobramycin) or vancomycin, and can be purchased premixed by the manufacturer. Such cement is only used prophylactically with primary total joint arthroplasty or revision for aseptic reasons, a practice common in Europe but less so in the United States. Some American authors propose antibiotic-loaded cement prophylaxis for patients at high risk, eg, those with immunosuppression, inflammatory cause of arthritis, or diabetes.⁵⁴

Vrabec et al,⁵⁵ in a study of low-dose tobramycin-loaded cement used for primary total knee arthroplasty, found a peak median intra-articular tobramycin concentration of 32 mg/L at 6 hours, declining to 6 mg/L at 48 hours with all serum levels 0.3 mg/L or less (unmeasureable) at similar time points.

Sterling et al,⁵⁶ studying primary total hip arthroplasties with low-dose tobramycin-loaded cement, found mean levels in drainage fluid of 103 mg/L at 6 hours, declining to 15 mg/L at 48 hours. Serum levels peaked at 0.94 mg/L at 3 hours, declining to 0.2 mg/L by 48 hours.

Although most of the antibiotic elution occurs early (within the first week), antibiotic can be found in joint aspirates up to 20 years later.⁵⁷ We are unaware of any well-documented cases of acute kidney injury ascribable to low-dose antibiotic-loaded cement used prophylactically. One case report making this assertion did not determine serum levels of aminoglycoside.⁵⁸

High-dose cement

High-dose antibiotic-loaded cement typically contains about 4 to 8 g of antibiotic per 40-g bag of cement and is used in the treatment of prosthetic joint infection to form the spacers. The antibiotic must be mixed into the cement powder by the surgeon in the operating room.

There is no standard combination or dosage. The choice of antibiotic can be tailored to the infecting organism if known. Otherwise, gram-positive organisms are most common, and vancomycin and aminoglycosides are often used together. This particular combination will enhance the elution of both antibiotics when studied in vitro, a process termed “passive opportunism.”⁵⁹ Other antibiotics in use include aztreonam, piperacillin, teicoplanin, fluoroquinolones, cephalosporins, and daptomycin, among others.

About 8 g of antibiotic total per 40-g bag is the maximum to allow easy molding.⁵² As an example, this may include 4 g of vancomycin and 3.6 g of tobramycin per 40 g. Given that 3 to 4 such bags are often used per joint, there is significant risk of systemic exposure.

Kalil et al⁶⁰ studied 8 patients who received high-dose tobramycin-loaded cement to treat periprosthetic joint infections of the hip or knee and found that 7 had detectable serum levels (mean 0.84 mg/L, highest 2.0 mg/L), including 1 with a level of 0.9 mg/L on day 38; 4 of these 8 developed acute kidney injury by AKIN criteria, although other risk factors for acute kidney injury existed. Nearly all had concomitant vancomycin (3 to 8 g) added to the cement as well.

Hsieh et al⁶¹ studied 46 patients with infected total hip arthroplasties treated with high-dose antibiotic-loaded cement spacers (vancomycin 4 g and aztreonam 4 g per 40-g bag) and found vancomycin levels in joint drainage higher than 1,500 mg/L on day 1, decreasing to 571 mg/L on day 7; serum levels were low (range 0.1–1.6 mg/L at 24 hours), falling to undetectable by 72 hours.

 

 

ANTIBIOTIC-LOADED CEMENT SPACERS AND ACUTE KIDNEY INJURY

Case reports have associated high-dose antibiotic-loaded cement spacers with acute kidney injury.

Curtis et al⁶² described an 85-year-old patient with stage 3 chronic kidney disease who was treated for an infected total knee arthroplasty with an antibiotic-loaded cement spacer (containing 3.6 g of tobramycin and 3 g of cefazolin per 40-g bag, 3 bags total) and developed stage 3 acute kidney injury. After 16 days and 3 hemodialysis sessions, the patient’s serum tobramycin level was still 2 mg/L despite receiving no systemic tobramycin.

Wu et al⁶³ reported a case of acute kidney injury that required dialysis after implantation of a tobramycin- and vancomycin-loaded spacer, with persistent serum tobramycin levels despite repeated hemodialysis sessions until the spacer was removed.

Chalmers et al⁶⁴ described 2 patients with acute kidney injury and persistently elevated serum tobramycin levels (3.9 mg/L on day 39 in 1 patient and 2.0 mg/L on day 24 in the other patient) despite no systemic administration.

In these and other case reports,^65–67 dialysis and spacer explantation were usually required. 


Comment. It is intuitive that acute kidney injury would more likely complicate revision total joint arthroplasties for infection than for primary total joint arthroplasties or revisions for aseptic reasons, given the systemic effects of infection and exposure to nephrotoxic or allergenic antibiotics. And the available data suggest that the risk of acute kidney injury is higher with revision for prosthetic joint infection than with revision for aseptic reasons. However, many of the studies were retrospective, relatively small, single-center series and used different definitions of acute kidney injury.

We are aware of 17 studies specifically addressing acute kidney injury or postoperative complications in general that may have included acute kidney injury.^{50,52,61,68–81} Ten of these studies found at least 1 case of acute kidney injury (Table 3). Of note, 7 studies totaling 219 patients reported no cases of acute kidney injury, although acute kidney injury per se was not mentioned and no definition of it was provided.^{50,61,76,77,79,80,82}

Luu et al⁸³ performed a systematic review of studies published between January 1989 and June 2012 reporting systemic complications (including acute kidney injury) of 2-stage revision arthroplasties including placement of an antibiotic-loaded cement spacer for treatment of periprosthetic joint infection. Overall, 10 studies were identified with 544 total patients. Five of these studies, with 409 patients, reported at least 1 case of acute kidney injury for a total of 27 patients, giving an incidence of 6.6% in these studies.^68–71 The remaining 5 studies, totaling 135 patients, did not report any cases of acute kidney injury,^{50,61,76–78} although that was not the primary focus of any of those trials.

Most notable from this systematic review, the study of Menge et al⁶⁹ retrospectively determined the incidence of acute kidney injury (defined as a 50% rise in serum creatinine to > 1.4 mg/dL within 90 days of surgery) to be 17% in 84 patients with infected total knee arthroplasties treated with antibiotic-loaded cement spacers. A mean of 3.5 bags of cement per spacer were used in the 35 articulating spacers, compared with 2.9 per nonarticulating spacer. These spacers contained vancomycin in 82% (median 4.0 g, range 1–16 g) and tobramycin in 94% (median 4.8 g, range 1–12 g), among others in small percentages. The dose of tobramycin in the spacer considered either as a dichotomous variable (> 4.8 g, OR 5.87) or linearly (OR 1.24 per 1-g increase) was significantly associated with acute kidney injury, although systemic administration of aminoglycosides or vancomycin was not.

Additional single-center series that were published subsequent to this review have generally used more current diagnostic criteria.

Noto et al⁷² found that 10 of 46 patients treated with antibiotic-loaded cement spacers had a greater than 50% rise in serum creatinine (average increase 260%). All spacers contained tobramycin (mean dose 8.2 g), and 9 of 10 also contained vancomycin (mean 7.6 g). All of the 9 patients with acute kidney injury with follow-up data recovered renal function.

Reed et al⁷⁵ found 26 cases of acute kidney injury (based on RIFLE creatinine criteria) in 306 patients with antibiotic-loaded cement spacers treating various periprosthetic joint infections (including hips, knees, shoulders, and digits) and compared them with 74 controls who did not develop acute kidney injury. By multivariable analysis, receipt of an ACE inhibitor within 7 days of surgery and receipt of piperacillin-tazobactam within 7 days after surgery were both significantly more common in cases with acute kidney injury than in controls without acute kidney injury.

Aeng et al⁷³ prospectively studied 50 consecutive patients receiving antibiotic-loaded spacers containing tobramycin (with or without vancomycin) for treatment of infected hip or knee replacements. Using RIFLE creatinine criteria, they found an incidence of acute kidney injury of 20% (10 of 50). Factors significantly associated with acute kidney injury included cement premixed by the manufacturer with gentamicin (0.5 g per 40-g bag) in addition to the tobramycin they added, intraoperative blood transfusions, and postoperative use of nonsteroidal anti-inflammatory drugs.

Geller et al,⁷⁴ in a multicenter retrospective study of 247 patients with prosthetic joint infections (156 knees and 91 hips) undergoing antibiotic-loaded cement spacer placement, found an incidence of acute kidney injury of 26% based on KDIGO creatinine criteria. Significant risk factors included higher body mass index, lower preoperative hemoglobin level, drop in hemoglobin after surgery, and comorbidity (hypertension, diabetes, chronic kidney disease, or cardiovascular disease). Most of the spacers contained a combination of vancomycin and either tobramycin (81%) or gentamicin (13%). The spacers contained an average of 5.3 g (range 0.6–18 g) of vancomycin (average 2.65 g per 40-g bag) and an average of 5.2 g (range 0.5–16.4 g) of tobramycin (average 2.6 g per bag).

As in Menge et al,⁶⁹ this study illustrates the wide range of antibiotic dosages in use and the lack of standardization. In contrast to the study by Menge et al, however, development of acute kidney injury was not related to the amount of vancomycin or tobramycin contained in the spacers. Eventual clearance of infection (at 1 and 2 years) was significantly related to increasing amounts of vancomycin. Multiple different systemic antibiotics were used, most commonly vancomycin (44%), and systemic vancomycin was not associated with acute kidney injury.

Yadav et al,⁸¹ in a study of 3,129 consecutive revision procedures of the knee or hip, found an incidence of acute kidney injury by RIFLE creatinine criteria of 29% in the 197 patients who received antibiotic-loaded cement spacers for periprosthetic joint infection compared with 3.4% in the 2,848 who underwent revision for aseptic reasons. In 84 patients with prosthetic joint infection having various surgeries not including placement of a spacer, the acute kidney injury rate at some point in their course was an alarmingly high 82%. In the group that received spacers, only age and comorbidity as assessed by Charlson comorbidity index were independently associated with acute kidney injury by multivariate analysis. Surprisingly, modest renal impairment was protective, possibly because physicians of patients with chronic kidney disease were more vigilant and took appropriate measures to prevent acute kidney injury.

Overall, the risk of acute kidney injury appears to be much higher during treatment of prosthetic joint infection with a 2-stage procedure using an antibiotic-loaded cement spacer than after primary total joint arthroplasty or revision for aseptic reasons, and may complicate up to one-third of cases.

 

 

REDUCING RISK DURING TREATMENT OF INFECTED REPLACEMENT JOINTS

Due to lack of appropriate data, how best to mitigate the risk of acute kidney injury is uncertain. In our opinion, however, the following measures should be considered (Table 4).

As in primary total joint arthroplasty in general, higher-risk cases should be identified based on age, body mass index, chronic kidney disease, comorbidities (hypertension, diabetes, established cardiovascular disease), and anemia.

Preoperative transfusion can be considered case by case depending on degree of anemia and associated risk factors.

All renin-angiotensin-aldosterone system inhibitors should be withheld starting 1 week before surgery.

Both nonselective and cyclooxygenase-2 selective nonsteroidal anti-inflammatory drugs should be avoided, if possible.

Strict attention should be paid to adequate intraoperative and postoperative fluid resuscitation.

Kidney function should be monitored closely in the early postoperative period, including urine output and daily creatinine for at least 72 hours.

Systemic administration of potentially nephrotoxic antibiotics should be minimized, especially the combination of vancomycin with piperacillin-tazobactam.⁸⁴ Daptomycin is a consideration.⁴³

If acute kidney injury should develop, serum levels of vancomycin or aminoglycosides should be measured if the spacer contains these antibiotics. The spacer may need to be removed if toxic serum levels persist.

TAKE-HOME POINTS

Acute kidney injury may complicate up to 10% of primary lower-extremity total joint arthroplasties and up to 25% of periprosthetic joint infections treated with a 2-stage procedure including placement of an antibiotic-loaded cement spacer in the first stage.

Risk factors for acute kidney injury include older age, obesity, chronic kidney disease, and overall comorbidity. Potentially modifiable risk factors include anemia, perioperative transfusions, aminoglycoside prophylaxis, perioperative renin-angiotensin system blockade, and postoperative nonsteroidal anti-inflammatory drugs. These should be mitigated when possible.

In patients with periprosthetic joint infection who receive antibiotic-loaded cement spacers, especially patients  with additional risk factors for acute kidney injury, strict attention should be paid to the dose of antibiotic in the spacer, with levels checked postoperatively if necessary. Nonnephrotoxic antibiotics should be chosen for systemic administration when possible.

Prospective randomized controlled trials are needed to guide therapy after total joint arthroplasty, and to verify the adverse long-term outcomes of acute kidney injury in this setting.