Obesity hypoventilation syndrome (OHS) is bound to be increasing because of the rising obesity epidemic but is underrecognized and “frequently underdiagnosed,” Saiprakash B. Venkateshiah, MD, said at the virtual annual meeting of the Associated Professional Sleep Societies.
The condition, which can cause significant morbidity and mortality, is defined by the combination of obesity and awake alveolar hypoventilation (PaCO2 ≥45 mm Hg), with the exclusion of alternate causes of hypoventilation. Sleep-disordered breathing (SDB) is almost universally present, with approximately 90% of individuals with OHS also having obstructive sleep apnea (OSA), most often severe, and approximately 10% having sleep-related hypoventilation, or a “pure hypoventilation subtype, if you will,” said Dr. Venkateshiah, assistant professor of medicine at Emory University, Atlanta.
The prevalence of OHS in the general population is unknown, but its prevalence in patients who present for the evaluation of SDB has ranged from 8%-20% across multiple studies, he said. Up to 40% of patients with OHS present for the first time with acute hypercapnic respiratory failure, which has an in-hospital mortality of 18%.
Postmenopausal women appear to have a higher prevalence, compared with premenopausal women and men, he noted, and women appear to be more likely than men to present with the clinical phenotype of OHS without associated OSA.
The arterial blood gas measurement needed to document alveolar hypoventilation and definitively diagnosis OHA is a “simple and economical test,” he said, “but it is logistically very difficult to obtain [these measurements] routinely in all patients in the clinic ... and is one of the reasons why OSH is underdiagnosed.”
Guideline advice
A practice guideline published in 2019 by the American Thoracic Society suggests that, for obese patients with SDB and a low to moderate probability of having OSH, a serum bicarbonate level be measured first. “In patients with serum bicarbonate less than 27 mmol/L, clinicians might forgo measuring PaCO2, as the diagnosis in them is very unlikely,” Dr. Venkateshiah said, referring to the guideline. “In patients with a serum bicarbonate greater than 27, you might need to measure PaCO2 to confirm or rule out the diagnosis of OHS.”
(Patients strongly suspected of having OHS, with more than a low to moderate probability – those in whom arterial blood gases should be measured – are “usually severely obese with typical signs and symptoms such as dyspnea, nocturia, lower-extremity edema, excessive daytime sleepiness, fatigue, loud disruptive snoring, witnessed apneas, as well as mild hypoxemia during wake and/or significant hypoxemia during sleep,” the ATS guideline says.)
The guideline panel considered the use of oxygen saturation measured with pulse oximetry during wakefulness to screen for OHS and decided to advise against it because of the paucity of evidence-based literature, Dr. Venkateshiah noted. (In making its five conditional recommendations, the guideline panel cited an overall very low quality of evidence.)
Symptoms of OHS overlap with those of OSA (for example, daytime hypersomnolence, witnessed apneas, loud snoring, and morning headaches), so “symptoms alone cannot be used to discriminate between the two disorders,” he advised. Signs of OHS commonly seen in clinical exams, however, are low resting daytime oxygen saturations and lower-extremity edema. A sleep study, he added, is needed to document and characterize SDB in patients with OHS.
Positive airway pressure therapy is the first-line treatment for OHS, and long-term outcomes of patients with OHS on PAP treatment are significantly better, compared with untreated individuals. There is no strong evidence to recommend one form of PAP therapy over another for patients with OHS and concomitant severe OSA, he said, but “the bottom line” from both short- and long-term randomized clinical trials comparing CPAP with noninvasive ventilation “is that CPAP is equivalent to noninvasive ventilation as far as outcomes are concerned.”
The ATS guideline panel recommends continuous positive airway pressure therapy for patients with OHS and severe OSA. And for OHS with nonsevere OSA, bilevel PAP is traditionally used – including pure hypoventilators, Dr. Venkateshiah said.
Weight-loss interventions are paramount, since “the primary driver of OHS is obesity,” he said at the meeting. There are only a few studies that have looked at bariatric surgery in patients with OHS, he said, “but they did note significant improvements in gas exchange, sleep apnea, lung volumes and pulmonary hypertension.”
The ATS guideline suggests weight-loss interventions that produce sustained weight loss of 25%-30% of the actual body weight. Such interventions are “most likely required to achieve resolution of hypoventilation,” Dr. Venkateshiah said.
OHS vs. COPD
In a separate presentation on OHS, Michelle Cao, DO, clinical associate professor at Stanford (Calif.) University, emphasized the importance of distinguishing the patient with OHS from the patient with hypercapnic chronic obstructive pulmonary disease (COPD). Spirometry and the flow volume curve can help rule out hypercapnic COPD and other conditions that cause daytime hypoventilation.
A study published in 2016 of 600 hospitalized patients determined to have unequivocal OHS found that 43% had been misdiagnosed as having COPD and none had been previously diagnosed with OHS, Dr. Cao noted. Patients in the study had a mean age of 58 and a mean body mass index of 48.2 kg/m2; 64% were women.
Dr. Venkateshiah and Dr. Cao had no relevant disclosures.