Clinical manifestations and diagnosis of obesity hypoventilation syndrome
- Amanda Piper, PhD
Amanda Piper, PhD
- Clinical Senior Lecturer
- Faculty of Medicine, University of Sydney
- Brendon Yee, MBChB, PhD
Brendon Yee, MBChB, PhD
- Associate Professor, University of Sydney
- Royal Prince Alfred Hospital Sydney, Woolcock Institute of Research
Obesity adversely impacts the respiratory system and in some circumstances is associated with the development of alveolar hypoventilation. When no better explanation for this hypoventilation can be found, the condition is referred to as the obesity hypoventilation syndrome (OHS). Although most patients with OHS present with chronic hypoventilation, in about a third of cases the diagnosis is made during a hospitalization for acute respiratory failure [1-3]. Individuals with OHS have considerably worse health status and access more health care resources compared to the general population, with differences apparent up to eight years before a diagnosis is made . Morbidity and mortality in untreated patients with OHS is high [1,2]. Even when sleep disordered breathing is treated with positive airway pressure therapy, mortality in those with severe OHS remains substantially worse than individuals with obstructive sleep apnea alone . The main cause of death is generally from cardiovascular disease [2,5]. Consequently, early diagnosis and commencement on appropriate therapy are considered crucial in order to minimize the adverse effects of this disorder.
The clinical manifestations and diagnosis of OHS are reviewed here, while the pathogenesis and treatment are discussed separately. (See "Pathogenesis of obesity hypoventilation syndrome" and "Treatment of the obesity hypoventilation syndrome" and "Noninvasive positive pressure therapy of the obesity hypoventilation syndrome".)
Obesity Hypoventilation Syndrome (OHS) exists when an obese individual (body mass index [BMI] >30 kg/m2) and sleep disordered breathing develops awake alveolar hypoventilation (PaCO2 >45 mmHg), which cannot be attributed to other conditions such as pulmonary disease, skeletal restriction, neuromuscular weakness, hypothyroidism, or pleural pathology [6-8].
The prevalence of OHS in the general population has not been studied. However, estimates based on rates of obesity and obstructive sleep apnea (OSA) in the community suggest 0.15 to 0.3 percent of the adult population in the United States are likely to have OHS . Obesity is the hallmark of OHS (BMI >30 kg/m2), and the prevalence of this disorder increases as BMI rises [9,10]. Prevalence rates among specific populations vary considerably, from around 8 percent in bariatric surgical patients to 16 percent of patients referred to sleep centers with symptoms of sleep apnea . In a study of hospitalized patients with a BMI >35kg/m2, the prevalence of OHS was 31 percent , while in another study of obese patients with hypoxemia, 51 percent were found to have OHS . In a single center study, 8 percent of ICU admissions fulfilled the criteria for OHS . Ethnic factors also affect prevalence rates. In Japanese patients presenting for investigation of OSA, 2.3 percent were found to have OHS  compared to 20 percent of predominantly African-American patients evaluated at a US sleep center .
About 90 percent of OHS individuals will have coexisting obstructive sleep apnea (OSA), and consequently the symptoms and many of the physical findings are indistinguishable from OSA [7,16]. These include excessive daytime sleepiness, loud snoring, choking during sleep, resuscitative snorting (ie, a loud snort that follows an apnea as the patient partially awakens and reopens the upper airway), fatigue, hypersomnolence, impaired concentration and memory, a small oropharynx, and a thick neck [7,16]. Unlike OSA, male gender does not appear to be a significant risk factor for OHS [5,14,17]. There is some evidence to suggest that women may be diagnosed later than men, and then only after presentation with acute respiratory failure [18,19]. (See "Clinical presentation and diagnosis of obstructive sleep apnea in adults".)
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- CLINICAL MANIFESTATIONS
- DIAGNOSTIC TESTS
- Serum bicarbonate
- Oxygen saturation by pulse oximetry
- Other blood tests
- Arterial blood gases
- Pulmonary function tests
- Chest radiograph
- Cardiac studies
- DIAGNOSTIC APPROACH
- SUMMARY AND RECOMMENDATIONS