Obesity Hypoventilation Syndrome

An obese patient who is sleepy during the day, wakes with headaches, or needs oxygen should not automatically be labelled as having uncomplicated obstructive sleep apnea. The finding that changes the picture is awake alveolar hypoventilation: carbon dioxide remains elevated while the patient is awake. OHS is clinically significant because oxygenation can look temporarily acceptable while ventilation is failing. Supplemental oxygen may raise the SpO2 without removing the excess CO2. A drowsy patient with obesity and a high oxygen saturation may therefore be deteriorating, not improving. The syndrome is diagnosed only after other causes of hypoventilation have been excluded. Treatment must support ventilation during sleep, address obstructive events when present, and pursue substantial sustained weight loss. The correct positive-airway-pressure modality depends on the sleep-study pattern; every patient with OHS does not require bilevel ventilation.