Obesity hypoventilation syndrome

Obesity hypoventilation syndrome (OHS) is a diagnosis of exclusion where the afflicted patient has an elevated BMI (>30 kg/m²) and chronic carbon dioxide retention. Most patients have obstructive sleep apnea and may develop cor pulmonale. The pathophysiology is complex and includes excessive load on the respiratory system, altered ventilator control, and functional respiratory impairment. Screening for OHS should include elevated serum bicarbonate levels in obese individuals; a low resting pulse oximetry reading (<94%) should also raise suspicion. OHS should be confirmed with an overnight polysomnography, ideally with CO₂ monitoring and an resting arterial blood gas documenting elevated carbon dioxide levels. Most patients can be adequately managed with positive airway pressure during sleep and bariatric surgery, or weight loss programs should be strongly encouraged.