obesitashypoventilationssyndrom

Obesity hypoventilation syndrome (OHS) is a respiratory disorder defined by obesity, daytime hypoventilation with hypercapnia, and the absence of other causes of hypoventilation. It typically occurs in individuals with a body mass index (BMI) of 30 kg/m² or greater and is frequently associated with sleep-disordered breathing.

Diagnosis is made when daytime arterial carbon dioxide tension (PaCO2) exceeds 45 mmHg in an obese patient, after other causes of hypoventilation have been excluded. Elevated serum bicarbonate reflects chronic hypoventilation. Polysomnography or nocturnal oximetry helps evaluate concomitant sleep apnea and nocturnal hypoventilation.

Pathophysiology involves increased work of breathing and reduced ventilatory drive due to excess body mass, leading to partial alveolar hypoventilation during wakefulness and sleep. Coexisting restrictive or obstructive lung disease, central factors, and obesity-related inflammation can contribute to the condition.

Management centers on noninvasive positive-pressure ventilation (NIV) as the mainstay, often combined with weight loss strategies and treatment of sleep apnea. Continuous positive airway pressure (CPAP) may help when obstructive sleep apnea is predominant; oxygen therapy is used cautiously to avoid worsening hypercapnia. Addressing comorbidities and supporting weight loss, including bariatric surgery in eligible patients, are important components of care.

Prognosis improves with treatment, while untreated OHS is associated with ongoing hypercapnia, hypoxemia, pulmonary hypertension, right heart strain, and increased mortality. OHS tends to be underrecognized in the obese population but responds well to appropriate ventilatory support and weight-management strategies.