Obesity Hypoventilation Syndrome

Obesity Hypoventilation Syndrome (OHS) refers to a state of chronic daytime hypoventilation associated with obesity. Criteria for the diagnosis include persistently elevated PaCO2 > 45 mmHg, a body mass index > 30 kg/m 2 and no other cause for hypoventilation. The exact pathophysiology has not been clearly defined, but the syndrome has been attributed to a combination of abnormal respiratory mechanics resulting in increased work of breathing, depressed central ventilatory control, and neurohormonal effects. Most patients with OHS have obstructive sleep apnea (OSA) and respond to CPAP therapy with significant improvement in daytime oxygenation and reduction in PaCO2. Those without OSA or who do not respond appropriately to CPAP, may require BIPAP therapy. Some OHS patients who initially require BIPAP can be switched to CPAP at a later time. Alternative methods of positive airway pressure treatment, such as average volume-assured pressure support or surgical interventions such as bariatic surgery or tracheostomy can be offered to patients who are refractory to CPAP or BIPAP.