Phenotypes of obesity hypoventilation syndrome: characteristics and outcomes.

Obesity hypoventilation syndrome (OHS) is defined by the combination of obesity (body mass index (BMI) ⩾30 kg·m2), sleep disordered breathing and daytime hypercapnia (arterial carbon dioxide tension (PaCO2) ⩾45 mmHg at sea level) during wakefulness occurring in the absence of an alternative neuromuscular, mechanical or metabolic explanation for hypoventilation. Patients with OHS can be classify by phenotypes depending on whether or not they have obstructive respiratory events: hypoventilation and no or no significant obstructive sleep apnoea (OSA) and hypoventilation and significant OSA; we also add a third phenotype, which is the hospitalized patient with acute-on-chronic-respiratory failure. We describe the mid and long-term outcomes with and without positive airway pressure (PAP) by these three phenotypes.