Daytime hypercapnia in adult patients with obstructive sleep apnea in China

To the Editor:Obstructive sleep apnea(OSA)is a common sleep-disordered breathing.Previous studies reported that the incidence of daytime hypercapnia in patients with OSA was 26.2%in China[1]and 14%in Japan.[2]However,Weitzenblum et al[3]demonstrated that daytime hypercapnia in patients with OSA might not be secondary to sleep apneas/hypopneas,but might due to the comorbidities,such as chronic obstructive pulmonary disease or severe obesity.Obesity hypoventilation syndrome(OHS)is defined as a conjunction of obesity(body mass index[BMI]≥30 kg/m^(2)),daytime hypercapnia(partial pressure of carbon dioxide in arterial blood[PaCO_(2)]≥45 mmHg)and sleep disordered breathing,after excluding other causes for alveolar hypoventilation.[4]Since patients with OHS were not completely excluded in previous studies,[1,2]we assumed that the incidence of daytime hypercapnia in Chinese patients with OSA might be low.