[Daytime hypercapnia in patients with obstructive sleep apnea hypopnea syndrome]

To evaluate the incidence and factors related to daytime CO2 retention (PaCO2 ≥ 45 mm Hg, 1 mm Hg = 0.133 kPa) in Chinese patients with obstructive sleep apnea hypopnea syndrome.

1441 patients with OSAHS had daytime arterial blood gas analysis were recruited from 2007 to 2009 in Peking University People's Hospital. 145 patients underwent pulmonary function test and had FEV1/FVC ratio over 70% were under further analysis. Sex, age, BMI, pulmonary function, polysomnography (PSG) and blood gas analysis results were recorded. Linear regression analysis was used to evaluate the relationship between PaCO2 levels and related parameters. Comparison was done between hypercanpnic and eucapnic patients.

Daytime hypercapnia occurred in 25.2% of the 1441 patients with OSAHS, and 26.9% in the 145 OSAHS patients who had lung function test and with FEV1/FVC ratio over 70%. PaCO2 was correlated with BMI, PaO2 and the severity of nocturnal hypoxemia as reflected by the mean SpO2 and SIT90. This was also confirmed by the comparison between the hypercapnic and eucapnic patients.

Hypercapnia occurs in a large part of patients with OSAHS and normal FEV1/FVC. BMI, nocturnal hypoxemia and daytime PaO2 level are all contributed to the development of daytime CO2 retention in OSAHS.