Prevalence of daytime hypercapnia or hypoxia in patients with OSAS and normal lung function

The purpose of this study was to determine factors increasing daytime PaCO2 or PaO2 in obstructive sleep apnoea syndrome patients (OSAS) with normal p ulmonary function tests. Anthropometric, pulmonary function tests, arterial blood gases and sleep polygraphic data were analysed retrospectively in 21 8 OSAS patients (apnoea-hypopnoea index > 15 h(-1); 18 females, 55 +/- 11 y ears): 125 patients had abnormal pulmonary function tests, i.e. one or more flow or volume under 80% or above 120% of predictive value (group 1) and 9 3 had normal pulmonary function tests (group 11). Hypercapnia was defined a s PaCO2 greater than or equal to6.0 kPa and hypoxia as PaO2 <9.3 kPa. Patie nts with abnormal pulmonary function tests were more hypoxic and hypercapni c, more obese, and had a higher apnoea-hypopnoea index (P < 0.05). Seventee n patients of group I and four of group 11 were hypercapnic (13.6% and 4.3% , respectively). Thirty-one patients in group 1 (24.8%) had a PaO2 <9.3 kPa and six (6.5%) in group II. Stepwise multiple regression analysis showed t hat in group 11, only two factors were correlated with PaCO2: mean apnoea d uration and FRC (respectively: c = 0.228, P < 0.001; c = 0.006, P = 0.0108) ; and only two with PaO2: mean apnoea dura:ion: (c = -0-218, P = 0.029) and BMI (c= - 3.72, P < 0.0001). Daytime hypercapnia is present in 4.3% and da ytime hypoxia in 6.5% of patients with occlusive sleep apnoea syndrome and normal pulmonary function tests. These alterations in blood gases in OSAS w ith normal pulmonary function tests should be considered as OSAS severity c riteria. (C) 2001 Harcourt Publishers Ltd.