Comparison of clinical characteristics in patients with obesity hypoventilation syndrome and obese obstructive sleep apnea syndrome: a case-control study.

INTRODUCTION: Obesity hypoventilation syndrome (OHS) can be overlooked unless clinicians have a high index of suspicion. The present case-control study aimed to compare characteristics of patients with OHS and obese obstructive sleep apnea syndrome (OSAS), and to identify determinants of hypercapnia in OSAS patients.
METHODS: Demographic and anthropometric features, pulmonary function tests, blood gas analysis and sleep parameters of 59 OHS patients were compared to 295 body mass index-matched OSAS patients.
RESULTS: The rate of hypertension (67.8% vs 53.2%, respectively, P=0.027) was higher in OHS than OSAS group. In OHS patients, FVC (%) (P<0.0001), FEV1 (%) (P=0.001) and PaO2 (P<0.0001) were lower, whereas PaCO2 and HCO3 levels were increased (P<0.0001). Daytime sleepiness was more frequent (89.8% vs 68.5%, respectively, P=0.002), and Epworth sleepiness scores were higher (14.0 vs 11.9, respectively, P=0.021) in OHS than OSAS patients. In polysomnography, lowest and mean SpO2 were decreased, and sleep time with SpO2 <90% was increased in patients with OHS (P<0.0001). Multivariate analysis showed that hypercapnia was associated independently with HCO3 (P<0.0001) and daytime SaO2 (P=0.003). Besides, HCO3 level ≥ 27 mEq/L had a sensitivity of 88.1% and specificity of 73.1%, and SaO2 ≤ 95% had a sensitivity of 64.4% and specificity of 73.9% for identifying OHS.
CONCLUSION: It was shown that OHS patients have increased rate of hypertension, daytime sleepiness and HCO3 , and decreased lung functions and PaO2 levels than OSAS patients. The present results support that elevated bicarbonate levels and decreased oxygen saturations in obese OSAS patients should prompt clinicians to predict OHS.