[Obesity and its respiratory effects detected through levels of partial pressure of carbon dioxide in the supine position].

INTRODUCTION: Obesity is a disease that is closely associated with deleterious respiratory effects such as the Obesity Hypoventilation Syndrome which conventionally includes awake hypercapnia. There are studies addressing the detection of daytime hypercapnia with the patient either in sitting or standing position. However, there are no studies in obese subjects with a normal daytime PaCO2 in whom the detection of hypercapnia is made in the supine position. It is feasible that the physiopathological changes that occur in obese patients when they adopt the supine position lead to increased PaCO2 levels or hypercapnia.

OBJECTIVE: To determine the levels of PaCO2 in obese patients with a normal daytime PaCO2 in the supine position using arterial blood gas test.

METHODS: Fifty patients with BMI > 30 Kg/m², with a normal daytime PaCO2 were included. Daytime arterial blood gas test was performed first with the patient in a standing position along with pulmonary function test. A second arterial blood gas test was made 15 minutes after the patient adopted the supine position. Polisomnography was performed.

RESULTS: Mean BMI was 40 kg/m2. PaCO2 levels in the standing position were less, statistically significant, than the PaCO2 levels in the supine position, 30.7 ± 2.5 mmHg vs 35.6 ± 6.7 mmH, p < 0.001.

CONCLUSIONS: We can achieve an early detection of Obesity hipoventilation syndrome in obese patients with a normal daytime PaCO2 by performing the arterial blood gas test in the supine position before these patients develop severe complications.