The influence of position on ventilation-perfusion distribution after abdominal surgery

Publisher Website
Google Scholar
Abstract
The effects of a change in position on gas exchange and ventilation perfusion (.ovrhdot.VA/.ovrhdot.Q distribution were studied in 12 patients, after abdominal surgery .ovrhdot.VA/.ovrhdot.Q distribution was determined from retention and excretion curves of six inert gases of different solubilities, in supine and sitting patients, during spontaneous breathing. Changing position from supine to sitting resulted in an increase in minute ventilation and a decrease in Paco2. With regard to .ovrhdot.VA/.ovrhdot.Qdistribution, an estimated shunt of 5.2% .+-. 3.4 was documented in all the patients in the supine position, and was associated with a large percentage of low .ovrhdot.VA/.ovrhdot.Q regions (20.0% .+-. 13.0) in six of them. Patients with associated estimated shunt and low .ovrhdot.VA/.ovrhdot.Q regions were those with the greatest amount of venous admixture (respectively: 27.3% .+-. 7.2, and 14.9% .+-. 3.0, for patients without low .ovrhdot.VA/.ovrhdot.Q regions, P < 0.01). When patients were placed in the sitting position, the estimated shunt was not reduced, but the percentage of low .ovrhdot.VA/.ovrhdot.Q decreased when it was documented. Despite the improvement of .ovrhdot.VA/.ovrhdot.Q distribution in the sitting position, the lack of significant change in Pao2 may be explained by the simultaneous decrease in Pvo2 caused by a decrease in cardiac output.