Changes in (a-A)CO2 difference and pulmonary artery pressure in anesthetized man.

Abstract

Arterial-alveolar CO2 differences were determined in 9 healthy subjects during 1% halothane (Fluothane) anesthesia. Pulmonary arterial pressures and systemic pressures were recorded at the same time. During the investigations pulmonary arterial pressures were changed either by rapid infusion of 1,000 ml saline solution or by tilting the patients in head-up or head-down positions. A linear relation between the pulmonary arterial mean pressure and the arterial-alveolar CO2 difference was found, irrespective of how the mean pulmonary arterial pressure was changed. This relation could be written as the formula [DELTA] CO2 = 0. 54 (22 - PPA)- The increased arterial-alveolar gradient for CO2 during anesthesia may be explained by a marked reduction of pulmonary capillary blood flow in the uppermost part of the lung, a reduction that is caused by a drop in pulmonary perfusion pressure.