Study of the oxygenation of cardiac patients submitted to extracorporeal circulation.

Studies were made on eight patients submitted to extracorporeal circulation to correct valvular defects. Whilst breathing 100% oxygen, the alveolar/arterial oxygen tension difference and the VD/VT relationship were determined before the operations and during the first three days of the post-operative period. On 26 occasions, the arterio/venous oxygen content difference was measured and used to calculate the total intrapulmonary shunt. In all patients, the alveolar/arterial oxygen tension difference was increased above normal before operation. The postoperative values were always higher than the preoperative ones. A significant mean increase was found on the second day. A slight but insignificant increase in the VD/VT relationship was found at each stage. In general, the values of the arterio/venous oxygen content difference were higher than the theoretical value of 5 vol.%. It is necessary to measure this difference in order to evaluate the true magnitude of the total intrapulmonary shunt despite the absence of clinical signs of low cardiac output.