Comparative effects of barbiturate or enflurane anesthesia with induced hypotension on intrapulmonary shunting.

Forty patients undergoing intracranial aneurysm clipping were operated on under either barbiturate anesthesia (in 22) or enflurane anesthesia (in 18). Cardiac output, arterial and mixed venous oxygen tension, and arterial, right atrial, pulmonary arterial, and pulmonary artery wedge pressures were measured. Cardiac index, intrapulmonary shunt fraction, and pulmonary vascular resistance were calculated. Hypotension to 60, 50, and 40 torr was induced with sodium nitroprusside. There was a decrease in shunt fraction with the induction of anesthesia in both groups. During induced hypotension there was a slight increase in shunting in the enflurane group. The venous oxygen content was significantly less than control values during the hypotensive period in both groups as a result of decreased cardiac output. The arteriovenous oxygen difference was significantly greater than control at the post-mannitol and hypotensive periods. Pulmonary vascular resistance was significantly less in the enflurane group.