The cardiovascular responses of aortic cross-clamping and declamping with normal and high ventricular filling pressures were compared during epidural and nitrous oxide-morphine anesthesia in 32 male patients undergoing reconstructive aortic surgery. The patients were divided into four groups. Groups I and II had lumbar epidural blocks with bupivacaine and received nitrous oxide in oxygen to breathe; groups III and IV were anesthetized with morphine (2 mg/ kg) and nitrous oxide. During aortic occlusion groups I and III received Ringer's lactate at a rate which maintained mean pulmonary capillary wedge pressure
3 to 4 torr above pre-anesthetic values whereas groups II and IV were given Ringer's lactate rates which kept
similar to pre-anesthetic values. Prior to cross-clamping mean arterial blood pressure and systemic vascular resistance were lower in groups I and II than in groups III and IV but cardiac output,
and pulmonary vascular resistance were similar in the four groups. Cross-clamping of the aorta produced no significant change in any cardiovascular variable measured in any group. Declamping did not significantly alter any variable in groups I and III but produced moderate hypotension in group IV and severe hypotension in group II as well as significant decreases in
in both groups. Our data demonstrate that aortic cross-clamping and release result in little change in cardiovascular dynamics in patients anesthetized with epidural or morphine-nitrous oxide and given balanced salt solutions intravenously in amounts adequate to increase left ventricular filling pressures prior to release of the aortic cross-clamp. Our findings also indicate that hypotension can occur in patients in whom left ventricular filling pressures are maintained at normal levels prior to cross-clamp release, especially in patients given epidural anesthesia.