Physiologic responses to operation in high risk surgical patients.

Fifty-three high risk surgical patients were studied using invasive cardiorespiratory monitoring to gain physiologic perspective of the perioperative period. Multiple hemodynamic and oxygen transport variables were tracked through the preoperative, intraoperative and postoperative periods using frequent sequential measurements. Impairment of cardiac and pulmonary function was measured intraoperatively, but this was compensated by therapy, so that oxygen delivery was maintained. Nonetheless, there was a decrease in oxygen consumption intraoperatively due to decreased oxygen extraction. Postoperatively, there was an increase in cardiac output, oxygen delivery and oxygen consumption. It is postulated that the fall in oxygen consumption intraoperatively may result in a metabolic debt and that a hyperdynamic postoperative state represents the physiologic response necessary to repair the damage caused intraoperatively by relative cellular hypoxia.