Hemodynamic and metabolic changes during and following operation.

During anesthesia and operation, there appears to be a common state wherein oxygen consumption is inadequate to meet intraoperative metabolic requirements. Although there is insufficient information to fully explain this problem, decreased intraoperative levels of cardiac output and oxygen delivery, altered intraoperative oxygen transport at the microcirculatory and cellular levels, and altered delivery of oxidative substrate are possible contributors. Anesthesia and operation thus appear to produce a physiologic pattern similar to other shock states. Postoperative physiologic changes include increased cardiac output and increased oxygen delivery, necessary to support increased oxygen consumption. These postoperative changes may represent compensatory physiologic responses to preoperative and intraoperative oxidative and metabolic deficits. There are also significant energy needs of the healing surgical wound. These additional energy requirements for wound healing add to the degree of increase in metabolism necessary for recovery from operation. The postoperative increase in oxygen consumption appears to be essential to reverse intraoperative deficits, and has been reported to have survival value. Clinically, a major goal of postoperative therapy should thus be to support these necessary physiologic compensations. Titration of postoperative therapy should therefore not be to "normal" physiologic endpoints, but to the supernormal cardiac output and oxygen transport necessary for recovery in postoperative patients.