After major surgery there is a signi®cant risk of major complications and even death, particularly in the elderly and patients with signi®cant cardiorespiratory disease. In the UK, recent large audits have shown a 30-day mortality rate of 5.6% for elective colorectal cancer surgery, 62 19.3% for emergency colorectal surgery, 62 7.3% for elective infrarenal aortic aneurysm and aorto-iliac occlusive disease surgery, 4 9±15% for oesophagectomy and 13±15% for elective gastrectomy. 34 Major surgery generates a strong systemic in¯ammatory response that in turn leads to an increase in oxygen requirement from an average of 110 ml min ±1 m ±2 at rest to an average of 170 ml min ±1 m ±2 in the postoperative period. 43 55 This substantial increase in oxygen demand is normally met by increases in cardiac output and tissue oxygen extraction. Most patients can meet the increased oxygen demand by increasing cardiac output and will usually do well after surgery. However, there remains a group who may not have the physiological reserve to increase cardiac output to the required level and this group of patients is at higher risk of complications after surgery. Trials have identi®ed high-risk patients and implemented strategies before surgery to increase oxygen delivery (DO 2 ) to the levels that major surgery demands. 15 30 55 67 Although some of these trials have demonstrated an improvement in outcome, the strategy remains controversial.The exact mechanisms that lead to postoperative complications are not completely understood, but an understanding of the existing knowledge on the pathogenesis of postoperative morbidity and mortality will help the clinician understand the rationale for increasing DO 2 and tissue perfusion in the high-risk surgical patient.In this paper we review the role of inadequate tissue perfusion and DO 2 in the development of complications after major surgery, the results of trials of preoperative interventions that aim to improve cardiac function and hence DO 2 , developments in the identi®cation of patients who are most likely to bene®t from these interventions and the role of¯uids and inotropes in optimization strategies.
Why do patients get major complications after major surgery?In patients undergoing major surgery, commonly monitored physiological variables such as heart rate, arterial pressure, central venous pressure (CVP), temperature and haemoglobin concentration are poor predictors of complications after surgery. Less commonly measured variables such as cardiac index (CI), DO 2 , gastric intramucosal pH (pHi) and stroke volume have been shown to be better predictors of postoperative outcome. 12 38 46 56 58 Survivors of major surgery and critical illness tend to have a higher CI, DO 2 and oxygen consumption (V Ç O 2 ) than non-survivors. 9 10 13 15 21 28 30 48 54 55 57 67 68 Moreover, normal values for these variables are not necessarily predictive of survival: in one series, 76% of patients who died after critical illness had achieved normal values. 11 The presence of an oxygen debt can be de...
