Monitoring of oxygen delivery in cardiac and vascular surgery

Monitoring the adequacy of oxygen (O2) delivery is of paramount significance in the perioperative period of surgical patients undergoing cardiac and major vascular surgery. These patients are at considerable risk for ischemic perioperative complications due to a high incidence of coronary artery disease. Monitoring the adequacy of global O2 delivery is based on observing stability of haemodynamics, absence of elevated lactate levels and preservation of O2 consumption. Monitoring the adequacy of regional O2 delivery focuses on the coronary, cerebral, splanchnic and renal circulation. Myocardial ischemia can be detected relatively easily by continuous ECG monitoring of leads II and V5 and in selected cases by transesophageal echocardiography. There are relatively few monitoring modalities clinically available at the present time to reliably assess adequacy of O2 delivery in the cerebral, splanchnic and renal circulation. Expecting relatively low intra- and postoperative haemoglobin levels per se does not necessarily mandate greatly exaggerated monitoring. However, continuous ECG monitoring of leads II and V5, invasive blood pressure measurement, determination of hourly urine production may be indicated in most patients. In high risk patients extended monitoring with a pulmonary artery catheter and transesophageal echocardiography may be indicated. Most important, however, is the clinical surveillance by an experienced physician integrating the information of all applied monitoring modalities who realizes early alterations indicating (potentially) compromised O2 delivery.