Monitoring Perioperative Ischemia

Abstract

surgery and whether perioperative ischemia leads to increased morbidity and mortality in patients with coronary artery disease (CAD) who are undergoing surgery. Based on previous studies, it is generally accepted that perioperative ischemia is common in patients with CAD undergoing noncardiac surgery. The incidence of ischemia during the operative period varies greatly with cardiac risk factors, type of surgery, duration of surgery, and the monitor used to detect ischemia. Because perioperative cardiac morbidity is the leading cause of death after anesthesia and surgery, it is prudent for the anesthesia clinician to have an understanding of the tools available for monitoring as well as their clinical utility. These tools are summarized, and recommendations are made regarding their use. Copyright © 2001 by W.B. Saunders Company. W y should we monitor for ischemia during Y Y surgery? Does perioperative ischemia lead to increased morbidity and mortality in patients with coronary artery disease (CAD) undergoing surgery? Slogoff and Keatsl addressed these questions in a prospective study involving 1,023 patients undergoing elective coronary artery bypass grafting (CABG). They found electrocardiographic (ECG) evidence of ischemia in 36.9% of their patients. Postoperative myocardial infarction (PMI) was 3 times more prevalent in patients with ischemia (6.9% v 2.5%). These results were confirmed in another 495 patients undergoing CABG; PMI occurred in 6.3% of the patients with ECG evidence of ischemia, compared with 1.8% of patients without ECG evidence of ischemia.2 An increase in PMI has also been demonstrated in patients with CAD undergoing noncardiac surgery. Mangano et a13 showed the incidence of preoperative, intraoperative, and postoperative ischemia to be 20%, 25%, and 41%, respectively, in men with cardiac risk factors who were undergoing major surgery. PMI conferred a 9-fold increase in the odds of having an ischemic event, defined as cardiac death, nonfatal myocardial infarction (MI), or unstable angina. Thus, it is generally accepted that perioperative ischemia is common in patients with CAD undergoing noncardiac surgery.The incidence of ischemia varies during the operative period, with preoperative rates ranging from 9.5% to 42%, 3-5 intraoperative rates of 18% to 74%,3-9 and postoperative rates of 2'7% to 41 %.3-5 These rates vary greatly with cardiac risk factors, type of surgery, duration of surgery, and the monitor used to detect ischemia. Because perioperative cardiac morbidity is the leading cause of death after anesthesia and surgery, it is prudent for the anesthesia clinician to have an understanding of the tools available for monitoring as well as their clinical utility. These tools are summarized, and recommendations are made regarding their use. Surface ElectrocardiographyStandard surface ECG is the most common perioperative technique used to monitor for myocardial ischemia. When ECG is used, more than 80% of ischemia episodes present as ST segment depressions. ST elevations are much less com-