We are disappointed that, in the 1990s, anesthesiologists still attempt to improve cardiac outcome by limiting therapeutic protocols to the intraoperative period. Recent work has demonstrated that postoperative myocardial ischemia (POMI) is the single most important predictor of poor cardiac outcome, defined as myocardial infarction, unstable angina, and sudden death. In studies in which researchers evaluate patients for POMI, it was determined that myocardial ischemia occurs most frequently within the first 36-48 h after surgery in 30-60% of the patients. [3-10]Patients who undergo vascular surgery are at risk of experiencing this higher incidence. [5-10]Poor cardiac outcome follows 24-36 h later in 10-50% of the patients. [3-10]Therefore, attempting to determine beneficial effects on cardiac outcome of a technique that is limited to the intraoperative period will not yield clinically useful results.
From the analysis of the natural history of myocardial infractions, it is clear that one has to implement therapeutic techniques both intraoperatively and postoperatively to derive beneficial effects. Our group and others suggested that epidural anesthesia and analgesia is effective in decreasing the incidence of postoperative myocardial ischemia. In addition, the physiologic basis for these results has been established. However, therapy must be provided for at least 72 h. The mechanisms that underly these beneficial effects are described, in part, by Go and Browner in the accompanying editorial to Bode's paper. However, they also fail to recognize the importance of the postoperative period. In the study by Christopherson et al. post-operative epidural therapy was limited to 24 h. Beyond that point, parenteral morphine was used intramuscularly. Likewise, Bode et al. administered parenteral morphine or meperidine intravenously to their patients for 12-24 h. Subcutaneous morphine or oral opioids were used thereafter. They acknowledged that an unspecified number of patients received epidural morphine. However, all epidural catheters were removed after 12-24 h, thereby limiting the most important benefit of this technique.
We suggest that the problem in analyzing perioperative cardiac outcome is not statistical power or analysis, as inferred by Go and Browner--it is protocol design. Therefore, we disagree with their closing statement that "additional randomized controlled trials comparing regional and general anesthesia to determine their effects on perioperative cardiac morbidity and mortality are unlikely to be useful. As of now, further trials are not needed." Conversely, we have an urgent need of randomized controlled trials that compare epidural anesthesia and analgesia with general anesthesia and parenteral analgesia throughout the postoperative period to further clarify this issue. The conclusion that there is no difference in cardiac outcome after general or epidural techniques is, in our view, premature and even incorrect.
A second concern we have with Bode's article is the use of pulmonary artery monitoring in every patient. This is not the standard of care for patients who undergo femoral-to-distal artery bypass surgery. Therefore, their results may not be applicable to routine practices for this procedure throughout the country. Because they neither specified a protocol of treatment for perioperative hemodynamic aberrations detected by pulmonary artery catheter monitoring, nor describe the number of therapeutic interventions per group, they may have introduced a bias in the way patients were treated.
Oscar A. de Leon-Casasola, M.D.; Mark J. Lema, Ph.D., M.D.; Department of Anesthesiology; Roswell Park Cancer Institute; Elm and Carlton Streets; Buffalo, New York 14263
(Accepted for publication April 18, 1996.)