In Reply:-Dr. Rigg et al. suggest that the relatively low cardiac morbidity and mortality observed in the study by Bode et al. [1] reflects the case mix of patients in that study. They hypothesize that studying only high-risk patients would generate a more accurate estimate of the effect of anesthesia choice on cardiac outcome.
To the extent that randomized controlled trials enroll less ill patients than are typically seen among the total surgical population, the low event rates seen in such studies may be partially an artifact. However, patients undergoing lower extremity vascular surgery, including those enrolled in trials, are already high-risk. [2] It is not at all clear how Rigg et al. would subclassify such patients into “high” high-risk and “low” high-risk, nor do they provide a source for these estimated event rates. And would patients at high high-risk, even if they could be identified, undergo elective vascular surgery? Most physicians would consider an expected perioperative mortality of 20% to be prohibitively great. A study enrolling such patients may take forever. Finally, there is little, if any, reason to believe that intraoperative anesthesia choice would reduce perioperative mortality rate, which has variety of causes, [3] by 25%.
Our review and informal meta-analysis were performed on published trials, weighted appropriately for sample size. [4] Because publication bias generally favors the publication of trials with positive results, inclusion of unpublished trials generally leads to a reduction in the summary effect size, not the converse. Similarly, although most of the trials had relatively few patients, small published trials generally overestimate the effect of a treatment. Although these potential biases would favor detecting a beneficial effect of regional anesthesia compared with general anesthesia, no significant benefit was found: 0%(95% CI, -3% to +3%) difference for in-hospital or short-term cardiac mortality and 1.5%(95%CI, -4% to +7%) difference for any cardiac event or death favoring general anesthesia. [5]
Despite the potential physiologic advantages from regional anesthesia compared with general anesthesia in patients undergoing vascular surgery, there has been no demonstrated statistical, and more importantly, clinical benefit on cardiac outcomes. There may, however, be other reasons to prefer one of the techniques. Nor does the lack of benefit mean that additional research in reducing perioperative car-diac morbidity and mortality is futile. Other strategies, such as those addressing the management of postoperative pain or perioperative myocardial ischemia, are promising. [6] As to further trials comparing the effects of currently available techniques of regional and general anesthesia on cardiac outcome, our conclusion still stands: none are needed.
Alan S. Go, M.D.
Warren S. Browner, M.D., M.P.H.
General Internal Medicine Section; Veterans Administration Medical Center, 111A1
4150 Clement Street; San Francisco, California 94121
(Accepted for publication February 3, 1997.)
