Abstract & Commentary
By Michael H. Crawford, MD, Professor of Medicine, Chief of Cardiology, University of California, San Francisco. Dr. Crawford is on the speaker's bureau for Pfizer. This article originally appeared in the October 2010 issue of Clinical Cardiology Alert. It was peer reviewed by Ethan Weiss, MD.
Source: Wijeysundera DN, et al. Outcomes and processes of care related to preoperative medical consultation. Arch Intern Med. 2010;170:1365-1374.
Patients undergoing major surgery tend to be older individuals with more comorbidities than the general non-surgical population. Thus, preoperative consultations by internal-medicine specialists are often requested by the surgeon or anesthesiologist. Such consultations clearly have a role in defining the risk-benefit ratio of surgery, but their value for altering the outcome of surgery is less well known. Thus, this group from Ontario, Canada, performed a population-based cohort study of patients over age 40 years undergoing major elective non-cardiac surgery, comparing outcomes in those who had preoperative consultations to those who did not. Since it would be expected that consultation patients would have more comorbidities and be at higher risk, a propensity score-matched pairs-cohort was constructed to account for these differences. The association between mortality and hospital stay was evaluated in this matched cohort of 191,852 patients.
Results: In the entire cohort (269,866), 39% underwent consultation, 94% of which were in the outpatient setting. As expected, there were differences between all measured characteristics, between those having a consultation and those not. In the matched cohort, these differences were markedly reduced. Consultation in the matched cohort was associated with higher rates of preoperative testing, use of beta-blockers or statins, and preoperative cardiac interventions. Also, consultation increased 30-day mortality (RR 1.16, 95% CI 1.07-1.25, NNH 516), one-year mortality (RR 1.08, NNH 227), and mean hospital stay (mean difference 0.67 days). As a control, consultation did not affect the incidence of postoperative wound infections. The authors concluded that medical consultation prior to major non-cardiac surgery increases pharmacologic therapy, testing, hospital stay, and mortality.
To those of us who spend a considerable amount of time doing preoperative consultations, this study is sobering. First, let me emphasize that this study does not say that preoperative consultations are worthless. At a minimum, they help define the risks of surgery and, therefore, may prevent some patients from having surgery in which the risk clearly outweighs the potential benefits. This study did not take this into account since the authors only studied patients who had surgery. However, in my experience, the number of patients not cleared for surgery is small (2%). Also, the propensity matching could not be done for about 8% of the patients in this study because their risk was so high, and few did not have consultations. Management of these patients may have been enhanced. However, in total, these two exceptions represent 10% of those undergoing surgery. In addition, propensity matching did not eliminate all the differences between the two groups, so there clearly was some residual confounding. The investigators admit this, but claim their sensitivity analyses suggest this residual confounding is small. Therefore, for the vast majority of preoperative patients, their results are likely to be valid; preoperative consultation increases costs and does not seem to change outcomes.
Why would mortality worsen with consultation? The authors suggest that this could be due to the increase in tests and therapy observed after consultations. The investigators noted that there was an increase in strokes related to beta-blocker use, which was increased in the consult group. This is consistent with recent data suggesting that perioperative beta-blockers can be harmful, especially if inappropriate hypotension and bradycardia occur. Also, consultation was associated with less epidural anesthesia use, which could increase complications. In addition, consultation was associated with less warfarin and low-molecular-weight heparin use in the first 30 days post-op all factors that could influence mortality.
On the other hand, although statistically significant, the changes in mortality and hospital stay were small and could be accounted for partially by inadequate matching of patients. Also, this is an administrative database study, so details like how many patients had myocardial infarction are not available. This renders the data less useful for analyzing the problem. Finally, once a patient is deemed at higher risk, short of cancelling surgery, there are not a lot of things to do to improve his/her risk that are proven effective. Variations in anesthesia technique and beta-blockers are frequently employed, but have little supporting data. Other approaches have even less supporting evidence. It may be that the best we can do is to do no harm. Resist the temptation to test and do procedures of dubious value in the perioperative setting. The best rule of thumb is to not do anything that the patient does not need anyway, regardless of surgery.