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Correspondence |
University Health Network, University of Toronto, Toronto, Canada, E-mail: scott.beattie{at}uhn.on.ca
We thank Drs. Lange, Roewer and Kehl for expressing interest in our recent paper, using our findings that beta blockers were unequally distributed between groups in our recent meta-analysis1 to highlight their recent investigations which suggest a negative interaction between beta blockers and ischemic preconditioning in vivo.2 Their findings are both interesting and intriguing, and come at a time when the efficacy of perioperative beta blockade has become increasingly controversial. The evidence cited refers to beta blockade in non-cardiac investigations, an important distinction since our report was limited to cardiac surgery. Coronary artery surgery has definitive periods of ischemia and reperfusion, a situation which is infrequent and unpredictable in noncardiac surgery. Secondly, we emphasize, that unlike beta blockade, there is no clinical evidence of an ischemic preconditioning like the effect of inhaled anesthetics in non-cardiac surgery.
Interestingly, there is clinical evidence that contradicts Dr. Lange et al.’s supposition, information which we were originally unable to report due to space constraints. Seventy-nine percent of the patients in the DeHert et al. studies (cited in our meta-analysis) were concomitantly using beta blockers, equally distributed between iv and inhaled anesthesia. (odds ratio 0.98; 95% confidence interval 59–1.64 P = 0.95). In these predominately beta blocked patients less troponin was released postoperatively in patients who received anesthesia with sevoflurane (weighted mean difference –2.95; 95% confidence intervals –3.3, –2.6 P = < 0.000001). These results suggest that ischemic-like preconditioning occurs in the presence of clinically beta-blocked patients.
This new controversy highlights the immediate need for safety and efficacy studies on combination therapies and drug interactions in both cardiac and non-cardiac surgery. However, on the available evidence it is premature to conclude that anesthetic preconditioning and beta blockers are incompatible.
References
1 Yu CH, Beattie WS. The effects of volatile anesthetics on cardiac ischemic complications and mortality in CABG: a meta-analysis. Can J Anesth 2006; 53: 906–18.
2 Lange M, Smul TM, Blomeyer CA, et al. Role of the beta 1-adrenergic pathway in anesthetic and ischemic preconditioning against myocardial infarction in the rabbit heart in vivo. Anesthesiology 2006; 105: 503– 10.[Medline]
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