Remifentanil for Regional Anesthesia

Abstract

In Response: The purpose of our study was not to compare midazolam with remifentanil, but to assess the sedative properties of remifentanil when given as analgesic supplementation during regional anesthesia. Midazolam was used as adjunct sedative drug to achieve a predefined level of sedation in all treatment groups before placement of the regional block and thereafter. Dr. Federolf pointed out the limitations of the remifentanil continuous infusion techniques for supplementing regional anesthesia procedures. We agree that remifentanil infusions induce a number of side effects, but their incidence should be compared with that of other opioid supplementations of regional anesthesia. Furthermore, the withdrawal of 13 patients from the remifentanil groups is a posteriori not unexpected, as this was a dose-finding study in which the continuous infusion was started with high infusion rates for the purpose of determining the 50% and 90% effective dose of the sedative effect. Dr. Federolf also misquoted the reduction in midazolam use seen with remifentanil infusions by using the differences between reported mean values in our original Table 1. A more accurate impression is obtained when comparing the ranges of total amount of midazolam used, regardless the type of surgery, and the percentage of patients requiring midazolam in the four groups of patients. Finally, the delayed return to alertness observed with remifentanil is easy to explain. Remifentanil was administered as a continuous infusion until the end of surgery. In contrast, midazolam supplementation occurred before the placement of the regional block and at the beginning of surgery. Considering the pharmacokinetic profile of midazolam, it is not unexpected that its plasma concentrations would have decreased to levels compatible with arousal at the end of surgery, at a time that the remifentanil concentrations had still to decrease. In selecting an appropriate adjunct to a regional anesthetic procedure, the anesthesiologist must balance the knowledge of the mechanism of action and therapeutic window of the particular drug against its side effects. Marilyn Lauwers, MD Frederic Camu, MD Department of Anesthesiology; Flemish Free University of Brussels School of Medicine; 1090 Brussels, Belgium