Do We Need to Intubate the Trachea 2 Minutes after Vecuronium 0.1 mg/kg in Elective Surgery?

To the Editor: We read with interest the article by Kim et al. (1) presenting a study where they measured the effect of different doses of ephedrine on intubating conditions 2 min after vecuronium 0.1 mg/kg. However, there are some aspects of their study that need explanation. What is the clinical reasoning behind the idea to decrease the time to intubate from 3–4 min to 2 min by using an additional drug—ephedrine—with potential side effects in elective patients when there is no need for rapid sequence induction? The more appropriate clinical means to decrease the onset time of vecuronium is to increase the dose to 0.15 mg/kg or—if the longer duration of action is considered to be a problem for very short procedures—simply wait for the appropriate onset of action to arrive. Since vecuronium is certainly not the muscle relaxant of choice for rapid sequence induction, we do not see the reason to decrease the onset time by 1–1.5 min in patients in which mask ventilation was not difficult. The authors state that they measured onset time at the adductor pollicis muscle commencing with submaximal currents of 20 mA in awake patients. Although they cite one study (2) that showed that submaximal stimulation can produce similar results in measuring train-of four ratios of NMB as supramaximal currents, this is not true for the determination of peak effect and onset time. The commencement of stimulation in awake patients, followed by stimulation in anesthetized patients, could have biased their results by altering the determination of peak effect and onset time, and gained—by rightfully interpreting their study setup—only 1 min of stimulation time in comparison to commencement in anesthetized patients. In addition, it obviously creates ethical problems. The interpretation of their results is confusing: they state that 70 and 110 μg/kg improved intubating conditions in comparison to placebo. However, they state as well that the intubating conditions were the same in all ephedrine groups! Why then not recommend 30 μg/kg ephedrine, since intubating conditions in that group was not different from the other groups? In addition, it would have been better had the authors measured onset time at the corrugator supercilii muscle, which better reflects onset and degree of NMB at the larynx than the adductor pollicis muscle. Their results show that ephedrine reduces onset time of vecuronium at the adductor pollicis muscle. We do not know whether it reduces onset time at the larynx, which is more important in relating intubating conditions to NMB. Furthermore, it reduces onset time of vecuronium after propofol application for anesthesia. Would ephedrine have changed the onset time of vecuronium had they used a hemodynamically more indifferent hypnotic drug, such as etomidate? In our mind, ephedrine is an efficient drug to counterattack the propofol-induced hypotension, but it should not be considered as a clinically valid choice to fasten onset of vecuronium. If for any reason, an onset time of 3 min to achieve good or excellent intubating conditions is not sufficiently short, rocuronium or a larger dose of vecuronium should be used. Thomas M. Hemmerling, MD, DEAA Guillaume Michaud Stephane Deschamps, DEES Guillaume Trager, DESS

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