Anesth Analg 2003;97:1544-1545
© 2003 International Anesthesia Research Society
LETTERS TO THE EDITOR
Do We Need to Intubate the Trachea 2 Minutes after Vecuronium 0.1 mg/kg in Elective Surgery?
Thomas M. Hemmerling, MD DEAA,
Guillaume Michaud,
Stephane Deschamps, DEES, and
Guillaume Trager, DESS
From the Neuromuscular Research Group (NRG), Department of Anesthesiology, Centre Hospitalier de l’Université de Montréal (CHUM) Hôtel-Dieu, Université de Montréal, Montréal, Canada
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.
References
- Kim KS, Cheong MA, Jeon JW, et al. The dose effect of ephedrine on the onset time of vecuronium. Anesth Analg 2003; 96: 1042–6.[Abstract/Free Full Text]
- Connelly NR, Silverman DG, O‘Connor TZ, Brull SJ. Subjective responses to train-of-four and double burst stimulation in awake patients. Anesth Analg 1990; 70: 650–3.[Abstract/Free Full Text]
Response
Kyo Sang Kim, MD PhD
Department of Anesthesiology, Hanyang University Hospital, Seoul, Korea
In Response:
I appreciate the comments by Dr. Hemmerling and colleagues and agree with the use of rocuronium for the rapid sequence induction. However, in many countries, the use of rocuronium may be limited to the induction of anesthesia because of its expense. In our country, the cost of rocuronium is four times higher than that of vecuronium. There are some limitations of clinical use by medical insurance companies, so we tried to reduce the onset time of vecuronium. We also wanted to evaluate whether a small dose of ephedrine reduced the onset time of vecuronium as with rocuronium (1,2).
In our study (3), the TOF stimulation was started 2 min before the administration of the study drug (placebo or ephedrine). That means the stimulation time before vecuronium was 3 min, not 1 min. I suspect that the time is not as short as the prestimulation time for the determination of peak effect and onset time (4). The use of less painful stimulation is important in awake patients for the neuromuscular monitoring. Brull et al. (5) reported that 12 healthy volunteers quantified (by 10-cm visual analog scale) the discomfort associated with TOF stimulation at 20, 30, and 50 mA, and the median VAS scores were 2, 3, and 6, respectively. In our study, any awake patient did not complain of discomfort by the stimulation of submaximal current. However, we also agree that a limitation of the current study may be the comparison of the first twitch of TOF stimulation due to the submaximal response of the twitch height.
There are no statistical differences of intubating conditions among ephedrine groups, but ephedrine 70 and 110 µg/kg (poor intubating conditions: 7% and 3%) improved intubating conditions in comparison to ephedrine 30 µg/kg (poor intubating conditions: 17%). The incidence of extreme changes (>30% from baseline) of MAP in ephedrine 110 µg/kg was 87%, whereas it was <10% in the other groups at 1 min after tracheal intubation. So we recommended that ephedrine 70 µg/kg given before the induction of anesthesia improved intubating conditions at 2 min after vecuronium by increased cardiac output without significant adverse hemodynamic effects.
References
- Szmuk P, Ezri T, Chelly JE, Katz J. The onset time of rocuronium is slowed by esmolol and accelerated by ephedrine. Anesth Analg 2000; 90: 1217–9.[Abstract/Free Full Text]
- Munoz HR, Gonzalez AG, Dagnino JA, et al. The effect of ephedrine on the onset time of rocuronium. Anesth Analg 1997; 85: 437–40.[ISI][Medline]
- Kim KS, Cheong MA, Jeon JW, Lee JH, Shim JC. The dose effect of ephedrine on the onset time of vecuronium. Anesth Analg 2003; 96: 1042–6.
- Hemmerling TM, Donati F, Babin D, Beaulieu P. Duration of control stimulation does not affect onset and offset of neuromuscular blockade at the corrugator supercilii muscle measured with phonomyography or acceleromyography. Can J Anaesth 2002; 49: 913–7.[Abstract/Free Full Text]
- Brull SJ, Ehrenwerth J, Silverman DG. Stimulation with submaximal current for train-of-four monitoring. Anesthesiology 1990; 72: 629–32.[ISI][Medline]
