Extradural clonidine for postoperative pain relief.

نویسندگان

  • B Cook
  • E Doyle
چکیده

Suxamethonium and auditory evoked potentials Sir,—I read with interest the article by Brunner and colleagues on the relationship between suxamethonium and cortical auditory evoked potentials [1]. The focus of the article was the hypothesis that suxamethonium may cause arousal of anaesthetized patients, but no plausible explanations were offered by the authors as to the possible mechanism. I suspect that the authors overlooked the effects of neuromuscular blockers on the muscles of the tympanum (tensor tympani and stapedius) which are the most sensitive muscles in the body to the action of blocking drugs. For example, there is considerable literature on the early diagnosis of my-asthenia gravis by testing the reflex tensioning of the middle ear ossicles with impedance techniques. Thus the effect of suxamethonium on the auditory evoked response may not be concerned with arousal. Instead it may merely be the result of abolishing the tensioning reflex mediated by the stapedius, allowing a much larger mechanical signal through to the inner ear and therefore causing a larger stimulus up the auditory nerve. The authors even cited a reference reporting the absence of the " arousal " effect of suxamethonium in the presence of previous non-depolarizing paralysis (ref. [10]) which is what one would expect: when the stapedius has been blocked totally, it cannot be blocked further. The results of this article are nevertheless interesting. The discussion section, however, might perhaps have been reduced to a single 10-line paragraph had the authors taken into account the physiology of the stapedius reflex. Sir,–Our study showed that suxamethonium had an arousal effect according to the auditory evoked response (AER). In the discussion section of our article, we outlined the possible causes of this effect and, according to the literature, felt that cortical stimulation secondary to increased muscle spindle activity after muscle fasciculation or direct spindle stimulation by suxame-thonium itself, may be responsible for the arousal pattern which we observed. Theoretically, as Dr Ponte points out, paralysis of the stapedius by suxamethonium could increase the input up the auditory nerve resulting in an AER response similar to that seen with arousal. However, if this were so, all neuromuscular blocking drugs would have an arousal effect on the AER. There is currently no evidence in the literature to support this theory. In fact, in an article published recently in this journal [1], Richmond and colleagues showed that vecuronium had no effect on the AER. Regarding the …

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عنوان ژورنال:
  • British journal of anaesthesia

دوره 76 1  شماره 

صفحات  -

تاریخ انتشار 1996