Neuromuscular TransmissionNeuromuscular monitoring: Old issues, new controversies
Introduction
Five years ago, an editorial in Anesthesiology opined: “… it is time to move from discussion to action and introduce objective neuromuscular monitoring in all operating rooms, not just those occupied by researchers and aficionados of muscle relaxants. …objective neuromuscular monitoring is an evidence-based practice and should consequently be used whenever a nondepolarizing neuromuscular blocking agent is administered [1].” By “objective,” the author meant the use of monitors that measured and displayed the train-of-four (TOF) ratio in real time. A similar editorial call for objective or quantitative monitoring in the British Journal of Anaesthesia appeared 3 years earlier with the dictum that “At a minimum, the clinician should always monitor the extent of neuromuscular recovery using objective means, whenever nondepolarizing neuromuscular block is not antagonized [2].”
Although these opinions probably represent the position of most academic neuromuscular “experts,” it is clear that in the real world of day-to-day practice, these suggestions have been widely ignored. A recent survey in the United Kingdom found that 62% of clinicians never use a peripheral nerve stimulator of any kind, and less than 10% used an objective monitor on a routine basis [3]. Studies from Denmark [4], Germany [5], and Mexico [6] report that routine monitoring of neuromuscular function was used by only 43%, 28%, and 2% of clinicians, respectively. This disconnect between editorial opinion and actual clinical practice raises a question of some importance. Is there a standard of care regarding the administration of neuromuscular blockers that anesthesia providers should be held to? The American Society of Anesthesiologists offers no help. Their publication “standards for basic anesthesia monitoring”1 makes no mention of neuromuscular monitoring. This is a little strange because the mission statement of the ASA that appears on the organization's Web site states: “The ASA is an educational, research, and scientific association…organized to raise and maintain the standards of the medical practice of anesthesiology and improve the care of the patient.”
Does the failure to monitor neuromuscular function have clinical consequences? In the absence of any “official” guidance, a review of this question still seems relevant 50 years after the intraoperative use of nerve stimulators was first suggested [7]. A prerequisite for this discussion is an understanding of how satisfactory recovery from neuromuscular block is now measured.
Section snippets
Clinical tests
In the decade after the introduction of d-tubocurarine into anesthesia practice, the clinician's ability to recognize residual neuromuscular block in the postoperative period was very limited. In a 1959 review on the then current state of the art of muscle relaxants, Cullen [8] wrote “In the absence of any ventilatory effort by the patient, no assessment (except by history) can be made of the cause for the apnea.” Nevertheless, in that year, Bendixen et al [9] suggested maximal negative
Postoperative residual curarization is not a rare occurrence
Almost 3 decades ago, Viby-Mogensen and coworkers [34] measured the prevalence of significant residual curarization in the recovery rooms of 3 university hospitals in Copenhagen. On different days chosen at random, these investigators studied every patient who received a nondepolarizing relaxant during anesthesia. The TOF fade ratio was determined immediately after arrival in the recovery area. Of 50 patients given neostigmine, 2.5 mg intravenously, at the end of anesthesia, 10 individuals
Does neuromuscular monitoring reduce the incidence of postoperative residual curarization?
It is a bit odd that, 50 years after the use of peripheral nerve stimulators were first suggested [7] as aids in monitoring neuromuscular function, use of these instruments is even being discussed. Nevertheless, the efficacy of these devices in preventing postoperative residual curarization is still a matter of controversy. “Common sense” suggests that even nonquantitative conventional PNS units that require a subjective evaluation of the evoked response should prove superior to “clinical”
How may new developments alter this discussion? The future of neuromuscular monitoring
It is clear that reversal of competitive neuromuscular block by cholinesterase inhibitors has its limitations. Once inhibition of true acetylcholinesterase is complete, giving additional neostigmine does not serve any useful purpose. If concentrations of blocking drug at the neuromuscular nicotinic receptors are high enough, recovery will be incomplete. Future progress in achieving rapid return of neuromuscular function will probably result from some form of “chemical reversal” of residual
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