• Takahiro Suzuki, Kazuhiko Munakata, Naoto Watanabe, Naoko Fukano, Shigeru Saeki, and Setsuro Ogawa.
• Department of Anesthesiology, Surugadai Nihon University Hospital, 1-8-13 Kanda-Surugadai, Chiyoda-ku, Tokyo 101-8309, Japan.
• J Anesth. 2003 Jan 1; 17 (2): 98-103.

PurposeIt has been suggested that the different degrees of fade induced by nondepolarizing neuromuscular blocking agents in repetitive muscular contractions may be due to the varying affinities or binding kinetics of presynaptic nicotinic receptors. We compared the degree of fade induced by mivacurium, cisatracurium, and d-tubocurarine in the cat muscular compound action potential (mCAP).MethodsIn 21 cats, mCAPs of the gastrocnemius muscle were evoked by paired (conditioning and test stimuli) and 2 Hz train-of-four (TOF) sciatic nerve stimulation. The interval between the paired stimuli was changed stepwise from 7 to 1000 ms. The ratios of the amplitude evoked by test stimulus to that evoked by the conditioning stimulus (M2/M1 ratios) and TOF ratios were measured. After baseline variables had been obtained, the cat received either mivacurium (0.08 mg x kg(-1), n = 7), cisatracurium (0.05 mg x kg(-1), n = 7), or d-tubocurarine (0.5 mg x kg(-1), n = 7). A series of M2/M1 ratios and TOF ratios were measured at various levels of partial block during recovery.ResultsAt 10% of baseline amplitude, all agents significantly depressed the M2/M1 ratios (i.e., fade) at relatively longer intervals of paired stimuli (mivacurium, > or = 100 ms; cisatracurium. > or = 40 ms; and d-tubocurarine, > or = 20 ms), when compared with baseline. The order of activity to produce fade was mivacurium < cisatracurium < d-tubocurarine. A similar result was obtained in TOF ratios measured at various levels of neuromuscular block.ConclusionOur results suggest that mivacurium shows a lesser degree of fade during partial neuromuscular block than cisatracurium and d-tubocurarine.

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