BACKGROUND: The doses of muscle relaxants used to facilitate tracheal intubation are 2 × ED₉₆. However, the potency needs to be measured on a molar basis rather than by the mass of the drug. The aim of this study was to compare the pharmacodynamics and intubation conditions of the muscle relaxants using a continuous infusion during induction.

METHODS: The time courses of the drug response and tracheal intubating conditions of the muscle relaxants by a continuous infusion were examined in 44 patients undergoing elective surgery. The neuromuscular effects of the relaxants were quantified by recording the twitch response of the adductor pollicis muscle after stimulating the ulnar nerve (0.1 Hz, 0.2 ms, supramaximal stimuli). The onset time and duration of each group were measured and the dose-response curves were determined by logistic regression analysis.

RESULTS: The doses (µmol/kg) for intubation were 1.08 ± 0.31 of rocuronium, 0.58 ± 0.10 of atracurium, 0.28 ± 0.06 of vecuronium and 1.36 ± 0.65 of succinylcholine. The relative potency of rocuronium, atracurium, vecuronium and succinylcholine was 1.00 : 1.86 : 3.86 : 0.79. There were no significant differences between any of the groups with regard to the onset time of the relaxants. The duration of the relaxants was succinylcholine (4 min 12 s), rocuronium (25 min 36 s), atracurium (34 min 28 s), and vecuronium (42 min 24 s). The intubation conditions of the succinylcholine group were inferior to those of the vecuronium group.

CONCLUSIONS: This method can be used to determine the potency and pharmacodynamics between the neuromuscular blockers. Further study will be needed to confirm these results and to evaluate the effect of the infusion rate on this model.