[Differential effects of muscle relaxants on the evoked electromyogram of the thenar and hypothenar muscles].

This study compares the neuromuscular blocking effect of nondepolarizing relaxants on the thenar and hypothenar muscles in 14 anesthetized patients with nitrous oxide-halothane. Vecuronium (60 micrograms.kg-1 iv) or pancuronium (60 micrograms.kg-1 iv) was given and supramaximal stimulation was applied to ulnar nerve at the wrist. The evoked compound action potentials were measured over the thenar and hypothenar muscles of the right hand simultaneously. During vecuronium blockade, the ratios of single twitch depression (T1/Tc) and train of four (T1/T4) of the thenar muscle were comparable with that of the hypothenar muscle. There was significant higher T1/Tc and T1/T4 ratio for the hypothenar muscle than for the thenar muscle within 60 minutes from pancuronium administration. These data suggest that relative potency of muscle relaxant on these two muscles seems to be drug specific. This phenomenon brings certain practical difficulties on monitoring of neuromuscular function with evoked electromyogram during anesthesia.