Frequency of train-of-four stimulation influences neuromuscular response

We have compared the effects of two different frequencies of train-of-four stimulation of the ulnar nerve (2-Hz stimulation once every 10 or 20 s) on onset time and potency of atracurium, vecuronium and mivacurium during balanced anaesthesia. The adductor pollicis EMG was recorded simultaneously in both hands of 24 children aged 2-12 yr. After administration of an ED50 dose of each blocker, onset times were mean 21 (SEM 10) s shorter (P < 0.05) and decreases in neuromuscular function were 22 (3)% greater (P < 0.001) in the hand which was stimulated once every 10 s. We conclude that it is not possible to compare potency estimates of neuromuscular blocking agents if different stimulation patterns have been used.