Mivacurium after atracurium in children

The effect of mivacurium after atracurium was evaluated in 36 children anesthetized with halothane-nitrous oxide-oxygen by measuring the force of contraction of the adductor pollicis during train-of-four stimulation at 0.1 Hz. The children were evaluated in two main groups. In Group 1 the effect of bolus doses of mivacurium after equipotent repeat doses of atracurium were evaluated. When the first twitch of the train-of-four response (T1) had recovered to 25% of control after a tracheally intubating dose of atracurium, a repeat dose of atracurium was given, on subsequent recovery to 25%, an equipotent dose of mivacurium was administered. In Group 2 when T1 had recovered to > 10% from 0.5 mg/kg atracurium, a mivacurium infusion was started; the initial infusion rate was 4 micrograms.kg-1.min-1 with adjustments made to maintain 90%-99% depression of T1. Patients were allowed to recover spontaneously from the effect of the relaxants. In Group 1 prolongation of the effect of mivacurium was noted after atracurium; the recovery indices (25%-75% and 5%-95%) of mivacurium were longer than those seen when mivacurium is the sole relaxant but shorter than atracurium. In Group 2, 15 min after the start of the mivacurium infusion, the dose requirement was 3.7 +/- 0.3 micrograms.kg-1.min-1 (approximately about one-third that required after a tracheally intubating dose of mivacurium). The infusion requirement increased gradually (P < 0.0001) until, at 90 min of infusion, it was 7.4 +/- 0.8 micrograms.kg-1.min-1. In Group 2 the recovery indices were similar to those seen when mivacurium is the sole relaxant given. When mivacurium is given after atracurium, evidence of the residual neuromuscular effects of the atracurium are detected beyond the usual recovery range.