Neuromuscular effects of 600 μg·kg−1 of rocuronium in infants during nitrous oxide‐halothane anaesthesia

Summary Rocuronium bromide (Zemuron) is a new steroidal nondepolarizing neuromuscular blocking drug. We were interested in determining the effect of a bolus of rocuronium in infants during halothane anaesthesia as we did previously in older children. Eighteen infants (2‐11 months) received a bolus of 600 μg·kg−1, which is equal to twice the dose of rocuronium estimated to produce 95% depression of neuromuscular function (ED95) in children (2‐12 yr). Neuromuscular blockade was monitored by recording the electromyographic activity of the adductor pollicis muscle resulting from supramaximal stimulation of the ulnar nerve at 2 Hz for 2 s at 10‐s intervals. Time (mean ± SEM, range) from administration of 600 μg·kg−1 rocuronium to 90% (B90) and 100% (B100) neuromuscular block was 37 ± 2 (20‐60) s and 64 ± 10 (20‐180) s, respectively. The time to recovery of neuromuscular transmission to 10% (T10) was 35.3 ± 3.0 (20.7‐57.8) min and to 25% of baseline (T25) was 41.9 ± 3.2 (24.3‐67.7) min. The recovery index (T25‐T75) was 26.6 ± 2.7 (11.7‐44.5) min, and the time to recovery of the train‐of‐four ratio (T4/T1) ± 0.75 was 82.1 ± 6.9 (53.2‐138.3) min. The plasma concentration of rocuronium when T1 had recovered to about 30% was 654 ± 34 (417‐852) ng·ml−1 which is similar to that observed in children. Six‐hundred μg·kg−1 of rocuronium has a rapid onset of effect in infants and prolonged duration of action in infants compared to children.