Atracurium Infusion Requirements in Children during Halothane, Isoflurane, and Narcotic Anesthesia

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Abstract
We were interested in determining the dose---response relationship of atracurium in children (2--10 yr) during nitrous oxide---isoflurane anesthesia (1%) and the atracurium infusion rate required to maintain about 95% neuromuscular blockade during nitrous oxide---halothane (0.8%), nitrous oxide---isoflurane (1%), or nitrous oxide---narcotic anesthesia. Neuromuscular blockade was monitored by recording the electromyographic activity of the adductor pollicis muscle resulting from supramaximal stimulation at the ulnar nerve at 2 Hz for 2 sec at 10-sec intervals. To estimate dose---response relationships, three groups of five children received 80,100, 150 μg/kg atracurium, respectively. During isoflurane anesthesia, the neuromuscular block produced by 80 μg/kg was 23.6% ± 6.5 (mean ± SEM), by 100 μg/kg was 45% ± 7.2, and by 150 μg/kg was 64% ± 8.7. The ED50 and ED95 (estimated from linear regression plots of log dose vs probit of effect) were 120 μg/kg and 280 μg/kg, respectively. At equipotent concentrations, halothane and isoflurane augment atracurium neuromuscular block to the same extent, compared to narcotic anesthesia. Atracurium steady-state infusion requirements averaged 6.3 ± 0.6 μg·kg2 · min-1 during halothane or isoflurane anesthesia; the requirements during balanced anesthesia were 9.3 ± 0.8 μg·kg-1·min-1 (P < 0.05). There was no evidence of cumulation during prolonged atracurium infusion.