MIVACURIUM-INDUCED NEUROMUSCULAR BLOCKADE DURING SEVOFLURANE AND HALOTHANE ANESTHESIA IN CHILDREN

The neuromuscular blocking effects of mivacurium during sevoflurane or halothane anaesthesia was studied in 38 paediatric patients aged 1-12 yr. All received premedication with midazolam, 0.5 mg.kg(-1) po and a n inhalational induction with up to 3 MAC of either agent in 70% N2O a nd O-2. The ulnar nerve war stimulated al the wrist by a train-of-four stimulus every ten seconds and the force of adduction of the thumb re corded with a Myotrace force transducer. Anaesthesia was maintained wi th a one MAC end-tidal equivalent of either volatile agent for five mi nutes before patients received mivacurium (0.2 mg.kg(-1)) iv. The onse t of maximal blockade occurred in 2.4 +/- 1.26 (mean +/- SD) min with halothane and 1.8 +/- 0.54 min with sevoflurane (NS). Four patients fa iled to achieve 100% block (3 halothane, 1 sevoflurane). The times fro m injection to 5, 75, and 95% recovery during sevoflurane (9.8 +/- 2.6 , 19.5 +/- 4.4, and 24.2 +/- 4.8 min) were greater than during halotha ne anaesthesia (7.2 +/- 2.2. 15.0 +/- 4.0, 19.2 +/- 4.9 min, respectiv ely (P < 0.005). AN patients demonstrated complete spontaneous recover y of neuromuscular function (T-1 > 95%, T-4/T-1 >75%) during the surge ry which lasted 24-63 min. All patients showed clinical signs of full recovery of neuromuscular blockade (i.e., headlift, gag, or cough). Ph armacological reversal war not required. It is concluded that followin g a single intubating dose of mivacurium, the time to maximum relaxati on was nor different during halothane and sevoflurane anaesthesia; rec overy times to 5.75 and 95% twitch height were longer during sevoflura ne anaesthesia and neuromuscular reversal was nor necessary.