Neuromuscular and clinical effects of mivacurium chloride in healthy adult patients during nitrous oxide-enflurane anaesthesia.

Abstract

We have studied the effects of mivacurium after induction of anaesthesia with alfentanil-propofol in healthy adult oral surgical patients. Anaesthesia was maintained with nitrous oxide and 0.75% (end-tidal) enflurane in oxygen after nasotracheal intubation. Recordings were made of the rectified compound adductor pollicis electromyogram in response to train-of-four (TOF) ulnar nerve stimulation. First and fourth TOF responses were defined as T1 and T4, with T1 suppression referenced to pre-mivacurium T1 height (Tc). Onset times (mean (SEM] to 90% T1 suppression were 2.5 (0.2), 2.1 (0.3) and 1.6 (0.1) min, respectively, after mivacurium 0.15 mg kg-1 (n = 18) and 0.2 mg kg-1 (n = 18) as 5-s boluses and 0.2 mg kg-1 over 30 s (n = 9). Intubating conditions 2 min after 0.15 mg kg-1 were good to excellent and not improved by a further 30-s delay or by use of a 0.2-mg kg-1 dose. Recovery to T1/Tc of 5% occurred on average in 12-13 min irrespective of dose. Thereafter, mivacurium infusions commenced at 8-10 micrograms kg-1 min-1 were adjusted at intervals of at least 3 min to achieve T1/Tc in the range 1-10%. Mean duration of infusion was 58 (3.4) min and mean infusion rate after a 15-min stabilization period was 6.6 (range 2.3-12.9) micrograms kg-1 min-1. On cessation of infusions, spontaneous recovery from T1/Tc 8% (1.0%) to T4:T1 = 0.7 took 17 (1.2) min. Neostigmine 0.04 mg kg-1 or edrophonium 0.75 mg kg-1 evoked recovery from T1/Tc 9% (SEM 1.2% and 1.0%, respectively) to T4:T1 = 0.7 in 11 (0.6) and 8 (0.9) min (both P less than 0.001 vs spontaneous recovery).