Time course and train-of-four fade of mivacurium block during sevoflurane and intravenous anaesthesia

BACKGROUND AND OBJECTIVE: Volatile anaesthetics inhibit nicotinic acetylcholine receptors at clinically relevant concentrations with higher affinity for the neuronal nicotinic receptor. The inhibitory effects of propofol on nicotinic receptors have only been documented at supraclinical concentrations. The aim of this study was to determine recovery properties and train-of-four (TOF) fade of mivacurium during sevoflurane and propofol anaesthesia, in order to examine any differences both in the enhancement of the neuromuscular block (postjunctional effects) and in TOF fade (prejunctional effects). METHODS: Twenty ASA I-II adult patients were randomly allocated to maintenance of anaesthesia with sevoflurane (end-tidal concentration 2%) or propofol. Neuromuscular block was assessed by acceleromyography and a single dose of mivacurium (0.15 mg kg(-1)) was administered (in the sevoflurane group after 30 min of exposure to sevoflurane). We measured time for recovery of the first twitch of the TOF (T1) from 25-75%, time from 25% recovery of T1 to achieving a TOF ratio (TOFR) of 0.8, TOFR at 50%, 75% and 90% recovery of T1, and height of T1 at TOFR of 0.7 and 0.9. Data were tested using t-test for independent samples. RESULTS: Recovery times (mean (95% confidence interval, CI)) of mivacurium in the sevoflurane group (T1 25-75%, 11.3 (8.1-14.5) min; T1 25%-TOFR0.8, 19.1 (15.7-22.5) min) were significantly longer (P < 0.05) than in the propofol group (T1 25-75%, 6.5 (5.2-7.7) min; T1 25%-TOFR0.8, 11.3 (7.8-10.3) min). No differences were found in the relations between TOFR and T1 or vice versa, between the groups. CONCLUSIONS: Recovery times after a single dose of mivacurium were prolonged by sevoflurane compared with propofol but no differences in TOF fade were observed between the two anaesthetics.