Potency and time course of mivacurium block during sevoflurane, isofluraneand intravenous anesthesia

Purpose: To determine the potency and time course of action of mivacurium n euromuscular block under routine clinical conditions during sevoflurane; is oflurane and intravenous anesthesia, Method: Patients were anesthetized with nitrous oxide 66% in oxygen and 1.5 MAC sevoflurane or isoflurane or a propofol infusion, neuromuscular block being monitored using mechanomyography. Potency was determined using admini stration of single doses of mivacurium of 40- 100 mu g.kg(-1) and construct ion of dose-response curves (n = 72). The onset and duration of action were determined following a bolus dose of 0.2 mg.kg(-1) of mivacurium (n 30), Results: The ED50 and ED95 (with 95% confidence limits) were estimated to b e 42 (35-51)and 86 (74-98) mu g.kg(-1), 52 (45-60) and 89 (72-110) mu g.kg( -1), and 53:(45-62) and 95 (81-112) mu g.kg(-1) during sevoflurane, isoflur ane and propofol anesthesia respectively (P < 0.05 between sevoflurane and propofol). Following administration of the 0.2 mg.kg(-1) dose, neither the times (mean +/- SD) to maximum block (1.6 +/- 0.31, 1.7 +/- 0.21 and 1.6 +/ - 0.45 min, respectively) nor the times to 25 and 90% recovery of T-1 (20 /- 4.5 and 33 +/- 8.8 min, 21 +/- 3.8 and 33 +/- 6.5 min, and 18 +/- 4.1 an d 28 +/- 5.8 min respectively) were different among groups, The times to re covery of TOF ratio to 0.8 were 40 +/- 10.0, 36 +/- 8.5 and 29 +/- 5.5 min in the sevoflurane, isoflurane and propofol groups respectively (P = 0.017 between the sevoflurane and propofol groups). Conclusions: Under usual conditions of clinical anesthesia the potency of m ivacurium was slightly enhanced during sevoflurane compared with intravenou s anesthesia but the duration of action was only minimally prolonged during sevoflurane and isoflurane anesthesia.