Comparison of the neuromuscular blocking effects of cisatracurium during isoflurane or propofol anesthesia in dogs

Objective To compare the neuromuscular blocking effects of cisatracurium during isoflurane versus propofol anesthesia in dogs. Study design Prospective, randomized study. Animals A total of 20 healthy, client-owned dogs (16 females, four males) weighing 12.5-22 kg and aged 1-8 years. Methods Dogs undergoing elective surgery were randomized in equal numbers to an isoflurane (ISO) or propofol (PPF) group. Other drugs used during anesthesia were equal between groups. Single-twitch (ST) stimulation was used to monitor neuromuscular response. After recording the baseline ST (T0), cumulative doses of cisatracurium (0.05 mg kg(-1)) were administered intravenously until ST/T0 <= 5%. Effective doses 50 (ED50) and 95 (ED95) of cisatracurium in each group were calculated from group dose-response curves. Recovery of ST (TR) was defined as spontaneous recovery of ST to 80-120% of T0 remaining stable for 2 minutes. The ST after each dose of cisatracurium, duration 25% (time after the last dose until 25% recovery of TR), recovery index (time to recovery from 25% to 75% of TR) and duration to TR (time after the last dose until recovery of TR) were recorded. Results Incremental doses of cisatracurium, median (range), were 2 (1-3) in ISO and 4 (2-5) in PPF to achieve >= 95% depression of ST/T0 (p < 0.01). ED50 and ED95 were 20 mu g kg(-1) and 117 mu g kg(-1) in ISO and 128 mu g kg(-1) and 167 mu g kg(-1) in PPF, respectively. The duration 25%, recovery index and duration to TR, median (range), were longer in ISO [22.6 (10.3-24.3), 5.3 (3.0-7.8) and 36.1 (20.1-49.7) minutes, respectively] than in PPF [10.2 (6.8-16.5), 3.0 (2.0-3.8) and 17.7 (14.2-28.7) minutes, respectively] (p < 0.01). Conclusions and clinical relevance Cisatracurium-induced neuromuscular blockade was significantly enhanced and prolonged by isoflurane compared with propofol.