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 µg kg-1 and 117 µg kg-1 in ISO and 128 µg kg-1 and 167 µg 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.