Speed of reversal of vecuronium neuromuscular block with different doses of neostigmine in anesthetized dogs.

Objectives: Neostigmine is routinely used to reverse non-depolarizing neuromuscular block. Given its indirect mechanism, a plateau may exist whereby increasing doses of neostigmine do not result in clinical benefit. This study was designed to measure the speed of reversal of vecuronium-induced neuromuscular block in isoflurane-anesthetized dogs after the administration of three doses of neostigmine as used in clinical practice.

Study Design: Prospective, crossover, randomized study.

Animals: Seven adult, mixed-breed dogs with a mean ± standard deviation (SD) age of 2.0 ± 0.8 years and weight of 19.1 ± 9.1 kg.

Methods: Dogs were anesthetized on three occasions with isoflurane and administered vecuronium (0.1 mg kg) intravenously (IV). The train-of-four (TOF) ratio was measured on the pelvic limb with acceleromyography. When the second twitch of the TOF had returned spontaneously, atropine (0.03 mg kg) and neostigmine (0.02, 0.04 or 0.07 mg kg) were administered IV. Time to reach a TOF ratio of ≥0.9 after neostigmine administration was recorded.

Results: Increasing the dose of neostigmine from 0.02 mg kg to 0.04 mg kg and 0.07 mg kg resulted in significant reductions in mean ± SD reversal times (10.5 ± 2.3, 7.4 ± 1.1 and 5.4 ± 0.5 minutes, respectively) (p < 0.0001) and smaller coefficients of variation (22%, 15% and 10%, respectively).

Conclusions And Clinical Relevance: Increasing the dose of neostigmine from 0.02 mg kg to 0.04 mg kg and 0.07 mg kg produced faster and less variable reversal of vecuronium-induced neuromuscular block in isoflurane-anesthetized dogs. No ceiling effect was observed at this dose range.