Neuromuscular block monitoring after the administration of 1 mg/kg intravenous cis-atracurium in the anaesthetized pig.

Neuromuscular blocking agents should be included as part of a balanced anaesthetic protocol to improve anaesthetic management, although doses are not always established for each species. Cis-atracurium is a benzylisoquinolinium neuromuscular blocking agent with an intermediate duration of action devoid of significant adverse effects previously used in pigs with a wide dosage range. Cis-atracurium was administered at 1 mg/kg bolus to sixteen pigs to establish its time profile and effects. The pigs were premedicated intramuscularly with 4 mg/kg azaperone, 8 mg/kg ketamine and 0.2 mg/kg morphine IM and maintained with isoflurane in oxygen. After cis-atracurium administration, neuromuscular monitoring via acceleromyography was started until the recovery of the 90% of the train of four ratio. Complete decrease in the train of four ratio was accomplished in eleven pigs. Onset of action was 70 s, with a recovery of the fourth twitch at 26 min and a recovery of a train of four ratio greater than 90% in 60 min. In conclusion, 1 mg/kg intravenous cis-atracurium in the pig allowed for a rapid onset of action and a complete recovery after 60 min although high variability in the time profile is seen.

Effects of neostigmine or edrophonium on force of contraction when administered at a train-of-four ratio of 0.9 in anesthetized dogs.

OBJECTIVE: Anticholinesterase drugs may produce paradoxical neuromuscular block when administered at shallow levels of neuromuscular block. The objective of this study was to evaluate the effects of neostigmine and edrophonium when administered at near-complete reversal from nondepolarizing block in anesthetized dogs. STUDY DESIGN: Incomplete crossover, randomized, blinded experimental study. ANIMALS: A total of 12 Beagle dogs. METHODS: Each dog was anesthetized twice with propofol and maintained with isoflurane and dexmedetomidine. Intravenous (IV) vecuronium (0.1 mg kg-1) was administered. When the mechanographic train-of-four (TOF) ratio had spontaneously recovered to ≥0.9, either neostigmine (0.04 mg kg-1) or edrophonium (0.5 mg kg-1) was administered IV, preceeded by atropine. Changes in twitch height or TOF ratio were measured for the next 10 minutes. Recurarization was considered to be present if values decreased by ≥10%. RESULTS: Data from four dogs in each treatment were excluded from analysis, resulting in data from five dogs administered both treatments, three dogs administered neostigmine and three dogs administered edrophonium. There was no difference between groups for age, weight, T1 and T4 twitch heights or TOF ratio values, before or after anticholinesterase administration. The TOF ratio decreased by 17% and 18% in two of the eight dogs administered neostigmine, resulting from a larger increase in T1 relative to T4. No reductions in individual twitch amplitudes were recorded in those dogs. When edrophonium was used, no cases of recurarization were observed. CONCLUSIONS AND CLINICAL RELEVANCE: The results support use of edrophonium for reversal of shallow neuromuscular block. The decreases in TOF ratio recorded after neostigmine does not necessarily indicate muscular weakness. Although the clinical implications are uncertain, the results suggest that, at these doses, edrophonium may be preferable to neostigmine for reversal of shallow neuromuscular block in dogs.

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-1) 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-1) and neostigmine (0.02, 0.04 or 0.07 mg kg-1) 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-1 to 0.04 mg kg-1 and 0.07 mg kg-1 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-1 to 0.04 mg kg-1 and 0.07 mg kg-1 produced faster and less variable reversal of vecuronium-induced neuromuscular block in isoflurane-anesthetized dogs. No ceiling effect was observed at this dose range.

Neuromuscular blocking agents and monitoring in the equine patient.

This article briefly reviews the physiology of the neuromuscular junction and the pharmacologic mechanisms of neuromuscular blocking agents. The clinical use of modern agents is discussed. Monitoring techniques used to assess the level of neuromuscular block and to exclude residual paralysis at the end of an anesthetic procedure are reviewed.