Retrospective evaluation of clinical use of cis-atracurium in horses

Background: To the authors’ knowledge, there are no reports describing the use of cis-atracurium in the horse. Objective: To describe the onset time and the duration of the neuromuscular blockade (NMB) of three different doses of cis-atracurium in horses and to determine the appropriate dose needed maintain a NMB. Study design: Retrospective study. Methods: Horses which received cis-atracurium as part of a balanced anaesthetic protocol at the Equine Teaching Hospital of the University of Liège between March 2014 and June 2017 were included in this study. A train-of-four (TOF) stimulation pattern was used to assess the NMB. The cis-atracurium induction dose, the onset and duration of action (when TOF count was under three twitches) of the first bolus, the number of supplementary boluses of cis-atracurium and the total dose of cis-atracurium administered per horse, the total duration of the NMB and the recovery time were recorded and analysed. Also the use of an antidote and any side effects produced by cis-atracurium were recorded. Results: From 37 horses that received cis-atracurium during this period, only 23 had a complete records and were included in the study. Three different doses of cis-atracurium were used to induce NMB: 100 μg/kg (n = 8) 75 μg/kg (n = 3) and 50 μg/kg (n = 12). Cis-atracurium 50 μg/kg failed to induce NMB in 3 horses. The onset of action was not significantly different between the three doses (5 minutes). The duration of the NMB was dose-dependent. The calculated dose of cis-atracurium necessary to maintain a NMB was 2.3 μg/kg/minute based on the sum of the induction dose and the supplementary boluses divided by the duration of the NMB. Main limitations: A further prospective study is needed to confirm the results. Conclusions: Cis-atracurium can be an alternative to other NMBA in horses.