Alfaxalone and medetomidine intravenous infusion to maintain anaesthesia in colts undergoing field castration

Abstract

Reasons for performing the study: The use of alfaxalone and medetomidine administered as an i.v. infusion to maintain anaesthesia has not previously been reported in the horse. Objectives: To investigate the use of alfaxalone in hydroxpropyl-beta-cyclodextrin (Alfaxan) and medetomidine infusion as a field anaesthetic for short-term surgical procedures in the horse. Hypothesis: Alfaxalone-medetomidine anaesthesia is suitable for short-term field anaesthesia in horses. Methods: Eleven healthy colts underwent 45min of anaesthesia with an i.v. infusion of alfaxalone (2mg/kg bwt/h) and medetomidine (5μg/kg bwt/h) for routine field castration. Horses were premedicated with i.v. acepromazine (0.03mg/kg bwt), medetomidine (7μg/kg bwt) and guaiphenesin (35mg/kg bwt) before i.v. induction with alfaxalone (1mg/kg bwt). Colts were intubated with an endotracheal tube and 100% oxygen insufflated at 10l/min. The physiological variables monitored included pulse rate, respiratory rate, direct arterial blood pressure, arterial blood gases and the quality of the inductions and recoveries were scored. Results: Overall, the anaesthetic period and surgical conditions were acceptable and the quality of the anaesthetic inductions and recoveries was good to excellent. All colts stood on their first attempt (mean ± s.d.) 37 ± 13.5min after the infusion was stopped. During anaesthesia, cardiopulmonary data, presented as range of mean values at each time point were: heart rate: 45-47 beats/min; mean blood pressure: 104-112mmHg; respiratory rate: 8 breaths/min; PaO2: 117-172mmHg; PaCO2: 50-56mmHg and pH7.34-7.37. Conclusions and potential relevance: The co-administration of alfaxalone and medetomidine as an i.v. infusion after anaesthetic induction with alfaxalone was suitable for short-term field anaesthesia in the horse. © 2012 EVJ Ltd.