Alfaxalone and medetomidine intravenous infusion to maintain anaesthesia in colts undergoing field castration.
Authors: Goodwin W A, Keates H L, Pearson M, Pasloske K
Journal: Equine veterinary journal
Summary
# Editorial Summary: Alfaxalone and Medetomidine Infusion for Equine Field Anaesthesia Maintaining surgical anaesthesia during field procedures such as castration has traditionally relied on inhalant gases or repeated bolus dosing, both of which present practical challenges in remote settings. Goodwin and colleagues evaluated a continuous intravenous infusion protocol combining alfaxalone (2 mg/kg/h) and medetomidine (5 µg/kg/h) in eleven healthy colts undergoing routine castration, following standard premedication and alfaxalone induction. All animals achieved excellent induction and recovery quality, standing unassisted within an average of 37 minutes post-infusion, whilst maintaining stable cardiopulmonary parameters throughout the 45-minute surgical period: heart rates of 45–47 beats/min, mean arterial pressures of 104–112 mmHg, and adequate oxygenation (PaO₂ 117–172 mmHg) despite a mild hypercapnia (PaCO₂ 50–56 mmHg). For practitioners conducting field surgery, this protocol offers a practical alternative to gas anaesthesia that requires only intravenous access and portable infusion equipment, with the added benefit of alpha-2 agonist properties providing analgesia and facilitating smooth recovery; however, the hypercapnia and modest bradycardia warrant careful patient selection and monitoring in animals with pre-existing cardiopulmonary compromise.
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Practical Takeaways
- •Alfaxalone-medetomidine infusion is a viable field anaesthetic option for short surgical procedures like castration in horses, providing stable maintenance and predictable recovery
- •This technique eliminates the need for volatile anaesthetics in the field setting, improving practicality for remote castrations while maintaining cardiopulmonary stability
- •Consistent first-attempt standing within 37 minutes post-procedure suggests good recovery quality suitable for field conditions where prolonged recovery supervision may be limited
Key Findings
- •Alfaxalone-medetomidine infusion maintained anaesthesia for 45 minutes of surgical time with acceptable anaesthetic conditions in 11 colts
- •All colts stood on first attempt with mean recovery time of 37 ± 13.5 minutes after infusion cessation
- •Cardiopulmonary parameters remained stable during anaesthesia: heart rate 45-47 bpm, mean blood pressure 104-112 mmHg, PaO₂ 117-172 mmHg
- •Induction and recovery quality was rated good to excellent in all animals using this alfaxalone-medetomidine protocol