Is isoflurane safer than halothane in equine anaesthesia? Results from a prospective multicentre randomised controlled trial.
Authors: Johnston G M, Eastment J K, Taylor P M, Wood J L N
Journal: Equine veterinary journal
Summary
# Editorial Summary Despite decades of experimental evidence favouring isoflurane over halothane in equine anaesthesia, a large prospective multicentre randomised controlled trial involving 8,242 horses failed to demonstrate an overall survival advantage for either agent as a maintenance anaesthetic across all surgical procedures and patient populations. Using mixed effects logistic regression to control for confounding variables, researchers found no significant difference in anaesthetic-related mortality between the two volatile agents overall; however, a clinically important secondary finding emerged showing that isoflurane significantly reduced mortality in younger horses (aged 2–5 years) and, notably, reduced death from cardiac arrest in high-risk cases regardless of age. These results suggest that while halothane remains a safe and acceptable choice for routine anaesthesia in adult horses, practitioners should consider isoflurane preferentially for juvenile patients and those with recognised risk factors for intraoperative cardiac complications, potentially influencing drug selection protocols in equine anaesthetic practice. The findings underscore the importance of large-scale clinical trials in challenging laboratory-based assumptions and highlight that safety profiles of anaesthetic agents may vary substantially depending on patient age and comorbidity status rather than applying uniformly across all equine populations.
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Practical Takeaways
- •Both halothane and isoflurane are viable maintenance agents for routine equine surgery, with no clear overall superiority of either drug
- •Consider isoflurane preferentially for young horses (2-5 years) and high-risk surgical cases where cardiac stability is a concern
- •Drug choice for anaesthetic maintenance in horses should be guided by individual patient risk factors rather than blanket protocol changes
Key Findings
- •No overall significant difference in death rates between isoflurane and halothane maintenance anaesthesia across all horses studied
- •Isoflurane significantly reduced death rates in horses aged 2-5 years compared to halothane
- •Isoflurane reduced death from cardiac arrest, particularly in high-risk cases
- •Halothane remains an acceptable maintenance anaesthetic agent for equine anaesthesia