Is isoflurane safer than halothane in equine anaesthesia? Results from a prospective multicentre randomised controlled trial.
BACKGROUND
Approximately 1 in 100 horses suffer unexpectedly from anaesthetic-related death. Identification and use of the safest anaesthetic drugs should support this aim. Experimental evidence has suggested that isoflurane should be a safer maintenance agent in equine anaesthesia than halothane.


OBJECTIVE
The death rate would be reduced in horses being maintained with isoflurane compared to halothane.


METHODS
A multicentre randomised controlled trial was undertaken to compare the effects of isoflurane and halothane for maintenance of equine anaesthesia for all types of operation. Data were analysed from 8242 horses in which anaesthesia was maintained with either halothane or isoflurane using mixed effects logistic regression models.


RESULTS
No overall benefit of either drug was detected. However, although not part of the primary hypothesis, data showed that the overall death rate was significantly reduced in horses age 2-5 years with isoflurane and that death from cardiac arrest was also reduced with isoflurane, particularly in high risk cases.


CONCLUSIONS
Halothane remains an acceptable anaesthetic for maintenance of anaesthesia in horses, but isoflurane may be safer in the young horse and in high risk cases.
Johnston
G M
GM
Department of Clinical Veterinary Medicine, University of Cambridge, Cambridgeshire CB3 0ES, UK.
Eastment
J K
JK
Taylor
P M
PM
Wood
J L N
JL
D000367:Age Factors; D000762:Anesthesia Recovery Period; D000769:Anesthesia, Inhalation / Q000401:mortality / Q000662:veterinary*; D018685:Anesthetics, Inhalation / Q000494:pharmacology*; D000818:Animals; D005260:Female; D006221:Halothane / Q000494:pharmacology*; D006736:Horses / Q000502:physiology* / Q000601:surgery; D007530:Isoflurane / Q000494:pharmacology*; D016015:Logistic Models; D008297:Male; D011446:Prospective Studies; D012307:Risk Factors; D012449:Safety; D016019:Survival Analysis
D018685:Anesthetics, Inhalation; D007530:Isoflurane; D006221:Halothane