Is isoflurane safer than halothane in equine anaesthesia? Results from a prospective multicentre randomised controlled trial

Abstract

Reasons for performing study: Approximately 1 in 100 horsessuffer 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. Hypothesis: 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 and potential relevance: Halothane remains anacceptable anaesthetic for maintenance of anaesthesia in horses, but isoflurane may be safer in the young horse and in high risk cases.

Management der Aufwachphase- mit oder ohne Hilfe?

“…Because morbidity data are scarce (Senior et al 2007), sample size estimations could be based on published mortality data. Mortality rate of healthy horses (ASA 1-2) undergoing general anaesthesia is 0.9 %, fractures being the cause in 23% of deaths (Johnston et al 2004), this leads to a frequency of 2 fractures per 1000 equine anaesthetics. To show if recovery with a head and tail rope is able to reduce the risk of a fracture from 2 per 1000 to 1 per 1000 anaesthetics, data of 47000 equine anaesthesia cases would be necessary (power 80%; confidence interval 95%) (Win Episcope 2.0), requiring a multicentre study.…”

“…The reason for this observation remains unclear, as assisted and unassisted recovery seem to be equally accepted methods for routine equine anaesthesia according to various textbooks (Doherty and Valverde 2006, Taylor and Clarke 2007). Within the extensive CEPEF studies no differentiation between assisted and unassisted recoveries or location of the participating equine practices and hospitals was made (Johnston et al 1995, Johnston et al 2002, Johnston et al 2004). The use of head and tail ropes cannot prevent the occurrence of fractures when the horse pushes itself up (Young andTaylor 1993, Bidwell et al 2007, personal observation), but it might help to reduce uncontrolled falls.…”

“…A large-scale, multicenter study -CEPEF (Confidential enquiry of perioperative equine fatalities) reported a death rate from non-colic-related anaesthetics of 0.9% (Johnston et al 1995), while the perianaesthetic mortality rate at a single, equine surgical practice seemed to be more favourable with 0.12%, because of preponderance of short procedures (Bidwell et al 2007). Thirty percent of all equine perioperative deaths are related to severe injury of the musculoskeletal system including fractures during the recovery phase, making recovery a critical part of equine anaesthesia (Johnston et al 1995, Johnston et al 2002, Johnston et al 2004, Bidwell et al 2007). …”

Anaesthetic management for hydropool recovery in 50 horses

“…The rate of equine fatalities directly related to anaesthesia ranges from 0.12-1% (Young et al 1990;Johnston et al 1991;Young et al 1993;Johnston et al 1995, Johnston et al 1995, Johnston et al 1996, Johnston et al 2002, Johnston et al 2004, Bidwell et al 2007). This is much hig-…”

Vasopressin is life threatening for horses under isoflurane anaesthesia

“…Approximately 0,2 % (Czupalla and Gerhards 2013) up to 1% of horses suffer from unexpectedly anaesthesia-related death (Johnston et al 2004). In small animals, the anaesthesia-related mortality is 1 in 1,000 dogs or cats (Dyson et al 1998).…”