18 Aug 2026
Kate Loomes BVSc(Hons), MSc CertAVP(EP), CertAVP(EM), DipECVAA, MRCVS previews her session from the first day of congress, where she will pose the question: is equine perioperative mortality decreasing?
Kate Loomes
Job Title
Image: highwaystarz / Adobe Stock
The annual congress of the BEVA in Birmingham this year has dedicated a stream to the topic of preventing pain and protecting patients and it is a privilege to have been invited to present a session on aspects of improving safety during equine general anaesthesia.
Over the years that I have been anaesthetising horses, several aspects of anaesthesia practice have evolved and will continue to evolve, including the agents in routine use, specialist knowledge and training pathways, and monitoring techniques. Embedded in these advancements, made by anaesthetists working with all species, has always been a strong sense of the prioritisation of safety.
The question is: is equine perioperative mortality decreasing?
To begin to answer this question, the results from two large-scale studies performed on a global platform and conducted approximately 20 years apart, are encouraging and indicate that equine perioperative mortality has decreased (Johnston et al, 2002; Gozalo-Marcilla et al, 2025). This is reassuring and potentially reflects advancements in knowledge and pharmaceutical options, together with investment in equipment and training.
These two studies are the second and fourth in the series of Confidential Enquiries into Perioperative Equine Fatalities (CEPEF) and report “non-colic” and “colic” fatalities during the perioperative period that included up to seven days post-anaesthesia. For horses undergoing “non-colic” procedures, the reported reduction in perioperative mortality was 0.3% (from 0.9% to 0.6%; Johnston et al, 2002; Gozalo-Marcilla et al, 2025).
After colic procedures, the reduction was greater, with a 3.6% reduction from 7.8% in 2002 (Johnson et al, 2002) to 4.2% more than 20 years later (Gozalo-Marcilla et al, 2025). For these emergency cases, earlier referral and the potential for shorter distances travelled due to a larger number of referral centres performing colic surgery may also have contributed to this fall in mortality.
While these reported improvements are encouraging, we know that the risk of equine general anaesthesia remains significantly higher than the risk in cats and dogs (Redondo, Martínez-Taboada, et al, 2024; Redondo, Otero et al, 2024). The physiological and anatomical challenges unique to horses make it difficult to compare species-specific anaesthetic risk.
In our efforts to improve safety and lower the occurrence of serious complication, assessment of risk needs to be considered for every individual patient.
The assessment of anaesthetic risk in horses has received research attention and augmentation of the traditional Association of Anesthesiologists (ASA) physical classification system to incorporate equine-specific information has been investigated (Hubbell et al, 2022). The Combined Horse Anaesthetic Risk Identification and Optimisation Tool (CHARIOT) used expert consensus and evidence-based information with the aim of identifying horses at increased anaesthetic risk prior to induction of anaesthesia so that measures might be implemented to potentially reduce morbidity and mortality (Hubbell et al, 2022).
Another facet of effective preparation for general anaesthesia is the use of a surgical safety checklist or pre-anaesthetic checklist. Checklists may serve as a cognitive aid and a formal or reproducible method of enhancing team coordination and communication. Implementation of a checklist aims to reduce frequency of human error, such as medication error and avoidable equipment problems, and some evidence indicates that checklists can be effective in reducing perioperative complications. The pre-anaesthetic checklist will be discussed during the BEVA session at congress with respect to usefulness in preventing harm to our patients.
Factors influencing anaesthetic risk have been extensively investigated in the literature and while some aspects are difficult to modify, the impact of others may be reduced if they are anticipated or if intervention is timely. The emergency status of a case and procedure type can influence anaesthetic risk and this association is likely to persist. Emergency procedures that did not include colic surgery incurred an anaesthetic or surgery-related mortality percentage of 2% (Mee et al, 1998a) compared to 0.63% associated with elective cases (Mee et al, 1998b).
Perioperative fatality is understandably higher for horses undergoing colic surgery and studies report figures including 4.2% (Gozalo-Marcilla et al, 2025), 4.3% (Mee et al, 1998a) and 7.8% (Johnston et al, 2002).
The length of postoperative period over which studies collect data varies. Studies may cease data collection at the time the horse returns to the stable (Dugdale et al, 2016), or continue to monitor for 48 hours postoperatively (Laurenza et al, 2020) and up to seven days postoperatively (Johnson et al, 2002; Gozalo-Marcilla et al, 2025). This variation in study design is likely to affect mortality and morbidity figures.
Horse factors such as older age (Johnston et al, 2002; Dugdale et al, 2016; Gozalo-Marcilla et al, 2025), higher ASA status (Johnston et al, 2002; Dugdale et al, 2016; Laurenza et al, 2020), increased bodyweight (Laurenza et al, 2020; Adami et al, 2020), draught breed type (O’Donovan et al, 2023) and pregnancy (Gozalo-Marcilla et al, 2025) have been shown to increase the risk of peri-anaesthetic mortality. Surgical procedure type can influence risk with arthrodesis/osteotomy procedures attracting a higher mortality percentage compared to arthroscopy (Bidwell et al, 2007).
Longer anaesthesia duration has been associated with poorer recovery quality (Young and Taylor, 1993; Dugdale et al, 2016), increased risk of neuromuscular complications and respiratory complications (Laurenza et al, 2020) and increased risk of death (Adami et al, 2020). Anaesthesia duration greater than three hours incurred 2.6 times the risk of mortality compared to durations of one to two hours (Gozalo-Marcilla et al, 2025). Interestingly, procedures lasting less than one hour also attracted a higher risk compared to the referent one to two hour duration (Gozalo-Marcilla et al, 2025).
The increasing complexity of surgical procedures being undertaken may impact anaesthesia time, although hopefully, an awareness of the importance of minimising anaesthesia duration may help to reduce any negative effect. Intraoperative infusion or additional doses of ketamine have been associated with higher mortality and poorer recovery quality respectively (Gozalo-Marcilla et al, 2025; Louro et al, 2022). Lateral recumbency body position was approximately four times less likely to be associated with mortality compared to dorsal recumbency (Dugdale et al, 2016).
Mortality and morbidity occurrence is often multifactorial and direct causation is often difficult to extract when several confounding factors may be involved. In addition to factors that influence anaesthetic risk, studies have investigated the cause and the timing of death and serious complications. When the mortality figures from CEPEF2 and CEPEF4 were stratified into cause of mortality, the incidence of cardiovascular collapse and cardiac arrest had reduced from 33.2% to 11.5% (Johnson et al, 2002; Gozalo-Marcilla et al, 2025).
The proportion of anaesthetic-related deaths due to cardiac arrest in earlier studies ranges from 33.2% to 47.6% (Johnston et al, 2002; Bidwell et al, 2007) and tended to be during a time when halothane was the most popular inhalant. Intraoperative cardiac arrest tended to occur early in the course of anaesthesia and may have been related to the almost universal use of halothane for maintenance of anaesthesia (Taylor et al, 2025).
Later studies, in which isoflurane was most frequently used, documented a lower proportion of deaths (11.1% to 11.5%) related to cardiac arrest and cardiovascular collapse (Laurenza et al, 2020; Gozalo-Marcilla et al, 2025).
It would seem that the proportion of deaths occurring intraoperatively has reduced and one single-centre retrospective study reported no intraoperative deaths in their population of horses (Dugdale et al, 2016). However, across the decades of equine anaesthetic risk surveillance, studies have consistently shown that the recovery phase persists to be a time of high risk of complication and death. Increased risk of mortality has been associated with poor recovery quality (Laurenza et al, 2020) suggesting that recovery quality and perioperative morbidity/mortality may be intertwined.
Methods aimed at improving recovery quality and ultimately recovery safety have been investigated in the literature. Systematic and structured reviews of this evidence have been undertaken to assess how various factors impact quality of recovery (Loomes and Louro, 2022; Gozalo-Marcilla and Ringer, 2021). Recovery complications can contribute significantly to overall mortality.
In a retrospective study of horses undergoing all types of surgery, 92% of non-fatal complications occurred during recovery and 88% of anaesthetic-related deaths happened in recovery (Laurenza et al, 2020).
In horses undergoing elective or non-colic surgery where the timeframe from premedication to return to the stable was analysed, 100% of deaths that occurred happened during recovery (Dugdale et al, 2016). When a longer timeframe extending to seven days postoperatively was analysed in non colic cases, 48.5% of deaths occurred during recovery (Gozalo-Marcilla et al, 2025).
Recovery catastrophes resulting in euthanasia may involve major orthopaedic injury. Two single-centre studies reported that 38% of anaesthetic-related deaths were due to fracture in recovery (Bidwell et al, 2007) and 71.4% of deaths in recovery were due to limb fracture or dislocation (Dugdale et al, 2016). It remains to be determined whether the flighty nature of the horse, which is often suggested to have the greatest influence on recovery quality, will limit future improvements (Dugdale et al, 2016).
One intervention aimed at improving recovery safety is the implementation of head and tail ropes, and this method of recovery assistance has gained research attention. In the global multicentre study of CEPEF4, 46.6% of horses recovered with head and tail rope assistance (Gozalo-Marcilla et al, 2025). In horses recovering after colic surgery, head and tail rope recovery assistance improved recovery quality (Louro et al, 2022) and reduced fatal complications (Nicolaisen et al, 2022), but other studies did not find that ropes provided an advantage (Rüegg et al, 2016).
It seems that rope assistance may well improve recovery in some horses, but cannot prevent fatalities in recovery (Lloyd and Murison, 2021). Review of the evidence suggests that the administration of alpha-2-adrenoreceptor agonists in recovery improves recovery quality (Loomes and Louro, 2022). Further to this, the administration of alpha-2-adrenoceptor agonists during recovery, alone or with acepromazine, has been associated with reduced odds of perioperative death (Gozalo-Marcilla et al, 2025).
Alongside evolving perianaesthetic management, conducting prospective large-scale studies aimed to investigate equine perianaesthetic management and outcomes should continue to be useful in detecting factors that influence anaesthetic safety.
In summary, safety has largely improved in most aspects of general anaesthesia resulting in lower fatality rates, but there are some aspects that are much harder to modify and these may limit our ability to mitigate anaesthetic risk entirely.
Kate Loomes completed an internship and residency in veterinary anaesthesia and analgesia at the University of Liverpool and joined Rainbow Equine Hospital soon after. Currently, Kate is involved in a multi-centre project to document and investigate equine perioperative complications and is interested in aspects of perioperative care and influences on anaesthetic risk.