Equine anaesthesia research highlights safety gains

General anaesthesia in horses is associated with fewer deaths now than two decades ago, reflecting significant advances in equine anaesthetic practice.

The findings are from a major international study led by an equine anaesthesia and analgesia expert at the Royal (Dick) School of Veterinary Studies.

This study, known as the Confidential Enquiry into Perioperative Equine Fatalities – phase 4 (CEPEF4), is the fourth edition in a series of large-scale, worldwide, multicentre studies which, since the 1990s, have examined the outcome at seven days after general anaesthesia in horses and identified relevant risk factors.

CEPEF4 analysed data from more than 47,000 procedures requiring general anaesthesia, collected from 28 countries in four continents between November 2020 and June 2023.

Overall mortality associated with general anaesthesia has decreased since the previous major enquiry in the early 2000s, the study found.

This study, undertaken by the CEPEF Community Interest Company (CEPEF CIC), could support evidence-based decision-making by vets and help owners to understand the benefits and risks of anaesthesia in horses.

Key findings

By comparing CEPEF4 data against earlier inquiries that used the same study design, with the benefit of modern information technology, experts were able to assess how outcomes following equine anaesthesia have changed over time, identifying where further improvements may still be needed.

The research team used veterinary records to track outcomes for individual cases, noting whether horses had survived for a 7-day period after surgery.

Findings show that death rates were lower than those reported in previous enquiries for horses undergoing anaesthesia for surgery or diagnostic imaging procedures, but they remain much higher than in other domestic species.

Patients suffering acute abdominal pain – such as those undergoing intestinal surgery for colic, mares having Caesarean sections, or foals requiring bladder rupture repair - have, as expected, higher death rates, the research team notes.

Risk factors

The study identified the recovery period as the most critical phase of anaesthesia. Horses are large prey animals, and waking and trying to stand after anaesthesia can be particularly hazardous, as their instinctive response can make them prone to panic, leading to injury.

For this reason, fractures during recovery remain the most common cause of death in otherwise healthy horses, the study found.

The results of CEPEF4 flag some well-known risk factors, and identify new ones. More comprehensive monitoring during anaesthesia – including close tracking of blood pressure, arterial blood gas and body temperature – was linked to lower odds of death, highlighting areas where clinical practice can continue to evolve.

Practices such as adequate analgesia during surgery, and mild sedation immediately before recovery were identified as protective factors.

Related studies

In a separate study using the same methodology, the team explored outcome following general anaesthesia in donkeys and donkey-horse hybrids. Similar death rates as in horses were reported.

In a research review, the team also investigates cases that do not result in postoperative death but may cause non-fatal complications affecting animal welfare, early hospital discharge, or long-term dysfunction.

Additionally, a narrative review traces the main milestones in equine anaesthesia since the first public demonstration in Vienna in 1847.

This work has been led in collaboration with colleagues from Taylor Monroe, Vetstream, the University of Zurich, and the Cardenal Herrera University, Spain (CEPEF CIC).

The research was supported by the Kate Borer-Weir Memorial Fund, the AVA Trust, and the Horse Trust. The research team also acknowledges the dedication and hard work of all contributors from the collaborating centres who submitted cases for the standing sedation study.

Related links

The main CEPEF4 paper

CEPEF 4 – meet the team

The Information Technology implementations

The donkey study

The post-operative complications review