Researchers assessed how outcomes following equine anaesthesia have changed over time. 

Overall mortality associated with general anaesthesia has decreased.

New research into equine anaesthesia has revealed falling mortality rates and factors influencing general anaesthesia outcomes.

The study, led by an equine anaesthesia and analgesia expert at the Royal (Dick) School of Veterinary Studies, is known as the Confidential Enquiry into Perioperative Equine Fatalities – phase 4 (CEPEF4).

CEPEF4 is the fourth edition in a series of large-scale studies that, since the 1990s, have examined the outcome at seven days after general anaesthesia in horses and identified relevant risk factors.

In the study, researchers assessed how outcomes following equine anaesthesia have changed over time, identifying where further improvements may still be required.

The team used veterinary records to track outcomes for individual cases, noting whether horses had survived for at least seven days after surgery.

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

They also reveal that patients suffering acute abdominal pain have, as was expected, higher death rates.

The study also looked at risk factors, identifying the recovery period as the most critical phase of anaesthesia.

As large prey animals, a horse’s instinct to stand after anaesthesia could make them prone to panic, leading to injury. For this reason, fracture during recovery remains the most common cause of death, the study found.

Comprehensive monitoring during anaesthesia was associated with lower odds of death. Practices such as adequate analgesia during surgery and mild sedation immediately before recovery were identified as protective factors.

A separate study using the same methodology explored outcomes following general anaesthesia in donkeys and reported similar death rates.

Dr Miguel Gozalo-Marcilla said of the findings: “CEPEF4 – The most updated equine anaesthesia mortality study - provides an evidence-based picture of the death rate in equine anaesthesia and identify the risks. 

“By bringing together data from 93 centres worldwide, CEPEF4 is the largest, confidential, observational, prospective, multicentre, cohort study and reflects a truly international team effort.”

The study, "The Confidential Enquiry into Perioperative Equine Fatalities: Phase 4 (CEPEF4)" – a worldwide observational, prospective, multicentre cohort study published in 2025 - is reported in Veterinary Anaesthesia and Analgesia.