Eating Green.

What’s the safest equine anesthetic available to veterinarians?

An article by Clare Illingworth, SPARK writer, University of Guelph.


Horses, like humans, are at risk from anesthetic-related complications during surgery. Historically, about one per cent of equine surgeries around the world end in mortality. A University of Guelph researcher is making progress in trying to further reduce that number, by determining the safest anesthetic available to veterinarians.

Prof. Wayne McDonell, Clinical Studies, looked at recovery rates in horses undergo-ing arthroscopy procedures (a technique that uses a video camera and long instruments to visualize joint spaces with minimal invasiveness) and found a certain anesthetic that appears to work best in elective surgeries.

“The type of anesthetic used can have great impact on the success of a surgery,” says McDonell. “There have been few studies that objectively compare inhaled anesthesia drugs and regimens during and after actual surgical procedures.”

Two inhalant anesthetics are popular with equine veterinarians. Halothane, the most common, is preferred because it’s effective and relatively inexpensive. Isoflu-rane is more frequently used in small animal surgeries and with critically ill horses, but it’s becoming a more popular choice for elec-tive surgeries because its cost is declining and many veterinarians say they’ve noticed fewer side effects in certain situations.
The problem, says McDonell, is that the benefits of both drugs are poorly researched in horses.

Both anesthetic types are inhaled gases that lower nerve impulses (the way the brain communicates with the body), ren-dering the horse unconscious and relaxed. The exact molecular process isn’t fully understood, but it is known that although both drugs require recovery time, horses receiving isoflurane tend to waken too soon, before the drug has been fully expelled.

“For this reason, veterinarians commonly use a sedative to allow the drug extra time to be expelled,” says McDonell. “The sedative prevents the drowsy horse from standing prematurely and injuring itself.”

This seems to work. Researchers studied eight horses undergoing two similar arthroscopic surgeries three months apart. The horses received halothane for one of the surgeries and isoflurane for the other, then were evaluated on reactions such as cardiovascular function, recovery characteristics, 48-hour post-recovery differences, gut mobility and overall well-being. Preliminary results show isoflurane involves fewer complications in recovery when coupled with a sedative.

“In the past, isoflurane was thought to be the poorer anesthetic choice because the recovery wasn’t handled properly,” says McDonell. “Now we know how to handle the post-operative care, and we’re having great success with recovery after post-arthroscopic surgeries.”

Others involved in this research include Profs. Carolyn Kerr and Melissa Sinclair and graduate student Sumit Durongphongtorn of the Department of Clinical Studies.

This research is sponsored by the Ontario Ministry of Agriculture and Food and the Ontario Horse Racing Industry Association.