Anesthetizing Horses in the Field for an Hour or More

Each week, only 10% of equine veterinarians anesthetize horses for more than 30 minutes, Hubbell said.

Photo: Paula da Silva

The longer a horse is under anesthesia, the greater the risk. And considering horses are some of the most vulnerable species when “knocked out” for surgery, equine veterinarians typically try to keep sedation periods as short as possible—most often less than 20 minutes. However, some procedures can take much, much longer.

To address some common issues with maintaining horses under prolonged anesthesia John Hubbell, DVM, MS, Dipl. ACVA, delivered a presentation for a veterinary audience at the 2013 American Association of Equine Practitioners' Convention, held Dec. 7-11 in Nashville, Tenn.

Hubbell, a professor of veterinary anesthesiology in the Department of Veterinary Clinical Sciences at The Ohio State University's College of Veterinary Medicine, started his presentation by reviewing guidelines he offered in an earlier lecture on producing 20 minutes of anesthesia in the field. Highlights included:

  • Completing a physical exam of the horse and recording findings;
  • Taking a complete medical history;
  • Performing basic blood prior to anesthesia;
  • Removing the horse’s halter to prevent potential facial paralysis; and
  • Monitoring and recording the horse’s heart and respiration rates every 10 minutes during the procedure (“Remember some horses will only breath two times per minute [under anesthesia],” he noted).

Each week, only 10% of equine veterinarians anesthetize horses for more than 30 minutes, Hubbell said. Of those, 50% use inhaled drugs rather than intravenous infusions tp maintain anesthesia, and a majority (85%) use an assistant to monitor the horse and administer additional anesthetic drugs.

Morbidity and mortality increase with the length of anesthesia, especially for large horses. “Warmbloods and drafts are at greatest risk,” Hubbell said, most likely because of the heightened difficulty of recovery of a large horse in a field situation.

Hubbell said planning ahead is essential when administering anesthesia longer than 20 minutes. He recommends:

  • Placing an intravenous catheter to allow drug administration during the procedure;
  • Selecting an operating field that’s free of obstructions and hard surfaces;
  • Estimating the horse’s weight and using that weight for appropriate drug dosing; and
  • Using protective padding under the horse’s head, point of the shoulder, and hip to help prevent injury.

Once a horse is anesthetized, the practitioner can use changes in respiration, muscle tone, or movement to monitor depth of anesthesia.

Hubbell recommends veterinarians purchase an oxygen tank and regulator to administer emergency oxygenation and ventilation because horses do not maintain “normal” blood oxygen tensions (the partial pressure of gases in the blood) under anesthesia when lying on their backs or sides. They tolerate the less than ideal oxygenation for short periods but can have issues if the recumbency is prolonged, he added.

“The availability of an oxygen source also would allow the veterinarian to breathe for the horse should respirations slow or cease,” he said. “A demand valve is a device similar to what scuba divers use that allows veterinarians to efficiently assist ventilation.”

Once the procedure is completed, the horse should be monitored during the recovery period until it stands and can walk steadily, Hubbell concluded.

About the Author

Michelle N. Anderson, Digital Managing Editor

Michelle Anderson serves as The Horse's digital managing editor. In her role, she produces content for our web site and hosts our live events, including Ask the Vet Live. A lifelong horse owner, Anderson competes in dressage and enjoys trail riding. She's a Washington State University graduate (Go Cougs!) and holds a bachelor's degree in communications with a minor in business administration and extensive coursework in animal sciences. She has worked in equine publishing since 1998. She currently lives with her husband on a small horse property in Central Oregon.

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