Anesthesia: Down, Not Out

Put a horse down. Euthanized. Humanely destroyed. The list goes on. It is how we in the business describe the unsavory, but sometimes necessary, task of killing a horse. Sometimes an animal becomes sick or crippled from a chronic problem, such as laminitis, and it is more humane to end the suffering; or a mare suffers complications from foaling and the only decision is how long until she dies. But one of the most controversial times of euthanizing a horse is when it is injured while in competition. Up goes the blue screen, in goes the needle, the suffering ends.

For years, there has been a movement to offer alternatives to euthanasia on the racetrack and at other competitive equine events. Offering these alternatives has been complicated by a number of facts, including the most compelling--horses at exercise are hard to sedate, and anesthetize, because of their increased heart and respiratory rates, and the increased adrenaline in their systems.

Veterinarians have noted that it can take twice the normal amount of sedation medication to take an excited, exercised horse to the point it is able to be handled safely.  Attempts have been made to define protocols for use on the racetrack in the face of catastrophic injury. These protocols include medications that would be simple to administer, would work in a distressed/excited horse, and would allow the horse to be recovered afterward without un-due trauma or continue under anesthesia for surgical intervention.

The Future is Here

Funding was provided from the American Quarter Horse Association to Washington State University for the study of anesthetizing horses immediately following strenuous exercise. While the study did not simulate the added dimension of injury, it was possible to exercise horses to fatigue on a treadmill or on a racetrack, then test various drug and anesthesia protocols, transportation, and recovery.

The Study

"We were looking at ways to try and save some of these horses who are breaking down on the racetrack," said Bob Schneider, DVM, MS, Diplomate ACVS, a professor of equine surgery at Washington State University. "We can't save all these horses at this point, but the first step is getting the horse off the track alive."

Schneider's colleagues in this study were Steve Greene, DVM, MS, Diplomate American College of Veterinary Anesthesia, an associate professor of anesthesiology, and Warwick Bayly, BVSc, MS, Diplomate ACVIM, a professor of equine medicine. The study was begun in October of 1995, and concluded in September of 1996. Results of the study have been sent to the AQHA and have been submitted for publication in a refereed veterinary journal.

The first step, according to Greene, was determining what drugs to use for sedating horses which have just finished strenuous exercise. Seven or eight different combinations of drugs were tried initially, and the ones that gave the best results were in a family known as Alpha-2 agonists; specifically, detomidine and medetomidine. Other medications did not give a "smooth induction" to these exercised horses, Greene said. (Alpha-2 drugs are named for the molecular site where they work.)

"It is necessary to produce smooth induction to anesthesia," he explained, noting that sedating a horse is necessary before the horse can be placed under drug-
induced anesthesia and placed in recumbency.

"We observed that Alpha-2 drugs gave a reasonable effect and required less than 2 cc of drug for sedation," Greene added.

After the horse was sedated for three to five minutes, an injectable anesthetic agent was given. The drug chosen was Telazol, which is approved for dogs and cats. Telazol is a combination of tiletamine (similar to ketamine) and zolazepam. This drug combination also only requires a small volume (5 cc), so it is quick and easy to administer. The time lapse gives the first drug time to calm the horse before it is anesthetized and helps insure that the Telazol can induce anesthesia and recumbency.

"The doses of these drugs are higher than used in the resting horse, but these are small volumes compared to what is used in elective procedures," said Bayly. "So, trying to get an injection into a moving, excited horse is not a problem because of the small volume."

The detomidine can be drawn into a syringe and ready to inject into the jugular vein during an emergency, said Greene. The needle can be left in and the Telazol injected. Telazol is a powder that can be reconstituted and saved one to two weeks for quick reaction times.

The pilot part of the research project involved exercising horses on a high-speed treadmill, explained Bayly. The speeds used took the horse to fatigue after two minutes of exercise in order to simulate racetrack exercise. The horse was backed off the treadmill, then given the sedative drug. This time lapse simulated the response time on the racetrack. Then the horse received drugs to induce anesthesia. After the combinations, dosages, and administration times were set into a protocol, six horses underwent the process. Some horses during the treadmill exercise were maintained on gas anesthesia after being anesthetized to simulate travel and time for a surgical procedure.

The next step was using Thoroughbred horses exercised on the university's racetrack. This allowed the researchers to determine the steps required to sedate, anesthetize, transport, and recover horses from a racetrack setting. Six horses also underwent this entire protocol.

"The horses were run full-out with a rider to simulate a race, and the horses were, indeed, excited and fatigued when they were pulled up," said Bayly.

"We took blood samples immediately when they were stopped and brought to the infield of the racetrack," said Greene. "We administered medetomidine about three minutes after they were stopped, let them become sedated (about three to five minutes) while we backed the ambulance nearby, then induced anesthesia with Telazol. Each horse became recumbent in a controlled way. Several horses were treated as if they had injuries so that a leg had a Kimzey splint or a Robert Jones bandage applied.

"The horse then had hobbles placed on his legs, was hoisted onto the specially designed ambulance with a lowered floor, and driven to the veterinary hospital," Greene said.

At the hospital, the horse was put in a surgery recovery stall and evaluated during recovery from anesthesia. There was no incidence of tying-up, and the average time to standing after reaching the recovery stall was about 65 minutes.

"The heart rate at the time they were given the medetomidine was high, usually greater than 160 (beats per minute)," said Bayly. "That indicates the horses were still in a highly excited state."

On-board heart rate monitors were used with the horses to ensure that the horses were exercised to the heart rate that racehorses reach while competing.

The question of tying-up has been raised for all horses undergoing anesthesia, and especially those which were in an excited state prior to induction. Horses were put on intravenous fluids after exercise and induction, but Bayly said this would simulate what a practitioner would do for any anesthetized horse.

Schneider added that in the normal horse undergoing surgery, tying-up is thought to be a problem more associated with blood pressure dropping during anesthesia. Since the blood pressure on these exercised horses is higher at induction, it might be that the tying-up will not be as much of a concern in these horses as with horses undergoing elective surgery, he explained.

The key to anesthetizing an acutely injured horse on the racetrack, or in any athletic competition, is to allow the horse to be removed to a more suitable setting for diagnosing and prognosing its injuries. This also allows the horse's regular attending veterinarian, trainer, and owner to offer input on the treatment of the animal.

Other Considerations

"Obviously, if a horse is anesthetized, you need a place to get him up," said Schneider. "An injured horse is not able to be recovered in the open. The racetracks need to find a place to recover these horses. This means some space requirements and a padded stall."

Schneider added that even after the injured horse is successfully removed from the track for evaluation, "ultimately the practitioner might make the same decision as the racetrack practitioner. But, there is more pressure on the track to get things moving. If the horse is gotten off the racetrack and into a controlled situation, this gives 60 minutes before the horse gets up to make decisions. Maybe no further anesthesia is needed because the leg is so shattered there is no shot to fix it, but this gives us time for positive, accurate assessment with cool heads not under pressure."

Schneider feels that this anesthesia protocol should be put in place at every track or event where there is a regulatory or attending veterinarian, especially at racetracks.

"It seems obvious to me that this is needed to improve the image of racing," said Schneider. "It shows the importance of the care of the horse by having a protocol and a recovery stall and having veterinarians make the decision off the track."

Bayly added, "There is no question that it is in the racetrack's best interest for the announcer to say the horse has been put on an ambulance and taken away for further evaluation."

There are many types of ambulances designed for loading injured horses, including the well-known Kimzey ambulance with a back-loading design and a floor that lets down on hydraulics to be level with the ground surface.

The group from Washington State designed their own ambulance during these studies. One of the most noticeable differences is the large size of the ambulance, which is necessary to allow the horse to lie in lateral recumbency (on its side). The ambulance loads from the side, has a center floor that drops to the ground surface, and features an overhead hoist like those found in surgical hospitals for moving horses. The researchers noted that this design was beneficial for the anesthetized horse's well-being, but that they are going to make other modifications to the ambulance.

In summing up the practicality of putting this protocol into practice at racetracks and at other top competitive equine events, Schneider said, "This to me seems so obvious that I find it hard to believe some people will disagree. Equine practice and horsemanship are steeped in tradition, but this study proves that it is safe to anesthetize excited horses. It is in the best interest of the horses, and in the best interest of racetrack management. But this can be used for any horse emergency, from a horse in a trailer accident to a Quarter Horse that is barrel racing."

The next step is to try the protocol in the "real world" of racing. The group is looking for regulatory veterinarians who would be willing to utilize this protocol during actual racing situations.

While this protocol will not save every horse that suffers a catastrophic injury while competing, it does offer trainers and owners the opportunity to have input in the decision of whether to euthanize the animal, or go to any extreme to try and save it. The extent of the injury, and the costs involved, always will be the final determinants, but at least with this new innovation, time is measured in minutes rather than seconds when the decision has to be made for euthanasia.

About the Author

Kimberly S. Brown

Kimberly S. Brown was the Publisher/Editor of The Horse: Your Guide To Equine Health Care from June 2008 to March 2010, and she served in various positions at Blood-Horse Publications since 1980.

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