
Horses are sedated and anesthetized commonly in equine practice, even for run-of-the mill emergencies. But for catastrophic emergencies with high hazard levels, practitioners must take a different approach.
“We need to make decisions of when not to sedate or what drug combinations should be used to minimize injury to either the horse or the emergency response team,” explained John Madigan, DVM, MS, Dipl. ACVIM, ACAW, Professor Emeritus, Department of Medicine and Epidemiology at the University of California’ Davis School of Veterinary Medicine, during the National Alliance of Equine Practitioners (NAEP) Saratoga Equine Practitioners Conference. “These decisions are based on observations made very early on the scene of these catastrophic emergencies.”
Using the example of a horse with trauma in recumbency, Madigan described his general approach, which first involves medically assessing the patient. Is the horse in cardiovascular compromise? Is he conscious and able to ambulate? Is there a reason he’s down (e.g., herpesvirus)? Madigan then assesses how compromised the horse is in terms of fatigue level, whether myopathy has started, the presence of limb instability, etc.
“We need to determine if the horse can handle what we’re about to do,” he explained. “We also have to take into consideration their behavior and level of fearfulness, especially in horses that are not typically handled.”
Should You Sedate?
Sedation might increase scene safety, but not always.
“While sedation may help decrease the horse’s anxiety and risk of additional trauma or corneal ulcers from hitting their head, etc., we can get a false sense of security from sedating them,” Madigan said.
The benefits of sedation include providing personnel and scene safety, decreasing the horse’s pain and anxiety, making the horse more tractable, and allowing the horse to be transported in recumbency or for aerial transport.
Contraindications for sedating include hypovolemia or other physical compromise and the risk of falling and getting into a worse situation, especially if there is water or a vertical drop.Further, if we are trying to help a down horse stand, sedation can weaken that effort.
“We also need to assess the environment,” Madigan continued. “If the horse needs to be able to walk up a hill during the rescue, then they cannot be sedated, especially if they are already weak. Sedation may take away the horse’s ability to stand when we need him to. If considering anesthesia, look around and determine if there is a suitable recovery area.
Further, the level of sedation can be highly variable and difficult to predict. There is a balance between too much (e.g., a yearling trapped in water with his head barely above the surface) versus not enough (e.g., dragging the yearling out of water and then having him freak out). Other factors that can affect a horse’s response to sedation include breed (e.g., Arabians), level of training and handling, cardiovascular stability and hydration status, and whether they are accustomed to the environment.
Choosing Sedatives and Anesthetics
Alpha-2 agonists, which have rapid and profound sedation but slow the heart rate, are common choices for sedation. Acepromazine will provide mild tranquilization but lowers blood pressure.
“The alpha-2s xylazine and detomidine can each be administered, but detomidine should be avoided if the horse might further be anesthetized with ketamine. The recoveries are not nice,” Madigan cautioned. “Romifidine can also be used as it produces a little less ataxia, but this medication must now be compounded.”
A “ketamine stun” at 0.1 mg/kg IV provides rapid onset of profound sedation, which might be useful in some situations in combination with alpha-2s.
If possible, consider a constant rate infusion of detomidine or xylazine with butorphanol.
“Regardless of what you choose, it is very important to wait until the horse’s head is below the withers,” said Madigan. “Then you can either attempt manipulation or induce anesthesia. But you still need to be prepared that the horse may come out of the initial sedation calmness.”
And while you can use reversal agents such as tolazine and yohimbine in emergencies, death is a real possibility.
“You better have a good reason to use these reversal agents,” Madigan said.
Anesthesia can be maintained with a xylazine/ketamine/valium mixture for up to two hours. For longer procedures, gas anesthesia and tracheal tube are needed. In this case, you must monitor anesthesia depth, looking at eye position, muscle tone, movement, palpebral and corneal reflex, blink, respiratory pattern and rate, and more.
Emergency Euthanasia via Intrathecal Route
Madigan encouraged conference attendees to review how to perform euthanasia, if indicated, using intrathecal lidocaine in an anesthetized horse—a procedure the AVMA approved in 2020. The Iowa State Large Animal euthanasia website has detailed images for the procedure.
Madigan advised practitioners to consult a field guide to equine emergency sedation and anesthesia (available at Loopsrescue.com) and the comprehensive details on managing emergencies at equine competitions/events in the conference proceedings. These step-by-step instructions will allow a coordinated team response directed by a single point person and a public information officer.
Related Reading
- Policies for Emergency Services in Equine Practice
- Disease Du Jour: Equine Disasters
- Equine and Livestock Evacuation Kit Essentials
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