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ABSTRACT
Anesthetization of large animals, such as the horse, is a challenge for veterinarians and compounding pharmacists. This article discusses the technique of intravenous anesthesia by using a combination of xylazine and ketamine in the horse for short-term unconsciousness; a combination of xylazine, diazepam, and ketamine for improved sedation and muscle relaxation; and a combination of xylazine, ketamine, and guaifenesin, referred to as Triple Drip, for the maximum 1-hour duration of unconsciousness. Compounding pharmacists that have the facilities and training required to prepare sterile compounds can greatly assist equine surgeons in the treatment of veterinarians' most challenging patients.
Prior to the 1970s, anesthetizing a horse in the field represented a high level of risk to both horse and veterinarian. Lateral recumbency (i.e., the horse lying on its side) produces ventilation and perfusion problems resulting in shunting of blood through the lungs and reducing oxygenation. When a horse was kept under anesthesia for too long it produced hypoxia and if for too brief a period, provided too shallow a plane of anesthesia, resulting in horses reaching a level of consciousness before the procedure was complete.
In 1977, a "new" era of safe anesthesia in horses began with the introduction of a new technique that utilized xylazine (an α-2 adrenergic agonist) and ketamine (a dissociative agent) to prepare short-term intravenous anesthesia. As the popularity of this technique grew, the safety and humanity of short-term equine anesthesia increased dramatically. Safety increased because the technique produced lateral recumbency with maintenance of reasonable cardiovascular function and acceptable respiratory depression. Recovery from anesthesia was generally smooth, with the horse rising to its feet 25 to 30 minutes after induction. The humanity of equine anesthesia increased because the institution of xylazine-ketamine anesthesia led to a dramatic reduction in the use of the paralyzing agent, succinylcholine, for equine restraint.
Xylazine-ketamine anesthesia has been administered to many horses during the past 30 years with relatively good results. Modifications of the xylazine-ketamine technique have been made as practitioners have encountered problems and subsequently adjusted the anesthetic protocol. The major problems associated with xylazine-ketamine anesthesia are related to (1) inadequate xylazine sedation...