Anesthetic Management of the Horse: Intravenous Anesthesia

Introduction For decades thiobarbiturates have been used to induce and maintain short term (15 30 minutes) general anesthesia in equids. Thiamylal is no longer commercially available, at least in the United States, but use of thiopental remains widespread. In earlier years these ultrashort acting barbiturates were the agents of choice to induce short term recumbency in tranquilized horses. Later guaifenesin and more recently xylazine (or other alpha-2 agonist type drugs) were administered in combination with or immediately prior to the intravenous injection of the thiobarbiturates to improve upon the quality of anesthetic induction and recovery. These improved techniques of general anesthesia facilitated surgical and other therapeutic procedures requiring more prolonged recumbency (e.g. 30 60 minutes). However, as duration of barbiturate administration increased, the duration of recovery from anesthesia became longer and the quality of recovery became more unpredictable and in some cases dangerous to the animal and associated personnel. Today, dissociative drugs such as ketamine have largely replaced thiobarbiturates for routine equine anesthetic management. This change has improved upon the qualitative consistency of both anesthetic induction and recovery. Because the dissociative agents have undesirable central nervous system excitatory properties their use in equids requires concurrent administration of other behavior modifying drugs such as an alpha-2 agonist (e.g. xylazine). A brief review and update of specific contemporary techniques follow.