Balancing Total Intravenous Anesthesia and Inhalant Anesthesia in Horses

1. Introduction
Intravenous drugs such as chloral hydrate, pentobarbital, and thiamylal were once commonly used for general anesthesia of horses but were often associated with prolonged or violent recoveries. When inhalant anesthetics such as halothane were introduced in the 1960s, the use of IV drugs for maintenance of anesthesia became less common.¹  In recent years, interest in IV anesthetic techniques has been renewed, both by recognition of the relatively high risk of morbidity or mortality with inhalant techniques and by the development of injectable drugs with fewer undesirable side effects and potentially improved recovery characteristics.²

In 2002, a large, multi-center prospective study reported peri-anesthetic mortality for horses to be 0.9% (1 death per 111 anesthetized horses).³ Subsequently, one individual equine hospital reported a much lower mortality rate of 0.12–0.24% (1 death per 417–833 cases).⁴ In the multi-center study, anesthesia induced and maintained using only IV drugs (total intravenous anesthesia [TIVA]) was reported to be associated with a lower risk of death (0.3%, or 1 death per 321 cases) than anesthesia induced with IV drugs and maintained with inhalant anesthesia.³  Recoveries from short-term IV anesthesia are often smoother and more controlled than recoveries from inhalant anesthesia.⁵  Other advantages of TIVA include the minimal equipment required compared with inhalant anesthesia and potentially reduced stress.⁶  The development of reversible or shorter-acting drugs such as α2 agonists, ketamine, and propofol has facilitated the use of TIVA for longer procedures than previously considered safe.⁷ [...]