Malignant hyperthermia in a horse anesthetized with halothane

Ahealthy, 565-kg, 14-year-old Quarter Horse gelding, negative for equine protozoal myelitis on serum Western blot and for hyperkalemic periodic paralysis (HYPP) by polymerase chain reaction, was selected for use in an electrophysiology study performed under inhalation anesthesia. The study was performed by following the guidelines of an Animal Use and Care Committee Protocol of the University of California at Davis (UCD 8578). Anesthesia was induced with halothane delivered via a face-mask. The horse was intubated 17 minutes later with an orotracheal tube and anesthesia was maintained with halo-thane by using a semiclosed, large-animal breathing circuit. Although muscle relaxation was otherwise good, the horse's ears remained tensed in a caudal direction throughout the study