EPIDURAL INJECTION OF KETAMINE FOR PERINEAL ANALGESIA IN THE HORSE

Objective-To determine the analgesic, sedative, and cardiopulmonary ef fects of epidural ketamine in the horse. Animal Population-Six healthy horses (three males and three females) weighing between 350 and 450 k g. Methods-Three doses of ketamine were selected (0.5, 1, and 2 mg/hg) . Two months before the beginning of experiments, the carotid artery w as exteriorized, and 1 week before experiments began, an epidural cath eter was placed percutaneously in all animals with the tip located 12 cm cranially in the midsacrum. One week later, either saline (control) or one of three doses of ketamine was injected epidurally. Each anima l received each ketamine dose and saline in random order at 1-week int ervals. Ketamine was diluted in saline 0.9% before the experiment, and the volume used was adjusted to horse size and correlated to clinical ly used volumes. All the animals received a standard noxious stimulus consisting of needle insertion into the skin and deep muscle using a 3 -point scale for scoring the response. A second scale was used to scor e the degree of sedation. The response to a noxious stimulus, the degr ee of sedation, and arterial blood pressure were assessed at previousl y determined intervals: before drug and 2, 5, 10, and 15 minutes and e very 15 minutes to 210 minutes after ketamine or saline administration . Arterial blood samples were drawn for blood gas analysis before drug and at 15, 30, 60, and 90 minutes. Results-All the tested doses of ke tamine were effective in producing analgesia of the tail, perineum, an d upper hindlimb. Total tail and perineal analgesia times were similar depending on dosage (30 minutes for 0.5 and 1.0 mg/kg and 75 minutes for 2.0 mg/kg). A sedative effect of ketamine was also observed in a d ose-response manner with a peak effect between 15 and 30 minutes posta dministration. No cardiopulmonary effects were observed with any dose of ketamine. Conclusions-Results indicate that epidurally administered ketamine in the horse produces local spinal and central nervous syste m effects with analgesia and sedation but minimal cardiopulmonary effe cts. Clinical Relevance-Further studies are required to determine whet her the analgesia is sufficient for surgery. (C) 1998 by The American College of Veterinary Surgeons.