CARDIOPULMONARY EFFECTS OF MEDETOMIDINE-KETAMINE IMMOBILIZATION WITH ATIPAMEZOLE REVERSAL AND CARFENTANIL-XYLAZINE IMMOBILIZATION WITH NALTREXONE REVERSAL - A COMPARATIVE-STUDY IN DOMESTIC SHEEP (OVIS-OVIS)

Eight healthy Suffolk sheep (Ovis ovis) were used in a crossover study to determine the cardiovascular and respiratory effects of i.m. carfe ntanil-xylazine and i.m. medetomidine-ketamine combinations. Anesthesi a was induced and maintained for 1 hr with medetomidine (125 mug/kg) a nd ketamine (2.5 mg/kg) or with carfentanil (10 mug/kg) and xylazine ( 0.2 mg/kg). Reversal of immobilization in the carfentanil/xylazine (CX ) group was achieved with i.v. naltrexone at 100 times the carfentanil dose. Reversal of immobilization in the medetomidine/ketamine (MK) gr oup was achieved with i.v. atipamezole at five times the medetomidine dose. Induction was rapid (<3 min) with both combinations. There were significant differences (P < 0.05) in heart rate, blood pressure, resp iratory rate, minute volume, Pco2, and arterial pH between treatments. Significant differences were not found between groups for Po2 or base excess. Immobilization with MK was characterized by hypertension, bra dycardia, hypercarbia, hypoxemia, and decreased pH. No significant cha nge occurred in respiratory rate or minute volume. All animals in the MK group had electrocardiogram (EKG) changes indicative of myocardial hypoxia. Hypoxemia in this group was severe and sustained until revers al with atipamezole. Hypoxemia was not related to respiratory depressi on and was probably due to changes in hemodynamics and positioning of the sheep in lateral recumbency. Immobilization with CX was characteri zed by hypotension, tachycardia, hypoxemia, decreased pH, and hypovent ilation as evidenced by decreased respiratory rate, decreased minute v olume, and increased Pco2. All animals in this group also developed EK G changes suggestive of myocardial hypoxia. Hypoxemia was most pronoun ced early in the immobilization period, with several animal developing apnea. Po2 increased gradually over the hour but remained significant ly lower than baseline throughout the immobilization period. Three ani mals in the CX group and one in the MK group developed severe hypotens ion. One animal in the CX group required reversal at 25 min postadmini stration because of sustained hypotension. Reversal was rapid. Within 3 min, animals of both treatment groups were attempting to attain ster nal recumbency. The results of this study demonstrate that both combin ations at the given doses have deleterious effects (hypoxemia) on the patient. Further studies are needed to better characterize the cardiov ascular effects of these agents.