The Cardiovascular Response of Sheep to Tiletamine–Zolazepam and Butorphanol Tartrate Anesthesia

Butorphanol tartrate (0.5 mg/kg intravenously [IV]) was administered to six ewes (group 1), 10 minutes before administration of tiletamine‐zolazepam (12 mg/kg IV). In six ewes (group 2), butorphanol tartrate and tiletamine‐zolazepam were administered simultaneously. Time of administration of butorphanol did not alter hemodynamics or duration of anesthesia significantly. Anesthesia was adequate for 25 to 45 minutes (mean, 31 min) in group 1. The sheep in group 2 were anesthetized effectively for 25 to 50 minutes (mean, 39 min). Neither dosing regimen caused significant changes in right atrial pressure, heart rate, pulmonary vascular resistance, or pulmonary capillary wedge pressure. Mean arterial blood pressure (MABP) decreased an average of 18% from baseline values of 113 mm Hg to a minimum of 84 mm Hg at minute 60 in group 1, and from 111 mm Hg to 92 mm Hg at minute 75 in group 2. The decrease was significant only for group 1. Cardiac output (CO) was significantly decreased 24% from 6.6 L/min at minute 45 in group 1, and 32% from 6.3 L/min at minute 15 in group 2. Systemic vascular resistance (SVR) was increased significantly at minute 15, 11% in group 1 and 37% in group 2. Mild respiratory acidosis was measured by significant decreases in arterial pO2 and pH and a significant increase in pCO2 without significant changes in HCO3. Results of this study show that (1) tiletamine‐zolazepam and butorphanol tartrate produce adequate anesthesia for 25 to 50 minutes; (2) the cardiovascular and anesthetic effects of the dosing schedules were similar; and (3) tiletamine‐zolazepam and butorphanol result in decreased CO and MABP with a concomitant increase in SVR, and mild respiratory acidosis.