Hemodynamic and respiratory effects of xylazine-morphine sulfate in horses

The cardiopulmonary effects of two xylazine-morphine sulfate drug combinations (mixtures) given IV were evaluated in horses. In horses given xylazine (0.66 mg/kg of body weight) and morphine sulfate (0.12 mg/kv) IV (experiment 1), there were significant (P less than 0.05) decreases in heart rate, cardiac output, and respiratory rate. Central venous pressure was significantly (P less than 0.05) increased. Arterial and pulmonary arterial blood pressures increased significantly (P less than 0.05) but transiently. Arterial blood gas tensions (PaCO2 and PaO2) and pH remained unchanged. In the horses given xylazine (0.66 mg/kg) and morphine sulfate (0.66 mg/kg) IV (experiment 2), the responses were qualitatively similar to those of experiment 1 horses, excluding lessened heart rate which was not significant). Horses in both experiments remained stationary and did not attempt to kick or strike for the duration of the experiment. Objective (trained personnel) and semiquantitative assessments of the analgesia in the horses during experiment 1 and those during experiment 2 indicated marked improvement in analgesia in the latter experiment.