Comparison of Dexmedetomidine/Morphine and Xylazine/Morphine as Premedication in Isoflurane-Anesthetized Sheep

In this study we investigated the sedative, anesthetic, and pulmonary histopathologic effects of dexmedetomidine/morphine (DM) and xylazine/morphine (XM) in sheep. We hypothesized that DM would provide profound sedation and better maintain physiologic parameters under anesthesia than XM in sheep undergoing laparoscopic surgery. Nineteen male sheep were premedicated with either DM (dexmedetomidine [0.006 mg/kg] and morphine [0.3 mg/kg]) or XM (xylazine [0.1 mg/kg] and morphine [0.3 mg/kg]). After DM or XM administration, 3 blinded veterinarians evaluated sedation scores (0 [no sedation], 1 [mild], 2 [moderate], 3 [severe]). Sheep were induced with intravenous tiletamine/zolazepam, intubated, and maintained with isoflurane in 100% oxygen. Anesthetic parameters were monitored for 60 min, including heart rate, respiratory rate, indirect blood pressure, oxygen saturation, end-tidal carbon dioxide, body temperature, arterial blood gas analysis, and isoflurane requirement. At the end of the procedure, the sheep were euthanized, and lung pathology (pulmonary edema) was assessed. The results showed that the sedation scores did not differ between DM (0.8 [0.4 to 1.0]) and XM (1.0 [1.0 to 1.0]). In addition, the anesthetic parameters were comparable between the groups, but the DM group exhibited a higher heart rate than the XM group. Finally, marked pulmonary changes, consistent with pulmonary edema, were observed in the XM group. In conclusion, DM and XM provided similar sedation and physiologic stability under isoflurane anesthesia, but DM may help minimize bradycardia and was associated with less evidence of pulmonary edema.