CARDIOPULMONARY EFFECTS OF MEDETOMIDINE-KETAMINE IN DOMESTIC SHEEP (OVIS-OVIS) MAINTAINED IN STERNAL RECUMBENCY

Five healthy Suffolk sheep (Ovis ovis) were used to determine selected cardiopulmonary effects of i.m. medetomidine-ketamine. The sheep were immobilized with medetomidine (125 mu g/kg) plus ketamine (2.5 mg/kg) and maintained in sternal recumbency for 1 hr. Reversal of medetomidi ne was achieved with atipamezole at five times the medetomidine dose. There were significant changes over time in heart rate, cardiac index, Pa-O2, Pa-CO2, pH, arterial blood pressure, systemic vascular resista nce, pulmonary vascular resistance, pulmonary venous admixture, oxygen delivery, and oxygen utilization. No significant change occurred in c entral venous pressure, stroke volume, base excess, or oxygen extracti on ratio. Pa-O2 decreased significantly, apparently because of a combi nation of hypoventilation and increased pulmonary venous admixture. Ca rdiac index decreased significantly as a result of decreased heart rat e; stroke volume was maintained at a relatively constant volume throug hout the immobilization. Oxygen delivery decreased significantly prima rily because of the decrease in cardiac index; arterial oxygen content was maintained at a relatively constant level throughout the immobili zation. Oxygen utilization also decreased significantly over time, and the oxygen extraction ratio remained at a constant level throughout t he study. The results of this study suggest that, although oxygen deli very decreases because of decreased cardiac index, oxygen demand also decreases; oxygen delivery is therefore consistent with oxygen demand. Further studies are needed to better characterize the cardiopulmonary effects of this drug combination in wild ruminants.