Cardiopulmonary evaluation of the use of medetomidine hydrochloride in cats

Objective To evaluate the cardiovascular effects of the alpha (2)-adrenergi c receptor agonist medetomidine hydrochloride in clinically normal cats. Animals-7 clinically normal cats. Procedure-Cats were anesthetized with isoflurane, and thermodilution cathet ers were placed for measurement of central venous, pulmonary, and pulmonary capillary wedge pressures and for determination of cardiac output. The dor sal pedal artery was catheterized for measurement of arterial blood pressur es and blood gas tensions. Baseline variables were recorded, and medetomidi ne (20 mug/kg of body weight, IM) was administered. Hemodynamic measurement s were repeated 15 and 30 minutes after medetomidine administration. Results-Heart rate, cardiac index, stroke index, rate-pressure product, and right and left ventricular stroke work index significantly decreased from baseline after medetomidine administration, whereas systemic vascular resis tance and central venous pressure increased. However, systolic, mean, and d iastolic arterial pressures as well as arterial pH, and oxygen and carbon d ioxide tensions were not significantly different from baseline values. Conclusions and Clinical Relevance-When administered alone to clinically no rmal cats, medetomidine (20 mug/kg, IM) induced a significant decrease in c ardiac output, stroke volume, and heart rate. Arterial blood pressures did not increase, which may reflect a predominant central alpha (2)-adrenergic effect over peripheral vascular effects.