CARDIOVASCULAR EFFECTS OF THE ALPHA(2)-ADRENERGIC RECEPTOR AGONIST MEDETOMIDINE IN CLINICALLY NORMAL CATS ANESTHETIZED WITH ISOFLURANE

Objective-To assess the cardiovascular effects of the alpha(2)-adrener gic receptor agonist medetomidine in healthy cats anesthetized with 2% isoflurane. Animals-11 clinically normal cats. Procedure-Cats were an esthetized with isoflurane, and catheters were inserted for measuremen t of aortic, left ventricular, and right atrial pressures. For data co llection, end-tidal isoflurane concentration was reduced to 2%, and en d-tidal CO2 was maintained at 35 to 40 mm of Hg by use of positive-pre ssure ventilation. After measurement of baseline data, medetomidine (0 .01 mg/kg of body weight, IM) was administered and data were collected continuously for 75 minutes. At the end of data collection, incisions were closed and cats were allowed to recover from anesthesia. Results -Medetomidine significantly increased mean arterial pressure and syste mic vascular resistance. The increase in mean arterial pressure was ma ximal at 17.8 +/- 7 minutes after medetomidine administration. Medetom idine also increased left ventricular peak systolic pressure, left ven tricular end diastolic pressure, and right atrial pressure. Medetomidi ne significantly decreased heart rate and mean aortic flow. Conclusion s-The low dosage of medetomidine (0.01 mg/kg, IM) promoted severe vaso constriction in isoflurane-anesthetized cats, and resulted in sustaine d increases in left ventricular preload and afterload.