Cardiopulmonary and analgesic effects of xylazine, detomidine, medetomidine, and the antagonist atipamezole in isoflurane-anesthetized swine.

The cardiovascular and respiratory effects of three alpha(2)-adrenergic agonists (xylazine 2mg/kg of body weight; detomidine, 40 micrograms/kg; medetomidine, 40 micrograms/kg) and their specific antagonist, atipamezole (200 micrograms/kg) were examined in young, isoflurane-anesthetized (1.3% end-tidal concentration) swine (weight range, 15 to 35 kg). The intravenous administration of all three alpha(2)-agonists caused an initial significant (P < 0.05) but short-lived increase in arterial blood pressure. Atipamezole also increased blood pressure, and this effect persisted throughout the period of observation. All agonists caused a sustained significant bradycardia, whereas atipamezole significantly increased heart rate (30 +/- 7 beats per min). The cardiac index tended to transiently decrease 5 to 10 min after agonist injection (significant only for xylazine at 2 min after injection) from an average pre-injection value of 166 ml/kg per min and did not change in response to atipamezole. None of the drugs significantly modified arterial blood gas (PaO2, PaCO2) or pH values. Xylazine and medetomidine but not detomidine or atipamezole manifested short-lived analgesic properties in response to clamping of the interdigital fold.