Ventilatory, hemodynamic and sedative effects of the α₂ adrenergic agonist, dexmedetomidine

Dexmedetomedine is a potent α₂ adrenergic agonist which can reduce anesthetic requirements by over 90% in rats and dogs. This study examined the effects of various doses of dexmedetomidine on the following monitored variables in New Zealand white rabbits: arterial blood gases, mean arterial pressure, respiratory rate, heart rate, and level of sedation. Following the percutaneous insertion of arterial and venous catheters, 21 rabbits received an infusion of saline or dexmedetomidine (20, 80 or 320 μg/kg). Monitored variables were recorded at 5, 15, 30 and 60 min following the infusion. Dexmedetomidine produced significant dose-dependent increases in PaCO₂ and level of sedation. There were significant decreases in heart rate, PaO₂ and respiratory rate. There was no significant change in mean arterial pressure even at the highest (320 μg/kg) dose. To examine the ability of an α₂ adrenergic antagonist to reverse the effects of dexmedetomidine, 5 rabbits initially received 320 μg/kg of dexmedetomidine as described above. Seven minutes after completion of the infusion, 900 μg/kg of the α₂ adrenergic antagonist, idazoxan, was administered. This resulted in a prompt and sustained reversal of the hypercarbia and sedation produced by the dexmedetomidine.