VENTILATORY EFFECTS OF DEXMEDETOMIDINE, ATIPAMEZOLE, AND ISOFLURANE IN DOGS

Dexmedetomidine (DMED) is a novel alpha(2) adrenergic agonist that has been shown to have potent analgesic and anesthetic sparing effects. T his study was designed to investigate the effects of DMED, both alone and combined with isoflurane, on resting ventilation, the hypercapnic response, and the hypoxic response in dogs. When given alone, 1-mu-g/k g decreased resting ventilation by 22% but at larger doses (10, 20, an d 100-mu-g/kg) resting ventilation increased, doubling at 100-mu-g/kg. Doses of 10-mu-g/kg and greater caused a maximum depression of 60% in the slope of the hypercapnic response, but no dose had a significant effect on the hypoxic ventilatory response. A dose of 3-mu-g/kg of DME D reduced isoflurane MAC from 1.3% to 0.37%, and the ventilatory effec ts of this 1 MAC combination were intermediate between the awake value s and those of isoflurane-anesthetized (1.3%) dogs. Atipamezole is a s pecific centrally acting alpha(2) receptor antagonist and when given w ith DMED in isoflurane-anesthetized dogs prevented the ventilatory dep ression. However, atipamezole alone also had ventilatory stimulating e ffects, which may indicate tonic alpha(2) adrenergic activity. The ven tilatory depression caused by DMED, either alone or combined with isof lurane, at doses that significantly reduce anesthetic requirements are relatively mild.