The effects of dexmedetomidine on the ventilatory response to hypercapnia in rabbits

Objective: Dexmedetomidine is a highly selective alpha(2)-adrenergic agonist that can reduce anesthetic requirements. This study, to assess. its effect on respiration, examined the effects of various doses of dexmedetomidine (1, 10, 30 and 50 mug/kg) on the respiratory response to carbon dioxide (CO2) breathing in rabbits. Design: Randomized prospective study. Setting: Animal laboratory at a university school of medicine. Intervention: From 28 animals, four groups of seven were randomly, assigned to receive different doses of dexmedetomidine (groups D I, D10, D30 and D50). Under inhalation of sevoflurane, each animal was tracheostomized and intubated with a 4 turn internal diameter (i.d.) endotracheal tube. Measurements and results: After end-tidal sevoflurane concentration had decreased below 0.03% and during quiet breathing (QB); respiratory rate (RR), tidal volume (V-T) and inspiratory time (T-I) were measured, from which minute ventilation (MV) and mean inspiratory flow (V-T/T-I) were calculated. After these measurements had been completed, each animal breathed the balloon gas (5% CO2 and 95% O-2) until the end-tidal CO2 (ETCO2) reached 10%. The respiratory measurements were repeated during the latter period. After the collection of these data, dexmedetomidine was infused intravenously and the same measurements were repeated 15 and 45 min after dexmedetomidine infusion. The slope of the ventilatory response to hypercapnia in D50 was significantly higher compared with D30 animals. In the range 1-30 mug/kg, during both QB and at 10% ETCO2, MV was decreased in a dose-dependent manner. Dexmedetomidine depressed both V-T and RR during QB and at 10% ETCO2. Conclusion: Dexmedetomidine depressed resting ventilation and the respiratory response to CO2, but it did not induce profound hypoxemia or hypercapnia in rabbits.