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 microg/kg) on the respiratory response to carbon dioxide (CO(2)) breathing in rabbits.


METHODS
Randomized prospective study.


METHODS
Animal laboratory at a university school of medicine.


METHODS
From 28 animals, four groups of seven were randomly assigned to receive different doses of dexmedetomidine (groups D1, D10, D30 and D50). Under inhalation of sevoflurane, each animal was tracheostomized and intubated with a 4 mm internal diameter (i.d.) endotracheal tube.


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% CO(2) and 95% O(2)) until the end-tidal CO(2) (ETCO(2)) 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 microg/kg, during both QB and at 10% ETCO(2), MV was decreased in a dose-dependent manner. Dexmedetomidine depressed both V(T) and RR during QB and at 10% ETCO(2).


CONCLUSIONS
Dexmedetomidine depressed resting ventilation and the respiratory response to CO(2), but it did not induce profound hypoxemia or hypercapnia in rabbits.
Saiseikai Nakatsu Hospital, Osaka, Japan.
Tomoyo
T
Nishida
Masaji
M
Nishimura
Kiyokazu
K
Kagawa
Yukio
Y
Hayashi
Takashi
T
Mashimo
D000316:Adrenergic alpha-Agonists / Q000494:pharmacology*; D000818:Animals; D001944:Breath Tests; D002245:Carbon Dioxide / Q000378:metabolism; D020927:Dexmedetomidine / Q000494:pharmacology*; D006935:Hypercapnia / Q000378:metabolism / Q000503:physiopathology*; D007564:Japan; D011817:Rabbits; D012119:Respiration / Q000187:drug effects*
D000316:Adrenergic alpha-Agonists; D002245:Carbon Dioxide; D020927:Dexmedetomidine