Respiratory reflexes in response to upper-airway administration of sevoflurane and isoflurane in anesthetized, spontaneously breathing dogs.
OBJECTIVE
To evaluate the respiratory effects occurring during administration of sevoflurane or isoflurane to the upper airway in dogs.


METHODS
A prospective, randomized study.


METHODS
Twelve healthy adult beagles (6 males, 6 females).


METHODS
At least 2 weeks after undergoing permanent tracheostomy, dogs were premedicated with acepromazine-buprenorphine, and anesthesia was induced with thiopental and maintained with alpha-chloralose. The upper airway was functionally isolated so that the inhalant could be administered to the upper airway while dogs were breathing 100% O2 via the tracheostomy. Respiratory reflexes in response to the administration of sevoflurane or isoflurane at concentrations of 1.2, 1.8, and 2.4 times the minimal alveolar concentration (MAC) (administered in 100% O2 at a flow rate of 5 L/min) were recorded. Reflexes in response to administration of each anesthetic were also recorded following upper-airway administration of lidocaine.


RESULTS
Respiratory reflexes elicited by upper-airway administration of each anesthetic were characterized by a dose-dependent increase in expiration time, with a resultant decrease in respiratory minute ventilation and increase in end-tidal PCO2. The magnitude of these responses was greater with isoflurane than with sevoflurane at 1.8 and 2.4 MAC. These reflexes were abolished after lidocaine nebulization into the upper airway.


CONCLUSIONS
Isoflurane induces greater reflex inhibition of breathing than does sevoflurane when the anesthetic is inhaled into the upper airway at concentrations used for mask induction.
Mutoh
T
T
Laboratory of Veterinary Surgery, Graduate School of Agricultural and Life Sciences, The University of Tokyo, Japan.
Kanamaru
A
A
Tsubone
H
H
Nishimura
R
R
Sasaki
N
N
D018685:Anesthetics, Inhalation / Q000494:pharmacology*; D000818:Animals; D004285:Dogs / Q000502:physiology*; D004305:Dose-Response Relationship, Drug; D005260:Female; D007530:Isoflurane / Q000494:pharmacology*; D008297:Male; D008738:Methyl Ethers / Q000494:pharmacology*; D011446:Prospective Studies; D011897:Random Allocation; D012018:Reflex / Q000187:drug effects*; D012132:Respiratory Muscles / Q000187:drug effects*; D000077149:Sevoflurane
D018685:Anesthetics, Inhalation; D008738:Methyl Ethers; D000077149:Sevoflurane; D007530:Isoflurane