Respiratory reflexes in spontaneously breathing anesthetized dogs in response to nasal administration of sevoflurane, isoflurane, or halothane

Objective—To characterize respiratory reflexes elicited by nasal administration of sevoflurane (Sevo), isoflurane (Iso), or halothane (Hal) in anesthetized dogs. Animals—8 healthy Beagles. Procedure—A permanent tracheostomy was created in each dog. Two to 3 weeks later, dogs were anesthetized by IV administration of thiopental and α-chloralose. Nasal passages were isolated such that inhalant anesthetics could be administered to the nasal passages while the dogs were breathing 100% O2 via the tracheostomy. Respiratory reflexes in response to administration of each anesthetic at 1.2 and 2.4 times the minimum alveolar concentration (MAC) and the full vaporizer setting (5%) were recorded. Reflexes in response to administration of 5% of each anesthetic also were recorded following administration of lidocaine to the nasal passages. Results—Nasal administration of Sevo, Iso, and Hal induced an immediate ventilatory response characterized by a dose-dependent increase in expiratory time and a resulting decrease in...