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 administra tion of sevoflurane (Sevo), isoflurane (Iso), or halothane (Hal) in anesthe tized 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 alpha -chloralose. Nasal passages were isolated such that inhalant anesthetics co uld be administered to the nasal passages while the dogs were breathing 100 % O-2 via the tracheostomy. Respiratory reflexes in response to administrat ion of each anesthetic at 1.2 and 2.4 times the minimum alveolar concentrat ion (MAC) and the full vaporizer setting (5%) were recorded. Reflexes in re sponse to administration of 5% of each anesthetic also were recorded follow ing administration of lidocaine to the nasal passages. Results-Nasal administration of Sevo, Iso, and Hal induced an immediate ven tilatory response characterized by a dose-dependent increase in expiratory time and a resulting decrease in expired volume per unit of time. All anest hetics had a significant effect, but for Sevo, the changes were smaller in magnitude. Responses to administration of each anesthetic were attenuated b y administration of lidocaine to the nasal passages. Conclusions and Clinical Relevance-Nasal administration of Sevo at concentr ations generally used for mask induction of anesthesia induced milder refle x inhibition of breathing, presumably via afferent neurons in the nasal pas sages, than that of Iso or Hal. Respiratory reflexes attributable to stimul ation of the nasal passages may contribute to speed of onset and could prom ote a smoother induction with Sevo, compared with Iso or Hal.