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  • Author or Editor: Arata Kanamaru x
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Abstract

Objective—To characterize and determine the sensory innervation of respiratory reflexes elicited by nasal administration of halothane to dogs.

Animals—10 healthy Beagles.

Procedure—Dogs underwent permanent tracheostomy and, 2 to 3 weeks later, were anesthetized with thiopental and α-chloralose administered IV. The nasal passages were functionally isolated so that halothane could be administered to the nasal passages while dogs were breathing 100% O2 via the tracheostomy. Respiratory reflexes in response to administration of halothane at concentrations of 1.25, 1.75, and 2.5 times the minimum alveolar concentration (MAC), and 5% (administered in 100% O2 at a flow rate of 5 L/min) were recorded. Reflexes in response to administration of 5% halothane were also recorded following transection of the infraorbital nerve, transection of the caudal nasal nerve, and nasal administration of lidocaine.

Results—Nasal administration of halothane induced an inhibition of breathing characterized by a dosedependent increase in expiratory time and a resultant decrease in expired volume per unit time. Effects were noticeable immediately after the onset of halothane administration and lasted until its cessation. Reflex responses to halothane administration were attenuated by transection of the caudal nasal nerve and by nasal administration of lidocaine, but transection of the infraorbital nerve had no effect.

Conclusions and Clinical Relevance—Nasal administration of halothane at concentrations generally used for mask induction of anesthesia induces reflex inhibition of breathing. Afferent fibers in the caudal nasal nerve appear to play an important role in the reflex inhibition of breathing induced by halothane administration. (Am J Vet Res 2000;61:260–267)

Full access
in American Journal of Veterinary Research

Abstract

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 expired volume per unit of time. All anesthetics had a significant effect, but for Sevo, the changes were smaller in magnitude. Responses to administration of each anesthetic were attenuated by administration of lidocaine to the nasal passages.

Conclusions and Clinical Relevance—Nasal administration of Sevo at concentrations generally used for mask induction of anesthesia induced milder reflex inhibition of breathing, presumably via afferent neurons in the nasal passages, than that of Iso or Hal. Respiratory reflexes attributable to stimulation of the nasal passages may contribute to speed of onset and could promote a smoother induction with Sevo, compared with Iso or Hal. (Am J Vet Res 2001;62:311–319)

Full access
in American Journal of Veterinary Research