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Hypersensitivity of Laryngeal C-Fibers Induced by Volatile Anesthetics in Young Guinea Pigs

Departments of Veterinary Surgery and Comparative Pathophysiology, Graduate School of Agricultural and Life Sciences, The University of Tokyo, Tokyo; and Division of Molecular Brain Science, Department of Brain Sciences, Kobe University Graduate School of Medicine, Kobe, Japan

Correspondence and requests for reprints should be addressed to Hirokazu Tsubone, D.V.M., Ph.D., Department of Comparative Pathophysiology, Graduate School of Agricultural and Life Sciences, The University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo 113-8657, Japan. E-mail: aahiro{at}mail.ecc.u-tokyo.ac.jp

Inhalation induction of anesthesia with a single volatile anesthetic is commonly used in children but is sometimes associated with increased cough, secretion, and airway obstruction, which may result in part from stimulation of laryngeal C-fibers. We examined the effects of two popular volatile anesthetics, halothane and sevoflurane, on laryngeal C-fiber responsiveness in urethane-anesthetized guinea pigs (from age 4–5 weeks). After administration of halothane or sevoflurane to the functionally isolated upper airway, laryngeal C-fiber afferents recorded from the internal branch of the superior laryngeal nerve and identified by a conduction velocity of less than 2.0 m/second were tested for responsiveness to chemical and mechanical stimuli. Halothane doubled C-fiber responsiveness to capsaicin injected into the left atrium or nebulized to the larynx and to laryngeal hyperinflation, compared with sevoflurane, but it had no effect on baseline activity. The data indicate that, compared with sevoflurane, halothane more markedly enhances laryngeal C-fiber sensitivity to chemical and mechanical stimuli in young guinea pigs, which would explain the greater number of respiratory-related complications in children during induction of anesthesia with this agent.

Key Words: airway irritation • laryngeal C-fibers • volatile anesthetics

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