DIFFERENCES IN RESPIRATORY REFLEX RESPONSES FROM THE LARYNX, TRACHEA AND BRONCHI IN ANESTHETIZED FEMALE SUBJECTS

Background: Animal studies show that airway receptors responsible for eliciting respiratory protective reflexes are not uniformly distribute d in the airways. Based on this information, it is possible that the p rotective reflex responses to airway irritation in humans may vary, de pending on the site of stimulation. The purpose of this study is to ex amine whether the protective reflex responses evoked from the larynx a re different from those evoked from the lower airways and to see how c hange in depth of anesthesia modifies the protective reflex responses evoked from individual sites. Methods: The airway mucosa of the larynx , tracheal carina, and bronchi were stimulated by injection of distill ed water (0.5 ml) at two different depths of sevoflurane anesthesia (1 .2 and 1.8 MAC) in 11 female subjects breathing spontaneously through the laryngeal mask airway. The respiratory responses were monitored by measuring ventilatory now and airway pressure. Results: At 1.2 MAC of sevoflurane anesthesia, both laryngeal and tracheal stimulation cause d protective responses, such as forceful expiratory efforts, apnea, an d spasmodic panting, whereas bronchial stimulation caused little or no such responses. There was no significant difference in the incidence of different types of reflex responses between the larynx and the trac hea. At 1.8 MAC of sevoflurane, the nature of the elicited responses w as very similar to that observed at 1.2 MAC of sevoflurane, showing li ttle dose-dependence of anesthetic effect. Conclusions: The respirator y reflex responses evoked by injection of water vary, depending on the site of stimulation. The incidence of various reflex responses was no t affected by the changing depth of anesthesia. The sensitivity to air way irritation seems to be greater at the larynx and trachea than at t he more peripheral airways.