Background: Laryngospasm frequently occurs during the administration of anesthesia and deep sedation to pediatric patients. Because of the high incidence and the severity of potential complications caused by inadequate ventilation in children, knowledge about laryngeal reflex responses is especially required in this population. Although of obvious clinical relevance, reflexes that involve the function of the larynx in anesthetized patients is a largely unexplored area, perhaps because it is difficult to assess laryngeal function in vivo. However, using a technique that combines assessment of laryngeal behavior obtained by endoscopic video images and simultaneous measurements of airflow permits a qualitative and quantitative assessment of reflex responses to evoked controlled stimulation of the larynx. Applying this technique, the effects of anesthetic agents administered in various doses and combinations can be evaluated. Prevention is the best “therapy” for laryngospasm. Various strategies have been promoted in the literature; however, their effectiveness on modifying laryngeal reflex responses has not been analyzed in a systematic manner. Working hypothesis: The therapeutic strategies tested in this project effectively reduce the incidence of laryngospasm in response to evoked laryngeal stimulation. Specific aims: We will investigate 1) the effects of varying concentrations of sevoflurane, 2) the administration of lidocaine, and 3) fentanyl in anesthetized healthy preschool-aged children undergoing elective surgery on the incidence of laryngeal (e.g., laryngospasm) and respiratory reflex responses to controlled stimulation of the larynx. We will also examine the modifying effect of remifentanil in patients with an upper airway infection anesthetized with propofol. Methods: An established technique of laryngeal stimulation will be used. With a laryngeal mask airway in situ, the mucosa of the larynx around the vocal cords is sprayed with a defined small amount of distilled water via a catheter inserted through the suction channel of a fiber bronchoscope. The response to this stimulation is assessed by analyzing the video images with the signal ventilatory airflow to determine the incidences of defined airway reflexes by a reviewer blinded to the patient’s treatment. Expected value of the proposed project: This project has implications for the clinical management of pediatric patients with and without upper respiratory infection at risk for laryngospasm. It will also provide novel quantitative and qualitative information on upper airway reflex responses in children anesthetized with drugs that are most commonly used in contemporary anesthesia practice.