RESUMO
BACKGROUND: Although topically applied laryngeal lidocaine is known to be effective in preventing the cardiovascular events associated with endotracheal intubation, it is still debated whether the mechanism of action of topically applied laryngeal lidocaine is via increased plasma concentration of lidocaine or via topically induced superficial anesthesia. The purpose of the present study is to observe vocal cord responses to stimulation and to find out whether topically induced superficial anesthesia with 10% lidocaine spray is effective under propofol anesthesia. METHODS: Twenty-four patients scheduled for operation on the upper or lower extremities were randomly allocated to two groups: (1) twelve patients who did not receive 10% lidocaine spray before the insertion of a laryngeal mask airway (LMA), (2) twelve patients who received 10% lidocaine spray before the insertion of LMA. The vocal cords of each patient were stimulated by the spraying of 0.2 ml distilled water or directly by bronchoscope tip, and the evoked responses were assessed by analyzing the hemodynamic and respiratory variables and vocal cord movement. The vocal cord movements elicited by the laryngeal stimulation were classified into four grades. RESULTS: There was a significant difference between the groups regarding vocal cord movement (P < 0.05). There were no differences between the groups regarding hemodynamic and respiratory variables. CONCLUSIONS: The result indicates that there is a topical anesthetic effect on the vocal cords by 10% lidocaine spray on the larynx.