Dose Response of Topical Anesthetic on Laryngeal Neuromuscular Electrical Transmission

Abstract

Our purpose was to determine the effect of a dose response to decreasing concentrations of topical anesthetic upon laryngeal neuromuscular electrical transmission. We performed a prospective study at a neurolaryngology referral center. Forty-three patients were divided into 5 groups. Each patient underwent laryngeal electromyography (EMG) of a thyroarytenoid muscle before and 60 seconds after topical laryngotracheal lidocaine hydrochloride, normal saline solution, or nothing was applied. The pretreatment and posttreatment measurements were recorded with the same indwelling EMG electrode. Group 1 (n = 12) received 4% lidocaine, group 2 (n = 9) received 2% lidocaine, and group 3 (n = 8) received 1% lidocaine. Group 4 (n = 5) received topical normal saline solution instead of lidocaine. A fifth group (group 5, n = 9) had 2 EMG recordings measured, each separated by 60 seconds, without topical anesthetic. Groups 1, 2, and 3 showed significant decreases in the maximum peak-to-peak amplitude of the EMG recording (48.5%, 49.7%, 44.7%, respectively). Groups 4 and 5 failed to show a significant change in peak-to-peak amplitude after 60 seconds. There was no dose response change in EMG with decreasing lidocaine concentrations. All concentrations of lidocaine administered in this study decreased the laryngeal neuromuscular electrical transmission as measured by laryngeal EMG. This group of patients did not exhibit any dose response to anesthetic concentration. This finding is clinically significant for both diagnostic and therapeutic uses of laryngeal EMG preceded by administration of topical anesthetic.