A New Method of Monitoring the Effect of Muscle Relaxants on Laryngeal Muscles Using Surface Laryngeal Electromyography

Abstract

n recent years, attempts have been made to find anondepolarizing muscle relaxant with a shortenough onset to replace succinylcholine as the mus-cle relaxant of choice for rapid sequence induction.The onset time of new muscle relaxants has beenmeasured mainly by mechanomyographically, elec-tromyographically or, more recently, by acceleromyo-graphically obtained responses of muscular sites, e.g.,the adductor pollicis muscle. They are easily accessi-ble, but not the site of interest for sufficient musclerelaxation at intubation: the larynx.Furthermore, the pharmacodynamic data obtainedby using different forms of neuromuscular monitoringcan vary quite substantially (1,2). Thus, when compar-ing the onset time or the clinical duration of a specificneuromuscular blockade at various sites, care must betaken to use similar forms of neuromuscular monitor-ing, e.g., electromyography (EMG) at all sites.EMG has long been a tool to measure responses oflaryngeal muscles, especially in surgery of the thyroidgland, where damage to the recurrent laryngeal nerveis a potential hazard. Various electrodes have beenused to obtain evoked electromyographic responses,such as hooked-wire electrodes endoscopically intro-duced into the adducting laryngeal muscles (cricothy-roid posterior) (3) or, more recently, a less invasive,easily attachable laryngeal electrode (4). This form ofmonitoring proved reliable in obtaining reproducableelectromyographic signals of the larynx.The purpose of this study was to develop a methodthat uses the attachable laryngeal surface electrode toobtain electromyographic responses of the adductinglaryngeal muscles, evoked by transcutaneous stimula-tion of the recurrent laryngeal nerve, and measure theonset of the neuromuscular blockade of rocuroniumand mivacurium; this was compared with the onset atthe adductor pollicis muscle using EMG via surfaceskin electrodes.