Surface vs intramuscular laryngeal electromyography

Purpose: To compare surface and intramuscular laryngeal electromyography (E MG) with adductor pollicis muscle EMG after 0.1 mg.kg(-1) cisatracunium. Methods: This prospective study included ten patients undergoing surgery wi th risk of damage to the recurrent laryngeal nerve (RLN), The tracheas were intubated after fentanyl/propoiol without the aid of muscle relaxation. A surface laryngeal electrode was attached to the tube and placed amidst the vocal cords; two straight needles were inserted endoscopically into the lek lateral cricoarytenoid muscle. Single twitch stimulation of the left RLN ( 0.1 Hz) was performed transcutaneously; skin EMG of the left adductor polli cis muscle was performed at 0.1 Hz. After supramaximal stimulation for 10 m in, 0.1 mg.kg(-1) cisatracurium was injected. Lag, onset time and peak effe ct were measured and compared. Results: Good correlation (r = 0.9, 0.8, p < 0.005) and good comparability of the two methods of laryngeal EMG (mean difference and limits of agreemen t: 0 +/- 28 sec for lag time, -2 +/- 84 sec for onset time) was shown, The mean surface laryngeal lag and onset times were 67 +/- 22 sec and 198 +/- 7 2 sec, compared with the adductor pollicis muscle (98 +/- 30 sec and 242 +/ - 59 sec) at P < 0.01. Peak effects at larynx (92 +/- 9%) and adductor poll icis muscle (95 +/- 3%) were similar Conclusion: Surface laryngeal EMG is comparable to intramuscular laryngeal EMG to determine degree and onset of the neuromuscular blockade, Increasing muscle relaxation does not cause the surface electrode to lose contact wit h the vocal cords and therefore underestimate onset time and peak effect.