Failed Vocalis Muscle Monitoring During Thyroid Surgery Resulting From Residual Muscle Relaxation

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We were not surprised by Ruebsam and Hoenemann’s reported case of a failure of recurrent laryngeal nerve (RLN) monitoring related to prolonged action of rocuronium.1 In our practice, we have noticed several similar cases related to prolonged action of neuromuscular blocking drugs at the vocalis muscle, in 1 case despite a train of 4 count of 4 at the adductor pollicis nearly an hour after administration of atracurium.
These observations led us to undertake a randomized controlled trial of routine administration of reversal agents at 30 minutes after induction of anesthesia.2 In this study, half of the participants (9 of 18) receiving placebo had inadequate neuromuscular function for effective RLN identification at a mean of 44.6 minutes after atracurium administration. We chose atracurium for our study because of a lesser variability of duration compared with rocuronium.3 The dose was a standard intubating dose of 0.4 mg/kg IV, equating to twice the ED95, compared with slightly less than this for rocuronium (0.44 mg/kg IV, 1.5 times ED95) in Ruebsam and Hoenemann’s case.1 All but one of the patients randomly assigned to receive routine reversal (neostigmine 2.5 mg IV and glycopyrrolate 0.4 mg IV) at 30 minutes after administration of atracurium were found to have adequate conditions for RLN identification (P = .002). We therefore suggest that all patients given nondepolarizing muscle relaxants be routinely reversed at 30 minutes after induction if RLN stimulation is to be attempted. This may be performed using neostigmine or sugammadex depending on the relaxant used and availability of sugammadex.
We also suggest modification of the algorithm presented by Ruebsam and Hoenemann1 to include assessment of a “laryngeal twitch.” This involves palpation of the postcricoid region of the larynx by the surgeon during ipsilateral RLN stimulation to determine whether posterior cricoarytenoid muscle contraction is occurring.4 The addition of palpation of contraction to electromyography assists the distinction between a functioning nerve with a misplaced or defective tube and a nerve that is not functioning.
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