-Original-

Anesthetic Considerations of Intraoperative Neuromonitoring in Thyroidectomy

Dai Namizato¹, Masae Iwasaki¹, Masashi Ishikawa¹, Ryuta Nagaoka², Yuki Genda¹, Hiroaki Kishikawa¹, Iwao Sugitani² and Atsuhiro Sakamoto¹

¹Department of Anesthesiology and Pain Medicine, Graduate School of Medicine, Nippon Medical School
²Department of Endocrine Surgery, Graduate School of Medicine, Nippon Medical School

Background: Intraoperative neuromonitoring (IONM) might reduce the incidence of injury to the recurrent laryngeal nerve (RLN) during thyroidectomy. Although dislocation of endotracheal tube surface electrodes can lead to false-positive IONM results (loss of signal), the risk factors for dislocation and the effects of muscle relaxants are unclear. Therefore, to identify factors that affect IONM results, we examined the frequency and risk factors for tube dislocation after cervical extension before surgery, the effect of sugammadex administration, and the correlation between IONM results and postoperative RLN palsy.
Methods: Thirty-nine patients scheduled for thyroidectomy from October 2016 to April 2017 were enrolled. All patients underwent standard IONM and pre- and postoperative laryngoscopy. Differences in patient characteristics in the tube dislocation group and non-dislocation group, and differences in amplitude during vagal stimulation before and after sugammadex administration, were assessed by the Mann-Whitney test or Fisher's exact test.
Results: Tube dislocation occurred in 27 patients (69%). Sterno-cricoid distance was significantly shorter in the dislocation group (n=27) than in the non-dislocation group (n=12) (43.88 [32.2-55.91] mm vs 49.46 [40.66-55.91] mm, respectively; p=0.048). Without sugammadex, amplitude during vagal stimulation was sufficient for monitoring. Nine patients had new-onset RLN palsy, which was transient in all patients. The sensitivity of IONM was 100%, the positive predictive value was 60%, and the negative predictive value was 100%.
Conclusions: The present findings suggest that anesthesiologists should use video laryngoscopy to correct tube dislocation and that a rocuronium dose of 0.6 mg/kg, without sugammadex, is adequate for IONM.

J Nippon Med Sch 2019; 86: 263-268

Keywords
intraoperative nerve monitoring (IONM), thyroid surgery, sevoflurane, neuromuscular blockage, video laryngoscope

Correspondence to
Dai Namizato, MD, Department of Anesthesiology and Pain Medicine, Graduate School of Medicine, Nippon Medical School, 1-1-5 Sendagi, Bunkyo-ku, Tokyo 113-8603, Japan
d-nami@nms.ac.jp

Received, February 15, 2019
Accepted, April 17, 2019