Abstract: 【Abstract】 Objective To investigate the optimal depth of endotracheal tube （ETT） which is closely related with the effectiveness of intraoperative neuromonitoring （IONM） for recurrent laryngeal nerve（RLN）during thyroid surgery in order to guarantee the accuracy of IONM for LRN especially when visible intubation devices are not available. Methods This clinical study involved two phases. In phase 1 study, 133 patients whose heights ranging from 145 cm to 180 cm were enrolled. Height and body weight were recorded；video intubation devices were utilized for intubation and observation；while the midline of the probe reaching the vocal cords opening level, the depth of ETT（Optimal depth） was also recorded and corresponding mean values for male and female were calculated separately. In phase 2 study, 35 patients with same inclusion criteria as in phase 1 study were intubated without any visible intubation devices and the ETTs were fixed in male or female to the depth according to the mean values of optimal depth obtained from phase 1 study, respectively；the success rate of electromyography （EMG） for laryngeal recurrent nerve monitoring was examined and compared to that in phase 1 study. Results Based on this certain study sample, the optimal depth of ETT in IONM for RLN shows positive correlation with patient height, the mean values are 21.7 cm and 19.7 cm in male and female, respectively. Fixing the ETT to the mean value of optimal depth either in male or in female can provide similar success rate of IONM for RLN when compared to direct localization with visible intubation devices. Conclusion In certain population，the mean value of optimal depth of ETT in IONM for RLN is 21.7 cm for male while 19.7 cm for female，one may fix the ETT to this mean value to achieve effective and satisfied IONM without the help of visible intubation devices.

Key words: EMG, IONM, Video laryngoscope, Endotracheal tube, RLN, Fiberscope

摘要： 【摘要】目的研究在全麻下接受甲状腺手术的特定人群中喉返神经监测时最适气管导管留置深度，以提供简便易行、成功率高的气管导管定位方案。方法168名身高145～180 cm患者入选本研究。其中133名纳入一阶段，采用可视喉镜暴露后行气管插管，记录当记录电极中点连线位于声带平面时气管导管的留置深度（可视喉镜定位导管深度）并分别计算其在男、女性的均数（最适深度）；余35名入选二阶段，采用普通喉镜暴露后分别基于男、女性“最适深度”置入气管导管，并记录导管到位率。结果“可视喉镜定位导管深度”与患者身高呈正相关；“最适深度”在本研究群体男、女性分别为21.7 cm和19.7 cm；基于“最适深度”进行气管导管定位与使用可视设备进行定位相比较，二种方法“导管到位率”无统计学差异。结论在全麻下接受甲状腺手术的特定人群中，当气管导管分别置入21.7 cm（男性）、19.7 cm（女性）时可成功进行术中喉返神经监测；没有可视设备时可基于推荐的“最适深度”进行气管导管定位，提高喉返神经监测成功率。

关键词: 喉返神经, 肌电图, 纤支镜, 术中神经监测, 气管内导管, 可视喉镜