Respiratory variation predicts optimal endotracheal tube placement for intra-operative nerve monitoring in thyroid and parathyroid surgery.

Background: Intra-operative nerve monitoring (IONM) of the recurrent laryngeal nerve (RLN) during thyroid and parathyroid surgery is thought to aid in identification and dissection of the RLN. While utilization of IONM is increasing, one area of variability in its application is the assessment of adequate endotracheal tube electrode placement for IONM during the case. The main objective of this study is to assess the overall success of utilizing respiratory variation to confirm proper endotracheal tube placement for RLN monitoring.
Methods: A prospective study of RLN monitoring during thyroid and parathyroid surgery at an academic referral center.
Results: Fifty-five cases were included. Fifty (91 %) achieved optimal respiratory variation during endotracheal tube position. Five (9 %) required repeat laryngoscopy to confirm correct endotracheal tube placement following patient positioning. For the respiratory variation group, average amplitude achieved during initial vagus, maximum vagus, initial RLN, and maximal RLN was 700 (± 474) mA, 921 (± 616) mA, 887 (± 584) mA, and 1330 (± 843) mA during evoked stimulation, respectively. For the repeat laryngoscopy group, average amplitude achieved during initial vagus, maximum vagus, initial RLN, and maximal RLN evoked stimulation was 591 (± 364) mA, 959 (± 306) mA, 771 (± 424) mA, and 1462 (± 855) mA during evoked stimulation, respectively. There was no statistical difference between the two groups for average initial vagus amplitude (p = 0.62), average maximum vagus amplitude (p = 0.89), average initial RLN amplitude (p = 0.67), or average maximum RLN amplitude (p = 0.74).
Conclusion: The findings of this study support the International Neural Monitoring Study Group recommendation that confirmation of endotracheal tube electrode placement be performed either by confirmation of adequate respiratory variation or by repeat direct laryngoscopy.