V/R Ratio Using Intra-Operative Nerve Monitoring During Esophageucomy Is a Possible Predictive Index to Predict Left Vocal Code Paralysis

Background Intraoperative nerve monitoring (IONM) during esophageal cancer surgery can help to identify and preserve the recurrent laryngeal nerve (RLN). During cervical lymph node dissection, a vagus nerve stimulation with an amplitude of less than 100 μV is considered a loss of signal, but the correlation with postoperative vocal cord paralysis (VCP) is not sufficient especially on the left side. To devise a useful parameter for prediction of left VCP, we measured the electromyographic (EMG) amplitude of the left RLN and vagus nerve (VN) using intermittent IONM. Methods We studied 39 consecutive patients who underwent esophagectomy with lymph node dissection around the left RLN. After lymph node dissection, the left RLN and left VN were stimulated, and the. EMG amplitude was measured using IONM. The VN/RLN ratio (V/R ratio) was calculated, and the presence of left VCP, diagnosed by laryngoscopy on the first postoperative day, was compared among the patients. Results Ten of the 35 patients had left VCP. In the VCP and non-VCP groups, the left VN amplitude was 190.0(0–1111) μV and 560.0(120–1200) μV, and the VR ratio was 0.26(0–0.75) and 0.71(0.24–1.0). Receiver operating characteristic curve analysis using the left VN amplitude and V/R ratio showed an (AUC) of 0.79 with a cutoff of 354 μV, and an AUC 0.90 with a cutoff of 0.50 (P < 0.03). When left VN amplitudes of <100 μV, <354 μV, and a V/R ratio of ≤0.50 were defined as left VCP, the accuracy was 82.0%, 74.4%, and 89.7%, respectively. Conclusion Using intermittent IONM, the V/R ratio with a cutoff value of 0.50 is a more useful parameter for prediction of VCP after esophagectomy than EMG amplitude during VN stimulation.