Individualized Supramaximal Stimulation Current During Continuous Neuromonitoring in Thyroid Surgery

Overview

Continuous intraoperative neuromonitoring (C-IONM) is increasingly used during thyroid surgery to detect early changes in recurrent laryngeal nerve function and reduce the risk of nerve injury. Current clinical practice recommends the use of fixed supramaximal stimulation currents; however, these recommendations are based on limited experimental evidence and may not account for individual variability between patients. This retrospective observational cohort study aims to determine patient-specific supramaximal stimulation currents (SSC) during C-IONM and to evaluate whether individualized stimulation provides monitoring quality comparable to conventional fixed-current stimulation while potentially reducing unnecessary stimulation intensity. The study also investigates factors influencing electromyographic response amplitudes during surgery and assesses the safety of individualized stimulation parameters.

Continuous intraoperative neuromonitoring (C-IONM) of the vagus nerve is increasingly used during thyroid surgery to facilitate early recognition of progressive recurrent laryngeal nerve (RLN) injury. Current international recommendations advocate the use of a fixed supramaximal stimulation current, typically between 1 and 2 mA. However, these recommendations are based on limited experimental and clinical evidence and do not account for potential interindividual differences in nerve excitability. The aim of this retrospective observational cohort study was to characterize the distribution of patient-specific supramaximal stimulation current (SSC) during C-IONM and to determine whether individualized SSC selection maintains monitoring performance compared with conventional fixed-current stimulation. Secondary objectives included evaluation of factors affecting electromyographic response amplitude and assessment of the safety of individualized stimulation. The study included consecutive adult patients undergoing thyroid surgery with C-IONM at a tertiary endocrine surgery center. Patients operated before implementation of an updated stimulation protocol constituted the control cohort and underwent monitoring using a fixed stimulation current of 1.5 mA. After protocol implementation, SSC was individually determined for each vagus nerve at the beginning of the procedure by gradually increasing stimulation current until no further increase in electromyographic response amplitude was observed. Continuous monitoring was subsequently performed using the individualized SSC. Neuromonitoring recordings were exported from the monitoring system, anonymized, and analyzed using dedicated Python software developed for this study. The software identified individual stimulation events, excluded incomplete or technically inadequate recordings, and extracted stimulation current and electromyographic amplitude for quantitative analysis. More than one million individual stimulation responses were evaluated. The primary objective was to determine the distribution of individualized SSC values and compare monitoring performance between individualized and fixed-current stimulation. Secondary analyses evaluated changes in response amplitude during surgery, variability between right and left vagus nerves, factors influencing amplitude, and the occurrence of monitoring-related adverse events. Statistical analyses included descriptive statistics, non-parametric comparisons, regression analysis, and multivariable modeling to identify independent predictors of electromyographic response amplitude.