Individualized Supramaximal Stimulation Current During Continuous Neuromonitoring in Thyroid Surgery (CIONM-SSC)

Patient-Specific Determination of Supramaximal Stimulation Current During Continuous Intraoperative Neuromonitoring of the Recurrent Laryngeal Nerve in Thyroid Surgery

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.

Study Overview

• Status: Completed
• Conditions: Thyroid Disease
• Intervention / Treatment: Procedure: Continuous intraoperative neuromonitoring with fixed stimulation current; Procedure: Continuous intraoperative neuromonitoring with individualized stimulation current

Detailed Description

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.

• Study Type: Observational
• Enrollment (Actual): 623

Contacts and Locations

Study Locations

• Poland
  • Gdansk, Poland, 80-135
    • The University Clinical Centre in Gdansk

Participation Criteria

Eligibility Criteria

• Ages Eligible for Study: Adult; Older Adult
• Accepts Healthy Volunteers: No

• Sampling Method: Non-Probability Sample

Study Population

The study population consisted of consecutive adult patients who underwent thyroid surgery with continuous intraoperative neuromonitoring (C-IONM) at the Department of Endocrine and General Surgery, Medical University of Gdańsk, Poland, between June 2020 and July 2024. Patients were identified retrospectively from the institutional thyroid surgery database and neuromonitoring records. Clinical and operative data were collected as part of routine clinical care. Participants were included consecutively during the study period.

Description

Inclusion Criteria:

• Adults aged 18 years or older.
• Patients undergoing thyroid surgery with continuous intraoperative neuromonitoring (C-IONM) of the vagus nerve.
• Availability of complete intraoperative neuromonitoring recordings suitable for analysis.
• Availability of complete clinical and operative data.

Exclusion Criteria:

• Age younger than 18 years.
• Incomplete or technically inadequate neuromonitoring recordings.
• Loss of signal or recurrent laryngeal nerve palsy preventing reliable amplitude analysis.
• Missing or incomplete clinical data required for the study.

Study Plan

How is the study designed?

Number of groups / cohorts

2

Cohorts and Interventions

Group / Cohort	Intervention / Treatment
Control cohort; Patients who underwent thyroid surgery with continuous intraoperative neuromonitoring (C-IONM) using a fixed vagus nerve stimulation current of 1.5 mA throughout the procedure. These patients were operated before implementation of the individualized stimulation protocol.	Procedure: Continuous intraoperative neuromonitoring with fixed stimulation current; Continuous vagus nerve stimulation during thyroid surgery using a fixed supramaximal stimulation current of 1.5 mA.
Individualized SSC cohort; Patients who underwent thyroid surgery with continuous intraoperative neuromonitoring (C-IONM) using an individually determined supramaximal stimulation current (SSC). SSC was established at the beginning of the procedure for each vagus nerve and subsequently used throughout continuous monitoring.	Procedure: Continuous intraoperative neuromonitoring with individualized stimulation current; Continuous vagus nerve stimulation during thyroid surgery using an individually determined supramaximal stimulation current established at the beginning of the procedure.

What is the study measuring?

Primary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Patient-specific supramaximal stimulation current	Distribution of the individualized supramaximal stimulation current required to achieve maximal electromyographic response during continuous intraoperative neuromonitoring of the vagus nerve.	During surgery
Patient-specific supramaximal stimulation current (SSC)	Distribution of the individualized supramaximal stimulation current (SSC) required to achieve maximal electromyographic response during continuous intraoperative neuromonitoring of the vagus nerve.	During surgery (at the beginning of continuous intraoperative neuromonitoring)

Secondary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Electromyographic response amplitude	Comparison of electromyographic response amplitudes between individualized and fixed stimulation current protocols during continuous intraoperative neuromonitoring.	During surgery

Collaborators and Investigators

• Sponsor: Medical University of Gdansk

Study record dates

Study Major Dates

• Study Start (Actual): June 18, 2020
• Primary Completion (Actual): July 25, 2024
• Study Completion (Actual): February 11, 2025

Study Registration Dates

• First Submitted: July 13, 2026
• First Submitted That Met QC Criteria: July 13, 2026
• First Posted (Actual): July 17, 2026

Study Record Updates

• Last Update Posted (Actual): July 17, 2026
• Last Update Submitted That Met QC Criteria: July 13, 2026
• Last Verified: July 1, 2026

More Information

Terms related to this study

• Keywords: Thyroidectomy; Thyroid surgery; Recurrent laryngeal nerve; Continuous intraoperative neuromonitoring; Supramaximal stimulation current
• Additional Relevant MeSH Terms: Endocrine System Diseases; Thyroid Diseases
• Other Study ID Numbers: KB/202/2025

Plan for Individual participant data (IPD)

• Plan to Share Individual Participant Data (IPD)?: YES
• IPD Plan Description: De-identified individual participant data underlying the reported results will be available upon reasonable request to the corresponding author, subject to approval from the hospital administration and applicable ethical and institutional regulations.

Drug and device information, study documents

• Studies a U.S. FDA-regulated drug product: No
• Studies a U.S. FDA-regulated device product: No