Submitted:
15 December 2025
Posted:
17 December 2025
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Abstract
Background/Objectives: Intraoperative neuromonitoring (IONM) has improved safety in thyroid and parathyroid surgery, yet intermittent IONM (I-IONM) may miss traction injuries developing between stimulations. We evaluated the feasibility and clinical utility of a trend-based intermittent monitoring mode (NIM Vital NerveTrend®) that records closely spaced stimulations and plots amplitude and latency over time.
Methods: We conducted a prospective observational study at a high-volume endocrine surgery unit (January–September 2025). Forty-four consecutive patients undergoing thyroidectomy and/or parathyroidectomy with NerveTrend® were enrolled. EMG responses were categorized as Green (amplitude >50% of baseline and latency < 110%), Yellow (amplitude < 50% or latency >110%), Red (amplitude < 50% and latency >110%), and Loss of Signal (LOS: amplitude < 100 µV). Primary outcomes included LOS prevalence and the association between stimulation frequency and the appearance of Yellow trends. Ethical approval: AVEN protocol 486/2024/OSS/AOUPR; informed consent obtained.
Results: Of 71 nerves at risk (NAR), 55 had a valid baseline and were analyzed; LOS occurred in 3/55 NAR (5.5%). The mean number of stimulations per NAR was 4.5 (range 1–9). Cases with both Green and Yellow points had a significantly higher mean number of stimulations than cases with only Green points (5.1 vs. 3.8; Student's t-test p = 0.0059). One Red measurement occurred in a case that progressed to LOS.
Conclusions: NerveTrend® provided near real-time functional feedback while maintaining the simplicity of I-IONM. Increased stimulation frequency was associated with early Yellow trend alerts, potentially signaling traction stress and enabling timely surgical adjustments. Larger multicenter studies and protocol standardization are warranted.
Keywords:
thyroidectomy
; parathyroidectomy
; intraoperative neuromonitoring
; NIM Vital
; NerveTrend
; recurrent laryngeal nerve
; EMG trend
; loss of signal
1. Introduction
Intraoperative neuromonitoring (IONM) has revolutionized thyroid surgery by enhancing identification and functional assessment of the recurrent laryngeal nerve (RLN). Intermittent IONM (I-IONM) remains widely used but may fail to capture progressive traction injuries occurring between stimulations. Continuous IONM[1] (C-IONM) provides real-time feedback but requires vagal clip electrodes and adds cost and complexity. The NIM Vital NerveTrend® mode (Medtronic, Jacksonville, FL) [2,3,4] bridges these approaches by plotting amplitude and latency trends from closely spaced, surgeon-triggered stimulations, offering near real-time feedback without a vagal electrode. We report our prospective experience with NerveTrend® in thyroid and parathyroid surgery at a high-volume center, focusing on feasibility, LOS prevalence, and the relationship between stimulation frequency and early trend alerts.
2. Materials and Methods
The protocol was designed as a prospective observational study conducted at the Department of General Surgery, Azienda Ospedaliero-Universitaria di Parma (January–September 2025).
We have standardized the use of NIM TriVantage® endotracheal tube with integrated electrodes and the neuromuscular management as INMSG recommendations [5,6,7]. The stimulations delivered with a monopolar probe at 1 mA, 100 µs pulse width, 4 Hz.
The monitoring protocol was the collection of a baseline established via repeated stimulations (≥20) of the vagus or RLN and subsequent stimulations performed at 3–5 min intervals or during traction-risk maneuvers at the same nerve site. Trend thresholds followed INMSG criteria: latency increase ≥10% and amplitude decrease ≥50% from baseline.
The results of stimulation were calssified as:
- − Green (amplitude >50% and latency <110% of baseline),
- − Yellow (amplitude <50% or latency >110%),
- − Red (amplitude <50% and latency >110%),
- − LOS (amplitude <100 µV).
The protocol was approved by AVEN (protocol 486/2024/OSS/AOUPR); written informed consent obtained from all participants.
Statistics: Descriptive analyses and Student’s t-test for group comparisons; significance set at p < 0.05.
3. Results
We collected Forty-four consecutive patients undergoing thyroidectomy and/or parathyroidectomy with IONM using NIM Vital NerveTrend®;44 patients (32 female, mean age 57.2 years; 12 male, mean age 53 years) treated with 26 total thyroidectomies, 15 hemithyroidectomies, 1 total thyroidectomy + parathyroidectomy, and 2 focused parathyroidectomies; five minimally invasive approaches[8,9](Table 1).
Table 1.
Demographic and clinical characteristics.
| Variable | Value |
|---|---|
| Number of patients | 44 |
| Mean age (years) | 56.2 |
| Sex | 32 F (72.7%); 12 M (27.3%) |
| Surgery type | 26 total thyroidectomies (59.1%); 15 hemithyroidectomies (34.1%); 1 total thyroidectomy + parathyroidectomy (2.3%); 2 parathyroidectomies (4.5%) |
| Minimally invasive approach | 5 cases (11.4%) |
| Preoperative cytology (Bethesda 2023) | 28 benign; 8 indeterminate(class 4); 8 malignant (class 6). |
| Preoperative therapy | 5 levothyroxine; 9 methimazole |
| Compressive symptoms | 13 (29.5%) |
Table 2.
Intraoperative NerveTrend® monitoring data.
| Variable | Value |
|---|---|
| Total nerves at risk (NAR) | 71 |
| NAR excluded (no valid baseline) | 16 (22.5%) |
| NAR analyzed | 55 (77.5%) |
| Loss of Signal (LOS) | 3 (5.5%) |
| Mean stimulations / NAR | 4.5 (range 1–9) |
| Mean Green measurements / NAR | 3.5 |
| Mean Yellow measurements /case | 2.0 |
| Cases with Red measurements | 1 (associated with LOS) |
| Comparison (only Green vs. Green+Yellow) | 3.8 vs. 5.1 stimulations; p = 0.0059 |
The nerves at risk were 71 total NAR: 16 excluded due to invalid baseline; 55 analyzed. LOS occurred in 3/55 NAR (5.5%). The mean stimulations in NAR were 4.5 (range 1–9). The mean number of Green measurements werre 3.5; in Yellow trends observed in 26 cases (mean 2 Yellow recordings / case). A total mean of 5.1 were recorded in Green+Yellow cases). One Red measurement was recorded in a case progressing to LOS.
Association between stimulation frequency and Yellow trends: Cases with Green+Yellow trends had a higher mean number of stimulations than cases with exclusively Green trends (5.1 vs. 3.8; p = 0.0059).
4. Discussion
Our experience supports the feasibility of NerveTrend® as a trend-based extension of I-IONM that provides actionable, near real-time feedback without a vagal electrode. The observed LOS rate (5.5%) aligns with reports for intermittent monitoring, while the association between higher stimulation frequency and Yellow trend alerts suggests that surgeons tend to increase monitoring during complex or traction-prone phases, potentially enabling early recognition of impending neuropraxia and adjustment of maneuvers. Randomized trials have shown that NerveTrend® may reduce progression to LOS and staged thyroidectomy compared with conventional I-IONM, and is non-inferior to continuous monitoring (NerveAssure®) regarding POD1 RLN injury risk. Our single-center cohort is limited by sample size, operator dependence, and exclusion of cases with invalid baseline due to interference. Standardized stimulation protocols and multicenter validation are needed.
5. Conclusions
NIM Vital NerveTrend® offers dynamic intraoperative feedback while preserving the simplicity of intermittent monitoring. Early Yellow trend alerts may flag traction stress, allowing timely modification of surgical maneuvers and potentially preventing LOS. Broader studies and protocol harmonization are warranted to define sensitivity, specificity, and clinical impact.
Author Contributions
Conceptualization, P.D.R.; methodology,P.D.R., E.B.; validation, T.L.,E.B.,G.P.; formal analysis, P.D.R.,L.P.; investigation, E.B.,L.P.; resources,E.B.,T.L.; data curation, E.B.,A.F.,C.M.; writing—original draft preparation, P.D.R.,G.P.; writing—review and editing, E.B.; visualization,E.B.,T.L.; supervision, E.B.,C.M. All authors have read and agreed to the published version of the manuscript.
Funding
This research received no external funding.
Institutional Review Board Statement
The study was conducted in accordance with the Declaration of Helsinki and approved by the Ethics Committee AVEN (protocol 486/2024/OSS/AOUPR).
Informed Consent Statement
Informed consent was obtained from all subjects involved in the study.
Data Availability Statement
De-identified datasets and study materials are available from the corresponding author upon reasonable request.
Acknowledgments
We thank the operating room staff and the anesthesia team for their support.
Conflicts of Interest
The authors declare no conflict of interest.
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