Chinese Guidelines on Intraoperative Neuromonitoring in Thyroid and Parathyroid Surgery (2023 Edition, English Full-Text Core Summary)

Basic Information

• Official Title: Chinese guidelines on intraoperative neuromonitoring in thyroid and parathyroid surgery (2023 edition)
• Issuing Bodies: Chinese Thyroid Association (College of Surgeons, Chinese Medical Doctor Association); Chinese Research Hospital Association Thyroid Disease Committee
• Publication: Gland Surgery, 2023, 12(8): 1031–1049 (English full text); corresponding Chinese version in Chinese Journal of Practical Surgery, 2023, 43(1)
• Scope: Applicable to open, endoscopic, and robotic thyroid/parathyroid surgery; covers recurrent laryngeal nerve (RLN), external branch of superior laryngeal nerve (EBSLN), vagus nerve (VN), and other cervical motor nerves; includes 42 evidence‑based recommendations graded by GRADE (Grade of Recommendation/Level of Evidence)
• Core Purpose: Standardize intraoperative neuromonitoring (IONM) workflows, reduce laryngeal nerve injury, and unify decision‑making for signal abnormalities and troubleshooting

1. Core Principles & Indications

1.1 Definition & Value

1.2 Indications (Strongly Recommended, Grade A/A)

• High‑risk cases: Thyroid cancer (especially with extrathyroidal extension), large goiters, revision surgery, severe inflammatory adhesion, retrosternal goiter, suspected non‑recurrent RLN (NRLN)
• Anatomical high‑risk features: High‑lying thyroid superior pole, short/thick neck, large thyroid‑to‑neck length ratio, EBSLN anatomical variants
• Patient‑related: Professional voice users, bilateral surgery, preoperative vocal cord dysfunction (VCD)
• All endoscopic/robotic thyroid surgeries (due to limited tactile feedback)

1.3 Contraindications

• Preoperative complete unilateral/bilateral VCP (no functional signal to monitor)
• Uncorrectable anatomical barriers (e.g., severe cervical distortion, unmanageable secretions interfering with electrodes)
• Patient refusal or inability to tolerate electrode placement

2. Standard IONM Workflow (Four‑Step Protocol, Grade A/A)

1. V1 (Pre‑dissection VN stimulation): Stimulate VN at cervical base; confirm baseline EMG amplitude/latency; rule out pre‑existing nerve dysfunction and validate system function.
2. R1 (Early RLN stimulation): Stimulate RLN at the first identified point (usually near the ligament of Berry); establish the reference signal for intra‑operative comparison.
3. R2 (Post‑dissection RLN stimulation): Stimulate RLN at the laryngeal entry point after thyroid mobilization/ligation; assess functional integrity after key dissection steps.
4. V2 (Post‑dissection VN stimulation): Re‑stimulate VN; compare with V1 to confirm no proximal nerve injury and intact neuromuscular transmission.

Key Parameters

• Stimulation: Bipolar probe, 1–3 mA (0.1–1.0 ms pulse width); avoid monopolar (high risk of current spread)
• EMG Thresholds: Loss of signal (LOS) = amplitude <100 μV; adverse event threshold = 50% drop in R1 amplitude (early warning for impending injury)
• Recording: Endotracheal tube surface electrodes (or thyroid cartilage needle electrodes); impedance <5 kΩ; bilateral recording recommended

3. Nerve‑Specific Monitoring Recommendations

3.1 Recurrent Laryngeal Nerve (RLN)

• NRLN Detection: Use monitoring point comparison + latency assessment (right‑sided NRLN: short latency, no descending cervical course; V1 absent/R1 present) (Grade A/A)
• Signal Abnormality Triage:
  • LOS with V1 intact → distal RLN injury (stretch, clamp, thermal, ligation)
  • LOS with V1 absent → proximal VN/root injury
  • Bilateral signal loss → check muscle relaxant, electrode position, or systemic neuromuscular dysfunction (Grade A/C)
   
• Injury Management: Suspend surgery for 20–30 min; release tension, irrigate, avoid repeated stimulation; persistent LOS → consider staged surgery or nerve repair (Grade A/B)

3.2 External Branch of Superior Laryngeal Nerve (EBSLN)

• High‑Risk Factors: High superior pole, large tumor, revision surgery, severe adhesion (Grade A/B)
• Monitoring Method: Stimulate EBSLN at superior pole; observe cricothyroid muscle (CTM) twitch + EMG response; absent twitch → immediate check for clamping/misligation (Grade A/B)
• Goal: Preserve vocal cord tension function (prevents voice fatigue, pitch loss)

3.3 Other Cervical Nerves

• Accessory, phrenic, hypoglossal, facial marginal mandibular nerves: Stimulate nerve trunks; record target muscle EMG; avoid thermal/stretch injury in lateral/central neck dissection (Grade B/C)

4. Troubleshooting & System Optimization (Grade A/B–B/C)

4.1 Common Signal Failures & Fixes

4.2 Anesthesia Requirements

• Total intravenous anesthesia (TIVA) preferred (reduces PONV and signal interference)
• Minimal neuromuscular blockade: Short‑acting agents (mivacurium); train‑of‑four (TOF) ratio ≥90% before stimulation
• Avoid laryngeal topical anesthesia (blocks signal transmission)

5. Graded Recommendations (Key Highlights, 42 Total)

High‑Priority Recommendations (Grade A/A–A/B)

1. Mandate the four‑step VN‑RLN‑VN protocol for all IONM cases (A/A)
2. Set 50% R1 amplitude drop as the RLN injury early warning threshold; suspend surgery if breached (A/B)
3. Use bipolar stimulation; avoid monopolar to prevent current spread (A/A)
4. For NRLN, combine monitoring point comparison + latency assessment (A/A)
5. Adjust endotracheal tube position for signal improvement; use electrode‑crossing to diagnose recording issues (A/B)
6. In EBSLN monitoring, act immediately on absent CTM twitch to avoid permanent injury (A/B)
7. Standardize IONM operating procedures to ensure reproducibility (A/A)

Quality & Training (Grade B/B–B/C)

• Surgeons must complete structured IONM training (didactic + proctoring) before independent use
• Record all stimulation sites, amplitudes, latencies, and adverse events in the operative note
• Regular system calibration and electrode quality control

6. Limitations & Clinical Caveats

• IONM is an adjunct to visual dissection, not a replacement; meticulous anatomical dissection remains paramount
• LOS positive predictive value for postoperative VCP is 10–90% (context‑dependent); false positives/negatives occur
• Bilateral RLN monitoring is strongly recommended for high‑risk cases to guide staged surgery