Video laryngeal mask-guided placement of electromyographic endotracheal tubes for intraoperative neuromonitoring during thyroidectomy: a simulator-based feasibility report

Dear Editor,

Recurrent laryngeal nerve (RLN) injury is a clinically significant complication of thyroidectomy. Intraoperative neuromonitoring (IONM) is widely used to facilitate RLN identification and to elucidate the intraoperative nerve injury mechanism. However, reliable IONM requires stable electromyographic (EMG) signal acquisition. In practice, the EMG endotracheal tube (EMG-ETT) is prone to malpositioning, displacement, or structural damage during insertion, which can compromise electrode contact and signal reliability [1,2]. Therefore, the tube must be precisely positioned and its location continuously verified to ensure dependable monitoring.

Several useful techniques for improving EMG-ETT placement, including the use of video stylets and fiberoptic bronchoscopy, have been described [3,4]. Nevertheless, these methods require additional equipment, repeated airway manipulation, or intermittent placement confirmation.

The SaCoVLM^TM is a third-generation video laryngeal mask airway with an integrated visualization system that enables real-time observation of the glottic structures [5]. We evaluated the feasibility of using the SaCoVLM as a conduit for guided EMG-ETT placement and continuous visualization in a simulated thyroidectomy setting.

We used a high-fidelity airway simulator (SimMan 3G, Laerdal) with a normal airway anatomy, with the head slightly extended to mimic the operative posture during thyroidectomy (Figs. 1A and B). After inserting a size 3 SaCoVLM, the glottic view was optimized by using the integrated video system. Two commercially available 6.0-mm internal diameter EMG-ETTs were tested sequentially: a Trivantage^TM EMG-ETT (Medtronic) and an NIM^TM Standard EMG-ETT (Medtronic). The four embedded surface electrodes are distributed along a longer contact segment in the Trivantage than in the NIM Standard tube. Each tube was advanced under direct visualization through the SaCoVLM device and the electrode band was aligned with the level of the vocal cords under continuous visual guidance (Figs. 1C and D). The tube position and electrode contact with the cords were observed in real-time, without requiring fiberoptic bronchoscopy or adjunctive devices.

Fig. 1.

Simulator-based demonstration of video laryngeal mask-guided placement of electromyographic endotracheal tubes (EMG-ETTs). (A) The Trivantage^TM EMG-ETT with attached electrode wires and cuff inflation line. The contact zone containing the surface electrodes on this tube design is longer than that in the NIM Standard EMG-ETT, providing a greater margin for rotational alignment. (B) Airway simulator positioned the head slightly extended to mimic the operative position for thyroidectomy. The SaCoVLM^TM is placed in the oral cavity and is connected to the ventilation circuit. (C) Endoscopic view through the SaCoVLM showing the Trivantage EMG-ETT advanced under direct visualization and the electrode band aligned at the vocal cord level, with adequate clearance and minimal resistance during passage. (D) Endoscopic view through the SaCoVLM showing a NIM Standard EMG-ETT advanced through the glottic inlet, with a comparatively tighter fit due to the shorter electrode segment and with the relatively larger cuff profile occupying more of the visual field.

In this simulated setting, both EMG-ETTs were successfully advanced through the SaCoVLM and were positioned at the vocal cord level on the first attempt. For both tube types, the glottic view remained unobscured on the SaCoVLM monitor throughout the insertion process, allowing real-time adjustment of the insertion depth and rotational orientation. However, the two tube designs displayed notable differences. The Trivantage EMG-ETT, with its longer surface electrode contact zone, demonstrated more accurate electrode-to-cord alignment and encountered less resistance during its passage through the laryngeal mask. In contrast, the NIM Standard EMG-ETT, with its shorter, more compact electrode segment, required more careful positioning to ensure adequate electrode contact, but could nonetheless be placed successfully under visual guidance. Under continuous video monitoring, tube movement could be recognized immediately and sustained electrode alignment could be confirmed. Direct observation of vocal cord movements also provided useful complementary information when interpreting IONM signals.

This technique offers several practical advantages during thyroid surgery requiring IONM. First, it provides direct visual guidance during EMG-ETT advancement, which may improve initial electrode positioning. Second, the integrated visualization system allows prompt detection of tube displacement and reduces the need for repeated airway manipulation for repositioning. Unlike intermittent fiberoptic bronchoscopy-based confirmation, the SaCoVLM provides uninterrupted visualization without requiring a separate device to be passed through the ETT lumen, thereby preserving ventilation capacity during the confirmation process. Third, continuous observation of the laryngeal inlet may assist in distinguishing tube displacement from true RLN injury [2]. Importantly, successful placement of two different EMG-ETT designs through the SaCoVLM indicates that this technique is applicable regardless of the specific tube used, suggesting generalizability in clinical practice. These features may be particularly relevant in cases where stable signal quality is critical for intraoperative decision-making.

Nevertheless, our findings are based on a technical evaluation using a simulator, rather than on human participants or clinical outcome data. Airway conditions in actual patients, including restricted mouth opening, difficult anatomy, presence of airway secretions, and surgical manipulations, may influence the feasibility of this approach and the image quality obtained. Additionally, as observations regarding the differences between the two EMG-ETT designs were based on a single simulated scenario, quantitative comparisons in clinical settings are warranted. Therefore, our findings should be interpreted as preliminary results. Future clinical studies should determine the success rate, safety, effect on EMG signal stability, and the potential role of this technique in real-world thyroid surgeries.

In conclusion, video laryngeal mask-guided EMG-ETT placement using the SaCoVLM was shown to be feasible with two different EMG-ETT designs in a simulated thyroidectomy model. This EMG-ETT placement approach may serve as a practical adjunct for accurate placement and continuous visual confirmation of tube positioning during IONM-guided thyroid surgeries.