Continuous Intraoperative Neuromonitoring (CIONM) of the Recurrent Laryngeal Nerve
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Continuous intraoperative nerve monitoring (CIONM) is an advanced tool to improve risk management of the recurrent laryngeal nerve (RLN) by ongoing determination of vagus amplitude and latency during thyroid surgery. The advantage of CIONM compared to intermittent nerve stimulation (IIONM) becomes apparent in technically demanding operations because CIONM provides instant alerts as soon as a surgical procedure impinges on the RLN. This is why CIONM is set to overcome the principal methodological limitation of IIONM, which is identification of RLN malfunction only after the damage has taken place.
Animal and human studies have consistently confirmed the feasibility, safety, and reliability of CIONM. By implication, accurate prediction of impending RLN injury hinges on the evaluation of wave changes which indicate nerve dysfunction that ultimately may result in complete loss of electromyographical (EMG) signal (LOS). “Combined events,” defined as concordant EMG changes in both amplitude (decreases to less than 50 % of initial baseline) and latency (increase to more than 110 % of initial baseline), typically precede postoperative vocal fold palsy and are reversible in 80 % of cases upon release of the nerve. CIONM also helps identifying functional nerve recovery with restitution of the amplitude to ≥50 % of its baseline so that surgical plans can be adjusted accordingly.
CIONM can prompt corrective actions before LOS occurs. Recent evidence suggests that CIONM may afford better nerve protection than IIONM, which resulted in permanent RLN palsy rates of 0 % with CIONM vs. 0.4 % with IIONM (P = 0.019).
KeywordsVagus nerve stimulation Continuous intraoperative nerve monitoring CIONM Combined EMG event Loss of signal Recurrent laryngeal nerve injury Thyroid surgery Vocal fold palsy
This video describes two surgical approaches to the carotid sheath; placement of the Advanced Periodic Stimulation (APS)® electrode on the vagus nerve; and calibration of the continuous intraoperative neuromonitoring system. The anterior (“midline”) approach to the right carotid sheath is the preferred approach in thyroid and parathyroid surgery. The anterior approach starts with midline incision of the superficial and middle layers of the cervical fascia. The left and right strap muscles are separated and mobilized along with the right thyroid lobe. Lateral retraction of the right strap muscles together with medial retraction of the right thyroid lobe reveals the carotid sheath. After the right vagus nerve has been identified, the probe for intermittent stimulation is used to confirm the functional integrity of the whole system, vagus nerve—recurrent laryngeal nerve—vocal muscle, by eliciting normal EMG signals. The carotid sheath is then entered, and a short segment of the vagus nerve is gently dissected free so that the electrode can embrace the nerve. Utmost care is to be used not to devascularize the vagus nerve. The vagus nerve is exposed with a nerve retractor, and the APS® electrode, with the enclosure tabs open, is placed on the nerve from a 45° angle. The APS® electrode is connected with the NIM 3.0 system so that the system can auto-calibrate baselines for amplitude and latency. To enable stable and reliable signals for neuromonitoring, the amplitude is calibrated to 500 μV at least. The vagus nerve is stimulated with a current of 1 mA at a frequency of 1 Hz. Once the system is calibrated, the left pane of the NIM 3.0 monitor shows a biphasic EMG tracing, and the right monitor pane displays separate lines for amplitude and latency. The probe for intermittent stimulation is used to document these baseline parameters. The lateral approach is more useful when there is extensive scarring in the central neck, large benign or malignant goiters reach out into the lateral neck, and for dissection of lateral neck nodes. In this video sequence, the left lateral approach is demonstrated. The superficial fascia of the neck is opened alongside a virtual line formed by the lateral border of the left sternohyoid muscle and the medial border of the left sternocleidomastoid muscle. Blunt separation of the muscles reveals the carotid sheath. Once the vagus nerve has been identified, its functional integrity is confirmed using a handheld stimulation probe, which is not to be seen here. As before, the carotid sheath is entered into through a short-range incision, and a short segment of the left vagus nerve is dissected free to embrace the APS® electrode. The APS® electrode is carefully placed on the nerve that is held into position by a nerve retractor. After the APS® electrode has been hooked up to the NIM 3.0 system, the system auto-calibrates baselines for amplitude and latency. As previously, a current of 1 mA at a frequency of 1 Hz is used to stimulate the vagus nerve. After calibration, the left pane of the NIM 3.0 monitor shows a biphasic EMG tracing, and the right monitor pane displays separate lines for amplitude and latency (MP4 446957 kb)
- 19.Dionigi G, Chiang F, Rausei S, Wu C, Boni L, Lee K, et al. Surgical anatomy and neurophysiology of the vagus nerve (VN) for standardised intraoperative neuromonitoring (IONM) of the inferior laryngeal nerve (ILN) during thyroidectomy. Langenbecks Arch Surg. 2010;395:893–9.CrossRefPubMedGoogle Scholar
- 35.Schneider R, Sekulla C, Machens A, Lorenz K, Thanh PN, Dralle H. Dynamics of loss and recovery of the nerve monitoring signal during thyroidectomy predict early postoperative vocal fold function. Head Neck. 2016;38:E1144–51.Google Scholar