We investigated the learning curve for using intraoperative neural monitoring technology in thyroid cancer, with a view to reducing recurrent laryngeal nerve injury complications. Radical or combined radical surgery for thyroid cancer was performed in 82 patients with thyroid cancer and 147 recurrent laryngeal nerves were dissected. Intraoperative neural monitoring technology was applied and the “four-step method” used to monitor recurrent laryngeal nerve function. When the intraoperative signal was attenuated by more than 50%, recurrent laryngeal nerve injury was diagnosed, and the point and causes of injury were determined. The time required to identify the recurrent laryngeal nerve was 0.5–2 min and the injury rate was 2.7%; injuries were diagnosed intraoperatively. Injury most commonly occurred at or close to the point of entry of the nerve into the larynx and was caused by stretching, tumor adhesion, heat, and clamping. The groups are divided in chronological order; a learning curve for using intraoperative neural monitoring technology in thyroid cancer surgery was generated based on the time to identify the recurrent laryngeal nerve and the number of cases with nerve injury. The time to identify the recurrent laryngeal nerve and the number of injury cases decreased markedly with increasing patient numbers. There is a clear learning curve in applying intraoperative neural monitoring technology to thyroid cancer surgery; appropriate use of such technology aids in the protection of the recurrent laryngeal nerve.
With the rise in the incidence of thyroid cancer, increasing numbers of patients are undergoing total thyroidectomy, with consequential voice changes due to recurrent laryngeal nerve (RLN) injury, which has a serious impact on the patient’s quality of life. In general, the reported RLN injury rate ranges from 1% to 13.3%. According to the Diagnosis and Treatment Guidelines for Patients with Thyroid Nodule and Differentiated Thyroid Cancer in China, the effective protection of the RLN is one of the key points in thyroid cancer surgery. In these guidelines, electrophysiological intraoperative neural monitoring (IONM) for RLN protection emerged after the regional protection method and fine dissection method. IONM has been developed over the past 30 years, and IONM has been clinically applied for nearly 20 years. Currently, IONM is considered required technology for thyroid operation in Europe and the USA and is rapidly being incorporated in China. Use of IONM is cost-effective for patients undergoing bilateral thyroid surgery [
We have started using IONM (via direct RLN stimulation) during thyroid cancer surgery in July 2012 and have monitored its use by surgeons up to July 2014, by which time the General Surgery Department has completed 82 thyroid cancer operations. We used this information to assess the learning curve for use of IONM in this context.
All cases included in this study were compatible with the International Standards Guidelines for Electrophysiological Recurrent Laryngeal Nerve Monitoring during Thyroid and Parathyroid Surgery [
Combined inhalation and intravenous anesthesia were adopted for thyroid cancer surgery. Short-acting muscle relaxant was used for intubation. No muscle relaxant was added during the operation. The NIM-Response 3.0 intraoperative nerve monitoring system (Medtronic; Dublin, Ireland) and laryngeal electromyography (EMG)-enhanced tracheal intubation tubes were used. During intubation, the blue zone was placed outside of the glottis to ensure that the two groups of electrodes leads on the intubation tubes were placed in contact with the vocal cords on both sides. The current intensity used for the stimulating electrode during surgery was 1.0–3.0 mA. The method for seeking the RLN is termed the “four-step method” [
The signal attenuation range was determined: if the degree to which the R2 signal was weaker than the R1 signal exceeded 50% [
If RLN injury was identified, 40 mg of methylprednisolone was immediately injected intravenously, during the operation, and ribbon gauzes soaked in dexamethasone were applied to the surface of the RLN for more than 10 min; they were then removed before suturing the incision. After the operation, 40 mg of methylprednisolone was administered once daily, via intravenous injection, for 2 successive days, and 0.5 mg mecobalamin tablets were administered orally twice a day until RLN function had recovered. If the patient’s voice was restored to normal and the closure of the vocal cords was considered normal upon fiberoptic laryngoscope examination, the patient’s RLN function was considered to have recovered completely.
Statistical software SPSS19.0 (SPSS, Inc., Chicago, IL, USA) was used to conduct the statistical analysis. The measurement data that were demonstrated as the mean ± standard deviation (SD), such as Baseline characteristics. One-way analysis of variance was used for time to identify among groups the recurrent laryngeal nerve by SPSS 19.0. Statistical significance was set at a P value of <0.05.
The details of the consecutive 82 cases are shown in Table
Characteristics of the patients.
Baseline characteristics | Number/mean ± SD |
---|---|
Age (years) | 46.6 ± 12.7 |
Sex ratio (F:M) | 2.9:1 |
Radical surgery (n): combined radical surgery (n) | 61:21 |
Tumor range (unilateral: bilateral) (n) | 62:20 |
Tumor size (cm) | 1.1 ± 0.8 |
Tumor number (n) | 1.4 ± 0.8 |
Retrieved cervical central lymph nodes (n) | 5.5 ± 3.8 |
Metastatic cervical central lymph nodes (n) | 1.7 ± 1.5 |
Dissected recurrent laryngeal nerve (n) | 147 |
pathological pattern (papillary/medullary) (n) | 81/1 |
F: female; M: male.
Mean operation time for all cases. The operative time decreased markedly after the first 10 cases.
Four patients were diagnosed with RLN injury intraoperatively (injury rate of 2.7%; 4/147). Fiberoptic laryngoscopy postsurgically indicated that the patients’ vocal cord motion had weakened or remained stable during 12 months. The signal attenuation range, injury point, injury cause, and RLN function recovery time after treatment are shown in Table
Case statistics of RLN injury.
Case | Lobe | Signal attenuation | Injury point | Injury cause | Recovery (months) |
---|---|---|---|---|---|
1 | Left | 70% | The point of entry into the larynx | Excessive stretching of RLN when picking up thyroid lobes | 0.5 |
2 | Left | 100% | 1 cm from the point of entry into the larynx | Tumor was adhered to RLN. | No recovery in 12 months. |
3 | Left | 90% | The point of entry into the larynx | Heat injury caused by ultrasound knife during separating. | 6 |
4 | Right | 90% | 1 cm from the point of entry into the larynx | Clamping of vessel to stop hemorrhage included and injured the RLN | 3 |
RLN: recurrent laryngeal nerve.
Groups were established based on chronological time, and each group consisted of surgery of 30 thyroid gland lobes. The time to identify the RLN during surgery and the number of injury cases (Table
Distribution of time to identify the RLN and injury across groups.
Group | Case | Time of seeking RLN (s) | Number of cases with injury |
---|---|---|---|
1 | 30 | 105 ± 34 | 2 |
2 | 30 | 100 ± 31 | 1 |
3 | 30 | 85 ± 24 | 1 |
4 | 30 | 50 ± 15 | 0 |
5 | 27 | 45 ± 9 | 0 |
| |||
Total | 147 | 78 ± 35 | 4 |
RLN: recurrent laryngeal nerve.
One-way analysis of variance for time to identify the recurrent laryngeal nerve among groups.
P value | Group 1 | Group 2 | Group 3 | Group 4 | Group 5 |
---|---|---|---|---|---|
Group 1 | / | 0.436 | 0.002 | 0.000 | 0.000 |
Group 2 | 0.436 | / | 0.020 | 0.000 | 0.000 |
Group 3 | 0.002 | 0.020 | / | 0.000 | 0.000 |
Group 4 | 0.000 | 0.000 | 0.000 | / | 0.448 |
Group 5 | 0.000 | 0.000 | 0.000 | 0.448 | / |
IONM was used for continuous monitoring during 82 thyroid cancer operations during which 147 thyroid lobes were removed. The time for identifying the RLN by means of IONM was 0.5–2 min, based on the fine dissection method. Among the 82 patients, 4 patients suffered RLN injury (injury rate: 2.7%), which was identified intraoperatively by IONM. The injury point was located near the larynx and the injury causes included stretching, tumor adhesion, heat, and clamping. All injuries were treated timely.
The reported complications of RLN injuries may be related to positioning of electrodes for IONM at the larynx, obstructing the endotracheal tube; the drugs used for anesthesia; and the effects of electrical stimulation at nerve structural and systemic levels [
Although RLN can be found relatively rapidly by using IONM intraoperatively, it has to be dissected after determining its position, to complete the exposure. This dissection process is very likely to cause injury. Using IONM can help to detect whether RLN function has been affected after performing separation and hemostasis.
In our study, the groups are divided in chronological order, with each group consisting of 30 RLNs; the time of seeking RLN and the number of injury case number have dropped obviously in the latter group. In addition, all injury cases occurred in the top 3 groups, which indicated that the use of IONM is beneficial to protection of the RLN. Understanding the learning curve for applying IONM technology may facilitate the use of IONM, which can assist in locating the RLN prior to exposing it via dissection, and it will be faster than locating it visually. More importantly, although macroscopic RLN injury, i.e., its complete disruption or mechanical damage, can be observed intraoperatively without IONM; in non-macroscopic RLN injury, the nerve appears to be in good condition, but is functionally damaged, and the existence, location, and cause of such injury can be difficult to judge without IONM. Without such knowledge, another such injury is likely to occur in subsequent operations. Using IONM, surgeon can determine the cause of injury and can try to avoid recurrence. The injury causes in the 4 cases in this study could be clearly determined, allowing surgeons to adjust their surgical technique, and, subsequently, no similar injuries occurred. With accumulation of operative cases, the RLN injury cases declined in this study.
It has been disputed whether using IONM can reduce RLN injury rate. Ide et al. [
The International Neural Monitoring Study Group has issued specific operation instructions [
Although the data presented in this study are not sufficient to conclude the impact of using IONM on RLN injury rate, it does indicate that there is a learning curve in use of IONM technology. According to our experience, the clinical application of IONM has the following significance: (1) it shortens the time for identifying the RLN; (2) it reduces RLN injury and predicts nerve function after surgery; (3) it helps to determine the RLN injury point and causes; (4) it assists in timeously identifying nerve injury on one side and judging whether the operation should be delayed for the other side; and (5) it helps to identify whether any voice change after surgery was caused by RLN injury.
Nevertheless, use of IONM has some limitations: (1) RLN injury cannot be completely avoided. With invasive neoplasm, adhesion or a large mass, and anatomic variation, such injury will occur during the process of tumor separation, even though the nerve position can be detected [
In conclusion, there is a technology learning curve in the application of IONM in thyroid cancer surgery, but the use of IONM may assist in protecting RLN during fine dissection.
The data used to support the findings of this study are available from the corresponding author upon request.
All procedures performed in this study were in accordance with the ethical standards of the institutional research committee and with the 1964 Helsinki Declaration and its later amendments or comparable ethical standards.
All authors declare that there are no conflicts of interest. No author has any financial relationship with the sponsoring organization.
This work was supported by the Beijing Municipal Administration of Hospitals’ Clinical Medicine Development Special Funding (ZYLX201504).