Cheng-Jing Tsai

Anatomical Variations of Recurrent Laryngeal Nerve During Thyroid Surgery: How to Identify and Handle the Variations With Intraoperative Neuromonitoring

Recurrent laryngeal nerve (RLN) palsy is the most common and serious complication after thyroid surgery. Visual identification of the RLN during thyroid surgery has been shown to be associated with lower rates of palsy, and although it has been recommended as the gold standard for RLN treatment, it does not guarantee success against postoperative vocal cord paralysis. Anatomical variations of the RLN, such as extra‐laryngeal branches, distorted RLN, intertwining between branches of the RLN and inferior thyroid artery, and non‐recurrent laryngeal nerve, can be a potential cause of nerve injury due to visual misidentification. Therefore, intraoperative verification of functional and anatomical RLN integrity is a prerequisite for a safe thyroid operation. In this article, we review the literature and demonstrate how to identify and handle the anatomical variations of the RLN with the application of intraoperative neuromonitoring in the form of high resolution photography, which can be informative for thyroid surgeons. Anatomical variations of the RLN cannot be predicted preoperatively and might be associated with higher rates of RLN injury. The RLN injury caused by visual misidentification can be rare if the nerve is definitely identified early with intraoperative neuromonitoring.

Intraoperative neuromonitoring for early localization and identification of recurrent laryngeal nerve during thyroid surgery.

Early and definite identification of the recurrent laryngeal nerve (RLN) is an important step to avoid inadvertent nerve injury during complicated thyroid operations. This study aimed to determine the feasibility of routine use of intraoperative neuromonitoring (IONM) to localize and identify the RLN at an early stage of thyroid surgery. This prospective study enrolled 220 consecutive patients (333 RLNs at risk) who underwent thyroid operations with application of IONM. The RLN was localized and identified routinely with a nerve stimulator after opening the space between the thyroid and carotid sheath. The success rates of early RLN localization and identification were evaluated. The current for localization and the amplitude of evoked laryngeal electromyographic signals were also recorded and analyzed. All RLNs, including 87 (26%) nerves that were regarded as difficult to identify, were successfully localized and identified. The stimulation level for RLN localization was 2mA in 315 nerves (95%) and 3mA in the other 18 nerves (5%). The signal obtained from RLN localization (amplitude = 932 ±436μV) showed a clear and reliable laryngeal electromyographic response that was similar to that from direct vagus (amplitude=811±389μV) or RLN stimulation (amplitude=1132±472μV). The palsy rate was 0.6% and no permanent palsy occurred. RLN injury is rare if the nerve is definitely identified early in the thyroid operation. The conclusion of this study is that IONM is a reliable tool for early RLN localization and identification, even in complicated thyroid operations.

Does extensive dissection of recurrent laryngeal nerve during thyroid operation increase the risk of nerve injury? Evidence from the application of intraoperative neuromonitoring

PURPOSE Extensive dissection of recurrent laryngeal nerve (RLN) is inevitable in some complicated thyroid operations. The study aimed to determine whether extensive dissection of RLN increases the risk of nerve injury. METHOD Three hundred thirty-one patients (506 nerves at risk) who underwent thyroid operations with intraoperative neuromonitoring were included. The study chiefly focused on the 101 RLNs on which extensive nerve dissection from the thoracic inlet to the entry of larynx was performed and for which the nerve exposure was longer than 5 cm. Electromyographic (EMG) signals were obtained from the RLN and vagus nerve before and after complete RLN dissection, and these were defined as R(1), V(1) and R(2), V(2) signals, respectively. The RLN palsy rates and the change of EMG signals were evaluated and analyzed. RESULTS Among 101 nerves with extensive dissection, 13 nerves were due to the operation for recurrent goiter; 41 nerves, for large goiter with substernal extension; and 47 nerves, for thyroid cancer with paratracheal nodal metastasis. No permanent palsy occurred, but 2 nerves experienced loss of EMG signal after complete RLN dissection from a large recurrent goiter and developed temporary palsy. The palsy rates were 2% (2/101) in the extensive dissection group and 2.5% (10/405) in the nonextensive dissection group (P = .77). Among 99 nerves with normal vocal function after operation, none experienced weakened signal after complete RLN dissection, and the mean amplitudes of R(2) and V(2) signals were not significantly different from those of R(1) and V(1) signals (R(2) vs R(1); 1038 vs 1030 μV; P = .74; V(2) vs V(1); 824 vs 816 μV; P = .75). CONCLUSIONS The results of this study suggest that careful surgical dissection is well tolerated by the RLN.

The effectiveness of dexmedetomidine infusion for sedating oral cancer patients undergoing awake fibreoptic nasal intubation.

Background and objective Dexmedetomidine is characterized with effects of sedation, analgesia, amnesia and lack of respiratory depression. Hence, it should be suitable for awake fibreoptic intubation (AFOI). Methods We enrolled 30 oral cancer patients with limited mouth openings who were undergoing AFOI for elective surgery. Patients were randomly allocated into two groups; the Dex group (n = 16) that received dexmedetomidine (1.0 μg kg−1) infusion and the Control group (n = 14) that received fentanyl (1.0 μg kg−1) infusion. Main outcomes were evaluated by grading scores presenting conditions for nasal intubation and postintubation. Other analysed parameters included airway obstruction, haemodynamic changes, consumption time for intubation, amnesia level and satisfaction. Results Intubation score (1–5) representing condition for nasal intubation was significantly better in the Dex group [2(1–3)] than in the Control group [3(2–5)] (P = 0.001). Postintubation score (1–3) representing tolerance to intubation also showed more favourable results in the Dex group [1(1–3)] than in the Control group [2(2–3)] (P = 0.002). The Dex group showed significantly reduced haemodynamic response to intubation than the Control group. Incidence requiring temporary haemodynamic support was higher in the Dex group but not of significance. Both levels of amnesia and satisfaction score were significant in the Dex group. Other analysed parameters such as consumption time for intubation, airway obstruction score and postoperative adverse events did not differ significantly. Conclusion Combination of dexmedetomidine loading with topical anaesthesia provides significant benefit for AFOI in intubation condition, patient tolerance, haemodynamic response, amnesia and satisfaction. Dexmedetomidine is effective for AFOI in anticipated difficult airway with only minor and temporary haemodynamic adverse effects.

Detecting and identifying nonrecurrent laryngeal nerve with the application of intraoperative neuromonitoring during thyroid and parathyroid operation

PURPOSE The nonrecurrent laryngeal nerve (NRLN) is a rare anatomical variant but associated with high risk of nerve injury during thyroid and parathyroid operations. Therefore, intraoperative detection and verification of NRLN are necessary. METHOD A total of 390 consecutive patients who underwent thyroid and parathyroid operations (310 RLNs dissected on the right side and 293 nerves on the left side) were enrolled. Electrically evoked electromyography was recorded from the vocalis muscles via an endotracheal tube with glottis surface recording electrodes. At an early stage of operation, vagal nerve was routinely stimulated at the level of inferior thyroid pole to ensure normal path of RLN. If there is a negative response from lower position but positive response from upper vagal stimulation, it indicates the occurrence of a NRLN, and we localize its separation point and path. RESULTS Four right NRLNs (1.3%) without preoperative recognition were successfully detected at an early stage of operation. Three patients were operated on for thyroid disease, one for parathyroid adenoma and all were associated with right aberrant subclavian artery. All NRLNs were localized and identified precisely with intraoperative neuromonitoring. Functional integrity of all nerves was confirmed by the intraoperative neuromonitoring and postoperative laryngeal examination. CONCLUSIONS Vagal stimulation at the early stage of operation is a simple, useful, and reliable procedure to detect and identify the NRLN.

Electromyographic endotracheal tube placement during thyroid surgery in neuromonitoring of recurrent laryngeal nerve

Intraoperative neuromonitoring (IONM) is widely used in thyroid surgery. This study aimed to investigate the influence of neck extension on electromyographic (EMG) endotracheal tube displacement and to determine the necessity of routinely checking the final electrode position after the patient had been fully positioned. A consecutive 220 patients undergoing thyroidectomy were enrolled. All patients were intubated with the EMG endotracheal tube under direct laryngoscopy. The electrode position and tube displacement were routinely checked and measured by laryngofiberoscopy before and after patient positioning. The patients were divided into two groups. In Group I (n = 110), the EMG tube was taped and fixed to the right mouth angle before full neck extension. In Group II (n = 110), the EMG tube was disconnected from the circuit tube and was not taped until full neck extension. In all patients, we ensured that the final electrode position was the optimal position with laryngofiberoscopic examination. The tube displacement after neck extension ranged from 16 mm upward to 4 mm downward in Group I and from 12 mm upward to 5 mm downward in Group II. The rate of tube displacement greater than 10 mm was 12.7% in Group I and 3.6% in Group II. Successful monitoring was achieved in all patients after the final optimal position of electrodes was ensured routinely. The electrode position can be severely displaced after the patient has been fully positioned. Verification of ideal position of electrodes before the beginning of the operation is a necessary step to guarantee functional intraoperative neuromonitoring.

A comparative study between 1 and 2 effective doses of rocuronium for intraoperative neuromonitoring during thyroid surgery

BACKGROUND The goal of this study was to explore an ideal application of rocuronium to enable adequate muscle relaxation for intubation without significantly affecting the evoked potentials measured by intraoperative neuromonitoring during thyroid surgery. METHODS A total of 80 patients were randomized to receive 1 (group 1, n = 40) or 2 (group 2, n = 40) effective doses (ED(95)) of rocuronium to facilitate electromyographic (EMG) endotracheal tube insertion. Evoked potentials were obtained every 5 minutes by stimulating the vagus nerve between the time period of 30 and 70 minutes after administration of rocuronium. The magnitude of evoked potentials at each time point and the tracheal intubating conditions were compared between groups. Accelerometry (twitch [% TW]) was used to monitor the quantitative degree of neuromuscular transmission at the adductor pollicis muscle. RESULTS At 30 minutes after administration of rocuronium, the rate of positive EMG response was 100% (40/40) in group 1 and 53% (21/40) in group 2 (P < .001). Positive EMG signals were obtained for all patients in group 2 until 55 minutes after administration of rocuronium. The mean amplitude detected from the time point of 30 to 60 minutes was greater in group 1 than in group 2 (P < .01). The time to tracheal intubation was 208 ± 59 seconds in group 1 and 114 ± 26 seconds in group 2 (P < .001). The overall intubating conditions were better in group 2 than in group 1 patients (P < .001). CONCLUSION A total of 1 ED(95) of rocuronium (0.3 mg/kg) is an optimal dose for intraoperative neuromonitoring during thyroid surgery. Positive and high EMG signals were obtained in all patients at an early stage of operation, and satisfactory intubating conditions were achieved in most patients.

Electromyographic study of differential sensitivity to succinylcholine of the diaphragm, laryngeal and somatic muscles: a swine model.

Neuromuscular blocking agents (NMBAs) might diminish the electromyography signal of the vocalis muscles during intraoperative neuromonitoring of the recurrent laryngeal nerve. The aim of this study was to compare differential sensitivity of different muscles to succinylcholine in a swine model, and to realize the influence of NMBAs on neuromonitoring. Six male Duroc‐Landrace piglets were anesthetized with thiamylal and underwent tracheal intubation without the use of an NMBA. The left recurrent laryngeal nerve, the spinal accessory nerve, the right phrenic nerve and the brachial plexus were stimulated. Evoked potentials (electromyography signal) of four muscle groups were elicited from needle electrodes before and after intravenous succinylcholine bolus (1.0 mg/kg). Recorded muscles included the vocalis muscles, trapezius muscle, diaphragm and triceps brachii muscles. The onset time and 80% recovery of control response were recorded and analyzed. The testing was repeated after 30 minutes. The onset time of neuromuscular blocking for the vocalis muscles, trapezius muscle, diaphragm and triceps brachii muscle was 36.3 ± 6.3 seconds, 38.8 ± 14.9 seconds, 52.5 ± 9.7 seconds and 45.0 ± 8.2 seconds during the first test; and 49.3 ± 10.8 seconds, 40.0 ± 12.2 seconds, 47.5 ± 11.9 seconds and 41.3 ± 10.1 seconds during the second test. The 80% recovery of the control response for each muscle was 18.3 ± 2.7 minutes, 16.5±6.9 minutes, 8.1±2.5 minutes and 14.8±2.9 minutes during the first test; and 21.5±3.8 minutes, 12.5 ± 4.3 minutes, 10.5 ± 3.1 minutes and 16.4 ± 4.2 minutes during the second test. The sensitivity of the muscles to succinylcholine, ranked in order, was: the vocalis muscles, the triceps brachii muscle, the trapezius muscle and the diaphragm. We demonstrated a useful and reliable animal model to investigate the effects of NMBAs on intraoperative neuromonitoring. Extrapolation of these data to humans should be done with caution.

Anaphylaxis to benzalkonium chloride-coated central venous catheter

Benzalkonium chloride (BAC) is commonly used as a bactericidal preservative and it may cause allergic reactions in some patients. An unusual case of anaphylactic shock in a 55-year-old woman following insertion of a central venous catheter (CVC) that was coated with BAC is presented. Assuming anaphylactic shock from the CVC, the catheter was removed immediately. Standard resuscitation was started with 100% oxygen, epinephrine, and saline infusion. The patient recovered without any sequelae. One month later, an intradermal skin test was positive for BAC.

Seizure after local anesthesia for nasopharyngeal angiofibroma.

We report a young male patient who experienced seizure after local injection of 3 mL 2% lidocaine with epinephrine 1:200,000 around a recurrent nasal angiofibroma. After receiving 100% oxygen via mask and thiamylal sodium, the patient had no residual neurologic sequelae. Seizure immediately following the injection of local anesthetics in the nasal cavity is probably due to injection into venous or arterial circulation with retrograde flow to the brain circulation. Further imaging study or angiography should be done before head and neck surgeries, especially in such highly vascular neoplasm.