Hsiu-Ya Chen

Standardization of Intraoperative Neuromonitoring of Recurrent Laryngeal Nerve in Thyroid Operation

BackgroundThe lack of standardized procedures of intraoperative neuromonitoring (IONM) during thyroid operations may lead to highly variable results, and many of these results can cause misleading information and, conversely, increase the risk of recurrent laryngeal nerve (RLN) injury. Therefore, standardization of IONM procedures is necessary.MethodsA total of 289 patients (435 nerves at risk) who underwent thyroidectomy by the same surgeon were enrolled in this study. Each patient was intubated with EMG endotracheal tube by the same anesthesiologist. Standardized IONM procedures were applied in each patient. The procedures include preoperative and postoperative video-recording of vocal cord movement, ensuring the correct position of electrodes after the neck was placed at full extension, vagal stimulation and registration of EMG signals before and after RLN dissection, and photographic documentation of the exposed RLN.ResultsFive patients encountered dysfunction of IONM, which was caused by malposition of electrodes and the problem was detected at once. One patient with non-RLN was detected at the earlier stage of operation. Eighteen nerves experienced loss of EMG signals during thyroid dissection, and the causes of nerve injuries were well elucidated with the application of our standardized IONM procedures.ConclusionsThe standardized IONM procedures are useful and helpful not only to eliminate false IONM results, but also to elucidate the mechanism of RLN injury. After ascertaining the surgical pitfalls and improving the surgical techniques, the palsy rate was significantly reduced in this study.

Intraoperative neuromonitoring for the early detection and prevention of RLN traction injury in thyroid surgery: A porcine model

BACKGROUND Operative traction of the thyroid lobe is a necessary component of thyroid surgery. This surgical maneuver can cause traction injury of the recurrent laryngeal nerve (RLN), and this complication has been reported to be the most common mechanism of nerve injury. The goal of this study was to investigate the electromyographic (EMG) signal pattern during an acute RLN traction injury and establish reliable strategies to prevent the injury using intraoperative neuromonitoring (IONM). METHODS Fifteen piglets (30 RLNs) underwent IONM via automated periodic vagal nerve stimulation and had their EMG tracings recorded and correlated with various models of nerve injury. RESULTS In the pilot study, a progressive, partial EMG loss was observed under RLN tractions with different tension (n = 8). The changes in amplitudes were more marked and consistent than were the changes in latency. The EMG gradually gained partial recovery after the traction was relieved. Among the nerves injured with electrothermal (n = 4), clamping (n = 1), and transection (n = 1) models, the EMG showed immediate partial or complete loss, and no gradual EMG recovery was observed. Another 16 RLNs were used to investigate the potential of EMG recovery after different extents of RLN traction. We noted the EMG showed nearly full recovery if the traction stress was relieved before the loss of signal (LOS), but the recovery was worse if prolonged or repeated traction was applied. The mean restored amplitudes after the traction was relieved before, during, and after the LOS were 98 ± 3% (n = 6), 36 ± 4% (n = 4), and 15 ± 2% (n = 6), respectively. CONCLUSION RLN traction injury showed graded, partial EMG changes; early release of the traction before the EMG has degraded to LOS offers a good chance of EMG recovery. IONM can be used as a tool for the early detection of adverse EMG changes that may alert surgeons to correct certain maneuvers immediately to prevent irreversible nerve injury during the thyroid operation.

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.

Vagal nerve stimulation without dissecting the carotid sheath during intraoperative neuromonitoring of the recurrent laryngeal nerve in thyroid surgery

Vagal nerve stimulation (VNS) has been recommended as a routine procedure during intraoperative neuromonitoring (IONM) of the recurrent laryngeal nerve (RLN). However, many surgeons have been discouraged from performing VNS because of the need for opening the carotid sheath. The purpose of this study was to investigate the feasibility and reliability of VNS without carotid sheath dissection.

Loss of signal in recurrent nerve neuromonitoring: causes and management

During recurrent laryngeal nerve (RLN) neuromonitoring in thyroid surgery, laryngeal electromyography (EMG) amplitude may be correlated with the number of muscle fibers participating in the polarization and these might be correlated with the function of RLN. If RLN is severely injured during the operation, most nerve fibers do not transmit nerve impulse and substantial decrease of EMG amplitude or loss of signal (LOS) will occur. True LOS at the end of an operation often indicates a postoperative fixed vocal cord, and the surgeon should consider the optimal contralateral surgery timing in patients with planned bilateral thyroid operation to avoid the disaster of bilateral vocal cord palsy. However, LOS recovery and false LOS may occur and may lead to an unnecessary 2(nd) operation. Therefore, a reliable modality for intraoperative LOS evaluation and management would afford the surgeon real-time information that could help guide surgical procedure and planning. The updated causes, algorithm, and management of LOS during RLN neuromonitoring are reviewed and summarized.

Stimulating dissecting instruments during neuromonitoring of RLN in thyroid surgery

During intraoperative neuromonitoring (IONM) of recurrent laryngeal nerve (RLN) in thyroid surgery, the need for frequent shifting between the dissecting instruments and stimulating probe is troublesome and time‐consuming. Therefore, use of these two instruments in combination would be a noticeable future direction. This study aimed to investigate the feasibility and safety of using stimulating dissecting instruments (SDIs) that combine the function of surgical dissection and nerve stimulation during IONM.

Reversal of rocuronium-induced neuromuscular blockade by sugammadex allows for optimization of neural monitoring of the recurrent laryngeal nerve

The use of neuromuscular blocking agent may effect intraoperative neuromonitoring (IONM) during thyroid surgery. An enhanced neuromuscular‐blockade (NMB) recovery protocol was investigated in a porcine model and subsequently clinically applied during human thyroid neural monitoring surgery.

Influence of intravenous anesthetics on neuromonitoring of the recurrent laryngeal nerve during thyroid surgery

Limited reports are available in the literature on the impact of intravenous administration of anesthetics on laryngeal electromyographic (EMG) activity. The purpose of this study was to determine the influence of the two commonly used intravenous anesthetics (propofol and thiamylal) on EMG amplitude evoked from the recurrent laryngeal nerve (RLN) during thyroid surgery. A total of 40 patients were randomized to receive a bolus of propofol (0.5 mg/kg; n = 20) or thiamylal (1.5 mg/kg; n = 20) to increase anesthetic depth when the surgeon found patient movement intraoperatively. Evoked potentials were obtained before and every 1 minute after the administration of each agent for up to 5 minutes by stimulating the RLN. The magnitude of evoked potentials at each time point and hemodynamic response were compared within groups. The mean amplitude of evoked potentials did not change significantly after administration of either propofol or thiamylal (p > 0.05 within groups). Mean arterial pressure measured from 1 minute to 5 minutes was significantly lower in the propofol group than in the thiamylal group (p < 0.05). Heart rate measured within 5 minutes did not differ significantly within groups. Low dose of propofol (0.5 mg/kg) or thiamylal (1.5 mg/kg) did not affect EMG readings during neuromonitoring of the RLN in thyroid surgery. Our results show that thiamylal provides better hemodynamic stability than propofol, and is therefore a preferable agent to increase anesthesia depth and prevent further patient movement during intraoperative neuromonitoring.

In response toReversal of rocuronium-induced neuromuscular blockade by sugammadex allows for optimization of neural monitoring of the recurrent laryngeal nerve: Letter to the Editor

Brunaud and Fuchs-Buder wrote a letter in response to our recent study to bring the selective sugammadex reversal approach for neural monitoring to the attention of readers. They stated that the need for sugammadex to restore neuromuscular function allowing adequate intraoperative neuromonitoring (IONM) is rather infrequent and observed in less than approximately 20% of patients. Consequently, compared to routine reversal of rocuronium neuromuscular blockade with sugammadex, a selective reversal approach may be sufficient and more cost-effective. First, we accept as true that recovery from rocuronium-induced neuromuscular blockade is significantly faster at the laryngeal muscles compared to the adductor pollicis muscle. Appropriate IONM may be allowed in most patients while the adductor pollicis is still paralyzed. However, the dose of rocuronium and the time of nerve stimulation is critical for successful IONM. In our previous study, in the patients who received a standard intubating dose of rocuronium (0.6 mg/kg), the rate of positive electromyographic (EMG) response from vagal stimulation was only 53% at 30 minutes after rocuronium injection; only at 55 minutes did the rate of positive EMG response reach 100% in these patients. Furthermore, the mean EMG amplitude was markedly lower from 30 to 60 minutes. Second, a higher initial EMG signal is also crucial as 1) it can be as a reference to be compared with the final signal to predict the outcome of vocal cord function, 2) it is helpful to map the path of the recurrent laryngeal nerve intraoperatively, and 3) it is useful to detect early adverse signal change to prevent imminent nerve injury, particularly for continuous IONM. Third, because sugammadex is currently an expensive product, a selective reversal approach may be more cost-effective. However, we have to emphasize that when a standard dose of rocuronium (0.6 mg/kg) is used for tracheal intubation, the recovery from neuromuscular blockade after rocuronium varies widely between subjects and may lead to a false-negative IONM result. If we take the cost of sugammadex into consideration, a reduced dosage of rocuronium (0.3 mg/kg) can be another option.