Abstract
A recurrent laryngeal nerve (RLN) injury resulting in vocal fold paralysis and dysphonia remains a major source of morbidity after thyroid and parathyroid surgeries. Intraoperative neural monitoring (IONM) is increasingly accepted as an adjunct to the standard practice of visual RLN identification. Endotracheal tube (ET) surface recording electrode systems are now widely used for IONM; however, the major limitation of the clinical use of ET-based surface electrodes is the need to maintain constant contact between the electrodes and vocal folds during surgery to obtain a high-quality recording. An ET that is malpositioned during intubation or displaced during surgical manipulation can cause a false decrease or loss of electromyography (EMG) signal. Since it may be difficult to distinguish from an EMG change caused by a true RLN injury, a false loss or decrease in EMG signal may contribute to inappropriate surgical decision making. Therefore, researchers have investigated alternative electrode systems that circumvent common causes of poor accuracy in ET-based neuromonitoring. Recent experimental and clinical studies have confirmed the hypothesis that needle or adhesive surface recording electrodes attached to the thyroid cartilage (transcartilage and percutaneous recording) or attached to the overlying neck skin (transcutaneous recording) can provide functionality similar to that of ET-based electrodes, and these recording methods enable access to the EMG response of the vocalis muscle that originates from the inner surface of the thyroid cartilage. Studies also indicate that, during surgical manipulation of the trachea, transcartilage, percutaneous, and transcutaneous anterior laryngeal (AL) recording electrodes could be more stable than ET-based surface electrodes and could be equally accurate in depicting RLN stress during IONM. These findings show that these AL electrodes have potential applications in future designs of recording electrodes and support the use of IONM as a high-quality quantitative tool in thyroid and parathyroid surgery. This article reviews the major recent developments of newly emerging transcartilage, percutaneous, and transcutaneous AL recording techniques used in IONM and evaluates their contribution to improved voice outcomes in modern thyroid surgery.
Highlights
Neural Monitoring for Improving Voice Outcomes After Thyroid Surgery thyroid surgery is among the most common and safe interventions in endocrine surgery, the risk of complications is still evitable due to the unique anatomical structure and physiological function of the thyroid gland (1)
This article presents a complete overview of state-of-the-art transcartilage, percutaneous, and transcutaneous anterior laryngeal (AL) recording techniques used in intraoperative neural monitoring (IONM) and compares their contribution to improved voice outcomes in modern thyroid surgery
In the current era in which quality of life is increasingly included as a surgical outcome measure, voice outcome after thyroidectomy is an important consideration for both patients and any clinician involved in managing such patients
Summary
Neural Monitoring for Improving Voice Outcomes After Thyroid Surgery thyroid surgery is among the most common and safe interventions in endocrine surgery, the risk of complications is still evitable due to the unique anatomical structure and physiological function of the thyroid gland (1). One major change in the past two decades is the growing acceptance of intraoperative neural monitoring (IONM) as a tool for minimizing surgical risk by assisting surgeons in the early localization and identification of the RLN and as a tool for assisting clinical decision-making by enabling real-time monitoring of evoked electrophysiologic laryngeal electromyography (EMG) responses during thyroid surgery. EMG recording during neuromonitored thyroid surgery is almost always performed using endotracheal tube (ET) surface electrodes placed in contact with vocal folds during intubation for general anesthesia because of the advantages including their noninvasiveness, wide commercial availability, and capacity to monitor larger areas of the target muscle (4, 5). An ET may be displaced by tracheal and neck extension, which inevitably raises the possibility of rotation or depth change (8–10) Both malpositioning and displacement can cause a false decrease or loss of EMG signal. In addition to the above issues of malpositioning or displacement that may occur during surgical manipulation, other disadvantages of ET include its high expense, the potential for accumulation of saliva to interfere with signal acquisition, and its limited use in pediatric patients and patients with airway abnormality
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