Proposals for Standardization of Intraoperative Facial Nerve Monitoring during Parotid Surgery

Abstract

Intraoperative facial nerve monitoring (FNM) has been widely accepted as an adjunct during parotid surgery to facilitate identification of the facial nerve (FN) main trunk, dissection of FN branches, confirmation of FN function integrity, detection of FN injury and prognostication of facial expression after tumor resection. Although the use of FNM in parotidectomy is increasing, little uniformity exists in its application from the literature. Thus, not only are the results of many studies difficult to compare but the value of FNM technology is also limited. The article reviews the current literature and proposes our standardized FNM procedures during parotid surgery, such as standards in FNM setup, standards in general anesthesia, standards in FNM procedures and application of stimulus currents, interpretation of electrophysiologic signals and prediction of the facial expression outcome and pre-/post-operative assessment of facial expressions. We hope that the FNM standardized procedures will provide greater uniformity, improve the quality of applications and contribute to future research.

Facial nerve monitoring in parotid gland surgery: Design and feasibility assessment of a potential standardized technique

“…This descriptive review article does not involve a series of patients, and it is not clear if they have encountered intra‐ or postoperative facial muscle palsies in their patients, due to this high‐energy delivery. We certainly do not do this type of approach based on the warning delivered by the system itself 9,10,22–29,31 …”

“…Even though there are significant differences in each process of stimulation of the RLN and the FN, a precise directive to advise what action to take if the parotid gland surgeon is faced with a loss of signal has not yet been described. Once the process of FN stimulation is started in the main trunk or in the subsequent branches, surgeons should keep in mind the initial responses of the nerve F 1 ‐pre‐dissection amplitude and latency to compare it with the final F 2 ‐post‐dissection numbers; however, just as in the RLN monitoring process, at any time the main trunk or particular branch can be stimulated and compared with the FN1 or a prior one, especially if the surgeon considers that trauma has been inflected to the nerve 20,22 …”

“…Different from the established and accepted guidelines for RLN neuromonitoring, there is not yet a multidisciplinary effort from parotid‐gland surgeons around the world to describe a given number to call a loss of signal during the FN monitoring process. An adaptation of the process learned from the RLN practice guides is useful, and it should be taken as a starting point for future reference building of individualized FN monitoring guidelines based on the experience gained and the few articles published so far in this matter 9,10,21,22 …”

“…Once it is set to go beyond 3 mA, the monitor will show a warning that such a higher level of energy may Note: Superior (Frontalis) and inferior (Mentalis) branches findings potentially harm the nerve. A recent review article by Chiang et al 22 describes their process of stimulation of the FN, starting with 10 mA just as the skin flap is raised; as the tragal pointer is approached, this is lowered to 3-5 mA. This descriptive review article does not involve a series of patients, and it is not clear if they have encountered intra-or postoperative facial muscle palsies in their patients, due to this high-energy delivery.…”

“…We certainly do not do this type of approach based on the warning delivered by the system itself. 9,10,[22][23][24][25][26][27][28][29]31 Loss of signal A loss of signal (LOS) status after trauma to the RLN is determined when these factors are present: a 50% reduction of the original amplitude numbers or a prolongation of the latency; a dramatic drop of the amplitude to 100 µV, usually meaning a severe trauma that definitively will not stand a chance to recover intra-operatively, along with the absence of ipsilateral contraction of the larynx when the nerve is directly stimulated, and the surgeon's finger is placed under the larynx without sensing any vocal cord mobility (Laryngeal twitch)…”