Kontinuierliches intraoperatives Neuromonitoring des Nervus facialis in der Parotischirurgie

Background: Postoperative facial palsy is the most common complication of parotidectomy. The aim of intraoperative neuromonitoring (IONM) is to lower the rate of paresis. However, in parotid surgery, this method has not developed further from pure differentiation of the nerve from the surrounding tissue. On the other hand, there has been significant progress in the field of IONM in recent decades. Especially in thyroid surgery and the surgery of the cerebello-pontine angle, a continuous analysis of the amplitudes and latencies takes place in real time, which is referred to as continuous IONM (cIONM). The analysis is made possible either by active continuous stimulation of the nerve or passively by the analysis of the generated nerve pattern. The aim is to recognize an impending nerve injury early and to modify the operative maneuver. This has demonstrated the reduction of the paresis rates in the mentioned surgeries. Furthermore, the cIONM offers predictive power regarding postoperative nerve function. The plausibility of the cIONM in parotid surgery has not yet been investigated. In our study, we aim to demonstrate the safe use of the Saxophone stimulation electrode on the facial nerve trunk. Methods: As part of a prospective study approved by the Ethical Committee of the Saxonian Chamber of Physicians (EK-BR-53 / 16-1) and pre-registered at the German Clinical Trial Register (DRKS-ID: DRKS00011051, http://www.drks.de), a parotidectomy with continuous stimulation of the facial nerve was performed in 40 patients using the Saxophone® electrode (AVALANCHE XT system, Dr. Langer Medical, Waldkirch, Germany). The data from these 40 operations (cIONM group) were compared with the data from another 40 parotidectomies that were only monitored by intermittent stimulation with the same system but without the use of a continuously stimulating electrode (iIONM group). All patients had normal facial nerve function preoperatively (HOUSE-BRACKMANN grade I). Results: The stimulation threshold of the cIONM group was significantly lower than that of the iIONM group (p<0.0001). The rate of early facial palsy was 50% in the cIONM and 30% in the iIONM group. In the long term, only 2.5% of the patients in the cIONM group and 10% of patients in the iIONM group showed facial palsy. There was no significant difference neither for early (p = 0.11) nor for long-term (p = 0.17) facial palsy between the two groups. In the cIONM group there was no correlation between the stimulation threshold (p = 0.74) or the stimulation duration (p = 0.51) and facial palsy. Conclusion: cIONM with the Saxophone electrode is safe in parotid surgery because it doesn’t cause more complications compared to a routine intermittent IONM. This is a prerequisite for the future development of this method. The goal is to identify the pattern of impending nerve injury, which could lead to a reduction of the rate of facial palsy using optic or acoustic warn signals. The cIONM is not a perfect method because disadvantages such as false negative alarms and technical artifacts are inevitable. Proper planning of the operation combined with meticulous preparation is essential.