[Signal evaluation of continuous vagal nerve stimulation for recurrent laryngeal nerve protection in thyroid surgery].
BACKGROUND
Newly developed vagal stimulation probes permit continuous intraoperative neuromonitoring of the recurrent laryngeal nerve during thyroid resection. A complete signal loss indicates an interrupted nerve conductance. There are no other criteria so far which may serve as warning criteria for imminent nerve function impairment.


METHODS
The vagal stimulation probe V3 was used in 50 patients with thyroid resection (96 nerves at risk) and recorded during the complete operation (V3, adhesive tube electrode, bipolar needle electrode; Fa. Inomed, Teningen, Germany). The signal parameters amplitude, latency and thresholds of nerve conductance were compared before start-ing thyroid resection and after finishing thyroid preparation. The changes of these parameters were analysed.


RESULTS
Complete signal loss was documented in 2 cases and vocal cord palsy confirmed laryngoscopically. Changes of the signal amplitude were seen in range from - 51% to + 243% after resection. The latencies (right vagal nerve 4.39 +/- 0.51 ms; left vagal nerve 6.78 +/- 0.75 ms) remained unchanged during the complete resection time. Lower threshold of nerve conduction varied from 0.5 to 2.5 mA, the upper threshold from 1.5 to 5.0 mA. All recorded changes of these parameters were not associated with laryngoscopic vocal cord disorders.


CONCLUSIONS
Continuous intraoperative neuromonitoring permits an immediate problem solving reaction of the surgeon in the case of complete signal loss. The parameters signal amplitude, latency and conduction threshold cannot be applied as additional warning criteria for nerve function impairment during thyroid resection.
Jonas
J
J
St. Marienkrankenhaus, Klinik für Allgemein-, Gefäss- und Visceralchirurgie, Frankfurt, Deutschland. jjonas047@gmx.de
D004867:Equipment Design; D005500:Follow-Up Studies; D006801:Humans; D007431:Intraoperative Complications / Q000175:diagnosis / Q000503:physiopathology*; D007828:Laryngoscopy; D016343:Monitoring, Intraoperative / Q000295:instrumentation*; D009431:Neural Conduction / Q000502:physiology; D011930:Reaction Time / Q000502:physiology; D012009:Recurrent Laryngeal Nerve / Q000503:physiopathology*; D061226:Recurrent Laryngeal Nerve Injuries; D015203:Reproducibility of Results; D012684:Sensory Thresholds / Q000502:physiology; D012815:Signal Processing, Computer-Assisted / Q000295:instrumentation*; D013965:Thyroidectomy; D055536:Vagus Nerve Stimulation / Q000295:instrumentation*; D014826:Vocal Cord Paralysis / Q000175:diagnosis / Q000503:physiopathology