Vocal cord paralysis predicted by neural monitoring electrophysiologic changes with recurrent laryngeal nerve compressive neuropraxic injury in a canine model

Background Recurrent laryngeal nerve (RLN) injury is a known complication of thyroid/parathyroid surgery. Intraoperative nerve monitoring (IONM) has been used to gain more information regarding the functional status of the RLN intraoperatively; however, the electromyography (EMG) parameters of RLN after nontransection neuropraxic compressive injury remain unknown. Methods We developed a canine model to identify IONM EMG correlates of postoperative vocal cord paralysis (VCP) using a standardized method to simulate surgical RLN compression sufficient to cause VCP. Results Compression nerve injury decreased EMG amplitude and increased EMG latency, with a 60% increase in RLN threshold stimulation compared to preinjury values. If RLN amplitude decreases by 80% with an absolute amplitude of 300 μV or less in combination with a latency increase of 10% or more, then nerve injury and associated VCP is likely. Conclusion These results may help surgeons to prognosticate postoperative neural function and intraoperative decision-making regarding contralateral thyroid surgery.