Objective Gradual impairment of nerve conduction is expected to be tightly associated with simultaneous gradual loss of vocal cord contractility, related to the fact that injured axons are connected to a defined number of muscle cells. In clinical studies, there is a time gap between observed adverse electromyographic (EMG) changes and examination of vocal cord function. This study evaluates the impact of intraoperative EMG changes on synchronous vocal cord contractility by simultaneous use of continuous intraoperative neuromonitoring (C‐IONM) and accelerometry for registration of actual vocal cord function at a given change of EMG amplitude. Methods EMG was obtained following vagus nerve stimulation by use of C‐IONM. A vocal cord accelerometer probe that could be attached to the vocal cords was developed based on a LIS3DH ultra low‐power high performance three axis linear accelerometer (STMicroelectronics, Geneva, Switzerland). Accelerometer data were registered continuously together with EMG data during traction injury of the recurrent laryngeal nerve (RLN) until an amplitude depression ≤100 μV. Results Six RLN from four immature domestic pigs were studied. Vocal cord contractility assessed by vocal cord accelerometry decreased in parallel with EMG amplitude, with significant correlations ranging from 0.707 to 0.968. Conclusion Decrease of EMG amplitude during traction injury to the RLN injury is closely associated with a parallel drop in vocal cord contractility. Level of Evidence NA Laryngoscope, 130:1090–1096, 2020
Objective: If bilateral thyroid surgery is planned and staged thyroidectomy considered in case of loss of neuromonitoring signal (LOS), a waiting time of 20 minutes is suggested for evaluation of early nerve recovery. This recommendation is based on clinical observations and has not been thoroughly validated experimentally. Methods: Sixteen pigs were randomly studied, and electromyogram (EMG) was continuously recorded during traction injury until an amplitude decrease of 70% from baseline (BL) (16 nerves) or LOS (16 nerves), and further during 40-minute recovery time. At the end of the experiments, vocal cord twitch was evaluated by videolaryngoscopy. Results: In the 70% group, 8 of 16 nerves recovered to or above an amplitude of 50% of baseline after 20 minutes and finally one more after 40 minutes. In the LOS group, only one nerve showed recovery after 20 minutes and one more after 40 minutes. Video-laryngoscopy revealed good or strong vocal cord twitches, in 10 of 14 nerves in the 70% group and in only 2 of 14 nerves in the LOS group. Conclusions: The overall intraoperative recovery was low after LOS. Even after 70% amplitude depression, only half of the nerves showed recovery to amplitudes ≥50% of BL. Nerve recovery is dynamic, and a waiting time of 20 minutes seems appropriate for the identification of early nerve recovery before decisions are taken to continue or terminate surgery. The final EMG amplitude was not always well correlated with estimated vocal cord twitch, evaluated by video-laryngoscopy. This observation needs further investigation. K E Y W O R D S intraoperative neuromonitoring, recurrent laryngeal nerve recovery, vocal cord twitch 1 | INTRODUCTION Implementation of continuous intraoperative neuromonitoring (C-IONM) gives the opportunity to real-time surveillance of the recurrent laryngeal nerve (RLN) during thyroid mobilization and nerve dissection. C-IONM compared to intermittent IONM (I-IONM) recognizes impending nerve injury and enables the assessment of intraoperative recovery of nerve function after loss of the
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