Spontaneous and evoked laryngeal electromyography of the thyroarytenoid muscles: a canine model for intraoperative recurrent laryngeal nerve monitoring.

OBJECTIVES: We sought to determine the feasibility of performing spontaneous and evoked intraoperative laryngeal electromyography (L-EMG) using nerve monitoring equipment and to compare recording electrode configurations and methods of recurrent laryngeal nerve (RLN) stimulation in dogs.

METHODS: Four beagles underwent crush injury of the left RLN, and 2 beagles underwent left RLN transection. Serial spontaneous and evoked L-EMG was recorded with the NIM-Response nerve monitoring system under sedation. Transesophageal, percutaneous, and direct open RLN stimulation was performed. Recordings of spontaneous and evoked responses were made with endotracheal tube surface electrodes and bipolar vocal fold needle electrodes. The L-EMG procedures were repeated every 1 to 2 weeks after injury, and intersubject and intertrial differences were evaluated.

RESULTS: Low-amplitude motor unit action potentials, polyphasic potentials, fasciculations, and fibrillations were detected in injured animals with bipolar needle recording electrodes with this system of spontaneous L-EMG. The surface recording electrodes did not detect pathologic waveforms. Percutaneous needle stimulation of the RLN is possible at currents slightly higher than those used for direct stimulation. Consistent, discrete, transesophageal stimulation of the RLN could not be reliably performed. Recording evoked responses with needle electrodes generated sharper waveforms, facilitating calculation of latency and wave duration. Evoked L-EMG utilizing surface recording electrodes limited the intertrial and intersubject variability of evoked amplitude.

CONCLUSIONS: Typical patterns of nerve injury can be detected with this system of intraoperative L-EMG in a canine model. Quantitative measures of amplitude, latency, and wave duration in healthy and injured canine RLNs may be determined with this system.