Translational study on recurrent laryngeal nerve temperature susceptibility

Background: Recurrent laryngeal nerve (RLN) injury is the most common and serious complication after thyroid surgery. However, little is known about the temperature threshold leading to RLN injury. In this study, we investigated threshold temperatures that cause RLN injury during thyroid surgery using continuous intraoperative neuromonitoring in swine models. Methods: Four pigs weighing 30 to 40 kg were used for this study. We applied automatic periodic stimulation to the vagus nerve and dissected the RLN. The operative field was then filled with water at various temperatures (1.9C to 87.4C). The threshold temperature was defined as the temperature measured before filling the operative field that was associated with adverse events (latency increase of more than 10% or amplitude decrease of more than 50%). Loss of signal was defined as the electromyography (EMG) signal disappearing and not recovering during 30 min of observation. Results: The low and high threshold temperatures were 2.5C and 81.5C, respectively. There were no adverse events at surrounding temperatures between 5.9C and 77.5C. The EMG signals in the RLNs exposed to the low threshold temperatures recovered, and there was no loss of signal. In contrast, the RLNs that showed adverse events at the high threshold temperatures showed loss of signal and no recovery of EMG signals. Conclusions: The RLN was found to be resistant to cold injury, whereas surrounding temperatures above 81.5C may cause permanent thermal injury to the RLN. The surrounding temperature should be controlled within the safe range during thyroid surgery to avoid RLN injury