Effectiveness of lidocaine infusion on the functionality of intraoperative monitoring of the recurrent laryngeal nerve during thyroid gland surgery

Abstract

Intraoperative nerve monitoring (INM) to assess for recurrent laryngeal nerve dysfunction during thyroid surgery is becoming the standard of care in many institutions. Successful provision of data analysis with the help of IONM requires complete relaxation of the larynx and suppression of the reflex. We investigated the role of intravenous lidocaine in providing such working conditions to ensure the least impact on hemodynamic changes and obtain better conditions for working with IONM. The study aims to evaluate the effect of lidocaine, administered intravenously in estimated doses, on the IONM and laryngotracheal reflexes during surgical interventions on the thyroid and parathyroid glands. Methods: Forty-six patients were randomly assigned to Group 1 where lidocaine was administered and Group 2 where no lidocaine was administered. All patients were anaesthetized with a narcotic analgesic and inhalation anaesthetic. The loading dose of lidocaine was administered at the rate of 1 mg/kg intravenously, and the maintenance dose was calculated at 1.5 mg/kg/hour. For IONM, a Dragonfly single-channel laryngeal surface electrode (C2 NerveMonitor; 8 channel system for intraoperative Neurophysiological Monitoring, GERMANY) attached to a cuffed ETT #7 (MEDICARE, China) was used during surgery the same to the manufacturer's instructions. Results: The number of patients who required StMC strength at 0.5 mA (the manufacturer's recommended strength is 1.5 mA) was significantly higher in the lidocaine group (P=0.001) than in the no lidocaine group (P=0, 00006). The same number of patients with < 50% DAIL at the end of surgery was significantly higher in group 1 than in group 2. In addition, the proportion of patients with hypotensive episodes and blood pressure medication requirements more than twice during surgery was significantly lower in group 1 than in group 2 (P < 0.05). Conclusions: Patients who were prescribed lidocaine intravenously were more resistant to laryngotracheal irritation during surgery, and this made it possible to maintain such a condition of the larynx, which was necessary to ensure increased relaxation of the larynx and suppression of reflexes when using IONM. Our ability to elicit a positive signal with StMC 0.5 mA intraoperatively and provide a DAIL < 50% before the end of surgery was statistically significant in the IV lidocaine group (group 1).