RESUMO
BACKGROUND: Intraoperative nerve monitoring (IONM) to assess the recurrent laryngeal nerve function during thyroid surgery is becoming the standard of care across many institutions. The successful deployment and data analysis from the IONM require complete laryngeal relaxation and reflex suppression. We investigated the role of intravenous lidocaine infusion (IVLI) to provide such operating conditions, under a lighter plane of anesthesia and fewer hemodynamic fluctuations. METHODS: Sixty-five patients were randomly assigned to lidocaine group (LG) or placebo group (PG) based on the computer-generated coding developed by the pharmacy department. The study medication (SM) was delivered by the pharmacist in a pre-filled coded syringe to the investigator 30 min prior to the surgery. All the patients were anesthetized by narcotic and inhalation based general anesthesia. The SM was administered at the rate of 1.5mg/kg/h following a loading dose of 1 mg/kg. Dragonfly® laryngeal surface electrode and Nerveana® nerve locator system were used for IONM during surgery. RESULTS: The proportion of patients requiring lower strength stimulating current (StMC) at 0.5 mA was significantly higher in the LG than in the PG (X2 (1, N = 61) = 10.1615, P = 0.001434). Similarly, the proportion of patients with the drop in the aggregate impedance level (DAIL) by < 50% at the end of surgery was significantly higher in the LG than in the PG (X2 (1, N = 61) = 15.982, P = 0.000064). In addition, the proportion of patients with the hypotensive episodes requiring rescue medications more than twice during surgery was significantly lower in the LG than in the PG (X2 (1, N = 61) = 0.0183, P < 0.05). CONCLUSIONS: The enhanced laryngeal relaxation and the reflex suppression afforded by the IVLI could have enabled a lower StMC to elicit a positive signal. The lower StMC promotes less intense laryngeal alterations as evidenced by the lower DAIL in the LG. IVLI can enhance the functionality of the IONM during prolonged operating time and the resultant increased number of IONM stimulations, while providing a stable hemodynamic environment.
RESUMO
Intra-operative nerve monitoring (IONM) is rapidly becoming a standard of care in many institutions across the country. In the absence of neuromuscular blocking agents to facilitate the IONM, the depth of anesthesia required to abolish the laryngo tracheal reflexes often results in profound hemodynamic instability during surgery, necessitating the use of large doses of sympathomimetic amines. The excessive alpha and beta adrenergic effects exhibited by these agents are undesirable in the presence of cardiovascular co-morbidities. Trying to strike a balance frequently results in an unsatisfactory intra-operative course. In the course of the near total thyroidectomy performed on a 60-year-old female, we employed lidocaine infusion at 1.5 mg/kg/hour following a bolus dose of 1 mg/kg. The troublesome laryngo tracheal reflexes were successfully blunted and we were able to moderate the depth of anesthesia resulting in stable hemodynamics. A bispectral index monitor was employed to guard against "recall" and a train of four monitor was used to ensure the absence of inadvertent neuromuscular blockade. During the surgery, there was loss of signal on the left recurrent laryngeal nerve (RLN). The signal strength was restored by rotating the endotracheal tube on its long axis to realign the electrode with the vocal cords under Glidescope(®) visualization.
