Efficacy of Intravenous Lidocaine in the Operative Management of Thyroid Surgery With Intraoperative Nerve Monitoring

Intra Operative Nerve Monitoring ( IONM) is rapidly becoming a standard of care in many institutions across the country. While the overall incidence of nerve palsy is low, when it occurs it is a devastating lifelong handicap . Several studies have documented that routine identification of the RLN with IONM has decreased the rates of permanent RLN palsy It is not designed to visualize the recurrent laryngeal nerve (RLN), but to allow intra-operative assessment of RLN function as well as to establish a prognosis in patients developing RLN paralysis. Complete functionality of the IONM depends on near total laryngeal relaxation and reflex suppression without the use of neuromuscular blocking agents (NMBAs). The depth of anesthesia required to meet that criteria often leads to hemodynamic instability.

When the IONM signal is unchanged after the resection, the surgeon can be reassured that postoperative vocal cord function is normal in 99.6% of cases. Where the IONM signal is absent or abnormal, 30-45% of the patients will develop vocal cord dysfunction postoperatively The successful deployment and data analysis from the IONM depends upon the complete laryngeal relaxation and reflex suppression. The IONM causes strong contractions of the vocal cords and is an independent cause of laryngeal alterations . The surgical procedure is a strong factor of stress to the larynx with a potentially traumatic manipulation at the level of the larynx . Complete functionality of the IONM constitutes before the full electromyographic recovery of the NMB at the adductor pollicis muscle , as the laryngeal muscles recover faster than the peripheral muscles . The anesthetic technique chosen should ensure absolute laryngeal reflex suppression as the effect of the short acting depolarizing muscle relaxant is wearing off immediately following intubation, until preferably the extubation. Be it total intravenous anesthesia or inhalation-based anesthesia, the depth required for reflex suppression can cause profound cardiovascular instability. While the attempts to titrate down the anesthetic depth can cause resurfacing of the troublesome laryngeal reflexes, attempts to counter the side effects with sympathomimetic agents can themselves result in a myriad of undesirable hemodynamic consequences. The resulting hemodynamic fluctuations can result in adverse outcomes in patients with significant cardiovascular co-morbidities.

Laryngoscopy with or without intubation, provokes a sympathoadrenal response. These events are especially detrimental in individuals who have limited myocardial reserve because of age or disease; these include geriatric population and those with significant coronary arteriosclerosis as in diabetes mellitus, sustained hypertension, angina, ischemic heart disease and cardiac dysrhythmias . IV lidocaine decreases the intracellular Ca2+ concentration in airway smooth muscle, decreases myofilament Ca2+ sensitivity and has been shown to suppress coughing and prevent reflex broncho constriction. Injected intravenously, lidocaine is variably effective in blunting the hemodynamic response to tracheal intubation .

IV lidocaine has analgesic, anti-hyperalgesic and anti-inflammatory properties. Local anesthetics can reduce the postoperative inflammatory response in several ways such as blocking neural transmission at the site of tissue injury and thus attenuating neurogenic inflammation. In addition because of anti-inflammatory properties of their own, they may inhibit the migration of granulocytes and release of lysosomal enzymes, consequently leading to a decreased release of pro-inflammatory cytokines. Pro-inflammatory cytokines can induce peripheral and central sensitization, leading to pain augmentation (hyperalgesia)

Because of its plasma half life of 8 min, an IV bolus of 1 - 1.5 mg/kg lidocaine must be followed by infusion of 1 - 4 mg/min in adults in order to maintain therapeutic levels of 1.5 - 4 μg/mL (15, 16). Lidocaine side effects have never been reported in its intended use, probably because the first clinical signs of toxicity occur at considerably high blood concentrations (> 5 μg/mL), which did not occur even when IV lidocaine was given continuously over 14 days . Lidocaine infusion at the rate of 1.5 mg/kg/h following a bolus of 1.5 mg/kg has been employed in a newborn to perform an intra-operative wake-up test during neurosurgery . It was also used during thyroidectomy in 60 y old patient with cardiac co morbidities This will be a prospective double blinded randomized controlled trial done at Bronx Lebanon Hospital Center. 60 consecutive patients undergoing thyroidectomy using nerve monitoring will be randomized into two groups of thirty each. One group will receive IV Lidocaine infusion during the surgery to facilitate the nerve monitoring. The other group will receive a placebo.