Lidocaine effects on the laryngeal chemoreflex, mechanoreflex, and afferent electrical stimulation reflex.

The use of lidocaine hydrochloride as either a topical or intravenous agent has become a common practice for minimizing laryngospasm and the reflex cardiovascular effects resulting from upper airway manipulation. The efficacy and mechanism of action of lidocaine for this purpose remain unclear. We evaluated the effect of lidocaine on the laryngeal chemoreflex (LCR), mechanoreflex (LMR), and superior laryngeal nerve electrical stimulation adductor reflex (SLN-ESAR) in piglets. Cardiopulmonary responses were used to assess LCR and LMR. Latency following SLN stimulation was used to assess SLN-ESAR. Intravenous lidocaine hydrochloride at 3 mg/kg produced no suppression of the LCR, LMR, or latency (SLN-ESAR onset latency before lidocaine 11.7 +/- 0.7 milliseconds, after lidocaine 12.2 +/- 0.5 milliseconds; peak latency before lidocaine 13.2 +/- 0.2 milliseconds, after lidocaine 13.4 +/- 0.4 milliseconds). Topically applied lidocaine at the same dose eliminated both LCR and LMR responses in all animals, with return of reflex responses 15 minutes after application. No effect on the SLN-ESAR was seen with application of topical lidocaine. This study supports topical lidocaine as a suppressant of laryngeal mucosal neuroreceptors without central neural reflex effects. Intravenous lidocaine did not affect peripheral neuroreceptors, nor did it significantly affect the latency of the SLN-ESAR neural reflex arc. Intravenous and topical lidocaine differ in mechanism of action and efficacy with regard to modulation of reflex effects induced by laryngeal stimulation.