Differences in cardiovascular response to airway stimulation at different sites and blockade of the responses by lidocaine

Background: Mechanical stimulation of the airways elicits abrupt cardiovasc ular responses (CVR) in anesthetized humans. We examined a potential differ ence in such responses by comparing changes in heart rate (HR) and arterial blood pressure (AP) responses to mechanical stimulation of three different parts of the airways, as well as the effects of localized airway anesthesi a with lidocaine on these responses. Methods: After induction of general anesthesia, the larynx under laryngeal mask insertion (L, n = 20), the trachea-carina under tracheal intubation (T , n = 20), or the bronchus under bronchial intubation (B, N = 20) of each p atient was mechanically stimulated in a similar manner. The same stimulatio n was repeated in 15 patients in each group after 5 mi of 4% Lidocaine had been sprayed onto the part of the airway being stimulated. To test the syst emic effect, intravenous Lidocaine 1 mg/kg was given to five patients in ea ch group, followed by the same airway stimulation. Consequent changes in HR and AP were continuously recorded and analyzed. Results: Significant increases in HR and AP in response to airway tactile s timulation differed in magnitude according to the stimulated sites (L > T g reater than or equal to B), These responses were completely blocked by topi cal application of lidocaine and partially blocked by intravenous lidocaine . Conclusions: We found that CVRs to tactile stimulation differ in their magn itude at three different sites within the airways, and localized anesthesia with lidocaine can abolish these responses in humans. The inhibition of li docaine could be mainly due to direct blockade of the mechanoreceptors of t he airways and partly to its systemic effect.