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

Mechanical stimulation of the airways elicits abrupt cardiovascular responses (CVR) in anesthetized humans. We examined a potential difference 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 anesthesia with lidocaine on these responses.

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 patient was mechanically stimulated in a similar manner. The same stimulation was repeated in 15 patients in each group after 5 ml of 4% lidocaine had been sprayed onto the part of the airway being stimulated. To test the systemic effect, intravenous lidocaine 1 mg/kg was given to five patients in each group, followed by the same airway stimulation. Consequent changes in HR and AP were continuously recorded and analyzed.

Significant increases in HR and AP in response to airway tactile stimulation differed in magnitude according to the stimulated sites (L > T > or = B). These responses were completely blocked by topical application of lidocaine and partially blocked by intravenous lidocaine.

We found that CVRs to tactile stimulation differ in their magnitude at three different sites within the airways, and localized anesthesia with lidocaine can abolish these responses in humans. The inhibition of lidocaine could be mainly due to direct blockade of the mechanoreceptors of the airways and partly to its systemic effect.