Airway anaesthesia and the cough reflex.

Topically and intravenously administered local anaesthetic agents are widely used to inhibit cough, but little quantitative, pharmacological data seems to be available. Various aspects of local anaesthetic agents as inhibitors of cough and other airway reflexes are discussed. Nebulized lidocaine dose-dependently inhibited both mechanically (trachea, carina) and ammonia vapour-induced cough. Lidocaine had a similar potency on each type of cough but inhibited that caused by mechanical stimulation for a significantly longer period of time. This observation supports the hypothesis of a more peripheral location for receptors mediating chemical cough. Nebulized tetracaine appeared to be more potent and to have a significantly longer duration of action than lidocaine. The Hering-Breuer inflation reflex was attenuated by both agents and in doses larger than those needed to inhibit cough. This observation is compatible with the view that the cough receptors are located close to the airway lumen and those mediating the Hering-Breuer reflex within the smooth muscle. Airway anaesthesia is commonly used to block the cough reflex during endoscopic procedures. Nebulized lidocaine has been reported also to suppress severe chronic cough but further studies on airway anaesthesia and cough in acute and chronic lung disease are warranted.