EFFECTS OF IV LIGNOCAINE ON AIRWAY REFLEXES ELICITED BY IRRITATION OF THE TRACHEAL MUCOSA IN HUMANS ANESTHETIZED WITH ENFLURANE

We have investigated the effects of bolus administration of lignocaine 1.5 mg kg-1 i.v. on respiratory responses to airway irritation induced by instillation of distilled water into the trachea in 10 patients anaesthetized with enflurane (1.5% end-tidal). Before administration of lignocaine, airway irritation elicited not only the cough reflex, but also other respiratory reflexes such as expiration, apnoea and spasmodic panting. Immediately after administration of i.v. lignocaine, when plasma concentrations of lignocaine exceeded 4.7 μg ml-1, tracheal irritation elicited only brief apnoea. Other reflex responses were suppressed completely; they recovered gradually with progressive decrease in plasma concentration of lignocaine. The apnoeic reflex was not eliminated at plasma lignocaine concentrations greater than 7.0 ug ml-1, whereas the expiration reflex, cough reflex and spasmodic panting were eliminated effectively by plasma concentrations of lignocaine greater than 3.5, 2.8 and 2.2 ug ml-1, respectively. © 1990 British Journal of Anaesthesia.