Plasma concentrations of lignocaine and its metabolites during fibreoptic bronchoscopy

Lignocaine metabolites are known to have both antiarrhythmic and toxic effects. Large plasma concentrations of these metabolites have been reported following endotracheal instillation of lignocaine. We measured plasma lignocaine monoethylglycinexylidide (MEGX), and glycinexylidide (GX) concentrations for up to 4h after fibreoptic bronchoscopy. The total dose of lignocaine required to suppress coughing varied between 230 mg and 364 mg. Small therapeutic lignocaine concentrations occurred transiently in nine of 19 patients after the bronchoscopy examination had finished. Only one patient achieved a plasma lignocaine concentration in the range of minor toxicity. Metabolite peaks occurred later and were of much smaller magnitude. They were unlikely to contribute to prophylaxis of cardiac arrhythmia or to toxicity. It would seem to be safe to use topical lignocaine in doses greater than the currently recommended maximum (200 mg) in conscious patients during fibreoptic bronchoscopy.