Plasma concentrations of lignocaine and its metabolites during fibreoptic bronchoscopy

Abstract

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 monoethyiglycinexylidide (MEGX), and glycinexylidide (GX) concentrations for up to 4 h after fibreoptic bronchoscopy. The total dose of lignocaine required to suppress coughing varied between 230 mg and 364 rag. Small therapeutic lignocaine concentrations occurred transiently in nine of 19 patients after the bronchotcopy examination had finished. Only one patient achieved a plasma lignocaine concentration in the range of minor toxidty. Metabolite peaks occurred later and were of much smaller magnitude. They were unlikely to contribute to prophylaxis of cardiac arrhythmia or to toxkity. It would seem to be safe to use topical lignocaine in dotes greater than the currently recommended maximum (200 mg) in conscious patients during fibreoptic bronchoscopy. © 1982 The Macmillan Press Ltd.