Serum concentrations of lignocaine and its metabolite monoethylglycinexylidide during fibre-optic bronchoscopy in local anaesthesia.

Fibre-optic bronchoscopy was performed in local anaesthesia using lignocaine. Serum concentrations of lignocaine and its active metabolite monoethylglycinexylidide (MEGX) were measured in 16 patients at regular intervals up to 120 min after administration. Lignocaine was administered as an aerosol in the upper respiratory tract and as a solution in the bronchial tree. The total dose of lignocaine ranged from 243 to 608 mg (2.4-8.0 mg kg-1 body weight). The dose of lignocaine given as an aerosol ranged from 163 to 508 mg (1.6-6.6 mg kg-1) and the dose given as a solution ranged from 60 to 180 mg (0.8-2.5 mg kg-1). The highest median serum lignocaine concentration, 10.5 mumol l-1, was measured 20 min after administration. None of the patients had toxic serum lignocaine levels (> 26 mumol l-1) or adverse effects. The highest median serum MEGX concentration, 1.7 mumol l-1, was measured 120 min after administration. The dose of lignocaine, expressed in mg per kg body weight correlated with serum lignocaine and serum MEGX (rs = 0.47 and rs = 0.39, respectively). Lignocaine is a clinically safe, local anaesthetic agent provided the total dose does not exceed 6-7 mg kg-1 body weight.