Effects of lidocaine at the plasma concentrations obtained by peridural injection on atrioventricular conduction disorders

The aim of this study was to measure plasma concentrations obtained during lidocaine extradural blocks, and to determine whether these concentrations were able to induce high degree AV blocks in patients with impaired AV conduction. In a preliminary study, 12 patients were given an extradural block with an initial bolus of 3.4 mg . kg-1 lidocaine. After repeat injections, the mean total dose was 4.7 mg . kg-1. Plasma lidocaine concentrations were determined over an 8 h period after the first injection. The study itself was carried out in 14 patients with conduction disturbances undergoing His-bundle exploration. After informed consent had been obtained, the patients received an intravenous bolus of lidocaine (1.6 mg . kg-1 over 30 s). After baseline values had been measured. His conduction and lidocaine plasma concentrations were recorded 2, 5, 10, 30 and 60 min after lidocaine injection. In the preliminary study, the peak plasma lidocaine concentration was obtained at the 15th min (1.22 +/- 0.81 microgram . ml-1). In the second series, no clinical disturbance was seen after the i.v. injection of lidocaine. The peak plasma lidocaine concentration was obtained at the 2nd min (3.05 +/- 1.44 micrograms . ml-1). No significant alteration of conduction occurred after intravenous lidocaine. It is therefore possible to conclude that bifascicular AV disturbances do not constitute a contraindication to extradural anaesthesia with lidocaine.