[Protective effect of lidocaine in maintaining the function of peripheral nerves]

The conduction preserving effect of lidocaine was investigated in sheathed vagus nerves of the rabbit. The nerves were preincubated for one hour in solutions containing either 5 (group I, n = 12) or 20 mmol/l glucose (group II, n = 12). Subsequently, the nerves were deprived of glucose, one half of each group being exposed to 0.1 mmol/l (ca. 0.0025 g/dl) lidocaine hydrochloride. Lidocaine prolonged significantly the 50% and 100% extinction times of compound action potentials of both myelinated A and unmyelinated C axons: In group I, conduction was blocked within 120 +/- 11 and 123 +/- 9 minutes (mean +/- SEM) respectively, whereas in group II conduction block occurred within 174 +/- 16 resp. 183 +/- 17 minutes. In contrast, A and C compound action potentials of nerves incubated without lidocaine were extinguished within 69 +/- 5 and 78 +/- 6 minutes, respectively (group I, p less than 0.001) or 106 +/- 9 minutes (group II, p less than 0.005). The results suggest that administration of subblocking concentrations of lidocaine by standard Bier block technique may increase the margin of safety during operations employing a pneumatic tourniquet, especially if the blood flow to the nerves is impaired by vascular diseases or local anaesthetics containing adrenaline.