Reversible conduction block in frog sclatic nerve for three different concentrations of bupivacaine

Abstract

We examined the effects of various concentrations of the bupivacaine commonly used for spinal anaesthesia on thereversibility of conduction block in isolated frog sciatic nerves measured by the extracellular recording technique. Seventy-twoisolated nerves were divided into 3 groups (n = 24), each of which was bathed in a different bupivacaine solution in a range ofconcentrations (10, 20 or 30 mM for 20 min). In each group, the extracellular action potentials were recorded before exposure tothe bupivacaine solution to provide the control data. The extracellular action potentials were recorded after 20 min exposure to thedrug by using a BIOPAC MP 100 acquisition system version 3.5.7 (Santa Barbara, USA). The nerves were washed continuously for3 h with Ringer’s solution and action potentials were recorded. The nerves were then soaked overnight at room temperature inRinger’s solution and tested for impulse recovery. The data were analysed with repeated-measures analysis of variance using SPSS9.05 for Windows. In the presence of 10 mM, 20 mM or 30 mM bupivacaine, the extracellular action potential amplitude decreasedby 23.21 ± 12.42%, 28.42 ± 17.51% and 39.45 ± 22.16%, respectively, relative to the control amplitude (P < 0.05); it recoveredto 89.21 ± 50.00%, 66.43 ± 30.10% and 47.12 ± 37.51% (P < 0.05), respectively, after 3-h of wash, and reached 110.31 ±50.13%, 90.60 ± 43.21% and 130.43 ± 56.32% (P < 0.05), respectively, after the overnight soaking process. This study showedthat exposing the nerve to high concentrations of bupivacaine causes an reversible impulse blockade and that bupivacaine does nothave neurotoxic effects on isolated frog sciatic nerves.