Reversible conduction block in isolated frog sciatic nerve by high concentration of bupivacaine

We evaluated the effects of a high concentration of bupivacaine commonly used for spinal anaesthesia on the reversibility of conduction block and compound nerve action potential (CNAP) parameters in isolated frog sciatic nerve measured by extracellular recording technique. Isolated frog sciatic nerves were bathed in 1.3% bupivacaine solution for 20 min. In each nerve, action potentials were recorded before exposure to bupivacaine solution, which served as the control data. The extracellular action potentials were recorded after 20 min in the drug by using a BIOPAC MP 100 Acquisition System Version 3.5.7 (Santa Barbara, USA). The nerves were washed for 3h continuously with Ringer's solution and action potentials were recorded. The nerve was then soaked overnight in Ringer's solution at room temperature and tested for impulse recovery. There were significant differences among the experiments regarding CNAP peak-to-peak amplitude, area and duration but conduction velocities among the experiments did not show any statistical difference. In the presence of bupivacaine the extracellular action potential amplitude decreased by 46.99+/-29.31% relative to the control amplitude (P<0.05), recovered to 47.10+/-26.90% after 3h of wash, and reached 123.20+/-39.70% after the overnight soak process. This study showed that exposing nerve to high concentration of bupivacaine causes reversible impulse blockade and that bupivacaine does not cause neurotoxic effect on isolated frog sciatic nerve.