Abstract

The blocking action of the local anesthetic (LA) drug bupivacaine applied to the isolated sheathed nerve trunk is potentiated by the use of alkaline media (increase in pH). There is a linear relationship between log-rate of block (min) and log-concentration of LA (uncharged concentration, mM). The linear regression equation for rate of block for slow conducting nerve fibers is steeper (faster rate of block) than that for fast conducting nerve fibers. Analysis of the effect of pH on the blocking action of LA drugs indicates the likelihood of support for our previous findings: (1) the rate of block of slow conducting fibers is faster than for fast conducting fibers, and (2) at steady-state equilibrium block fast conducting fibers are more profoundly blocked than slow conducting fibers because of a lower safety margin for transmission in fast fibers.