Abstract

Carbonation can mean either the use of carbonate salts of the local anesthetics (LA) or aerating a solution of LA with carbon dioxide (CO₂) gas. Both methods were found to potentiate the nerve blocking effects of bupivacaine on isolated nerve preparations. The molecular CO₂ in such solutions readily diffuses through tissue membranes resulting in an increase in intracellular hydrogen ion concentration; this leads to an increase in the protonated form of LA and thus to a potentiation of nerve block. In addition we present evidence that there is a decrease in the hydrogen ion concentration immediately outside the cell membrane subsequent to CO₂ diffusion that increases the concentration of the uncharged form of LA outside the cell and this favors LA diffusion into the cell. There is no evidence that carbonation, per se, alters the diffusion characteristics of the membranes, changes the nerve membrane sensitivity, or alters LA behavior except as caused by changes in hydrogen ion concentration.