RT Journal Article SR Electronic T1 Differential Sensitivity of Fast and Slow Fibers in Mammalian Nerve: IV. Effect of Carbonation of Local Anesthetics (LA) JF Regional Anesthesia: The Journal of Neural Blockade in Obstetrics, Surgery, & Pain Control JO Reg Anesth Pain Med FD BMJ Publishing Group Ltd SP 68 OP 75 DO 10.1136/rapm-00115550-198510020-00004 VO 10 IS 2 A1 Gissen, Aaron J. A1 Covino, Benjamin G. A1 Gregus, Joseph YR 1985 UL http://rapm.bmj.com/content/10/2/68.abstract AB 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.