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Differential Sensitivity of Fast and Slow Fibers in Mammalian Nerve: IV. Effect of Carbonation of Local Anesthetics (LA)
  1. Aaron J. Gissen, MD*,
  2. Benjamin G. Covino, PhD, MD and
  3. Joseph Gregus
  1. From the Department of Anesthesia, Brigham and Women's Hospital, Boston, Massachusetts
  2. *Professor of Anesthesia at Harvard Medical School, Boston, MA.
  3. Professor of Anesthesia at Harvard Medical School, Chairman of Department of Anesthesia at Brigham and Women's Hospital, Boston, MA.
  4. Research Associate, Department of Anesthesia, Brigham and Women's Hospital, Boston, MA.


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.

  • Nerve transmission block
  • Effect on block of pH
  • pCO2
  • carbonate salts of LA

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