Pleural permeability to local anesthetics--the influence of concentration, pH, and local anesthetic combinations.

The transpleural passage of lidocaine, bupivacaine-lidocaine mixtures, and of bupivacaine, with and without epinephrine, was studied in vitro using pleural from piglets. Our objective was to ascertain whether changing physical parameters of local anesthetics such as pH, concentration, and addition of epinephrine might influence the transfer. Rate of transfer is linearly related to concentration at a given pH, but raising the pH increases the rate for bupivacaine. No change in rate was detectable when the pH of lidocaine was increased or in the rate of transfer of bupivacaine when bupivacaine and lidocaine were mixed. The mixture did however facilitate lidocaine flux. Epinephrine [1:200,000] lowers the pH of the solution dramatically but does not statistically change the transpleural passage of bupivacaine. We conclude that the onset of interpleural blockade may be shortened by using more concentrated solutions of bupivacaine whose pH have been modified by the addition of alkali, by using the higher concentrations of lidocaine or by mixing lidocaine with bupivacaine.