Anesthetics produce pain on skin infiltration (1,2). The relation of this local anesthetic-induced pain to pH of the local anesthetic solution has, however, not been evaluated. Commercial preparations of local anesthetics are prepared as acidic solutions of the salts to promote solubility and stability. Further increases of acidity in local anesthetic solutions containing epinephrine are avoided by the addition of epinephrine to plain lidocaine (3); sodium bicarbonate can also be used to increase pH. Such increases in pH, by increasing the ratio of nonionized to ionized local anesthetic, alter the pharmacologic properties of local anesthetics. For example, addition of sodium bicarbonate to preparations of local anesthetics increases spread and duration of sensory blockade and lessens the time to onset of anesthesia (4,5). The present double-blind, randomized study was designed to determine the relation between pH of anesthetic solutions and production of pain associated with infracutaneous injection of the local anesthetic, lidocaine.
Address correspondence to Dr. McKay, Department of Anesthesia, Brigham and Women's Hospital, 75 Francis Street, Boston, MA 02115.
© 1987 International Anesthesia Research Society