[pH-adjusted lidocaine HCl with or without epinephrine for epidural anesthesia]

Preparations of local anesthetics are prepared as acidic solutions of the salts to promote solubility and stability. In solution, these salts exist as both nonionized and ionized forms. The ratio depends on the pH of the solution, and it is only the non-ionized form that permeates the nerve membrane and sheath. This study of epidural analgesia was undertaken to determine the effect of increasing the pH of the lidocaine HCl by the addition of sodium bicarbonate. Parameters studied included the time of onset of analgesia (time between the completion of injection and the loss of scratch sensation at the left L1 dermatome), the spread of sensory blockade, the degree of motor block, and the blood pressure and heart rate. Eighty seven adult patients undergoing epidural anesthesia were divided into four groups. Group 1 patients were given 2% lidocaine HCl solution plus 1.5 mL normal saline per 10 mL of lidocaine (pH 5.55). Group 2 patients were given 2% lidocaine HCl solution plus 1.5 mL 7% sodium bicarbonate per 10 mL of lidocaine (pH 7.04). Group 3 received 2% lidocaine HCl solution with 1:200000 epinephrine plus 1.5 mL normal saline per 10 mL of lidocaine (pH 5.68). Group 4 received 2% lidocaine HCl solution with 1:200000 epinephrine plus 1.5 mL 7% sodium bicarbonate per 10 mL of lidocaine (pH 7.11). The time of onset of analgesia and the spread of sensory blockade were more rapid in groups 2 and 4. The degree of motor block was more pronounced in these two groups, as were the changes in blood pressure and heart rate.