Effects of pH adjustment and carbonation of lidocaine during epidural anesthesia for foot or ankle surgery.

We examined the onset and the quality of sensory and motor block of the lumbosacral roots during epidural anesthesia performed for foot or ankle surgery with lidocaine HCl, pH adjusted, or carbonated lidocaine in a randomized, double-blind study. Forty-five patients received 20 mL of one of three solutions: control group (n = 15), 20 mL of 2% lidocaine with epinephrine (5 micrograms/mL) plus 2 mL of NaCl 0.9% (pH 4.58 +/- 0.10); pH adjusted group (n = 15) 20 mL of lidocaine with epinephrine (5 micrograms/mL) plus 2 mL of 8.4% sodium bicarbonate (pH 6.47 +/- 0.16); and carbonated group (n = 15) 20 mL of 1.73% carbonated lidocaine with epinephrine (5 micrograms/mL) plus 2 mL of 0.9% NaCl (pH 6.42 +/- 0.04). Onset time of sensory block of the L4-S1 roots and maximum cephalad spread were similar in the three groups. Surgical anesthesia was significantly poorer with lidocaine HCl compared to the carbonated solution with eight patients requiring fentanyl supplementation versus one in the carbonated group. Complete motor block was observed in eight patients of the carbonated group compared to three in the pH adjusted group (P < 0.01) and one in the control group (P < 0.005). Lidocaine venous blood levels were comparable in the three groups. When compared to lidocaine HCl, only carbonated lidocaine, but not the pH adjusted solution, significantly improved epidural block of the L4-S1 roots.