Abstract

Controversial results have been published in the literature concerning the efficacy of alkalinization of solutions of local anesthetics to shorten the time to onset of sensory block. Fifty-two parturients scheduled for cesarean section at term under epidural anesthesia were randomly allocated to one of four groups: group 1, 0.5% plain bupivacaine (pH = 5.38 ± 0.05); group 2, 0.5% bupivacaine pH-adjusted with 1.4% sodium bicarbonate (pH = 6.87 ± 0.01); group 3, 0.5% bupivacaine with 1:200,000 epinephrine (pH = 4.80 ± 0.04); and group 4, 0.5% bupivacaine pH-adjusted with 1:200,000 epinephrine (pH = 6.68 ± 0.01). The time to onset of the sensory block was evaluated using a nerve stimulator technique. Motor blockade was assessed using Bromage's scale. No differences in the characteristics of the onset of the sensory block were observed with epinephrine-containing solutions nor with pH-adjusted local anesthetics. The maximal degree of motor blockade was not significantly different in the four groups. We conclude that alkalinization of a 0.5% bupivacaine solution is not an effective way to shorten the latency of epidural block for cesarean section.