Onset of epidural blockade after plain or alkalinized 0.5% bupivacaine.

This double-blind study investigated the effect of adding 1.4% bicarbonate to 0.5% bupivacaine on onset time of sensory and motor blockade after epidural administration. Forty patients were randomly divided into one of two groups. Group 1 received 20 mL of 0.5% bupivacaine (pH, 5.58 +/- 0.12) and group 2 received 20 mL of 0.5% bupivacaine + 0.6 mL of 1.4% bicarbonate (pH, 6.53 +/- 0.06). Onset of temperature sensation loss occurred at L-1 after 5 min in both groups. The first signs of motor impairment were seen after 4 min in three patients in group 1 and two patients in group 2. Maximum motor blockade was reached after 30 min in group 1 and after 36 min in group 2. No difference in motor blockade or upward spread of anesthesia was noted between the two groups. The authors conclude that alkalinization of 0.5% bupivacaine offers no improvement in the onset of epidural blockade.