The Influence of p H-Adjusted 2-Chloroprocaine on the Quality and Duration of Subsequent Epidural Bupivacaine Analgesia during Labor

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Abstract
A randomized, double-blind study was performed to determine whether pH-adjustment of 2-chloroprocaine hastens the onset of epidural analgesia, and improves the quality and duration of subsequent epidural bupivacaine analgesia during labor. One milliliter of either 8.4% sodium bicarbonate or normal saline was added to a 30-ml vial of 2% 2-chloroprocaine. At 0, 5, and 7 min, each patient received 2, 5, and 3 ml of 2-chloroprocaine, respectively. At 22 min, any patient who did not yet have satisfactory analgesia received an additional 5 ml of 2-chloroprocaine. At 35, and, again, at 36 min, each patient received 5 ml of 0.25% bupivacaine. The median onset of 2-chloroprocaine analgesia was slightly more rapid in the bicarbonate group than in the saline-control group (12 versus 14 min, P < .05). Two of 31 women in the bicarbonate group, versus 10 of 31 women in the saline-control group, required an additional 5 ml of 2-chloroprocaine at 22 min to achieve satisfactory analgesia (P = .01). There was no significant difference between groups in median duration of subsequent bupivacaine analgesia (60 min in each group) or mean (±SD) dosage of bupivacaine during the first stage of labor (64 ± 43 versus 72 ± 57 mg). Also, there was no significant difference between groups in pain scores over time. The authors conclude that pH-adjustment of 2-chloroprocaine: 1) slightly hastened the onset of epidural analgesia during labor; 2) significantly decreased the number of women who required additional 2-chloroprocaine to achieve satisfactory analgesia; and 3) did not significantly affect the quality or the duration of subsequent epidural bupivacaine analgesia.