Epidural ropivacaine for the initiation of labor epidural analgesia: A dose finding study

The purpose of our study was to determine the lowest concentration of ropivacaine that offers pain relief for the initiation of labor epidural analgesia. Women in active labor were enrolled in this prospective, randomized, double-blinded study to receive either ropivacaine 0.20% (Group I), ropivacaine 0.15% (Group II), or ropivacaine 0.10% (Group III). After placement of the epidural catheter, 13 mL of the study medication was administered. Fifteen minutes later, the adequacy of analgesia was assessed. If the woman reported that her degree of analgesia was not adequate, an additional 5 mL of the study medication was given, the degree of pain relief was reassessed 15 min later, and the study was concluded. A sequential study design was used to assess the success rates. We found that 26 of 28 (93%) women in Group I had adequate analgesia, compared with only 18 of 28 (64%) in Group II (P = 0.014) and 4 of 12 (33%) in Group III(P = 0.003). We conclude that rogivacaine 0.20% offers adequate analgesia significantly more often than either ropivacaine 0.15% or ropivacaine 0.10%. If one selects ropivacaine as the sole local anesthetic for the initiation of labor epidural analgesia, the minimal concentration should be 0.20%. Implications: The lowest effective concentration of ropivacaine for the initiation of labor epidural analgesia has not been determined. We found that ropivacaine 0.20% offers adequate analgesia significantly more often than either ropivacaine 0.15% or ropivacaine 0.10%. If one selects ropivacaine as the sole local anesthetic for the initiation of labor epidural analgesia, the minimal concentration should be 0.20%.