Epidural ropivacaine infusion for postoperative analgesia after major lower abdominal surgery--a dose finding study

Ropivacaine exhibits less cardiotoxicity and causes less motor block than bupivacaine when used in equianalgesic doses. This makes ropivacaine potentially well suited for epidural infusion for postoperative analgesia. The aim of this study was to determine which of three concentrations of epidurally administered ropivacaine infused for postoperative analgesia would attenuate intravenous opioid analgesia requirements while also minimizing motor block. Forty ASA I-III patients, having major lower abdominal surgery, completed the study. They were randomly assigned to one of four treatment groups: Group S, control, epidural saline (n = 10); Group 1, epidural 0.1% ropivacaine (n = 10); Group 2, epidural 0.2% ropivacaine (n = 10); and Group 3, epidural 0.3% ropivacaine (n = 10). The study was double-blind. Initial epidural analgesia was established with 0.5% ropivacaine, and then general anesthesia induced for surgery. Once in the recovery room, epidural infusions were commenced at 10 mL/h and maintained at that rate for 21 h. Intravenous patient controlled analgesia (PCA) morphine was used as required by the patients for supplemental analgesia. Total PCA morphine use was more over the 21-h period in Group S than all the ropivacaine groups, being significantly so for Group 2 (median values: Group S, 43.3 mg; Group 1, 18.7 mg; Group 2, 7.5 mg; Group 3, 19 mg; for Group 2, P = 0.03). Visual analog scale (VAS) scores on coughing were significantly lower (i.e., less pain) than control for all ropivacaine groups after 4 h of infusion and also for Groups 2 and 3 after 8 h of infusion. (Median VAS (mm) on coughing at 8 h: Group S = 70, Group 1 = 56, Group 2 = 32, Group 3 = 0; for Groups 2 and 3, P < 0.05 compared to Group S). There was a dose-related increase in the amount of motor block, with Group 3 having significantly more motor block than all other groups at 4 and 8 h.(ABSTRACT TRUNCATED AT 250 WORDS)