Ropivacaine or 2% mepivacaine for lower limb peripheral nerve blocks

Background: Intra- and postoperative clinical properties of sciatic-femoral nerve block performed with either ropivacaine at different concentrations or mepivacaine have been evaluated in a multicenter, randomized, blinded st udy., Methods: Adult patients scheduled for foot and ankle surgery were randomize d to receive combined sciatic-femoral nerve block with 225 mg of either 0.5 % (n = 83), 0.75% (n = 87), or 1% (n = 86) ropivacaine, or with 500 mg of 2 % mepivacaine (n = 84). A thigh tourniquet was used in all patients. Onset time, adequacy of surgical anesthesia, time to offset of nerve block, and t ime until first postoperative requirement for pain medication were evaluate d by a blinded observer. Results: The adequacy of nerve block was similar in the four treatment grou ps (the ratios between adequate:inadequate: failed blocks were 74:9:0 with 0.5% ropivacaine, 74:13:0 with 0.75% ropivacaine, 78:8:0 with 1% ropivacain e, and 72:12:0 with 2% mepivacaine), The onset of the block was slower with 0.5% ropivacaine than with other anesthetic solutions (P < 0.001). Regardl ess of the concentration, ropivacaine produced a longer motor blockade (10. 5 +/- 3.8 h, 10.3 +/- 4.3 h, and 10.2 +/- 5.1 h with 0.5%, 0.75%, and 1% ro pivacaine, respectively) than with mepivacaine (4.3 +/- 2.6 h; P < 0.001). The duration of postoperative analgesia was shorter after mepivacaine (5.1 +/- 2.7 h) than after ropivacaine (12.2 +/- 4.1 h, 14.3 +/- 5 h, and 14.5 /- 3.4 h, with 0.5%, 0.75%, or 1% ropivacaine, respectively; P < 0.001). Pa in relief after 0.5% ropivacaine was 14% shorter than 0.75% or 1% ropivacai ne (P < 0.05). During the first 24 h after surgery, 30-37% of patients rece iving ropivacaine required no analgesics compared with 10% of those receivi ng mepivacaine (P < 0.001). Conclusions: This study suggests that 0.75% ropivacaine is the most suitabl e choice of local anesthetic for combined sciatic-femoral nerve block, prov iding an onset similar to mepivacaine and prolonged postoperative analgesia .