Interscalene brachial plexus anaesthesia with 0.5%, 0.75% or 1% ropivacaine: a double-blind comparison with 2% mepivacaine

We have compared interscalene brachial plexus block performed with ropivaca ine or mepivacaine in 60 healthy patients undergoing elective shoulder surg ery. Patients were allocated randomly to receive interscalene brachial plex us anaesthesia with 20 ml of 0.5% ropivacaine (n = 15), 0.75% ropivacaine ( n = 15), 1% ropivacaine (n= 15) or 2% mepivacaine (n = 15). Readiness for s urgery (loss of pinprick sensation from C4 to C7 and inability to elevate t he limb from the bed) was achieved sooner with 1% ropivacaine (mean 10 (SD 5) min) than with 0.5% ropivacaine (22 (7) min) (P<0.001) or 2% mepivacaine (18 (9) min) (P<0.02). Postoperative analgesia was similar with the three ropivacaine concentrations (11.5 (5) h, 10.7 (2) h and 10 (2.4) h with 0.5% , 0.75% and 1% concentrations, respectively) and nearly two-fold longer com pared with 2% mepivacaine (5.1 (2.7) h) (P<0.001).