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 withropivacaine or mepivacaine in 60 healthy patients undergoing electiveshoulder surgery. Patients were allocated randomly to receive interscalenebrachial plexus 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 surgery (loss of pinprick sensation from C4 to C7 andinability to elevate the 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). Postoperativeanalgesia 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 compared with 2% mepivacaine (5.1(2.7) h) (P < 0.001).