A double-blind study of axillary brachial plexus block by 0.75% ropivacaine or 2% mepivacaine

Axillary brachial plexus block using 20 mL of 0.75% ropivacaine or 2% mepivacaine was compared in a prospective, randomized, double-blind study of two groups of 15 patients. The times to onset of sensory and motor block and to resolution of motor block, as well as the time to onset and degree of post-operative pain were recorded by an observer blinded to the identity of drug. Times to onset of sensory block were similar in the two groups (ropivacaine 10 min, mepivacaine 8 min). Resolution of motor block in the operated hand and the time to first requirement of post-operative analgesia occurred later with ropivacaine (9 h 50 min and 10 h) than with mepivacaine (3 h 50 min and 6 h), P<0.01 for both measurements. Nine patients who received ropivacaine and two patients who received mepivacaine did not require further post-operative analgesia (P<0.05). Ropivacaine is less toxic than other long-acting local anaesthetics, and 0.75% ropivacaine may be better for brachial plexus block when fast onset is required and prolonged pain relief is useful.