Alkalinization of local anesthetics. Which block, which local anesthetic?

A number of clinical studies have been performed in an attempt to establish the effects of alkalinization on potency of local anesthetics. Conflicting results were obtained probably because different studies used different methods as well as different definitions of the effects. To determine the efficacy of alkalinization using different local anesthetic solutions and different regional blocks, 180 patients were studied in a randomized, double-blind fashion. The local anesthetic solutions studied were bupivacaine, mepivacaine, and lidocaine; the regional blocks studied were epidural block, axillary brachial plexus block, and femoral and sciatic nerve block.

In this study, 180 patients receiving epidural block (n = 60), sciatic and femoral nerve block (n = 60), and brachial plexus block (n = 60) were randomized to receive, in a double-blind fashion, a plain or a pH-adjusted solution of 2% mepivacaine, 2% lidocaine, or 0.5% bupivacaine. Onset of sensory analgesia, onset of maximum effect (peak effect or complete analgesia), duration of the block, onset, duration and density of motor block were evaluated using pinprick (Hollmen scale) and a 10-point decimal scale (Seow scale).

concerning epidural block, the alkalinization of the local anesthetic shortened significantly the onset of sensory analgesia in the dermatome corresponding to the lumbar interspace used for epidural puncture (L3-L4) and increased the spread of the epidural block in all the groups. The onset of sensory analgesia at L4 level ranged from 10 minutes for plain bupivacaine to 3 minutes for alkalinized lidocaine, whereas the onset at T10 level ranged from 16 minutes for plain bupivacaine and mepivacaine to 12.3 minutes for alkalinized lidocaine. The effects of alkalinization were more evident with lidocaine and bupivacaine. Concerning femoral and sciatic nerve blocks, a statistically significant shorter onset of sensory analgesia and motor block were observed with mepivacaine. Concerning brachial plexus axillary block, the effects of alkalinization were more evident with lidocaine.

Alkalinization produced the best results with lidocaine and bupivacaine for epidural block, with lidocaine for brachial plexus block, and with mepivacaine for sciatic and femoral nerve blocks.