Brachial plexus blockade for evaluation of local anaesthetic agents

Brachial plexus block (axillary approach) has been compared with ulnar nerve block for the evaluation of local anaesthetic drugs. Duration of analgesia is the same in both techniques with the same drugs. Following axillary nerve block the median, ulnar and radial nerves are blocked for a different time. The onset of motor block is faster following axillary nerve block, according to muscle power, but not according to action potentials in the e.m.g. Once all the nerves are blocked, no differences exist for the duration of muscle paralysis. The rate of techinical failure is higher with brachial plexus blocks compared with single nerve blocks. Larger amounts of local anaesthetic solutions are necessary for plexus blockade and this may cause toxic effects. The volunteer's comfort is less after plexus block because of more widespread paralysis. Therefore, ulnar nerve block and extradural block are in many respects the most suitable techniques for evaluation of new local anaesthetic agents.