Among the criticisms which are levelled against regional anaesthesia, the time spent waiting for the onset of analgesia and the need to accept a certain rate of failure are frequently cited.One of the authors had occasion in 1963, to observe the rapidity of action of carbonated local analgesic solutions (lignocaine and prilocaine) in extradural blockade as done by Bromage, who subsequently reported his findings 192. Compared with the conventional hydrochloride salts of local analgesics the carbonic salts shortened the latency of the agent by one third and produced a more intense sensory and motor blockade. There was a tendency to wider spread of analgesia even with a reduced total dose. The results were so impressive that they encouraged us to try these same solutions in peripheral nerve blocks. For our investigation we chose regional analgesia of the brachial plexus. Theory of carbonated local analgesic solutionsIt has been known for a long time that the hydrogen ion concentration is an important factor in the uptake of local analgesic agents. Bignon in 18923 mentioned cocaine with alkali added, and in 1910 Gros4 suggested how alkalinised solutions worked. The theory of carbonated local analgesics has been ably put forward by Bromagel. Carbonated solutions, in this case lignocaine carbonate, have a relatively high pH of 6.5 and are thus less demanding on the buffering capacity of the tissues (pH 7.4) than the commonly available local analgesics. Of these, the solutions containing vasoconstrictor agents have a pH of 4 and even those containing no vasoconstrictor are not higher than a pH of 6. In carbonated solutions the free base is liberated quickly due to rapid buffering, and the liberated carbon dioxide diffuses very rapidly causing a fall in the intracellular pH in the vicinity. Thus the analgesic base is brought closer to the nerve membrane in a higher concentration for combination with the receptor5.6. In addition carbon dioxide appears to have a direct effect on nerve fibres by stabilizing excitable tissue.