AN EVALUATION OF TWO NEW LOCAL ANAESTHETICS FOR MAJOR CONDUCTION BLOCKADE

Two new local anaesthetic agents, one fast acting (lidocaine hydrocarbonate) and one long acting (bupivacaine hydrochloride), have been compared with the established agents lidocaine hydrochloride and mepivacaine hydrochloride for epidural anaesthesia and supraclavicular brachial plexus block in 320 patients. Carbonated lidocaine was very quick acting and produced surgical anaesthesia 30 per cent faster than any of the other agents tested in both epidural and brachial plexus blockade, and its quality of anaesthesia was the most intense and reliable. Bupivacaine had the slowest onset and it produced less intense motor blockade. Duration of action was about the same for the two lidocaine salts, but mepivacaine lasted about 20 per cent longer, while bupivacaine lasted about 90 per cent longer than lidocaine in epidural analgesia. In brachial plexus anaesthesia all the agents lasted longer than in epidural analgesia: lidocaine and mepivacaine lasted twice as long, but bupivacaine lasted three times as long. The average duration of brachial plexus anaesthesia with bupivacaine was more than ten hours, but the individual results were widely scattered, and the standard deviation exceeded two hours. A mixture containing 1 per cent carbonated lidocaine and 0.25 per cent bupivacaine gave the best clinical compromise in brachial plexus anaesthesia. With this mixture anaesthesia was complete in 71/2 minutes, and lasted for 71/2 hours. The basis for the behavior of the two new drugs is discussed, and it is concluded that they both fill a real but specialized clinical need.