Differential neural effects of epidural anesthetics

The purpose of this investigation was to clarify in a laboratory model the sites of action of epidurally administered local anesthetics. This report describes such a a model, which is capable of monitoring sites of altered electrophysiologic activity induced by epidural anesthetic agents. Evoked potential response alterations measured from electrodes positioned along the conducting pathways were assessed in six monkeys following epidural injections of 0.5 per cent bupivacaine, 3 per cent chloroprocaine, and 1 per cent etidocaine. Bupivacaine in ten studies was found to cause its major effects at the dorsal root entry zone and the long tracts of the spinal cord white matter, associated with variable peripheral nerve alterations. Chloroprocaine effects in six studies were limited to alteration of responses recorded from the dorsal root zone and peripheral nerve. In contrast, etidocaine in eight studies caused marked attenuation of the responses recorded from the long tracts of the spinal cord white matter, associated with only minimal corresponding changes at the dorsal entry zone or peripheral nerve levels. These findings illustrate the capability of this experimental model to demonstrate relatively selective effects along the sensory and motor pathways for epidurally injected local anesthetic agents.