Intrathecal and epidural narcotics.

This paper presents an overall review of epidural and intrathecal narcotics. The early laboratory studies and initial clinical applications are presented. This is followed by a description of the mechanism of action of narcotics acting both intrathecally and epidurally, and some of the similarities and differences between narcotics and local anesthetic drugs. Technique, dosages, indications, and contraindications are also discussed. Pain is described as an unpleasant sensory and emotional experience associated with, or described in terms of, actual or potential tissue damage.' Drugs that relieve suffering from pain are termed analgesics. Stimulation of specialized receptors (nocicep-tors) which are present in almost every organ system, or their afferent neurons, can result in the transmission of a pain impulse. 2 Inhibition of generation , transmission or preception of the pain impulse can be produced by analgesics. In general, the narcotic analgesics exert their dominant effects at the level of the spinal cord and central (brain) centers. It has been well established that specific opiate receptors exist in the brain, primarily in the limbic system, spinoreticular tracts (such as peri-aqueductal gray, medial thalmic nuclei, hypothala-mus and substantia gelatinosa), spinal trigeminal nucleus, nucleus tractus solitarii, and vagus nerve. 2 Although there are considerable choices for analgesic therapy, there is no ideal method or ideal drug. With the demonstration of anesthetic and analgesic drug effects in the spinal cord it became apparent that spinal sites were important in mediating analgesic effects. As the body of knowledge about the mechanism of drug-induced analgesia increases, the effects at the spinal cord level assume even greater importance. Researchers have placed heavy emphasis on the interaction of narcotic analgesics with areas of the spinal cord that are thought to function in the transmission of information about painful events in the periphery. One of the primary aims of anesthesia is to provide intraoperative analgesia. However, the potential side effects of narcotics, in particular respiratory depression, have tempered analgesic treatment of postoperative pain. In 1979, intrathecal and epidural narcotics were introduced that produced intense and very prolonged analgesia. 8 This report will outline this development, and discuss the use, mechanism of action, benefits, and adverse side effects of these narcotics. History Clinical application of intraspinal narcotics for pain relief is based on animal work that demonstrated abundant opiate receptors in Rexed's lam-inal 1, 2, 5, of the dorsal horn of the spinal gray matter. 4 The identification by Snyder of specific …