Spinal opiate analgesia: its present role and future in pain relief.

Narcotics have been shown to act selectively upon nociceptive synaptic junctions in laminae 1 and 2 of the dorsal horn of the spinal cord. Subarachnoid or epidural injection of narcotics can produce selective segmental analgesia of great intensity and prolonged duration that is free of motor or sympathetic blockade. However, poorly lipid-soluble drugs, such as morphine, that tend to linger in the water phase of the CSF may spread rostrally to involve opiate receptors in brain stem nuclei. Delayed respiratory depression and lifethreatening apnoea is therefore the greatest danger. Other undesirable side effects include itching, nausea and vomiting and urinary retention. All side-effects are antagonized by naloxone. Intraspinal narcotic analgesia has many useful applications for the relief of acute or chronic pain. Obstetrical pain is less amenable to this approach. Effective and safe management of acute pain requires that the patients be under adequate surveillance to avoid the danger of insidious respiratory depression. Chronic malignant pain is well controlled by relatively small doses of narcotic, and these patients can be managed at home on a long-term basis.