Intrathecal and epidural opioids

Abstract

NTRASPINAL ANESTHESIA was first described by Bier and others of surgical anesthesia following intrathecal injection of the local anesthetic, cocaine. 1 Near the turn of the century, opioids (morphine) and o~z-adrenergic agonists (epinephrine) were injected intrathecally 2 but were soon abandoned because they did not produce surgical anesthesia. Use of these agents was rediscovered in the late 1970s, when they produced analgesia, not anesthesia, after intrathecal injection in animals) Within a few years, this led to clinical use of intrathecal morphine for analgesia. 4 Over the last 15 years, epidural and spinal injection of opioids have been reported for the treatment of acute and chronic pain in thousands of research reports and are a common practice in modern anesthesia care. The purpose of this article is to review intrathecal and epidural opioids in terms of their mechanism of action and clinical use, their interactions with other anesthetics and analgesics, and their effect on patient outcome, with a focus on perioperative use. MECHANISM OF ACTION Opioids act on three major classes of receptors, classified originally by pharmacological means, and termed mu (#), delta (5), and kappa (K). The endogenous ligands for these receptors are endorphins (#), enkephalins (5), and dynorphins (K), although at high enough concentrations, each of these peptides can interact with all opioid receptors. Pharmacological and molecular techniques have now distinguished several subtypes of each of these receptors, although all clinically used opioids are capable of stimulating all opioid receptor types and subtypes.