Fentanyl: clinical use as postoperative analgesic--epidural/intrathecal route.

The administration of epidural and intrathecal opioids for the management of postoperative pain is well established. Fentanyl, because of its greater lipophilicity, offers a number of advantages over morphine for epidural analgesia, including a lower incidence of side effects and reduced risk of delayed-onset respiratory depression. The relatively short duration of action of epidural fentanyl makes this agent more ideally suited for continuous infusion or patient-controlled epidural analgesia (PCEA). The effective doses and adverse effects profile of epidural fentanyl are reasonably well understood. Because of the lack of spread through the cerebrospinal fluid (CSF) and hence the segmental nature of the analgesia achieved, location of epidural catheter placement is of paramount importance when this agent is used. Prolonged epidural infusion of fentanyl may result in high systemic concentrations not dissimilar to IV infusion, and, therefore, the greatest efficacy of epidural fentanyl administration may be in combination with low concentrations of bupivacaine, an approach that achieves a synergistic effect. 2-Chloroprocaine has been shown to antagonize epidural fentanyl analgesia. Intrathecal fentanyl for postoperative analgesia is limited by its short duration of action with single-bolus administration. The widespread international increase in the use of epidural fentanyl for postoperative analgesia promises further improvements and refinement in techniques.