Devices for administering PCA are electronically controlled infusion pumps that deliver a preset dose of narcotic into a patient’s indwelling intravenous catheter upon patient request. The devices all contain delay intervals or lockout times during which patient demands for more narcotic are not met. These devices eliminate the delay between the onset of pain and the administration of analgesic agents, a common problem inherent with on-demand analgesic orders in busy hospital wards. Patient-controlled analgesia has excellent patient acceptance. Compared with conventional intramuscular injections, serum narcotic levels have significantly lower variability in patients using PCA (42). Patients using PCA have improved analgesia, a lower incidence of postoperative pulmonary complications, and less confusion than those given intramuscular narcotics (45). The total dose of narcotic used is lower with PCA than with conventional intramuscular depot injection.
The use of PCA does not eliminate the adverse side effects of narcotics. Potentially life-threatening respiratory depression is seen in as many as 0.5% of patients using PCA. The use of a continuous narcotic infusion in addition to demand dosing is associated with a fourfold increase in respiratory depression. Elderly patients and those with preexisting respiratory compromise are at risk for respiratory depression (42).
Carefully supervised regimens using continuous infusions, on-demand intramuscular therapy, or fixed dosage schedules (every 4-hour dosing) with on-demand supplementation can have analgesic efficacy comparable with PCA. The type of close supervision required to achieve adequate on-demand analgesia without PCA is difficult to maintain. Use of PCA shortens the time between the onset of pain and the administration of pain medication, provides more continuous access to analgesics, and allows for an overall steadier state of pain control.
Anesthetics and narcotics administered either in the epidural space or intrathecally are among the most potent analgesic agents available; the efficacy of these agents is greater than that provided by intravenous PCA techniques. These drugs can be administered in several ways, including a single-shot dose given by epidural or intrathecal injection, intermittent injection given either on schedule or on demand, and continuous infusion.
Because of the risk of central nervous system infections and headaches, intrathecal administration is usually limited to a single dose of narcotic, local anesthetic, or both. In comparison with epidural administration, duration of action for a single dose is increased via the intrathecal route as a result of the high concentrations of drug attained in the cerebrospinal ﬂuid. The risk of central nervous system and respiratory depression, and systemic hypotension, is increased. The low doses of opioids required for intrathecal analgesia are sufficient to be associated with an increased risk of respiratory depression (46). Some investigators warn against the use of intrathecal spinal analgesia outside the intensive care setting.
Epidural administration is the preferred approach and provides extended (>24 hours) pain control during the postoperative period. Relative contraindications are the presence of coagulopathy, sepsis, and hypotension. Both anesthetic and narcotic agents are used with excellent efficacy. Among the anesthetic agents, bupivacaine is the most popular, providing excellent analgesia with minimal toxicity. Epidural analgesia is most suited for pain control in the lower abdomen and extremities. Potential adverse effects of epidural anesthetic agents include urinary retention, motor weakness, hypotension, and central nervous system and cardiac depression. In contrast to anesthetic agents, opioids offer excellent analgesia without accompanying sympathetic blockade. Epidural opioids tend to have a much longer duration of action, and hypotension is a rare complication. Compared with epidural anesthetics, there is a higher incidence of nausea and vomiting, respiratory depression, and pruritus (47).