Severe pain is a common sequela of intrathoracic, intra-abdominal, and major bone or joint procedures. About 60% of such patients perceive their pain to be severe, 25% moderate, and 15% mild. In contrast, following superficial operations on the head and neck, limbs, or abdominal wall, less than 15% of patients characterize their pain as severe. The factors responsible for these differences include duration of operation, degree of operative trauma, type of incision, and magnitude of intraoperative retraction. Gentle handling of tissues, expedient operations, and good muscle relaxation help lessen the severity of postoperative pain. Objective measures of pain remain elusive.
While factors related to the nature of the operation influence postoperative pain, it is also true that the same operation produces different amounts of pain in different patients. This varies according to individual physical, emotional, and cultural characteristics. Much of the emotional aspect of pain can be traced to anxiety. Feelings such as helplessness, fear, and uncertainty contribute to anxiety and may heighten the patient’s perception of pain.
It was once thought that anesthesia and analgesia in neonates and infants was too risky and that these young patients did not perceive pain. It is now known that reduction of pain with appropriate techniques actually decreases morbidity from major surgery in this age group.
The physiology of postoperative pain involves transmission of pain impulses via splanchnic (not vagal) afferent fibers to the central nervous system, where they initiate spinal, brain stem, and cortical reflexes. Spinal responses result from stimulation of neurons in the anterior horn, resulting in skeletal muscle spasm, vasospasm, and gastrointestinal ileus. Brain stem responses to pain include alterations in ventilation, blood pressure, and endocrine function. Cortical responses include voluntary movements and psychologic changes, such as fear and apprehension. These emotional responses facilitate nociceptive spinal transmission, lower the threshold for pain perception, and perpetuate the pain experience.
Postoperative pain serves no useful purpose and may cause alterations in pulmonary, circulatory, gastrointestinal, and skeletal muscle function that contribute to postoperative complications. Pain following thoracic and upper abdominal operations, for example, causes voluntary and involuntary splinting of thoracic and abdominal muscles and the diaphragm. The patient may be reluctant to breathe deeply, promoting atelectasis. The limitation in motion due to pain predisposes to venous stasis, thrombosis, and embolism. Release of catecholamines and other stress hormones by postoperative pain causes vasospasm and hypertension, which may in turn lead to complications such as stroke, myocardial infarction, and bleeding. Prevention of postoperative pain is thus important for reasons other than the pain itself. Effective pain control may improve the outcome of major operations.
Close attention to the patient’s needs, frequent reassurance, and genuine concern help to minimize postoperative pain. Spending a few minutes with the patient every day in frank discussions of progress and any complications does more to relieve pain than many physicians realize. Patients with preoperative drug and substance abuse still have postoperative pain needs and may require more medication than others. Communication among the patient care team can help in the understanding of specific pain-control needs.
Opioids are the mainstay of therapy for postoperative pain. Their analgesic effect is via two mechanisms:
A direct effect on opioid receptors
Stimulation of a descending brain stem system that contributes to pain inhibition
Although substantial relief of pain may be achieved with opioids, they do not modify reflex phenomena associated with pain, such as muscle spasm. Opioids administered intramuscularly, while convenient, result in wide variations in plasma concentrations. This, as well as the wide variations in dosage required for analgesia among patients, reduces analgesic efficacy. Physician and nurse attitudes reflect a persistent misunderstanding of the pharmacology and psychology of pain control. Frequently, the dose of opioid prescribed or administered is too small and too infrequent. When opioid usage is limited to temporary treatment of postoperative pain, drug addiction is extremely rare.
Morphine is the most widely used opioid for treatment of postoperative pain. Morphine may be administered intravenously, either intermittently or continuously. Except as discussed below in the section on patient-controlled analgesia (PCA), continuous intravenous administration requires close supervision and is impractical except in the PACU or intensive care unit. Side effects of morphine include respiratory depression, nausea and vomiting, and clouded sensorium. In the setting of severe postoperative pain, however, respiratory depression is rare, because pain itself is a powerful respiratory stimulant.
Meperidine is an opioid with about one-eighth the potency of morphine. It provides a similar quality of pain control with similar side effects. The duration of pain relief is somewhat shorter than with morphine. Like morphine, meperidine may be given intravenously, but the same requirements for monitoring apply.
Other opioids useful for postoperative analgesia include hydromorphone and methadone. Hydromorphone is usually administered in a dose of 1-2 mg intramuscularly every 2-3 hours. Methadone is given intramuscularly or orally in an average dose of 10 mg every 4-6 hours. The main advantage of methadone is its long half-life (6-10 hours) and its ability to prevent withdrawal symptoms in patients with morphine dependence. Patients who use methadone preoperatively should be continued postoperatively on their usual dose to avoid withdrawal; most clinics maintain records on their patients and should be consulted to confirm the appropriate replacement.
C. Nonopioid Parenteral Analgesics
Ketorolac tromethamine is a nonsteroidal anti-inflammatory drug (NSAID) with potent analgesic and moderate anti-inflammatory activities. It is available in injectable form suitable for postoperative use. In controlled trials, ketorolac (30 mg) demonstrated analgesic efficacy roughly equivalent to that of morphine (10 mg). A potential advantage over morphine is its lack of respiratory depression. Gastrointestinal ulceration, impaired coagulation, and reduced renal function—all potential complications of NSAID use—have not yet been reported with short-term perioperative use of ketorolac.
Within several days following most abdominal surgical procedures, the severity of pain decreases and oral analgesics suffice for control. Aspirin is often avoided as an analgesic postoperatively, since it interferes with platelet function, prolongs bleeding time, and interferes with the effects of anticoagulants; however, in some settings aspirin is used to diminish the risk of cardiovascular complications by these mechanisms. For most patients, a combination of acetaminophen with codeine (eg, Tylenol No. 3) or propoxyphene (Darvocet-N 50 or -N 100) suffices. Hydrocodone with acetaminophen (Vicodin) is a synthetic opioid with properties similar to those of codeine. For more severe pain, oxycodone is available in combination with aspirin (Percodan) or acetaminophen (Percocet, Tylox). Oxycodone is an opioid with slightly less potency than morphine. As with all opioids, tolerance develops with long-term use.
E. Patient-Controlled Analgesia
Patient-controlled analgesia puts the frequency of analgesic administration under the patient’s control but within safe limits. A device containing a timing unit, a pump, and the analgesic medication is connected to an intravenous line. By pressing a button, the patient delivers a predetermined dose of analgesic (usually morphine, 1-3 mg). The timing unit prevents overdosage by interposing an inactivation period (usually 6-8 minutes) between patient-initiated doses. The possibility of overdosage is also limited by the fact that the patient must be awake in order to search for and push the button that delivers the morphine. The dose and timing can be changed by medical personnel to accommodate the needs of the patient. This method appears to improve pain control and even reduces the total dose of opioid given in a 24-hour period. The addition of a background continuous infusion to the patient-directed administration of analgesic appears to offer no advantage over PCA alone.
F. Continuous Epidural Analgesia
Opioids are also effective when administered directly into the epidural space. Topical morphine does not depress proprioceptive pathways in the dorsal horn, but it does affect nociceptive pathways by interacting with opioid receptors. Therefore, epidural opioids produce intense, prolonged segmental analgesia with relatively less respiratory depression or sympathetic, motor, or other sensory disturbances. In comparison with parenteral administration, epidural administration requires similar dosage for control of pain, has a slightly delayed onset of action, provides substantially longer pain relief, and is associated with better preservation of pulmonary function. Epidural morphine is usually administered as a continuous infusion at a rate of 0.2-0.8 mg/h with or without the addition of 0.25% bupivacaine. Analgesia produced by this technique is superior to that of intravenous or intramuscular opioids. Patients managed in this way are more alert and have better gastrointestinal function. Side effects of continuous epidural administration of morphine include pruritus, nausea, and urinary retention. Respiratory depression may occur.
Intercostal block may be used to decrease pain following thoracic and abdominal operations. Since the block does not include the visceral afferent nerve fibers, it does not relieve pain completely, but it does eliminate muscle spasm induced by cutaneous pain and helps to restore respiratory function. It does not carry the risk of hypotension—as does continuous epidural analgesia—and it produces analgesia for periods of 3-12 hours. The main disadvantage of intercostal blocks is the risk of pneumothorax and the need for repeated injections. These problems can be minimized by placing a catheter in the intercostal space or in the pleura through which a continuous infusion of bupivacaine 0.5% is delivered at a rate of 3-8 mL/h.
Direct administration of a combination of short- and long-acting local anesthetics can help significantly in management of postoperative pain in a variety of settings. Optimally, wound infiltration or local nerve block should occur following the induction of intravenous anesthesia and prior to skin incision but may still be beneficial after incision.
Patients at the extreme of ages, who underwent acute/emergency surgery or had a poor preoperative functional and nutritional status require special postoperative consideration.
Infants and children can be both more easily taken out of equilibrium and yet can return to health more quickly. Reassessment should occur more frequently with calculation of fluid needs tailored to their body surface area and losses. The nursing ratio is expected to be higher for more critically ill children. Elderly patients tend to have more complex preoperative medical issues, require a careful preoperative functional assessment of their nutritional reserve, and may have a more sensitive response to sedatives and other medications with a prolonged return to full mental function. Careful attention to even small changes in status should trigger thoughtful appraisal of the patient.