Effect of analgesic treatment on the physiological consequences of acute pain

Physiological responses to acute pain are described, and the effects of different analgesic techniques on these responses are discussed. The body's response to acute pain can cause adverse physiological effects. Pain can impede the return of normal pulmonary function, modify certain aspects of the stress response to injury, and alter hemodynamic values and cardiovascular function. It can produce immobility and contribute to thromboembolic complications. In addition, pain can slow a patient's recovery from surgery and contribute to increased morbidity. Fewer pulmonary complications occur when adequate analgesia is provided through the use of epidural narcotics and local anesthetics, particularly if the injury or surgery involves the lower part of the body. Continuous morphine infusions, intercostal nerve blocks, and transcutaneous electrical stimulation do not alter the frequency of pulmonary complications. The effectiveness of patient-controlled analgesia in reducing postoperative pulmonary complications is still not known. Epidural local anesthetic therapy inhibits the stress response, particularly in operations involving the lower abdomen or extremities; this technique is less effective during major abdominal procedures. Suppression of endocrine-metabolic changes following lower abdominal surgery requires neural block to the fourth thoracic segment. Epidural narcotics partially inhibit the stress response after lower abdominal or extremity surgery but not after upper abdominal or thoracic surgery. Local anesthetics applied to the surgical site, intercostal nerve blocks, and intrapleural and intraperitoneal administration also do not modify the stress response. Adequate analgesia through the use of local anesthetics and narcotics postoperatively generally results in improved cardiovascular function, decreased pulmonary morbidity and mortality, earlier ambulation, and decreased likelihood of deep vein thrombosis. Some data suggest that improved patient outcome occurs with adequate analgesia. Block of afferent and efferent neural pathways by local anesthetics seems to be the most effective analgesic modality in lessening the physiologic response to pain and injury.