Acute pain is the symptom of a larger disease process, and is usually nocioceptive in nature. This means that a noxious (unpleasant) event stimulates the intact nervous system to produce the sensation of pain. Examples of this noxious event include a surgical incision, labor pain, acute pancreatitis or a myocardial infarction.

Acute pain can be somatic or visceral or neuropathic in origin. Somatic pain is sharp and well localized in nature, usually to an external site. Visceral pain tends to be dull and vaguely localized to a deep site, and is frequently associated with nausea. Acute pain is self-limiting, and resolves when the noxious stimulus ceases.

Physiological and psychological responses to acute pain are directed toward escape from the painful situation. Acute pain usually triggers a neuroendocrine stress response, which is proportional to the intensity of the pain. This is a variant of the fight-or-flight response. Catecholamines are released, increasing heart rate, blood pressure, and systemic vascular resistance. Other effects of this catecholamine release may include urinary retention, ileus, stress ulcers, increased work of breathing, nausea, and constipation.

The predominant emotional response to acute pain is anxiety, although anger toward caretakers may also be expressed. These emotional responses indicate that the patient believes the pain to be temporary and "fixable", and represent an attempt to escape from the painful stimulus.

Acute pain usually responds well to non-steroidal pain relievers and/or narcotics. Frequently, neural blockade can effectively relieve acute pain and de-
crease the likelihood of developing a chronic pain syndrome.