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INTRODUCTION

Pain is the most common presenting symptom of disease. It is defined as an unpleasant sensory and emotional experience, associated with actual or potential tissue damage. There are sound medical and legal reasons to treat pain aggressively in hospitalized patients. The Joint Commission, which certifies health care institutions in the United States, mandates that all patients have the right to adequate pain assessment and management (Table 48-1).

TABLE 48-1Joint Commission Pain Assessment and Management Standards for Hospitals

In the inpatient setting, patients may be more concerned about pain relief than the outcome of their underlying illness. Poor pain control has adverse physiologic consequences that lead to worse outcomes (Table 48-2).

TABLE 48-2Physiologic Consequences of Uncontrolled Pain

In postoperative patients, better analgesia improves cardiovascular, respiratory, endocrine, immunologic, gastrointestinal, and hematologic status. Following many common surgeries, acute pain that is not satisfactorily treated may become persistent.

PATHOPHYSIOLOGY: NOCICEPTIVE AND ANTI-NOCICEPTIVE PATHWAYS

Nociception, the perception of noxious stimuli, is a preconscious neural activity that is normally necessary, but not sufficient, for pain. It is more accurate to refer to nociceptive pathways, rather than pain pathways. The peripheral nerve fibers acting as nociceptors are lightly myelinated A-delta and unmyelinated C fibers, which are triggered or sensitized (peripheral sensitization) by several substances, including adenosine triphosphate (ATP), prostanoids, bradykinin, serotonin, histamine, and hydrogen ions. Heat, pressure, or nerve damage also results in activation.

The primary nociceptors synapse ...

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