Pain Assessment and Pain Mechanisms
Mechanisms
Pain is an unpleasant sensory and emotional experience associated with, or resembling that associated with, actual or potential tissue damage. Nociceptive pain arises from tissue injury (somatic: sharp, well localized; visceral: cramping, poorly localized, may be referred). Neuropathic pain follows a lesion or disease of the somatosensory nervous system; patients describe burning, shooting, or electric pain, often with allodynia or hyperalgesia. Nociplastic pain reflects altered nociception without clear tissue or nerve damage, as in fibromyalgia.
Know the four steps: transduction, transmission (A-delta fibers fast and sharp; C fibers slow and dull), modulation in the dorsal horn, and perception. Gate control theory explains why rubbing, heat, cold, or TENS can reduce pain: large Aβ fibers close the dorsal horn gate.
Assessment
Self-report is the gold standard. Match the tool to the patient: 0–10 numeric rating scale, Wong-Baker FACES, FLACC or NIPS for young children, PAINAD for advanced dementia, CPOT or BPS for ventilated or sedated adults. Document location, quality, timing, aggravating and relieving factors, severity, functional impact, and the patient's own goal. Reassess after every intervention per policy - roughly 15–30 minutes after an IV opioid and 1 hour after an oral dose.
Traps
Vital signs are not a pain scale. A calm, quiet patient - or one who is sedated or paralyzed - may still have severe pain. Never equate tolerance or physical dependence with addiction. Do not assume older adults, infants, or patients with cognitive impairment feel less pain; they are consistently undertreated.
Rule of thumb: treat the report and the function, not the number. A 4/10 pain that prevents coughing and deep breathing needs more aggressive analgesia than a 4/10 in a patient who is comfortable and ambulating.