Pain Management and Pathophysiology

Study Notes

Pain is a personal, subjective sensory and emotional experience associated with actual or potential tissue damage.
It's defined as "whatever the experiencing person says it is, existing whenever he says it does." (McCaffery, 1999).
All pain is real.
Medically, pain is an unpleasant sensation ranging from mild, localized discomfort to agony.
Pain has physical (nerve stimulation) and emotional components.
Pain can be localized or diffuse.

Pain transmission involves three components: peripheral nervous system (afferent pathways), central nervous system and descending control system (efferent pathways).
Nociceptors (pain receptors) are nerve endings that respond to intense stimuli.
Nociceptors in every part of the body except large internal organs respond to inflammation, ischemia or stretching.
Stimuli (mechanical, thermal, or chemical) trigger electrical activity (action potentials).
Two types of afferent nerve fibers (Aδ and C fibers) transmit pain signals:
- Aδ fibers are smaller and myelinated, transmitting "fast pain" rapidly and precisely.
- C fibers are larger and unmyelinated, transmitting "slow pain" (dull, aching, burning) more diffusely.
When nociceptors are stimulated, histamine and other algogenic (pain-causing) substances are released.
These substances cause vasodilation (redness, warmth) and increased vascular permeability (swelling). Key chemicals include histamine, bradykinin, acetylcholine, serotonin, and substance P.

Tissue damage stimulates nociceptors, transmitting pain signals to spinal cord dorsal horn, then lamina II (substantia gelatinosa).
Signals are relayed to other parts of the spinal cord (reticular formation, hypothalamus, limbic system, cerebral cortex).

Descending fibers originate in the lower and midbrain, terminating in the dorsal horn of the spinal cord.
These fibers block nociceptors.
Endorphins and enkephalins reduce or inhibit pain transmission and perception. Endorphin receptors are present in ascending and descending pathways.

Peripheral nerve fibers carrying pain signals to the spinal cord can be modified before transmission to the brain.
Gating mechanisms can either permit or inhibit pain transmission.
Larger fibers (A-alpha and A-beta) inhibit pain transmission (gate closed), while smaller fibers (A-delta and C) facilitate it (gate open).

Mechanical stimuli (trauma, surgery, inflammation, pressure on pain receptors, tumor pressure, muscle spasms).
Thermal stimuli (extreme heat or cold).
Chemical stimuli (tissue ischemia, lactic acid, chemicals, muscle spasms).

Classified by duration (acute or chronic).
Classified by location (cutaneous, deep, visceral, radiating, referred, intractable, neuropathic, phantom).

Pain Intensity: The duration or intensity a person is willing to endure. Influenced by destruction, consciousness, activity, and expectations. Assess using pain scales.
Pain Threshold: The smallest stimulus that elicits a pain response.
Pain Tolerance: The maximum intensity or duration of pain a person can endure.
Location: Determined by where the patient points to the affected area. Referred pain is felt in an area distant from the stimulus.
Quality: Patients describe the pain in their own words (burning, aching, throbbing, stabbing, etc.).
Aggravating/Alleviating Factors: Factors that increase or reduce pain (activity, medication, heat/cold, massage, etc.).

Autonomic nervous system response (e.g., dilated pupils, increased heart rate, blood pressure).

Pain History: Previous pain treatments, when and what analgesics were last taken, and allergies.
Location: Defining the location of the pain.
Intensity: Using a scale (0-10).
Quality: Describing the pain.
Pattern: Onset, duration, recurrence.
Precipitating and alleviating factors: Identifying factors that increase or decrease pain.
Associated symptoms: Identifying other symptoms that accompany the pain.
Effects on ADLs: Assessing impact on daily activities.
Coping resources: Identifying resources for coping with pain.
Affective responses: Assessing feelings like anxiety, fear.

Examples of potential diagnoses related to pain: ineffective airway clearance, activity intolerance, immobilization, self-care deficit, ineffective coping, deficient knowledge.