Pain and Its Management
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Approach to the patient
Pain is the most common symptom that brings a pt to a physician’s attention. Management depends on determining its cause, alleviating triggering and potentiating factors, and providing rapid relief whenever possible. Pain may be of somatic (skin, joints, muscles), visceral, or neuropathic (injury to nerves, spinal cord pathways, or thalamus) origin. Characteristics of each are summarized in Table 5-1.
Neuropathic Pain Due to damage of peripheral or central nociceptive pathways. Definitions: neuralgia: pain in the distribution of a single nerve, as in trigeminal neuralgia; dysesthesia: spontaneous, unpleasant, abnormal sensation; hyperalgesia and hyperesthesia: exaggerated responses to nociceptive or touch stimulus, respectively; allodynia: perception of light mechanical stimuli as painful, as when vibration evokes painful sensation. Reduced pain perception is called hypalgesia or, when absent, analgesia. Causalgia is continuous severe burning pain with indistinct boundaries and accompanying sympathetic nervous system dysfunction (sweating; vascular, skin, and hair changes—sympathetic dystrophy) that occurs after injury to a peripheral nerve.
Sensitization refers to a lowered threshold for activating primary nociceptors following repeated stimulation in damaged or inflamed tissues; inflammatory mediators play a role. Sensitization contributes to tenderness, soreness, and hyperalgesia (as in sunburn).
Referred pain results from the convergence of sensory inputs from skin and viscera on single spinal neurons that transmit pain signals to the brain. Because of this convergence, input from deep structures is mislocalized to a region of skin innervated by the same spinal segment.
Chronic Pain The problem is often difficult to diagnose with certainty, and pts may appear emotionally distraught. Several factors can cause, perpetuate, or exacerbate chronic pain: (1) painful disease for which there is no cure (e.g., arthritis, cancer, chronic daily headaches, diabetic neuropathy); (2) perpetuating factors initiated by a bodily disease that persist after the disease has resolved (e.g., damaged sensory or sympathetic nerves); (3) psychological conditions. Pay special attention to the medical history and to depression. Major depression is common, treatable, and potentially fatal (suicide).
Nociceptive stimulus usually evident
Usually well localized
Similar to other somatic pains in pt’s experience
Relieved by anti-inflammatory or narcotic analgesics
Most commonly activated by inflammation
Pain poorly localized and usually referred
Associated with diffuse discomfort, e.g., nausea, bloating
Relieved by narcotic analgesics
No obvious nociceptive stimulus
Associated evidence of nerve damage, e.g., sensory impairment, weakness
Unusual, dissimilar from somatic pain, often shooting or electrical quality
Only partially relieved by narcotic analgesics; may respond to antidepressants or anticonvulsants