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SOURCE

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Source: Herndon CM, Strickland JM, Ray JB. Pain management. In: DiPiro JT, Talbert RL, Yee GC, Matzke GR, Wells BG, Posey LM, eds. Pharmacotherapy: A Pathophysiologic Approach. 10th ed. New York, NY: McGraw-Hill; 2017. http://accesspharmacy.mhmedical.com/content.aspx?bookid=1861&sectionid=146063604. Accessed January 23, 2017.

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DEFINITION

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  • Pain is an unpleasant, subjective, sensory, and emotional experience associated with actual or potential tissue damage or described in terms of such damage.

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ETIOLOGY

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  • Pain can occur from many causes, for example:

    • Surgery.

    • Trauma.

    • Labor.

    • Medical procedures.

    • Illnesses.

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PATHOPHYSIOLOGY

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  • Nociceptive (adaptive) pain is somatic (from skin, bone, joint, muscle, or connective tissue) or visceral (from internal organs).

    • Free nerve endings known as nociceptors can be stimulated by mechanical, thermal, and chemical impulses.

      • Action potentials transmitted along afferent nerve fibers to spinal cord and then ascend to higher centers.

      • The thalamus may act as relay station and pass impulses to central structures, where pain is processed further.

    • Body modulates pain through several processes, including endogenous opioid system.

  • Maladaptive (pathophysiologic) pain often described as chronic pain.

    • Neuropathic pain (eg, postherpetic neuralgia, diabetic neuropathy) results from nerve damage.

    • Maladaptive pain can be centralized, where no nerve injury or inflammation exists but a centrally mediated disturbance in pain processing within the CNS leads to pain hypersensitivity (eg, fibromyalgia, irritable bowel syndrome, tension-type headache).

  • Acute pain (eg, surgery, trauma, labor, and medical procedures) usually is nociceptive.

  • Chronic pain can be nociceptive, neuropathic, or centralized.

  • Cancer pain includes both chronic and acute pain caused by the disease itself, treatment, or diagnostic procedures.

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EPIDEMIOLOGY

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  • Greater than 100 million persons in the United States live with chronic pain.

  • The economic burden of chronic pain exceeds 500 billion US dollars annually.

  • Each year, 25 million Americans experience acute pain due to injury or surgery, and one-third of Americans experience severe chronic pain at some point in their lives.

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CLINICAL PRESENTATION

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  • Patients may be in obvious acute distress or appear to have no noticeable suffering.

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SIGNS AND SYMPTOMS
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  • Acute pain may be:

    • Sharp or dull.

    • Burning.

    • Shock-like.

    • Tingling.

    • Shooting.

    • Radiating.

    • Fluctuating in intensity.

    • Varying in location.

    • Occurring in timely relationship with obvious noxious stimulus.

  • Chronic pain can present similarly and often occurs without time relationship to noxious stimulus.

  • Over time, chronic pain presentation may change (eg, sharp to dull, obvious to vague).

  • Acute pain can cause:

    • Hypertension.

    • Tachycardia.

    • Diaphoresis.

    • Mydriasis.

    • Pallor.

    • These signs seldom present in chronic pain.

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DIAGNOSIS

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MEANS OF CONFIRMATION AND DIAGNOSIS
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  • Pain is subjective sensation; there are no specific laboratory tests for pain. Diagnosis based on:

    • Patient description.

    • History.

    • Physical exam.

  • Pay attention to mental factors that may lower pain threshold, example:

    • Anxiety.

    • Depression.

    • Fatigue.

    • Anger.

    • Fear.

  • Behavioral, cognitive, social, and cultural factors may ...

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