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Source: Baumann TJ, Strickland JM, Herndon DM. Pain Management. In: DiPiro JT, Talbert RL, Yee GC, Matzke GR, Wells BG, Posey LM, eds. Pharmacotherapy: A Pathophysiologic Approach. 8th ed. Accessed June 20, 2012.

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

  • Pain can occur from many causes, for example:
    • Surgery
    • Trauma
    • Labor
    • Medical procedures
    • Illnesses

  • Nociceptive (acute) 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.
  • Neuropathic and functional pain often described as chronic pain.
    • Neuropathic pain (e.g., postherpetic neuralgia, diabetic neuropathy) results from nerve damage.
    • Functional pain (e.g., fibromyalgia, irritable bowel syndrome, tension-type headache) involves abnormalities in nervous system.
  • Acute pain (e.g., surgery, trauma, labor, and medical procedures) usually is nociceptive, but can be neuropathic.
  • Chronic pain can be nociceptive, neuropathic/functional, or both.

  • In a survey, 1 in 4 Americans reported pain that lasted for >24 hours in previous month; in those reporting pain, 42% stated that it lasted >1 year.
  • 76.5 million Americans report they are in chronic pain.
  • 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.

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

Signs and Symptoms

  • 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 (e.g., sharp to dull, obvious to vague).
  • Acute pain can cause:
    • Hypertension
    • Tachycardia
    • Diaphoresis
    • Mydriasis
    • Pallor
    • These signs seldom present in chronic pain.
  • Neuropathic pain often chronic, not well described, and not easily treated with conventional analgesics.

Means of Confirmation and Diagnosis

  • Pain is subjective sensation; diagnosis based on:
    • Patient description
    • History
    • Physical exam
  • Baseline pain description can be obtained by assessing PQRST characteristics:
    • Precipitating factors
    • Quality
    • Radiation
    • Severity
    • Temporal factors
  • Pay attention to mental factors that may lower pain threshold, example:
    • Anxiety
    • Depression
    • Fatigue
    • Anger
    • Fear
  • Behavioral, cognitive, social, and cultural factors may also affect pain experience.

Laboratory Tests

  • Perform individual tests as required to identify potential underlying causes.


  • Performed as required to identify underlying causes.

Diagnostic Procedures

  • Performed as required to identify underlying causes.

Differential Diagnosis


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