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When pain presents itself, one's first instinct is to find relief from the pain. Pain is extremely subjective and very difficult to define, thus becoming whatever the patient perceives it to be. Pain disables millions of people to some extent, many receiving inappropriate analgesic regimens. Pain has a tremendous impact on society. Pain is the number one reason why people seek medical advice.(1)
The pathophysiology of pain perception is very complex and not well understood. Stimulation of receptors known as nociceptors is the first step leading to a pain sensation. Bradykinins, hydrogen ions, potassium ions, prostaglandins, histamine, leukotrienes and serotonin sensitize nociceptors. Once sensitized and activated, the receptor sends an action potential along A-delta or C afferent nerves to the spinal cord. A-delta fiber stimulation results in sharp localized pain whereas stimulation of C fibers results in a dull, diffuse, aching pain. These afferent, nociceptive nerve fibers synapse in the dorsal horn of the spinal cord. The pain transmission will eventually reach the brain via ascending pathways that allow the brain to distinguish sharp localized pain from dull aching pain.(2)
Acute pain is generally of sudden onset which serves as notification of tissue injury. This tissue injury can result from trauma, surgery, damaged to various parts of the body as a result of cancer, or numerous other stimuli. Acute pain is usually accompanied with physical indications of increased autonomic activity such as an elevation in heart rate and blood pressure. Once the pain stimuli is eliminated, the pain sensation is usually reduced.
Chronic pain can be chronic lower-back pain, chronic headaches, peripheral neuralgia, herpetic neuralgia, cancer pain, or phantom limb pain. Chronic pain is generally associated with a chronic disease and lacks a clear etiology. This is pain that exists past the normal expected healing time.
Pain can present itself as somatic, visceral, or neuropathic. Somatic pain can be mild to severe and is generally characterized as being a dull, sharp, or aching pain. Visceral is described as being diffuse or gnawing. Both of these types of pain respond well to opioids. Neuropathic pain is a result of a peripheral nerve injury and can be burning, shooting, tingling, or numbing. Neuropathic pain usually requires more nontraditional analgesics.
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