A patient who has chronic pain is very different from a patient who has acute pain. Acute pain is pain that is the result of tissue injury, such as injury from trauma or surgery (American Pain Society [APS], 2008). Patients expect that when their injury heals, the pain will resolve. As the pain decreases, the patient is able to resume their normal everyday activities and level of functioning. Acute pain serves the purpose of warning the person that an injury has occurred and appropriate action is needed (e.g., treatment or moving away from the source of the pain).
Chronic pain is a different life experience. Chronic pain is pain that lasts beyond the normal healing period of 3 to 6 months (APS, 2008). It is the result of injury or potential tissue damage (APS, 2008). Chronic, persistent pain has many different sources, and the pain that the patient complains of may be in several different areas of the body. Chronic, persistent pain may exist even though there is no detectable physical source for the pain (Marcus, 2000).
The average patient with chronic pain may rate his pain level at high intensity, yet be able to function at some level. This is confusing for health care providers who expect a patient who rates his/her pain intensity at 7 out of 10 to be showing signs of severe pain, such as grimacing, moaning, or guarding the painful area. The patient with chronic pain has learned to adapt both consciously and unconsciously. Functionality is a better measure of pain relief in patients with chronic pain (ASPMN, 2010; Marcus, 2000). Physiologically, the patient with chronic pain may not have increases in blood pressure or heart rate when they are experiencing their normal daily chronic pain. Discussing the different types of chronic pain will provide insight into the causative factors for the pain.
There are several different types of chronic pain. Exhibit 1.1 identifies the two main categories, nociceptive and neuropathic pain. Figure 1.1 further classifies chronic pain into mixed and visceral pain.
Differences Between Nociceptive and Neuropathic Pain Nociceptive
—Produced by peripheral mechanoreceptors, thermoreceptors, and chemoreceptors. —Serves to warn the body that injury has occurred. —Pain is proportionate to receptor stimulus.
—Caused by damage to the peripheral or central nervous system. —May involve an inflammatory process that perpetuates the pain stimulus.
—Nociceptive input not required for pain to occur. —Pain is of higher intensity and disproportionate to pain stimulus.
Pain f h
Postherpetic Lower back neuralgia pain
Rheumatoid Pancreatitis arthritis Bladder pain
Noncardiac chest pain Abdominal pain syndrome
Figure 1.1 ■ Pain classification. IBS — irritable bowel syndrome.
Nociceptive pain is the result of tissue damage, surgery, or injury. When patients have surgery or sprain an ankle, nociceptive pain is the result. Almost everybody has experienced some type of nociceptive pain.
Thie stimulus for nociceptive pain is generated from various sources and specialized sites located throughout the body. Activation of thermoreceptors (heat), mechanoreceptors (tissue injury, pressure), and chemoreceptors (chemical irritants) can all create nociceptive pain. This means that when a patient burns a hand, has a crush injury, or has an infection, a nociceptive pain stimulus is produced. The pain stimulus is then passed along the peripheral nervous system by a voltage-gated sodium channel that allows an influx of sodium ions into the neural cell, also creating an action potential that allows the stimulus to pass to the central nervous system. Once the pain stimulus reaches the spine, if the pain stimulus is sustained, the pain signal is transmitted past the dorsal horn of the spine, through the limbic system, and into the cerebral cortex. There the stimulus is recognized as pain and translated, and an appropriate response is provided (see Figure 1.2).
Nociceptive pain is often acute and the pain will diminish as healing occurs. This type of pain serves as a warning signal to the body, which can identify the injury and protect itself. Exceptions to the short-term nature of the pain are chronic degenerative conditions such as osteoarthritis or rheumatoid arthritis, which can produce long-term pain. Outside of chronic, incurable degenerative conditions such as arthritis, it is reasonable to expect that most acute, nociceptive pain will resolve once healing takes place.
For treatment, analgesics typically are quite effective in reducing the intensity of nociceptive pain, with a 2-point reduction on the Numeric Rating Scale (NRS) or 30% reduction in intensity considered a good response. Nonopioid analgesics, such as ibuprofen or acetaminophen, work well for mild and moderate pain, especially that which is aching in nature or related to an inflammatory process.
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