What Is Pain?
Pain has been characterized in a variety of ways. There are physical definitions such as an unpleasant sensation; a warning that something is wrong; or the body's response to a thermal, chemical, or mechanical injury. There are also definitions that attempt to provide a meaning or explanation. For example, pain is a punishment; it lets the body know it is alive; it is a teacher helping to modify future behavior; or it is "all in one's head."
Two definitions have become particularly influential among health care providers, educators, and researchers. The International Association for the Study of Pain (IASP) proposes that pain is an unpleasant sensory and emotional experience associated with actual or potential tissue damage. Margo McCaffery suggested as early as 1968 the widely accepted definition, "Pain is whatever the experiencing person says it is, existing whenever the experiencing person say it does" (McCaffery and Beebe 1989, p. 7). Both definitions point to the fact that pain is much more than tissue damage that triggers a response from the nervous system. The management of pain therefore involves more than treating the tissue injury. The individual's cultural background, present circumstances, and state of mind all require assessment and attention. It has become clear that cultural learning leads to differences in the way that people express pain. Furthermore, it is also becoming increasingly accepted among the medical community that, in contrast to previous medical beliefs, children feel pain even when they are too young to express it effectively. Elderly people may also have different, less obvious, ways of expressing pain, especially if affected by Alzheimer's disease. Health care providers are therefore improving their expertise in recognizing signs of pain across a broad span of patients.
How Does Pain Work?
Research about pain is still limited, but is going forward on many fronts. A major focus is the search for a molecular description of how a pain stimulus is signaled to the brain and how the brain signals its response. Until that process has been firmly identified, caregivers and researchers can utilize the following overview of pain pathways.
Cell damage occurs. Proteins trigger specific channels that set off the pain signal. As chemicals are released the area becomes inflamed and swollen. Identification of the specific pain channels may lead to the development of highly selective local anesthetics with reduced side effects for the rest of the body.
When the tissue damage threshold is reached, nerve fibers in the area carry a message to the spinal column. There are three types of nerve fibers, each of which has a distinctive role in producing pain sensations. Small, myelinated fibers known as A delta carry localized and sharp thermal and mechanical impulses to the neospinothalamic tract. The small, unmyelinated C fibers carry aching, throbbing, burning, dull, unlocalized messages to the paleospinothalamic tract and on to the brain stem and thalamus. A beta fibers, which are large and myelinated, serve to inhibit impulses from the A delta and C fibers, thereby modulating the number and intensity of impulses sent up the spinal tracts.
The physiologist Patrick Wall, one of the world's foremost authorities on pain, describes what happens in the dorsal horn of the spinal cord, "If the input message comes only from the large A beta fibers as a result of touch, the cell fires briefly and then is turned off. If, however, the input volley comes from tissue damage detection fibers, A delta and C, the cell fires more vigorously and exaggerates the output. During all this time, the brain is sending down control messages to amplify, diminish, or ignore the signal" (Wall 2000, p. 40). An example of this occurs when hitting one's shin on a sharp object. The immediate response is to reach down and rub the area. The rubbing message is carried by the A beta fibers closing the gate to messages from the A delta and C fibers.
Once in the spinal cord the messages cross to the opposite side of the spinal column. Next they travel upward through the spinothalamic tract, conveying information about the nature and location of the stimulus to the thalamus, cerebral cortex, and spinoreticular tract. This process activates autonomic and limbic (motivational-affective) responses in the brain stem and thalamus. Messages descend the spinal cord as a result of these responses.
It is in the brain stem and the cerebral cortex that the pain messages are analyzed. Here the body meets the mind. While little research is available, there are theories and some pieces of the puzzle to suggest what is happening.
Endorphins. Endorphins are important pieces of the puzzle. Scientists know something of the body's defenses against pain. Some neuropeptides, such as Substance P, appear to be pain specific transmitters. Other peptides, such as the endorphins and enkephalins, provide profound analgesic (pain-relieving) effects. Morphine and other opioid medications were in use long before the opioid receptor sites in neural tissue were discovered in the 1970s. The word endorphin was coined as a contraction to the terms endogenous (meaning "a natural property of the body") and morphine. Methods to turn on secretion of the endorphins have been studied. Massaging or moving a painful part may owe some of its effectiveness to stimulating endorphin production. The "runner's high," a good feeling as a result of exercise, has also been attributed to endorphin release.
Placebo response. Less well explained is the "placebo effect." This occurs when a treatment produces an effect primarily because of its intent rather than its specific therapeutic physical or chemical properties (e.g., taking a pill that actually contains no medicine). People sometimes report that they feel better even though they have had only the expectation and appearance of a treatment. The double-blind research technique that pits a new drug against an inactive substance has been developed to offset the placebo effect. The placebo would be expected to produce no effects. In actuality, however, placebo users frequently report positive effects. An important aspect of the placebo effect seems to be that the person trusts the person administering the treatment and believes that the treatment will be effective. The placebo effect can be a useful supplement to therapeutic treatment but its effectiveness differs markedly from person to person and is not entirely reliable.
Both the presence of endorphins and the well-documented placebo response point to the power of the mind-body connection in pain management.
Use of Noninvasive Pain Control Measures
The first methods of pain control probably included stimulation of the skin with heat, cold, massage, and vibration, all of which have the ability to relieve pain without causing injury, at a low cost, and with little experience. Other types of stimulation of the skin include massage with mentholbased lotions, transcutaneous electrical nerve stimulation (an electrical current administered through skin patches), and acupressure (gentle pressure applied to acupuncture points).
Rubbing a bumped shin or applying a cool cloth to a forehead works to relieve discomfort. A parent's kiss to make everything "all better" helps a child through a painful experience. It reminds the individual that the presence of a loved one has a role in relieving pain.
Assisting the patient to focus attention on stimuli other than pain is another effective noninvasive pain control measure. Because the pain stimulus does not go away, but instead becomes "more bearable," this strategy has the advantage of being under the patient's control. It is also inexpensive. Many patients use the distraction strategy without realizing it by watching television, reading, doing crossword puzzles, listening to music, or attending to the company of friends and relatives. Meditation and guided visual imagery are also in this group of therapies. A disadvantage is that the existence of the pain may be doubted by others if the patient can be distracted. Distraction requires concentration and may drain the energy resources of the patient, perhaps leading to increased fatigue and irritability. The method is particularly effective for brief painful episodes.
Freedom from skeletal muscle tension and anxiety produces the relaxation response, characterized by specific physiological responses (decreased oxygen consumption, decreased respiratory rate, decreased heart rate, decreased muscle tension, normal blood pressure, and increased alpha brain waves) and a lowering of the subjective sense of distress. Conscious attempts can be made to interrupt the cycle of pain that leads to anxiety and muscle tension with increased pain as a result. The relaxation response requires active patient involvement. Many patients need specific instruction to invoke the relaxation response effectively. Some techniques include deep breathing exercises, jaw relaxation, review of peaceful past experiences, and a meditative or progressive relaxation script or tape.
Use of medication. While the noninvasive therapies are useful for mild pain, they should be considered supplements to the effective management of moderate to severe pain. Moderate to severe pain are often treated with medication and invasive pain control measures.
The World Health Organization developed the "analgesic ladder" to illustrate a systematic plan for the use of pain medication. Mild pain is treated with medications such as aspirin, acetominophen, and non-steroidal anti-inflammatory drugs (NSAIDs). Maximum recommended doses of these drugs restrict amounts in order to prevent toxicity and damage to the liver and kidneys. As pain increases, opioids such as oxycodone may be used. Severe pain requires morphine or other long-acting opioids. The dose is matched to the pain level. Although there are side effects to these drugs, the amount of drug is not limited. If pain level increases, the route by which the medication is given may change from the slower acting oral route to a faster route, whether transdermal, transmucosal, or intravenous. It is important to avoid routes that actually cause pain, such as intramuscular injection.
For continuous pain, medical practitioners often maintain that continuous pain medication should be available. This requires drugs that are long acting and given on a continuous schedule. The goal is to keep pain in check, rather than waiting until it is out of control before administering more medication.
Side effects of the drugs should be anticipated and prevented. The most common and preventable side effect of the opioids is constipation. Prevention includes adequate fluid and fiber intake and the possible use of stool softeners and laxatives.
It is important to remember that withstanding pain uses energy. When pain is first adequately relieved with medication, the patient may sleep for an extended period of time. This sleeping does not indicate that too much medication is being taken, it means that the person's body is recuperating and regaining energy. This sleepiness can lead family and caregivers to fear that the disease is progressing or that too much medication is being given. If the person arouses easily, then it is an indication that he or she is not taking too much medication.