Learning Objectives
By the end of this section, you will be able to:
- Define pain and its causes
- Differentiate among types of pain
Pain is an important communication tool that bodies use to indicate that something is wrong. Although everyone experiences pain, the perception of pain is unique and varies from person to person. “Pain is whatever the experiencing person says it is, existing whenever they say it does” (McCaffery, 1968). Pain may be classified according to a variety of factors, such as location, onset, duration, and cause. Being able to differentiate between the types and characteristics of pain is a crucial skill when assessing pain.
What Is Pain?
Generally, pain is an uncomfortable or unpleasant sensation that typically signifies injury or illness. The purpose of pain is to tell the individual that something is not right within their body and requires further attention. For example, if a person touches a hot stove, they feel a burning sensation (pain) on the skin that tells them to stop touching the stove. If a person’s knee hurts when walking after a fall, their body is telling them not to put weight on that knee.
Pain is a physiological process caused by interaction with nociceptors. A nociceptor is a type of sensory receptor that responds to potentially damaging stimuli by sending nerve signals to the spinal cord and brain in a process called nociception. There are several types and functions of nociceptors:
- Thermal nociceptors are activated by noxious heat or cold, such as a hot pan.
- Mechanical nociceptors are activated by excess pressure or mechanical deformation, such as a finger getting caught in a car door. They also respond to incisions that break the skin surface.
- Chemical nociceptors are activated by a wide variety of spices commonly used in cooking. For example, capsaicin is a compound in chili peppers that causes a burning sensation of the mucous membranes. It is also used in common over-the-counter creams for pain relief because when it is applied to the skin, it blocks the transmission of pain impulses.
Nociceptors detect noxious stimuli and transduce them into electrical energy. An action potential is created and transmitted along nociceptor fibers. There are two types of nociceptor fibers, A-Delta and C (Kendroud et al., 2022). A-Delta fibers are fast-conducting fibers associated with the initial sensation of sharp, stinging, or pricking pain. C fibers are slower-conducting fibers associated with the secondary sensation of diffuse, dull, burning, or aching pain. The pain impulse is transmitted along these nociceptor fibers to the dorsal horn in the spinal cord, and then from the spinal cord to the thalamus, where pain messages are relayed to the cerebral cortex. The cerebral cortex perceives pain impulses, so it is then that the person has conscious awareness of pain. Figure 7.2 illustrates this process.
Types of Pain and Their Causes
Pain can be a normal response to an illness or injury and may not require medical treatment. This type of pain may be referred to as normal pain, which is of the severity and duration that you would expect to experience according to the cause of the pain. Examples of normal pain may be a skinned knee, minor burn, pulled muscle, or tension headache, or even more severe such as the pain of a sprained ankle, broken bone, labor and delivery, or recovery from surgery. Although medical treatment may be necessary to treat the underlying problem, the associated pain typically does not warrant further medical treatment. On the contrary, abnormal pain moves beyond the expected severity and duration expected from the cause of the pain and may require additional medical treatment. Examples of abnormal pain may be fibromyalgia, neuropathic pain, chronic back pain, and migraines, which are complex pain conditions characterized by chronic pain with varying intensity.
There are several different types of pain, each with its own indications for treatment and management. Pain may be characterized according to onset and duration, such as acute, chronic, or breakthrough. Pain may also be categorized as neuropathic or nociceptive, according to the type of damage that causes it. The types of pain are not isolated; sources of pain may fall into more than one of these categories. It is important to identify the type of pain in order to develop an individualized plan of care to treat and manage it.
Acute Pain
When pain is short in duration, typically lasting from minutes up to three to six months (depending upon the reference source), it is considered acute pain. It comes on suddenly and tends to be associated with a specific soft-tissue injury, such an ankle sprain, or a temporary illness, such as gastritis. This type of pain may be sharp, throbbing, burning, stabbing, or tingling; it may manifest as weakness or numbness. Acute pain typically produces a physiological response resulting in vital sign changes, such as increased pulse, respirations, and blood pressure. Generally, once the injury heals or illness subsides, the pain subsides as well. Examples of acute pain include pain that results from surgery, cuts, burns, labor and delivery, and broken bones.
Nurses can identify acute pain by assessing the symptoms, intensity, and location of the pain, as well as the associated injury or illness. Blood tests, x-rays, computed tomography (CT scans), magnetic resonance imaging (MRIs), ultrasounds, dye-injection studies, and nerve conduction studies may also be helpful for diagnostic testing. Acute pain may be treated with rest, heat or ice, anti-inflammatory medications, physical therapy, exercise, stress reduction, bioelectric therapy (electrical impulses used to stimulate nerves and muscles), muscle relaxants, and short-term use of narcotics (International Association for the Study of Pain, 2021).
Do not ignore acute pain. If left untreated, acute pain may turn into chronic pain. For example, a broken bone that is left untreated may result in the bone not healing, leading to worsening pain over time. Acute pain may also turn into chronic pain when repeated or continuous nerve stimulation alters the pain pathways in the central nervous system. For example, repetitive knee injuries may result in subsequent arthritis over time.
Chronic Pain
By contrast, chronic pain is longer in duration, typically identified as pain lasting longer than six months. It often results from health conditions, such as arthritis, fibromyalgia, cancer, diabetes, and musculoskeletal deformities. Other causes of chronic pain include normal aging, wear and tear on bones and joints, nerve damage, and injuries that fail to heal properly. Chronic pain does not typically result in vital sign changes because the body has adjusted to the new normal of chronic pain.
Chronic pain may be categorized as constant or intermittent. Constant pain is continuous, though the intensity of the pain may vary at times. Back injuries, for instance, may result in chronic pain; the pain may worsen or lessen with certain movements, but it is constant. Intermittent pain comes and goes. Migraines, for example, may be considered chronic pain if the person has experienced them over a time period longer than three months; the migraines themselves come and go, however, so they are considered intermittent.
Chronic pain may alter in severity, depending on the day. Some days the pain may be mild or nonexistent, and other days the pain may be severe and debilitating. Due to its chronic nature, this pain may considerably affect the quality of one’s life. It can have physical effects, such as tense muscles, limited mobility, a lack of energy, and changes in appetite. It may also cause emotional effects, such as depression, anger, anxiety, and fear of reinjury. When managing chronic pain, it is important to assess one’s ability to perform activities of daily living, as well as assess for signs of depression and anxiety. Early intervention is key to preserving quality of life and mental well-being.
Breakthrough Pain
A sudden increase in pain that lasts for a short time is called breakthrough pain. It may be caused by stress, illness, or activity, by the wearing off of pain medicine, or for no known reason. Breakthrough pain may occur with acute or chronic pain. Acute surgical pain, for instance, may be well controlled with oral analgesics, but the patient may experience a sudden increase in pain after physical therapy exercises that result in the need for additional doses of pain medications between the regular doses of oral analgesics. In contrast, a patient diagnosed with rheumatoid arthritis may experience chronic pain that is well controlled with the patient’s regular pain medication regimen; a flare-up of pain may require additional therapeutic medications to be added to the regimen until the breakthrough pain subsides.
Neuropathic Pain
Damage to nerves or other parts of the nervous system can result in neuropathic pain. It may be characterized as shooting, stabbing, sharp, or burning pain. Some people may even describe the pain as an electrical shock or say it feels like “pins and needles.” Common causes of neuropathic pain include cancer, stroke, limb amputation, radiation, chemotherapy, and diabetes.
Neuropathic pain is a type of chronic pain that can be so severe that it becomes debilitating. It may interfere with the ability to perform everyday tasks and be severe even with normal movement. As a result, the person may experience mobility issues. Neuropathic pain may also affect sensitivity: for example, it can interfere with a person’s ability to feel hot and cold sensations, which may result in injury. The person may touch a hot pan, not be able to sense that it is hot, and end up with severe burns to their fingers.
Following an amputation, patients may experience a type of neuropathic pain known as phantom pain in which the patient perceives the pain to be coming from the missing body part. Approximately 80 percent of patients who undergo an amputation will experience phantom pain (Cleveland Clinic, 2021). Phantom pain is caused by the brain misinterpreting the pain signals, but the pain is real. It may last for seconds, hours, days, or longer, and may be described as burning, aching, pinching, itching, tingling, shooting, stabbing, throbbing, or twisting. Diagnose phantom pain by conducting a physical exam and ruling out other medical causes, such as infections.
Nociceptive Pain
Pain caused by damage to the body tissue, typically from injury to joints, muscles, skin, tendons, or bones, is called nociceptive pain. It is often described as sharp, achy, or throbbing. Nociceptive pain may be either acute or chronic. For example, a scrape to the knee, a twisted ankle, or a blow to the head may be characterized as acute nociceptive pain. If the blow to the head were to result in subsequent migraines lasting longer than three months, it would then be characterized as chronic nociceptive pain.
There are two types of nociceptive pain. The first, somatic pain, is experienced in the muscles, skin, or bone. This pain is focused on a specific area of the body and is typically more intense than visceral pain. It is often characterized as cramping, aching, or gnawing. Examples include pain resulting from headaches, the motion of injured limbs, or cuts in the skin. The other type of pain, visceral pain, is experienced in the internal organs; the exact location may be difficult to identify. Visceral pain is oftentimes described as aching, cramping, or as pressure in the body. Examples include pain caused by endometriosis, bladder infection, and irritable bowel syndrome. (Table 7.1) displays the defining characteristics of nociceptive and neuropathic pain.
| Nociceptive Pain | Neuropathic Pain | |
|---|---|---|
| Somatic Pain | Visceral Pain | |
| Arises from the muscles, skin, or bone | Arises from the internal organs | Arises from damage to the nervous system |
| Characterized as cramping, aching, gnawing | Characterized as achy, pressure, cramping | Characterized as shooting, stabbing, sharp, burning, electric-like sensation, “pins and needles” |
| Examples: infection, postoperative, fracture | Examples: endometriosis, irritable bowel syndrome, pancreatitis | Examples: neuropathy, phantom limb pain, shingles |
Referred Pain
When the pain in one part of the body is caused by pain in a different location in the body, it is considered referred pain. Referred pain can happen if the brain incidentally sends a pain signal to a different part of the body. Although referred pain may be felt anywhere, areas such as the shoulders, neck, back, teeth, and jaws are common sites of referred pain. Referred pain is typically the result of an overlapping dermatome, specific regions of the skin that connect to a single spinal nerve root. Due to the shared neural pathways, the individual may feel the pain in a different portion of the dermatome supplied by the same nerve root. For example, a person having a heart attack may experience shoulder pain, whereas pain in the lower back may be caused by kidney pain.