References:
- Kozier & Erb’s Fundamentals of Nursing: Concepts, Process, and Practice, 11th Edition, ISBN 9780135428733, by Audrey Berman, Shirlee J. Snyder, and Geralyn Frandsen (Ch. 30, pp. 651 - 690)
Pain is an unpleasant and highly personal experience that may be imperceptible to others, while consuming all parts of an individual’s life. The best definition of pain comes from Margo McCaffery, an internationally known nurse expert on pain. Her often-quoted definition of pain states, “pain is whatever the person says it is, and exists whenever he says it does.” This definition certainly portrays how subjective pain is. Another widely agreed-on definition of pain is “an unpleasant sensory and emotional experience associated with actual or potential tissue damage, or described in terms of such damage.” Three aspects of these definitions have important implications for nurses:
- Pain is a physical and emotional experience. It is not only in the mind nor only in the body.
- It is a response to actual or potential tissue damage, so laboratory or radiographic reports may not be abnormal despite the real pain.
- Pain is described in terms of such damage (e.g., neuropathic pain). Given that some clients are reluctant to diagnose the presence of pain unless asked, nurses will be unaware of a client’s pain until they assess for it. Nonverbal clients or those unable to communicate (e.g., intubated clients, preverbal children) are at risk for undertreatment of pain.
Pain interferes with functional abilities and quality of life. Severe or persistent pain affects all body systems, causing potentially serious health problems while increasing risk of complications and delays in healing. Pain management is the alleviation of pain or a reduction in pain to a level of comfort that is acceptable to the client. Effective pain management is an important aspect of nursing care to promote healing, prevent complications, reduce suffering, and prevent the development of incurable pain states. To be a true client advocate, nurses must realize their role as advocates for pain relief.
Persistent Pain
Even if the original cause of pain heals, the changes in the nervous system resulting from suboptimal pain management may increase the risk for the development of persistent or chronic pain. Persistent pain also contributes to insomnia, weight gain or loss, constipation, hypertension, deconditioning, chronic stress, and depression. These effects can interfere with work, recreation, domestic activities, and personal care activities to the point at which many sufferers question whether life is worth living.
The Nature of Pain
Although pain is a universal experience, the nature of the experience is unique to the individual based, in part, on the type of pain experienced, the psychosocial meaning, and the response. Adding to the complexity, pain may be a physiologic warning system alerting the nurse to a problem or unmet need demanding attention; or it may be a diseased, malfunctioning segment of the nervous system.
Types of Pain
Pain may be described in terms of:
- Location: while posing its own set of problems, the location of pain is nonetheless important. For example, many types of headaches can be identified and each one may have different clinical needs. Chest pain also involves a difficult task of differentiating between cardiac and noncardiac pain. Pain may also be referred, commonly in visceral (organ-originating) pain.
- Duration: Acute pain lasts for less than 3 months, whether it has a sudden or slow onset, and regardless of intensity. Chronic pain, also known as persistent pain, is caused by pain signals firing in the nervous system beyond 3 months to even years. Each of these produce different physiologic and behavioral responses.
| Acute Pain | Chronic Pain |
|---|---|
| Mild to severe | Mild to severe |
| Sympathetic nervous system response: increase in HR, RR, BP; diaphoresis; and dilated pupils | Parasympathetic nervous system response: normal vital signs; dry, warm skin; pupils dilated or normal |
| Related to tissue injury; resolves with healing | Continues beyond healing |
| Restlessness, anxiety | Depressed, withdrawn |
| Client reports pain | Client does not mention pain unless asked |
| Pain behavior are displayed: crying, driving area, holding area | Pain behavior often absent |
- Intensity: most practitioners classify the intensity of pain by using a numeric scale—0 (no pain) to 10 (worst pain imaginable). Linking the rating to health and functioning scores, pain in the 1 to 3 range is considered mild pain, a rating of 4 to 6 is moderate pain, and pain reaching 7 to 10 is viewed as severe pain and is associated with the worst outcomes.
- Etiology:
- Nociceptive pain is experienced when an intact, properly functioning nervous system sends signals that tissues are damaged, requiring attention and proper care. Subcategories of nociceptive pain include somatic and visceral.
- Somatic pain originates in the skin, muscles, bone, or connective tissue, e.g., the sharp sensation of a paper cut or aching of a sprained ankle.
- Visceral pain results from activation of pain receptors in the organs or hollow viscera and tends to be characterized by cramping, throbbing, pressing, or aching qualities. Often visceral pain is associated with feeling sick (e.g., sweating, nausea, or vomiting) as in the examples of labor pain, angina pectoris, or irritable bowel.
- Neuropathic pain is associated with damaged or malfunctioning nerves due to illness (e.g., post-herpetic neuralgia, diabetic peripheral neuropathy), injury (e.g., phantom limb pain, spinal cord injury pain), or undetermined reasons. Neuropathic pain is typically chronic; it is often described as burning, “electric-shock,” or tingling, painful numbness, dull, and aching. Episodes of sharp, shooting pain can also be experienced. Neuropathic pain tends to be difficult to treat.
- Nociceptive pain is experienced when an intact, properly functioning nervous system sends signals that tissues are damaged, requiring attention and proper care. Subcategories of nociceptive pain include somatic and visceral.
Concepts Associated with Pain
- Cancer-related pain: Pain associated with the disease, treatment, or some other factor in individuals with cancer. Can be acute, recurrent, or chronic.
- Intractable pain: A pain state (generally severe) for which no cure is possible even after accepted medical evaluation and treatments have been implemented. The focus of treatment turns from cure to pain reduction, functional improvement, and the enhancement of quality of life.
- Pain threshold is the least amount of stimuli required to produce a sensation that can be called pain. It may vary from individual to individual, and may be related to age, gender, or race, but it changes little in the same individual over time.
- Pain tolerance is the maximum amount of painful stimuli that an individual is willing to withstand without seeking avoidance of the pain or relief. Pain tolerance varies significantly among individuals, even within the same individual at different times and in different circumstances. For example, a woman may tolerate a considerable amount of labor pain because she does not want to alter her level of alertness or the health of her baby. She likely would not tolerate a fraction of that pain during a routine dental procedure before requesting appropriate pain relief medicine.
- Procedural pain: Pain associated with any medical intervention. Nurses need to anticipate type of expected pain and provide appropriate interventions.
The following states indicate abnormal nerve functioning, and the associated cause needs to be identified and treated (as soon as possible) before irreversible damage occurs:
- Allodynia: Sensation of pain from a stimulus that normally does not produce pain (e.g., light touch).
- Dysesthesia: An unpleasant abnormal sensation that can be either spontaneous or evoked.
- Hyperalgesia: Increased sensation of pain in response to a normally painful stimulus.
The following concepts are important reasons to prevent pain or treat it as soon as possible to prevent the amplification, spread, and persistence of pain:
- Sensitization: An increased sensitivity of a receptor after repeated activation by noxious stimuli.
- Windup: Progressive increase in excitability and sensitivity of spinal cord neurons, leading to persistent, increased pain.
Physiology of Pain
The transmission and perception of pain are complex processes. The central nervous system’s structure constantly changes, and the constituency and function of its chemical mediators are not well understood. The extent to which pain is perceived depends on the interaction between the body’s analgesia system, the nervous system’s transmission, and the mind’s interpretation of stimuli and its meaning.
Nociception
The peripheral nervous system includes specialized primary sensory neurons that detect mechanical, thermal, or chemical conditions associated with potential tissue damage. When these nociceptors are activated, signals are transduced and transmitted to the spine and brain where the signals are modified before they are ultimately understood and then “felt.” The physiologic processes related to pain perception are described as nociception. Four physiologic processes are involved in nociception:
- Transduction: nociceptors can be excited by mechanical, thermal, or chemical stimuli. Inflammation, pressure, distension, destruction, chemical irritation (e.g., lactic acid), and ischemia. During the transduction phase, harmful stimuli trigger the release of biochemical mediators, such as prostaglandins, bradykinin, serotonin, histamine, and substance P, which sensitize nociceptors. Painful stimulation also causes movement of ions across cell membranes, which excites nociceptors.
- Pain medications can work during this phase by blocking the production of prostaglandin (e.g., nonsteroidal anti-inflammatory drugs [NSAIDs]) or by decreasing the movement of ions across the cell membrane (e.g., topical local anesthetic). Another example is the topical analgesic capsaicin, which depletes the accumulation of substance P and blocks transduction.
- Transmission: The second process of nociception, transmission of pain, includes three segments. (1) Pain impulses travel from the peripheral nerve fibers to the spinal cord (dorsal horn); (2) pain impulses travel through an ascending pathway in the spinal cord to the brain; and (3) transmission of information to the brain where pain perception occurs.
- Pain control can take place during the second process of transmission. For example, opioids block the release of neurotransmitters, particularly substance P, which stops the pain at the spinal level. The gabapentinoids (i.e., gabapentin and pregabalin) treat neuropathic pain by inhibiting the transmission of painful stimuli in the dorsal horn (Polomano et al., 2017).
- Perception: The third process, perception, is when the client become conscious of the pain. Complex activities in the CNS shape the character and intensity of pain perceived and give meaning to the pain. This shapes the behavioral response that follows.
- Nonpharmacologic interventions such as distraction, imagery, massage, and acupuncture have been used to influence pain perception.
- Modulation: Often described as the “descending system,” this final process occurs when neurons in the brain send signals back down to the dorsal horn of the spinal cord. These descending fibers release substances such as endogenous opioids, serotonin, and norepinephrine, which can inhibit or reduce the ascending painful impulses in the dorsal horn. In contrast, excitatory amino acids (e.g., glutamate, N-methyl-d-aspartate [NMDA]) can increase these pain signals.
- The effects of excitatory amino acids tend to continue, while the effects of the inhibitory neurotransmitters (endogenous opioids, serotonin, and norepinephrine) tend to be short lived because they are reabsorbed into the nerves.
- Tricyclic antidepressants can relieve pain by blocking the resorption of norepinephrine and serotonin, making them more available to fight pain; or NMDA-receptor antagonists (e.g., ketamine, dextromethorphan) or opioids may be used to help diminish the pain signals.