Pain is (1) a universal, self-defined experience that is described as mild to severe discomfort; (2) a protective mechanism in response to noxious stimuli; and (3) a stressor that can lead to physical disorders related to undernutrition, immobility, and immune suppression. Pain cannot be objectively measured. The definition of a client’s pain is affected by his or her cultural background and by the nurse’s biases and expectations.

Pain can be described by its cause or origin and by its description or nature. Pain categorized by its origin is nociceptive (normal processing of noxious stimuli) or neuropathic, which is abnormal processing of stimuli by the peripheral nervous system (PNS) or the central nervous system (CNS). Nociceptive pain is (1) cutaneous, caused by stimulation of nerve endings in the skin and resulting in a “burning” or “prickling” sensation; (2) somatic, a nonlocalized discomfort originating in support structures, such as tendons, ligaments, and nerves; or (3) visceral, a less localized discomfort in the internal organs.

Neuropathic pain arises from damage to the peripheral or central nervous system. Two forms of neuropathic pain are allodynia (a nonpainful stimulus felt as painful in spite of the tissue appearing normal) and paresthesia (abdominal sensations, such as burning, prickling, or tingling). Neuropathic pain includes centrally-generated pain (phantom pain, spinal cord injury) or peripherally-generated pain (diabetic neuropathy, trigeminal neuralgia).

Pain in the abdomen may be “referred” pain, localized where the affected organ was located during fetal development. A trigger point is a hypersensitive point that causes a local twitch when stimulated. Hyperalgesia is extreme sensitivity to pain.

Pain can also be characterized by its duration. Acute pain is pain identified by a sudden onset and short duration, of mild to severe intensity, with a steady decrease in intensity over a period of time. The pain goes away once the noxious stimulus (needle stick, burn, fracture, etc.) is removed. Recurrent acute pain is identified by repetitive painful episodes that may recur over a prolonged period or throughout the client’s lifetime, such as migraine headaches, sickle cell anemia pain crises, or angina pectoris. Chronic pain is a long-term (6 months or longer), persistent, nearly constant, or recurrent pain that produces significant negative effects on the client’s lifestyle. Chronic malignant pain is a result of progressive tissue injury, such as cancer or a burn. Chronic nonmalignant pain (CNP) occurs in people who do not have progressive tissue injury, such as neuralgia, low back pain, or arthritis. CNP can lead to activity intolerance, functional impairments, role change, social isolation, sleep deprivation, and depression. The term intractable pain refers to pain that is resistant to all therapies.

The processes involved in nociception (process by which the individual becomes aware of pain) are transduction, transmission, perception, and modulation. Transduction begins when a noxious stimulus occurs, with tissue damage, leading to the cellular release of prostaglandins (PG), bradykinin (BK), serotonin (5HT), substance P (SP), and histamine (H). Transmission of pain occurs when the stimulus travels through the afferent (ascending) pathway to the spinal cord, then to the brain where the pain is perceived. The transmission of pain depends upon where the stimulus is applied. For example, cutaneous pain is transmitted quickly, but visceral pain is slower. Ischemic pain, occurring when the blood supply of an area is restricted or cut off completely, leads to inadequate oxygenation of the tissue and inadequate waste removal. The most common examples are muscle cramps, sickle cell pain crisis, angina pectoris, and myocardial infarction.

Perception occurs when an individual develops a conscious awareness of pain. The person becomes aware of the intensity, location, and quality of pain, interpreting the information in the light of previous experience. Modulation refers to activation of descending neural pathways that inhibit transmission of pain. The efferent (descending) fibers release endogenous opioids (enkephalins and endorphins) that produce analgesia.

According to the Gate Control Theory of Pain, pain has cognitive, sensory, emotional, and physiological components. According to this theory, large-diameter nerve cells in the dorsal horn of the spine block transmission of pain impulses to the brain. Stimulants, such as cutaneous massage, opioids release, and excessive stimulation activate these cells to “close the gate.” Several nonpharmacologic modalities support this theory, such as massage, acupuncture, and acupressure.

A person’s pain threshold is the level of intensity at which pain becomes appreciable or perceptible. Pain tolerance is the level of intensity or duration of pain the client is willing or able to endure. Several factors affect pain threshold and pain tolerance, including age, gender, stress, anxiety, previous experience with pain, cultural norms, and cultural attitudes.

Pain assessment includes both subjective and objective pain assessment. Subjective data includes the intensity, location, and quality of pain (radiating, burning, diffusing); factors accompanying the pain (for example, nausea, constipation, dizziness), and factors alleviating the pain (such as lying down, avoiding certain foods, or taking medication).

Pain assessment tools include pain intensity scales, such as the verbal rating scale (VRS) or the numeric rating scale (NRS), a pain diary, and psychosocial pain assessment. The pain intensity scales use adjectives for clients to rate the severity of pain. They can be modified for children, for example, the Wong/Baker Faces Pain Rating Scale. Pain diaries are used to record the date and time of pain, the intensity, the situation, how the client was feeling, what the client was thinking about, client activities to ease the pain, and how effective the pain control strategy was. The questions addressed with psychosocial pain assessment revolve around how the client and family understand the medical diagnosis, previous experiences with pain, usual coping mechanisms, concerns of the client and family about pain medications, and family understanding of the differences between tolerance, dependence, and addiction.

The nursing diagnoses for clients with pain are Acute Pain and Chronic Pain. Pain may also be the cause of a nursing diagnosis, such as Impaired Physical Mobility or Activity Intolerance. After finding appropriate nursing diagnoses, the nurse works with the client to develop expected outcomes.

The relationship between the client and the nurse is crucial when dealing with pain. Much of the treatment for pain incorporates client education to identify causes, assess and describe pain accurately, prevent reoccurrence, and treat effectively. Both pharmacologic and nonpharmacologic interventions are effective.

The principles for pain control are to assess the pain accurately, treat the cause, individualize analgesics, use the least invasive route of administration of medications, administer analgesics at regularly scheduled intervals rather than on an as-needed (PRN) basis, give the client control (for example, patient-controlled analgesia, (PCA), and titrate doses to provide maximum pain relief and minimum side effects). The World Health Organization (WHO) has established principles for pharmacologic interventions for pain. Nonopioid medications are tried first, followed by opioids if these do not work, and by adjuvant medications (tricyclic antidepressants, anticonvulsants, corticosteroids, antihistamines, neuroleptics, and psychostimulants) to enhance the analgesic efficiency of opioids if opioids alone do not work. Adjuvant medications work by enhancing the analgesic efficacy of opioids, to treat symptoms that exacerbate pain, and to provide analgesia for specific types of pain.

Examples of nonopioid medications are nonsteroidal anti-inflammatory drugs (NSAIDs), aspirin, and acetaminophen. NSAIDs inhibit the synthesis of prostaglandin, resulting in an anti-inflammatory effect. NSAIDs are useful for mild pain, but can cause gastrointestinal, hematologic, liver, and renal problems. Aspirin can cause multiple side effects, including tinnitus and vertigo, nausea and vomiting, and bleeding disorders. Acetaminophen is useful for mild pain and does not cause bleeding problems, but it is not an anti-inflammatory. Examples of opioid medications are morphine, methodone, hydromorphone, codeine, and meperidine. The most common side effects are respiratory depression, constipation, and physical dependence. Another form of pain relief is local anesthesia.

Non-pharmacological interventions for pain include client education; distraction; reframing (replacing negative thoughts with positive thoughts); biofeedback; cutaneous stimulation, transcutaneous stimulation; and complementary and alternative therapies, such as acupuncture and acupressure, herbs, nutrition, physical stimulation, relaxation techniques, environment manipulation, and transcutaneous electrical nerve stimulation (TENS).