Pain Management Nursing CE Course Part 1: The Pathophysiology and Classification of Pain (All Users)

1.0 ANCC Contact Hours AACN Category A

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3-Part Module Series on Pain Management. Please visit the following links to visit Part 2 and Part 3 modules.

For RNs/LPNs:

For APRNs:

Part 1: The Pathophysiology and Classification of Pain  


By the completion of this module, the learner should be able to:

  • Define pain and discuss the pathophysiology of pain and pain processes.
  • Describe the four main categories of pain: acute, chronic, nociceptive, and neuropathic pain.
  • Identify the core components of a comprehensive pain assessment and describe the use of pain assessment scales and tools.

This 3-part series on pain management strives to provide a thorough review of the principles of pain management, the critical assessment, non-pharmacological and pharmacological interventions, as well as strategies to safeguard patient care, improve patient outcomes, and uphold the practice of the healthcare professional, specifically the nurse and advanced practice nurse. 

Pain is always subjective and described as an individual experience for each patient. In 1968, Margo McCaffery, a pioneer and well-known expert in the care of patients with pain, defined pain as "…whatever the experiencing person says it is, existing whenever he says it does" (McCaffrey, 1968). The International Association for the Study of Pain (IASP, 2017) defines pain as "an unpleasant sensory and emotional experience associated with actual or potential tissue damage." Pain cannot be objectively measured and is instead dependent upon the individual's self-report. It is a complex perception that has physiological, behavioral, and psychological components, with wide variability in how each person experiences pain from a distinct stimulus (National Institute of Neurological Disorders and Stroke, [NINDS], 2019b). 

Pathophysiology of Pain

The etiology of pain is usually complex and multifaceted, thereby heightening the importance of proper clinical assessment, diagnosis, and identification of underlying and contributing conditions to reduce pain to an acceptable level. There are several processes associated with nociceptors, the sensory impulses that carry pain signals. Basic knowledge of each of these, as well as a proper understanding of the most common pain terminology, helps when determining the etiology of pain, assessing, and identifying the most common symptoms to facilitate the selection of the most optimal interventions to alleviate pain (NINDS, 2019b). Table 1 describes the primary pain processes, and Figure 1 demonstrates a graphic representation of the pain pathway.

Categories of Pain

Pain is categorized by duration (acute or chronic), origin (nociceptive or neuropathic), or by the disease or condition that causes it (cancer, diabetes, rheumatoid arthritis, etc.). Nociceptive pain includes somatic pain (skin, muscles, and soft tissues) and visceral pain (internal organs and lining of body cavities) (Ignatavicius & Workman, 2015). A description of each of these categories of pain will be defined in the next section of this module.

Acute Pain

Acute pain is a warning sign or protective response that something in the body has been damaged, notifying the individual to respond to or escape the painful stimuli. It usually has a direct cause, resulting from disease, inflammation, or injury to tissues. The etiology of acute pain may be surgery, burns, invasive procedures, childbirth, or trauma. It is temporary and self-limiting, meaning it is confined to a defined period and often resolves with tissue healing. Acute pain may be accompanied by anxiety or emotional distress (NINDS, 2019b). Physiological responses to acute pain include activation of the sympathetic nervous system, or the body's inherent fight or flight response. Manifestations of the sympathetic response may include tachycardia, hypertension, increased respiratory rate, dilated pupils, diaphoresis, anxiety, and muscle tension. Behavioral responses to acute pain may include restlessness, grimacing, moaning, flinching, guarding, apprehension, and an inability to concentrate. Acute pain is usually treatable, and interventions are aimed at managing the underlying problem. If left untreated or unrelieved, acute pain can lead to the development of chronic pain (Ignatavicius & Workman, 2015). 

Chronic Pain

Chronic pain is a widely prevalent condition, as it is one of the most common reasons people utilize health care services in the US. According to the 2016 National Health Interview Survey, 50 million US adults (20.4% of the adult population) have chronic pain. Nearly 20 million of these have "high-impact chronic pain," which is defined as pain severe enough to impair life and work activities (Dahlhamer et al., 2018). Unlike acute pain, chronic pain is not protective, and the onset is gradual. It is ongoing and frequently recurs, usually lasting greater than three months and persisting beyond tissue healing. Chronic pain is often poorly localized and can be challenging to describe. While chronic pain does not have the physiological response on the sympathetic nervous system that acute pain does, it is associated with significant morbidity, including physical and mental health conditions. Patients with chronic pain are at higher risk for developing depression, fatigue, decreased level of functioning, impairment of activities of daily living, disability, and financial burden. It can interfere with personal and intimate relationships and contribute to social isolation or emotional distress. Chronic pain is usually not life-threatening, and management is aimed at symptomatic relief. It is more resistant to medical treatment than acute pain, as it does not always respond to interventions. If the underlying etiology cannot be identified, controlling the long-term effects of the pain is very challenging. In some cases, chronic pain is considered idiopathic; this is without an identifiable cause, or when the pain exceeds typical pain levels associated with the underlying condition (Ignatavicius & Workman, 2015).

Some of the most common conditions causing chronic pain include low back pain (lumbago), arthritis, headaches, and fibromyalgia. Low back pain is one of the leading causes of disability in Americans, as nearly 80% of adults experience low back pain at some point in their lifetime (NINDS, 2019a). It has profound effects on patients, families, work productivity, and the economy. Determining the cause of low back pain can be difficult and costly. In the US, direct healthcare expenditure associated with low back pain can range from $50 to $90.7 billion annually. When combined with costs due to loss of work productivity, total costs are estimated to reach $635 billion each year. Low back pain can result from a prior injury that did not resolve or heal entirely, from poor body mechanics and posture, or wear-and-tear associated with aging leading to osteoarthritis and degenerative disc disease (Yang et al., 2018). Cancer-related pain is often considered a chronic pain condition and is attributed to tumor invasion, nerve compression, bone metastases, or as a byproduct of treatment, such as radiation therapy (Ignatavicius & Workman, 2015). 

Fibromyalgia is a poorly understood chronic pain condition that affects about 4 million adults in the US. The etiology is not known. Still, the disease is characterized by abnormal pain perception processing. Patients experience a multitude of symptoms, including diffuse musculoskeletal pain and stiffness, fatigue, exercise intolerance, headaches, sleep disturbances, and problems with memory and concentration. Fibromyalgia more commonly affects middle-aged women, as well as those who have rheumatoid arthritis or lupus. The condition is often treated with a combination of pharmacological and non-pharmacological interventions. Analgesic medications may be prescribed or purchased over the counter. Recommended lifestyle modifications include aerobic exercise, stress management, cognitive-behavioral therapy, and sleep hygiene (The Centers for Disease Control and Prevention [CDC], 2017). Table 2 provides a quick comparison chart of the features of acute and chronic pain.

Nociceptive Pain

Nociceptive pain is the normal response that arises from damage or injury to tissues caused by noxious stimulus. There are two main categories of nociceptive pain: somatic and visceral. Somatic pain may be further subdivided into cutaneous or superficial (skin and subcutaneous tissues) and deep somatic (bone, musculoskeletal, blood vessels, and connective tissues).  Somatic pain is generally well-localized and may be described as sharp, burning, dull, or aching. A few examples include incisional pain, wound complications, muscle spasms, and peripheral vascular disease. Visceral pain is located within internal organs and the linings of the body cavities, such as the stomach or intestines. Visceral pain is usually poorly localized, diffuse, and described as deep cramping, sharp, or shooting. A few examples of visceral pain include colitis, pancreatitis, bladder spasms, and appendicitis (Ignatavicius & Workman, 2015). As displayed in Figure 2, visceral pain can cause referred pain in other body locations separate from the site of the noxious stimulus.

Neuropathic Pain

Neuropathic pain results from damage to or dysfunction of the nervous system, inducing hyperalgesia, or pain that is out of proportion to the injury. Neuropathic pain is usually described as intense, shooting, burning, and can be characterized by sensory abnormalities, such as paresthesia (numbness, tingling, or "pins and needles"). Allodynia, or pain due to a stimulus that does not usually provoke pain, is another common manifestation of neuropathic pain. Neuropathic pain typically responds to adjuvant drugs such as antidepressants, anticonvulsants, antispasmodic agents, and skeletal muscle relaxants, which will be discussed among other pain treatments in a separate module. Many types of neuropathic pain are chronic, unrelenting, persistent, and long-lasting. Some of the most common types of neuropathic pain conditions include postherpetic neuralgia (PHN), trigeminal neuralgia (TN), diabetic neuropathy, and phantom limb pain, which are outlined below (Ignatavicius & Workman, 2015).

Postherpetic Neuralgia (PHN)

PHN is a highly painful and debilitating complication of the herpes zoster (Shingles) virus, which results from damage to the sensory nerves, affecting the nerve fibers and skin. It is characterized by a pain that persists beyond the resolution of the Shingles rash. The risk for PHN increases with age, and hyperalgesia and allodynia following the resolution of the skin rash are among the most prominent clinical manifestations. Treatment is challenging, and effective relief from symptoms often requires multiple pharmacological options. Common treatments include Lidocaine (Lidoderm) patch, nortriptyline (Pamelor), amitriptyline (Elavil), duloxetine (Cymbalta), venlafaxine (Effexor), Gabapentin (Neurontin), Pregabalin (Lyrica), Tramadol (Ultram), and opioids. The role of opioid use in patients with PHN is controversial (Ignatavicius & Workman, 2015). The CDC (2019) recommends that all adults aged 50 and older receive the recombinant zoster vaccine (RZV, Shingrix), administered as two doses, two to six months apart. For healthy adults aged 60 and older, zoster vaccine live (ZVL, Zostavax) can be used (CDC, 2019).

Trigeminal Neuralgia (TN)

TN, or tic douloureux, is a type of chronic pain that affects the fifth cranial nerve, inducing excruciating, shock-like burning pain to the face. It usually affects one side of the face near the jaw or cheek, and the intensity of the pain is so severe that it can be physically and mentally debilitating. TN pain can be sporadic and intermittent, often referred to as "attacks of pain," and may be triggered by contact with the face or cheek (such as brushing teeth, applying makeup, eating, etc.). Diagnosis and treatment of the condition are equally complex, but management usually includes pharmacological medications such as anticonvulsants and tricyclic antidepressants. Non-pharmacological modalities are often used in conjunction with drugs, which may include acupuncture, biofeedback, and electrical stimulation of the nerves, in addition to nutritional therapy. In extreme cases, when other treatments fail, neurosurgical approaches may be considered (NINDS, 2019c).

Diabetic Neuropathy

Diabetic neuropathy is nerve damage that is caused by diabetes. Over time, elevated blood glucose levels can induce damage to the nerves. There are a few different types of diabetic neuropathies, but the most common is peripheral neuropathy affecting the legs, feet, and toes. People with diabetes may also experience focal neuropathies such as damage to a single nerve in a specific body part, called entrapment syndromes. The most common entrapment syndrome is carpal tunnel syndrome. Autonomic neuropathy is also seen in diabetics, which is damage to the nerves that control the internal organs. Autonomic neuropathy can lead to digestive dysfunction, bladder dysfunction, or ocular retinopathy. These conditions can contribute to the overall morbidity among this population (National Institute of Diabetes and Digestive Kidney Diseases [NIDDK], 2018).

Phantom Limb Pain

Phantom limb pain is felt after the loss of a body part and is most commonly described as stabbing, shooting, burning, and throbbing pain. Allodynia is a common manifestation. Risk factors include older age at the time of amputation, lower limb amputation, and bilateral limb amputation (Ignatavicius & Workman, 2015). 

Risk Factors for Pain

Several risk factors increase the risk for the development of pain. Some of the most common include:

  • Advancing age;
  • Lower socioeconomic status, such as those living in poverty;
  • Various occupational-associated risks (i.e., manual labor involving heavy lifting, or inactivity due to a desk job, poor posture, and improper body mechanics); 
  • Less than a high school education;
  • Public health insurance;
  • Sedentary lifestyle, being overweight or obese;
  • Presence of specific underlying health conditions such as cancer (tumor invasion, nerve compression, bone metastases, associated infections, immobility, prescribed treatments), arthritis, fibromyalgia, and neuropathy;
  • Trauma;
  • Surgery;
  • Invasive diagnostic or treatment procedures (Dahlhamer et al., 2018; NINDS, 2019b).

Factors Affecting the Pain Experience

At all stages of the pain assessment, the nurse and APRN must be cognizant of the various factors that can affect the patient's pain experience, which can make the diagnostic work-up more complex. Some of the most common factors that can impact an individual's pain experience are listed in Table 3.

Risk Factors for the Undertreatment of Pain

Undertreatment of pain is a serious complication and can lead to increased anxiety with acute pain and depression with chronic pain. According to the US Department of Health and Human Services (USDHHS, 2019), some of the most common risk factors associated with the undertreatment of pain include:

  • Older age (older adults);
  • Cultural and societal attitudes of pain;
  • Lack of knowledge and education regarding pain and appropriate management;
  • Fear of addiction (among patients and providers);
  • Stigma;
  • Exaggerated fear of respiratory depression;
  • Barriers to accessing care (lack of insurance coverage and payment for pain modalities or pain specialist)
  • Specific populations: infants and children, elderly adults, and patients with substance abuse disorders (USDHHS, 2019).

Pain Assessment

All patients should be screened for the presence of pain, which is the critical first step to a comprehensive pain assessment. Since pain is a subjective experience, a thorough and reliable assessment of pain is vital to diagnose pain and determine the most effective treatment plan accurately. The pain assessment is comprised of the following components:

  • A pain interview using a validated pain assessment scale; 
  • A thorough history and physical examination, inclusive of a review of prior pain experiences and treatments, as well as a functional assessment of abilities and deficits; 
  • A psychosocial assessment;
  • Opioid assessment and identification if the patient is opioid-tolerant (Rabow et al., 2020). 

Scales and Tools

The patient's self-report of pain severity should be evaluated using an appropriate scale, such as the Numeric Rating Scale (NRS), where 0 refers to "no pain" and 10 denotes "the worst pain imaginable." Other pain severity scales include the Visual Analogue Scale (VAS) and the Defense and Veterans Pain Rating Scale (DVPRS). Pain severity scales for individuals who have difficulty communicating verbally, such as older adults with cognitive impairments and dementia, include the FACES Pain Scale (displayed in Figure 3), the Adult Non-Verbal Pain Scale (NVPS), and the Pain Assessment in Advanced Dementia Scale (PAINAD). The FACES scale is also widely utilized in pediatric pain assessment. Pain severity scales that allow for pain assessment using various physical features representative of pain include the Behavioral Pain Scale (BPS) and the Critical Care Pain Observation Tool (CPOT). In conjunction with the pain severity assessment scales described above, there are additional assessment tools that help to define and classify the pain. The OPQRST tool is one of the most common instruments utilized, which reviews the following features of pain: provocation and palliation of symptoms, quality, region and radiation, severity, and timing (University of Florida Health, 2020). An overview of the clinical use and application of the OPQRST tool is outlined in Table 4.

In addition to the above, it is also helpful to ask patients about the setting of pain, such as how the pain affects the individual’s daily life or activities of daily living (ADLs).  Some questions to ask include:

  • “Where are you when the symptoms occur?”
  • “What are you doing when the symptoms occur?”
  • “How does the pain affect your sleep?”
  • “How does the pain affect your ability to work or interact with others?”

 (UF Health, 2020)

History and Physical Examination

The patient's medical and surgical history, in addition to prior trauma or injuries, should be evaluated. An allergy and medication history, including the use of any over-the-counter medications and supplements, is critical. The nurse or APRN should assess the patient's history with prior or current pain relief measures, including pharmacological and non-pharmacological modalities. Information regarding the patient's prior experience with opioids should be explored during the initial pain assessment to determine if the patient is opioid-tolerant and to identify risks for opioid use disorders, in the event that opioids become part of the pain management plan.  Behaviors complement self-report and assist in pain assessment of both nonverbal and verbal patients. Direct observation of the patient's nonverbal behavioral manifestations may indicate the presence of pain. Facial expressions (grimacing, wrinkled forehead, wincing), body movements (restlessness, pacing, guarding), and audible expressions (crying, wincing, moaning) can all indicate the presence of pain. Other physical examination findings that can indicate pain include decreased attention span and changes to vital signs. Blood pressure, pulse, and respiratory rate increase temporarily with acute pain. However, eventually, vital signs will stabilize with the persistence of pain and chronic pain. Therefore, physiologic indicators might not be an accurate measure of chronic pain or pain that is present over time (Bickley, 2016).

The nurse or APRN should perform a focused physical assessment of the systems related to the reported pain, including the neurological system and musculoskeletal system. In patients with clinical suspicion for neuropathic pain, signs of nerve injury may or may not be seen on the neurological exam. Some patients may demonstrate sensory deficits to provoked pain, such as a dull, pinprick, and sharp touch, or alterations in temperature or vibration. Allodynia or hyperalgesia may be present, as an exaggerated response to stimuli. Further, autonomic changes in the temperature and color of the extremities, as well as hair and nail growth, can accompany neuropathic pain. The patient should be evaluated for any impairments in mobility, such as gait disturbance, imbalance, loss of muscle tone, reflexes, coordination, and grip strength (Bickley, 2016).

Psychosocial Examination

Pain can impair many aspects of a patient's psychological function and social wellbeing. The patient should be screened for the presence of any psychosocial impacts of pain, such as disturbances in sleep, mood, activity, energy, appetite, and overall functioning. The patient's ability to fulfill activities of daily living, in addition to work responsibilities, should be explored. Pain can also impair cognition, memory, and negatively impact relationships with family, friends, and colleagues. Suicidal ideation is essential to assess, as chronic pain is often accompanied by depressive symptoms (Bickley, 2016).

Assessment of Pain in Older Adults

It is well documented that the incidence of pain is high among the older adult population. However, they receive fewer analgesics and are at heightened risk for the undertreatment of pain. Older adults tend to report less pain than younger adults, which may be related to beliefs about pain, concerns about reporting pain, or cognitive deficits. Research demonstrates that many older adults hold beliefs that pain is something that must be lived with, and that reporting pain is an unacceptable sign of weakness. Pain may be associated with being a "bad" patient, or may signify impending death or serious illness, and therefore is ignored. Fear of becoming addicted to narcotics and opioids may also contribute to the older adult's reluctance to report pain. Those with cognitive impairments, hearing or visual deficits, as well as dementia, are at risk for undertreated pain. Special consideration should be given to the older adult population when assessing for pain. Appropriate pain scales should be utilized within this population and the scale should be explained each time it is used. Attention should be paid to nonverbal indicators of pain as part of the pain assessment in these patients, such as facial expressions, body movements, grimacing, guarding, and behavioral changes. It may be helpful to avoid the use of the word pain, and instead use verbal descriptions such as "ache," "sore," or "hurt" (Ignatavicius & Workman, 2015).

For additional information, proceed to the second part of this 3-part series entitled, Part 2: The Non-Opioid Management of Pain.


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