Learning Objectives
By the end of this section, you will be able to:
- Describe the physiologic process of pain
- Analyze the gate control theory of pain
- Identify the classifications of pain
In order to assess and manage pain effectively, nurses must first understand the physiologic process of pain. Painful stimuli travel through the central nervous system via the pain pathway to the brain where the brain processes and initiates a response. The body’s response to pain is dependent on the classification of pain and any factors affecting pain.
Pain can be classified by duration, location, and cause. Pain can be acute, chronic, localized, referred, or idiopathic. Nurses must know how to classify pain to effectively treat the pain. Pain can also be affected by biological, psychological, and social factors. The patient’s age, attitude, emotions, or culture can affect how they perceive pain and how they want the pain to be treated. All these factors play a role in how nurses approach pain management for each patient.
The Physiologic Process of Pain
Pain can be processed physiologically and emotionally through the body. Pain motivates the individual to withdraw from dangerous stimuli, to protect a damaged body part while it heals, and to avoid similar experiences in the future. Pain can resolve after the stimulus is removed and the body has healed, but sometimes pain persists. Pain can also occur in the absence of a stimulus, damage, or disease.
Sensory receptors in the peripheral nervous system called nociceptors play an important role in the pain process. A nociceptor is designed to respond to potentially damaging stimuli by sending nerve signals to the spinal cord and brain. The process by which painful stimuli are detected by nociceptors and begin to send the pain signals from the peripheral nervous system to the brain is called nociception (Chen et al., 2023). After nociception occurs, the body processes the pain through four major steps: transduction, transmission, perception, and modification (Figure 30.2).
Transduction of Pain
The starting point of the body passing painful stimuli to the brain is called transduction of pain. It occurs when activated nociceptors in the peripheral nervous system send a pain signal to the central nervous system, starting in the dorsal root of the spinal cord (Yam et al., 2018). Activation of nociceptors can occur internally or externally, such as from a cut from a knife, an infection, or a sprained ankle (Answine, 2018).
There are several types and functions of nociceptors:
- Thermal nociceptors are activated by 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.
Transduction of pain is the first step of the pain process. Once the spinal cord receives the pain signal, the next step is transmitting the pain signal from the spinal cord to the brain.
Transmission of Pain
The spinal cord, brain stem, and cerebral cortex are all involved in the transmission of pain (Yam et al., 2018). After the nociceptive signal is activated, transmission of pain sends the pain signal through the central nervous system. The pain signal is sent from the spinal cord to the nucleus of the brain stem, which initiates the brain’s perception of pain (Chen et al., 2023). The pain signal is categorized as a thermal, mechanical, or chemical nociceptor. The brain then localizes the pain and creates an appropriate physical or emotional response (Answine, 2018).
Perception of Pain
After the brain stem receives the pain signal, it is sent to the cerebral cortex where the brain perceives the severity of the pain. When the brain receives the nociceptive signal, it perceives the message as pain to activate the body’s defense to the perceived threat (Yam et al., 2018). The perception of pain occurs when the brain becomes aware of the pain through the cerebral cortex and determines an appropriate response to protect the body (Answine, 2018). For example, when a person stubs their toe, the brain perceives the painful stimuli and signals the body to take action. The person may grab their foot or cry out to express their pain. Individuals may perceive pain differently and perception can be altered due to many different factors. Past experiences, external factors, other health issues, and environmental differences are just a few things that can affect the perception of pain.
Modification of Pain
There are many factors that can affect the perception of pain; and there may be situations where the brain may modify pain signals in order to protect the body. The modification of pain occurs when the brain changes the intensity of the pain signal based on the situation that originated the pain signal (Answine, 2018). For example, a person may get injured from a dog bite, but the brain chooses to ignore the pain signal so the person can run away from the dog.
A chemical called a neurotransmitter carries messages between neurons to communicate throughout the body. Many neurotransmitters, such as norepinephrine and serotonin, can be involved in modifying the pain signals the brain receives (Answine, 2018). Nonpainful signals, such as electrical nerve stimulation, touch, or pressure can help counteract the severity of the pain signals. This is part of the gate control theory of pain.
The Gate Control Theory of Pain
The gate control theory of pain was developed by Ronald Melzack and Patrick Wall in 1965. Their research helped explain how sensory and psychological aspects affect how patients perceive pain (Campbell et al., 2020). The gate control theory states that the central nervous system can use neurological “gates” to determine when pain is felt. These “gates” determine which pain signals are allowed through to the brain and acts as a survival mechanism for the body (Cleveland Clinic, 2022). When the “gates” are open, the pain signal can travel to the brain and be perceived as pain. When the “gates” are closed, the pain signal is blocked from traveling to the brain. If the body perceives pain in two different locations at the same time, one “gate” may close to prioritize a response for the other cause of pain. Individuals can also use methods such as massage and acupuncture to help the body close these “gates” to decrease painful stimuli.
Link to Learning
Watch this video to better understand the gate control theory of pain.
The gate control theory states that different pain signals can be transmitted to the brain faster than others can. Signals such as touch or sensation can be received by the brain faster than signals that send pain or temperature to the brain (Cleveland Clinic, 2022). Stimulating signals such as pressure can help decrease the pain signals to the brain. This explains why clutching an injured extremity can help decrease the pain sensation.
The gate control theory acknowledges that there are many factors that can affect pain (Trachsel et al., 2023). Factors such as mental health disorders, mindset, stress, or lifestyle choices have been shown to affect how the brain perceives pain. These factors can prevent the “gates” from closing, which can increase the pain intensity and frequency.
Factors Affecting the Theory of Pain
Biological, psychological, and social factors can all affect how a patient perceives pain (Table 30.1). Nurses must consider these factors while assessing and providing holistic nursing care for patients experiencing pain.
| Biological Factors | Psychological Factors | Social Factors |
|---|---|---|
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Age is a significant biological factor in the perception of pain. Newborns and infants can feel pain but are unable to verbalize it. School-aged children and adolescents may try to be “brave” and rationalize the pain. Older adults are at increased risk for undertreatment of pain because they are less likely to report it and pain can present atypically with confusion and agitation. Older adults and patients with diabetes/neuropathy may also feel pain differently due to decreased sensations.
Psychological factors also play a considerable role in pain perception. A patient’s expectations of pain can often increase or decrease the severity. If a patient believes they will have a lot of pain, their perception can increase. In contrast, if a patient believes an intervention will be effective, their pain may decrease (Heshmat, 2023). For example, a patient who believes physical therapy will decrease their pain may have better pain outcomes than a patient who believes physical therapy will not have any effect on their pain. The interpretation of pain can also have an impact on pain perception. How pain affects a patient’s quality of life can change their perception of pain. For example, a patient who is having pain from chronic arthritis may perceive their pain differently than a patient who is having pain from delivering a baby (Heshmat, 2023).
It is important for nurses to understand how social factors can affect a patient’s perception of pain. Factors such as culture and socioeconomic status can influence how a patient perceives and articulates their pain (Heshmat, 2023). Certain cultures may be more expressive in their pain than others, and patients may hide their pain in fear of judgment of their socioeconomic status. For example, people from Asian cultures are more stoic and less vocal, while people from Middle Eastern cultures may be more vocal about their pain.
The complex interactions between factors affecting pain and individual perception can create a wide range of reactions to pain (Trachsel et al., 2023). Pain management must be multimodal and different for each patient to effectively treat pain.
Emotional State
Pain is always defined as a sensory and emotional experience. The patient’s emotional state and pain go hand in hand, especially in patients with chronic pain. Research has shown that patients with chronic pain have higher rates of negative emotions such as anxiety, depression, and frustration (Gilam et al., 2020). Both negative and positive emotions can shape a patient’s perception of pain. Research has also shown that patients with negative emotions such as anxiety tend to have a lower pain threshold (Heshmat, 2023), but positive emotions can decrease pain severity. This is why patients who practice relaxing activities such as listening to music can have reduced pain (Kober et al., 2020).
Social and Cultural Environment
Social and cultural environments can play a large role in the perception of pain. Factors such as a patient’s home environment and social support can affect pain perception. Patients who have supportive social circles have been shown to have improved pain outcomes. Social isolation can contribute to poor pain outcomes, especially in chronic pain and older adult patients (Chadwick et al., 2022).
Other patient populations who can be affected by social factors include
- patients with a history of addictive disease;
- patients who are nonverbal, cognitively impaired, or unconscious;
- patients who endure pain without complaining due to cultural or religious beliefs;
- patients who are non-English speaking, where communication is a barrier; and
- patients who are uninsured or underinsured, where cost of medications is a barrier.
Nurses need to be aware of the impact of social environment and culture on pain management. Providing culturally competent care is essential to effective pain management for all patients.
Cultural Context
Cultural Competence in Pain Management
Cultural competence is essential in effective pain management. Patients who are non-English speaking are at higher risk for experiencing undertreated pain due to communication barriers. Interpreters can be helpful in ensuring patients are able to effectively express their pain and communicate their needs. Cost and availability are two cited barriers to having interpreters readily available in healthcare settings (Yelton & Jildeh, 2023). However, any intervention to ensure cultural competence in healthcare settings should be explored regardless of barriers. Cultural practices and beliefs play a big role in how a patient perceives pain and their expectations of pain management. Lack of understanding of cultural differences can damage the provider-patient relationship and create barriers to effective pain management. For example, some Asian cultures may not express their pain and appear reserved despite being in severe pain. Religion can also play a role in perception of pain. Some religions may believe that pain is a test of faith or part of the path God has planned for them. If nurses are not aware of these cultural differences, the patient could experience ineffective pain management (Givler et al., 2023). The different cultures and personal experiences of nurses can affect how pain is perceived in patients. Nurses should be aware of how their personal beliefs and experiences can impact how they care for patients who are different from them.
Classification of Pain
Classifying pain can help effectively evaluate and treat pain. Pain can be classified based on the severity, duration, or location. The World Health Organization (WHO) developed the analgesic ladder (Figure 30.3) in 1986 to help select analgesics for patients with cancer pain, but it can be broadened for managing pain appropriately for all patients. The ladder classified pain into three categories: mild, moderate, and severe. The WHO defines pain severity based on the type of medication needed to treat the pain. For example, mild pain may require only nonopioid analgesics while severe pain requires opioid medications such as morphine or fentanyl (Anekar et al., 2023).
Pain can also be classified based on the duration or location of pain. Using tools such as pain location charts can help patients pinpoint the location of their pain, which may give healthcare providers a better idea of the cause of pain. The duration of pain can also help determine the potential cause and effective pain management strategies. For example, acute abdominal pain may indicate appendicitis whereas chronic back pain could indicate a past injury.
Duration
The duration of pain can determine the treatment method. Acute, chronic, or breakthrough pain are all defined based on the duration of time the pain persists. Acute pain is defined as Pain that is short in duration and caused by an acute event. For example, acute pain can be caused by an acute event such as a car accident or sports injury. Chronic pain is defined as pain that lasts longer than six months. Patients with chronic illnesses often experience chronic pain that can vary in severity. For example, patients with chronic pancreatitis often experience chronic abdominal pain that is caused by the inflammation of the pancreas. Acute pain that exists along with chronic pain is called breakthrough pain. Breakthrough pain persists even when interventions are present to treat chronic pain (Robertson, 2022). Patients receiving pain medication for chronic abdominal pain caused by pancreatitis may also experience breakthrough pain. If patients are receiving pain interventions but are still having severe pain, they may need to be hospitalized for further management to treat the breakthrough pain.
Acute Pain
Acute pain is a short-lived response that alerts the brain to an acute event caused by injury, trauma, surgery, or illness (Dowell et al., 2022). Acute pain can last a few seconds or a few months and is usually resolved when the acute event is treated (International Association for the Study of Pain [IASP], 2021a). Symptoms of acute pain can include numbness, tingling, sharp, throbbing, and stabbing pain (IASP, 2021a). Acute pain may cause appetite changes, sleep disturbances, diaphoresis, changes in vital signs, and behaviors such as distraction, guarding, protectiveness, and restlessness. Examples of acute pain include postoperative pain; burns; acute musculoskeletal pain from conditions such as strains, sprains, and fractures; pain associated with labor and delivery; and pain from traumatic injury.
Because acute pain can vary in severity, the type of treatment may vary based on individual patient needs (Robertson, 2022). Treatment for acute pain may include rest, ice or heat, physical therapy, nonopioid medications, or exercise (IASP, 2021a). The first step in treating acute pain is identifying the cause and ensuring that patients receive treatment before the pain becomes severe. Acute pain is often resolved when the cause is treated, so identifying the cause is an important first step in treating acute pain.
Chronic Pain
Chronic pain is ongoing and persistent for longer than six months and is not always confined to a specific area of the body. Chronic pain often affects an individual’s psychological, social, and behavioral responses that can influence daily functioning. Causes of chronic pain can include chronic disease, injury, inflammation, or an unknown cause (Dowell et al., 2022). Chronic medical problems, such as osteoarthritis, spinal conditions, fibromyalgia, and peripheral neuropathy, are common causes of chronic pain. Chronic pain can continue even after the original injury or illness that caused it has healed or resolved.
It is estimated that one in five adults in the United States experiences chronic pain (Dowell et al., 2022). People who have chronic pain often have physical effects that are stressful on the body. These effects include tense muscles, limited mobility, lack of energy, and appetite changes. Emotional effects of chronic pain include depression, anger, anxiety, and fear of reinjury. These effects can limit a person’s ability to return to their regular work or leisure activities. Multiple factors can lead to chronic pain becoming more centralized, which can result in a decreased pain threshold. This can cause patients to experience an increased severity of pain and to need complex pain management (Dydyk & Grandhe, 2023).
Link to Learning
Chronic pain affects so many individuals in the United States and throughout the world. Observing a patient interview with someone who experiences chronic pain can be useful for nurses to understand how chronic pain affects everyday life and the many different ways to manage chronic pain.
Location
Pain can be defined based on location. Sometimes it is easy for patients to identify the location of their pain and sometimes it may be difficult. Pain perceived at a location other than the site of the painful stimulus is called referred pain. The abdomen, extremities, and head are common areas to experience pain. Pain location charts can be helpful for patients to describe their pain (Figure 30.4).
Identifying the location of a patient’s pain can better help healthcare providers effectively assess and manage pain. Pain location charts show areas of the body, and the patient can point to a specific area where they are feeling their pain. Areas of pain such as knee pain can result from different causes based on location (Askinazi, 2023). For example, pain above the knee can be caused by inflammation while pain at the kneecap can be caused by a stress fracture. Location may be hard to determine for certain types of pain, but it can be helpful in the pain assessment and treatment plans.
Cutaneous Pain
Pain that is perceived from the skin is called cutaneous pain. Cutaneous pain is often acute pain that is resolved after the underlying injury or condition is treated. However, sometimes cutaneous pain can become chronic. Cutaneous nociceptors respond to heat, cold, and mechanical and chemical stimuli. Causes of cutaneous pain can include diabetes, autoimmune diseases, and other painful skin conditions (Gudin et al., 2022).
Patients who have diabetes often experience skin infections that can become painful. Other skin conditions such as shingles and dry skin can cause cutaneous pain. Shingles is caused by the virus that causes chickenpox and creates a vesicular rash that is painful and itchy. Autoimmune diseases such as lupus can cause inflammation, rash, and lesions that can cause cutaneous pain (Stucky & Mikesell, 2022). Many patients who experience cutaneous pain can also experience pain elsewhere in their body at the same time. Cutaneous pain can often be easy to identify due to outward signs of the cause of pain, such as cuts, burns, swelling, rashes, and bruising.
Visceral Pain
Visceral structures are internal organs such as the stomach, kidneys, spleen, and appendix. Visceral structures are highly sensitive to stretch, ischemia, and inflammation. When these internal organs are injured or damaged it creates visceral pain (Ford, 2019). Visceral pain is diffuse, difficult to locate, and often referred to as a distant, usually superficial, structure. It may be accompanied by nausea and vomiting and vital signs changes. Visceral pain may be described as sickening, deep, squeezing, aching, pressure, and dull. Visceral pain can be caused by gallstones, appendicitis, or irritable bowel syndrome (Santos-Longhurst, 2018).
Visceral pain can be difficult to locate due to the pain being internal, and patients often struggle to pinpoint an exact location. Unlike cutaneous pain, visceral pain does not typically show any outward signs of the cause of pain, which can make it difficult to locate.
Somatic Pain
Pain initiated by stimulation of nociceptors in ligaments, tendons, bones, blood vessels, fascia, and muscles is called somatic pain; it is a dull, aching, poorly localized pain. Somatic pain can be aching, deep, or superficial. For example, a ligament tear will cause deep somatic pain whereas a burn will cause superficial somatic pain. Somatic pain can be caused by broken bones, muscle stress, connective tissue diseases, joint pain, cuts, or burns (Santos-Longhurst, 2018). Somatic pain may show outward signs of the cause of pain such as a broken bone, cuts, burns, swelling, or bruising. Deep somatic pain may show no outward signs of the cause of pain, so further diagnostic testing may be needed to identify the location.
Referred Pain
Pain can radiate from one area to another. For example, back pain caused by a herniated disk can cause pain to radiate down an individual’s leg. Referred pain is different from radiating pain because it is perceived at a location other than the site of the painful stimulus. For example, pain from retained gas in the colon can cause pain to be perceived in the shoulder. Referred pain can happen because all nerves are connected and sometimes the brain sends a pain signal to a different area from where the pain started (Watson, 2019).
Referred pain can be felt anywhere, which is why it can be difficult to diagnose. Common areas of referred pain are shoulders, neck, back, and jaw (Watson, 2019). For example, lower back pain can indicate that there is something wrong with the kidneys, and jaw pain could be an early sign of a heart attack. It is important that nurses are aware of these signs to help identify and treat serious conditions such as a heart attack.
Etiology
The etiology of pain describes the specific cause of pain. Pain can result from various health conditions such as genetics, trauma, degenerative diseases, cancer, surgical procedures, infection, mechanical cause, or an unknown cause (Arumugam et al., 2019). Nociceptive, neuropathic, and idiopathic pain are all types of pain resulting from a specific cause. These causes can include heat, cold, chemicals, or neurological damage. The cause of pain can also be unknown.
Nociceptive Pain
Pain caused by stimulation of pain receptors by a mechanical or chemical cause such as heat or cold is called nociceptive pain (Ford, 2019). Because nociceptors are found everywhere in the peripheral nervous systems, nociceptive pain originates in the peripheral nervous system (Dydyk & Grandhe, 2023). The severity of nociceptive pain is directly related to the degree of injury. For example, stubbing a toe may cause mild pain while burns from a house fire may cause severe pain.
Nociceptive pain can be acute, chronic, somatic, or visceral depending on the duration and location of the pain. Nociceptive pain is usually acute, but sometimes the nociceptors may remain more sensitive to pain after the cause of pain has been resolved (Jacques, 2023). For example, a past head injury may have chronic pain due to frequent headaches even after the injury is treated.
Treatment of nociceptive pain is dependent on the duration and location of the pain. Acute nociceptive pain may only need mild pain interventions, such as an ice pack for a stubbed toe. Chronic or more severe nociceptive pain may require a combination of pharmacological and alternative pain management (Jacques, 2023).
Neuropathic Pain
Pain caused by neurological damage or dysfunction is called neuropathic pain. Neuropathic pain can be peripheral and centralized, and it is estimated that 10 percent of adults in the United States experience neuropathic pain (Dydyk & Grandhe, 2023). Neuropathic pain results in stimulation from something that is not considered painful, but due to the neurological damage, the body perceives the stimuli as painful (Yam et al., 2018). Neuropathic pain can result from conditions such as diabetes, neurological disorders, cancer, trauma, or toxins.
Neuropathic pain can be described as burning, numbness, tingling, shooting, or stabbing and can occur in response to nonpainful stimuli such as temperature changes. Diabetes is one of the most common causes of neuropathic pain. Patients who have diabetes can develop numbness and tingling in their lower extremities due to decreased circulation. This can lead to pain, decreased sensation, and injury to the lower extremities. Central nervous systems disorders such as multiple sclerosis and Parkinson disease can cause neuropathic pain. Patients receiving cancer treatment such as radiation or chemotherapy may also experience neuropathic pain due to their treatments (Santos-Longhurst, 2018).
Neuropathic pain is generally undertreated because it typically does not respond to traditional analgesics. Medications such as tricyclic antidepressants and gabapentin are typically used to manage this type of pain. These medications work on blocking the sensation to the affected nerves. Many patients are not aware that their chronic condition could lead to neuropathic pain. Nurses should provide education for patients with these conditions to ensure that their pain is managed effectively.
Patient Conversations
Assessing Neuropathic Pain in Patients Who Have Diabetes
Scenario: The nurse is caring for an established patient with diabetes who was admitted for hyperglycemia. The nurse is providing discharge education about the patient’s diabetes home management and the patient is asking about pain management.
Patient: I often have numbness and tingling in my feet, and it really bothers me. Why is that happening?
Nurse: Are you having any pain right now?
Patient: No, not right now. But the pain comes and goes a lot when I am at home.
Nurse: That kind of pain is common in patients with diabetes. Diabetes can cause decreased circulation in your legs, which can lead to the numbness and tingling.
Patient: No one has told me that before.
Nurse: Have you ever spoken to your doctor about this pain?
Patient: No, I haven’t seen my doctor in a long time. I probably should make an appointment with them.
Nurse: Many typical pain medications will not be effective for this type of pain, but there are some medications that are very effective. Let me help you set up an appointment with your doctor and we can work on getting you the right treatment plan for your pain.
Patient: Thank you very much. I had been taking Motrin but that was not helping. I am glad to hear there is something that may help my pain.
Idiopathic Pain
Sometimes patients can have pain without a known cause. This is called idiopathic pain, a chronic pain that is from an unknown origin. Idiopathic pain from an injury or medical condition may also persist long after the cause is healed. Medical conditions in which idiopathic pain may be present include fibromyalgia, multiple sclerosis, headaches, joint disorders, peripheral neuropathy, and irritable bowel syndrome (Jacques, 2021). Patients may often experience idiopathic facial pain in the jaw, ears, or cheeks. Patients may feel dull, aching, throbbing, or tingling sensations in their face without any identified cause of pain (Cleveland Clinic, 2021).
Idiopathic pain can be difficult to diagnose. The symptoms of idiopathic pain can often be similar to those of other conditions. Healthcare providers tend to rule out other medication conditions before idiopathic pain is diagnosed. Because the underlying cause is not known, idiopathic pain can also be difficult to treat. A combination of medications and alternative therapies such as acupuncture, biofeedback, and meditation can help reduce pain (Cleveland Clinic, 2021).