Overview of Pain

module 1

Protection

Function of pain

• Warning signal about an unmet need, or malfunction of the nervous system secondary to a disease process

• Motor, sensory, or emotional response to a subjective feeling

Warning/Symptoms of Disease

Function of pain

• A symptom is a warning about a disease or condition

• Disease entity that can be treated

Response to Injury

Function of pain

• Reaction to different types of injury

  • Thermal injuries, e.g., sunburn

  • Mechanical injury, e.g., fracture

  • Chemical injury, e.g., inhalation of toxic fumes

  • Ischemic injury, e.g., lack of oxygen to body tissues

Cognitive factors influencing perception of pain

• An alert, oriented patient can recognize pain, report pain, and implement behaviors to prevent or relieve pain.

• Non-alert patients may have impaired ability to perceive, report, prevent, or relieve pain.

• Patients with Alzheimer disease or other cognitive disorders may not be able to express the location of pain, prevent pain, or relieve pain, but they are capable of perceiving and experiencing pain.

Affective/Behavioral factors influencing perception of pain

• behaviors include:

  • physical: grimaces, clenched teeth, guarding, bent posture, and restlessness

  • verbal: crying, moaning, screaming

  • psychological: anger, irritability, despair

Sensory factors influencing perception of pain

• Any loss of sensory function directly influences the patient’s awareness of pain. When patients cannot sense pain, they cannot communicate pain, prevent it, or respond to it.

• Patients in pain may feel like their senses are overstimulated or demonstrate sensitivity to light, sound, and smells

Pattern Theory

Theory of pain that proposed the physiologic basis of pain and provided the foundation for the gate control theory of pain

• When injury occurs, sensations relay a unique pattern or sequence of signals to the brain.

• The brain deciphers the pattern and correlates it with the sensation.

• The pattern determines whether the brain interprets the stimuli as pain.

Gate Control Theory of Pain

Theory of pain that looked at pain via the mind-body perspective, explaining the influence of cognitive and emotional factors on pain perception

• Tissue damage causes a stimulus to be sent to the brain, which first travels to three locations in the spinal cord.

• One of these locations, the dorsal horn of the spinal cord, provides a gating mechanism.

• The signals at this gate determine whether or not pain is felt. If the gate closes, the impulses are not transmitted to the brain and no pain is perceived. If the signals reach a specific level of intensity, the gate opens, allowing the signal to reach the brain and pain to be felt.

• State-of-mind and lifestyle choices can affect the intensity of the stimuli. For example, depression may cause the gate to remain open more often

Neuromatrix Theory

Theory of pain that proposed that the central nervous system, rather than injury at the periphery, is responsible for pain sensation

• Pain is a complex issue that cannot be explained solely by physical factors.

• Perception of painful stimuli results from the neuromatrix, a unique genetically controlled network of neurons affected by an individual’s subjective physical, psychological, cognitive, and life experiences.

• Input from the periphery, such as tissue trauma, can initiate or affect but not create a neurosignature (the signal created by the neuromatrix).

• Specific neurosignatures elicit corresponding sensations, and alterations in signals yield memories of the experience, allowing the same sensation to be felt if the same circumstance occurs in the future

Nociceptors

a peripheral nerve ending, or sensory neuron, that initiates the sensation of pain by sending “threat” stimuli to the spinal cord and brain and is sensitive to thermal, mechanical, and chemical stimuli

• distributed throughout the body in joints, muscles, skin, and viscera, but density differs in each area

  • Highest density: Skin, extremely sensitive to pain

  • Lower density: Joints and tissues, less sensitive than skin

  • Lowest density: Internal organs, respond only to painful stimuli, e.g., on palpation or when infection is present

Nociception

the process by which pain is conducted from the periphery to the central nervous system

• begins with the conversion of the noxious stimuli (injury) to an electrical impulse, which is transmitted from one neuron (nerve) to the next with the help of neurotransmitters

Lobes involved in nociception

• Brainstem: pain signals travel from the spinal cord to the brain, including the brainstem, thalamus, and cerebral cortex

• Occipital lobe: processes the pain (cause of pain or reaction of pain) from the body and generates the actual experience of pain

• Parietal lobe: helps the person localize where on the body injury occurred

• Frontal lobe: conveys the degree of unpleasantness of the pain experience

• Temporal lobe: allows the person to plan ways of removing or getting away from the pain

• Cerebellum: the relay station that distributes sensory signals to several other regions of the brain

Four Steps of Nociception

transduction, transmission, perception, and modulation

Transduction

• Injury occurs and nociceptors identify pain stimuli and convert it to an electrical impulse

• Injured tissues release neurotransmitters that are part of the inflammatory response

• Neurotransmitters assist with transmission of pain signals across neurons

• Inflammatory response is a significant cause of generalized pain

Transmission

• Pain signal is transmitted through the afferent nerve to the spinal cord and brain

• Signals travel two pathways:

  • A-delta fibers:

    • Larger fibers and rapid conduction

    • Pain translated as sharp, acute pain

  • C fibers:

    • Smaller fibers and slow conduction

    • Pain translated as diffuse, dull, and longer-lasting pain

• Both A-delta and C fibers carry pain impulses from the spinal cord to the cerebral cortex of the brain

Modulation

• Once pain is recognized, the brain changes pain perception by sending inhibitory signals via the spinal cord

• This signal results in the release of analgesic neurotransmitters called endogenous opioids

  • Enkephalins influence the emotional perception of pain.

  • Beta-endorphins reduce pain via the central and peripheral nervous systems.

  • Dynorphins modulate pain through stimulation or reduction, depending on which receptors are activated

Perception

• Brain translates afferent nerve signals as pain and person perceives pain

• Limbic system controls emotional reactions

• Somatosensory cortex perceives location, intensity, and quality of pain

  • Pain threshold: lowest intensity at which the brain recognizes pain; varies per person

  • Pain tolerance: intensity or duration of pain that a person can, or is willing to, endure; varies per person

Bradykinin

A peptide produced in the blood that mediates the inflammatory response and stimulates pain receptors

Substance P

A neuropeptide that transports pain impulses from the periphery to the central nervous system

Histamine

An amine released by immune cells in response to inflammation

Serotonin

A neurotransmitter released from the brainstem and dorsal horn that inhibits pain transmission

Cytokines

Proteins secreted by immune system cells that control inflammation

Electrolytes

Molecules that activate nerve endings (synapses) that respond to painful stimuli by changing ionic movement into and out of nerve cells

Prostaglandins

Hormone-like compounds derived from fatty acids that are thought to increase sensitivity to pain by stimulating pain receptors on neurons (nerve cells)

Nociceptive pain

occurs when nociceptors encounter harmful stimuli such as trauma, inflammation, or tissue damage

• most common type felt as sharp, burning, aching, cramping, or stabbing sensations

• visceral pain - from organs. occurs from pancreatitis, inflammatory bowel disease, bladder distention, and cancer

• somatic pain - from skin, muscles, joints, and bones. occurs from sunburn, lacerations, fractures, sprains, arthritis, bone cancer

• referred pain - from location of the body other than where it originated

• radiating pain - extends from the source of pain to an adjacent area of body

Neuropathic pain

nerve injury or impairment

• serves no purpose in relation to the body’s warning system or defenses

• felt as numbness, tingling, burning, aching, crushing, stabbing, or shooting

• primary causes are inflammation or metabolic disease

• caused by tumors, trauma, infection, chemotherapy, phantom limb pain

Psychogenic pain

no physical source and is caused, increased, or prolonged by mental, emotional, or behavioral factors

• often presents as headache, back pain, or stomach pain

Acute pain

• transient

• < 3 months

• fast onset

• identifiable cause

• diminishes as injury heals

• associated with conditions such as acute injury or trauma, surgery, and childbirth

Chronic pain

• persistent pain

• > 3 months

• intermittent or continuous pain

• does not always have an identifiable cause

• can lead to disability, affecting quality of life

• associated with conditions such as arthritis, fibromyalgia, and neuropathy

• can be further divided into cancer and noncancer pain

Breakthrough pain

can occur in patients with cancer or noncancer pain (acute or chronic), and it is associated with surgery, injury, or a fluctuation in pain from an existing condition

• Transient, worsening pain exacerbation that generally lasts 30 minutes or less

• exacerbation of pain even though background pain is controlled

Idiopathic pain

chronic pain with no identifiable cause or pain that remains beyond healing from a medical condition or injury

• examples : migraine headache and fibromyalgia

Physiologic factors of pain

age, fatigue, genes, neurologic function

Social factors of pain

previous experience, family and social network, spiritual factors

Psychological factors of pain

attention (increased attention to pain is linked to increased pain), anxiety and fear, coping

Cultural factors of pain

gender, familial factors, ethnicity

SOCRATES for pain assessment and history

S = site

O = onset

C = character

R = radiation

A = associations

T = time course

E = exacerbating/relieving factors

S = severity

ABCDE method for pain management

Assess the patient about their pain frequently

Believe the patient and their family and how it can be relieved

Choose pain control that is appropriate

Deliver interventions in a timely manner

Evaluate how your intervention helped your patient