Understanding Pain: Nociceptive & Neuropathic

Pain

• Pain is defined as "unpleasant sensory and emotional experience associated with actual or potential tissue damage" (IASP).
• The patient's subjective experience of pain is also considered (The Joint Commission).
• Pain serves to protect the body.
  • It alerts the body to a dangerous situation.
  • It allows the body to remove itself from the situation.

Types of Pain

• Nociceptive Pain:
  • Treated with over-the-counter (OTC) analgesics.
    • NSAIDs
    • Tylenol
  • Prescription analgesics, including opioids:
    • Morphine
• Neuropathic Pain:
  • Treated with anticonvulsants:
    • Neurontin
    • Lyrica

Nociceptive Pain

• Nociception: Pain receptors (nociceptors) respond to painful stimuli.
• Nociceptors transduce painful stimuli into action potentials.
• Chemical mediators involved in transduction include:
  • Prostaglandins
  • NSAIDs (inhibit prostaglandins)
  • Lactate
  • Kinins
  • K+, H+
  • Histamine
  • Serotonin

Neuroanatomy of Pain

• Nociceptors are pain receptors.
• Nociceptive pain is pain resulting from actual or perceived tissue injury.

Nociceptive Pain Pathway

• Transduction: The process of converting painful stimuli to action potentials.
• Transmission: Spinal nerves transmit signals to the anterolateral tract and then to the thalamus.
• Perception: The brain interprets the signal as pain.
• Modulation: The process of suppressing or enhancing pain signals.

Transmission

• Spinal nerves transmit pain signals to the anterolateral tract, then the thalamus.
• Sensory fibers ascend.
  • Aδ fibers (10%): fast, large, myelinated; sharp, stinging pain; highly localized
  • C fibers (90%): slow, small, unmyelinated; dull, aching pain; poorly localized, lingering
• Spinal neurotransmitters include:
  • Excitatory: Substance P, glutamate, histamine
  • Inhibitory: Endorphins, norepinephrine, GABA, serotonin

How Does the Brain Localize Pain?

• Nociceptor pathways are organized in an anatomical order in the spinal cord and somatosensory cortex.
  • Dermatome map
• Primary sensory cortex localizes pain.

Perception

• Neural processing of pain sensation is influenced by:
  • Awareness
  • Emotion/mood
  • Prior experience
  • Expectation
  • Culture
  • Physical status
  • Sex/gender

Perception Concepts

• Pain threshold: The minimum intensity of a stimulus needed to produce pain.
• Pain tolerance: The maximum intensity of pain that a person can tolerate.
• Pain expression: The quantity and quality of pain.

Opioids

• Analgesia: Relieving pain
• Agents that bind to receptors: Morphine, naloxone, endorphins
• Manifestations: Diuresis, sedation, decreased respiratory rate (RR), pupil constriction, constipation, and nausea/vomiting (N/V)
  • Other less common pain meds

Acute Pain

• Etiology: Tissue injury
• Characteristics: Pain resolves as injury heals; less than 3 months' duration
• Clinical Manifestations (CM): Self-report and SNS stimulation; increased heart rate (HR), RR, and blood pressure (BP); pallor/diaphoresis, hyperglycemia, dilated pupils, nausea/vomiting (N/V), and urine retention.
• Treatment Implications (TI): Short-acting opioid/non-opioid relief to maintain function/healing.

Chronic Pain

• Etiology: Underlying disease or unclear cause, comorbidities such as sleep disturbance and depression
• Characteristics: >6 months; increased peripheral transduction sensitivity, abnormal central responsiveness
• Clinical Manifestations (CM): Non-SNS responses, such as mood disturbances, inability to function, chronic hyperglycemia, fatigue/sleep problems, and weakened immune systems
• Treatment Implications (TI): Multimodal/Long-acting pain meds, including opioids, antidepressants, and anticonvulsants, to maintain function/quality of life.

Referred Pain

• Etiology: Injury at a different site.
• Characteristics: Referred to tissue in the same sensory dermatome; visceral nociceptor activity and primary somatic afferent nerves in the posterior horn of the spinal cord.
• Clinical Manifestations (CM): Various clinical manifestations
• Treatment Implications (TI): Relief of underlying injury

Treatment Implications for Pain

• Interrupt Peripheral Transmission:
  • Thermal treatment: ↓ inflammation/swelling
  • Local anesthetics: ↓ pain stimulus
  • Splinting: ↓ further tissue injury/inflammation
  • NSAIDs: ↓ prostaglandins ⇒↓ inflammation/pain
• Altering Perception & Integration:
  • Medications: Opioids/Non-opioids, anticonvulsants, antidepressants
  • Non-medications: Distraction, imagery, relaxation, biofeedback, hypnosis

Neuropathic Pain

• Etiology: Possible tissue injury to the nerves; nerve damage or dysfunction, altered central processing of nociceptive input
• Characteristics: Shooting, burning, electric shock-like, tingling/pins-and-needles pain
• Treatment Implications (TI): Maintain functional ability and quality of life with anticonvulsants and antidepressants (TCAs).

Explore the different types of pain, including nociceptive and neuropathic pain. Learn about the mechanisms behind nociception, the role of chemical mediators, and common treatments for each type of pain. Discover how pain serves as a protective mechanism for the body.