MH

Pain Assessment

Development of Pathologic Pain

  • Pain develops through two main pathways: nociceptive and/or neuropathic processing.

  • Patients present with diverse symptom types, leading to varied clinical responses to therapy.

  • Accurate pain assessment is crucial for developing effective non-pharmacologic and/or pharmacologic strategies to achieve improved clinical outcomes.

Neuroanatomic Pathways

  • Pain receptors (nociceptors) detect painful sensations.

  • Transmit signals via primary sensory (afferent) fibers (Aδ and C fibers).

  • Enter the spinal cord through posterior nerve roots into the dorsal horn via the tract of Lissauer.

  • Fibers synapse with interneurons in the substantia gelatinosa (Lamina II) of the spinal cord.

  • Pain signals then cross the spinal cord and ascend to the brain via the anterolateral spinothalamic tract.

  • The pathway continues through the medulla and thalamus, ultimately reaching the cerebral cortex, where pain is perceived.

Physiology of Pain: Nociceptors and Nerve Fibers

  • Nociceptors:

    • Specialized nerve endings designed to detect painful sensations.

    • Transmit sensations to the central nervous system (CNS) using two primary sensory (afferent) fibers: Aδ and C fibers.

  • Aδ Fibers:

    • Myelinated and larger in diameter.

    • Transmit pain signals rapidly to the CNS.

    • Result in localized, short-term, and sharp sensations.

  • C Fibers:

    • Unmyelinated and smaller.

    • Transmit signals more slowly.

    • Sensations are diffuse and aching, persisting after the initial injury.

  • Peripheral sensory Aδ and C fibers:

    • Enter the spinal cord via posterior nerve roots within the dorsal horn, traveling through the tract of Lissauer.

  • Substantia Gelatinosa:

    • A specific area of the spinal cord (considered Lamina II) where Aδ and C fibers synapse with interneurons.

    • This area receives sensory input from various body regions.

  • After synapsing, pain signals cross to the contralateral side of the spinal cord and ascend to the brain via the anterolateral spinothalamic tract.

Nociception Process and Phases

  • Nociceptive Pain:

    • Develops when functioning and intact nerve fibers in the periphery and CNS are stimulated.

    • Triggered by external events causing actual or potential tissue damage.

  • Nociception is divided into four phases:

    1. Transduction

    2. Transmission

    3. Perception

    4. Modulation

Phase 1: Transduction

  • Occurs in response to noxious (harmful) stimuli.

  • Injured tissue releases a variety of chemical mediators, including:

    • Substance P

    • Histamine

    • Prostaglandins

    • Serotonin

    • Bradykinin

  • These neurotransmitters propagate the pain message.

  • An action potential moves along afferent nerve fibers to the spinal cord, terminating in the dorsal horn.

Phase 2: Transmission

  • The pain impulse moves from the spinal cord to the brain.

  • In the dorsal horn, a second set of neurotransmitters (Substance P, glutamate, and adenosine triphosphate (ATP)) carries the pain signal.

  • If the pain signal is not stopped, it ascends via various fibers within the spinothalamic tract to the thalamus.

Phase 3: Perception

  • This is the conscious awareness of the pain signal.

  • Cortical structures, such as the limbic system, contribute to the emotional response to pain.

  • Pain is only perceived as a painful experience when it reaches the cerebral cortex. The perception of pain is highly individualized and influenced by psychological and cultural factors.

Phase 4: Modulation

  • This phase involves the body's natural pain-inhibiting processes.

  • Descending pathways from the brainstem release neurotransmitters such as serotonin, norepinephrine, GABA, and endogenous opioids (e.g., endorphins, enkephalins) into the spinal cord.

  • These neurotransmitters inhibit pain transmission by blocking the release of pain-producing substances from the afferent nerve fibers or by decreasing the excitability of postsynaptic neurons in the dorsal horn.

  • This process can reduce or alter the perceived pain.

Types of Pain

  • Acute Pain:

    • Short-term, self-limiting, dissipates after injury heals.

    • Serves as a warning sign; identifiable cause.

    • Example: surgery, trauma, kidney stones.

  • Chronic Pain (Persistent Pain):

    • Pain continues for 6 months or longer, typically after the injury has healed.

    • Can be malignant (cancer-related) or non-malignant (arthritic, back pain).

    • Does not stop when injury heals; can be difficult to treat.

    • Often accompanied by symptoms such as fatigue, insomnia, weight changes, depression, and irritability.

  • Nociceptive Pain:

    • Arises from actual or threatened damage to non-neural tissue.

    • Usually responsive to opioids and non-opioid medications.

    • Divided into:

    • Somatic Pain:

      • Originates from musculoskeletal tissues or body surface.

      • Usually well-localized and described as throbbing, aching, or gnawing.

      • Examples: tissue injury, bone metastasis, surgical incision.

    • Visceral Pain:

      • Originates from internal organs (e.g., stomach, intestine, gallbladder).

      • Often poorly localized, dull, aching, squeezing, or cramping.

      • Can be referred to other body sites.

      • Examples: tumor pressing on an organ, bowel obstruction, appendicitis.

  • Neuropathic Pain:

    • Caused by a lesion or disease of the somatosensory nervous system.

    • Implies an abnormal processing of pain messages from damage to nerve fibers.

    • Often perceived as burning, shooting, tingling, or electrical-like sensations.

    • Difficult to treat; often requires adjuvant analgesics.

    • Examples: diabetic neuropathy, shingles (postherpetic neuralgia), sciatica, phantom limb pain.

  • Referred Pain:

    • Pain felt at a particular site but originates from another location.

    • Both sites are innervated by the same spinal nerve, making it difficult for the brain to differentiate the origin.

    • Example: myocardial infarction pain refers to the left arm or jaw.

  • Breakthrough Pain (BTP):

    • A transient flare of moderate to severe pain superimposed on a persistent pain syndrome.

    • Can be predictable (e.g., with movement or dressing changes) or unpredictable.

    • Requires rapid-onset, short-acting medication.

Clinical Manifestations of Pain

  • Physiologic Responses (Acute Pain):

    • Sympathetic nervous system activation:

    • Tachycardia

    • Increased blood pressure

    • Tachypnea

    • Pupil dilation

    • Diaphoresis

    • Muscle tension

    • Anxiety, fear

    • These responses may lessen over time, even with persistent pain, as the body adapts.

  • Behavioral Responses (Acute Pain):

    • Crying, groaning, moaning

    • Guarding, grimacing

    • Restlessness, agitation

    • Inability to concentrate

    • Changes in appetite

  • Behavioral Responses (Chronic Pain):

    • Often subtle and less obvious than acute pain.

    • Bracing, rubbing

    • Diminished activity, reduced range of motion

    • Sighing

    • Changes in sleep patterns

    • Isolation, withdrawal

    • Flat affect, decreased spontaneity

    • Depression, anxiety, fear of re-injury.

Pain Assessment Approaches

  • Pain is always subjective; it is whatever the experiencing person says it is.

  • Believe the patient's self-report of pain.

Subjective Data - Pain History

  • Location:

    • Where is your pain? Ask the patient to point.

  • Intensity/Severity:

    • How bad is your pain? Use a pain rating scale.

  • Quality:

    • What does your pain feel like? (e.g., sharp, dull, throbbing, burning)

  • Onset:

    • When did the pain start?

  • Duration:

    • How long does it last? Is it constant or intermittent?

  • Timing (Pattern):

    • What makes the pain better or worse? Does it follow a pattern?

  • Alleviating and Aggravating Factors:

    • What relieves the pain? What causes it to worsen?

  • Associated Symptoms:

    • Any other symptoms accompanying the pain (e.g., nausea, fatigue, numbness)?

  • Impact of Pain on Activities of Daily Living (ADLs):

    • How does the pain affect sleep, appetite, mood, personal hygiene, walking, social interactions?

  • Patient's Goals:

    • What is a realistic pain goal for the patient? (e.g., function improvement, pain reduction to a tolerable level)

Objective Data - Physical Examination

  • Observe the patient for nonverbal behaviors of pain. (Note: The absence of these behaviors does not mean the absence of pain).

  • Vital Signs:

    • While vital signs can indicate acute pain (e.g., increased heart rate, blood pressure, respirations), they are not reliable indicators for chronic pain due to adaptation.

  • Musculoskeletal Examination:

    • Inspect and palpate joints and muscles for swelling, tenderness, guarding, or limited range of motion.

  • Neurological Examination:

    • Assess sensation, motor strength, and reflexes if neuropathic pain is suspected.

  • Abdominal Examination:

    • Palpate for tenderness, guarding, distention, or masses in cases of visceral pain.

  • Facial Expression:

    • Grimacing, clenched teeth, furrowed brow.

  • Body Movement:

    • Restlessness, pacing, guarding a painful area, stooped posture, reduced mobility.

Pain Rating Scales

  • Unidimensional Scales:

    • Measure only pain intensity.

    • Numeric Rating Scale (NRS):

    • A scale from 0 to 10 (or 0 to 5).

    • 0 = no pain, 10 = worst possible pain.

    • Commonly used for adults and children \ge 10 years.

    • Verbal Descriptor Scale (VDS):

    • Uses words to describe pain intensity (e.g., no pain, mild, moderate, severe, worst pain possible).

    • Visual Analog Scale (VAS):

    • A 10-cm line on which the patient marks pain intensity.

    • 0 = no pain, 10 = worst possible pain.

  • Multidimensional Scales:

    • Measure pain intensity, quality, impact on function, and emotional response.

    • McGill Pain Questionnaire (MPQ):

    • Comprehensive tool; describes sensory, affective, and evaluative aspects of pain.

    • Brief Pain Inventory (BPI):

    • Assesses pain severity and interference with daily activities.

Pain Assessment in Specific Populations:

  • Infants and Children:

    • FLACC Scale (Face, Legs, Activity, Cry, Consolability):

    • Used for nonverbal children aged 2 months to 7 years.

    • Scores range from 0 to 10 (no specific LaTeX instruction was provided for 2 months and 7 years, so I kept them as regular numbers, if they are part of a math expression, they should be in LaTeX. The scale range 0 to 10 is a range so it is represented in LaTeX as 0 to 10).

    • Wong-Baker Faces Pain Rating Scale:

    • Uses 6 faces ranging from happy (no pain) to crying (worst pain).

    • Suitable for children \ge 3 years.

  • Older Adults:

    • Many older adults may underreport pain due to fear of addiction, belief that pain is a normal part of aging, or cognitive impairment.

    • PAINAD (Pain Assessment IN Advanced Dementia) Scale:

    • Observational tool for assessing pain in nonverbal patients with advanced dementia.

    • Assesses breathing, negative vocalization, facial expression, body language, and consolability.

    • Scores range from 0 to 10 (no specific LaTeX instruction was provided for the numbers. The range 0 to 10 is represented in LaTeX as 0 to 10).

  • Patients with Communication Barriers:

    • Consider behavioral cues, vital signs, and involve family members for insights.