Chapter 4 Pain PDF

Chapter 4 Pain 1 of 36  Pain  A complex constellation of unpleasant sensory, emotional and cognitive experiences  Provoked by real or perceived tissue damage  Manifested by certain autonomic, psychological, and beh...

Chapter 4 Pain 1 of 36  Pain  A complex constellation of unpleasant sensory, emotional and cognitive experiences  Provoked by real or perceived tissue damage  Manifested by certain autonomic, psychological, and behavioral reactions. Terman GW, Bonica JJ. Spinal mechanisms and their modulation. In: Loeser JD, Butler SH, Chapman CR, Turk DC, eds.Bonica’s Management of Pain. 3rd ed. Philadelphia, Pennsylvania, USA: Lippincott Williams and Wilkins; 2003:73 2 of 36  Pain  Pain is complicated Difficult to assess Often reported with no physiological evidence Subjective Environmental influences  Distracting stimuli - auditory and visual  Malenbaum, S., et al. (2008). Pain in its Environmental Context: Implications for Designing Environments to Enhance Pain Control. Pain. 134(3):241–244. Individual responses  Influenced by personality, emotions, cultural norms Research is limited Ethical restrictions Minimize animal subjects' pain and suffering Not many humans volunteer for pain studies 3 of 36  Pain  Pain is a body defense mechanism Warns of problem  Nociceptive pain Pain caused by a specific tissue Stimulation of pain receptors (the origin of stimulus) Mechanoreceptors, thermoreceptors, photoreceptors Chemoreceptors, osmoreceptors Bruises, burns, fractures, joint damage (arthritis or sprains)  Neuropathic pain Damage to the actual nerve Not to any receptor 4 of 36  Pain  Neuropathic pain Painful diabetic neuropathy Post herpetic neuralgia Pain from shingles  Caused by varicella-zoster virus, type of herpes virus) May continue after blisters and other symptoms have ended Post amputation phantom limb pain Pain from spinal cord injury Neuralgia of a single nerve following injury Cervical and lumbar radiculopathy Post stroke pain Complex regional pain syndrome RSD and causalgia 5 of 36  Pain  Pain threshold Level at which body first perceives stimulus as painful  Pain perception Interpretation of pain Very subjective  Pain tolerance Ability to cope with pain Genetic (2014 paper) American Academy of Neurology (AAN). "Low tolerance for pain? The reason may be in your genes." ScienceDaily. ScienceDaily, 20 April 2014. www.sciencedaily.com/releases/2014/04/140420193428.htm Determined by degree of pain, intensity, duration Varies between individuals 6 of 36  Causes of Pain  Inflammation  Infection  Ischemia and tissue necrosis  Stretching of tissue - “No pain, no gain” Stretching of tendons, ligaments, joint capsule  Chemicals  Burns  Muscle spasm  Thalamic Pain Syndrome (TPS) After a thalamic stroke (ischemic or hemorrhagic) Resultant lesions in the thalamus causing pain 7 of 36  Types of Pain  Somatic pain – nociceptive (receptor) Cutaneous Bone, muscle Carried by sensory afferent fibers May be acute or chronic  Visceral pain – nociceptive (receptor) Originates in organs Carried by sympathetic afferent fibers May be acute or chronic Often diffuse and vague 8 of 36  Types of Pain  Acute pain Usually nociceptive Sudden, severe, short term Indicates tissue damage Localized or generalized Physiologic stress response ↑ blood pressure, heart rate Skin → cool, pale, moist ↑ respiratory rate ↑ skeletal muscle tension Vomiting may occur 9 of 36 Strong emotional response may occur  Types of Pain  Chronic (1/2) Often neuropathic Over extended time; may be recurrent Usually more difficult to treat than acute pain Usually generalized → specific cause may be unclear Possible contributing causes Fatigue, irritability, depression Sleep disturbances Anorexia 10 of 36  Types of Pain  Chronic (2/2) Affects activities of daily living (ADL’s) May experience periods of acute pain (exacerbations) Usually reduces tolerance to additional pain Pain causes 11 of 36 Nociceptive Pain Pathways: Receptors  Nociceptors Pain receptors Types of nociceptors 1. Thermal  Extreme temperatures 2. Chemical  Acids or chemicals produced by body – Bradykinin, histamine, prostaglandin 3. Mechanical (Physical)  Pressure 4. Polymodal  Various stimuli 5. Silent  Normally unresponsive to noxious mechanical stimulation 12 of 36  Awakened during inflammation and after tissue injury Nociceptive Pain Pathways: Fibers  Afferent fibers Myelinated - A delta fibers (Aδ) Transmit impulses very rapidly (3 - 30 m/s) Diameter: 1 - 5 microns Acute pain  Sudden, sharp, localized Unmyelinated - C fibers Transmit impulses slower (0.5 – 2.0 m/s) Diameter: 0.2 – 1.5 microns Chronic pain  Persistent, diffuse, dull, burning, or aching sensation 13 of 36 Nociceptive Pain Pathways: Tracts  Spinothalamic bundle (Anterolateral system) Carries signals to spinal cord and then to brain Neospinothalamic tract (Lateral spinothalamic tract) Fast impulses (Aδ); localize acute pain/temperature (3 – 30 m/s) Paleospinothalamic tract (Anterior spinothalamic tract) Slower impulses (mostly C but some Aδ) Chronic/dull pain, crude touch and pressure (0.5 – 2.0 m/s) Archispinothalamic tract (Multisynaptic propriospinal pathway) Slower impulses (mostly C); chronic/dull pain (0.5 – 2.0 m/s) Visceral, emotional and autonomic reactions to pain  Spinoreticular tract - Increases level of arousal/alertness in response to pain/temperature Travels to Reticular Formation and Reticular Activating System  Spinotectal tract Enables orientation of the eyes and head toward relevant stimulus Travels to midbrain 14 of 36 Nociceptive Pain Pathways: Tracts 15 of 36 Nociceptive Pain Pathways: Brain  Reticular formation (RF) Throughout the brainstem Blocks certain incoming pain  Thalamus – relay center  Reticular activating system (RAS) Diffuse area of brain Creates awareness of stimuli  Somatosensory cortex Parietal lobe → perception & localization  Hypothalamus → stress response  Limbic system → emotional response 16 of 36 Pain Pathways 17 of 36  Pain Pathways  Dermatome Area of skin Innervated by single spinal nerve Somatosensory cortex → “mapped” Corresponds to source of pain stimuli  Reflex “response” Involuntary muscle contraction Away from pain source To guard against movement 18 of 36 Theories of Pain: Gate Control (1/3)  Gate-Control Theory “Gates” built into pain pathway Synapses act as gates Modifies pain stimuli conduction and transmission in spinal cord and brain Use enkephalins Opiate-like blocking agents Gates open Pain impulses transmitted from periphery to brain Gates closed Reduces or modifies the passage of pain impulses 19 of 36 Theories of Pain: Gate Control (2/3)  Gate-Control Theory → Gate open 20 of 36 Theories of Pain: Gate Control (3/3)  Gate-Control Theory → Gate closed 21 of 36 Theories of Pain: Neuromatrix (1/2)  Neuromatrix (Body-self) Theory Explains Nociceptive and Neurogenic pain Pain not generated by a “one way” path Brain has at least 3 neural networks → Neuromatrix Various inputs to neuromatrix triggers outputs Only one output is pain Different pains have specific neuro-signatures Pain can be produced in absence of sensory signals First proposed to explain phantom limb pain 22 of 36 Theories of Pain: Neuromatrix (2/2)  Neuromatrix (Body-self) Theory “Pain” “Affect” 23 of 36  Theories of Pain: Glial Cell (1/2)  Glial Cell Theory Little to no role in basic pain Function in neuropathic pain Activated glial cells → amplify pain Astrocytes, microglia in CNS Satellite cells in dorsal root and trigeminal ganglia Release proinflammatory biochemicals Damaged, dying and dead neurons release activators Repeated opioids activate glial cells Activated glial cells  Amplify pain  Suppress opioid analgesia Chronic pain → Gliopathy 24 of 36  Theories of Pain: Glial Cell (2/2)  Glial Cell Theory Theorized associations: 25 of 36 Signs, Symptoms and Diagnosis of Pain (1/2)  Location  Descriptive terms Aching, burning, sharp, throbbing, widespread Cramping, constant, periodic, unbearable, moderate  Timing of pain Association with an activity  Physical evidence of pain May not be any Pallor and sweating High blood pressure or tachycardia 26 of 36 Signs, Symptoms and Diagnosis of Pain (2/2)  Nausea and vomiting May occur with acute pain  Fainting and dizziness May occur with acute pain  Anxiety and fear Seen with chest pain or trauma  Clenched fists or rigid faces  Restlessness or constant motion  Guarding area to prevent receptor stimulation 27 of 36  Pain and Children  Infants → look for physiological response Tachycardia Increased blood pressure Facial expressions Crying  Variations at different developmental stages Different coping mechanisms Range of behavior Difficulty describing pain  Older children Withdrawal and lack of communication 28 of 36  Referred Pain  Pain perception Site distant from source Characteristic of viscera  Pain source may be difficult to determine  Cause? Convergence Theory Multiple neural inputs  Somatic and visceral  Go to specific spinal cord area/segment Brain misinterpretation 29 of 36  Phantom Pain  Pain perceived from missing body part  Common if chronic pain has occurred  Following an amputation Pain, itching, tingling  Often non-responsive to pain therapies  May resolve Weeks to months  Not fully understood  Neuromatrix theory 30 of 36  Headache  Sinuses, eyes  Muscle spasm and tension From emotional stress  Temporal Temporomandibular joint syndrome (TMJ)  Migraine Cerebral vascular and metabolic changes (biochemical)  Intracranial headaches Increased pressure inside the skull 31 of 36  Managing Pain  Remove cause of pain as soon as possible  Ice Impulses from temperature receptors close gates  Transcutaneous electrical stimulation (TENS) Alternate sensory stimulation at site blocks pain  Analgesics Oral, parenteral, transdermal Classified by ability to relieve Mild pain → NSAID’s (not Tylenol - acetaminophen)  Aspirin (Bayer, Bufferin, Excedrin)  Ibuprofen (Advil, Motrin IB), Naproxen (Aleve) Moderate pain → opiates (Percocet, Oxycontin) Severe → opiates (Vicodin, Demerol) 32 of 36  Managing Pain  Endogenous pain control Opioids Secreted by interneurons of CNS Block conduction of pain impulses to brain Enkephalins → spinal cord Endorphins → brain stem Dynorphin → brain/spinal cord Resemble morphine  “Morphine-like” substances 33 of 36  Managing Pain  Sedatives and anti-anxiety drugs Adjuncts to analgesic therapy Promote rest and relaxation May reduce analgesic dosage  Chronic and increasing pain Often seen with cancer Stepwise therapy to address pain Tolerance to narcotics develops Increase dose requirements New drug may be required Combination drugs 34 of 36  Managing Pain  Severe pain Patients administer opiate medication as needed Patient-controlled analgesia (PCA) Lessen overall consumption of narcotics  Intractable pain Cannot be controlled with medication Surgical intervention Rhixotomy – cut spinal nerve Cordotomy – cut spinal cord Injections – inject at spinal nerve of spinal cord 35 of 36  Managing Pain  Anesthesia Local anesthesia Skin or mucous membranes Spinal or regional anesthesia Block pain from legs or abdomen Injected into spinal cord region General anesthesia Gas or IV - Loss of consciousness Neuroleptanesthesia Sedated consciousness  Detached, pain-free state Opioids for pain Neuroleptics for sedation (antipsychotic) Quick recovery to full consciousness 36 of 36