The Physiology Of Pain

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Understanding the pain pathway is the first step to effective pain management in veterinary patients.

The Physiology Of Pain

  1. 1. The Physiology of Pain Kristen Cooley BA, CVT, VTS (Anesthesia) Globe University Madison, WI
  2. 2. What is Pain? <ul><li>sensory and emotional </li></ul><ul><li>actual or potential </li></ul>
  3. 3. What is Pain? <ul><li>Often over looked </li></ul><ul><li>In 2000 JCAHO </li></ul><ul><ul><li>mandated pain be 5 th vital sign </li></ul></ul><ul><li>2003 AAHA followed suit </li></ul>
  4. 4. Noxious stimulus <ul><li>Pain causing </li></ul><ul><ul><li>Intensity </li></ul></ul><ul><ul><ul><li>Chemical </li></ul></ul></ul><ul><ul><ul><li>Mechanical </li></ul></ul></ul><ul><ul><ul><li>Thermal </li></ul></ul></ul>
  5. 5. Nociceptor <ul><li>Pain detecting </li></ul><ul><ul><li>Found throughout the body </li></ul></ul>
  6. 6. Nociception <ul><li>The activity by a noxious stimulus </li></ul>
  7. 7. Definitions <ul><li>Allodynia </li></ul><ul><ul><li>Not typically painful </li></ul></ul><ul><li>Hyperalgesia </li></ul><ul><ul><li>Exaggerated response </li></ul></ul><ul><li>Hyperesthesia </li></ul><ul><ul><li>Increased sensitivity </li></ul></ul>
  8. 8. Types of pain <ul><li>Peripheral pain </li></ul><ul><ul><li>Visceral </li></ul></ul><ul><ul><ul><li>Abdominal or thoracic organs </li></ul></ul></ul><ul><ul><ul><ul><li>Poorly localized </li></ul></ul></ul></ul><ul><ul><ul><ul><li>Referred </li></ul></ul></ul></ul><ul><ul><li>Somatic </li></ul></ul><ul><ul><ul><li>Superficial </li></ul></ul></ul><ul><ul><ul><ul><li>Skin </li></ul></ul></ul></ul><ul><ul><ul><li>Deep </li></ul></ul></ul><ul><ul><ul><ul><li>tendons, joints, muscle, periosteum </li></ul></ul></ul></ul><ul><ul><ul><ul><ul><li>Easily localized </li></ul></ul></ul></ul></ul>
  9. 9. Types of pain <ul><li>Neuropathic pain </li></ul><ul><ul><li>Damage to peripheral nerves or spinal cord </li></ul></ul><ul><ul><li>Often difficult to treat appropriately </li></ul></ul>
  10. 10. Factors affecting pain <ul><li>Stress </li></ul><ul><ul><li>Exacerbates pain </li></ul></ul><ul><ul><ul><li>Environmental changes </li></ul></ul></ul><ul><ul><ul><li>Physiologic changes </li></ul></ul></ul><ul><li>Anxiety </li></ul><ul><ul><li>Exacerbates pain </li></ul></ul><ul><ul><li>Pain recognition </li></ul></ul><ul><ul><ul><li>Anxiolytics </li></ul></ul></ul><ul><ul><ul><li>Too much sedation can mask signs of pain </li></ul></ul></ul><ul><ul><ul><ul><li>This is inhumane </li></ul></ul></ul></ul>
  11. 11. Factors affecting pain <ul><li>Wind-up </li></ul><ul><ul><li>Sensitize to subsequent stimuli </li></ul></ul><ul><ul><li>Glutamate </li></ul></ul><ul><ul><ul><li>Activates NMDA receptor </li></ul></ul></ul><ul><ul><li>Initiates an intracellular cascade </li></ul></ul><ul><ul><ul><li>Increases membrane sensitivity to stimuli </li></ul></ul></ul><ul><li>‘ Central sensitization’ </li></ul><ul><ul><li>Less tolerant </li></ul></ul><ul><ul><li>Maladaptive </li></ul></ul>
  12. 12. Types of Pain <ul><li>Acute </li></ul><ul><li>Injury </li></ul><ul><li>Surgery </li></ul><ul><li>Inflammation </li></ul><ul><li>Infection </li></ul><ul><li>Limits mobility </li></ul><ul><li>Temporary </li></ul><ul><li>Chronic </li></ul><ul><li>Age related disorders </li></ul><ul><li>Slow to develop </li></ul><ul><li>May learn to cope </li></ul>
  13. 13. Types of Pain <ul><li>Adaptive </li></ul><ul><li>Normal response </li></ul><ul><ul><li>Tissue damage </li></ul></ul><ul><li>Protects from further injury </li></ul><ul><li>Inflammation is a large component </li></ul><ul><li>Maladaptive </li></ul><ul><li>Abnormal response </li></ul><ul><ul><li>No real purpose </li></ul></ul><ul><li>Stimulus is gone but pain persists </li></ul><ul><ul><li>Inappropriately managed adaptive pain </li></ul></ul>
  14. 14. The Pain Pathway <ul><li>Transduction </li></ul><ul><ul><li>Signal formation </li></ul></ul><ul><ul><ul><li>Chemical signal </li></ul></ul></ul><ul><ul><ul><ul><li>Inflammatory mediators </li></ul></ul></ul></ul><ul><ul><ul><li>Electrical activity </li></ul></ul></ul><ul><ul><ul><ul><li>Recognizable by nervous system </li></ul></ul></ul></ul>Transduction
  15. 15. The Pain Pathway <ul><li>Transmission </li></ul><ul><ul><li>How the signal is sent </li></ul></ul><ul><ul><ul><li>Transmitted through PNS </li></ul></ul></ul><ul><ul><ul><ul><li>A-delta </li></ul></ul></ul></ul><ul><ul><ul><ul><ul><li>Fast, small, myelinated </li></ul></ul></ul></ul></ul><ul><ul><ul><ul><ul><li>Acute pain </li></ul></ul></ul></ul></ul><ul><ul><ul><ul><li>C-fibers </li></ul></ul></ul></ul><ul><ul><ul><ul><ul><li>Slow, large, unmyelinated </li></ul></ul></ul></ul></ul><ul><ul><ul><ul><ul><li>Chronic pain </li></ul></ul></ul></ul></ul>Transmission
  16. 16. The Pain Pathway <ul><li>Modulation </li></ul><ul><ul><li>Signal processing </li></ul></ul><ul><ul><ul><li>Spinal cord </li></ul></ul></ul><ul><ul><ul><ul><li>Dorsal horn </li></ul></ul></ul></ul><ul><ul><ul><ul><li>Endogenous systems </li></ul></ul></ul></ul>Modulation
  17. 17. The Pain Pathway <ul><li>Cross section of the spinal cord </li></ul><ul><ul><li>Dorsal horn </li></ul></ul><ul><ul><ul><li>Modulation </li></ul></ul></ul>Tissue trauma Signal enters dorsal horn Reflex activity exits ventral horn To higher levels of CNS
  18. 18. The Pain Pathway <ul><li>Perception </li></ul><ul><ul><li>Receiving and interpretation </li></ul></ul><ul><ul><ul><li>Successful transduction, transmission, & modulation of a painful stimulus </li></ul></ul></ul><ul><ul><ul><li>Conscious, subjective, and emotional </li></ul></ul></ul>Modulation Perception
  19. 19. The Pain Pathway & Drugs <ul><li>Transduction (formation) </li></ul><ul><ul><li>Drugs that work “on site” </li></ul></ul><ul><ul><ul><li>Local anesthetics </li></ul></ul></ul><ul><ul><ul><ul><li>Lidocaine, bupivacaine </li></ul></ul></ul></ul><ul><ul><ul><ul><ul><li>Block sodium channels </li></ul></ul></ul></ul></ul>
  20. 20. Transduction & drugs <ul><li>NSAIDS </li></ul><ul><ul><li>Carprofen, meloxicam, ketoprofen </li></ul></ul><ul><ul><ul><li>Inhibit the production of prostaglandins from inflamed tissue </li></ul></ul></ul>
  21. 21. Arachidonic Acid COX-1 COX-2 <ul><li>Prostaglandins for homeostatic </li></ul><ul><li>functions </li></ul><ul><ul><li>Integrity of GI mucosa </li></ul></ul><ul><ul><li>Modulate renal blood flow </li></ul></ul><ul><ul><li>Regulate platelet function </li></ul></ul><ul><li>Prostaglandins in </li></ul><ul><li>inflammation </li></ul><ul><li>Pain </li></ul><ul><li>Edema </li></ul><ul><li>Fever </li></ul>Inhibition undesirable Inhibition desirable 5-LOX <ul><li>Leukotrienes </li></ul><ul><li>GI Ulcers </li></ul><ul><li>DJD </li></ul>NSAIDS COX-3
  22. 22. Transduction & drugs <ul><li>Steroids </li></ul><ul><li>Intra-articular opioids </li></ul><ul><ul><li>Opioid receptors can be found in inflamed joints </li></ul></ul>
  23. 23. The Pain Pathway & Drugs <ul><li>Transmission (sent) </li></ul><ul><ul><li>Drugs that stop nerve impulses </li></ul></ul><ul><ul><li>Local anesthetics </li></ul></ul><ul><ul><ul><li>Locally and systemically (lidocaine only) </li></ul></ul></ul><ul><ul><ul><ul><li>Preferential tx </li></ul></ul></ul></ul><ul><ul><ul><ul><li>Great for pancreatitis pain </li></ul></ul></ul></ul><ul><ul><ul><li>Do not give bupivicaine IV! </li></ul></ul></ul><ul><li>Alpha-2 agonists </li></ul>
  24. 24. The Pain Pathway & Drugs <ul><li>Modulation (processing) </li></ul><ul><ul><li>Opioids </li></ul></ul><ul><ul><ul><li>Raise threshold </li></ul></ul></ul><ul><ul><ul><ul><li>Methadone, morphine… </li></ul></ul></ul></ul><ul><ul><li>Alpha-2’s </li></ul></ul><ul><ul><ul><li>Decrease signal </li></ul></ul></ul><ul><ul><ul><ul><li>Dexmedetomidine </li></ul></ul></ul></ul><ul><ul><li>Local anesthetics </li></ul></ul><ul><ul><ul><li>Blocks sodium channels </li></ul></ul></ul><ul><ul><ul><ul><li>Lidocaine, bupivacaine </li></ul></ul></ul></ul><ul><ul><li>NSAIDS </li></ul></ul><ul><ul><ul><li>Carprofen, meloxicam </li></ul></ul></ul><ul><ul><li>Tricyclic antidepressants </li></ul></ul><ul><ul><ul><li>Amitriptaline </li></ul></ul></ul><ul><ul><li>NMDA antagonists </li></ul></ul><ul><ul><ul><li>Decreases wind-up </li></ul></ul></ul><ul><ul><ul><ul><li>Ketamine, methadone </li></ul></ul></ul></ul>
  25. 25. The Pain Pathway & Drugs <ul><li>Perception </li></ul><ul><ul><li>General anesthetics </li></ul></ul><ul><ul><ul><li>Injectables </li></ul></ul></ul><ul><ul><ul><li>Inhalants </li></ul></ul></ul><ul><ul><li>Opioids </li></ul></ul><ul><ul><li>Alpha-2’s </li></ul></ul>Z z z z z z z
  26. 26. Pre-emptive Analgesia <ul><li>Pain meds given in anticipation of pain </li></ul><ul><ul><li>intensity and duration </li></ul></ul><ul><ul><li>Chronic pain state </li></ul></ul><ul><ul><li>Does not eliminate post-op pain it just makes it easier to control! </li></ul></ul>
  27. 27. Balanced Analgesia <ul><li>Simultaneous administration of two or more analgesic drug classes or techniques </li></ul><ul><ul><li>Synergism </li></ul></ul><ul><ul><li>Additive </li></ul></ul><ul><ul><li>Pain pathway </li></ul></ul>
  28. 28. Pre-emptive and balanced analgesia <ul><li>Utilizes lower doses </li></ul><ul><ul><li>Less unwanted side effects </li></ul></ul><ul><li>More complete analgesia </li></ul><ul><li>Suppresses the stress response </li></ul><ul><ul><li>Decreases chronic pain state </li></ul></ul><ul><li>Shorten recovery </li></ul>
  29. 29. Consequences of pain
  30. 30. Is pain beneficial? <ul><li>NO! </li></ul><ul><ul><li>Decrease quality of life </li></ul></ul><ul><ul><li>Prolongs healing </li></ul></ul><ul><ul><ul><li>Injury, illness, surgery </li></ul></ul></ul><ul><li>All tissue injury causes pain </li></ul><ul><ul><li>Routine or quick procedures </li></ul></ul><ul><ul><li>Skill of individual </li></ul></ul>
  31. 31. Recognition of pain <ul><li>Subjective </li></ul><ul><ul><li>Know what is normal </li></ul></ul><ul><ul><ul><li>Species </li></ul></ul></ul><ul><ul><ul><li>Breed </li></ul></ul></ul><ul><ul><ul><li>Individual </li></ul></ul></ul><ul><ul><li>Use common sense </li></ul></ul><ul><ul><li>Big picture </li></ul></ul><ul><ul><li>Pre-emptive techniques </li></ul></ul><ul><ul><li>Remember that it is better to treat pain that isn’t there than to not treat pain that is </li></ul></ul>
  32. 32. Recognition of pain <ul><li>Can be difficult to asses </li></ul><ul><ul><li>Prey species </li></ul></ul><ul><ul><li>Stoicism is innate and evolutionary </li></ul></ul>
  33. 33. Pets in pain <ul><li>Assess: </li></ul><ul><ul><li>Body posture </li></ul></ul><ul><ul><li>Appearance </li></ul></ul><ul><ul><li>Locomotion </li></ul></ul><ul><ul><li>Behavior </li></ul></ul><ul><ul><li>Activity level </li></ul></ul><ul><ul><li>Daily habits </li></ul></ul><ul><ul><li>Response to people </li></ul></ul>
  34. 34. Physiologic signs of pain <ul><li>Increase in monitoring parameters </li></ul><ul><ul><li>blood pressure </li></ul></ul><ul><ul><li>heart rate </li></ul></ul><ul><ul><li>respiratory rate </li></ul></ul><ul><li>Peripheral vasoconstriction </li></ul><ul><li>Stress leukogram </li></ul><ul><ul><li>These signs do not rule pain in or out! </li></ul></ul>
  35. 35. Common behavioral responses to pain <ul><li>Pain recognition </li></ul><ul><ul><li>Whine, whimper </li></ul></ul><ul><ul><ul><li>Intermittent vocalization </li></ul></ul></ul><ul><ul><ul><ul><li>Continuous vocalization </li></ul></ul></ul></ul><ul><ul><li>Arched or abnormal posture </li></ul></ul><ul><ul><ul><li>Standing with head down, bowing/praying position, hunched </li></ul></ul></ul><ul><ul><li>Guarding of injured tissue </li></ul></ul><ul><ul><ul><li>Abdominal splinting/muscle tensing </li></ul></ul></ul><ul><ul><ul><ul><li>Reaction to palpation of site around injured tissue </li></ul></ul></ul></ul><ul><ul><ul><ul><ul><li>Snapping/reacting when approaching injured tissue </li></ul></ul></ul></ul></ul>Dogs are pack animals, they share emotions with pack members to receive support
  36. 36. Behavioral responses to pain <ul><ul><li>Restlessness </li></ul></ul><ul><ul><ul><li>Frequent position changes </li></ul></ul></ul><ul><ul><ul><ul><li>Inability to sleep </li></ul></ul></ul></ul><ul><ul><li>Behavior change </li></ul></ul><ul><ul><ul><li>Animal becomes timid or aggressive </li></ul></ul></ul><ul><ul><li>Increased heart rate and blood pressure </li></ul></ul><ul><ul><li>Hypersalivation </li></ul></ul><ul><ul><li>Appetite reduction </li></ul></ul><ul><ul><li>Dilated pupils </li></ul></ul><ul><ul><li>Altered voiding behavior </li></ul></ul>
  37. 37. Behavioral responses to pain <ul><li>Pain recognition </li></ul><ul><ul><li>Over grooming </li></ul></ul><ul><ul><ul><li>Growling at nothing </li></ul></ul></ul><ul><ul><ul><ul><li>Purring </li></ul></ul></ul></ul><ul><ul><li>Hiding </li></ul></ul><ul><ul><ul><li>Aggression </li></ul></ul></ul><ul><ul><li>Squinting </li></ul></ul><ul><ul><ul><li>Refusal to change body position </li></ul></ul></ul><ul><ul><li>Guarding injured tissue </li></ul></ul><ul><ul><ul><li>Skin flicking, muscle tensing </li></ul></ul></ul><ul><ul><li>Desperate attempts to flee </li></ul></ul><ul><ul><li>Reduced grooming </li></ul></ul><ul><ul><li>Appetite reduction </li></ul></ul><ul><ul><li>Pupil dilation </li></ul></ul><ul><ul><li>Salivation </li></ul></ul><ul><ul><li>Restlessness </li></ul></ul><ul><ul><ul><li>Inability to sleep </li></ul></ul></ul><ul><ul><ul><ul><li>Sleeping all the time </li></ul></ul></ul></ul><ul><ul><li>Increased heart rate and blood pressure </li></ul></ul>Cats are more solitary animals, they are generally more stoic than dogs; showing pain highlights a cats vulnerability
  38. 38. Common procedures & pain <ul><li>No/temporary pain </li></ul><ul><ul><li>PE </li></ul></ul><ul><ul><li>Nail trim </li></ul></ul><ul><ul><li>Suture removal </li></ul></ul><ul><li>Analgesics typically not necessary </li></ul><ul><ul><li>Don’t forget about stress! </li></ul></ul><ul><li>Minor pain </li></ul><ul><ul><li>Suturing </li></ul></ul><ul><ul><li>Urinary catheterization </li></ul></ul><ul><ul><li>IV catheterization </li></ul></ul><ul><ul><li>Dental cleaning </li></ul></ul><ul><li>Mild analgesics beneficial </li></ul><ul><ul><li>Decrease stress of animal and handler </li></ul></ul>
  39. 39. Common procedures & pain <ul><li>Moderate pain </li></ul><ul><ul><li>OHE/castration </li></ul></ul><ul><ul><li>Declaw </li></ul></ul><ul><ul><li>Extractions </li></ul></ul><ul><li>Analgesics are necessary! </li></ul><ul><ul><li>Butorphanol alone is not adequate for these procedures! </li></ul></ul><ul><li>Severe pain </li></ul><ul><ul><li>Fracture repair </li></ul></ul><ul><ul><li>Cruciate repair </li></ul></ul><ul><ul><li>Amputation </li></ul></ul><ul><ul><li>Ear canal ablation </li></ul></ul><ul><li>Analgesics are essential! </li></ul><ul><ul><li>Multi-modal is best </li></ul></ul>
  40. 40. Pain Scoring <ul><li>Assigns a numerical value to observed behaviors </li></ul><ul><li>Makes pain assessment more objective </li></ul><ul><li>Helps puts everybody on the same page </li></ul>
  41. 41. Pain Scoring <ul><li>Comfort </li></ul><ul><li>Movement </li></ul><ul><li>Appearance </li></ul><ul><li>Behavior </li></ul><ul><li>Interaction </li></ul><ul><li>Vocalization </li></ul><ul><li>Heart rate </li></ul><ul><li>Trust your instincts </li></ul><ul><ul><li>If you feel that an animal is uncomfortable it probably is </li></ul></ul><ul><ul><li>Pain scores help you to communicate this to the doctor </li></ul></ul><ul><ul><li>Decreases stress! </li></ul></ul>
  42. 42. Questions?

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