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Pain Management

Pain Management. Why Treat Pain?. Animals feel pain just like us Unethical not to address pain Animal owner and public concerns Many anesthetics have no analgesic effect Which do? Pain results in poor anesthetic recovery. MYTHS. “Anesthetics mask symptoms”

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Pain Management

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  1. Pain Management

  2. Why Treat Pain? • Animals feel pain just like us • Unethical not to address pain • Animal owner and public concerns • Many anesthetics have no analgesic effect • Which do? • Pain results in poor anesthetic recovery

  3. MYTHS “Anesthetics mask symptoms” “Patient will harm itself if there’s no pain” “Pain is difficult to assess”

  4. The Truth! • Pain is BAD: • Decreased cardiovascular function • Decresed appetite • Slows wound healing • Decreased immune function • Greater chance of infection • Increased fear and anxiety

  5. Use of Analgesics in Practice • Overall = poor • 13-26% dog and cat spay/neuters receive analgesics • 50-70% of non-neutering soft tissue surgery • >80% orthopedic surgery and severe trauma • Why not better? • DEA / theft concerns • Older vets not trained that way • Older drugs dangerous • Animals are stoic

  6. Pain Perception • Pain sensor nerve fiberspinal cordbrain • Neurotransmitters>> • Somatic ( superficial ) pain • Visceral ( internal organ ) pain • Bone pain

  7. Classification of Pain • Intensity (scale of 1-10) • Acute, sharp, sudden, short • Surgical pain • Responds well to drug tx • Chronic, dull, prolonged • Cancer or arthritis • Doesn’t always respond well to tx • Referred (from somewhere else) • Hyperesthesia (increased sensitivity) • Neuropathic (Nerve damage) • Poorly responsive

  8. Degree and Type of Pain Depend On • The procedure • The animal • Pain is an individual experience • Tailor analgesic protocol to the patient • Analgesic administration • Timing • Dosage

  9. Preemptive Analgesia • If the body doesn’t sense the pain during the procedure, the pain will be easier to deal with post-operatively • A patient in surgical anesthesia is not aware of pain, but the body is still responding sensitizes the nervous system

  10. Preemptive Analgesia Results In • Marked decrease in amount of analgesic medication needed post-operatively • Increased patient comfort

  11. Balanced Anesthesia • Several anesthetic drugs are combined into anesthetic protocol • Include analgesic • Synergism • Smaller dosages needed • Decreased potential for side effects

  12. Monitoring Signs of Pain Facial Expression Vocalization Body Posture Abnormal Gait Decreased Activity Level Attitude Appetite Grooming Urination/Defecation Habits

  13. Methods of Pain Control • Non-pharmacological methods: • Endorphins = The body’s natural painkillers • Good nursing care • Comfortable bedding • Clean and dry • Easy access to bathroom, food, water • TLC • Rotate recumbency • Allow time to sleep

  14. Non-pharmacological Methods • Apply cold to site (acute- 1st 24 hours) • Decreases inflammation • Numbs • Apply heat to site (chronic) • Massage • Acupuncture/acupressure • Complementary methods • Herbs, laser, magnetic, chiropractic

  15. Pharmacologic Methods • Opioids • 2 agonists • Steroids • NSAIDS • Local anesthetics • Chondroprotective drugs

  16. Opioids

  17. Opiate Receptors MOA? 4 types of receptors: mu kappa sigma delta Should we be wondering why fraternities/sororities name themselves after receptors of pain??

  18. Opioids:Backbone of Analgesia • Pure Agonists • Morphine, oxymorphone, meperidine, hydromorphone, fentanyl • Partial agonists, mixed agonist-antagonists • Buprenorphine • Butorphanol • Pure Antagonists (reversal of agonists) • Naloxone • ABUSE POTENTIAL

  19. Opioid Administration • Systemic: IV, SQ, IM, CRI • Intra-articular injection • Local injection • Epidural injection • Transdermal fentanyl patch

  20. Opioid Effects • GOOD: • Great analgesia • Variable muscle relaxation • Sedation • BAD: • Respiratory depression • GI effects • Vomiting • Defecation followed by constipation

  21. Opioids (other effects) • Excitement • Panting • Vocalization • Noise sensitivity • Depression of the cough center • Advantage for?

  22. Fentanyl Patch • Lag time: • apply 6-12 hours prior to surgery in cats, • 12-24 hours in dogs • Lasts about 3 days (up to 6 in cats) • Variation in absorption rate • Dose of patch (in micrograms/hr) • Avoid heat sources • Excessive amounts can cause ataxia, sedation in dogs, excitement, disorientation, wide-eyed stare in cats • Remove patch, can reverse

  23. Fentanyl Patch • Applied to dorsal neck or shoulders, lateral thorax • Clip hair, clean skin with water only • Do not cut patch • Can remove just part of backing if small animal • Apply patch, hold firmly 2 minutes • Bandage

  24. Opioid Partial Agonists • Buprenorphine • Buprenex® • 4-8 hour duration

  25. Opioid Mixed Agonist-Antagonist • Butorphanol • (Torbutrol®, Torbugesic®) • For mild to moderate pain • Duration 1 to 4 hours IM, SQ • Less abuse potential than agonists

  26. Opioid Antagonists • Naloxone • Used to reverse opiates/opioids • Remember: Reverses analgesia too! • May not last as long as the agonist • Relapse =“renarcotization” • Partial reversal with butorphanol possible

  27. Alpha-2 Agonists“thiazines”

  28. Alpha-2 Agonists • MOA? • Examples: • Xylazine (Rompun®) • Medetomidine (Domitor®) Engages receptors in CNS >> decrease norepinephrine

  29. Xylazine: Good Things • Moderate analgesia • Potent sedative effect • Good muscle relaxation

  30. Xylazine: Bad Things • Bradycardia due to stimulation of the vagus nerveheart block • Profound cardiac disturbances! • Sensitizes the heart to catecholaminesArrhythmias • Decreased cardiac output • Hypotension (BP decreases by 1/4-1/3) #1 ?

  31. Xylazine: More Bad Things • Vomiting (sometimes used as emetic)

  32. Xylazine: Reversal? • Yohimbine is reversal agent • Mixed Alpha- antagonist (blocker) • Trade name “Yobine”

  33. Medetomidine Common name? • =DOMITOR® • More specific to CNS alpha-2 receptors • Alpha-2 so has reversal agent • (Antisedan®) Name?

  34. Steroids= corticosteroids,glucocoticoids • Examples: • Prednisone = Prednisolone • Dexamethasone • Betamethasone • Solu-Delta-Cortef • Solu-Medrol • Decrease pain by decreasing inflammation

  35. Steroids: MOAinhibit phospholipase A2>>> inhibits prostoglandin/leukotrienes Steroids inhibit here Phospholipase A2 COX-2 NSAIDS inhibit here COX-1

  36. Side Effects and Toxicity • Iatrogenic hyperadrenocorticism • “Cushings Dz” • Polyphagia • PU/PD • Glaucoma and cataracts • Gastric ulceration • Delayed wound healing • Immunosuppression

  37. More ! • Insulin resistance • Hepatopathy • CNS: restlessness, seizure activity • Infection

  38. Non-Steroidal Anti-inflammatory Drugs ( NSAIDS ) • Aspirin • Carprofen - Rimadyl ® • Etodolac - Etogesic® • Ketoprofen - Ketofen ® • Phenylbutazone – “Bute” • Flunixin - Banamine ® • (Acetaminophen - Tylenol ®)

  39. NSAIDS • Most have effective somatic (superficial) analgesic effect • Some have good visceral analgesic effect also • All take 30-60 minutes to take effect, even if injected • All have antiinflammatory properties • Reduce fevers

  40. NSAIDS • MOA: cyclooxygenase inhibitors >> prostaglandin inhibitors • Many side effects are due to “good” prostaglandin inhibition (COX 1): • GI upset/ ulceration • Renal toxicity • Impaired platelet function

  41. NSAIDS: MOAinhibit cyclooxygenase>>> inhibits prostoglandin/thromboxane Steroids inhibit here Phospholipase A2 COX-2 NSAIDS inhibit here COX-1

  42. NSAIDS - Metabolism • Metabolized by the liver • Variation in metabolism between species • Aspirin half-life 12 hours in dogs, 1 hour in horses, 38 hours in cats • Many NSAIDS toxic to cats due to inability to metabolize them • Acetaminophen is toxic in dogs AND cats!

  43. NSAIDS Inhibit Production of Protective GI Prostaglandins • Erosion/ulceration of GI tract • Stomach upset • Inappetance • Vomiting • Diarrhea • Melena ?

  44. Prostaglandins in the Kidneys • Cause dilation of renal vasculature, allowing perfusion despite decreased blood pressure due to • Shock • Dehydration • Blood loss • Anesthesia • Inhibition of prostaglandin production can cause kidney cell death due to lack of perfusion • Only an issue if decreased BP

  45. NSAIDS • Cyclooxygenase inhibition decreased thromboxane decreases platelet adhesion/clumpingdecreases clot formation and thromboemboli

  46. TYPES of NSAIDs

  47. Phenylbutazone • COX1 and 2 Inhibitor • Very Potent • Commonly used in horses • Not recommended in dogs • GI side effects common • NEVER IN CATS!

  48. Aspirin • COX1 and 2 Inhibitor • Very short half-life in horses • Commonly used in dogs • Buffered only • With food • Use with caution in cats • Can’t metabolize well • Half-life 38 hours • Dosed every 48-72 hours

  49. Neither Ibuprofen Nor Naproxen Is Recommended for Use in Cats Ibuprofen = “Advil” COX1 + COX2 Inhibitors Officially not recommended in dogs. most do OK if used like aspirin

  50. Ketoprofen • Ketofen® (COX1 and COX2) • Licensed in horses • Approved for use in dogs and cats in Canada, Europe • Good analgesia, potent antipyretic • Injectable • Limit use • Blood clotting

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