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Pain Management

Pain Management. Dr. J.M. Roesner, DVM, DABVP Dr. Vanessa Lee, DVM. Ethics and Economics of Pain Management Pain Pathway and Strategies for Pain Reduction NSAIDS Tepoxalin Parting Thoughts. AVMA Position.

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Pain Management

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  1. Pain Management Dr. J.M. Roesner, DVM, DABVP Dr. Vanessa Lee, DVM

  2. Ethics and Economics of Pain Management • Pain Pathway and Strategies for Pain Reduction • NSAIDS • Tepoxalin • Parting Thoughts

  3. AVMA Position “Animal pain and suffering are clinically important conditions that adversely affect an animals quality of life. Drugs, technique or husbandry methods used to prevent and control pain must be tailored to individual animals.” (JAVMA 2001:218:1694)

  4. Untapped Market: 60% or more of DJD dogs are not treated or managed by a DVM. (JAVMA 2002:221:215-222)

  5. “Ethical Economics”

  6. Types of Pain

  7. 1. Somatic • Skin, musculoskeletal • Dull, aching, localizable

  8. 2. Visceral • Compression, distension, infiltration of pelvic, abdominal or thoracic organs • May be difficult to localize

  9. 3. Neuropathic • Nerve compression, damage infiltration, +/-hyperalgesia • Severe burning or tingling (Tranquilly, Teton Press)

  10. NMDA Receptor

  11. Pain Pathway

  12. Pain Pathway Continued: “First Pain” – A-delta, fast “Second Pain” - C fibers, slow Dorsal Root Ganglia – contains afferent cell bodies

  13. Pain Pathway Continued: Dorsal Horn of Spinal Cord (2nd order Neurons) Site of Synapse of First Order Neurons: A: excitatory and inhibitory interneurons B: propriospinal neurons (segmental reflex activity) C: projecting neurons to supraspinal centers (midbrain, cortex) Spinothalamic, Spinocervical, Spinomesencephalic

  14. Pain Pathway Continued: 3rd order neurons are within: • Medulla • Pons • Midbrain • Thalamus • Hypothalamus • Cerebral Cortex

  15. Pain Pathway Continued: Descending inhibitory influences occur within cortex, thalamus, midbrain, rostral medulla and brain stem.

  16. Nociception: A: Transduction: receptor translates physical energy into electrical energy B: Transmission: A delta and C fibers propagate impulses C: Modulation: endogenous descending analgesic systems (opiod, serotonergic and noradrenergic) inhibit stimuli processing in spinal dorsal horn cells.

  17. Pain Recognition •  HR,  BP,  RR, peripheral vasoconstriction • Restless • Sedentary hunched •  Appetite • Purring, vocalization • Pain scores – VAS & NRS

  18. Pain has negative consequences on healing, morbidity & mortality.

  19. Assume an animal is painful if you would be in a similar circumstance.

  20. Preemptive Analgesia • Rx Prior to stimulus • Minimizes likelihood of chronic pain • Pain is easier to prevent than to alleviate (windup) • e.q. premed opiods, NSAIDS, Alpha 2 agonists, local blocks, epidurals

  21. Multimodal Analgesia • Synergistic • Decreased potential for adverse reactions • Effective • E.g NSAID   transduction • Local Block  stops transmission • Opiod and Alpha 2 agonist   modulation

  22. Multimodal Analgesia • Decreases nociceptor sensitization (inflammation) • Decreases wind up (neuroplastic changes in cord) • Decreases tachyphylaxis • Decreases neuroendocrine response • Decreases convalescent time • Improves healing (perfusion) • Improves immune function

  23. Sites of Drug Intervention in Pain Processing

  24. Inhibit Transduction(peripheral sensitization of nociceptors) • Local anesthetics • Opiods • NSAIDs • Corticosteriods

  25. Inhibit Transmission(impulse conduction) • Local anesthetics • Alpha 2 agonists

  26. Modulation of Spinal Pathway(inhibit central sensitization) • Local anesthetics • Opiods • Alpha 2 agonists • Trycyclic antidepressants • Cholinesterase inhibitors • NMDA antagonists • NSAIDs • Anticonvulsants

  27. Inhibit Perception • General anesthetics • Opiods • Alpha 2 agonists • Benzodiazepams • Phenothiazines

  28. Epidural

  29. Epidural • Lidocaine Bupivicaine 1 ml/4.5 kg or 1 ml/3.5 kg for abdominal • Morphine • Fentanyl • Alpha 2 Agonists • Buprenorphine

  30. Distal Radial/Ulnar & Median Nerve Block

  31. Articular Blocks - Stifle

  32. Dental Blocks

  33. Intercostal Blocks

  34. CRI’s • Can overcome short +/- ½ limitations • Morphine, Ketamine, Butorphanol • Calculator programs available

  35. Transdermal • Fentanyl or lidoderm patches • Topical gabapentin • Emla cream

  36. Drugs to Consider: • Tramadol • Amatidine • Dextromethorphan • Gabapentin • IV lidocaine

  37. Butorphanol (Plumb 2005) • Kappa agonist, mu antagonist, sigma agonist • NOT adequate for severe pain • NOT adequate for bone pain • Controlled (C-IV) • Short duration of analgesia (best in CRI, has a ceiling effect)

  38. Analgesic Doses • D: 0.1-1.0 mg/kg (SQ, IM, IV) • C: 0.1-1.0 mg/kg (SQ, IM, IV) • H: 0.1 (SQ, IM, IV) • Ferret: 0.05-0.1 mg/kg (SQ, IM, IV) • Rabbit, Rodent: 0.4 mg/kg (IV, SQ, IM) • Avian: 2-4 mg/kg

  39. Buprenorphine (Plumb 2005) • Partial mu agonist, weak kappa antagonist • Long duration • Sublingual and buccal use in cats • Scheduled C-III • May decrease analgesia from pure mu agonists (controversial, may be species dependent) • Contra indicated in patients on MAOI • Ceiling effect

  40. Analgesic Doses • D: 0.005-0.03 mg/kg (IV, SQ, IM) • C: 0.005-0.03 mg/kg (IV, SQ, IM or buccal • Ferret: 0.01-0.05 mg/kg (IV, SQ, IM) • H: 0.004-0.02 mg/kg (IV, SQ, IM) • Rabbit: 0.02-0.05 mg/kg (IV, SQ, IM) • Rodent: 0.1-0.05 mg/kg (IV, SQ, IM)

  41. Fentanyl (Plumb 2005) • Pure mu agonist • CRI or patch • Class C-II • Alters amylase and lipase • Do not combo with MAOI • Some variation in patch absorption with individual and site • Dosing see pg. 328 Plumb

  42. Tramadol (Plumb 2005) • Mu agonist, SSRI, decreases norepinephrin reuptake • Caution with combo in SSRI, MAOI, TCA, SAME, digoxin • Synergistic with NSAIDS • Naloxone does not fully reverse • Inexpensive, unscheduled • Analgesic doses: PO D: 1-4mg/kg q 8-12 C: 4 mg/kg q 12 • Injectable form available in Europe

  43. Ketamine (Plumb 2005) • NMDA receptor antagonist, dissociative anesthetic • Decreases “wind up” in spinal cord processing of pain • Doses are lower for analgesia than anesthesia • Adverse effects are less than when used as an anesthetic, but still present • Use as adjunct with narcotics

  44. Analgesic Doses • D: 0.1-1 mg/kg PO,IM, SQ q 4-6 h CRI 0.1-0.3 mg/kg h • C: 0.1-1 mg/kg IM,SQ q 4-6 h CRI 0.1-0.3 mg/kg h • Exotic Species-little analgesic data extrapolate from anesthetic doses

  45. Amantidine (Plumb 2005) • NMDA receptor antagonist, antiviral • Oral, inexpensive, gel cap • Use as an adjunct in pain management (especially with opioids, NSAIDS) • Drug interactions: TMS, quinidine, thiazide, diuretics, triamterene, CNS stimulants, anticholinergics • Analgesic Doses: D: 1.25-4 mg/kg PO q 12-24 h, C: 3 mg/kg PO q 24h

  46. Dextromethorphan • NMDA antagonist, SSRI, antitussive • Conflicting pain data • Caution mixing with MAOI and SSRI (serotonin syndrome) • Doses: Dog: 1-2 mg/kg q 12h

  47. Gabapentin (Plumb 2005) • Analgesic, anticonvulsant, psychiatric Rx • Oral, fairly expensive • Adjunct in management of chronic pain • Mechanism unknown • Drug interactions: antacids decrease absorption, may increase AUC when combined with morphine or hydrocodone • False positive for protein on urine multistix

  48. Analgesic Dose • D: 3 mg/kg PO q 24 h • C: 3 mg/kg PO q 24 h • Anectdotal: can be used in transdermal prep applied to trigger points for fibromyalgia and migraines in man

  49. Amitriptyline (Plumb 2005) • Tricyclic antidepressant • Mechanism unclear: blocks amine pump (increase NE, serotonin), sedation, anticholinergic • Adjunct in chronic pain, antipuritic • Caution in patients with seizures, MAOIs, glaucoma, thyroid disease, cardiac or metabolic disease • May alter blood glucose levels • Analgesic Doses: D: 1-2 mg/kg PO q 12-24h C: 0.5-2 mg/kg PO q 24 h

  50. Lidocaine (Marc Raffe personal communication) • Local anesthetic, CRI useful in analgesia, antiarrythmic • Do not use lidocaine with epinephrine IV • Cats may be more sensitive to CNS depression • Emla cream • Dose CRI: Dog: 2 mg/kg/hour • MLK Protocol: Morphine 0.1 mg/kg/h, Medetomidine 1 mcg/kg/h, Lidocaine 2 mg/kg/h, Ketamine 0.2 mg/kg/h

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