5 regional anesthesia


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5 regional anesthesia

  1. 1. Spinal,epidural and caudal anesthesia [email_address]
  2. 2. HISTORY <ul><li>1885 Corning - First attempt with epidural cocaine </li></ul><ul><li>1891 Quincke - Describes the lumbar puncture technique </li></ul><ul><li>1901 use of cocaine as an epidural agent for humans and dogs reported </li></ul><ul><ul><li>Alternative to general anesthesia </li></ul></ul><ul><ul><li>1921 Pagis - First lumbar anesthesia for surgery </li></ul></ul><ul><ul><li>1927 E.R. Frank describes use of procaine as a successful alternative </li></ul></ul><ul><li>1947 Lidocaine commercially available </li></ul><ul><li>1949 Curbelo - First continuous lumbar analgesia with Touhy needle </li></ul><ul><li>1963 Bupivicaine commercially available </li></ul><ul><li>1979 Cousins - Epidural opioids provide analgesia </li></ul><ul><li>1983 Yaksh - Different spinal receptor systems mediating pain </li></ul><ul><li>1985 University of Kiel, Germany, Anesthesiology managed acute post-operative pain service </li></ul><ul><li>Interest wanes as inhalant anesthesia gains favor </li></ul>Cousins & Bridenbaugh, 3rd Edition
  3. 3. Current Role <ul><li>Significant role in modern veterinary and human anesthesia and analgesia </li></ul><ul><li>Important aspect of “balanced anesthesia” concept </li></ul>
  4. 4. Indications <ul><li>Surgery caudal to the umbilicus </li></ul><ul><ul><li>Up to and including thoracic limb if using morphine </li></ul></ul><ul><li>Peritonitis </li></ul><ul><li>Severe pancreatitis </li></ul><ul><li>Caudal trauma </li></ul><ul><li>High risk anesthetic candidates </li></ul><ul><ul><li>Dystocia </li></ul></ul><ul><li>Preemptive analgesia </li></ul>
  5. 5. Contraindications <ul><li>Absolute </li></ul><ul><ul><li>Patient refusal. </li></ul></ul><ul><ul><li>Localized infection at skin puncture site. </li></ul></ul><ul><ul><li>Generalized sepsis (e.g., septicemia, bacteremia). </li></ul></ul><ul><ul><li>Coagulopathy </li></ul></ul><ul><ul><li>Increased intracranial pressure. </li></ul></ul>
  6. 6. Contraindications <ul><li>Relative </li></ul><ul><ul><li>Localized infection peripheral to regional technique site. </li></ul></ul><ul><ul><li>Hypovolemia. </li></ul></ul><ul><ul><li>Central nervous system disease. </li></ul></ul><ul><ul><li>Chronic back pain. </li></ul></ul><ul><ul><li>Inexperience of operator </li></ul></ul>
  7. 8. Segmental level required for surgery
  8. 9. Segmental level required for surgery <ul><li>Operative Site ----------------------------- Level </li></ul><ul><li>Lower extremities T-12 </li></ul><ul><li>Hip T-10 </li></ul><ul><li>Vagina, uterus T-10 </li></ul><ul><li>Bladder, prostate T-10 </li></ul><ul><li>Lower extremities with tourniquet T-8 </li></ul><ul><li>Testis, ovaries T-8 </li></ul><ul><li>Lower intraabdominal T-6 </li></ul><ul><li>Other intraabdominal T-4 </li></ul>
  9. 18. Local Anesthetics <ul><li>Aminoamide-linked drugs : Bupivicaine, lidocaine </li></ul><ul><li>Aminoester-linked drugs : procaine , tetracaine </li></ul><ul><li>Agents reversibly bind to neuronal voltage-gated sodium channels and block nerve impulse conduction </li></ul><ul><li>Affect segmental nerve roots </li></ul><ul><li>Individual pharmacodynamics of agents depend on lipid solubility, dissociation constant, protein-binding characteristics </li></ul>
  10. 19. Local Anesthetics <ul><li>Effects based on myelination and size </li></ul><ul><li>Smaller sensory and ANS fibers affected 1 st </li></ul><ul><li>Sensation disappears in following order: </li></ul><ul><ul><li>Pain </li></ul></ul><ul><ul><li>Cold </li></ul></ul><ul><ul><li>Warmth </li></ul></ul><ul><ul><li>Touch </li></ul></ul><ul><ul><li>Joint </li></ul></ul><ul><ul><li>Deep pressure </li></ul></ul><ul><li>Recovery in reverse order </li></ul>
  11. 20. Local Anesthetics <ul><li>surface anaesthesia ——tetracaine </li></ul><ul><li>infiltration anaesthesia ——procaine, lidcaine etidocaine, ropivacaine, </li></ul><ul><li>conduction anaesthesia ——lidcaine, procaine, bupivacaine , etidocaine </li></ul><ul><li>spinal(subarachnoidal) anaesthesia——lidcaine, tetracaine, procaine </li></ul><ul><li>epidural anaesthesia ——lidcaine, tetracaine, procaine, bupivacaine ,ropivacaine, etidocaine </li></ul>
  12. 38. Spinal anesthesia <ul><li>Spinal anesthesia involves administering local anesthetic into the subarachnoid space. </li></ul><ul><li>The spinal canal extends from the foramen magnum to the sacral hiatus. The boundaries of the bony canal are the vertebral body anteriorly, the pedicles laterally, and the spinous processes and laminae posteriorly </li></ul>
  13. 39. Spinal anesthesia <ul><li>Three interlaminar ligaments </li></ul><ul><li>supraspinous ligament </li></ul><ul><li>interspinous ligament </li></ul><ul><li>ligamentum flavum </li></ul>
  14. 40. Spinal anesthesia <ul><ul><li>The spinal cord is invested in three meninges </li></ul></ul><ul><ul><li>The pia mater </li></ul></ul><ul><li>The dura mater </li></ul><ul><li>The arachnoid </li></ul>
  15. 41. Spinal anesthesia <ul><li>subarachnoid space </li></ul><ul><li>Extends from the attachment of the dura at S-2 to the cerebral ventricles above. The space contains the spinal cord, nerves, cerebrospinal fluid (CSF), and blood vessels that supply the cord. </li></ul>
  16. 42. Spinal anesthesia <ul><li>Physiological changes </li></ul><ul><li>Neural blockade </li></ul><ul><li>Cardiovascular. Hypotension </li></ul><ul><li>Respiratory </li></ul><ul><li>Visceral effects </li></ul><ul><li>Neuroendocrine </li></ul><ul><li>Thermoregulation </li></ul><ul><li>Central nervous system effects </li></ul>
  17. 43. Spinal anesthesia <ul><li>Determinants of spread  Major factors   Baricity of solution   Position of patients (except isobaric solution)   Dose and volume of drug injected (except isobaric)  Minor factors   Level of injection   Speed of injection/barbotage   Size of needle   Physical status of patients   Intra-abdominal pressure </li></ul><ul><li>Determinants of duration  Drug used  Dose injected  Presence of vasoconstrictors  Total spread of blockade </li></ul>
  18. 44. Spinal anesthesia <ul><li>Complications </li></ul><ul><li>Neurologic </li></ul><ul><li>Transient paresthesias , Spinal hematoma , back pain , Bloody tap , Transient neurologic syndrome , Postdural puncture headache </li></ul><ul><ul><li>Cardiovascular </li></ul></ul><ul><li>Hypotension , Bradycardia </li></ul><ul><ul><li>Respiratory </li></ul></ul><ul><ul><li>Apnea , Dyspnea </li></ul></ul><ul><ul><li>Visceral </li></ul></ul><ul><li>Nausea and vomiting , Urinary retention </li></ul><ul><li>Infection </li></ul>
  19. 45. Spinal anesthesia <ul><li>16ga=1.191mm </li></ul><ul><li>18ga=1.024mm </li></ul><ul><li>20ga=0.812mm </li></ul>
  20. 46. Epidural anesthesia <ul><li>Needle selection </li></ul><ul><ul><li>Shorter bevels </li></ul></ul><ul><ul><li>Steel stylet </li></ul></ul><ul><ul><li>Longer length </li></ul></ul><ul><ul><li>Duller tip </li></ul></ul><ul><li>Correct placement of needle </li></ul><ul><li>Hanging drop technique </li></ul><ul><li>Air leakage </li></ul><ul><li>Loss of resistance </li></ul><ul><li>Whoosh test </li></ul>
  21. 47. Epidural anesthesia <ul><li>Epidural anesthesia is achieved by introducing local anesthetics into the epidural space </li></ul><ul><li>Physiology </li></ul><ul><li>Neural blockade </li></ul><ul><li>Cardiovascular </li></ul><ul><li>Respiratory </li></ul><ul><li>Coagulation </li></ul><ul><li>Gastrointestinal </li></ul>
  22. 48. Epidural anesthesia <ul><li>Determinants of the level of epidural blockade </li></ul><ul><li>Volume of local anesthetic </li></ul><ul><li>Age. </li></ul><ul><li>Pregnancy </li></ul><ul><li>Speed of injection. </li></ul><ul><li>Position </li></ul><ul><li>Spread of epidural blockade. </li></ul><ul><li>Determinants of onset and duration of epidural blockade </li></ul><ul><li>Selection of drug . </li></ul><ul><li>Addition of epinephrine </li></ul><ul><li>Addition of opioid. </li></ul><ul><li>pH adjustment of solution. </li></ul>
  23. 49. Epidural anesthesia <ul><li>Complications </li></ul><ul><li>Dural puncture </li></ul><ul><li>Bloody tap </li></ul><ul><li>Catheter complications : The catheter can be inserted into an epiduralvein , Inability to thread the epidural catheter , Catheters can break off or become knotted , Cannulation of the subdural space </li></ul><ul><li>Intravascular injection </li></ul><ul><li>Unintentional subarachnoid injection </li></ul><ul><li>Local anesthetic overdose. </li></ul><ul><li>Epidural hematoma </li></ul><ul><li>Postdural puncture headache. </li></ul><ul><li>Epidural abscess </li></ul><ul><li>Direct spinal cord injury </li></ul>
  24. 50. Caudal anesthesia <ul><li>Caudal anesthesia is obtained by placing local anesthetic into the epidural space in the sacral region </li></ul><ul><li>Complications The complications of caudal anesthesia are similar to those of epidural anesthesia </li></ul>
  25. 51. Caudal anesthesia
  26. 52. Caudal anesthesia
  27. 53. <ul><li>Thank you ! </li></ul>
  28. 54. Fossum, Fundamentals of orthopedic surgery and fracture management, p. 825 Techniques in Small animal Surgery , 2 nd Edition, 2002. Drug Dose Onset (min) Duration (hours) Lidocaine 2% 1 ml/ 3.4 -4.5 kg 10 1-1.5 Bupivacaine (0.25 or 0.5%) preservative free 1ml/4.5kg 20-30 4.5-6 Fentanyl 0.001 mg/kg 4-10 6 Oxymorphone 0.1 mg/kg 15 10 Morphine (preservative free) 0.1 mg/kg 0.03 mg/kg (cats) 23 20 Buprenorphine 0.003-0.005 mg/kg diluted w/saline 30 12-18
  29. 55. Techniques of Administration <ul><li>Lateral recumbency </li></ul><ul><ul><li>Ideal if lateralized orthopedic problem </li></ul></ul><ul><ul><li>Surgical site down for maximal infiltration of agent (at least 5min) </li></ul></ul><ul><li>Sternal </li></ul><ul><ul><li>Potentially easier </li></ul></ul><ul><ul><li>Pelvic limbs drawn cranial </li></ul></ul><ul><ul><ul><li>Stretches out ligamentum flavum </li></ul></ul></ul><ul><ul><ul><li>Expands intervertebral space </li></ul></ul></ul>
  30. 56. Needle Selection con’t… Patient size Gauge and length Alternative gauge and length Cats and small dogs 25 G; 1” 22 G; 1.5” Medium to large dogs 22 G; 2.5” 21 G; 2.5” Very fat, large or giant breed dogs 21 G; 3”
  31. 57. Injection/dose precautions <ul><li>If intrathecal reduce dose by 40-75% of epidural </li></ul><ul><li>Reduce dose by up to 75% in pregnant patients </li></ul><ul><ul><li>Engorgement of epidural vessels </li></ul></ul><ul><ul><ul><li>Decreases volume of space </li></ul></ul></ul><ul><ul><ul><li>Increased absorption </li></ul></ul></ul>
  32. 58. Post injection <ul><li>Keep head elevated for 10 min. </li></ul><ul><li>Place affected limb down for 5 min. </li></ul>
  33. 59. Agents <ul><li>Local anesthetics </li></ul><ul><li>Opioids </li></ul><ul><li>α -2 agonists </li></ul><ul><li>Dissociatives </li></ul>
  34. 60. Preservatives <ul><li>Prudent to choose preservative free when possible </li></ul><ul><li>No reports of neurotoxicity in animals after one dose </li></ul><ul><ul><li>formaldehyde </li></ul></ul><ul><ul><li>phenol </li></ul></ul><ul><li>Avoid especially with: </li></ul><ul><ul><li>Repeated injections </li></ul></ul><ul><ul><li>Intrathecal injections </li></ul></ul><ul><li>Avoid antioxidant Na metabisulfite (in local anesthetics that contain epinephrine) intrathecally </li></ul><ul><ul><li>Not a true preservative </li></ul></ul>
  35. 61. Local Anesthetics: Disadvantages <ul><li>Relatively short duration of action </li></ul><ul><li>Possibility of unwanted motor blockade </li></ul><ul><li>Potential blockade of spinal sympathetic nerves </li></ul><ul><ul><li>Cause or aggravate hypotension </li></ul></ul>
  36. 62. Local Anesthetics <ul><li>Lidocaine </li></ul><ul><ul><li>Quick onset of action </li></ul></ul><ul><ul><li>Short-acting </li></ul></ul><ul><li>Bupivacaine </li></ul><ul><ul><li>More potent </li></ul></ul><ul><ul><li>Slower onset </li></ul></ul><ul><ul><li>Analgesia with minimal motor blockade </li></ul></ul><ul><ul><li>High affinity for Na channels (potential for cardiotoxicity) </li></ul></ul>
  37. 63. Lidocaine: Dosages <ul><li>Lidocaine for injection or preservative free 1.0-2.0% </li></ul><ul><ul><li>Single LS injection </li></ul></ul><ul><ul><li>1ml/5kg lean body weight for caudal procedures </li></ul></ul><ul><ul><li>1ml/3.5kg lean BW for abdominal procedures </li></ul></ul>
  38. 64. Bupivacaine: dosages <ul><li>Bupivacaine with epinephrine: 0.25-0.50% </li></ul><ul><ul><li>Single LS injection </li></ul></ul><ul><ul><li>1ml/5kg lean body weight for caudal procedures </li></ul></ul><ul><ul><li>1ml/3.5kg lean BW for abdominal procedures </li></ul></ul><ul><li>Bupivacaine preservative free (no epi) </li></ul><ul><ul><li>1ml/5-3.5kg lean BW </li></ul></ul><ul><ul><li>+/- CRI 0.1-0.4mg/kg/day </li></ul></ul><ul><ul><li>*CVT XIII p. 127, B. Hansen </li></ul></ul>
  39. 65. Duration of action <ul><li>Lidocaine </li></ul><ul><ul><li>~1 hour </li></ul></ul><ul><li>Bupivacaine </li></ul><ul><ul><li>~4-6 hour </li></ul></ul>
  40. 66. Toxicity <ul><li>Seizures </li></ul><ul><ul><li>Crossing of BBB </li></ul></ul><ul><ul><li>Treat with diazepam </li></ul></ul><ul><li>Respiratory depression </li></ul><ul><ul><li>artificial ventilation and oxygen </li></ul></ul><ul><li>Cardiovascular depression </li></ul><ul><ul><li>Hypotension </li></ul></ul><ul><ul><li>Myocardial depression </li></ul></ul>
  41. 67. Opioids <ul><li>Morphine, Fentanyl, oxymorphone, meperidine, buprenorphine </li></ul><ul><li>Selectively block pain conduction without: </li></ul><ul><ul><li>Motor, sensory or sympathetic blockade </li></ul></ul><ul><ul><li>Central effects </li></ul></ul><ul><li>MAC reduction </li></ul><ul><li>Hemodynamic stability </li></ul><ul><li>Blockade of autonomic response to noxious stimuli </li></ul>
  42. 68. Opioids mechanism of action <ul><li>Bind at opioid receptors on interneurons of superficial laminae of dorsal horn of spinal cord segments </li></ul><ul><ul><li>Pre/postsynaptic inhibition of afferent transmission (glutamate & substance P) </li></ul></ul><ul><ul><li>Better for dull aching post-op pain than acute intraoperative </li></ul></ul><ul><li>Must cross dura to CSF and spinal cord </li></ul><ul><ul><li>Diffuse across meninges into CSF then SC* </li></ul></ul><ul><ul><ul><li>Arachnoid mater is main meningeal diffusion barrier </li></ul></ul></ul><ul><ul><li>Travel thru perineurium of spinal nn. along n. root into SC </li></ul></ul><ul><ul><li>Absorbed by spinal segmental aa. or epidural vv. and then to brain and SC </li></ul></ul><ul><ul><li>*Quandt & Rawlings, “Reducing Post-operative pain for dogs: Local Anesthetic and Analgesic Techniques,” Compendium , pp. 101-111,1996. </li></ul></ul>
  43. 69. Opioid Agents <ul><li>More lipophilic = quicker onset = shorter acting </li></ul><ul><li>Most to least lipid soluble </li></ul><ul><ul><li>Fentanyl </li></ul></ul><ul><ul><li>Buprenorphine </li></ul></ul><ul><ul><li>Oxymorphone </li></ul></ul><ul><ul><li>Morphine </li></ul></ul>
  44. 70. Morphine <ul><li>Least lipid-soluble </li></ul><ul><li>Peak effect ~90 min. </li></ul><ul><li>May persist for 24 hours </li></ul><ul><li>Cephalad migration independent of volume </li></ul>
  45. 71. Other Opioid Agents <ul><li>Fentanyl </li></ul><ul><ul><li>Little use as a single agent </li></ul></ul><ul><ul><li>Does not extend more than 2 spinal segments from site </li></ul></ul><ul><ul><li>Useful in combination with morphine </li></ul></ul><ul><li>Buprenorphine </li></ul><ul><ul><li>Local action </li></ul></ul><ul><ul><li>Slightly longer acting than fentanyl </li></ul></ul><ul><li>Oxymorphone </li></ul><ul><ul><li>Has been used successfully </li></ul></ul><ul><ul><li>Slightly less duration than morphine </li></ul></ul>
  46. 72. Side Effects of Opioids <ul><li>Pruritis at affected dermatomes </li></ul><ul><ul><li>Especially with morphine </li></ul></ul><ul><li>Delayed respiratory depression </li></ul><ul><ul><li>Up to 24 hours with morphine </li></ul></ul><ul><ul><li><2% of humans </li></ul></ul><ul><ul><li>Not clinically significant in companion animals </li></ul></ul><ul><li>Posterior ataxia </li></ul><ul><li>Urine retention </li></ul><ul><ul><li>Detrusor m. weakness </li></ul></ul><ul><ul><li>Up to 24 hrs post morphine/oxymorphone </li></ul></ul><ul><ul><li>*Hansen, B. “Epidural Anesthesia,” Current Veterinary therapy , XIII. p. 128 </li></ul></ul>
  47. 73. Intrathecal Injections <ul><li>Accidental entrance into subarachnoid space </li></ul><ul><li>May see significant central effects </li></ul><ul><ul><li>Dogs: sedation and miosis </li></ul></ul><ul><ul><li>Cats: agitation and mydriasis </li></ul></ul><ul><li>Respiratory depression </li></ul><ul><li>Hyperesthesia </li></ul><ul><li>If aware of intrathecal location: </li></ul><ul><ul><li>Reduce by 30-75% of epidural dose </li></ul></ul><ul><ul><li>Preservative-free, w/o epinephrine </li></ul></ul>
  48. 74. Opioids and MAC <ul><li>Morphine proven to reduce halothane MAC in dogs </li></ul><ul><ul><li>42% reduction in HL </li></ul></ul><ul><ul><li>35% reduction in FL </li></ul></ul><ul><li>Morphine proven to reduce isoflurane MAC in cats </li></ul><ul><ul><li>31% reduction using tail clamp </li></ul></ul><ul><ul><li>*J.E. Ilkiw, Balanced Anesthetic techniques in dogs and cats , pp. 31-36., 1999 </li></ul></ul>
  49. 75. Synergism of Opioids and Locals <ul><li>Post-op combination of morphine and bupivacaine </li></ul><ul><ul><li>Superior analgesia to morphine alone </li></ul></ul><ul><ul><li>Longer than 24 hours of analgesia </li></ul></ul><ul><ul><li>*Torske & Dyson, “Epidural Analgesia and Anesthesia,” Veterinary Clinics of N. America ., p. 859-874, vol. 30, no. 4, July 2000. </li></ul></ul>
  50. 76. α 2 -agonists <ul><li>Xylazine, medetomidine, clonidine, detomidine </li></ul><ul><li>Cross dura to bind α 2 adrenoreceptors and act at dorsal horn (similar to opioids) </li></ul><ul><li>Work best when combined with other agents ie. Morphine </li></ul><ul><ul><li>*Hansen, B. “Epidural Anesthesia,” Current Veterinary therapy , XIII. p. 128 </li></ul></ul>
  51. 77. α 2 -agonists dosages <ul><li>Medetomidine and Morphine </li></ul><ul><ul><li>0.005mg/kg medetomidine </li></ul></ul><ul><ul><li>0.1mg/kg morphine </li></ul></ul><ul><ul><li>Effects for 13 hours </li></ul></ul>
  52. 78. Dissociatives <ul><li>Ketamine </li></ul><ul><ul><li>Blockade of α adrenoreceptors </li></ul></ul><ul><ul><li>Selective suppression of dorsal horn </li></ul></ul><ul><ul><li>Interactions with opioid receptors </li></ul></ul><ul><ul><li>1-2 hour duration </li></ul></ul><ul><ul><li>2.0mg/kg </li></ul></ul>
  53. 79. Combinations <ul><li>Opioids and ketamine </li></ul><ul><li>Opioids and local anesthetics </li></ul><ul><li>Alpha-2 and opioids </li></ul><ul><li>Bupivacaine, lidocaine and opioids </li></ul><ul><li>Etc. </li></ul>
  54. 80. Conclusions <ul><li>Epidurals are an important part of pain management </li></ul><ul><li>Multimodal therapy </li></ul><ul><li>Easy to implement </li></ul>