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Regional Anesthesia Spinal and epidural (caudal) Anesthesia Dr. Mohamed Abdelraheem

Regional Anesthesia Spinal and epidural (caudal) Anesthesia Dr. Mohamed Abdelraheem. Objectives Describe anatomy of spinal canal Identify anatomic landmarks for proper placement of a spinal needle Define appropriate steps for placement of spinal, epidural, or caudal needle

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Regional Anesthesia Spinal and epidural (caudal) Anesthesia Dr. Mohamed Abdelraheem

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  1. Regional Anesthesia • Spinal and epidural (caudal) Anesthesia • Dr. Mohamed Abdelraheem

  2. Objectives • Describe anatomy of spinal canal • Identify anatomic landmarks for proper placement of a spinal needle • Define appropriate steps for placement of spinal, epidural, or caudal needle • Distinguish level of anesthesia after administration of regional • State factors affecting level and duration of spinal vs. epidural block • Explain potential complications and corresponding treatments associated with administration of regional anesthetics

  3. Spinal Anatomy • 33 Vertebrae • 7 Cervical • 12 Thoracic • 5 Lumbar • 5 Sacral • 4 Coccygeal • High Points: C5 & L5 • Low Points: T5 & S2

  4. Spinal Cord • Adult • Begins: Foramen Magnum • Ends: L1 • Newborn • Begins: Foramen Magnum • Ends: L3 • Terminal End: Conus Medullaris • Filum Terminale: Anchors in sacral region • Cauda Equina: Nerve group of lower dural sac Spinal Cord

  5. Saggital Sections • Supraspinous Ligament • Outer most layer • Intraspinous Ligament • Middle layer • Ligamentum Flavum • Inner most layer

  6. Space that surrounds the spinal meninges • Potential space • Ligamentum Flavum • Binds epidural space posteriorly • Widest at Level L2 (5-6mm) • Narrowest at Level C5 (1-1.5mm) Epidural Space

  7. Spinal Meninges • Dura Mater • Outer most layer • Fibrous • Arachnoid • Middle layer • Non-vascular • Pia • Inner most layer • Highly vascular • Sub Arachnoid Space • Lies between the arachnoid and pia

  8. Vasoconstrictors • Prolong duration of spinal block • No increase in duration with lidocaine & bupivacaine • Significant increase with tetracaine (double duration) Spinal Pharmacology

  9. Factors Effecting Distribution • Site of injection • Shape of spinal column • Patient height • Angulation of needle • Volume of CSF • Characteristics of local anesthetic • Density • Specific gravity • Baracity • Dose • Volume • Patient position (during & after) Spinal Pharmacology

  10. Anesthesia level is determined by patient position • Uptake of local anesthetic occurs by diffusion • Elimination determines duration of block • Lipid solubility decreases vascular absorption • Vasoconstriction can decrease rate of elimination Spinal Pharmacology

  11. Blockade of Sympathetic Preganglionic Neurons • Send signals to both arteries and veins • Predominant action is venodilation • Reduces: • Venous return • Stroke volume • Cardiac output • Blood pressure • T1-T4 Blockade • Causes unopposed vagal stimulation • Bradycardia • Associated with decrease venous return & cardioaccelerator fibers blockade • Decreased venous return to right atrium causes decreased stretch receptor response Cardiovascular Effects

  12. Treatment • Best way to treat is physiologic not pharmacologic • Primary Treatment • Increase the cardiac preload • Large IV fluid bolus within 30 minutes prior to spinal placement, minimum 1 liter of crystalloids • Secondary Treatment • Pharmacologic • Ephedrine is more effective than Phenylephrine Hypotension

  13. Healthy Patients • Appropriate spinal blockade has little effect on ventilation • High Spinal • Decrease functional residual capacity (FRC) • Paralysis of abdominal muscles • Intercostal muscle paralysis interferes with coughing and clearing secretions • Apnea is due to hypoperfusion of respiratory center Respiratory System

  14. Spinal Technique • Preparation & Monitoring • EKG • NBP • Pulse Oximeter • Patient Positioning • Lateral decubitous • Sitting • Prone (hypobaric technique)

  15. Midline Approach • Skin • Subcutaneous tissue • Supraspinous ligament • Interspinous ligament • Ligamentum flavum • Epidural space • Dura mater • Arachnoid mater • Paramedian or Lateral Approach • Same as midline excluding supraspinous & interspinous ligaments Spinal Technique

  16. Spinal Anesthesia Levels

  17. Indications & Advantages • Full stomach • Anatomic distortions of upper airway • TURP surgery • Obstetrical surgery (T4 Level) • Decreased post-operative pain • Continuous infusion Spinal Anesthesia

  18. Contraindications • Absolute: • Refusal • Infection • Coagulopathy • Severe hypovolemia • Increased intracranial pressure • Severe aortic or mitral stenosis • Relative: • Use your best judgment Spinal Anesthesia

  19. Complications • Failed block • Back pain (most common) • Spinal head ache • More common in women ages 13-40 • Larger needle size increase severity • Onset typically occurs first or second day post-op • Treatment: • Bed rest • Fluids • Caffeine • Blood patch Spinal Anesthesia

  20. Fluid Test for CSF Return • Clear • Free flow • Aspiration into syringe • Litmus Paper • Urine dip stick • Temperature • Taste… If you’re man enough… Spinal Anesthesia

  21. Increase pressure of CSF by placing blood in epidural space • If more than one puncture site use lowest site due to rosteral spread • May do no more than two • 95% success with first patch • Second patch may be done 24 hours after first Blood Patch

  22. Spread of Local Anesthetics • First to cauda equina • Laterally to nerve rootlets and nerve roots • May defuse to spinal cord • Primary Targets: • Rootlets • Roots • Spinal cord Spinal Anesthesia

  23. Epidural Anatomy • Safest point of entry is midline lumbar • Spread of epidural anesthesia parallels spinal anesthesia • Nerve rootlets • Nerve roots • Spinal cord

  24. Epidural Anesthesia • Order of Blockade • B fibers • C & A delta fibers • Pain • Temperature • Proprioception • A gamma fibers • A beta fibers • A alpha fibers

  25. Test Dose: 1.5% Lido with Epi 1:200,000 • Tachycardia (increase >30bpm over resting HR) • High blood pressure • Light headedness • Metallic taste in mouth • Ring in ears • Facial numbness • Note: if beta blocked will only see increase in BP not HR • Bolus Dose: Preferred Local of Choice • 10 milliliters for labor pain • 20-30 milliliters for C-section Epidural Anesthesia

  26. Distances from Skin to Epidural Space • Average adult: 4-6cm • Obese adult: up to 8cm • Thin adult: 3cm • Assessment of Sensory Blockade • Alcohol swab • Most sensitive initial indicator to assess loss of temperature • Pin prick • Most accurate assessment of overall sensory block Epidural Anesthesia

  27. Complications • Penetration of a blood vessel • Hypotension (nausea & vomiting) • Head ache • Back pain • Intravascular catheterization • Wet tap • Infection Epidural Anesthesia

  28. Caudal Anesthesia • Anatomy • Sacrum • Triangular bone • 5 fused sacral vertebrae • Needle Insertion • Sacrococcygeal membrane • No subcutaneous bulge or crepitous at site of injection after 2-3ml

  29. Post Operative Problems • Pain at injection site is most common • Slight risk of neurological complications • Risk of infection • Dosages • S5-L2: 15-20ml • S5-T10: 25ml Caudal Anesthesia

  30. Blockade of 5 Nerves • Tibial nerve • Largest • Heal & medial side sole of foot • Superficial perineal nerve • Branch of common perineal • Dorsal (top) portion of foot • Saphenous nerve • Branch of femoral nerve • Medial side of leg, ankle, & foot • Sural nerve • Branch of posterior tibial nerve • Posterior lateral half of calf, lateral side of foot, & 5th toe • Deep perineal nerve • Continuation of common perineal nerve Ankle Block

  31. Ankle Block

  32. Brachial Plexus • Musculocutaneous Nerve • Median Nerve • Ulnar Nerve • Radial Nerve

  33. Axillary Block • Position • Head turned away from arm being blocked • Abduct to 90º • Forearm is flexed to 90º • Palpate brachial artery for pulse

  34. Advantages • Provides anesthesia for forearm & wrist • Fewer complications than a supraclavicular block • Limitations • Not for shoulder or upper arm surgery • Musculocutaneous nerve lies outside of the sheath and must be blocked separately • Complications • Intravascular injection • Elevated bleeding time increases risk for hematoma Axillary Block

  35. Dosing • Lidocaine 1% 30-40ml • Etidocaine 1% 30-40ml • Bupivacaine 0.5% 30-40ml • Note 40ml is most common dose Axillary Block

  36. Other Blocks

  37. Basic Labs: • Platelet counts >50,000 (minimum), prefer >100,000 • Prothrombin time (PT) & Partial thrombin time (PTT) • Note that PT & PTT require approx. 60-80% loss of coagulation activity before becoming abnormal • Thrombin time • Hemoglobin & Hematocrit • Bleeding time Regional Anesthesia in the Anticoagulated Patient

  38. Heparin: Reverse with FFP or Protamine • IV discontinue 4 hours prior to block • SQ can block one hour prior to dose • Do not D/C cath until 4 hours after heparin D/C’d & obtain normal lab values • Lovenox (LMWH): No Reversal • Stop 10 days prior to surgery • Post op D/C cath 2 hours prior or 10 hours after first dose • Coumadin: Reverse with Vit K or FFP • Stop 7 days prior to surgery • Check PT/INR Regional Anesthesia in the Anticoagulated Patient

  39. Plavix: No Reversal • Stop 5-10 days prior to surgery • NSAIDS: No Reversal • May be safe for regional block • Ideal to stop 5 days prior to surgery • ASA: No Reversal • Stop 7-10 days prior to surgery Regional Anesthesia in the Anticoagulated Patient

  40. Objectives • Classify each local as an ester or amide • State the mechanism of action for local anesthetics • State the metabolism for esters & amides • Identify ranking of absorption by arterial flow for give anatomic regions • Discuss how lipid solubility and vasoconstriction affect the potency and duration of locals • Discuss the etiology of an allergic reaction to local anesthetics • Understand how pKa effects speed of onset of locals Local Anesthetics

  41. Speed of Onset • Based on pKa • Lower pKa equals more un-ionized at pH 7.4 • Un-ionized drug penetrates lipid bilayer of nerve • More un-ionized form of local equals faster penetration, which equals quicker onset of action • Local anesthetics + NaHCO3 (High pH) = more un-ionized Local Anesthetics

  42. Local Anesthetics

  43. Esters • Procaine • Chloroprocaine • Tetratcaine • Cocaine • Metabolism • Hydrolysis by psuedo- cholinesterase enzyme • Amides • Lidocaine • Mepivacaine • Bupivacaine • Etidocaine • Prilocaine • Ropivacaine • Metabolism • Liver Local Anesthetics

  44. Toxicity & Allergies • Esters: Increase risk for allergic reaction due to para-aminobenzoic acid produced through ester-hydralysis • Amides: Greater risk of plasma toxicity due to slower metabolism in liver Local Anesthetics

  45. Local Anesthetics • Potency • The greater the oil/water partition coefficient the greater the lipid solubility • The more lipid soluble the greater the potency

  46. Duration of Action • The degree of protein binding is the most important factor • Lipid solubility is the second leading determining factor • Greater protein bound + increase lipid solubility = longer duration of action Local Anesthetics

  47. Characteristics of Local Anesthetic Agents

  48. Determinants of Blood Concentrations • Loss of local anesthetic is primarily through vascular absorption • Vasoconstrictors decrease the rate of absorption & increase duration of action • Ranking rate of absorption by arterial blood flow • Highest to lowest • Tracheal • Intercostal muscles • Caudal • Paracervical • Epidural • Brachial plexus • Subarachnoid • Subcutaneous Local Anesthetics

  49. Hyperbaric • Typically prepared by mixing local with dextrose • Flow is to most dependent area due to gravity • Hypobaric • Prepared by mixing local with sterile water • Flow is to highest part of CSF column • Isobaric • Neutral flow that can be manipulated by positioning • Very predictable spread • Increased dose has more effect on duration than dermatomal spread • Note: Be cognizant of high & low regions of spinal column Local Anesthetics & Baracity

  50. Mechanism of Action • Un-ionized local anesthetic defuses into nerve axon & the ionized form binds the receptors of the Na channel in the inactivated state

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