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

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