Neuraxial anaesthesia (Spinal, epdiural and caudal anesthesia)

Anatomy, Indication, contraindication, complications of spinal, epidural and caudal anesthesia

1. Neuraxial anesthesia(Spinal, Epidural & Caudal block) Dr. Tenzin Yoezer KGUMSB

2. Role of neuraxial anesthesia in anesthetic practice Studies have shown – reduces postop morbidity when used alone or in combination with GA Less convincing studies – it is associated reduced periop mortality Reduces the incidence of venous thrombosis, PE, cardiac complication, bleeding and transfusion, vascular graft occlusion, pneumonia, respiratory depression in the Upper abdominal and thoracic surgery Allows earlier return of bowel function Propose mechanism: avoidance of large dose of anesthetics and opioids, reduces hypercoagulable state, increases tissue blood flow, improving oxygenation from decreased splinting, enhances persistalsis , suppressing neuroendocrine stress hormone

3. The elderly sick patient SA needs little or no sedation – reduces postop delirium and cognitive dysfunction

4. Anatomy

5. Spinal cord

6. Dural sacextends : adult – S2 child – S3

7. Blood supply of spinal cord Supplied by 2 arteries: a) Single spinal artery – arises from vertebral artery Supplies anterior 2/3 b) Paired posterior spinal arteries – supplies posterior 1/3 Receives additional supply from intercostal artery from thoracic and lumbar 0ne important radicular artery arising from aorta – artery of Adamkiewz / arteria radicularis magna Typically unilateral and nearly arises from left side Provides major supply to anterior spinal cord Injury to this artery – anterior spinal artery syndrome

8. Mechanism of action Principal action is at nerve root Blockade of posterior nerve root – somatic and visceral sensation Anterior nerve root blockade – motor and autonomic outflow Somatic blockade Interrupts afferent transmission and abolishes efferent impulses Smaller and myelinated fibers – easily blocked Differential blockade – size and character of fiber, conc. of L A Judged by temperature sensitivity 2 segment cephalic whereas sensation block(pain ,light touch) is usually several more cephalic than motor blockade

9. Autonomic blockade Sympathetic outflow – thoracolumbar Exist from T1 – L2 Small and myelinated B fiber Parasympathetic outflow – craniosacral Neuraxial doesn't ’ t block vagus nerve Physiological response to neuraxial blockade is result of decreased sympathetic tone or unopposed parasympathetic tone, or both.

10. Cardiovascular manifestation Variable BP drop and decrease in HR Determined by level of block More cephalic – more extensive sympathetic block Vasomotor tone is primarily determined by sympathetic fibers from T5- L1 Blocking those fibers – vasodilation of venous capacitance vessels and pooling of blood in lower extremities and viscera. Effect of arterial vasodilation may be minimized by compensatory vasoconstriction above the block High spinal – blocks compensatory vasoconstriction and blocks cardiac sympathetic accelerator fibers (T1 – T4) Unopposed vagal tone – sudden cardiac arrest

11. Mx of hypotension and bradycardia Left uterine displacement in preganant woman Head-down position – autotransfusion IVF bolus 5-10 mL/kg Phenyephrine – direct alpha adrenergic, Vasoconstriction, increase SVR, reflexively increase bradycardia Ephedrine – direct and indirect beta adrenergic effect Increase heart contractility and HR,vasocontriction Epinephrine – 2-5 mcg bolus vasopressor

12. Pulmonary manifestation Minimal physiological alteration – diaphragm is innervated by C3-C5 Even with high thoracic – Vt is unchanged. Small decrease in vital capacity – loss of abdominal muscles But have to outweigh the advantages in severe chronic lung disease – reply on intercostal and abdominal muscles In high spinal – impairs intercostal and abdominal muscles - impairs effective cough and clearing of secretion Surgery above umbilical – instead of SA, thoracic epidural with diluted LA and opioids may be helpful Epidural analgesia – improves pulmonary outcome by reducing incidence of pneumonia and respiratory failure, improves oxygenation, decreases duration of ventilatory support

13. GI manifestation Neuraxial block-induced sympathectomy allows vagal dominance Leads to active peristalsis Therefore improves operative condition during intestinal surgery when used adjunct to GA Post op epidural analgesia – earlier return of GI function ** reduced hepatic blood flow due to decrease MAP

14. Urinary tract manifestation Little effect on kidney function – RBF is maintained with autoregulation Urinary retention – blockade of both sympathetic and parasympathetic outflow of lumbosacral Thus need urinary catheter/ minimal use of fluid

15. Metabolic and endocrine Surgical trauma and activation of somatic and visceral afferent nerve – activation of systemic neuroendocrine stress response Releases adrenocorticotropic hormones, cortisol, epinephrine, norepinephrine, vasopressin, RAS With neuraxial blockade: Partial suppression – major invasive abdominal/thoracic surgery Total blockade – lower extremities surgery

16. Clinical consideration to SA & EA Absolute ci controversial Lack of consent Infection at the site of injection Coagulopathy/bleeding diathesis Severe hypovolemia Increase ICP Relative CI Sepsis Uncooperative Preexisting neurology deficit Demyelinating lesion Stenotic valvular heart lesions LVO obstruction(hypertrophic obstructive cardiomyopathy) Severe spinal deformity Prior back surgery Complicated surgery Prolong operation Major blood loss Maneuvers that compromise respiration

17. Neuraxial blockade in the setting of Anti- cogulant and antiplatelet agent American society if reginal and Pain medicine issue guideline Incidence of epidural haematoma – 1:150,000

18. Oral antiplatelet drugs Ticlopidine – 14 days Clopidogrel – 7days Prasugrel – 7-10 days Ticagrelor – 5 days Abiciximab – 48 hr Eptifibatide – 8 h Metabolite of clopidogrel and prasugrel inhits P2Y12 receptors – inhibits platelet aggregation

19. Standard UFH Mini-dose SC prophylaxis – not CI

20. Patient position Sitting – “angry cat back” Lateral decubitus – fetal position Buie’s ( Jacknife ) position

21. Factors influencing level of spinal block Most important factors Baricty of anesthetic solution Position of the patient During injection Immediately after injection Drug dose: large dose more cephalic Site of injection Other factors Age CSF Curvature of the spine Drug volume Intra-abdominal pressure Needle direction: cephalic vs lateral/ caudad Patient height pregnancy

22. Position of the spine With normal spine anatomy: apex of thoracolumbar curvature is T4 In supine position hyperbaic solution produce block below T4 “Glass spine effect”

23. Specific gravity of CSF = 1.003 to 1.008 at 37 o C Hyperbaracity = adding glucose Hypobaricity = adding steril water/fentanyl Lumbar CSF inversely correlates with dermatomes spread Increase abdominal pressure – decrease CSF – greater dermatomal spread Eg : epidural vein engorgement, pregnancy, ascites, large abdominal tumor, obesity Age related low volume CSF Kyphoscolosis – low volume CSF

24. Spinal anesthetic agents

25. Epidural anesthesia

26. Epidural anesthesia Performed at lumbar, thoracic, cervical, sacral( caudual block) Content of epidural space: Nerve root - travel in the space laterally Fatty connective tissue Lymphatics Venous ( Batsons ) plexus Septa/connective tissue bands – reason for unilateral block

27. Angulation of epidural needle Note that acute angle (30 -50oC is required for thoracic whereas only slightly cephalid orientation is required for cervical and lumbar

28. Epidural activation Volume and conc. in epidural is larger- high chance of toxicity if given intrathecally or intravascular if full dose given To safegaurd – test dose / increamental dose Classic test dose: 3 mL of 1.5% lidocaine with 1:200,00 epiephrine (0.005 mg/mL) Intravacular injection: tachycardia, increasing size of T wave

29. Caudad block

30. Dosage – 0.5 -1 mg/kg of 0.125% to .25% bupi / ropi with or without epinephrin ***Armitage formula: 0.25% 0f bupi 0.5 mL/kg for lumbosacral 1 mL/kg for thoraco -lumbar 1.25 mL/kg for mid thoraci Opiods , morphine can be included Anorectal surgery: 15-20mL of 1.5% to 2% lidocaine with or without epi May add 50-100mcg Fentanyl **Avoid caudal block in Pionidal cyst- risk of infection

31. Factors affecting level of block Is not predictable as SA Generally in Aduly 1-2 mL of LA per segment block is accepted Eg : to achieve T4 sensory level from L4/5 would injection require 12-24 mL For segmental or analgesic block, less volume is required

32. Factors affecting level of block 1) Age – dose requirement decreases with age (probably due to age related decrease in the size of compliance of epidural space) 2) Height – shorter require 1mL/segment, taller 2mL/segment 3) Gravity 4) Additive to LA – Opioids affects quality of block than duration Epinephrine 5mcg/mL prolongs duration by decreasing vascular absorption and reduces peak systemic blood volume

33. Epidural agents Following initial 1-2mL/segment, repeated dose on fixed interval until desired dose is achieved Once some regression in sensory level has occurred – 1/3 or ½ of initial activation dose is reinjected at incremental dose Previously chlorprocaine with bisulfite was associated with neurotoxicity, with EDTA severe backache(?local hypocalcemia) Surgical anesthesia – 0.5% Bupivacaine 0.75% Bupi no longer used in obstetric – cardiac arrest after accidental IV injection 0.0625% Bupi fro Labour analgesia Ropivacaine produces less motor block than at Bupi at similar conc maintaining satisfactory sensory block

34. LA pH adjustment LA solution is acidic for cheamically stable and bacteriostatic Addition of epinephrine makes more acidic than palin Weak bases – primarily exist as ionic form Onset of action is slow with low pH Need incharged ion to cross lipid membrane Addition of NaHCO2 (1mEq/10mL) speeds onset With Bupivacaine above pH 6.8, NaHCO2 precipitates and thus not added

35. Failed epidural block 1) False epidural space – Soft ligament Entry into paraspinous muscle Intrathecal Subdural Intravenous 2) Unilateral block – withdraw 1-2 cm Reinject and turn pt to unblocked side 3) Segmental sparing – due to septation Additional LA and turning to unblocked side 4) Sacral sparing – large nerve root of L5, S1, S2 and delay onset Elevate the bed and reinject the LA 5) Visceral pain during traction despite good block – visceral fibers that travel with vagus nerve isresponsible

36. Caudual block

37. Commonly employed to peadiatric surgery with GA in surgeries below diaphragm – mainly to avoid toxic effect from GA In adult used in anorectal surgery Needle/catheter penetrates sacrococcygeal ligament Dural sac extends till S1 in adult and S3 in infants ( high chance of intrathecal injection)

38. Complication of neuraxial block Large survey shows low incidence of serious compliction ASA closed claim project data over 20yr(1980 – 1999): Regional anesthesia accounts for 18% liability Temporary/ nondisabling -13% Permanent nerve injury – 10% Permanenant brain damage – 8% Other permanent injuries – 4% Majority of claim involved lumbar epidural (42%), spinal anesthesia (34%). Occurs mostly in obstetric patients

39. A) Complication associated with excess responses to appropriately placed drug 1) High neural blockade can occur both in SA and EA Casues : Excessive dose Failure to reduce standard doses in selected pts ( elderly, pregnant, obese, short stature) Unusual sensitivity/ speed of LA Clinical features: Dyspnea,numbness or weakness of UL, nausea, hypotension Mx : Reassurance to pt O2 Treatment of bradycardia and hypotension

40. 2) High spinal 3) Total spinal SA ascending into cervical levels cases severe hypotension, bradycardia, and respiratory insufficiency Unconsciousness, apnea, and hypotension resulting from high level of anesthesia are referred to as “HIGH SPINAL”, or when it extends to cranial nerves – ”TOTAL SPINAL” Apnea is result of severe sustained hypotension and medullary hypoperfusion Mx of high/total spinal: Supporting ventilation Supplementing oxygen Supporting circulation- fluids, vasopressors, fluid Intubation if necessary/ indicated

41. 4) Cardiac arrest during SA High incidence -1:1500 Many cases were preceded by bradycardia. Many cases in young and healthy pts Prevention: Correction of hypovolemia Prompt treatment of hypovolemia and bradycardia

42. 5) Urinary retention Blockade of S2-4 roots – decrease urinary bladder tone and inhibits voiding reflex Other complications: 6) Anterior spinal artery syndrome 7) Horner syndrome

43. B) Complication associated with needle or catheter insertion 1) Inadequate anesthesia or analgesia Inversely proportional to experience Movement of needle during injection Incomplete entry of needle opening into the space Injection of LA solution into nerve root sleeve

44. 2) Intravascular injection CNS – tinnitus, metallic test, circumoral numbness,seizure , unconscious CVS – hypotension, arrhythmias, depressed contractility Common in epidural and caudual since SA uses small dose Prevention: Aspirating before injection Test dose Incremental dose Mx - ACLS 20% Lipid emulsion (1.5 mL/kg bolus, 0.25 mL/kg/min or 15 mL/kg/h) Rank of LA potency is same rank in producing seizure and cardiac toxicty Levobupivacaine , Ropivacaine , Bupivacaine, Tetracaine >lidocaine, mepivacaine > chloroprocaine

45. 3) Total spinal anesthesia Accidental injection into intrathecal during epidural and caudal 4) Subdural injection Can happen during several attempts for EA Onset is 15- 30 minutes ( compared to rapid onset in intrathecal) and is patchy block Can manifest as high spinal block 5) Back ache Due to tissue trauma while inserting needle Bruising and local inflammatory response with or without reflex muscle spasm Usually mild and self limiting May last for few weeks – subsides by PCM, NSAIDs Have to consider epidural haematoma or abscess *** majority of the population has chronic backache

46. 6) Neurological injury a) nerve root damage b) Spinal cord injury c) cauda equinal syndrome More perplexing /distressing Must rule out epidural hematoma and abscess Nerve Root or Cord(if above L1 in adult and L3 in children) may be injured Most resolve spontaneously but, some are permanent If sustained paresthesia during procedure – immediately withdraw needle. Stop injection immediately if there is pain 7) Dural puncture/leak PDPH Diplopia Tinnitus

47. 8) Epidural/spinal hematoma Needle or Cather trauma to epidural vein Incidence of Spinal hematoma – 1: 150,000 For epidural hematoma – 1: 220,000 Onset is sudden ( compared to epidural abscess) Red flag symptoms: Sharp back ache and leg pain with motor weakness or sphincter dysfunction, or both If suspected: urgent CT/ MRI Neurological consultation Outcome – good neurological outcome in prompt surgical decompression Prevention: avoid neuraxail with coagulopathy, significant thrombocytopenia, platelet dysfunction, those on fibrinolytic or thrombolytic therapy

48. 9) Meningitis and arachnoiditis Due to contamination of the equipment, solution or organism tracked in from the skin Indwelling catheter may colonize with skin organism Strict aseptic technique- esp in obstetric where family members want to see the procedure Family members should also wear mask and gown

49. 10 ) Epidural abscess Spinal epidural abscess is rare but potentially devastating complication Incidence varies from 1:6500 to 1:500,000 epidural Most commonly seen in epidural catheter There are 4 classic stages of EA: 1 st stage – back pain that is intensified by percussion over the spine 2 nd stage – nerve root or radicular pain 3 rd stage – motor and sensory deficit or sphincter dysfunction 4 th stage – paraplegia or paralysis

50. Prognosis correlates with degree if neurological dysfunction at the time of diagnosis Clue – fever and back pain after epidural anesthesia Once suspected, remove epidural catheter and tip send for culture Injection site – examined for signs of infection: pus if present for culture Blood culture If highly suspicious start antibiotic that covers staphylococcus ( aureus and epidermis) MRI/CT spine to rule out Urgent consultation with neurosurgical and infectious specialist Surgery – in addition to pus drainage, laminectomy Prevention: Minimizing catheter manipulation and maintaining closed system Using micropore (0.22um) bacterial filter Removing after defined time( some clinician remove after 4 days)

51. 11) Shearing of an epidural catheter Risk of shearing and breaking of epidural catheter if withdrawn through needle If catheter breaks off within space – observe the patient If superficial – remove surgically

52. C) Complication associated with drug toxicity 1) LAST Excessive absorption of LA from epidural or caudal Rare if appropriate dose is administered 2) Transient neurological symptoms(TNS) Also referred as transient radicular irradiation Characterized by back pain radiating to leg without sensory or motor deficit, occurring after resolution of SA and resolving within few days Commonly associated with hyperbaric lidocaine (12%), tetracaine (2%), Bupivacaine(1%), mepivacaine , prilocaine , procaine, subarachnoid ropivacaine Pathogenesis – conc dependent neurotoxicity of LA Incidence is greatest among outpatient, particularly male pt undergoing surgery in lithotomy position. Less incidence among other than lithotomy position 3) Cauda equina syndrome

53. Thanks Morgan and Makill