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🏥 Neuraxial Anesthesia: Spinal and Epidural — A Professor's Lecture

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PART I: FOUNDATIONAL ANATOMY — Know This Cold

Layers Traversed (Posterior → Anterior)

Critical Landmarks

• Tuffier's line (intercristal/bicristal line): connects the two iliac crests → crosses at L4 spinous process or L4–L5 interspace in adults
• Conus medullaris terminates at L1 in adults (L3 in neonates) — always insert below L2 to avoid cord injury
• Dural sac terminates at S2 — caudal punctures above this risk dural puncture

The Epidural Space

• Posteriorly: Ligamentum flavum and laminae
• Anteriorly: Posterior longitudinal ligament + vertebral bodies
• Laterally: Pedicles and intervertebral foramina

📌 Professor's pearl: The epidural space is a potential space with sub-atmospheric (negative) pressure at lumbar levels — the basis of the "hanging drop" technique. It communicates freely with the paravertebral spaces through the intervertebral foramina, explaining why large epidural volumes can spread widely and why one-sided blocks occur when septa are present.

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PART II: SPINAL ANESTHESIA (Subarachnoid Block)

Mechanism of Action

Indications

• Lower abdominal surgery (hernia, appendectomy)
• Urological procedures (TURP, cystoscopy) — awake patient monitors for TUR syndrome
• Obstetric: Cesarean section, instrumental delivery
• Lower extremity orthopedic surgery (hip, knee arthroplasty)
• Perineal/anorectal/perianal surgery
• Gynecological procedures

Absolute Contraindications

• Patient refusal
• Local infection at needle site
• Severe hypovolemia/hemodynamic instability
• Raised intracranial pressure
• Coagulopathy (INR >1.4, platelets <80,000)

Relative Contraindications

• Fixed cardiac output states (severe AS, HOCM)
• Prior spine surgery
• Anatomical abnormalities (severe scoliosis, spina bifida)
• Demyelinating disease (controversial)

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THE PROCEDURE — Step by Step

Step 1: Pre-procedure Checklist

• Informed consent, IV access established, monitoring applied (SpO₂, NIBP, ECG)
• Resuscitation equipment checked: airway cart, vasopressors (ephedrine 5–10 mg aliquots or phenylephrine 50–100 µg), atropine
• Preload with 500–1000 mL crystalloid (co-load is now preferred over pre-load)

Step 2: Positioning — Two Options

• Patient sits at edge of table, feet on a stool
• Arms folded over a pillow, chin tucked to chest
• Patient "arches back like an angry cat"
• Advantage: maximally opens interspaces, easier landmark palpation in obese patients, produces gravity-dependent pooling of hyperbaric solution (useful for saddle block)

• Patient lies in fetal position, knees drawn to chest
• The side to be operated on placed dependently (for unilateral block with hyperbaric solution)
• Advantage: better tolerated in anxious or pre-sedated patients

Step 3: Sterile Preparation

• Full sterile gown and gloves, mask, hat — this is central neuraxial anesthesia; treat it as an operating procedure
• Cleanse skin with chlorhexidine 0.5–2% in alcohol (preferred over povidone-iodine; superior bacterial kill, but allow to dry completely — avoid intrathecal contamination)
• Drape the field

Step 4: Identify the Interspace

• Palpate Tuffier's line → L4–L5 interspace
• Preferred interspace in adults: L3–L4 or L4–L5 (below the conus)
• Identify midline using spinous process tips

Step 5: Local Infiltration

• Raise a skin wheal with 1–2 mL of 1–2% lidocaine using a 25G needle
• Infiltrate subcutaneous tissues and deeper interspinous ligament

Step 6: Needle Selection — Critical Choice

Rule: Always use a 25G or smaller pencil-point needle (Whitacre or Sprotte) in ambulatory patients and anyone at risk for PDPH (young women, obstetric patients).

Step 7: Needle Insertion — Midline Approach

1. Insert the introducer (22G) first, anchored firmly in the interspinous ligament
2. Insert the spinal needle through the introducer, bevel/opening oriented longitudinally (parallel to dural fibres) — this separates rather than cuts the longitudinal fibres, reducing PDPH
3. Advance with slow, steady pressure — you will feel two distinct "pops":
   • First pop: Through the ligamentum flavum
   • Second pop: Through the dura-arachnoid (entry into subarachnoid space)
4. Remove the stylet and wait for free flow of clear CSF — this confirms subarachnoid placement

📌 If no CSF appears: Rotate needle 90°; if still absent, suspect bevel against dura → slightly advance or withdraw. Never inject without confirming CSF.

Paramedian (Lateral) Approach

• Useful in elderly patients with calcified interspinous ligaments, kyphoscoliosis
• Insert 1 cm lateral and 1 cm caudal to spinous process tip, angle medially and cephalad
• Avoids supraspinous and interspinous ligaments
• Goes directly to ligamentum flavum and dura

Step 8: Drug Injection

• Attach pre-drawn syringe (or use the barbed/Luer-lock connection)
• Aspirate 0.2–0.5 mL CSF to confirm position ("barbotage" can help mixing but is not mandatory)
• Inject slowly at 0.2 mL/sec — too rapid → turbulent spread, unpredictable block height
• Re-aspirate at end to confirm continued intrathecal position

Step 9: Positioning After Injection

• Position the patient immediately for the desired block level (within 5–10 min before drug fixes to tissue)
• Hyperbaric solutions: dependent spread → patient positioning controls level
• Isobaric solutions: less gravity-dependent spread, more predictable height based on dose

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Drugs and Doses for Spinal Anesthesia

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Factors Controlling Block Height (Miller's Table 41.3)

• Baricity of solution — most reliable method of controlling spread
• Patient position during and after injection
• Dose — higher dose → more cephalad spread
• Site of injection — higher interspace → higher block

• Age (elderly → smaller doses needed; reduced CSF volume)
• Height (minimal effect clinically)
• Pregnancy (raised intraabdominal pressure → reduced subarachnoid volume)
• Obesity → reduced subarachnoid space
• CSF volume varies: neonates 10 mL/kg → adults 1.5–2 mL/kg

Required Dermatomal Levels for Common Surgeries

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PART III: EPIDURAL ANESTHESIA

How Epidural Differs from Spinal

Indications

• Labor analgesia (most common use worldwide)
• Major abdominal, thoracic, pelvic surgery
• Postoperative pain management (catheter technique)
• Chronic pain management
• Thoracic epidural for ICU patients (reduces post-thoracotomy pulmonary complications)

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THE PROCEDURE — Step by Step

Step 1: Pre-procedure (Same as Spinal)

Step 2: Positioning

• Lateral decubitus (preferred for catheter placement): Spine flexed maximally (chin to chest, knees to abdomen) → widens the interspinous spaces and pulls the spinal cord anteriorly, expanding the posterior epidural space
• Sitting position: Excellent for obese patients and thoracic epidurals

Step 3: Sterile Preparation

Step 4: Needle — The Tuohy Needle

• Curved Huber tip — deflects the catheter cephalad once the epidural space is entered
• Markings at 1-cm intervals — allow precise depth tracking
• Fitted with a Luer-lock cap for the LOR syringe

Step 5: Identify the Epidural Space — Two Techniques

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1. Advance the Tuohy needle through skin and into the interspinous ligament (depth ~3–4 cm in average adult)
2. Remove the stylet; attach the LOR syringe (glass syringe preferred — low friction, clear visualization) filled with:
   • Air (2–3 mL): historically used; risk of pneumocephalus, venous air embolism, patchy block
   • Saline (2–3 mL): now preferred — no compressibility artifacts, denser tactile feedback, no gas complications
3. Apply constant gentle forward pressure on the plunger while simultaneously advancing the needle millimeter by millimeter
4. As long as the needle tip is in the ligamentum flavum → high resistance → plunger springs back
5. The moment the needle tip enters the epidural space → sudden loss of resistance → the syringe plunger advances freely with no springback

📌 Tactile teaching: Imagine pressing your thumb on a syringe filled with air — while in the ligament it feels like pressing against a hard rubber ball. When the epidural space is entered, that resistance vanishes completely in a split second. You will feel this the first time you do it correctly and never forget it.

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• Fill the hub of the needle with a drop of saline
• As needle advances through ligamentum flavum, the drop remains stationary
• On entering the epidural space (sub-atmospheric pressure) → the drop is "sucked in" by negative pressure
• Less reliable, requires adequate negative pressure (works less well in thoracic region or obese patients)
• Historical use; LOR has largely replaced it

Step 6: Depth Assessment

• Average depth to epidural space in adults: 4–6 cm (midline lumbar)
• Rule of thumb: approximately equal to the distance from the skin to the ligamentum flavum
• Depth > 7–8 cm: high risk of false loss of resistance or intravascular placement
• Note the depth marking on the needle for subsequent catheter placement

Step 7: Catheter Insertion

1. Through the Tuohy needle, thread a 20G epidural catheter
2. Advance catheter 4–6 cm beyond the needle tip (so 2–4 cm remains in the epidural space)
3. Hold the catheter firmly while removing the needle — catheter must not be pulled back through the needle (shearing risk)
4. Fix catheter at skin — most institutions use transparent dressings with a strain-relief loop

Step 8: Test Dose — Non-Negotiable

⚠️ Professor's warning: In parturients receiving oxytocin or during uterine contractions, tachycardia may be present at baseline, reducing the sensitivity of the epinephrine test dose. In beta-blocked patients, the HR criterion may be unreliable. Always combine with clinical assessment.

Step 9: Epidural Drug Administration

• Detect intravascular/intrathecal catheter migration between doses
• Titrate to the desired level
• Avoid catastrophic total spinal or LAST

• Fentanyl 50–100 µg (bolus) or 2–4 µg/mL (infusion) — rapid analgesia, reduces LA requirements
• Morphine 2–5 mg — long duration (12–24 h postoperative analgesia), delayed respiratory depression
• Clonidine 75–150 µg — enhances analgesia, useful in opioid-resistant patients

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PART IV: PHYSIOLOGICAL EFFECTS OF NEURAXIAL BLOCKADE

Cardiovascular

• Sympathetic block → arterial vasodilation (↓ SVR) and venodilation (↓ preload)
• Block of T1–T4 (cardiac accelerator fibers) → bradycardia — can be profound and sudden
• Hypotension is the most common complication — treat with:
  • Vasopressors: Phenylephrine (first-line in obstetrics — preserves uteroplacental flow) or ephedrine (mixed α/β — better for bradycardic patients)
  • Volume: crystalloid co-load
  • Positioning: left uterine displacement (obstetrics), Trendelenburg position

Respiratory

• Up to T4 level: minimal respiratory compromise — diaphragm (C3–C5) is unaffected
• Intercostal muscle paralysis begins at T1 — reduces forced expiration, cough effectiveness
• Total spinal anesthesia → diaphragmatic paralysis → respiratory arrest — manage with IPPV
• Patient subjective feeling of "can't breathe" is almost always from proprioceptive loss (can't feel chest moving), not true hypoventilation

Gastrointestinal

• Sympathetic block → parasympathetic dominance → increased peristalsis, contracted gut (good for surgical exposure)
• Nausea often from hypotension → treat hypotension first

Urinary

• S2–S4 block → detrusor paralysis → urinary retention — catheterize all surgical patients receiving neuraxial anesthesia; monitor ambulatory patients carefully

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PART V: COMPLICATIONS — Recognition and Management

Hypotension

• Most common (20–33% of spinals for CS)
• Treat: phenylephrine infusion (100–150 µg/min titrated) now preferred over ephedrine in obstetrics; crystalloid co-load

Post-Dural Puncture Headache (PDPH)

• Occurs after dural puncture → CSF leaks → intracranial hypotension → traction on meningeal vessels and nerves
• Character: bilateral, frontal/occipital, postural (worse upright, better supine), may radiate to neck, tinnitus, diplopia (CN VI palsy)
• Incidence: 0.1–0.5% with 25–27G pencil-point spinal needles; up to 70% with 16G Tuohy (wet tap)
• Treatment:
  • Conservative: bed rest, hydration, caffeine, analgesics
  • Definitive: Epidural Blood Patch (EBP) — 15–20 mL autologous blood injected epidurally at the puncture level; 85–98% success rate

High/Total Spinal

• Excessive cephalad spread → hypotension, bradycardia, respiratory arrest, loss of consciousness
• Management: Secure airway immediately, CPR if needed, vasopressors, atropine

Local Anesthetic Systemic Toxicity (LAST)

• Most commonly from accidental intravascular injection
• Prodrome: circumoral numbness, metallic taste, tinnitus, agitation
• Severe: seizures, cardiovascular collapse (bupivacaine most cardiotoxic)
• Management: Airway/ABC, Intralipid 20% (1.5 mL/kg bolus), ACLS (avoid vasopressin, calcium channel blockers, lidocaine)

Epidural Hematoma

• Rare but catastrophic — most common with anticoagulated patients
• Presentation: back pain + progressive leg weakness/sensory loss
• Emergency: MRI, neurosurgical decompression within 6–8 hours to prevent permanent paraplegia
• Prevention: follow ASRA guidelines on anticoagulation timing

Transient Neurological Symptoms (TNS)

• Buttock/leg pain after spinal anesthesia (most common with lidocaine 5% hyperbaric)
• Self-limiting (24–72 hours), no permanent deficit
• Management: NSAIDs, reassurance
• Reason lidocaine is largely replaced by bupivacaine or chloroprocaine for ambulatory spinal

Cauda Equina Syndrome

• Permanent motor/sensory deficit of sacral nerve roots
• Associated with continuous spinal catheters and repeated dosing of 5% hyperbaric lidocaine
• Mechanism: pooling of high-concentration local anesthetic around sacral roots

Epidural Abscess

• Back pain + fever + neurological deficit days after epidural
• Diagnosis: MRI (most sensitive)
• Management: urgent surgical drainage ± antibiotics

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PART VI: COMBINED SPINAL-EPIDURAL (CSE) TECHNIQUE

Needle-Through-Needle Technique

1. Place Tuohy needle in epidural space (LOR confirmed)
2. Pass a long spinal needle (127 mm Whitacre) through the Tuohy needle until dura is punctured → CSF confirmed
3. Inject spinal dose (reduced — e.g., 7.5–10 mg hyperbaric bupivacaine for CS instead of 12.5–15 mg)
4. Remove spinal needle; thread epidural catheter
5. If spinal block inadequate → extend via epidural catheter

• Cesarean section (most common obstetric use — denser faster block than epidural alone)
• Long orthopedic cases (spinal provides initial block; epidural extends it)
• Labor analgesia (CSE provides fastest onset)

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PART VII: COMPARISON TABLE — SPINAL vs. EPIDURAL

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PART VIII: PROFESSOR'S KEY EXAMINATION POINTS

🧠 The examiner will ask these — know them precisely:

1. Why inject below L2? Spinal cord ends at L1 — below this is cauda equina, which is more resilient to needle injury than the cord itself
2. Why use pencil-point needles? They separate dural fibres longitudinally rather than cutting them → less CSF leak → less PDPH
3. What confirms subarachnoid placement? Free flow of clear CSF — never inject without this
4. What is the test dose and why? 3 mL lidocaine 2% + 15 µg epinephrine → detects intravascular (tachycardia) and intrathecal (motor block) placement
5. Hyperbaric bupivacaine mechanism? Denser than CSF → sinks dependently → gravity + patient position control spread
6. Why does epidural onset take 10–20 min? Drug must diffuse across dura, traverse epidural fat, and penetrate nerve roots — not in CSF, so no direct bathing of neural tissue
7. Ephedrine vs. phenylephrine for neuraxial hypotension? Phenylephrine = pure α-agonist = vasoconstriction without tachycardia, preserves uteroplacental flow → first-line in obstetrics. Ephedrine = mixed α+β = may cause fetal acidosis if used as primary agent in obstetrics, but preferred if bradycardia accompanies hypotension
8. ASRA anticoagulation guidelines: LMWH: wait 12 h (prophylactic) or 24 h (therapeutic) after last dose before neuraxial; catheter removal also requires these intervals
9. What is Batson's plexus? The valveless epidural venous plexus — explains why intravascular catheter placement is common (veins are thin-walled, multiple, engorged in pregnancy), and also why metastatic cancer can spread via this route
10. What is cauda equina syndrome? Permanent sacral nerve root damage from pooling of concentrated local anesthetic — avoid continuous spinal with lidocaine 5%

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• Miller's Anesthesia, 10e, Chapters 41 & 45
• Morgan & Mikhail's Clinical Anesthesiology, 7e, Chapter 45
• Barash's Clinical Anesthesia, 9e, Chapter 10
• Sabiston's Textbook of Surgery, Chapter 20

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Neuraxial Anesthesia: Spinal & Epidural — A Complete Lecture

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LECTURE 1: ANATOMY — The Foundation of Everything

Surface Landmarks

📌 Professor's pearl: Tuffier's line crosses L4, not L5 as many students say. It is the spinous process of L4, so the interspace immediately below it is L4–L5, and the interspace above is L3–L4. Your safest working interspaces in adults are L3–L4 and L4–L5 — both are below the conus medullaris.

Layers Traversed — Posterior to Anterior

1. Skin → local anesthetic wheal here
2. Subcutaneous fat → minimal resistance
3. Supraspinous ligament → connects tips of spinous processes; firmer resistance begins
4. Interspinous ligament → between adjacent spinous processes; softer, "spongy" feel
5. Ligamentum flavum → the most important tactile landmark: dense, rubbery yellow elastic fibers; thickest posteriorly (3–5 mm at lumbar level); produces a distinct, gritty resistance you will feel as "pushing through cartilage"
6. Epidural space → low/sub-atmospheric pressure; contains fat, Batson's venous plexus, lymphatics, nerve roots
7. Dura mater → tough, fibrous outer meningeal layer
8. (Subdural space — potential; clinically hazardous if a catheter enters here)
9. Arachnoid mater → delicate, the true barrier to CSF
10. Subarachnoid space → contains CSF — the target of spinal anesthesia
11. Pia mater → adherent to the cord

The Effect of Patient Flexion — Why We Flex the Spine

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LECTURE 2: SPINAL ANESTHESIA (Subarachnoid Block)

What It Is and How It Works

• Onset is rapid — 3–5 minutes
• Block is dense — profound sensory and motor blockade
• Only tiny volumes are needed (1.5–4 mL)
• Duration is fixed — one shot, cannot extend it (unless catheter used)

Indications

• Urological: TURP, cystoscopy (awake patient monitors for TUR syndrome/hyponatremia)
• Lower abdominal: hernia repair, appendectomy
• Orthopedic: hip arthroplasty, knee arthroplasty, femur fixation
• Obstetric: Cesarean section (most common use worldwide), instrumental delivery
• Gynecological: hysterectomy, D&C
• Perineal/anorectal: hemorrhoidectomy, pilonidal sinus (saddle block)
• Vascular: lower limb bypass

Contraindications

• Patient refusal
• Infection at the injection site (local sepsis)
• Uncorrected hypovolemia / hemodynamic instability
• Raised intracranial pressure
• Coagulopathy: INR >1.4, platelets <80,000, therapeutic anticoagulation

• Fixed cardiac output (severe aortic stenosis, HOCM) — sudden vasodilation may be lethal
• Prior back surgery at the same level
• Pre-existing neurological disease (controversial — document carefully)
• Severe scoliosis or spinal deformity
• Uncooperative patient

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STANDARD PROCEDURE — Step by Step

✅ Step 1: Pre-Procedure Setup

1. IV access secured (18G minimum — you may need to give vasopressors fast)
2. Monitoring: SpO₂ continuous, NIBP q2 minutes, ECG, capnography if sedated
3. Resuscitation drugs drawn up and labeled:
   • Ephedrine 5–10 mg/mL aliquots
   • Phenylephrine 50–100 µg/mL aliquots
   • Atropine 0.6 mg
   • Intralipid 20% available
4. Airway equipment immediately accessible
5. Fluid co-load: 500–1000 mL crystalloid (Hartmann's or normal saline) running as you start — co-load is now preferred over pre-load as it is more effective
6. Discuss with patient: procedure, expected sensations (warmth, heaviness in legs), what to report

✅ Step 2: Patient Positioning

✅ Step 3: Sterile Preparation

• Sterile gown, sterile gloves, mask, hat — all mandatory
• Skin preparation: chlorhexidine 0.5–2% in 70% isopropyl alcohol (preferred over povidone-iodine — superior bacterial kill, reduced PDPH risk with iodine contamination of CSF)
• CRITICAL: Allow the solution to completely air dry (30–60 seconds) before proceeding — wet chlorhexidine is neurotoxic
• Apply fenestrated sterile drape

✅ Step 4: Landmark Identification

• Palpate Tuffier's line → finger on L4 spinous process
• Count down to identify L4–L5 space or up to L3–L4 space
• Mark or indent the target interspace with a thumbnail
• Confirm midline by symmetrical palpation of both sides of the spinous processes

✅ Step 5: Local Anesthetic Skin Infiltration

• 25G needle, 1–2 mL of 1–2% lidocaine
• Raise a skin wheal at the marked entry site
• Infiltrate deeper into the interspinous ligament — this significantly reduces procedural pain and patient movement

✅ Step 6: Needle Selection

✅ Step 7: Needle Insertion — Midline Approach

1. Insert the introducer (22G, 2 cm) firmly into the interspinous ligament, angled slightly cephalad (5–15°) to follow the downward angulation of the spinous processes
2. Pass the spinal needle through the introducer
3. Orient the bevel/opening parallel to the long axis of the spine (longitudinal) — this ensures dural fibers are spread, not cut, minimizing CSF leak
4. Advance with steady, slow pressure:
   • Supraspinous ligament → slight resistance
   • Interspinous ligament → firmer; needle feels "anchored like an arrow in a target"
   • Ligamentum flavum → distinct gritty, firm resistance
   • Pop #1 (subtle): through ligamentum flavum
   • Pop #2 (distinct): through dura-arachnoid — entry into subarachnoid space
5. Remove the stylet and wait for free-flow of clear CSF — this is your non-negotiable confirmation of correct placement
   • If no CSF: rotate needle 90° (bevel may face bone), aspirate gently, advance 1 mm
   • Never inject without confirming CSF

✅ Paramedian Approach (When Midline Fails)

• Entry point: 1–2 cm lateral and 1 cm caudal to the inferior edge of the superior spinous process
• Needle directed medially and cephalad (10–25°) toward the midline
• Bypasses supraspinous and interspinous ligaments entirely — goes directly to ligamentum flavum
• If bone encountered shallowly: redirected upward (hitting lower lamina medially)
• If bone encountered deeply: redirected slightly more craniad toward midline (hitting lower lamina laterally)

✅ Step 8: Drug Injection

1. Attach the pre-drawn syringe with a Luer-lock connection — prevents accidental dislodgment
2. Aspirate 0.2–0.5 mL CSF to reconfirm placement
3. Inject at 0.2 mL/second (slow, steady) — rapid injection creates turbulent flow and unpredictable spread
4. At completion, re-aspirate a small volume of CSF to confirm continuous intrathecal position
5. Remove the needle and the introducer as a unit

✅ Step 9: Positioning After Injection

• Position the patient immediately — the drug is mobile in CSF for 5–10 minutes before it fixes to neural tissue
• Hyperbaric solution + supine: drug gravitates to the natural lumbar lordosis → mid-lumbar level; tilting table Trendelenburg raises the level
• Hyperbaric + sitting for 3 min: drug pools in sacrum → saddle block
• Isobaric solution: less gravity-dependent, height determined primarily by dose
• Assess sensory level at 5 and 10 minutes using cold (ice or alcohol swab) or pinprick

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Drug Doses for Spinal Anesthesia

⚠️ Lidocaine and TNS: Lidocaine 5% hyperbaric carries a high risk of Transient Neurological Symptoms (burning buttock/leg pain for 24–72h). It has largely been replaced by bupivacaine or chloroprocaine for ambulatory procedures. Never use concentrated lidocaine for continuous spinal — this causes cauda equina syndrome.

Intrathecal Adjuvants

📌 Pearl on morphine: Hydrophilic → stays in CSF longer → delayed respiratory depression up to 24 hours. Use only when close monitoring is available. Fentanyl is lipophilic → rapid uptake into neural tissue → limited spread, minimal delayed respiratory depression.

Factors Controlling Block Height

• Pregnancy/obesity: Raised intraabdominal pressure compresses epidural veins → reduced CSF volume → higher than expected block → use reduced doses
• Elderly: Reduced CSF volume and spinal compliance → more sensitive → reduce dose 20–30%
• Height: Minimal clinical effect compared to baricity

Required Dermatomal Levels

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LECTURE 3: EPIDURAL ANESTHESIA

How Epidural Differs Conceptually from Spinal

• Diffuse through the ligamentum flavum
• Traverse the epidural fat
• Penetrate the dura and nerve root sheaths

• Slow onset (10–20 minutes vs 3–5 min for spinal)
• Variable block density (not bathing in CSF)
• Need for large volumes (10–20 mL vs 1.5–4 mL)
• Ability to do segmental blocks — drug confined to the injected level

The Epidural Space — Anatomy Detail

• Batson's venous plexus — valveless, distensible veins (engorged in pregnancy) → most common site of inadvertent intravascular catheter placement
• Epidural fat (filled with fat in children → explains weight-based dosing)
• Lymphatics
• Nerve root sleeves as they exit the foramina

📌 Why do one-sided epidural blocks happen? Fluoroscopic and cadaveric studies have demonstrated fibrous septa and connective tissue bands within the epidural space that can restrict local anesthetic spread to one side. This explains patchy or unilateral blocks and is not a technique failure — it's anatomy.

Indications

• Labor analgesia — the most common use globally
• Major abdominal surgery (provides superior postoperative analgesia vs. parenteral opioids)
• Thoracic epidural for thoracotomy, esophagectomy, major lung resection — reduces postoperative ventilation time and pulmonary complications
• Major pelvic surgery
• Postoperative pain management (catheter-based, multi-day)
• Chronic pain management

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STANDARD PROCEDURE — Step by Step

✅ Step 1: Pre-Procedure Setup

✅ Step 2: Positioning

✅ Step 3: Sterile Preparation

✅ Step 4: The Tuohy Needle — Know Your Tool

• Curved Huber tip — deflects the catheter cephalad once it exits the needle tip into the epidural space
• 1-cm graduation markings on the shaft — track exact depth
• Wings on some (Weiss needle) for one-handed technique
• Supplied with a stylet to prevent tissue coring during insertion

✅ Step 5: Needle Insertion to Ligamentum Flavum

1. After skin wheal and deep infiltration with lidocaine, insert the Tuohy needle (with stylet in place) at the target interspace — L3–L4 or L4–L5 for lumbar; direct slightly cephalad
2. Advance through supraspinous ligament, interspinous ligament, until increased resistance of the ligamentum flavum is distinctly felt
3. Remove the stylet
4. Attach the Loss of Resistance (LOR) syringe

✅ Step 6: Identifying the Epidural Space — Loss of Resistance

• Glass syringe (low friction, precise feedback) filled with 2–3 mL saline + small air bubble
• The air bubble must compress → tells you the fluid is not compressible when in a closed space
• Apply constant gentle forward pressure on the plunger with thumb while advancing the needle 1–2 mm at a time
• In the ligamentum flavum: high resistance — plunger springs back, the air bubble compresses
• The moment the tip enters the epidural space: sudden, complete loss of resistance — the saline flows freely, the air bubble no longer compresses
• Stop advancing immediately — you are in the epidural space

• Same technique with 2–3 mL air
• Risk: pneumocephalus, venous air embolism, patchy block from air pockets
• LOR with saline has replaced this in most centers

📌 Teaching moment: LOR with saline can cause confusion if you cannot tell whether free-flowing fluid is saline from your syringe or CSF from an accidental dural puncture (wet tap). This is why some practitioners leave a small air bubble in the syringe — if you get wet tap, you will see CSF mixed with saline flowing freely and clear.

• Fill the Tuohy needle hub with a saline drop
• In the ligamentum flavum: drop remains stationary
• On entering epidural space (negative/sub-atmospheric pressure): drop is sucked inward
• Less reliable in obese patients (positive epidural pressure), and during general anesthesia, and at thoracic level
• Largely replaced by LOR

✅ Step 7: Depth of the Epidural Space

• Average depth skin-to-epidural space (lumbar, midline): 4–6 cm in adults
• Greater in obese patients (up to 8 cm)
• Note the depth marking on the needle
• A mnemonic: "4, 5, 6 cm deep in most adults" — if you are beyond 8 cm without LOR, stop and reassess

✅ Step 8: Catheter Insertion and Fixation

1. Stabilise the Tuohy needle carefully — any movement at this point risks dural puncture or vascular entry
2. Thread the 20G epidural catheter through the needle with a smooth, continuous motion
3. Advance the catheter 4–6 cm beyond the needle tip (so 2–4 cm lies within the epidural space — just enough for secure placement without coiling into a vessel or nerve root)
4. Hold the catheter firmly while withdrawing the needle — never pull the catheter back through the needle (shearing risk)
5. If the patient reports sharp radiating pain or paresthesia down a leg during catheter threading → catheter is contacting a nerve root → withdraw 0.5–1 cm
6. Secure catheter at skin with adhesive tape; draw the catheter up the back and over the shoulder; apply transparent dressing with strain-relief loop

✅ Step 9: The Test Dose — Never Skip This

⚠️ Limitations of the epinephrine test dose: In parturients, uterine contractions cause natural tachycardia — false positive rate is higher. In patients on beta-blockers, the heart rate criterion is abolished — false negatives occur. Rely also on clinical assessment and incremental dosing, not the test dose alone.

✅ Step 10: Incremental Drug Administration

• Divide total dose into 5 mL aliquots
• Aspirate before each aliquot (even negative aspiration is not 100% reliable — catheters can be partly intravascular)
• Wait 3–5 minutes between aliquots, monitoring blood pressure, heart rate, sensory level
• If signs of intravascular injection at any point (tinnitus, metallic taste, numbness of tongue, agitation, HR rise): stop immediately
• If signs of intrathecal injection (rapidly ascending motor block): manage as high spinal

📌 Morgan & Mikhail's principle: "Each incremental dose is its own test dose." This incremental approach is the single most important safety practice in epidural anesthesia.

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Epidural Drug Doses

• 1 to 2 mL per spinal segment to be blocked (e.g., L4–L5 to T4 = ~10–12 segments = 10–24 mL)
• Shorter patients: 1 mL/segment; taller patients: 2 mL/segment
• Elderly patients: dose requirements decrease with age (reduced epidural space compliance)

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LECTURE 4: PHYSIOLOGICAL EFFECTS OF NEURAXIAL BLOCKADE

Cardiovascular — The Dominant Effect

1. Arteriolar vasodilation → ↓ SVR → ↓ blood pressure
2. Venous vasodilation → ↓ venous return → ↓ preload → ↓ cardiac output
3. Bradycardia when T1–T4 (cardiac accelerator fibers) are blocked — can be sudden and profound

📌 The Bezold-Jarisch reflex: In high spinal with severe preload reduction, decreased right heart filling activates ventricular mechanoreceptors → paradoxical bradycardia and vasodilation → can cause cardiac arrest even in healthy young patients. Treat aggressively with atropine, ephedrine, or epinephrine.

Respiratory

• Diaphragm (C3, C4, C5) is never blocked by lumbar neuraxial anesthesia
• Intercostal muscles (T1–T11) → paralyzed in very high blocks → reduces cough, forced expiration
• Patient subjectively feels they cannot breathe → this is almost always proprioceptive loss (cannot feel chest move), not true hypoxia → reassure and give oxygen
• True respiratory arrest occurs only with total spinal (cervical/brainstem level)

Gastrointestinal

• Sympathetic block (T5–L1) → parasympathetic dominance → increased peristalsis, small contracted bowel
• Excellent surgical conditions for abdominal surgery
• Nausea most commonly from hypotension — treat the hemodynamics first

Urinary

• S2–S4 block → detrusor muscle paralysis → urinary retention
• All patients receiving neuraxial anesthesia for surgical procedures should be catheterized
• For ambulatory patients: must void spontaneously before discharge

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LECTURE 5: COMPLICATIONS — Recognition and Management

1. Hypotension (Most Common)

• Incidence: 15–33% for spinal anesthesia; 20–30% for epidural
• Prevention: crystalloid co-load + vasopressor infusion in high-risk patients (obstetric CS)
• Treatment: phenylephrine infusion, ephedrine, IV fluids, Trendelenburg

2. Post-Dural Puncture Headache (PDPH)

• Bilateral, frontal or occipital, may extend to neck
• Postural — the hallmark: worse within 15 minutes of sitting/standing, relieved within 30 minutes of lying flat
• May include: tinnitus, diplopia (CN VI palsy from traction), photophobia, nausea

• 25–27G pencil-point (Whitacre/Sprotte): < 1%
• 25G Quincke cutting: ~2–5%
• 16G Tuohy wet tap: up to 70%

• Conservative: bed rest, adequate hydration, regular analgesics (paracetamol, NSAIDs, caffeine 300–500 mg oral or IV)
• Definitive: Epidural Blood Patch (EBP)
  • 15–20 mL autologous blood drawn aseptically, injected epidurally at the puncture site or one level below
  • Blood clots within the epidural space, sealing the dural tear
  • Success rate: 85–98% after first patch
  • Wait 24–48 hours before performing (earlier patches have lower success rates)
  • Always obtain informed consent — risks include repeat dural puncture, backache, very rarely neural injury

3. High / Total Spinal

1. Call for help immediately
2. Secure the airway — rapid sequence intubation
3. CPR if cardiac arrest
4. Vasopressors (epinephrine, phenylephrine)
5. Atropine for bradycardia
6. Maintain supine position (avoid Trendelenburg which worsens cephalad spread of remaining drug)

📌 Pearl: Total spinal is almost entirely preventable. Use correct dose, confirm intrathecal placement before injection, use incremental epidural dosing, always use the test dose.

4. Local Anesthetic Systemic Toxicity (LAST)

• CNS prodrome: circumoral numbness, metallic taste, tinnitus, lightheadedness, visual disturbance, agitation
• CNS toxicity: seizures, loss of consciousness
• Cardiovascular toxicity: arrhythmias (bupivacaine most dangerous — binds cardiac sodium channels with high affinity), VT, VF, cardiac arrest

1. Stop injecting immediately
2. Airway, 100% oxygen
3. Seizures: benzodiazepines (midazolam 2–5 mg IV) or propofol (low dose)
4. Intralipid 20% — the antidote:
   • Bolus: 1.5 mL/kg over 1 minute
   • Infusion: 0.25 mL/kg/min for at least 10 minutes
   • "Lipid sink" theory — the lipid emulsion sequesters the hydrophobic local anesthetic
5. ACLS for cardiac arrest — prolonged resuscitation may be needed (bupivacaine cardiotoxicity is reversible with lipid rescue)
6. Avoid: vasopressin, calcium channel blockers, beta-blockers, high-dose propofol during LAST

5. Epidural Hematoma

6. Transient Neurological Symptoms (TNS)

• Burning/aching pain in buttocks, thighs, calves; begins 6–24 hours after spinal recovery
• Most associated with 5% hyperbaric lidocaine (and lithotomy position)
• No neurological deficit — purely sensory, self-limiting (24–72 hours)
• Treatment: NSAIDs, reassurance
• Prevention: avoid lidocaine 5% — use bupivacaine or chloroprocaine instead

7. Cauda Equina Syndrome

• Permanent motor and sensory deficit of sacral nerve roots
• Classic association: continuous spinal catheter + repeated doses of 5% hyperbaric lidocaine
• Drug pools around sacral roots (dependent, immobile in lateral/prone position) → direct neurotoxicity
• Prevention: never use concentrated lidocaine for continuous spinal; use bupivacaine

8. Epidural Abscess

• Back pain + fever + progressive neurological deficit, typically days to weeks after epidural
• Risk factors: prolonged catheter in situ (>96h), immune compromise, diabetes, bacteremia
• Organism: most commonly Staphylococcus aureus
• Diagnosis: MRI with gadolinium (most sensitive)
• Treatment: urgent neurosurgical drainage + IV antibiotics

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LECTURE 6: COMBINED SPINAL-EPIDURAL (CSE) TECHNIQUE

• Rapid, dense onset of spinal anesthesia
• Unlimited duration and flexibility of epidural

Needle-Through-Needle Technique (Standard)

1. Identify epidural space with Tuohy needle via LOR — but do not inject anything yet
2. Pass a long spinal needle (127 mm, 25–27G Whitacre) through the Tuohy needle until the dura is punctured — CSF flows
3. Inject the intrathecal dose (typically reduced — e.g., 7.5–10 mg hyperbaric bupivacaine for CS rather than 12.5–15 mg for spinal alone)
4. Remove the spinal needle, thread the epidural catheter
5. If the spinal block is inadequate (insufficient height or premature regression): extend via epidural catheter

Applications

• Cesarean section — most common obstetric application
• Labor analgesia (CSE gives faster, more complete onset than epidural alone for the first 15 minutes)
• Long orthopedic procedures (total hip/knee in elderly) — spinal for initial block, epidural for extension and postoperative analgesia

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LECTURE 7: MASTER COMPARISON TABLE

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LECTURE 8: EXAMINATION ESSENTIALS — 10 Questions Your Examiner Will Ask

🧠 Know these exactly. These are the questions that separate pass from distinction.

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