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Epidural Anaesthesia - Comprehensive Exam Guide

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1. Anatomy of the Epidural Space

• Posteriorly: ligamentum flavum and vertebral laminae
• Laterally: pedicles and intervertebral foramina
• Anteriorly: posterior longitudinal ligament and vertebral bodies

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2. Indications

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3. Contraindications

• Patient refusal
• Infection at the injection site (local sepsis)
• True allergy to local anaesthetics
• Raised intracranial pressure (risk of brainstem herniation with dural puncture)
• Coagulopathy / uncorrected anticoagulation

• Systemic sepsis / bacteraemia
• Spinal deformity (scoliosis, previous spinal surgery)
• Hypovolaemia / haemodynamic instability (sympathetic block exaggerates hypotension)
• Neurological disease (controversial - medicolegal concern)
• Patient inability to cooperate
• Anticoagulant therapy (requires timing as per ASRA guidelines - see below)

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4. Equipment

Needles

• Tuohy needle (most common): 17-18 gauge, 3-3.5 inches, blunt bevel with a 15-30° curve (Huber tip). The curve directs the catheter cephalad and theoretically deflects the dura rather than puncturing it.
• Crawford needle: straight, thin-walled - higher risk of dural puncture.
• Weiss winged needle: wings aid in controlled advancement.

Catheters

• 19-20 gauge catheter threaded through the 17-18 gauge needle
• Advanced 2-6 cm into the epidural space (too short = dislodgement; too long = unilateral block, vascular cannulation, knotting)
• Single-port (end-hole) or multi-port (closed tip with side holes) - side-port catheters have fewer paresthesias and lower intravascular puncture rate

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5. Levels and Needle Angulation

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6. Patient Positioning

• Sitting (preferred for obese patients, easier midline identification): patient arches back ("rainbow"), feet supported, assistant in front
• Lateral decubitus (preferred for hip fractures, labour, uncooperative patients): hips and knees flexed to chest to flex lumbar spine
• Lateral position is preferred for children - bending moves spinal cord forward, expanding the epidural space

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7. Approaches

• Calcified supraspinous / interspinous ligaments (elderly patients)
• Thoracic epidural (avoids acute spinous process angulation)
• Patient cannot flex adequately

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8. Identifying the Epidural Space

Loss of Resistance (LOR) - Most Common

1. Needle advanced to ligamentum flavum with stylet in situ
2. Stylet removed, glass syringe filled with saline or air attached
3. Within the ligament: resistance to injection is felt
4. Advance slowly, millimetre by millimetre with continuous or intermittent pressure
5. On entering epidural space: sudden loss of resistance - syringe empties freely

• Air: simpler, easier to recognise dural puncture (instant CSF flow)
• Saline: associated with fewer complications (less risk of air emboli, pneumocephalus, incomplete blocks, pain)
• A recent meta-analysis found no statistically significant advantage of one over the other; outcomes are similar with either technique (Barash 9e, p. 2825)

Hanging Drop Technique

1. Needle tip within ligamentum flavum, hub filled with saline
2. Drop "hangs" at hub while in ligament
3. On entering epidural space: negative pressure sucks the drop in
4. More reliable for thoracic epidural (more consistent negative pressure there)
5. Risk: if needle plugged, drop not drawn in → accidental dural puncture may occur

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9. Activating the Epidural (Test Dose and Incremental Dosing)

Test Dose

• Intrathecal injection → dense spinal block within 2-3 min (lidocaine 45 mg)
• Intravascular injection → heart rate increase ≥20% within 1 min (epinephrine 15 mcg)

• False positives: uterine contractions causing HR increase in laboring women
• False negatives: beta-blockade blunts HR response
• Aspiration alone is unreliable (false-negative aspirations occur with both needles and catheters)

Incremental Dosing

• Each dose is a test dose - inject in 5 mL fractions
• Large enough to produce mild symptoms (tinnitus, metallic taste) of inadvertent IV injection
• Small enough to avoid seizures or cardiovascular collapse

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10. Drugs for Epidural Anaesthesia

Local Anaesthetics

• 0.5%: sympathetic + sensory + motor block (surgical)
• 0.25%: sensory block without significant motor block
• 0.0625%: preganglionic sympathetic block only (labour analgesia)

Adjuvants

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11. Factors Affecting Spread of Epidural Block

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12. Complications

Immediate/Technical

Physiological Effects / Cardiovascular

• Sympathetic blockade → vasodilation → hypotension (more predictable than spinal, develops over 10-20 min)
  • Treat with IV fluids, vasopressors (phenylephrine for non-obstetric, ephedrine if bradycardia also present)
• Block of cardiac accelerator fibres (T1-T4) → bradycardia (less common than spinal)

Delayed Complications

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13. Epidural vs. Spinal - Key Exam Comparison

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14. Anticoagulation and Neuraxial Timing (ASRA Guidelines)

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15. Benefits of Epidural Analgesia (Post-operative)

• Reduced postoperative pulmonary complications after thoracic and abdominal surgery (preserves pulmonary function, facilitates physiotherapy)
• Reduced opioid requirements → less nausea, sedation, ileus
• Better pain control at rest and on movement
• Earlier mobilisation
• May reduce risk of deep vein thrombosis
• May improve outcomes in high-risk cardiac patients undergoing major surgery

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High-Yield Exam Facts

1. Ligamentum flavum is the key structure - it provides the resistance before LOR
2. Tuohy needle is standard; blunt curved tip to deflect dura
3. Catheter advanced 2-6 cm into epidural space (not more)
4. Test dose = 3 mL of 1.5% lidocaine + 15 mcg epinephrine
5. Epinephrine marker: HR rise ≥20% within 60 seconds indicates IV placement
6. Sodium bicarbonate speeds onset but do NOT add to bupivacaine (precipitates at pH >6.8)
7. Bupivacaine 0.75% is contraindicated in obstetrics
8. Epidural haematoma is a surgical emergency - laminectomy within 6-8 hours of onset
9. Hanging drop is more reliable at thoracic level (more consistent negative epidural pressure)
10. Unilateral block: withdraw catheter 1-2 cm, turn patient with unblocked side down, reinject
11. Sacral sparing (L5/S1): raise head of bed and reinject with additional local anaesthetic
12. Epidural acts primarily on spinal nerve roots (but also spinal cord and paravertebral nerves)
13. Rate of serious neurological complications from central neuraxial blockade: <4 per 10,000

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Spinal Anaesthesia - Comprehensive MD Anaesthesiology Exam Guide

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1. Definition and Historical Context

• Procaine: Braun 1905
• Tetracaine: Sise 1935
• Lidocaine: Gordh 1949
• Bupivacaine: Emblem 1966

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2. Anatomy Relevant to Spinal Anaesthesia

• Spinal cord terminates at L1 in adults (L3 in neonates - descends with growth)
• Thecal sac ends at S2 in adults
• Between L1 and S2 lies the cauda equina bathed in a relatively large volume of CSF - this is why lumbar puncture below L1 minimises spinal cord injury risk
• Tuffier's line (intercristal/bicristal line): connects the two iliac crests and crosses the spine at L4-L5 interspace (or L4 spinous process) in adults - used as a landmark for needle insertion

• Volume: 120-150 mL total; approximately 25-35 mL in the lumbosacral space
• Density: 1.00059 g/mL at 37°C
• Production: ~0.35 mL/min by choroid plexus

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3. Indications

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4. Contraindications

• Patient refusal
• Local infection at the puncture site
• True allergy to local anaesthetics
• Raised intracranial pressure (risk of brainstem herniation)
• Coagulopathy / therapeutic anticoagulation
• Severe hypovolaemia / haemodynamic instability

• Systemic sepsis / bacteraemia (avoid until antibiotics started and response demonstrated)
• Spinal deformity, previous spinal surgery
• Neurological disease (medicolegal concern, not absolute)
• Patient inability to cooperate
• Anticoagulant therapy (timing per ASRA guidelines)
• Severe aortic stenosis / fixed cardiac output states (cannot compensate for sympathetic block)

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5. Equipment: Spinal Needles

Needle Tip Types

• The arachnoid mater cells are oriented parallel to the long axis of the spine. A parallel-bevel cutting needle slits these cells narrowly; pencil-point needles separate rather than cut. This minimises CSF leakage.
• For cutting-tip needles: orienting the bevel parallel to the long axis of the spine (i.e., parallel to the dural fibres) reduces PDPH risk by more than half.

• Larger gauge → better tactile feel but higher PDPH rate (~40% with 22G cutting)
• Smaller gauge → lower PDPH (<2% with 29G) but higher failure rate
• Optimal balance: 25-26G pencil-point needle - lowest combined risk of PDPH and failure

• Orient cephalad to ensure adequate spread and reduce risk of local anaesthetic pooling around cauda equina
• Orienting to one side can achieve a more pronounced unilateral block

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6. Patient Positioning

• Easier midline identification (especially obese patients)
• Greatest lumbar flexion - maximally opens interspaces
• Preferred for saddle block (hyperbaric solution pools in sacral region while patient remains seated)

• Preferred for hip fractures, labour, uncooperative or haemodynamically compromised patients
• Thin patients and those with BMI <25 are more comfortable laterally
• Used for unilateral spinal (hyperbaric drug pools in dependent side)

• Jackknife position - described for specific perineal/sacral procedures

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7. Approaches

• Needle inserted in midline with slight cephalad angulation (10-15°)
• Path: skin → supraspinous ligament → interspinous ligament → ligamentum flavum → dura → arachnoid → CSF
• Characteristic "pop" or "give" as needle passes through ligamentum flavum then dura

• Skin entry 1 cm lateral to the superior edge of the inferior spinous process
• Needle angled 10-15° off the sagittal plane, cephalomedially
• Bypasses calcified supraspinous/interspinous ligaments (elderly)
• Useful for thoracic level access
• Does not traverse supraspinous or interspinous ligaments
• If bone contacted, walk cephalad up the lamina

• After "pop", remove stylet - CSF should appear at hub
• Small gauge → longer wait for CSF flow, especially in lateral position
• If no CSF: rotate in 90° increments; advance slightly; if still no CSF, withdraw and restart
• Confirm CSF by free flow and ability to aspirate before injecting

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8. Baricity and Spread - The Core MD Concept

• Hyperbaric solutions flow to dependent (lower) regions by gravity
• Hypobaric solutions float to non-dependent (upper) regions
• Isobaric solutions are not significantly influenced by gravity

1. CSF volume (decreased volume → higher block)
2. Baricity of the local anaesthetic solution

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9. Other Factors Affecting Block Height

Drug Factors (controllable)

• Dose - primary determinant of duration and quality
• Volume × Concentration = Dose (inextricably linked)
• Baricity - most clinically important for spread control
• Temperature - warming increases hypobaricity

Patient Factors (not fully controllable)

• CSF volume: reduced by: pregnancy, obesity, increased intraabdominal pressure, Valsalva - all increase spread
• Age: decreased CSF volume and compliance with age → increased spread
• Height: taller patients need more drug to achieve same level
• Pregnancy: engorged epidural veins reduce CSF volume + thoracic kyphosis effect

Technical Factors

• Level of injection: more cephalad injection → higher block (especially with isobaric solutions)
• Speed of injection: slower injection may paradoxically increase spread; very fast injection can cause discomfort
• Barbotage (repeated CSF aspiration/reinjection): does NOT consistently affect block height
• Needle orifice orientation: affects hypobaric solutions more than hyperbaric (cephalad orientation → more cephalad spread for hypobaric)

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10. Pharmacology of Intrathecal Local Anaesthetics

Classification by Duration

Key Drugs

• Highly protein-bound, lipid-soluble amide
• pKa 8.1 → slow onset
• 0.5% hyperbaric (with 8% glucose): surgical anaesthesia; onset ~20 min, duration up to 225 min
• 0.5% isobaric: slightly longer duration than hyperbaric equivalent
• 0.75% not FDA-approved for obstetric neuraxial use (enhanced cardiotoxicity in pregnant patients)
• Epinephrine only slightly prolongs duration (~15 min)

• Intermediate duration (50-100 mg, ~1-1.5 hours)
• Traditionally 5% in 7.5% glucose - associated with Transient Neurological Symptoms (TNS) and cauda equina syndrome with continuous spinal technique
• Popularity has declined; still used by some practitioners

• Ultra-short-acting; rapid metabolism by pseudocholinesterase
• 30-60 mg preservative-free preparation → reliable short-duration spinal; faster recovery than lidocaine
• TNS can still occur
• Gaining popularity for ambulatory surgery

• Less cardiotoxic than bupivacaine; greater motor-sensory differentiation
• Potency = 0.6× that of bupivacaine
• Equivalent doses → less motor block and earlier recovery

Spinal Additives

• Lipophilic (fentanyl, sufentanil): rapid CSF uptake into neural tissue and vasculature → limited rostral spread → lower risk of delayed respiratory depression; relative intrathecal:IV potency = 10-20:1
• Hydrophilic (morphine): slow CSF uptake → wide rostral spread → risk of late respiratory depression (up to 18-24 h); relative intrathecal:IV potency = 200-300:1

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11. Physiology of Spinal Block - Differential Blockade

1. Preganglionic sympathetic fibres (B fibres) - smallest, blocked first
2. Temperature / pain (C and Aδ fibres)
3. Touch, pressure (Aβ fibres)
4. Motor (Aα fibres) - largest, blocked last

• Sympathetic block is typically 2 dermatomes HIGHER than sensory block
• Sensory block to cold is 1-2 dermatomes higher than pinprick
• Pinprick is 1-2 dermatomes higher than touch
• Motor block is 2 dermatomes LOWER than sensory block

Cardiovascular Effects of Sympathetic Blockade

• Sympathetic fibres leave cord at T1-L2
• Vasodilation is predominantly venous (capacitance vessels) → reduced preload → reduced cardiac output
• Hypotension is more marked with higher block levels
• Cardiac accelerator fibres: T1-T4 - block causes bradycardia (Bezold-Jarisch reflex also contributes - venous pooling → decreased ventricular filling → paradoxical bradycardia)
• Sudden asystole can occur from loss of cardiac sympathetic + unopposed vagal activity at SA node

• Crystalloid/colloid preload or co-load
• Left lateral tilt in obstetric patients (aortocaval decompression)
• Phenylephrine (first-line in obstetrics - preserves uteroplacental blood flow)
• Ephedrine (when bradycardia also present - mixed α/β agonist)
• Atropine 0.6 mg for bradycardia
• Head-down tilt / leg elevation (increases venous return)

Respiratory Effects

• Low/mid lumbar block: minimal respiratory effects
• T10: intercostal muscle weakness
• High thoracic/total spinal: loss of diaphragmatic function (C3-C5) → apnoea
• Patients with high block may describe difficulty breathing due to loss of chest wall proprioception, even if diaphragm intact

Gastrointestinal Effects

• Sympathetic fibres T5-L1 inhibit peristalsis → their blockade increases gut motility
• Vagal tone becomes dominant → contracted, hyperperistaltic bowel (good surgical condition for bowel surgery)
• Nausea during spinal (especially with opioid addition or hypotension)

Urinary Effects

• Sacral (S2-S4) parasympathetic blockade → urinary retention
• Detrusor muscle paralysis - catheterisation may be required

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12. Block Monitoring

1. Sensory level: cold sensation (ethyl chloride) - most sensitive; pinprick - standard
2. Motor block: modified Bromage scale
3. Sympathetic block: HR and BP changes
4. Adequate block: sensory level 2-3 segments above expected surgical stimulus + inability to straight-leg raise (ensures lumbar roots blocked)

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13. Complications

Immediate

Post-procedure

Post-Dural Puncture Headache (PDPH)

• Postural - worsens upright, relieved lying flat (pathognomonic)
• Frontal or occipital distribution
• Associated: nausea, tinnitus, diplopia, CN VI palsy (longest intracranial course), hearing loss, neck stiffness
• Onset: usually 24-72 hours post-puncture; >90% begin within 3 days
• Spontaneous resolution: 72% by 7 days, 87% by 6 months

• Young age (especially 18-30 years)
• Female sex
• Low BMI
• Larger needle gauge
• Cutting needle tip
• Bevel perpendicular to spine axis
• History of PDPH or chronic headaches

1. Conservative: bed rest (relieves symptoms, does not shorten duration), adequate hydration (no strong evidence but practised), analgesics (paracetamol, NSAIDs, opioids)
2. Caffeine (weak evidence - some temporary relief via vasoconstriction)
3. Epidural blood patch (EBP) - definitive treatment:
   • 10-20 mL autologous blood injected into epidural space at or one level below puncture site
   • Clot seals dural tear; also transiently raises epidural pressure
   • Success: 75-90% permanent relief with single patch
   • Second patch effective for incomplete relief
   • Timing: more effective if performed ≥72 hours after puncture (allow some CSF pressure to restore)
   • Complication: back pain during injection (stop if severe); rarely epidural haematoma

Transient Neurological Symptoms (TNS)

• Buttock and lower extremity pain radiating symmetrically, without neurological deficit
• Onset 6-36 hours after recovery from spinal, resolves within 1-7 days
• Strongly associated with lidocaine (especially 5% hyperbaric): incidence 10-40%
• Also with: lithotomy position, ambulatory surgery, obesity, same-day procedures
• Mechanism: direct neurotoxicity of concentrated lidocaine at cauda equina
• Treatment: NSAIDs, reassurance; self-limiting
• This is why lidocaine's popularity for spinal has declined

Cauda Equina Syndrome (CES)

• Permanent neurological injury: saddle anaesthesia, bowel/bladder dysfunction, lower limb weakness
• Associated with continuous spinal anaesthesia using micro-catheters + hyperbaric 5% lidocaine (drug pooled in sacral space → neurotoxic concentrations)
• Micro-catheters for continuous spinal now largely abandoned because of this

Neurological Complications (General)

• Rate of serious neurological complications from central neuraxial blockade: <4 per 10,000
• Risk increased in elderly and those with pre-existing spinal pathology
• Epidural haematoma: rare; increased by anticoagulation; surgical emergency (laminectomy within 6-8 h)
• Meningitis: usually from contamination (Streptococcus viridans from operator's oral flora - hence face mask mandatory)
• Epidural abscess: rare; fever, back pain, neurological deterioration

Hearing Loss

• Transient low-frequency hearing loss from decreased CSF pressure affecting inner ear (endolymph-perilymph pressure differential)
• More common with large-gauge needles
• Usually resolves within ~1 month; permanent loss reported rarely

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14. Combined Spinal-Epidural (CSE)

• Spinal needle passed through epidural needle (needle-through-needle technique) into CSF
• Advantages: speed + reliability of spinal + flexibility + duration of epidural catheter
• Epidural injection after spinal → increases spinal block height (volume effect compresses dural sac)
• Application: labour analgesia (spinal component for rapid onset, epidural for maintenance), prolonged surgeries, caesarean section
• Risk: epidural drugs may enter intrathecal space via dural hole → potentiated effect; always titrate carefully

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15. Saddle Block

• Targeted block of sacral roots (S1-S5) only
• Patient remains seated for 5-10 min after injection of hyperbaric solution
• Drug stays in sacral (dependent) region
• Uses: anorectal surgery, perineal/perianal procedures, operative vaginal delivery
• Saddle block for vaginal delivery: hyperbaric tetracaine 3-4 mg or bupivacaine 2.5-5 mg ± fentanyl 12.5-25 mcg ± sufentanil 5-7.5 mcg

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16. Unilateral and Selective Spinal Anaesthesia

• Small-dose hyperbaric solution + lateral position for 10-15 min → preferential block of dependent side
• e.g., 4-5 mg hyperbaric bupivacaine for knee arthroscopy
• Benefits: less haemodynamic instability, faster recovery, earlier discharge
• Selective spinal: minimum dose to anaesthetise only the surgical area

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17. Continuous Spinal Anaesthesia

• Large-bore needle (or micro-catheter) threaded into subarachnoid space
• Allows titration of dose (useful in elderly, high-risk cardiac patients)
• Micro-catheters (≤28G) largely abandoned due to cauda equina syndrome
• Currently: 17-19G catheters via large-bore needles used (accepted high PDPH risk)
• Application: elderly patients with severe cardiac disease for major surgery

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18. High-Yield MD Exam Facts Summary

1. August Bier (1898) performed the first spinal anaesthetic in humans (cocaine)
2. CSF density = 1.00059 g/mL at 37°C
3. Spinal cord ends at L1 in adults; thecal sac ends at S2
4. Tuffier's line = intercristal line = L4-L5 interspace in adults
5. Two most important determinants of block height: CSF volume + baricity
6. Sympathetic block is 2 segments HIGHER than sensory; motor is 2 segments LOWER
7. Cardiac accelerator fibres = T1-T4; sympathetic outflow = T1-L2
8. Hyperbaric → dependent regions; hypobaric → non-dependent; isobaric → gravity-independent
9. Pencil-point needles (Whitacre, Sprotte) reduce PDPH vs Quincke (cutting)
10. Optimal needle: 25-26G pencil-point (lowest combined PDPH + failure risk)
11. Cutting needle bevel parallel to long axis of spine → reduces PDPH by >50%
12. Needle side-port cephalad orientation → ensures adequate spread, prevents cauda equina pooling
13. TNS: strongly associated with lidocaine (10-40%), especially in lithotomy; self-limiting 1-7 days
14. Cauda equina syndrome: concentrated hyperbaric lidocaine via micro-catheter → permanent deficit
15. PDPH: postural headache; onset 24-72 h; epidural blood patch 20 mL = definitive treatment; single EBP cures 75-90%
16. EBP is more successful when performed ≥72 h after dural puncture
17. PDPH associated with cerebral venous thrombosis (aOR 19.0) and meningitis (aOR 39.7) - serious!
18. Phenylephrine is first-line vasopressor for spinal hypotension in obstetrics
19. Epidural injection after spinal raises block height (CSE effect)
20. Total spinal → presents as apnoea not just hypotension; treat with airway + CPR
21. Morphine intrathecal: delayed respiratory depression up to 18-24 hours post-injection
22. Relative intrathecal:IV potency: morphine 200-300:1; fentanyl 10-20:1
23. Aseptic technique mandatory; face mask worn to prevent Streptococcus viridans meningitis
24. Rate of serious neurological complications: <4 per 10,000 neuraxial blocks

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