Neuraxial anaesthesia

11 min read Last updated April 8, 2026

Surgical approach (context: procedures commonly performed under neuraxial)

  • Lower limb orthopaedics (e.g. THR/TKR): positioning (lateral/supine), tourniquet use, cementation, significant blood loss possible
    • Tourniquet pain may occur despite dense block; consider sedation/analgesia or convert
  • Lower abdominal surgery (e.g. hernia, TURP, cystoscopy): lithotomy common; irrigation fluids and reflexes (TURP syndrome) relevant
    • Lithotomy can increase venous return and affect block height; be cautious with haemodynamics
  • Obstetrics (LSCS): rapid access, left uterine displacement, potential for major haemorrhage; neonatal considerations
    • High neuraxial block and aortocaval compression are key causes of maternal collapse
  • Perineal/anal surgery: often short; can use saddle block; prone/jack-knife positioning may be used
    • Saddle block targets S2–S5; avoid excessive cephalad spread

Anaesthetic management (generic template for neuraxial cases)

  • Type of anaesthesia: neuraxial (spinal/epidural/CSE/caudal) ± sedation; be ready to convert to GA
    • GA backup plan: airway strategy, aspiration risk, haemodynamic support, analgesia plan
  • Airway: usually no airway device; if deep sedation or conversion—SGA/ETT as indicated
    • Sedation can cause airway obstruction in supine pregnant/obese patients—use minimal effective dose
  • Duration: spinal typically 1.5–3 h (drug/dose dependent); epidural/CSE can be topped up for longer cases
    • Plan for surgical duration uncertainty: choose epidural/CSE if prolonged/variable
  • How painful: depends on surgery; neuraxial provides dense intra-op analgesia; post-op analgesia best with epidural infusion/opioid adjuncts
    • Tourniquet and visceral traction pain may break through—treat with opioids, ketamine, LA supplementation, or convert
  • Monitoring: standard + close BP cycling (e.g. every 1–2 min initially for obstetrics); consider arterial line for high-risk
    • Hypotension is common early—anticipate and treat promptly
  • Haemodynamics: preload/coload strategy, vasopressors (phenylephrine/ephedrine/metaraminol), uterine displacement in pregnancy
    • Phenylephrine first-line for spinal hypotension in obstetrics (maintains fetal pH better than ephedrine in many studies)

Definition and scope

  • Neuraxial anaesthesia = local anaesthetic ± adjuncts delivered around the spinal cord/nerve roots to produce sensory ± motor ± sympathetic block
  • Techniques: spinal (intrathecal), epidural, CSE, caudal; continuous spinal (selected cases)

Relevant anatomy (high-yield)

  • Layers (midline): skin → subcut → supraspinous → interspinous → ligamentum flavum → epidural space → dura → arachnoid → CSF → pia
  • Epidural space contents: fat, lymphatics, segmental arteries, epidural venous plexus (engorged in pregnancy), nerve roots
  • Spinal cord ends: conus medullaris ~L1 in adults (range T12–L3); dural sac ends ~S2
    • Hence spinal/epidural typically at L3/4 or L4/5 (Tuffier’s line = iliac crests ≈ L4 spinous process/space; variable)
  • Dermatomes (approx): T4 nipple, T6 xiphisternum, T10 umbilicus, L1 inguinal, S2–4 perineum
  • Sympathetic outflow: T1–L2; cardioaccelerator fibres T1–T4 (block → bradycardia/hypotension)

Physiology and pharmacology

  • Block components: sympathetic (earliest) > sensory > motor; differential block depends on fibre type and concentration
  • Spinal spread determinants: baricity, dose/volume, patient position, CSF volume (reduced in pregnancy/obesity), height (minor), injection speed (minor)
    • Hyperbaric solutions tend to follow gravity; isobaric less position-dependent
  • Epidural spread determinants: volume more important than dose; age, pregnancy, injection site, catheter direction; patchy block common
  • Local anaesthetic choice: bupivacaine/levobupivacaine/ropivacaine; lignocaine (faster, shorter); chloroprocaine (rapid, short; obstetric top-ups in some units)
  • Adjuncts: opioids (fentanyl/diamorphine/morphine), clonidine, adrenaline; benefits vs side effects (pruritus, PONV, urinary retention, respiratory depression—especially intrathecal morphine)
    • Intrathecal morphine: excellent prolonged analgesia but requires respiratory monitoring (delayed depression)

Indications and advantages

  • Indications: lower limb surgery, lower abdominal/urological, obstetrics (labour analgesia, LSCS), vascular (selected), chronic pain procedures
  • Advantages: avoids airway instrumentation, reduced surgical stress response, excellent analgesia, reduced thromboembolism in some settings, earlier mobilisation (with appropriate regimen)
  • Obstetrics: awake mother, reduced aspiration risk vs GA, improved uteroplacental perfusion if hypotension avoided

Contraindications (absolute vs relative)

  • Absolute: patient refusal, infection at site, uncorrected severe hypovolaemia/shock, true LA allergy (rare), raised ICP due to mass lesion/obstructed CSF flow
  • Anticoagulation/antiplatelets: not absolute per se—follow ASRA/ESAIC/RCoA guidance; key issue is risk of neuraxial haematoma
    • Always document: drug, dose, last dose time, renal function, platelet count/trend, traumatic attempt, catheter in/out times
  • Relative: sepsis/bacteraemia, fixed cardiac output states (severe AS/HOCM), severe coagulopathy/thrombocytopenia, severe spinal deformity/previous surgery, neurological disease (risk/benefit and documentation)
  • Raised ICP: spinal may precipitate herniation if mass effect; isolated idiopathic intracranial hypertension is different (often safe but individualised)

Preparation, consent, and safety

  • Consent: benefits, alternatives (GA), common side effects (hypotension, urinary retention, pruritus), significant risks (PDPH, nerve injury, infection, haematoma, high/total spinal, LAST)
  • Equipment: resuscitation drugs, vasopressors, airway kit, intralipid, sterile neuraxial pack, appropriate needles/catheters, ultrasound (optional), labels for syringes
  • Asepsis: hat/mask, sterile gloves/gown, skin prep (chlorhexidine in alcohol—allow to dry), sterile drapes; minimise contamination of catheter/needle hub
  • WHO checklist and neuraxial drug safety: separate neuraxial drugs from IV drugs; clear labelling; avoid look-alike ampoules

Technique essentials

  • Positioning: sitting or lateral; optimise flexion; maintain comfort and stillness; in pregnancy avoid aortocaval compression (wedge/tilt)
  • Spinal: identify interspace, infiltrate skin, introducer if needed, pencil-point needle reduces PDPH, confirm free-flow CSF, inject calculated dose, position appropriately
    • Assess block: cold/light touch (sensory), Bromage (motor), haemodynamics; allow time for onset before incision
  • Epidural: Tuohy needle to ligamentum flavum, loss of resistance (saline commonly), thread catheter 3–6 cm into space, aspirate, test dose (unit policy), incremental dosing
    • Test dose aims: detect intrathecal or intravascular placement; interpret cautiously in pregnancy/β-blockade
  • CSE: spinal through epidural needle (needle-through-needle) or separate interspaces; advantages: rapid onset + ability to extend duration
  • Failure management: recognise early; troubleshoot (position, catheter pullback, additional volume, change solution); low threshold to convert to GA if unsafe delay

Haemodynamic effects and treatment

  • Mechanism: sympathetic block → venodilation (↓ preload) ± arteriolar dilation (↓ SVR); high block may impair cardiac accelerator fibres (bradycardia) and venous return
  • Risk factors for severe hypotension: high block, hypovolaemia, pregnancy, elderly, baseline high sympathetic tone, aortocaval compression, rapid onset (spinal > epidural)
  • Treatment: left uterine displacement (if pregnant), rapid fluids (coload), vasopressors (phenylephrine/metaraminol; ephedrine if bradycardic), atropine for bradycardia, escalate early
    • If severe bradycardia/asystole: treat as peri-arrest—CPR, adrenaline; consider high/total spinal and manage airway/ventilation

Complications (recognition and management)

  • High/total spinal: hypotension, bradycardia, dyspnoea, upper limb tingling, nausea, LOC; manage with airway/ventilation, vasopressors, fluids, left tilt, call for help
  • PDPH: postural headache ± neck stiffness, photophobia, tinnitus; risk reduced with pencil-point small gauge; treat with hydration/caffeine/simple analgesia; epidural blood patch if severe/persistent
    • Consider differential: meningitis, intracranial pathology, pre-eclampsia, cerebral venous sinus thrombosis (postpartum)
  • Neuraxial haematoma: severe back pain, motor weakness, sensory loss, sphincter dysfunction; emergency MRI and neurosurgical decompression ideally within hours
    • Time-critical: treat as emergency; stop epidural infusion; urgent escalation
  • Epidural abscess/meningitis: fever, back pain, neurological deficit; urgent imaging, microbiology, antibiotics ± surgery
  • Nerve injury: direct trauma, ischaemia, haematoma/abscess, positioning; document neuro exam, early senior review, exclude compressive causes
  • LAST: tinnitus, metallic taste, seizures, arrhythmias; prevent with incremental dosing/aspiration; treat with airway/oxygen, benzodiazepines, intralipid, follow ALS modifications
  • Urinary retention: common with neuraxial opioids and sacral block; catheterisation may be required
  • Inadequate/patchy block: common with epidurals; manage systematically; do not persist if surgery urgent or patient distressed

Special situations

  • Obstetrics: reduced CSF volume and epidural vein engorgement → greater spread; hypotension prevention critical; intrathecal opioids improve quality
  • Cardiac disease: fixed output lesions (severe AS) poorly tolerate sympathectomy; consider graded epidural/combined techniques with invasive monitoring or alternative
  • Sepsis: avoid in uncontrolled sepsis/shock; if benefits outweigh risks (e.g. source control) ensure haemodynamic optimisation and senior decision-making
  • Anticoagulated patient: timing around DOACs/LMWH/warfarin and catheter removal is critical; if neurological symptoms occur treat as haematoma until proven otherwise
You are asked to perform a spinal anaesthetic for an elective total hip replacement. Talk me through your preparation, technique, and how you will manage hypotension.

Structure: assess → plan → perform safely → confirm block → manage physiology → contingency.

  • Pre-op assessment: indication, comorbidities (AS, anticoagulants), baseline BP, airway (backup GA), neurological history; check Hb, platelets, coagulation/anticoagulant timing
  • Consent: benefits/alternatives; risks—hypotension, PDPH, nerve injury, infection, haematoma, high spinal, failure and conversion to GA
  • Preparation: IV access, fluids available, vasopressors drawn up and labelled, monitoring, oxygen, intralipid available, aseptic setup
  • Technique: L3/4 or L4/5, sitting/lateral; skin LA; pencil-point needle; confirm CSF; inject appropriate hyperbaric bupivacaine dose ± opioid; position and reassess
  • Block assessment: sensory level (cold), motor (Bromage), haemodynamics; ensure adequate level for surgery before incision
  • Hypotension management: treat promptly—fluids (coload), vasopressors (metaraminol/phenylephrine), address bradycardia with atropine; consider high spinal if severe symptoms
  • Contingency: if inadequate block—supplement (opioids/ketamine), consider conversion to GA; ensure analgesia plan post-op
Explain the physiological basis of hypotension and bradycardia after spinal anaesthesia, and how you would treat each.

Examiners want mechanism + targeted treatment + escalation.

  • Hypotension: sympathetic block (T1–L2) → venodilation (↓ preload) ± arteriolar dilation (↓ SVR) → ↓ CO/BP; worsened by hypovolaemia and aortocaval compression
  • Bradycardia: block of cardioaccelerator fibres (T1–T4) + reduced venous return triggering vagal reflexes (e.g. Bezold–Jarisch) → profound bradycardia/asystole in severe cases
  • Treat hypotension: left tilt (if pregnant), rapid fluids, vasopressors (phenylephrine/metaraminol; ephedrine if low HR), oxygen, reassess block height
  • Treat bradycardia: atropine; if severe with hypotension use ephedrine/adrenaline; prepare to manage high/total spinal with airway support
  • Escalation: call for help early, consider peri-arrest algorithm if deteriorating; do not delay airway management if consciousness/ventilation compromised
A patient develops sudden breathlessness and cannot lift their arms shortly after an intrathecal injection. What is your diagnosis and immediate management?

This is a classic high/total spinal scenario: diagnose clinically and resuscitate.

  • Diagnosis: high/total spinal (rapid sympathectomy + cervical/thoracic spread causing upper limb weakness, dyspnoea, hypotension, bradycardia, possible LOC)
  • Immediate actions: call for help; ABC approach; high-flow oxygen; support ventilation (bag-mask) and proceed to RSI/intubation if needed
  • Circulation: left uterine displacement if pregnant; rapid IV fluids; vasopressors (phenylephrine/metaraminol) and treat bradycardia (atropine; adrenaline if severe)
  • Reassurance and sedation once ventilated: patient may feel unable to breathe due to intercostal block despite diaphragmatic function—do not dismiss; treat clinically
  • Ongoing: invasive BP if unstable, consider ICU; document event and debrief
Discuss post-dural puncture headache: risk factors, features, differential diagnosis, and management including epidural blood patch.

Common FRCA topic: define, recognise, exclude dangerous causes, treat stepwise.

  • Pathophysiology: CSF leak → low CSF pressure → traction on pain-sensitive structures; compensatory cerebral vasodilation
  • Features: postural headache (worse upright, better supine) ± neck stiffness, nausea, photophobia, tinnitus; typically within 24–72 h
  • Risk factors: young age, female/pregnancy, large cutting needle (Quincke), multiple attempts, previous PDPH; pencil-point and small gauge reduce risk
  • Differential (especially postpartum): pre-eclampsia, migraine, meningitis, intracranial haemorrhage, cerebral venous sinus thrombosis
  • Initial management: explanation, simple analgesia, hydration, caffeine (short-term benefit), avoid dehydration; assess severity and impact
  • Epidural blood patch: indication—severe/persistent PDPH affecting function; technique—aseptic epidural at/near level, inject autologous blood (commonly ~15–20 mL) until pressure/discomfort; monitor and advise
    • Risks: back pain, repeat dural puncture, infection, haematoma, neurological symptoms; consent and follow-up required
You are asked to site an epidural for labour. How do you confirm correct placement and avoid intrathecal/intravascular injection?

Key themes: technique, aspiration, incremental dosing, interpretation of test dose, vigilance.

  • Correct placement: identify epidural space with loss of resistance (often saline); thread catheter 3–6 cm; secure; aspirate for blood/CSF (not fully sensitive)
  • Test dose: unit policy dependent; aims to detect intrathecal (rapid dense motor block) or intravascular (tachycardia/CNS symptoms) injection; interpret carefully in labour (pain/anxiety) and with β-blockers
  • Incremental dosing: give small aliquots with frequent aspiration and monitoring; observe for rapid onset motor block, tinnitus/metallic taste, circumoral numbness, tachyarrhythmia
  • Avoidance strategies: meticulous aspiration, fractionated dosing, use of adrenaline-containing solutions where appropriate, continuous monitoring after top-ups
  • If suspected intrathecal/intravascular: stop injection, call for help, manage high spinal or LAST as indicated; do not leave patient unmonitored
A patient with an epidural catheter develops new leg weakness and severe back pain 12 hours post-op. What is your differential and immediate plan?

This is a time-critical neuraxial emergency until proven otherwise.

  • Differential: neuraxial haematoma, epidural abscess, intrathecal migration/high local anaesthetic dose, nerve root injury, spinal cord ischaemia, compartment/positioning neuropathy
  • Immediate actions: stop epidural infusion; assess and document neuro status (motor, sensory, reflexes, sphincters); check coagulation/platelets and anticoagulant timing; urgent senior review
  • Escalate: treat as haematoma until excluded—urgent MRI spine and neurosurgical/spinal referral; aim for decompression within hours if confirmed
  • If infection suspected: cultures, inflammatory markers, start antibiotics after discussion; imaging still urgent
  • Analgesia: provide alternative analgesia while epidural stopped; maintain haemodynamic stability
Compare spinal and epidural anaesthesia: onset, density, dosing principles, failure patterns, and complications.

A classic compare-and-contrast viva: be structured.

  • Onset: spinal rapid (minutes); epidural slower (10–20+ min depending on drug/concentration/volume)
  • Density: spinal usually denser sensory/motor block; epidural more titratable and can be predominantly sensory with low-concentration infusions
  • Dosing: spinal—small dose in CSF (baricity and dose important); epidural—larger volumes, spread volume-dependent, incremental top-ups possible
  • Failure: spinal failure less common but can occur (wrong space, no CSF, inadequate dose); epidural failure/patchy block more common (catheter malposition, unilateral block, septae)
  • Complications: spinal—PDPH, high spinal, hypotension; epidural—LAST (intravascular), catheter-related issues, haematoma/abscess, dural puncture; both—nerve injury
How do you assess the level of neuraxial block and decide if it is adequate for surgery?

Examiners want practical bedside tests and understanding of modality vs surgical stimulus.

  • Sensory testing: cold (alcohol swab/ice) correlates with spinothalamic; light touch correlates more with dorsal columns and may better reflect surgical tolerance for some procedures
  • Motor testing: Bromage score; inability to straight-leg raise suggests significant motor block (but motor block is not required for all surgery)
  • Autonomic clues: hypotension, warm peripheries; but do not rely solely on haemodynamics to infer level
  • Match to surgery: e.g. LSCS needs T4 (light touch); hip surgery typically T10–L1 sensory with good femoral/obturator coverage; perineal surgery needs S2–S5
  • If inadequate: allow time, adjust position (spinal), supplement epidural, add systemic analgesia/sedation cautiously, or convert to GA

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