Epidural anaesthesia and analgesia

[1]

Why this is examined / one-line answer

Epidurals are high-stakes: labour analgesia, major open abdominal/thoracic analgesia, and surgical anaesthesia. Examiners want thoracic vs lumbar differences, test dose logic, failure modes, absolute vs relative contraindications, ASRA anticoagulation principles, and a crisp high-block algorithm. One-liner: I place a catheter with LOR, exclude intravascular and intrathecal placement with aspiration and a test dose, titrate to dermatomes, and I never ignore anticoagulation timing or a progressive neurological deficit. [1]

Anatomy and physiology of block

Epidural space: from foramen magnum to sacral hiatus, outside dura, containing fat, veins, lymphatics, nerve roots. LA spreads segmentally along roots; height depends mainly on mass and volume, injection site, age, pregnancy (engorged veins shrink effective volume), and catheter position — not baricity (spinal concept). [1]

Order of fibre sensitivity (teaching): sympathetic → sensory → motor (concentration-dependent). Low-concentration infusions aim for analgesia with motor sparing; surgical anaesthesia needs higher concentration/mass. [1]

Thoracic vs lumbar epidural

CSE combines rapid spinal onset with epidural titration (separate topic). [1]

Indications

• Labour analgesia; conversion to CS anaesthesia with top-up
• Postoperative analgesia: open major abdominal, thoracic, some vascular
• Surgical anaesthesia when titratable lower-density block preferred
• Selected trauma (rib fractures) — risk–benefit with anticoagulation [1]

Absolute and relative contraindications

Absolute (classic teaching):

• Patient refusal
• Local infection at insertion site
• Raised intracranial pressure with herniation risk
• True allergy to LA (rare)
• Uncorrected frank coagulopathy / therapeutic anticoagulation outside safe windows
• Inadequate monitoring / no resuscitation facilities [1]

Relative:

• Systemic sepsis (risk of epidural abscess)
• Fixed cardiac output states (severe AS) — sympathectomy poorly tolerated
• Progressive neurological disease (document carefully)
• Severe hypovolaemia (correct first)
• Anatomical difficulty / previous spinal surgery
• Thrombocytopenia — many units use platelet thresholds (e.g. ≥70–80 × 10⁹/L for insertion, higher caution in rapidly falling counts — follow local + ASRA spirit) [1]

Technique essentials

1. Consent: benefits, failure, PDPH, hypotension, rare nerve injury/haematoma/abscess, motor block.
2. Monitoring, IV access, resuscitation drugs.
3. Position: sitting or lateral; asepsis.
4. Tuohy needle via midline or paramedian.
5. Loss of resistance to saline (or air — saline preferred by many to avoid pneumocephalus/patchy air).
6. Thread catheter 3–5 cm in space (more → knot/migration risk; less → dislodge).
7. Aspirate (blood/CSF).
8. Test dose then incremental therapeutic dosing.
9. Secure, label epidural line, dedicated pump, no IV injection ports without anti-error system. [1]

Test dose

Purpose: detect intrathecal or intravascular catheter before large dose. [1]

Classic adult test dose teaching: lidocaine 45–60 mg (e.g. 3 mL of 1.5–2%) ± adrenaline 15 microg (1:200,000). [1]

Limitations: beta-blockers blunt HR response; labouring women have HR variability; negative test ≠ guaranteed safe forever — always fractionate large top-ups. Aspiration is mandatory but imperfect.[2]

Top-up and dosing principles

• Mass (mg) = concentration × volume drives density and spread.
• Labour analgesia: low-concentration LA + opioid (e.g. bupivacaine/levobupivacaine/ropivacaine 0.0625–0.1% with fentanyl) via infusion/PCEA/programmed intermittent boluses.
• Surgical top-up: higher concentration (e.g. lidocaine 2% ± adrenaline, or ropivacaine/bupivacaine surgical strengths) in divided doses to T4 for CS.
• Postoperative: dilute LA ± opioid infusion; motor and BP checks.
• Warm solutions may speed onset slightly — minor point.
• Max LA dose ceilings still apply across all sites; watch for LAST.[2]

Failure modes

High block / total spinal

Presentation: rapid ascending numbness, arm weakness, dyspnoea, whisper voice, bradycardia, profound hypotension, apnoea, unconsciousness, cardiac arrest. [1]

Management:

1. Call for help; stop further LA.
2. 100% oxygen, support ventilation, intubate if needed (DAS mindset if difficult).[3]
3. Left tilt if pregnant.
4. Vasopressors (phenylephrine/metaraminol/adrenaline as severity demands); fluids.
5. Atropine/glycopyrrolate for bradycardia.
6. CPR if no output — treat as perioperative arrest.
7. Reassure: dense block usually recedes over hours if ventilation/circulation supported.
8. After recovery: review catheter, document, follow neurology.

Anticoagulation timing — ASRA principles (not a full table dump)

You must show you know principles; quote exact hours from current ASRA/local app in clinical practice.[1]

Principles:

1. Epidural haematoma is rare but catastrophic — prevention is timing.
2. Consider drug, dose (prophylactic vs therapeutic), renal function, and combination therapy.
3. Insertion and catheter removal are both high-risk moments — same discipline.
4. After traumatic tap, delay anticoagulation restart.
5. LMWH: classic teaching gaps between dose and neuraxial procedure (prophylactic vs therapeutic differ; twice-daily regimens more restrictive).
6. Unfractionated heparin IV: stop infusion, check aPTT normalised before neuraxial.
7. DOACs: longer holds, renal adjustment — do not guess.
8. Antiplatelet: aspirin alone often acceptable; dual therapy and potent P2Y12 agents are problematic.
9. Neurological observation protocol after removal.
10. If haematoma suspected → immediate MRI and surgical decompression — hours matter for recovery. [1]

Complications (structured)

Common: inadequate block, hypotension, pruritus (opioids), urinary retention, motor block, shivering.
PDPH: after wet tap — postural headache; conservative then epidural blood patch.
LAST: intravascular injection — lipid ready for large top-ups.[2]
Haematoma/abscess: back pain, bilaterally progressive motor/sensory loss, bowel/bladder — emergency.
Nerve injury: rare; document baseline deficits.
Epidural-related maternal fever: inflammatory; distinguish from chorioamnionitis clinically.
Wrong-route injection: systems design (NRFit, labelling).

Monitoring after epidural

• BP, HR, sensory level, motor score (Bromage), sedation if opioid, respiratory rate.
• Labour: CTG collaboration with midwifery/obstetrics.
• Post-op: APS review; anticoagulation plan written before catheter out. [1]

SAQ scaffold

1. Thoracic vs lumbar indications (3)
2. Test dose composition and interpretation (3)
3. Absolute contraindications (3)
4. High spinal management (4)
5. ASRA anticoagulation principles (3)
6. Haematoma red flags (2) [1]

Viva stems

“Top-up for CS — patient says she cannot breathe.” — high block algorithm.
“When can I remove the epidural on enoxaparin?” — ASRA timing principles + local chart.
“Unilateral labour epidural.” — failure mode actions.
“Wet tap — next?” — resite, counsel PDPH, follow-up.
“Why thoracic for laparotomy?” — segmental analgesia, less lower limb block, better dynamic pain control. [1]

Common traps

• Large single-shot top-up without fractionation.
• Ignoring anticoagulation for catheter removal.
• Calling every fever chorioamnionitis without thought — and the reverse.
• Missing LAST while chasing high spinal (or vice versa).
• Documenting “working epidural” with patient still in severe pain. [1]

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Red flags

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References

1. [1]Horlocker TT et al. Regional Anesthesia in the Patient Receiving Antithrombotic or Thrombolytic Therapy: American Society of Regional Anesthesia and Pain Medicine Evidence-Based Guidelines (Fourth Edition) Reg Anesth Pain Med, 2018.PMID 29561531
2. [2]Neal JM et al. The Third American Society of Regional Anesthesia and Pain Medicine Practice Advisory on Local Anesthetic Systemic Toxicity: Executive Summary 2017 Reg Anesth Pain Med, 2018.PMID 29356773
3. [3]Frerk C, Mitchell VS, McNarry AF, et al. Difficult Airway Society 2015 guidelines for management of unanticipated difficult intubation in adults Br J Anaesth, 2015.PMID 26556848