Anaesthetic Management: Electrical Burn Posted for Amputation

1. Understanding the Pathophysiology (Determines Anaesthetic Risk)

• Low-voltage (<1000 V): injury limited to contact site
• High-voltage (>1000 V): deep tissue destruction extending into muscle around long bones; commonly requires amputation

2. Pre-operative Assessment

Cardiovascular

• ECG is mandatory. Most common dysrhythmia: sinus tachycardia with ST/T-wave changes
• Conduction defects (heart blocks) are common
• Cardiac standstill / ventricular fibrillation are the most serious complications
• Myocardial injury behaves like contusion, not MI — minimal haemodynamic consequence but dysrhythmia risk persists
• Cardiac enzymes may be unreliable (normal CK/troponin does NOT exclude conduction system injury)
• Patients without ECG changes on presentation are unlikely to develop life-threatening arrhythmias → guides monitoring intensity

Renal

• High-voltage injury → rhabdomyolysis → myoglobinuria → acute tubular necrosis
• Check urine colour (dark/cola = myoglobinuria), serum creatinine, electrolytes, myoglobin/CK
• Urine output target ≥1–2 mL/kg/hr if myoglobinuria is present (vs 0.5 mL/kg/hr standard)
• Established AKI significantly alters drug choice and dosing

Fluid Status

• Formula-based resuscitation (Parkland etc.) is inadequate in electrical burns — surface burn underestimates total injury (deep visceral injury + rhabdomyolysis)
• Assess volume status: look for hypovolaemia from fluid shifts and third-spacing

Musculoskeletal / Neurological

• Assess for compartment syndrome (fasciotomy may have already been done)
• Tetanic muscular contractions during electrocution can cause vertebral fractures → spine clearance if high-voltage mechanism
• Evaluate for blunt thoracic/abdominal trauma and spinal cord injury (event-related fall or forceful ejection)
• Peripheral neuropathy at the amputation site is likely → affects regional technique planning

Airway

• If burns involve the face/neck/airway: assess for inhalation injury, oropharyngeal/supraglottic oedema
• Contractures from prior burn wound management may restrict neck movement → anticipate difficult airway

Metabolic / Haematological

• Hypermetabolic state in major burns → increased O₂ demand, altered drug pharmacokinetics
• Anaemia (chronic in post-burn patients awaiting amputation)
• Electrolytes: hypernatraemia if hypertonic saline was used; hyperkalaemia risk from tissue necrosis and rhabdomyolysis
• Blood glucose disturbance; hepatic function altered in extensive burns

3. Key Pharmacological Considerations

Succinylcholine — CONTRAINDICATED

• Denervated and chronically damaged muscle upregulates extrajunctional acetylcholine receptors
• Succinylcholine causes massive potassium efflux → potentially fatal hyperkalaemia
• Onset of risk: ~48–72 hours post-burn and persists for months (until wound healed)
• If the patient presents >48 hours after injury (which is typical for an elective/semi-elective amputation posting), succinylcholine is absolutely contraindicated
• Use rocuronium (1.2 mg/kg for RSI) with sugammadex reversal available

Other NMBDs

• Burns patients are resistant to non-depolarising neuromuscular blockers — require higher doses (up to 2–3× normal) due to receptor upregulation
• Monitor with peripheral nerve stimulator meticulously

Volatile Agents

• Ketamine is historically favoured in burn patients — preserves cardiovascular tone, provides analgesia, useful for induction and TIVA
• Sevoflurane/isoflurane: standard; no absolute contraindication
• Propofol: caution with haemodynamic instability and propofol infusion syndrome risk in prolonged cases

Opioids & Analgesia

• Markedly increased opioid requirements in chronic burn patients (tolerance, hypermetabolic clearance)
• Multimodal approach: ketamine (sub-anaesthetic infusion), regional blocks, NSAIDs (if renal function permits), paracetamol
• Pre-operative pain management should be optimised — uncontrolled pre-op pain predicts difficult intraoperative anaesthesia

4. Anaesthetic Technique Options

Regional Anaesthesia (Preferred adjunct / possible primary technique)

• Neuraxial (spinal/epidural): excellent for lower limb amputations; provides dense block, post-op analgesia, attenuates sympathetic response
  • Spinal: reliable, dense motor block — preferred for below-knee/transtibial
  • Epidural: allows titration and post-op catheter analgesia — preferred for above-knee or bilateral
  • Relative contraindications: coagulopathy, local infection at site, haemodynamic instability, uncleared spinal injury
• Peripheral nerve blocks:
  • Upper limb: brachial plexus block (infraclavicular/axillary) for hand/forearm amputation — also provides vasodilation, beneficial for circulation to stump
  • Lower limb: femoral + sciatic, or adductor canal + popliteal sciatic depending on level
  • Continuous nerve catheters provide post-operative analgesia and may reduce phantom limb pain development
• Benefits of regional: reduces opioid consumption, haemodynamic stability, reduced volatile requirement, may reduce incidence of phantom limb pain (controversial but biologically plausible)

General Anaesthesia

• Often required or combined with regional for proximal amputations and in uncooperative/haemodynamically unstable patients
• Induction: ketamine (1–2 mg/kg IV) ± propofol titrated to haemodynamic state; or etomidate (1 single dose) if severely compromised (note: adrenal suppression concern with etomidate infusion)
• Airway: RSI if full stomach risk, airway involvement, or delayed gastric emptying (common in major burns)
  • Use rocuronium (not succinylcholine)
  • Have video laryngoscope and difficult airway equipment immediately available
• Maintenance: volatile agent or TIVA; ketamine infusion (0.1–0.5 mg/kg/hr) reduces volatile requirements and provides analgesia

5. Intraoperative Monitoring

6. Intraoperative Management

Haemodynamics

• Expect significant blood loss in amputation — have blood products available (cross-matched blood, FFP)
• Vasopressors/inotropes on standby (noradrenaline preferred)
• Tourniquet use: helpful to reduce blood loss but may not be feasible if extensive proximal tissue damage

Arrhythmia Management

• Ongoing ECG monitoring; have defibrillator available
• Pre-treat magnesium deficiency if present (common in burns)
• Avoid hypokalaemia (proarrhythmic)

Temperature

• Warm IV fluids, forced-air warming, increase theatre temperature
• Burn patients lose thermoregulatory capacity — hypothermia worsens coagulopathy and cardiac excitability

Electrolytes / Metabolic

• Monitor K⁺ closely — risk of hyperkalaemia (rhabdomyolysis, tissue necrosis, succinylcholine effects if inadvertently given)
• Correct metabolic acidosis — lactic acidosis common from tissue hypoperfusion
• Glucose management: target normoglycaemia

7. Post-operative Management

Analgesia

• Continue regional catheter if placed (epidural or peripheral nerve catheter)
• IV ketamine infusion (sub-anaesthetic) as adjunct
• Opioids titrated to effect — expect high requirements
• Phantom limb pain: early regional analgesia (pre- and post-op nerve blocks/catheters) reduces but doesn't eliminate risk
  • Consider gabapentin/pregabalin perioperatively
  • NMDA antagonists (ketamine, memantine) — supportive role

Ventilation

• Extubate early if airway not compromised and haemodynamics stable
• If inhalation injury or large fluid shifts: consider planned post-op ventilation in ICU

Fluid Management

• Continue goal-directed fluid therapy based on urine output and haemodynamic targets
• If myoglobinuria persists: sodium bicarbonate IV to alkalinise urine (targets urine pH >6.5) + maintain high urine output
• Avoid nephrotoxic drugs (aminoglycosides, NSAIDs if AKI)

ICU Disposition

• High-voltage electrical burn with amputation warrants ICU post-operative care in most cases
• Monitor for: ongoing dysrhythmias, AKI progression, electrolyte disturbances, wound-related sepsis, DIC

8. Summary of Key Anaesthetic Pitfalls

• Miller's Anesthesia, 2-Volume Set 10e — Electrical Injury and Burn Anesthesia
• Standard anaesthetic principles for trauma and burn patients