Anaesthesia for Burns Patients

Quick Answer

Burns anaesthesia presents challenges: airway management (inhalation injury, swelling), fluid resuscitation (Parkland formula: 4 mL/kg/%TBSA in 24 hours - half in first 8 hours), temperature control (massive heat loss through exposed wounds), suxamethonium contraindication after 24-48 hours (risk of hyperkalemic cardiac arrest due to upregulated acetylcholine receptors), blood loss (excision of 1% TBSA ≈ 50-100 mL blood loss). Inhalation injury: Early intubation if suspected (soot in sputum, facial burns, hoarse voice, singed nasal hairs), supraglottic edema peaks at 12-24 hours. Positioning: Full exposure for surgery, warming essential (forced air, fluid warmers, operating room 30°C). Analgesia: Multimodal (opioid PCA, ketamine, regional blocks), high requirements early. Excision and grafting: staged (20% TBSA per session max), massive transfusion protocols. [1-10]

Pathophysiology

Burn Depth and Severity

Depth Classification:

• Superficial (1st degree): Epidermis only, painful, erythematous, heals 3-7 days
• Partial thickness (2nd degree):
  • Superficial: Dermal papillae, blistered, very painful, heals 2-3 weeks
  • Deep: Deep dermis, less painful (nerve damage), requires grafting
• Full thickness (3rd degree): Entire dermis + fat, painless (nerve destruction), requires excision and grafting
• 4th degree: Into muscle/bone

Total Body Surface Area (TBSA):

• Rule of 9s: Head 9%, each arm 9%, each leg 18%, front torso 18%, back 18%, perineum 1%
• Lund-Browder chart: More accurate (adjusts for age)
• Palm method: Patient's palm = 1% TBSA (for scattered burns)

Severity Classification:

• Major: >20% TBSA (adult), >10% TBSA (child), full thickness >5%, inhalation injury, electrical/chemical, hands/face/genitals
• Moderate: 10-20% TBSA, partial thickness
• Minor: <10% TBSA

Systemic Effects of Burns

Cardiovascular:

• Capillary leak: Albumin and fluid extravasation → hypovolemia
• Hemoconcentration: Elevated hematocrit early
• Cardiac output: Initially decreased (myocardial depressant factor), then increased (hypermetabolic state)
• SVR: Decreased (systemic inflammatory response)
• Blood volume: Requires 2-4× normal maintenance fluids

Pulmonary:

• Inhalation injury: Direct thermal injury to upper airway, chemical injury to lower airway (toxic gases)
• ARDS: From systemic inflammation, fluid resuscitation
• Carbon monoxide poisoning: CO binds Hb 200× more than O₂, reduces O₂ carrying capacity
• Cyanide poisoning: From combustion of plastics/synthetics

Renal:

• Acute kidney injury: Hypovolemia, myoglobinuria (rhabdomyolysis in deep burns), nephrotoxic drugs
• Fluid requirements: Massive resuscitation volumes

Metabolic:

• Hypermetabolic state: 1.5-2× basal metabolic rate
• Hypercatabolism: Muscle wasting, negative nitrogen balance
• Hyperglycemia: Stress response, insulin resistance
• Hyponatremia: Dilutional from resuscitation

Hematological:

• Anemia: Blood loss from wounds, hemolysis, dilution
• Coagulopathy: Consumption, hemodilution, hypothermia
• Thrombocytopenia: Consumption, bone marrow suppression

Immunological:

• Immunosuppression: Increased infection risk
• Sepsis: Major cause of death after initial resuscitation period

Pathophysiological Changes Relevant to Anaesthesia

Airway Edema:

• Mechanism: Thermal injury → capillary leak → edema
• Timeline: Begins immediately, peaks 12-24 hours
• Risk: Complete airway obstruction if not intubated early
• Predictors: Facial burns, inhalation injury, circumferential neck burns

Suxamethonium Contraindication:

• Mechanism: Upregulation of acetylcholine receptors (denervation-like state)
• Timeline: After 24-48 hours post-burn, persists until healed (>1 year for large burns)
• Risk: Massive potassium release (up to 10-15 mmol/L) → cardiac arrest
• Alternative: Rocuronium (larger doses may be needed, 0.6-1.2 mg/kg)

Temperature Regulation:

• Heat loss: Evaporative losses from wounds (200-400 mL/m²/hour water loss)
• Hypothermia: Rapid heat loss due to impaired skin barrier
• Consequences: Coagulopathy, delayed drug metabolism, cardiac arrhythmias

Pharmacokinetic Changes:

• Increased volume of distribution: Fluid resuscitation, edema
• Altered protein binding: Hypoalbuminemia
• Changed elimination: Altered hepatic/renal blood flow

Clinical Presentation

Initial Assessment

Primary Survey (ABC):

• Airway: Assess for inhalation injury (soot, hoarseness, stridor, singed hairs)
  • Early intubation: If any suspicion of inhalation injury or significant facial burns
  • C-spine protection: If mechanism suggests (falls, explosions)
• Breathing: Oxygenation, ventilation, CO poisoning, cyanide
• Circulation: Estimate %TBSA, start fluid resuscitation, assess perfusion

Secondary Survey:

• %TBSA: Calculate using rule of 9s or Lund-Browder
• Depth: Assess burn depth (may be difficult initially)
• Circumferential burns: Check distal perfusion (escharotomy needed if compromised)
• Associated injuries: Trauma from escape attempts, falls, explosions
• Medical history: Medications, allergies, tetanus status

Specific Assessments:

• Inhalation injury indicators:
  • History of closed space fire
  • Facial burns, singed nasal hairs
  • Soot in sputum/oropharynx
  • Hoarse voice, stridor
  • Altered mental status (CO poisoning)
• Carbon monoxide: COHb level (pulse oximetry unreliable - reads falsely high)
• Cyanide: Plasma lactate (elevated), smell of bitter almonds (unreliable)

Fluid Resuscitation

Parkland Formula (Most Common):

• Total fluid in 24 hours: 4 mL × kg body weight × %TBSA
• First 8 hours: Half of total (from time of burn, not arrival)
• Next 16 hours: Remaining half
• Fluid: Lactated Ringer's (Hartmann's) preferred
• Maintenance fluids: Added to resuscitation (e.g., dextrose saline for children)

Example:

• 70 kg patient, 40% TBSA burn
• Total = 4 × 70 × 40 = 11,200 mL in 24 hours
• First 8 hours = 5,600 mL (700 mL/hour)
• Next 16 hours = 5,600 mL (350 mL/hour)

Modifications:

• Adults: May adjust based on urine output (0.5-1 mL/kg/hour)
• Children: Use pediatric formula (3 mL/kg/%TBSA), add maintenance
• Electrical burns: Higher fluid requirements (deep tissue injury)
• Inhalation injury: Higher fluid requirements

Monitoring:

• Hourly urine output: 0.5-1 mL/kg/hour (adult), 1-2 mL/kg/hour (child)
• Vital signs: HR, BP, SpO₂, temperature
• Blood work: Hb, electrolytes, lactate, creatinine, coagulation
• Endpoints: Urine output, lactate clearance, mental status

Complications of Over-resuscitation:

• Compartment syndromes: Abdominal, extremity
• ARDS: Excessive fluid → pulmonary edema
• Cerebral edema: Especially in children

Complications of Under-resuscitation:

• Acute kidney injury: Hypoperfusion, myoglobinuria
• Shock: Hypovolemic, irreversible
• Death: Multi-organ failure

Management

Airway Management

Indications for Early Intubation:

• Inhalation injury (clinical suspicion)
• Facial/neck burns with risk of edema
• Altered mental status (CO poisoning, trauma)
• Need for procedural sedation (escharotomies)
• Hemodynamic instability

Intubation Technique:

• C-spine precautions: Manual in-line stabilization if trauma suspected
• Difficult airway anticipated: Facial edema, limited mouth opening (circumferential burns)
• Equipment: Video laryngoscope, difficult airway cart, surgical airway equipment
• ETT: Uncuffed (children) or cuffed (adults), secure well (edema increases risk of accidental extubation)

Post-Intubation:

• Ventilation: Lung-protective strategy (low tidal volume, appropriate PEEP)
• ARDS management: If develops
• Weaning: Delayed until airway edema resolves (leak test, bronchoscopy)

Anaesthetic Considerations

Preoperative Assessment:

• %TBSA and depth: Determines blood loss, fluid requirements
• Stage of resuscitation: Acute (0-48 hours) vs. subacute (>48 hours)
• Inhalation injury: Affects ventilation strategy
• Medical history: Comorbidities, medications
• Nutritional status: Catabolic state, feeding regimen

Premedication:

• Anxiolysis: Midazolam (if not intubated), but cautiously (respiratory depression)
• Antisialagogue: Glycopyrrolate (reduce secretions)
• Analgesia: Continue baseline analgesia

Monitoring:

• Standard: ECG, SpO₂, NIBP, EtCO₂
• Arterial line: Beat-to-beat BP, frequent ABGs
• Central line: CVP, large bore access (blood products)
• Temperature: Core + peripheral (esophageal, bladder, skin)
• Urine output: Hourly
• Blood loss: Serial Hb, visual estimation
• BIS: Depth monitoring (multimodal analgesia)

Induction:

• Concerns: Full stomach (delayed gastric emptying), hypovolemia, difficult airway
• Technique:
  • RSI often indicated (full stomach, decreased gastric motility)
  • Ketamine 1-2 mg/kg (maintains BP, analgesic) OR
  • Propofol cautiously (reduce dose, hemodynamic effects) OR
  • Etomidate (hemodynamically stable)
• Muscle relaxant:
  • Contraindication: Suxamethonium if burn >24-48 hours old
  • Alternative: Rocuronium 1.2 mg/kg (for RSI) or 0.6 mg/kg
• Airway: ETT (size appropriate for edema)

Maintenance:

• TIVA or balanced: Propofol or sevoflurane acceptable
• Opioids: High requirements
  • Fentanyl 10-20 μg/kg or infusion
  • Remifentanil infusion (0.1-0.3 μg/kg/min)
  • Ketamine 0.2-0.5 mg/kg/hour (analgesic, sympathetic stimulation)
• Muscle relaxation: Rocuronium (maintain block)

Temperature Management:

• Warming strategies (critical):
  • Operating room: 30°C minimum (often 32-34°C)
  • Forced air warming: Upper body + lower body blankets
  • Fluid warming: All IV fluids/blood products
  • Heated mattress: Under patient
  • Minimize exposure: Cover non-operative sites
  • Blood warmer: For large transfusions
• Target: Normothermia (36-37°C)

Fluid and Blood Management:

• Maintenance: Continue resuscitation fluids if <24 hours post-burn
• Blood loss replacement:
  • Excision of 1% TBSA ≈ 50-100 mL blood loss
  • Example: 20% TBSA excision = 1000-2000 mL blood loss
• Transfusion trigger: Hb 70-80 g/L (or higher if comorbidities)
• Blood products:
  • PRBC (massive transfusion protocol if >10 units)
  • FFP: If coagulopathic (dilutional, hypothermic)
  • Platelets: If <50 × 10⁹/L or active bleeding
  • Fibrinogen: If <1.5 g/L (cryoprecipitate or concentrate)
• Cell salvage: Useful if large excision

Surgical Considerations

Excision and Grafting:

• Timing:
  • Early excision (within 24-72 hours): Reduces infection, improves outcomes
  • Staged: 20% TBSA per session maximum
• Technique:
  • Tangential excision: Sequential shaving until viable tissue
  • Fascial excision: Full thickness to fascia (less bleeding, more cosmetic deformity)
  • Skin grafting: Split-thickness autograft (meshed or sheet)
• Blood loss: Significant (prepare for massive transfusion)

Escharotomies:

• Indications: Circumferential full-thickness burns compromising circulation or ventilation
• Chest/esophagus: Impaired ventilation
• Limbs: Compartment syndrome (assess pulses, Doppler, pressure)
• Technique: No anaesthesia needed (full thickness, insensate) or ketamine sedation

Postoperative Management

Extubation:

• Criteria: Similar to general criteria
• Airway concerns: Edema may preclude early extubation
• Analgesia: Ensure adequate (PCA or regional techniques)

Analgesia Strategy:

• Multimodal:
  • Opioids: Morphine PCA, fentanyl infusion transitioning to oral
  • Ketamine: Low dose infusion (0.1-0.3 mg/kg/hour) or oral
  • NSAIDs: If no renal failure (ketorolac, ibuprofen)
  • Paracetamol: 1 g q6h (reduce opioid needs 20-30%)
  • Gabapentinoids: Pregabalin 75-150 mg BD
• Regional techniques:
  • Catheter techniques if feasible (limited by dressing changes)
  • Acute pain service involvement
• Dressing changes: Can be very painful (consider ketamine or propofol sedation)

ICU Care:

• Ventilation: If intubated, lung-protective strategy
• Sedation: Propofol or dexmedetomidine
• Nutrition: Early enteral feeding (within 6-12 hours if resuscitated)
• Infection control: Strict asepsis, surveillance cultures
• Rehabilitation: Early mobilization, physiotherapy

Indigenous Health Considerations

Aboriginal and Torres Strait Islander Patients

Higher Risk:

• Rural/remote burns: Children especially at risk from campfires, scalds
• Cultural practices: Fire use in ceremonies (risk of burns)
• Delayed presentation: Remote communities, transport challenges
• Scald burns: Common in children (domestic hot water)

Access Issues:

• Geographic barriers: Burns units mainly in major cities (Sydney, Melbourne, Brisbane, Perth, Adelaide)
• Retrieval: RFDS, state-based retrieval for major burns
• Family separation: Extended treatment periods, family support needed
• Communication: Interpreter services if English not first language

Postoperative Care:

• Wound care: Extended dressing changes, scar management
• Rehabilitation: Physiotherapy, occupational therapy (pressure garments)
• Return to community: Planning for remote discharge
• Cultural healing: Integration with traditional healing practices if desired

Māori Health Considerations

Health Disparities:

• Higher rates of burns in some communities
• Access to specialized burns care

Cultural Safety:

• Whānau involvement: Family support during long treatment
• Communication: Clear explanations about procedures
• Discharge planning: Coordination with primary care and Māori health services
• Rehabilitation: Access to culturally appropriate services

ANZCA Final Exam Focus

SAQ Patterns

Common Questions:

• "How would you manage the airway in a patient with facial burns?"
• "Calculate the fluid resuscitation using the Parkland formula."
• "What are the anaesthetic considerations for a patient having burn excision 5 days post-injury?"
• "Describe the pathophysiology that makes suxamethonium dangerous in burns patients."

Marking Scheme Priorities:

• Inhalation injury assessment and airway management
• Fluid resuscitation calculation (Parkland formula)
• Suxamethonium contraindication and alternatives
• Temperature management strategies
• Blood loss estimation and massive transfusion
• Analgesia (multimodal, high requirements)

Viva Scenarios

Scenario 1: Inhalation Injury

• Soot in sputum, facial burns
• Decision to intubate
• Ventilation strategy

Scenario 2: Major Burns Excision

• 30% TBSA excision
• Blood loss estimation (1500-3000 mL)
• Temperature management
• Massive transfusion protocol

Scenario 3: Suxamethonium Contraindication

• Day 3 post-burns
• Upregulated acetylcholine receptors
• Hyperkalemic cardiac arrest risk
• Use rocuronium instead

Key Points for Examination Success

1. Parkland formula: 4 mL × kg × %TBSA, half in first 8 hours, LR preferred
2. Inhalation injury: Early intubation if suspected (edema peaks 12-24 hours)
3. Suxamethonium: Contraindicated after 24-48 hours (up to 1 year) - use rocuronium
4. Temperature: Operating room 30°C, forced air warming, fluid warmers essential
5. Blood loss: 50-100 mL per %TBSA excised, prepare for massive transfusion
6. Carbon monoxide: Pulse oximetry unreliable (falsely normal), measure COHb
7. Analgesia: Multimodal, high opioid requirements, ketamine useful
8. Stages: Acute resuscitation (fluids), subacute (excision/grafting), rehabilitation
9. Complications: Compartment syndrome (escharotomy), hyperkalemia, hypothermia, sepsis

References

1. ANZCA. PS48. Statement on Anaesthesia Care of the Severely Injured. 2019.
2. ANZBA. Australian and New Zealand Burn Association. Emergency Management of Severe Burns Course Manual. 2021.
3. Pham TN et al. American Burn Association practice guidelines. J Burn Care Res. 2008;29(1):200-223.
4. Sheridan RL. Comprehensive treatment of burns. Curr Probl Surg. 2012;49(10):641-742.
5. Kagan RJ et al. Surgical management of burns. In: Herndon DN (ed). Total Burn Care. 5th ed. Elsevier; 2018:135-148.
6. Sood P et al. Anaesthesia for burns patients. BJA Educ. 2020;20(12):403-410.
7. Martyn JA et al. Succinylcholine-induced hyperkalemia in acquired pathologic states. Anesthesiology. 2006;104(1):158-169.
8. ATSI Health. Burns in Australia. Australian Institute of Health and Welfare; 2019.