ANESTHETIC MANAGEMENT OF BURNS PATIENT

MD Anaesthesiology Exam Notes

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1. EPIDEMIOLOGY & SIGNIFICANCE

• Burns are the second most common cause of accidental death, after motor vehicle accidents
• 11 million new burns annually worldwide; ~180,000 deaths per year
• Children (high BSA:mass ratio) and elderly (thinner skin) are at greatest risk for major burns
• Second- or third-degree burns involving >20% TBSA require specialized burn center care
• The anesthesiologist is involved at multiple stages: resuscitation, airway management, operative debridement/grafting, ICU care, and repeated dressing changes

Morgan & Mikhail's Clinical Anesthesiology, 7e; Barash Clinical Anesthesia, 9e

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2. CLASSIFICATION OF BURNS

• Head & neck: 9%
• Each upper limb: 9%
• Chest (anterior): 9%; Abdomen (anterior): 9%
• Upper back: 9%; Lower back: 9%
• Each thigh: 9%; Each lower leg + foot: 9%
• Perineum: 1%

Morgan & Mikhail's Clinical Anesthesiology, 7e

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3. PATHOPHYSIOLOGY OF MAJOR BURNS

3.1 Two Temporal Phases

Phase 1: Burn Shock / Ebb Phase (0–48 hours)

• Massive release of inflammatory mediators (histamine, prostaglandins, reactive oxygen species, cytokines, DAMPs)
• Capillary leak with loss of plasma proteins into interstitium — both injured and non-injured tissue
• Hypovolemia, hemoconcentration, raised haematocrit
• Cardiac output falls up to 50–60% within 30 minutes (normovolemic hypoperfusion = "burn shock")
• Massive vasoconstriction
• Reduced urine output; risk of acute kidney injury
• Loss of endothelial barrier function → transcapillary fluid loss + evaporative loss through broken skin

Phase 2: Hypermetabolic State / Flow Phase (48–72 hours onward)

• Inflammatory cytokines drive systemic vasodilation
• Hyperdynamic circulation: raised CO, tachycardia
• Elevated basal body temperature; markedly increased O₂ consumption
• Muscle protein catabolism; severe negative nitrogen balance
• Impaired immune function; risk of sepsis
• This phase can persist for months to years after injury — highlighting need for aggressive nutritional support

Barash Clinical Anesthesia, 9e; Morgan & Mikhail's Clinical Anesthesiology, 7e; Miller's Anesthesia, 10e

3.2 Local Burn Wound

• Zone of coagulation (central, irreversible)
• Zone of stasis (potentially salvageable)
• Zone of hyperaemia (peripheral, recovers)

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4. INHALATION INJURY

4.1 Three Types (may coexist)

4.2 Diagnosis of Inhalation Injury

• Burns in an enclosed space
• Unconsciousness at scene
• Singed nasal vibrissae / facial hair
• Carbonaceous (sooty) sputum
• Hoarse voice, stridor
• Soot/erythema in oropharynx
• Facial/neck burns

• Flexible bronchoscopy — gold standard (diagnoses and grades severity, predicts mortality/ICU LOS)
• ABG: PaO₂, HbCO level, carboxyhemoglobin, methemoglobin
• Pulse oximetry is unreliable (cannot distinguish HbO₂ from HbCO)
• CXR, CT thorax

Barash Clinical Anesthesia, 9e

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5. CARBON MONOXIDE AND CYANIDE POISONING

5.1 Carbon Monoxide (CO) Poisoning

• CO binds haemoglobin with affinity ~250× greater than O₂ → reduces O₂ carrying capacity
• Shifts oxyhaemoglobin dissociation curve to the left → impairs O₂ release to tissues
• Pulse oximetry is falsely normal — SpO₂ reads HbCO as oxyhaemoglobin

• 100% O₂ via tight-fitting non-rebreather mask (t½ of HbCO falls from 5 hours in room air → 60–90 min on 100% O₂)
• If HbCO >20%: intubate + mechanically ventilate with FiO₂ 1.0
• Hyperbaric oxygen (HBO) therapy — indicated for significant CO poisoning; multiple sessions needed

5.2 Cyanide Poisoning

• From combustion of plastics, synthetics (polyurethane, nylon)
• Blocks cytochrome c oxidase → histotoxic hypoxia
• Suspect when: lactic acidosis, altered consciousness despite normal SpO₂/PaO₂
• Treatment: sodium thiosulphate + hydroxocobalamin (or dicobalt edetate)

Morgan & Mikhail's Clinical Anesthesiology, 7e

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6. FLUID RESUSCITATION

6.1 Indications

• Adults: burns >15% TBSA
• Children: burns >10% TBSA
• First-degree burns are excluded from TBSA calculation

6.2 Standard Formulas

Parkland Formula (most widely used)

• Total volume in first 24h = 4 mL × kg × % TBSA (Lactated Ringer's / Plasmalyte)
• Half given in first 8 h (from time of burn, not hospital arrival)
• Remaining half over next 16 h
• Second 24 hours: 0.8 mL/kg/% TBSA (5% dextrose) + 0.015 mL/kg/% TBSA (5% albumin)

Modified Brooke Formula

• 2 mL × kg × % TBSA in first 24 h
• Half in first 8 h, remainder over next 16 h
• Second 24 h: colloid added

Muir & Barclay Formula (UK)

• Colloid-based (fresh frozen plasma or albumin)

Barash Clinical Anesthesia, 9e; Miller's Anesthesia, 10e

6.3 Monitoring Adequacy of Resuscitation

• Target urine output: 0.5–1.0 mL/kg/h (adults), 1.0 mL/kg/h (children)
• If UO >1 mL/kg/h → slow infusion rate
• Adjuncts: invasive arterial monitoring, CVP, cardiac output monitoring

6.4 Fluid Creep

• Phenomenon where administered volumes exceed calculated goals (often >6 mL/kg/% TBSA in 24 h vs. Parkland's 4 mL/kg)
• Occurs due to: miscalculating TBSA (including first-degree), sedation-related hypotension treated with fluids, pressure to respond to any hemodynamic change
• Consequences of fluid creep:
  • Pulmonary oedema / ARDS
  • Abdominal compartment syndrome (ACS)
  • Conversion of partial to full-thickness burns
  • Raised intraocular pressure
  • Muscle compartment syndromes requiring fasciotomy

6.5 Choice of Fluid

• Balanced crystalloids (Ringer's Lactate / Plasmalyte) are preferred for initial resuscitation
• Avoid:
  • Normal saline (hyperchloraemic acidosis)
  • Hypertonic saline (increased AKI risk)
  • Blood transfusion in early phase (increased mortality)
  • Albumin/colloid in early phase — controversial (capillary leak may allow oncotically active molecules to extravasate)
• Colloids may be used after 12–24 h to reduce total fluid load

6.6 Abdominal Compartment Syndrome (ACS)

• Risk when: circumferential abdominal burns OR >6 mL/kg/% TBSA administered
• Monitor: intravesical (bladder) pressure via Foley catheter connected to pressure transducer
  • Zero at pelvic brim; instil 20 mL fluid; measure after 60 s
  • IAP >20 mmHg = ACS → abdominal decompression
• Risk of Pseudomonas infection if laparotomy near burned tissue

Morgan & Mikhail's Clinical Anesthesiology, 7e; Miller's Anesthesia, 10e

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7. AIRWAY MANAGEMENT IN BURNS

7.1 Indications for Early Intubation

Critical principle: Upper airway oedema progresses relentlessly during fluid resuscitation. Early intubation is safer than delayed; a patent airway today may be impassable in 4–6 hours.

7.2 Approach to Intubation

• Awake fibreoptic intubation (AFOI) is technique of choice for anticipated difficult airway (facial burns, oropharyngeal oedema, limited neck mobility)
• Rapid sequence induction (RSI) appropriate for early presentations (<48 h) without oedema
• Use succinylcholine only within first 24–48 hours (see muscle relaxant section)
• Have surgical airway (cricothyrotomy kit / tracheostomy) immediately available
• Video laryngoscopy as alternative
• Document airway carefully — multiple providers will manage over time

7.3 Tube Choice and Ventilation

• Use uncut ETT (swelling makes tube shortening dangerous)
• Secure tube carefully (circumferential burns make adhesive tape unreliable — use ties)
• Tracheostomy may be necessary for long-term ventilation (>2 weeks)
• Protective ventilation:
  • Tidal volume 6 mL/kg ideal body weight
  • PEEP 5–8 cmH₂O (higher if inhalation injury + ARDS)
  • Permissive hypercapnia if needed
  • Target SpO₂ >95% based on co-oximetry, not pulse oximetry

Barash Clinical Anesthesia, 9e; Morgan & Mikhail's Clinical Anesthesiology, 7e

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8. MUSCLE RELAXANTS IN BURNS

8.1 Mechanism of Altered Response

• Both fetal (α₂βγδ) and mature (α₂βεδ) subtype isoforms proliferate
• Increased quantal content of evoked ACh release (noted by 72 hours post-injury)
• Changes in diaphragm acetylcholinesterase content and molecular forms

• Resistance to non-depolarising neuromuscular blockers (NDNMBs)
• Hypersensitivity / exaggerated response to succinylcholine

8.2 Succinylcholine

• Mechanism: Upregulated extrajunctional receptors release massive K⁺ on depolarisation
• Serum K⁺ may reach 13 mEq/L → ventricular tachycardia, ventricular fibrillation, cardiac arrest
• Magnitude of hyperkalaemia does not correlate with burn size (lethal hyperkalaemia reported with as little as 8% TBSA burn)
• Burns involve >25% TBSA typically to show clear resistance; but CONTRAINDICATION applies to ALL burns after 48 h

Other conditions causing nAChR upregulation (same succinylcholine risk): spinal cord injury, prolonged immobility, stroke, Guillain-Barré syndrome, multiple sclerosis, prolonged NDNMB exposure

Miller's Anesthesia, 10e; Morgan & Mikhail's Clinical Anesthesiology, 7e

8.3 Non-Depolarising Neuromuscular Blockers

• Resistance typically seen when burns involve >25% TBSA
• May require 2–5× normal dose to achieve adequate relaxation
• Recovery to pre-burn neuromuscular function can take months to years
• Mandatory quantitative neuromuscular monitoring (TOF ratio, PTC) — wide inter-individual variation
• Drug choice: rocuronium (high-dose for RSI if sux contraindicated: 1.2 mg/kg), vecuronium, cisatracurium (useful in multi-organ failure — Hofmann elimination)

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9. PHARMACOKINETICS IN BURNS

9.1 Absorption

• Delayed gastric emptying (early phase)
• Increased skin absorption of topical agents

9.2 Distribution

• Increased volume of distribution (Vd) for hydrophilic drugs (oedema expands extracellular space)
• Hypoalbuminaemia (capillary leak, catabolism) → increased free fraction of protein-bound drugs
• Raised α₁-acid glycoprotein → increased binding of basic drugs (e.g., lidocaine)
• Anaemia in later phases

9.3 Metabolism

• Phase 1 (ebb): reduced hepatic blood flow → reduced drug metabolism
• Phase 2 (flow): hypermetabolic state → markedly increased hepatic blood flow and enzyme activity → increased clearance of many drugs
• Induction of CYP450 enzymes

9.4 Elimination

• AKI (early) reduces renal clearance
• Polyuria (later hypermetabolic phase) increases renal drug clearance
• Altered morphine pharmacokinetics confirmed in burns patients during surgery

• Opioids: may need higher doses in hypermetabolic phase; titrate carefully
• Propofol: increased clearance in hypermetabolic phase
• Ketamine: often drug of choice (see below) — maintains haemodynamic stability
• Midazolam: increased Vd — higher loading doses

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10. PREOPERATIVE ASSESSMENT

10.1 History

• Time, mechanism (thermal/chemical/electrical), place (open vs. enclosed space)
• Estimate % TBSA, depth of burns
• Associated trauma (fall, blast, explosion)
• CO/cyanide exposure history
• Comorbidities (especially cardiac, respiratory, renal, diabetes)
• Current medications, known allergies
• Volume of fluid given so far; response; urine output

10.2 Examination

• Airway: facial burns, singed vibrissae, oropharyngeal soot/oedema, mouth opening, neck mobility
• Respiratory: RR, SpO₂, breath sounds, stridor
• Cardiovascular: HR, BP, perfusion — signs of burn shock or hyperdynamic state
• Neurological: GCS, orientation — CO poisoning?
• Fluid status: UO, skin turgor, mucous membranes
• Sites for vascular access: IV lines may need to be placed through or near burned skin

10.3 Investigations

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11. INTRAOPERATIVE ANESTHETIC MANAGEMENT

11.1 Timing of Surgery

• Emergency: escharotomy (circumferential burns causing compartment syndrome), airway burns, blast injuries
• Early (days 1–5): early excision and grafting (EEG) — reduces SIRS, hospital stay, mortality
• Repeated: multiple sequential grafting procedures often required for major burns
• Burns patients may return to OR 5–20 times; cumulative pharmacological exposures matter

11.2 Temperature Management

• Critical priority: burns patients cannot regulate temperature
• OR temperature should be maintained at ≥37–40°C for all burn procedures
• All IV fluids must be warmed
• Forced-air warming blankets, radiant warmers
• Wrap non-operative extremities
• Hypothermia worsens: coagulopathy, cardiac dysfunction, drug metabolism, infection risk

11.3 Positioning and Access

• Venous access through burned skin is acceptable in emergency (secure carefully)
• Intra-osseous access if peripheral IV impossible
• Central venous access may be required
• Arterial line preferred for continuous BP monitoring + ABG sampling
• Position carefully — pressure areas, padding (especially over bony prominences adjacent to grafted areas)

11.4 Choice of Anesthetic Technique

General Anaesthesia

• Most common approach for operative procedures
• Induction agents:
  • Ketamine — drug of choice in haemodynamically unstable burn patients
    • Sympathomimetic → maintains HR and BP
    • Bronchodilator → useful in inhalation injury
    • Good analgesic and amnestic
    • Combine with benzodiazepine to prevent emergence delirium
    • Dose: 1–2 mg/kg IV or 4–6 mg/kg IM (useful when IV access difficult)
  • Propofol — use cautiously in haemodynamically unstable patients; TIVA possible
  • Etomidate — useful in haemodynamically compromised patients; avoid repeated doses (adrenal suppression)
  • Thiopentone — used for rapid sequence induction; hypotension risk in hypovolaemia
• Maintenance:
  • Volatile agents (sevoflurane, isoflurane, desflurane) — all acceptable
  • TIVA with propofol + remifentanil — useful to avoid volatile agent pollution in prolonged procedures
  • Ketamine infusion as adjunct
• Analgesia:
  • Multimodal approach essential
  • Opioids: morphine, fentanyl, hydromorphone — titrate to effect; tolerance develops rapidly
  • Ketamine (sub-anaesthetic doses 0.1–0.5 mg/kg/h) — opioid-sparing
  • NSAIDs/COX inhibitors (with caution — AKI risk, gastric effects)
  • Paracetamol
  • Dexmedetomidine — sedation + analgesia, reduces opioid requirement

Regional Anaesthesia

• Technically challenging (burned/scarred skin, oedema)
• Useful for: limb procedures, donor site harvesting, dressing changes
• May mask symptoms of compartment syndrome — caution in early post-burn period
• Examples: peripheral nerve blocks (femoral, sciatic, brachial plexus), spinal/epidural

11.5 Muscle Relaxation Summary (Intraoperative)

• <48 h from burn: succinylcholine acceptable for RSI
• >48 h from burn: use rocuronium (1.2 mg/kg) for RSI; sugammadex available for reversal
• Higher doses of NDNMBs required (>25% TBSA)
• Quantitative TOF monitoring mandatory
• Avoid vecuronium/pancuronium in hepatic/renal failure (accumulation)
• Cisatracurium preferred in multi-organ failure

11.6 Monitoring

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12. SPECIAL OPERATIVE SITUATIONS IN BURNS

12.1 Escharotomy

• Indicated for circumferential full-thickness burns causing compartment syndrome of limbs, chest, or abdomen
• Full-thickness burns are insensate — no anesthesia needed for escharotomy of full-thickness burns
• Deep partial-thickness burns may retain sensation — local anaesthesia/IV analgesia may be required
• Chest escharotomy: releases respiratory restriction, improves compliance

12.2 Excision and Skin Grafting

• Major surgical blood loss expected — have cross-matched blood immediately available
• Blood transfusion threshold: Hb <7–8 g/dL (liberal in paediatrics, cardiac disease)
• Tumescent epinephrine infiltration of donor/recipient sites reduces blood loss
• Prone positioning for back/buttock grafts — airway access critical
• Temperature management especially important during long procedures

12.3 Dressing Changes

• Can be extremely painful — require sedation/analgesia/GA
• Options: ketamine IM or IV, dexmedetomidine, nitrous oxide (Entonox), intranasal fentanyl/midazolam in children
• Psychological preparation and distraction therapy adjuncts

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13. PAEDIATRIC BURNS — SPECIAL CONSIDERATIONS

• Use Lund-Browder chart (not Rule of Nines) for TBSA estimation
• Children <30 kg: add 5% dextrose to IV fluids (hypoglycaemia risk)
• Target UO: 1.0 mL/kg/h (vs 0.5 mL/kg/h in adults)
• Maintenance fluids: 4-2-1 rule; avoid hypotonic solutions postoperatively (hyponatraemia risk from SIADH)
• Greater risk of hypothermia (high BSA:mass ratio)
• Succinylcholine restriction same as adults (>48 h post-burn)
• Morphine remains first-line opioid in most burn centres for children with major burns

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14. POSTOPERATIVE CARE

14.1 ICU Management

• Most major burn patients go to burns ICU post-operatively
• Continue temperature management — maintain normothermia
• Mechanical ventilation: protective strategy (TV 6 mL/kg IBW, PEEP 5–8 cmH₂O)
• Sedation and analgesia: opioid infusions (morphine/fentanyl), ketamine adjunct, dexmedetomidine
  • Opioid tolerance develops rapidly — dose escalation common
  • Avoid prolonged benzodiazepine use (delirium, withdrawal)
• Nutritional support: critical in hypermetabolic phase — early enteral nutrition via NG tube
  • High protein (1.5–2 g/kg/day), high caloric (25–35 kcal/kg/day) requirements
  • Continue nutrition perioperatively when possible
• Infection control: burns are a portal for sepsis
  • Regular wound inspection, cultures
  • Systemic antibiotics for confirmed sepsis — not prophylactically
  • Topical antimicrobials: silver sulfadiazine, mafenide acetate

14.2 Pain Management

• Multimodal approach throughout hospitalisation
• Background continuous pain + procedural pain (dressing changes, physiotherapy) — both must be addressed
• Regional techniques where anatomically feasible
• Psychological support integral to pain management

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15. COMPLICATIONS OF BURNS AND ANESTHESIA

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16. ELECTRICAL BURNS — SPECIAL CONSIDERATIONS

• Entry and exit wounds may underestimate true extent of injury
• Massive deep tissue destruction despite normal-appearing skin
• Rhabdomyolysis and myoglobinuria → AKI → target UO 1–2 mL/kg/h + alkalinise urine
• Cardiac arrhythmias (VF, heart block) — continuous ECG monitoring, 24-h observation post-exposure
• Spinal cord injury risk (tetanic muscle contractions)
• Cataracts (delayed)
• Succinylcholine risk applies as with thermal burns >48 h

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17. HIGH-YIELD EXAM POINTS (SUMMARY)

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SOURCES

• Miller's Anesthesia, 10th Edition (Miller et al.) — Chapters 24, 34
• Morgan & Mikhail's Clinical Anesthesiology, 7th Edition — Chapter 39 (Burns)
• Barash, Cullen & Stoelting's Clinical Anesthesia, 9th Edition — Chapter on Trauma/Burns
• Miller's Anesthesia, 10e (Block 17) — Fluid Management in Burns

1. Epidemiology & Classification — degrees of burns, Rule of Nines, Lund-Browder for children
2. Pathophysiology — two-phase model (ebb/burn shock vs. hypermetabolic/flow phase), local burn zones
3. Inhalation Injury — three types, diagnosis (flexible bronchoscopy gold standard), clinical indicators
4. CO & Cyanide Poisoning — HbCO levels/effects, unreliable pulse oximetry, management with HBO
5. Fluid Resuscitation — Parkland formula (4 mL/kg/%TBSA), fluid creep, ACS (bladder pressure >20 mmHg), colloid vs. crystalloid
6. Airway Management — early vs. delayed intubation, AFOI, RSI technique, protective ventilation
7. Muscle Relaxants — succinylcholine contraindicated after 48 h (lethal hyperkalaemia up to K⁺ 13 mEq/L), NDNMB resistance >25% TBSA, duration of risk up to 2 years
8. Pharmacokinetics — altered Vd, hypoalbuminaemia, hypermetabolic clearance
9. Preoperative Assessment — history, examination, investigations
10. Intraoperative Management — temperature (OR at 40°C), ketamine as drug of choice, monitoring, muscle relaxant protocol
11. Special Situations — escharotomy, excision/grafting, dressing changes
12. Paediatric Considerations — dextrose supplementation, higher UO target
13. Postoperative/ICU Care — ventilation, nutrition, infection control
14. Electrical Burns — rhabdomyolysis, cardiac arrhythmias
15. High-Yield Exam Summary Table — all key numbers and facts in one place