Assessment and Resuscitation of the Acute Burns Patient - Anaesthetic Perspective

1. Primary Survey (ABCDE)

A - Airway (Most Critical Decision)

• Hoarse voice or stridor
• Dyspnea or tachypnea
• Altered level of consciousness
• History of exposure in an enclosed space
• Suspected smoke inhalation
• Moderate-to-severe facial or oropharyngeal burns
• Circumferential neck burns
• Visible airway injury on laryngoscopy
• Oropharyngeal soot, singed nasal/facial hair
• Burns ≥40% TBSA
• Hemodynamic instability, dysphagia

Facial burns alone (singed hair, nasal vibrissae) are NOT a mandatory indication for intubation. A hoarse voice, dyspnea, or altered consciousness are the key triggers. - Morgan and Mikhail's Clinical Anesthesiology, 7e, p.1561

• Awake intubation with generous topical anaesthesia ± sedation is preferred when a difficult airway is anticipated with partial obstruction
• RSI with video laryngoscopy is acceptable if intubation is performed early (before significant edema develops)
• If "can't intubate, can't oxygenate" develops, follow the failed airway algorithm - surgical airway is rarely but definitionally indicated

No single feature adequately predicts the need for intubation; when in doubt, early intubation is encouraged. Flexible laryngoscopy can substitute for empirical intubation in mild/inconclusive cases. - Rosen's Emergency Medicine, p.835

B - Breathing

• Supplemental humidified oxygen to maintain SpO2 >92% in all suspected inhalation injury
• Lung-protective ventilation: Tidal volume 6-8 mL/kg, plateau pressures <35 cmH2O, PEEP ~8 cmH2O

• Permissive hypercapnia is acceptable
• Bronchoscopy is the gold standard to diagnose inhalation injury, determine severity, and clear debris
• Inhaled beta-agonists for bronchoconstriction
• Nebulised heparin (5,000-10,000 IU) + N-acetylcysteine reduces duration of mechanical ventilation
• Corticosteroids are not recommended empirically

C - Circulation and Haemodynamics

• Cardiac output falls by up to 50% within 30 minutes of major burn
• Mechanism: massive burn-induced vasoconstriction → normovolaemic hypoperfusion ("burn shock")
• If adequate crystalloid resuscitation is given, cardiac function normalises within 48 hours, then transitions to hyperdynamic physiology as healing begins

• Two large-bore IV catheters - through unburned tissue if at all possible
• IV access through burned tissue is acceptable if necessary

2. Burn Size Assessment - Rule of Nines

Important: First-degree burns (epidermal only, no blistering) are excluded from TBSA calculations used for fluid resuscitation formulae. Including them leads to fluid creep. - Morgan and Mikhail's, p.1558

• Superficial (1st degree): Epidermal only - not included in TBSA
• Partial thickness (2nd degree): Into dermis - painful, blistered
• Full thickness (3rd degree): All skin layers destroyed - insensate, leathery

3. Fluid Resuscitation

• Adults: burns >20% TBSA
• Children: burns >10% TBSA

• Hypertonic saline (increased acute kidney failure risk in burns)
• Blood products during initial resuscitation (increased mortality)
• Albumin (no outcomes benefit vs. crystalloid)
• Hydroxyethyl starch

Resuscitation Formulae (first 24 hours from time of injury):

Time is calculated from the time of injury, not time of arrival. If a patient arrives 4 hours post-burn, the first 8-hour volume must be delivered in the remaining 4 hours. - Rosen's Emergency Medicine, p.836

Monitoring Adequacy of Resuscitation:

• Urine output is the primary endpoint: target 0.5-1.0 mL/kg/h in adults; 1.0 mL/kg/h in children; 1-2 mL/kg/h in infants <1 year
• If urine output >1.0 mL/kg/h in adults, slow the infusion rate

Complications of Over-Resuscitation:

• Fluid creep: Volume administered far exceeds calculated goal (often due to miscalculation from including 1st-degree burns, or sedation-induced hypotension prompting excess fluids)
• Abdominal Compartment Syndrome (ACS): Risk with circumferential abdominal burns or >6 mL/kg/%TBSA received. Measure bladder pressure via Foley catheter; intra-abdominal pressure >20 mmHg warrants decompression
• Pneumonia and ARDS: Excess fluid promotes pulmonary edema, especially in the context of inhalation injury

4. CO and Cyanide Poisoning

• CO binds haemoglobin with ~250× the affinity of oxygen
• Carboxyhemoglobin (HbCO) shifts O2-Hb dissociation curve leftward (reduced O2 delivery)
• Pulse oximetry is falsely normal - it cannot distinguish HbO2 from HbCO. Always get ABG/VBG for direct HbCO measurement
• HbCO >10%: clinically significant (smokers have baseline up to 10%)
• HbCO >20%: intubate and ventilate with 100% O2
• HbCO >60%: lethal
• Hyperbaric oxygen is indicated for all significant CO poisonings and requires multiple sessions to reduce long-term neurological sequelae

5. Anaesthetic Drug Considerations

Succinylcholine and the Hyperkalemia Window

"Beyond 48 h following a major burn injury, succinylcholine administration can produce lethal hyperkalemia. This risk persists for up to 2 years following burn injury." - Morgan and Mikhail's Clinical Anesthesiology, 7e, p.1561

Temperature Management

• Burns patients cannot thermoregulate
• All resuscitation and care environments must be maintained near 40°C
• Use radiant warming, forced-air warming devices, and fluid warmers

Analgesia

• Multimodal analgesia is preferred (opioid + adjuncts)
• IV morphine: 2-4 mg IV in adults, 0.05 mg/kg in children <50 kg
• Caution with regional techniques in the early post-burn period - they may mask symptoms of compartment syndrome

6. Indications for Admission / Burns Unit Transfer

• Partial or full thickness >10% TBSA (all ages) or >20% TBSA (adults)
• Burns involving face, hands, feet, genitalia, perineum, or major joints
• Full thickness burns >5% TBSA
• Circumferential burns of limbs or chest
• Chemical or electrical burns
• Inhalation injury
• Significant co-morbidities or extremes of age

Summary: Anaesthetic Priorities at a Glance

1. Airway first - anticipate a difficult, evolving airway; intubate early if any signs of inhalation injury or airway compromise
2. 100% O2 always initially - treats CO poisoning and hypoxia simultaneously
3. LR resuscitation using Parkland (4 mL/kg/%TBSA) or modified Brooke (2 mL/kg/%TBSA); titrate to urine output 0.5-1 mL/kg/h
4. Succinylcholine is safe in first 48 hours only - use NDMR (rocuronium) beyond 48 hours
5. Pulse oximetry unreliable with CO poisoning - ABG mandatory
6. Avoid fluid creep - monitor for abdominal compartment syndrome
7. Warm everything - patient, IV fluids, environment