Burn assessment and fluid resuscitation

Burn assessment and initial resuscitation

Major burns cause capillary leak and can threaten the airway, circulation and limb perfusion. Start an ABCDE assessment, identify associated trauma, provide appropriate oxygen and analgesia, and contact a burn service early. Burn depth and surface area guide referral and fluid estimates; ongoing physiological reassessment determines whether the initial treatment is adequate.

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Burn Depth Classification & Surface Area Assessment

Accurate assessment of burn depth and percentage of Total Body Surface Area (%TBSA) governs fluid resuscitation, transfer to a specialized burn centre, and operative indications.

Classification of Burn Depth

1. Superficial (Epidermal):
   • Depth: Confined to the epidermis.
   • Appearance: Erythematous, dry, no blisters; brisk capillary refill.
   • Sensation: Exquisitely painful (e.g., sunburn).
   • Healing: Heals within 3 to 7 days via re-epithelialization without scarring.
   • Critical Rule: Superficial epidermal burns are NOT included in %TBSA fluid calculations.
2. Superficial Partial-Thickness:
   • Depth: Epidermis and upper layers of papillary dermis.
   • Appearance: Pale pink, blistered, moist, weeping; brisk capillary refill.
   • Sensation: Intensely painful and sensitive to air/touch.
   • Healing: Heals in 10 to 14 days with minimal to no hypertrophic scarring.
3. Deep Partial-Thickness:
   • Depth: Extends into reticular dermis; sparse hair follicles and sweat glands remain.
   • Appearance: Blotchy red, pale white, dry or broken blisters; sluggish or absent capillary refill.
   • Sensation: Dull pressure sensation; diminished or absent pinprick sensation.
   • Healing: Takes $> 3\text{ weeks}$ to heal; severe scarring; typically requires tangential excision and split-thickness skin grafting.
4. Full-Thickness:
   • Depth: Entire epidermis, dermis, and reaches subcutaneous fat/fascia.
   • Appearance: Dense white, waxy, leathery, charred black or dark brown; completely dry; absent capillary refill.
   • Sensation: Completely anaesthetic to pinprick (pain receptors destroyed); hairs pull out freely without resistance.
   • Healing: Loss of dermal regenerative structures prevents healing from within the wound. These burns usually require excision and skin coverage; the burn team individualises timing and treatment to wound extent, location and patient stability.

Estimation of Burn Size (%TBSA)

• Wallace Rule of Nines (in adults):
  • Head and neck: $9\%$
  • Each upper limb (circumferential): $9\%$ (anterior $4.5\%$, posterior $4.5\%$)
  • Anterior torso (chest and abdomen): $18\%$
  • Posterior torso (upper and lower back): $18\%$
  • Each lower limb (circumferential): $18\%$ (anterior $9\%$, posterior $9\%$)
  • Perineum and genitalia: $1\%$
• Palmar Surface Method: The surface area of the patient's entire hand (palm plus all five fingers) represents approximately $1\%$ TBSA. Used for measuring scattered, patchy, or irregular burns.

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Inhalation Injury & Airway Management

Inhalation injury can substantially worsen burn outcomes. It encompasses supraglottic thermal injury, subglottic chemical tracheobronchitis, and systemic toxicity (carbon monoxide and hydrogen cyanide).

Clinical Indicators of Inhalation Injury

• History of exposure to fire or explosion within an enclosed space.
• Deep facial, perioral, or neck burns; singed nasal hairs or eyebrows.
• Soot deposits in the oral cavity, palate, or posterior pharynx.
• Carbonaceous (soot-tinged) sputum or brassy cough.
• Voice alteration: hoarseness, muffled voice, brassy cough.
• Inspiratory stridor or wheezing.
• Carboxyhaemoglobin ($COHb$) level $> 10\%$ on blood gas analysis.

Time-Critical Airway Intervention

Upper-airway injury can cause progressive oedema, including during fluid resuscitation. Reassess voice, swelling, respiratory effort and consciousness; a reassuring initial conversation does not exclude later deterioration.

• Early expert airway assessment: Progressive hoarseness, increasing oropharyngeal swelling, obstruction, respiratory failure or inability to protect the airway can require early intubation by an experienced team. Plan before access becomes difficult, with a tube appropriate to the patient and anticipated bronchoscopic care.
• Continual observation: Facial burns, soot or singed hairs are warning signs that require assessment and monitoring; they do not individually mandate intubation. Do not wait for stridor or exhaustion when a threatened airway is already apparent. Protect the cervical spine when the mechanism suggests associated trauma.

Carbon Monoxide & Cyanide Poisoning

• Carbon monoxide binds haemoglobin with an affinity 240 times that of oxygen, shifting the oxyhaemoglobin dissociation curve to the left and poisoning cellular cytochrome oxidase. Standard pulse oximetry ($SpO_2$) cannot distinguish carboxyhaemoglobin from oxyhaemoglobin and reads falsely normal.
• Management: Administer 100% high-flow oxygen via a non-rebreather mask (reduces $COHb$ half-life from 300 minutes on room air to 60–90 minutes). For severe poisoning ($COHb > 25\%$, neurological deficit, pregnancy), consider hyperbaric oxygen.
• Cyanide toxicity: Enclosed-space smoke exposure with altered consciousness, cardiovascular collapse or marked unexplained lactic acidosis raises suspicion. A lactate of at least 10 mmol/L supports concern in smoke inhalation, but is not diagnostic alone. When suspicion is high, give hydroxocobalamin 5 g IV over 15 minutes with resuscitation and urgent toxicology advice; do not delay treatment to obtain lactate. Seek Australian Poisons Information Centre advice on 13 11 26.

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Fluid Resuscitation & The Parkland Formula

Systemic capillary leak ("burn shock") occurs in major burns ($> 20\%\text{ TBSA}$ in adults, $> 10\%\text{ TBSA}$ in children), leading to massive fluid extravasation into interstitial spaces.

Modified Parkland estimate and reassessment

The NSW burn network’s February 2026 estimate is 3 mL × weight in kg × %TBSA over 24 hours, for burns exceeding 20% in adults or 10% in children. Use the number 36 for 36%, not 0.36. Half is allocated to the first eight hours from injury and half over the following sixteen; subtract fluid already given.

For a 70-kg adult with 36% burns, the estimate is 3 × 70 × 36 = 7,560 mL, with 3,780 mL in the first eight hours. If two hours have elapsed with no fluid, 3,780/6 = 630 mL/h initially. Adjust to perfusion, urine output, electrolytes and specialist review rather than treating the estimate as a fixed endpoint. Typical urine-output goals are 0.5 mL/kg/h in adults and 1 in children, who also need maintenance fluid. Avoid fluid overload and hypothermia.

Cool the burn with running cool water for twenty minutes, with benefit up to three hours after injury. Do not use ice; remove jewellery and protect the remainder of the patient from hypothermia. Chemical and electrical burns need specific assessment.

Circumferential Burns & Emergency Escharotomy

Full-thickness burns produce a tough, leathery, inelastic coagulum called an eschar. During fluid resuscitation, massive third-space oedema accumulates beneath the unyielding eschar, causing a tourniquet effect.

Indications

1. Circumferential Torso Burns: Causes severe restriction of chest wall compliance, resulting in high peak airway pressures, hypoventilation, respiratory acidosis, and impaired venous return.
2. Circumferential Extremity Burns: Causes compression of neurovascular bundles, resulting in peripheral compartment syndrome with digital cyanosis, paresthesias, pain on passive extension, loss of Doppler ultrasound signals, and pulselessness.

Surgical Technique

• Escharotomy: Urgent specialist assessment for impaired limb perfusion or restricted ventilation. Insensate eschar does not mean the surrounding tissue is painless; provide analgesia and monitored procedural care. Escharotomy releases burned skin; fasciotomy addresses a deeper compartment syndrome.
• Extremities: Mid-lateral and mid-medial longitudinal incisions along the limb, extending across the entire burned area into healthy tissue. Incisions must penetrate the full depth of the leathery eschar down into subcutaneous fat until the wound edges pop open and tissue tension is relieved. Avoid superficial nerves (e.g., common peroneal nerve at the fibular neck, ulnar nerve at the elbow).
• Chest: Longitudinal incisions along the anterior axillary lines connected by a transverse incision across the upper chest/epigastrium ("shield" incision).

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Primary references (checked 7 October 2026): NSW 2026 burn fluids; NSW February 2026 burn management; NSW October 2026 burns protocol; hydroxocobalamin prescribing information.