Burn Depth Classification

🟢 Lite — Quick Review (1h–1d)

Burns are tissue injuries from heat, chemicals, electricity, radiation, or friction causing cellular damage and protein denaturation. TBSA (Total Body Surface Area) estimates extent using the Rule of Nines: each limb 9%, anterior trunk 18%, posterior trunk 18%, head 9%, perineum 1%. Parkland Formula calculates fluid: 4 × weight (kg) × %TBSA burned; give half in the first 8 hours.

Burn depth classification: Superficial (1st degree) heals in 3–7 days; partial-thickness (2nd degree) heals in 7–21 days; full-thickness (3rd degree) requires surgical excision and grafting. Suspect inhalation injury with facial burns, singed nasal hairs, or carbonaceous sputum — this dramatically increases mortality. Circumferential full-thickness burns need urgent escharotomy to prevent compartment syndrome.

🟡 Standard — Regular Study (2d–2mo)

Burn Depth Classification

Burns are classified by depth into four degrees. Superficial (1st degree) involves only the epidermis — presents with erythema, pain, and no blisters. Healing occurs spontaneously within 3–7 days without scarring. Superficial partial-thickness (2nd degree) extends into the dermis — produces blisters, intense pain, and blanching. These heal within 7–14 days with minimal scarring if infection is prevented. Deep partial-thickness burns damage hair follicles and sweat glands; they appear mottled, have reduced sensation, and may require 3–4 weeks to heal with significant scarring risk. Full-thickness (3rd degree) destroys all skin layers — the skin appears leathery, waxy, or charred, and is painless due to nerve destruction. Fourth-degree burns extend into subcutaneous tissue, muscle, or bone.

Estimating TBSA

The Rule of Nines divides the adult body into 11 regions of 9% each plus the perineum at 1%. In children, the head accounts for 18% because it is proportionally larger; each lower limb is 13.5% and trunk percentages are adjusted accordingly. The Lund-Browder chart provides age-adjusted percentages and is preferred in pediatric patients. When calculating fluid requirements, do not include first-degree burns in %TBSA calculations.

Fluid Resuscitation

The Parkland Formula is the standard: Volume (ml) = 4 × body weight (kg) × %TBSA burned. Administer half the total volume in the first 8 hours post-burn and the remaining half over the next 16 hours. This calculates crystalloid requirement for the first 24 hours; additional maintenance fluids should be provided. The formula is a starting point — titrate based on urine output (target: 0.5–1.0 ml/kg/hr in adults, 1.0–1.5 ml/kg/hr in children).

Inhalation Injury

Suspect inhalation injury when the patient was trapped in an enclosed space fire, has facial burns, singed nasal hairs, singed eyebrows, carbonaceous sputum, hoarseness, or stridor. Bronchoscopy confirms the diagnosis. Inhalation injury increases mortality significantly and requires early airway securing, humidified oxygen, and bronchodilators.

Surgical Considerations

Circumferential full-thickness burns form a rigid eschar that restricts chest expansion or causes limb compartment syndrome. Escharotomy (incision through eschar) or fasciotomy (release of fascial compartment) is performed emergently at the bedside under sedation. Early excision of dead tissue and skin grafting reduces infection risk and hospital stay. Infection remains the leading cause of mortality after successful initial resuscitation.

🔴 Extended — Deep Study (3mo+)

Chemical and Electrical Burns

Chemical burns require immediate, prolonged irrigation with water or saline for 20–30 minutes. The specific agent matters: hydrofluoric acid requires calcium gluconate gel or injection; alkalis cause penetrating injuries that continue damaging tissue until neutralized. Do not attempt chemical neutralization reactions as they may generate heat and worsen injury. Electrical burns often appear deceptively minor on the skin surface while causing extensive deep tissue necrosis along the current path through muscle and nerves. These patients require cardiac monitoring (arrhythmias are common), serial CK measurements to detect rhabdomyolysis, and evaluation for visceral injuries. Tetanus prophylaxis and broad-spectrum antibiotics are indicated.

Common Mistakes in Exam and Practice

A frequent error is underestimating fluid requirements by using incorrect body weight or failing to subtract first-degree burns from the %TBSA figure. Students also confuse superficial and deep partial-thickness burns — the presence of blanching and pain sensation differentiates them clinically, and this distinction determines whether conservative management is appropriate or surgical intervention is needed. Another trap: calculating the Parkland formula but forgetting that the first 8-hour period starts from the time of burn injury, not from arrival at hospital — if the patient presents late, the bolus dose must be adjusted accordingly.

Exam Strategy

For the Saudi GP Board, burns questions frequently test TBSA calculation using the Rule of Nines, Parkland formula application with correct timing of fluid administration, and recognition of inhalation injury indicators. Electrical burns appear in scenario-based questions emphasizing hidden deep tissue damage. Focus on distinguishing burn depths by clinical features — this consistently appears in clinical vignette questions.

Worked Example

A 70-kg adult sustains burns to both anterior upper limbs, anterior trunk, and perineum. Calculate fluid requirement using Parkland Formula.

%TBSA: each upper limb 9% (18% total), anterior trunk 18%, perineum 1% = 37%
Total fluid = 4 × 70 × 37 = 10,360 ml in 24 hours
First 8 hours: 5,180 ml
Next 16 hours: 5,180 ml (2,590 ml per 8-hour block)

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Burn Depth Classification