4. Thermal burns

1. Definition

• Thermal burn → tissue damage from heat: flame, hot liquid (scald), steam, hot object (contact), flash
• Protein coagulation starts above 44 °C; damage rises with temperature and time of exposure
• Burn disease → general reaction of the body to an extensive burn

2. Aetiology and risk factors

• Children → scalds
• Adults → flame
• Epilepsy, alcohol, elderly, house fires

3. Pathogenesis

Local: zones of injury (Jackson)

1. Zone of coagulation → dead tissue, must be debrided
2. Zone of stasis → impaired blood flow; may survive or die (cooling, fluids, no infection save it)
3. Zone of hyperaemia → minimal injury, recovers in 7–10 days

General

• Increased capillary permeability → loss of plasma into tissues and from the wound
• Hypovolaemia, haemoconcentration → burn shock
• Hypermetabolism, catabolism
• Immunosuppression → infection, sepsis
• Burn shock develops when burns are > 15% total body surface area (TBSA) in adults, > 10% in children and the elderly

4. Classification

Depth (local burns)

• First degree (superficial, epidermal) → erythema, pain, no blisters; heals in 3–7 days without scar
• Second degree (superficial partial thickness) → epidermis and papillary dermis; blisters, wet pink base, blanches, very painful; heals in < 2 weeks
• Third degree A (deep partial thickness) → reticular dermis; blotchy red or white, reduced sensation; heals in > 3 weeks with scarring, often needs grafting
• Third degree B (full thickness) → whole dermis; white, leathery or charred eschar, painless, no blanching; needs excision and grafting
• Fourth degree → subcutaneous fat, muscle, bone; charring
• Partial thickness → heals from surviving skin appendages (hair follicles, sweat glands)
• Depth may progress over the first 48–72 h

Extent

• Rule of nines (adults):
  • Head and neck → 9%
  • Each upper limb → 9%
  • Front of trunk → 18%
  • Back of trunk → 18%
  • Each lower limb → 18%
  • Perineum → 1%
• Palm method → patient's palm with fingers ≈ 1% TBSA
• Lund and Browder chart → most accurate; corrects for age (larger head in children)
• First-degree burns → not counted in TBSA

Severity

• Minor → partial thickness < 10% TBSA in adults, < 5% in children or elderly, full thickness < 2%
• Major → larger area, special areas (face, hands, feet, perineum, major joints), inhalation injury, electrical or chemical burns
• Baux score → age + % TBSA; add 17 for inhalation injury (revised Baux)

5. Clinical picture: stages of burn disease

1. Burn shock → first 48–72 h; hypovolaemia, oliguria, haemoconcentration, thirst, restlessness
2. Acute burn toxaemia → days 3–10; absorption of toxic products from the wound; fever, tachycardia, confusion, anaemia
3. Septicotoxaemia → from week 2 until wounds close; wound infection, sepsis, wasting (burn cachexia)
4. Convalescence → wounds healed; scars, contractures

6. Diagnosis

• History → agent, time, enclosed space (inhalation risk)
• Signs of inhalation injury:
  • Burns to face, singed nasal hair
  • Soot in the mouth, carbonaceous sputum
  • Hoarse voice, stridor
  • Fire in an enclosed space
• Carboxyhaemoglobin (COHb) level, arterial blood gas
• Full blood count, haematocrit, urea, electrolytes, creatine kinase
• Bronchoscopy → confirms airway injury

7. Treatment

First aid

• Stop the burning process; remove clothing and jewellery
• Cool with running tap water for 20 min (useful within 3 h); no ice
• Cover with cling film or a clean dressing
• Keep the patient warm

General treatment

• Primary survey (ABCDE):
  • Airway → early intubation in inhalation injury before oedema closes the airway
  • Breathing → 100% oxygen for carbon monoxide poisoning
  • Circumferential chest burn → escharotomy to allow ventilation
• Fluid resuscitation → burns > 15% TBSA in adults, > 10% in children
• Parkland formula → 4 mL × body weight (kg) × % TBSA of Hartmann's (Ringer's lactate) in 24 h
  • Half in the first 8 h from the time of the burn
  • Half in the next 16 h
  • Current guidance (Advanced Burn Life Support) → start at 2 mL × kg × % TBSA in adults
• Titrate to urine output → 0.5 mL/kg/h in adults, 1 mL/kg/h in children
• Analgesia → intravenous opioids
• Tetanus prophylaxis
• Early enteral nutrition → high protein and calorie
• Stress ulcer prophylaxis → prevents Curling's ulcer
• Venous thromboembolism prophylaxis
• No routine prophylactic systemic antibiotics → treat proven infection only

Local treatment

• Clean, debride loose skin and large or tense blisters
• Superficial burns → non-adherent dressing, moisturiser
• Partial and full thickness → topical antimicrobials (silver sulfadiazine, silver dressings)
• Closed method → dressings; open method → exposure (face, perineum)
• Escharotomy → circumferential full-thickness burn of a limb or chest; incise the eschar to release constriction
• Early tangential excision and split-thickness skin grafting → within 3–5 days for deep burns
• Large burns → temporary cover with allograft, xenograft or skin substitutes
• Physiotherapy, splinting, pressure garments → prevent contractures and hypertrophic scars

Referral to a burns centre

• Partial thickness > 10% TBSA
• Face, hands, feet, genitalia, perineum, major joints
• Full-thickness burns at any age
• Electrical, chemical and inhalation injuries
• Burns with major trauma or serious comorbidity

8. Complications

• Hypovolaemic shock, acute kidney injury
• Respiratory failure, acute respiratory distress syndrome (ARDS)
• Wound infection, sepsis (Pseudomonas, Staphylococcus aureus)
• Curling's ulcer → stress ulcer of the stomach or duodenum
• Compartment syndrome
• Hypertrophic scars, keloids, contractures
• Marjolin's ulcer → squamous cell carcinoma in a chronic burn scar

9. Prognosis

• Depends on age, % TBSA, depth, inhalation injury
• Revised Baux score > 140 → survival unlikely