25.1 Burns, Inhalation Injury, Drowning, Hypothermia, Heat Illness and Decompression Illness

25.1 Burns, Inhalation Injury, Drowning, Hypothermia, Heat Illness and Decompression Illness

Burns

Assessment

• Depth: superficial (epidermal, red, painful; not counted in burn size), superficial partial-thickness (blisters, painful, blanching), deep partial-thickness (mottled, reduced sensation), full-thickness (white or leathery, painless).
• Size (total body surface area, TBSA): the Wallace rule of nines in adults (head 9%, each arm 9%, front of trunk 18%, back 18%, each leg 18%, perineum 1%), the Lund and Browder chart (adjusts for age, as children have relatively larger heads), and the patient's palm with fingers (about 1%) for small or scattered burns.
• Referral criteria include large burns, burns to the face, hands, feet, perineum or joints, circumferential and electrical or chemical burns, inhalation injury and burns in young children or the elderly.

Pathophysiology

Burns cause local and systemic release of inflammatory mediators, increased capillary permeability and loss of plasma into the tissues, maximal in the first 8-12 hours and lasting about 24-48 hours. This causes burn shock (hypovolaemic and distributive), followed by a hypermetabolic phase with raised cardiac output, oxygen consumption and catabolism that can last months.

Fluid Resuscitation

• Usually needed above about 15% TBSA in adults and 10% in children.
• Parkland formula: $\text{Volume (mL)} = 4 \times \text{weight (kg)} \times \%\text{TBSA}$ of crystalloid (Hartmann's) over 24 hours, with half in the first 8 hours from the time of the burn and half over the next 16 hours.
• The formula is only a starting point. Titrate to urine output of about 0.5 mL/kg/h in adults (about 1 mL/kg/h in children under 30 kg, higher in electrical injuries with myoglobinuria).
• "Fluid creep" (over-resuscitation) causes oedema, abdominal and limb compartment syndromes and pulmonary complications. Albumin may be added after about 12-24 hours to reduce crystalloid requirements.
• Children need maintenance fluid with glucose in addition to resuscitation fluid.

Airway and Inhalation Injury

Upper airway thermal injury causes oedema that progresses over 24-48 hours, especially with fluid resuscitation. Signs: facial and neck burns, singed nasal hairs, soot in the mouth, hoarse voice, stridor, carbonaceous sputum.

Early intubation with an uncut tube (to allow for facial swelling) is indicated for stridor or airway compromise, deep facial or circumferential neck burns, reduced consciousness, or the need for safe transfer. Delayed intubation can become impossible.

Lower airway injury results from chemical irritants in smoke, causing bronchospasm, impaired ciliary function, mucosal sloughing, casts and pneumonia. Diagnosis is by bronchoscopy. Treatment includes lung-protective ventilation, bronchodilators, and nebulised heparin and N-acetylcysteine in some centres.

Smoke Toxins

Circumferential Burns

Full-thickness circumferential burns of the chest restrict ventilation and those of limbs cause ischaemia; escharotomy releases them.

Anaesthesia for Burn Patients

• Suxamethonium: safe in the first 24-48 hours; avoid from about 48 hours until the burn has healed (and for some time after) because of upregulated extrajunctional receptors and hyperkalaemia.
• Resistance to non-depolarising blockers develops from about 1 week, requiring larger doses (up to two to five times).
• Increased opioid requirements (tolerance, hypermetabolism).
• Blood loss during excision and grafting is large (about 2-4% of blood volume per 1% TBSA excised in some estimates); use tourniquets, topical adrenaline and tranexamic acid.
• Temperature control: warm the theatre (about 28-32 °C), warm fluids and use active warming, as burned patients lose heat rapidly.
• Monitoring may be difficult (ECG needle electrodes, alternative oximetry sites).

Electrical Injury

Low-voltage (below 1,000 V) alternating current causes arrhythmias, especially ventricular fibrillation; high-voltage injury and lightning cause deep tissue damage disproportionate to skin burns, rhabdomyolysis, compartment syndrome and asystole. Lightning causes massive direct current and may cause respiratory arrest that outlasts cardiac arrest. Monitor the ECG, check creatine kinase, and maintain high urine output if myoglobinuria is present.

Drowning

Drowning is respiratory impairment from submersion or immersion in liquid. The key injury is hypoxia.

• Resuscitation: start with 5 rescue breaths because the arrest is hypoxic, then standard CPR. Do not attempt to drain water from the lungs.
• Salt and fresh water aspiration both wash out surfactant and cause pulmonary oedema and ARDS; the distinction is clinically unimportant.
• Consider cervical spine injury only if the history suggests diving or trauma.
• Hypothermia may protect the brain in cold-water immersion; prolonged resuscitation may be appropriate.

Accidental Hypothermia

ECG: bradycardia, J (Osborn) waves, prolonged intervals, atrial fibrillation.

Management:

• Handle gently (movement can trigger ventricular fibrillation), remove wet clothes, insulate, and use active external rewarming (forced air) for mild and moderate hypothermia.
• In cardiac arrest, ERC guidance limits defibrillation to three attempts and withholds adrenaline when the core temperature is below 30 °C, and doubles the interval between adrenaline doses (6-10 minutes) between 30 and 35 °C.
• Extracorporeal life support (venoarterial ECMO or cardiopulmonary bypass) is the preferred rewarming method for hypothermic cardiac arrest or unstable patients; survival with good neurological outcome is possible after prolonged CPR.
• A serum potassium above about 12 mmol/L suggests asphyxia or a non-survivable injury; scores such as HOPE help decide on ECLS.
• "Nobody is dead until warm and dead" applies, within these limits.

Heat Illness

• Heat exhaustion: core temperature usually below 40 °C, normal mental state; rest, cooling and fluids.
• Heat stroke: core temperature above about 40 °C with central nervous system dysfunction (confusion, seizures, coma). Exertional heat stroke affects athletes and soldiers; classic heat stroke affects the elderly in heat waves. Complications include rhabdomyolysis, acute kidney injury, liver failure, DIC and ARDS.
• Treatment: rapid cooling (cold-water immersion is the most effective for exertional heat stroke; evaporative cooling, ice packs), aiming for a core temperature of about 38.5-39 °C within 30 minutes. Antipyretics are ineffective; dantrolene is not recommended.
• Differential diagnosis: malignant hyperthermia, neuroleptic malignant syndrome, serotonin syndrome, thyroid storm and sympathomimetic toxicity.

Decompression Illness

Includes decompression sickness (nitrogen bubbles forming in tissues and blood during or after ascent from depth) and arterial gas embolism (from pulmonary barotrauma during rapid ascent).

• Decompression sickness: joint pain ("the bends"), skin mottling, neurological symptoms (spinal cord), and pulmonary "chokes".
• Arterial gas embolism: sudden neurological deficit or loss of consciousness within minutes of surfacing.
• Treatment: 100% oxygen, fluids, lie flat, and urgent hyperbaric oxygen recompression. Air transfer should be at low altitude or with a cabin pressurised to sea level.
• Flying is avoided for at least 12-24 hours after diving (longer after multiple dives or dives needing decompression stops) to prevent decompression sickness.