Surgery chapters
Burn pathophysiology, systemic effects and fluid resuscitation formulas
How a burn causes local tissue damage, capillary leak and burn shock, its effects on the airway, lungs, gut, immunity and metabolism, and how to calculate and monitor resuscitation fluids (Parkland, ATLS, Muir and Barclay).
- A burn has a central zone of coagulation, a salvageable zone of stasis and an outer zone of hyperaemia. Inflammatory mediators make capillaries leak, so fluid and protein shift out of the vessels and cause burn shock once burns exceed about 15% TBSA in adults (10% in children).
- Parkland formula: 4 mL × kg × % TBSA of Ringer's lactate in 24 hours, half in the first 8 hours from the time of burn; ATLS now starts at 2 mL (adults) and 3 mL (children).
- The best guide to resuscitation is urine output: about 0.5 mL/kg/h in adults and 1 mL/kg/h in children.
On this page
Overview
A major burn is not just a skin wound. It sets off a body-wide inflammatory reaction that makes capillaries leak, leading to burn shock, and later to infection, gut failure and a large rise in metabolic rate. Early deaths come from airway and inhalation injury and under-resuscitation; later deaths from sepsis and multiorgan failure. Fluid resuscitation guided by formulas and urine output is the key early treatment.
Local effects: zones of a burn (Jackson)
| Zone | Position | What happens |
|---|---|---|
| Zone of coagulation | Centre | Proteins coagulated; tissue dead and cannot recover |
| Zone of stasis | Around it | Reduced blood flow; tissue can survive if perfusion is maintained, but dies with shock, infection, oedema or poor resuscitation |
| Zone of hyperaemia | Outer | Increased blood flow from inflammation; recovers fully |
Good fluid resuscitation and cooling aim to save the zone of stasis. If it is lost, a burn becomes deeper and larger.
Inflammation and burn shock
Mechanism:
- Heat damages proteins and stimulates pain fibres; complement and the clotting (Hageman factor) and kinin cascades are activated.
- Mast cells release histamine and cytokines such as TNF-α; neutrophils release oxygen radicals and proteases.
- Capillary permeability rises sharply, so water, salts and even large proteins leak out.
- Leaked protein and damaged collagen raise the tissue oncotic pressure, pulling out more fluid. Oedema forms.
Results:
- Loss of plasma (not red cells) from the circulation, so haematocrit rises.
- Fluid loss is proportional to the burn area and is greatest in the first 8 hours, continuing for about 24–36 hours.
- Around 10–15% TBSA, the loss is enough to cause hypovolaemic (burn) shock.
- Above about 25% TBSA, the leak also occurs in vessels far from the burn (generalised oedema).
Burn shock is due to loss of plasma through leaky capillaries, not to bleeding. Blood loss is not a feature of the early burn; if a burn patient is hypotensive early, look for another injury.
Systemic effects of a major burn
| System | Effect |
|---|---|
| Airway | Heat injury of the upper airway causes swelling that can block it within hours (usually 4–24 h) |
| Lungs | Smoke particles injure the lower airways: inflammation, mucosal sloughing, plugging, pneumonia, ARDS; signs may take 24 hours to 5 days |
| Metabolic poisoning | Carbon monoxide and hydrogen cyanide from fires in enclosed spaces |
| Chest wall | Full-thickness eschar on the chest restricts breathing (needs escharotomy) |
| Circulation | Burn shock; circumferential full-thickness eschar on a limb acts like a tourniquet as the limb swells |
| Kidneys | Acute kidney injury from hypovolaemia, or from myoglobin and haemoglobin in deep and electrical burns |
| Gut | Mucosal ischaemia, ileus, bacterial translocation, stress ulceration (Curling's ulcer), abdominal compartment syndrome |
| Immune system | Cell-mediated immunity falls; infection from the wound, lungs, lines and catheters; sepsis is the main late killer |
| Metabolism | Hypermetabolic, catabolic state: raised energy use, protein breakdown, weight loss; continues until the wound is closed |
| Blood | Raised haematocrit early; later anaemia; coagulation changes |
| Electrolytes | Hyperkalaemia risk (cell damage); use suxamethonium with caution in major and electrical burns because it can raise potassium further |
Airway and inhalation injury
Suspect if:
- Trapped in a closed space with smoke or hot gases; altered consciousness.
- Burns of the face and neck, singed nasal hair, burns of the palate or nasal mucosa.
- Soot in the mouth or nose, carbonaceous sputum.
- Hoarseness, change in voice, stridor (late signs).
Management:
- Early intubation is safest before swelling makes it impossible; have a surgical airway (cricothyroidotomy) ready.
- Use a large tube (ATLS advises at least 7.5 mm internal diameter in adults).
- Humidified oxygen, physiotherapy, nebulisers, bronchoscopy as needed.
Stridor or voice change in a patient with facial burns means the airway is closing: intubate now. Symptoms of laryngeal oedema are late, so act on the history and signs.
Carbon monoxide and cyanide
- CO binds haemoglobin with about 240 times the affinity of oxygen and shifts the dissociation curve to the left.
- Pulse oximetry reads falsely normal because it cannot tell carboxyhaemoglobin from oxyhaemoglobin. Measure carboxyhaemoglobin (HbCO) on arterial blood gas.
- HbCO above 10% suggests significant exposure; high levels cause headache, confusion, coma and death.
- Treat with 100% oxygen by non-rebreathing mask: the half-life of HbCO falls from about 4 hours on room air to about 40 minutes on 100% oxygen.
- Cyanide blocks mitochondrial respiration, causing persistent unexplained lactic (metabolic) acidosis; seek specialist advice.
"Cherry-red" skin colour in CO poisoning is rare. A normal SpO2 does not exclude CO poisoning.
Fluid resuscitation
Who needs IV fluids?
- Bailey & Love: consider IV fluids for burns over 15% TBSA in adults and 10% TBSA in children.
- ATLS: start formal burn fluid resuscitation when deep partial plus full-thickness burns exceed 20% TBSA.
- Smaller burns can often be managed with oral fluids; oral fluids must contain salt (oral rehydration solution), because plain water can cause hyponatraemia.
Which fluid?
- Ringer's lactate (Hartmann's solution), warmed, is the fluid of choice. Crystalloids are cheap and as effective as colloid in the first 24 hours.
- Colloid (human albumin solution or plasma) is avoided in the first 12 hours or so because protein leaks out; some units add it later.
- Hypertonic saline reduces oedema in some centres but needs careful sodium monitoring.
Formulas
| Formula | Fluid | Volume | Timing |
|---|---|---|---|
| Parkland | Ringer's lactate | 4 mL × kg × % TBSA in 24 h | Half in first 8 h (from the burn), half in next 16 h |
| ATLS / ABA consensus | Ringer's lactate | 2 mL × kg × % TBSA (adults); 3 mL (children); 4 mL (high-voltage electrical) | Half in first 8 h, then adjust to urine output |
| Muir and Barclay | Colloid (albumin or plasma) | One portion = 0.5 mL × kg × % TBSA | Six portions over 36 h: three 4-hour blocks, two 6-hour blocks, then one 12-hour block |
| Children's maintenance (added to resuscitation fluid) | Dextrose-saline | Per 24 h: 100 mL/kg up to 10 kg; plus 50 mL/kg between 10 and 20 kg; plus 20 mL/kg above 20 kg | Over 24 h |
The 8 hours are counted from the time of the burn, not from arrival in hospital. A patient who arrives late must "catch up".
A 70 kg man has 30% TBSA partial and full-thickness flame burns.
Total in 24 h = 4 × 70 × 30 = 8,400 mL Ringer's lactate
First 8 h = 8,400 ÷ 2 = 4,200 mL → 4,200 ÷ 8 = 525 mL/h
Next 16 h = 4,200 mL → 4,200 ÷ 16 = 262.5 mL/h (about 260 mL/h)
Same patient (needs 4,200 mL in the first 8 hours) arrives 2 hours after the burn having had no fluid.
Time left in the first 8 h = 8 − 2 = 6 h
Rate = 4,200 ÷ 6 = 700 mL/h for the next 6 hours, then 262.5 mL/h for 16 hours
70 kg man, 30% TBSA, ATLS adult rate of 2 mL:
Total = 2 × 70 × 30 = 4,200 mL in 24 h
First 8 h = 2,100 mL → 262.5 mL/h, then titrate up or down to urine output
A 20 kg child has a 20% TBSA scald.
Resuscitation (ATLS 3 mL) = 3 × 20 × 20 = 1,200 mL in 24 h → first 8 h 600 mL = 75 mL/h
(Parkland 4 mL would give 4 × 20 × 20 = 1,600 mL)
Maintenance = (100 × 10) + (50 × 10) = 1,500 mL in 24 h = 62.5 mL/h of dextrose-containing fluid
Target urine output = 1 mL/kg/h = 20 mL/h
70 kg adult, 30% TBSA.
One portion = 0.5 × 30 × 70 = 1,050 mL
Six portions over 36 h (three 4-h, two 6-h and one 12-h block) = 6 × 1,050 = 6,300 mL in total
Formulas give only a starting rate. Never give the full volume blindly; adjust hourly to the patient's response.
Monitoring resuscitation
- Insert a urinary catheter in all patients needing burn resuscitation.
- Urine output is the key measure:
| Patient | Target urine output |
|---|---|
| Adult | 0.5 mL/kg/h (ATLS: about 30–50 mL/h); Bailey & Love gives 0.5–1.0 mL/kg/h |
| Child under 30 kg | 1 mL/kg/h |
| High-voltage electrical burn with dark urine | Higher (about 100 mL/h in adults; ATLS) until the urine clears |
- Bailey & Love: if output is low, raise the infusion by 50%; if there are signs of hypoperfusion, give a 10 mL/kg bolus; if output exceeds 2 mL/kg/h, slow the infusion.
- Other measures: haematocrit, acid–base status (lactate, base deficit), mental state. Tachycardia is a poor guide in burns (pain and anxiety also cause it).
- Diuretics and glycosuria make urine output misleading.
A 70 kg adult: 0.5 × 70 = 35 mL/h
Dangers of getting it wrong
- Under-resuscitation: kidney injury, conversion of the zone of stasis, deeper burns, multiorgan failure.
- Over-resuscitation ("fluid creep"): severe oedema, pulmonary oedema, abdominal and limb compartment syndrome, deepening of burns.
Nutrition in burns
- Major burns are hypermetabolic and catabolic; feed early.
- Bailey & Love: adults over 15% TBSA (children over 10%) have raised nutritional needs; a nasogastric tube is advised for large burns and feeding should start within about 6 hours to protect the gut mucosa.
- Energy needs are estimated with formulas such as Curreri (adults 16–59 years: 25 kcal/kg + 40 kcal per % TBSA).
- Early wound excision and closure is the most effective way to stop the catabolic drive.
70 kg adult, 30% TBSA: (25 × 70) + (40 × 30) = 1,750 + 1,200 = 2,950 kcal/day
Expect: the three zones of a burn and the salvageable zone of stasis, capillary leak as the cause of burn shock with rising haematocrit, the thresholds for IV fluids (15% adults, 10% children), Parkland formula (4 mL × kg × % TBSA, half in the first 8 hours from the time of burn) with a numerical calculation, Ringer's lactate as the fluid of choice, the newer ATLS 2 mL and 3 mL rates, urine output as the best monitor (0.5 mL/kg/h adult, 1 mL/kg/h child), carbon monoxide and the falsely normal pulse oximeter, early intubation for airway burns, Curling's ulcer and hypermetabolism.
Quick revision
- Zones: coagulation (dead), stasis (salvageable), hyperaemia (recovers).
- Burn shock = capillary leak of plasma; haematocrit rises.
- IV fluids: over 15% TBSA adults, over 10% children (Bailey & Love); over 20% (ATLS).
- Parkland: 4 × kg × % TBSA; half in first 8 h from the burn; Ringer's lactate.
- ATLS: 2 mL adults, 3 mL children, 4 mL electrical; titrate to urine.
- Urine: 0.5 mL/kg/h adult, 1 mL/kg/h child.
- CO: 100% oxygen; SpO2 falsely normal; measure HbCO.
- Stridor or voice change after a face burn: intubate early.
- Sepsis is the commonest late cause of death.
Written by The House Job from standard surgical references (Bailey & Love; ATLS Student Course Manual).
FAQ
Why does a burn patient go into shock without bleeding?
Inflammatory mediators make the capillaries leaky, so plasma water, salt and protein move from the blood into the tissues. The circulating volume falls even though red cells stay in the vessels.
Is the Parkland formula 2 mL or 4 mL?
The classic Parkland formula is 4 mL × kg × % TBSA. ATLS now advises starting adults at 2 mL and children at 3 mL to avoid over-resuscitation, then adjusting to urine output. Check your local unit's protocol.
When does the first 8-hour period start?
From the time of the burn injury, not from the time the patient reaches hospital.
What is the best way to judge whether burn resuscitation is adequate?
Hourly urine output through a urinary catheter, aiming for about 0.5 mL/kg/h in adults and 1 mL/kg/h in children.