Burns & Fluid Resuscitation

A burn is a wound that continues to evolve for two or three days after the injury, and almost everything that is done in the first forty-eight hours is aimed at stopping that evolution.

The organising tool is a three-part assessment: depth decides healing, area decides fluid, and the airway decides whether either matters.

Every examination question in this chapter is testing one of those three. Depth questions ask whether the burn will heal or needs grafting. Area questions ask for a fluid calculation. Airway questions ask whether the patient will still have one in two hours.

1. What a Burn Actually Does

The classical description is of three concentric zones, and it explains why burns get worse before they get better.

The zone of coagulation is the central area of irreversible protein denaturation. It is dead at the moment of injury and nothing will recover it.

The zone of stasis surrounds it. Perfusion here is reduced but the tissue is alive, and this is the only zone that treatment can influence.

The zone of hyperaemia is the outermost area of vasodilatation, which recovers unless something goes badly wrong.

The whole purpose of resuscitation is to save the zone of stasis. Hypotension, hypoxia, oedema and infection all convert it to coagulation, which is why an inadequately resuscitated burn deepens over the following days.

Systemically, a large burn releases inflammatory mediators that increase capillary permeability throughout the body, not merely at the burn site.

Fluid therefore leaks into the interstitium everywhere, producing burn shock, which is a distributive and hypovolaemic shock combined. Loss is greatest in the first eight hours, which is why resuscitation formulas front-load the volume.

Later, from about forty-eight hours, the picture reverses into a hypermetabolic state with tachycardia, raised temperature, catabolism and enormous energy requirements.

2. Depth Decides Healing

Depth determines whether the burn heals from surviving epidermal appendages or requires grafting, and it is assessed by appearance, capillary refill and sensation.

The counterintuitive point is that the most painful burn is not the deepest one. A superficial partial thickness burn exposes intact nerve endings in a moist bed and is agonising, whereas a full thickness burn has destroyed the nerve endings and is painless.

A patient describing a painless burn is describing a serious one.

Superficial epidermal burns, the classic sunburn, are excluded from the burn surface area calculation entirely, which is a common source of arithmetic error.

Deep partial thickness burns are the difficult group. They sit at the boundary of grafting, may be revised in depth over forty-eight hours, and are increasingly excised and grafted early rather than allowed to heal slowly with contracture.

3. Area Decides Fluid

Three methods are used, and the choice depends on the size and pattern of the burn.

The rule of nines assigns nine per cent or a multiple of it to each region in an adult: head and neck nine, each arm nine, each leg eighteen, front of trunk eighteen, back of trunk eighteen, and perineum one.

The rule of the palm takes the patient's own palm with fingers as approximately one per cent, and is best for small or scattered burns.

The Lund and Browder chart is the most accurate and the only method valid in children, because it adjusts for age.

Children have proportionally much larger heads and smaller legs, so the adult rule of nines overestimates the leg contribution and underestimates the head, producing a materially wrong fluid volume in exactly the patients least able to tolerate error.

An infant's head is closer to eighteen per cent than nine, with each leg nearer thirteen.

4. Fluid Resuscitation

The Parkland formula remains the calculation the examination expects: four millilitres of Ringer lactate per kilogram per per cent burn in the first twenty-four hours, with half given in the first eight hours and half over the following sixteen.

The eight hours run from the time of the burn, not from the time of arrival. A patient reaching hospital four hours after injury must receive the first half in the remaining four hours, and this is a favourite question.

Ringer lactate is chosen over normal saline because large volumes of saline produce hyperchloraemic metabolic acidosis, and over colloid in the first day because leaking capillaries allow protein to escape into the interstitium.

Current burn practice has moved away from starting at four millilitres. The American Burn Association guideline recommends beginning at two millilitres per kilogram per per cent in adults and titrating upwards, because the traditional formula consistently produced over-resuscitation.

That phenomenon is called fluid creep, and its consequences are real: pulmonary oedema, abdominal compartment syndrome, and conversion of the zone of stasis by tissue oedema. The safest position for an examination is to know the Parkland calculation and to know that it is a starting point.

The formula is a starting estimate, and urine output is the endpoint that actually governs. Titrate to 0.5 millilitres per kilogram per hour in adults, and around 1 millilitre per kilogram per hour in children.

Maintenance fluid is given in addition in children, because they have limited glycogen reserves and become hypoglycaemic without it.

Resuscitation formulas are indicated above roughly fifteen to twenty per cent burn in adults and ten per cent in children. Smaller burns are managed with oral fluid.

5. The Airway Decides Everything

Inhalation injury is the single greatest predictor of mortality in burns, and the decision it demands must be made early.

Suspect it from the circumstances rather than from the examination: fire in an enclosed space, loss of consciousness, facial burns, singed nasal hair, soot in the mouth or sputum, hoarseness and stridor.

Airway oedema develops over hours and is worsened by the resuscitation fluid itself. An airway that looks manageable on arrival may be unintubatable four hours later.

Therefore intubation is performed early on suspicion, not late on evidence. Waiting for stridor means attempting intubation through a swollen airway, and it is the classic avoidable death in burn care.

Carbon monoxide poisoning must be considered separately. It binds haemoglobin with an affinity vastly greater than oxygen, and produces headache, confusion and eventually coma.

Pulse oximetry is falsely normal in carbon monoxide poisoning, because the oximeter cannot distinguish carboxyhaemoglobin from oxyhaemoglobin. Diagnosis requires co-oximetry, and treatment is one hundred per cent oxygen, which shortens the half-life substantially.

Cyanide toxicity occurs when synthetic materials burn, and should be suspected in a persistent lactic acidosis that does not respond to fluid and oxygen. Hydroxocobalamin is the antidote of choice in burns because it does not impair oxygen carriage.

6. Escharotomy and Compartment Problems

Full thickness burn produces eschar, which is inelastic. When it is circumferential, the tissue beneath swells against a rigid casing.

On a limb this produces a compartment syndrome, with progressive pain, loss of distal pulses and neurological deficit, and the pulse is a late sign rather than an early one.

On the chest it restricts ventilation, producing rising airway pressures and inadequate chest expansion in a ventilated patient.

Escharotomy is an incision through the eschar down to subcutaneous fat, performed at the bedside along the mid-medial and mid-lateral lines of a limb. It requires no anaesthesia in a full thickness burn because the eschar is insensate.

Escharotomy is not fasciotomy. Escharotomy releases burnt skin; fasciotomy opens muscle compartments and is needed in electrical injury and in deep thermal burns with muscle involvement.

Abdominal compartment syndrome is a recognised consequence of over-resuscitation, presenting with a tense abdomen, rising airway pressures, falling urine output and a raised intra-abdominal pressure.

7. Wound Care, Infection and Nutrition

First aid is cool running water for twenty minutes, effective for up to three hours after injury, followed by covering with clean film or a sterile sheet.

Ice is not used, because it causes vasoconstriction in the zone of stasis and deepens the burn. Hypothermia is a genuine risk in a large burn, so the patient is kept warm even while the wound is cooled.

Silver sulfadiazine is the traditional topical agent. It does not penetrate eschar well and can cause transient leucopenia. Mafenide penetrates eschar but is painful and inhibits carbonic anhydrase, producing metabolic acidosis.

Prophylactic systemic antibiotics are not given. They select resistant organisms without reducing burn wound infection, which is prevented by early excision, topical agents and wound care.

Burn wound infection is diagnosed by change in the wound, systemic deterioration and quantitative culture rather than by surface swabs, which grow colonisers. Pseudomonas aeruginosa is the classic late organism.

Tetanus prophylaxis is given, since burns are tetanus-prone wounds.

Early excision and grafting of deep burns reduces infection, hospital stay and mortality, which reversed the older practice of waiting for eschar to separate.

Nutrition is a major intervention rather than supportive care. The hypermetabolic response can double resting energy expenditure, so high-calorie, high-protein enteral feeding is started early, and the enteral route is strongly preferred.

Curling ulcer is the stress gastric ulceration of major burns, and proton pump inhibitor prophylaxis is standard.

8. Grafting and the Late Burn

A burn that will not heal within about three weeks is grafted, because healing beyond that point occurs through granulation and contracture rather than through epithelial resurfacing.

A split thickness graft takes epidermis with part of the dermis. It survives on a poorly vascularised bed, the donor site re-epithelialises from remaining appendages and can be reharvested, and it can be meshed to cover a large area from a small donor.

The price is contraction and poor colour match, because less dermis is transferred.

A full thickness graft takes the whole dermis. It contracts far less and matches better, which is why it is used on the face and over joints, but it needs a well-vascularised bed and the donor site must be closed directly, limiting its size.

Graft take fails for four reasons, and they are worth knowing as a list because the question is usually which one applies: haematoma or seroma lifting the graft off its bed, shear from inadequate immobilisation, infection, and an avascular recipient bed such as exposed bone or tendon without periosteum or paratenon.

Hypertrophic scars stay within the boundary of the original wound and often regress; keloids extend beyond it and do not. Both are commoner in darker skin and across the sternum, shoulders and earlobes.

Marjolin ulcer is squamous cell carcinoma arising in a chronic burn scar, typically decades later, and any non-healing ulceration in an old scar must be biopsied rather than dressed.

9. Electrical and Chemical Burns

Electrical injury is dangerous because the visible wound bears no relation to the damage. Current passes through tissues of least resistance, principally nerve, blood vessel and muscle, so deep muscle necrosis can lie beneath minor entry and exit wounds.

Muscle necrosis releases myoglobin, which precipitates in renal tubules and causes acute kidney injury. Urine appears dark and dipsticks positive for blood without red cells on microscopy.

Management is aggressive fluid to maintain a high urine output, well above the standard burn target, with a low threshold for fasciotomy and cardiac monitoring for arrhythmia.

Fluid requirements in electrical injury cannot be estimated from surface area, because the surface area does not reflect the injury.

Chemical burns are irrigated copiously with water, and neutralising agents are avoided, because the neutralisation reaction is exothermic and adds a thermal burn to the chemical one.

Alkalis penetrate more deeply than acids because they cause liquefactive necrosis, whereas acids cause coagulative necrosis that limits their own penetration.

Hydrofluoric acid is the exception requiring a specific antidote. Fluoride ion binds calcium, causing severe pain, hypocalcaemia and arrhythmia, and treatment is topical or injected calcium gluconate.

10. Referral and Special Populations

Transfer to a burn centre is indicated for burns over a defined proportion of surface area, any full thickness burn, burns of the face, hands, feet, perineum or over joints, electrical and chemical burns, inhalation injury, and burns in the very young or very old.

The special sites are listed not because they are large but because the functional and cosmetic consequences of poor healing are disproportionate.

Non-accidental injury must be considered in children. Suspicious features include a scald with a clear immersion line and no splash marks, burns to the buttocks or both feet in a stocking distribution, cigarette burns, and a history inconsistent with the pattern or changing between tellings.

In India, kerosene stove burns, sari and dupatta ignition, and self-inflicted or homicidal burns in young married women make every major burn a medicolegal case, requiring a dying declaration where the patient may not survive and notification to the police.

11. Worked Examples

Example 1. A 60 kg man has burns to the whole of both legs and the front of the trunk. He arrives three hours after injury. Calculate the resuscitation.

Both legs give thirty-six per cent and the anterior trunk eighteen, so the total is fifty-four per cent.

Parkland gives 4 multiplied by 60 multiplied by 54, which is 12,960 millilitres over twenty-four hours. Half of that, 6,480 millilitres, must be delivered within eight hours of the burn.

Three of those eight hours have already passed, so the first half must run over the remaining five hours, at approximately 1,296 millilitres per hour, with the remaining 6,480 over the subsequent sixteen. Urine output then governs the actual rate.

Example 2. A man rescued from a house fire has soot in the mouth, hoarseness and oxygen saturation of 99 per cent on air. He is talking normally.

The saturation is falsely reassuring. Pulse oximetry cannot distinguish carboxyhaemoglobin from oxyhaemoglobin, so a normal reading does not exclude carbon monoxide poisoning, and co-oximetry is required.

The soot and hoarseness indicate inhalation injury with an airway that will swell over the next several hours, worsened by the resuscitation fluid he is about to receive. He should be intubated early and given one hundred per cent oxygen. Waiting until he develops stridor means intubating a closed airway.

Example 3. A patient with a circumferential full thickness burn of the forearm develops increasing pain and reduced sensation. The radial pulse is still palpable.

This is compartment syndrome beneath an inelastic eschar. The presence of a pulse is not reassurance, because pulselessness is a late sign that appears only when compartment pressure exceeds arterial pressure.

Escharotomy is performed at the bedside along the mid-medial and mid-lateral lines, incising through eschar to subcutaneous fat. No anaesthesia is required through insensate full thickness burn, and fasciotomy is added only if muscle compartments remain tight afterwards.

Summary

• Depth decides healing, area decides fluid, the airway decides whether either matters.
• The zone of stasis is the only zone treatment can save; hypotension, hypoxia and infection convert it.
• Capillary leak is systemic, greatest in the first eight hours, hence front-loaded fluid.
• A hypermetabolic state follows from about forty-eight hours.
• The most painful burn is superficial partial thickness; full thickness is insensate.
• Full thickness burn is white or leathery, non-blanching and needs grafting.
• Superficial epidermal burns are excluded from the area calculation.
• Rule of nines for adults, rule of palm for scattered burns, Lund and Browder for children.
• Children have proportionally larger heads and smaller legs, so the adult rule misleads.
• Parkland is 4 mL per kg per per cent Ringer lactate, half in the first eight hours.
• The eight hours run from the burn, not from arrival.
• Current guidance starts at 2 mL per kg per per cent to avoid fluid creep.
• Urine output of 0.5 mL per kg per hour in adults governs, not the formula.
• Children need maintenance fluid in addition, to avoid hypoglycaemia.
• Intubate early on suspicion of inhalation injury, never late on evidence.
• Pulse oximetry is falsely normal in carbon monoxide poisoning.
• Suspect cyanide when lactic acidosis persists despite oxygen and fluid.
• Circumferential eschar causes compartment syndrome; the pulse is a late sign.
• Escharotomy releases skin; fasciotomy opens muscle and is needed in electrical injury.
• Cool with running water for twenty minutes, never ice.
• Prophylactic systemic antibiotics are not given.
• Early excision and grafting reduces infection, stay and mortality.
• Nutrition is a therapeutic intervention, and the enteral route is preferred.
• Curling ulcer is the stress ulceration of major burns.
• Split thickness grafts survive poor beds and can be meshed; full thickness grafts contract less.
• Graft take fails from haematoma, shear, infection or an avascular bed.
• Hypertrophic scars stay within the wound; keloids extend beyond it.
• Marjolin ulcer is squamous carcinoma in an old burn scar and must be biopsied.
• Electrical injury damage far exceeds the visible wound; watch for myoglobinuria.
• Irrigate chemical burns, never neutralise, because neutralisation is exothermic.
• Alkalis penetrate deeper than acids through liquefactive necrosis.
• Hydrofluoric acid needs calcium gluconate.
• Consider non-accidental injury from immersion lines and absent splash marks.