Major burns don't happen very often but sometimes clothing gets set alight (whether deliberately or accidentally) and patients suffer significant burns. A major burn is classed as anything greater than 10% body surface area in a child (or 15% in an adult), or an airway burn.
There are some excellent summaries on major burns including:
- The BMJ ABC
- BMJ Burn Circulation Review (including worked examples)
- Burn Journal
- Anaesthetic Update
Pathophysiology of Burns
The first thing that happens is the burn makes capilliaries become leaky. Plasma is lost and water is drawn out with it causing a hypovolaemic distributive shock. This lasts for 3- 36 hours.
Because water is drawn out of the tissue, the patient becomes very oedematous.
Burns damage the red blood cells, and make them fragile, so anaemia can result
Jackson's Burn Model is used to understand burn pathophysiology. There are three main areas in a burn:
- Zone of hyperaemia: this is the outer ring of erythema. The tissue here is unaffected, and viable.
- The zone of vascular stasis is the next ring in. This tissue has been affected by the burn and may recover, but may not. Making sure the patient is adequately hydrated will affect this zone of stasis.
- The central zone of necrosis is irreversibly damaged. This thermally coagulated tissue behaves like cutaneous gangrene. It has
no blood supply - so if it remains dry, it is inhospitable to bacterial
growth. If it remains moist, bacteria resistent to antibiotics will
proliferate. These micro-organisms can release exotoxins, leading to
deepening of the burn wound, local cellulitis and sepsis.
This damaged tissue also has an inflammatory response, releasing leukotrienes, prostaglandins, oxygen free radicles and histamine into the circulation. This leads to increased capillary permeability. The effects are very similar to the effects seen in sepsis.
Stridor, hoarse voice, singed nasal hairs are all listed as "red flags" when assessing the airway in a burns patient. There are no studies looking at the predictive value of these signs in airway injury, but as a small amount of swelling can significantly affect the airway diameter, especially in children, it pays to be vigilant. I have been told by a burns anaesthetists that the only way to reliably assess the degree of airway swelling is to have a look - either when you intubate, or with a bronchoscope / naso-endoscope. Accessing these tools can be tricky so I suspect most places will err on the side of caution.
In any patients with features suggestive of inhalational injury we should measure carboxyhaemoglobin values.
Remember that many people with burns may have been involved with explosions or other traumas.
Circumferential chest burns can cause problems with ventilation, and may require urgent treatment.
Managing circulation can be difficult in burns. Initial fluid requirements can be very high due to burn shock and altered vascular permeability. Later, fluid causes massive oedema and further management difficulties.
Assessing burn depth and area covered is the first step to calculating fluid requirements.
Assessing Burn Depth
As much as we all like a fancy test or gadget to help us, clinical assessment is the only way of assessing burn depth.
There are four things we can assess to help us gauge the depth of the burn - which nearly fit an ABBC approach!
Appearance - this can be difficult as burns are often covered with soot or dirt, and blisters obscure the burn base.
Blanching - capillary refill can be assessed - preferably by pressing on the burn with a sterile cotton bud (or wound swab).
Bleeding - I have never seen bleeding assessed before, but it is suggested that you can test bleeding with a 21 gauge needle. Brisk bleeding on superficial pricking indicates the burn is superficial or superficial dermal. Delayed bleeding on a deeper prick suggests a deep dermal burn, while no bleeding suggests a full thickness burn.
Sensation - You should test sensation with a needle. Painful burns are superficial or superficial dermal burns. Non-painful burns indicate a deep dermal injury, while full thickness injuries are insensate. However oedema can blunt sensation.
Assessing Burn PercentageLund and Browder charts are better and more accurate than Wallace's rule of nines (covered in minor burns). Remember not to include simple erythema in your calculations!
- The Parkland formula is as good as any other methods at calculating fluid requirements, and I find it easier to remember than the others.
The Parkland formula is for crystalloid only. Children require maintenance fluid in addition.
- High tension electrical injuries require more fluid (up to 9 mlx(burn area)x(body weight) in the first 24 hours).
- Inhalation injuries may increase fluid requirements by 50%.
Infection is common, but the role of prophylactic antibiotics is unclear.
Tetanus cover should be provided.
Deep dermal or full thickness burns are inelastic, and will not stretch. Oedema and swelling beneath this tissue increases tissue pressures. To allow adequate skin perfusion and ventilation, division of the burn may be needed. In an escharotomy only the burnt tissue is divided - not any fascia. In a fasciotomy underlying fascia is divided too.
Escharotomies should be performed with cautery (as they tend to bleed), ideally in aseptic conditions in theatre.
And all of this is summarised beautifully on Academic Life in EM. And not so beautifully below.