Burns: Pathophysiology, Assessment and Treatment
Updated: 18 hours ago
Burn injuries remain one of the most common and physiologically demanding forms of trauma encountered in emergency and critical care settings, arising from thermal, chemical, electrical, or radiation sources across domestic, occupational, and disaster contexts. Given the breadth of mechanisms, the complexity of the underlying physiology, and the high stakes of delayed or inadequate treatment, a structured understanding of burn injuries is essential for clinicians across prehospital, emergency, and critical care settings.
Pathophysiology
The pathophysiology of burn injury operates on two levels: a local tissue response confined to the site of injury, and a systemic response capable of affecting the entire body. Understanding both is essential to anticipating how a burn will evolve in the hours and days following the initial injury.
Local Response
Think of a burn as a bullseye with three rings. The centre (zone of coagulation) is the point of maximum contact and where the burn is at its worst; cells here are dead from the heat and the tissue cannot be recovered. Around this is the zone of stasis, where cells are damaged yet still salvageable, though blood flow is insufficient; if oxygen and perfusion aren't restored, these cells will die and the burn will effectively deepen. This is why fluid resuscitation in burns care matters so much. The outer ring is the zone of hyperaemia, which typically recovers on its own without serious medical intervention, presenting as inflamed and irritated tissue.
Systemic Response
When a burn involves a sufficiently large total body surface area (generally cited as greater than 15 to 20% in adults), local inflammatory mediators released at the wound site (histamine, prostaglandins, cytokines) spill into systemic circulation, triggering a body-wide response. This produces a generalised increase in capillary permeability, allowing fluid, electrolytes, and protein to shift out of the intravascular space throughout the body, not just at the burn site. The result is a rapid decline in circulating volume, which, if not treated with aggressive fluid resuscitation, progresses into hypovolaemic shock.
Total Body Surface Area Calculation
The rule of nines is the most widely used method for estimating what percentage of the body has been burned, giving clinicians a quick sense of severity. It divides the body into anatomical regions, each representing approximately 9% (head and neck 9%, each arm 9%, anterior and posterior torso 18% each, each leg 18%, groin 1%). For example, a patient with burns covering the entire anterior trunk (18%) and the whole of one arm (9%) has an estimated total body surface area of 27%, already well above the threshold at which systemic capillary leak and fluid shifts become clinically significant, warranting formal fluid resuscitation.
In practice: that same 27% TBSA figure is the difference between a burn managed with local wound care alone, and one that needs formal fluid resuscitation started immediately. The calculation isn't academic, it changes what you do next.
Assessment and Treatment
Primary Survey and Initial Assessment
As with any major trauma, assessment of the burn patient begins with a standard airway-breathing-circulation approach, with particular attention to the airway in patients with suspected inhalation injury. Facial burns, singed nasal hairs, soot in the oropharynx, and a history of exposure in an enclosed space should raise immediate concern for airway involvement, and supplementary oxygen should be delivered as soon as possible. Once airway, breathing, and circulation are addressed, the burn itself is assessed: mechanism of injury, depth, total body surface area, and any associated trauma.
Burn Depth Classification
• Superficial (first-degree): extends to the epidermis; identified by redness, pain, no blistering. A sunburn is the classic example; these typically heal on their own within days, without scarring
• Superficial partial-thickness (second-degree): extends into the upper dermis; identified by pain, blisters, blanching with pressure, and moisture. Heals in approximately 2 to 3 weeks with minimal scarring
• Deep partial-thickness (second-degree): extends deeper into the dermis; pale or mottled, less painful due to nerve damage, and does not blanch. Healing is slow and often requires medical or surgical intervention
• Full-thickness (third-degree): destroys the entire dermis; characterised by a leathery texture, white or charred appearance, and painless at the centre due to destroyed nerve endings. Requires surgical intervention and grafting
• Fourth-degree: extends into fascia, muscle, or bone; associated with high morbidity, often requiring amputation or extensive reconstruction
Fluid Resuscitation
For patients with burns exceeding the systemic threshold (generally greater than 15 to 20% total body surface area in adults), fluid resuscitation is the cornerstone of early treatment. In the prehospital setting, simplified formulas are favoured to reduce cognitive load under time pressure, such as the PHIFTEEN-B formula used by the Queensland Ambulance Service (15 mL per hour for each 1% of TBSA burned), delivered as sodium chloride 0.9%. Large fluid volumes also carry risk in their own right: interstitial oedema and tissue swelling can complicate airway management, underscoring why fluid rates must be reviewed regularly and tailored to the individual patient rather than applied rigidly.
Wound Care
Initial wound management involves cooling the burn with cool (not ice-cold) running water for 20 minutes, which is still beneficial up to 3 hours after injury, removing adherent clothing and jewellery, and covering the wound to reduce contamination and pain. Superficial and superficial partial-thickness burns are typically managed with topical dressings and analgesia, while deep partial-thickness and full-thickness burns often require early surgical intervention and skin grafting to reduce infection risk and improve functional outcomes.
Pain Management and Infection Prevention
Burns are among the most painful traumatic injuries due to exposure of nerve endings in partial-thickness wounds, requiring aggressive multimodal analgesia. Given the loss of the skin's protective barrier, infection is a leading cause of morbidity in burn patients; careful aseptic wound technique and vigilant monitoring for signs of sepsis are essential throughout the treatment course.
Burn severity unfolds over hours and days, not just at the moment of injury.
Conclusion
Burn severity unfolds over hours and days, not just at the moment of injury, making the zone of stasis, systemic capillary leak, and hypermetabolic response as clinically important as the wound itself. Accurate total body surface area calculation, timely fluid resuscitation, and depth-appropriate wound care remain the pillars of treatment, alongside airway vigilance and infection prevention.
References
Queensland Ambulance Service. Clinical Practice Guidelines: Trauma/Burns. https://www.ambulance.qld.gov.au/__data/assets/pdf_file/0019/219133/CPG_Burns.pdf
Australian and New Zealand Committee on Resuscitation (ANZCOR). Guideline 9.1.3: First Aid for Burns. https://www.anzcor.org/home/first-aid/guideline-9-1-3-first-aid-for-burns
Acute and Chronic Thermal Burn Evaluation and Management. StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing. https://www.ncbi.nlm.nih.gov/books/NBK430730/
Parkland Formula. StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing. https://www.ncbi.nlm.nih.gov/books/NBK537190/
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Disclaimer: This article is general education for students. It is not medical advice, and it does not replace your service's clinical practice guidelines, your educators or your local protocols.
