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Burn Injuries

Emergency Medicine
Surgery
Military Medicine
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Introduction

Burns are devastating injuries that can lead to severe disfigurement and are accompanied by a high mortality rate, particularly in the elderly or those patients with large surface area burns (1–3). The body’s response to burn injuries can be local or systemic [4]. Burn injuries are classified based on the percent total body surface area affected (TBSA) and depth of injury.
Usually burn injuries that are larger than 20% lead to a complex physiologic systemic reaction. The systemic effects are related to fluid shifts and the release of inflammatory mediators which can lead to burn shock. There is also an impairment of immune function, hypermetabolism, and potentially death if not properly treated[5,6].
Burns greater than 20% require complex fluid management and additional fluid resuscitation. Factors that seem to increase the risk of death related to the burn injury are age, presence of inhalation injury and size of the injury (%TBSA). The Baux score was initially described as age + %TBSA to approximate the mortality of a patient at the time of presentation.  As an example, a patient who is above the age of 60 with a TBSA of 40% and an inhalation injury has a mortality risk of >90% [4,7]. This is relevant during times of war with mass casualty. An important component of military burn care is to triage and identify patients with the highest chance of survival in the setting of limited resources [8].
The goal of this publication is to provide a brief review regarding the basic principles of burn care in the acute setting.

Classification of burn injuries and relevant definitions

Soft tissue injury is clinically graded based on depth (See table 1 for clinical appearance of burn injury based on degree) [5]. Anatomy of healthy skin is shown in figure 1.[3]
Figure 1. Anatomy of healthy skin and classification of burns according to depth.
From Greenhalgh DG. Management of Burns. Longo DL, editor. N Engl J Med. 2019 Jun 13;380(24):2349–59. Massachusetts Medical Society. Reprinted with permission from Massachusetts Medical Society
Third degree burn injuries can lead to injury of nerve endings, and as a result, some patients may not experience pain. The total body surface area (TBSA) is quantified based on age-adjusted charts (Lund-Browder diagrams or modifications thereof) or can be estimated according to the Wallace rule of nines which is used only in adults (Figure 2, Lund-Browder diagram)[2,5]. First degree burns are not included in the %TBSA estimation.
Figure 2. Zones of injury in burns.
From the article Orgill DP. Excision and Skin Grafting of Thermal Burns. N Engl J Med. 2009 Feb 26;360(9):893–901. Massachusetts Medical Society. Reprinted with permission from Massachusetts Medical Society
Burn wounds require constant evaluation as some wounds may progress to deeper injuries over the course with inadequate resuscitation or local wound care. This is explained by the model put forward by Jackson et al. which describes a central area of coagulation necrosis (punctum maximum of burn injury) which is irreversibly damaged but surrounded by potentially salvageable tissue (zone of stasis) if proper treatment is applied (Figure 3) [9].
Figure 3. Lund and Browder chart and rule of 9s.
From the article Orgill DP. Excision and Skin Grafting of Thermal Burns. N Engl J Med. 2009 Feb 26;360(9):893–901. Massachusetts Medical Society. Reprinted with permission from Massachusetts Medical Society
Burns can be classified according to mechanism of injury. The most common mechanism is fire/flame followed by scald and contact with hot objects. Other mechanisms are electrical, chemical, and radiation induced burns [7].
Table 1. Grading of burn injuries.
GradeDepthSensitivity/PainBlanching and capillary refillClinical appearanceTreatmentPrognosis
Superficial (1st degree)EpidermisPainfulBlanches with quick capillary refillErythema, no blistering, edemaSupportive (analgesia)Heals w/o scarring (1 week)
Superficial partial thickness (2a)Epidermis and papillary dermisPainfulBlanches with slow capillary refillErythema, edema, blistering, pinkTopical antimicrobials, occlusive dressingHeals w/o scarring, hypo/hyperpigmentation possible (1-2weeks)
Deep partial thickness (2b)Epidermis, papillary and reticular dermisMinimal painNo, sluggish refillBlistering (easily rupture), dark red appearance (“cherry-red”)Topical antimicrobials, occlusive dressing, may need graftingScarring, healing process takes several weeks (2-4 weeks) May require surgical intervention
Full thickness (3rd degree)Epidermis, dermis, and subcutaneous tissuesNo painabsentNecrotic tissue (white/black/gray leather like appearance), dryRequires excision and graftingDoes not heal without intervention, debridement and grafting necessary
Deep tissue injury (4th degree)Epidermis, dermis, subcutaneous tissues and muscle, fascia, bone)No painabsentNecrotic tissue (white/black/gray leather like appearance), drySurgical removal of necrotic tissue, amputation or flap coverage may be necessarySame as 3rd degree, may require amputation of affected extremities

Thermal injuries

Most thermal injuries are related to scalds caused by spillage of hot drinks or liquids or hot bathing water. Scald burns injuries tend to be more superficial in nature. Flame burns are caused by exposure to fire and can be often associated with an inhalation injury. Flame burns can be devastating depending on the duration of the thermal exposure and the extent burned. Contact burns occur after direct contact with a hot surface for a prolonged period of time and are often deep dermal or full thickness burns [10].

Electrical burn injury

3-4% of all burns are caused by electrocution. Mechanistically, an electric current travel though the body from the point of entry to a point of exit, damaging tissue in-between as heat is generated. The amount of tissue damage is proportional to the amount of energy that passes through the body. High voltage injuries are defined by >1000V traveling through the body [9].
Deep tissues such as muscle and bone are often injured. Patients who sustain electrocution injury may present with cardiac arrythmia and close monitoring can be necessary. Some patients who have electrical burn injuries in an extremity may present with a compartment syndrome secondary deep muscle and tissue damage.

Chemical and radiation induced burn injury

Approximately 3% of all burn injuries are related to contact with chemical agents such as acids or bases. Chemical burn injuries are often caused by prolonged exposure to chemicals. Despite removal of the inciting agent, there still may be ongoing tissue damage at the time of the patient’s presentation. Removal of all affected clothing and copious irrigation with water to remove the inciting agent are important initial steps in management. In some cases of chemical burn injuries, there are specific antidotes available. Hydrofluoric acid burn injuries require the application of calcium gluconate as either a topical gel or via injection [11].
Radiation related burn injuries can be seen after exposure to UV-radiation (e.g., sun burns) or ionizing radiation for example in workers in the nuclear industry. Damage related to ionizing radiation directly damages DNA. The depth of injury depends on total energy exposure, duration of exposure, and the type of particle that the body is exposed to. Radiation burn injuries can result in any degree of burn injury.

Inhalational injury

An inhalation injury is defined as any direct injury to the respiratory tract caused by a thermal and chemical component which are toxic products of combustion at the time of the burn injury. Patients with inhalation injury may require invasive ventilation support. This is because of respiratory distress caused by airway edema from direct tissue insult. Clinical signs that may suggest an underlying inhalation injury are singed nasal hairs, soot in the oropharynx, hoarseness, tachypnea, and facial or neck burns.
Diagnosis is made via history and bronchoscopy or laryngoscopy which can show carbonaceous deposits inside the oropharynx.[3] Direct systemic toxicity can result from inhalation of toxic gases such as carbon monoxide and cyanide. Of note, a common clinical scenario is a patient who smokes while on home supplemental oxygen and suffers a flash burn. These patients often do not sustain smoke inhalation injuries and are unlikely to require intubation as deeper airways are rarely affected.
Patients with burns related to flames may have been exposed to smoke for a prolonged period and carbon monoxide (CO) poisoning must be considered in case of gas exchange issues. The affinity of CO to hemoglobin is significantly higher comparted to oxygen and thus peripheral oxygenation will be impaired. Levels can only be quantified using carboxyhemoglobin measurements. CO poisoning is treated with administration of 100% O2 to reduce the amount of CO bound to hemoglobin by accelerating the dissociation of CO from hemoglobin[3].

Escharotomies

In the case of a circumferential burn injury involving deep dermal or full thickness burns, the skin can lose its compliance.  Depending on the location, this can result in limited chest expansion, abdominal compartment syndrome or limb ischemia which may then require incision of the stiff eschar (escharotomies) to relive tension. Incisions are made longitudinally through the stiff eschar to healthy soft tissue. The incisions are typically placed in the medial or lateral mid-axial lines.
If a compartment syndrome has developed, fasciotomies may be necessary. Importantly, the effects of stiff circumferential eschar (e.g., blood flow limitation in extremities) often develops after large volume fluid resuscitation is started. Due to the systemic inflammatory state, capillary leakage can lead to extravasation of fluid and increase compartmental pressures.
Alongside a stiff burn eschar, this can lead to significant increase in compartment pressures with obstruction of venous outflow and reduction in arterial perfusion. This can lead to irreversible necrosis of muscle fibers after approximately 6 hours of warm ischemia time. The early clinical signs of compartment syndrome in an extremity are pain that worsens with active or passive movement of muscles, hard musculature, and tenderness to palpation with paresethesias. Initially pulses can still be maintained. In the later stages, the pain worsens, and muscle become weak due to paralysis. This can be accompanied by loss of pulses, pallor, cold extremity etc. (acute limb ischemia, 6 Ps).
For limb rescue, fasciotomies should be performed with longitudinal incision of the muscle fascia which will relieve compartment pressures and thus improve perfusion.

Burn shock

Most deaths related to burn injury happen within the first 3 days after injury and are attributed to the acute sequalae from burn shock[12]. This makes burn injuries a special category of traumatic injuries with a very complex systemic response to the initial injury.
Burn shock is a combination of relative hypovolemia (wound related volume loss) and distributive shock (capillary leakage in both burned and unburned tissue) with release of pro-inflammatory mediators leading to cardiac dysfunction[13]. Adequate modern critical care measures have significantly improved survival rates following major burns, mainly owing to improved care of burn shock and development of fluid resuscitation protocols with avoidance of over resuscitation.

Acute management of burn injuries

Initial assessment and triage
Initial assessment should follow standard trauma assessment guidelines. The burning process should be stopped as soon as possible. A primary survey must be performed (ABCDEF: Airway (check need for intubation, tracheostomy, coniotomy), breathing, circulation (hemodynamic monitoring, check perfusion of extremities and assess need for escharotomies), neurologic disability, exposure with environmental control, fluid resuscitation) to stabilize the patient for more detailed assessment[7].
While the burn patient is being assessed, normothermia should be maintained as hypothermia is common, especially in larger %TBSA burns as the protective thermoregulatory effect of the skin is lost.
Airway and breathing
In burn patients, airway and circulatory assessment should be prioritized. This includes potential intubation for patients sustaining an inhalation injury, which may be suspected in larger %TBSA burns, and those presenting with respiratory distress. Factors such as carbon monoxide and cyanide poisoning may also complicate peripheral tissue oxygenation. Circular burns leading to restriction of chest expansion must be considered and may need additional intervention such as escharotomies.
Patients with larger TBSA burns require large volume resuscitation. Early intubation may be preferred in these patients because of possible impeding respiratory compromise resulting from upper airway edema making intubation more difficult at later stages. Factors that may indicate need for intubation are all burns >40%TBSA, head and neck burns, presence of inhalation injury or signs thereof, any signs of respiratory distress, or an inability to protect the airway because neurological status.[3]
In intubated patients who sustained inhalation injury acute respiratory distress syndrome (ARDS, respiratory failure in the setting of hypoxemia and bilateral lung infiltrates on imaging classified into mild, moderate and severe passed on P/F ratio) may develop and lung protective low tidal volume ventilation (4-8cc of predicted body weight) is indicated.

Circulation and fluid resuscitation

Patients with large surface area burns and/or deep burns may develop burn shock with circulatory impairment. Thus, adequate fluid resuscitation is key in the initial phase of burn care. 
For minor burns outpatient management is appropriate and aggressive fluid resuscitation is not needed. Minor burns for adults without significant comorbidities are defined as partial thickness burns <10%TBSA or full thickness <1%TBSA without significant comorbidities[14]. In children or the elderly, >10% TBSA burns are considered severe.
For adults, major burns are defined as any burn >20%TBSA, full thickness burns >5%TBSA, high voltage electrical burns, and relevant burn injuries affecting the face (eyes, ears) and genitalia[15].
Severe burn injuries (>20%TBSA) are a multisystem disease, and these patients require large resuscitation volumes. The amount of fluid that is given is based on the %TBSA which is estimated based on age adjusted charts (e.g., Lund-Browder). Once the total body surface area has been determined, the initial fluid rates are calculated.
For the initial burn resuscitation, crystalloids such as lactate ringer’s solution (LR) are often used in combination with colloids (e.g., albumin) for rescue in patients who do not respond to traditional crystalloids-based resuscitations and show drop in hourly UOP off despite administration of crystalloids and/or persistent hypotension. Colloids were shown to reduce total fluid requirements per %TBSA[3]. The infusion rate of LR is titrated to a UOP of approximately 0.5cc/kg/h per American Burn association guidelines.
The fluid needed within the first 24 hours can be approximated by using a modified Parkland formula.  Based on this formula American burn association guidelines recommend giving 2 cc x %TBSA x kg body weight within the first 24 hours [16,17]. First half of the volume should be given in the first 8 hours and the remainder over the course of 16 hours.  Fluid boluses should be avoided as this can lead to over-resuscitation. For example. in a 80kg male with a 40% burn he would require 6400 cc of fluids in 24 hours.
After the initial resuscitation efforts, fluid resuscitation continues for a goal of 30-50cc of urine per hour with goal of euvolemia. Over resuscitation which should be avoided due to potential complications such as compartment syndrome and pleural effusions or pulmonary edema that can severely complicate the clinical course [13].  Different parameters of volume status should be obtained and guide resuscitation efforts. Other parameters of resuscitation aside from UOP and hemodynamics are to trend metabolic endpoints such as lactate, base deficit, and blood pH.
Central venous/mixed venous oxygenation (SvO2) can also help guide resuscitation (reference 65-70%). The volume status can also be assessed using hemodynamic parameters for example via bedside transthoracic echocardiography by assessing IVC filling, especially in patients with heart failure or reduced renal function. Invasive measures can be the ventral venous pressure which may be reflective of resuscitation status [18].

Further considerations

After the initial phase of stabilization and resuscitation, major burns require multidisciplinary care. Multiple organ systems are affected in burns and the patient’s complex management includes pain control, management of possible coagulopathy and DVT prophylaxis, prevention of infectious complications and nutritional support (hypermetabolic state of severely burned patients).  The hypermetabolic state in burn patients is important to consider when discussing nutritional support. Burn patients are prone to malnutrition due to the increase energy requirements that is caused by a perpetual state of systemic inflammation aimed at optimizing wound healing conditions.

Burn wound coverage and management

Initial emergency wound management includes cleansing and assessment of the burn injury. Management of burn wounds is based on the depth of the injury. For management strategies, it is important understand how depth affects the ability of the wound to heal. Superficial wounds affect the epidermis only and do not damage the underlying dermis (divided into the more superficial papillary dermis and below reticular dermis). Barrier function of the skin remains intact, and the wound is dry without formation of blisters. First degree burns can be treated with either an unscented lotion or an emollient such as vitamin A and D ointment or a petroleum based topical.
If the superficial dermal layer is damaged, the burn is classified as a superficial partial thickness burn. The epidermal layer is destroyed, and interstitial fluid can be seen in the wound with  blisters formation [3]. The neurovascular bundle of the reticular dermis is intact, and thus the wound is very painful and blanches with pressure. This type of wound can heal via re-epithelialization.
Stem cells that reside within the wound edges migrate leading to re-epithelialization of the defect. This process does not need any surgical intervention, but cellular migration can be supported by keeping the micromilieu moist. Dressings are aimed at keeping a moist milieu to support re-epithelialization [19]. Blisters and sloughed off skin should unroofed/removed as inflammatory mediators can impair wound healing. This explains why deeper wounds take longer to heal or do not re-epithelialize properly. The deeper the burn, the more skin adnexa are lost. Thus, if a wound takes longer to heal (2-3 weeks), excision and skin grafting may need to be considered [3]. Dressings for superficial or deep partial thickness burns are often dressings that create a moist microenvironment and prevent infection. For such wounds antibiotic ointments or silver sulfadiazine with fine mesh gauze are often used.
Full thickness burns (destruction of epidermis and dermis in its entirety) do not heal sufficiently (destruction of hair follicle stem cells) on their own and require debridement and skin grafting.
Of note, these injuries destroy the deep dermal neurovascular plexus and thus are painless and do not blanch with application of direct pressure. Such wounds heal with significant scar formation and contraction as all stem cells for direct re-epithelialization have been destroyed. The burn eschar often needs excision and debridement as it is a great nidus for infection.

Excision and grafting in the acute setting

Deep second degree and third-degree burns need to be excised.  Early excisional debridement (tangential/fascial excision) of full thickness burn injuries is preferred to
  • remove necrotic tissue and minimize systemic release of inflammatory mediators and
  • minimize nidus for infection.
Early aggressive surgical intervention was shown to decrease length of hospital stay and also reduce overall mortality while increasing the requirement for blood transfusions [20,21]. Debrided wounds should be definitively covered as soon as possible, at best during the time of initial debridement.
Several options are available for coverage of the wounds in the early stages. The type of surgery depends on the extent (%TBSA, depth) of the burn injury, location and whether a suitable recipient wound bed is available. For wound coverage of larger surface area burns with well vascularized wound bed, split thickness skin grafts are commonly used (if donor sites are available) to cover larger surface area burns. A split thickness skin graft is taken from a healthy portion of the patient’s integument (harvested with a dermatome, thickness 0.15-0.6 mm) and transferred to the debrided burn wound bed [22].
These grafts are often meshed to maximize the surface area that can be covered and minimize donor site morbidity. The donor sites heal on their own via direct re-epithelialization from wound edges and dermal appendages within 2-3 week. If needed, these sites can be used multiple times as donor sites. In patients without available donor sites, dermal substitutes such as BTM (biodegradable temporizing matrix) can be used.
BTM is a synthetic polyurethane bilayer dermal template that provides a scaffold for ingrowth of recipient site cells that can be used in patients with deep dermal and full thickness wounds [23]. Following grafting, a multilayered dressing is often applied which consists of a primary non-adherent dressing, secondary antimicrobial dressing and tertiary dressing to absorb wound exudate.
Small burns may be closed directly after debridement, larger defects on bones or other non-vascularized areas (e.g., with exposed vasculature, nerves) may require local soft tissue re-arrangement or free flap reconstruction once the patient has been stabilized.

Summary

  • Burn injuries are one of the most devastating traumatic injuries with high rate of morbidity and mortality proportional to age, %TBSA and depth of injury
  • Major burns (>20%TBSA) often have profound systemic impact and typically require ICU level of care
  • Early initiation of fluid resuscitation and wound care efforts are essential. Early debridement was shown to improve mortality and reduce hospital length of stay
  • Reconstruction can be challenging in patients with large surface area burns when autologous donor sites are depleted. In these cases, synthetic dermal substitutes have emerged as a viable substitute
  • Rehabilitation of major burn victims can take weeks to years and often involves a multidisciplinary team consisting of physical and occupational therapists, social workers, nurses, and surgeons

References 

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