Pathophysiology

The severity of a thermal injury depends upon the size of the burn, depth of injury, and the area of the body affected. While smaller burns are often limited to a local cutaneous response, larger burns trigger a systemic response. More specifically, burn injuries ≥20 % total body surface area (TBSA) result in a significant, generalized capillary leak, leading to a decrease in intravascular volume. The resulting decrease in cardiac output and hypovolemic state, combined with a robust sympathetic response, lead to hypoperfusion of the skin and viscera, further affecting the depth of the burn. Furthermore, depression of the central nervous system (CNS), acute renal failure, and cardiovascular collapse will ultimately ensue if aggressive and adequate fluid resuscitation is not provided.

Initial Clinical Evaluation

The depth of the burn injury depends on the temperature, duration of exposure, and specific characteristics of the affected skin. Although wound depth can be indeterminate initially, monitoring the response to wound care for several days can aid in the determination of a wound’s true depth of injury.

Burn wounds are commonly classified as: first degree, superficial partial thickness, deep partial thickness, and full thickness. Burns limited to the epidermis are considered superficial (i.e., first degree), and most heal within 3–4 days following desquamation and without significant scarring. They do not blister, are often erythematous and painful, and, thus, are treated with soothing lotions that frequently contain aloe vera to optimize epithelialization and provide patient comfort. In contrast, superficial partial thickness burns characteristically involve the upper layers of the dermis, form blisters, and are quite painful. Following blister debridement, the wound typically appears pink and moist, is hypersensitive to touch, demonstrates increased perfusion, and blanches with pressure. Healing requires re-epithelialization from the skin appendages (i.e., hair follicles, sweat glands, and sebaceous glands) and wound perimeter, which usually occurs within 2–3 weeks without functional impairment. Deep partial thickness burns extend into the deeper dermal layers, but also blister. They are a mottled pink to white color, dry, and variably painful. Capillary refill and sensation to light touch are diminished. Without surgical intervention, healing usually occurs within 3–8 weeks and results in severe scarring, contraction, and risk for loss of function. Full-thickness burns extend through the entire dermis, and thus are white (or black), dry, leathery, firm, and insensate to touch. Classically, the dead and denatured dermis remains structurally intact, forming an eschar. Similar to deep partial thickness burns, operative intervention is required to avoid significant wound contracture and delayed healing.

While burn depth plays a crucial role in wound management, the most important feature in predicting mortality is the overall burn size as a percentage of the victim’s TBSA (American Burn Association 2012). Most commonly, the “rule of nines” is utilized to provide a preliminary estimate of a burn size. In adults, each upper extremity and the head and neck account for 9 %, while each lower extremity, the anterior torso, and the posterior torso each account for 18 % (Fig. 1). For smaller burns, one can use the palm of the patient’s hand to represent 1 % TBSA and calculate the burn size accordingly.

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Patient Management

Airway management – For unconscious patients, basic life support measures and standard ABCs as advocated in ATLS and ABLS are followed, and the airway should be immediately addressed. This may include supplemental oxygen via face mask or intubation based upon the extent of injury and mental status. However, minor burn injuries sparing the respiratory tract rarely affect the airway, oxygenation, or ventilation, and supplemental oxygen is likely unnecessary.

Inhalation injury – Inhalation injuries occur in approximately one third of all major burns and significantly increase mortality (American Burn Association 2012). Similar to cutaneous burn injury, inhalation injury is a graded phenomenon and can be separated into three distinct components: carbon monoxide (CO) poisoning, upper airway thermal burns, and inhalation of products of combustion. Diagnosis of inhalation injury relies upon a thorough history and physical exam, and is often suggested by exposure to fire in a closed space, carbonaceous sputum, and an elevated carboxyhemoglobin (COHb). It rarely results from outdoor exposure to fire and smoke. All patients involved in a fire within a closed space should be evaluated for an inhalation injury and administered 100 % supplemental oxygen via a tight-fitting mask or an endotracheal tube, as the oxygen rapidly accelerates the dissociation of CO from hemoglobin. Early clinical signs and symptoms of inhalation injury include copious mucus production, carbonaceous sputum, and hoarseness. The characteristic airway damage results in wheezing, air hunger, atelectasis, and, in severe cases, airway edema and acute respiratory distress syndrome (ARDS). Symptoms may appear immediately or up to 12–48 h following injury, although more severe disease is associated with earlier onset of symptoms. Work-up includes a CXR and arterial blood gas with a COHb level. More severe injury is commonly associated with a decreased partial pressure of oxygen to fractional inspiration of oxygen ratio (PaO₂:FiO₂) and may require mechanical ventilatory support. Elevated COHb levels often cause neurologic symptoms, which sequentially worsen with increasing levels ranging from a simple headache to confusion, lethargy, coma, and eventually death (Mosier and Gibran 2011). Conversely, the absence of neurologic deficits correlates with a good prognosis. Hyperbaric oxygen remains controversial in the treatment of CO poisoning. It may be appropriate in the patient with severe neurologic impairment, as it can more rapidly lower COHb levels. However, the risks of barotrauma, isolation from nursing staff, and the ability to perform critical care may be too significant for a patient with combined burn injury undergoing resuscitation.

We utilize fiber-optic bronchoscopy to verify the diagnosis of inhalation injury and to assess the degree of airway edema, microbial contamination, and mucosal damage, although some argue that it should only be performed when the diagnosis is in question. Regardless, oxygen and supplemental airway and ventilator support is the mainstay of treatment. Mild cases of smoke poisoning can be managed with humidified air, pulmonary toilet, and bronchodilators. More severe cases with significant oropharyngeal edema and face and neck burns require early intubation before it becomes emergent and oral airway access is not obtainable (Fig. 2). Once an endotracheal tube is placed, it should typically remain for 2–5 days, allowing for the edema to subside. The patency of the airway can be verified by testing for a cuff leak around the endotracheal tube when the cuff is deflated. In the absence of a cuff leak, significant airway edema may still be present. In isolated inhalation injury or with an associated small burn injury, a short course of corticosteroids may be considered to decrease airway edema and facilitate extubation.

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Resuscitation – The massive shifts of fluid and electrolytes from the intravascular to the extravascular space, associated with burns ≥ 20 % TBSA, begin immediately following burn injury, while reversal typically initiates on postburn day 3 and may not be completely restored until 7–10 days following injury. Resuscitation can be achieved using a variety of algorithms, which target maintaining normal renal, cardiac, and respiratory functions. The initial resuscitation requirements for patients with ≥ 20 % TBSA burns are most commonly calculated using the Baxter (or Parkland) formula. Specifically, the predicted first 24-h fluid requirements are equal to 4 mL/kg body weight/%TBSA burn. Half of the volume is administered over the first 8 h post injury, and the remainder over the next 16 h. The subsequent ongoing resuscitation is then modified according to the patient’s clinical status, including blood pressure, heart rate, central venous pressure, and urine output. The urine output, in particular, remains the simplest and most reliable indicator of the resuscitation’s adequacy in patients with preserved renal function. We target a urine output of 30–50 mL/h measured by Foley catheter in adult patients and 0.5–1 mL/kg/h for children. For patients with larger burn injuries, colloid solutions should be considered to decrease complications associated with large volume resuscitation. While some institutions utilize high dose vitamin C and FFP, we find 5 % albumin works well in maintaining euvolemia without worsening systemic edema.

Wound Management

As a part of the initial wound assessment, the burn injury should be cleansed thoroughly with soap and water, and then dried with a clean towel. Some wounds can be managed at the bedside, while others may require the use of a shower table to adequately address the initial cleaning. Small blisters can be left intact, while large, flaccid blisters should be debrided. Debridement of dead skin and blisters can be achieved with forceps and scissors.

Escharotomy – During the initial wound evaluation, the burn depth, TBSA involved, and adequacy of perfusion should all be determined. For full-thickness burns involving the circumference of an extremity, the extremity should be elevated to decrease edema, and distal pulses must be routinely and continually monitored. Furthermore, substantial burn injuries to the torso may significantly impair chest wall compliance and effective ventilation. While it appears structurally similar to intact skin, eschar no longer retains the natural elasticity of healthy skin and contributes to an increased pressure. Following burn injury, the accumulation of local edema may eventually exceed capillary and venous pressure and approach arterial pressure, resulting in distal hypoperfusion and ischemia. Compartment syndrome is present in a tense and edematous extremity with pallor, pain, paresthesias, and pulselessness. Pulses may be monitored via palpation, but faint or non-palpable pulses should be more thoroughly evaluated using a Doppler. If clinical suspicion escalates or Doppler signals weaken, escharotomy should be performed. Escharotomy is performed by incising the insensate eschar using either a scalpel or electrocautery. Releasing incisions along the medial and lateral aspects of an extremity should be performed with attention to the degree of release that is achieved. In extreme cases, fasciotomies may be required as well if compartment pressures are not sufficiently improved following escharotomy. If the burn injury involves the majority of the trunk, a chest wall escharotomy via incisions along the bilateral anterior axillary lines, with subcostal and subclavicular connections, may improve pulmonary function and decrease intra-abdominal pressure (Fig. 3).

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Daily burn wound care – Once a wound has undergone its initial cleansing, a topical agent and dry gauze should be placed. The dressing should cover the entire wound, protect the body, keep the wound moist, prevent evaporative heat and water loss, and allow for maximum mobility. Often the initial topical agent of choice, silver sulfadiazine is soothing to the wound, has broad-spectrum antimicrobial activity, does not penetrate eschar, and has minimal systemic absorption. Mafenide acetate is also commonly used, provides reliable Gram-negative coverage, penetrates eschar well, and is our preferred topical agent following excision and grafting. Superficial wounds may be covered with bacitracin, neomycin, or polymyxin B in conjunction with basic ointments or lotions to maintain a moist and optimal environment for re-epithelialization. Methicillin-resistant Staphylococcus aureus (MRSA) wound colonization may be treated with mupirocen. Regardless of the topical agent or type of dressing used, wound mobility must be maintained, and involved extremities should be consistently elevated. Wounds with modest drainage should undergo daily dressing changes, while those with significant drainage likely require two changes daily. Routine dressing changes remove debris and promote re-epithelialization with minimal scarring. When the depth of injury is indeterminate, routine dressing changes may continue for several days before the final determination of the need for surgical intervention is made.

Surgical burn wound management – Operative debridement is often necessary for deep partial thickness burns and full-thickness burns. The decision to operate often hinges on the determination of how quickly a wound would heal without surgery. The acceptable timeframe is typically estimated at 2–3 weeks, while surgical intervention is preferred in wounds requiring longer. However, early excision of the eschar and skin grafting is often essential for optimal healing by decreasing inflammation and the risk for hypertrophic scarring. Early burn excision and grafting is the single largest advancement in burn care, improving survival, reducing infection rates, and shortening hospital stays (Mosier and Gibran 2009). The standard of care today includes early excision, as early as post-injury day 3, and coverage with autografts (Mosier and Gibran 2009; Kagan et al. 2009; Sterling et al. 2011). The two main surgical approaches to burn wound excision are fascial excision and tangential excision. Fascial excisions yield a well-vascularized wound bed and tend to readily accept grafts, although at a cost of significant cosmetic deformities. Tangential excisions are often more cosmetically appealing, but they can be difficult to assess suitability for graft acceptance. With either approach, hemostasis is crucial and can be achieved using a variety of techniques, including use of tourniquets, clysis with dilute epinephrine solution under the burn wound, and topical measures such as laparotomy pads soaked in thrombin and epinephrine solution, pressure, and selective use of cauterization. When necessary, temporary coverage with a biologic dressing or cadaveric allograft can be performed until autografting can be achieved.

Once the wound bed has been adequately prepared, skin grafts are the gold standard for definitive wound closure and should yield a > 90 % success rate. Full-thickness skin grafts produce fewer contractions and are typically used to cover small defects on the hand or face. However, they also create a larger donor wound, may lengthen healing time, and increase the risk of hypertrophic scarring. In contrast, split-thickness skin grafts are at a higher risk for contraction (the thinner the graft, the higher the risk), but the resulting donor site wound is less substantial. Depending on the distribution of the burn injury, the anterolateral thigh is often the preferred donor site. Once harvested, skin grafts can be applied as a sheet (or unmeshed) graft, or they can be meshed by varying ratios (1:1 to 4:1). The advantages to meshing include the ability to cover larger areas from a smaller starting donor site and allowance of spontaneous drainage from the wound (decreasing the incidence of seromas and hematomas and consequently improving graft survival). Once the autograft is secured, an overlying dressing should be placed to prevent shearing. Options include wet dressings, greasy gauze, a non-adherent dressing (i.e., Conformant) with an outer antimicrobial wet dressing, or negative pressure wound therapy. For wounds crossing joints, we utilize splints to improve immobilization of the wound and simultaneous mobilization of the extremity, while awaiting graft adherence. Once graft acceptance has been demonstrated, physical therapy becomes the focus of the recovery process.

Supplemental Considerations

Significant burn injuries create a hypermetabolic state with greater alteration to systemic physiology than any other condition or injury. A multidisciplinary team approach to care utilizing a nutritionist, pharmacist, social worker, and physical and occupational therapy in addition to the intensivist burn surgeon, as is provided in verified burn centers, is uniquely suited to deliver high quality care of the burn injured patient (Mosier and Gibran 2011). Additional concerns beyond the burn wound include nutrition, infection prevention, thermoregulation, and pain management.

Nutrition – Early supplemental nutrition is crucial in order to adequately compensate for the increased metabolic demands of patients with larger burn injuries. Although smaller burns do not require significant changes in a patient’s normal intake, patients with moderate (10–29 %TBSA) to large (>30 % TBSA) burns require oral supplements, and temporary feeding tubes should be strongly considered. Nutritional requirements should be assessed within hours of injury and plans initiated shortly thereafter. Oral diets and supplements serve as the primary source of nutrition, as the injury itself rarely results in a contraindication to enteral feeding. The addition of tube feedings, even for short intervals, can easily and quickly improve caloric and protein intake. Furthermore, tube feedings can be cycled at night in order to allow for oral intake during the day. They can also be adjusted to meet the specific metabolic needs of each individual patient. For patients with extended hospital stays, nutritional lab values should be considered to assess the adequacy of the dietary regimen.

Infection – Significant progress has been made toward reducing infection rates in burn patients. In addition to the improved surgical treatment paradigm, the development and understanding of antimicrobials has also expanded. However, the risk of infection remains a constant threat to any burn patient and can affect any number of sites, including the wound, lungs, and urinary tract. Pneumonia, cellulitis, and urinary tract infections were the most prevalent complications in burn centers in 2012 (American Burn Association 2012). While specifically identified infections require appropriate antimicrobial coverage, the routine use of prophylactic systemic antibiotics promotes development of multidrug resistant organisms, has not been shown to reduce infection rates, and is not recommended. Topical antimicrobials, however, deliver high concentrations of antimicrobial agents to the wound surface and, thus, have become the gold standard for treating the wound.

Temperature regulation – Intact skin not only serves as a physical barrier important to prevent water loss and evaporation, but also as a means of thermoregulation. When the barrier is disrupted by a significant burn injury, the body immediately begins to lose substantial amounts of heat and water via evaporation, which normally serves as a means of cooling in non-injured skin. Although heat and water loss cannot be completely prevented, the application of wound dressings, linens, and warming blankets can all serve as adjuncts to help restore and maintain normothermia. In addition, ambient temperatures should be adjusted to a higher baseline, which is especially important during wound care and operative interventions to prevent hypothermia.

Pain management – Pain from large burn injuries can typically be controlled with narcotics. Although minor burns may only require acetaminophen, more significant injuries often necessitate the use of morphine or hydromorphone. Once oral intake has been established, oral pain medications can and should be administered. Pain medications should target background pain, breakthrough pain, and procedural pain. Thus, patients undergoing routine dressing changes should receive supplemental pain medications at that time, and patients with significant background pain benefit from use of long-acting pain medications. It is not uncommon for substantial doses of narcotics and anxiolytics to be required when burn injuries are large or involve sensitive areas of the body.