Chapter 95. Thermal Injuries

The very young and very old are at increased risk of domestic burns.1,2 Active young adults in industrial jobs are at modest increased risk. In developed countries, about 70% of pediatric burns are caused by hot liquid. Flame injuries are more common in older children and young working adults. Scalding and flame injuries each account for approximately half of burn injuries in the elderly, with kitchen and bathing accidents being predominant. Approximately 20% of burns in younger children involve abuse or neglect.

The development of an envelope of cornified skin was a crucial component of the adaptation of aquatic sea animals to the land environment. The vapor and fluid barrier created by the epidermal layer facilitates the maintenance of fluid and electrolyte homeostasis within very narrow limits. The dermis provides strength and flexibility, and the reactive dermal vasculature facilitates control of internal body temperature within very narrow limits. The appendages provide lubrication and prevent desiccation. All of these critical functions are lost when substantial areas of the skin are burned.

There is both a local and a systemic response to the burn wound.3,4 The local response consists of coagulation of tissue with progressive thrombosis of surrounding vessels in the zone of stasis over the first 12–48 postinjury hours. An ability to truncate this secondary microvascular injury and its associated tissue loss is a major area of ongoing investigation. In larger burns, a systemic response develops that is driven initially by release of mediators from the injured tissue, with a secondary diffuse loss of capillary integrity and accelerated transeschar fluid losses. This systemic response is subsequently fueled by by-products of bacterial overgrowth within the devitalized eschar.

Burn wounds are initially clean but are rapidly colonized by endogenous and exogenous bacteria.5 As bacteria multiply within the eschar over the days following injury, proteases result in eschar liquefaction and separation. This leaves a bed of granulation tissue or healing burn, depending on the depth of the original injury. In patients with large wounds involving 40% or more of the body surface, the infectious challenge generally cannot be localized by the immune system, leading to systemic infection. This explains the rare survival of patients managed in an expectant fashion with burns of this size.

The systemic response to injury is characterized clinically by fever, a hyperdynamic circulatory state, increased metabolic rate, and muscle catabolism.6 This stereotypical response to injury has been retained by all mammalian species. It is effected by a complex cascade of mediators, including changes in hypothalamic function resulting in increases in glucagon, cortisol, and catecholamine secretions; deficient gastrointestinal barrier function with translocation of bacteria and their by-products into the systemic circulation; bacterial contamination of the burn wound with systemic release of bacteria and bacterial by-products; and some element of enhanced heat loss via transeschar evaporation. It is likely that this response has significant survival value, but control of some of the adverse aspects of this response, particularly muscle catabolism, is an active area of ongoing investigation.7,8

(See Box 95-1)

Burns are classified by depth:

• First degree: Red, dry, and painful and are often deeper than they appear, sloughing the next day (Fig. 95-1A).
• Second degree: Red, wet, and very painful with enormous variability in their depth, ability to heal, and propensity to hypertrophic scar formation (see Fig. 95-1B).
• Third degree: Leathery, dry, insensate, and waxy (see Fig. 95-1C).
• Fourth degree: Involve underlying subcutaneous tissue, tendon, or bone (see Fig. 95-1D).

Circumferential burns require special monitoring and possible surgical decompression. If across the torso, they will interfere with ventilation. If they involve an extremity, limb-threatening ischemia may occur during resuscitation.

Although lightning strikes carry large amounts of energy, measured in millions of volts, human injuries are rare, with only about 50 people so injured annually in the United States and a fatality rate of only about 10%. Injury can rarely occur from direct strike, and is usually fatal. More commonly, people are injured by current flow around the skin envelope, or side flash, when a nearby object is struck. Destructive burns are unusual. Serious injury is more often the result of associated blunt trauma or occasional cardiac arrest. In most survivors, lingering symptoms are nonfocal, neurologic in nature, often preceded by an immediate but transient loss of consciousness.9 The most common physical finding in those injured by side flash is an evanescent serpiginous cutaneous erythema, as noted in Figure 95-2.

In the outpatient setting, patient selection should ensure that major complications are few (Table 95-1). The most common issues that arise are wound sepsis, excessive pain and anxiety, and underestimation of burn depth.10 The most common wound infection in this setting is streptococcal cellulitis, which presents initially with surrounding erythema that progresses to lymphangitis and systemic toxicity (Fig. 95-3). These patients often need admission for antibiotics, observation, and sometimes surgery. In some situations, adequate pain and anxiety management is very difficult in the outpatient setting, especially around dressing changes. This can be addressed with judicious medication and sometimes carefully monitored membrane dressings. Some patients will require admission. It is common for burn depth to be underestimated initially, with areas of full-thickness injury not appreciated for several days. These patients may require admission for surgery.

As burns increase in size and depth, the local injury is accompanied by an increasing degree of systemic derangement. Classically, this response has two phases. An initial “ebb” phase of reduced perfusion and metabolic rate, which lasts 24–48 hours, is followed by a “flow” phase of protein catabolism and a hyperdynamic circulation.11 This later phase lasts until well after wound closure. Management of this physiology is an essential part of inpatient burn care. Those with large burns are susceptible to a host of other complications related to sepsis and organ failure. Careful monitoring and early intervention are essential to successful outcomes (Table 95-1).

Patient Evaluation and Treatment Planning

In both outpatient and inpatient settings, a careful evaluation of the patient is essential for treatment planning. Patient evaluation is organized into a primary and a secondary survey, following the guidelines of the American College of Surgeons Committee on Trauma and the Advanced Burn Life Support Course of the American Burn Association. As in trauma, the primary survey begins with an assessment, and control if necessary, of the airway. Deeper burns of the face and neck can result in progressive airway edema. Occasionally, a child will aspirate hot liquids resulting in very severe upper airway edema mandating urgent intubation.

A burn-specific survey evaluates the issues uniquely associated with burn injury (^ch95etb1.1). This may take just a few seconds if the burn is small, but will be much more time consuming in the more seriously injured.12 In those with small injuries, essentials include a detailed determination of the mechanism of injury, a screen for associated trauma, consideration of the possibility of abuse (Fig. 95-4), and a detailed assessment of the burn wound. Delayed presentation for care, confusing stories, sharply demarcated margins, immersion patterns, and contact injuries are physical findings suggesting for abuse or neglect.13 All such children should be admitted for evaluation.

After the patient has been evaluated, the burn wound should be examined for size, extent, depth, and circumferential components.14 Burn extent is best estimated using a chart based on the Lund–Browder diagram that compensates for the changes in body proportions with age (^ch95efg4.1). An alternative is a modified “rule-of-nines,” in which the head and neck is given 18% (instead of the adult 9%), each lower extremity is given 15% (instead of the adult 18%), each upper extremity is given 10% (instead of the adult 9%), and the anterior and posterior torso are each given 16% (instead of the adult 18%). For scattered or irregular burns, the entire palmar surface of the patient's hand represents approximately 1% of the body surface over all ages.

Burn depth is classified as first, second, third, or fourth degree (Fig. 95-1A–D). First-degree burns are red, dry and painful and are often deeper than they appear, sloughing the next day. Second-degree burns are red, wet and very painful. There is an enormous variability in their depth, ability to heal, and propensity to hypertrophic scar formation. Third-degree burns are leathery, dry, insensate, and waxy. Fourth-degree burns involve underlying subcutaneous tissue, tendon, or bone.

Near or completely circumferential burns should be identified for special monitoring, as they may need to be decompressed in the hours following injury to avoid ischemia (extremities) or failure of ventilation (torso).

The majority of burns can be successfully managed in the outpatient setting. However, poorly provided outpatient burn care can be frustrating and painful for patients and providers. The key is careful patient selection (^ch95etb1.2) and a detailed care plan, especially an inpatient care plan (^ch95etb1.3).

Patient Outcomes

Burn wounds and grafts typically develop some degree of hypertrophic scarring.15 This involves a gradual increase in vascularity and collagen deposition in the months following healing. Some wounds will demonstrate significant contracture formation, with important functional and esthetic consequences (Fig. 95-5). Many patients will have bothersome pruritus and sometimes temporary neuropathic pain if burns are deep. A long-term follow-up plan, consisting of scar management strategies, rehabilitation, reconstructive surgery, and emotional support will facilitate optimal outcomes. This care is best provided in a multidisciplinary burn clinic, ideally part of a comprehensive burn program. With such supports in place, the long-term outcome for most patients is surprisingly good. When managed in a comprehensive follow-up program, even those who have suffered devastating burns tend to become happy and productive again.16,17

Outpatient Burns

Practice patterns vary widely, but certain characteristics are universal.18 The wound should be kept generally clean and regularly inspected for infection. Desiccated exudates and topical medications should be periodically cleansed. Burns selected for outpatient management tend to be small and superficial with a corresponding low risk of infection, so clean rather than sterile technique is reasonable. If topical agents rather than membrane dressings are used, wounds may be cleansed with lukewarm tap water and a bland soap. Soaking adherent dressings prior to removal will decrease the pain associated with daily wound care. The wound is gently cleansed with a gauze or clean washcloth, inspected for any sign of infection, patted dry with a clean towel and redressed. It is important to instruct each patient to return promptly if they notice erythema, swelling, increased tenderness, lymphangitis, odor, or drainage so that infectious complications can be addressed early. Most small burns are adequately managed with a daily cleansing and dressing change. In some cases, a membrane dressing is applied once it is clear that early surgery is not needed, early infection is unlikely, and wounds are superficial. Pain and anxiety can be an issue for many. Some will benefit from an oral narcotic given 30–60 minutes prior to a planned dressing change. If dressings are occlusive, pain between dressing changes tends to be modest.

Increasing pain and anxiety associated with dressing changes; inability to keep scheduled follow-up appointments; delayed healing; signs of infection or a wound, which appears deeper than appreciated at the time of the initial examination, should prompt early return and specialty evaluation. Wounds selected for outpatient management are usually fairly superficial and heal within two weeks, but patients with mid and deep dermal injuries may have a deeper component with resulting scarring that may benefit from specialty evaluation. Finally, wounds of the face, ears, hands, genitals, and feet have functional and cosmetic importance out of proportion to their wound size. In some cases, early specialty evaluation may be prudent, as initial care can have an impact on long-term outcome.19

Inpatient Burns

A system of burn center verification has evolved to ensure that the patients requiring care of more serious injuries receive coordinated efforts by experienced providers. Burn center referral criteria can be found at www.ameriburn.org (^ch95etb1.4). Care of severe burns can be divided into phases, each with important objectives (^ch95etb1.3).20 Critical care is an important component, especially in the first three phases. Verified burn programs are required to have embedded burn intensive care units.

Topical Medications and Membranes

There is an increasingly confusing array of wound medications and membranes available for burn wounds. Wound medications and membranes provide three benefits: (1) pain control, (2) prevention of wound desiccation, and (3) reduction of wound colonization.

Topical wound medications range from aqueous solutions through antibiotic-containing ointments and debriding enzymes. Most topical agents in outpatient use have a viscous carrier that prevents wound desiccation and a more or less broad antibacterial spectrum that reduces wound colonization. A gauze wrap minimizes soiling of clothing and protects the wound from trauma. Silver sulfadiazine is in common use because it is painless on application and has a broad spectrum of antibacterial activity. Superficial burns are commonly treated with a clear, viscous antibacterial ointment containing low concentrations of various antibiotics. Wounds around the eyes can be treated with topical ophthalmic antibiotic ointments. Significant ear burns should be treated with mafenide acetate, as it is the only agent that will penetrate the relatively avascular cartilage.

Wound membranes provide transient physiologic wound closure while the underlying wound heals.21 Physiologic closure implies a degree of protection from mechanical trauma, vapor transmission characteristics similar to skin, and a physical barrier to bacteria. The major benefit of wound membranes is that, when successful, they minimize wound manipulations. These membranes help create a moist wound environment with a low bacterial density and are generally intended for use on selected clean superficial wounds and donor sites. Occlusive synthetic membranes must be used with caution if wounds are not clearly clean and superficial, as submembrane infection can occur, deepening underlying wounds and causing systemic infection and toxicity.

There have been a plethora of burn prevention efforts, which have met with mixed success. They can be based on (1) public education, (2) legislation, or (3) engineering.22 Public education campaigns depend for their success on an educated literate community. The “stop, drop, and roll” campaign in elementary schools is an excellent example. Legislation is often more effective. Examples include safe factory set points for home water-heaters and flammability standards for children's bedclothes. Engineering solutions are perhaps the most effective. Examples are common in industry, and include physical isolation of high-power lines and “child-proof” cigarette lighters. Often all the three are combined, a current example being the fire-safe cigarette. A self-extinguishing cigarette has been engineered and, in some places, its sale is mandated after public education influenced the legislative process.