Epidemiology

Approximately 500,000 patients sustain nonfatal burn injuries in the United States each year.¹ Only 6% of these patients require hospitalization, so most are treated as outpatients.

Serious burns are some of the most challenging critical care cases. Approximately 8% of all burns result in death. Furthermore, care must be optimized because long-term disability can be moderated if initial resuscitation is adequate, infections are minimized, and specialty care by burn experts is promoted.

Pathophysiology

Knowing the anatomy of the skin is essential to understanding burn pathophysiology (Fig. 189.1). Burns are classified according to the depth of injury (Table 189.1 and Fig. 189.2). First- and second-degree burns are partial-thickness burns and have a better prognosis. Full-thickness burns (third and fourth degree) are insensate and require skin grafts (unless <1 cm) or reconstruction because of destruction of the epidermis and dermis. Based on the depth of the burn, the ability to heal can be predicted. Because the dermis itself is the living tissue, the depth of burn into the dermis determines how likely wounds are to heal and what degree of scarring can be expected.

Fig. 189.1 Schematic representation of a cross section of human skin.

The two major layers of human skin, the epidermis and the dermis, overlie subcutaneous fat and muscle. Arterioles (red), venules (blue), and lymph vessels (yellow) of the dermis form a lower and an upper vascular plexus. Capillary loops extend toward the epidermis from the upper plexus of blood vessels into the dermal papillae, approximately one loop per dermal papilla. Sensory and autonomic nerves (yellow fibers) are also arranged in a lower and an upper plexus at the junction of the dermis and subcutaneous fat and in the upper dermis. Sweat glands and hair follicles with their associated sebaceous glands are also integral components of skin.

(From Adkinson NF, Yunginger JW, Busse WW, et al, editors. Middleton’s allergy: principles and practice. 6th ed. St. Louis: Mosby; 2003.)

Fig. 189.2 Depth of burns.

First-degree burns are confined to the epidermis. Second-degree burns extend into the dermis (dermal burns). Third-degree burns are full-thickness burns through the epidermis and dermis. Fourth-degree burns involve injury to underlying tissue structures such as muscle, tendon, and bone.

(From Townsend CM, Beauchamp RD, Evers BM, et al, editors. Sabiston textbook of surgery. 17th ed. Philadelphia: Saunders; 2004.)

The severity of the burn depends on the duration of contact with the burn agent, the heat and conductivity of tissues, the heat of the burn agent, heat transfer (conduction, convection, or radiation), and the heat capacity of the burn agent.

Burns damage by two methods: first, by direct injury to the cellular structure of the tissue and, second, by the release of local mediators. Three zones are discussed with burn injuries: the zone of coagulation, the zone of stasis, and the zone of hyperemia. The zone of coagulation is the necrotic area of cell death as a result of direct thermal injury. Surrounding this area is the zone of stasis, which has decreased blood flow and is at risk for cell death within 24 hours but may initially appear as living tissue. Cell mediators such as thromboxane A₂ are predominantly responsible for transforming this area into the zone of coagulation. Outside this zone is the zone of hyperemia. The zone of hyperemia is defined as the outside area of tissue affected by the burn, usually blanching on touch, but with intact blood flow and high potential to recover from the initial insult.

The secondary effects of burns, such as histamine release and edema, are thought to result from cellular mediators. Aggregated platelets from the burn release serotonin, whereas histamine is derived from mast cells within the burned skin.

Presenting Signs and Symptoms

Frequently, occupational exposure causes burns. Direct contact with flame, scalds, injuries caused by heated equipment or arc welding, gasoline fires, and cooking accidents are all common. In children or elderly patients with burn injuries, the concern for abuse is always present (see the “Red Flags” box).

One issue that is often of concern is the depth of burns. Determining between deep partial-thickness and superficial partial-thickness burns is difficult because it may take time for a definitive area of demarcation to develop. The usual method of distinction, blistering (which occurs with deep partial-thickness burns, or second-degree burns), can be delayed; however, it is the only distinction that is available early. Third-degree burns are insensate.

With all burn patients, assessment of the airway is critical. Signs of deep injury are stridor, soot in the mouth, and singed nasal hairs; any of these signs should indicate the need for close monitoring and more aggressive airway management. Swelling can occur rapidly in burned tissues, so signs of airway involvement should suggest earlier intubation because decompensation may occur rapidly.

Differential Diagnosis and Medical Decision Making

In each patient with a burn, the airway is still the most important component. Burn victims are often also subject to smoke inhalation or thermal injury to respiratory tissue from superheated air, and these injuries take priority over any others. Carbon monoxide, cyanide, and other inhaled toxins should be considered. The most threatening injuries are deep burns, burns covering a significant proportion of body surface area, and respiratory burns (Box 189.1).

Aside from the ABCs (airway, breathing, circulation), the most important aspect of burn assessment is estimation of burn depth and burn surface area. Burn depth can be assessed by evaluating the degree of blanching, noting the presence of blistering of the skin, and checking for the presence of pain. Total burn surface area is best assessed by using a Lund and Browder chart (Fig. 189.3). Alternatively, a patient’s palmar surface (not including the fingers) can be used as a crude measure of 1% of the patient’s body surface area.

Fig. 189.3 A, The Lund and Browder charts are somewhat more accurate than the rule of nines in estimating the total body surface area burned. B, The proportion of total body surface area of individual areas, according to age. When compared with adults, children have larger heads and smaller legs. Other areas are relatively equivalent throughout life. The rule of nines is not accurate in determining the percentage of total body surface area burned in children. Ant, Anterior; L, left or lower; Post, posterior; R, right; U, upper.

(From Roberts JR, Hedges J, editors. Clinical procedures in emergency medicine. 4th ed. Philadelphia: Saunders; 2004.)

Children’s body surface area is significantly different from that of adults. A child’s head and torso account for a much larger percentage of body surface area than in an adult. Patients with serious burns need specific burn unit care and require transfer if such care is unavailable at the institution.

In patients with severe burn injuries, burn shock can occur. Hypovolemic shock develops from alterations in capillary permeability. Cell death can result in severe hyperkalemia, although this condition is usually a delayed finding.

Treatment

The first intervention for burn victims is assessment of the airway. Smoke inhalation is a common issue, so all patients who do not need immediate intubation should be given 100% humidified oxygen via a nonrebreather mask. Because edema can progress in minutes to hours and the full extent of respiratory damage may not become evident until 12 hours after the initial injury, patients with evidence of airway damage should be intubated prophylactically, before the airway becomes edematous (see the “Priority Actions” box).

Because of the expected hypovolemic state of these patients, two large-bore intravenous lines should be placed. Although placement of intravenous lines through burned skin is not optimal given that they allow another portal for infection into an open wound, it is preferable to having no intravenous access at all.

Fluid requirements are a key facet in the management of a burn patient. Two specific formulas are most commonly used. The Parkland formula is used to estimate fluid replacement in adults. This formula gives suggested fluid replacement in addition to maintenance fluid amounts over a 24-hour period; half of this fluid should be given over the first 8 hours, with the remaining half administered over the following 16 hours. The original Parkland formula used lactated Ringer solution as the fluid of choice.²

For children, the Galveston formula is recommended for calculation of fluid repletion. The Galveston formula suggests that lactated Ringer solution with 5% dextrose should be used as the fluid of choice because of the lack of glycogen stores in the pediatric population. Again, half of the total amount should be given in the first 8 hours, with the remainder administered within the next 16 hours. Maintenance fluid should be also added, and particular attention should be paid to maintaining body temperature (see the “Facts and Formulas” box).

Despite these formulas, fluid resuscitation is more accurately based on appropriate urine output, which is 0.5 mL/kg/hr in adults and up to 1 mL/kg/hr in children. When one is uncertain about the patient’s fluid status, as may occur with congestive heart failure or pulmonary edema, a Swan-Ganz catheter may be necessary to provide guidance. Some controversy exists about the optimal fluid to use in burn patients. Although current guidelines specify crystalloid only initially, more recent studies suggest a probable role for colloid solutions.^3,4

All burns should be gently cleansed of debris with normal saline solution. Superficial burns (superficial second- and first-degree burns) should be dressed with topical antimicrobial dressings, with frequent dressing changes planned (every 6 hours). A degree of controversy exists about the best antimicrobial dressing. No clearly superior agent has been reported in the literature.⁵ One commonly used agent, silver sulfadiazine, should not be applied to the face because of concerns about staining. A good option, particularly for the face, is a simple, over-the-counter antibiotic ointment. For mild burns, aloe vera cream is also acceptable. Biosynthetic dressings are another option, but because of cost and availability, these dressings are usually limited to inpatient burn management. A recent study showed a combination of hyaluronic acid plus silver sulfadiazine to be superior to just silver sulfadiazine alone.⁵

Deeper burns may require débridement and grafting. Specific recommendations should be discussed with the local burn center. If burns are in areas that can be elevated, they should be; this approach decreases the amount of subsequent edema that develops in the burn areas. Controversy also exists about whether burn blisters should be sterilely incised or left alone. No definitive data on the subject are available, but the general consensus appears to be that unless a blister prevents the application of a dressing, it should be left intact.

Pain management is beneficial to the patient and is important to address early. Third-degree (full-thickness) burns are insensate, but more superficial burns are exquisitely painful. Most burns vary in depth and are painful, so early intravenous administration of morphine or hydromorphone (Dilaudid) is indicated for patients with extensive or deep burns. First-degree burns can be managed with oral nonsteroidal antiinflammatory medications as a first-line therapy, although narcotics may be required. Superficial partial-thickness burns require oral narcotics for pain control.

Occasionally, a burn covers such a large area that it poses a risk for respiratory or vascular compromise. For example, a circumferential burn on an extremity can compromise the vascular supply to that extremity, whereas a nearly circumferential full-thickness burn on the chest can prevent chest movement and result in an inability to ventilate. Through escharotomies these constricting bands of tissue can be released (Table 189.2). The basic method of performing an escharotomy is to incise the constricting band of tissue down to subcutaneous fat. Fasciotomies for compartment syndrome may also be required with thermal burns that cause edema and subsequent increased compartmental pressure.

Table 189.2 Eschar Treatment

Much discussion has centered around empiric antibiotic administration. No data support the empiric use of antibiotics for acute burn wounds, except in topical form, as recommended for superficial burn wounds.⁶

Application of cold inhibits the production of lactate, release of histamine and thromboxane, and sequelae such as edema, microvascular congestion, and progressive ischemia. Cold should be used for small burns but not for large burns because hypothermia could result. Ice should not be applied directly because frostbite can increase tissue injury. Cold water can help relieve the pain of first- and second-degree burns, but patients with significant burns involving more than 9% of their total body surface area should not have cold applied.

Follow-Up, Next Steps in Care, and Patient Education

Patients with major burns should receive care in a specialized burn center (see Box 189.1). Minor burns can be cared for on an outpatient basis with close follow-up and instructions for assessing for infection. Patients should be informed of what to expect over the days and weeks following their burn (see the “Patient Teaching Tips” box). All patients with concern for possible nonaccidental burns should be evaluated by both social services and law enforcement, and patients with self-inflicted injuries should be referred for psychiatric care. Any pediatric patient suspected of suffering abuse should be admitted to the hospital, even if the burn itself does not meet admission criteria, so that social services can ensure the child’s safety (see the “Red Flags” box).