INCIDENCE

The precise number of burns that occur in the United States each year is unknown because only 21 of 50 states mandate the reporting of burn injury. An estimated total number of burns has been obtained by extrapolation of those data. At present, 1.25 million is regarded as a realistic estimate of the annual incidence of burns in the United States, 80% of which involve less than 20% of the total body surface. Approximately 190–263 patients per million population are estimated to require admission to a hospital for burn care each year. In the population of burn patients requiring hospital care, there is a smaller subset of approximately 20,000 burn patients who, as defined by the American Burn Association (Table 1), are best cared for in a burn center each year. This subset consists of 42 patients per million population with major burns, and 40 patients per million population having lesser burns but a complicating cofactor.

Table 1 Burn Center Referral Criteria

a If the mechanical trauma poses the greater immediate risk, the patient may be stabilized and receive initial care at a trauma center before transfer to a burn center.

MECHANISM OF INJURY

Certain populations are at high risk for specific types of injuries that require treatment by the trauma/critical care surgeon. Scald burns are the most frequent form of burn injury overall, causing 58% of burn injuries and over 100,000 emergency department visits annually. Sixty-five percent of children age 4 and under who require hospitalization for burn care have scald burns, the majority of which are due to contact with hot foods and liquids. The occurrence of accidental tap water scalds can be minimized by adjusting the temperature settings on hot water heaters or by installing special faucet valves that prevent delivery of water at unsafe temperatures. Scald burns with injury typically involving the feet, posterior legs, buttocks, and sometimes the hands are most often caused by immersion in scalding water by an abusive caretaker. It is important that the trauma/critical care surgeon identify and report child abuse, because when abuse is undetected and the child is returned to the abusive environment, repeated abuse is associated with a high risk of fatality.

Fire and flame sources cause 34% of burn injuries and are the most common causes of burns in adults. One-fifth to one-quarter of all serious burns are related to employment. Kitchen workers are at relatively high risk for scald injury, and roofers and paving workers are at greatest risk for burns due to hot tar. Workers involved in plating processes and the manufacture of fertilizer are at greatest risk for injury due to strong acids, and those involved with soap manufacturing and the use of oven cleaners are at greatest risk of injury due to strong alkalis.

Electric current causes approximately 1000 deaths per year. Young children have the highest incidence of electric injury caused by household current as a consequence of inserting objects into an electrical receptacle or biting or sucking on electric cords and sockets. Adults at greatest risk of high-voltage electric injury are the employees of utility companies, electricians, construction workers (particularly those manning cranes), farm workers moving irrigation pipes, oil field workers, truck drivers, and individuals installing antennae. Lightning strikes result in an average of 107 deaths annually. The vast majority (92%) of lightning-associated deaths occur during the summer months among people engaged in outdoor activities such as golfing or fishing.

Abuse is a special form of burn injury, affecting the extremes of age. Child abuse is typically inflicted by parents but also perpetrated by siblings and child care personnel. The most common form of thermal injury abuse in children is caused by intentional application of a lighted cigarette. Burning the dorsum of a hand by application of a hot clothing iron is another common form of child abuse. Scald burns, as previously discussed, are also common. In recent years, elder abuse by caretakers or family members has become more common, and it too should be reported and the victim protected.

PATHOPHYSIOLOGY

GRADING OF BURN WOUND DEPTH

The injuries that will be apparent on examination are the consequences of the level of tissue destruction. Wounds that are superficial are associated with hyperemia, fine blistering, increased sensation, and exquisite pain upon palpation. The wounds are hyperemic, warm, and readily blanch. These types of injuries represent firstdegree burns or are alternatively termed superficial partial-thickness injuries. With a second degree or deeper partial-thickness burn, the wound presents with intact or ruptured blisters or is covered by a thin coagulum termed “pseudoeschar.” The key physical finding is preservation of sensation in the burned tissue, although it is reduced (Table 2). With proper care, superficial and even deeper partial-thickness injuries are capable of spontaneous healing without grafting. The risk of infection in deep partial-thickness wounds is significant, and if an infection develops it can lead to a greater depth of skin loss. A full-thickness wound occurs when the injury penetrates all layers of the skin or extends into the subcutaneous or deeper tissues. These wounds will appear pale or waxy, be anesthetic, dry, and inelastic, and contain thrombosed vessels. Occasionally in children or young women, the initial appearance of a wound may be more that of a brick red coloration. Such wounds will have significant edema and are inelastic and insensate. Full-thickness wounds are infection-prone wounds, as they no longer provide any viable barrier to invading organisms and if left untreated become rapidly colonized and a portal for invasive burn wound sepsis.

Table 2 Clinical Characteristics of Burn Injuries

RESUSCITATION PRIORITIES

Fluid Administration

Immediately following burn injury, the changes induced in the cardiovascular system must receive therapeutic priority. In all patients with burns of more than 20% of the total body surface area and those with lesser burns in whom physiologic indices indicate a need for fluid infusion, a large-caliber intravenous cannula should be placed in an appropriately sized peripheral vein, preferably underlying unburned skin. If there are no peripheral veins available, central venous access is indicated. Lactated Ringer’s solution should be infused at an initial rate of 1 liter/hr in the adult and 20 ml/kg/hr for children who weigh 50 kg or less. That infusion rate is adjusted following estimation of the fluid needed for the first 24 hours following the burn.

Resuscitation fluid needs are proportional to the extent of the burn (combined extent of partial- and full-thickness burns expressed as a percentage of total body surface area) and are related to body size (most readily expressed as body weight) and age (the surface area per unit of body mass is greater in children than in adults). The patient should be weighed on admission and the extent of partial- and full-thickness burns estimated according to standard nomograms (Figure 1). The fluid needs for the first 24 hours can be estimated on the basis of the Advanced Burn Life Support and Advanced Trauma Life Support consensus formula (Table 3).

Figure 1 Example of a form used for documenting extent of burn. Figure outlines are filled in with a blue pencil and a red pencil to indicate distribution of partial-thickness and full-thickness burns, respectively. Note the columns indicating how the percentage of total body-surface area represented by body-part surface changes with time.

(Used with permission from Martin RR, Becker WK, Cioffi WG, and Pruitt BP Jr: Thermal Injuries. In Wilson RF and Walt AJ, editors: Mangement of Trauma: Pitfalls and Practice, 2nd ed. Baltimore, Williams and Wilkins, 1996, p. 765.)

Table 3 Fluid Required for the First 24 Hours Post-Burn

Adults = 2–4 ml LR/%TBSAB/Kg, BW Children = 3–4 ml LR/%/TBSAB/Kg, BW + maintenance in children <30 kg

BW, Body weight; LR, lactated Ringer’s; TBSAB, total body surface area burned.

Because of the greater surface area per unit of body mass in children, the volume of fluid required for the first 24 hours is relatively greater than that for an adult. In all patients, one-half of the estimated volume should be administered in the first 8 hours after the burn. If the initiation of fluid therapy is delayed, the initial half of the volume estimated for the first 24 hours should be administered in the hours remaining before the 8th post-burn hour. The remaining half of the fluid is administered over the subsequent 16 hours.

The limited glycogen stores in a child may be rapidly exhausted by the marked stress hormone response to burn injury. Serum glucose levels in the burned child should be monitored, and 5% dextrose in lactated Ringer’s administered if serum glucose decreases to hypoglycemic levels. In the case of small children with small burns, the resuscitation fluid volume as estimated on the basis of burn size may not meet normal daily metabolic requirements. In such patients, maintenance fluids should be added to the resuscitation regimen.

The infusion rate is adjusted according to the individual patient’s response to the injury and the resuscitation regimen. The progressive edema formation in burned and even unburned limbs commonly make measurements of pulse rate, pulse quality, and even blood pressure difficult and unreliable as indices of resuscitation adequacy. Therefore, hourly urine output should be used as a measure of the adequacy of resuscitation. The fluid infusion rate is adjusted to obtain 30 ml of urine per hour in the adult and 1 mg/kg of body weight per hour in children weighing less than 30 kg. The administration of fluid is increased or decreased only if the hourly urinary output is one-third or more below, or 25% or more above, the target level for 2 successive hours. If in either adults or children the resuscitation volume infused in the first 12 hours will result in administration of 6 ml or more per percent of body surface area burned per kilogram of body weight in the first 24 hours, human albumin diluted to a physiologic concentration in normal saline should be infused and the volume of crystalloid solution reduced by a comparable amount.

Restoration of functional capillary integrity occurs at or near 24 hours after burn injury. Consequently, the volume of fluid needed for the second 24 hours post-burn is less, and colloidcontaining fluids can be infused to reduce further volume and salt loading. Human albumin diluted to physiologic concentration in normal saline is the colloid-containing solution of choice, infused in a dosage of 0.3 ml per percent of burn per kilogram of body weight for patients with 30%–50% burns, 0.4 ml per percent of burn per kilogram of body weight for patients with 50%–70% burns, and 0.5 ml per percent of burn per kilogram of body weight for patients whose burns exceed 70% of the total body surface area. Water containing 5% dextrose is also given in the amount necessary to maintain an adequate urinary output. The colloid-containing fluids for children are estimated according to the same formula, but half normal saline is infused to maintain urinary output and avoid inducing physiologically significant hyponatremia by infusion of large volumes of electrolyte-free fluid into the relatively small intravascular and interstitial volume of the child. Fluid infusion “weaning” should also be initiated during this time period, to further minimize volume loading. In a patient who is assessed to be adequately resuscitated, the volume of fluid infused per hour should be arbitrarily decreased by 25%–50%. If urinary output falls below target level, the prior infusion rate should be resumed. If urinary output remains adequate, the reduced infusion rate should be maintained over the next 3 hours, at which time another similar fractional reduction of fluid infusion rate should be made. This decremental process will establish the minimum infusion rate that maintains resuscitation adequacy in the second post-burn day.

Fluid management after the first 48 hours post-burn should permit excretion of the retained fraction of the water and salt loads infused to achieve resuscitation, prevent dehydration, and electrolyte abnormalities, and allow the patient to return to pre-burn weight by post-burn day 8–10. Infusion of the large volumes of lactated Ringer’s required for resuscitation commonly produces a weight gain of 20% or more and a reduction of serum sodium concentration to approximate that of lactated Ringer’s—that is, 130 mEq/l. Correction of that relative hyponatremia is facilitated by the prodigious evaporative water loss from the surface of the burn wound, which is the major component of the markedly increased insensible water loss that is present following resuscitation. Inadequate replacement of insensible water loss makes hypernatremia the most commonly encountered electrolyte disturbance in the extensively burned patient following resuscitation. Such hypernatremia should be managed by provision of sufficient electrolyte-free water to allow excretion of the increased total body sodium mass and replace insensible water loss to the extent needed to prevent hypovolemia.

Electrolyte abnormalities are frequently encountered in the immediate post-burn period. Hyperkalemia is frequently encountered and is typically a laboratory sign of hemolysis but may also be a sign of muscle destruction by high-voltage electric injury or a particularly deep thermal burn. Hyperkalemia may also occur in association with acidosis in patients who are grossly under-resuscitated. In the case of patients with high-voltage electric injury, emergency debridement of nonviable tissue and even amputation may be necessary to remove the source of the potassium. Hypophosphatemia is also extremely common after burn resuscitation due to either prolonged administration of parenteral nutrition or failure to supply sufficient phosphate to meet the needs of tissue anabolism following wound closure. Hypophosphatemia can be prevented and treated by appropriate dietary phosphate supplementation.