The extent of tissue injury caused by a burn is quantified by the surface area (SA) and the depth of injury. Determination of the extent of injury provides a basis for estimation of fluid requirements for resuscitation and for determining an overall care plan. In addition, in that a positive correlation exists between extent of injury and mortality, this determination provides information on prognosis. For estimation of the extent of SA involved, a Lund & Browder chart or Berkow’s formula should be used. The “rule of nines” cannot be used in children <15 years of age. The distribution of SA by age is shown in the chart in Table 32.1.

Evaluation of depth of injury is readily determined at the extremes of depth, such that partial-thickness injury is easy to differentiate from full-thickness injury. A first-degree burn is characterized as erythematous, painful, and dry, while a thirddegree burn, also known as a full-thickness burn, is leathery, dry, and insensate. Burn injuries at an intermediate depth of partial thickness are more difficult to assess. They are divided into superficial and deep partial-thickness wounds. Whether superficial or deep, these wounds appear very similar on physical examination. They are erythematous, moist, and sensate. Evaluation of these wounds is complicated by the fact that
they evolve over time, are frequently not homogeneous with regard to depth, and dynamically change over the first days after injury. Previous attempts to use advanced instrumentation, such as laser Doppler and infrared sensing devices, did not demonstrate proven value in routine evaluation of this depth of injury. However, a more recent report suggests that laser Doppler imaging may be useful in estimating depth of injury in children (1). The importance of differentiating depth of injury relates to the fact that a superficial partial-thickness burn will reepithelialize in 2 weeks, whereas a deep partialthickness wound heals by epithelialization and contraction. To avoid scarring, the deeper wound must be treated by skin grafting. Except for small-SA wounds, full-thickness wounds should either should be excised and closed primarily or grafted with the patient’s skin. A cross section of skin with indication of the various depths of injury is depicted in Figure 32.1.

The depth of the injury in burns that are caused by scalding, flame, or contact with a hot object is directly related to the temperature, duration of exposure, and thickness of the tissue. Three zones of injury have been identified in burn-injured skin. The outer zone of coagulative necrosis includes necrotic tissue that is irreversibly damaged by heat or chemical. Below that is the zone of stasis in which some viable tissue remains. This dynamic region is subject to further necrosis if it is not protected from further physical damage. Care must be taken to avoid aggressive methods of debridement and harsh cleansing agents. In addition, delivery of nutrient blood flow and oxygen is important in this region, and compromised cardiac output due to inadequate resuscitation can increase the depth of injury. The zone adjacent to the zone of stasis is the zone of hyperemia, and is characterized by increased blood flow and local inflammatory response to the injury.

Chemical burns cause denaturation of protein and disruption of cellular integrity. The degree of injury is dependent on the time of exposure, the strength of the agent, and the solubility of the agent in tissue. Alkaline agents tend to penetrate deeper into tissues than do acids, with an exception being hydrofluoric acid, which penetrates lipid membranes readily.

Electrical injury accounts for 2%-3% of the burns in children that require evaluation in an emergency department (2). Electricity is the flow of electrons, the force (or gradient) behind the flow is the voltage, the volume of the flow is the current measured in amperes, and the resistance to that flow is measured in ohms. Electrical injury can occur from direct contact or by an arc such as a lightning strike. Direct contact often causes damage at the entry and exit sites and along the path of the current. Arcs associated with high voltage can be extremely hot and cause deep thermal burns at the entrance site as well as current injury along the path. Domestic electricity in North America ranges 120/240 V. Low voltage is defined as <500-1000 V and is usually associated with less morbidity (less tissue injury from burns or blunt trauma) if there is no cardiac or respiratory arrest. Electricity occurs in two forms, alternating current (AC) where the current flows back and forth, and direct current (DC) where flow is in one direction. AC is in common use in North America and standardly runs at 60 cycles per second or 60 Hz (3). Battery power and lightning are examples of DC current. AC is more dangerous at a given voltage because of its ability to produce a tetanic muscular contraction that can prevent the victim from letting go and prolong the contact with electricity.