Burns and Frostbite

Published on 07/03/2015 by admin

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Last modified 07/03/2015

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Chapter 66 Burns and Frostbite

Shawn P. Fagan, MD , Jeremy Goverman, MD, FACS

1 What determines the degree of tissue destruction after a thermal injury?

The degree of tissue injury is directly related to the temperature and duration of contact with the heat source. Children are particularly susceptible to thermal injury because of the thinner dermal layer. At 156° F (68.9° C), it requires less than 1 second to have a full-thickness thermal injury. As temperature of the heat source decreases, the time necessary for a clinical significant thermal injury is prolonged. This is evident by the 10 seconds required to produce a full-thickness thermal injury at 130° F (54.4° C). For this reason, the American Burn Association recommends setting the thermostat of a household water heater to 120° F (48.9° C) to prevent clinically significant thermal injuries in the household.

2 What determines the physiologic impact of a thermal injury on the human body?

The physiologic impact of the thermal injury is directly related to the extent of second- and third-degree thermal injury. This is why most burn fluid resuscitative formulas are based on the extent of second- and third-degree thermal injury. Of interest, the depth of thermal injury does not affect the physiologic consequences but may affect the wound management techniques required for effective wound healing. Most second-degree thermal injuries can be managed until healing with topical antimicrobials, whereas third-degree thermal injuries, dependent on size, generally require excision of nonviable tissue and closure with skin grafts.

3 How are thermal injuries classified?

Thermal injuries are classified by the depth of injury to the underlying skin’s structure. The skin is composed of an outer epidermis and inner dermis. The regenerative capacity of the skin, the stem cells, reside in the dermis and hair follicles. Thus the ability to heal a thermal injury is directly related to the degree of damage of the dermis and the presence of hair follicles at the site of thermal injury. Burn wounds are classified from first through fourth degree:

First degree: Thermal injury only affects the epidermis—sunburn.

Second degree: Thermal injury affects the epidermis and superficial dermis. The injury results in blistering and mild to moderate edema to the affected area. The wound is painful because of damaged nerves but should heal with simple topical antimicrobials in approximately 14 to 21 days.

Third degree: The thermal injury affects both the epidermis and dermis. A true third-degree thermal injury should be without pain because of the complete destruction of the sensory nerves. However, few thermal injuries are composed of only one class of injury. The majority of deep thermal injuries are a mixture of depths, thus making lack of sensation a poor marker to classify depth of injury. A more specific marker of a third-degree thermal injury is the white and leathery appearance. Healing of a third-degree thermal injury will require excision and grafting.

Fourth degree: Thermal injuries that affect structure deep to the skin–fat, fascia, muscle, and/or bone. Treatment and presentation are similar to those of third-degree thermal injuries.

4 What are the initial steps in the management of an individual who had a thermal injury?

The management of a thermally injured patient should proceed in a similar manner as the clinician would evaluate any trauma patient with the understanding of a few burn-specific nuances. The first step is to stop the burning process. This may be as simple as removing smoldering clothing or copious irrigation of chemical or radiation injuries. As the burning process is being addressed, the patient should undergo a primary survey consisting of airway, breathing, circulation, disability, and exposure.

Airways can be challenging in a burn patient. Therefore clinicians must be aware of potential inhalation injuries that may affect the supraglottic airway (airway obstruction) and/or infraglottic airway (chemical pneumonitis). Children are particularly susceptible to supraglottic obstruction because of progressive edema and relatively narrow upper airways. Individuals demonstrating airway compromise or having large thermal injuries should have an endotracheal tube placed to avoid airway issues. The important point to remember is that maximal edema occurs approximately 24 hours after thermal injury.

Appropriate and rapid resuscitation is critically important to avoid future morbidity and mortality after a thermal injury. Studies have demonstrated that the timing of initial resuscitation is directly related to mortality. Delay in resuscitation must be avoided, but the rate of fluids administered must be appropriate. Recently, studies have demonstrated increased morbidity and mortality associated with overresuscitation. Thus calculating the estimated fluid requirement for a thermally injured patient should be performed early in the evaluation process and titrated on the basis of urine output and normalization of resuscitative laboratory results.

It is critically important not to be distracted by the extent or depth of thermal injury during the initial evaluation. All thermally injured patients should have a comprehensive trauma evaluation to avoid missed injuries. It is not uncommon for thermal injuries to be associated with significant trauma.

5 What is burn shock?

Classically, burn shock was simply defined by a state of hypovolemia. However, it is now realized that burn shock is a complex process not only affecting preload but also influencing cardiac output and systemic vascular resistance. During the first 8 hours after thermal injury a substantial increase in capillary permeability occurs resulting in a state of intravascular volume depletion. This relative intravascular volume depletion is coupled with a decrease in cardiac output and increased systemic vascular resistance. The degree of impaired cardiac output and increased vascular tone cannot be completely attributed to the state of post–burn injury hypovolemia. Therefore a goal-directed approach to the resuscitation of a thermally injured patient is warranted. The specific impairment (preload, cardiac output, systemic vascular resistance) should be identified and appropriate therapeutic measures initiated to improve the specific problem. Simply stated, burn shock is not simply a state of hypovolemia.

6 How do you determine the initial fluid requirements of a thermally injured patient?

Although burn shock can influence preload, cardiac output, and systemic vascular resistance, burn patients do differ from other intensive care unit populations with the substantial intravascular fluid depletion that occurs over the first 24 hours. This is directly related to increased capillary permeability. Therefore thermally injured patients require a considerable amount of volume administration in the first 24 hours.

The Parkland Burn Center published the most widely used burn resuscitation formula. The formula states that the total amount of lactated Ringer’s solution necessary during the first 24 hours is directly related to the size of thermal injury (second and third degree) and the preburn weight (kilograms) of the patient. The Parkland formula is 2 to 4 mL/kg body weight/Total body surface area (TBSA) thermal injury. Half of the volume is administered during the first 8 hours from time of injury with the remaining amount administered over the following 16 hours. The formula is an estimate of the fluids necessary during the initial 24 hours; therefore the rate of fluid administration must be adjusted on the basis of the monitoring of resuscitative parameters with the primary goal of avoiding overresuscitation.

Some centers modify the resuscitative formula for children because of the larger surface area per kilogram body weight compared with an adult. The Galveston resuscitation formula is based on TBSA affected by thermal injury but also includes a maintenance infusion rate. The Galveston formula is 5000 mL lactated Ringer’s/TBSA thermal injury +1200 mL/TBSA. In addition, infants and young children should have a continuous source of glucose administered via the maintenance fluids. Similar to that for adults, the resuscitative formula is an estimate of the fluids necessary during the first 24 hours; adjustment must be made on the basis of response to the initial resuscitation.

7 Should a primary survey be repeated during the first 24 hours after thermal injury?

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