A burn injury involves damage to body tissue, typically caused by heat, chemicals, electricity, or radiation. The initial assessment determines the necessary treatment and patient disposition. Accurately determining the extent and depth of the damage is necessary for predicting outcomes and guiding immediate care. Burn size and severity directly influence the risk of complications like fluid loss and infection.
Assessing Burn Severity
The first step in calculating burn severity is determining the depth of tissue damage, categorized into three main types. A superficial burn affects only the epidermis, similar to a mild sunburn. These burns appear red, are painful, and typically do not form blisters, healing without scarring in days.
A partial-thickness burn extends through the epidermis and into the underlying dermis layer of the skin. This type of burn is characterized by the formation of blisters, a weeping or moist appearance, and a mottled red-to-pink color. Partial-thickness burns cause intense pain and may take up to three weeks to heal, often resulting in some degree of scarring.
The most serious injury is a full-thickness burn, which destroys both the epidermis and the entire dermis, potentially extending into the underlying fat, muscle, or bone. The affected area may appear waxy white, charred black, or leathery brown. Paradoxically, due to the destruction of nerve endings, this burn itself may lack sensation, although the surrounding, less-deep areas can be very painful. Full-thickness burns do not heal naturally and require specialized medical intervention.
Calculating Total Body Surface Area
Once the depth of the injury is determined, the next calculation involves estimating the percentage of the body affected, known as the Total Body Surface Area (TBSA). The “Rule of Nines” is a standard method used for a rapid TBSA estimate in adults. This rule segments the adult body into areas that each represent 9% or a multiple of 9% of the total surface area.
For an adult, the entire head and neck account for 9%, the entire front of the torso is 18%, and the entire back of the torso is also 18%. Each entire arm, including the hand, represents 9% of the TBSA. Each entire leg, front and back, is assigned 18%, and the area of the genitals (perineum) accounts for the final 1%. These percentages allow quick summation of the total affected area.
For small, scattered, or irregular burns, the “Rule of Palms” offers a useful alternative. The patient’s palm, excluding the fingers, represents approximately 1% of their TBSA. The non-burned palm is used as a template to cover and count the area of the burn injury. This method is helpful for estimating smaller burns where the Rule of Nines might be imprecise.
Adjusting Calculations for Children
The Rule of Nines, which is reliable for adults, becomes inaccurate for pediatric patients because a child’s body proportions are significantly different. Infants and toddlers have a proportionally larger head and smaller legs compared to adults.
In an infant, the head can account for as much as 18% of the TBSA, which is double the adult value. Conversely, the legs of a young child account for a smaller percentage than the 18% assigned to an adult leg.
A modified approach recognizes that for each year of age over one, a percentage point is subtracted from the head and added to the legs until adult proportions are reached. This proportional adjustment ensures an accurate TBSA estimate, which is important for determining the child’s fluid needs.
When to Seek Emergency Medical Attention
The combination of burn depth and size determines when a burn injury requires immediate professional medical care. Any full-thickness burn, regardless of its size, necessitates emergency medical attention. The destruction of the skin barrier in these deep injuries creates a high risk of infection and severe fluid loss.
The size of a partial-thickness burn is a major factor in seeking emergency care. A partial-thickness burn covering more than 10% of the TBSA in an adult is considered a major burn requiring specialized treatment. Burns involving sensitive areas also warrant immediate attention due to the high risk of functional impairment. These locations include the face, hands, feet, major joints, and genitals.
Other types of burn injuries necessitate a professional evaluation due to unique risks. This includes all electrical burns, chemical burns, and any burn with a risk of inhalation injury, such as those occurring in an enclosed space. Burns in infants and the elderly are also considered more serious, even if small, due to the patient’s compromised ability to compensate for the injury.