TBSA quantifies the extent of burn injuries across a patient’s skin. Calculating this percentage is the first step in assessing burn severity and determining immediate medical treatment. A precise TBSA estimate is necessary for guiding fluid resuscitation, which involves administering intravenous fluids to counteract the massive fluid loss that occurs in severe burns. Accurately gauging the injury size informs decisions regarding specialized burn center referral and helps predict patient outcomes.
The Role of Burn Depth in TBSA Calculation
An accurate TBSA calculation requires correctly classifying the depth of the injury, as not all burns are included in the final percentage. Only partial-thickness (second-degree) and full-thickness (third-degree) burns are counted when estimating TBSA. These deeper burns damage the skin barrier, leading to fluid shifts and the risk of shock.
Superficial (first-degree) burns, such as a mild sunburn, are excluded from the TBSA calculation. These injuries involve only the outermost layer of skin (the epidermis), are characterized by redness, and do not cause the fluid loss seen in deeper burns. Excluding these areas ensures the TBSA measurement accurately reflects the injury’s demand for fluid replacement and specialized care.
Standard Methods for Adult Assessment
The most widely used method for rapidly assessing TBSA in adults is the Rule of Nines (Wallace Rule of Nines). This system divides the body into sections assigned a value of 9% or a multiple of nine. Its simplicity makes it an effective tool for emergency medical providers who need to quickly triage a patient and begin treatment, especially fluid administration.
The entire head and neck region represents 9% of the body’s surface area. Each complete arm, including the hand, is also 9% (4.5% for the front and 4.5% for the back).
The trunk is divided into segments totaling 36%. The entire anterior torso (chest and abdomen) accounts for 18%, and the entire posterior torso (back) accounts for 18%. The genital and perineal area is a singular region that accounts for the remaining 1%.
Each full leg, including the foot, represents 18% of the TBSA (9% for the front and 9% for the back). By summing the percentages of only the burned sections, providers quickly determine the total percentage affected by second- and third-degree burns.
Adapting Calculation for Children
The Rule of Nines is inaccurate for infants and young children because their body proportions differ significantly from adults. Children have a proportionally larger head and smaller surface area in their lower extremities. Using the adult Rule of Nines on a child could result in an inaccurate, potentially underestimated TBSA, leading to inadequate fluid resuscitation.
The Lund-Browder chart is the preferred and more accurate method for estimating TBSA in pediatric patients. This chart addresses anatomical differences across age groups by assigning variable percentages to different body parts. For example, a newborn’s head may represent about 18% of the TBSA, while an older child’s head accounts for a smaller percentage as they grow.
The chart includes an age-correction factor, meaning the assigned percentages for the head and legs change depending on the child’s age. As a child gets older, the relative percentage assigned to the head decreases, and the percentage assigned to the legs increases. This adjustment ensures the calculated TBSA accurately reflects the extent of the injury in a developing body.
Using the Palm as a Quick Estimate
The Palmar Method provides a simple, rapid estimation of burn size, often used for smaller or irregularly shaped burns. This technique uses the patient’s own hand as a measuring tool. The entire palmar surface of the hand, from the wrist crease to the fingertips, is approximated to be 1% of their TBSA.
If only the palm is used (excluding the fingers and wrist), it represents a smaller surface area, approximated at 0.5% of the TBSA. This method is less precise than the Rule of Nines or the Lund-Browder chart. It serves to quickly gauge the size of scattered or small burns (under 15% TBSA) when a formal assessment is not immediately feasible.