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Total Body Surface Area
Total Body Surface Area
The surface of an object is the outermost layer which is used to describe its texture, form or size. The area of the surface, or surface area, is the number of square units (measured in inches, feet, yards, miles, etc.) needed to completely cover the surface of the object. In the body, the epidermis makes up the outermost layer, and the surface area is essentially a measurement of how much exposed skin the body has.
Total Body Surface Area (TBSA) measures the area of a burn injury in comparison with the entire surface area of the body. This relationship is used by medical professionals to determine the severity of the burn. This allows medical professionals to treat burn patients effectively to ensure the highest likelihood of recovery.
TBSA Measurement Techniques
Because of the difficulty in measuring the surface area of irregular objects (such as the curvature of the body) and because these calculations often need to be made quickly, several methods have been developed to assist medical professionals with determining TBSA. The three most common methods are the Rule of Nines, the Lund and Browder Chart, or using the patient’s palm.
The Rule of Nines
The Rule of Nines divides the body into 11 sections that are each estimated to account for 9% of the body’s total surface area. The sections are listed below.
- Upper back
- Lower back / buttocks
- Arm (x2)
- Front leg (x2)
- Back leg (x2)
Zones can be broken down into smaller sections or added together. For example, the front and back of the arms are each 4.5%; each leg is 18%. The groin accounts for the 1% of TBSA not accounted for by the other 11 zones.
While the Rule of Nines is easy to remember and a good rule of thumb in an emergency, critics point out that this rule does a poor job of accounting for differences between age groups. In particular, the Rule of Nines fails to account for the changing relationship between the head and the rest of the body as one grows older. For this reason, the Rule of Nines does not make accurate estimates for young children and should only be used for adults.
Lund and Browder Chart
In an effort to make a more reliable TBSA chart, two medical researchers (Lund, C.C. and Browder, N.C.) released their paper “The estimation of areas of burns” in the 1944 edition of the Surgery, Gynecology & Obstetrics Journal. Since its printing, the Lund and Browder Chart has become one of the most widely used methods for determining the size of a burn injury.
Similar to the Rule of Nines method, the Lund and Browder Chart divides the body into zones and estimates the amount of surface area that each zone accounts for. The chart is a picture of the body from both front (anterior) and back (posterior) angles, and the zones of the body are divided accordingly.
There are three zones of the body that the Lund and Browder Chart varies depending on age. These areas are the head, thighs and lower legs. The head ranges from 19% of TBSA for a newborn baby down to 9% of TBSA for an individual age fifteen and older. As the percentage of the head decreases with age, the percentage of the thighs and lower legs increases. The thighs increase from 11% to 18% and the lower legs increase from 10% to 13% of TBSA from the age of zero to fifteen. The full breakdown of each zone is found in the chart below.
While the Lund and Browder Chart aims to create an accurate reflection of TBSA, not everyone agrees that it is successful in its aim. One critique of this chart is that it was designed based upon the average body of various age groups in 1944. Average bodies today are substantially different than they were seventy years ago. The change in body size likely skews the percentages for each of the body’s zones, but it is unclear if the change is enough to cause life-threateningly erroneous results. After all, this technique is still an estimation of TBSA, not any type of genuine measurement.
The Patient’s Palm
A final method for calculating TBSA is using the patient’s palm as a measuring tool. The palm is roughly 1% of TBSA regardless of the age of the patient. Using the palm as a reference, professional medical providers can estimate the percentage of the body that has been burned. This technique is most effective when burns cover less than 15% or more than 85% of TBSA. When burns cover more than half the body, professional medical providers measure the area that is not burned and subtract that percentage from 100.
Because the palm method does not require access to any charts, it can be used in the field to make calculations on children (or anyone who the Rule of Nine is ineffective for).
Impact of TBSA
A serious potential complication of burn injuries is dehydration. The skin is the primary organ responsible for retaining bodily fluids. When it is sufficiently injured, the skin loses its capacity to retain fluids and the body can become dehydrated as a result. Measuring the surface area of the burn is an important step in determining the level of fluid replacement and extent of treatment that a burn patient needs. The skin is still able to retain fluids if the burn is a first degree burn, so only burns of the second degree or worse are used to calculate TBSA. The American Burn Association burn center referral criteria advises that burns greater than 10 percent TBSA be referred to a burn center.
There is also a direct relationship between burn TBSA and mortality rates in burns. The table below uses data from 2002 through 2011 collected by the American Burn Association. While the data is not a random sample and only includes patients that were admitted to burn centers for treatment, the conclusions remain logically consistent and compelling.