Purpose: An accurate measurement of body surface area (BSA) involved in patients injured by burns is critical in determining initial fluid requirements, nutritional needs and criteria for tertiary center admissions.  Appropriate fluid resuscitation using the Parkland formula has been shown to improve outcomes but the formula relies on a precise estimate of the BSA involved. The “rule of nines” and Lund-Browder charts are commonly used to calculate the BSA, however both were formulated on small sample sizes and their accuracy in all patient populations remains to be proven.  With the continued rise in obesity, the preceding methods need to be validated for obese patients, given that altered BSA distribution has been observed in this patient population.  Inaccurate estimates of the BSA burned may lead to gross errors in treatment paradigms resulting in worse outcomes.

 Methods:  Detailed BSA measurements were obtained from 125 adult patients according to linear formulas defined by DuBois & DuBois (1917) for calculating BSA of individual body segments (head, arms, hands, trunk, thigh, legs, and feet).  Patients were sub-grouped based on BMI with 42 normal weight / overweight patients (BMI < 29.9), 42 obese patients (BMI 30.0 – 39.9) and 41 morbidly obese patients (BMI > 40.0).  Hip to waist ratios were calculated. The contribution of individual body segments to the total BSA was determined based on BMI, and the validity of existing measurement tools were examined, namely the rule of nines and Lund-Browder chart.

 Results:  The groups were relatively homogeneous with the obese and morbidly obese populations being comprised of a higher percentage of females.  Hip / Waist ratios were statistically different (p < .001) for normal weight patients (1.21) when compared to obese (1.14) and morbidly obese patients (1.15). As BMI increased the surface area (SA) of the head, in relation to the total BSA increased, while trunk SA, leg SA and hand SA decreased (p<.001).  Significant error was found when comparing all groups to the ‘rule of nines’ and Lund-Browder chart, which overestimated the contribution of the head and arms to the TBSA while underestimating the trunk and legs for all BMI groups.  A new rule is proposed to minimize error assigning 5% of the total BSA to the head, 15% of the total BSA to the arms across all BMI groups, and alternating the contribution of the trunk / legs as follows: normal weight 35% / 45%, obese 40% / 40%, and morbidly obese 35% / 45%.

 Conclusions: The determination of total BSA burned remains integral in the treatment of burn patients.  Current modalities used to determine total BSA burned are subject to significant error, which is magnified as BMI increases.  New methods for efficient and accurate evaluation of total BSA burned in normal weight and obese patients are needed. We feel this new algorithm is simple to use and will allow for better surface area estimates in patients regardless of BMI.