Percentage of burned body surface area determination in obese and nonobese patients

Abstract

Background: The measurement of burn surface area is important during the initial management of burn patients for estimating fluid requirements and determining hospital admission criteria. The "rule of nines" is commonly used for this purpose. However, the proportional contribution of various major body segments to the total body surface area changes with obesity. Similarly infants have very large heads, altering the overall contribution of other body segments to the total body surface area.

Methods: Detailed body surface area measurements were made in 47 patients: 18 were of normal weight, 6 were moderately obese, and 23 were seriously obese. Published tables of similar measurements for infants were reviewed to determine how the rule of nines applied to these populations. The contribution of the major body segments to the overall body surface area was calculated and compared to estimates that would be derived for these segments from the rule of nines.

Results: The rule of nines provides reasonable estimates of body surface area for patients ranging from 10 to 80 kg. For obese patients weighing more than 80 kg a rule of fives is proposed: 5% body surface area for each arm, 5 x 4 or 20% for each leg, 10 x 5 or 50% for the trunk, and 2% for the head. For infants weighing less than 10 kg a rule of eights applies: 8% for each arm, 8 x 2 or 16% for each leg, 8 x 4 or 32% for the trunk, and 20% for the head.

Conclusion: Various body parts differentially contribute to the total body surface area. Because these relationships remain relatively constant throughout growth, the rule of nines provides reasonable estimates for the determination of burned body surface area for most children and adults. These relationships break down for infants and obese adults and the proposed modifications to the rule of nines provide better estimates of surface area for these groups.