Related Experiment Video
Updated: Oct 16, 2026
Rat Burn Model to Study Full-Thickness Cutaneous Thermal Burn and Infection
Published on: August 23, 2022
Percentage of burned body surface area determination in obese and nonobese patients
1VAMC Greater Los Angeles Health Care System, Los Angeles, California 90099-5786, USA.
Insights
The rule of nines accurately estimates burn surface area for most patients, but modifications are needed for infants and obese adults. New "rule of fives" and "rule of eights" offer improved accuracy for these specific populations.
Area of Science:
- Burn management
- Body surface area estimation
- Pediatric and adult medicine
Background:
- Accurate burn surface area (BSA) measurement is critical for initial burn patient management, including fluid resuscitation and hospital admission decisions.
- The "rule of nines" is a widely used method for BSA estimation, but its accuracy is compromised in infants and obese individuals due to altered body segment proportions.
- Obesity and infant physiology significantly change the proportional contribution of body segments to total body surface area, impacting the "rule of nines" reliability.
Purpose of the Study:
- To evaluate the accuracy of the "rule of nines" in estimating body surface area (BSA) for normal weight, obese, and infant populations.
- To develop and propose modified BSA estimation methods for infants and obese adults where the "rule of nines" is less reliable.
- To compare calculated BSA measurements with those derived from the "rule of nines" in diverse patient groups.
Main Methods:
- Detailed body surface area measurements were conducted on 47 patients, categorized by weight: 18 normal weight, 6 moderately obese, and 23 seriously obese.
- Published body surface area data for infants were reviewed to assess the applicability of the "rule of nines" in this demographic.
- The proportional contribution of major body segments to overall BSA was calculated and compared against "rule of nines" estimations.
Main Results:
- The "rule of nines" provides adequate BSA estimates for patients weighing between 10 and 80 kg.
- For obese patients over 80 kg, a "rule of fives" is proposed: 5% per arm, 20% per leg, 50% for the trunk, and 2% for the head.
- For infants under 10 kg, a "rule of eights" is suggested: 8% per arm, 16% per leg, 32% for the trunk, and 20% for the head.
Conclusions:
- Body segment contributions to total body surface area (BSA) vary, necessitating adjustments to standard estimation methods.
- While the "rule of nines" is generally reliable for children and adults, its accuracy diminishes in infants and obese adults.
- The proposed "rule of fives" for obese adults and "rule of eights" for infants offer more precise BSA estimations, improving burn management for these populations.
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.
Related Concept Videos
01:21Drug Dosing: Obese Patients
01:22Burn Injuries
The damage results in the death of skin cells, which can lead to a massive loss of fluid. Dehydration, electrolyte imbalance, and renal and circulatory failure follow, which can be fatal. Burn patients are treated with intravenous fluids to offset...
01:25Pharmacokinetics in Obese Patients: Drug Absorption and Distribution