The rule of fives in burns is a method for estimating the percentage of total body surface area (TBSA) affected by a burn in obese patients (typically those weighing over 80 kg). It's a modification of the more common rule of nines, which can be less accurate in obese individuals due to the altered proportions of their body surface areas.
Explanation of the Rule of Fives
The rule of fives assigns the following percentages to different body regions:
- Each arm: 5% TBSA
- Each leg: 20% TBSA (5 x 4)
- Trunk: 50% TBSA (10 x 5)
- Head: 2% TBSA
Why Use the Rule of Fives for Obese Patients?
The standard rule of nines, while widely used, assumes a certain body proportion that doesn't always hold true for obese individuals. Specifically, the trunk often makes up a larger percentage of the total body surface area in obese patients, while the head and legs may make up a smaller percentage. The rule of fives attempts to compensate for these differences, offering a more accurate estimate of burn size in this population.
Example
Let's say an obese patient has burns covering their entire left arm and the front of their trunk. Using the rule of fives:
- Left arm: 5%
- Front of trunk: 25% (half of the 50% total for the trunk)
- Estimated TBSA burned: 5% + 25% = 30%
Important Considerations
- Approximation: The rule of fives is still an estimate. The actual TBSA burned can vary.
- Lund-Browder Chart: The Lund-Browder chart is generally considered more accurate, especially for children, and can be used in conjunction with or instead of the rule of fives, regardless of patient weight. This chart accounts for the changing proportions of body surface areas with age.
- Medical Expertise: TBSA estimations should always be performed by trained medical professionals. These estimations are crucial for fluid resuscitation and overall burn management.
