The Harris-Benedict formula, when used for burn patients, is typically modified by multiplying the basal metabolic rate (BMR) by activity and injury factors to estimate caloric needs.
While the original Harris-Benedict equation calculates BMR, its application to burn patients requires adjustments due to the hypermetabolic state induced by burn injuries. Therefore, it's used as a component within a larger calculation.
Here's how it works:
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Calculate Basal Metabolic Rate (BMR) using the Harris-Benedict Equation: The original Harris-Benedict equations are:
- For Men: BMR = 88.362 + (13.397 x weight in kg) + (4.799 x height in cm) - (5.677 x age in years)
- For Women: BMR = 447.593 + (9.247 x weight in kg) + (3.098 x height in cm) - (4.330 x age in years)
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Apply Activity Factor: This factor accounts for the patient's activity level before the burn. Examples include:
- Confined to bed: 1.2
- Ambulatory: 1.3
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Apply Injury Factor: This is crucial for burn patients to account for the increased metabolic demands due to the burn. The injury factor varies depending on the severity of the burn (Total Body Surface Area or TBSA). The reference mentions:
- Use of a global "injury factor".
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Calculate Total Energy Expenditure (TEE): TEE = BMR x Activity Factor x Injury Factor
Important Considerations:
- Variability: The Harris-Benedict equation, even with adjustments, may not be the most accurate predictor of energy expenditure in burn patients. Indirect calorimetry is often considered the gold standard for determining energy needs.
- Other Formulas: The provided reference also mentions the Toronto formula, which is another, more complex, equation specific to burn patients, incorporating TBSA, energy intake, body temperature, days post-burn, and the Harris-Benedict equation. This highlights that several formulas are used, and the Harris-Benedict is often just one component.
- Individualization: Regardless of the formula used, nutritional support should be individualized based on the patient's response, clinical status, and monitoring parameters.
Therefore, while a direct "Harris-Benedict formula for burns" doesn't exist as a single equation, the original Harris-Benedict formula is used to calculate the BMR, which is then factored into a larger calculation that accounts for activity and the burn injury. The overall estimated energy expenditure is then used to guide nutrition for burn patients.
