You calculate fluid overload, expressed as percent fluid overload (%FO), using a specific formula that considers fluid intake, output, and baseline body weight.
Fluid Overload Calculation Formula
The formula for calculating percent fluid overload (%FO) is:
%FO = [∑ daily (fluid intake (L) - total output (L)) / baseline body weight (in kilograms)] x 100
- ∑ daily (fluid intake (L) - total output (L)): This part calculates the cumulative daily fluid balance. You subtract the total fluid output (e.g., urine, drainage) from the total fluid intake (oral, intravenous) each day and sum these daily differences over the period you're assessing.
- Baseline body weight (in kilograms): This is the patient's weight before the period of fluid accumulation. It's crucial for normalizing the fluid imbalance to the individual's body size.
- x 100: This converts the result into a percentage.
Example Calculation
Let's say we want to calculate the %FO for a patient:
- Baseline body weight: 70 kg
- Day 1: Fluid intake = 3L, Fluid output = 2L
- Day 2: Fluid intake = 2.5L, Fluid output = 1.5L
- Day 3: Fluid intake = 2L, Fluid output = 2L
- Calculate daily fluid balance:
- Day 1: 3L - 2L = 1L
- Day 2: 2.5L - 1.5L = 1L
- Day 3: 2L - 2L = 0L
- Sum the daily fluid balances: 1L + 1L + 0L = 2L
- Apply the formula:
- %FO = [2L / 70 kg] x 100 = 2.86%
In this example, the patient has a fluid overload of 2.86%.
Importance of Accurate Measurement
Accurate measurement of both fluid intake and output is crucial for accurate fluid overload calculation. This includes all sources of intake (oral, IV, medications) and all routes of output (urine, stool, drains, emesis).
