1. What is the Water Deficit Formula?

The Water Deficit Formula calculates the free water deficit (FWD) in hypernatremia, which estimates the amount of free water needed to correct serum sodium to normal levels (140 mmol/L).

2. How Does the Calculator Work?

The calculator uses the Water Deficit formula:

Where:

• \( FWD \) — Free Water Deficit (L)
• \( TBW \) — Total Body Water (L)
• \( Na \) — Serum Sodium (mmol/L)

Explanation: The formula estimates the volume of free water required to correct hypernatremia by normalizing serum sodium to 140 mmol/L.

3. Importance of Water Deficit Calculation

Details: Accurate water deficit calculation is crucial for proper management of hypernatremia, guiding fluid replacement therapy, and preventing complications from overly rapid correction.

4. Using the Calculator

Tips: Enter Total Body Water in liters, Serum Sodium in mmol/L. All values must be valid (TBW > 0, Na > 0).

5. Frequently Asked Questions (FAQ)

Q1: How is Total Body Water (TBW) estimated?
A: TBW is typically estimated as 60% of body weight in kg for men and 50% for women, though this varies with age and body composition.

Q2: What is the normal range for serum sodium?
A: Normal serum sodium ranges from 135-145 mmol/L. Values above 145 mmol/L indicate hypernatremia.

Q3: How quickly should water deficit be corrected?
A: Correction should be gradual, typically over 48-72 hours, with a maximum sodium correction rate of 0.5 mmol/L per hour to avoid cerebral edema.

Q4: Are there limitations to this formula?
A: This formula provides an estimate and doesn't account for ongoing losses. Clinical judgment and frequent monitoring are essential.

Q5: What fluids are used to correct water deficit?
A: Typically, hypotonic fluids like 5% dextrose in water or half-normal saline are used, depending on the clinical situation.