1. What is the Water Deficit Calculation?

The Free Water Deficit (FWD) calculation estimates the amount of free water needed to correct hypernatremia. It helps clinicians determine appropriate fluid replacement therapy for patients with elevated sodium levels.

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 equation calculates the volume of free water required to normalize serum sodium concentration to 140 mmol/L.

3. Importance of FWD Calculation

Details: Accurate FWD estimation is crucial for safe correction of hypernatremia, preventing complications from overly rapid sodium correction such as cerebral edema.

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 target rate for sodium correction?
A: Sodium should be corrected slowly, typically not faster than 0.5 mmol/L per hour or 10-12 mmol/L per 24 hours to avoid complications.

Q3: When should this calculation be used?
A: This calculation is used for patients with hypernatremia (Na > 145 mmol/L) to guide free water replacement therapy.

Q4: Are there limitations to this equation?
A: This formula assumes no ongoing water losses and may need adjustment for patients with significant ongoing fluid losses.

Q5: How should the calculated deficit be administered?
A: The calculated deficit is typically replaced over 48-72 hours with frequent monitoring of sodium levels and clinical status.