Free Water Deficit Calculator
Calculate free water deficit for hypernatremia correction and fluid replacement therapy
Calculate Free Water Deficit
Select patient category to determine total body water coefficient
Patient's current body weight
Laboratory serum sodium measurement
Target sodium level (normal: 135-145 mEq/L)
Free Water Deficit Results
Formula used: FWD = TBW × ((Current Na ÷ Desired Na) - 1)
Calculation: Enter values to see calculation
TBW coefficient: 60% for adult male
Example Calculation
Patient: 70 kg adult male with serum sodium 147 mEq/L
TBW: 70 kg × 0.6 = 42 L
FWD: 42 × ((147 ÷ 140) - 1) = 42 × 0.05 = 2.1 L
Result: Patient needs 2.1 liters of free water replacement
TBW Coefficients
These coefficients represent the percentage of body weight that is water
Sodium Reference Ranges
Normal
135-145 mEq/L
Mild Hypernatremia
146-149 mEq/L
Moderate Hypernatremia
150-159 mEq/L
Severe Hypernatremia
≥160 mEq/L
Correction Guidelines
Chronic Hypernatremia
Correct at 0.5 mEq/L per hour
Acute Hypernatremia
Correct at 1-2 mEq/L per hour
Avoid Rapid Correction
Risk of cerebral edema
Understanding Free Water Deficit
What is Free Water Deficit?
Free water deficit is the volume of water needed to correct hypernatremia by diluting sodium to normal levels. It's essential for fluid replacement therapy in dehydrated patients.
Clinical Applications
- •Hypernatremia management
- •Dehydration assessment
- •Fluid replacement planning
- •ICU fluid management
Calculation Steps
- Calculate Total Body Water (TBW) = Weight × Coefficient
- Determine sodium ratio = Current Na ÷ Desired Na
- Apply formula: FWD = TBW × (Ratio - 1)
- Plan correction rate based on chronicity
Important Considerations
- • TBW varies by age, sex, and body composition
- • Chronic cases require slower correction
- • Monitor for signs of cerebral edema
- • Adjust for ongoing losses
⚠️ Medical Disclaimer
This calculator is for educational and reference purposes only. It should not replace professional medical judgment, clinical assessment, or established treatment protocols.
Healthcare providers must:
- Consider patient-specific factors and comorbidities
- Monitor electrolytes and neurological status closely
- Adjust correction rates based on clinical response
- Account for ongoing fluid losses and requirements
- Follow institutional protocols for hypernatremia management
Always consult with a physician or qualified healthcare provider before making any treatment decisions.