Free Water Deficit Calculator
Calculate fluid replacement needs for hypernatremic patients
Patient Parameters
Calculation Results
About Free Water Deficit
What is Hypernatremia?
Hypernatremia is defined as serum sodium concentration >145 mmol/L. It represents a deficit of water relative to sodium in the extracellular fluid. This condition often occurs in patients with inadequate water intake, excessive water loss, or both.
Calculation Formula
The free water deficit is calculated using the Adrogue-Madias formula:
Where Total Body Water (TBW) is estimated as:
- Adult Males: TBW = Weight (kg) × 0.6
- Adult Females: TBW = Weight (kg) × 0.5
- Elderly Males: TBW = Weight (kg) × 0.5
- Elderly Females: TBW = Weight (kg) × 0.45
- Children: TBW = Weight (kg) × 0.65
Clinical Considerations
Rate of Correction: Hypernatremia should be corrected slowly to avoid cerebral edema. The maximal rate of sodium correction should not exceed 0.5 mmol/L per hour or 12 mmol/L per 24 hours.
Fluid Selection: The preferred fluid for replacement is water, either orally or intravenously as 5% dextrose in water (D5W).
Monitoring: Serum sodium should be monitored every 2-4 hours during acute correction. Adjust fluid administration based on patient response and ongoing losses.
References & Clinical Guidelines
- Adrogue HJ, Madias NE. Hypernatremia. N Engl J Med. 2000;342(20):1493-1499.
- Sterns RH. Disorders of plasma sodium. N Engl J Med. 2015;372(1):55-65.
- Palevsky PM, et al. KDOQI Clinical Practice Guideline for Hemodialysis Adequacy: 2015 update.
- Al-Absi A, Gosmanova EO. A clinical approach to the treatment of chronic hypernatremia. Am J Kidney Dis. 2020;76(1):143-150.