Free Water Deficit
Estimates the water volume needed to correct hypernatremia.
When to use
Adults with hypernatremia to plan free water replacement with gradual correction.
Pearls and pitfalls
- Total body water is estimated at 60% of weight in young men, 50% in young women and 45% to 50% in older adults.
- Correct hypernatremia slowly, usually with a fall of up to 10 mmol/L in 24 hours.
- The deficit is an estimate and should be reassessed with serial sodium and fluid balance.
- Do not replace the whole deficit at once; adjust for ongoing losses and clinical conditions.
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Formula
Free water deficit (L) = total body water (fraction × weight) × (sodium/140 − 1).
Evidence
Estimate based on total body water and serum sodium, described in hypernatremia management.
References
- Adrogue HJ, Madias NE. Hypernatremia. N Engl J Med. 2000;342(20):1493-1499. doi:10.1056/NEJM200005183422006
Frequently asked questions
What is Free Water Deficit?
Estimates the water volume needed to correct hypernatremia. Adults with hypernatremia to plan free water replacement with gradual correction.
How is the result calculated?
Free water deficit (L) = total body water (fraction × weight) × (sodium/140 − 1).
How should the result be interpreted?
Estimate based on total body water and serum sodium, described in hypernatremia management.
What are the sources?
Adrogue HJ, Madias NE. Hypernatremia. N Engl J Med. 2000;342(20):1493-1499.