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Free water deficit in hypernatremia
Water needed to correct hypernatraemia.
Free water deficit in hypernatremia
Total body water fraction
Body weight
Measured serum sodium
mEq/L
Complete the fields above to see the result.
When to use
- Estimating the water deficit and replacement volume in a hypernatraemic patient.
Formula
Free water deficit (L) = TBW fraction x weight(kg) x (serum Na / 140 - 1).
Pearls and pitfalls
- The deficit accounts only for the existing water shortfall; ongoing insensible and urinary losses must be added.
- Overly rapid correction of chronic hypernatraemia risks cerebral oedema.