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Free Water Deficit Calculator

About this Calculator

The Free Water Deficit calculator helps clinicians determine the amount of free water needed to correct hypernatremia. This calculation is essential for safe and effective treatment of disorders of sodium concentration. The calculator uses patient demographics to estimate total body water (TBW) percentage, along with current and target sodium levels, to compute the water deficit or excess.

Free Water Deficit (L) = TBW × Weight × ( Current Na⁺ Target Na⁺ - 1)

Interpretation of Results

  • Negative Result: Indicates a free water deficit. The calculated value represents the amount of free water needed to correct the hypernatremia. Treatment should be administered gradually to prevent rapid changes in serum sodium.

  • Positive Result: Indicates water excess. This suggests the need for water restriction or other interventions to correct hyponatremia.

  • Clinical Considerations: The correction rate for sodium should not exceed 10-12 mEq/L in 24 hours to prevent central pontine myelinolysis. Consider dividing the calculated deficit into portions for safer administration over 48-72 hours.

kg
mEq/L
mEq/L
Free Water Deficit
-
 
Total Body Water Percentages
Adult Male: 60%
Adult Female: 50%
Elderly Male: 50%
Elderly Female: 45%
Child: 60%

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