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Fluid Deficit Calculator

Estimate the free water deficit in patients with hypernatremia (high sodium).

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Formula

TBW * (1 - (Target Na / Current Na))

Calculates the volume of water needed to return serum sodium to a target level.

Worked Example

70kg Male, 160 Na, Target 140 -> ~6.1 L water deficit.

Frequently Asked Questions

What is the goal of free water replacement?

The goal is to safely lower serum sodium. Correcting too quickly can cause cerebral edema, so a standard target is often a 10-12 mEq/L drop per 24 hours.

What is TBW?

Total Body Water (TBW) is the estimated percentage of body weight that is water. It varies by gender and age (Adult Male: 0.6, Female: 0.5; Elderly Male: 0.5, Female: 0.45).

How should the deficit be replaced?

Deficits are usually replaced over 48-72 hours using oral water or IV D5W, following institutional protocols.

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