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Fluids & Electrolytes

Free Water Deficit (Hypernatraemia)

Estimates the free-water deficit in a hypernatraemic child, to guide the volume needed to return sodium to 140 mEq/L.

Scope: Uses TBW = 0.6 × weight (term infants/children). Neonates and the elderly use different fractions. Add maintenance + ongoing losses separately.

Inputs

FieldUnitNotes
Weight kg 0.5–150
Measured sodium mEq/L 145–200
Total body water fraction Young infants run a higher TBW

FAQ

What is the Free Water Deficit (Hypernatraemia)?

Estimates the free-water deficit in a hypernatraemic child, to guide the volume needed to return sodium to 140 mEq/L.

What inputs does the Free Water Deficit (Hypernatraemia) need?

Weight (kg), Measured sodium (mEq/L), Total body water fraction.

Are there any limitations?

Uses TBW = 0.6 × weight (term infants/children). Neonates and the elderly use different fractions. Add maintenance + ongoing losses separately.

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