Free Water Deficit in Hypernatremia & Safe Hourly Infusion Calculator

Estimate TBW × ((Current Na / Target Na) − 1) in liters and mL/hr.

Estimated Free Water Deficit
5.14 L
Total Body Water (TBW) 45 L
Safe Correction Horizon (≤0.5 mEq/L/hr) 32 hours
Deficit Replacement Rate (Excl. Insensible) 160.71 mL/hr
Inputs
kg
Patient body weight in kilograms.
fraction
Total body water fraction (0.6 adult male, 0.5 adult female/elderly).
mEq/L
Measured hypernatremic serum [Na⁺] in mEq/L.
mEq/L
Target serum [Na⁺] in mEq/L.
Results & Graph
Estimated Free Water Deficit
5.14 L
Total Body Water (TBW)
45 L
Safe Correction Horizon (≤0.5 mEq/L/hr)
32 hours
Deficit Replacement Rate (Excl. Insensible)
160.71 mL/hr

Estimated Free Water Deficit

Graph 1 • Body Weight Kg Sensitivity Recalculates the domain equation across 50% to 150% of the primary input while holding other parameters constant.
0 L 4.2 L 8.3 L 50%: 2.57 L 2.6 50% 75%: 3.86 L 3.9 75% 100%: 5.14 L 5.1 100% 125%: 6.43 L 6.4 125% 150%: 7.71 L 7.7 150%
Graph 2 • Primary & Supporting Metric Comparison Compares the primary output alongside supporting domain benchmarks.
Estimated Free Water Deficit 5.14 L Total Body Water (TBW) 45 L Safe Correction Horizon (≤0.5 mEq/L/hr) 32 hours Deficit Replacement Rate (Excl. Insensible) 160.71 mL/hr
Graph 3 • Exact Output Table & Units Displays each calculated output in its exact domain unit.
Estimated Free Water Deficit5.14 LTotal Body Water (TBW)45 LSafe Correction Horizon (≤0.5 mEq/L/hr)32 hoursDeficit Replacement Rate (Excl. Insensible)160.71 mL/hr
Summary: At TBW = 45 L and serum Na = 156 mEq/L, free water deficit is 5.14 L (5143 mL), replaced at ~161 mL/hr over 32 hrs (0.5 mEq/L/hr max rate).
Summary: At TBW = 45 L and serum Na = 156 mEq/L, free water deficit is 5.14 L (5143 mL), replaced at ~161 mL/hr over 32 hrs (0.5 mEq/L/hr max rate).
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Formula & Mathematical Methodology: Free Water Deficit Reference Equation

TBW = Weightkg × WaterFraction
FreeWaterDeficitL = TBW × [ (SerumNa / TargetNa) − 1 ]
TBW = Weight_kg × WaterFraction; FreeWaterDeficit_L = TBW × [ (Serum_Na / Target_Na) − 1 ]
  • bodyWeightKg: Body Weight Kg (kg)
  • totalBodyWaterFraction: Total Body Water Fraction (fraction)
  • currentSerumSodiumMeqL: Current Serum Sodium Meq L (mEq/L)
  • targetSerumSodiumMeqL: Target Serum Sodium Meq L (mEq/L)

Rounding: Laboratory and clinical equations retain full floating-point precision and round displayed results to 2 decimal places.

Worked Example: Reference Calculation: Free Water Deficit

Estimate TBW × ((Current Na / Target Na) − 1) in liters and mL/hr.

  1. Enter the reagent concentrations, assay readings, or clinical laboratory parameters.
  2. Compute the standard formula: TBW = Weight_kg × WaterFraction; FreeWaterDeficit_L = TBW × [ (Serum_Na / Target_Na) − 1 ].
  3. Review the primary result, supporting reference intervals, and 3 SVG visualizations.
Result: Evaluates Free Water Deficit via TBW = Weight_kg × WaterFraction; FreeWaterDeficit_L = TBW × [ (Serum_Na / Target_Na) − 1 ].

Frequently Asked Questions

What formula is used by the Free Water Deficit in Hypernatremia & Safe Hourly Infusion Calculator?

It computes TBW = Weight_kg × WaterFraction; FreeWaterDeficit_L = TBW × [ (Serum_Na / Target_Na) − 1 ] and plots three custom SVG graphs showing parameter sensitivity and component breakdowns.

Can I compare different reagent dilutions or lab scenarios side by side?

Yes. Use the "Compare (0/3)" button to pin up to 3 scenarios side by side.

Are entered values stored on any server?

No. Every calculation runs 100% locally in your browser.

Health & Fitness · Pharmacology & Critical Care

Free Water Deficit in Hypernatremia & Safe Hourly Infusion Calculator: inputs, method, and how to read the result

Estimate TBW × ((Current Na / Target Na) − 1) in liters and mL/hr.

Choose inputs for the case you are checking

The defaults are illustrative. Replace them with values for your case and keep the units shown beside each field.

  • Body Weight Kg: Patient body weight in kilograms.
  • Total Body Water Fraction: Total body water fraction (0.6 adult male, 0.5 adult female/elderly).
  • Current Serum Sodium Meq L: Measured hypernatremic serum [Na⁺] in mEq/L.
  • Target Serum Sodium Meq L: Target serum [Na⁺] in mEq/L.

What the calculation includes

With the default values shown, Estimated Free Water Deficit is 5.14 L. The calculation follows Free Water Deficit Reference Equation; the formula and variable definitions above show how the inputs combine.

One-input check: With the other defaults held constant, changing Body Weight Kg from 75 kg to 83 kg changes Estimated Free Water Deficit from 5.14 L to 5.69 L. This is a comparison inside the calculator's stated model, not a prediction.

Where to use caution

  • Uses standard IUPAC atomic weights, 25°C (298.15 K) reference thermodynamics, and published clinical literature equations.
  • Educational and laboratory reference tool only; clinical scoring calculators do not replace professional medical judgment or institutional protocols.

Scope: IUPAC / NIH Laboratory & Clinical Reference Standard Check the assumptions and limitations against your situation before relying on the estimate.

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