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(Young male: 0.60 | Elderly male: 0.50 | Young female: 0.50 | Elderly female: 0.45)
Free Water Deficit (L) = TBW × [(Na_current / Na_target) − 1]
Correction rate (chronic): ≤0.5 mEq/L/hr; max 8–10 mEq/L per 24h
Correction rate (acute, <48h): up to 1–2 mEq/L/hr
Endocrinology
Free Water Deficit — Hypernatremia Management
Calculate free water deficit and correction rate for hypernatremia
Please enter sodium between 130 and 200 mEq/L.
Please enter target sodium between 135 and 145 mEq/L.
Please enter weight between 1 and 200 kg.
TBW Fractions Used:
Young male: 0.60 | Elderly male: 0.50
Young female: 0.50 | Elderly female: 0.45
Young female: 0.50 | Elderly female: 0.45
✓ Free Water Deficit Results
⚠ Monitoring: Check serum sodium every 2–4 hours during active correction. Avoid over-rapid correction (risk of cerebral oedema). Add 30–40 mL/hr to the calculated rate for ongoing insensible losses.
Hypernatremia Severity Reference
| Na (mEq/L) | Severity | Symptoms | Action |
|---|---|---|---|
| 145–149 | Mild | Thirst, malaise | Oral rehydration |
| 150–159 | Moderate | Weakness, lethargy | Oral or IV rehydration |
| 160–169 | Severe | Confusion, seizure risk | IV D5W, slow correction |
| ≥170 | Critical | Coma, herniation risk | ICU, careful IV D5W |
Formulas
TBW (L) = TBW_fraction × Weight (kg)(Young male: 0.60 | Elderly male: 0.50 | Young female: 0.50 | Elderly female: 0.45)
Free Water Deficit (L) = TBW × [(Na_current / Na_target) − 1]
Correction rate (chronic): ≤0.5 mEq/L/hr; max 8–10 mEq/L per 24h
Correction rate (acute, <48h): up to 1–2 mEq/L/hr
