Free Water Deficit
Estimates the water deficit underlying hypernatremia, as a starting point for correction planning.
Formula
Free water deficit = Total body water fraction × Weight × (Current Na / 140 − 1)
Result
Enter all values to see the result.
Limitations
- Uses a fixed total-body-water fraction by sex (0.6 male, 0.5 female) and does not adjust for age or body composition, both of which shift true total body water.
- Estimates the total deficit only — it does not specify a safe correction rate, which must be limited separately (commonly no more than 8–10 mEq/L per 24 hours to avoid cerebral edema from overly rapid correction).
- Does not account for ongoing free water losses (e.g. diabetes insipidus, osmotic diuresis) that continue during correction.
References
- Standard total-body-water-based free water deficit formula; used alongside Corrected Sodium and safe correction-rate limits.
Clinical Context & Relevant Topics (3)
Disease ReferenceTonicity assessment, etiologic classification, 3% hypertonic saline bolus protocols, individualized ODS-safe correction limits, DDAVP relowering, DI diagnostics, and evidence-aware hypernatremia correction.
Bedside recognition and organ-support priorities for thyroid storm, myxedema coma, adrenal crisis, pheochromocytoma crisis, and severe hypercalcemia.
Sepsis-AKI microcirculatory decoupling, KDIGO staging, Furosemide Stress Test (FST), urine microscopy, and the AEIOU dialysis threshold framework.
Relevant Clinical Pathways (8)
Decision ProtocolsFrom urgent 'AEIOU' indication screening and modality selection to vascular access, dosing, and anticoagulation.
From emergent cardiac membrane stabilization to intracellular shifting, elimination, and dialysis triggers.