💧 Free Water Deficit (Hypernatraemia)
Estimate the free water deficit in hypernatraemia to plan fluid replacement.
Free Water Deficit (Hypernatraemia)
Weight (kg)
Current sodium (mmol/L)
Total body water factor
When to use
Guide water replacement in hypernatraemia.
How it works
Deficit = TBW × (Na/140 − 1), where TBW = body-water factor × weight (0.6 male, 0.5 female/elderly).
Key points
- Add ongoing and insensible losses to the calculated deficit.
- Lower sodium by ≤ 10–12 mmol/L per 24 h in chronic cases.
- Over-rapid correction risks cerebral oedema.
References
Decision support for licensed clinicians only; not a substitute for clinical judgement, diagnosis or local protocols.