Medical calculators
Free Water
Free Water Deficit
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Anatium is a study resource, not medical advice. Nothing here is a diagnosis, a prescription or a substitute for a clinician who has seen the patient. Check every number against a current local protocol before it touches anyone, and never act on a result you cannot reproduce yourself.
How it is calculated
Free Water Deficit = TBW × ((Na/140) - 1). TBW ≈ 0.6 × weight (male) or 0.5 × weight (female). Lower sodium by no more than about 0.5 mmol/L per hour and 10 mmol/L per day where hypernatraemia has lasted over 48 hours or its duration is unknown, and add ongoing losses to this deficit.
About
How much water-only replacement a hypernatraemic patient needs, and over what time.
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