Free Water Deficit
Estimates free water needed to correct hypernatremia based on total body water and measured sodium
- Highest activation tier
- Recommended
- How it is scored
- Scored in code; a stated value is compared only from the structured summary or a supplied value
- Scoring type
- formula
- Care settings
- ICU, Inpatient
When it activates
Scribeable activates a calculator from the encounter. The Free Water Deficit can activate when the transcript or pasted chart context documents any of these:
- Hypernatremia requiring correction
- Sodium >145 mEq/L
- Dehydration with elevated sodium
- Free water replacement planning
A coded diagnosis can also activate it. ICD-10 prefixes carried by the registry: E23.2, E87.0.
Inputs the note needs
3 inputs. Each is resolved from the transcript, the pasted chart context and charted labs; at this calculator’s tier a missing input is never requested, and a missing required input keeps the score out of the draft.
| Input | Type | Unit / options | Guidance |
|---|---|---|---|
| Measured serum sodium in mEq/L | lab | mEq/L | |
| Body weight in kilograms | vital | kg | |
| Biological sex (TBW factor: 0.6 men, 0.5 women) | history |
Scoring
Free water deficit (L) = TBW × ((Na / 140) − 1); TBW = weight_kg × 0.6 (men) or 0.5 (women)
Free H₂O deficit = (0.6 if male else 0.5) × Body weight in kilograms × ((Measured serum sodium in mEq/L/140) − 1); sex=Biological sex (TBW factor: 0.6 men, 0.5 women)
Interpretation
Replace deficit gradually: target Na decrease ≤10–12 mEq/L per 24 hours to avoid cerebral edema. Account for ongoing insensible losses. Use D5W or enteral free water. Recheck Na every 4–6 hours during active correction. In elderly patients, use TBW factor 0.5 for men, 0.45 for women.
Evidence
Sources carried in Scribeable's citation registry for this calculator; guideline version: Adrogue-Madias 2000.
- Adrogue HJ, Madias NE. Hypernatremia (Free Water Deficit calculation)Adrogue & Madias (Free Water Deficit) 2000 · 2000 · link last verified 2026-03-28
How Scribeable handles it in the note
When an encounter activates the Free Water Deficit (its highest tier is recommended), Scribeable does not ask you for missing inputs. The score is computed in code from whatever inputs resolve from the transcript, the pasted chart context or charted labs; a computed value is written into the draft only when every required input already resolves.
The score is computed in code from the resolved inputs, not recalled by the language model. A stated Free Water Deficit value is compared against the computed one when the draft's structured summary carries it; a disagreement found there is flagged to the second drafting pass, which is instructed to correct the score and its interpretation, unless Scribeable has supplied the computed value to that pass, in which case the value the draft writes is checked against the supplied one and a detected difference is shown beside the note for you to adjudicate rather than silently rewritten.
Classified as a deterministic formula: a spare suggestion is easy to ignore, so activation is permissive.
See it activate on your own encounter
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