Renal Emergency Medicine Anaesthesia / Critical Care Standard — widely used clinical formula

Free Water Deficit in Hypernatraemia

Calculates the estimated free water deficit in patients with hypernatraemia to guide fluid replacement therapy.

Score interpretation

Mild Free Water Deficit (< 2 L) 0–2

Estimated free water deficit < 2 L.

→ Oral rehydration if patient can drink. If IV: 5% dextrose or 0.45% NaCl. Correct sodium no faster than 10–12 mmol/L per 24h to avoid cerebral oedema. Monitor Na⁺ every 4–6h.

Moderate Free Water Deficit (2–5 L) 2–5

Estimated free water deficit 2–5 L. Significant hypernatraemia.

→ IV fluid replacement required. Target correction rate 10–12 mmol/L/24h (0.5 mmol/L/hour maximum). Use 5% dextrose or 0.45% NaCl. Identify and treat underlying cause (DI, diarrhoea, inadequate intake).

Severe Free Water Deficit (> 5 L) ≥ 5

Severe hypernatraemia with large free water deficit.

→ HDU/ICU monitoring. Slow correction essential — rapid correction risks cerebral oedema. Nephrology/endocrinology review if central or nephrogenic DI suspected. Vasopressin (desmopressin) if central DI.

Interpretation bands for the Free Water Deficit. Apply clinical judgement and local guidance.

References

Adrogue HJ, Madias NE. Hypernatremia. N Engl J Med. 2000;342(20):1493–1499.

Curated clinical cross-links plus same-class fallbacks.

Calculators

Drugs

Pathways

Decision support only — verify against a current formulary, NICE, or your local guideline before clinical use.

Score interpretation

References

Related