Renal & Electrolytes

Sodium Deficit Calculator

Sodium needed to reach a target level, from total body water; correct slowly to avoid osmotic demyelination.

Reviewed by Alex G, BSN, RN, CEN, CCRN, CMC, NREMT-P · From the Reference tab of the app

Turn on JavaScript to use this calculator, or open it in the web app.

Formula

TBW * (Target Na - Current Na)

How it is used

• Total body water is about 60% of weight in younger men and 50% in younger women; use 50% and 45% in older men and women.
• Chronic hyponatremia: raise sodium by no more than 8 mEq/L in any 24 h (the exam-safe answer; guideline upper limits run 10–12) to avoid osmotic demyelination.
• The deficit ignores ongoing losses and water shifts; the Adrogué–Madias calculator predicts the change per liter, and serial sodium checks guide the rate.

Same formula as the app. Open it in the web app.

Related one-pagers

• Electrolyte ImbalancesHypernatremia is always hypertonic and nearly always a water deficit in someone who cannot drink. ICU causes: fever, osmotic diuresis (glucose, mannitol, high-protein feeds), loop diuretics, lactulose and sodium loads (bicarbonate, hypertonic saline).
• DKA and HHSFluid restores perfusion and GFR, lowers counter-regulatory hormones and improves insulin sensitivity; alone it lowers glucose about 50–70 mg/dL per hour (2024 consensus). After 500–1,000 mL/h for 2–4 h (about 1 L/h in severe hypovolemia), the rate follows blood pressure, heart rate, urine output and sodium, replacing half the deficit in 8–12 h and the rest by 24–48 h (2024 consensus and Fig. 4). The 2009 consensus then switched to 0.45% saline at 250–500 mL/h if corrected sodium was normal or high.
• Toxidromes and AntidotesLithium (label target 0.8–1.2 mEq/L) is handled like sodium, so dehydration, AKI, thiazides, ACE inhibitors, ARBs and NSAIDs raise levels. Acute overdose in a lithium-naive patient causes vomiting and diarrhea with high levels that redistribute; chronic toxicity causes tremor, hyperreflexia, ataxia, confusion and seizures at lower levels, because lithium is already in the brain. Give isotonic saline, stop interacting drugs, irrigate the bowel for large sustained-release ingestions (charcoal does not bind lithium) and dialyze by EXTRIP; cerebellar deficits can persist (label).
• ABG Interpretation in 6 Steps

Related calculators

• Anion Gap
• BUN/Cr Ratio
• Corrected Calcium
• Corrected Sodium (Hyperglycemia)
• Creatinine Clearance (Cockcroft-Gault)
• CRRT Effluent Dose (mL/kg/h)
• Fractional Excretion of Sodium (FENa)
• Fractional Excretion of Urea (FEUrea)

For education and exam preparation only. Follow your institution’s protocols. For education and exam preparation only. Verify results independently and follow your institution’s protocols. Not a substitute for clinical judgment.