How this calculator works
The Adrogue-Madias equation estimates the effect of one litre in a closed system. Potassium in the infusate is included. Scaling this change to an hourly flow is only an initial mathematical approximation; urine output, ongoing losses and changes in body water can make actual sodium changes very different. The user supplies the desired change. No safe rate or regimen is selected. The result is an estimate for information only and is not medical advice.
Formula
Change after 1 L = (infusate Na + infusate K - serum Na) / (TBW + 1). Approximate rate (mL/h) = specified hourly change / change after 1 L × 1000. TBW = weight × selected water fraction.
Worked example
At 70 kg and a 0.60 fraction, TBW is 42 L. Serum Na 120 and fluid Na 154 with no K give 34/43 = 0.790698 mmol/L after 1 L. A specified 0.25 mmol/L/h corresponds mathematically to 316.176 mL/h.
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Frequently asked questions
Does this recommend a safe correction limit?
No. Appropriate targets depend on symptoms, duration and clinical risk. Monitoring and reassessment are essential.
Why enter fluid composition directly?
Sodium and potassium content vary by product and additives. Use the composition on the prescribed solution label.
What does the older-adult option mean?
The cited adult review subtracts five percentage points from the usual 0.60 male or 0.50 female fraction. Custom fractions require clinical judgement.