Expected sodium change per liter of fluid (Adrogué-Madias)
Predicts how much 1 liter of a chosen fluid will change serum sodium, and the volume to reach a safe target.
Inputs
1 of 6SexUsed by the equation
years
Actual (total) body weight
mEq/L
Fluid
Positive to raise, negative to lower.
mEq/L
Patient values are shared with every calculator.
When to use
- Planning saline for hyponatremia or free water for hypernatremia.
Pearls and pitfalls
- Limit correction of chronic hyponatremia to 8 mEq/L in 24 hours (lower if high ODS risk).
- The formula ignores ongoing losses and urine output; check sodium every 2 to 4 hours.
- Brisk water diuresis after the cause resolves can overcorrect quickly.
Why use
Turns a fluid choice into an expected sodium change you can check against the 24-hour limit.
ΔNa per L = (infusate Na + infusate K − serum Na) ÷ (TBW + 1); TBW = weight × 0.6 (men), 0.5 (women, older men), 0.45 (older women)