Correcting hyponatremia too quickly is one of the few harms in medicine that's almost entirely preventable by pacing the plan correctly. This calculator turns a current sodium, a target sodium, and a correction window into a rate you can check against widely cited safe limits, and estimates how much of a given IV fluid is needed using the Adrogué-Madias equation.
Why correction rate matters
Hyponatremia causes brain cells to swell as water shifts to balance the lower extracellular sodium concentration. Over hours to days, brain cells adapt by extruding osmoles and shrink back toward normal volume. If chronic hyponatremia is then corrected too quickly, the brain — now adapted to a lower osmolality — can lose water faster than it can re-accumulate osmoles, causing myelin damage in the pons and elsewhere: osmotic demyelination syndrome (ODS). The safe correction limit exists specifically to give brain cells time to re-equilibrate.
Most guidelines cite a limit of roughly 8 mEq/L per 24 hours for higher-risk patients and up to 10-12 mEq/L per 24 hours for lower-risk patients, with a further absolute cap of about 18 mEq/L over 48 hours. This calculator applies the more conservative 8/10 mEq/L per 24h thresholds by default.
Inputs and what they mean
Current sodium and target sodium (mEq/L) define the planned total change; correction window (hours) spreads that change over time to produce a rate. On the Fluid Volume tab, weight and sex estimate total body water, and the IV fluid selection sets the infusate's sodium concentration used in the Adrogué-Madias equation.
The Adrogué-Madias equation assumes a closed system with no ongoing free-water losses (for example, from a large osmotic diuresis in hyperglycemia, or after relief of urinary obstruction) — in practice, actual sodium rise can outpace the estimate in these settings, which is exactly why frequent lab rechecks matter more than the initial plan.
Limits and edge cases
This calculator is a planning aid, not a substitute for serial serum sodium measurements — actual correction rate depends on ongoing renal water handling, which can change unpredictably (for example, a sudden water diuresis as vasopressin suppression occurs). It does not account for patient-specific ODS risk factors such as alcohol use disorder, malnutrition, liver disease, hypokalemia, or a baseline sodium below 105 mEq/L, all of which argue for a more conservative target. It also does not model acute (well-tolerated, symptomatic within 48 hours) hyponatremia, where faster initial correction may be appropriate under close monitoring. Always interpret results alongside frequent lab monitoring and clinical judgment.