How fast can serum sodium be safely corrected?

In chronic hyponatraemia, serum sodium should rise by no more than about 8 mEq/L in any 24-hour period, and 6 mEq/L in patients at high risk of osmotic demyelination such as those with alcoholism, malnutrition, hypokalaemia or advanced liver disease. Correcting faster risks osmotic demyelination syndrome.

What is the Adrogue-Madias formula?

The Adrogue-Madias formula predicts the change in serum sodium from one litre of a chosen infusate: delta sodium equals (infusate sodium plus infusate potassium minus serum sodium) divided by (total body water plus one). It lets you estimate the infusion rate needed to raise sodium by a target amount.

What is osmotic demyelination syndrome?

Osmotic demyelination syndrome, formerly called central pontine myelinolysis, is irreversible brain injury caused by overly rapid correction of chronic hyponatraemia. Symptoms include dysarthria, dysphagia, quadriparesis and locked-in syndrome, often appearing days after the correction. Slow, monitored correction prevents it.

Why does potassium appear in the formula?

Replacing a potassium deficit raises serum sodium too, because potassium is osmotically active and shifts water. The Adrogue-Madias formula adds infusate potassium to infusate sodium so that potassium replacement is accounted for, preventing inadvertent overcorrection.

Does the formula account for ongoing urine losses?

No. The Adrogue-Madias formula assumes a closed system and ignores ongoing renal water and electrolyte losses. When a patient begins a brisk water diuresis, sodium can rise far faster than predicted, so frequent re-measurement every 2 to 4 hours during active correction is essential.

What is the Hyponatraemia Correction Rate Calculator?

Calculate a safe sodium correction rate for hyponatraemia (no more than 6 to 8 mEq/L per 24 hours) and the infusion rate of hypertonic, normal or half-normal saline using the Adrogue-Madias formula. Helps prevent osmotic demyelination syndrome. It runs free in your browser on Gera Tools, with nothing uploaded.

Hyponatraemia Correction Rate Calculator

Name: Hyponatraemia Correction Rate Calculator
Creator: Gera Tools
License: https://creativecommons.org/licenses/by/4.0/

Get one useful tool a week

Like this tool? Enter your email and we'll send you one genuinely useful Gera tool a week — plus a link to come back to this one. No spam, one-click unsubscribe any time.

Safe sodium correction for hyponatraemia

The danger in treating chronic hyponatraemia is not the low sodium itself but correcting it too quickly, which can cause irreversible osmotic demyelination syndrome. This calculator does two things: it states the maximum safe 24-hour rise for the patient, and it uses the Adrogué–Madias formula to estimate the infusion rate of a chosen saline that will reach that target without overshooting.

How it works

The safe ceiling is a fixed clinical limit. This tool uses 8 mEq/L per 24 hours as the standard cap and a stricter 6 mEq/L per 24 hours for patients at high demyelination risk — those with alcoholism, malnutrition, liver disease, or severe hypokalaemia.

The infusion side uses Adrogué–Madias to predict how much one litre of infusate will move the sodium:

ΔNa per litre = (infusate_Na + infusate_K − serum_Na) / (TBW + 1)
TBW = weight_kg × factor   (male 0.6, female 0.5, elderly 0.5 / 0.45)

Dividing the daily target by ΔNa per litre gives the litres of infusate to run over 24 hours, and dividing by 24 gives the hourly rate. Hypertonic 3% saline (513 mEq/L Na) raises sodium fastest per litre; normal 0.9% saline (154 mEq/L) raises it more gently; 0.45% saline may not raise it at all if the patient is excreting concentrated urine.

Which infusate to choose

The Adrogué–Madias formula makes the choice explicit by showing the predicted rise per litre for each option:

Infusate	Sodium content	Typical use case
3% NaCl	513 mEq/L	Symptomatic hyponatraemia needing urgent correction
0.9% NaCl	154 mEq/L	Hypovolaemic hyponatraemia; milder deficits
0.45% NaCl	77 mEq/L	Rarely used; may worsen hyponatraemia in some patients

If the patient also needs potassium replacement, the formula’s infusate_K term captures its contribution to serum sodium, preventing inadvertent overcorrection when potassium is replaced alongside saline.

Worked example

A 70 kg man (TBW = 42 L) with serum sodium of 115 mEq/L and potassium of 4.0 mEq/L:

ΔNa per litre of 3% saline = (513 + 0 − 115) / (42 + 1) = 398 / 43 ≈ 9.3 mEq/L per litre
Target rise 8 mEq/L in 24 hours → 8 / 9.3 ≈ 0.86 litres over 24 hours ≈ 36 mL/hr

Running 3% saline at roughly 36 mL/hr for 24 hours is expected to raise sodium by about 8 mEq/L — right at the safe limit. In practice, start lower and re-check every 2-4 hours.

Critical monitoring notes

Treat the predicted rate as a starting point, not a guarantee. The formula assumes a closed system — it ignores ongoing urinary water and electrolyte losses. The most common cause of inadvertent overcorrection is a brisk water diuresis that begins once circulating volume is restored (SIADH correction, resolution of pain or nausea, or glucocorticoid administration). If the sodium is rising faster than planned, administer DDAVP and electrolyte-free water to slow the rise. Frequent measurement — every 2 to 4 hours during active correction — is not optional; it is the safety check the formula cannot replace.