Sodium Correction Rate Calculator — Hyponatraemia Treatment
Calculate the intravenous fluid infusion rate required to raise serum sodium from its current value to a target in a specified time window. Based on the Adrogue-Madias equation, with real-time safety warnings when the projected 24-hour correction exceeds guideline limits.
mEq/L
mEq/L
kg
Patient type
Infusate
hrs
Within safe correction rate limit (≤10 mEq/L per 24 h)
- 1
Estimated total body water (TBW)
70 × 0.6 = 42 L - 2
ΔNa per litre of infusate
(513 − 120) ÷ (42 + 1) = 9.14Adrogue-Madias: sodium rise per litre of this infusate. - 3
Total sodium rise required
130 − 120 = 10 mEq/L - 4
Total volume to infuse
10 ÷ 9.14 × 1000 = 1,094 mL - 5
Infusion rate
1,094 mL ÷ 24 hr = 46
How does this calculator work?
Infusion rate (mL/hr) = [target ΔNa / ((Na_infusate − Na_serum)/(TBW+1))] × 1000 / hours. TBW = weight × 0.6 (adult males). Limit the sodium rise to ≤10 mEq/L per 24 h in chronic hyponatraemia to avoid osmotic demyelination syndrome. Use 3% saline for symptomatic cases; monitor serum sodium every 2–4 hours during active correction.
Formula
How this is calculated
The Adrogue-Madias equation predicts how much each litre of intravenous fluid will change the serum sodium: ΔNa per litre = (Na_infusate − Na_serum) / (TBW + 1). From this, the total volume needed to achieve the desired rise is calculated: total volume (L) = target ΔNa / ΔNa per litre. Dividing by the number of hours gives the infusion rate in L/hr (or mL/hr after multiplying by 1000).
For hyponatraemia, the choice of infusate matters greatly. Isotonic saline (154 mEq/L) raises sodium only modestly unless the patient's sodium is very low or TBW is large. Hypertonic 3% saline (513 mEq/L) is effective at low infusion rates and is the standard rescue fluid for symptomatic severe hyponatraemia. The calculator supports both, along with half-normal saline (used when a slower, gentler rise is needed) and 5% saline for extreme cases.
The most critical safety constraint in treating hyponatraemia is the rate of sodium rise. Raising sodium too quickly in chronic hyponatraemia (>48 hours' duration) risks osmotic demyelination syndrome (ODS), also called central pontine myelinolysis — a potentially fatal or permanently disabling neurological condition caused by rapid shifts in brain cell volume. Guidelines (2014 European Hyponatraemia Guidelines; US expert consensus) recommend a maximum rise of 10–12 mEq/L in the first 24 hours and 18 mEq/L in 48 hours for most patients, with even stricter limits (8 mEq/L per 24 h) for those at highest ODS risk (alcoholism, malnutrition, liver disease, hypokalaemia). This calculator highlights corrections that exceed these limits and is intended as a decision-support tool only.
Frequently asked questions
In chronic (>48 h) hyponatraemia, brain cells adapt to low sodium by exporting osmolytes (taurine, myoinositol, potassium), reducing intracellular osmolality to prevent swelling. Rapidly restoring sodium causes these osmolytes to re-enter slowly while water follows sodium quickly, shrinking brain cells and stripping myelin from pontine axons — osmotic demyelination syndrome. Acute hyponatraemia (<48 h, clearly documented) has not allowed time for adaptation and can be corrected more quickly.
3% saline contains 513 mEq/L of sodium — about 3.3 times the concentration of normal saline. It is used in symptomatic severe hyponatraemia (seizures, coma, respiratory failure) to achieve a rapid initial rise of 1–2 mEq/L/hr for the first 2–3 hours. It is usually given through a central line and requires ICU-level monitoring. Once symptoms resolve, the rate is reduced to stay within 24-hour safety limits.
Over-rapid correction risks ODS: dysarthria, dysphagia, spastic quadriparesis and an "locked-in" state can develop 2–6 days after treatment. If overcorrection is detected (sodium rising faster than the target rate), it can sometimes be partially reversed by re-lowering sodium with hypotonic fluids or desmopressin — a strategy that requires specialist input immediately.
Also known as
TG we-Calculate Editorial Team. (2026). Sodium Correction Rate Calculator — Hyponatraemia Treatment [Online calculator]. TG we-Calculate. https://we-calculate.com/calculator/sodium-correction-rate-calculator
TG we-Calculate Editorial Team. "Sodium Correction Rate Calculator — Hyponatraemia Treatment." TG we-Calculate. 2026. https://we-calculate.com/calculator/sodium-correction-rate-calculator.
TG we-Calculate Editorial Team, "Sodium Correction Rate Calculator — Hyponatraemia Treatment," TG we-Calculate, 2026. [Online]. Available: https://we-calculate.com/calculator/sodium-correction-rate-calculator
@misc{wecalculate_sodium_correction_rate_calculator, title = {Sodium Correction Rate Calculator — Hyponatraemia Treatment}, author = {{TG we-Calculate Editorial Team}}, howpublished = {\url{https://we-calculate.com/calculator/sodium-correction-rate-calculator}}, year = {2026}, note = {TG we-Calculate} }
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