Adrogué–Madias Predicted Sodium Change Calculator

Overview

Estimates the change in serum sodium after one litre of an infusate using the Adrogué–Madias equation. The calculator is intended to make the underlying equation transparent while preserving the requirement for clinical assessment and source-data verification.

Clinical Significance

The equation provides an initial estimate only. Actual sodium change can differ substantially because of urine electrolyte losses, ongoing water gain or loss, changing vasopressin activity and treatment dynamics.

When to Use

• Plan an initial fluid strategy for dysnatraemia with close biochemical monitoring.
• Use a patient-specific total-body-water estimate.
• Recalculate from observed sodium response and ongoing inputs and outputs.

How It Is Calculated

• Predicted ΔNa after 1 L = (infusate Na + K − serum Na) ÷ (total body water + 1).
• MedicalC validates required values, applies the stated equation and rounds only the displayed result.
• Review intermediate measurements and assumptions whenever the result appears discordant with the clinical picture.

Interpretation

• The equation provides an initial estimate only. Actual sodium change can differ substantially because of urine electrolyte losses, ongoing water gain or loss, changing vasopressin activity and treatment dynamics.
• Interpret trends only when the same technique, units and clinical conditions are reasonably comparable.

Worked Example

Enter the required measurements in the displayed units. MedicalC applies: Predicted ΔNa after 1 L = (infusate Na + K − serum Na) ÷ (total body water + 1). Confirm the result against the original observations before using it in a clinical decision.

Patient Considerations

• Consider age, body size, pregnancy, organ support, medication, rhythm, ventilation, measurement conditions and acute physiological change where relevant.
• Use the earliest reliable values for prognostic trauma scores unless the score definition specifies otherwise.
• Repeat calculations only when a changed result could influence care and the source data remain valid.

Limitations

• The equation can underpredict or overpredict correction.
• It does not incorporate urinary electrolyte-free water clearance.
• It must not be used to bypass safe correction-rate limits or frequent monitoring.

Clinical Pearls

• Treat the calculator as a transparent equation, not an autonomous recommendation.
• Record the exact time and method of important measurements.
• Resolve a clinically implausible result by checking inputs before assuming unusual physiology.

Common Mistakes

• Entering values in the wrong unit.
• Combining measurements obtained at different clinical time points.
• Applying a published threshold outside its validated population or setting.
• Allowing a score to delay urgent treatment.

Evidence Base

The calculator implements the stated published or established relationship. Principal source: Adrogué HJ, Madias NE. Aiding fluid prescription for the dysnatremias. Intensive Care Med. 1997.

References

1. Adrogué HJ, Madias NE. Aiding fluid prescription for the dysnatremias. Intensive Care Med. 1997. — Primary publication, authoritative guideline or recognised specialty source.