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Abstract: TH-PO1124

New Sodium Equation with Built-In Rate of Correction to Simplify Therapeutic Orders for Hyponatremia or Hypernatremia

Session Information

Category: Fluid, Electrolytes, and Acid-Base

  • 704 Fluid, Electrolyte, Acid-Base Disorders


  • Chen, Sheldon, MD Anderson, Houston, Texas, United States

Both hyponatremia and hypernatremia occur frequently in hospitalized patients. To understand these disorders, investigators have mathematically modeled the serum sodium concentration in humans. Edelman published the seminal equation (J Clin Invest 37: 1236-56, 1958), and others have refined it for clinical use.


The model has been expanded to incorporate time, and then a term explicitly appears for a rate of sodium correction, a key consideration to avoid treatment complications like osmotic demyelination. The equation is solved for the fluid administration rate to assist the clinician with the hospital order in the management of dysnatremia. To handle the calculations, we programmed the equation into a spreadsheet that aggregates the relevant data, e.g., urine [Na+K], and provides immediate results to facilitate patient care on rounds.


Entering baseline data on the inputs and outputs of Na/K/water along with the patient's body weight, a clinician can use the new sodium equation to aim for a desired serum [sodium] over a safe timeframe. The formula returns the infusion rate for any treatment fluid such as normal saline, hypertonic saline, or 5% dextrose in water. The formula can also calculate treatment in terms of the dosage of salt tablets. With a slight modification, it can handle an abrupt water diuresis and appropriately decrease the IV fluid rate so that hyponatremia is not overcorrected. Demonstrating efficacy, the new sodium equation has performed well in real-life cases of hyponatremia and hypernatremia.


The proposed equation improves upon existing sodium equations by accounting for all inputs and outputs, if known, and incorporating a rate of correction. The quantitative approach provides a rational and effective basis for prescribing intravenous fluids and salt tablets in the hospital.