Is there a proven formula based on Na+ deficit for the dose and rate of administration of hypertonic saline?

Updated: Aug 16, 2019
  • Author: Christie P Thomas, MBBS, FRCP, FASN, FAHA; Chief Editor: Vecihi Batuman, MD, FASN  more...
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Answer

Formulas for the dose and rate of hypertonic saline have been proposed based on a Na+ deficit to calculate the rate of administration of hypertonic fluids. [17] However, they have not been prospectively studied. Despite the correct use of these formulas, hyponatremia is often corrected too rapidly. Therefore, these formulas should serve only as guidelines. Patients still require frequent retesting of their serum Na+ concentration. [20]

The approximate Na+ deficit can be estimated by using the following formula (0.5 L/kg for females):

  • Na+ Deficit (mEq) = (Desired Na+ - Measured Na+) x 0.6 L/kg x Weight (kg)

Three-percent hypertonic saline has 513 mEq/L each of Na+ and Cl- and has an osmolality of 1026 mOsm/L. The volume of hypertonic saline needed to correct that deficit can be calculated as follows:

  • Volume of 3% Saline = (Na+ Deficit)/513 mEq/L Na+

Assuming a rate of correction of chronic hyponatremia of 0.5 mEq/L per hour, the amount of time needed to correct a given degree of hyponatremia is as follows:

  • Time Needed for Correction = (Desired Na+ - Measured Na+)/0.5 mEq/L per hour

The rate of infusion of hypertonic saline is as follows:

  • Rate = (Volume of 3% Saline)/(Time Needed for Correction)


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