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Expected Sodium change

This formula will provide the expected rate of change of plasma sodium concentration for a given infusion tonicity and a given urine composition

Input:
Sex
Weight
Vol Infusate
Vol Urine
Na Infusate mEq/L
Na Serum mEq/L
Na Urine mEq/L
K Infusate mEq/L
K Urine mEq/L
Results:
TBW
Vol Delta
Na Change
mEq/L
Decimal Precision:

Formula:

TBW = Sex * Weight

VolDelta = VolInfusate - VolUrine

NaChange = ((VolInfusate * (NaInfusate + KInfusate)) - (VolUrine * (NaUrine + KUrine)) - (VolDelta * NaSerum)) / (TBW + VolDelta)

Reference:

  1. Barsoum NR, Levine BS. Current prescriptions for the correction of hyponatraemia and hypernatraemia: are they too simple?. Nephrol Dial Transplant. 2002 Jul;17(7):1176-80.
  2. Medscape renal calculators

 

*Please note: this calculator is intended for educational usage only and should never be used to replace clinical decision making by a qualified practitioner.