In cases of volume depletion there is loss of both sodium and water. The deficit of sodium can be estimated if the serum sodium is known.
sodium deficit in mEq =
= (140 - (current serum sodium in mEq/L)) * 0.6 * (body weight in kilograms)
• 140 is the mean normal serum sodium in mEq/L
• 0.6 * body weight in kilograms is the estimate of total body water
In cases of severe volume depletion, the body weight is reduced. If the patient's usual body weight is known, this can be used in the calculation. If it is not known then adjustments may need to be made to correct for the differences.
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Specialty: Endocrinology, Clinical Laboratory