Hypertonic Saline Infusion for Hyponatremia: Limitations of the Adrogué-Madias and Other Formulas

Abstract

Hypertonic saline infusion is used to correct hyponatremia with severe symptoms. The selection of the volume of infused hypertonic saline (VInf) should address prevention of overcorrection or undercorrection. Several formulas computing this VInfhave been proposed. The limitations common to these formulas consist of (1) failure to include potential determinants of change in serum sodium concentration ([Na]) including exchanges between osmotically active and inactive sodium compartments, changes in hydrogen binding of body water to hydrophilic compounds, and genetic influences and (2) inaccurate estimates of baseline body water entered in any formula and of gains or losses of water, sodium, and potassium during treatment entered in formulas that account for such gains or losses. In addition, computing VInffrom the Adrogué-Madias formula by a calculation assuming a linear relation between VInfand increase in [Na] is a source of errors because the relation between these two variables was proven to be curvilinear. However, these errors were shown to be negligible by a comparison of estimates of VInfby the Adrogué-Madias formula and by a formula using the same determinants of the change in [Na] and the curvilinear relation between this change and VInf. Regardless of the method used to correct hyponatremia, monitoring [Na] and changes in external balances of water, sodium, and potassium during treatment remain imperative.