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

Hypertonic saline infusion is used to correct hyponatremia with severe symptoms. The selection of the volume of infused hypertonic saline (V-Inf) should address prevention of overcorrection or undercorrection. Several formulas computing this V-Inf have 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 V-Inf from the Adrogue-Madias formula by a calculation assuming a linear relation between V-Inf and 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 V-Inf by the Adrogue-Madias formula and by a formula using the same determinants of the change in [Na] and the curvilinear relation between this change and V-Inf. Regardless of the method used to correct hyponatremia, monitoring [Na] and changes in external balances of water, sodium, and potassium during treatment remain imperative.