Quantitative approaches to the analysis and treatment of the dysnatremias

Recent new insights into the determinants of the plasma water sodium concentration ([Na(+)](pw)) have played an important role in advancing our understanding of the pathogenesis and treatment of the dysnatremias. Central to these recent advances is the recognition of the full significance of the Edelman equation discovered 50 years ago. Although Edelman et al showed empirically that the [Na(+)](pw) is related to the total exchangeable sodium (Na(e)), total exchangeable potassium (K(e)), and total body water (TBW) by the following equation: [Na(+)](pw) = 1.11(Na(e) + K(e))/TBW - 25.6 (Eq. 1), the significance of the nonzero values of the slope and y-intercept in the Edelman equation has been unrecognized and ignored. It recently has been shown that the slope and y-intercept in this equation are determined quantitatively by several additional physiologic parameters that play an important role in modulating the [Na(+)](pw) and in the generation of the dysnatremias. By defining all the physiologic parameters that determine the magnitude of the [Na(+)](pw), this analysis has also proven to be an indispensable tool for deriving new formulas to aid the clinician in both interpreting the pathogenesis and treating the dysnatremias. In this article, the role of quantitative analysis in the diagnostic and therapeutic approach to the dysnatremias is discussed.