Abstract: PO1430
Reconsidering the Edelman Equation: Impact of Individual Total Body Cation Content and Body Weight
Session Information
- Fluid, Electrolyte, and Acid-Base Disorders: Clinical - 1
October 22, 2020 | Location: On-Demand
Abstract Time: 10:00 AM - 12:00 PM
Category: Fluid, Electrolyte, and Acid-Base Disorders
- 902 Fluid, Electrolyte, and Acid-Base Disorders: Clinical
Authors
- Vuurboom, Mart D., Amsterdam UMC Locatie AMC, Amsterdam, North Holland, Netherlands
- Wenstedt, Eliane, Amsterdam UMC Locatie AMC, Amsterdam, North Holland, Netherlands
- Vogt, Liffert, Amsterdam UMC Locatie AMC, Amsterdam, North Holland, Netherlands
- Olde Engberink, Rik Hg, Amsterdam UMC Locatie AMC, Amsterdam, North Holland, Netherlands
Background
Treatment of hypo- and hypernatremia is guided by formulas that are based on the Edelman equation, including Adrogue-Madias’ and others. This equation is the result of a unique study in which serum sodium concentration ([Na+]), total body exchangeable Na+ and potassium (K+) and total body water (TBW) were measured in a highly heterogeneous population. However, the Edelman equation does not account for the recently uncovered body compartment where Na+ can be temporarily stored and released without affecting TBW.
Methods
We performed a post-hoc analysis of original data from the Edelman study. In a linear regression model, the effects of important clinical characteristics on the relation between (Nae+Ke)/TBW and serum [Na+] were examined: sex, age, body weight and presence of edema. Using piecewise regression, we analyzed differences in slope and y-intercept for increasing values of (Nae+Ke)/TBW. Serum [Na+] was calculated by multiplying serum water [Na+] by 0.93.
Results
Data was available for 85 measurements in 82 patients; 57 males, 25 females, with a mean age of 57±15 years. Serum [Na+] ranged from 103 to 150 mmol/L. The association between serum [Na+] and (Nae+Ke)/TBW was different for high and low weight categories (table). Sex, age or presence of edema did not alter the association. In piecewise regression, a significant change in slope was found at 149 mmol/L (Nae+Ke)/TBW (figure; 1.12 vs 0.56, p = 0.01).
Conclusion
The coefficients of the Edelman equation are significantly affected by weight and total body cation content. The less steep slope for the higher (Nae+Ke)/TBW and high weight groups may reflect an increase in osmotically inactive Na+ storage. This may explain the inaccuracy of Edelman based formulas in daily clinical practice.