Monitoring Urine Flow to Prevent Overcorrection of Hyponatremia: Derivation of a Safe Upper Limit Based on the Edelman Equation  Florian Buchkremer, MD, Stephan Segerer, MD, Andreas Bock, MD  American Journal of Kidney Diseases  Volume 73, Issue 1, Pages 143-145 (January 2019) DOI: 10.1053/j.ajkd.2018.05.017 Copyright © 2018 National Kidney Foundation, Inc. Terms and Conditions

Figure 1 Depictions of theoretical calculations based on the Edelman equation. (A) Δ[Na]plasma (change in plasma sodium concentration) as a function of urine volume (Vurine) and different total-body water (TBW) levels (20, 30, 40L). The lower the TBW, the higher the Δ[Na]plasma. (Baseline [Na]plasma [plasma sodium concentration] set at 127mmol/L, [Na]urine [sodium concentration in urine] + [K]urine [potassium concentration in urine] at 20mmol/L). (B) Δ[Na]plasma as a function of Vurine and different [Na]urine + [K]urine (20, 60, 100mmol/L). The lower the urinary concentration, the higher the Δ[Na]plasma. (Baseline [Na]plasma = 127mmol/L, TBW=40L). (C) Δ[Na]plasma as a function of Vurine and different baseline [Na]plasma concentrations (127, 100mmol/L). The higher the baseline [Na]plasma, the higher the Δ[Na]plasma. (TBW=40L, [Na]urine + [K]urine = 20mmol/L). (D) TBW estimation according to Watson et al9 for a 160-cm woman in comparison to estimates of 0.4, 0.5, and 0.6 times body weight (BW). Calculating TBW as 0.4 × BW systematically underestimates TBW compared to the reference formula, up to a BW of ∼100kg. (E) Δ[Na]plasma as a function of Vurine per kg of BW. Vurine of ∼24mL/kg leads to Δ[Na]plasma of +8mmol/L. (TBW = 0.4 × BW, [Na]urine + [K]urine = 20mmol/L, baseline [Na]plasma = 127mmol/L; values were set to provide an upper boundary for urine flow). American Journal of Kidney Diseases 2019 73, 143-145DOI: (10.1053/j.ajkd.2018.05.017) Copyright © 2018 National Kidney Foundation, Inc. Terms and Conditions