Hyponatremia in cancer patients: Strategy for safe correction in the hospital

Abstract

Hyponatremia is a common but challenging disorder to treat. The pathogenesis and the workup can be unexpectedly complicated, and the available therapies are manifold. Instead of trying to wrangle all of the aspects of hyponatremia into a comprehensive algorithm, we describe a general strategy that goes back to the first principles embodied in the model discovered by Edelman and colleagues back in 1958. The so-called Edelman equation underpins our modern understanding of [sodium] disorders, and it has engendered pretty much all of the [sodium] equations that are in clinical use. As the dysnatremias have a quantitative basis, a numerical approach seems prudent. We developed a predictive [sodium] equation that simultaneously considers all of the ongoing inputs and outputs of Na/K/H2O that would perturb the serum [Na] and also factors in the element of time that would determine the rate of [Na] correction. Our equation solves for the rate of intravenous fluid (or salt tablet) administration, because that information helps clinicians the most when prescribing therapy for inpatients. With the rate of [Na] correction built in, the equation also aims to safeguard against overcorrection. Since the equation is programmable into a clinical calculator, our renal fellows find it easy to use on their own. However, all of the [sodium] equations are fallible, because their data are no longer valid when the clinical parameters change, as they are likely to do. Nevertheless, we believe that the quantitative approach to hyponatremia has much to offer in terms of efficacy and safety.

Safely correct hyponatremia with continuous renal replacement therapy: A flexible, all‐purpose method based on the mixing paradigm

“…These values are controversial (Nguyen et al, 2016; Nguyen & Kurtz, 2004a), so until better measurements are made, it may be prudent to just denote them as $$$ m $$$ and $$$ b $$$, as in $$$ \left[\mathrm{Na}\right]=m\cdotp \frac{\mathrm{Na}+\mathrm{K}}{\mathrm{TBW}}+b $$$. Most sodium equations assume $$$ m=1 $$$ and $$$ b=0 $$$ (Chen, 2019; Chen et al, 2021; Chen & Shey, 2018; Mohiuddin et al, 2022); these values are used throughout, except where noted. Note: $$$ m $$$ is a scalar (unitless), and $$$ b $$$ has units of mEq/L.…”

Ratio Profile: Physiologic Approach to Estimating Appropriate Intravenous Fluid Rate to Manage Hyponatremia in the Syndrome of Inappropriate Antidiuresis

“…To infer the total Na+K mass, we can compute Na p × TBW. In a sense, the Edelman equation is describing the effect of osmosis to equilibrate the concentrations of the two major tonic cations: sodium in the extracellular fluid and potassium in the intracellular fluid, as weighted by the sizes of their 4 respective compartments (6). The extracellular space is about one-third of TBW, while the intracellular space is about two-thirds of TBW, so the intracellular [K] is not budged as much by a perturbation like the infusion of an intravenous (IV) fluid.…”

“…Let us say that she started with a plasma sodium of 140 mEq/L and had a TBW of 42 L. Then, the equation would be calculated as: The D[Na] p is 10:8 mEq/L, which can be verified by the Barsoum-Levine Equation (10): All of the practical sodium equations exploit the principle that all gains and losses (iv fluids, oral intake, urine, stool, etc.) can be separated into their Na/K/H 2 O components and sorted into their proper place in the Edelman fraction (6,8,9,11,12).…”

“…They can be answered by the Edelman equation. The numerator tracks all of the cationic solutes, and the denominator tracks all of the water(6,9). The tracking version of the Edelman equation can be conceptualized asNa new = Initial Na+K amount + Na+K solutes gained by IV fluid − Na+K solutes lost by urine Initial TBW + Volume gained by IV fluid − Volume lost by urine For example, if a liter of NS is given to a patient, then her numerator increases by 154 mEq, and the denominator increases by 1 L. Over the same time, if she produces half a liter of urine with a Na+K u = 100 mEq/L, then her numerator decreases by 50 mEq, and the denominator decreases by 0.5 L. Combine all the input and output data with initial conditions, and the Edelman equation can predict, in theory, the new plasma sodium.…”

Improving on the Adrogué–Madias Formula

“…It may not be completely foolproof, but the general equation is worth adopting now. Lastly, more capable sodium equations exist (20,24,(26)(27)(28)(29)(30), but the A-M…”