Sodium Concentration Measurement during Hemodialysis through Ion-Exchange Resin and Conductivity Measure Approach: In Vitro Experiments

Abstract

Sodium measurement during hemodialysis treatment is important to preserve the patient from clinical events related to hypo- or hyper-natremia Usually, sodium measurement is performed through laboratory equipment which is typically expensive, and requires manual intervention. We propose a new method, based on conductivity measurement after treatment of dialysate solution through ion-exchange resin. To test this method, we performed in vitro experiments. We prepared 40 ml sodium chloride (NaCl) samples at 280, 140, 70, 35, 17.5, 8.75, 4.375 mEq/l, and some “mixed samples”, i.e., with added potassium chloride (KCl) at different concentrations (4.375-17.5 mEq/l), to simulate the confounding factors in a conductivity-based sodium measurement. We measured the conductivity of all samples. Afterwards, each sample was treated for 1 min with 1 g of Dowex G-26 resin, and conductivity was measured again. On average, the difference in the conductivity between mixed samples and corresponding pure NaCl samples (at the same NaCl concentration) was 20.9%. After treatment with the exchange resin, it was 14.7%, i.e., 42% lower. Similar experiments were performed with calcium chloride and magnesium chloride as confounding factors, with similar results. We also performed some experiments on actual dialysate solution during hemodialysis sessions in 15 patients, and found that the correlation between conductivity measures and sodium concentration improved after resin treatment (R=0.839 before treatment, R=0.924 after treatment, P<0.0001). We conclude that ion-exchange resin treatment coupled with conductivity measures may improve the measurement of sodium compared to conductivity measures alone, and may become a possible simple approach for continuous and automatic sodium measurement during hemodialysis.

Finite-Element Modeling of Time-Dependent Sodium Exchange across the Hollow Fiber of a Hemodialyzer by Coupling with a Blood Pool Model

“…Correlation accounts for the presence of offset and gain between the 2 compared variables, but the high estimated R 2 value could only be obtained in the case of very similar time dynamics. Values of the regression coefficients are similar to values reported in the literature for the relationship between sodium concentration and conductivity in dialysate: for example, Tura et al (35) reported σ Dial = 0.08•Na Dial + 2.87. The value of the obtained regression slope, 0.092 (mS/cm)/mM, and the presence of a 1.068 mS/cm offset can be explained by the influence of ions other than sodium on total conductivity, as already mentioned in the Methods section.…”

How Geometry Affects Sensitivity of a Differential Transformer for Contactless Characterization of Liquids

“…Therefore, this measurement method has potential in biotechnology and medical technology for the contactless determination of biomass within single-use bioreactors [1,18] or for obtaining tissue information [19][20][21][22][23]. In addition, the differential transformer approach is investigated with respect to continuous in-line monitoring of the sodium concentration in human blood, by measuring the blood plasma conductivity, mainly influenced by the sodium concentration [24][25][26][27]. Continuous monitoring of plasma sodium concentration is particularly important in continuous renal replacement therapy, especially in patients with severe dysnatremia, since both a large deviation from the physiological plasma sodium level [26,[28][29][30] and a rapid change in the concentration can lead to dangerous complications such as central pontine myelinolysis [31,32].…”

Zero Diffusive Sodium Balance in Hemodialysis Provided by an Algorithm‐Based Electrolyte Balancing Controller: A Proof of Principle Clinical Study

“…Because the conductivities of single ions cannot be measured independently of their counter ions, the conductivities of KCl and NaCl solutions have to be used instead. σ K / σ Na depends only slightly on the actual ion strength and can be deduced from in vitro measurements: Tura et al found conductivities of 12.93 and 15.92 mS/cm, for a 140 mmol/L sodium chloride or potassium chloride solution respectively. This leads to σ K / σ Na = 1.231.…”