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Extracellular resistance is sensitive to tissue sodium status; implications for bioimpedance-derived fluid volume parameters in chronic kidney disease.

ABSTRACT: Multifrequency bioimpedance spectroscopy (BIS) is an established method for assessing fluid status in chronic kidney disease (CKD). However, the technique is lacking in predictive value and accuracy. BIS algorithms assume constant tissue resistivity, which may vary with changing tissue ionic sodium concentration (Na⁺). This may introduce significant inaccuracies to BIS outputs. To investigate this, we used ²³Na magnetic resonance imaging (MRI) to measure Na⁺ in muscle and subcutaneous tissues of 10 healthy controls (HC) and 20 patients with CKD 5 (not on dialysis). The extracellular (Re) and intracellular (Ri) resistance, tissue capacitance, extracellular (ECW) and total body water (TBW) were measured using BIS. Tissue water content was assessed using proton density-weighted MRI with fat suppression. BIS-derived volume indices were comparable in the two groups (OH: HC - 0.4?±?0.9 L vs. CKD 0.5?±?1.9 L, p?=?0.13). However, CKD patients had higher Na⁺ (HC 21.2?±?3.0, CKD 25.3?±?7.4 mmol/L; p?=?0.04) and significantly lower Re (HC 693?±?93.6, CKD 609?±?74.3 Ohms; p?=?0.01); Ri and capacitance did not vary. Na⁺ showed a significant inverse linear relationship to Re (r_s?=?- 0.598, p?+ (x) is described through equation y?=?- 7.39x?+?814. A 20% increase in tissue ionic Na⁺ is likely to overestimate ECW by 1.2-2.4L. Tissue Na⁺ concentration has a significant inverse linear relationship to Re. BIS algorithms to account for this effect could improve prediction accuracy of bioimpedance derived fluid status in CKD.

SUBMITTER: Mitsides N

PROVIDER: S-EPMC7007413 | biostudies-literature | 2020 Feb

REPOSITORIES: biostudies-literature

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Extracellular resistance is sensitive to tissue sodium status; implications for bioimpedance-derived fluid volume parameters in chronic kidney disease.

Mitsides Nicos N McHugh Damien D Swiecicka Agnieszka A Mitra Roshni R Brenchley Paul P Parker Geoff J M GJM Mitra Sandip S

Journal of nephrology 20190618 1

Multifrequency bioimpedance spectroscopy (BIS) is an established method for assessing fluid status in chronic kidney disease (CKD). However, the technique is lacking in predictive value and accuracy. BIS algorithms assume constant tissue resistivity, which may vary with changing tissue ionic sodium concentration (Na+). This may introduce significant inaccuracies to BIS outputs. To investigate this, we used 23Na magnetic resonance imaging (MRI) to measure Na+ in m ...[more]

PMID: 31214996

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Project description:BackgroundIt is becoming increasingly evident that the accurate assessment of fluid status is critical to ensure optimal care in patients undergoing hemodialysis (HD). Various fluid parameters, including overhydration (OH) and overhydration/extracellular water (OH/ECW%), which can be obtained using a bioimpedance spectroscopy device have been used to indicate the hydration status in such patients. This study aimed to explore the effect of these fluid parameters on cardiovascular events and determine which parameter was a better predictor of cardiovascular events (CVEs).MethodsA total of 227 patients who underwent HD at the Hangzhou Hospital of Traditional Chinese Medicine were enrolled in this prospective study between December 2017 and August 2018. Clinical data were collected, and the fluid status of patients was assessed using a body composition monitor. The patients were followed up until December 2020. The primary outcomes were CVEs. The association between fluid parameters and CVEs was analyzed using Cox proportional hazards models. The areas under the curve (AUCs) of receiver operating characteristic analysis and improvement in the global chi-squared value were used to compare the predictive values of fluid parameters for CVEs.ResultsDuring a median follow-up of 31 months, 66 CVEs were recorded. The patients with a higher absolute hydration index (OH) and a relative hydration index (OH/ECW%) exhibited an increased risk of developing CVEs. After adjusting for confounding factors, both OH [hazard ratio (HR) 1.279 per L, 95% confidence interval (CI) 1.047-1.562; p = 0.016] and OH/ECW% (HR 1.061 per %, 95% CI 1.017-1.108; p = 0.006) were independently associated with CVEs. The predictive ability of the absolute hydration index was superior to the relative hydration index based on AUC calculations for CVEs. Furthermore, a greater change in χ2 in predicting CVEs was noted for the absolute hydration index.ConclusionsBoth absolute hydration index and relative hydration index were found to be independent predictors of CVEs in univariate and multivariate analyses. Furthermore, the absolute hydration index had a better additive predictive value than the relative hydration index in predicting CVEs.

Dataset Information

Extracellular resistance is sensitive to tissue sodium status; implications for bioimpedance-derived fluid volume parameters in chronic kidney disease.

Publications

Extracellular resistance is sensitive to tissue sodium status; implications for bioimpedance-derived fluid volume parameters in chronic kidney disease.

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