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      Classification of Hydration in Clinical Conditions: Indirect and Direct Approaches Using Bioimpedance

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          Abstract

          Although the need to assess hydration is well recognized, laboratory tests and clinical impressions are impractical and lack sensitivity, respectively, to be clinically meaningful. Different approaches use bioelectrical impedance measurements to overcome some of these limitations and aid in the classification of hydration status. One indirect approach utilizes single or multiple frequency bioimpedance in regression equations and theoretical models, respectively, with anthropometric measurements to predict fluid volumes (bioelectrical impedance spectroscopy—BIS) and estimate fluid overload based on the deviation of calculated to reference extracellular fluid volume. Alternatively, bioimpedance vector analysis (BIVA) uses direct phase-sensitive measurements of resistance and reactance, measured at 50 kHz, normalized for standing height, then plotted on a bivariate graph, resulting in a vector with length related to fluid content, and direction with phase angle that indexes hydration status. Comparison with healthy population norms enables BIVA to classify (normal, under-, and over-) and rank (change relative to pre-treatment) hydration independent of body weight. Each approach has wide-ranging uses in evaluation and management of clinical groups with over-hydration with an evolving emphasis on prognosis. This review discusses the advantages and limitations of BIS and BIVA for hydration assessment with comments on future applications.

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          A new method for monitoring body fluid variation by bioimpedance analysis: the RXc graph.

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            Importance of Whole-Body Bioimpedance Spectroscopy for the Management of Fluid Balance

            Introduction: Achieving normohydration remains a non-trivial issue in haemodialysis therapy. Preventing the deleterious effects of fluid overload and dehydration is difficult to achieve. Objective and clinically applicable methods for the determination of a target representing normohydration are needed. Methods: Whole-body bioimpedance spectroscopy (50 frequencies, 5–1,000 kHz) in combination with a physiologic tissue model can provide an objective target for normohydration based on the concept of excess extracellular volume. We review the efficacy of this approach in a number of recent clinical applications. The accuracy to determine fluid volumes (e.g. extracellular water), body composition (e.g. fat mass) and fluid overload was evaluated in more than 1,000 healthy individuals and patients against available gold standard reference methods (e.g. bromide, deuterium, dual-energy X-ray absorptiometry, air displacement plethysmography, clinical assessment). Results: The comparison with gold standard methods showed excellent accordance [e.g. R 2 (total body water) = 0.88; median ± SD (total body water) = –0.17 ± 2.7 litres]. Agreement with high-quality clinical assessment of fluid status was demonstrated in several hundred patients (median ± SD = –0.23 ± 1.5 litres). The association between ultrafiltration volume and change in fluid overload was reflected well by the method (median ± SD = 0.015 ± 0.8 litres). The predictive value of fluid overload on mortality underlines forcefully the clinical relevance of the normohydration target, being secondary only to the presence of diabetes. The objective normohydration target could be achieved in prevalent haemodialysis patients leading to an improvement in hypertension and reduction of adverse events. Conclusion: Whole-body bioimpedance spectroscopy in combination with a physiologic tissue model provides for the first time an objective and relevant target for clinical dry weight assessment.
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              Effect of fluid management guided by bioimpedance spectroscopy on cardiovascular parameters in hemodialysis patients: a randomized controlled trial.

              Fluid overload is the main determinant of hypertension and left ventricular hypertrophy in hemodialysis patients. However, assessment of fluid overload can be difficult in clinical practice. We investigated whether objective measurement of fluid overload with bioimpedance spectroscopy is helpful in optimizing fluid status. Prospective, randomized, and controlled study. 156 hemodialysis patients from 2 centers were randomly assigned to 2 groups. Dry weight was assessed by routine clinical practice and fluid overload was assessed by bioimpedance spectroscopy in both groups. In the intervention group (n = 78), fluid overload information was provided to treating physicians and used to adjust fluid removal during dialysis. In the control group (n = 78), fluid overload information was not provided to treating physicians and fluid removal during dialysis was adjusted according to usual clinical practice. The primary outcome was regression of left ventricular mass index during a 1-year follow-up. Improvement in blood pressure and left atrial volume were the main secondary outcomes. Changes in arterial stiffness parameters were additional outcomes. Fluid overload was assessed twice monthly in the intervention group and every 3 months in the control group before the mid- or end-week hemodialysis session. Echocardiography, 48-hour ambulatory blood pressure measurement, and pulse wave analysis were performed at baseline and 12 months. Baseline fluid overload parameters in the intervention and control groups were 1.45 ± 1.11 (SD) and 1.44 ± 1.12 L, respectively (P = 0.7). Time-averaged fluid overload values significantly decreased in the intervention group (mean difference, -0.5 ± 0.8 L), but not in the control group (mean difference, 0.1 ± 1.2 L), and the mean difference between groups was -0.5 L (95% CI, -0.8 to -0.2; P = 0.001). Left ventricular mass index regressed from 131 ± 36 to 116 ± 29 g/m(2) (P < 0.001) in the intervention group, but not in the control group (121 ± 35 to 120 ± 30 g/m(2); P = 0.9); mean difference between groups was -10.2 g/m(2) (95% CI, -19.2 to -1.17 g/m(2); P = 0.04). In addition, values for left atrial volume index, blood pressure, and arterial stiffness parameters decreased in the intervention group, but not in the control group. Ambulatory blood pressure data were not available for all patients. Assessment of fluid overload with bioimpedance spectroscopy provides better management of fluid status, leading to regression of left ventricular mass index, decrease in blood pressure, and improvement in arterial stiffness. Copyright © 2013 National Kidney Foundation, Inc. Published by Elsevier Inc. All rights reserved.
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                Author and article information

                Journal
                Nutrients
                Nutrients
                nutrients
                Nutrients
                MDPI
                2072-6643
                10 April 2019
                April 2019
                : 11
                : 4
                : 809
                Affiliations
                [1 ]Department of Kinesiology and Public Health Education, University of North Dakota, Grand Forks, ND 58202-7166, USA; henry.lukaski@ 123456und.edu
                [2 ]Nephrology Service, University Hospital of Grand Canary and Faculty of Science, University Los Palmas, 35019 Los Palmas, Grand Canary, Spain; nvegdia@ 123456gobiernodecanarias.org
                [3 ]Antonio Talluri, Fatbyte, Inc., 50012 Bagno a Ripoli, Florence, Italy; info@ 123456fatbytesrl.com
                [4 ]Department of Electronic Engineering, Universitat Politècnica de Catalunya, 08034 Barcelona, Spain
                Author notes
                [* ]Correspondence: lexa.nescolarde@ 123456upc.edu ; Tel.: +34-93-4137286
                Article
                nutrients-11-00809
                10.3390/nu11040809
                6521329
                30974817
                6ebdaff9-7eb0-47ef-8622-fedbef37120e
                © 2019 by the authors.

                Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license ( http://creativecommons.org/licenses/by/4.0/).

                History
                : 05 March 2019
                : 08 April 2019
                Categories
                Review

                Nutrition & Dietetics
                fluid overload,resistance,reactance,bioelectrical impedance vector analysis,bioelectrical impedance spectroscopy,malnutrition

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