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

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.

Comparison of the Effect of Different Resistance Training Frequencies on Phase Angle and Handgrip Strength in Obese Women: A Randomized Controlled Trial

“…The bioimpedance vector analysis (BIVA) is used in clinical and sports fields to study the change in body fluids and nutritional state [10][11][12][13]. It represents the raw bioimpendance parameters (resistance (R) and reactance (Xc)) as a point on the R-Xcgraph in which both length and slope are considered.…”

Nocturnal thoracic volume overload and post‐discharge outcomes in patients hospitalized for acute heart failure

“…[5][6][7][8][9] The high rates of rehospitalization and mortality may indicate that the current guidelines for discharge, typically based on clinical assessment of volume status, are insufficient for AHF patient stabilization. 10 Daytime measures of haemodynamic parameters, such as blood pressure, left ventricular ejection fraction (LVEF), and cardiac output, are important determinants of prognosis in patients with heart failure. 11 We have previously demonstrated that daytime measures of pulsatile haemodynamics, such as carotid-femoral pulse wave velocity (CFPWV), backward (Pb) amplitude of the reflection wave, carotid pulse pressure, 12,13 and electromechanical activation time (EMAT), 9 a measure of the ventriculo-arterial coupling, were independently associated with post-discharge outcomes in patients with AHF.…”

Assessment of Hydration Status in Peritoneal Dialysis Patients: Validity, Prognostic Value, Strengths, and Limitations of Available Techniques

“…There are mainly four methods of body fluid volume assessment: (a) prediction of TBW with function of single-frequency (50 kHz), (b) use of low (1–5 kHz) and high (100–500 kHz) frequencies and (c) bioimpedance spectroscopy (BIS) where a broad band of frequencies (1–1,000 kHz) is used (Low-frequency currents (<5 kHz) pass through the ECV (they cannot pass the cell membrane), while high-frequency currents pass though both ECV and intracellular volume compartments [41]. A variable amount of very low-frequency current, regardless at which frequency the current is introduced, can penetrate the membranes of muscle cells, particularly when the current is parallel to the muscle fiber [42]) and (d) bioimpedance vector measurement (BIVA), where continuous bivariate vector of impedance (resistance and reactance) is evaluated, compared with the deviation from a reference healthy population [43]. These methods can be applied segmentally or as a whole body measurement [44], while the results can be presented as absolute volumes or vector distribution [45, 46].…”

“…In general, BIS prediction equations could involve 5 different errors: impedance measurement error, regression error (standard error against the reference method), intrinsic error of the reference method, electric-volume model error (e.g., anisotropy of tissues), and biological variability of healthy and diseased subjects. On the contrary, vector analysis (BIVA) seems to engage only mainly measurement error and biological variability, as there is no need for body weight measurement and use of regression equations [43].…”