Related Experiment Video
Updated: Aug 18, 2026
Evaluation of Fluid Overload by Bioelectrical Impedance Vectorial Analysis
Published on: August 17, 2022
Whole body--single frequency bioimpedance
1Department of Medical and Surgical Sciences, Nephrology Clinic, University of Padova, Padova, Italy.
Background:
The postdialysis target weight is determined as the lowest weight a patient can tolerate without intradialytic symptoms or hypotension. Patterns of electrical properties of tissues allow a direct monitoring of fluid status without the need of the body weight.
Methods:
Whole body impedance is measured from skin electrodes on hand and foot. Impedance (Z vector) is a combination of resistance, R, i.e. the opposition to the flow of an injected alternating current, at any current frequency, through intra- and extracellular ionic solutions, and reactance, Xc, i.e. the dielectric component of cell membranes and organelles, and tissue interfaces. Measurements at 50 kHz current frequency are done with the best signal to noise ratio.
Results:
Cyclical tissue hydration changes in hemodialysis patients are detectable as changes in the whole body impedance, which can be utilized with patterns of impedance vector analysis in monitoring the prescription of optimal hydration independent of the body weight. Wet-dry weight prescription based on impedance vector analysis should bring abnormal vectors back into the reference, 75% tolerance ellipse, where tissue electrical conductivity is restored.
Conclusions:
Identification and ranking of normal versus abnormal tissue hydration can be obtained from impedance vector patterns without the need of equations.
