Bioimpedance Can Solve Problems of Fluid Overload

Abstract

Bioimpedance (BI) techniques for measuring normal hydration status (NHS) can be generally classified as (1) by frequency as single frequency at 50 kHz, BI analysis, and multifrequency BI spectroscopy and (2) by method as whole body (wrist to ankle) measurement and calf BI spectroscopy. The aim of this article was to review current BI methods for clinical practice in patients with end-stage of kidney disease. BI vector analysis using whole-body single-frequency BI at 50 kHz may be useful for population studies to indicate a range of degree of fluid loading and of nutritional status. Whole body multifrequency BI spectroscopy is used to estimate extracellular (ECV), intracellular fluid volume, and total body water in dialysis patients. The whole-body BI model is used in the body composition monitor (BCM). The whole-body BI model is established with ECV, intracellular fluid volume, and body weight based on parameters from regression analysis in healthy subjects to calculate fluid overload in dialysis patients. Calf BI methods have been developed to measure NHS by 2 ways: (1) continuous measurement of the intradialytic resistance curve until flattening occurs; (2) calf normalized resistivity in the range of healthy subjects (18.5 × 10(-2) Ω m(3)/kg in male and 19.1 × 10(-2) Ω m(3)/kg in female). In general, for population studies, BI vector analysis or ECV/total body water may be useful; BCM is a commercially available device that can certainly guide volume reduction safely over time. For more exact measure of fluid overload, calf BI methods appear to be most accurate, but these are at present research tools. BI techniques are not only useful in assessing NHS but also in the study of nutrition and body composition.