Bioimpedance and the Duration of the Hemodialysis Session

Abstract

Bioelectrical impedance analysis (BIA) is composed of resistance (R) and reactance (Xc). The aim of this study was to investigate whether BIA may be influenced by the duration of hemodialysis (HD) sessions. Eleven uremic patients underwent one 4-hour and one 8-hour bicarbonate HD session. Volume of blood and dialysate processed, volume of ultrafiltration (V(UF)), and dialysate electrolyte concentrations were prescribed to be the same. R and Xc were determined at the start and the end of each session, injecting 800 μA at 50 kHz alternating sinusoidal current (BIA 101; Akern, Italy). Mean pre- and postdialysis body weights and V(UF) were not significantly different in the 4-hour and 8-hour treatments. Postdialysis R, ΔR (the difference between post- and predialysis R values), and percent increase of R values were significantly higher in the 8-hour sessions, when compared with the corresponding values of the 4-hour sessions (p < 0.0001, 0.02, and 0.02, respectively). In conclusion, this study shows that 8-hour HD sessions were associated with postdialysis R, ΔR, and percent increase of R values significantly higher than the corresponding ones of 4-hour sessions. If higher R values may represent a proxy of a correct dry body weight, it remains a matter of future research.

Kinetics of Plasma Refilling During Hemodialysis Sessions with Different Initial Fluid Status

“…This method may be replaced by a more elaborate method of segmental bioimpedance that may provide more exact data especially during the volume perturbation caused by UF. [33][34][35][36] Nevertheless, whole-body bioimpedance seems to be sufficient for studying the relations between Kr values and volume of body compartments in the clinical setting. However, more precise information about the change of fluid volume in different body segments would be interesting for further understanding of the refilling kinetics.…”

Effect of change in fluid distribution in segments in hemodialysis patients at different ultrafiltration rates on accuracy of whole body bioimpedance measurement

“…This has potential clinical relevance, since maintenance of central blood volume is essential to maintain cardiac output and blood pressure. Basile et al (1) demonstrated intradialytic changes in whole body resistance using whole body bioimpedance at 50 kHz to be significantly greater in an 8-h dialysis treatment (at a low rate of ultrafiltration) than in a 4-h treatment (at a high rate of ultrafiltration) with the same ultrafiltration volume, presumably because relatively more fluid was removed from the leg in the longer dialysis treatment. Their paper provides evidence that change in whole body resistance during different dialysis durations and rate of ultrafiltration does not proportionally reflect fluid removal from the body.…”

“…Therefore, knowledge of the effect of changes in fluid distribution occurring during the HD treatment on the accuracy of measurements is relevant. Whole body techniques assume that body segments (arm, trunk, and leg) can be modeled as a cylinder with uniform conductivity (1,19,20,26). However, the obvious differences in cross-sectional area between the trunk and limbs affect the accuracy of this method when nonphysiological changes in the distribution of ECV occur (20,28).…”