Bioimpedance monitoring of cellular hydration during hemodialysis therapy

Abstract

Introduction The aim of this paper is to describe and demonstrate how a new bioimpedance analytical procedure can be used to monitor cellular hydration of End Stage Renal Disease (ESRD) patients during hemodialysis (HD). Methods A tetra-polar bioimpedance spectroscope (BIS), (UFI Inc., Morro Bay, CA), was used to measure the tissue resistance and reactance of the calf of 17 ESRD patients at 40 discrete frequencies once a minute during dialysis treatment. These measurements were then used to derive intracellular, interstitial, and intravascular compartment volume changes during dialysis. Findings The mean (± SD) extracellular resistance increased during dialysis from 92.4 ± 3.5 to 117.7 ± 5.8 Ohms. While the mean intracellular resistance decreased from 413.5 ± 11.7 to 348.5 ± 8.2 Ohms. It was calculated from these data that the mean intravascular volume fell 9.5%; interstitial volume fell 33.4%; and intracellular volume gained 20.3%. Discussion These results suggest that an extensive fluid shift into the cells may take place during HD. The present research may contribute to a better understanding of how factors that influence fluid redistribution may affect an ESRD patient during dialysis. In light of this finding, it is concluded that the rate of vascular refill is jointly determined with the rate of "cellular refill" and the transfer of fluid from the intertitial compartment into the intravascular space.

Keywords: Hypotension; adequacy of dialysis; drugs and dialysis; hemodynamics.

Figure 1

Electrode placement.

Figure 2

General equivalent circuit model of current conduction through tissue.

Figure 3

Equivalent circuit diagram used in BIS analysis for intracellular, interstitial, and intravascular volumes.

Figure 4

Extra-vascular soft tissue compartment of BIS model.

Figure 5

Mean ± SE extracellular (Re-increasing trace) and intracellular (R_i-decreasing trace) resistances for the 17 HD sessions vs. elapsed time.

Figure 6

Individual subject R_e (red-positive) and R_i (green-negative) resistance changes during HD.

Figure 7

Continuous bioimpedance records of interstitial (V_i – bottom trace), cellular (V_c – middle trace) and vascular (V_b – top trace) compartmental fluid volumes during first 180 min of 17 selected HD therapy sessions.

Figure 8

A. Pre–post vascular volume (mL) for each of 17 subject HD sessions, Pre: dark, Post: light. B. Pre–post cellular volume (mL) for each of 17 subject HD sessions, Pre: dark, Post: light. C. Pre–post interstitial volume (mL) for each of 17 subject HD sessions, Pre: dark, Post: light.

Figure 9

Group mean +/− SE interstital (V_i – bottom trace), cellular (V_c – middle trace), and vascular (V_b – top trace) intracellular volumes (Expressed as percentage of total calf volume) vs. elapsed time.