M. Fenech et al., Fluid volumes determination by impedance spectroscopy and hematocrit monitoring: Application to pediatric hemodialysis, ARTIF ORGAN, 25(2), 2001, pp. 89-98
A method for extracting fluid volumes from multifrequency bioimpedance, whi
ch takes into account the body geometry and the presence of nonconducting e
lements, was tested on 12 young dialyzed patients against correlations for
total body water volumes (TBW) from Watson et al. and Humes et al. Our calc
ulations of TBW from impedance were found to overestimate Humes' values by
0.25 L (0.8%) postdialysis and by 2.08 L (6.5%) predialysis. Extracellular
water (ECW) was found to contribute an average of 93% of ultrafiltered volu
me. Intracellular water volume (ICW) determination from impedance was found
to be too imprecise to predict its variation during dialysis; therefore, I
CW variations were calculated as the difference between ultrafiltration and
ECW changes. The continuous recording of hematocrit by an optical device m
onitored changes in plasma and interstitial volumes. In most cases, ultrafi
ltration was compensated mainly by a contribution from interstitial fluid,
and the drop in plasma volume was generally moderate.