Extra- and intracellular volume monitoring by impedance during haemodialysis using Cole-Cole extrapolation.

A method is presented for monitoring the relative variation of extracellular and intracellular fluid volumes using a multifrequency impedance meter and the Cole-Cole extrapolation technique. It is found that this extrapolation is necessary to obtain reliable data for the resistance of the intracellular fluid. The extracellular and intracellular resistances can be approached using frequencies of, respectively, 5 kHz and 1000 kHz, but the use of 100 kHz leads to unacceptable errors. In the conventional treatment the overall relative variation of intracellular resistance is found to be relatively small.

Extracellular and intracellular fluid volume monitoring during dialysis by multifrequency impedancemetry.

Impedance techniques can, in principle, permit non-invasive monitoring of extracellular (Ve) and intracellular (Vi) fluid volumes during dialysis. The authors present a method that determines the resistances Re and Ri of extracellular and intracellular compartments, respectively, by extrapolating impedance measurement toward zero, as well as infinite frequencies, according to the Cole-Cole model of biologic issues. These measurements were made using a XITRON 4000 B impedance meter (Xitron Technologies Inc., San Diego, CA) at frequencies ranging from 5 kHz to 1 MHz. The fact that the body is not a cylindric, homogeneous conductor is taken into account by introducing shape factors ke and ki and different resistivities pe and pi for the extracellular and intracellular fluid compartments. Assuming that these four unknown parameters can be regarded as constant during dialysis, the authors obtain: [formula: see text] where subscript o denotes initial values at start of dialysis. Impedances were measured at 30 min intervals on 11 pediatric patients and two adults, whereas total body water volume was determined by measuring urea in collected dialysate. Without ultrafiltration, Ve and Vi do not change significantly in percentage whereas, in the presence of ultrafiltration, Ve decreased by 15% to 25%. In cases when Vi does not change, it is possible to determine Ve and its variation during dialysis.