[Determination of dry weight of hemodialyzed patients on the basis of the ratio of extracellular fluid volume to total body fluid volume as measured by multifrequency impedance].

Whole body impedometry is relatively new non-invasive method to measure the distribution of total body water (TBW) between extra- and intracellular compartment (VEC, VIC). Having applied linear regression analysis onto the relation of the ratio of the extracellular volume to the volume of total body water (VEC/TBW) and the age in a group of healthy individuals very narrow scatter from the regression line was found. This line can thus be used as an indicator of normohydration status with respect to age. Assuming that the relation of VEC/TBW vs. age is the same in dialysed patients and that the state of normohydration corresponds to the so called dry weight, the VEC/TBW value can be used as a novel indicator of dry weight. Any deviation of the pre-dialysis VEC/TBW value from normal could easily be used to establish the desired ultrafiltration and dry weight. With regard to the known inaccuracy with which the dry weight is determined from purely clinical assessment this approach may lead to substantial objectivisation in determination of this principal parameter. It may be especially helpful in case of newly admitted patients. The suggested new approach to dry weight determination is supported by the finding of statistically significant relation between post-dialysis deviation of the VEC/TBW ratio from the normal value vs. blood volume reduction at the end of the dialysis session. Patients classified at the end of a dialysis session as still overhydrated by their VEC/TBW deviation from normal showed little or no reduction in their blood volume. An investigation of the Vena Cava Inferior diameter in a subgroup of these patients confirmed this finding showing no decrease at the end of dialysis. On the contrary, the patients whose post-dialysis VEC/TBW value was normal or below normal showed both significant reduction in their blood volume as well as decrease in the Vena Cava Inferior diameter.