Assessment of postdialysis dry weight: a comparison of techniques

Because clinical indices of hydration state are insensitive, the estimation of correct postdialysis dry weight is still major problem. Recently, some new techniques have been introduced to assess postdialysis dry weight more accurately. The plasma concentrations of the biochemical markers atrial natriuretic peptide (ANP) and cGMP are related to intravascular hydration state. The echographically measured inferior caval vein diameter (VCD) is linked to right atrial pressure and blood volume (BV). Regional noninvasive conductivity measurements provide information about regional extracellular fluid volume (EFV). In this study of postdialysis ANP and cGMP concentrations, VCD and EFV yielded postdialysis diagnoses of hydration state in 18 patients on maintenance dialysis. In order to verify the established diagnosis, hemodynamic and BV changes during dialysis were studied. In postdialysis underhydrated patients, differentiated according to VCD and EFV standards, a pronounced decrease in BV, stroke volume, and left ventricular end-diastolic diameter compared with postdialysis normohydrated patients was observed. Hemodynamic and BV changes during dialysis were identical in the groups selected according to postdialysis ANP level. Only a difference in BV decrease was demonstrated between the groups selected according to postdialysis cGMP. Predialysis and postdialysis VCD correlated well with the corresponding EFV (r = 0.7 and r = 0.8, respectively). Because VCD and EFV were related and interpretation yielded diagnoses of postdialysis hydration state that were substantiated by the finding of classical hemodynamic features of underhydration, both are an asset in the diagnosis of postdialysis dry weight. cGMP values are less informative, and ANP does not provide any information at all.