[Estimation of urea distribution volume in hemodialysis patients]

Background: On-line urea clearance estimation, currently available on some dialysis monitors, makes it possible to calculate the dialysis dose Kt and thus allows to estimate Kt/V for each session, providing an estimation of urea distribution volume (V) at equilibrium assumed equal to total body water.

Methods: Three methods suitable for routinely estimating V, using the anthropometric Watson formula (V(Wat)), the body composition monitor (BCM) device (Fresenius Medical Care) based on bio-impedance analysis (V(imp)) and the indirect estimation (V(Daug)) obtained from measurement of Kt/(Kt/V)(sp) ratio respectively are compared during 25 dialysis sessions in 15 patients to a direct estimation (V(DDQ)) obtained by direct quantification of dialysis (DDQ) considered as the gold standard in hemodialysis patient..

Results: V(Watson) overestimates V(DDQ) by about 20%. The values of V(imp) (29.1±5.6 L) and V(Daug) (29.5±4.6 L) are in agreement with V(DDQ) (29.9±5.2 L). Correlation coefficient with V(DDQ) is better for V(imp) (r=0.94) than for V(Daug) (r=0.85).

Conclusion: Bio-impedancemetry using BCM and indirect method using the second generation Daugirdas equation are two methods of clinical interest for estimating V. Bio-impedancemetry does not require blood sample, but it needs to have a specific device at disposal.