Reconciliation between urea kinetics and direct dialysis quantification.

ABSTRACT

Previous studies comparing urea kinetic model (UKM) and direct dialysate quantification technique (DDQ) found statistically different results as far as the urea distribution volume (V) and protein catabolic rate (PCR) are concerned. In these studies, however, the true values for both the dialyser urea clearance (K) and urea concentration (C) were not used. The aim of this study was to compare UKM and DDQ using for both methods a variable-volume single-pool (VVSP) model as well as plasma water C and effective K. The study was performed during paired filtration dialysis (PFD) sessions because this technique allows bloodless measuring of K. Twenty dialysis patients were studied during a single PFD session. Dialysate and ultrafiltrate C and urea mass transfer rate were measured every 15 min to compute averaged K and total urea removal. Blood samples were obtained as for a three-point UKM, and an iterative technique was used for both methods. The results (means +/- SD) obtained with UKM were as follows K = 176 +/- 23 ml/min; V = 29986 +/- 7620 ml, PCR = 65 +/- 15 g/day, Kt/V = 1.04 +/- 0.17. These results were not statistically different from those obtained using DDQ. In conclusion, when methodological errors are avoided, DDQ and UKM provide very similar results. This study shows also that PFD is very useful for studying solute kinetics during dialysis.