Chronic hemodialysis: Kt/V or solute removal index to evaluate the effective delivered dose?

A standard for quantifying the hemodialysis dose has not yet been defined. Many authors suggest the use of an alternative method to Kt/V: the solute removal index (SRI). We compared three methods based on blood-side urea determinations with the direct quantification method (DDQ) for estimating the delivered dialysis dose, expressed as SRI as well as Kt/V. Eight patients underwent three consecutive dialysis sessions, with the same dialytic efficiency. For each patient and each dialytic session the SRI and Kt/V were determined using the DDQ method and the single pool variable volume kinetic model, in its classical version (SPVV) as well by using the postdialysis urea value determined 30 min after the end of the session (eqSPVV). Double pool Kt/V was also estimated by the Daugirdas-Schneditz rate equation. Our results showed that the SPVV kinetic model significantly overestimated the delivered dialysis dose, the mean value of SRI and Kt/V were respectively 8.9% and 17% higher than those obtained by DDQ. The eqSPVV allowed the SRI to be estimated with a difference of -0.3% and Kt/V with a difference of -2% in comparison with DDQ. By using the Daugirdas-Schneditz rate of equation, which does not require blood samples to be drawn after the end of the session, the difference in Kt/V value was 3%. Therefore, both the eqSPVV kinetic model and the Daugirdas method allow quantification of the delivered dialysis dose with results similar to those determined by DDQ, which cannot be routinely applied. Kt/V seems the best marker for dialytic doses quantification.