On-line assessment of delivered dialysis dose.

Background: The adequacy of the delivered dialysis dose is essential to prevent patient morbidity and mortality. The determination of effective ionic dialysance (D) is easy, non-invasive and inexpensive, and its use instead of effective urea clearance (K) in kinetically determining apparent" urea distribution volume (Vt) is likely to lead to a correct Kt/V, even though the Vt value may be incorrect. The aim of this study was to test the possibility of using the measurement of D to monitor Kt/V on-line during each dialysis treatment.

Methods: Forty-four patients were dialyzed using a monitor equipped with specially designed "Diascan Module" (COT; Hospal) that measures effective D by means of a single conductivity probe. Vt was calculated according to the SPVV three BUN method urea kinetic model using D instead of K values. One month later, Kt/V was calculated as Dt/V, using actual D and T values and the predetermined Vt values updated for the current final body wt. Both the Dt/V and Kt/V determined according to the Smye and Daugirdas methods were compared with the Kt/V determined using the SPVV kinetic model (Kt/Veq)

Results: The Kt/V values calculated using ionic dialysance and predetermined Vt were approximately equivalent to those of Kt/Veq (1.14 +/- 0.16 vs. 1.14 +/- 0.17, mean difference 0.00 +/- 0.07), as were those determined according to the Smye and Daugirdas methods (1.10 +/- 0.18 and 1.13 +/- 0.17, mean difference -0.03 +/- 0.06 and 0.01 +/- 0.06, respectively).

Conclusion: Once Vt has been determined, the evaluation of ionic dialysance in stable patients makes it possible to calculate the Kt/V accurately at each dialysis session without blood or dialysate sampling, and at no additional cost.