Kinetics of urea and beta-microglobulin during and after short hemodialysis treatments

Daily short hemodialysis (HD) is often prescribed by simply doubling treatment frequency and halving treatment time; however, the effect of this prescription approach on the equilibrated HD dose (urea eKt/V) and whole body clearance for beta(2)-microglobulin has not been established.

We compared urea and beta(2)-microglobulin kinetics during and 60 minutes after a short HD treatment and a conventional HD treatment in a crossover study on 22 maintenance HD patients: 16 male and 6 female, 61 +/- 18 (mean +/- standard deviation) years of age. One patient in each treatment modality was excluded from certain analyses because of missing data. Short and conventional HD treatments were essentially identical, except for treatment times, which were 116 +/- 14 and 241 +/- 27 minutes, respectively. Blood samples were collected at regular intervals during and after treatments, and additional blood and dialysate samples were collected at 60 minutes of treatment to evaluate dialyzer clearances.

Plasma water urea clearances measured directly across the dialyzer during short and conventional HD treatments were not different (255 +/- 23 mL/min and 255 +/- 28 mL/min, respectively). The 60-minute postdialysis blood urea nitrogen concentration rebounded more (P < 0.01) after short HD than conventional HD (5.9 +/- 3.1 vs. 4.0 +/- 1.5 mg/dL, respectively). Calculated urea eKt/V values using the Daugirdas-Schneditz rate equation were not different from those measured during conventional HD using the 60-minute postdialysis concentration but significantly overestimated measured urea eKt/V values during short HD. Postdialysis rebound of beta(2)-microglobulin concentrations was variable but similar after short and conventional HD treatments (0.1 +/- 3.4 vs. 0.7 +/- 1.8 mg/L, respectively). Whole body clearances of beta(2)-microglobulin calculated from predialysis and immediate (10-second) postdialysis serum concentrations during short and conventional HD treatments were not different from each other (42.9 +/- 24.1 vs. 41.9 +/- 22.4 mL/min, respectively).

These observations show that the Daugirdas-Schneditz rate equation is accurate in predicting urea eKt/V during conventional, but not during short, HD. In contrast, whole body clearances of beta(2)-microglobulin during short and conventional HD treatments were similar. We conclude that calculation of accurate estimates of urea eKt/V, but not clearances of beta(2)-microglobulin, differ during short and conventional HD treatments.