S. Brunet et al., Diffusive and convective solute clearances during continuous renal replacement therapy at various dialysate and ultrafiltration flow rates, AM J KIDNEY, 34(3), 1999, pp. 486-492
Clearances of several solutes (urea, creatinine, phosphate, urates, beta(2)
-microglobulin [beta(2)-M]) were measured during venovenous continuous rena
l replacement therapy (CRRT) at Various ultrafiltration (Q(UF); 0 to 2 L/h)
and dialysate flow rates (Q(D); 0 to 2.5 L/h). Preset Multiflow-60 and Mul
tiflow-100 hollow-fiber dialysers (M-60 and M-100; Hospal-Gambro, St-Leonar
d, Canada) were compared (five patients for each type). First, we evaluated
the impact of predilution on convective clearances: a progressive decrease
in patient clearances, similar for both filters, was observed, reaching a
maximum of 15%, 18%, and 19% for urea, urates, and creatinine, respectively
, with predilution at a Q(UF) of 2 L/h. Second, we compared convective and
diffusive clearances. Because effluent to plasma ratio (E/P) remained at 1
for small solutes (urea, creatinine, phosphate, urates) during convection,
clearances were equal to the effluent rate for both dialyzers. However, we
observed greater diffusive clearances for small molecules with M-100 than w
ith M-60 at a Q(D) of 1.5 to 2.5 L/h, the difference being more significant
as molecular weight increased. For beta(2)-M, diffusive clearance was very
low and rapidly reached a plateau of 8 and 12 mL/min for M-60 and M-100, r
espectively at a Q(D) greater than 1.5 L/h. Convective clearances for beta(
2)-M increased nonlinearly up to 20 +/- 2 mL/min at a progressively greater
Q(UP) (from 0.5 to 2 L/h) for both M-60 and M-100. This nonlinear increase
was attributed to an increase of almost 40% in UP for beta(2)-M from a Q(U
F) of 0.5 to 2 L/h. Third, the interaction between convection and diffusion
was assessed by measuring solute clearances at a fixed Q(UF) (1 and 2 L/h)
and variable Q(D) (0.5 to 2.5 L/h). For small molecules, no significant in
teraction between convection and diffusion was noticed with M-100, whereas
only a small interaction was noticed with M-60. However, for beta(2)-M, the
addition of diffusion (Q(D), 0.5 to 2.5 L/h) did not result in any signifi
cant increase in total clearances over convective clearances for M-60 and M
-100. This observation suggests that the diffusive clearances for Sp-M obse
rved with M-60 and M-100 at a Q(UF) of 0 L/h and at various Q(D) probably o
ccurs by convective fluxes across the membrane. These results demonstrate t
hat convection is more efficient than diffusion in removing mixed-molecular
-weight solutes during CRRT. (C) 1999 by the National Kidney Foundation, In
c.