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Quantitative analysis of convective dose in hemofiltration and hemodiafiltration: “Predilution” vs. “postdilution” reinfusion.

Authors :
Colussi, Giacomo
Frattini, Gianmaria
Source :
Hemodialysis International. Jan2007, Vol. 11 Issue 1, p76-85. 10p. 10 Graphs.
Publication Year :
2007

Abstract

In hemofiltration (HF) and hemodiafiltration (HDF), removal of medium and high-molecular-weight solutes is greatly enhanced by convective mechanisms as compared with simple diffusion; increasing convective flows may allow greater removal rates of these solutes. Use of “predilution” (pre-H[D]F) may allow higher ultrafiltration rates than the “postdilution” mode (post-H[D]F); yet, the dilution of plasma water may have unpredictable effects on “endogenous” water convection. We have applied a mathematical analysis to evaluate and compare endogenous water convective flow rates in pre-H(D)F vs. post-H(D)F. Endogenous plasma water recovered in ultrafiltrate was calculated according to patient (hematocrit, total protein level) and session parameters (blood flow, ultrafiltration rate, programmed weight loss), in absolute terms and as a fraction of endogenous plasma water delivery to the filter. Maximally efficient post-H(D)F was modelled according to a preset postfilter hematocrit or filtration fraction. Nomograms were constructed expressing endogenous water convective fluxes in relation to parameters of interest (ultrafiltration rate, blood flow, hematocrit) with both post-H(D)F and pre-H(D)F, and “efficiency” of pre-H(D)F vs. post-H(D)F (as the ratio of endogenous water convective flow rate with the 2 techniques) as a function of the ultrafiltration/reinfusion rate. In post-H(D)F, the model predicts maximal ultrafiltration rates within the limits of a preset hemoconcentration at the filter outlet; additionally, the model allows to calculate ultrafiltration/reinfusion quantities to be set in pre-H(D)F to equal and overcome maximal convective efficiency of post-H(D)F. This “equivalence” ultrafiltration rate may greatly vary according to patient's hematocrit and blood flow, so that the ultrafiltrate-reinfusate volume available in the system dictates, in any patient, which mode of reinfusion may attain higher “endogenous” convective flow rates. Pre-H(D)F may allow higher fractional and absolute “endogenous” convective flow rates as compared with post-H(D)F, provided that adequate amounts of reinfusate are available. For lower reinfusate volumes than “equivalence” values, post-H(D)F remains a better option. [ABSTRACT FROM AUTHOR]

Details

Language :
English
ISSN :
14927535
Volume :
11
Issue :
1
Database :
Academic Search Index
Journal :
Hemodialysis International
Publication Type :
Academic Journal
Accession number :
23709969
Full Text :
https://doi.org/10.1111/j.1542-4758.2007.00157.x