Data acquisition system for dialysis machines. A model for membrane hydraulic permeability.

ABSTRACT

Membrane permeability is a key determinant of dialyzer performance; in vivo, membrane hydraulic permeability is affected by the formation of a protein cake on its surface, reducing ultrafiltration and convective fluxes. The purpose of this work was to evaluate the real hydraulic permeability of high flux polysulfone membrane under conditions of hemodiafiltration, and to consequently develop a mathematical model to estimate ultrafiltration Kuf and protein adsorption Kc coefficients. The DIB08 data acquisition system adapted to the Fresenius 2008E dialysis machine (Fresenius, Bad Homburg, Germany) allowed the recording of useful information for dialysis quantification, which was then processed by a bedside computer. The system was able to evaluate Kuf(t) profile, by calculation from the transmembrane pressure over time (TMP(t)) and ultrafiltration rate (Quf)Kuf (t) = Quf/TMP (t). Subsequent modeling of Kuf involved the determination of two key parameters Kufhd (dialyzer permeability during diffusion only) (in mL/h/mmHg), and Kc (protein adsorption coefficient) (in mL/h/mmHg2). The model chosen was the following Kuf (t) = Kuf0 x (1 - (Kc/Kuf0) x In(t + 1)) where Kuf0 represents the initial Kuf obtained at the beginning of the session. Thirty-one sessions were evaluated by real kinetic analysis, from which the mathematical model was derived. It included 27 postdilutional on-line hemodiafiltration and four hemodialysis sessions performed in four patients with nonreused HF80s dialyzers. For the analysis, three subgroups were defined Group 1, first session of the week (Monday or Tuesday); Group 2, second session of the week (Wednesday or Thursday); and Group 3, third session of the week (Friday or Saturday). Results of Kuf and Kc obtained by real kinetic analysis are presented. The midweek session was associated with a higher membrane hydraulic permeability, most likely relative to lesser ultrafiltration rates and an associated relative decrease in membrane protein coating, represented by Kc. The described data acquisition system allowed the assessment of real time membrane hydraulic permeability and the subsequent development of a mathematical model to estimate this fundamental parameter as it functions to hemodialyzer performance.