A New Semiempirical Mathematical Model for Prediction of Internal Filtration in Hollow Fiber Hemodialyzers

Abstract

The potential of convective solute transport for blood purification has been widely explored. New techniques (such as hemodiafiltration), based on a combination of diffusion and convection techniques, have been developed. Owing to the internal filtration/backfiltration (IF/BF) phenomenon, high-flux dialysis also relies on a convective component, which, however, is hard to quantify and thus optimize. In this work, we developed a mathematical model designed to supply the clinician with a quantification of the IF/BF fluxes taking place during high-flux dialysis. IF fluxes are predicted based on the machine settings and blood hematocrit/protein concentration. The hydraulic characteristics of commercial dialyzers were derived from bloodless bench tests. Moreover, an in vitro blood test was conducted on a 1.8 m² polysulfone dialyzer using an established scintigraphic analysis, for verification of model prediction accuracy. Results of simulations show that the IF/BF rate is sensitive to the blood flow rate and (to a lesser extent) to the dialysate flow rate. Increasing net ultrafiltration rates resulted in parallel increases of direct filtration and simultaneous decreases of BF. IF/BF is rather influenced by blood composition, due to the complex dependence of oncotic pressure and blood viscosity upon hematocrit and plasma protein concentration. Simulation results showed an excellent agreement with the experimental results obtained with scintigraphy, with only a 3% prediction error. With respect to some previous works, this model is simpler in its theoretical approach. It allows implementation into a user-friendly software tool and might be used to predict the convective component in high-flux dialysis and possibly to optimize it.

Technical Breakthroughs in the Wearable Artificial Kidney (WAK)

“…This intermittent change in gradient and the bidirectional flux across the membrane suggest that this device may perform a different type of hemodiafiltration, similar in some aspects to that described by Fiore et al and called "internal hemodiafiltration" (26,27). However, the WAK pump pulsatile flow pattern causes intermittent opposite phase changes in TMP and thus differs from other types of hemodiafiltration described (27).…”

The Rise of Expanded Hemodialysis

“…This mechanism, although invisible, makes it possible to achieve a significant amount of convection inside the dialyzer where filtration takes place in the proximal part and backfiltration compensates in the distal part. The ultrafiltration control system of the dialysis machine regulates the process and provides the exact amount of net filtration required for the scheduled weight loss of the patient [18,19,20]. There is no need for complicated equipment, but a blood flow of 300 mL/min or higher and a dialysate flow of 500 mL/min or higher are adequate.…”

Pulse Push/Pull Hemodialysis: Convective Renal Replacement Therapy

“…Using this model, internal filtration volumes and reinfusion rates were determined during internal HDF and post-dilution HDF modes, and revealed that differences between total convections (4.1 and 5.4 L/h for iHDF and HDF) well reflected differences between 2M clearance rates (123±11 and 149±26 ml/min for iHDF and HDF, respectively) (Lucchi et al, 2004). In a study conducted using in vitro scintigraphy method to verify this semi-empirical model, the model was found to show excellent accuracies of around 97% and a prediction error of only 3% (Fiore et al, 2006). In addition to the mathematical model, methods for performing indirect measurements of the internal filtration have also been proposed.…”