Effect of Hollow Fiber Length on Solute Removal and Quantification of Internal Filtration Rate by Doppler Ultrasound

Abstract

Renal replacement therapy with dialyzers capable of enhanced internal filtration (IF) can be an alternative to standard hemodiafiltration, as it provides convective solute removal comparable to that of hemodiafiltration by a simple procedure. In this study, we clinically evaluated the effect of the hollow fiber length in the dialyzer, a crucial factor influencing the rate of IF, by comparing two commercial dialyzers (BS-1.6U, BS-1.6UL, Toray, Japan) which differed in the fiber length, but had the same surface area and inner diameter of their hollow fibers. We showed that in the dialyzer with the longer fibers, the pressure profile along the dialyzer was significantly altered, and the solute clearance tended to be increased. In addition, we successfully quantified the IF rate with a Doppler ultrasound in the experimental circuit, by measuring the blood flow velocities along the bundle of fibers. We showed that the changes in the blood flow velocity were more marked in the dialyzer with the longer fibers; the calculated IF rates in the dialyzers with the shorter and longer fibers were 11.1 mL/min and 37.7 mL/min, respectively, which seemed to be compatible with the solute clearances. This simple and readily applicable method is expected to be useful in the development of modified dialyzers to fully exploit the benefits of IF in renal replacement therapy.

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

“…Similarly, mass conservation for the flow of plasma proteins in the blood compartment gives: (14) which yields:…”

“…The interaction between these factors is rather complex and it involves nonlinear relationships resulting in different effects. In the past, experimental quantification of IF/BF was carried out in vitro by measuring the local concentration of a marker molecule [12] , by scintigraphic methods [13] , or by echo-Doppler blood velocity measurements [14] . But applying such methods systematically in vivo does not seem to be feasible, due to equipment complication and/or to the requirement of additional competencies.…”

Pulse Push/Pull Hemodialysis: Convective Renal Replacement Therapy

“…Obviously, dialyzer length effectively regulates dialysate pressure drops. In one study conducted to clarify the effect of dialyzer length on solute clearance, middle-to-large uremic molecules, such as 2M and alpha-1 microglobulin ( 1M), were shown to be better cleared by a 250 mm dialyzer than a 195 mm dialyzer (Sato et al, 2003). Dialysate pressure drop can also be manipulated by modulating membrane packing density.…”

“…Thus, changes in blood velocity along a dialyzer provide information on blood volume changes and on amounts of forward and backward filtration. In one study, the internal filtration rate of a 250 mm dialyzer was found to be 37.7 ml/min by Doppler ultrasonography, but only 11.1 ml/min for a standard 195 mm dialyzer (Sato et al, 2003). Doppler ultrasonography is straightforward, non-invasive, and easily used at bedside (Mineshima, 2011).…”

Modeling of Internal Filtration in Theranova Hemodialyzers

“…While several previous studies have estimated internal filtration rates for standard high-flux filters [17][18][19] , a similar quantitative assessment for the HRO filter class has not been performed. Therefore, the aim of this study was to quantify convective volumes for 2 HRO filters, Theranova 400 and Theranova 500 (Baxter International Inc., Deerfield, IL, USA), when used under typical HD operating conditions.…”