Hemodialysis Membranes

Ofsthun, Norma J.; Karoor, Sujatha; Suzuki, Masatoshi

doi:10.1002/9780470276280.ch19

Cited by 4 publications

(5 citation statements)

References 54 publications

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“…So far we have examined only the concentration gradient as the driving force, but in HD another force is involved to enhance the transport of larger solutes from the blood to dialysis fluid compartment. Ultrafiltration is a pressure-driven mechanism to increase flux (fluid transport) across the membrane and instead of hydraulic permeability (flux units of L/m 2 /h) the volumetric filtration rate per mmHg is expressed in the form of the KUF (in mL/h/mmHg) [ 6 , 7 , 17 , 30 ]. It is a value derived from in vitro measurements whereby bovine or human blood is ultrafiltered at different transmembrane pressures [ 31 ].…”

Section: Membrane Separation Determinants Based On Fluxmentioning

confidence: 99%

“…For the so-called high-flux membranes, at lower TMPs (∼0–100 mmHg), a linear relationship exists between the ultrafiltration rates (UFRs), but plateaus at relatively high TMPs (>150 mmHg); the KUF is derived from the linear part of the plot. It should be noted that the KUF is not normalized with respect to surface area and it is a property of the dialyser, not just the membrane; a dialyser with membranes containing relatively small pores can have a high KUF if the surface area is large [ 7 , 30 ].…”

Section: Membrane Separation Determinants Based On Fluxmentioning

confidence: 99%

“…To summarize, the concept of flux, fundamental to the functioning and designation of various HD therapy modalities that derive their names from this term, is a highly complex and multifactorial transport phenomenon. The hydraulic permeability—flux—of a membrane varies with the membrane thickness, pore size distribution and pore density [ 7 ]. Thus it is not the easiest of concepts to comprehend, or to describe or control in real life.…”

Section: Membrane Separation Determinants Based On Fluxmentioning

confidence: 99%

“…The size—and geometry—of the pores of each membrane depend on the production process of the manufacturer. The main determinants are the choice of the polymer systems and the thermodynamic membrane ‘spinning’ conditions [ 6 , 7 , 69 , 70 ].…”

Section: Membrane Separation Determinants Based On Selectivitymentioning

confidence: 99%

“…As in the body, the primary driving force in HD is diffusion, created by the net movement of substances from a region of higher concentration (blood) to a region of lower concentration (dialysis fluid). Further, when transmembrane pressure (TMP) is applied to increase the flow of fluid across the membrane to enhance solute removal, flux is then represented as mL/h/mmHg, the ultrafiltration coefficient (KUF) and a measure of the water or hydraulic permeability of the membrane [ 6 , 7 ].…”

Section: Introductionmentioning

confidence: 99%

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Flummoxed by flux: the indeterminate principles of haemodialysis

Bowry¹,

Kırçelli

Misra

2021

Clinical Kidney Journal

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In haemodialysis (HD), unwanted substances (uraemic retention solutes or ‘uraemic toxins’) that accumulate in uraemia are removed from blood by transport across the semipermeable membrane. Like all membrane separation processes, the transport requires driving forces to facilitate the transfer of molecules across the membrane. The magnitude of the transport is quantified by the phenomenon of ‘flux’, a finite parameter defined as the volume of fluid (or permeate) transferred per unit area of membrane surface per unit time. In HD, as transmembrane pressure is applied to facilitate fluid flow or flux across the membrane to enhance solute removal, flux is defined by the ultrafiltration coefficient (KUF; mL/h/mmHg) reflecting the hydraulic permeability of the membrane. However, in HD, the designation of flux has come to be used in a much broader sense and the term is commonly used interchangeably and erroneously with other measures of membrane separation processes, resulting in considerable confusion. Increased flux is perceived to reflect more ‘porous’ membranes having ‘larger’ pores, even though other membrane and therapy attributes determine the magnitude of flux achieved during HD. Adjectival designations of flux (low-, mid-, high-, super-, ultra-) have found indiscriminate usage in the scientific literature to qualify a parameter that influences clinical decision making and prescription of therapy modalities (low-flux or high-flux HD). Over the years the concept and definition of flux has undergone arbitrary and periodic adjustment and redefinition by authors in publications, regulatory bodies (US Food and Drug Administration) and professional association guidelines (European Renal Association, Kidney Disease Outcomes Quality Initiative), with little consensus. Industry has stretched the boundaries of flux to derive marketing advantages, justify increased reimbursement or contrive new classes of therapy modalities when in fact flux is just one of several specifications that determine membrane or dialyser performance. Membranes considered as high-flux previously are today at the lower end of the flux spectrum. Further, additional parameters unrelated to the rate of diffusive or convective transport (flux) are used in conjunction with or in place of KUF to allude to flux: clearance (mL/min, e.g. of β2-microglobulin) or sieving coefficients (dimensionless). Considering that clinical trials in nephrology, designed to make therapy recommendations and guide policy with economic repercussions, are based on the parameter flux they merit clarification—by regulatory authorities and scientists alike—to avoid further misappropriation.

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Section: Membrane Separation Determinants Based On Fluxmentioning

confidence: 99%

Section: Membrane Separation Determinants Based On Fluxmentioning

confidence: 99%

Section: Membrane Separation Determinants Based On Fluxmentioning

confidence: 99%

Section: Membrane Separation Determinants Based On Selectivitymentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Flummoxed by flux: the indeterminate principles of haemodialysis

Bowry¹,

Kırçelli

Misra

2021

Clinical Kidney Journal

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Medical Applications of Membranes

Baker

2012

Membrane Technology and Applications

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Synthetische Membranen für die Wasseraufbereitung: aktueller Stand und Perspektiven

Fane

Wang

2015

Angewandte Chemie

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Membrantechnologien für die Aufbereitung von Meer‐ oder Abwasser bieten beste Möglichkeiten, den steigenden Wasserbedarf der Menschheit zu decken. Obwohl die Entsalzung mittels Umkehrosmose (RO, reverse osmosis) und die Abwasserreinigung in Membranbioreaktoren fest etablierte Verfahren sind, gibt es bei verschiedenen Membrantechnologien reichlich Spielraum für Verbesserungen, vor allem hinsichtlich Trenneigenschaften, Energiebedarf und Kosten. Wir sind jetzt in der Lage, ideale Membraneigenschaften anzugeben, und Fortschritte in der Materialwissenschaft und Chemie führen zu immer wirksameren Membranen. Wichtig ist, dass Entwicklungen im Bereich der Membranmaterialien auch von apparativen Verbesserungen der Membrantechnik begleitet werden. Es ist wahrscheinlich, dass Limitierungen in der Fluidmechanik und beim Stoffübergang eine Obergrenze der Membranleistung festlegen werden. Dennoch kann in den nächsten 20 Jahren mit großen Fortschritten gerechnet werden. Dabei dürfte die Umkehrosmose die zentrale Technologie für die Wasserentsalzung und ‐aufbereitung bleiben.

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Hemodialysis Membranes

Cited by 4 publications

References 54 publications

Flummoxed by flux: the indeterminate principles of haemodialysis

Flummoxed by flux: the indeterminate principles of haemodialysis

Medical Applications of Membranes

Synthetische Membranen für die Wasseraufbereitung: aktueller Stand und Perspektiven

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