Dialyzers surface area

Factors that influence drug dialyzability in chronic ambulatory peritoneal dialysis include drug-specific characteristics (e.g., molecular weight, solubility, degree of ionization, protein binding, and VD) and intrinsic properties of the peritoneal membrane (e.g., blood flow, pore size, and peritoneal membrane surface area). 

In the microadaptation of this method, 50 pi of the sample is prediluted to 1.0 ml. This total volume is added to the sample cup. The analysis rate is reduced to twenty determinations per hour, which, along with the larger sample pick-up tube, results in the complete utilization of the diluted sample. Apparently the membrane area in a single dialyzer unit allows a sufficiently adequate amount of urea to transfer to the recipient stream to conduct the analysis. This compares with the need for additional dialyzing surface required in the microadaptation of the glucose method. 

In this equation./ A is the surface area X is the thickness of the dialyzing membrane/ and D is the diffusivity of a given solute in the dialyzing membrane. Solute diffusivity is primarily determined by molecular weight. 

EIGURE 6.1 Plot of dialysis clearance (CL]j) vs. dialyzer blood flow (Q). The theoretical curves were fit to experimental data points to obtain estimates of the permeability coefficient-surface area product (P-S) for each solute. Flow-limited clearance is indicated by the dashed line. The data were generated with a Kolff-Brigham type hemodialysis apparatus. (Reproduced with permission from Renkin EM. Tr Am Soc Artific Organs 1956 2 102-5.)... 

An analysis of relative dialysis clearance and dialyzer permeability coefficient-surface area products that was made for the closely related compounds procainamide (PA) and N-acetylprocainamide (NAPA) is summarized in Table 6.3. Dialyzer clearance measurements of PA (CLpa) and NAPA (CLmapa)... 

TABLE 6.3 Dialyzer Permeability Coefficient-Surface Area Products for PA and NAPA S... 

An example of a hemodialyzer is shown in Figure 45-17. The most important fimctional part is the dialyzer membrane. Biocompatibihty of the dialyzer membrane is an essential requirement because of high surface areas and long contact times with blood. The most important physiological interactions that occur, apart from protein fouling of tubing and membranes, are complement activation and induction of cytokine release. 

Dialysis membranes are classified as conventional (standard), high-efficiency, and high-flux. Conventional dialyzers, mostly made of cuprophane, have small pores that limit clearance to relatively smaU molecules such as urea and creatinine. High-efficiency membranes have large surface areas and thus have a greater ability to remove water, urea, and other small molecules from the blood. High-flux... 

The sample volume has no influence on the dialysis factor. This implies that for a fixed dialyzer, the ratio of membrane surface area to sample volume will not affect the dialysis factors. 

Fresh high-flux dialysis membranes achieve approximately 23—37% reductions in plasma P2M levels [344]. However, dialyzer reuse significantly impairs the removal of P2M [345]. Indeed, it has been recognized that non-specific adsorption of middle molecules on the surface of these synthetic high-flux membranes, rather than difiusion through the membrane, can account for significant amounts of the device s clearance [346, 347]. With the surface area of membranes in the dialysis device amounting to less than 2 m, the adsorption capacity of the device is obviously too small. 

The specific immersion wetting enthalpies of kaolinite, illite, and their organo-philic derivatives were investigated in methanol and benzene in our earlier publications [35,37,38]. These data reveal that the heat of immersion in methanol is the highest in the case of the dialyzed hydrophilic mineral, and with increasing surface modification its value decreases. The comparison of immersion wetting enthalpies relative to unit mass of the adsorbent is justified only when the specific surface area of the adsorbent is constant. It is also known, on the other hand, that the value of liquid sorption capacity, is a function of surface modification 02 = where 2flm,2 is the hydrophobic surface area and a is the total... 

The performance of the hollow-fiber dialyzers depends on many fiber properties such as fiber dimension, surface area, porosity and water permeability. 

For some people, it s unbelievable and may sound like a surprise 900 different types of dialyzers are commercially available worldwide in 2014. They differ in geometric design, membrane polymer and surface area, capillary geometry and... 

Adsorption onto the membrane does contribute to the removal of noxious compounds, such as interleukin-1 and interleukin-6 (lL-1, lL-6), tumor neaosis factor (TNF), peptides and 62-microglobuhn [71], As a result of the restricted surface area of dialyzers, however, adsorption capacity will rapidly be saturated. Acceptable rates of net removal by adsorption can only be achieved if the surface area is drastically increased by specifically designed devices [75, 76] or blood purification systems combining filtration and adsorption mechanisms in two devices, either arranged in parallel or in series. 

Example 8.1.20 Countercurrent dialysis may be explored to eliminate substantially 0.05M sodium phosphate from a Img/ml solution of bovine serum albumin (BSA) and 25 mM Tris buffer at a pH of 7 (via NaOH). The dialyzing buffer composition is 25 mM Tris and the pH is 7 (via HCl). The dialysate flow rate is lOOml/min. The membrane module has 0.2 surface area. The value of Kic for the phosphate salt for one membrane module is 0.020 cm/min and that for two modules in series is 0.015 cm/min. Determine the values of (C,yo/C r) for sodium phosphate using the expression developed in Problem 8.1.22 for the following cases (a) feed flow rate, lOcm /min (b) feed flow rate, 20 cm /min (c) feed flow rate, 10 cm /min and two membrane modules in series. Comment on the effects of feed flow rate and putting membrane modules in series. 

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