Membrane hemofiltration

Fig. 5. Cross section of blood-clogged hemofiltration acryUc hoUow-fiber membrane. The spheroids are red blood ceUs. Courtesy of I. Cabasso.

Fig. 14. Mass transfer across hemodialysis and hemofiltration hoUow-fiber membranes.

In the hemofiltration HF (i.e., ultrafiltration see Section 8.3) of blood, using an appropriate membrane, all of the solutes in plasma below a certain molecular weight will pass into the filtrate at the same rate, irrespective of their molecular sizes, as occurs in the human kidney glomeruli. Since its first proposal in 1967 [14], HF has been studied extensively [15-17]. Although a dialysate solution is not used in HF, the correct amount of substitution fluid must be added to the blood of the patient, either before or after filtration, to replace all the necessary blood constituents that are lost in the filtrate. This substitution fluid must be absolutely sterile, as it is mixed with the patient s blood. For these reasons, HF is more expensive to perform than hemodialysis, and so is not generally used to the same extent. 

Walch et al.58) in Hoechst fabricated a membrane for hemofiltration from 2,2,4-trimethylhexamethylenediamine-2,4,4-trimethylhexamethylenediamine-terephthalic acid copolymer 13. The membrane has an ultrafiltration capacity for cattle blood of 1640 1/m2 day bar, a retention value of 44 % for dextran 7000, and molecular weight limit of 58000 + 6000. 

A 13-year-old boy underwent a 17-hour craniotomy in an attempt to resect an arteriovenous malformation with propofol-based anesthesia. He developed frank propofol infusion syndrome after 74 hours of postoperative propofol sedation in the neurosurgical ICU (used to manage intracranial hypertension). Echocardiography showed severe biventricular dysfunction despite extraordinary pharmacological support. Extracorporeal circulation with membrane oxygenation (ECMO) was instituted at the bedside via cannulation of the left femoral vessels. Hemofiltration... 

As mentioned already, the artificial kidney is a classic example of chemical engineering prowess. The proper design of such devices requires a description of both water and solute transport to and from blood, across membranes, and to and from an adjacent fluid known as the dialysate. Variations on this theme include hemodilution, hemoconcentration, and hemofiltration. Applications of these same principles have been used to examine continuous ambulatory peritoneal dialysis. Oxygenation of blood,... 

Brunet P, Jaber K, Berland Y, Baz M. Anaphylactoid reactions during hemodialysis and hemofiltration role of associating AN69 membrane and angiotensin I-converting enzyme inhibitors. Am J Kidney Dis 1992 19 444-7. 

Hemofiltration (HF) is a similar modaUty whereby solute is removed by convection. The hemofiltration apparatus differs from HD in that no dialysate circuit is present. Rather, blood within the cartridge is subject to pressure across a high-flux (large pore) membrane creahng an ultrafiltrate of solutes and water while cells and large solutes remain in the blood and return to the circulation. Hemofiltration typically requires replacement of fluid and electrolytes lost in the ultrafiltrate. 

Sutures, dressings, hemofiltration membranes Biodegradable tissue engineering scaffolds and devices... 

Clarification of rough beer, vinegar and pasteurization of clarified beer by cross-flow ultrafiltration are also very common processes utilizing hollow fiber ultrafiltration. As seen in Table 1, an important number of membrane manufacturers specialize in medical and pharmaceutical applications. In pharmaceutical and biotechnology industries, hollow fiber membranes are used for the concentration, separation, and purification of physiological activators such as antibiotics, vaccines, enzymes, proteins and peptides, as well as blood purification (hemofiltration). As a physical barrier for bacteria and viruses, membranes are also a popular option for the production of purified water for hospitals and pharmacies. 

Two membrane-based therapies, hemodialysis and hemofiltration, are used as substitutes for renal function. On comparing these substitution therapies with the natural kidney, it should be remembered that each therapy functions for four to six hours, three times per week, in contrast to the continuous performance of their natural counterpart. Hemodialysis and hemofiltration may also be used to augment normal renal function in the cases of drug detoxification and fluid removal, respectively. 

Figure 1 Relative permeability spectra for synthetic and natural membranes. Curves (1) and (2) represent the glomerular membrane for neutral and anionic solutes, respectively (8), curve (3) hemofiltration membranes (.91, and curve (4) hemodialysis membranes (10), Reproduced with permission from Ref. 52. Copyright 1980 Kidney International.

Blends of isotactic and atactic polymethylmethacrylate (PMMA) in solution have been used to form semipermeable membranes, for both hemodialysis and hemofiltration. Details of the polymer properties are not available (18). 

Polysulfone. Polysulfone homo- (19) and copolymers have been formed into hollow fiber membranes for hemofiltration by solution extrusion, followed by coagulation and washing. Equilibrium water absorption by these membranes varies between 0.85 and 2.1 percent. The water-equilibrated polymers are glassy at room temperature. Sieving properties of copolymer hemofilters prepared with a 2-phenyl-2-phenoxy propane segment have been characterized (2). The hydrophobicity of this polymer is reflected in a significantly altered rejection spectrum in the presence of protein when compared to saline solutions. 

As outlined earlier, hemodialysis and hemofiltration require the removal of solutes smaller than albumin from blood. Solute mass transfer rates across hemodialysis membranes cannot exceed the diffusivity of the solute In water. Solute diffusivity decreases with Increasing molecular diameter (Stokes-Einstein relationship) consequently, solute mass transfer rates for hemodlalyzers intrinsically decrease with increasing molecular size. In addition to limitations Imposed by diffusion In solution, mass transfer is further limited by diffusion resistance in the membrane as well as boundary layer effects resulting from laminar flow both of these effects are also functions of molecular size. The quantitation of mass transfer In hemodlalyzers has been reviewed extensively (22). 

One aspect of RRT that is overlooked by most clinicians is which hemodialyzer or hemofilter is used during the treatment. The material used to make the membranes of hemodialyzers (for hemodialysis) and hemofilters (for hemofiltration) varies by manufacturer, and recent evidence suggests that which membrane material is used may influence the outcomes of patients with ARF. When blood comes into contact with these membranes, the complement cascade is activated, resulting in an immune reaction. Each type of membrane induces complement to a different degree. Those that cause less of a complement cascade are termed biocompatible, while membranes that induce a large reaction are considered bioincompatible. Bio-... 

Kronfol NO, Lau AH, Barakat MM. Aminoglycoside binding to polyacrylonitrile hemofilter membranes during continuous hemofiltration. ASAIO Transactions 1987 33 300-303. 

Development of a Cellulose Acetate Membrane and a Module for Hemofiltration... 

Figure 14. Structure of the developed module for hemofiltration, Daicel Hemo-Fresh 1, unit compartment 1.1, membrane 1.2 substrate cloth 1.3, heat-sealed side edge 1,4, smooth-surfaced and corrugate-shaped blood compartment spacer 2, PET spacer between unit compartments 3, polyurethane end seal 4, case 5, cap.

A new cellulose acetate membrane for hemofiltration was developed by employing the mixtures of liquids of opposite properties for both solvent for cellulose diacetate and additive to the polymer solution. The additive was composed of water and organic solvents of limited water solubility. The role of the additive is likely to have somewhat different aspect from that of other additives known so far. 

A new high performance module, Daicel HemoFresh (a registered trademark) for hemofiltration, is characterized by both superior membrane performance and good blood compatibility. It is now being confirmed clinically that this module is superior to other hemofilters so far available with regard to UFR, permeation of undesirable solutes, clotting, hemolysis and the amount of blood left behind in the module. 

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