Liquid purification or separation – Constituent mixture variation responsive – With membrane
Reexamination Certificate
1999-12-30
2001-11-13
Drodge, Joseph W. (Department: 1723)
Liquid purification or separation
Constituent mixture variation responsive
With membrane
C210S252000, C210S321710, C210S321800, C210S321890, C210S323200, C604S006090
Reexamination Certificate
active
06315895
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to hemodiafiltration devices and methods and, more particularly, to a new hemodiafiltration cartridge and its method of use.
BACKGROUND OF INVENTION
Current treatment for End Stage Renal Disease (ESRD)essentially consists of hemodialysis process, wherein blood to be cleaned flows on one side of a semipermeable membrane and a physiologic solution, a dialysate, flows on the other side of the membrane, whereby toxins in the blood are transferred from one side to the other. The primary driving force in this treatment is diffusion. This process is generally effective in removing small Molecular Weight (MW) toxins such as urea and creatinine. However, this process is much less effective in removing middle range MW substances, e.g., substances having a molecular weight higher than about 1 kDa, because of a low diffusion coefficient of such substances.
To a much lesser extent hemodiafiltration is used as a treatment modality. In hemodiafiltration, diffusion is combined with filtration to remove toxins from the blood. Sterile non-pyrogenic replacement fluid is added to the blood either prior to or after it enters a hemodiafiltration cartridge. The replacement fluid replaces plasma water which is filtered across the semi-permeable membrane during the hemodiafiltration process. The advantage of hemodiafiltration over hemodialysis is the use of filtration in conjunction with diffusion to remove toxins. As a result of this combination, hemodiafiltration is more efficient at removing small molecules, e.g., creatinine and urea, as well as removing much greater quantities of middle range MW substances, by filtration.
State of the art designs for hemodiafiltration filters are substantially equivalent to those of high flux dialyzers. Such filters consist of bundles of hollow fibers in a cylindrical housing. During operation of the hemodiafiltration system, replacement fluid is injected into the blood either upstream (pre-dilution) or downstream (post-dilution) of the filter cartridge.
Diafiltration devices using pre-dilution or post-dilution schemes have inherent efficiency limitations. Pre-dilution schemes allow for relatively unlimited filtration, however, because the blood is diluted prior to reaching the filter, the overall mass transfer of solutes is decreased. Post-dilution schemes have the advantage of keeping blood concentrations high, resulting in more efficient diffusion and convection of solutes, however, the increased concentration of blood cells and the resultant higher blood viscosity during filtration, poses a limit on the amount of water that can be filtered.
SUMMARY OF INVENTION
It is an object of some aspects of the present invention to provide a hemodiafiltration cartridge that enables a higher toxin removal rate and higher toxin removal efficiency than that of prior art hemodiafiltration devices. The present invention reduces and/or eliminates the above mentioned drawbacks of prior art hemodiafiltration devices by providing a scheme in which blood is diluted after it is partially, but not fully, diafiltered. The scheme of the present invention combines the benefits of predilution schemes, e.g., high filtration rate, with the benefits of post dilution schemes, e.g., high diffusive and convective efficiencies. The device of the present invention may be adapted to operate in conjunction with a dual-stage hemodiafiltration machine, or a standard dialysis machine using dual-stage hemodiafiltration, such as the machines described in PCT patent application No. PCT/US99/17468 and in PCT patent application No. PCT/US99/25804, assigned to the assignee of the present application, the disclosures of both of which are incorporated herein by reference in their entirety. Alternatively, by making appropriate alterations in a dual-stage device according to the present invention, e.g., by allowing direct flow of dialysate fluid between the two stages of the dual-stage device, the present invention may be adapted for use in conjunction with a standard dialysis machine using single stage diafiltration.
A hemodiafiltration cartridge in accordance with the present invention has blood and dialysate inlet and outlet ports. The cartridge of the present invention includes two housings, for example, two cylindrical housings, corresponding to two hemodiafiltration stages, wherein the first stage has a blood inlet and a dialysate outlet, and the second stage has a blood outlet and dialysate inlet.
In an embodiment of the present invention, the blood inlet and outlet ports and the dialysate inlet and outlet ports are located on one side, e.g., at the top, of the cartridge. Each of the two hemodiafiltration stages of the present invention may contain longitudinal bundles of high flux, semi-permeable, hollow fibers, which may be sealed off from the dialysate compartments at each end by a potting compound such as polyurethane. The blood inlet may include a header member that may be attached to a casing of the cartridge, at the fiber ends.
In one embodiment, the two stages are produced separately and then assembled together. Alternatively, the two stages may be manufactured as a single unit. The method of production does not affect the resultant dual-stage cartridge.
In an embodiment of the present invention, the cartridge includes two additional ports, preferably at the second end, e.g., the bottom end, of the cartridge. One of these additional ports may be a substitution fluid inlet where sterile replacement fluid is mixed with the blood. This mixing may take place in a common header space, between the first and second stages, where the blood exits the hollow fibers of the first stage and enters the fibers of the second stage.
The other additional port may be an inter-dialysate port, for example, a dual aperture port, which directs dialysate fluid exiting the second stage of the cartridge to cycle through the controlling machine, where the flow rate of the dialysate may be metered, and returns the dialysate to the first stage. While the total level of filtration of the cartridge is generally controlled by the dialysate inlet and outlet rates, the inter-dialysate port enables control of the individual filtration rates of the two cartridge stages. This port may also enable modification of the dialysate flow rate or dialysate composition between the two stages. In an alternative embodiment of the invention, the dialysate fluid exiting the second stage may be directed to flow directly into the first stage, e.g., by providing an aperture-connecting cap to the dual-aperture port.
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“Thoughts and Progress”,Artificial Organs,11(2):188-190, New York, 1987.
“Centralized On
Collins Gregory R.
Summerton James
Cecil Terry K
Darby & Darby
Drodge Joseph W.
Nephros, Inc.
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