Dual-stage filtration cartridge

Details Dual-stage filtration cartridge Dual-stage filtration cartridge

2001-10-30

2004-04-13

Kim, John (Department: 1723)

Liquid purification or separation

Processes

Liquid/liquid solvent or colloidal extraction or diffusing...

C210S321600, C210S321640, C210S321720, C210S321800, C210S321810, C210S321880, C210S321890, C210S321900

Reexamination Certificate

active

06719907

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to filtration devices and methods and, more particularly, to a filtration cartridge and its uses as a hemodiafilter in one application and a fluid filter that produces sterile fluid in another application.
BACKGROUND OF INVENTION
The most common treatment for End Stage Renal Disease (ESRD) essentially consists of a hemodialysis process, wherein blood to be cleaned flows on one side of a semi-permeable 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.
Two primary needs must be met for hemodiafiltration to be effective. The first is for a patient treatment diafilter that allows for high filtration rates and as a result increased clearances of toxins. The second is for a sterilizing filter or series of filters that can provide large volumes of sterile infusion fluid in a continuous manner.
Regarding the first need, state of the art designs for hemodiafilters are substantially equivalent to those of high flux dialyzers. Such filters consist of a bundle 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 by diffusion is decreased. In other words, the efficiency of the removal of the toxins is less than desired. 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. This is typically limited to approximately 25% of the blood flow.
With respect to the second need, hemodiafiltration requires large volumes of sterile infusion fluid be available, therefore the standard methodology of IV infusion (hanging one liter saline bags) is not appropriate. Instead a method in which sterile fluid is produced in a continuous manner is generally required to satisfy this need.
There are methods where non-sterile infusion fluid for hemodiafiltration is filtered through one or a series of filters to render it sterile before infusion into the patient's bloodstream. The filtration arrangement in these processes must remove endotoxins, bacteria, and other pyrogen-inducing compounds. If a filter should fail during the process, a patient may suffer a septic or pyrogenic reaction due to inadequately filtered fluid.
Several filtration techniques and devices do currently exist. For example on-line production of substitution fluid is described in D. Limido, et al.,
“Clinical Evaluation of AK
-100
ULTRA for Predilution HF with On
-
Line Prepared Bicarbonate Substitution Fluid. Comparison with HD and Acetate Postdilution HF
”, International Journal of Artificial Organs, Vol. 20, No. 3 (1997), pp. 153-157. Another sterility filter is described in U.S. Pat. No. 4,784,768 to Mathieu. Most prior art schemes have key drawbacks, they either rely on a single filter to sterilize the fluid or they use two separate filters in series increasing the cost and complexity.
The need exists for a filter that provides redundant sterile filtration and produces physiologic fluid suitable for patient infusion.
SUMMARY OF INVENTION
In attempting to meet the first need of providing a diafilter that accommodates high filtration rates, one embodiment of the diafilter reduces and/or eliminates the drawbacks of prior art hemodiafiltration devices by providing a scheme in which blood is diluted after it is partially, but not fully, diafiltered. The diafiltration scheme of the present invention combines the benefits of pre-dilution schemes, e.g., high filtration rates, with the benefits of post-dilution schemes, e.g., high diffusive and convective efficiencies. The present diafilter can be adapted to operate in conjunction with conventional diafiltration machines, including but not limited to Fresenius 4008 On-Line Plus, Gambro AK 200 Ultra. Alternatively, the diafilter may be used with conventional hemodialysis machines, including but not limited to, Fresenius 2008H, Baxter SPS 1550, Cobe Centry System 3, etc, that have been modified to provide a source of replacement fluid. For example, a pump or valve meters dialysate from a tee in the main dialysate stream and passes it through sterilizing filters.
When serving as a diafiltration cartridge, the present invention has blood and dialysate inlet and outlet ports. The cartridge includes a single housing, for example, a cylindrical housing, which houses two hemodiafiltration stages, wherein the first stage has a blood inlet and the second stage has a blood outlet. Accordingly, the present invention accomplishes dual-stage diafiltration within a single cylindrical housing having a cylindrical hollow fiber bundle disposed therein. The diafilter thus has the appearance of a traditional dialyzer with the exception that the construction of its two ends or header caps differs from that of a traditional dialyzer design. The first end cap includes both the blood inlet and blood outlet ports separated by an internal wall and seal, which is designed to segregate the filter into first and second diafiltration stages. The second end cap serves as blood/replacement fluid mixing chamber and has an inlet port for receiving substitution fluid.
In the diafilter embodiment of the present invention, the blood inlet and outlet ports are located at a first end of the cartridge. The dialysate outlet is preferably also located at or near the first end of the cartridge. For example, in one exemplary embodiment, the blood inlet and outlet ports and dialysate outlet are located at the top (first end) of the cartridge. The main cylindrical housing contains a longitudinal bundle of high flux semi-permeable hollow fibers sealed off from the dialysate compartments at each end by a potting compound, such as polyurethane. The substitution fluid inlet and the dialysate inlet are located at or near an opposite second end, e.g., the bottom of the cartridge. At the substitution fluid inlet port a sterile replacement fluid is mixed with the partially diafiltered blood. This occurs in a common header region where the blood exits the hollow fibers of the first stage and enters the hollow fibers of the second stage. The dialysate flow is common to the two filter stages and runs counter-current to blood flow in the first stage and co-current to blood flow in the second stage.
The counter-current flow in the first stage keeps a maximum conc

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