CA1122536A

CA1122536A - Twin pack hemodialyzer

Info

Publication number: CA1122536A
Application number: CA308,856A
Authority: CA
Inventors: Finley W. Markley
Original assignee: US Department of Energy
Current assignee: US Department of Energy
Priority date: 1977-08-08
Filing date: 1978-08-08
Publication date: 1982-04-27
Also published as: AU3866178A; BE869564A; GB2001867B; DK347678A; GB2001867A; FR2399850A1; IT7826608A0; JPS5635465B2; SE7808391L; DE2833966A1; NO782688L; JPS5430699A; IT1098382B

Abstract

ABSTRACT OF THE DISCLOSURE

The present invention relates to an improved design for a hemodialyzer which provides for increased contact between the blood and the dialysate fluid across the semipermeable mem-brane by increasing the blood flow path in the dialyzer unit, while at the same time increasing the blood velocity through the unit to prevent buildup of fibrin on the semipermeable membrane surfaces. The hemodialyzer of the present invention includes two independent stacks of parallel flattened semi-permeable membrane tubes disposed within a dialyzer casing.
The dialysate fluid flows through the casing within the interior of the flattened tubes, while the blood flows through the casing around and between the semipermeable membrane tubes, the two independent stacks of the tubes being arranged within the casing such that the blood passes through each of the two independent stacks in succession.

Description

TW~N PACK HEMODIALYZER

This invention relates to an improved apparatus for use in the cleansing of impurities from the blood by hemo-dialysis.
The cleansing of cell waste and impurities from the blood by the process of hemodialysis has been known and routinely conducted for many years, with hemodialyzers, commonly referred to as artificial kidneys, being used successfully to treat patients suffering from kidney mal-function or kidney disease. In recent years, efforts to further develop and improve hemodialyzers have been directed toward increasing the efficiency of the hemo-dialyzer unit, improving the units from the standpoint of providing for less stress on the patient and improved safety in the use of the devices, lowering the expense involved in hemodialysis treatment and making hemodial-ysis treatment available to more of those in need of such treatment.
The hemodialyzers presently being used in this country fail to fully satisfy the needs of the vast num-ber of kidney patients in several important respects.Hemodialyzer machines presently used are expensive and hence require a large initial investment for the basic machine and other associated equipment which is necessary for the hemodialysis treatment. A blood pump is generally required because of the flow resistance caused by the large size of the present machines, which size often makes a blood transfusion necessary because of the loss of blood to the blood priming volume of the machines.
In-hospital treatment or the presence of trained medical personnel is often necessary for hemodialysis treatment, l~Z2536 as is the essential rebuilding of the hemodialyzer units under sterile conditions following each hemodialyzer treatment. Partially resulting from these mentioned considerations, the cost of continuing hemodialysis treatments is prohibitive to many patients in need of such periodic treatment and the number of hemodialyzer units available is severely limited in relation to the vast number of those suffering from kidney disorders.
Hemodialyzers are presently being developed in attempts to alleviate some of these problems. One development effort has been directed toward de~ising a small, pumpless, efficient and less expensive hemodialyzer which can be made more widely available and which can make hemodialysis treatment possible for more patients at 3 lower yearly cost. ThiS effort has resulted in the development of a series of models of small pumpless hemo-dialyzers which can meet some of the present needs of kidney patients. The knowledge and advanced technology obtained in the development of each of these hemodialyzer models has enabled the development of the series of pro-gressively more refined and efficient hemodialyzer models, each replacing earlier models and successively offering improvements to the more basic earlier model. The present invention is an improved model in this series of hemodial-yzers.
The present invention is an improved hemodialyzer closely related to a series of models of hemodialyzers of which the present inventor was a coinventor. Two earlier model hemodialyzers, subject of U. S. patent 3,522,885 and U. S. patent 3,56;,258, were small pumpless disposable ~. ZZ~i3~i units consisting of a series of parallel tubes arranged in a stack within a rectangular shaped casing. The blood and the dialysate fluid passed either within the tubes or across and around the exterior of the tubes, with the hemodialyzer of U. S. patent 3,565,258 providing for the passing of dialysate fluid within the supported tubes while the blood flowed across the dialyzer casing between and around the tubes. While this latte~ model proved to be a satisfactory design and underwent clinical testing, it remained desirable to improve the design and increase the efficiency of the hemodialyzer.
An improved design over the dialyzer of U. S. pa-tent 3,565,258 became the subject of another hemodialyzer invented by the present applicant, U. S. patent 3,778,369, which design provided for at least one baffle extending from a side wall of the casing across the width of each of the flattened tubes such that the blood flowing through the dialyzer would flow around the baffles and across the tubes a multiple number of times. The baffles served to lengthen the flow path of the blood passing through the hemodialyzer unit, thereby increasing the amount of contact between the blood and the dialysate fluid across -the semipermeable membrane. While this latter hemo-dialyzer ~las proved to be satisfactory, improvements in the design of hemodialyzers and increases in the efficiency of the hemodialysis are never ending goals.
Therefore it is an object of the present invention to provide a hemodialyzer which is small, can be operated without the need of a blood pump and can be discarded after use.
It is also an object of the present invention to provide a hemodialyzer which has improved efficiency of dialysis and improved operation characteristics.
In accordance with the present invention, a hemodialyzer is provided in which two completely independent stacks of parallel flattened semipermeable membrane tubes are disposed within a .
casing. The two stacks are separated by a solid plate extending from one wall of the casing across the width of the stack to a point near to but not touching the opposite wall o the casing so as to leave a gap between the plate and the opposite wall and thereby divide the interior of the casing into two sections, with each section containing one of the -two independent stacks.
The sections communicate only along the gap between -the plate and the casing wall. The hemodialyzer has associa-ted therewith means for passing dialysate fluid through the casing within the tubes, with that means including a dialysate inlet at one end of the casing and a dialysate outlet at the opposite end of the casing.
The hemodialyzer has associated therewith means for passing blood through the casing around and between the tubes such that the blood flows across and between the tubes in a first of the two independent stacks of tubes and subsequently acxoss and between the tubes in a second of the two independent stacks of tubes, with that means including a blood inle-t near the same end of the casing as the dialysate outlet and a blood ou-tlet near the same end of the casing as -the dialysate inlct.
~ The bloocl and dialysate fluid are separa-ted by and make contact across the semipermeable membrane across which active dialysis takes place.
The blood flow through this hemodialyzer design can generally be described as across and between the tubes in a first of ~hc two independent stacks of tubes and subsequently across and between the tubes in a second of the two independent stacks.
The dialysate fluid passes through the dialyzer within the tubes of both of the two independent stacks with the volume of dialy-sate which passes through the tubes of one of the two independent stacks not passing through the tubes of the other stack.
A better understanding of the features of the present in-vention and the inherent advantages can be obtained from a D reading of the following description of the invention wi-th reference to the drawings, in which:

~2536 Fig. 1 is a perspective view of a hemodialyzer cons-tructed in accordance with the preferred embodiment of the present invention which has an end removed to expose the interior structure of the hemodialyzer.
Fig. 2 is an end view of a hemodialyzer constructed in accordance with the preferred embodiment of the present invention with the end partially broken away to e~pose the interior structure of the hemodialyzer.
Fig. 3 is a vertical section of the end of the hemo-dialyzer taken along the line 3--3 of Fig. 2.
Fig. 4 is a horizontal section taken along the line 4--4 of Fig. 2.
Fig. S is a vertical section of an alternative embodiment of the present invention, appearing with Fig. 1.
While the invention is here described in connection with a preferred embodiment, it will be understood that is not intended to limit the invention to only that specific embodiment, but it is intended to cover all alternatives, modifications and equivalents as may be included within the spirit and scope of the invention as defined by the appended claims.
The construction and operation of the present inven-tion can best be understood by referring first to Fig. 1 wherein there is shown a hemodialyzer unit in accordance with a preferred embodiment of the present invention with the end thereof removed to expose the interior structure.
The hemodialyzer in accordance with the present invention includes a casing indicated generally at 11. A plurality of flattened semipermeable membrane tubes, such as tubes 13, are arranged in parallel and form two independent ~Z536 stacks indicated generally a~ 15 and 17. The two stacks 15 and 17 of the parallel flattened semipermeable mem-brane tubes 13 are disposed separately within the casing 11. As illustrated in Fig. 1, it is preferred that these two stacks be arranged one on the other.
Means are provided for passing dialysate fluid through the hemodialyzer and the casing within the tubes 13. While any of various means well known and fully understood by those skilled in the art can be used for passing the dialysate fluid through the hemodialyzer, one such possible means will be described below. It should be appreciated, however, that the means described herein are only one possibility of many available in the art which would be readily adaptable for use with the present hemodialyzer. Referring to Fig. 3 where the example of a means for passing the dialysate fluid through the hemodialyzer can most easily be visualized, there is shown on one end of the casing 11 a dialysate inlet 19.
Referring momentarily to Fig. 4, there is shown on the opposite end of the casing 11 a dialysate outlet 21 con-structed in the identical manner to the dialysate inlet 19. Consequently the description will be limited to the dialysate inlet 19, it being understood that the struc-ture of the dialysate outlet 21 is identical to that of the inlet 19.
Referring again to Fig. 3, it can be appreciated that the dialysate inlet 19 is adapted to be connected to tubing appropriate for the carrying of dialysate fluid from an appropriate reservoir by a pump to the hemo-dialyzer. Dialysate inlet 19 therefore is shown as an ~ZZS36 approximately tubular structure. The dialysate inlet 19opens to a dialysate inlet plenum 23 which communicates with the interior of the semipermeable membrane tubes through the openings at their ends. The dialysate inlet plenum 23 serves to distribute the dialysate fluid to all the tubes in both of the stacks of tubes 15 and 17. As indicated by the arrows in Fig. 3, dialysate fluid would enter the inlet 19, distribute through the dialysate inlet plenum 23 and pass therefrom to the interiors of the semipermeable membrane tubes 13, the dialysate fluid flowing through all the tubes in both stacks lS and 17.
Referring again momentarily to Fig. 4, it can be appreci-ated that after the dialysate fluid flows along the length of the tubes 13 it will exit from the tubes at the ends opening to a similar dialysate outlet plenum 25 located at the opposite end of the casing ll and communi-catng with dialysate outlet 21 from which the dialysate fluid will exit from the hemodialyzer.
It is, o course, essential that there be no inter-mingling of the fluids in the hemodialyzer casing.
Therefore the dialysate fluid must flow through the hemodialyzer casing only within the tubes while the blood flows through the hemodialyzer casing only around and outside of the tubes. Any such intermingling of the dialysate fluid and the blood is prevented by a barrier 27 located at the ends of the tubes near the dialysate -inlet plenum 23. This barrier 27 sealingly separates the dialysate inlet plenum from the interior portions of the dialysate casing through which the blood flows. The ends of the tubes 13 project through the barrier 27 and ~2ZS36 open to the dialysate inlet plenum 23, thus permitting the flow of dialysate fluid from the plenum through the tubes. A similar barrier 29 is located at the opposite end of the casing 11 and sealingly separates the interior of the dialysate casing from the dialysate outlet plenum 25. The position and relation of the two barriers can best be seen from Fig. 4. While the barrier can be any sort of a structure which will seal the ends of the tubes and separate the plenum from the interior of the dialy-sate casing, it has been found that a layer of epoxyembedding the ends of the tubes 13 works particularly well and enables construction of a dialyzer in accordance with the present invention through uncomplicated straight-forward technigues. Such a barrier has been constructed and used in accordance with the dialyzers subject of the previous U. S. patents discussed above.
Means are also provided for passing blood through the dialyzer casing around and between the tubes 13.
While many of the well-known prior art techniques for introducing blood into a dialyzer casing and removing blood therefrom can be adapted for use with the hemo-dialyzer in accordance with the present invention, one such example which can readily be employed with the present invention can best be appreciated by first referring to Fig. ~ where there is shown near one end of the hemodialyzer casing 11 a blood inlet 31. While the inlet can be located near either end of the casing 11, it is preferred that the inlet 31 be located on the same end of the casing as the dialysate outlet 21. The blood outlet 33 will correspondingly be located on the opposite ~ZZS3~

end of the casing 11, such end being the same end of the casing 11 as the dialysate inlet 19.
This arrangement is preferred, as the blood entering the dialyzer throu~h inlet 31 contains the highest con-centrations of impurities. ~he blood containing the high concentration of impurities then undergoes active dialysis exchange across the semipermeable membrane near the dialy-sate outlet 21 where the dialysate will have already removed a portion of impurities from the blood, thereby providing the dialysate with a higher degree of impurities than the dialysate contains at the dialysate inlet 19.
Near the blood outlet 33 the blood will have undergone dialysis in flowing through the dialyzer from the inlet 31 and the concentration of impurities in the blood will have been reduced. The dialysate entering the hemo-dialyzer through the inlet 19 will, of cour~e7 contain no impurities. This dialysate with no impurities then undergoes active hemodialysis across the membrane with the blood near the blood outlet 33, which blood having already undergone dialysis in its passage through the dialyzer will have a reduced concentration of impurities.
A high differential of impurity concentration in the blood as opposed to in the dialysate is thereby maintained throughout the hemodialyzer unit. If the blood and dialysate were introduced on the same end of the dialyzer unit, the concentration of impurities in the dialysate near the outlet would be fairly high for having undergone dialysis with the blood as it passes through the hemo-dialyzer, while the concentration of impurities in the blood will have been reduced through dialysis as it ~lZ2S3~i passes through the hemodialyzer. Consequently, the con-centrations in the blood and dialysate near the outlet would have tended to equalize, reducing the concentration differential, and reducing the efficiency of dialysis at the latter portion of the flow path. Therefore it is preferred that the blood inlet be located on the end of the hemodialyzer casing adjacent the dialysate outlet.
nhile the blood inlet 31 and outlet 33 can be any of a variety of structures which are adaptable or permit connection to blood-carrying tubing, a particular inlet and outlet which are readily adaptable and found to be highly useful in the present apparatus are those blood inlet and blood outlet ports described in the applicantls previous U. S. patent 3,778, 369 These previously des-cribed blood ports are tapered so as to provide advan-tageous distribution of the blood across the entire stack of tubes. The structure and advantages obtained thereby are fully described in the mentioned U. S. patent and the advantages obtained thereby are also provided when these particular blood ports are employed in the apparatus of the present invention. The preferred use of these tapered slit blood ports is indicated by the tapered blood inlet 31 and the tapered blood outlet 33 as illus-trated in Fig. 2.
Referring again to Fig. 1, it can be appreciated that the b~ood inlet leads to a blood inlet plenum indicated at 35 which serves to distribute the blood along the height and length of the first stack of tubes 15.
Following distribution of the blood through the blood 3~ inlet plenum 35, the blood can 10~ across the surfaces ~z~

of the semipermeable membrane tubes 13 between and around the tubes of the first stack 15 and subsequently across and around the semipermeable membrane tubes of the second stack 17 to the blood outlet plenum 37 which serves to collect the blood. The blood then flows from the outlet plenum 37 through the blood outlet.
In accordance with the hemodialyzer of the present invention, the blood passes through the casing around and between the tubes in a manner such that the blood passes in succession through each of the two independent stacks.
The essential features and the clearest explanation of the blood flow can best be understood by referring to Fig. 5 wherein there is shown another embodiment of the present invention. In Fig. 5, identical numerals will be used to identify the similar components of the hemo-dialyzer unit although in this particular embodiment these components may be arranged somewhat differently. Accor-dingly, it can be appreciated that flattened semiper-meable membrane tubes 13 are arranged in parallel to form a stack, and two independent stacks, a first stack 15 and a second stack 17 independent of the first, are disposed within the hemodiaiyzer casing indicated generally at 11.
In this particular embodiment, it can be seen that the first stack 15 and the second stack 17 are arranged side by side in the casing 11. Blood flow through the hemo-dialyzer in accordance with this embodiment can be represented by the small arrows and can be seen to be from the blood inlet 31 to a blood inlet plenum 35 along the length of one side of the casing 11 wherein the blood distributes along the length and height of the first l~ZZS36 stack of tubes 15. Blood flow is then around and between the tubes 13 in the first stack 15 and in succession around and between the tubes 13 in the second stack 17 to the blood outlet plenum 37 which serves to collect the blood and permit its exit from the hemodialyzer casing through the blood outlet 33. Blood flow can generally be described as from the blood inlet plenum 35, through the first stack of tubes 15, across the small gap 39 (some-what exaggerated in the drawing) and in succession through the second stack of tubes 17 to the blood outlet plenum 37.
In conducting hemodialysis, blood is normally main-tained at a slight positive pressure compared to the dialysate fluid in order that excess water can be driven across the semipermeable membrane from the blood. As a result of this blood pressure, the casing 11 of the embodiment illustrated in Fig. 5 tends to bulge where the blood passes across the gap or intermediate plenum 39 from the one stack of tubes to the other. The bulge at the top of the casing at point 41, illustrated by the dotted line and arrow in Fig. 5, and bulge in the bottom of the casing at point 43, similarly illustrated by the dotted line of the casing and small arrow, causes a path to open between the stack of tubes and the top surface or bottom surface of the casing. Blood flow then tends to be along the top and bottom surfaces of the dialyzer casing rather ~han through the interior of the two stacks 15 and 17. Dialysis across the semipermeable membrane tubes 13 is therefore reduced due to the preferential blood flow path along the top and bottom surface of the casing.

~3~

Therefore a preferred embodiment which offers other advantages over and above the embodiment of Fig. 5 is one in which the two independent stacks of parallel semiper-meable membrane tubes are arranged one on the other.
Such a preferred embodiment is illustrated in Figs. 1-4.
As is illustrated in Fig. 1, it is preferred that the stacks 15 and 17 be arranged one on the other. As can be seen from Fig. 1 blood flow is then from the blood inlet plenum 35 across the stack of tubes 15 to the intermediate plenum 39, downward in the intermediate plenum 39 to the level of the stack of tubes 17, and in succession across the stack of tubes 17 to the outlet plenum 37. The flow of blood in the intermediate plenum 39 exerts a pressure on the side 45 of the casing 11 in a manner similar to that described in connection with the embodiment of Fig. 5. However, any tendency for ~his side of the casing to bulge will not hinder the normal blood flow path. Blood flow must still be across the stack 15 to the intermediate plenum 39 and the bulging of the side 45 o the casing 11 merely enlarges the inter-mediate plenum 3g rather than creating a preferential blood flow path which will avoid the semipermeable mem-brane tube surfaces. The blood must still flow across the tubes of stack 17 from the intermediate plenum 39 to the outlet plenum 37.
The two stacks of tubes 15 and 17, although being one on the other, are separate and independent stacks, the two stacks being separated such that the blood must pass in succession through each of the two independent stacks. Such separation and blood flow can ~e ~12;~536 accomplished by means such as, for example, a solid plate 47 disposed between the two stacks. The two stacks 15 and 17 are then separated by solid plate 47 which extends from one wall 49 of the casing. The solid plate 47 extends from the wall 49 of the casing, such wall forming a side of the casing the same as that on which the blood inlet and blood outlet lie, across the width of the stacks 15 and 17 to a point near to but not touching the opposite wall 45 of the casing so as to leave a gap for the intermediate plenum 39 between the edge of the plate 47 and the opposite wall 45. The interior of the casing 11 is thereby divided by the plate 47 into two sections, each section containing one of the two independent stacks 15 or 17. It can then be appreciated that the two sec-tions containing the stacks 15 and 17 communicate only along the gap or intermediate plenum 39 between the plate 47 and the casing wall 45. 8100d flow then must be across the stack of tubes 15 from the blood inlet plenum 35 to the intermediate plenum 39 and back across the second stack of tubes 17 to the blood outlet plenum 37.
Such blood flow can perhaps be most clearly understood by considering the blood flow as following the small arrows illustrated in Fig. 2.
As was mentioned previously, the blood flowing through the dialyzer is at a slightly higher pressure than the dialysate in order to drive excess water from the blood to the dialysate fluid. As a consequence, it is preferred that support members be inserted within the tubes to hold the interior walls of the tubes apart and provide a flow path for the dialysate fluid. The blood will force the membrane down onto the support member to open a flow path for the blood while the support mem-ber will retain a flow path for the dialysate fluid.
While many types of support members can be used, a nonwoven plastic mesh support has been found to be par-ticularly useful. While such support members are well known in the art, a full description of the support members and their function can be obtained from a reading of two previous U. S. Patents, No. 3,788,482 and No. 3,565,258.
~ everal significant advantages are offered by a hemodialyzer in accordance with the present invention.
In addition to the advantage offered by the preferred embodiment as mentioned above, other advantages over previous dialyzer designs can be seen from the following considerations. In comparison with a hemodialyzer con-taining only a single stack of tubes, for a volume flow of blood through the dialyzer unit per unit time remaining ~he same, the path length in the dialyzer of the present invention is increasad. Correspondingly, the blood velocity must be increased, which increase in velocity helps prevent the buildup of fibrin on the semi-permeable membrane surface. The buildup of fibrin is undesirable for several reasons, among which are the buildup of fibrin on the semipermeable membrane surface will reduce the dialysis efficiency of the membrane and, perhaps more importantly, the buildup of fibrin on the semipermeable membrane surface can lead to the formation of a blood clot which would prove highly dangerous to the 3~ patient undergoing hemodialysis treatment. With the ~:IZ2536 increase in path length for the blood flowing through the hemodialyzer unit in accordance with the present inven-tion, the blood also will pass across two independent stacks of tubes, thereby coming in contact with dialysate fluid across the semipermeable membrane tubes over a path length double that of a single stack unit. The increase in contact of the blood with dialysate fluid across the semipermeable membrane will, of course, increase the efficiency of dialysis occurring in the hemodialyzer unit.
While the invention has been described in conjunc-tion with specific embodiments and a preferred embodiment thereof, many alternatives, modifications and variations as well as other advantages will be evident to those skilled in the art in light of the foregoing description.
Accordingly, it should be unde}stood that the invention is not intended to be limited to the details given herein but it is intended to embrace all such alternatives, modifications and variations as fall within the spirit and scope of the appended claims.

Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A hemodialyzer comprising:
a casing;
two independent stacks of parallel, flattened semi-permeable membrane tubes disposed in said casing, said two stacks being separated by a solid plate extending from one wall of the casing across the width of the stack to a point near to but not touching the opposite wall of said casing so as to leave a gap between said plate and said opposite wall and thereby divide the interior of said casing into two sections, each section containing one of the two independent stacks, which sections communicate only along the gap between the plate and the casing wall;
means for passing dialysate fluid through said casing within said tubes, said means including a dialysate inlet at one end of said casing and a dialysate outlet at the opposite end of said casing; and means for passing blood through said casing around and between said tubes such that the blood flows across and between the tubes in a first of the two independent stacks of tubes and subsequently across and between the tubes in a second of the two independent stacks of tubes, said means including a blood inlet near the same end of the casing as said dialysate outlet and a blood outlet near the same end of said casing as said dialysate inlet.

2. The hemodialyzer of Claim 1 wherein said two independent stacks are arranged one on the other.