Blood Treating And Filtering Apparatus

Abstract

Stored human blood is treated preliminary to blood transfusions by passing it through a mat of glass wool or other fibrous material which removes from the blood the storage-generated platelet leukocyte aggregates present therein. It is filtered during open heart surgery by passing it through the same material for removal of aggregates and leukocytes and separation of entrained air.

Parent Case Text

This application is a continuation-in-part of the patent application of Roy L. Swank, Ser. No. 826,480, filed May 21, 1969 for "Blood Treating Method and Apparatus," now abandoned.

Description

In blood transfusions and heart surgery it has become routine to employ blood bank blood. This is prepared by withdrawing blood from donors, adding heparin or other preservative, and then storing the blood under carefully controlled conditions until its use is required.

Whether it is used directly in transfusions or in heart surgery, there sometimes have been observed in the patient an ensuing cessation of circulation and other reactions not attributable to mismatching of blood types. Although the cause of this regrettable result has been unknown, it has been recognized as a function of blood storage duration. Accordingly, it has been common practice to discard blood bank blood after it has been stored for a predetermined time.

Another difficult problem exists when handling blood during heart surgery, kidney dialysis, etc. In these procedures not only is the blood altered to produce harmful constituents, but it becomes contaminated with extraneous material such as epithelium, pieces of muscle, fat emboli, fragments of suture material and entrained air. This foreign material must be removed in order successfully to consummate the surgical procedure.

It is the general object of this invention to provide method and apparatus for treating blood to be used in transfusions and heart surgery which will overcome the foregoing problem, reducing the likelihood of transfusion reactions due to circulatory failure and related conditions, and enabling the use of blood bank blood even though it has been stored for long periods of time.

Another object is the provision of a continuous, high capacity, blood filter which contemporaneously filters and deaerates the blood.

In the drawings:

FIG. 1 is a longitudinal sectional view of the herein described blood treating apparatus, as used in transfusing blood;

FIGS. 2 and 3 are plan views of support elements employed in the apparatus of FIG. 1;

FIGS. 4 and 5 are graphs illustrating the effect of fiber diameter and filter density on the performance of filters contained in the apparatus; and

FIGS. 6, 7 and 8 are sectional, exploded and schematic views illustrating respectively, the construction and application of a modified form of the apparatus, as used in heart surgery.

It has been discovered that when blood bank blood is stored, its leukocyte and platelet components are altered, developing characteristics which are responsible for the transfusion complications described above. The alteration is evidenced in two ways. First, some of the platelets become adhesive. Second, some of the platelets form aggregates with some of the leukocytes. The aggregates primarily are responsible for the adverse results occurring when old blood is used in blood transfusions.

In view of the correlation between the altered component content of the stored blood and the occurrence of transfusion complications when such blood is applied in medical practice, the importance of removing these altered components prior to transfusion and during heart surgery becomes strikingly apparent.

The present invention provides an efficient method and apparatus for accomplishing the removal of such components.

FIGS. 1--3 illustrate apparatus for use particularly in transfusions. The apparatus comprises a tube 10 which may be made of rigid material such as glass, but which preferably is made of a nonpyrogenic, sterilizable, resilient material such as polyethylene plastic. Such material makes of the tube a hand pump so that the flow of blood through the apparatus may be increased by slowly compressing the tube sidewalls in the manner shown in dotted outline in FIG. 1.

Since the blood preferably passes through the apparatus by gravity flow, tube 10 normally is arranged vertically and has at its upper end an inlet port and at its lower end an outlet port.

To facilitate application of the apparatus in blood transfusions, the inlet port of the tube preferably is fitted with a hollow, penetrating spur 12 adapted to pierce the cap 14 of a bottle 16 of blood bank blood.

Spur 12 preferably extends inwardly within tube 10 and accordingly acts as a metering device by which drop flow of blood may be monitored. The open lower end of tube 10 is fitted with a cap 18 having an integral valve chamber 20 and a stub exhaust conduit 22. A ball valve assembly 24 is seated within the valve chamber better to control the flow of blood during pumping of tube 10. The ball valve assembly may be omitted, however, where the head of blood in container 16 is sufficient to prevent reverse flow.

A rubber tube or other conduit 26 is attached to stub conduit 22. It conveys the blood to the patient, usually through an interposed flow valve.

Tube 10 thus provides a housing for filter elements which selectively remove the undesirable altered components of the stored blood. To this end there are welded or otherwise secured to the inner sidewalls of the lower portion of the tube, below the pumping area, an upper support 28, an intermediate support 30, and a lower support 32. Upper support 28 is illustrated in detail in FIG. 2 while lower supports 30, 32 which may be substantially identical, are illustrated in FIG. 3. All three supports may be made from substantially rigid plastic.

Support 28 mounts a blood clot filter screen 34 of stainless steel or other suitable material. It has a screen size dimensioned to screen out any clots which may be present in the blood.

Support 28 also guides the blood to the central area of the tube To this end it comprises a ring 36 which is glued or otherwise affixed to the inner walls of tube 10 and an inwardly projecting, annular flange 38. The latter has inwardly extending projections 40, particularly evident in FIG. 2.

Supports 30, 32, on the other hand, serve the function of supporting the filter material. Each comprises a ring 42 mounting a characteristic pattern of crosspieces 44. Ring 42, like ring 36, is glued or otherwise fastened to the inner wall of the tube.

The three support rings thus provide three chambers 46, 48, 50 of progressively smaller volume. These chambers contain the filter material determining the desired performance of the filter.

Chambers 46, 48 contain the filter material 52 responsible for removing the blood aggregates and the altered leukocytes and platelets. For use in this application, the filter material must adhere these storage-altered components selectively; must permit free passage of the other blood components; must have a large area of absorbing surface; must not be nonpyrogenic; must not pack; must not collapse nor plug; and must not be affected adversely by repeated subjection to heat and chemical sterilization.

To meet the foregoing requirements, the filter material is used as filaments or fibers which may be formed into a resilient mat compressible as required to produce passageways or channels of optimum size. The diameter or cross-sectional area of the individual particles of the material is of primary importance in determining its suitability.

In general, as will be demonstrated hereinafter, the material should comprise fibers or filaments having lengths of not less than 100 microns and diameters of less than 60 microns, preferably less than 30 microns. Such fibers are sufficiently large so that they will not pass through the filter and into the bloodstream of the patient. They are sufficiently small in diameter so that the storage-altered aggregates can completely surround them with overlapping portions which stick to each other, anchoring the aggregates to the fibers.

Material suitable for the present invention purpose thus are fibrous or filamentous polyester resins (Dacron and kodel), filter polyamide resin (Nylon), filamentous polyacrylic resin (Orlon), glass wool, steel wool, cotton, and cellulose (paper). However, the fibrous or filamentous materials meeting the above noted requirements may also be used.

In achieving the purposes of the invention, it further is desirable that the upstream portion of the filter material should be rather loosely packed to allow penetration of the large aggregates and their distribution through the entire filter, thus increasing its capacity. Downstream, there should be provided a quantity of the filter material which is relatively closely packed. This provides the large surface area necessary to selectively absorb the storage altered components of smaller size.

Chamber 46, and to a certain extent the interior of dome-shaped clot filter 34, receive the more loosely packed filter material. The central opening and inwardly directed projections 40 of support 28 allow the filter material to fluff up above the support, without freely escaping from the chamber below.

Chamber 48 receives the more tightly packed filter material. In general, it may be packed to advantage from two to four times more densely than the filter material contained in chamber 46, i.e. to a density of from 0.1 to 0.4 grams per cubic centimeter.

Chamber 50 receives a sponge filter 54 having for its function preventing fragments of the filer material contained in the superimposed chambers from reaching conduit 26, and hence the blood stream of the patient. The sponge filter preferably has a pore size of 60 to 100 pores per square inch. It preferably comprises porous polyurethane or other porous plastic. In the alternative, it may comprise a stainless steel screen or sponge.

The importance of filter element diameter and degree of compression in chamber 48 has been determined by tests, the results of which are shown in FIGS. 4 and 5.

To determine the effect of filter material diameter, the apparatus of FIG. 1 was filled with filter materials of varying identity and cross-sectional dimensions. Blood bank blood outdated by several weeks was gravitated through the apparatus at room temperature.

The treated blood then was tested for the presence of residual storage-altered components, i.e. adhesive platelets, and leukocytes and aggregates of the same by passing it through the pressure test apparatus described in the patent of Roy L. Swank, U.S. Pat. No. A 3,266,299, and measuring the developed filtration pressure. The results follow in Table 1 --------------------------------------------------------------------------- and are graphed in FIG. 4. 67 TABLE I

Material Average Fiber Filtration Diameter (microns) Pressure (mm. Hg) __________________________________________________________________________ Nylon 58.+-. 6 180 Nylon 42.+-. 4 96 Nylon 26.+-. 2 27 Nylon 20.+-..+-.2 16 Nylon 14.+-. 1 10 20 Dacron 13.+-. 1 23 Dacron 17.+-. 1 , 25 Dacron 20.+-. 4 , 39 Glass wool 10.+-. 2 24 Steel wool 28.+-. 4 , 36 Stainless Steel Wool 50.+-. 10 , 120 Cotton 20.+-. 4 , , 33 Verel 20.+-. 5 , 25 Kodel 20.+-. 5 , 25 Cellulose 30 and smaller , 40 (defiberized paper) __________________________________________________________________________

It will be observed from the table and graph that the efficiency of the treatment is affected markedly by the diameter of the packing fibers. To be effective, the fibers should have diameters of less than 60 microns, preferably less than 30 microns. As the diameter decreases, the efficiency of the altered blood component removal increases dramatically.

To test the effect of filter material compression in chamber 48, samples of clot-free blood were allowed to flow gravitationally through the filter packed with packings of varying density. In each case the same amount of blood was employed and the time noted for passage through the filter. The results are given in FIG. 5.

It will be noted that a marked point of inflection occurs at a density of about 0.2 grams per cc. In general, best results are obtained where the density of the filtering material lies within the range of from 0.1 to 0.4 grams per cc. At lower densities, efficient filtration is not obtained. At higher densities, the filtration rate is too slow to be practical.

In the use of the filter stored blood contained in the container 16 passes through hollow spur 12 which meters it dropwise into resiliently collapsible tube 10. There it passes first through clot filter 34, which screens out the clots, and onto flange 38 of support 28, which directs it centrally of the tube.

Within clot filter 34, and to a greater extent within camber 46 through which it next flows, the blood contacts loosely packed filter material 52 contained in camber 46. This removes the larger aggregates.

Next, it flows through more tightly packed filter material 52 contained in chamber 48 which selectively removes the storage-altered leukocytes and aggregates of smaller size.

Next it passes through sponge or screen filter 54 which prevents particles of the filter material from leaving the apparatus and entering the bloodstream of the patient.

While this is occurring, the upper resiliently deformable portion of the tube 10 may be slowly compressed and allowed to re-expand. This pumps the blood through the filter and makes possible rapid transfusion in emergency situations.

FIGS. 6, 7 and 8 illustrate apparatus useful for filtering blood during open heart surgery, kidney dialysis procedures, etc. The general arrangement of the various units employed in the system is illustrated particularly in FIG. 8.

A conduit 110 may be tied to the superior or inferior vena cava 112 using known techniques. A branch conduit 114 having a suction tip 115 made of stainless steel or other inert material is placed in the chest cavity for removal of accumulated blood.

Conduit 110 and 114 merge to form main conduit 116 which transfers the blood to a reservoir 118 of suitable capacity.

The blood then passes through a first pump 120, an oxygenator 122 and a second pump 124. The latter discharges it into the herein described blood treating and filtering apparatus 126. It should be noted, however, that this apparatus may be located variously in the system to meet the needs of various situations. Typical alternate locations are illustrated in dotted outline.

The oxygenated, treated, and filtered blood then continues through conduit 116, the discharge end of which is tied into the femoral or other artery 128.

The construction and manner of assembly of blood treating and filtering unit 126 is shown in detail in FIGS. 6 and 7.

The unit comprises an upstream end piece 130, a downstream end piece 132 and a tubular body 134. End pieces 130, 132 may be made from stainless steel or plastic, while body 134 may be made from transparent plastic or glass.

The upstream end piece 130 is provided with a central inlet port 136 with outwardly projecting nipple 138 for attachment of one segment of conduit 116. The downstream end piece 132 is provided with a discharge port 140 communicating with a nipple 142 designed to receive another length of conduit 116.

These three elements of the unit, i.e. upstream and downstream end pieces 130, 132, and body 134 provide a central chamber 144 arranged for horizontal flow of the blood. The chamber is sealed by providing in the inner face of the end piece 130 an annular groove 146 seen clearly in FIG. 7. A similar groove, not visible in the same figure, is present in end piece 132. Seal rings 148, 150 are seated in the grooves.

The entire assembly then is clamped together with the parts in sealed relationship by suitable means such as bolts 152 penetrating one of the end pieces and threaded into the other.

Housed within chamber 144 in laterally spaced relation to the two end pieces is a blood treating and filtering assembly comprising a mat 154 of filter material, a perforated, upstream filter-material retainer 156, a screen 158, and a downstream filter-material retainer 160.

Retainers 156, 160 serve to locate filter element 154 centrally in the path of flow of the blood. They may be fabricated from suitable durable inert material such as stainless steel or plastic.

Screen 158 serves to screen out pieces of filter material 154 which otherwise might be entrained in the blood. It may be made of fine mesh stainless steel, Nylon or other suitable material.

Baffle means prevent channeling of the blood through the central part of filter 154 and insure that the blood diffuses through the entire filter area, thus insuring efficient filtration. In the illustrated form of the invention, the baffle means comprises a central, unperforated section 156a of perforated retainer 156. This is located directly opposite inlet port 136.

Further to improve the efficiency of the filter, and to enable it to remove entrained air, the subassembly including elements 154, 156, 158 and 160 are maintained spaced apart from end pieces 130, 132. This provides an infeed recess 144a and an outfeed recess 144b.

Although various structural arrangements may be provided for accomplishing this purpose, a preferred arrangement comprises forming infeed end plate 130 with a peripheral boss 162 and outfeed end plate 132 with a similar peripheral boss 164. These serve as spacers by providing shoulders against which the margins of retaining plates 156, 160 bear in the final assembly of the apparatus.

Recess 144a, cooperating with baffle area 156a of retaining plate 156, serves the valuable function of causing distribution of the blood over the entire filter area.

Recess 144b at the downstream end of the unit serves the valuable function of providing an air trap which permits removal of entrained air from the blood. Such air, when it reaches the downstream end of the unit, will bubble upwardly to the top of recess 144b. There it passes through a port 166 located at the to of end piece 132. A nipple 168 is received in the port and mounts a valve 170 which may be used to exhaust the air as desirable or necessary.

Thus in the application of the form of the invention illustrated in FIGS. 6, 7 and 8, blood entering through inlet port 136 spreads out over the area of the filter in recess 144a, and passes through filter 154, into recess 144b where the entrained air bubbles upwardly and escapes via port 166.

The filter element removes the altered leukocytes and platelets, the leukocyte-platelet aggregates, the fat emboli, the epithelium, the pieces of muscle and suture material, and other debris from the blood. This all is accomplished efficiently, continuously and at a high rate sufficient to accommodate the needs of open heart surgery techniques.

Claims

Having thus described my invention in preferred embodiments, I claim as new and desire to protect by Letters Patent:

1. Apparatus for treat, preliminary to medical application, human blood containing platelet-leukocyte aggregates, the apparatus comprising:

a. a vessel having an inlet port near one end and an outlet port near the other end,

b. within the vessel between the inlet and outlet ports, a filter assembly comprising

1. a blood clot filter member,

2. downstream from the blood clot filter member a first meat of finely subdivided blood-contact material comprising a solid fibrous material the fibers of which are nondegrading to the blood and characterized by the ability selectively to adhere the aggregates,

3. downstream from the first mat a second mat of finely subdivided blood-contact material comprising a solid fibrous material the fibers of which are nondegrading to the blood and characterized by the ability selectively to adhere the aggregates, the second mat having a density greater than the first mat for selectively removing aggregates of smaller size,

4. downstream from the second mat fiber filter member for filtering from the blood fragments of mat fiber filter material,

c. means for introducing stored blood into a inlet port and for passing it through the filter assembly,

d. and means for withdrawing the treated blood from the outlet port.

2. The apparatus of claim 1 wherein the vessel has resiliently deformable sidewalls on the upstream side of the filter assembly adapted to be compressed and re-expanded for pumping blood through the apparatus.

3. The apparatus of claim 1 including

a. a first perforate support member between the blood clot filter member and the first mat, supporting the blood clot filter member and compressing the first mat, and

b. a second perforate support member between the first and second mats supporting the first mat and compressing the second mat.

4. The apparatus of claim 3 wherein the blood clot filter member comprises a dome-shaped screen support at its open end on the first support member, the latter having a central opening through which the first mat projects into the spacing defined by the screen.

5. The apparatus of claim 4 including inwardly extending projections on the first support member engaging the first mat to prevent free escape of the latter into the space defined by the screen.

6. The apparatus of claim 1 including valve means adjacent the outlet port operable to prevent back flow of blood from the outlet port into the vessel.

7. The apparatus of claim 1 wherein the second mat of fibrous material has a density of about 0.1 to 0.4 grams per cc.

8. The apparatus of claim 1 wherein the mat fiber has a diameter not substantially great than about 30 microns, the density of the second mat is about 0.2 grams per cc. and the density of the first mat is about 1/4--1/2the density of the second mat.

9. A high volume, continuous blood filter comprising:

a. upstream and downstream end pieces,

b. a tubular body secured between the end pieces to form a chamber,

c. an inlet port at the center of the upstream end piece,

d. an outlet port below the top of the downstream end piece,

e. the inlet and outlet ports thereby enabling substantially horizontal blood flow through the chamber,

f. a quantity of blood-filter material between the end pieces,

g. upstream perforated, filter-material-retaining means locating the filter material in the path of the blood flow,

h. means spacing apart the downstream retaining means and end piece and forming therebetween a recess at the downstream end of the chamber for separating and collecting air entrained in the blood, and

i. air-exhaust port means communicating with the top of the recess for exhausting collected air therefrom.

10. The blood filter of claim 9 wherein spacing means comprises a peripheral boss on the downstream end piece projecting inward therefrom for abutment by the downstream retaining means.

11. The blood filter of claim 9 including means spacing apart the upstream retaining means and end piece and forming therebetween a recess at the upstream end of the chamber.

12. The blood filter of claim 11 wherein the spacing means comprises a peripheral boss on the upstream end piece projecting inward therefrom for abutment by the upstream retaining means.

13. The blood filter of claim 9 including baffle means opposite the inlet port for diffusing the blood laterally over the entire area of the blood filter material.

14. The blood filter of claim 13 wherein the baffle means comprises an imperforate central portion of the upstream retaining means.