Blood storage container

Abstract: A blood storage container (1) includes a blood storage chamber (7) having a blood outlet port (6), a blood inlet chamber (5) disposed upstream of the blood storage chamber with respect to a direction in which blood to be stored flows, a blood debubblizer (8) for debubblizing the blood, the blood debubblizer being disposed between the blood inlet chamber and the blood storage chamber, and an air bubble stop unit (9) for preventing air bubbles in the blood from flowing therethrough, the air bubble stop unit being disposed down­ stream of the blood debubblizer. The air bubble stop unit has mesh screens of different mesh sizes which are supported in a frame (11) that is detachably disposed in the blood storage chamber.

Description: The present invention relates to a blood storage container, and more particularly to a blood storage container for use in an open-type pump oxygenator circuit or the like. When a surgical operation is effected on the chest of a patient, an oxygenator is often used recently in connection with an extracorporeal blood circulation circuit in bypassing relation to the lung of the patient, and carbon dioxide is removed from the blood of the patient and fresh oxygen is added to the blood by the oxygenator. The extracorporeal blood circulation circuit includes a blood storage container for temporarily storing the blood so that air bubbles produced during the circulation of the blood will be removed from the blood, or the rate of circulation of the blood will be prevented from dropping due to the bending of a tube of the extracorporeal blood circulation circuit. Blood storage containers now in use in the arm are roughly classified into a closed-type soft bag container which is made of a soft material and stores the blood in a hermetically sealed condition, and an open-type hard shell container which is made of a hard material and stores the blood in an open or vented condition. The soft bag container is advantageous in that it has no blood-air interface, but disadvantageous in that it cannot hold a large amount of blood and cannot give an exact indication of how much blood is stored therein. The hard shell container can store a large amount of blood and allows the user to know the exact amount of blood stored therein. Other advantages of the hard shell container are that it can easily be united with an oxygenator, thus permitting an extracorporeal blood circulation circuit to be arranged with ease, and also the blood can easily be debubblized when the extracorporeal blood circulation circuit is set up and primed. Japanese Laid-Open Patent Publication No. 59-57661, for example, proposes a hard shell blood storage container which utilizes these advantages. The conventional blood storage container which is united with an oxygenator, however, has no mechanism for removing air bubbles from the blood that ingresses into the container. Air bubbles must be removed from the blood in order to prevent the patient from suffering embolism. Therefore, the extracorporeal blood circulation circuit should be provided with a debubblizing mechanism in another region than the blood storage container. It is nevertheless preferable to provide the blood storage container with a debubblizer for removing air bubbles from the stored blood, so that the extracorporeal blood circulation circuit will be made compact as a whole. Japanese Laid-Open Patent Publication No. 62-258671 discloses a blood storage container which incorporates a blood debubblizer therein. The disclosed blood debubblizer comprises a foamed body integral with the blood storage container. The foamed body is of a hydrophobic nature to allow air bubbles in the blood to grow and be removed with a view to protecting the patient from embolism. The foamed body positioned in the blood storage container is effective in removing relatively large air bubbles from the blood which has entered from a blood inlet into the foamed body. However, some very small air bubbles in the blood may pass through the foamed body and remain in the blood which returns into the body of the patient. When this happens, the patient may be afflicted with embolism owing to those very small air bubbles that remain trapped in the blood. Further, US-A-4 704 203 discloses a debubblizer in the form of a three-dimensional foamed body which is of a generally porous material and substantially occupies the entire interior volume of the chamber. The porous material of the foamed body has preferably been treated with a surface-active agent reducing the surface tension, e.g. making it hydrophobic. This causes the bubbles to burst and allows removing these from the blood. This debubblizer is not provided for a blood storage container directly, but is to be used in extra-corporeal blood circuits. It only allows removing relatively large air bubbles from the blood, whereas small air bubbles may pass through the foamed body and eventually enter into the body of a patient together with the returned blood. The different densities of the different layers of the debubblizer do not essentially influence this result. In DE-A-2 844 073 and US-A-3 507 395 both mesh screens are described, whereas the latter document only discloses a mesh for trapping solid particles in the blood, the former document teaches use of combined hydrophobic and hydrophilic filter media. These filter media do not comprise a three-dimensional foamed body, but are more or less of the mesh or similar types. It is therefore a principal object of the present invention to provide a blood storage container for use with an extracorporeal blood circulation apparatus or the like for removing tiny air bubbles and also foreign matter substantially completely from the blood stored in the container. A blood storage container according to the invention comprises a chamber and a blood debubblizer for debubblizing the blood in the form of a three-dimensional foamed body. As claimed, the chamber is provided as a blood inlet chamber. The blood debubblizer is provided downstream of the blood inlet chamber and upstream of a blood storage chamber having a blood outlet port. Further, the foamed body of the blood debubblizer is of a hydrophobic nature for attracting air bubbles. An air bubble stop unit is provided between the blood debubblizer and the blood storage chamber for preventing remaining smaller air bubbles flowing therethrough by trapping and removing these. According to the invention the air bubble stop unit comprises mesh screens which are treated such that they are hydrophilic. According to the invention two different filter media are provided, namely the blood debubblizer and the air bubble stop unit comprising mesh screens, in combination with their hydrophobic and hydrophilic natures, respectively. The hydrophobic nature of the debubblizer is promoted to positively attract air bubbles contained in the blood, thus allowing the air bubbles to grow and be removed from the blood. Accordingly, the blood debubblizer removes relatively large air bubbles from the blood. The hydrophilic air bubble stop unit can easily catch air bubbles with the very fine mesh screens and therefore removes very small or minute air bubbles from the blood. The blood flows very smoothly through the blood debubblizer and the air bubble stop unit and downstream of these is completely free of air bubbles. Advantageously the mesh screens can include a mesh screen of larger mesh size and a mesh screen of smaller mesh size, the air bubble stop means including a frame in which the mesh screens are supported. Further, the mesh screen of larger mesh size can be positioned upwardly of the mesh screen of smaller mesh size. Alternatively the mesh screen of smaller mesh size is positioned upwardly of the mesh screen of larger mesh size. In preferred embodiments of the present invention the mesh screens have mesh sizes ranging from 50 to 300 mesh size, the mesh screen of larger mesh size may have a mesh size ranging from 50 to 300, preferably from 75 to 250, or from 50 to 175, preferably from 75 to 150. According to one embodiment of the present invention the mesh screens are detachably mounted in the blood storage chamber. The above and other objects, features and advantages of the present invention will become more apparent from the following description when taken in conjunction with the accompanying drawings in which preferred embodiments of the present invention are shown by way of illustrative example. In the drawings: FIG. 1 is a perspective view of a blood storage container according to the present invention; FIG. 2 is a perspective view of an air bubble stop unit of the blood storage container; FIG. 3 is a perspective view of an air bubble stop unit according to another embodiment of the present invention; FIG. 4 is a side elevational view, partly in cross section, of an extracorporeal blood circulation apparatus in which the blood storage container of the present invention is incorporated; and FIG. 5 is a schematic perspective view of the extracorporeal blood circulation apparatus shown in FIG. 4. FIG. 1 shows a blood storage container 1 according to the present invention which is to be incorporated in an extracorporeal blood circulation apparatus (described later on). The blood storage container 1 is of the hard shell type to be assembled in the extracorporeal blood circulation apparatus which includes an oxygenator. The blood storage container 1 basically comprises a container casing 2 and a cover 3 (FIG. 4) for closing the upper opening of the container casing 2. The container casing 2 is made of a hard material such as polyvinyl chloride, polystyrene, polycarbonate, or the like. The container casing 2 should preferably be transparent so as to allow the user to visually observe the blood stored in the container casing 2. As shown in FIGS. 4 and 5, the container casing 2 has a pair of blood inlet ports 4 defined in the bottom of one end thereof, a blood inlet chamber 5 communicating with the blood inlet ports 4 and having a bottom which is substantially at the same level as the blood inlet ports 4, and a blood storage chamber 7 communicating with the blood inlet chamber 5 and having a bottom extending from the blood inlet chamber 5 downwardly along a curved surface toward the other end of the blood storage chamber 7 remote from the blood inlet chamber 5, the blood storage chamber 7 having a blood outlet port 6 in a lower portion thereof. A blood debubblizer 8 is positioned between the blood storage chamber 7 and the blood inlet chamber 5. An air bubble stop unit 9 is detachably disposed on a downstream side of the blood debubblizer 8 which faces the blood storage chamber 7. The blood debubblizer 8 and the air bubble stop unit 9 are prevented from being displaced toward the blood outlet port 6 by means of locking members 10 vertically attached to the inner surfaces of side walls of the blood storage chamber 7. When blood containing air bubbles flows into the blood inlet chamber 5, the blood debubblizer 8 removes the air bubbles from the blood as it flows therethrough, and hence supplies the debubblized blood into the blood storage chamber 7. The blood debubblizer 8 is in the form of a three-dimensional foamed body which is of a hydrophobic nature to allow air bubbles in the blood to grow and be removed. The air bubble stop unit 9 may be made of any of various materials insofar as they allow liquids to flow therethrough. However, the resistance to liquid flows of the material of the air bubble stop unit 9 should be small enough not to develop any appreciable pressure loss in a blood flow upon contact with the blood flow through the air bubble stop unit 9. As shown in FIG. 2, the air bubble stop unit 9 has a frame 11 including a crisscross inner frame member, a mesh screen 12 of a larger mesh size disposed in an upper portion of the frame 11, and a mesh screen 13 of a smaller mesh size disposed in a lower portion of the frame 11. The mesh sizes of the mesh screens 12, 13 should be in the range of from 50 to 300 mesh, and more preferably in the range of from 75 to 250 mesh as a whole. More specifically, the mesh size of the mesh screen 12 should range from 50 to 300 mesh, and preferably from 50 to 175 mesh, and more preferably of 100 mesh, and the mesh size of the mesh screen 13 should range from 125 to 300, and more preferably from 150 to 250 mesh. Each of the mesh screens 12, 13 is of a plain weave woven of polyester filaments. The mesh screen 12 should preferably have a filament diameter of 55 µm and a thickness of 95 µm, and the mesh screen 13 should preferably have a filament diameter of 45 µm and a thickness of 75 µm. In the embodiment shown in FIG. 2, the width between adjacent filaments of the mesh screen 12, i.e., the mesh opening, is 199 µm with an opening area of 61 %, whereas the mesh opening of the mesh screen 13 is 124 µm with an opening area of 54 %. The material of the mesh screens 12, 13 should not activate the blood constituents upon contact with the blood. Examples of the material of the mesh screens 12, 13 include polyvinyl chloride, polyethylene, polypropylene, polyester, polycarbonate, or the like. The mesh screens 12, 13 may be coated with a polymer so that they will become hydrophilic. Generally, mesh screens are hydrophobic and do not allow blood to flow easily therethrough particularly during an initial phase of usage thereof. However, by making the mesh screens 12, 13 hydrophilic, they allow blood to flow easily therethrough even during an initial period of usage thereof. The polymer to be coated on the mesh screens 12, 13 to render them hydrophilic should contain hydroxymethylmethacrylate (HEMA) and methylmethacrylate (MMA). The desired hydrophilic nature is obtained by a polymer containing MMA and HEMA at proportions of 92 and 8, respectively. It is most preferable to coat the blood debubblizer 8 with silicone so as to make it hydrophobic and also to make the air bubble stop unit 9 hydrophilic. By doing so, the hydrophobic nature of the blood debubblizer 8 is promoted to positively attract air bubbles contained in the blood, thus allowing the air bubbles to grow and be removed from the blood. The air bubble stop unit 9 which is rendered hydrophilic can easily catch air bubbles with the very fine mesh screens. The blood flows very smoothly through the blood debubblizer 8 and the air bubble stop unit 9 because the blood storage container 1 is used with the oxygenator which is of the head perfusion type. The mesh screen 12 of larger mesh size may be disposed in the lower portion of the frame 11, and the mesh screen 13 of smaller mesh size may be disposed in the upper portion of the frame 11. Alternatively, the mesh screen 13 of smaller mesh size may be disposed in each of the upper and lower portions of the frame 11. If the mesh screen 12 of larger mesh size is disposed in the lower portion of the frame 11 and the mesh screen 13 of smaller mesh size is disposed in the upper portion of the frame 11, then since air bubbles contained in the blood move up when the blood flows through the mesh screens 12, 13, the air bubbles are removed by the upper mesh screen 13 of smaller mesh size, whereas the pressure loss of the blood flowing through the lower mesh screen 12 is prevented from being lowered by the mesh screen 12 which is of larger mesh size. Mesh screens for removing air bubbles and foreign matter from the blood may include a mesh screen 13 of smaller mesh size, a mesh screen 12 of larger mesh size, and a mesh screen of intermediate mesh size, which are positioned in juxtaposed relation in a frame 11, as shown in FIG. 3. The blood storage container 1 thus constructed is used with an extracorporeal blood circulation apparatus A illustrated in FIGS. 4 and 5. The extracorporeal blood circulation apparatus A comprises a heat exchanger 20 and an oxygenator 21 which is coupled to the blood storage container 1 of the present invention. Blood B flows from the superior and inferior vena cava of a patient (not shown) into a blood supply port 22 through medical tubes (not shown). The blood B is then supplied to the oxygenator 21 through gaps between tubes 23 stored in the heat exchanger 20. At this time, water W maintained at a predetermined temperature flows in the tubes 23 through water ports 24, 25. Therefore, the blood B flowing through the gaps between the tubes 23 is heated or cooled to the predetermined temperature by the water W. The blood B then flows from the heat exchanger 20 into the oxygenator 21 through joint tubes 26. Oxygen is added to and carbon dioxide is removed from the blood B in a gas exchange chamber 28 surrounded by a housing 27 of the oxygenator 21. More specifically, a bundle of hollow filamentary membranes 29 which is disposed in the chamber 28 is supplied with a gas C containing oxygen from a gas inlet port 30 through a gas supply chamber 31. Therefore, oxygen and carbon dioxide are exchanged in the blood B through the hollow filamentary membranes 29. A gas C containing carbon dioxide is discharged from a gas discharge chamber 32 through a gas outlet port 33. The blood B with oxygen added thereto by the oxygenator 21 is directed through joint tubes 34 and the blood inlet ports 4 into the blood inlet chamber 5 of the blood storage container 1. At this time, the flow of the blood B is smoothed by mesh screens 36 fitted in the blood inlet ports 4. Relatively large air bubbles are then removed from the blood B by the blood debubblizer 8. Very small or minute air bubbles which have not been removed from the blood B by the blood debubblizer 8 are then trapped and removed by the air bubble stop unit 9. Therefore, the blood B which is completely free of air bubbles is sent to the blood storage chamber 7. Inasmuch as the mesh screen 12 of large mesh size is disposed in the upper portion of the frame 11 of the air bubble stop unit 9 and the mesh screen 13 of small mesh size is disposed in the lower portion of the frame 11, even if the mesh screen 13 happens to be clogged by small air bubbles or foreign matter that may have been contained in the blood B, the blood B is directed toward the mesh screen 12 positioned above the mesh screen 13. Therefore, the blood B is not prevented from flowing through the air bubble stop unit 9. The blood outlet port 6, a BCP port 38 for protecting the heart muscles of the patient, and a port 40 which receives a thermistor probe 39 are defined in the lower portion of the blood storage container 1 near the heat exchanger 20, these ports being successively arranged upwardly in the order named. The blood B stored in the blood storage container 1 will be supplied to the aorta of the patient by means of a pump (not shown) communicating with the blood outlet port 6. As described above, the air bubble stop unit 9 composed of the mesh screens is disposed downstream of the blood debubblizer 8. Even if the blood that has flowed into the blood inlet chamber 5 contains air bubbles, relatively large air bubbles are trapped and removed by the blood debubblizer 8 as the blood flows therethrough. Minute air bubbles which are not removed by the blood debubblizer 8 and hence remain in the blood are then trapped by the air bubble stop unit 9. Therefore, any blood which contains air bubbles is not returned from the blood storage container 1 to the patient, and the patient is prevented from suffering embolism. Since the mesh screens of the air bubble stop unit 9 have mesh sizes ranging from 50 to 300 mesh, minutes air bubbles which may have been contained in the blood having passed through the blood debubblizer 8 can completely be removed from the blood without developing a substantial pressure loss in the blood. Since the mesh screens of the air bubble stop unit 9 have different mesh sizes, even if the mesh screen of smaller mesh size are clogged with air bubbles, foreign matter, or the like, the blood is allowed to flow through the mesh screen of larger mesh size. Therefore, the air bubble stop unit does not interrupt the flow of the blood therethrough. It is possible to remove minute air bubbles mainly with the mesh screen of smaller mesh size, and to minimize a pressure loss in the blood with the mesh screen of larger mesh size. Accordingly, the blood can flow at all times without an obstruction, while at the same time minute air bubbles can be completely removed from the blood and any pressure loss in the blood is held at a minimum. The air bubble stop unit 9 may be installed inversely so that the mesh screens 12, 13 will be positioned upside down. Although certain preferred embodiments have been shown and described, it should be understood that many changes and modifications may be made therein without departing from the scope of the appended claims.

Claims: A blood storage container (1) comprising a chamber (5), a blood debubblizer (8) for debubblizing the blood in the form of a three-dimensional foamed body, characterised in that the chamber (5) is provided as a blood inlet chamber, the blood debubblizer (8) is provided downstream of the blood inlet chamber (5) and upstream of a blood storage chamber (7) having a blood outlet port (6) and the foamed body of the blood debubblizer (8) is of a hydrophobic nature for attracting air bubbles, an air bubble stop unit (9) is provided between the blood debubblizer (8) and the blood storage chamber (7) for preventing remaining smaller air bubbles flowing therethrough by trapping and removing these, the air bubble stop unit (9) comprising mesh screens (12, 13) which are treated such that they are hydrophilic. A blood storage container according to claim 1, wherein said mesh screens (12, 13) include a mesh screen of larger mesh size (12) and a mesh screen of smaller mesh size (13), said air bubble stop unit (9) including a frame (11) in which said mesh screens are supported. A blood storage container according to claim 2, wherein said mesh screen of larger mesh size (12) is positioned upwardly of said mesh screen of smaller mesh size (13). A blood storage container according to claim 2 or 3, wherein said mesh screen of smaller mesh size (13) is positioned upwardly of said mesh screen of larger mesh size (12). A blood storage container according to any of claims 3 to 4, wherein said mesh screens (12, 13) have mesh sizes ranging from 50 to 300 mesh size. A blood storage container according to claim 5, wherein said mesh screen of smaller mesh size (13) has a mesh size ranging from 125 to 300, preferably from 150 to 250. A blood storage container according to claim 5 or 6, wherein said mesh screen of larger mesh size (12) has a mesh size ranging from 50 to 175, preferably from 75 to 150. A blood storage container according to any of claims 2 to 7, wherein said mesh screens (12, 13) are detachably mounted in said blood storage chamber (7).

Inventors: KUROO' TAKESHI C O TERUMO KABU, OSHIYAMA HIROAKI C O TERUMO KA, KUROO', TAKESHI C/O TERUMO KABUSHIKI KAISHA, OSHIYAMA, HIROAKI C/O TERUMO KABUSHIKI KAISHA
Applicants: TERUMO CORP, TERUMO KABUSHIKI KAISHA
Application year: 1989
Main classification: A61M1
IPC codes: A61M1