BLOOD STORAGE TANK

Abstract: An object of a blood storage tank in accordance with the present invention is to remove bubbles in a blood in an extracorporeal circulation circuit and to secure a predetermined quantity of the blood. In the blood storage tank described above, a defoaming member is disposed in a blood path between a blood inflow portion having a blood inlet and a blood storage portion having a blood outlet in such a manner as to cross transversely the entire width of the blood path and a rib having a predetermined height is disposed across the full width of the blood path while kept in contact with the surface of the defoaming member on the side of the blood storage portion. According to this structure the blood is caused to stay in the defoaming member for a predetermined time by the rib and during which, bubbles in the blood are removed reliably.

Description: The present invention relates to a blood reservoir for use with an artificial lung, the blood reservoir including a debubblizing filter for reliably removing air bubbles from blood stored in the blood reservoir. When a surgical operation is effected on the chest of a patient, an extracorporeal blood circulation circuit including an artificial lung is used in recent years 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 artificial lung. The extracorporeal blood circulation circuit includes a blood reservoir for temporarily storing the blood so that air bubbles produced during the circulation of the blood will be removed from the blood, or for supplying stored blood to make up for m reduction in the rate of circulation of the blood. Blood reservoirs now in use in the art are roughly classified into a soft bag type which is made of a soft material, and a hard shell type which is made of a hard material. The soft bag reservoir 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 reservoir 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 reservoir are that it can easily be united with an artificial lung, thus permitting an extracorporeal blood circulation circuit to be simplified, 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(1984)-57661, for example, proposes a hard shell blood reservoir combined with an artificial lung. It is very important that a hard shell blood reservoir be capable of reliably removing air bubbles which have been introduced into the blood through a blood extracting tube. If the blood containing air bubbles were returned to the patient, then the patient would suffer from the danger of embolism. The hard shell blood reservoir therefore has a debubblizing filter for removing air bubbles from the stored blood. One known hard shell blood reservoir with a debubblizing filter, which is combined with an artificial lung, is a blood reservoir LPM 50 (manufactured by Baxter Travenol Laboratories, Inc.) as shown in FIG. 1 of the accompanying drawings. The blood reservoir, denoted at 2, has a blood debubblizing filter 8 disposed in a blood inlet chamber 6 near a blood inlet port 4 and held in contact with the bottom of the blood inlet chamber 6. Blood B which has been introduced from an artificial lung 10 through a heat exchanger 12 into the blood reservoir 2 flows into a blood storage chamber 14 without being subjected to a large resistance by the debubblizing filter 8. Since the blood B is not kept in effective contact with the debubblizing filter 8, the debubblizing filter 8 fails to debubblize the blood B effectively. Air bubbles, particularly small air bubbles, contained in the blood B therefore tend to be carried into the blood storage chamber 14 by the flow of the blood B. In view of the aforesaid drawbacks of the conventional blood reservoirs, it is an object of the present invention to provide a blood reservoir which includes a debubblizing filter that can effectively be kept in contact with introduced blood for a greater debubblizing capability, so that air bubbles contained in the blood can effectively be removed. To achieve the above object, there is provided in accordance with the present invention a blood reservoir comprising a blood inlet chamber having a blood inlet port, a blood storage chamber communicating with the blood inlet chamber and having a blood outlet port in a lower end which is positioned downwardly of the blood inlet chamber, and a blood debubblizing filter extending fully across a blood passage of the blood inlet chamber which leads to the blood storage chamber, characterized by a rib held against the side of the debubblizing filter closer to the blood storage chamber and extending fully across the blood passage, the rib projecting a predetermined distance upwardly from the bottom of the blood inlet chamber. The rib has a height ranging from 1 mm to 50 mm. The debubblizing filter comprises a first foamed body disposed closer to the blood inlet port, and a second foamed body disposed closer to the blood storage chamber, the first foamed body having a mesh number larger than the mesh number of the second foamed body. The rib may include irregular surface portions transversely across the blood passage. FIG. 1 is a schematic elevational view of a conventional blood reservoir; FIG. 2 is a side elevational view, partly in cross section, of an artificial lung apparatus incorporating a blood reservoir according to the present invention; FIG. 3 is a vertical cross-sectional view of the blood reservoir of the invention; FIG. 4 is a cross-sectional view taken along line IV - IV of FIG. 3; FIG. 5 is a cross-sectional view of a blood inlet chamber in a blood reservoir according to a comparative example; FIG. 6 is a cross-sectional view of a blood inlet chamber in a blood reservoir according to another embodiment of the present invention; and FIG. 7 is a diagram of a blood circuit employed in a blood circulation experiment conducted on the blood reservoir according to the present invention. Preferred embodiments of a blood reservoir according to the present invention will be described in detail with reference to the accompanying drawings. FIG. 2 shows a blood reservoir 20 according to the present invention which is combined with an artificial lung 21 for exchanging oxygen and carbon dioxide in blood B and a heat exchanger 28 for keeping the blood B at a predetermined temperature. The blood reservoir 20 will first be described with reference to FIGS. 3 and 4. The blood reservoir 20 is a blood reservoir of the hard shell type for use in an extra corporeal blood circulation circuit. As shown in FIG. 3, the blood reservoir 20 has a pair of blood inlet ports 22a, 22b, a blood inlet chamber 24 communicating with the blood inlet ports 22a, 22b and having a bottom which is substantially at the same level as the blood inlet ports 22a, 22b, a blood storage chamber 26 communicating with the blood inlet chamber 24 and having a bottom extending progressively downwardly from the blood inlet chamber 24, and a blood outlet port 28 defined in the lower end of the blood storage chamber 26. The blood reservoir 20 comprises a container housing 30 of a hard material such as hard polyvinyl chloride, polystyrene, polycarbonate, or the like. The container housing 30 has an upper opening closed by a cover 32. The container housing 30 should preferably be transparent so as to allow the user to visually observe the blood B stored in blood reservoir 20. The blood inlet ports 22a, 22b are connected to blood outlet tubes 34a, 34b (see FIG. 2) from the artificial lung 21. The blood inlet chamber 24 communicating with the blood inlet ports 22a, 22b defines a blood passage extending from the blood inlet ports 22a, 22b to the blood storage chamber 26. The blood inlet chamber 24 is higher in position than the blood storage chamber 26, and has a bottom which is substantially at the same level as the blood inlet ports 22a, 22b, as described above. The bottom of the blood inlet chamber 24 may be flat or semicylindrical in shape. However, the flat bottom is preferable since a blood debubblizing filter (described later) can easily be placed thereon. The blood storage chamber 26 communicating with the blood inlet chamber 24 serves to store the blood B which has flowed into the blood reservoir 20. The bottom of the blood storage chamber 26 extends progressively downwardly from the blood inlet chamber 24. The blood B which is temporarily stored in the blood reservoir 20 is discharged out from the blood outlet port 28 defined in the lower end of the blood storage chamber 26. The blood reservoir 20 also has a blood debubblizing filter 36 disposed in the housing 30 and extending transversely fully in and across the blood passage defined by the blood inlet chamber 24. The debubblizing filter 36 serves to remove air bubbles from the blood B which has flowed into the blood inlet chamber 24 so that the blood B free of air bubbles can be delivered into the blood storage chamber 26. The debubblizing filter 36 is generally in the form of of foamed bodies which are of a hydrophobic nature to allow air bubbles in the blood to grow and be removed. The foamed body is of a three-dimensional mesh structure. In the illustrated embodiment, the debubblizing filter 36 is composed of a foamed body 38a of a larger mesh number and a foamed body 38b of a smaller mesh number, the foamed bodies 38a, 38b are arranged side by side. The foamed body 38a is positioned closer to the blood inlet ports 22a, 22b, whereas the foamed body 38b is positioned closer to the blood storage chamber 26. The mesh number referred to above represents the number of interstices or openings occurring per length of 25.4 mm (1 inch), and is originally an indication of the size of openings of a screen or sieve. The debubblizing filter 36 is held in intimate contact with the bottom of the blood inlet chamber 24 and extends across the full width of the blood passage so that the incoming blood B will be in full contact with the debubblizing filter 36. The debubblizing filter 36 is also held in intimate contact with the side walls of the housing 30. The upper end of the debubblizing filter 36 is preferably held in intimate contact with the cover 32 mounted on the top of the housing 30 in order to prevent the debubblizing filter 36 from being moved by the blood flow or to prevent the blood B from flowing out beyond the upper end of the debubblizing filter 36. In order to prevent the debubblizing filter 36 from being moved, the housing 30 has four ridges 40a through 40d projecting from the inner side surfaces of the housing 30 on both lateral sides of the debubblizing filter 36 at the opposite surfaces thereof. The housing 30 also has a rib 42 projecting a certain height from the bottom of the blood inlet chamber 24. The rib 42 is disposed at the edge of the debubblizing filter 36 near the blood storage chamber 26, i.e., on the downstream side of the debubblizing filter 36 with respect to the blood flow, and extends the full width of the blood passage defined by the blood inlet chamber 24. The rib 42 is held in contact with the foamed body 38b. The artificial lung 21 coupled to the blood reservoir 20 comprises a housing 50 and attachment covers 52a, 52b closing the upper and lower ends, respectively, of the housing 50. The housing 50 accommodates therein a number of hollow fiber membranes 54 which are vertically disposed in spaced relation to each other. The hollow fiber membranes 54 have opposite open ends held in the housing 50 by partitions 56a, 56b in a fluidtight manner, with the open ends remaining open. The attachment cover 52a, the housing 50, and the partition 56a jointly define a gas inlet space 58 communicating with the hollow spaces in the hollow fiber membranes 54 and connected to a gas inlet port 60. The other attachment cover 52b, the housing 50, and the partition 56b jointly define a gas outlet space 62 communicating with the hollow spices in the hollow fiber membranes 54 and connected to a gas outlet port 64. The inner wall surface of the housing 50, the partitions 56a, 56b, and the outer wall surfaces of the hollow fiber membranes 54 jointly define a blood chamber 66 connected to a blood inlet tube 68 communicating with the heat exchanger 23 and the blood outlet tubes 34a, 34b which communicate with the blood reservoir 20. The blood outlet tubes 34a, 34b of the artificial lung 21 are joined in a fluidtight manner to the blood inlet ports 22a, 22b of the blood reservoir 20. The blood outlet tubes 34a, 34b and the blood inlet ports 22a, 22b may be joined by threaded interfitting engagement, tapered interfitting engagement, fitting engagement through an O-ring, ultrasonic or high-frequency bonding, or adhesive bonding. The artificial lung 21 is of the type which delivers a gas G containing oxygen such as air into the hollow fiber membranes 54 and allows the blood B to flow outside of the hollow fiber membranes 54 for a gaseous exchange between the gas G and the blood G. Alternatively, the artificial lung 21 may be of the type which delivers the blood B into the hollow fiber membranes 54 and the gas G containing oxygen around the hollow fiber membranes 54 for a gaseous exchange between the gas G and the blood B, or of the type which includes flat membranes for a gaseous exchange. Preferably, the artificial lung 21 should be of the type which passes the blood B around the hollow fiber membranes 54 as described above in this embodiment. With the artificial lung 21 of this type being employed, since any pressure loss across the artificial lung 21 is small, a blood circulation circuit incorporating the blood reservoir 20 is not required to have a blood delivery pump in front of the artificial lung 21, but the blood B can be fed by gravity from the patient to the artificial lung 21 and the blood reservoir 20. The heat exchanger 23 is coupled to the blood inlet tube 68 of the artificial lung 21. The heat exchanger 23 has a number of heat exchanging tubes 72 disposed in a casing 70 in spaced relation to each other and extending in the longitudinal direction of the casing 70. The opposite open ends of the heat exchanging tubes 72 are held on side walls of the casing 70 by partitions (not shown) in a fluidtight manner, with the open ends of the tubes 72 remaining open. The partitions, the side walls of the casing 70, and the outer wall surfaces of the heat exchanging tubes 72 jointly define a space 74 which communicates with a blood inlet port 76 and the blood inlet tube 68 of the artificial lung 21. The inner spaces in the heat exchanging tubes 72, which are isolated from the space 74 in a fluidtight manner, communicate with a water inlet port 77 communicating with the exterior of one of the partitions of the casing 70 and a water outlet port (not shown) communicating with the exterior of the other partition of the casing 70. Warm or cold water W is supplied from the water inlet port 77 into the heat exchanging tubes 72, and warms or cools the blood B held in contact with the heat exchanging tubes 72. The heat exchanger 23 may be of the type in which the blood B is passed through the heat exchanging tubes 72 and a cooling or warming medium is passed around the heat exchanging tubes 72. The heat exchanger 23 and the blood reservoir 20 further have ports 78, 80, respectively, for the insertion of temperature sensor probes. The blood reservoir of the above embodiment is basically constructed as described above. Operation and advantages of the blood reservoir will be described below. The blood reservoir 20, the artificial lung 21, and the heat exchanger 23 which are combined together serve as an artificial lung apparatus. The blood B is introduced from the blood inlet port 76 into the casing 70 of the heat exchanger 23, and warmed or cooled by the water W flowing through the heat exchanging tubes 72 while the blood B is flowing toward the blood inlet tube 68 of the artificial lung 21. Then, the blood B flows from the blood inlet tube 68 into the housing 50 of the artificial lung 21. During passage through the blood chamber 66, a gaseous exchange is effected between the blood B and the gas G containing oxygen which flows through the hollow fiber membranes 54, thereby removing excessive carbon dioxide from the blood B and adding oxygen to the blood B. The blood B to which oxygen is added flows out of the artificial lung 21 from the blood outlet tubes 34a, 34b and flows into the blood reservoir 20 through the blood inlet ports 22a, 22b. The blood B introduced from the blood inlet ports 22a, 22b now reaches the debubblizing filter 36 in the blood inlet chamber 24. Since the side of the debubblizing filter 36 closer to the blood storage chamber 26 is held against the rib 42 which extends the full width of the blood passage defined by the blood inlet chamber 24 and projects upwardly a certain distance from the bottom of the blood inlet chamber 24, the blood B is temporarily forced to stay and be deflected just in front of the rib 42 while in contact with the debubblizing filter 36. Accordingly, the blood B passes through the debubblizing filter 36 in a sufficient period of time and is kept in contact with the debubblizing filter 36 through a sufficient area or at a sufficient frequency. Therefore, air bubbles contained in the blood B contact the cells of the foamed bodies 38a, 38b of the debubblizing filter 36 and are combined into larger air bubbles, which are moved from the blood B into an upper space in the blood reservoir 20 and are reliably removed. Inasmuch as the two foamed bodies 38a, 38b have different mesh number which become smaller in the direction in which the blood B flows, the pressure loss across the debubblizing filter 36 is not increased, and the air bubbles in the blood B are brought into sufficient contact with the cells of the foamed bodies 38a, 38b, with the result that the blood B is effectively debubblized. The rib 42 is required to extend the full transverse width of the blood passage defined by the blood inlet chamber 24. In this embodiment in which the blood inlet chamber 24 has a flat smooth bottom, as shown in FIG. 4, the rib 42 has to extend continuously up to the opposite lateral sides of the housing 30. More specifically, as shown in FIG. 5, if a rib 82 projecting from the bottom of the housing 50 is of a discontinuous shape and does not extend the entire transverse region of the blood passage defined by the blood inlet channel 24, the blood B flowing through the blood inlet chamber 24 passes through the recesses of the rib 82 when the blood B is to contact the debubblizing filter 36. Therefore, the rib 82 is not effective to keep the blood B in contact with the debubblizing filter 36. However, as shown in FIG. 6, providing a rib 84 extends the entire transverse region of the blood passage of the blood inlet chamber 24, the rib 84 is not required to be of a constant height, but may have irregular surface portions of different heights of different heights projecting upwards in the blood passage, and yet can maintain the blood B in sufficient contact with the debubblizing filter 36. If the height of the rib 42 or 82 were less than 1 mm, it would not be able to force the blood B to stay or be deflected in contact with the debubblizing filter 36. If the height of the rib 42 or 82 were in excess of 50 mm, it would tend to keep the blood B excessively in the blood inlet chamber 24, thus increasing the priming volume of the blood reservoir 20. Therefore, the rib 42 or 82 should preferably be of a height ranging from 1 mm to 50 mm, more preferably ranging from 1 mm to 20 mm, and most preferably ranging from 2 mm to 10 mm. The rib 42 or 82 may be formed integrally with the housing 30 when the housing 30 is injection-molded, or may be separately formed and then bonded to the housing 30 by high-frequency fusion, thermal fusion, or adhesive bonding. At any rate, it is necessary that the rib 42 or 82 be held in intimate contact with the bottom in a fluidtight fashion in the blood passage of the blood inlet chamber 24. The blood B from which air bubbles have been removed by the debubblizing filter 36 flows from the blood inlet chamber 24 into the blood storage chamber 26. After the blood B has temporarily been stored in the blood storage chamber 26, it is delivered to the patient's body from the blood outlet port 38 in the lower end of the blood storage chamber 26. An experiment conducted on the blood reservoir of the present invention will be described below. As shown in FIG. 7, there was employed a blood reservoir 20 having a storage capacity of 4 ℓ and including a blood inlet chamber 24 having a length of 30 mm, a width of 160 mm, and a flat bottom. The blood passage extending from the blood inlet chamber 24 to the blood storage chamber 26 had a rib 42 extending across the blood passage fully in its transverse direction and projecting a height of 3 mm from the bottom of the blood inlet chamber 24. The blood reservoir 20 also had a debubblizing filter 36 held closely against the rib 42 and composed of a foamed body 38a (having a thickness of 15 mm) made of a polyurethane foam having a mesh number of 13, the foamed body 38a being positioned closer to the blood inlet ports 22a, 22b, and a foamed body 38b (having a thickness of 15 mm) made of a polyurethane foam having a mesh number of 8, the foamed body 38b being held closely against the foamed body 38a and positioned closer to the blood storage chamber 26. An experimental blood circuit was constructed of the blood reservoir 20 and a blood storage tank 88 having a storage capacity of 20 ℓ and connected to the blood reservoir 20 by a roller pump 86. Using the experimental blood circuit, a blood circulation experiment was carried out at a blood flow rate of 4 ℓ/min. to determine how air bubbles were mixed into the blood B in the blood storage chamber 26 of the blood reservoir 20. A comparative blood circulation experiment was also conducted using the same blood reservoir as the blood reservoir 20 except that no projecting rib 42 was disposed on the bottom of the blood inlet chamber 24, and also using the same experimental blood circuit as described above, and it was determined how air bubbles were mixed into the blood in the blood storage chamber of the blood reservoir. It was found as the results of the experiments that the debubblizing filter 36 in the blood reservoir 20 having the rib 42 was more effective in removing air bubbles from the blood than the debubblizing filter in the comparative blood reservoir having no rib 42. Substantially no air bubbles were found flowing into the blood storage chamber 26. With the present invention, as described above, the blood remains in contact with the debubblizing filter over a long period of time, and the deflected blood flow causes the blood to be kept in contact with the debubblizing filter through an increased area or at an increased frequency. The blood is thus debubblized by the debubblizing filter so effectively that even small air bubbles can sufficiently be removed from the blood. Since the blood remains in sufficient contact with the debubblizing filter, the debubblizing filter does not develop an excessive pressure loss which would otherwise be brought about by an increased thickness of the debubblizing filter. Consequently, air bubbles can effectively be removed from the blood while at the same time maintaining a required amount of flood. As a result, it is possible to achieve safer extracorporeal circulation of blood when the blood reservoir is incorporated in an extracorporeal blood circulation circuit.

Claims: A blood reservoir (20) comprising a blood inlet chamber (24) having a blood inlet port (22a(b)), a blood storage chamber (26) communicating with the blood inlet chamber and having a blood outlet port (28) in a lower end which is positioned downwardly of said blood inlet chamber, and a blood debubblizing filter (36) extending fully across a blood passage of said blood inlet chamber which leads to said blood storage chamber, characterized by a rib (42) held against the side of said debubblizing filter (36) closer to said blood storage chamber (26) and extending fully across said blood passage, said rib (42) projecting a predetermined distance upwardly from the bottom of said blood inlet chamber (24). A blood reservoir according to claim 1, wherein said rib (42) has a height ranging from 1 mm to 50 mm. A blood reservoir according to claim 1, wherein said debubblizing filter comprises a first foamed body (38a) disposed closer to said blood inlet port (22a(b)), and a second foamed body (38b) disposed closer to said blood storage chamber (26), said first foamed body (38a) having a mesh number larger than the mesh number of said second foamed body (38b), said mesh number being defined as the number of interstices or openings occuring per length of 25.4 mm. A blood reservoir according to claim 1, wherein said rib (42) includes irregular surface portions of different heights projecting upwards in the blood passage.

Inventors: HUKASAWA HIROMICHI, HUKASAWA, HIROMICHI
Applicants: TERUMO CORP, TERUMO KABUSHIKI KAISHA
Application year: 1988
Main classification: A61M1
IPC codes: A61M1