CA1182401A

CA1182401A - Arterial blood filter with improved gas venting

Info

Publication number: CA1182401A
Application number: CA000418338A
Authority: CA
Inventors: Duane D. Dickens; Francis M. Servas
Original assignee: Shiley Inc
Current assignee: Shiley Inc
Priority date: 1981-12-23
Filing date: 1982-12-22
Publication date: 1985-02-12
Also published as: DE3278279D1; JPS58112549A; EP0174420A3; ES279722Y; JPS6314992B2; US4411783A; ES278937U; EP0082721B1; ES279722U; EP0174420A2; ES278937Y; EP0082721A1

Abstract

ARTERIAL BLOOD FILTER WITH IMPROVED GAS VENTING
Abstract A novel liquid filter of the "outside-in" type is disclosed, comprising a hollow tubular housing, a concentrically disposed perforated tubular core surrounded by a cylindrical filter element and communicating with a liquid outlet in the bottom wall of the housing, and a filter element cap covering the upper ends of the perforated core and filter element. A gas vent is located at the highest point in the top wall of the housing, which is at the center of the top wall. The liquid inlet and filter element cap are designed to provide for establishment of a stable swirling flow outside the filter element and above the filter element cap.
An improved means of bonding upper and lower cup-like portions together to form a hollow tubular housing with high resistance to rupture under pressure is also disclosed. The filter of the invention is particularly suited for use in extracorporeal blood flow circuits, most particularly as an arterial blood filter located downstream from a blood oxygenator.

Description

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ARTl~RIAL BLOOD F:[LTER WITH I~lPRO~lED GAS VENTING

~ lood filters are widely used in extracorporeal hlood flow circuits, such as those employed in hemodialysis treatments or cardiopulmonary bypass operations (e.g. open heart surgery). These filters are typically disposable, i.e. not re-sterilized and re-used, and are thus manufactured in mass production from inexpensive materials. In cardiopulmonary bypass circuits, blood filters are usually included both upstream and downstream oE a blood oxygenator. ~n arterial blood filter, located downstream from the oxyyenator, is intended to serve a critically important safety function by removing any solid or gaseous emboli, particles, bubbles, etc., that may for example have escaped through the oxygenator or be~n generated by cavitation behind a pump, from the arterialized blood befors it is returned to the patient. Failure to effectively remove such emboli, particles, bubbles, etc., can obviously have disastrous consequences.
As an additional safety factor, an arterial blood filter positioned downstream from a pump must have a very high resistance to rupture under an excessive internal pressurization caused for example by an unexpected blockage of the return line to the patient. In a disposable arterial filter, the high resistance to rupture must be accomplished without markedly raisin~ the cost of manufacture.

One known type of arterial blood filter (see e.g. U.S. Patents 3,701,433 and 3,939,078) comprises a hollow tubular housing, an upwardly-extending perforated tubular core concen-trically disposed within the housing and surrounded by a cylindrical. filter element, e.g. a pleated layer or array of layers wrapped into a cylindrical configuration, a Eilter element cap covering the uppe.r ends of the perforated core and filter element, a gas vent in the top wall of the housing, a blood inlet in communication with the space between the filter element and the side wall of the housing, and a blood outlet in communication with the space within the perforated core. The flow of blood through the cylindrical filter element is lS substantially radial, from the outside of the cylindrical element to the ins.ide thereof. Although th.ls known type of arterial blood filter has been used for many years with conslderable benefit to mankind, it is nevertheless in need of improvement.
The input blood upstream of the filter element tends to develop regions of churning Elow, which interfere with the orderly passage of gaseous emboli and bubbles to the vent. As a result, one must rely excessively upon the layer in the filter element having the smallest pore size, e.g. a woven filter screen, to prevent the passage of gaseous emboli and bubbles through the filter element and to the patient.
Consequently, the probability of such passage occurring is higher than if a smooth orderly gas venting were provided. Furthermore, the development of regions of churning flow may give rise to excessive destruction of blood components.

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It is an object of the present invention to provide a disposable blood filter, suitable for use in an extracorporeal blood flow circuit, in which yas bubbles and gaseous emboli in the blood input are vented in a highly predict.able manner along orderly pathways. This and other objects of the invention are achieved with a novel liquid filter, suitable for use in an extracorporeal blood flow circuit, comprising a hollow tubular housing having a side wall, a top wall having a highest point at the center thereof and a bottom wall, a perforated tubular core concentrically disposed within said housing, a cylindrical filter element surrounding said core and displaced from said side wall, a filter element cap covering the upper ends of said core and said filter element and displaced from said top wall, a gas vent in sai.d top wall at said highest point, a substantially horizontal liquid inlet in said si.de wall adjac~nt said top wall, and a filtrate outlet in said bottom wall of said housing in communication with the space within said core, with the upper surface of said filter element cap being symmetrical about the longitudinal axis of said housing, having a highest point at its center, and being without any points of localized minimum height, and with said inlet being adapted to direct the incoming flow of liquid in a non-perpendicular manner against the side wall of the housing, wh~3reby a swirling flow of liquid is established outside said filter element and above said filter element cap. The establlshment of a swirling flow or vortex creates a negative pressure gradient in all directions towards the centrally located vent, thereby providing orderly pathways for the movement of gaseous emboli and gas bubbles in the input liquid to the vent.
In a preferred embodirnent of the novel filter, the upper surface of the filter element cap includes a generally conical central portion generally overlying the perforated tubular core, and a relatively flat peripheral portion surrounding said central portion.
The cylindrical filter element preferably comprises an array of layers, with said array being provided with a plurality o~ longitudinal pleats and wrapped ~nto a cylindrical configuration. More preferably, the array consists of three layers, a woven screen middle layer of synthetic polymeric filaments having a pore size of from about 15 microns to about 50 mlcrons and identical inner and outer supporting sheets of open mesh extruded synthetic polymeric netting of much greater pore size. In one embodiment of the novel filter, an arxay of layers comprising the filter element is provided with not more than about 12 longitudinal pleats per inch of outer circumference of the perforated tubular core and includes a woven screen of synthetic polymeric monofilaments having a pore size of from about 15 microns to about 25 microns. In this embodiment, the small pore size woven screen provides an optimal barrier against passage of yaseous emboli, while the rela-tively open p].eat configuration eliminates -the risk of capturiny yaseous ernboli between pleats and provides for the ready and easy priminy of the :Ellter.
Ano-ther aspect of a novel filter of -the invention relates -to -the manner in which upper and lower mating cup-like portions are bonded together at a seam to form a hollow tubular housing haviny an excellent resis-tance to rupture a-t the seam under excessive internal pressurization.
According to-this otheraspect, there is provided in a hollow tubular housiny comprisiny an upper cup-li.ke por-tion, havincJ
a top wall, a downwardly-extendincJ side wall and an open bottom end, secured to a lower cup-like po:r-tion haviny a bottom wall, an upwardly-ex-tendiny side wall and an open -top end, -the lmprovemen-t wherein -the lowermos-t portion oE said upper portion includes inner and ou-ter downwardly-extendiny annular rims defininy a Eirst annular yroove between -them, the up~permost por-tion of said lower por-tion includes inner and outer upwardly-ex-tending annular rims defining a second annular groove he-tween -them, wi-th said outer annular rim of said lower portion received within said firs-t annular groove and with said inner annular rim oE said upper portion received wi-thin said second annular groove, said two outer annular rims are bonded tocJe-ther and said outer upwarclly-extendiny annular rim is bonclecl to saicl inner clownwardly-extencliny annular rim, whereby a double shear seal capable oE withstandiny elevated pressure is ob-tained.

`s The invention will be clescribed in detail with reference to a preferred embodiment thereof, which is a disposable arterial blood Eilter for use in an extracorporeal blood Elow circuit including a blood oxygenator. Reference -to this embodiment does not limit the scope of the invention, which is limited only by the scope of the claims.
In the drawings:
Figure 1 is an exploded perspective view of an arterial blood filter of the invention;
Figure 2 is a longitudinal sectional view oE the filter of Figure l;
Figure 3 is a sectional view along line 3--3 in Figure 2;
and Figure ~ is a -transverse sectional view through a portion o -the filter element of -the Eilter of Figure 1.

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A disposable blood filter 1 of the inventlon is shown in FIGS. 1 and 2. :[t is an arterial blood filter, i.e. suitable to be :Lncluded in an extracorporeal blood flow circuit downstream of a blood oxygenator.
Filter 1 comprises a hollow l:ubular housing 3 having a top wall 5, side wall 7 and bottom wall 9, a vertically-extending perforated tubular core 11 concentrically disposed within housing 3, a cylindrical filter element 13 surrounding and supported by tubular core 11, and a filter element cap 15 covering the upper ends of tubular core 11 and filter element 13. Tubular housing 3 ls formed from cup-like upper and lower portions 17 and lg secured together in a manner to be described below at seam 21. Side wall 7 of housing 3 extends upwardly to include the short vertically-ex-tending portion 23 of upper portion 17. Top wall 5 o tubula~ housin~ 3 is upwardly inclined con-tinuously from its circumferential perimeter to a highest point a-t the center of the wall, at whi.ch highest point gas vent 28 is located. Gas vent 28 compxises a Luer fitting. Filter 1 also includes outlet 29 in bottom wall 9, which communicates with the interior of tubular core 11, and hori~ontal inlet 31 in side wall 3 adjacent top wall 5. The downwardly-extending annulqr rim 45 of filter element cap 15terminates at edge 47, which is bevelled (see FIG. 2) so that ga.s bubbles and gaseous emboli cannot be trapped beneclth it. Lower portion 19 is slightly tapered (see FIG. 2), for reasons that will be explained below.

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Cylindrical filter element 13 is shown in FIG.
1 and, in a transverse sectional view, FIG. 4. It comprises an array of three superimpo.sed layers 33, 35 and 37 folded together in a plurality of longi-tudinal pleats and wrapped int:o a cylindrical con-figuration wikh opposed ends sealed at a seam by conventional means. Middle layer 35, the principal filtering layer, is a woven screen of nylon filaments having a pore size of about 20 microns. (In another preferred embodiment of the invention, woven nylon screen 35 has a pore size of about 40 microns.) Identical layers 33 and 37 on either side of screen 35 are made of extruded open mesh polypropylene nettiny having a pore size of about 1000 microns. Layers 33 and 37 serve to support screen 35 against collapse at the substantial flow rates experienced during operation o~ t~le arterial Eilter 1. Additionally, the upstream open mesh layer serves to trap any solid d~bris that may be present in the blood. The layers in the array may be rendered hydrophillic by treatment with a we-tting ayent, for example a hydro phill~c non-ionic polyethylene oxide homopolymer such ~J~ as a Polyox resin (Union Carbide Corp., New York, N.Y.), a blood-compatible surfactant or a purified plasma protein such as heparin or albumin. Cylindrical filter element 13 preferably has an open pleat configuration in use. That is, a substantial space S (see FIG. 4) is left between adjacent pleats. Thus, as one example only, filter element 13 may be provided with 29 longitudinal pleats,evenly distributecl along a 2.64 inch circumference (corresponding to a 0.84 inch diameter) of the outer surface of perforated core 11. The advantages of the open pleat filter element configuration are discussed above.
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Of critical importance to ~he present inven-tion is the deslgn of filter element cap 15. The upper surface of cap 15 is s~metrical about the longitudinal aY~is of tubular housiny 3 and has its hiyhest point 39 at its center. The assembly of core 11, filter element 13 and cap 15 is positively fixed sy~netrically with respect to the longitudinal axis of housing 3 by means of thre~e evenly circumferentially distributed spacers 81, 83 and 85 provided in the cap 15, each oE which contacts an adjacent portion of side wall 7 of housing 3 in the region of seam 21. Further-more, there are no localized points or regions of minimum height (i.e., dimples, grooves, valleys, etc.) upon the upper surface of cap 15~ The upper surface of the filter element cap may be continuously inclined from its perimeter to i-ts center point or, alternatively, its peripheral portion may be campletely fla-t. Pxeferably, as shown in FIG. 2, said upper sur~ace includes a generally conical central portion 41 generally overlying tubular core 11, and a relatively flat peripheral portion ~3 surrounding central portion 41. More preferably, the ratio of the height ~l of the upper surface of cap 15 to the diameter D of said surface (see FIG. 2) is from about 0.10 to about 0.25.
Other designs for the upper surface of cap 15 are possible. Thus, as only one additional eYample, said surface may include a generically hemispherical central portion generally overlying the perforated tubular core, and a relatively flat peripheral portion.
As is shown in FIGS. 1 to 3, horizontal inlet 31 is so situated that the input blood does not directly impinge on cap 15 or element 13, but instead first contacts, in a non-perpendicular manner, the inner surfac~ of side wal:L 7 of housing 3. In the filter shown in FIGS. 1 to 3, the input blood contacts side wall 7 at an acute angle. Other designs are possible in which the input blood contacts the side wall in an essentially tangential manner.
The net effect of the configuration of elements in filter 1, particularly filter element cap 15 and inlet 31, is the establishment over a wide range of blood throughput flow rates of a stable swirling flow of blood, i.e. a vortex, between filter element 13 and side wall 7 and between filter element cap 15 and top wall 5. As a consequence, a negative pressure gradient towards the vent, which provides the driving force for gas bubble and gaseous emboli removal, exists -throughout the swirling blood. This negative pressure yradient creakes an orderly system of pathways for gas buhble and gaseous emboli removal at the centrally located vent 28. The input stream of blood through inlet 31 is directed away from vent 28 and thus does not interfere with the venting.
In operation as an arterial blood filter in an extracorporeal blood flow circuit including a blood oxygenator, inlet 31 is connected to a line leading from the oxygenator, outlet 29 is connected to a line leading to the patient, Luer cap 27 is removed from Luer fitting 28, a stopcock (not shown) is installed on fitting 28 and the stopcoc~ is connected to a vent line leading to a non-pressuriæed por-t on the blood oxygenator or a cardiotomy reservoir.

The extracorporeal circuit is primed with saline solution before the circulation of the patient's blood through it commences. The stc)pcock installed on fitting 28 is in the open position during filtration of the patient's blood but must be closed prior to stopping the extracorporeal circuit punnp to prevent backflow of blood in the filter. During steady-state filtration, the entire space within housing 3 above filter element cap 15 is filled with the patient's blood.
As one example only of the filter 1 shown in FIGS. 1 to 4, filter element 13 is provided with 29 longitudinal pleats evenly distributed along the outer circumference of perforated tube 11, tube 11 has an outer diameter of 0.84 inch, H is 0.35 inch and D is 2.035 inches. The average inner diameter of s.ide wall 7 between rounded shoulder q9 and seam 21 is 2.18 inches. In a Eilter 1 of the inven-tion having these dimensions, excellent results are obtained at blood throughput flow rates of from about 1 liter/minute to about 6 liters/minute.
Filter 1 is manufactured by conventional methods.
~pper cup-like portion 17, is prepared as a single piece including inlet 31 and fitting 28. Lower cup-like portion 19 is prepared as a single piece including outlet 29. Portions 17 and 19, as well as cap 15, are made of an inexpensive clear plastic material, preferably a thermoplastic such as a polycarbonate, while core 11 is also made of an inexpensi~e plastic material, preferably polyproplene. The slight --ll--upward/outward taper of lower portion 19 results from its manufacture by injection molding, which is preferred because of its low cost. This taper is beneficial to the function of the filter since it acts to equalize the pressure gradient across filter element 13 at different longitudinally displaced locations.
In assembling the filter, filter element cap 15 is first held upside down and filled, between tubular projection 51 and rim 45, with a hot melt adhesive 55 such as ethylene vinyl acetate. Perforated core 11 (carrying filter element 13) is then lowered onto cap 15. Core 11 loosely receives projection 51, which filter element 13 rests upon annular flange 53 of cap 15 and fits loosely within rim 45. Core 11 (carrying filter element 13) and cap 15 are held together in their des~red perpendicular relative con~
f.iguration by a suitable fixture (not shown). ~fter adhesive 55 has hardened, the resulting assembly i5 removed from the fixture holding it. Lower cup-like portion 19 is filled with a hot melt adhesive 57, e.~.
ethylene vinyl acetate, between tubular projection 59 and side wall 7 below shoulder 49. The assembly of core 11, filter element 13 and cap 15 is then lowered onto lower portion 19, with core 11 loosely receiving projection 59 and filter element 13 fitting loosely within side wall 7 below shoulder ~9. Filter element 13 rests upon a substantial number, for example twenty-four, of equally distributed radially-extending ribs, e.~. 61, 63, in single piece construction with portion 19 and extending upwardly from slightly -12~

inclined lower wall 9. Provision of these ribs improves the bonding of ~ilter element 13 to lower portion 19. The assembly of core 11, fil~er element 13 and cap 15 ls held tog~ther with lower portion 19 in the desired concentric relative configuration by a suitable fixture (not shown~. After adhesive 57 has hardened, the resulting assembly is removed from the fixture holding it.
As can be seen in FIG. 2, upper cup-like portion 17 contains inner and outer downwardly-extending annular rims 65 and 67 defining annular groove 69 between them, while lower cup-like portion 19 contains inner and outer upwardly-extending annular rims 71 and 73 defining annular groove 75 be-tween them. A silicone rubber "O"-ring 77 is held within groove 75. Portion 17 and 19 are adapted to be joined together, thereby forming seam 21, with rim 73 recei.ved within groove 69 and rim 65 received within groove 75. After such joining has been accomplished, rim 73 is bonded to rim 67 and to rim 65, preferably by ultrasonic bonding, with portions 17 and 19 held under compression so that ring 77 i5 compressed within groove 75. The result is a triple hermetic seal between portions 17 and 19.
The dou~le shear seal provided by the bonding of rim 73 to rims 65 and 67 imparts an excellent burst resistance to seam 21 of filter 1; internal pressures far in excess of 50 psi can be tolerated without bursting. If desired, a triple shear seal may be provided by additionally bonding rim 71 to rim 65.

After the bonding of upper portion 17 to lower portion 19 is completed, Luer cap 27 is installed on Luer fitt1ng 28 and plastic protective caps are placed over inlet 31 and outlet 29. The filter is then sterilized and packaged in a sterile con-dition, _ g. in a clear plastic peel-open pouch, for distribution to the ultimate user, who disposes of it after a single use.

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A liquid filter suitable for use in an extracorporeal blood flow circuit comprising a hollow tubular housing having a side wall, a top wall having a highest point at the center thereof and a bottom wall, a gas vent in said top wall at said highest point, a perforated tubular core concentrically disposed within said housing, a cylindrical filter element surrounding said core and displaced from said side wall, a filter element cap covering the upper ends of said core and said filter element and displaced from said top wall, a substantially horizontal liquid inlet in said side wall adjacent said top wall, and a filtrate outlet in said bottom wall of said housing in communication with the space within said core, with the upper surface of said filter element cap being symmetrical about the longitudinal axis of said housing, having a highest point at its center, and being without any points of localized minimum height, and with said inlet being adapted to direct the incoming flow of liquid in a non-perpendicular manner against the side wall of said housing, whereby a swirling flow of liquid is established outside said filter element and above said filter element cap.

2. A filter of claim 1 wherein said upper surface of said filter element cap is continuously inclined from the perimeter to the center of said cap.

3. A filter of claim 1 or 2 wherein said upper surface includes a generally conical central portion generally overlying said perforated tubular core, and a relatively flat peripheral portion surrounding said central portion.

4. A filter of claim 1 wherein said filter element comprises an array of layers, with said array being provided with a plurality of longitudinal pleats.

5. A filter of claim 4 wherein one of said layers is a woven screen of synthetic polymeric monofilaments having a pore size of from about 15 microns to about 50 microns.

6. A filter of claim 5 wherein said array is provided with not more than about 12 longitudinal pleats per inch of outer circumference of said perforated tubular core.

7. A filter of claim 6 wherein one of said layers is a woven screen of synthetic polymeric monofilaments having a pore size of not more than about 25 microns.

8. In a hollow tubular housing comprising an upper cup-like portion, having a top wall, a downwardly-extending side wall and an open bottom end, secured to a lower cup-like portion having a bottom wall, an upwardly-extending side wall and an open top end, the improvement wherein the lowermost portion of said upper portion includes inner and outer downwardly-extending annular rims defining a first annular groove between them, the uppermost portion of said lower portion includes inner and outer upwardly-extending annular rims defining a second annular groove between them, with said outer annular rim of said lower portion received within said first annular groove and with said inner annular rim of said upper portion received within said second annular groove, said two outer annular rims are bonded together and said outer upwardly-extending annular rim is bonded to said inner downwardly-extending annular rim, whereby a double shear seal capable of with-standing elevated pressure is obtained.

9. The improvement of claim 8 wherein additionally said two inner annular rims are bonded together, whereby a triple shear seal is obtained.

10. The improvement of claim 8 or 9 wherein said upper and lower portions are made of plastic and said annular rims are bonded by ultrasonic bonding.

11. A filter of claim 4 wherein at least one of said layers has been rendered hydrophillic by treatment with a wetting agent.