GB2153247A - Filter - Google Patents

Abstract

A filter for biological fluids and solutions comprises a casing enclosing filter medium in the form of hollow fibres, both ends of which are sealed to the outlet end of the casing. The central tubular part of the casing 30 shown is made of porous hydrophobic plastics to act as an air vent. In another embodiment only part of the tubular part of the casing acts as an air vent while the rest is transparent to allow inspection of the medium. The filter can be primed in 15 seconds and used in non-vertical positions. <IMAGE>

Description

SPECIFICATION Hollow fiber filter element Background of the Invention This invention relates to an in-line filter system for parenteral solution administration sets, and in particular, to a filter element which employs hollow fiber filter membranes.

Filtration of parenteral solutions prior to delivery of the solution to a patient is becoming increasingly important and critical. For example, the removal of micron (1 X10-6 meters size particles is now deemed important.

Such particles can include particulate matter suspended in the solution, bacteria or even dust trapped in the administration set during assembly.

The common open mesh filter is not capable of filtering and removing micron-size particles.

It is therefore an object of this invention to provide a parenteral solution filter which can remove micron-size particles.

Prior art patents disclose the use of hollow fiber filters for micron-size filtration. Such fibers may be spun or drawn from polymeric materials such as polyethylene. U.S. Patents 3,503,515; 3,702,658; 3,730,959; and 3,760,949 discloses such filter elements.

These filters are constructed in a manner similar to the casing and tube-type heat exchanger in which there is a tubular or cylindrical casing within which the tubing is positioned and secured at each end by a header with liquids flowing through both the tubes and the casing. In the filter system the solution flows into the casing, is filtered as it passes through the fiber wall and the filtrate exits from the open ends of the fiber.

Recently, filtration and separation devices have been developed in which the fibers are looped or doubled back on themselves so as to form a U-shape with both open ends of each fiber being positioned at the outlet end of the casing. The fiber ends are sealed or "potted" in a header at the outlet end.

During operation, solution enters the casing, flows about the looped fibers and flows through the fiber wall from outside the fiber into the bore of the fiber. As the solution flows through the fiber wall, it is filtered and the filtrate flows along the tube bore to open tube ends for delivery to the patient.

Such filters are effective for removing micron size particles. Furthermore, these filters have a high surface area to fluid volume ratio (A/V), and as such, the filters are comparatively small in size.

In some filters air may become trapped within the element either from air initially in the element prior to priming or air which separates during filtration and which accumulates within the element. Air trapped within the casing substantially decreases the efficiency of the filter as the air may mask filter surface, and thus reduce the total effective filter surface area.

In order to minimize air accumulation and masking, filters have been developed in which an air vent is provided in one end of the filter casing, usually the inlet end, which is opposite the filtrate or outlet end. Thus air will rise to the top of the element for venting. Such filters are usually used in a generally vertical orientation where the vent is at the top of the filter casing.

In practice, filter elements are positioned immediately upstream of the injection needle and many nurses would like to tape the filter element to the patient or place it in a position other than vertical. However, in such a situation, the air vent may not be at the top, and thus air venting will not be maximized.

It is therefore the object of this invention to provide a hollow fiber filter element which can be positioned at attitudes other than vertical during use, or at any attitude.

Medical personnel find that it is sometimes desirable to visually check the operation of the filter for blockage, particulate build-up, etc.

It is therefore another object of this invention to provide a ventable filter element which can be visually checked by attending medical personnel.

Furthermore, the time required to prime or reprime a filter element is deemed important.

Priming refers to the initial filling of the filter element, Repriming refer to refilling of the filter element as may be necessary when a solution supply bottle empties, supply is interrupted, etc. In general, priming and repriming times are related to available gas venting area and the condition of the filter. Repriming takes longer than priming since the filter has been wetted. Medical personnel believe that priming or repriming should take less than 15 seconds.

It is yet a further object of this invention to provide a ventable and transparent filter element which can be primed or reprimed in less than about 15 seconds.

These and other objects of this invention will become apparent from the following description and appended claims.

Summary of the Invention There is provided by this invention hollow fiber filter elements which can be used at attitudes other than vertical and which can be checked visually, or at any attitude.

The filter includes a casing having a hydrophobic venting section which permits air or gas to flow through the casing wall but will not permit liquid to pass therethrough. The filter exhibits a high flow rate over a prolonged time since air or gas accumulation is minimized, and thus the element is less prone to reduction in filtration area due to air or gas masking.

In one embodiment; the entire casing is a venting section. In another embodiment, the casing also includes a transparent viewing portion which permits the filter operation to be visually checked by attending medical personnel. The hydrophobic venting section comprises at least about 10 percent of the casing surface area so as to assure venting and the ability to position the element at attitudes other than vertical.

Furthermore, filter elements of this type can be primed or reprimed in less than about 15 seconds.

Brief Description of the Drawings Figure 1 shows a solution administration set which includes the filter element in accordance with one embodiment of the invention, wherein the entire casing is a venting section; Figure 2 is a sectional view of the filter element in Fig. 1, which can be used at any attitude; Figure 3 shows a solution administration set which includes the filter element in accordance with a second embodiment of the invention, including a casing having a venting section, and further including a viewing section; and Figure 4 is a sectional view showing the details of the filter element in Fig. 3.

Description of the Preferred Embodiment Referring now to Figs. 1 and 3, an administration set 10 of the type commonly used to deliver biological fluids to a patient is shown.

The system include a connector 12 for connection to a fluid source 13, such as a therapeutic solution. From the connector fluid flows through a drip chamber 14, check valve 16 and to a Y-shaped injection site 18, where medicaments can be added to the solution.

Fluid exiting the injection site flows through a flow controller 20 to another Y-shaped injection site 22. Fluid then flows to the filter element 24 (Fig. 1), or to the filter element 25 (Fig. 2).

The filtered solution or filtrate exiting the filter element flows to a needle adapter 26, and thereafter, to a patient. This is a gravity flow system and the rate of flow is dependent on factors such as fluid source height or pressure head, pressure losses in the system, efficiency of the filter element, and the like.

The filter elements 24, 25 disclosed herein will deliver at least 300 millimeters of solution per hour for between 24 and 48 hours under a pressure or head equivalent to 18 inches water between the inlet and outlet. In actual levels with of water, an initial flow rate of 450 ml/hour and a flow rate of 390 ml/hour after 48 hours have been noted.

Referring now to Figs. 2 and 4, the filter elements 24, 25 are shown in cross section.

Such filters are commonly three to six inches long and perhaps one-half inch in diameter.

The elements 24, 25 include an inlet end or header 28 and an outlet end or header 32.

Filter element 24 includes a tubular casing or body 30. Filter element 25 includes a tubular casing or body 31. Bundles of looped or Ushaped hollow fibers, such as 34, 36, 38 and 40, are positioned within the casing 30, 31 with both open ends of each fiber potted in the sealant 42. For example, ends 34a and 34b of fiber 34 are open to the outlet head 32.

The casing 31 of the filter element 25 includes a venting section 31 a positioned adjacent the inlet end 28 and a transparent viewing section 31 bat the outlet end.

With either filter element 24, 25 in operation fluids enter inlet 28 and are filtered by flowing through the walls of the fibers, such as 34, into the bore of the fiber. The filtrate or filtered solution exits the fiber end, such as 34a and 34b, and exits the filter element through outlet 32.

The hollow fibers are a polymeric material, typically a porous polyolefin. for example, polyethylene. The pore size is usually about 0.2 micron. The fibers have an outside diameter of between about 0.01 and 0.02 inch and a wall thickness of between 0.001 and 0.005 inch. The fibers are typically impregnated with a surfactant to render them hydrophilic and facilitate flow of aqueous solutions therethrough. An exemplary surfactant is a mixture of monoesters of sorbitan with capric.

lauric, myristic, palmitic and/or oleic acids.

More specifically: Sorbitan caprate 1.1 % by weight Sorbitan laurate 43.5% by weight Sorbitan myristate 27.8% by weight Sorbitan palmitate 19.2% by weight Sorbitan oleate 8.4% by weight Other analogous esters may be used, pure or mixed, preferably monoesters or carbohydrates, such as sorbitan, glucose, fructose, or other metabolizable carbohydrates of preferably five to six carbon atoms.

The casing 30 of the filter 24 and the venting section 31 a of the casing 31 in the filter element 25 are each a hyrophobic, rigid, extruded tubular member made of polyethylene or polypropylene. The material is not wettable with water and has a pore size of about 0.2 micron or less so as to filter out particles of about 0.2 micron or greater.

With respect to the filter element 24 illustrated in Figs. 1 and 2, air or gas which accumulates within the filter element 24 between the casing 30 and the fibers can pass through the casing wall. In this way, gas does not accumulate within the element, does not mask filter surface area and therefore will not reduce filter efficiency. Furthermore, since gas can pass through the entire casing wall, the filter can be oriented at any attitude between horizontal and vertical and be effective. This gives both the nurse and patient wide latitude in using the filter. For example, a nurse could tape the filter to the patient's arm if so desired.

Air or gas separated during filtration tends to rise within the casing and move toward a high point. Thus, with respect to the filter element 25 such as illustrated in Figs. 3 and 4, in operation the filter 25 is positioned so as to maintain the venting section 31 a above the non-venting outlet end 32. Generally, the longitudinal axis of the filter 25 is tilted with respect to the horizontal so that air or gas can rise and accumulate in the venting section, pass through the venting section 31 a and vent the filter.

Thus air or gas which accumulates within the filter element 25 between the casing 31 and the fibers can pass through the venting section 31 a. Filter efficiency is substantially increased. Furthermore, gas can pass through the venting system, and the filter can be oriented at attitudes other than vertical. This gives both the nurse and patient substantial latitude in using the filter. Thus a nurse may be able to tape the filter to the patient's arm if so desired.

The fact that gas can pass through the casing 30 of the filter element 24 and through the venting section 31 a of the filter element 25 minimizes priming and the elements 24, 25 are essentially self-priming.

Referring once more to the filter element 25, the transparent viewing section 31 b may be made of a transparent acrylic or transparent rigid polyvinylchloride.

The lengths of the venting section 31 a and viewing section 31 b may vary depending upon the specific filter. In order to function properly, the venting section comprises at least about 10% of the surface area of the casing. In such a filter the casing would be 1 0% venting and 90% transparent. However, it is believed that commercial filter casings will be about 50% venting and 50% transparent to effect a balance between venting and viewing.

In filter elements 25 of the type described, the priming and/or repriming time will be less than about 15 seconds. It should also be noted that as the portion of the venting surface which comprises the casing 31 increases, the extent to which casings 31 can be oriented away from the vertical will increase.

The potting compounds for forming the seal 42 in both filter elements 24, 25 may be polyurethane, but other compounds, such as epoxies, hot melts and silicone can be used.

Filters 24, 25 of the preferred embodiments when tested, have exhibited a 480 ml/hr flow rate initially and 390 ml/hr flow rate after 48 hours, using water.

Using the standard TPN solution (8% amino acid, 50% dextrose, balance water), the flow rate was maintained at 3.5-4 ml/minute for between 24 and 48 hours. However, when conventional filters are used with TPN, the initial flow rate is 3-4 ml/minute, and after 24 hours, the flow rate was 1.5-2 ml/minute.

From the foregoing, it is seen that substantial benefits may be gained using the filter elements 24, 25 of this invention, including increased flow rates, reduced orientation requirements and self-priming.

The fibers shown in Figs. 2 and 4 are looped and U-shaped. However, with slight modifications several other fiber arrangements can be used. For example, straight fibers extending from one end of the filter to the other can be used. Looped U-shaped fibers with the looped or bight portion being pinched closed can be used. Similarly, single fibers where one end is open and the other end closed by pinching or plugging can be used.

In the previously described embodiments, the filtered liquid flows from outside the hollow fiber, through the fiber wall and into the bore of the fiber. However, it should be understood that filters can be fabricated in which the flow is reversed so that solution enters the fiber bore and flows through the fiber wall for filtration.

Regardless of the fiber shape or the flow path, it is important that the casing permits venting of accumulated air and gas and, in the embodiment shown in Figs. 3 and 4, that the internal filter functioning can be observed.

It will be appreciated that numerous changes and modifications can be made to the embodiments disclosed herein without departing from the spirit and scope of the invention.

Claims (19)

1. A filter element for use in filtering biological liquids, said element including a sealed casing having a liquid inlet and a liquid outlet, and filter means filteringly positioned between said inlet and outlet so that unfiltered liquid entering the casing flows through the filter means; wherein said casing includes a venting section; said venting section comprising at least about 10% of the casing surface area and being fabricated of a hydrophobic polymeric material which resists the flow of liquid therethrough and said material having a pore size of about 0.2 micron, so as to permit gas within said housing to pass through said housing wall and vent the housing.

2. The filter element as in Claim 1, wherein the casting is entirely a venting section.

3. The filter as in Claim 1, wherein said filter means comprises at least one hollow fiber having a bore and a wall and such that unfiltered liquid entering the casing flows through the wall of the hollow fiber.

4. The filter element as in Claim 1, said casing further comprising a viewing section; said viewing section being transparent so that functioning of the filter element can be visually monitored; and said filter element exhibiting priming and repriming times of less than about 15 seconds.

5. A filter element as in Claim 3, wherein said hollow fiber means includes a plurality of looped U-shaped fibers, each having two open ends with both of said ends positioned at one of said inlet and said outlet.

6. A filter element as in Claim 5, wherein said open ends are positioned at the outlet end, whereby liquid entering said inlet passes through said fiber wall into said fiber bore and flows from said filter element through the open ends of said filter.

7. A filter element as in Claim 1, wherein said casing is generally cylindrical in shape and the inlet and outlet are located at the cylinder ends.

8. A filter element as in Claim 1, wherein said casing is a rigid, extruded, polymeric tube having an inside diameter of between about one-fourth and one-half inch and wall thickness of about 1/16 inch.

9. A filter element as in Claim 8, wherein said polymeric material is selected from polypropylene and polyethylene.

10. A filter element as in Claim 1, wherein said element is nonpositional and can be oriented at substantially any attitude during use.

11. A filter element as in Claim 1, wherein the filter element is substantially selfpriming.

12. A filter element as in Claim 1, wherein the flow rate of water through said element at a pressure of 18 inches of water is at least 300 ml/hour during at least 24 hours of use.

13. A filter element as in Claim 3, wherein said flow rate is at least 300 ml/hour for 48 hours.

14. A filter element as in Claim 1, wherein said filter tubes: (a) are polyethylene; (b) have an outside diameter between about 0.0010-0.020 inch; (c) have a wall thickness of about 0.001-0.005 inch; (d) the surface of said fiber having been treated with a surfactant to render the tube hydrophobic; (e) a pore size of about 0.22 micron; and (f) said tubes being sealed to said housing using a potting compound.

15. A filter element as in claim 1, wherein said venting section comprises about 50% of the casing surface area.

16. A filter element as in Claim 1, wherein said venting section is adjacent the liquid inlet.

17. A filter element as in Claim 16, wherein said transparent viewing section is adjacent the liquid outlet.

18. A filter element as in Claim 1, and in combination therewith a fluid administration set for delivering fluids to the filter and delivering fluids from the filter to the patient wherein said filter element can be positioned at vertical and other attitudes.

19. A filter element as in Claim 18.

wherein the filter element can be positioned at attitdudes wherein the venting section is above the outlet so that gas will rise through the filter to the venting section for escape