Filter for use in the filtration of blood

The considerable risk of brain damage is a serious problem with the use of cardiopulmonary circulatory methods, although these have been much improved in recent years. Medical World News, July 17, 197θ »page 29, reports that several studies in cardiac surgery patients have focused on neurological complications, many of which suffer in the postoperative period, with impaired consciousness and behavioral disorders being the most common sequelae. No one has been able to explain the cause of this phenomenon.

In The Annala of Thoracic Surgery, Volume 9, so-called No. 3, March 197Ο, pages 221-228, and Surgery, Gynecology & Obstetrics, September, 1969, Volume 129, pages 5θ551θ, Patterson and Kessler reported the results obtained from the experiments, investigating the effect of oxidants on blood during cardiopulmonary rotation therapy. Patterson and Kessler pointed out that while cardiopulmonary rotation therapy has proven to be a significant therapeutic treatment, the most commonly used oxidants altered the blood in some way, ultimately resulting in damage to the saturated tissue. The composition of the toxic substance was not known, but the evidence blamed the particulate matter, especially the micro-plugs, which consisted of silicone, gas, aggregation of blood components, and denatured lipoproteins. Utilizing ultrasound technology in a specially designed test chamber, Pat52274 terson and Kessler showed that blood oxidizers produced large amounts of microplugs, and in addition, they found that the mixing ratio of oxygen and blood was strikingly proportional to the formation of microplugs. However, the filters used in this work did not successfully remove large amounts of microplugs from the blood compared to the canine lung used as a filter.

This work led Patterson, Brenan, and Kessler to equate microplugs with the marked decrease in brain metabolism observed after cardiopulmonary rotation therapy. In their experiments with experimental dogs, which included partial cardiopulmonary rotation and baseline cerebral blood flow studies and cerebral metabolism values ​​for oxygen, glucose, CO 2 and lactate, under rotation. Mean cerebral blood flow decreased by 25%, cerebral metabolic values ​​for oxygen decreased by 45%, oxygen COp production decreased by 50%, and glucose metabolism decreased by 6%, and these changes were not immediately reversible. The researchers then placed the filter in the artery, after which the particle number averaged only 240 minutes and there was no decrease in cerebral blood flow, in fact there was a small increase. A similar increase was observed in the flow of experimental animals that were connected to the pump oxidant only briefly, after which the connection was immediately disconnected. In addition, with the filter in the circulatory system, cerebral metabolic values ​​for oxygen and glucose decreased by only 9 1 »and 16% and returned to normal values ​​1 1/2 hours later.

The filter used in these studies was a round plate of stainless steel mesh, 15.24 cm in diameter (6), with a uniform aperture size of 25 microns. Although this filter is suitable for dogs, it could not pass blood at the flow rates required by adults without severe hemolysis due to its relatively small surface area, as reported by Patterson and Twichell in an unpublished bulletin. For adults, high blood flow values ​​are necessary to avoid injury. In addition, the stainless steel filter is not suitable for use with human blood because it is too expensive to be discarded after use and is too difficult and time consuming to clean for new use.

According to the invention, there is provided a filter element through which human blood can pass at a high flow rate without substantially removing normal and desirable constituents and which can be used in human circulatory systems to remove microstrugs and has a filter plate and means for directing blood through a filter plate placed on the blood flow line and is mainly characterized by that the filter is a square mesh plastic mesh woven from long polyester fibers with an aperture size of about? 5^-Between 5O microns and where the proportion of open area is between about? 5 “4θ $ and where the fibers ,, 3 are locked in place at their intersections. The filter element is usable, it can be discarded after use because it is made of cheap plastic material. The plastic material is inert to blood and the pore size of the filter element is constant and does not change in use or under the influence of temperature, partly due to the nature of the plastic fiber material and partly due to the way the fibers are attached to each other.

The diameter of the long fibers is important in determining both the pore size and the percentage of open area, the latter being important for maintaining a high blood flow through the filter.

As used herein, the term filter plate, or filter plate, refers to a filter plate in a filter element. The term filter element refers to a filter plate disposed in a structure that ensures the flow of liquid through the filter plate when the element is placed in the housing across the line of flow from the inlet end to the outlet end. The term filter unit refers to a filter element plus a housing having at least an inlet side and an outlet side.

Most of the long polyester fibers available today are polyesters of ethylene glycol and terephthalic acid, available under the trademark Dacron. Long polyester fibers can also be prepared from polymers of alkene glycols and dicarboxylic acids, usually aromatic acids, but also cycloaliphatic and aliphatic acids, such as propylene glycol-1,2, butene glycol-2,3 and 1,2 and pentene glycol-1,2-2,3 and 1-3, esterified with terephthalic acids substituted with terephthalic acid or alkyl, or with adipic or cork acids, or with cyclohexane-1,4-dicarboxylic acid. Long polyester fibers of ethylene glycol and terephthalic acid are preferred because they are readily available and inexpensive. However, polyesters of other glycols and acids may be used.

Exemplary screen fabrics of long polyester fibers used as filter elements in accordance with the invention are made of a long polyester fiber having a diameter of 40 microns, a mesh size of 53 microns and an open area of ​​33%, a 44 micron mesh and 27% open area, and a 37 micron mesh and 23% mesh. in the open field.

The long fibers are locked in place at their intersections. Locking not only increases strength and rigidity, but also prevents pore size change during use, which is very important. If the pores are too small, less than about 25 p »they remove important blood components such as blood cells, which of course is not desirable. If, on the other hand, they are too large, they will pass the micro-plugs they are supposed to stop.

Such filter plates can be fitted to discardable filter elements of any design and shape. In order to obtain the largest possible open area and a large flow value in the confined space, the filter plate is preferably corrugated or corrugated, in order to obtain a large surface area for the flow. A suitable shape of the filter element is one in which the filter plate is folded into a corrugated cylinder, the open ends of which are closed by end caps, limiting the passage of the filter flow line through the filter, the filter flow line in communication with the at least one end cover.

The end caps are preferably also made of a plastic material, e.g. polyester resin. The end caps can be bonded to the filter plate, using a potting mixture or a common type of binder. However, to ensure a bacterial-tight bond, it is best to solder the end caps to the filter plate, and a polyolefin such as polyethylene or polypropylene is preferred for this purpose. Other plastic materials that can be used as end caps include e.g. polyamides, polyvinyl chloride, polyvinylidene chloride, polycarbonates, and Teflon, polytetrafluoroethylene, and Kel-P, polytrifluorochloroethylene, but these are more difficult to bond.

In order for the filter plate to retain its shape better, especially the corrugated shape, it is preferable to use a porous support outside the filter plate and in close proximity to or in contact with the filter plate both above and below the flow direction. The support material is stiffer than the filter plate and preferably flexible and preferably also plastic, so that it can be bonded to the same end cap in the filter element. The preferred support material is Vexar mesh (extruded polypropylene mesh). Any torn plate having an uneven surface, e.g., with recesses, ridges, etc., can be used. Examples include polypropylene sheet, polyethylene sheet, polyvinylidene chloride sheet, polyvinyl chloride sheet, and other types of plastics commonly used for end caps and useful when they have an uneven surface that provides conduction and prevents the backing sheet from clogging.

Preferred embodiments of the invention are shown in the drawings, in which Figure 1 shows an enlarged top view of a filter sheet made of long polyester fibers according to the invention, Figure 2 shows an isometric view of a filter element having a filter plate according to Figure 1, Figure 4 shows a longitudinal sectional view of a filter unit, Fig. 5 shows a cross-sectional view taken along line 3-3 of Fig. 2 and in the direction of those lines; Fig. 5 shows an isometric view of a second embodiment of a filter element according to the invention; Fig. 6 shows a longitudinal sectional view of Fig. 5 along line 6-6; shows a cross-sectional view of the filter element of Figure 5 taken along line 7-7 and seen in the direction of the arrows.

The filter plate shown in Fig. 1 is a sinter-bonded, square-meshed mesh made of long poly5'52274 ester fibers with a pore size of 4, μ, a long fiber diameter of 4 ja μ, and an open area portion of 27 Weft fibers 1 are bonded to warp fibers 2 at their intersection 3 .

In the filter element 5 shown in Figures 2-4, the corrugated filter plate 6 is bent into a cylinder, the open ends of which are closed by end caps 7 »8 made of polypropylene. The end cover 7 has a central hole 9 and an annular connecting piece 10 projecting in one piece, which leads directly to the outlet opening of the housing of the filtration unit. On the outside and inside of the filter plate there are corrugated, protective support plates 11,12 made of Vexarpolypropylene mesh, 50 mesh dimensions, and concentrically in relation to this corrugated combination of three plates there is a rigid, perforated polypropylene core 14. The end caps are soldered to the plate 6 and Vex 12.

The filtration unit shown in Figures 3 and 4 includes a filter housing 15 »made in two parts 16,17» soldered together in their respective parts 18,19. Each housing part 16,17 is provided in one piece with a connecting line 20,21, which provide connection possibilities in a circulatory system, such as a cardiopulmonary circulatory system or a transfusion system. The connecting cables shown are for hose 27 with an inside diameter of 9.53 mm (3/8). The housing parts are made of plastic, such as polypropylene. The connecting line 20 of the shown embodiment acts as the inlet side and the connecting line 21 as the outlet side, but if desired, the liquid can also flow in the opposite direction without having to make any changes in the shown structure.

The filter element 5 is fixed at the end of the end cover 7 to the wall of the housing at the connection point 28 by means of an annular connecting piece 10 which fits tightly to the connection point and is connected to it. Thus, a leak-free and hakteeritiivis, the direct connection of the filter element 5 from the inner side 26 and the line 27, which is attached to the trunk line 39, 21 of the press.

The connecting line 20 has an inwardly extending, curved closure portion 29 which extends into the recess 40 of the end cap 8 in contact therewith and extends over the segment at the point adjacent the air hole 30 and directs flow from the inlet duct 31 out of the air hole. This makes it easier to remove gas, e.g. air, from the filtration unit when it starts operating without being disturbed by the flow of liquid inside,

An air hole 30 is formed in the recess 32 of the housing portion 16 in an outwardly extending protrusion 33 through which a conical bore 34 extends.

The upper end of the protrusion 33 has four outwardly extending lugs or protrusions 36 positioned to engage the internal double thread 37 of the removable cover 38. · an air hole forming a leak-proof and bacteria-tight seal.

Obviously, this is. a simple filtration unit which can be easily made of plastic by extrusion or compression molding or by molding as two housing parts, one cover and one filter element, and that all parts are permanently bonded together. The device can thus be mass-produced at low cost according to easily reproducible standards and can be discarded after use. Its small capacity, less than 500 cm 2, and preferably less than 250 cm 2, makes it particularly suitable for any type of circulatory system.

If desired, the connecting cables 20,21 can be equipped with Luer locks so that they can be more easily connected to the standard connectors of other types of medical equipment. The air hole protrusion 35 shown has a Luer lock connector for a standard Luer lock cover.

The filter element 50 of Figures 5-7 has a three-layer combination with a filter plate 6 and support plates 11, 12 in a corrugated, roof slate form, with the corrugated bends 51 overlapping in the plane of the filter element. The combination is heat-sealed at 52 along its four sides (or three sides if folded over itself). The element has a conduit connection through a tube 53 which extends into the open interior 54 of the element and terminates in the form of a hood tip 55. The only way to and from the pipe is through the filter plate 6. The pipe 53 can act as an outlet pipe for filtering the flow in normal operation, but it can also act as an inlet pipe, whereby the flow through the filter plate 6 takes place in the opposite direction. This type of filter element is particularly useful in a flexible, bag-type filter unit, where the tube 53 may extend beyond the bag 56 (shown in broken lines in Figure 5) and may be heat sealed to the bag in the same manner as the filter element. At one end of the bag is an inlet pipe 57 (or outlet pipe) which connects to the other side of the filter element.

This type of filter element is particularly useful for filtering blood, allowing it to be built into a regular blood bag, but can also be used in other ways, and any type of filter plate can be used as well as any type of housing.

The corrugated shape of the filter plate of this element gives a large surface area and the corrugated roof ridge arrangement makes it possible to use a flat bag without the need for a support interior, as the spaces between the racks act as wires, while the roof-edge overlapping structure provides structural support. The outer support layers of the three-layer combination are made of a thermosetting material, whereas the filter plate does not react under conditions where the outer layers soften, so that the latter can be soldered together by a leak-free heat seal through the pores of the filter plate without damaging the filter plate. Heat seals are easily obtained by high frequency heating and lime heat seals can be formed simultaneously, also heat seals with the pipe.

By using the filter elements according to the invention in a filter unit having the same structure as shown in Figures 5-4, significant results have been obtained in connection with cardiopulmonary treatment. The following examples illustrate the use using a filtration unit with an external size of 6x9 cm in a filter unit with a liquid volume of 240 cm and made entirely of polypropylene, with the exception of a square-mesh mesh filtration element made of long polyester fibers. The total area of ​​the filter plate in the filter element was 645 cm.

The device was tested in a cardiopulmonary circuit in which the other end of a double-ended roller pump recirculated blood through a plastic tube about 500 cm long with a diameter of 9.55 nm (5 / θ) and the cardiotomy suction reservoir rose above the 7θ pump. Blood pressure was measured before and after the filter. The other end of the pump was used to circulate blood in a circuit that was otherwise similar except that it did not have a filter. 750 cm 2 of donated human blood was drained into each circuit. Leakings were continued for 4 hours at 4 l / min. flow value. Blood was sampled periodically for hematocrit, blood fluid hemoglobin, blood fluid electrophoresis, blood fluid lipoprotein electrophoresis, cholestorol, and platelets. The pressure drop across the filter was measured at the end of the spill and also at the end of it, when the flow value was changed from 0 to 6 l / min. In three experiments, there was an increase in hemoglobin in the blood fluid in the bed over four hours and a flow rate of 4 l / min. approximately the same whether or not a filter was used, indicating that the filter had little detrimental effect. The proportion of platelets decreased at the end of the experiments in 42-66 ^ circuits with a filter and 46-6Ο already in the circuit without a filter, again indicating that there was little detrimental effect as a filter.

During the four hours of 4 l / min venting, there was a pressure drop across the filter in the range of 8-40 millimeters of mercury in five different experiments. The total amount of protein in the blood fluid decreased by an average of 10 Jo in the circuit without filter and 11% in the circuit with filter. Protein fractions decreased

4-19 Already inconsistent. Blood fluid cholesterol decreased by an average of 5 J ° i if the filter was omitted, and 15 Jo when the filter was used.

The filter has been used in conjunction with cardiopulmonary rotation therapy in a series of trials performed on a small group of patients who underwent open heart surgery and has functioned satisfactorily. None of the patients showed signs of cerebral tolerance lesions.