GB2077621A - Dialysing and ultra-filtering device - Google Patents

Abstract

A dialysing and ultra-filtering device comprises hollow, i.e. capillary, fibres 3 of Cellophane (Registered Trade Mark) or the like, mounted for passage of hematic liquid within a chamber through which dialysing solution passes, wherein the chamber is defined by a container 1 having the shape of a parallelepipedic substantially crushed box; the fibres are disposed between two opposite ends (heads) 22, 24 of the box and on the two smaller sides at right angles to the heads provision is made for orifices 18, 20 for the inflow and outflow, respectively, of the dialysing solution, which thus passes through the container along paths perpendicular to the capillaries. A baffle in the chamber parallel to the two larger sides of the box may divide the dialysate solution flow into parallel streams. <IMAGE>

Description

SPECIFICATION Dialysing and ultra-filtering device The present invention relates to a dialysing and ultra-filtering device which uses hollow fibres of regenerated cellulose ("cellophane" (Registered Trade Mark)) or the like, particularly for extra-corporeal hemodialysis, the hematic content of which is extremely low and constant (insensitive to pressure variations) and the clinical performances of which are very high relative both to the hematic content and to the dialysing area.Such a device is of a type adapted to be used with a system for circulating the electrolytic solution in a single flow with monitoring (commonly called "artificial kidney") of usual type, and so provided with: a tube supplying the fresh dialysing solution, to which the device is connected; a heating and thermostating system for the said solution; and a suction pump which is applied to the tube for the outflow of the dialysing solution exhausted by the device itself, to bring about in the latter a depression which increases the rate of ultra-filtration, whenever required .

There are in existence dialysing or ultrafiltering devices which use capillaries of regenerated cellulose, and which all have, in varying degrees, one or more of the following drawbacks: 1 - low dialytic output per unit of dialysing area; 2 - ease of coagulation of the blood inside the capillaries; 3 - difficulty of removal of any air which may have entered the actual capillaries; 4 - high consumption of dialysing solution; 5 - overall size and shape which cause difficulties as regards storage, transport and sterilisation; 6 - difficulty of obtaining adequate ultrafiltration.

As to the low yield per unit of dialysing area the following may be stated: The use of hollow, i.e. capillary, fibres of cellulose acetate for the making of dialysers goes back many years. With cellulose acetate capillaries dialysers have been constructed made of a bundle of hollow fibres, having a substantially cylindrical shape, which is contained in an envelope of also cylindrical shape. Numerous other dialysers also, recently constructed with hollow cellophane fibres have a similar geometry, while others are made up of several cylindrical bundles placed side by side. On the axial part of the bundle the capillaries are packed more closely than on the periphery.It follows from this that the dialysing solution (dialysate) preferably circulates at the periphery of the bundle, while the blood preferably circulates in the axial portion, because at the centre it finds the shortest path, the inlet nozzle and the outlet one being disposed centrally at the extremities of the cylinder. This is obviously a first factor which restricts dialytic outputs.

A second restricting factor for the dialytic output lies in the fact that in almost all models of dialysers which use hollow fibres the flow of dialysate (i.e. of the dialysing solution) and of blood are parallel or, in some models, almost parallel. The dialysate does not encounter any obstacle on its path and adopts laminar progress, and this is a considerable obstacle to dialytic exchanges.

A third important factor being an obstacle to dialytic exchanges lies, in many models, in the length of the hollow fibres and it is well known that, dialysing areas being equal, dialytic output is the greater as the fibres themselves are the shorter. Indeed, in the case of very long hollow fibres, the blood is already purified half way along the travel in the fibres, and along the following path (final section) the passage of solutes outwards is practically insignificant. The same may be said of the path of dialysing solution: the longer such a path, the smaller the dialytic efficiency, areas and other parameters being equal.

A fourth factor responsible for the poor dialytic yield, which is found in almost all hollow fibre dialysers, is the presence of "dead spaces" where the circulation of the dialysate stagnates as a consequence of the geometry of the devices themselves. In those parts, dialytic exchanges stop immediately after the start of the first stages of dialysis.

Other obstacles to dialytic exchanges consist in irregularities in the openings of the capillaries (ovalised, half-moon-shaped, comma-shaped) which create preferential paths for the blood which flows in them at low speed, while, on the other hand, the rate of flow is high in the capillaries the mouths of which are perfectly circular.

As regards the coagulation of blood in the capillaries the following is observed.

The irregularities of the mouths of the capillaries to which reference has been made above, together with the tortuous path of some hollow fibres, constitute an obstacle to the path of the blood. It follows therefrom that its flow slows down in them to the point of stopping, coagulation then taking place. In addition to impeding dialysis, reducing the effective exchange area, this phenomenon prevents the complete restitution of the blood to the patient at the end of the actual dialysis.

This brings about a subtraction from the amount of blood at each dialysis which, in patients who are repeatedly hemodialysed (chronic patients), is the cause of rapid development of anemia.

The coagulation of blood in capillaries takes place also further to the penetration of air in them, both at the start of and during dialysis, and their length and the tortuous path prevent the removal of the air.

As to the importance of the presence of air in the capillaries, the following is observed.

The phenomenon of penetration of air into the capillaries may take place, it has been said, both at the start of dialysis, or during it and, once it has taken place, it is all the more difficult to remove the air the longer the capillaries, and the more tortuous their path is. This drawback involves a reduction of the area actually useful for dialytic exchanges and it brings about the stopping of the circulation of the blood which has entered the initial tract of the hollow fibres containing the air bubbles, and its subsequent coagulation with the consequences which have been mentioned hereinabove. To avoid such a drawback, some appliances are supplied with liquid (formaldehyde solution) and they must be used with an air "trap" inserted on the arterial line of flow of blood to the dialysers.This is a further complication of the dialytic procedure which is already complex in itself.

As regards the high consumption of dialysing solution, it is observed that the irregularities of the and in the bundle of capillaries to which reference has been made, and the constructional geometry of many dialysers with hollow fibres bring about - as has been said - that the capillaries are soaked in irregular manner by the dialysate and that the flow of the latter is laminar. To obviate these drawbacks and perform clinically satisfactory dialyses it is therefore necessary - for many devices - for the flow of dialysate to be very high, with drawbacks of supplying and costing problems.

The overall size and the shape produce difficulties in storage, transport and sterilisation. The elongated cylindrical shape of almost all dialysers with hollow fibres, with the electrolytic solution nozzles disposed at right angles to the axis of the cylinder, give a structure of substantial overall size and of difficult storage and transport, and also of difficult positioning for sterilisation. The same may be said also of the shape recently provided, in which the nozzles have the same position, and the shape is that of a parallelepiped with a square base, but relatively high, this being the case also of those formed of several cylinders placed side by side.

The difficulty of obtaining adquate ultrafiltration is a typical drawback of dialysers with capillaries formed of cellulose acetate, the permeability of which to water is decidedly smaller than that of cellophane. The difficult passage of water brings about that it becomes necessary to have very high gradients of trans-membrane hydrostatic pressure and therefore considerable depression in the dialysate compartment. This facilitates the boiling of the solution with the formation of air bubbles which reduce dialytic exchanges. The difficulty of ultra-filtration requires, however, that particularly efficient suction pumps should be fitted in monitoring systems, and the latter are not usually equipped with such pumps.

The present invention has for its object a dialysing and ultra-filtering device which is extensively free from such drawbacks and, in particular, there has been obtained a dialysing and ultra-filtering device with hollow fibres characterised in: a) - a high dialytic output per unit of dialysing area; b) - an almost complete absence of blood coagulation inside the capillaries; c) - an extreme simplicity of operation and commissioning; d) - an extreme facility of removal of the air that may have entered the capillaries; e) - a normal consumption of dialysing solution; f) - overall size and shape such as to facilitate storage, transport and sterilisation; g) - great ease of regulation of ultra-filtration with low gradients of trans-membrane hydrostatic pressure.

In addition to the above-named advantages which distinguish it from the other similar dialysers, it exhibits (as others do) a low hematic content and an absolute constancy in spite of variations in the hematic flow and trans-membrane pressure.

To achieve the above aims and advantages, in the dialysing and ultra-filtering device according to the invention - comprising hollow (i.e. capillary) fibres of cellophane or the like, included within a chamber through which the dialysing solution flows, while the blood to be purified is made to pass through the fibres provision is made for a container in the form of a substantially crushed parallelepipedic box, closed by two opposite sides, between which the capillaries or relatively short hollow fibres extend, and having on the two smaller sides at right angles to said end sides orifices for the inflow and outflow respectively of the dialysing solution, which thus flows through the container with paths perpendicular to the capillaries and with substantially whorling movements.

Advantageously the capillaries extend between two collectors or dispensing chambers extending along the two end sides. In addition, one of the two collectors is connected to the inflow connection at one end of the actual collector, while the other collector is connected to the outflow connection situated at the end opposite that which corresponds to the end of the input collector where the inlet connection is. In this way there are obtained equal paths of equal resistance for all the capillaries, without preferential paths or dead zones. The collectors may have a decreasing section in conformity with the distance of the relevant connection.

Advantageously also the inflow and outflow orifices for the dialysing solution (dialysate) are combined with appropriate dispensing collectors; an input connection is connected to one end of a first collector, while an outlet connection is connected to one end of the other of the collectors corresponding to the end opposite to that which is fitted with a connection of said first collector. Thus also for the dyalisate preferential paths and dead areas are avoided.

The hollow, and thus capillary, fibres may be subdivided into two sections by a diaphragm or parallel divisions, and in an intermediate position between the two principal fascias of the container. This promotes dialytic exchanges as it reduces the sectional area of the path for the dialysate, increasing the speed. The dividing wall may vary in thickness.

The heads of the capillaries are formed by the incorporation of the end portion of the capillaries in a hardened or machined mass.

The invention will be better understood on following the description and attached drawing, which shows a non-limitative practical embodiment of the invention itself. In the drawing: Figure 1 shows a diagram of the paths, in cross-section, of the box; Figure 2 shows the assembly in cross-section along a plane parallel with the front portions; Figures 3 and 4 show enlarged local sections along lines 111-Ill and IV-IV of the Fig.

1; Figure 5 shows a diagram of the paths of the blood.

As shown in the illustrations the device comprises, as essential constituent element, a central container 1 in the shape of a cigar box in which two bundles of capillaries 3 and 5 are placed in such a way that they extend along the inside of the box in the direction of its greatest dimension, and in such a way that their inlet and outlet ends are incorporated in an upper and a lower head 7 and 9, and open out onto the external faces of the said heads 7 and 9, which correspond to the extreme sections of the box having smaller length and height. On the sides 1 A of the box having a smaller height and a greater length, holes 10 and 12 are provided from which, and, out of which, there enters or flows out the dialysate into and from the chamber defined by box 1.

Such holes 10 and 12 are opened into two spouts 14,1 6 delimited by walls 1 4A and 1 6A and which, when the device has been assembled, constitute the dispensing chamber 14 and the collecting chamber 16 for the actual dialysate, connected to the inlet 18 for the dyalising solution and respectively to the outlet 20 for the spent dialysate. The front walls of the box 1 have ribs adapted to strengthen the structure, enabling it to withstand the variations of pressure of the dialysate.

The two heads 7 and 9 may be made by a process of centrifuging a polymerizable fluid mass which encompasses the ends of the capillaries or hollow fibres and becomes hardened there; means are provided for preventing or limiting the penetration of the mass between the capillaries, and provision is made for machining for shaping the heads by removing material from the front faces where the capillaries thus properly open out.

A couple of covers 22 and 24 are intended to close the ends of the box 1 in the vicinity of the heads 7 and 9, forming with them the dispensing (26) and collection (28) chambers for the blood, said chambers 26 and 28 being connected to the dialysate connections 30 and 32. Said connections 30 and 32 are at one end of the relevant dispensing chamber, the cross-section of which may increase (cf.

Fig. 5) as it come closer to the appropriate connection (30, 32).

With the arrangement described (cf. also Fig. 5) there is ensured a substantial evenness of resistance in all the likely paths of the blood.

The said parts mentioned above are assembled and joined preferably by soldering, with adhesives or as fitting-in parts, and parts 14A, 16A, 22, 24 are assembled with seals such as 34 and 36.

The inside of the container 1 is filled with the the two bundles or groups of capillaries 3 and 5, divided by a baffle or division 40, and developed according to an orientation that is perpendicular to that along which the dialysate flows through the holes 10 and 12, as a consequence of which the two flows - kept separate from each other - of the hematic liquid and of dialysing solution are substantially perpendicular to each other, as may be seen from the arrows on the diagram of Fig.

1. The baffle or divider 40 separates the capillaries into two groups 3 and 5, and forces the dialysate to follow two parallel paths in a relatively restricted space, made such by this baffling and by the capillaries, practically indeformable by the stresses bound with the dialysate itself. In such a manner, and due also to the position of the capillaries - which are at right angles to the path of the dialysate - there is achieved a turbulence adapted to facilitate dialytic exchanges.

As already indicated, Fig. 1 is a diagrammatic representation of the dialyser, the arrows fD representing the path of the dialysate, and the arrows fE that of the blood. The latter enters from the inflow nozzle 30 at the bottom, is diffused in the dispensing chamber 26, and from the latter passes into the capillaries 3, 5 disposed along the direction of the greatest length of the device and towards the top of the figure. From capillaries 3, 5 the blood passes into the collection chamber 28 and reaches the outflow nozzle 32, with paths equal for all the capillaries. The dialysate comes in from the nozzle 18 on the right at the bottom, spreads into the dispensing chamber 14 through which it passes upwards; from it it passes into the dialysis chamber through the double row of holes 10 and it passes through it transversally, crossing the capillaries 3, 5.From this chamber the dialysate reaches through holes 12 the collection chamber 16 and flows to the outflow nozzle 20.

Thus, the dialysing solution also follows equal paths without following preferential courses.

From that which has been described it follows that in the dialysing and ultra-filtering device of the type indicated the compartment in which the blood flows to be dialysed and ultra-filtered is formed of the multiple sections of the double row of hollow, i.e. capillary, fibres 3 and 5, said blood entering from the bottom and coming out at the top, being purified and ultra-filtered, this ultra-filtering being of clinical standard, representing the removal of water and of molecules weighing less than 20,000 dantons. Capillaries 3,5 exhibit a rectilinear path and at their ends are welded together and to the inner wall of the device, with the heads 7, 9, where the capillaries are embedded along a stretch long enough to prevent the blood from permeating through the gaps between the capillaries and between the latter and the inner walls of the device.The material for welding and for the formation of the heads 7, 9 may consist of polyurethane, biocompatible or at least nontoxic, having, when polymerisation is complete, a minimum cession, in accordance with the provisions ruling on the matter. Heads 7, 9 may be formed with the centrifuging of the arrangement, the polyurethane mass being fluid and said capillaries being closed as a result of previous centrifuging to prevent the penetration of the fluid mass in them; processing by machining to remove the layer of excess polyurethane completes the heads.

The dialysing solution circulating outside the capillaries follows a path at right angles to them and - flowing away from the dispensing chamber 14 and reaching the dialysis chamber through the double set of holes 10 ensures uniform dispensing and thus ensures that the capillaries are wetted externally along their entire length by a substantially equal flow.

The above-listed aims are achieved through the implementation of the geometry which consists in the arrangement in the two contiguous sections of rectilinear capillaries, with the inlet and outlet apertures for the blood perfectly circular; through the length of capillaries which is less than that of almost all the other similar devices; through the provision of a path for the blood which is at right angles to that of the dialysate and through the presence of the baffle between the two sections of capillaries which, jointly, facilitate the turbulence of their flow even at a relatively slow speed; through a short path for the dialysate between the holes 10 and 12; through the total elimination of dead spaces both from the blood compartment and from the dialysate compartment, and, finally, through the even distribution of the blood and dialysate at all the places where dialysis can take place.

By using the greater part of the components and by adopting a baffle or divider 40 of varying thickness it is possible to vary the minimum of tubular or capillary fibres 5, and thus vary dialysing area.

It is understood that the drawing shows - only an exemplification given only as a practi-.

cal demonstration of the invention, while it is possible to vary the form and arrangement of the said invention without, on that account, departing from the scope of the concept which is at the basis of the actual invention.

Claims (9)

1. Dialysing and ultra-filtering device for haemodialysis and extra-corporeal ultra-filtration, comprising hollow, i.e. capillary, fibres of cellophane or the like, enclosed within a chamber through which the dialysing solution flows, the hematic liquid to be purified being made to pass into the fibres, characterised in that, in a container (1) having the shape of a substantially crushed parallelepipedic box, and between two opposite ends (7, 9) the capillaries or hollow fibres (3, 5) extend, and in that, on two smaller sides (1A) at right angles to the heads (7, 9), openings are provided for the inflow (10) and, respectively, for the outflow (12) of the dialysing solution, which thus passes through the container with paths perpendicular to the capillaries.

2. A device according to the foregoing claim, in which the capillaries (3, 5) extend between two dispensing chambers or collectors (26, 28) extending along the two heads (7, 9), characterised in that one of the two collectors (26) is connected to the inlet connection (30) at one end of the collector (26) itself, while the other collector (28) is connected to the outflow connection (32) situated at the end opposite that corresponding to the end of the inlet collector (26) where the inlet connection is situated.

3. A device according to Claim 2, charac-i terised in that the collectors (26, 28) have a cross-section which increases towards the appropriate connection.

4. A device according to Claim 1, characterised in that the inlet openings (10) and outflow openings (12) for the dialysing solution or dialysate are combined with appropriate dispensing collectors (14, 16).

5. A device according to Claim 4, characterised in that an inflow connection (18) is connected to one end of a first (14) collector of the pair (14, 16), while an outflow connection (20) is connected to one end of the other collector (16) of the pair (14, 16), correspond ing to the end opposite that which is provided with a connection (18) of said first collector (14).

6. A device according to the foregoing claims, characterised in that the hollow, i.e.

capillary, fibres (3, 5) are divided into two courses by a diaphragm or baffle (40), parallel with, and in an intermediate position between the two principle sides of the container.

7. A device according to the foregoing claims, characterised in that the baffle or divider (40) is exchangeable, to obtain a variation of the dialysing area.

8. A device according to the foregoing claims, characterised in that the heads are formed of a hardened, machined, mass.

9. A dialysing and ultra-filtering device with capillaries, particularly for example for extra-corporeal haemodialysis, the whole as described above and represented in exemplification on the attached drawing.