GB2058604A - Purification system for use in blood treatment - Google Patents

Abstract

In a purification system for blood treatment the dialysate or ultrafiltrate 1 from the blood treatment system is purified and returned 10 to the treatment system to the patient during treatment. Reverse osmosis is a suitable purification method. Because a reverse osmosis purification system 7, 8 has a very pure output 10 there is no need for the pathway 1, 2, 3, 5, 6 from the treatment system to the purification system 7, 8 to be kept sterile, and the initial charge 4 to this pathway may be tap-water. The rejected fraction from the reverse osmosis is recycled 9. Because the dialysate or ultrafiltrate is recycled the volume of waste liquid built up during treatment is much reduced, thereby alleviating the disposal problem. The waste materials will accumulate in a reservoir 3 in the non-sterile part of the fluid circuit. The system can be compact and easy to use, and can be powered by normal mains electricity. <IMAGE>

Description

SPECIFICATION Purification system for use in blood treatment This invention relates to purification systems used in conjunction with blood treatment apparatus and to methods of purifying the dialysate or ultrafiltrate obtained in blood treatments.

Dialysis and haemofiltration (the latter is also known as diafiltration) are both now well known as treatments for patients having renal failure.

In the first of these treatments, blood from the patient is passed through a dialysis device made up of a semi-permeable membrane on the other side of which is a flow of dialysate which is a controlled solution of certain salts which it will exchange through the semi-permeable membrane with the patient's blood and take from the blood toxic and noxious materials. The blood is then returned directly to the patient.

The output of dialysate in such a process is of high volume and contains undesirable and perhaps infectious materials. Precautions have to be taken in the continuous after-treatment and disposal of this waste, but the main difficulty with the system is the extremely high volumes of very highly controlled dialysate which are required.

In haemofiltration (diafiltration) blood from the patient is passed over a membrane to the other side of which a very reduced pressure is applied.

The membrane is such that as a result water is sucked out of the blood and with it some of the soluble materials having a molecular weight of below that of proteins that is to say all the toxic and noxious materials which it is desired to remove. Also removed however are beneficial salts and, partly because the blood is highly concentrated by the passage through the haemofilter and partly for the replacement of the necessary desirable salts, the blood which has passed through the diafilter is then reconstituted by the addition of an infusate containing salts. The infusate must of course be sterile and added under sterile conditions.The volume of permeate (impure product from the haemofilter) is here much lower than that of impure dialysate in a dialysis process but again there is a problem of disposal and there is also a problem of the supply of a sufficient, quite large, quantity of sterile infusate to the blood return line.

The problem of suppling a large quantity of highly sterile medium has previously been tackled by regeneration processes in the best known of which, the Redy process, the dialysate/permeate is circulated in a closed system which includes as part of it an ion exchange/enzyme packed cartridge, the output from which is, after addition of essential salts, returned either as dialysate or to the blood return line of the haemofilter. The cartridges are designed to have a capacity to cope with one treatment and cannot themselves be regenerated. They are large and heavy which causes handling and storage problems and being for use once only make the treatment quite costly.

More subtle disadvantages are that any interruption to the steady flow of medium through the cartridges can cause clogging and also that the ion exchange/enzyme material is very susceptible to damage by traces of common sterilising agents.

It can be seen that these processes although removing one disadvantage have incurred others, the economic and handling disadvantages which have been pointed out.

The present invention is a novel approach to the purification of dialysate or permeate materials in which a continuously operable purifying unit is used which has a highly pure output. Then, the circuit in which the purification device is contained need not be an entirely closed circuit (in the sense of an enclosed sterile circuit) bu#t may be one which is in part "open" and which can be charged initially with a quantity of dialysate medium, that is to say water, which is of only moderate purity.

If this charge is placed in an open reservoir from which the feed to the purifying device is taken and the purifying device and reservoir form part of a circuit which includes a dialysate or ultrafiltrate output side, this dialysate or ultra-filtrate passing to the reservoir, then it can be seen that in continuous operation of the purifying device there will be continuous production of sterile purifying medium and a gradual accumulation of noxious and toxic substances in the reservoir. The purified medium is returned to a return line of the blood treatment device.At the end of the treatment the material in the reservoir is simply discarded (having taken any necessary precautions for its sterilisation and being rendered harmless) and it can be seen that this is the only waste product from the process single charge of medium which may be according to the length of treatment from approximately seven litres to seventeen litres - which is quite a different disposal problem from that involved in the continuous disposal of a flow of waste material in conventional dialysis or haemofiltration systems.

The balance between net transfers occurring in the dialysis apparatus or haemofilter is carefully controlled so as to remove from the patient during each treatment some desired volume of liquid.

With proper management this parameter can be used to control the duration of the treatment. The present system allows particularly readily for the determination of when a desired amount of liquid has been removed from the patient since it will by the nature of the circuit described, accumulate in the reservoir. Thus by the amount by which the volume in the reservoir has increased during the treatment, so by that amount has the patient lost liquid.

At least two types of known purifying systems produce a highly pure output on the one hand and a recyclable impure output on the other hand. The first of these is a continuous distillation system but its energy consumption may be excessive in the present context. A preferred purification system in the present invention is a reverse osmosis system, with the feed from the reservoir being subjected to high pressure across a reverse osmosis semi permeable barrier, at the other side of which pure medium will be found. The "blow-by" (the impure product) from the reverse osmosis process is recycled to the reservoir and in a particularly convenient arrangement this blow-by which will still be at a very high pressure can be used to drive the dialysate or permeate from the dialyser or haemofilter towards the reservoir.Between the purifying device and the return side of the dialyser or haemofilter one has therefore a closed sterile line into which is introduced through a metering pump or valve a concentrate to replace the desired salts which will have been removed in the purification process. In the case of the dialyser the line is taken to the dialysate side and the salts will pass by osmosis into the bloodstream; in the case of the haemofilter the line is taken to the return line through which blood passes back directly to the patient.

The attached drawings show diagrammatically two embodiments of the invention one with a dialyser and the other with a haemofilter.

Fig. 1 is an "open" portion of circuitry which is common to both embodiments, Fig. 2 is a diagram of circuitry particular to a dialyser and Fig. 3 is a diagram of circuitry particular to a haemofilter.

In Fig. 1 output of impure dialysate from a dialyser or of impure permeate from a haeomofilter is taken by line 1 to a pump 2 whence it passes to an open reservoir 3 which is initially charged with a known volume of medium or permeate medium. The reservoir is "open" in the sense that it need not be enclosed and sterile, and the medium originally charged to it neither need be particularly pure (it may be for example ordinary tap water) nor need it be sterile. Feed is taken from the tank by line 5 which goes to a high pressure pump 6 from which it is fed through the units 7 and 8 of a continuously operable purification device which gives a highly pure output of medium. A reverse osmosis device is preferred because the impure product known as "blow by", can be passed by line 9 to the pump 2 which it may in fact power, the pump 2 taking the form for example of an ejector pump.Pure and sterile medium is passed by line 10 to the remaining part of the circuit, as shown in Fig. 2 or Fig. 3. It will be seen that impurities separated from the dialysate or permeate brought into the circuitry via line 1 are separated from it in the purification device 7, 8 and are recirculated within the "open" part of the circuit which is that part forming a recycling loop in Fig. 1. However the pure and sterile product of the purification process is recycled to a return line of the blood purification device in a manner which will be described.

In Fig. 2 the situation is seen with line 10 feeding towards a dialyser 11, the return line of which is indicated at 12. At 13 a proportionating pump or valve incorporates minor proportions of a concentrate of desirable salts brought in from line 14. The purified and refreshed dialysate circulates past the semi-permeable membrane behind which is blood, the blood input side to the dialyser from the patient being seen at 15 and the return side to the patient at 16. The dialysate having picked up impurities from the blood passes through line 1 into the purifying circuit and its impurities are taken from it and returned into the reservoir 3.

In the haemofiltration circuit seen in Fig. 3 output 10 of the purifying device is seen to be fed to a blood return line 18 of a haemofilter 19 and since it is then going direct into the patient, as a safety measure a biological filter 17 is incorporated in the line. As in the arrangement of Fig. 2 a proportionating valve or pump adds a minor proportion of a concentrate of desired mineralsfrom line 14.

The medium, newly refreshed with desirable salts, is thus-mixed and passed to the patient down return line 20. The blood input side of the haemofilter is seen at 21.

The impure permeate product of the haemofiltration process is taken from line 22 to line 1 and then as previously described around the circuitry seen in Fig. 1 so that impurities become concentrated in the reservoir 3.

Dotted line 23, Fig. 3 indicates two possible positions of a bypass operable in the event of pressure surges in the line 10.

It can be seen that in the circuit described there is firstly a single charge of permeate medium or dialysate medium which is placed in the reservoir.

There is no need for a continuing and running supply of that medium. This medium is recirculated both through the "open" part of the circuit and through the sterile blood purification device (or through the patient) being repurified in every passage, with impurities being concentrated in the reservoir which forms part of the "open" circuit. It follows from this also that there is no need for continuous disposal of waste. The waste is contained at the end of the treatment entirely in the charge remaining in the reservoir and can be treated and disposed of in a single operation, and its volume is low.

Furthermore, the desired extent of the treatment can be determined by simple volumetric measurement of the charge which is at any given time in the reservoir. If a treatment is desired to continue until such time as say 1 litre of liquid has been removed from the patient then this is readily determined from the volume of medium in the reservoir.

The system as described can therefore be embodied in highly portable and very easily used apparatus devoid of previous need either for very large quantities of purified medium or of the need for heavy and single-use ion exchange/enzyme cartridges. The reservoir can be charged by the patient himself from any source of reasonably clean water for example from the tap, and the sole power required, at least with reverse osmosis purification, is power to work the high pressure pump 6 which lies easily within the capacity of a normal domestic or hotel electrical power supply.

Claims (9)

1. Apparatus for purifying dialysate or permeate materials from a blood-treatment means which includes a purification device characterised in that the purification device (8) is continuously operable, the impure output side (9) of which forms part of a recycling circuit (9, 3) in which impurities accumulate and which includes a reservoir (3) for dialysate or permeate medium, and the sterile output side (10) of which is to be connected to a return line (12, 18) of the bloodtreatment means (11, 19).

2. Apparatus according to Claim 1 wherein the device (8) is a reverse-osmosis apparatus.

3. Apparatus according to Claim 1 or Claim 2 wherein the blood-treatment means is a dialyser (11) and the sterile output of the purification device (8) is to be returned to the dialysate side (12)thereof.

4. Apparatus according to Claim 1 or Claim 2 wherein the blood-treatment means is a haemofilter (1 9) and the sterile output side of the purification device (8) is to be returned to the return line (1 8, 20) to the patient from the haemofilter.

5. Apparatus according to any one of the preceding claims wherein metering means (13) control injection of concentrate (14) of desired salts into the sterile output (10) of the purification device (8).

6. Method of purifying dialysate or permeate materials from a dialyser or haemofilter during blood treatment characterised in that impurities and pure dialysate or permeate medium are separated from each other in a continuously operable purification device (8), preferably by reverse osmosis, to form a sterile output and an impure output, the sterile output is returned to a return line (12, 1 8) of the dialyser or haemofilter, the impure output being cycled with material to be purified in a circuit including a reservoir (3) containing a charge (4) of dialysate or permeate medium and the purification device (8).

7. Method according to Claim 6 wherein when reverse osmosis is used the high pressure of the impure output is used in pump (13) to drive itself and material to be purified to the reservoir (3).

8. Method according to Claim 6 or Claim 7 wherein the initial charge (4) of medium in the reservoir is neither sterile nor specially purified.

9. Method according to Claim 6, Claim 7 or Claim 8 wherein the course of the blood treatment of the patient is monitored by reference to the volume of medium accumulated in the reservoir (3).