Abstract:
Apparatus is disclosed for the safety monitoring of a dialyzer including at least one holder for holding a container for a powdered substance in which the holder includes a supply end for supplying a liquid to the container and a delivery end for delivering liquid containing the powdered substance from the container to a concentrate pump. The apparatus includes a first supply conduit for supplying water to the supply end of the holder for delivery to the container, a first delivery conduit for delivering the water containing the powdered substance from the delivery end of the holder to the concentrate pump, and a second supply conduit which is connectable to either the delivery end of the holder or to the first delivery conduit. Methods for the safety monitoring of dialyzers are also disclosed.

Description:
CROSS-RELATED APPLICATIONS 
     The present application is a continuation of application Ser. No. 09/582,595, filed Jun. 28, 2000, U.S. Pat. No. 6,428,706 which is a 371 of PCT/SE99/00062 filed Jun. 28, 2000. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to a holder for a powder cartridge in a dialysis machine and in particular to safety considerations in connection with such a holder and the use of such a powder cartridge. More particularly, the present invention relates to an improved conduit layout in connection with such a holder in order to increase safety. 
     The term “dialysis machine” is intended to cover not only a machine intended for hemodialysis but also machines for hemofiltration and for hemodiafiltration, as well as for peritoneal dialysis. 
     BACKGROUND OF THE INVENTION 
     European Patent Application No. 278,100 describes a dialysis machine of the type to which the present invention may be applied. This application thus describes a dialysis machine which includes a preparation unit for dialysis solutions where the preparation occurs on-line starting from concentrates in liquid and powder form positioned in separate cartridges or vessels. 
     A dialysis machine comprises basically two parts; namely, a first blood part for transport of blood from a patient through an extracorporeal circuit comprising a dialyzer, and a second liquid part for preparing a dialysis solution and transporting this solution to the dialyzer, and then to a drain. 
     The dialyzer generally comprises a semi-permeable membrane which divides the dialyzer into a blood-containing part and a dialysate-containing part. The transport of molecules and substances occurs through the membrane for conditioning the blood, in order to replace the function of the kidney. 
     The present invention relates to the liquid part of the dialysis machine which prepares the dialysis solution. In this part of the dialysis machine, purified water is supplied from an external source such as an RO-unit, and is mixed with concentrate in suitable proportions so that a dialysis solution is prepared. The dialysis solution comprises sodium-, bicarbonate, potassium, calcium, magnesium, chloride and acetate ions in suitable concentrations, as well as possibly glucose and other ions, all dissolved in water. The concentrations of the ions in the dialysis solution are generally mirror-images of the concentrations in blood, where the mirror line is the normal concentration in blood of the ions. Thus, if an ion concentration is increased in the blood over the normal concentration, the ion concentration in the dialysis solution is decreased in relation to the normal concentration. The pH of the solution is adjusted to about 7.1-7.4. 
     With the most common form of treatment occurring today, bicarbonate dialysis, the dialysis solution is prepared by mixing two liquid concentrates into the main flow of water; i.e., a B-concentrate comprising substantially bicarbonate and an A-concentrate comprising the remaining components. The B-concentrate can also contain sodium chloride. These concentrates are metered in ratios of between about 1:25 and 1:40 depending on the concentration and the desired content of the dialysate, respectively. The metering occurs either volumetrically or by measuring the conductivity and controlling metering pumps so that the correct conductivity is obtained, i.e. feedback control of the metering pumps. 
     The reason for the division into A- and B-concentrates is that calcium precipitates to form calcium carbonate in the presence of bicarbonate, meaning that these two substances cannot be mixed until immediately before use, and then only in low concentrations. Magnesium also causes similar problems. 
     European Patent Application No. 278,100 describes the use of one or more powder cartridges as a replacement for the aforementioned concentrate. The powder cartridges are coupled into the dialysis machine and water is allowed to pass through the cartridges in order to form substantially saturated solutions of the powder contents at the outlets. These saturated solutions are metered into the main flow of water instead of the above-mentioned concentrates. For a little less than 10 years, there has been a bicarbonate cartridge on the market which is sold under the trademark BiCart® by GAMBRO AB, as a replacement for the B-concentrate. The B-concentrate was the concentrate which was the most difficult to handle, since the bicarbonate solution was close to its saturation limit, and when storing in cold spaces easily formed precipitates. Additionally, containers were required which were sealed against carbon dioxide, since otherwise decomposition into sodium carbonate occurred, with subsequent pH increase. 
     Now there is also another type of cartridge on the market which contains sodium chloride. This cartridge replaces the larger amount of ions in the A-concentrate. The remaining ions and substances are contained in a little bag of only about half a liter, called an ion bag. 
     A dialysis machine which is adapted to use these three components must also have the possibility of using the still generally occurring liquid-formed concentrates. For this purpose there are two hollow rods which are removable and can be fitted into an A-concentrate canister or a B-concentrate canister, respectively. The machine then includes sensors which detect if the rods are positioned in the machine or not. Also there are separate holders for the above-mentioned cartridges. If the holders are folded out and contain a cartridge, this condition is detected by sensors. 
     One problem which arises with dialysis machines of this type, which are intended to be used for a plurality of different types of concentrates, is that it is possible to mix up the rods and to put the rod for the B-concentrate into the A-concentrate canister and vice versa. This error condition is detected by the electronics in the dialysis machine in that the conductivity value which is expected after the mixing-in does not occur. Thus, the conductivity for the A-concentrate is significantly higher than the conductivity for the B-concentrate. 
     Another potential for error is the case where the dialysis machine is provided with both cartridges of the powder type and the corresponding rod is put into a container with concentrate. In order to resolve this error condition, the liquid is taken to the bicarbonate cartridge through the rod, to the upper end of the cartridge. If the rod is put into a container with bicarbonate this has no great practical significance, and the only thing that happens is that an additional amount of bicarbonate, is dissolved in the cartridge so that the outgoing solution is substantially saturated. Normally the machine detects this in that the rotational speed for the B-metering pump is lower than when using normal B-concentrate. If, however, A-concentrate comes into a bicarbonate cartridge, gas formation (carbon dioxide) occurs which rapidly results in an alarm condition. 
     The same or similar conditions exist with the use of a sodium bicarbonate cartridge. If the corresponding A-rod is put into a B-canister, gas formation occurs (carbon dioxide) which rapidly results in an alarm condition. 
     However, the situation is different if the A-rod corresponding to the A-cartridge is put into a concentrate container containing A-concentrate. The A-concentrate contains substantially sodium chloride and in this respect the situation is the same as with bicarbonate. The A-concentrate however also contains magnesium, potassium, calcium, acetic acid and possibly glucose. Magnesium, potassium and calcium are present in only relatively small amounts, such that they do not have a noticeable effect on the conductivity measurements. If the machine is now adjusted for dialysis with a bicarbonate cartridge, a sodium chloride cartridge and a small bag containing other ions, the machine meters the necessary amount of ions from the small bag, i.e. magnesium, potassium and calcium. This means that the dialysis solution in principle contains double the amount of magnesium, potassium and calcium than was intended. Apart from the fact that this gives rise to incorrect treatment, it can be life-threatening for certain patients. A construction which makes this error condition impossible would be desirable. 
     One object of the present invention is to provide a dialysis machine having improved safety. 
     Another object of the present invention is to provide a dialysis machine which is intended for use of both liquid concentrate as well as at least one powder cartridge for sodium chloride, where it is impossible to unintentionally supply A-concentrate and at the same time use the powder cartridge. 
     SUMMARY OF THE INVENTION 
     In accordance with the present invention, these and other objects have now been realized by the invention of apparatus for the safety monitoring of a dialyzer comprising at least one holder for holding a container for a powdered substance, the holder including a supply end for supplying a liquid to the container and a delivery end for delivering the liquid containing the powdered substance from the container to a concentrate pump, the apparatus comprising a first supply conduit for supplying water to the supply end of the holder for delivery to the container, a first delivery conduit for delivering the water containing the powdered substance from the delivery end of the holder to the concentrate pump, and a second supply conduit connectable to either the delivery end of the holder or to the first delivery conduit. In a preferred embodiment, the apparatus includes a first rod connectable by the second supply conduit to the delivery end of the holder and to the first delivery conduit. In a preferred embodiment, the container includes an upper end and a lower end, the supply end of the holder comprising an upper arm for attachment to the upper end of the container and the delivery end of the holder comprising a lower arm for attachment to the lower end of the container, and wherein at least one of the upper and lower arms is movable between a first position cooperating with the second supply conduit for connecting the first rod to the concentrate pump and a second position for connecting with the delivery end of the holder. In a more preferred embodiment, the apparatus includes a flush and disinfecting conduit, and the other of the upper and lower arms is also movable between a first position cooperating with the flush and disinfection conduit and a second position. 
     In accordance with one embodiment of the apparatus of the present invention, the at least one holder comprises a first holder and the apparatus includes a second holder for holding a second container for a powdered substance, the second holder including a supply end for supplying a liquid to the second container and a delivery end for delivering the liquid containing the powdered substance from the second container to a second concentrate pump, and including a third holder for an ion bag. 
     In accordance with another embodiment of the apparatus of the present invention, the supply end of the holder comprises an upper supply arm and the delivery end of the holder comprises a lower delivery arm. 
     In accordance with the present invention, a method has also been devised for the safety monitoring of a dialyzer comprising at least one holder for holding a container for a powdered substance including a supply end and a delivery end, the holder including a supply end for supplying a liquid to the container and a delivery end for delivering the liquid containing the powdered substance from the container to a concentrate pump, the method comprising providing a first holder arm for the supply end of the holder and attaching the first holder arm to the supply end of the container, providing a second holder arm for the delivery end of the holder and attaching the second holder arm to the delivery end of the container, supplying a liquid substantially comprising water from a source through a first supply conduit to the supply end of the container, and delivering the liquid containing the powdered substance through a first delivery conduit to a concentrate pump from the delivery end of the container. Preferably, the method includes folding the second holder arm and connecting the folded second holder arm to a first rod for feeding the liquid containing the powdered substance through a second supply conduit directly to the first delivery conduit. 
     In accordance with one embodiment of the method of the present invention, the container includes an upper end and a lower end, the supply end comprising the upper end of the container and the delivery end comprising the lower end of the container. 
     The objects of the present invention are fulfilled by safety apparatus for a dialysis machine comprising at least one holder for a container or cartridge containing a substance in powder form. According to the present invention, the apparatus comprises a first supply conduit, which leads from a water source to a supply end of the cartridge holder, a delivery conduit for delivering solution from a delivery end of the cartridge holder to a concentrate pump, and a second supply conduit, which is connectable to the delivery end of the cartridge holder, as well as to the delivery conduit and the concentrate pump. 
     Preferably, the cartridge holder includes an upper holder arm intended to cooperate with an upper end of the cartridge and a lower holder arm intended to cooperate with the lower end of the cartridge, and at least one of the holder arms is maneuverable between a first position where it cooperates with the second supply conduit in order to connect the A-rod to the concentrate pump, and a second position where it cooperates with the delivery end of the cartridge. The second holder arm of the cartridge holder cooperates, in a first position, with a flush and disinfection conduit. The dialysis machine may further comprise at least one additional cartridge holder and a holder for an ion bag. Moreover, the supply end of the cartridge holder comprises an upper supply arm, and the delivery end of the cartridge holder comprises a lower delivery arm. 
     In another aspect of the present invention, there is provided a method of activating a safety arrangement for a dialysis machine comprising at least one holder for a cartridge containing a substance in powder form. The invention comprises the steps of: activating a first holder arm for cooperation with the supply end of the cartridge; activating a second holder arm for cooperation with the delivery end of the cartridge; supplying substantially water from a water source to the supply end of the cartridge by means of a separate first supply conduit; and delivering solution from the delivery end of the cartridge by means of a delivery conduit to a concentrate pump. 
     Preferably, the second holder arm is folded in for connection with an A-rod for feeding concentrate through a second supply conduit directly to the delivery conduit and the concentrate pump. The supply end is the upper end of the cartridge and the delivery end is the lower end of the cartridge. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will be more fully appreciated with reference to the following detailed description, which, in turn, refers to the drawings wherein: 
     FIG. 1 is a schematic representation of the portion of a dialysis machine in which the dialysis solution is prepared according to the state of the art. 
     FIG. 2 is a schematic representation similar to FIG. 1, but modified in order to achieve improved safety in accordance with the present invention; and 
     FIG. 3 is a side, elevational view of a holder for the powder cartridges, which can be used in the present invention. 
    
    
     DETAILED DESCRIPTION 
     The present invention is described below in more detail with reference to a preferred embodiment intended to be used on the dialysis machine GAMBRO AK 200 which is sold by GAMBRO AB. The principles of the present invention can be used on other types of dialysis machine without modification in a manner which will be apparent to one of ordinary skill in the art. 
     FIG. 1 is a flow diagram of the above-mentioned dialysis machine, where only the part of the dialysis machine is shown which is relevant to the present invention, namely the part where the preparation of the dialysis solution occurs. 
     The dialysis machine is connected by means of tubes to an outlet for purified water which is normally found in a dialysis clinic. The water normally comes from a RO-unit and is, practically speaking, free of ions and other impurities. 
     The water enters a main conduit  1  in a dialysis machine according to FIG.  1  through an inlet conduit  2 . The inlet conduit  2  opens into a water vessel  3  where the water is heated to the temperature of use, normally about 37° C. During a normal dialysis treatment which continues over four hours, about 120 l of water is used. Thus ½ liter of dialysis solution has to be prepared per minute (500 ml/minute). Other speeds of dialysis solution preparation can be used, but the normal range is from about 300 to 700 ml/minute. 
     The heated water from the water vessel  3  then passes through a conduit  4  and reaches a first metering point  5  where a first concentrate is metered into the main flow, normally the A-concentrate. Additionally, there is a second metering point  6  where a B-concentrate is metered in. Between the metering locations there is a first conductivity sensor  7 . After the second metering point  6  there is a restrictor valve  8 , a powerful pump  9  and a second conductivity sensor  10 . The inverse metering order can also be used. 
     A first metering pump  11  is connected to the first metering point  5  and a second metering pump  12  is connected to the second metering point  6 . 
     In the heating vessel there are two rods,  13  and  14 . These rods pass through holes in the front of the machine and through holes in the water vessel and extend below the water level in the water vessel  3  as shown in FIG.  1 . The rods are removable and the rod  13  is marked with a red color and is intended to be put into a canister with A-concentrate. The rod  14  is marked with a blue color and is intended to be put into a canister with B-concentrate. 
     When the machine is used for the preparation of a dialysis solution starting from concentrate in powder form, the rods,  13  and  14 , are positioned in the water vessel as shown in FIG.  1 . Additionally, one or two cartridges are arranged in separate cartridge holders. In FIG. 1 the dialysis machine is shown arranged for preparing dialysis solution starting from two powder cartridges and an ion bag. 
     A conduit  15  extends from the rod  13  and opens into the upper end of a sodium chloride cartridge  16  inserted in a holder comprising brackets or arms  17  and  18 , which is described in more detail below. The lower end of the sodium chloride cartridge  16  is connected by means of a conduit  19  to the suction side of the first metering pump  11 . The conduit  19  suitably includes a particle filter  20  for preventing powder from passing out of the cartridge  16  and reaching the pump. 
     In the same way, a conduit  21  leads from the B-rod  14  and opens into the upper end of a bicarbonate cartridge  22  arranged in a second holder,  23  and  24 . From the lower end of the bicarbonate cartridge  22  there is a conduit  25  which leads to the second concentrate pump  12 . The conduit  25  preferably contains a particle filter  26 . 
     Finally, there is a small bag  27 , below referred to as an ion bag, which contains about ½ liter of liquid with other components which are not provided from the powder cartridges. The ion bag  27  is arranged in a third holder  28 . A conduit  29  leads from the ion bag and opens into a third concentrate pump  30 . The concentrate pump  30  pumps the contents through a conduit  31 , which opens into the conduit  19 . The degree of concentration in the ion bag is, for example, 1:400 or at least 1:150. 
     The function of the dialysis machine according to FIG. 1 is as follows. 
     Water enters through the inlet  2  to the water vessel  3 . A level sensor  32  ensures that the water level in the vessel is substantially constant by means of an inlet valve  33  controlled by the level sensor  32 . The water vessel is open to the atmosphere. Water passes from the water vessel into the main conduit  1 , and through the main conduit  4  to the mixing points,  5  and  6 , and further through the restrictor arrangement  8  and the pump  9 . The water flow is thus controlled by the powerful pump  9  so that the desired amount of dialysis solution is produced, normally about 500 ml/minute. 
     Water passes through the rod  13 , which is in the water vessel  3  with its tip lowered into the water, through the conduit  15  to the upper end of the first holder,  17  and  18 . The water enters into the upper end of the sodium chloride cartridge  16  and passes through the sodium chloride powder therein and out through the particle filter  20  to the conduit  19 . The conduit  19  thus contains water substantially saturated with sodium chloride. This saturated sodium chloride solution in the pump  19  is pumped through the first metering pump  11  to the first metering point  5  in the main conduit,  1  and  4 . Thereafter, the mixture of concentrate and water in the conduit  4  passes to the first conductivity sensor  7  where the conductivity is measured. The conductivity is substantially proportional to the concentration of sodium chloride and the pump  11  is controlled by the conductivity cell  7  so that the desired conductivity is obtained after the dilution of the sodium chloride, normally about 12 mS/cm. 
     The control takes place by means of a control processor comprising a computer  35  connected to the respective sensors and actuators. Moreover, the computer  35  comprises a supervisory processor or portion, that supervises the control processor and the dialysis machine operation, as is conventional in the art. 
     The second rod  14  is similarly put into the water container  3  with the tip positioned in the water. The water thus passes through the rod  14  and the conduit  21  to the upper part of a cartridge  22  with bicarbonate powder, the cartridge  22  being arranged in the second holder. The water passes through the powder and out through the bottom of the cartridge through the filter  26  to the conduit  25 . The conduit  25  thus contains water substantially saturated with sodium bicarbonate, which by means of the second concentrate pump is metered into the second metering point  6 . By this second metering of substantially saturated sodium bicarbonate, the conductivity in the solution rises from about 12 mS/cm to about 15 mS/cm, which is measured with the second conductivity sensor  10 . The increase in conductivity controls the metering pump  12  so that the correct amount of bicarbonate is metered in. 
     Normally, the metering pumps are controlled so that the concentration of bicarbonate ions in the finally prepared dialysis solution is about 35 mmol/l and that of the sodium ions about 140 mmol/l. 
     In the manner described above, sodium chloride and sodium bicarbonate have been metered into the main conduit, these being the two main ingredients in the dialysis solution, i.e. the substances which are present in the highest concentration. 
     The remaining ions and substances which are to be included in the final dialysis solution are metered in with a third metering pump  30 . An ion bag  27  is positioned in a third holder  28 . The contents of the ion bag  27  are fed out through the holder to the conduit  29  which leads to the third metering pump  30  and through the conduit  31  to the conduit  19 . In this way, the solution which reaches the inlet of the first concentrate pump  11  will have about the same composition as the contents in an A-concentrate, although normally with another dilution. In principle it is possible to let the third concentrate pump  30  and its outlet conduit open at any point in the main conduit  1 , or even after the metering pump  11 . The addition of the conductivity from the contents in the ion bag is relatively small. An example of the contents in the ion bag is described below. 
     FIG. 3 shows a holder for one of the cartridges  16  and  22 . The holder consists of an upper bracket,  17  and  23 , and a lower bracket,  18  and  24 . The brackets are pivotable between a folded-out position, as shown in FIG. 3, where the brackets cooperate with a powder cartridge, and a folded-in position which is shown in dashed lines in FIG. 3, where the brackets cooperate with separately arranged connection tubes,  41  and  42 , arranged on the side surface of the dialysis machine. The connection tubes,  41  and  42 , may be joined with one another by means of a conduit  43 . 
     During normal operation water enters through the conduit,  15  and  21 , to the pivotal holder and reaches the upper end of the cartridge holder. Water is supplied with a speed of about 10 to 20 ml/min, which is controlled by the output metering pump. The water drips down into the upper end of the container and reaches the water level  44  which is shown in FIG.  3 . The container is filled with powder or particles consisting of sodium chloride or sodium bicarbonate (or some other substance). The powder level is shown by the dashed line  45 . The powder level sinks during the treatment from an upper level just below the water level  44  until the powder has run out and is near to the bottom surface of the cartridge. The water which is fed into the cartridge thus has to pass through the powder bed  45  in order to reach the outlet  46 . The solution thereby becomes saturated, or substantially saturated, when it reaches the outlet  46  and is led further through the conduit,  19  and  25 , to the respective concentrate pump. 
     When the dialysis machine is adapted for treatment by using liquid concentrates, the brackets,  17  and  23 , and  18  and  24 , are pivoted inwardly to the positions,  47  and  48 , shown in dashed lines. The water is then led directly from the conduit,  15  and  21 , through the connection tube  41 , the conduit  43 , the connection tube  42  to the outlet conduit,  19  and  25 . This is shown in FIG. 1 by means of the dashed lines marked  17  and  23 , and  18  and  24 . Additionally, FIG. 3 shows a position sensor  49  which detects when the brackets  47  and  48  are close to the sensor  49 . The sensor  49  can be a magnetic relay which is actuated by small permanent magnets,  50  and  51 , arranged in the brackets so that when the permanent magnets,  50  and  51 , are close to the sensor  49  an electrical contact is made. If both the holder arms,  47  and  48 , are pivoted inwardly the sensor  49  is thus activated. Other forms of sensor can of course be used, such as mechanical, electrical, etc. The sensor  49  can consist of two discrete sensors which are connected in parallel or in series. 
     If the dialysis machine according to FIG. 1 is to be used only with liquid concentrates, the holder arms or brackets,  23  and  24 , and  17  and  18 , are thus inwardly pivoted. The rod  13  is placed in an A-concentrate container and the rod  14  is placed in a B-concentrate container. The contents in the containers is sucked through the conduit  15 , the holder  17 , the holder  18  and the conduit  19  to the pump  11 . The contents of the B-concentrate canister are sucked through the rod  14 , the conduit  21 , the holder arms,  23  and  24 , and the conduit  25  to the pump  12 . In this position of operation the pump  30  is not in motion. 
     If the dialysis machine is now by mistake applied for dialysis with powder cartridges,  16  and  22 , and an ion bag  27  and then the second (blue-marked) rod  14  is lowered into a concentrate container, there will be no direct difficulties which are not immediately detected by the dialysis machine. Firstly, it will be noted that the rods are not positioned in their respective holders. If, however, this mechanical detection for any reason does not work, the following possible situations will occur. 
     If the B-rod  14  is placed in an A-concentrate container the conductivity sensor  10  will detect a high conductivity, whereby the pump  12  reduces its speed to the point where it lies outside the set predetermined range. In this condition a rotational speed alarm is given. The reason is that the A-concentrate container contains concentrate with sodium chloride in high concentration which gives a high conductivity. Since the A-concentrate has a low pH-value, a large build-up of carbon dioxide gas will occur in the bicarbonate cartridge, which soon leads to an alarm. 
     If the B-rod  14  by mistake would be put into a B-canister containing sodium bicarbonate solution with a concentration of 840 g/10 l, which is a normal concentration, there will be no great problem. The bicarbonate solution from the canister will of course pass through the cartridge  22 , but only receives a minimal addition of bicarbonate so that the outgoing solution will be saturated in the conduit  25 , which depending on the temperature can be an extra addition of about 10% to 20%. The mixing of the dialysis solution occurs entirely satisfactorily. It also occurs that the B-canister contains bicarbonate with a concentration of 660 g/10 l, and moreover sodium chloride with a concentration of about 350 g/10 l. The conductivity for this solution is, however, so large that the same happens as if the rod  14  is put into an A-canister, i.e. the conductivity sensor  10  detects such a high conductivity that the pump  12  is driven with such a low speed that it lies outside its normal operating range and a rotational speed alarm is given. 
     When the holders,  23  and  24 , and  17  and  18 , are open, it is indicated for the dialysis machine that the machine is arranged for preparing a dialysis solution starting from powder cartridges for sodium chloride and sodium bicarbonate as well as an ion bag. For this, it is programmed into the dialysis machine that the conductivity values for the conductivity sensors,  7  and  10 , are to control the pumps,  11  and  12 , at a predetermined speed in the range of about 10 to 20 ml/min, e.g. about 16 ml/min for the bicarbonate cartridge. Since the concentration in the conduit  25  can vary somewhat depending on temperatures and other factors, there is an allowable variation range for the pump  12 , normally +/−20%. If the pump goes outside this range, an alarm signal is given. The same is true for the pump  11  but with correspondingly different values. 
     Thus, it is clear from the above that no large problems are present concerning the B-rod  14  which leads to the B-concentrate pump  12  and which are not taken care of by the normal safety system of the dialysis machine. 
     If the red A-rod  13  is mistakenly put into a B-concentrate canister the conductivity sensor  7  and the pump  11  will lie outside their predetermined ranges, whereby an alarm signal is given. Moreover, gas formation occurs since the acidic solution from the ion bag meets bicarbonate solution in the conduit  19  after the connection to the conduit  31 , leading to an alarm situation. 
     If, however, the A-rod  13  is put into an A-concentrate canister, the following situation will occur. The A-concentrate contains substantially sodium chloride with a concentration of about 200 g/l. Furthermore there is magnesium, potassium and calcium and acetic acid in lower concentrations. When this solution reaches the cartridge  16 , additional sodium chloride is added until the solution becomes saturated with sodium chloride. The saturated sodium chloride solution reaches the conduit  19 . Also the pump  30  meters in magnesium, potassium and calcium from the ion bag  27  through the conduit  31  to the conduit  19 . The conduit thus contains magnesium, potassium and calcium both from the A-canister and from the ion bag  27 . 
     The conductivity sensor  7  thus detects a somewhat higher conductivity than normal and the pump  11  reduces speed slightly. This reduction is, however, moderate and within the error tolerance of this pump of +/−10%. The machine thus accepts the obtained solution without giving any alarm signal. However, the content of potassium, magnesium and calcium is about 50% higher than originally set, since the contribution from the ion bag  27  consists of 100% and the contribution from the A-concentrate container, depending on its degree of concentration, is up to at least 50%. Such an increase of, in particular, the content of potassium ions can be life-threatening for the patient. 
     In order to solve this problem it is possible to use ion-selective meters which measure the concentration of potassium, magnesium and/or calcium. Such meters are, however, expensive and complicated to use. 
     Since the calcium content is raised, it may be possible to indicate this error since calcium carbonate might precipitates. This, however, takes a long time and is difficult to measure. 
     In accordance with the present invention the above problem is solved in the following way. The problem occurs due to the fact that the dialysis machine has to be adapted for using both liquid concentrate for the A-concentrate and a combination of powder-formed and liquid-formed concentrate by means of the powder cartridge  16  and the ion bag  27 . Thus there have to be two conduit paths which fulfil this need. In accordance with the present invention, the conduit  15  from the rod  13  runs through upper arm  17 . The upper arm  17  is moved to connect to the lower pivotal arm  18  of the first holder via the connection tubes  41  and  42  and conduit  43  of FIG.  3 . The upper holder arm&#39;s  17  connection to the cartridge  16  is joined with a separate conduit  55  to the main conduit  1  or the water vessel  3 , as shown in FIG.  2 . Due to this coupling, the characteristic is obtained that when the powder cartridge  16  is coupled-in, the water transport occurs through the separate conduit  55  to the upper end of the cartridge  16  and out through the lower end of the cartridge to the conduit  19 . Even if the rod  13  is put into a container, there is no transport through the rod  13  since the conduit  15  ends in a connection tube  56 , which is open to the atmosphere. When the cartridge  16  is not located in the holder,  17  and  18 , the holder is closed, whereby the connection tube  56  is connected to the conduit  19 . If the rod  13  is therefore in an A-canister, the contents are led from the A-canister through the rod  13 , the conduit  15 , the connection tube  56  and the holder arm  18  to the conduit  19  and the pump  11 . In this way the possibility is obtained of using both liquid-formed concentrate and powder cartridges for the A-concentrate, whereby at the same time the above-mentioned risk of possible incorrect operation is completely removed. 
     The reason for the present arrangement in respect of the holders and the rod  14  in connection with the bicarbonate cartridge is that the holders must be able to be disinfected and flushed between treatments. This occurs simply by folding-in of the holder brackets,  23  and  24 , and the use of the short circuiting conduit  43  in the arrangement of FIG.  1 . As a result of the different coupling of the holder arms,  17  and  18 , in connection with the sodium chloride cartridge  16  according to the present invention, there is no longer this possibility and a new disinfection construction has to be achieved. 
     In order to allow flushing of the holder arms,  17  and  18 , special measures have therefore been taken, as shown in FIG.  2 . The lower holder arm  18  is flushed automatically by means of the rod  13 , the conduit  15 , the holder arm  18 , the conduit  19 , the pump  11 . The upper holder arm is connected through a flush conduit  52  with a connection tube  53 , which in turn is connected with the conduit  29  when the ion bag  27  is not in the third holder, as is shown by the dashed line  54 . Thus, the upper holder arm  17  of the first holder is flushed by water passing through the conduit  51  to the upper holder arm  17  and from there through the conduit  52  to the connection tube  53  and to the conduit  29  as well as through the pump  30  to the conduit  31 . By means of this special arrangement of the flush conduit  52  it is possible to flush the upper holder arm  17  and the holder  28  at the same time with the aid of the pump  30 . The same flow path is used for disinfection. 
     As an example, the following composition is given for the contents in the ion bag  27  per 500 ml: 
     KCl, about 30 g 
     CaClx2H 2 O, about 44 g 
     MgClx6H 2 O, about 20 g 
     Acetic acid, about 36 g 
     The above substances are dissolved in water so that the volume is about 500 ml. 
     The sodium chloride cartridge contains about 1200 g of sodium chloride in powder form. The bicarbonate cartridge  22  contains about 650 g of sodium bicarbonate in powder form. 
     The contents in the ion bag  27  can be varied within wide limits in order to be adapted to the particular needs of the patient. Since the bag is as small as about ½ liter, a larger number of different compositions can be stored at the hospital or the dialysis clinic without the storage space becoming too large. In this way, individualised treatment can be carried out more easily. Since sodium chloride and sodium bicarbonate are taken from the powder cartridges under control of the pumps,  11  and  12 , with the aid of the conductivity sensors,  7  and  10 , individualisation of the concentration of bicarbonate ions and sodium ions is made possible as well as profiling the concentration of these ions during operation. 
     A dialysis machine contains many more components than have been described above, such as a number of valves, pumps, sensors and measurement devices. These arrangements are, however, not described in the present application since they are not required for understanding the invention. 
     The present invention can also be used in connection with other types of holders for powder cartridges. 
     The ion bag  27  can, for example, be replaced by an arrangement as disclosed in European Patent Application No. 443,324, where the contents of the ion bag  27  are prepared on-line. 
     The present invention has been described above with reference to a preferred embodiment of the invention. The various features of the invention can be combined in different ways and be adapted to different types of dialysis machines, as is obvious for a skilled person reading this description. Such modification are intended to be encompassed by the invention. The invention is only limited by the appended claims.