Dialysis device with controlled composition of dialysis solution.

The invention relates to a dialysis machine according to the preamble of claim 1.

Dialysis devices of the type mentioned at the outset are known. As a detector, which is arranged upstream of the dialyzer, they usually have a conductivity measuring cell with which the temperature-compensated conductivity value of the dialysis solution can be measured. This conductivity value reflects the exact electrolyte composition of the dialysis solution, so that a change in this value indicates a change in the electrolyte content of the dialysis solution.

The detector itself serves both to set the electrolyte content of the dialysis solution and to switch off the entire device, provided that a critical condition for the patient could thereby be generated.

In order to regulate the electrolyte composition of the dialysis solution, the conductivity measuring cell used as a detector controls a pump which pumps the concentrate from a concentrate storage container into the mixing device. The mixing device, on the other hand, is provided with a tap water connection via which tap water is supplied in a controlled manner. Controlled mixing and heating of tap water and concentrate takes place in the mixing device itself, the desired composition of the dialysis solution being obtained at the outlet of this device.

This dialysis solution is passed through the dialyzer, in which the blood is cleaned of substances that are harmful to the urine and the withdrawal of liquid.

As a result of the high level of exchange (clearance) of the dialyzers used today, substances that are sensitive to urine are removed from the blood very quickly, and the dialysis time is thereby reduced. In the case of highly effective dialyzers, the treatment time can be reduced to 3 x 2 hours per week, during which not only the urinary substances, such as urea, but also the excess fluid are removed.

The removal of the excess liquid requires a very precise control of the liquid balance, which is why this method can only be carried out with liquid-balancing devices. Despite this precise balance, patients still experience dialysis-typical discomfort, such as headache, vomiting and muscle cramps, which is referred to as "disequilibrium syndrome". The reason for this is probably due to the rapid withdrawal of sodium ions from the blood, which occurs due to the difference in concentration of sodium in the blood (extracorporeal circulation) and in the dialysis fluid. The greater the exchange capacity of the dialyzer, the lower the permissible gradient of the sodium concentration between the blood and the dialysis fluid. For example, a maximum difference of 10 mmol / 1 sodium should be allowed for normal dialyzers, which is reduced by half for high-performance dialyzers.

However, the sodium content in the patient's blood now differs and is usually still outside the normal range of 135 - 147 mmol / l. In order to avoid the dialysis symptoms described above, it is advantageous to work with a sodium concentration in the dialysis fluid of about 144 mmol / l. The consequence of this is that the patient becomes thirsty during the treatment and absorbs a relatively large amount of liquid until the next dialysis treatment, that is to say is watered over. Overweight of up to 6 kg was not infrequently observed. This increased amount of liquid must then be ultrafiltered within the treatment period of about 2-3 hours, the required amount of sodium being removed together with this amount of liquid. However, this method of treatment is not so precise that the above symptoms could be avoided.

Furthermore, the strong over-watering of the organism that occurs between the treatments is in no way beneficial, but on the other hand cannot be avoided with the methods used today.

Devices (for example Seratron from Cordis-Dow) have therefore already been developed which, based on a dialysis solution with a specific composition, change this composition over the dialysis time, this change taking place according to a specific program. This process is known as "sodium modeling". This program has the disadvantage, of course, that it is by no means tailored to the individual circumstances. As a result of the fixed initial concentrations, there are already difficulties in patients with different sodium levels. In addition, this program does not take into account the differences between the exchange performance of the individual dialyzers, so that disequilibrium symptoms cannot be avoided here either.

The experts have found the determination of sodium elimination during dialysis to be impossible, since even with a very low measurement error of 1% over the duration of dialysis, a high absolute deviation, ie sodium loss or increase, could result. Accordingly, the determination of sodium elimination during dialysis was dispensed with (see HG Sieberth et al, "Current Problems of Dialysis and Renal Failure" 3rd Symposium, Innsbruck 1969, p. 206-214, especially p. 211, 3rd paragraph).

As a result of these metrological difficulties, experts have generally operated with certain predetermined dialysis solution compositions which are either constant or variable according to a certain program (sodium modeling). As a result, the patient has so far been subjected to a certain dialysis solution composition, but the composition has not been adapted to the patient, since this was not considered possible.

The invention is therefore based on the object of providing a dialysis device of the type mentioned at the outset, with which the electrolyte composition of the untreated and treated liquids passed through the dialyzer can be determined and, if appropriate, the composition of the dialysis liquid can be adjusted to the needs of the patient.

This object is achieved by the characterizing features of claim 1.

It has now surprisingly been found that the electrolyte content of those flowing through the dialyzer _FLiquids, that is, the blood and the dialysis solution, upstream and downstream of the dialyzer can be determined with a sensor arranged upstream and downstream of the dialyzer in such a way that the composition of the dialysis solution can be adapted exactly to the needs of the patient by appropriate regulation .

According to a first embodiment, an evaluation unit is initially provided in connection with the two sensors mentioned above, which can display the difference in the composition of the electrolyte content both differentially and integrally for certain, preselectable periods in a downstream differentiating unit, ie comparator. Accordingly, the difference in the electrolyte content of the liquids flowing through the dialyzer can be monitored and recorded integrally for the time of the dialysis treatment.

According to a second embodiment, the value determined by the evaluation and differentiation unit is used to regulate the composition of the dialysis fluid in such a way that the patient's electrolyte balance is adjusted to the value desired by the doctor. The composition of the dialysis solution will therefore be regularly controlled in such a way that the electrolyte composition of the patient's blood usually corresponds to that of a healthy person who does not suffer from kidney failure. On the other hand, however, special electrolyte compositions of the blood which are adapted to the patient and in which the patient usually feels good, ie are not subjected to metabolic disorders, can also be adjusted.

The dialyzer according to the invention works in the following way:<ul id="ul0001" list-style="none"><li>The dialysis apparatus according to the invention can initially be used to preselect the electrolyte concentration of the dialysis solution with which the patient is initially treated. Such an initially set dialysis solution enters the dialyzer and is used in the dialyzer for exchange purposes along the dialysis membrane. If this dialysis solution has a difference in the concentration of the electrolytes compared to blood on the inlet side, this concentration difference is reduced to a difference of about 5% in a dialyzer with a high exchange rate until the blood emerges. This latter difference is due to the plasma anions present in the blood, which are less able to penetrate the semipermeable membrane. This permanent difference is about 5% of the absolute concentration and is explained by the Gibbs-Donnan theory.</li></ul>

From this it can already be seen that such a concentration difference is generally undesirable in the dialysis treatment of a patient, since — as explained above — strong changes in the electrolyte balance of the patient lead to the unpleasant disequilibrium symptoms.

As a result, the concentration of the electrolytes of the dialysis solution at the outlet of the dialyzer is measured with the second detector, taking into account the concentration difference obtained and mentioned above at the outlet of the dialyzer. This value thus differs from the value of the concentration of the dialysis solution obtained at the dialyzer inlet, provided that there is a difference in the concentration of the electrolytes between the dialysis solution and the blood. Accordingly, by feeding these two values, which are obtained by measuring the electrolyte concentrations upstream and downstream of the dialyzer, into the control unit according to the invention, the mixing device, in particular its pump, can be controlled, with which the concentrate is conveyed into the mixing device.

Thus, according to the invention, the electrolyte concentration during dialysis can be regulated continuously at a certain value or else according to a chronological sequence of values, this regulation being based directly on the electrolyte concentration present in the blood. This regulation has the advantage that - unlike the previously used regulations - the electrolyte concentration in the blood is the control constant.

It is advantageously sufficient that only one concentrate solution is used to produce the dialysis liquid, which is diluted with tap water in a ratio of about 1:34. As a rule - as already explained in the introduction - the concentration of the dialysis fluid during dialysis treatment will fluctuate at most by approximately + 8%, so that the influence on the other electrolytes, for example potassium or calcium, is practically negligible.

On the other hand, however, different concentrates with different electrolytes can also be used, in which case each concentrate container is connected to a pump, by means of which the specific concentrate quantities are fed to the mixing device. The pumps themselves are controlled by regulating devices that are connected to ion-selective sensors or detectors. With such an ion-selective sensor, the specific concentration of a certain electrolyte can be determined and regulated as desired and independently of the other electrolytes.

In a further embodiment, a sensor or detector is provided for determining the total electrolyte content upstream and downstream of the dialyzer. This arrangement of the two sensors is advantageously each connected to a temperature sensor which is arranged adjacent. These temperature sensors are used for temperature compensation of the determined values, for example the electrochemical potentials or the conductivity value. However, if the temperature of the dialyzing solution supplied essentially corresponds to the body temperature of the patient, this temperature compensation can be omitted.

These sensors are connected to an actual value device, which in turn is connected to a preprogrammed target value device. If the actual value deviates from the target value, the composition of the dialysis solution is corrected by regulating the pump delivering the concentrate solution to the mixing device until the actual value matches the target value.

Either the conductivity measurement or else the determination of the potentials of the ions, in particular the sodium ion, by means of ion-selective electrodes can advantageously be used to determine the total ion concentration. The latter method has the advantage over the former method that several types of ions can be measured selectively and regulated with the aid of the device according to the invention. On the other hand, the electrodes used are much more susceptible and unstable than the ion conductivity measuring cell, so that the conductivity will be given preference in a conventional dialysis.

Moreover, ion-selective electrodes show a potential drift when they are exposed to different pressures, for example negative pressure, which is applied to the dialyzer to produce the ultrafiltration on the dialysis liquid side. According to a further embodiment, this behavior is taken into account, the measurement being carried out in a pressure-balanced manner. For this purpose, lines branching off from the lines of the dialysis solution are provided upstream and downstream of the dialyzer and can be shut off by means of shut-off elements. Synchronized with these shut-off devices, at least one pump is provided downstream, which overcomes the negative pressure prevailing in the dialysis solution line. The measuring arrangement consisting of at least one detector is connected to this pump. According to this embodiment, measurement is carried out alternately, ie the detector is alternately charged with untreated and treated dialysis solution.

In a further embodiment, at least one of the detectors mentioned above can also be provided in the extracorporeal blood circuit on the dialyzer. In particular, a sensor at the inlet and a sensor at the outlet of the dialyzer can be provided in the extracorporeal blood circuit.

Furthermore, the sensors provided in the extracorporeal blood circuit can be separated from the blood by means of plasma filters, so they are only exposed to the plasma which essentially contains the electrolytes to be determined.

These measurements can either take place in on-line operation or blood samples from the extracorporeal circuit can be branched off by means of lines branching off the extracorporeal circuit, which lines can be closed by metering valves.

Further features, details and embodiments of the invention are explained on the basis of the following description with reference to the drawing.

Show it:<ul id="ul0002" list-style="none"><li>Figure 1 is a schematic representation of a first embodiment of a dialyzer, each with a detector upstream and downstream of the dialyzer in the dialysis solution line.</li><li>Fig. 2 is a schematic view of a further embodiment, each with a branch in the dialysis solution line^G upstream and downstream of the dialyzer, the branching lines leading to a detector;</li><li>Fig. 3._.is a schematic view of a third embodiment, in addition to the embodiments shown in Figures 1 and 2 has detectors_ which are provided in the extracorporeal blood circuit; and .</li><li>_Fig. 4 is another schematic view of an embodiment that is substantially similar to FIG. 3.</li></ul>

1 shows the dialyzer according to the invention at 10. This dialyzer essentially consists of a unit 12 for producing the dialyzing solution and a dialyzer 14, which is connected to the unit 12 and to which a pump 16 is connected downstream for generating a negative pressure in the dialyzer on the side of the dialyzing liquid.

The unit 12, which is shown in simplified form, has as its main component a mixing device 18, which is not explained in greater detail and which is connected via a line 20 to a container 22 containing a concentrate solution. A controllable pump 24 is arranged in this line 20, with which the concentrate solution can be conveyed into the mixing device.

The mixing device 18 is also connected via a line 26 to a fresh water supply 28. The water arriving in the mixing device 18 is heated to approximately the body temperature of the patient by a heating block, not shown. The pump 24 then sucks concentrate out of the container 22, which is then mixed in the mixing device with the heated tap water.

In this mixing device, excess gas dissolved in the dialysis solution, which would otherwise be released in the dialyzer 14, is also separated, since there is a certain negative pressure.

A line 30 leads from the mixing device 18, via which the dialyzing solution produced is conveyed to the dialyzer 14. A first detector 32 is provided in this line 30, with which at least one concentration parameter of the electrolytes contained in the dialysis fluid can be measured. Usually this will be the concentration of the sodium salt, since this makes up at least 90% of the conductivity value. However, the sum of all concentration parameters can preferably also be measured, since usually all concentrations are present in the same ratio to one another. This is due to the fact that only a concentrate solution is presented.

However, as will be explained below, the use of such a concentrate solution, which contains all the electrolytes in the mixture, is not absolutely necessary. It is conceivable that the electrolyte salt is present in the form of a concentrate and is fed to the mixing system 18 in each case via a conveyor system which essentially corresponds to the line 20 and the pump 24. A sodium salt, in particular sodium chloride, in the form of its concentrate and the other electrolytes can advantageously be present in a further concentrate. However, the use of a certain concentrate is particularly preferred, as shown in FIG. 1 shown, since the sodium ion concentration in the dialysis fluid changes at most by a maximum of 10% during dialysis, which of course also results in a relative change of the same size in the other electrolytes, which, however, is tolerated in the organism without great difficulty.

A concentration parameter of the dialysis solution is therefore measured in the detector 32, which is arranged upstream of the dialyzer 16. If a conductivity measuring cell is used as the detector 32, which is in itself preferred, the conductivity of the entire dialysis solution is measured here. The measured value obtained is compensated for with the aid of a temperature detector 34 connected to the detector 32. The detector 32 is also connected to a control unit 36 ​​which can control the pump 24 in accordance with the measured value determined in the detector 32.

The temperature detector 34 is followed by a bypass valve 38 arranged in the line 30, from which on the one hand the line 30 continues to the dialyzer 14 and on the other hand branches off a bypass line 40. This_BYpass line 40 is connected to a further bypass valve 42, which is arranged downstream of the dialyzer in line 44. Both bypass valves are electrically connected to a control device 46, which is also electrically connected to the detector 32 and the temperature detector 34. If the temperature or the measured value measured in the detector 32 deviates from the target value, then the control unit 46 controls the bypass valves in such a way that the dialysis fluid which does not yet correspond to the desired conditions is led past the dialyzer 14 through the bypass line 40. This prevents dialysis fluid of the wrong composition or temperature from reaching the dialyzer. If, however, the composition and the temperature of the dialysis fluid are correct, it reaches the dialyzer 14 and then through a further temperature detector 48 and detector 50 with which in turn at least one concentration parameter in the dialysis fluid can be measured. As stated, these detectors are arranged downstream of the dialyzer 14 in the line 44. These detectors 48 and 50 are connected to the pump 16, which in the line system extending from the unit 12 to the pump 16, in which the dialysis liquid is conveyed, applies a certain negative pressure which is used to control the ultrafiltration.

The detectors 32, 34, 48 and 50 are each connected via lines 52, 54, 56 and 58 to an evaluation unit 60 which is followed by a differentiating unit 64 via a line 62. From this differentiating unit 64, as indicated by the line 66, a signal is sent to the control unit 36, provided that there is a difference in the differentiating unit 64 that deviates from the set value.

The embodiment shown in FIG. 1 has the following mode of operation:<ul id="ul0003" list-style="none"><li>In the unit 12, a dialysis solution is first prepared in the usual way. When this dialysis solution leaves the unit 12, the bypass valves 38 and 42 are switched to bypass until the detector 32 displays the concentration value which is fixed therein, but which can be changed by the higher-level differentiation unit 64.</li></ul>

Once the desired dialysis solution has been prepared, it is conveyed by means of the pump 16 through the dialyzer 14 with the generation of a negative pressure, the bypass valves 38 and 42 of course being switched over. This is where the control according to the invention of the content of the dialysis solution begins. If the detector 50 outputs a signal to the evaluation unit and subsequently to the differentiating unit 64, which deviates by a certain amount compared to the signal emitted by the detector 32, that is to say a difference value is formed that controls the value fixed in the differentiating unit 64 this differentiating unit 64 turns on the control unit 36, as shown at 66, which in turn starts or stops the pump 2 * 4, depending on whether a higher or lower concentrated dialysis solution is to be produced.

The difference in the differentiating unit 64 is selected such that the difference in concentration of the sodium ions contained in the dialysing liquid upstream and downstream of the dialyzer is not more than 5 mmol / l, preferably not more than 1-2 mmol / 1 and in particular about 0 mmol / 1 . Unless a difference is found upstream and downstream of the dialyzer, the ultrafiltrate drawn off from the blood by the dialyzer 14 has practically the same electrolyte composition as the blood itself, which is essentially the goal.

In a further development of this embodiment shown in FIG. 1, the bypass valves 38 and 42 and the bypass line 40 can be used to check the detectors 32, 34, 48 and 50. The detectors 32 and 50 as well as 34 and 48 are compared with one another in that pure dialysis solution is pumped past the dialyzer 14 through line 30, line 40 and line 44. In this checking state, which is carried out regularly, for example approximately every 10-15 minutes, the respective values ​​of the detectors in the evaluation unit 60 are set to zero, so that an absolute calibration of the detectors used is unnecessary and there is only an identical concentration dependency of the detectors got to.

After calibration, ie after the bypass valves 38 and 42 have been appropriately switched over, the patient is dialyzed again. The dialysis fluid pumped out by the pump 16 is then passed into the drain. `

All detectors which can be used to determine ion concentrations in liquids are suitable as detectors 32 and 50. These include conductivity measurement, electrochemical measurement of individual ion types or the sum of all ions, spectrographic measurement, magnetic measurement and the like. The preferred detectors include the conductivity measuring cell and ion-selective electrodes.

The use of the conductivity measuring cell is known in today's dialysis machines. For example, a conductivity measuring cell is used to monitor the conductivity value to be set upstream of the dialyzer, it being used only for the purpose of monitoring a value that has been set once. Regulation of this value is at best provided in the prior art by means of the sodium modeling mentioned above, which is not based on the respective conditions which result from the electrolyte concentration in the patient and the dialyzers used. Ion-selective electrodes are also known, for example from Cammann, Working with ion-selective electrodes, 2nd ed. 1977, Springer-Verlag, Berlin, and and from D-PS 2215378, to which express reference is made as a disclosure. Such ion selective electrodes are made from an ion exchange material that is either cationic or anionic active. Such materials include, for example, quaternary ammonium groups, phosphonium ions, or sulfonium ions, which can have organic radicals, for example. Long-chain aliphatic markaptans, alkylated phenols or macrocyclic ethers, for example crown ethers, can also be used. In particular, it is possible to create membrane electrodes which respond to alkali ions and contain complexes of crown ether or analog compounds, in particular valinomycin. A.

Furthermore, divalent or polyvalent metal ions can also be determined so that practically every possible metal ion can be measured.

Other cation sensitive materials include metal chelates or ion exchange salts or ion exchange materials. Valinomycin is particularly preferred for the measurement of potassium ions, a dioxakorksäurediamidiamid for the measurement of sodium ions, likewise a dioxakorksäurediamidderivat for calcium ions, which differs from the above diamide. On the other hand, sodium ions can also be determined with a Na-selective glass, which is preferred over ion-selective electrodes on an organic basis because of its insensitivity. The pH value can also be determined with a pH-selective glass electrode, which is also commercially available and is described, for example, in D-AS 2134101, to which reference is made for reasons of disclosure.

Organic ion-selective electrodes are usually made in the form of thin membranes made of PVC material to which a plasticizer is added. Such polymeric materials and the production and addition of plasticizers are for example in DP_S 2215378, to which reference is made.

An ion-selective electrode produced in this way is connected by means of the usual lead, for example an electrolyte solution as a current key (saturated KCl solution) to a lead electrode, which in turn is connected to a commonly used measuring and amplifier device, which according to the invention is referred to as evaluation unit 60.

According to the exemplary embodiment shown in FIG. 1, detectors 32 and 50 of the same composition are preferably used, ie either conductivity measuring cells or ion-selective electrodes.

Due to the constant composition of the concentrate solution contained in the container 22, the overall composition of the dialysis fluid can be controlled via a sodium-selective electrode.

2 shows a further embodiment of the invention, the same reference numerals being used for the same parts. This embodiment in turn has a unit 12 for producing the dialysis liquid. The line 30, which is connected directly to the dialyzer to which the line 44 connects, goes off from this unit 12. The lines 30 and 44 each have a branching line 68 and 70, which unite to form a line 72. The line 68 is advantageously arranged immediately upstream and the line 70 immediately downstream of the dialyzer 14.

Since a vacuum is generated in the dialysis solution lines 30 and 44 by the pump 16, the lines .68 and 70 are shut off by shut-off devices 74 and 76 and are advantageously opened and closed alternately. In order to suck fresh or used dialysis solution into line 72, a pump 78 is provided in this line 72, which overcomes the negative pressure in lines 30 and 44. This pump 78 is followed by a storage vessel 80, in which pressure equalization takes place, for example through an opening 82 provided in the storage vessel 80. Detector 84 is provided downstream of this storage vessel, the function and structure of which correspond to the detectors 32 and 50 and which is temperature compensated by a temperature detector 86. The evaluation unit 60 with the usual control is in turn connected to these detectors 84 and 86. As can be seen from the exemplary embodiment shown in FIG. 2, this embodiment only works with one detector, which can alternately be charged with fresh or used dialysis solution, and thus manages with one detector. This embodiment is also considered to be within the scope of the invention. However, no further detector is required in the line 30 leading directly to the dialyzer 14 to continuously check the overall composition of the dialysis solution. However, this line 30 preferably has such a detector, which corresponds to the detector 32 shown in FIG. 1, in particular a conductivity measuring cell with which strong fluctuations in the dialysis solution can be determined immediately, so that the dialysis device can be interrupted.

According to this preferred embodiment, a conductivity measuring cell can therefore be provided in the line 30, while an ion-selective electrode can be considered as the detector 84, which is always calibrated with fresh dialysis solution due to the alternating operation and only the difference between the used dialysis solution conveyed by the line branch 70 in relation to the fresh dialysis solution. Such in Fig. 2nd The embodiment shown has the advantage that the dialysing devices commonly used today can be connected to an externally provided detector device, in particular an ion-selective measuring arrangement, only the hose system connected to the dialyser 14 having to have two connections which connect the lines to the lines 68 and make 70. On the other hand, a conventional conductivity measuring cell can of course also be provided as the detector 84.

The embodiments shown in FIGS. 3 and 4 are special further developments of the embodiments shown in FIGS. 1 and 2 and should therefore be considered in connection with them. For reasons of simplification, the respective device arrangements which are provided in the dialysis solution circuit are omitted.

According to the embodiment shown in FIG. 3, the blood circuit of the dialyzer 14 is connected to at least one detector which is present in the blood _Eelectrolyte ratios, conductivity measurements, the hematocrit value or the pH value can be determined.

The dialyzer 14 has an extracorporeal line 88 for supplying blood and a line 90 for removing the blood from the dialyzer 14. A line 92 branches off from line 88, in which a shut-off element 94 is provided. This is followed by a pump 96, which is advantageously designed as a hose pump. Downstream of this pump, a vent valve 98 is provided adjacent to line 92, with which the blood in line 92 is pressure-equalized. This is in turn followed in line 92 by detector 100, which corresponds in type, composition and construction to detectors 32 and 50 and which in turn can advantageously be temperature compensated by temperature detector 102.

In a further embodiment, also shown in FIG. 3, line 90 also has a branching line 104, in which, in turn, a shut-off element 106, a pump 108, a vent valve 110 and detectors 112 and 114 are arranged. The spout is connected to the latter detector.

The embodiment shown in FIG. 3 works as follows:<ul id="ul0004" list-style="none"><li>By means of the shut-off devices 94 and 106, which are opened at certain time intervals or are open continuously, only a correspondingly qerinqe amount of blood is sucked in by the pump 96. Downstream of the pump, the blood in line 92 is pressure-balanced so that the pressure-sensitive measurement with ion-selective electrodes, if these are used, is not disturbed or changed. The in the detectors 100 and 112 Measured data determined are output to the evaluation unit 60 via an electrical line 116 or 118.</li></ul>

This is followed again by the processing of the measured values ​​according to FIG. 1.

A preferred embodiment consists in that the embodiment shown in FIG. 1 or 2 is combined with the embodiment shown in FIG. 3 in such a way that only one of the measuring arrangements according to FIG. 3 which branches off either line 88 or line 90, be used.

On the other hand, the embodiment shown in FIG. 3 can also be constructed essentially in accordance with the embodiment of FIG. 2, the shut-off elements 94 and 106 corresponding to the shut-off elements 74 and 76 and the detectors 100, 102, 112 and 114 each being combined to form one detector , which corresponds to the detectors 84 * and 86. This device then operates alternately like the embodiment shown in FIG. 2, since only one of the shut-off devices is opened or is closed while the other shut-off device is closed or open.

In the embodiment shown in FIG. 4, which for reasons of simplification only has a branch 92 in the line 88, a hemofilter 122 is provided upstream of the shut-off device 94, with which the plasma is filtered off from the blood cells, so that only the plasma is measured is subjected to the detector 100. 4 corresponds to the arrangement according to FIG. 3. The embodiment according to FIG_Fig. 4 changed compared to the embodiment shown in Figure 3 in that a hemofilter 122 is arranged in the line 92 through which the blood plasma can be subjected to the desired values.

The embodiment shown in FIG. 3 allows both the measurement of the electrolytes contained in the blood and the hematocrit value, which can be measured by means of the conductivity and a measured variable with which the water withdrawal from the patient can be determined. It increases with increasing patient water deprivation and thus gives an indication of the amount that has been ultrafiltered. Furthermore, a certain increased hematocrit value, which is preferably measured by means of a conductivity measuring cell as detector 100 or 112, represents a critical point from which the so-called hypovolemic shock can be transferred to the patient when the tolerance limit of the volume withdrawal is reached . Accordingly, such an increase in hematocrit can be used to control ultrafiltration and further increase the safety of such devices.

Such a combination of the embodiments shown in FIGS. 3 and 4 with the embodiments shown in FIGS. 1 and 2 has the advantage that more than one detector. is present in the measuring system, so that the precision and thus the measuring sensitivity of the entire system are multiplied by the factor by averaging<maths id="math0001" num=""><img file="EP0097366A2_D0001.tif" /></maths> increased, where n is the number of detectors.

On the other hand, however, the embodiment shown in FIG. 3, each with a measuring arrangement at the entrance and exit of the blood from the dialyzer 14 alone, can be sufficient to fine-tune the composition of the dialyzer, i.e. a connection with the embodiments shown in FIGS. 1 and 2 may not be necessary .

In a further preferred embodiment, it has been found that, advantageously with a detector 32 and a control unit 36, which controls the pump 24 and thus the concentrate flow, the lower electrolyte composition still tolerated by the patient is initially produced and monitored, for example a dialysis fluid with a Sodium content of 135 mmol / 1. In this embodiment it is provided that from the container 22 a further line corresponding to the line 20 and a further pump corresponding to the pump 24 are arranged for fine regulation of the composition of the dialysis solution. This further pump is controlled by a unit which also corresponds to the control unit 36 ​​and the differentiating unit 64. This version has the advantage because_ß the monitoring and fine adjustment of the dialysis solution do not overlap and are separate from each other. In this case, the detector 32 can either be used alone or a further detector can be provided upstream of the dialyzer 14, which has the same or different properties as the detector 32.

The above description relates to a dialyzer which falls under the term "device for purifying blood". In this respect, of course, such an application of the invention is not only limited to dialysis, but also extends to other devices for purifying blood, for example to hemofiltration. In hemofiltration, plasma is filtered from the quasi-solid components of the blood in a hemofilter. In this case, the hemofilter used corresponds to the dialyser 14 mentioned above. In the case of hemofiltration, the substituate solution is added to the blood downstream of the hemofilter in accordance with the amount of plasma withdrawn. In this case, according to the arrangement shown in FIGS. 1 to 4, a detector at the blood inlet and a detector at the blood outlet of the hemofilter and a detector at the plasma outlet are provided in accordance with a first embodiment. The substituate is in turn added in the form of a concentrate which is used to prepare the substituate. Instead of such a concentrate, it is of course also possible to use ready-made solutions whose composition corresponds to the lower value tolerated by the patient. A fine adjustment of this composition, which is formed from a concentrate, is then carried out again, the difference between the measured values ​​at the blood inlet and the blood outlet or the absolute measured value at the plasma outlet being measured, for example. On the other hand, however, the blood input and plasma outlet can also be compared in terms of their measured values.

With such a hemofiltration arrangement, it is possible in direct operation to change and adapt the composition of the substituate solution in accordance with the conditions present during hemofiltration.

It should also be added that each of the above-described devices for purifying blood can have up to four measuring points which are connected to at least one detector. In such an embodiment, the measuring points are tapped one after the other according to a specific circuit method and in one or more _Dif reference units evaluated.

Furthermore, it should also be noted that the evaluation unit 60 and possibly the differentiating unit 64 can be used to measure the electrolyte concentrations of the untreated and treated liquids passed through the dialyzer. For example, the electrolyte concentration at the input and at the output of the dialyzer 14 can be measured directly and the difference between these values ​​can be determined and displayed integrally, both differentially and over a certain period of time. According to this embodiment, there is therefore no change in the composition of the dialysis solution by appropriate control of the unit 12 for generating the _Danalysis solution provided.

This embodiment is thus a pure measuring device for measuring and for the differential and / or integral display of the electrolyte balance, in particular the sodium balance.