DIALYSIS APPARATUS HAVING AN APPARATUS FOR DETERMINING AT LEAST TWO HEMODIALYSIS PARAMETERS

Abstract

The invention relates to a dialysis device comprising a device for determining at least one first and second haemodialysis parameter, and a method for determining at least one first and second haemodialysis parameter during a dialysis treatment with a dialysis device. The device 20 for determining at least one first and second haemodialysis parameter comprises a device 21 for generating a change in a physical or chemical parameter of the dialysis fluid in the dialysis fluid system 6 in the form of a bolus, and a device 22 for detecting a change over time in the physical or chemical parameter of the dialysis fluid in the dialysis fluid system 6. Furthermore, the dialysis device has a computing and evaluating unit 23 that is configured such that, on the basis of the change in the physical or chemical parameter in the form of a bolus, for at least one dialysis condition at least one value for the clearance of the dialysis treatment is determined, and, on the basis of at least one value for the clearance, a first and second haemodialysis parameter is determined. The dialysis device according to the invention and the method according to the invention are characterised in that boluses of different sizes, in particular boluses having different area contents, are administered to determine the haemodialysis parameter.

Claims

1. A dialysis device configured for connecting a dialyser that is divided by a semipermeable membrane into a first compartment, which is part of an extracorporeal blood circuit, and a second compartment, which is part of a dialysis fluid system of the dialysis machine, comprising a device for determining at least one first and second haemodialysis parameter, the device for determining a haemodialysis parameter comprising: a device for generating a change over time in a physical or chemical parameter of a dialysis fluid in a dialysis fluid feed line to the dialyser in the dialysis fluid system in the form of a bolus, a device for detecting a change over time in the physical or chemical characteristic of the dialysis fluid attributable to the bolus in a dialysis liquid discharge line from the dialyser in the dialysis fluid system, a computing and evaluating unit cooperating with the device for generating a change over time in a physical or chemical parameter and the device for detecting a change over time in a physical or chemical parameter that is configured such that, on the basis of a change in the physical or chemical parameter, at least one value for the clearance of the dialysis treatment is determined, and, on the basis of the at least one value for the clearance, at least one haemodialysis parameter is determined, wherein the device for generating a change in a physical or chemical parameter is designed such that, to determine a first haemodialysis parameter, at least one bolus for determining the first haemodialysis parameter is generated having a first size, the computing and evaluating unit being configured such that, on the basis of the change in the physical or chemical parameter in the form of at least one bolus for determining the first haemodialysis parameter, at least one value for the clearance of the dialysis treatment is determined, on the basis of which value or values the first haemodialysis parameter is determined, and in that, to determine a second haemodialysis parameter, at least one bolus for determining the second haemodialysis parameter is generated having a second size, the computing and evaluating unit being configured such that, on the basis of the change in the physical or chemical parameter in the form of at least one bolus for determining the second haemodialysis parameter, at least one value for the clearance of the dialysis treatment is determined, on the basis of which value or values the second haemodialysis parameter is determined, the first size being larger than the second size or the distance between the first sizeand a reference value being greater than the distance between the second size and a reference value.

2. The dialysis device according to claim 1, wherein the at least one bolus for determining the first haemodialysis parameter is characterised by a first area, and the at least one bolus for determining the second haemodialysis parameter is characterised by a second area, the first area content of the first area being greater than the second area content of the second area.

3. The dialysis device according to claim 1, wherein the first haemodialysis parameter is a blood flow in the vascular access or a recirculation flow in a vascular system.

4. The dialysis device according to claim 3, wherein the dialysis device is configured for connection to an extracorporeal blood circuit that comprises a first bloodline and a second bloodline that is to be connected to an inlet or outlet of the first compartment of the dialyser and in that for determining the blood flow in the vascular access, the device for generating a change in a physical or chemical parameter is designed such that, for a first dialysis condition, a first bolus having the first area contentand, for a second dialysis condition, a second bolus having the first area content is generated, the computing and evaluating unit being configured such that, on the basis of the change in the physical or chemical parameter in the form of the first bolus having the first area content under the first dialysis condition, a first value for the clearance is determined and, on the basis of the change in the physical or chemical parameter in the form of the second bolus under the second dialysis condition, a second value for the clearance is determined, on the basis of which values the blood flow in the vascular access is determined, or to determine the blood flow in the vascular access, the device for generating a change in a physical or chemical parameter is designed such that a bolus having the first area content is generated for a second dialysis condition, the computing and evaluation unit being configured such that, on the basis of an estimate of the clearance for the first dialysis condition, a first value for the clearance is determined and, on the basis of the change in the physical or chemical parameter in the form of the bolus having the first area content under the second dialysis condition, a second value for clearance is determined, on the basis of which values the blood flow in the vascular access is determined, wherein, under the first dialysis condition, the first bloodline conveys blood from a downstream portion of a vascular access of the patient and the second bloodline conveys blood towards an upstream portion of the vascular access and, under the second dialysis condition, the first bloodline conveys blood from an upstream part of the vascular access and the second bloodline conveys blood towards a downstream portion of the vascular access.

5. The dialysis device according to claim 1, wherein the second haemodialysis parameter is the dialysis dose Kt/V, K being the clearance, t the dialysis time and V the urea distribution volume.

6. The dialysis device according to claim 5, wherein for determining the dialysis dose Kt/V, the device for generating a change in a physical or chemical parameter is designed such that a bolus is generated having the second area content, the computing and evaluating unit be configured such that, on the basis of the change in the physical or chemical parameter in the form of the bolus having the second area content, a value for the clearance is determined, on the basis of which value the dialysis dose Kt/V is determined.

7. The dialysis apparatus according to claim 1, wherein a controlling and computing unit cooperating with the device for generating a change in a physical or chemical parameter and the device for detecting a change over time in a physical or chemical parameter is provided, which controlling and computing unit is configured such that the generation and detection of the change in the physical or chemical parameter is started during the blood treatment to determine the first or second haemodialysis parameter.

8. The dialysis machine according to claim 7, wherein the controlling and computing unit is configured such that, to determine the first haemodialysis parameter, the generation and detection of the change in the physical or chemical parameter is started only once or only twice during the blood treatment and/or in that, to determine the second haemodialysis parameter, the generation and detection of the change in the physical or chemical parameter is started multiple times during the blood treatment.

9. The dialysis apparatus according to claim 4, wherein, to determine the first haemodialysis parameter, the device for generating a change in a physical or chemical parameter is designed such that the substance concentration of a substance in the dialysis fluid, is increased to determine the first and second values of the clearance under the first and second dialysis conditions or the value of the clearance under the second dialysis condition or decreased to determine the first and second values of the clearance under the first and second dialysis conditions or the value of the clearance under the second dialysis condition and/or to determine the second haemodialysis parameter, the device for generating a change in a physical or chemical parameter is designed such that the substance concentration of a substance in the dialysis fluid, is increased for a previous measurement and decreased for a subsequent measurement or decreased for a previous measurement and increased for a subsequent measurement.

10. A dialysis system comprising the dialysis device according to claim 1, and comprising a dialyser that is divided by a semipermeable membrane into a first compartment, which is part of an extracorporeal blood circuit, and a second compartment, which is part of a dialysis fluid system of the dialysis apparatus, and comprising an extracorporeal blood circuit that comprises a first bloodline and a second bloodline that is connected to an inlet or outlet of the first compartment of the dialyser.

11. A method for determining at least one first and second haemodialysis parameter during a dialysis treatment with a dialysis device comprising the following method steps: Generating at least one change over time in a physical or chemical parameter of a dialysis fluid in a dialysis fluid feed line to a dialyser in a dialysis fluid system in the form of a bolus, Detecting at least one change over time in the physical or chemical parameter of the dialysis fluid attributable to the at least one bolus in a dialysis fluid discharge line from the dialyser in the dialysis fluid system, Determining at least one value for the clearance of the dialysis treatment on the basis of the at least one change in the physical or chemical parameter in the form of a bolus, and determining at least one haemodialysis parameter on the basis of the at least one value for the clearance, wherein, to determine a first haemodialysis parameter, at least one bolus for determining the first haemodialysis parameter is generated having a first size, at least one value for the clearance of the dialysis treatment being determined on the basis of the change in the physical or chemical parameter in the form of at least one bolus for determining the first haemodialysis parameter, on the basis of which value the first haemodialysis parameter is determined, and in that, to determine a second haemodialysis parameter, at least one bolus for determining the second haemodialysis parameter is generated having a second size, at least one value for the clearance of the dialysis treatment being determined on the basis of the change in the physical or chemical parameter in the form of at least one bolus for determining the second haemodialysis parameter, on the basis of which value the second haemodialysis parameter is determined, the first size being larger than the second size or the distance between the first size and a reference value being greater than the distance between the second size and a reference value.

12. The method according to claim 11, wherein the at least one bolus for determining the first haemodialysis parameter is characterised by a first area and the at least one bolus for determining the second haemodialysis parameter is characterised by a second area, the first area content of the first area being greater than the second area content of the second area.

13. The method according to claim 11, wherein the first haemodialysis parameter is a blood flow in the vascular access or a recirculation flow in a vascular system.

14. The method according to claim 13, wherein, to determine the blood flow in the vascular access, a first bolus having the first area content is generated for a first dialysis condition and a second bolus having the first area content is generated for a second dialysis condition, a first value for the clearance being determined on the basis of the change in the physical or chemical parameter in the form of the first bolus having the first area content under the first dialysis condition and a second value for the clearance being determined on the basis of the change in the physical or chemical parameter in the form of the second bolus under the second dialysis condition, on the basis of which values the blood flow in the vascular access is determined, or to determine the blood flow in the vascular access for a second dialysis condition, a bolus having the first area content is generated, a first value for the clearance being determined on the basis of an estimate of the clearance for the first dialysis condition and a second value for the clearance being determined on the basis of the change in the physical or chemical parameter in the form of the bolus having the first area content under the second dialysis condition, on the basis of which values the blood flow in the vascular access is determined, wherein, under the first dialysis condition, the first bloodline conveys blood from a downstream portion of a patient’s vascular access and the second bloodline conveys blood towards an upstream portion of the vascular access and, under the second dialysis condition, the first bloodline conveys blood from an upstream portion of the vascular access and the second bloodline conveys blood towards a downstream portion of the vascular access.

15. The method according to claim 12, wherein the second haemodialysis parameter is the dialysis dose Kt/V, where K is the clearance, t is the dialysis time and V is the urea distribution volume, and in that, to determine the dialysis dose Kt/V, a bolus having the second area content is generated, a value for the clearance being determined on the basis of the change in the physical or chemical parameter in the form of the bolus having the second area content, on the basis of which value the dialysis dose Kt/V is determined.

16. A computer program product that comprises commands that, when the program is executed by a computer, cause the computer to carry out a method according to claim 11 for determining at least one first and second haemodialysis parameter during a dialysis treatment with a dialysis device.

17. The dialysis apparatus according to claim 4, wherein, to determine the first haemodialysis parameter, the device for generating a change in a physical or chemical parameter is designed such that the substance concentration of a substance in the dialysis fluid, that is a Na concentration, is increased to determine the first and second values of the clearance under the first and second dialysis conditions or the value of the clearance under the second dialysis condition or decreased to determine the first and second values of the clearance under the first and second dialysis conditions or the value of the clearance under the second dialysis condition and/or to determine the second haemodialysis parameter, the device for generating a change in a physical or chemical parameter is designed such that the substance concentration of a substance in the dialysis fluid, that is a Na concentration, is increased for a previous measurement and decreased for a subsequent measurement or decreased for a previous measurement and increased for a subsequent measurement.

Description

[0084] In the following, an embodiment of the invention will be described in detail making reference to the drawings.

[0085] In which:

[0086] FIG. 1 is a simplified schematic view of an embodiment of the dialysis device according to the invention,

[0087] FIG. 2A shows the device for specifying a dialysis condition of the dialysis device, a first dialysis condition being specified,

[0088] FIG. 2B shows the device for specifying a dialysis condition of the dialysis device, a second dialysis condition being specified,

[0089] FIG. 3 shows the change over time in the physical or chemical parameter of the dialysis fluid at the inlet and outlet of the dialyser,

[0090] FIG. 4 shows the first and second change over time in the physical or chemical parameter of the dialysis fluid at the inlet of the dialyser for determining a first haemodialysis parameter, a positive bolus being administered,

[0091] FIG. 5 shows the change over time in the physical or chemical parameter of the dialysis fluid at the inlet of the dialyser for determining a second haemodialysis parameter,

[0092] FIG. 6 shows the first and second changes over time in the physical or chemical parameter of the dialysis fluid at the inlet of the dialyser for determining a first haemodialysis parameter, a negative bolus being administered,

[0093] FIG. 7 shows a sequence of positive and negative boluses for continuously determining the second haemodialysis parameter during the blood treatment,

[0094] FIG. 8 shows the conductivity of the dialysis liquid measured in an experiment upstream and downstream of the dialyser.

[0095] FIG. 9 shows a flow chart to illustrate the determination of a first dialysis parameter on the basis of a first and second measurement of a first and second clearance value under a first and second dialysis condition,

[0096] FIG. 10 shows a flow chart to illustrate the determination of a first dialysis parameter on the basis of an estimate of a first clearance value and a measurement of a second clearance value under a first and second dialysis condition.

[0097] FIG. 1 is a simplified schematic representation of the components of an embodiment of the dialysis device according to the invention that are essential to the description of the invention. Because the measurement methods for determining the haemodialysis parameters as such are known from the prior art, only those aspects of the method that are essential to the invention are described.

[0098] While operating, the dialysis device is connected to a dialyser and an extracorporeal blood tubing system. The dialysis device is programmed to be able to carry out the method according to the invention to determine the dialysis parameters if it is connected both to a dialyser and an extracorporeal blood tubing system and to a patient.

[0099] The dialysis device according to the invention may be equipped with a dialyser 1 that is divided by a semi-permeable membrane 2 into a first compartment 3 and a second compartment 4. The first compartment 3 of the dialyser 1 is part of an extracorporeal blood circuit 5 shown in dotted lines in FIG. 1, and the second compartment 4 of the dialyser 1 is part of a dialysis fluid system 6 shown in dotted lines.

[0100] The extracorporeal blood circuit 5 comprises a first bloodline 7, at one end of which a first cannula 8 is connected, and a second bloodline 9, at the one end of which a second cannula 10 is connected. The first cannula 8 is connected to a downstream portion 11 of a patient’s vascular access 12, and the second cannula 10 is connected to an upstream portion 13 of the patient’s vascular access 12. The direction of the blood flow in the vascular access is designated by an arrow. The other end of the first bloodline 7 is connected to an inlet 3a of the first compartment 3 and the other end of the second bloodline 9 is connected to an outlet 3b of the first compartment 3 such that the patient’s blood flows from the downstream portion 11 of the vascular access into the first compartment 3 and flows from the first compartment 3 into the upstream portion 13 of the vessel access 12. The blood is conveyed in the extracorporeal blood circuit 5 using a blood pump 14.

[0101] The dialysis device can have a device 15 for specifying a first and a second dialysis condition that is shown in a highly simplified manner in FIGS. 1A and 1B. The device 15 for specifying a dialysis condition is designed such that a first dialysis condition can be specified under which the first bloodline 7 conveys blood from the downstream portion 11 of the vascular access 12 and the second bloodline 8 conveys blood towards the upstream portion 13 of the vascular access 12 and a second dialysis condition can be specified under which the first bloodline 7 conveys blood from the upstream portion 13 of the vascular access 12 and the second bloodline 9 conveys blood towards the downstream portion 11 of the vascular access 12. FIG. 2A shows the direction of blood flow under the first dialysis condition, and FIG. 2B shows the direction of blood flow under the second dialysis condition. The blood flow is reversed in the line portions on the vascular side.

[0102] The device 15 for specifying a dialysis condition may comprise an automatically operable arrangement of valves that allow portions of the bloodlines on the device side and on the patient side to be swapped, as shown in dotted lines in FIGS. 1A and 1B.

[0103] The device 15 may also be a manually operable device that is not connected to the dialysis device, in particular a control device of the dialysis device. The dialysis device may have an input device with which the medical personnel can input which dialysis condition is to be present. The input device can also indicate which dialysis condition was specified or that the dialysis condition was changed, for example from a first dialysis condition to a second dialysis condition. An example of such a device is the so-called Twister® from Fresenius Medical Care Deutschland GmbH.

[0104] The dialysis fluid is provided using a device 16 for providing dialysis fluid, to which a dialysis fluid feed line 17 is connected, which dialysis fluid feed line leads to an inlet 4a of the second compartment 4 of the dialyser 2. A dialysis fluid discharge line 18 is connected to the outlet 4b of the second compartment 4, which leads to a drain that is not shown. The dialysis fluid is conveyed through the second compartment 4 of the dialyser 1 in the dialysis fluid system 6 by means of a dialysis fluid pump 19.

[0105] The dialysis device has a device 20 for determining a first haemodialysis parameter and a second haemodialysis parameter. In the present embodiment, the first haemodialysis parameter is the dialysis dose Kt/V and the second haemodialysis parameter is the blood flow in the vascular access Qa (blood access flow).

[0106] The device 20 for determining haemodialysis parameters comprises a device 21 for generating a change over time in a physical or chemical parameter of the dialysis fluid in the dialysis fluid system 6 in the dialysis fluid feed line 17 upstream of the second compartment 4 and a device 22 for detecting the change over time in the parameter in the dialysis fluid discharge line 18 downstream of the second compartment 4 attributable to the change over time in the parameter upstream of the dialyser. Furthermore, the parameter can also be recorded in the dialysis fluid feed line 17 upstream of the second compartment 4 of the dialyser 1.

[0107] The change over time in the parameter upstream of the dialyser 1 is also referred to below as the input bolus and the change over time in the parameter downstream of the dialyser is referred to as the output bolus. The output bolus is the system’s response to the input bolus.

[0108] In the present embodiment, the physical or chemical parameter is the concentration c of a substance in the dialysis liquid, in particular the Na concentration, that is changed upstream of the dialyser 1, i.e., increased or decreased for a predetermined time interval. In the present embodiment, the device 21 for generating a change over time in a physical or chemical parameter is a component of the device 16 for providing the dialysis fluid, which allows the Na concentration of the dialysate to be changed for a predetermined time interval.

[0109] In the present embodiment, the device 22 for detecting the physical or chemical parameter has a conductivity sensor 22A that measures the conductivity of the dialysis fluid in the dialysis fluid discharge line 18 as a variable correlating with the Na concentration. The device 22 for detecting the physical or chemical parameter may have a further conductivity sensor 22B that measures the conductivity of the dialysis fluid in the dialysis fluid feed line 17. If the form of the input bolus is known, the conductivity sensor 22B in the dialysis fluid feed line 17 is not needed. Otherwise, the conductivity in the dialysis fluid feed line 17 can be measured using the conductivity sensor 22B.

[0110] FIG. 3 shows the input bolus and output bolus. The bolus in the present embodiment is characterised by the area content of the area, which is between the graph of a function describing the change over time in the physical or chemical parameter, for example the Na concentration c(t) or the conductivity, and the graph of a reference function. The area content is a measure of the size of the bolus, i.e., a larger bolus has a larger area content than a smaller bolus. The reference function may be a linear function: f(t) = mt+B, where m is the slope of the function and B is a predetermined base value. The slope is 1 in the present embodiment. The base value B may be the Na concentration (conductivity) of the blood before the bolus is administered. The area content of the input and output bolus can be determined by calculating the integral in a given integration interval.

[0111] Alternatively or in combination, other variables may also be used to characterise the bolus and thus to determine the haemodialysis parameters. An alternative characteristic variable for the bolus may be the amplitude and duration of the bolus. The area content can be estimated from the amplitude and duration. The amplitude and duration of the bolus alone can be meaningful variables if a relationship between the size and duration of a bolus is known.

[0112] The determination of haemodialysis parameters based on the area content of the bolus is described below. The other variables can be used in a comparable manner.

[0113] The dialysis device has a computing and evaluating unit 23 that cooperates with the device 21 for generating a change in a physical or chemical parameter and the device 22 for recording the parameter, which computing and evaluating unit may be part of a central computing and controlling unit 24 of the dialysis device. The central computing and controlling unit 24 is connected via control and signal lines S.sub.1 to S.sub.6 to the dialysis fluid pump 19, the blood pump 14, the device 15 for specifying the dialysis condition, the device 21 for generating a change in a physical or chemical parameter (input bolus) and the conductivity sensors 22A and 22B of the device 22 for detecting the parameter (output bolus). The computing and controlling unit 24 is configured such that the individual components of the dialysis device are controlled during the dialysis treatment such that the method steps described below for determining the haemodialysis parameters are carried out.

[0114] The individual method steps of a first embodiment for determining a first dialysis parameter are shown in FIG. 9.

[0115] The computing and controlling unit 24 may have, for example, a general processor, a digital signal processor (DSP) for continuously processing digital signals, a microprocessor, an application-specific integrated circuit (ASIC), an integrated circuit consisting of logic elements (FPGA) or other integrated circuits (IC) or hardware components to perform the individual method steps for controlling the blood treatment device. A data processing program (software) may run on the hardware components in order to carry out the method steps.

[0116] In addition, an input unit 25 is provided that is connected to the computing and controlling unit 24 via a signal line S.sub.7. Using the input unit 25, the medical personnel can make inputs relating to the determination of the haemodialysis parameters. The input unit 25 may have a keyboard. A display unit 26 is provided for displaying the haemodialysis parameters. The input and display unit may also be designed as a touch-sensitive screen 27 (touchscreen).

[0117] At the beginning of the dialysis treatment or after a predetermined time interval has elapsed or after a button 25A has been pressed on the touchscreen 27 by the medical personnel, the blood flow in the vascular access Qa (blood access flow) is determined (step 101).

[0118] The device 15 for specifying the dialysis condition specifies the first dialysis condition (FIG. 2A) in order to determine a first value for the clearance (dialysance) (step 102). The device 21 for generating a change in a physical or chemical parameter then generates an input bolus I having a predetermined area content ΔM.sub.1 (step 103) (FIG. 3). The device 22 for detecting a physical or chemical parameter then detects the input bolus I having the area content ΔM.sub.1 upstream of the dialyser 1 and the output bolus II having the area content ΔM.sub.2 downstream of the dialyser by measuring the conductivity of the dialysis fluid using the conductivity sensors 22A and 22B upstream and downstream of the dialyser 1. The measured values are stored in a memory 23A of the computing and evaluating unit 23 (step 104).

[0119] The amount of substance ΔM1 that is fed upstream of the dialyser and the amount of substance ΔM2 that is discharged downstream of the dialyser are calculated as follows:

[00005]$\Delta \text{M1=Qd*}\int \text{dcDi*dt}$

[00006]$\Delta \text{M2=Qd*}\int \text{dcDo*dt}$

where Qd is the dialysis fluid flow, cDi is the dialysate concentration at the inlet and cDo is the dialysate concentration at the outlet of the second compartment 4 of the dialyser 1 and t is the time.

[0120] The computing and evaluating unit 24 can calculate a first value for the dialysance D according to the following equation (step 105):

[00007]$\text{D=Qd*}\left(\Delta \text{Mi-}\Delta \text{Mo}\right)\text{/}\Delta \text{Mi}$

[0121] To determine the dialysance, more complex equations can be used that take other parameters into account, such as the ultrafiltration rate (Qf) and/or substituate rate (Qs). These equations for determining dialysance have been known for a long time and are described in the specialist literature. A more complex equation of this kind may look as follows, for example: D= (Qd+Qs+Qf)*(1- ΔM2/ΔM1) and is included as embodiments in equation (3).

[0122] The dialysis fluid flow Qd is predetermined by the dialysis fluid pump 19, which is controlled by the controlling and computing unit 24 with the corresponding flow rate.

[0123] After the first value for the dialysance has been determined, the device 21 for specifying the dialysis condition specifies the second dialysis condition (step 106) (FIG. 2B) in order to be able to determine a second value for the clearance (dialysance). The device 21 for generating a change in a physical or chemical parameter then generates an input bolus having a predetermined area content (step 107). The second input bolus preferably has the same or at least approximately the same area content as the first input bolus. The conductivity sensor 22A upstream of the dialyser 1 then detects the input bolus and the conductivity meter 22B downstream of the dialyser detects the output bolus (step 108).

[0124] As already stated above, the dialysis device may also be programmed such that the input boluses are not measured directly, but can also be calculated over time when the amount of sodium added is known. The same applies if the flows and the behaviour of the dialysis fluid in the dialysis fluid system is known for other variables characterising the input boluses.

[0125] After ΔMI and ΔM2 are calculated according to equation (1) or equation (2), the computing and evaluating unit calculates the second value D′ for the dialysance according to equation (3) (step 109).

[0126] The computing and evaluating unit now calculates the blood flow in the vascular access Qa according to the following equation (step 110):

[00008]$\text{Qa= D*D′ /}\left(\text{D}-\text{D′}\right),$

where D is the first value of the dialysance and D′ is the second value of the dialysance.

[0127] More complex equations can also be used that take other parameters into account, such as the ultrafiltration rate (Qf) and/or blood water flow (bwf). These equations for determining dialysance have been known for a long time and are described in the specialist literature. A more complex equation of this kind may look as follows, for example: Qa = 1/bwf * (D-Qf)*D′/(D-D′) and is included as embodiments in equation (3).

[0128] The blood flow in the vascular access Qa is displayed on the display unit 26 (step 11).

[0129] FIG. 4 shows the input bolus for the first and second clearance measurements. The area content is designated as A in FIG. 4 and the base value is designated as B. The device 21 for generating the input bolus increases the substance concentration of the dialysis fluid cD, in particular the Na concentration, from the basic value B to a maximum value MAX, i.e., the blood flow in the vascular access Qa is determined with two positive boluses that are characterised by the same area content A.

[0130] FIG. 6 shows an alternative embodiment having a negative input bolus for the first clearance measurement and a negative input bolus for the second clearance measurement. In FIG. 6, the area content is once again labelled A and the base value B. The device 21 for generating the input bolus reduces the substance concentration of the dialysis fluid cD, in particular the Na concentration, from the basic value B to a minimum value MIN, i.e., the blood flow in the vascular access Qa is determined with two negative boluses that are characterised by the same area content A.

[0131] Before the clearance measurements for determining the first haemodialysis parameter are carried out, the dialysis fluid flow and/or the blood flow may be increased to a predetermined value by the computing and controlling unit 24 increasing the speed of the dialysis fluid pump 19 or the blood pump 14. After the clearance measurement, the dialysis fluid flow and/or the blood flow can again be reduced to the previously set value.

[0132] After the clearance measurements, the computing and controlling unit 24 can also specify an operating mode for determining the first haemodialysis parameter, which operating mode causes a reduction in the concentration of the substance administered, in particular the salt added. Measures for reducing the salt content in the dialysate over a predetermined period of time or with a predetermined profile are described, for example, in DE 3 223 051 A1.

[0133] The method for clearance measurement as such is described in EP 0 911 043 B1, and the method for determining the blood flow Qa (blood access flow) in the vascular access on the basis of two successive clearance measurements as such is described in detail in EP 0 928 614 B1.

[0134] The above-described determination of the blood flow in the vascular access is carried out automatically only once during the dialysis treatment or after the button 25A is pressed by the medical personnel.

[0135] The dialysis device according to the invention not only provides for the determination of the blood flow in the vascular access, but also the determination of the dialysis dose kt/V during the dialysis treatment.

[0136] During the dialysis treatment, the device 21 for generating a physical or chemical property generates an input bolus, preferably under the first dialysis condition, by increasing or decreasing the Na concentration of the dialysis liquid based on the basic value B.

[0137] FIG. 5 shows an input bolus A′, the Na concentration being increased. The device 22 for detecting a physical or chemical parameter then detects the input bolus upstream of the dialyser 1 and the output bolus downstream of the dialyser by measuring the conductivity of the dialysis fluid using the conductivity sensors 22A, 22B upstream and downstream of the dialyser 11. The measured values are stored in the memory 23A of the computing and evaluating unit 23, and the dialysance D (clearance K) is calculated according to equation (3). After the dialysance D (clearance K) has been determined, the computing and evaluating unit 23 calculates the dialysis dose Kt/V, which is displayed by the display unit 26.

[0138] While the first haemodialysis parameter (blood access flow) is only determined on the basis of an input bolus that has the area content A, the second haemodialysis parameter (dialysis dose) is only determined on the basis of an input bolus that has the area content A′, the area content A being at least 2.5 times as large, in particular at least 2.7 times, in particular at least 3 times as large as the area content A′ (FIG. 4, FIG. 5).

[0139] The quotient between the area content A and A′ of the input bolus for determining the first and second haemodialysis parameters can be determined as a function of the signal-to-noise ratio. The quotient can be calculated using an algorithm as a function of the signal-to-noise ratio, or the corresponding values can be stored in the memory 23A of the computing and evaluating unit 23. The memory 23A can also store values that specify a specific pulse shape and/or pulse duration for the input bolus.

[0140] While the blood flow in the vascular access Qa is determined with a relatively large bolus, the dialysis dose Kt/V is determined with a relatively small bolus. Based on the large bolus, the blood flow in the vascular access can be determined with a high degree of accuracy. In general, a one-time determination of the blood flow in the vascular access is sufficient, preferably at the beginning of the dialysis treatment. In contrast, the dialysis dose is preferably determined multiple times during the dialysis treatment.

[0141] FIG. 7 shows a sequence of input boluses for determining the dialysis dose. A positive bolus for a previous measurement is followed by a negative bolus for a subsequent measurement, a positive Na bolus being associated with an increase in the Na concentration and a negative Na bolus being associated with a decrease in the Na concentration.

[0142] Other sequences can alternatively or additionally be programmed. In the case of an alternating sequence between positive and negative boluses, every second bolus may be directed upwards, and in the case of a sequence of positive boluses, all boluses may be directed to values greater than the baseline. The dialysis machine is preferably controlled according to alternating boluses or solely with positive boluses. FIGS. 3 to 7 are for illustrative purposes only.

[0143] FIG. 8 shows the conductivity measured in an experiment upstream and downstream of the dialyser as a function of time t. The measured conductivity correlates with the concentration of the substance (Na concentration) in the dialysis fluid. In FIG. 8, the substance concentration (conductivity) upstream of the dialyser 1 (input bolus) is denoted by cdi and the substance concentration (conductivity) downstream of the dialyser (output bolus) is denoted by cdo.

[0144] Upper and lower limits that are not exceeded or fallen short of when generating a positive or negative bolus can be specified for the conductivity. The limits can be specified such that there is no burden on the patient.

[0145] In the embodiment described above, the first clearance value is determined on the basis of the change in a physical or chemical property of the dialysis fluid. An alternative embodiment for determining the blood flow in the vascular access Qa provides for the estimation of the first clearance value D instead of the measurement. FIG. 10 shows the individual method steps of the alternative embodiment. Method steps 100 and 101, and 103 to 108 correspond to method steps 100, 101, and 105 to 110 of the first embodiment (FIG. 9). In this regard, reference is made to the description of the first embodiment for determining the first clearance value. Instead of method steps 102, 103 and 104 of the first embodiment, the first clearance value D is estimated in the second embodiment (step 102). The computing and evaluating unit 23 can determine an estimated value for the first clearance value according to the method described in EP 1 698 360 B1 or calculate said value according to the equations published in Sargent, A. & Gotch, F., ‘Principles and biophysics of Dialysis’ in ‘Replacement of renewal function by dialysis’, 4th ED.

[0146] A second aspect of the invention provides that the distance between the first size (A) of the first bolus and a reference value is greater than the distance between the second size (A′) of the second bolus and a reference value. According to the second aspect, a reference value is defined, the size of the at least one bolus for determining the first haemodialysis parameter and the size of the at least one bolus for determining the second haemodialysis parameter being related to the reference value. In the present embodiment, this reference value is the noise in the system, the distance from the reference value being the signal-to-noise ratio. For an accurate measurement, the largest possible signal-to-noise ratio is sought, which increases with the size of the bolus, but which also increases the burden on the patient. The individual method steps of the second aspect of the invention correspond to those of the first aspect, the dialysis device for determining the first haemodialysis parameter, in particular the blood flow in the vascular access Qa, specifying a bolus that has a greater signal-to-noise ratio than the bolus for determining the second haemodialysis parameter, in particular the dialysis dose.