Device for identifying the direction of liquid flow through a dialyser

Abstract

The invention relates to a device and a method for detecting the direction of fluid flow through a dialyser 1 which comprises a blood chamber 4, through which blood flows, and a dialysate chamber 3, through which dialysate flows, which are separated from one another by a semi-permeable membrane 2. In addition, the invention relates to an extracorporeal blood treatment device comprising a device for detecting the flow direction. A first aspect of the invention is to measure the clearance in order to detect the flow direction and to compare the measured clearance with a specified limit value, a flow direction in countercurrent flow being concluded if the clearance is greater than the specified limit value. This aspect is based on the finding that in the case of blood treatment in practice with operation of the dialyser in co-current flow, clearance values above a certain limit value can no longer be achieved. A second aspect of the invention is to measure the clearance to detect the flow direction and to change the flow rate of the dialysate. Checking the flow direction according to the second aspect is based on the comparison of the measured change in clearance with a calculated expected value of the change in clearance for operation of the dialyser in both countercurrent flow and co-current flow. The invention according to the second aspect is based on the finding that the amount of the relative change in clearance in the event of a change in dialysate rate is always greater in the case of operation in co-current flow than in countercurrent flow.

Claims

1. A device for detecting the direction of fluid flow through a dialyzer, the device comprising a dialyzer that comprises a blood chamber, through which blood flows at blood flow rate Q.sub.bw, and a dialysate chamber, through which dialysate flows at an initial dialysate flow rate Q.sub.d,0, the blood chamber and the dialysate chamber being separated from one another by a semi-permeable membrane, a control unit for changing the flow rate of the dialysate through the dialysate chamber of the dialyzer from the initial dialysate flow rate to a second dialysate flow rate, Q.sub.d,0+Q.sub.d, selected by a user while maintaining the blood flow rate Q.sub.bw unchanged, a measuring unit that measures clearance at any dialysate flow rate, the measuring unit comprising: i) at least one conductivity sensor in a dialysate flow path upstream of the dialyzer, which measures a first conductivity of the dialysate, the dialysate having a first concentration of a substance, the first conductivity measured before the dialysate enters the dialyzer, and ii) at least one conductivity sensor in a dialysate flow path downstream of the dialyzer, which measures a second conductivity of the dialysate, the dialysate downstream of the dialyzer having a second concentration of the substance, the device being configured to measure the second conductivity after the dialysate leaves the dialyzer, the measuring unit being configured to calculate: i) a first clearance value, K.sub.diff,1, based on a difference between the first conductivity and the second conductivity measured at the initial dialysate flow rate Q.sub.d,0; and ii) a second clearance value K.sub.diff,2, based on a difference between the first conductivity and the second conductivity measured at the second dialysate flow rate Q.sub.d,0+Q.sub.d, and an arithmetic and evaluation unit, comprising a microprocessor and a memory, the arithmetic and evaluation unit: i) calculating a change in clearance values, K.sub.diff1, by subtracting the first clearance value K.sub.diff,1 from the second clearance value K.sub.diff,2; ii) calculating a countercurrent mass transfer coefficient, k.sub.oA.sub. based on K.sub.diff,1, Q.sub.d,0, and Q.sub.bw; iii) calculating a co-current mass transfer coefficient, k.sub.oA.sub. based on K.sub.diff,1, Q.sub.d,0, and Q.sub.bw; iv) calculating a first expected change in a clearance value, {acute over (K)}.sub.diff1, when the dialysate and blood flow are in countercurrent flow; v) calculating a second expected change in clearance value, {acute over (K)}.sub.diff2, when the dialysate and blood flow are in co-current flow; and vi) comparing K.sub.diff1 to each of {acute over (K)}.sub.diff1 and {acute over (K)}.sub.diff2, where if K.sub.diff1 is Closer to {acute over (K)}.sub.diff1 than {acute over (K)}.sub.diff2, the arithmetic and evaluation unit determines that the dialysate flow and blood flow are in countercurrent flow, but if K.sub.diff1 is closer to {acute over (K)}.sub.diff2 than {acute over (K)}.sub.diff1, the arithmetic and evaluation unit determines that the dialysate flow and blood flow are in co-current flow, wherein arithmetic and evaluation unit is configured to generate a control signal indicating co-current flow or countercurrent flow, and wherein the device further comprises a display unit, the display unit being configured to receive the control signal and, based on the control signal, display whether the operation of the dialyzer is in co-current flow or countercurrent flow.

2. The device according to claim 1, wherein the arithmetic and evaluation unit is configured to calculate the countercurrent mass transfer coefficient k.sub.0A.sub. based on K.sub.diff,1, Q.sub.d,0, and Q.sub.bw, by using a first equation, the first equation being $k_0{A}_{}=\frac{Q_{\mathrm{bw}}{Q}_{d,0}}{Q_{d,0}-Q_b}\ln \left(\frac{\frac{K_{\mathrm{diff},1}}{Q_{d,0}}-1}{\frac{K_{\mathrm{diff},1}}{Q_{\mathrm{bw}}}-1}\right).$

3. The device according to claim 1, wherein the arithmetic and evaluation unit is configured to calculate the co-current mass transfer coefficient k.sub.0A.sub. based on K.sub.diff,1, Q.sub.d,0, and Q.sub.bw, by using a second equation, the second equation being ${\left(k_{0}A\right)}_{}=-\frac{Q_{\mathrm{bw}}{Q}_{d,0}}{Q_{d,0}+Q_{\mathrm{bw}}}\ln \left(1-K_{\mathrm{diff},1}\left(\frac{1}{Q_{\mathrm{bw}}}+\frac{1}{Q_{d,0}}\right)\right).$

4. The device according to claim 1, wherein the arithmetic and evaluation unit is configured to calculate the first expected change in the clearance value, {acute over (K)}.sub.diff1, by using a third equation, the third equation being ${\left({\tilde{K}}_{\mathrm{diff},2}\right)}_{}=Q_{\mathrm{bw}}\frac{e^{{}_{}}-1}{e^{{}_{}}-\frac{Q_{\mathrm{bw}}}{Q_{d,0}+Q_d}},{}_{}={\left(k_{0}A\right)}_{}\frac{\left(Q_{d,0}+Q_d\right)-Q_{\mathrm{bw}}}{Q_{\mathrm{bw}}\left(Q_{d,0}+Q_d\right)}.$

5. The device according to claim 1, wherein the arithmetic and evaluation unit is configured to calculate the second expected change in the clearance value, {acute over (K)}.sub.diff2, by using a fourth equation, the fourth equation being ${\left({\tilde{K}}_{\mathrm{diff},2}\right)}_{}=Q_{\mathrm{bw}}\frac{1-e^{-{}_{}}}{1+\frac{Q_{\mathrm{bw}}}{Q_{d,0}+Q_d}},{}_{}={\left(k_{0}A\right)}_{}\frac{\left(Q_{d,0}+Q_d\right)+Q_{\mathrm{bw}}}{Q_{\mathrm{bw}}\left(Q_{d,0}+Q_d\right)}.$

Description

(1) An embodiment of the invention is described in the following with reference to the drawings, in which:

(2) FIG. 1 is a greatly simplified schematic view of the essential components of an extracorporeal blood treatment device and

(3) FIG. 2 shows the relative change in clearance in the event of a change of dialysate rate for the operation of the dialyser in co-current flow and in countercurrent flow.

(4) FIG. 1 is a greatly simplified schematic view of only those components that are essential to the invention of an extracorporeal blood treatment device. In the present embodiment, the device for detecting the direction of fluid flow through the dialyser of the extracorporeal blood treatment device is a component of the blood treatment device. The device for detecting the flow direction through the dialyser can, however, also constitute a separate unit.

(5) The extracorporeal blood treatment device, which is a haemodialysis device in the present embodiment, has a dialyser 1, which is separated by a semi-permeable membrane 2 into a blood chamber 4 and a dialysate chamber 3. The blood chamber 4 has a first port 4A and a second port 4B, while the dialysate chamber 3 has a first port 3A and a second port 3B.

(6) The fluid system has a device 5, which is only shown schematically, by means of which fresh dialysate is produced from water and concentrates. The device 5 for preparing fresh dialysate allows a quick change, in particular an increase in the concentrate composition, in order to produce a concentrate bolus.

(7) The device 5 for preparing fresh dialysate is connected via a first dialysate line 6 to the first port 3A of the dialysate chamber 3. A second dialysate line 7, in which a dialysate pump 8 is connected, leads from the second port 3B of the dialysate chamber 3 to an outlet 9. This part of the blood treatment device constitutes the dialysate system I.

(8) An arterial blood line 10, in which a blood pump 11 is connected, leads from the patient to the first port 4A of the blood chamber 4, while a venous blood line 12, which leads back to the patient, leaves from the second port 4B of the blood chamber 4. This part of the blood treatment device constitutes the extracorporeal blood circuit II.

(9) During the extracorporeal blood treatment, dialysate flows through the dialysate chamber 3 and blood flows through the blood chamber 4. In the process, dialysate and blood flow along the membrane 2 of the dialyser 1. In order to increase the efficiency of the treatment, the dialyser 1 is generally operated in countercurrent flow. In the process, dialysate and blood flow along the membrane in opposite directions. The dialyser can, however, also in principle be operated in co-current flow.

(10) The blood treatment device has a central control unit 13, which is connected to the dialysate pump 8 and the blood pump 11 via control lines 8, 11.

(11) The first and second dialysate lines 6, 7 are hose lines, to which the dialyser 1 is connected. Connectors, which are not shown, in particular Hansen couplings, which are generally colour coded, serve to connect the hose lines 6, 7 to the ports 3A, 3B of the dialyser 1.

(12) The device for detecting the flow direction through the dialyser 1, which in the present embodiment is a component of the blood treatment device, has an arithmetic and evaluation unit 14, which is connected to the central control unit 13 of the blood treatment device via a data line 15. The arithmetic and evaluation unit 14 can, however, also be a component of the central control unit 13. In addition, the device for detecting the flow direction has a control unit for changing the dialysate rate by a specified amount, which in this embodiment is a component of the central control unit 13 of the blood treatment device, but can also be a separate unit.

(13) The dialysate system I can comprise a device 16 for reversing the flow direction, which has an arrangement of valves 16A, 16B, 16C, 16D. The valves are preferably electromagnetically or pneumatically actuated valves which are controlled via control lines 16A, 16B, 16C, 16D by the central control unit 13 of the blood treatment device.

(14) The valve 16A is arranged in the first dialysate line 6 and the second valve 16B is arranged in the second dialysate line 7. Upstream of the first valve 16A, a first line branch 6A branches off from the first dialysate line 6 and leads to the second dialysate line 7 upstream of the second valve 16B. The third valve 16C is connected in the first line branch 6A. Downstream of the first valve 16A, a second line branch 6B branches off from the first dialysate line 6 and leads to the second dialysate line 7 downstream of the second valve 16B. The fourth valve 16D is connected in the second line branch 6B. In the process, the terms upstream and downstream of the valves relate to the flow direction when the fluid flow is not reversed.

(15) In normal operation, the dialyser 1 is operated in countercurrent flow. For this purpose, the central control unit 13 opens the first and second valve 16A, 16B and closes the third and fourth valve 16C, 16D. Consequently, the first port 3A is the inlet and the second port 3B is the outlet of the dialysate chamber 3. To reverse the flow direction, the control unit 13 closes the first and second valve 16A, 16B and opens the third and fourth valve 16C, 16D. Then the first port 3A is the outlet and the second port 3B is the inlet of the dialysate chamber 3.

(16) The device for detecting the flow direction of the dialyser has a measuring unit for measuring the clearance, which measuring unit has means to measure a physical and/or chemical property of the dialysate. In the present embodiment, the physical and/or chemical property of the dialysate is the concentration of a substance in the dialysate, for example the sodium concentration. To measure the physical and/or chemical property, means 17 are provided, which comprise a first sensor 17A and a second sensor 17B. In order to determine the Na concentration, the first sensor 17A measures the conductivity of the dialysate in the first dialysate line 6 upstream of the dialyser 1, while the second sensor 17B measures the conductivity of the dialysate in the second dialysate line 7 downstream of the dialyser 1. The sensors 17A, 17B are connected to the arithmetic and evaluation unit 14 via data lines 17A, 17B.

(17) In addition, a display unit 18A and an alarm unit 18B are provided and are connected via data lines 19A and 19B to the arithmetic and evaluation unit 14. The display unit 18A displays the operation of the dialyser in co-current flow or countercurrent flow. The alarm unit 18 gives an alarm if an incorrect operation of the dialyser 1 is ascertained.

(18) Firstly, the theoretical principles of the detection of the flow direction through the dialyser are explained.

(19) In countercurrent flow operation, the effective dialyser parameter (mass transfer coefficient) K.sub.0A can be calculated from a first measurement of the diffusive clearance K.sub.diff,1 when the dialysate flow Q.sub.d,0 and blood (water) flow Q.sub.bw are known (Sargent/Gotch Principles and Biophysics of Dialysis in Replacement of Renal Function by Dialysis):

(20) $\begin{array}{cc}{k}_0{A}_{}=\frac{Q_{\mathrm{bw}}{Q}_{d,0}}{Q_{d,0}-Q_b}\ln \left(\frac{\frac{K_{\mathrm{diff},1}}{Q_{d,0}}-1}{\frac{K_{\mathrm{diff},1}}{Q_{\mathrm{bw}}}-1}\right)& \mathrm{Equation}\left(1\right)\end{array}$

(21) In co-current flow operation, the corresponding correlation is:

(22) $\begin{array}{cc}{\left(k_{0}A\right)}_{}=-\frac{Q_{\mathrm{bw}}{Q}_{d,0}}{Q_{d,0}+Q_{\mathrm{bw}}}\ln \left(1-K_{\mathrm{diff},1}\left(\frac{1}{Q_{\mathrm{bw}}}+\frac{1}{Q_{d,0}}\right)\right)& \mathrm{Equation}\left(2\right)\end{array}$

(23) Assuming that the mass transfer coefficient K.sub.0A remains constant in the event of a change of dialysate flow Q.sub.d, in the event of a change in the dialysate flow by Q.sub.d the expected value of the diffusive clearance {tilde over (K)}.sub.diff,2 can now be calculated both for countercurrent flow operation and for co-current flow operation:

(24) $\begin{array}{cc}{\left({\tilde{K}}_{\mathrm{diff},2}\right)}_{}=Q_{\mathrm{bw}}\frac{e^{}-1}{e^{}-\frac{Q_{\mathrm{bw}}}{Q_{d,0}+Q_d}},{}_{}={\left(k_{0}A\right)}_{}\frac{\left(Q_{d,0}+Q_d\right)-Q_{\mathrm{bw}}}{Q_{\mathrm{bw}}\left(Q_{d,0}+Q_d\right)}& \mathrm{Equation}\left(3\right)\\ {\left({\tilde{K}}_{\mathrm{diff},2}\right)}_{}=Q_{\mathrm{bw}}\frac{1-e^{}}{1+\frac{Q_{\mathrm{bw}}}{Q_{d,0}+Q_d}},{}_{}={\left(k_{0}A\right)}_{}\frac{\left(Q_{d,0}+Q_d\right)+Q_{\mathrm{bw}}}{Q_{\mathrm{bw}}\left(Q_{d,0}+Q_d\right)}& \mathrm{Equation}\left(4\right)\end{array}$

(25) The device according to the invention and the method according to the invention can be used not only for detecting the flow direction for haemodialysis (HD), but also for haemodiafiltration (HDF). In the case of an HDF treatment having a predilution or post dilution, the diffusive proportion of the clearance is extracted from the total clearance K.sub.m determined from the measurements. This is possible using the following equation and so the equations (1) to (4) can also be applied to HDF procedures.

(26) $K_{\mathrm{diff}}=\frac{Q_{\mathrm{bw}}+Q_s}{Q_b-Q_f-\left(1-\right)Q_s}\left(\frac{Q_{\mathrm{bw}}+Q_s}{Q_b}{K}_m-Q_f-Q_s\right),$

(27) =1 with HDF predilution

(28) =0 with HD and HDF post dilution

(29) Q.sub.bw denotes the blood water flow, Q.sub.b the blood flow, Q.sub.d the dialysate flow, Q.sub.f the filtrate flow and Q.sub.S the substitute flow.

(30) The general case of haemodiafiltration (HDF) is described in detail in Gross, Maierhofer et al. Online clearance measurement in high-efficiency hemodiafiltration (Kidney International (2007) 72, 1550-1553).

(31) Following a second determination of the diffusive clearance K.sub.diff,2 at a dialysate flow of Q.sub.d,0+Q.sub.d the real change in the diffusive clearance K.sub.diff=K.sub.diff,2K.sub.diff,1 for co-current flow operation and countercurrent flow operation can now be compared with the expected change ({tilde over (K)}.sub.diff) for co-current flow operation and countercurrent flow operation.
({tilde over (K)}.sub.diff).sub.=({tilde over (K)}.sub.diff,2).sub.({tilde over (K)}.sub.diff,1).sub. and
({tilde over (K)}.sub.diff).sub.=({tilde over (K)}.sub.diff,2).sub.({tilde over (K)}.sub.diff,1).sub.

(32) FIG. 2 shows the relative change in clearance in the event of a change in dialysate rate Q.sub.d by 200 ml/min, 100 ml/min (reduction) and +300 ml/min (increase) from a specified, original dialysate rate Q.sub.d of 500 ml/min and a specified blood flow rate Q.sub.b of 300 ml/min with operation of the dialyser 1 in countercurrent flow and with operation in co-current flow for a haemodialysis treatment (HD). The clearance K at the original dialysate rate of 500 ml/min is entered on the x axis. The determined values of the clearance K are between 60 and 200 ml/min. It can be seen that in the event of a blood treatment in practice with operation of the dialyser in the co-current flow, clearance values above a limit value of 185 ml/min can no longer be achieved. Furthermore, it can be seen that the amount of the relative change in clearance in the event of a change of the dialysate rate with operation in co-current flow is always greater than countercurrent flow.

(33) For dialysers typically used in haemodialysis having a mass transfer coefficient K.sub.0A of 300-1200 ml/min, a clearance K of at least 150 ml/min is also to be expected in co-current flow before the change in dialysate rate Q.sub.b. Therefore, in the present example, in the event of changes in the dialysate rate Q.sub.b of 200 and +300 ml/min (to 300 and 800 ml/min) the difference in clearance change between co-current and countercurrent flow lies outside of the error tolerance of a clearance determination on the basis of conductivity.

(34) The central control unit 13 and the arithmetic and evaluation unit 14 are configured such that the individual steps of the method according to the invention for detecting the flow direction are carried out.

(35) In the embodiment, it is assumed that the dialyser 1 is intended to be operated in countercurrent flow. Countercurrent flow operation is therefore the normal operation. This is to be checked in the present embodiment.

(36) In the event of a certain blood flow rate Q.sub.b and a certain dialysate rate Q.sub.d,0, which are specified for the blood treatment, the measuring unit measures the diffusive clearance K.sub.diff,1. For this purpose, by means of a short-term change in the concentration composition in the device 5 in order to prepare fresh dialysate in the dialysate circuit I upstream of the dialyser, a concentrate bolus is produced which is measured by the sensors 17A and 17B of the measuring unit upstream and downstream of the dialyser 1. The sensor 17A upstream of the dialyser 1 can also be omitted if the value of the bolus is known. The measuring unit then calculates the clearance K.sub.diff,1 from the ascertained measured values. The calculation of the clearance from the measured values forms part of the prior art (DE 39 38 662 A1, DE 197 47 360 A1).

(37) Firstly, the arithmetic and evaluation unit 14 compares the measured clearance K.sub.diff,1 with a specified limit value, which is above 160 ml/min, preferably above 175 ml/min, most preferably above 185 ml/min. If the clearance K.sub.diff,1 is above the limit value, the arithmetic and evaluation unit 14 concludes operation in countercurrent flow, since such a high value for the clearance cannot be achieved in co-current flow operation, which can, however, be checked again subsequently. Otherwise, co-current flow operation is concluded, which likewise can be checked again.

(38) The dialysate rate Q.sub.d is now changed by a specified amount, i.e. the dialysate rate Q.sub.d is increased or reduced, the blood flow rate Q.sub.b being maintained. After the change in dialysate rate Q.sub.d, the clearance K.sub.diff,2 is measured again by the measuring unit.

(39) The measured values K.sub.diff,1 and K.sub.diff,2 saved in a memory (not shown) of the arithmetic and evaluation unit 14. From the measured values K.sub.diff,1 and K.sub.diff,2 the arithmetic and evaluation unit 14 calculates the amount of the change in clearance (K.sub.diff).sub. resulting from the change in dialysate rate of Q.sub.d by the specified amount Q.sub.d to Q.sub.d,0+Q.sub.d whilst maintaining the blood flow rate Q.sub.b for the assumed case of operation of the dialyser 1 in countercurrent flow:
(K.sub.diff).sub.=K.sub.diff,1K.sub.diff,2

(40) After determining the amount of the change in clearance ({tilde over (K)}.sub.diff).sub. on the basis of the clearance measurements before and after the change in dialysate rate Q.sub.d, the expected value of the clearance change is calculated both for the case of countercurrent flow ({tilde over (K)}.sub.diff).sub. and for the case of co-current flow ({tilde over (K)}.sub.diff).sub..

(41) For this purpose, firstly, the mass transfer coefficient K.sub.0A of the dialyser 1 is calculated according to equation (1) for countercurrent flow and equation (2) for co-current flow from the previously measured clearance K.sub.diff,1, the adjusted dialysate rate Q.sub.d,0 and blood flow rate Q.sub.b, and the blood water flow Q.sub.bw.

(42) Subsequently, the expected value of the clearance ({tilde over (K)}.sub.diff,2).sub. for countercurrent flow after the change in dialysate flow is calculated from the dialysate rate increased by the specified amount Q.sub.d to Q.sub.d,0+Q.sub.d, the unchanged blood flow rate Q.sub.b, the blood water flow Q.sub.bw and the previously determined mass transfer coefficient K.sub.0 according to equation (3), and the expected value of the clearance ({tilde over (K)}.sub.diff,2).sub. for co-current flow after the change in dialysate flow is calculated from the dialysate rate increased by the specified amount Q.sub.d to Q.sub.d,0+Q.sub.d, the unchanged blood flow rate Q.sub.b, the unchanged blood water flow Q.sub.bw and the previously determined mass transfer coefficient K.sub.0A according to equation (4).

(43) The arithmetic and evaluation unit 14 subsequently calculates the amount of the difference between the expected value of the clearance ({tilde over (K)}.sub.diff,2).sub. for countercurrent flow after the change in dialysate rate and the clearance measured before the change in dialysate rate in order to determine the amount of the expected change in clearance for countercurrent flow, and calculates the amount of the difference between the expected value of the clearance ({tilde over (K)}.sub.diff,2).sub. for co-current flow after the change in dialysate rate and the clearance measured before the change in dialysate rate in order to determine the amount of the expected change in clearance for co-current flow.

(44) Subsequently, the arithmetic and evaluation unit 14 calculates the amount of the difference between the measured change in clearance and the expected value of the change in clearance for the case of countercurrent flow and calculates the amount of the difference between the measured change in clearance and the expected value of the change in clearance for the case of co-current flow.

(45) The two difference values are then compared to one another. If the amount of the difference for countercurrent flow is smaller than the amount of the difference for co-current flow, the arithmetic and evaluation unit 14 concludes operation in countercurrent flow, which is the desired operation in the present embodiment. If, on the other hand, the amount of the difference for co-current flow is smaller than the amount of the difference for countercurrent flow, operation in co-current flow is concluded, which is not the desired operation in the present embodiment, i.e. it would be an erroneous state.

(46) Moreover, the arithmetic and evaluation unit 14 generates a control signal indicating the operating state, which the display unit 18A receives and so the countercurrent flow or co-current flow operation is displayed.

(47) If the dialyser 1 is incorrectly connected to the dialysate lines 6, 7, i.e. if the ports have been mixed up, the arithmetic and evaluation unit 14 generates a control signal, which the alarm unit 18B receives. The alarm unit 18B then gives an alarm. Moreover, the arithmetic and evaluation unit 14 generates a control signal, which the central control unit 13 receives. Then the control unit 13 carries out an intervention in the machine control system. This intervention can be that the performance of the blood treatment is interrupted. Alternatively, it is possible to reverse the flow direction by activating the corresponding valves 16A-16D, and so the dialyser is actually operated in countercurrent flow.