RECIRCULATION MEASUREMENT BY MEANS OF DIFFUSION EQUILIBRIUM

Abstract

An extracorporeal blood treatment machine includes a dialyzer and a sensor device downstream of the dialyzer on a dialysis fluid side. The machine is connected to a control and computing unit configured to qualitatively and quantitatively determine at least one preferably selected or selectable blood component in the used dialysis fluid. The control and computing unit is adapted to put the machine into a mode in which a dialysis fluid amount is confined within the dialyzer at least until the concentrations of the blood component on the dialysis fluid side and on the blood side of the dialyzer are in equilibrium, and thereupon to switch the machine into a mode in which the dialysis fluid flow is permitted to leave the dialyzer to feed the confined dialysis fluid amount as a dialysis fluid bolus to the sensor device for determining the blood component concentration contained in the bolus.

Claims

1. An extracorporeal blood treatment machine comprising a dialyzer and a sensor device that is downstream of the dialyzer on a dialysis fluid side and is electrically connected to a control and computing unit, which is provided and configured to both qualitatively and quantitatively determine, based on measurement signals of the sensor device, a blood component in a used dialysis fluid, the control and computing unit further configured to: put the extracorporeal blood treatment machine into a first mode in which a dialysis fluid amount is confined within the dialyzer at least until a concentration of the blood component on the dialysis fluid side is in equilibrium with a concentration of the blood component on a blood side of the dialyzer, which equilibrium is no longer changing or is only still changing to an unsubstantial degree, wherein a time period within which the equilibrium is established is determined by a time value, and thereupon switch the blood treatment machine into a second mode in which a dialysis fluid flow is permitted to leave the dialyzer in order to feed a previously confined dialysis fluid amount as a dialysis fluid bolus to the sensor device for determining a concentration of the blood component contained in the dialysis fluid bolus, and calculate a current recirculation value from said concentration of the blood component contained in the dialysis fluid bolus and from a number of further machine and/or adjustment parameters.

2. The extracorporeal blood treatment machine according to claim 1, wherein a concentration of said blood component in the used dialysis fluid corresponds to a maximum peak in a sensor signal of the sensor device directly after a release of the dialysis fluid bolus from the dialyzer.

3. The extracorporeal blood treatment machine according to claim 1, wherein a calculation of the current recirculation value takes place using a calculation model defined by the following formula: $R=\frac{1-\frac{c_{\mathrm{DO}}.Math.Q_D}{c_{\mathrm{sys}}.Math.K_D}}{1-\frac{c_{\mathrm{DO}}.Math.Q_D}{c_{\mathrm{sys}}.Math.K_D}+\frac{c_{\mathrm{DO}}.Math.Q_D}{c_{\mathrm{sys}}.Math.Q_B}}$ with TABLE-US-00002 R recirculation rate cDO concentration of a substance at the dialysate output csys c_sys systemic concentration of a blood component which is not affected by recirculation (concentration in the patient) QD dialysis fluid flow rate QB blood flow rate in the extracorporeal blood line system KD theoretical clearance of the dialyzer K0A dialyzer-specific.

4. The extracorporeal blood treatment machine according to claim 3, wherein: the dialyzer comprises a dialysis fluid inlet for fresh dialysis fluid, a dialysis fluid outlet for used dialysis fluid, and a filter membrane which separates a dialysis fluid membrane side, at which the dialyzer is connected to a dialysis fluid circulation via a dialysis fluid inlet line and a dialysis fluid outlet line, from a blood membrane side at which the dialyzer is connected or connectable to an extracorporeal blood circulation; a bypass line is provided by which the dialysis fluid membrane side is bypassable in a bypass mode so as to temporarily confine dialysis fluid present in the dialyzer, for which purpose at least one respective check valve is provided at the dialysis fluid inlet line and the dialysis fluid outlet line between the bypass line and the dialyzer; and the control and computing unit is configured or adapted to be equipped with a memory unit, wherein the extracorporeal blood treatment machine further comprises: a data set stored or storable on the memory unit and indicating a number of blood flow values suited for different parameters of the blood treatment machine in the extracorporeal blood circulation and corresponding time values within which, in the dialyzer, with an appropriately adjusted blood flow value, assuming a maximally possible recirculation value, a concentration equilibrium of at least one selected or selectable blood component between blood in the extracorporeal blood circulation and dialysis fluid confined in the dialyzer is completed exclusively due to diffusion; and the calculation model stored on the memory unit, by which the control and computing unit, taking into account a concentration of the blood component, calculates an actual recirculation value, for which purpose the control and computing unit, for determination of the blood component in the blood of the patient, switches the extracorporeal treatment machine into the bypass mode for a duration of the time value and operates the extracorporeal blood circulation at a blood flow value indicated and, directly after termination of the bypass mode, metrologically determines, by the sensor device, a concentration bolus produced by the bypass mode in the used dialysis fluid draining from the dialyzer.

5. The extracorporeal blood treatment machine according to claim 4, wherein the memory unit is steadily integrated in the extracorporeal blood treatment machine.

6. A method for monitoring a recirculation rate in an extracorporeal blood treatment by using the extracorporeal blood treatment machine in accordance with claim 1, comprising the following steps: determining a time value as a function of an adjusted blood flow value within which a concentration equilibrium of a previously selected blood component occurs: operating the extracorporeal blood treatment machine in the bypass mode in which, by maintaining the blood flow value, a dialysis fluid is confined within a dialyzer for the determined time value, switching to a release mode in which the dialysis fluid is released in a direction of an outlet of the dialyzer; capturing a measurement peak in a scope of a sensory measurement of a blood component-equivalent measurement parameter in the dialysis fluid after switching to the release mode; and calculating the recirculation rate by a calculation model.

7. The method for monitoring a recirculation rate according to claim 7, wherein the step of calculating the recirculation rate takes place using a calculation model defined by the following formula: $R=\frac{1-\frac{c_{\mathrm{DO}}.Math.Q_D}{c_{\mathrm{sys}}.Math.R_D}}{1-\frac{c_{\mathrm{DO}}.Math.Q_D}{c_{\mathrm{sys}}.Math.K_D}+\frac{c_{\mathrm{DO}}.Math.Q_D}{c_{\mathrm{sys}}.Math.Q_B}}$ with TABLE-US-00003 R recirculation rate cDO concentration of a substance at the dialysate output csys c_sys systemic concentration of a blood component which is not affected by recirculation (concentration in the patient) QD dialysis fluid flow rate QB blood flow rate in the extracorporeal blood line system KD theoretical clearance of the dialyzer K0A dialyzer-specific.

Description

BRIEF DESCRIPTION OF THE DRAWING FIGURES

[0046] The invention will be described in detail in the following by means of a preferred embodiment with reference to the enclosed drawing figures, of which:

[0047] FIG. 1 a first embodiment of an extracorporeal blood treatment machine according to the invention;

[0048] FIG. 2 a second embodiment of an extracorporeal blood treatment machine according to the invention;

[0049] FIG. 3 a third embodiment of an extracorporeal blood treatment machine according to the invention;

[0050] FIG. 4 a chronological sequence of the measurements at a sensor device of a dialysis machine where the sensor device is arranged directly behind or before the valve of the dialysis fluid outlet line.

[0051] The Figures are merely of schematic nature and serve exclusively for the understanding of the invention. The same elements are designated with the same reference numbers.

DETAILED DESCRIPTION

[0052] FIG. 1 illustrates a first embodiment of an extracorporeal blood treatment machine (dialysis machine) 1 according to the invention, having a dialyzer 2 comprising a dialysis fluid inlet 4 and a dialysis fluid outlet 6. The dialyzer 2 is further equipped with a filter membrane 8 separating a dialysis fluid membrane side 10, which is in fluid connection with a dialysis fluid inlet line 12 and a dialysis fluid outlet line 14 of a dialysis fluid circulation 16, from a blood membrane side 18. The dialysis fluid inlet line 12 and the dialysis fluid outlet line 14 are connected to the dialysis fluid inlet 4 and the dialysis fluid outlet 6 of the dialyzer 2. The blood membrane side 18 is in fluid connection with an extracorporeal blood circulation 20. In the dialysis fluid circulation 16, a bypass line 22 is further provided, by means of which the dialysis fluid membrane side 10 of the dialyzer 2 may be bypassed, i.e. be circumvented fluidically. In the dialysis fluid inlet line 12 and the dialysis fluid outlet line 14 a respective valve 24, 26 is provided by means of which the dialysis fluid inlet line 12 and the dialysis fluid outlet line 14 may be opened and/or closed and thus either release the flow path for fresh dialysis fluid with opened valves 24, 26 through the dialysis fluid inlet line 12, the dialysis fluid membrane side 10 of the dialyzer 2, and the dialysis fluid outlet line 14, or close the flow path by closing at least the valve 24, ideally both valves 24, 26.

[0053] In the first embodiment of the dialysis machine 1 according to the invention a sensor device 28 is positioned downstream of the dialysis fluid outlet 6 and upstream of the valve 26. It is, for instance, configured as an optical sensor device and performs, in the dialysis fluid flowing past, measurements by means of UV/VIS spectroscopy as a function of the absorption range of the specific blood component to be measured at the wavelength absorbable by this blood component, so as to enable a concentration determination of this blood component or a corresponding parameter determination. Concentration/parameter determinations by absorption measurement are generally known and will therefore not be explained here in detail. Apart from optical measurement methods, alternative measurement methods, for instance, by conductivity determination, are also conceivable. The measured values generated at the sensor device 28 are transmitted to and evaluated by a control and computing unit 30.

[0054] The control and computing unit 30 is in mutual information exchange at least with the valves 24, 26 and the sensor device 28, i.e. it receives and transmits information from the valves 24, 26 and the sensor device 28 and/or to the valves 24, 26 and the sensor device 28. Furthermore, the control and computing unit 30 is connected to or equipped with a memory unit 32. At least one data set by which the dialysis machine 1 can be controlled as a function of the predetermined and/or received information is stored and/or storable on this memory unit 32.

[0055] The dialysis machine 1 further comprises a further valve 34 in the bypass line 22 which is also in information exchange contact with the control and computing unit 30 and may be controlled, i.e. opened and closed, by it. The valve 34 is provided to release or to block the flow path for fresh dialysis fluid via the bypass line 22. The fresh dialysis fluid is obtained from a dialysis fluid providing unit/dialysis fluid source 36. A balancing chamber 38 which balances fresh dialyzing fluid flowing into the dialysis fluid inlet circulation 16 and (used) dialysis fluid flowing out thereof is positioned downstream of the dialysis fluid source 36. The balancing chamber 36 is arranged fluidically such that it is positioned between the dialysis fluid source 36 and a mouth position of the bypass line 22 in the dialysis fluid inlet line 12, and between a mouth position of the bypass line 22 into the dialysis fluid outlet line 14 and a drain.

[0056] On the blood membrane side 18 of the dialyzer 2 the extracorporeal blood circulation 20 is connected to the dialyzer 2. The blood circulation 20 comprises at least one arterial blood line 40 which connects a patient's arterial access to a blood-side dialyzer input and at which a blood pump 42 is arranged, and a venous blood line 44 which connects a blood-side dialyzer output to a patient's venous access. The blood pump 42 is also in (mutual) information exchange contact with the control and computing unit 30 and is controlled by it.

[0057] FIG. 2 illustrates a second embodiment of a dialysis machine 1 according to the invention, which differs from the dialysis machine 1 of the first embodiment merely in that the sensor device 28 is not arranged upstream of the valve 26, but is positioned fluidically between the valve 26 and the balancing chamber 38, especially between the mouth position of the bypass line 22 into the dialysis fluid outlet line 14 and the balancing chamber 38.

[0058] FIG. 3 illustrates a third embodiment of a dialysis machine 1 according to the invention, which differs from the dialysis machine 1 of the first embodiment merely in that the sensor device 28 is not arranged upstream of the valve 26, but is positioned downstream of the balancing chamber 38.

[0059] In operation of the dialysis machine 1 (all embodiments), a patient is first connected to the extracorporeal blood circulation 20. Subsequently, the control and computing unit 30 retrieves a target blood flow value and a time value for the duration of a bypass mode from the data set which is stored on the memory unit 32. Patient-dependent minimal and maximal upper limits for the target blood flow value may be taken into account in the data set. The time value for the duration of the bypass mode is preferably chosen/determined such that, during the bypass mode, an (approximate) diffusion equilibrium is reached for the blood component to be measured in the dialyzer 2 even under the worst circumstance, namely a maximally possible recirculation or a recirculation to be expected maximally (e.g. recirculation of 20 percent to 30 percent). Here, the rule applies that the lower the blood flow value and the larger the dialyzer, the longer it takes until the (approximate) diffusion equilibrium has been reached. Depending on the specific blood component to be measured/to be determined, which is chosen optionally prior to the treatment from a plurality of possible blood components, the output time value may additionally be larger or smaller.

[0060] After the control and computing unit 30 has retrieved the target time value and the target blood flow value and/or they were input manually, it sets the blood pump 42 to the target blood flow value. Once the target blood flow value has been reached and a predetermined value for the dialysis fluid flow through the dialysis fluid circulation 16 has also been reached, the dialysis machine 1 is switched to the bypass mode by the control and computing unit 30. This means that, for the duration of the bypass mode, the valves 24, 26 are closed, i.e. the dialysis fluid present between the valves 24, 26 is confined, and the valve 34 in the bypass line 22 is opened, so that the flow path of the fresh dialysis fluid leads from the dialysis fluid source 36 via the bypass line 22 to the drain. For the duration of the bypass mode, the blood pump 42 is now operated at the rate set while the dialysis fluid on the dialysis fluid membrane side 10 is stationary. Consequently, the blood component to be measured/determined passes from the blood flowing through the blood membrane side 18 of the dialyzer 2 via the filter membrane 8 into the dialysis fluid which is stationary on the dialysis fluid membrane side 10 of the dialyzer 2. Thus, the blood component to be measured/determined will enrich in the stationary dialysis fluid until a diffusion equilibrium has been (substantially) reached on the blood membrane side 18 and the dialysis fluid membrane side 10. Since the blood in the extracorporeal blood circulation 20 flows on continuously, the diffusion equilibrium concentration of the blood component to be measured/determined corresponds at that time substantially to the available concentration of the blood component to be measured/determined in the blood of the extracorporeal blood circulation 20, which corresponds at that time in turn to the available concentration of the blood component to be measured in the blood of the patient's body. Consequently, the diffusion equilibrium concentration of the blood component to be measured/determined in the stationary dialysis fluid corresponds to the concentration of the blood component to be measured in the blood of the patient's body.

[0061] Once the diffusion equilibrium has been (almost) reached and/or once the predetermined time value for the bypass mode, within which the diffusion equilibrium is deemed to have been reached, has been reached, the control and computing unit 30 ends the bypass mode. Consequently, it closes the valve 34 in the bypass line 22 and opens at the same time the valves 24, 26 in the dialysis fluid inlet line 12 and the dialysis fluid outlet line 14, so that fresh dialysis fluid flows from the dialysis fluid source 36 again through the dialysis fluid membrane side 10 of the dialyzer 2. The dialysis fluid that had been stationary before on the dialysis fluid membrane side 10 consequently flows through the dialysis fluid outlet line 14 in the direction of the drain, passing the sensor device 28. The sensor device 28 measures, as a consequence of the enrichment of the blood component to be measured, a peak (light absorption peak in place of the concentration of this blood component) whose maximum may be evaluated as a diffusion equilibrium concentration of the blood component. In conclusion, after the measurement of the peak maximum the concentration present in the blood of the patient's body of the blood component to be measured/determined is thus known, and in the subsequent and/or continuing blood treatment the actual recirculation may be calculated in a known way.

[0062] FIG. 4 illustrates the chronological sequence of the measurement (absorption value of the blood component to be measured) at a sensor device 28 of a dialysis machine 1 in which the sensor device 28 is arranged directly behind the valve 26 of the dialysis fluid outlet line 14 and before or behind the mouth position of the bypass line 22 in the dialysis fluid outlet line 14 (the temporary offset of the peak with a displacement of the sensor device 28 in downstream direction is unconsidered as being negligible in FIG. 4 for the sake of convenience). The checkered area is the duration in which the bypass mode is active, i.e. no dialysis fluid flowing from the dialysis fluid membrane side 10 flows past. Before and during the bypass mode the sensor device 28 consequently measures in the dialysis fluid a constant parameter for the concentration for a particular blood component since the dialysis fluid and/or the dialysis fluid fraction in which the blood component to be measured enriches due to diffusion is confined between the valves 24, 26 and fresh dialysis fluid from the dialysis fluid source 36 does not flow around the sensor device. The concentration thus measured may be considered as the concentration of the blood component to be measured at the dialyzer output under the normal, known treatment/operating conditions (c.sub.do).

[0063] After the termination of the bypass mode the sensor device measures a distinct peak in the concentration of the blood component to be measured since, after the opening of the valve 26, the previously confined dialysis fluid fraction now flows past the sensor device 28. It has to be noted that, for the case in which the sensor device 28 is arranged directly behind the valve 26, the peak maximum corresponds almost to the diffusion equilibrium concentration. If there is a larger distance between the valve 26 and the sensor device 28, the peak maximum decreases due to diffusion, so that appropriate mathematical correction measures are used for determining the diffusion equilibrium concentration. The diffusion equilibrium concentration measured/determined of the blood component to be measured corresponds to the systemic blood component concentration c.sub.sys.

[0064] Once the concentration bolus of the blood component to be measured/determined in the dialysis fluid has passed the sensor device 28 completely, the measured/determined concentration of the blood component again corresponds to c.sub.do.

[0065] With the known equation (5) according to the foregoing description the recirculation R may now be calculated.