Patent Application
20100168925
The present invention relates to an arrangement for controlling an extracorporeal blood-treating apparatus, and in particular a hemodialysis apparatus or hemofiltration apparatus or hemodiafiltration apparatus, which has a dialyzer or filter that is divided by a semi-permeable membrane into a first and a second chamber. The present invention also relates to an extracorporeal blood-treating apparatus having a control arrangement of this kind and to a method of controlling an extracorporeal blood-treating apparatus.
Hemodialysis is well known as an extracorporeal blood treatment process, in which the blood to be treated flows, in an extracorporeal blood circuit through the blood chamber of a dialyzer, which is divided by a semi-permeable membrane into a blood chamber and a dialysis fluid chamber, at a given blood flowrate, while dialysis fluid flows through a dialysis fluid chamber of the dialyzer at a given dialysis fluid flowrate. As well as hemodialysis, hemofiltration is also well known as a blood treatment process. Hemodiafiltration is a combination of both hemodialysis and hemofiltration.
The metabolic exchange in the dialyzer is of both a convective and a diffusive nature. In diffusive metabolic exchange, for the substance concerned, the mass transfer per unit of time through the membrane is proportional to the concentration gradient between the blood and the dialysis fluid; in convective metabolic exchange, the mass transfer depends on the quantity of filtrate because the concentration of filterable substances both in the blood and in the filtrate is the same (Blutreinigungsverfahren [Blood cleansing processes], Georg-Thieme-Verlag, Stuttgart, N.Y., 4th. ed. 1990, pages 11 to 13).
Because the concentration gradient becomes steadily smaller during the dialysis treatment, a fixed numerical value cannot be given for the amount of substance exchanged per unit of time. Clearance forms a measurable indicator of the performance of a dialyzer that is not dependent on concentration. The clearance of a substance is that part of the total flow through the dialyzer that has been entirely freed of the substance concerned. Dialysance is another term for defining the performance of a dialyzer, in a way which also takes substances that are contained in the dialysis fluid into account.
For ultrafiltration equal to 0, the following is found for the determination of dialysance D or clearance K for a given substance.
Dialysance D is equal to the ratio between the mass transport Qb(cbi−cbo) on the blood side for the substance concerned and the difference cbi−cdi in the concentration of the substance between the blood and the dialysis fluid at the given input of the dialyzer.
For reasons of mass balance, it is true that
Q
b(cbi−cbo)=−Qd(cdi−cdo) (2)
For dialysance on the dialysate side, the following equation follows from (1) and (2):
The notation in (1) to (3) is as follows:
Qb=effective blood flowrate
Qd=dialysis fluid flowrate
Cb=concentration of the substance in the volume of the blood in which it is dissolved
Cd=concentration of the substance in the dialysis fluid
i=inlet of the dialyzer
o=outlet of the dialyzer.
EP 0 428 927 A1 describes a method of in vivo determination of parameters of hemodialysis in which dialysate electrolyte transfer is measured at each of two different dialysate input concentrations. On the assumption that the input concentration in the blood is constant, dialysance is determined by this known method of determining the difference between the differences in dialysis fluid ion concentration on the inlet side and outlet side of the dialyzer at the times of the first and second measurements, dividing this difference by the difference between the dialysis fluid ion concentrations on the input side at the times of the first measurement and the second measurement, and by multiplying the result by the flowrate of the dialysis fluid.
Another method of determining dialysance is described in U.S. Pat. No. 6,702,774 B1. In this known method, a given amount of a substance, whose dialysance is to be determined, is added upstream of the dialyzer as a bolus, and dialysance is calculated from the amount of the substance which is added upstream of the dialyzer, the integral of the concentration of the substance over time downstream of the dialyzer, and the flowrate of the dialysis fluid.
There is also a method of determining the maximum dialysance of a dialyzer which is known from DE 197 39 100 C1.
Sigdell and Tersteegen have studied the relationship between clearance and dialysance on the one hand, and blood and dialysis fluid flowrates on the other hand for dialysis without ultrafiltration (Sigdell, J., Tersteegen, B.: Clearance of a Dialyzer under varying Operation Conditions; Artificial Organs 10(3): 219-225, 1986). Sigdell and Tersteegen found that in practice, to increase clearance or dialysance, it appears not to make sense to set a dialysis fluid flowrate of more than twice the blood flowrate. Various methods have been proposed as ways of taking the effect of ultrafiltration on clearance into account. However, at the typical flowrates (Qf=15 ml/min, Qd=500 ml/min, Qb=300 ml/min), the effect of ultrafiltration is relatively small and can be ignored. Werynski and Waniewski have found a general expression for the relationship between flowrates and the resultant clearance and have dealt with hemodiafiltration. They included hemodialysis as a special case (Wernyski, A. and Waniewski, J.: Theoretical Description of Mass Transport in Medical Membrane Devices, Artificial Organs 19(5), pp. 420-427 (1995)).
The known pieces of dialysis apparatus are operated at a blood flowrate which is set by the treating physician within predetermined limits, with the dialysis fluid flowrate likewise being set within predetermined limits, which are generally between 500 ml/min and 800 ml/min. This gives the dialysis dose, which is calculated from the quotient of the product of the clearance K and the effective treatment time T divided by the volume of distribution V (KT/V).
There is today a demand in practice for the quotient (K T/V) for urea to be higher than a pre-stipulated limiting value, and in particular to be higher than 1.3. The volume of distribution V depends on the patient in this case, which means that when treating the blood the physician can pre-stipulate only the clearance K, which is dependent on the flowrates of the blood and the dialysis fluid, and the treatment time T. Consequently, for the required dialysis dose to be achieved, there is a given value for clearance or dialysance which should be ensured to apply during a treatment and which can be found by calculation for a desired treatment time. If however the blood flowrate or the dialysis fluid flowrate changes during the treatment, it is not possible to ensure that a given clearance is obtained.
U.S. Pat. No. 5,092,836 describes a method of hemodialysis which is intended to allow a saving to be made of dialysis fluid. This method does not contemplate the pre-stipulation of a fixed value for the blood flowrate or the dialysis fluid flowrate. Instead, the intention is for a dialysis fluid flowrate to be pre-stipulated which is in a constant ratio to the pre-stipulated blood flowrate.
Also, there is known from WO 2004/022135 A1 a dialysis apparatus in which dialysance is measured and, by varying the rate of ultrafiltration, it is ensured that both the dialysis dose KT/V and the desired loss of weight by the patient are obtained at the same time.
U.S. Pat. No. 5,744,031 describes a method of controlling a blood treatment process in which, to determine dialysance, a measurement is made of conductivity, the value measured for dialysance being compared with a desired value to enable the blood flowrate or dialysis fluid flowrate to be altered in such a way that the actual value for dialysance corresponds to the desired value. This known method is disadvantageous inasmuch as a measurement of conductivity is required during the blood treatment to allow dialysance to be determined. However, a continuous measurement of conductivity not only involves greater cost and complication but also sets limits to how fast regulation can be, because a relatively large amount of time is required for the individual measurements if it is to be possible for the measured variables to be sensed with the requisite accuracy.
Both for hemodialysis and also for hemofiltration and a combination of the two processes, i.e. hemodiafiltration, the relationship between the flowrates on the one hand and clearance, and dialysance on the other hand is known from US 2003/0230533 A1, which is hereby incorporated by reference.
One aspect of the present invention is to provide an arrangement for controlling an extracorporeal blood-treating apparatus which allows optimized blood treatment with a pre-stipulated clearance or dialysance. A further aspect of the present invention is to provide a blood-treating apparatus having such a control arrangement. Another aspect of the present invention is to specify a method of controlling an extracorporeal blood-treating apparatus which makes possible optimized blood treatment with a pre-stipulated clearance or dialysance. A further aspect of the present invention is to provide a computer software product for such a control arrangement.
The control arrangement according to the present invention and the method according to the present invention are intended for an extracorporeal blood-treating apparatus which make take the form both of a hemodialysis apparatus and of a hemofiltration apparatus. The control arrangement according to the present invention and the method may also be intended for a hemodiafiltration apparatus.
The different instances of application differ in that different flowrates, which each have an effect on dialysance or clearance, play a part in the individual treatment processes. In this way, provision is made in hemodiafiltration not only for changing the blood flowrate and the dialysis fluid flowrate but also for changing the ultrafiltration flowrate or the substituent flowrate. However, since the dependence of dialysance or clearance on the individual flow rates is known for all the instances of application, there is no fundamental difference between the alternative embodiments of the control arrangement according to the present invention.
In the general case of extracorporeal blood treatment which covers all the treatment processes, what will be referred to will be an exchanging unit, which may take the form either of a dialyzer or a filter in the case of hemodialysis or hemofiltration, respectively. The extracorporeal hemodialysis apparatus for example, to which one embodiment relates, has a dialyzer, which is divided by a semi-permeable membrane into a blood chamber and a dialysis fluid chamber, a blood pump for pumping blood through the blood chamber at a given blood flowrate Qb, and a dialysis fluid pump for pumping dialysis fluid through the dialysis fluid chamber at a given dialysis fluid flowrate Qd.
The control arrangement according to the present invention may form an independent assembly or may be part of the extracorporeal blood-treating apparatus. Because major components of the control arrangement according to the present invention, such for example as a control unit (microprocessor) and a memory unit, are parts of the known blood-treating apparatus, the control arrangement according to the present invention can be provided in the known blood-treating apparatus at no great technical cost or complication. If all the hardware required is available, the provision of the computer software product according to the present invention may be all that is required.
The arrangement and method according to the present invention assume that different flows or flowrates are pre-stipulated before the treatment, and/or different flows or flowrates, such as blood flowrates or dialysis fluid flowrates, are altered during the treatment. When a blood flowrate, for example, is pre-stipulated or changed respectively before or during the blood treatment, the dialysis fluid flowrate is pre-stipulated or changed in such a way that a desired clearance or dialysance is maintained, preferably for a pre-stipulated period of treatment. Basically, the dialysis fluid flowrate may only be pre-stipulated but need not be set automatically. Preferably however the dialysis fluid flowrate at which the desired clearance or dialysance is maintained is also set by the apparatus. This may be done automatically or after confirmation by a user.
The blood flowrate may be changed during the blood treatment once or more than once but basically even continuously, the dialysis fluid flowrate then always being set in such a way that the desired clearance or dialysance is maintained, preferably within the pre-stipulated period of treatment. Conversely, when there is a change in the dialysis fluid flowrate the blood flowrate is set such that the desired clearance or dialysance is maintained, preferably within the pre-stipulated period of treatment. What is crucial is that the flowrate in the given case is determined not on the basis of a measurement of clearance or dialysance, such as a measurement of conductivity for example, but on the basis of the known dependence of clearance or dialysance on the flowrates. In this way it is possible for the flowrates to be adjusted quickly and continuously to ensure that clearance or dialysance is as desired during the treatment.
Basically, both the dialysis fluid flowrate and also the blood flowrate may be changed. In practice however, the blood flowrate is generally changed and then the dialysis fluid flowrate is only adjusted to suit.
The desired clearance or dialysance is preferably entered prior to the blood treatment from an input unit and is stored in a memory unit. The desired dialysance or clearance thus constitutes a desired value (i.e. a setpoint) for the control system.
A further possible embodiment makes provision not for entering desired values for clearance or dialysance, but for the measurement of these parameters. Clearance or dialysance is preferably measured at the beginning of the dialysis treatment, with control then taking place over the course of the treatment without any further measurement of dialysance or clearance. The measured value thus constitutes the desired value that is to be achieved by the blood treatment even if the dialysis fluid flowrate or the blood flowrate is changed during the treatment. The actual methods of measuring dialysance or clearance are part of the prior art.
The relationship between the desired clearance or dialysance on the one hand and, for example, the blood flowrate or dialysis fluid flowrate on the other hand, can be defined by an equation. This equation includes only the parameters of blood flowrate and dialysis fluid flowrate and a coefficient k0A, which is dependent in essence on the surface area and on the resistance to diffusion of the semi-permeable membrane of the dialyzer. This coefficient k0A can be pre-stipulated and stored for various types of dialyzers before the blood treatment begins. It is however also possible for the coefficient k0A to be determined by measuring the clearance or dialysance at a pre-stipulated blood flowrate and dialysis fluid flowrate and calculating the coefficient from an equation which defines the relationship between clearance or dialysance and between blood flowrate and dialysis fluid flowrate.
An embodiment of the present invention is described in detail below by reference to the drawings.
a is a simplified schematic view of the conditions which apply to the liquids or fluids in hemofiltration when there is predilution.
b is a simplified schematic view of the conditions which apply to the liquids or fluids in hemofiltration when there is postdilution.
The relationship in extracorporeal blood treatment between dialysance or clearance and the flowrates will be explained below. The dependence of dialysance or clearance on the flowrates is described in detail in US 2003/0230533 A1, the disclosure of which is hereby incorporated by reference.
a and 2b are similarly schematic views of a hemofiltration apparatus in which a hemofilter 201, which is divided by a semi-permeable membrane 202 into two chambers 203 and 204, is provided as an exchanging unit. On the blood side, the terminology that applies is the same as in
Also shown in
The relationship between the flowrates and dialysance will be described below. It is assumed that a given dialysance and at least one of the flowrates are pre-stipulated to allow at least one of the other flowrates to be calculated so that the desired dialysance will be maintained. The relationship which is detailed below covers the case where a given dialysance and at least one of the flowrates is pre-stipulated during the treatment. If a given dialysance is pre-stipulated during the treatment, the relevant flowrates can be calculated, thus allowing the desired dialysance to be maintained. This calculation may be made whenever one of the flowrates has changed, without the need for a conductivity measurement.
The diffusive proportion Ddiff of the dialysance is calculated from equation (4):
where k=1 is predilution and k=0 is postdilution.
The filter coefficient k0A, which is assumed to be constant between the two points in time 1 and 2, is calculated as follows:
The above equations show the relationship between the flowrates Qf, Qs, Qd and Qb and the parameters k0A, D and Ddiff.
In accordance with the present invention, at least one of the flowrates is pre-stipulated, with at least one of the other flowrates being determined from the above equations, thus allowing the desired dialysance D to be obtained. The determination of the flowrates from the above equations can be performed numerically by known methods of calculation.
In what follows, a method of determining dialysance D which is known from US 2003/0230533 will be described in brief by reference to
Where α is the Gibbs-Donnan coefficient.
After an initial determination of the ion dialysance D, it is possible for further values of dialysance to be calculated for later points in time at which at least one of the flowrates Qs, Qf, Qd and Qb has changed. However, this presupposes that the flowrates Qs, Qf, Qd and Qb are known at a time before they change. The initial determinations of dialysance at the flowrates Qf1, Qs1, Qd1 and Qb1 can be performed by known methods on the basis of a measurement of conductivity. These methods are part of the prior art and thus there is no need for any further description of them. A method of this kind is described in, for example, EP 0 428 927 A1 or US 2003/0230533.
In what follows, the relationship described above between clearance or dialysance and the individual flows, i.e. flowrates, will be explained by reference to
The extracorporeal blood-treating apparatus, which is a hemodialysis apparatus, has a dialyzer 1 which is divided by a semi-permeable membrane 2 into a blood chamber 3 and a dialysis fluid chamber 4. From a patient, an arterial blood line 5, into which a blood pump 6 is connected, runs to an inlet of the blood chamber 3, while a venous blood line 7 runs to the patient from an outlet of the blood chamber 3.
Fresh dialysis fluid is supplied from a source 8 of dialysis fluid. From the source 8 of dialysis fluid, a dialysis fluid inlet line 9 runs to an inlet of the dialysis fluid chamber 4 of the dialyzer 1, while a dialysis fluid outlet line 10 runs from an outlet of the dialysis fluid chamber 4 to a discharge outlet 11. Connected into the dialysis fluid outlet line 10 is a dialysis fluid pump 12.
The dialysis apparatus has a control unit 13 which is connected to the blood pump 6 and the dialysis fluid pump 12 by control lines 14, 15, respectively. The control unit 13 generates control signals for operating the blood and dialysis fluid pumps 6, 12 at pre-stipulated pumping rates, which means that a pre-stipulated blood flowrate Qb is established in the arterial blood line 5 and a pre-stipulated dialysis fluid flowrate Qd is established in the dialysis fluid outlet line 10.
Arranged in the dialysis fluid inlet line 9, at the inlet of the dialysis fluid chamber 4, are a conductivity sensor 16 for determining the input concentration cd, of a given substance in the dialysis fluid upstream of the dialysis fluid chamber 4 and, in the dialysis fluid outlet line 10, at the outlet of the dialysis fluid chamber 4, a conductivity sensor 17 which measures the output concentration cdo of the given substance in the dialysis fluid downstream of the dialyzer, during the dialysis treatment.
The measured values from the conductivity sensors 16, 17 are fed via signal lines 18, 19, respectively, to an arrangement 21 for determining the clearance K or dialysance D. Via a data line 22 that runs to the control unit 13, the arrangement 21 for determining clearance or dialysance receives the control signals for the blood pump 6 and dialysis fluid pump 12 which pre-stipulate the blood flowrate Qb, and dialysis fluid flowrate Qd respectively. From the arrangement 21, the control unit 13 receives, via the data line 22, the clearance or dialysance that is determined by the arrangement 21.
Arrangement 23 is provided to allow the concentration of Na in the dialysis fluid upstream of the dialyzer 1 to be changed. Via a control line 20, the arrangement 23 is connected to the control unit 13.
An input unit 24 is also connected to the control unit 13 by a data line 25. A desired clearance K or dialysance D can be entered from the input unit 13. It is also possible for a desired blood flowrate Qb or dialysis fluid flowrate Qd to be entered to enable either one or both of the parameters to be pre-stipulated and/or to be changed during the treatment. Also provided is a memory unit 26 which is connected to the control unit 13 by data line 27. The values entered from the input unit 24 are stored in the memory unit 26 and can be read from the memory unit 26 by the control unit 13.
The dialysis apparatus permits various modes of operation which will be described in detail below. However, it is not a prerequisite of all the modes of operation for dialysance or clearance to be measured. Therefore, the arrangement for measuring clearance or dialysance which is formed by the components identified by reference numerals 21, 23, 16 and 17 can also be dispensed with for the relevant modes of operation.
The dialysis apparatus also has other components, e.g. a drip chamber, shut-off members, etc. which are known to the person skilled in the art but which have not been shown for the sake of greater clarity. The dialysis apparatus may also have an ultrafiltration arrangement.
Using the input unit 24, which has, for example, screen input facilities or a keyboard, the user enters the desired clearance K or dialysance D as well as various other parameters for the hemodialysis. It is also possible for the duration T of the treatment and a desired blood flowrate Qb and/or dialysis fluid flowrate Qd to be entered. The values are stored in the memory unit 26 and can be read off by the control unit 13.
The control unit 13 has a calculating unit 13′ which, from the desired clearance or dialysance and the blood flowrate, calculates that dialysis fluid flowrate that is required to enable the desired clearance or dialysance to be achieved. If what the user pre-stipulated was not the blood flowrate but the dialysis fluid flowrate, then the calculating unit 13′ would calculate the blood flowrate that is required to enable the desired clearance or dialysance to be achieved.
Using the coefficient k0A, the calculation of the required dialysis fluid flowrate Qb or blood flowrate Qd is performed on the basis of the following equation:
In this equation, k0A is a coefficient that depends in essence on the active surface area A of the semi-permeable membrane of the dialyzer (in m2) and on the resistance to diffusion R of the membrane of the dialyzer (in m2 min/ml=104 min/cm) (k0A=A/R).
Whereas the equations given previously define the relationship in which dialysance or clearance stands in a general form, equation (9) defines this relationship for the special case of hemodialysis. Numerical methods which are familiar to the person skilled in the art are generally employed to solve the equation.
The coefficient k0A is a characteristic typical of the dialyzer which is read from the memory unit 26 by the control unit 13. A plurality of coefficients k0A which are associated with different types of dialyzers may be stored in the memory unit 26. Using the input unit 24, the user is able to enter a given type of dialyzer before the treatment begins, thus enabling the control unit 13 to read the coefficient that applies in the given case from the memory unit 26.
Due to the relationship given in equation (9) between blood flowrate and also dialysis fluid flowrate and clearance or dialysance, a reduction in blood flowrate leads to an increase in dialysis fluid flowrate if the desired clearance or dialysance is to be achieved. Conversely, an increase in blood flowrate leads to a reduction in dialysis fluid flowrate if the pre-stipulated clearance or dialysance is to be achieved. If on the other hand it is not the blood flowrate but the dialysis fluid flowrate which is changed, then an increase in dialysis fluid flowrate leads to a reduction in blood flowrate and a reduction in dialysis fluid flowrate leads to an increase in blood flowrate.
If a change is made to the dialysis fluid flowrate or blood flowrate during the treatment, which change may be made in individual steps or continuously, the blood flowrate or dialysis fluid flowrate, in the respective cases, is always adjusted by the control unit 13 such that the desired clearance or dialysance is maintained over the pre-stipulated treatment time.
When controlling the pumping rate of the blood pump 6 and dialysis fluid pump 12, the control unit 13 takes account of the fact that for the blood flowrate and dialysis fluid flowrate there are certain respective minimum or maximum flowrates which must not be dropped below or exceeded. The blood flowrate in particular should not exceed a certain upper limiting value which depends on the vascular access. In the event that the achieving of the desired clearance or dialysance should make it necessary for the respective flowrates for the blood or the dialysis fluid to be exceeded or dropped below, the control unit 13 signals this fault condition to the user. What may be provided for this purpose is for example an alarm arrangement (not shown) which gives an audio and/or visual alarm. The control unit 13 can then pre-stipulate a longer or a shorter treatment time to enable a setting to be made for the flowrate that is within the pre-stipulated limits for blood flowrate and dialysis fluid flowrate.
In what follows, an alternative embodiment of the control arrangement will be described which makes use of the arrangement for measuring dialysance.
The basis for the measurement of dialysance is that the input concentration cdi, such as, for example, as the concentration of Na in the dialysis fluid, upstream of the dialyzer 1 is changed for a short time by the arrangement 23 for changing the composition of the dialysis fluid and the input concentration cdi and output concentration cd, in the dialysis fluid are measured upstream and downstream of the dialyzer by the conductivity sensors 16, 17, respectively. The values measured are processed by the arrangement 21 for determining clearance or dialysance, which has a calculating unit 21′ to calculate the clearance or dialysance.
The calculation of clearance K or dialysance D for a given blood flowrate and dialysis fluid flowrate can be performed using equations (1) to (3). This method of determining clearance or dialysance is described in detail in EP 0 428 927 A1, which is hereby incorporated by reference.
A further method of determining clearance or dialysance, which is distinguished by having a particularly short measuring time, is known from U.S. Pat. No. 6,702,774 B1, which is likewise hereby incorporated by reference. Due to the short measuring times, the application of this method is given preference in the case of the control arrangement according to the present invention.
The control unit 13 controls the arrangement 21 for determining clearance or dialysance at the beginning of the treatment, and the arrangement 21 thus determines clearance or dialysance at the blood flowrate and dialysis fluid flowrate which are pre-stipulated at the beginning of the treatment. The value determined for clearance or dialysance is then read off by the control unit, which calculates the coefficient k0A on the basis of equation (9), which is then available for the continued calculation of the flowrates from equation (9). This embodiment has the advantage that the type of dialyzer does not have to be entered from the input unit 24 and there does not have to be a table in which different coefficients are assigned to different types of dialyzers stored in the memory unit 26.
A further alternative embodiment provides for the desired clearance or dialysance not to be entered from the input unit 24, but rather to be pre-stipulated by the control unit 13 at the beginning of the treatment. What the control unit 13 may pre-stipulate as clearance or dialysance is the value that the arrangement 21 for determining clearance or dialysance determined at, for example, the beginning of the treatment.
The formal provisions which have been described by reference to hemodialysis can also be applied to hemofiltration. The control arrangement for a hemofiltration apparatus therefore differs from the control arrangement described above only in that, as well as the blood flowrate, account is also taken of the ultrafiltration flowrate and/or the substituent flowrate in the evaluation of the flowrates, but account is not taken of the dialysis fluid flowrate. In hemodiafiltration, account is taken not only of the blood flowrate and the dialysis fluid flowrate but also of the ultrafiltration flowrate and/or the substituent flowrate. If one of the flowrates, such as the dialysis fluid flowrate for example, is altered, the calculating unit 13′ of the control unit 13 calculates, on the basis of the relationship defined in equations (4) to (6), one of the other flowrates, such for example as the blood flowrate or ultrafiltration flowrate or substituent flowrate, at which there is an assurance of the desired clearance or dialysance being achieved during the blood treatment, but without the need for measurements of conductivity to be made continuously. All that is required in this case is for clearance or dialysance to be measured once for a set of flowrates Qf1 and/or Qs1 and/or Qd1 and/or Qb1, so that, if there is a change in a flowrate, another flowrate can be adjusted in the appropriate way simply on the basis of a calculation of the parameters. If this measurement is made by the arrangement 21 for determining clearance or dialysance, by making the measurement of conductivity after a brief change in the composition of the dialysis fluid or substituent fluid. The calculation of whichever is the other flowrate, which is intended to counteract the alteration in the one flowrate in order to ensure that the pre-stipulated clearance or dialysance is achieved, will be made whenever the one flowrate has been altered.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2006 026 999.3 | Jun 2006 | DE | national |
| 10 2006 038 545.4 | Aug 2006 | DE | national |
This is a 371 national phase application of PCT/EP2007/004993 filed Jun. 6, 2007, claiming priority to German Patent Application No. 10 2006 026 999.3 filed Jun. 8, 2006, and German Patent Application No. 10 2006 038 545.4 filed Aug. 17, 2006.
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/EP07/04993 | 6/6/2007 | WO | 00 | 7/28/2009 |
