Method for operating a blood treatment apparatus, control unit and treatment apparatus for executing the method

Abstract

A method for operating a blood treatment apparatus including an extracorporeal blood circuit having a blood filter with a blood chamber and a dialysate chamber, between which a membrane is arranged. The method encompasses operating a blood pump from a first time point, at which an ultrafiltration pump is stopped, at least until a second time point, at which at least one of the following conditions is met for the first time after the first time point: a time interval after has elapsed, the blood pump has conveyed a volume after, a measurement of a fluid in the extracorporeal blood circuit exceeds or falls below a threshold.

Claims

1. A method for operating a blood treatment system, the method comprising: at the end of a blood treatment session, continuing to operate a blood pump from a first time point signifying (i) regular completion of the blood treatment session or (ii) manual termination of the blood treatment session by a user, at which an ultrafiltration pump is stopped, at least until a second time point, at which at least one of the following conditions is first met after the first time point: (a) a time interval has elapsed; (b) the blood pump has conveyed a volume after the first time point; and (c) a measurement value of a fluid in an extracorporeal blood circuit of the blood treatment system exceeds or falls below a certain threshold, wherein before the first time point, the ultrafiltration pump and the blood pump are running, and wherein at the first time point, the ultrafiltration pump stops running and the blood pump continues running.

2. The method according to claim 1, wherein the first time point occurs after at least one of: an ultrafiltration goal has been met; and a prescribed treatment time has been reached.

3. The method according to claim 1, wherein the method comprises operating the blood pump after the first time point at least until condition (c) of claim 1 has been met and at least until at least one of the conditions (a) and (b) of claim 1 is met.

4. The method according to claim 1, wherein after the second time point the ultrafiltration pump is reactivated.

5. The method according to claim 4, wherein a target rate of the ultrafiltration pump is calculated based on a flow rate, the measurement value of the fluid in the extracorporeal blood circuit and/or on water available in the extracorporeal blood circuit.

6. The method according to claim 1, wherein after the second time point, a fluid content of the extracorporeal blood circuit is returned to a patient by introducing a substituate into an arterial section of the extracorporeal blood circuit.

7. The method according to claim 6, wherein for at least some of a time period, during which the fluid content of the extracorporeal blood circuit is returned to the patient, at least one of the following is operated: the ultrafiltration pump; the blood pump; and a substituate pump.

8. The method according to claim 7, wherein during return of the fluid content of the extracorporeal blood circuit to the patient, the ultrafiltration pump is operated, after the ultrafiltration pump was stopped at the first time point and was reactivated no earlier than the second time point, at least until at least one of the following conditions is met: (d) the measurement value of the fluid in the extracorporeal blood circuit of the blood treatment system exceeds or falls below a certain threshold; (e) a rinsing fluid volume introduced into the arterial section exceeds a certain value; and (f) a detected pressure exceeds a certain value.

9. The method according to claim 8, wherein the substituate is introduced into the arterial section by the blood pump and wherein after the ultrafiltration pump has stopped due to at least one of the conditions (d), (e) and (f) of claim 8 being met, the blood pump continues running until at least one of the following conditions is met: (g) a measurement value recorded in a venous section of the extracorporeal blood circuit exceeds or falls below a certain threshold; and (h) the rinsing fluid volume introduced into the arterial section exceeds a certain value.

10. The method according to claim 7, wherein a pressure difference is generated in a blood filter of the extracorporeal blood circuit with a lower pressure in a dialysate chamber and a higher pressure in a blood chamber of the extracorporeal blood circuit, wherein the pressure difference is, at least partially, generated by at least one pump of the following pumps: the ultrafiltration pump; the substituate pump; and the blood pump.

11. The method according to claim 10, wherein a flow rate of the at least one pump is between 30 and 280 ml/min.

12. The method according to claim 10, wherein at least one of the following ratios is in a value range of 0.01 to 0.8: a first flow rate ratio of the ultrafiltration pump to the blood pump; and a second flow rate ratio of the ultrafiltration pump to the substituate pump.

13. The method according to claim 6, wherein a first flow rate ratio of the ultrafiltration pump to the blood pump and/or a second flow rate ratio of the ultrafiltration pump to a substituate pump increases while substituate is introduced into the arterial section.

14. The method according to claim 6, wherein a first flow rate ratio of the ultrafiltration pump to the blood pump and/or a second flow rate ratio of the ultrafiltration pump to a substituate pump is varied while substituate is introduced into the arterial section of the extracorporeal blood circuit in order to regulate hematocrit in a venous section of the extracorporeal blood circuit to a pre-determined value.

15. The method according to claim 1, wherein the extracorporeal blood circuit comprises a blood filter having a blood chamber and a dialysate chamber between which a membrane is arranged, wherein the blood chamber is connected to an arterial section which leads to the blood chamber, and to a venous section which leads away from the blood chamber, and wherein the dialysate chamber is connected to a dialysis inlet line which leads to the dialysate chamber and to a dialysate outlet line which leads away from the dialysate chamber.

16. A medical treatment apparatus comprising: an extracorporeal blood circuit with a conduit interior; a blood pump which is arranged at or in the extracorporeal blood circuit for conveying blood within the conduit interior of the extracorporeal blood circuit; and a control unit configured to: at the end of a blood treatment session, continuing to operate the blood pump from a first time point signifying (i) regular completion of the blood treatment session or (ii) manual termination of the blood treatment session by a user, at which an ultrafiltration pump is stopped, at least until a second time point, at which at least one of the following conditions is first met after the first time point: (a) a time interval has elapsed; (b) the blood pump has conveyed a volume after the first time point; and (c) a measurement value of a fluid in the extracorporeal blood circuit exceeds or falls below a certain threshold, wherein before the first time point, the ultrafiltration pump and the blood pump are running, and wherein at the first time point, the ultrafiltration pump stops running and the blood pump continues running.

17. The medical treatment apparatus according to claim 16, which comprises or is connected to at least one pump for generating a pressure difference in a blood filter of the extracorporeal blood circuit, with a lower pressure in a dialysate chamber and a higher pressure in a blood chamber of the extracorporeal blood circuit.

18. A non-transitory computer readable medium storing instructions that are executable by one or more processors configured to perform operations comprising: at the end of a blood treatment session, continuing to operate a blood pump from a first time point signifying (i) regular completion of the blood treatment session or (ii) manual termination of the blood treatment session by a user, at which an ultrafiltration pump is stopped, at least until a second time point, at which at least one of the following conditions is first met after the first time point: (a) a time interval has elapsed; (b) the blood pump has conveyed a volume after the first time point; and (c) a measurement value of a fluid in an extracorporeal blood circuit exceeds or falls below a certain threshold, wherein before the first time point, the ultrafiltration pump and the blood pump are running, and wherein at the first time point, the ultrafiltration pump stops running and the blood pump continues running.

Description

DESCRIPTION OF DRAWINGS

(1) Hereafter, the method is explained based on preferred implementations thereof with reference to the accompanying drawings.

(2) FIG. 1 shows, schematically simplified, the execution of a method from the prior art by means of a known medical treatment apparatus.

(3) FIG. 2 shows, schematically simplified, an exemplary implementation of a medical treatment apparatus while executing the method.

(4) FIG. 3 shows a further method from the prior art, executed by a known medical treatment apparatus.

(5) FIG. 4 shows the comparison between a traditional blood return with NaCl and a blood return by an implementation of the method.

(6) FIG. 5 illustrates the time period of blood pump operation in accord with aspects of the present disclosure.

DETAILED DESCRIPTION

(7) During or after a blood treatment session, the blood or blood mixture in the extracorporeal blood circuit (and in particular in the blood filter) is typically returned to the patient. This usually takes place by introducing substituate into the extracorporeal blood circuit, whereby the blood present therein is displaced downstream and, thus, is re-infused into the patient, e.g. through the venous patient connection.

(8) In some cases, due to the introduction of substituate, a diffuse transition region from blood to substituate develops, in which blood is mixed with substituate. The blood/substituate mixture present downstream of the blood filter (post-filter), thus, often contains substituate. A large amount of substituate may be needed to rinse out the extracorporeal blood circuit all the way to the venous patient connection. Additionally, some of this substituate is reintroduced to the patient, which is often undesired, particularly in dialysis patients.

(9) Methods for removing blood from an extracorporeal blood circuit are shown in FIGS. 1 and 2. A conventional method is shown in FIG. 1. FIG. 2 shows an implementation of the method for removing blood and/or a blood mixture, which occurs in some implementations after a blood treatment session. Alternatively, it may occur during a blood treatment session. Both FIGS. 1 and 2 show schematically simultaneous reinfusion (also referred to as online closed circuit) and residual blood distribution at a time point at which half of the conventional reinfusion volume (e.g., about 200 ml) has been reinjected.

(10) FIG. 1 shows an extracorporeal blood circuit 1, which is connected or connectable via a double needle access to the vascular system of the patient (not shown). The blood circuit 1 is disposed optionally in sections thereof in or on a blood cassette 2. It is connected to a blood treatment apparatus 4. Controlling or regulating the blood treatment apparatus 4 may be carried out by a control or regulating unit 29.

(11) The extracorporeal blood circuit 1 includes an arterial patient tube 6 and an arterial connection needle 5 (as an example of an access device) of an arterial section 9 or of an arterial patient line or blood line 9. The extracorporeal blood circuit 1 further includes a venous patient tube clamp 7 and a connection needle 27 (as an example of a further or second access device) of a venous section 23 or of a venous patient line or blood line 23.

(12) A blood pump 11 is provided in the arterial section 9, a substituate pump 17 is connected to a substituate line 17a. The substituate line 17a may be connected to a substituate source via an optional, preferably automatic substituate port 18, herein shown as not connected. By means of the substituate pump 17, substituate may be introduced via pre-dilution or via post-dilution through associated lines 13 or 14, respectively, into line sections, e.g., into the arterial section 9 or into a venous section 23a, respectively (between the blood chamber 19a and an optional single needle chamber 36) of the extracorporeal blood circuit 1.

(13) A blood filter 19 is provided in the blood circuit 1. It includes the blood chamber 19a which is connected to the arterial section 9 and to the venous section 23. A dialysate chamber 19b of the blood filter 19 is connected to a fresh dialysis liquid inlet line 31a which leads to the dialysate chamber 19b and to a spent dialysate outlet line 31b which leads away from the dialysate chamber 19b.

(14) The fresh dialysis liquid inlet line 31a optionally includes a valve V24 by means of which the flow within the fresh dialysis liquid inlet line 31a may be stopped. The spent dialysate outlet line 31b optionally includes a valve V25 by means of which the flow within the spent dialysate outlet line 31b may be stopped.

(15) The fresh dialysis liquid inlet line 31a is further optionally connected to a compressed air source 26 (not shown here, see however FIG. 3) by means of another internal valve of the device. The compressed air source 26 may be provided as a part or component of the treatment apparatus 4 or may be a separate part therefrom. A pressure sensor 37 (herein not shown, see however FIG. 3) may be provided downstream of the compressed air source 26.

(16) The arrangement of FIG. 1 encompasses an optional arterial detector 15 for detecting air and/or blood. The arrangement of FIG. 1 further encompasses one, two or more pressure sensor(s) 33a, 33b, 33c, e.g. at the points shown in FIGS. 1 and 2.

(17) In order to empty the blood chamber 19a of the blood filter 19 from blood after the treatment, substituate may be added in pre-dilution to the blood circuit 1 and to the blood chamber 19a, as shown in FIG. 1, by the substituate pump 17 through the addition site 13.

(18) Alternatively, or in addition, the substituate may be introduced without operating or not by exclusive operation of the substituate pump 17, but rather by (exclusively or additionally) operating the blood pump 11. To this end, e.g. the arterial patient hose clamp 6 is closed and substituate is introduced into the extracorporeal blood circuit 1 via a supply line 8 from a storage container for the substituate.

(19) The substituate/blood content, thus produced, is conveyed along the conduit interior of the extracorporeal blood circuit 1 by operating the blood pump 11 and/or the substituate pump 17. The substituate/blood content is pressed or conveyed through the blood filter 19, a venous air separation chamber 21 and the venous section 23 of the extracorporeal blood circuit 1 in order to remove the blood from the extracorporeal blood circuit 1 in the direction towards the venous connection needle 27, from the blood filter 19.

(20) A venous substituate-blood detector 25 is optionally arranged in the venous section 23 of the extracorporeal blood circuit 1 as an example of a detection device, which detects the presence of substituate at a pre-determined position of the conduit interior of the extracorporeal blood circuit 1. The blood pump 11 and/or the substituate pump 17 optionally continues conveying the substituate/blood content until the blood, which was present in the venous section 23 of the extracorporeal blood circuit 1, is removed from it and returned to the vascular system of the patient via the venous connection needle 27 and/or until the presence of substituate (or the decrease of the hematocrit in the conduit interior, for example down to 2%) is detected in the conduit interior at the venous substituate/blood detector 25. The conveying operation of all pumps may be stopped at this point. An optical and/or acoustical signal may be output.

(21) FIG. 1 shows a distribution of residual blood after conveying half of the amount of the reinfusion fluid, which is conventionally required for removing blood from the blood tubing set 1. The hematocrit HKT at the venous substituate/blood detector 25 amounts to, at the point in time represented in FIG. 1, 100% of the original HKT value present in the extracorporeal blood circuit 1 immediately before the completion of the blood treatment method. The hematocrit HKT at the venous substituate/blood detector 25 is thus the original HKT value in the extracorporeal blood circuit 1 immediately before the completion of the blood treatment method. Therefore the hematocrit HKT is given in FIG. 1 as HKT 100% at the venous substituate/blood detector 25. All of the percentage values concerning HKT in FIG. 1 and in FIG. 2 are relative values: The percentage values given at the indicated points of the blood tubing circuit 1 indicate which fraction the HKT measurable at those points represents relative to the HKT present in the conduit interior at the end of the treatment, which is in this case when the ultrafiltration pump stops.

(22) The hematocrit HKT of the blood present in the extracorporeal blood circuit 1 is described with HKT and a percentage value at the various points in FIG. 1. The percentage describes the relation of the current hematocrit HKT at the indicated points to the original hematocrit present in the extracorporeal blood circuit 1 immediately before completion of the blood treatment method. If for example the hematocrit HKT in the extracorporeal blood circuit 1 is 42% before the completion of the blood treatment, then HKT 100% means that the hematocrit HKT is still at 42%.

(23) By infusing substituate using the substituate pump 17 through the addition site 13 for pre-dilution, a mixture in the extracorporeal blood circuit 1 occurs or develops at the transition from substituate to blood, in particular in the blood filter 19, which mixture influences the measurable HKT.

(24) In FIG. 1, the hematocrit HKT at the entry of the blood chamber 19a of the blood filter 19 is 2% of the original value. The hematocrit HKT increases across the blood chamber 19ainitially to 10% and then at the venous end of the blood chamber 19a to 20% of the original measurable value. In the venous section 23, the hematocrit HKT further increases first to first 40% shortly after the blood filter 19, then to 60% in section 23a, to 80% after the air separation chamber 21 up to 100% at the venous substituate/blood detector 25 (in both FIG. 1 and FIG. 2. the indicated percentages refer to the ratio of the currently present hematocrit HKT to the original hematocrit HKT, see supra, and are thus relative values). It is now clear that in the prior art the mixing of substituate and blood takes place over a longer distance, such that a substantial volume of substituate must be infused for achieving a complete or an almost complete reinfusion of blood.

(25) The method illustrated in a snapshot in FIG. 2just as in FIG. 1shows a residual blood distribution after conveying half of the fluid, which is conventionally reinfused. Unlike FIG. 1, there is a pressure difference in the blood filter 19 with a lower pressure in the dialysate chamber 19b and a higher pressure in the blood chamber 19a. The pressure difference may be e.g. created by generating an absolute or a relative negative pressure in the dialysate chamber 19b of the blood filter 19, e.g. by removing liquid from the dialysate chamber 19b through the valve V25 by means of an ultrafiltration pump (UF-pump 40, not shown, see FIG. 3). The pressure difference may be generated alternatively or additionally through a flow resistance downstream of the blood chamber 19a, e.g. in the venous section 23a, if at the same time fresh dialysis liquid is introduced into the blood chamber 19a, e.g. by means of the substituate pump 17 and/or the blood pump 11 or by another pump not shown in this implementation.

(26) By means of the pressure difference, the liquid is removed from the extracorporeal blood circuit 1 (see arrow in the blood filter 19). This means that during the blood return, the hematocrit HKT in the extracorporeal blood circuit 1 is generally or at some times higher than in FIG. 1. This is seen at the blood filter 19, at the entry of which, just like in FIG. 1, a hematocrit HKT of 2% (of the original value) may be observed. At the exit of the filter 19, the hematocrit HKT is already 50% compared to 20% (of the original value, respectively) in the method shown in FIG. 1. This is due to the fact that water has been removed from the blood/substituate mixture in the blood filter 19.

(27) At the points in FIG. 1, at which the hematocrit HKT is 40%, 60% and 80%, it is 70%, 80% or 90% in FIG. 2. The transition from blood to substituate is thus sharper than in the conventional method of FIG. 1. Less substituate is required for flushing out the blood/substituate mixture all the way to the venous patient connection. Furthermore, the blood/substituate mixture downstream of the filter 19 contains less substituate.

(28) FIG. 3 shows an exemplary device behavior during a blood return known in the art. A bag 50 containing physiological saline which is placed at the arterial section 9 is a source for substituate with which the blood is displaced from the extracorporeal blood circuit 1. Unlike in FIGS. 1 and 2, the substituate is conveyed into the blood filter 19 with the aid of a blood pump 11.

(29) In this implementation, no patient blood is cleaned in the blood filter 19 anymore, the dialysate chamber 19b and the membrane of the blood filter 19 are not perfused anymore so that the amount of water (plasma) in the patient blood is not reduced any further. Hence, the flow rate of the blood pump 11 reaches the patient (the flow rate is e.g. 30 to 200 ml/min). The valves V24 and V25 are both closed, and the UF pump 40 is switched off.

(30) The arterial blood pump 11 conveys NaCl solution into the extracorporeal blood circuit 1. In this, the flow rate is e.g. 30 to 200 ml/min.

(31) The device behavior during the blood return in an exemplary implementation may also be illustrated with reference to FIG. 3. The dialysate chamber 19b is optionally not perfused anymore in an implementation, i.e., there is no flowexcept through the membraneinto the dialysate chamber. The amount of water (the plasma fraction) of the patient blood is further reduced. In this, the valve V24 is closed and the valve V25 is open. The UF pump 40 is switched on and pumps at e.g. 1 to 80 ml/min to generate a negative pressure in the dialysate chamber 19b and thereby removes water from the blood chamber 19a across the membrane. The arterial blood pump 11 here conveys for example NaCl solution from the bag at the arterial section 9 into the extracorporeal blood circuit 1 at a flow rate of e.g. 30 to 280 ml/min.

(32) The flow rate within the extracorporeal blood circuit 1 across the membrane of the filter 19 to the treatment apparatus 4 is in this example equal to the conveying rate of the UF pump 40. The flow rate which reaches the patient is in this example the flow rate conveyed by the arterial pump minus the flow rate conveyed by the UF pump. The flow rate into the vascular system of the patient (the sum of arterial and venous flow rates) is here e.g. 30 to 200 ml/min.

(33) FIG. 4 shows a comparison between a blood return in the prior art and an exemplary implementation of the method.

(34) In this example, the method, advantageously reduces the required amount of substituate from the usual 390 ml to only 300 ml.

(35) The continuous line (line 1) describes the flow rate present at the entry of the blood filter 19. This flow rate is optionally unchanged during the entire blood return in both the prior art and in the exemplary implementation of the method and may be 100 ml/min.

(36) In the prior art, the conveying rate of the UF pump during the blood return is 0 ml/min, as seen in the thin, short dashed line (line 2). There is no flow across the filter membrane. Therefore, the flow rate at the entry of the blood filter 19 (line 1) is the same here as the flow rate at the exit of the filter 19.

(37) In the prior art, this results in an absolute hematocrit HKT at the venous patient connection (line 5, long-dashed line), in this case at the venous substituate/blood detector 25, which is 40% at the beginning of the blood return. Due to the desired displacement of the blood by the substituate, the hematocrit HKT decreases at the detector 25 during the blood return until the hematocrit reaches a pre-determined value of e.g. 2% there. In the prior art, 390 ml physiological saline solution must be introduced into the extracorporeal blood circuit in order to reach this value of 2% (see x-axis of the diagram of FIG. 4).

(38) In the implementation of the method which is exemplarily illustrated in FIG. 4, the flow rate at the filter exit (line 4, dot-dashed) is lower than the flow rate at the filter entry (line 1), because the UF pump 40 removes water from the dialysate chamber 19b. The flow rate of the UF pump 40 is shown in the bold, short-dashed line (line 3). Here, it is clear that the flow rate of the UF pump 40 increases across or during the blood return (line 3) with the result that the flow rate decreases at the filter exit (line 4). Water is removed from the blood/substituate mixture in the blood filter 19 by the UF pump 40, which causes the hematocrit HKT at the venous patient connection 27 to decrease to the pre-determined value (e.g. 2%) earlier already, namely after infusing only 300 ml substituate (line 6, dashed). Thus, for an almost complete reinfusion of the blood volume contained in the extracorporeal blood circuit 1, less substituate is infused than in the prior art.

(39) In one example, blood is treated until an ultrafiltration goal is met and the ultrafiltration pump 40 is stopped at a time t.sub.UF-stop (FIG. 5). Subsequently, blood flow continues in the extracorporeal circuit 1, preferably without ultrafiltration taking place. To this end, the blood pump 11 is active while the ultrafiltration pump is preferably deactivated (preferably at least until t.sub.BP-min). In this way, concentrated blood in the blood filter 19 is displaced by fresh blood from the patient. A blood measurement device, such as a blood volume monitor (e.g. CritLine), measures the hematocrit, alternatively a default value for the hematocrit is used (such a default value may be 35% and may be set by the clinician). The blood pump operates at least until t.sub.BP-min (FIG. 5), at which point in time at least a certain minimum volume V.sub.post-UF-stop has been conveyed by the blood pump since t.sub.UF-stop, or a minimum time interval T.sub.post-UF-stop has elapsed since t.sub.UF-stop or a blood measurement, such as a hematocrit measurement value, falls below a certain threshold. Between t.sub.UF-stop and t.sub.BP-min, the ultrafiltration pump is preferably deactivated.

(40) After t.sub.BP-min, the blood flow in the extracorporeal blood circuit 1 may be stopped and the arterial section 9 can be connected to a substituate supply, such as a bag of saline solution, or substituate may be provided by a substituate pump 17. Depending on the blood flow rate and the measured hematocrit value or default hematocrit value, the blood treatment apparatus 4 calculates a target ultrafiltration rate. In this, an ultrafiltration factor cf_UF is used as a safety parameter. The factor cf_UF describes the fraction of the water in the extracorporeal blood circuit 1, which may safely be removed from the extracorporeal blood circuit 1. In one implementation, cf_UF is 20%. This means that the water safely available in the extracorporeal blood circuit 1 is considered to be 20% of V.sub.EBC. The target ultrafiltration rate Q.sub.UF is thus Q.sub.UF=Q.sub.BPcf_UF or Q.sub.UF=Q.sub.BP20%. Once blood return starts, for example by starting the blood pump 11, the ultrafiltration pump 40 will run at the target ultrafiltration rate. The ultrafiltration pump 40 runs until at least one of the following criteria is met, which takes into account the amount of blood in the blood filter 19: (a) a pre-determined hematocrit is detected; (b) the blood volume monitor (e.g. CritLine) measures a predefined saturation level; (c) a user selectable relative blood volume; (d) a default or user selectable preset substituate volume; and (e) a predefined post-arterial pump pressure, dialysate pressure, transmembrane or venous pressure is detected.

(41) When the ultrafiltration pump 40 is stopped, the blood pump 11 continues running until blood is no longer sensed at the venous clamp or a set volume of substituate is processed. The described process may also be used in conjunction with priming solutions created online by a dialysis machine.

(42) The present methods and devices are not limited to the above-described implementations, which are given for illustration only.

LIST OF REFERENCE NUMERALS

(43) 1 extracorporeal blood circuit 2 blood cassette 4 treatment apparatus, blood treatment apparatus 5 access device, e.g. arterial connection needle 6 arterial patient hose clamp 7 venous patient hose clamp 8 supply line 9 arterial section or arterial blood line or arterial patient line 11 blood pump 13 addition site for substituate (pre-dilution) 14 addition site for substituate (post-dilution) 15 arterial air/blood detector 17 second conveying device, e.g. a substituate pump 17a substituate line 18 automatic substituate port 19 blood filter, filter 19a blood chamber 19b dialysate chamber 21 venous air separator chamber 23 venous section or venous blood line 23a venous section 25 venous substituate/blood detector 26 compressed air source 27 access device, e.g. venous connection needle, venous patient connection 29 control or regulating unit 31a fresh dialysis liquid inlet line 31b spent dialysate outlet line 33a, b, c pressure sensors 35 single needle valve 36 single needle chamber 37 pressure sensor 40 ultrafiltration pump (UF pump) V24 valve V25 valve 50 bag HKT hematocrit