Generating medical fluid for renal replacement therapy

Abstract

A system is configured to generate a medical fluid for renal replacement therapy by on-line mixing of fluids. The system comprises a first flow path (12), a second flow 5 path (16), a first sensor (20) in the first flow path, and a second sensor (20') in the second flow path. The first and second sensors measure a composition-related parameter. The system is operable to convey at least one of the fluids to the first and second sensors in a calibration phase, and determine a conversion function for converting between a first signal of the first sensor and a second signal of the second 0 sensor, based the first and second signals during the calibration phase. In a production phase, the system is operable to control at least one pump based on converted measurement values given by operating the conversion function on measurement values in the first signal from the first sensor.

Description

[0001] GENERATING MEDICAL FLUID FOR RENAL REPLACEMENT THERAPY

[0002] Technical Field

[0003] The present disclosure relates to the field of renal replacement therapy and in particular to generation of a medical fluid for use in such therapy.

[0004] Background Art

[0005] Renal replacement therapy (RRT) is a therapy that replaces the normal bloodfiltering function of the kidneys. It is used when the kidneys are not working well, which is known as kidney failure and includes acute kidney injury (AKI) and chronic kidney disease (CKD). RRT involves removal of water from the blood of the patient suffering from kidney failure, as well as exchange of solutes with the blood. One example of RRT is extracorporeal blood therapy, in which blood is circulated outside of the patient and interfaced with one or more medical fluids. Modalities of extracorporeal blood therapy include hemodialysis (HD), hemofiltration (HF) and hemodiafiltration (HDF). Another example of RRT is peritoneal dialysis (PD), in which a medical fluid is infused into the peritoneal cavity of the patient to interface with the blood of the patient through the peritoneal membrane.

[0006] Medical fluids used in HD and PD are commonly known as dialysis fluids. In HF, the medical fluid is known as replacement fluid, since it is infused into the blood of the patient to replace fluid removed during therapy. In HDF, both dialysis fluid and replacement fluid are used.

[0007] Extracorporeal blood therapy by HD, HF or HDF is performed differently for treatment of patients with AKI compared to patients with CKD, by use of a different type of dialysis machine. Generally, compared to CKD patients, AKI patients are treated continuously over a longer period of time and at lower fluid flow rates. Such continuous treatment is commonly known as CRRT (Continuous Renal Replacement Therapy). To ensure precise and consistent monitoring and control of fluid removal, known as ultrafiltration, AKI machines are typically provided with scales that are used for measuring the weight of fresh treatment fluid and the weight of spent treatment fluid during therapy. CKD machines instead use flow meters or volumetric pumping to control ultrafiltration.

[0008] PD machines, also known as cyclers, may include at least one scale to measure the weight of fresh treatment fluid infused into the peritoneal cavity and the weight of spent treatment fluid withdrawn from the peritoneal cavity. Over time, RRT consumes large quantities of medical fluid. In some modalities of RRT, pre-made medical fluid is delivered in prefilled bags to the point of care. For example, conventional PD is performed by use of prefilled bags. AKI machines are configured to use prefilled bags of medical fluid, by staff arranging a prefilled bag on one of the scales before treatment, and replacing the prefilled bag as required. On the other hand, CKD machines have integrated capability to generate medical fluid on- demand by mixing one or more concentrates with water, so-called on-line fluid generation. Recently, PD machines with integrated capability of on-line fluid generation have been proposed.

[0009] There is a general desire to advance on-line generation of medical fluid for all types of RRT. Given the installed base of dialysis machines, it would also be desirable to provide a simple technique of re-configuring existing dialysis machines to produce their own medical fluid.

[0010] Summary

[0011] It is an objective to at least partly overcome one or more limitations of the prior art.

[0012] A further objective is to expand the number of machines that may be used for online generation of medical fluid for RRT.

[0013] Another objective is to enable accurate on-line generation of medical fluid at low cost.

[0014] One or more of these objectives, as well as further objectives that may appear from the description below, are at least partly achieved by a system for generating medical fluid for renal replacement therapy, a control method, a computer-readable medium, and a disposable arrangement, embodiments thereof being defined by the dependent claims.

[0015] Still other objectives and aspects, as well as embodiments, features and technical advantages, may appear from the following detailed description, from the attached claims as well as from the drawings.

[0016] Brief Description of the Drawings

[0017] FIG. l is a schematic diagram of an example system for generating medical fluid.

[0018] FIG. 2 A is a flow chart of an example method of operating the system of FIG. 1, and FIG. 2B is a flow chart of an example implementation of a data collection step in the method of FIG. 2 A.

[0019] FIG. 3 is a graph of calibration data obtained during a calibration phase. FIG. 4 is schematic diagram of a control system for generating a control signal for a pump in the system of FIG. 1.

[0020] FIGS 5A-5B are schematic diagrams of a disposable arrangement and a machine, respectively, for use in the system of FIG. 1.

[0021] FIG. 6 is a schematic diagram of a variant of the system in FIG. 1.

[0022] FIG. 7 is a flow chart of a method of operating the system in FIG. 6.

[0023] FIG. 8 is a flow chart of an example method of configuring systems for generating medical fluid.

[0024] FIG. 9 is a schematic diagram of an example water supply device comprising a reusable sensor.

[0025] FIGS 10A-10B are side views of a re-usable sensor before and after manipulation of a disposable line set to encase a fluid within the sensor.

[0026] FIG. 11 is a flow chart of an example procedure of performing fluid control during interruption of dialysis therapy.

[0027] FIG. 12 is a schematic diagram of a sub-system for generating liquid concentrate from dry concentrate.

[0028] Detailed Description of Example Embodiments

[0029] Embodiments will now be described more fully hereinafter with reference to the accompanying drawings, in which some, but not all, embodiments are shown. Indeed, the subject of the present disclosure may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure may satisfy applicable legal requirements. Like numbers refer to like elements throughout.

[0030] Also, it will be understood that, where possible, any of the advantages, features, functions, devices, and / or operational aspects of any of the embodiments described and / or contemplated herein may be included in any of the other embodiments described and / or contemplated herein, and / or vice versa. In addition, where possible, any terms expressed in the singular form herein are meant to also include the plural form and / or vice versa, unless explicitly stated otherwise. As used herein, "at least one" shall mean "one or more" and these phrases are intended to be interchangeable. Accordingly, the terms "a" and / or "an" shall mean "at least one" or "one or more," even though the phrase "one or more" or "at least one" is also used herein. As used herein, except where the context requires otherwise owing to express language or necessary implication, the word "comprise" or variations such as "comprises" or "comprising" is used in an inclusive sense, that is, to specify the presence of the stated features but not to preclude the presence or addition of further features in various embodiments. It will furthermore be understood that, although the terms first, second, etc. may be used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another. For example, a first element could be termed a second element, and, similarly, a second element could be termed a first element, without departing the scope of the present disclosure. As used herein, the terms "multiple", "plural" and "plurality" are intended to imply provision of two or more elements, whereas the term "set" implies provision of at least one element. The term "and / or" includes any and all combinations of one or more of the associated listed elements.

[0031] Well-known functions or structures may not be described in detail for brevity and / or clarity. Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs.

[0032] The present disclosure relates to a technique for on-line generation of medical fluid for use in renal replacement therapy (RRT). As used herein, RRT refers to any therapy that replaces or supplements the normal blood-filtering function of the kidneys in a patient. RRT may involve removal of water from the blood of the patient, as well as exchange of solutes with the blood.

[0033] As used herein, on-line fluid generation refers to the generation of medical fluid on the fly, by mixing various constituents in adequate proportions. On-line fluid generation may comprise on-demand fluid generation, in which the production rate of the medical fluid is adjusted to match the consumption rate of the medical fluid, for example by on-going RRT. It is also conceivable to implement the on-line fluid generation to be independent of the consumption rate of the medical fluid, for example by providing the generated medical fluid to a storage vessel or reservoir.

[0034] The medical fluid may be any fluid that is consumed as part of RRT and is also referred to as "treatment fluid". In the context of extracorporeal blood therapy, the medical fluid may be a dialysis fluid, which is interfaced with blood in a filtration unit, commonly known as a "dialyzer". Alternatively or additionally, the medical fluid may be a so-called replacement fluid or substitution fluid, which is infused into the blood upstream or downstream of the dialyzer, for example as part of hemofiltration (HF) or hemodiafiltration (HDF), as is well known in the art. In the context of PD, the medical fluid may be a dialysis fluid, which is infused into the peritoneal cavity of the patient and which interfaces with the blood of the patient through the peritoneal membrane that lines the peritoneal cavity.

[0035] Medical fluids for use in RRT have well-defined compositions, which are tailored to the specific therapy and to the patient. In on-line generation, the composition of the medical fluid may be given by medical guidelines and / or be set by a caretaker for a specific patient or group of patients. Medical guidelines may also define allowable deviations from nominal concentrations of various solutes in the medical fluid.

[0036] As used herein, a "disposable device" (or part / arrangement / sensor, etc.) is a device that is intended to be used only for a limited time, after which the device is replaced for a new disposable device. Depending on disposable device, the limited time may correspond to a single treatment session or a predefined number of treatment sessions, or be given by a predefined maximum time period. In another alternative, a disposable device may be replaced whenever a new patient is to be treated.

[0037] As used herein, a "re-usable device" (for example, a sensor) is a device that has a longer operative life than a corresponding device that is disposable. Thus, the re-usable device is retained for continued use for its intended purpose when the disposable device is discarded and replaced for a new disposable device. In some embodiments, the reusable device is not intended to be replaced at all. Thus, its operative life is endless, at least in theory. Colloquially, such a device is often referred to as being "permanent" or "permanently installed", although the device will be replaced if it is deemed to be malfunctioning.

[0038] As used herein, a "treatment session" or "session" refers to a time period during which a patient is subjected to RRT by use of a dialysis machine. The time period starts when the patient is connected to the dialysis machine and ends when the patient is disconnected from the dialysis machine.

[0039] In the technique proposed herein, a medical fluid is generated as a mixture of two or more constituent fluids. For example, the medical fluid may be a dialysis fluid, which is generated by mixing water and one or more concentrates. One way to generate dialysis fluid is to use conductivity as feedback for the dosing of the respective concentrate. This is common practice in CKD machines. Such a CKD machine comprises an internal mixing system for producing dialysis fluid on-line by mixing water and one or more concentrates. The concentrate(s) may be supplied in separate containers or bags, which are fluidly connected to the CKD machines. The mixing system comprises a plurality of permanent components, including fluid paths, valves, pumps and sensors, including one or more conductivity sensors. The CKD machine further comprises an internal cleaning system, which is operable to intermittently clean and disinfect the mixing system to ensure to ensure bacterial inactivation of the mixing system. The cleaning system may, for example, be activated after each treatment session. The use of the cleaning system also ensures proper composition of the dialysis fluid. If the mixing system is used continuously, without cleaning, the internal dimensions of the fluid paths and sensors may change from buildup of deposits. For example, deposits inside a conductivity sensor may cause a drift in measured conductivity, for example by changing the distance between electrodes (cell constant) in the conductivity sensor and / or the dimension of the flow path through the conductivity sensor. Deposits may also affect the electrode contact to the fluid.

[0040] As noted in the Background section, it is desirable to advance on-line production of dialysis fluid. There is a huge installed base of dialysis machines in medical facilities all over the world. Existing AKI machines and PD machines are configured to use prefilled bags of dialysis fluid. There is thus a demand for a simple technique of reconfiguring existing dialysis machines for on-line production of dialysis fluid, by mixing of water and one or more concentrates, where the respective concentrate is supplied to the dialysis machine in a container or bag.

[0041] The present Applicant has considered designing a disposable arrangement with fluid paths tailored to enable on-line generation of dialysis fluid by mixing within the disposable arrangement. Such a disposable arrangement is commonly denoted "line set" although it need not only include fluid lines. The disposable arrangement is installed in engagement with pumps on a dialysis machine and connected to sources of water and concentrate(s), whereupon the dialysis machine is operated to dose and mix the water and the concentrate(s) in fluid paths within the disposable arrangement, to produce dialysis fluid on-line. The disposable arrangement may be replaced after a treatment session or at regular time intervals, to ensure the sterility of the dialysis fluid.

[0042] One problem in this context is that the dosing of concentrate(s) is conventionally based on conductivity measurements, which calls for a conductivity sensor of high accuracy. Such conductivity sensors are expensive. If the disposable arrangement were to include one or more expensive conductivity sensors, which are thus discarded after short-time usage, the cost of dialysis treatment would increase drastically. There are also cheap conductivity sensors available on the market. However, inexpensive conductivity sensors generally lack the required accuracy for controlling the dosing of concentrate(s).

[0043] One solution to this problem might be to use concentrate(s) with highly well- defined composition. If the composition of the respective concentrate is known with high accuracy, it would be possible to dose water and concentrate(s) in well-defined proportions without the use of conductivity feedback, provided that the water and concentrate(s) are dosed by high accuracy pumps. However, recalling that concentrates are supplied in containers or bags, the composition of the respective concentrate is likely to change over time as a result of water transport through the container wall. To ensure high accuracy in composition, the self-life of the concentrate containers needs to be short and / or the containers need to include a highly efficient water vapor barrier. Both of these alternatives will increase the cost of concentrate and thus the cost of treatment.

[0044] The technique proposed herein is based on the insight that it would be possible to include a less accurate conductivity sensor in the disposable arrangement if this sensor could be calibrated, whenever necessary, by use of a more accurate conductivity sensor. Thus, the less accurate sensor ("first sensor") is a relatively cheap device and could be part of the disposable arrangement to be discarded after use. The more accurate sensor ("second sensor") would be more expensive and used for a longer period of time than the less accurate sensor. The less accurate sensor is thus arranged to be used for controlling the mixing for production of the dialysis fluid and is exposed to the majority of the fluid transported through the disposable arrangement. The more accurate sensor is fluidly connected to the disposable arrangement and used for calibrating the less accurate sensor during start-up and / or on a periodical basis.

[0045] The proposed technique has the potential of expanding the number of machines that are capable of on-line generation of dialysis fluid, including existing dialysis machines that were originally configured to use prefilled bags of dialysis fluid. By expanding on-line generation of dialysis fluid, the need to use prefilled bags of dialysis fluid will be reduced, resulting in environmental benefits such as reduced transport space and reduced consumption of plastic material. Further, the staff is relieved of the need to store, administrate and handle heavy prefilled bags, for example in an intensive care unit.

[0046] Although conductivity sensors are discussed above, the proposed technique is applicable to any type of sensor that is capable of measuring a fluid parameter that ties to the composition of the fluid that is subjected to the measurement. As used herein, such a fluid parameter is denoted a composition-related parameter (CRP). Alternatively, the fluid parameter may be denoted a concentration-related parameter. In some embodiments, the CRP represents electrical conductivity, or equivalently resistivity, which corresponds to the concentration of ions that carry electrical current in the fluid subjected to the measurement. In a variant, the CRP represents the concentration of a substance or solute in the fluid. In a medical fluid, such a substance may be an electrolyte such as bicarbonate, sodium, potassium, calcium, magnesium, chloride, etc. The concentration of any such substance may be measured by an ion-selective sensor. If the medical fluid is generated for use in PD, a substance acting as an osmotic agent, for example glucose, may be present in the medical fluid, and the CRP may represent the concentration of the osmotic agent. In a further alternative, the CRP may represent the concentration of hydrogen ions, for example in the form of a pH value. Thus, in some embodiments, a CRP sensor may be represented by a conductivity sensor, a resistivity sensor, an ion-selective sensor, a glucose sensor, a pH sensor, or any combination thereof. It is to be understood that the above-mentioned first and second sensors may be of different types. As an alternative to the listed examples of CRP sensors, the second sensor may be a LIBS (Laser-Induced Breakdown Spectroscopy) sensor, a BGA (Blood Gas Analyzer) sensor, or any other type of sensor that is conventionally used for high accuracy concentration measurements in fluids.

[0047] Further, the proposed technique of calibrating a first sensor by use of a second sensor and then using the first sensor to control mixing of fluids for production of medical fluid may be applicable also in situations when both of the first and second sensors are disposable components or re-usable components. Likewise, the proposed technique is not limited to the first sensor being included in a disposable arrangement with fluid paths tailored to enable on-line generation of medical fluid by mixing within the disposable arrangement.

[0048] Various embodiments will now be described with reference to FIG. 1, which illustrates an example system 1 for on-line generation of medical fluid for any type of RRT. In the illustrated example, the medical fluid is generated by mixing two fluids Fl, F2 ("constituent fluids"). The medical fluid is supplied to a receiving device 30. In some embodiments, the medical fluid is a dialysis fluid for use in extracorporeal blood therapy, such as HD or HDF, and the receiving device 30 comprises a dialyzer. In some embodiments, the medical fluid is a replacement fluid for use in HF or HDF, and the receiving device 30 comprises an infusion port on a blood withdrawal line and / or on a blood return line. In some embodiments, the medical fluid is a dialysis fluid for use in PD, and the receiving device 30 comprises a disposable fluid circuit, which is attached to a PD cycler. It is also conceivable that the receiving device 30 corresponds to the peritoneal cavity as such. In some embodiments, which are applicable to all types of RRT, the receiving device 30 is a reservoir for collecting the medical fluid for subsequent use in RRT. In such embodiments, the medical fluid is not generated on- demand. The reservoir may or may not be connected to or part of a system for dialysis therapy.

[0049] The fluids Fl, F2 are held in a respective container 3a, 3b. The containers 3a, 3b may be rigid or flexible and may be of any material, for example plastics. In some embodiments, the first fluid Fl in the first container 3a is water, and the second fluid F2 in the second container 3b is a liquid concentrate. The system 1 further comprises a pump arrangement 4 comprising pumping devices ("pumps") Pl, P2. The respective pump Pl, P2 may be of any type. In the example of FIG. 1, it is assumed that at least pump P2 is occluding, which means that it blocks fluid passage when disabled. If the fluid paths in the system 1 are defined by a disposable arrangement (below), the pumps Pl, P2 are typically peristaltic pumps, which engage the outside of dedicated tubing. The pumps Pl, P2 are operated in response to control signals Cl, C2.

[0050] A main fluid line 12 extends from the first container 3a to an outlet for medical fluid, here comprising a connector 12a for connection to a corresponding connector 30a of the receiving device 30. The main fluid line 12 forms a main supply path ("first flow path") for the medical fluid. A connecting fluid line 13 extends from the second container 3b to a junction 13b on the main fluid line 12. The system 1 is configured to allow a flow of F2 to meet and form a mixture with a flow of Fl in the main fluid line 12, within and downstream of junction 13b. The mixing of Fl and F2 may or may not be completed at junction 13b but is completed at the CRP sensor 20 (below). In the illustrated example, the pump Pl is arranged in the main fluid line 12 to define the flow rate of medical fluid ("main flow rate"), and the pump P2 is arranged in the connecting fluid line 13 to define the flow of F2. Thus, the pump P2 is operable to control the amount of F2 admixed into Fl within the main fluid line 12.

[0051] Although not shown in FIG. 1, the system 1 may include one or more devices configured to promote the mixing, for example inside the junction 13b. In some embodiments, the junction 13b is a 3-way connector. A non-limiting example of a 3- way connector with a mixing-enhancement device is disclosed in W02009 / 030973, which is incorporated herein by reference. In a variant, the mixing-enhancement device may be separate from and located downstream of the junction 13b. Such a separate device may be configured to increase the Reynolds number of the mixture and / or at least one of the incoming fluid flows. Alternatively, the separate device may be configured as a conventional static mixer, or a recirculation circuit in which the mixture is circulated to promote mixing before being conveyed to receiving device 30.

[0052] A diversion line or drain line 16 ("second flow path") extends from the main fluid line 12 towards a drain 17, or alternatively towards a receptable (not shown) for collection of discarded fluid. A valve arrangement 15 is arranged in the main fluid line 12 to selectively divert fluid from the main fluid line 12 into the diversion line 16, by opening a passage from the main fluid line 12 into the diversion line 16. In some embodiments, the valve arrangement 15 is operable to direct all incoming fluid either along the main fluid line 12 towards the receiving device 30 or into the diversion line 16. The valve arrangement 15 may include any number of valves and is operated based on one or more control signals, collectively represented as control signal C3. If the fluid paths are defined by tubing, the valve arrangement 15 may comprise pinch valves, which engage the outside of the tubing.

[0053] A first CRP sensor 20 is arranged in the main fluid line 12, either intermediate the pump Pl and the valve arrangement 15, as shown, or intermediate the junction 13b and the pump Pl. A second CRP sensor 20' is arranged in fluid communication with the diversion line 16. The CRP sensors 20, 20' are configured to output a respective measurement signal SI, SI' which is indicative of a composition-related parameter of passing fluid. In some embodiments, both the output signals SI, SI' represent the same composition-related parameter, for example conductivity.

[0054] As noted, the first fluid Fl may be water, which is a major constituent of any medical fluid. To sustain continued generation of medical fluid, the container 3a may need to be replenished. To this end, the system 1 comprises a water supply device 10, which is configured to generate water of sufficient quality for use in medical fluid. The supply device 10 is connected to the container 3a by a water supply line 11. The supply device 10 is operable to supply water to the container 3a, subject to a control signal C4, to completely or at least partly refill the container 3 a during a refill phase. The refill phase may be selectively initiated when the container 3a is deemed to be (sufficiently) empty. The amount of fluid in the container 3 a may be determined by the control device 40 based on a signal S2 from a scale 2a (below). Alternatively, the amount of fluid in the container 3 a may be estimated by determining and integrating the flow rate of Fl in the main fluid line 12. The flow rate may be given by a flow meter (not shown) or estimated based on the pumping speeds of the pumps Pl, P2.

[0055] In the illustrated example, the system 1 comprises a disposable arrangement, which is engaged with a machine. The disposable arrangement and the machine will be described in more detail below with reference to FIGS 5A-5B. In the illustrated example, the first CRP sensor 20 is disposable and thus included in the disposable arrangement, whereas the second CRP sensor 20' is a re-usable sensor and thus not included in the disposable arrangement. To enable replacement of the disposable arrangement, the system 1 includes a plurality of connectors. Connector 1 la is configured for releasable connection to the water supply device 10. Connector 13a is configured for releasable connection to the container 3b. Connector 16a is configured for releasable connection to the re-usable CRP sensor 20'. As already noted, the system 1 also includes a connector 12a for releasable connection to the receiving device 30.

[0056] In the illustrated example, the system 1 comprises scales 2a, 2b which are configured to provide a respective weight signal S2, S3 representing mass. The containers 3 a, 3b are arranged on a respective scale 2a, 2b. Instead of being hung from the scales 2a, 2b, as shown, the containers 3a, 3b may be placed to rest on the scales 2a, 2b. Scales are commonly included in machines for AKI therapy and PD therapy and used to monitor the amount of fluid in different containers, for example for the purpose of determining the amount of fluid ("ultrafiltrate") that is extracted from the patient during therapy. A control device 40 is configured to control the operation of the system 1. If the system 1 is operated by a dialysis machine, the control device 40 may be a controller of the dialysis machine or a separate controller. The control device 40 is configured to receive measurement signals (here SI', SI, S2, S3), and output control signals (here Cl, C2, C3, C4). The control device 40 may be configured to generate the control signals in accordance with a control program and based on the measurement signals. The control program comprises computer instructions. The control device 40 comprises processing circuitry that includes one or more processors 41 and computer memory 42. The control program is stored in the memory 42 and executed by the processor(s) 41. The control program may be supplied to the control device 40 on a computer-readable medium, which may be a tangible (non-transitory) product (e.g., magnetic medium, optical disk, read-only memory, flash memory, etc.) or a propagating signal. Although not shown in FIG. 1, the control device 40 may be connected to one or more input devices that enable an operator to input control data, as well as one or more UI devices for providing feedback data to the operator. For example, the input device(s) may comprise a keyboard, keypad, computer mouse, control button, touch screen, printer, microphone, etc., and the UI device(s) may comprise a display device, a touch screen, an indicator lamp, an alarm device, a speaker, etc. The operator may be a clinically experienced person, such as a physician or a nurse, or a patient.

[0057] FIG. 2A is a flowchart of an example method 200 of operating a system for online generation of medical fluid. The method is generically applicable to any such system but will be described with reference to the system 1 in FIG. 1. The method 200 is performed by the control device 40. The method 200 comprises a calibration phase, CP, and a production phase, PP. The calibration phase is at least performed at start-up of the system 1. One or more calibration phases may also be performed during operation of the system 1, by the system 1 being transitioned from the production phase to the calibration phase, and the production phase being resumed after completion of the calibration phase. For example, the system 1 may enter the calibration phase at regular intervals, or whenever a new container 3b of liquid concentrate has been installed. Alternatively or additionally, the system may enter the calibration phase whenever the speed of a pump in the pump arrangement is found to deviate from an operative speed range. The operative speed range may be defined as a range of allowable speed values for the respective pump, or as an allowable change of the speed of the respective pump, for example in relation to the initial speed of the respective pump when the current production phase was started.

[0058] The system 1 may also repeat the calibration phase whenever a first CRP sensor 20 has been discarded and replaced for a new first CRP sensor. This calibration phase is used for determining a conversion function (below) between the signal SI of the first CRP sensor 20 and the signal SI' of the second CRP sensor 20'.

[0059] In the illustrated example, the calibration phase comprises a step 201 of operating the valve arrangement 15 and the pump arrangement 4, via control signals C1-C3, to convey at least one of the constituent fluids Fl, F2 to the first and second CRP sensors 20, 20'. Step 201 thus ensures that both sensors 20, 20' are exposed to a fluid of the same composition. In step 202, calibration data from the signals SI, SI' during step 201 is processed to determine a conversion function for converting signal values in the signal SI into signal values in the signal SI'. In the production phase, step 203, the valve arrangement 15 and the pump arrangement 4 are operated, via control signals Cl- C3, to pump the constituent fluids Fl, F2 through the main fluid line 12 to provide a medical fluid at the outlet 12a. Thereby, the mixture of Fl and F2 is only passed through the first sensor 20, and the generation of the medical fluid is controlled based on the signal SI from the first sensor 20. Specifically, as represented by steps 203a- 203c, the pump arrangement 4 is at least partly controlled based on converted signal values given by operating the conversion function on the signal values in the signal SI .

[0060] Steps 203a-203c represent an example control sequence, which is repeatedly performed by the control device 40 to operate the system 1 during the production phase, via the control signals Cl, C2. In step 203a, a measured CRP value is obtained from the first sensor 20. In step 203b, a converted CRP value is generated by operating the conversion function on the measured CRP value from step 203a. The converted CRP value thereby estimates the CRP value that would have been measured by the second sensor 20'. In step 203c, one or more pumps in the pump arrangement in the system 1 is controlled based on the converted CRP value from step 203b to generate the medical fluid with a target composition, for example given by a target CRP value. In the specific example of FIG. 1, the pump Pl may be operated to generate a target flow rate, and the pump P2 may be operated to achieve a converted CRP value that matches the target CRP value.

[0061] FIG. 2B is a flow chart of an example of the data collection step 201. In step 201a, the system is operated to generate and supply a test fluid to both sensors 20, 20'. In step 201b, a first CRP value for the test fluid is obtained from the first sensor 20, and a second CRP value for the test fluid is obtained from the second sensor 20'. The first and second CRP values both represent the test fluid and form a data pair. In the following, such a data pair is denoted "sampled data pair" or SDP. Depending on implementation, step 201b may result in a single SPD or a plurality of SDPs for the test fluid. For example, a single SPD may be given as an average of signal values within a time window in the respective signal SI, SI' ("temporal average"). As indicated by an arrow in FIG. 2B, steps 20 la-20 lb may be repeated any number of times, for different test fluids. Each test fluid has a unique composition and is a unique combination of the available fluids. In the example of FIG. 1, a test fluid may include only Fl (no F2), only F2 (not Fl), or a mixture of Fl and F2. Different test fluids may be formed by mixtures of Fl and F2 at different proportions.

[0062] FIG. 3 is a graph with CRP values in the output signal SI on the x-axis, and CRP values in the output signal SI' on the y-axis. Sampled data pairs for different test fluids are indicated by dots. Each sampled data pair is determined by temporal averaging. Sampled data pair Ml is given by CRP1, CRP1' and is obtained by conveying Fl to both sensors 20, 20'. Sampled data pair M2 is given by CRP2, CRP2' and is obtained by conveying a mixture of Fl and F2 to both sensors 20, 20'. A conversion function CF is determined by fitting a linear function to Ml, M2, for example by linear regression. As indicated by dashed dots M3, M4, further SDPs may be provided by step 201 and used by step 202 to determine the conversion function. The conversion function need not be linear, but may be non-linear, for example a polynomial function, a spline function, etc. It is conceivable to define the conversion function based one the SDP for a single test fluid, by assuming that the conversion function intersects the x-axis or y-axis at a particular CRP value, for example in the origin (0,0).

[0063] The accuracy of the conversion function affects the composition accuracy of the medical fluid. The calibration phase may be tailored to improve the accuracy of the conversion function. This may be achieved by performing step 201 to convey a test fluid that has same composition as the intended medical fluid (i.e., the target composition) through the sensors 20, 20' and by using an SDP for this test fluid in step 202. Thus, the medical fluid is provided as a test fluid in the calibration phase. Further, this SDP may be given an increased weight compared to SDPs for other test fluids when determining the conversion function. It is also conceivable to convey one or more test fluids with a composition near and / or around the target composition, to increase the number of SDPs to be used in step 202. However, the consumption of the constituent fluids increases with the number of test fluids, and so does the duration of the calibration phase. Thus, in some embodiments, the number of test fluids is in the range of 2-5.

[0064] In a non-limiting example, a least mean square approach is used to determine the conversion function. If the correlation between CRP values from the sensors 20, 20' is expected to be linear, the following conversion function is applicable: y = k ■ x + m, with x being a CRP value from sensor 20, y being a CRP value from sensor 20', and k and m being gain and offset for the linear correlation. The values of k and m may be obtained by minimizing the error vector e in the following equation:

[0065] Y = ■ 0 + e, with y being a vector containing CRP values from sensor 20', being a regression matrix, and 0 being a linear correlation vector containing values of k and m. Assuming that step 201 has resulted in three SDPs: CRP1:CRP1', CRP2:CRP2', CRP3:CRP3', we have the following data elements:

[0066] It can be shown that the error vector e is minimized for 0 = (<X>-1■ <X>)-1■ <X>-1■ Y, which thus yields the values of k and m for the conversion function.

[0067] In the specific example of FIG. 1, it is only possible to convey Fl or a mixture of Fl and F2 through the sensors 20, 20'. If pump Pl is operated and pump P2 is disabled, Fl will be conveyed through the main fluid line 12 into the diversion line 16. If both pumps Pl, P2 are operated a mixture of Fl and F2 will be conveyed into the diversion line 16. The proportions between Fl and F2 are adjustable via the speed of the respective pump Pl, P2. A detailed example of step 201 is presented below with reference to FIG. 7.

[0068] In the system 1 of FIG. 1, the sensors 20, 20' are arranged to be connected in series when the valve arrangement 15 is open to the diversion line 16. Thereby, the same fluid will inherently pass through both sensors 20, 20' in step 201. In some embodiments, the CRP values of an SDP may be obtained simultaneously from the sensors 20, 20', by waiting until the signal values are sufficiently stable in both SI and SI' and then extracting a respective CRP value from SI and SI'. It is also conceivable to obtain the CRP values of an SDP at different time points, by accounting for the location of the respective sensor 20, 20'. In FIG. 1, a CRP value may be extracted from output signal SI at a first time point and from output signal SI' at a second time point, where the second time point differs from the first time point by a time offset that corresponds to the distance between the sensors 20, 20' along the flow path. The time offset may be calculated as a function of the current flow rate of fluid. For example, the time offset may be estimated by assuming a plug flow along the flow path. In one example, the time offset is given by V / D, where V is the volume of the flow path between the sensors 20, 20' and D is the flow rate.

[0069] It may be noted that the sensors 20, 20' need not be fluidly connected in series during step 201. In an alternative (not shown), the system 1 is instead be configured with the sensors 20, 20' in parallel flow paths, and the valve arrangement 15 is operable to either direct fluid to the sensor 20 or to the sensor 20'. In such a variant, the CRP values of an SDP are obtained with relatively large time separation.

[0070] To the extent that the present description refers to determining or establishing a flow rate of fluid, this may be done in different ways. In a first example, the system may include one or more flow meters. For example, a flow meter may be arranged in the main fluid line 12 downstream of the pump Pl or in the connecting line 13. In a second example, the flow rate may be given by the pumping speed of a pump. For example, the pump Pl and / or the pump P2 may be a volumetric pump with a known stroke volume, and the flow rate may be calculated as the product of stroke volume and number of strokes per time unit (pumping speed). Alternatively, the pumping speed may be converted to flow rate based on tabulated data. In a third example, the flow rate may be determined based on the weight signals S2, S3 from the scales 2a, 2b. Thus, the flow rate of fluid Fl is given by the weight change of the container 3 a, and the flow rate of fluid F2 is given by the weight change of the container 3b.

[0071] FIG. 4 is a schematic view of a control system 400 for operating the system 1 during the production phase. The control system 400 uses feedback control and may be part of the control device 40. In the example of FIG. 4, the control system 400 is configured to generate the control signal C2 for the pump P2 in FIG. 1, and receive the signal SI from the sensor 20. The control system 400 comprises a target unit 401, which is configured to generate a target signal SI that represents the target composition of the medical fluid to be generated in the production phase. The target signal SI may designate a target CRP value. The control system 400 further comprises a subtraction unit 402, which is configured to output an error signal E, which represents the momentary difference between the target signal SI and an actual value signal SI. Each signal value in the actual value signal SI is a converted CRP value (cf. step 203b). A controller 403 is configured to generate the control signal C2 based on the error signal E. The controller 403 may be of conventional type, for example a P, PI, or PID controller. A calculation unit 404 is configured to generate the actual value signal SI based on the signal SI from sensor 20, by use of the conversion function, CF. Thus, the calculation unit 404 may perform steps 203a-203b in FIG. 2A, whereas step 203c is performed by the combination of the target unit 401, the subtraction unit 402, and the controller 403. It is conceivable that the target flow rate of the medical fluid is changed in the production phase, for example in accordance with a predefined schedule or by intervention by an operator, for example via an input device (not shown) connected to the control device 40. In the system 1 of FIG. 1, the control device 40 will adjust the target flow rate by changing the speed of the pump Pl. Likewise, the target composition of the medical fluid may be changed in the production phase. This corresponds to a change in the target signal SI in FIG. 4. In some embodiments, the control device 40 may operate the valve arrangement 15, via control signal C3, to intermittently divert the medical fluid into the diversion line 16 whenever the target flow rate or the target composition is to be changed, to mitigate the risk that a mixture of incorrect composition is conveyed to the receiving device 30 while the speed of pump Pl or pump P2 is adjusted.

[0072] In some embodiments, the control device 40 performs a monitoring procedure in the production phase, in which the speeds of the pumps in the pump arrangement are evaluated in relation to a set of speed limits for detection of operational error. Errors in the system 1, for example a kinking of a fluid line or a mechanical failure of a pump, may cause the speed of a pump to change significantly. The set of speed limits defines the maximum and / or minimum speed limit for the respective pump. If the current speed of a pump is found to be below its minimum speed limit or above its maximum speed limit, the control device 40 may stop the pumps Pl, P2 and / or cause an alarm to be generated via a UI device (not shown). As an alternative or supplement to monitoring pump speeds, weight changes of the containers 2a, 2b given by the output signals S2, S3 of the scales 2a, 2b may be evaluated for detection of operational error.

[0073] In some embodiments, the control device 40 performs a verification operation during the production phase, in which the valve arrangement 15 is operated to direct at least part of the medical fluid into the diversion line 16. Thereby, the medical fluid is directed through both the first sensor 21 and the second sensor 21'. The verification operation may be performed periodically or be triggered by an event, such as a gradual drift or a step-change in the speed of one or more pumps. As part of the verification operation, the control device 40 obtains current CRP values (first and second measurement values) from the signals SI, SI' for the medical fluid, and evaluates the current CRP values for detection of an unexpected deviation. If an unexpected deviation is found, the control device 40 may take dedicated action, for example generate an alarm on its UI device (not shown) or perform a calibration phase for determination of an updated calibration function to replace the calibration function currently in use. The dedicated action may also include the valve arrangement 15 being operated to divert the medical fluid into the diversion line 16, at least if the magnitude of the unexpected deviation is large, for example in relation to a threshold value. In one example, the control device 40 may evaluate the current CRP values by operating the conversion function on the CRP value from the signal SI to calculate a current converted CRP value, and evaluate this current converted CRP value in relation to the current CRP value from the signal SI'. An unexpected deviation may be detected if the difference between these CRP values exceeds a threshold value.

[0074] FIG. 5 A shows an example of the above-mentioned disposable arrangement la, also denoted "disposable part" herein. The disposable part la may be a unitary component, as shown, or an aggregation of connectable sub-parts. The disposable part la is provided as a dedicated accessory for installation on a machine. In the illustrated example, the disposable part la comprises the water supply line 11, the container 3a, the main fluid line 12, the connecting fluid line 13, the junction 13b, the CRP sensor 20, and the diversion line 16. Connector 1 la is arranged on the end of line 11 for connection to the water supply device 10, connector 13a is arranged on the end of line 13 for connection to the container 3b, connector 12a is arranged on the end of line 12 for connection to the receiving device 30, and connector 16a is arranged on the end of line 16 for connection to the CRP sensor 20'. The provision of connector 13a makes it possible for an operator to remove the container 3b when empty and re-attach a new container 3b full of fluid F2. The disposable part la is discarded after use, for example after completion of a treatment session, after a predetermined maximum time of use, or whenever a new patient is to be treated.

[0075] In the disposable part la, the fluid lines may be defined by plastic tubing. As noted above, the pumps Pl, P2 may be peristaltic pumps which engage the outside of the tubing to generate a moving compression of the tubing to force fluid to move along the tubing. Conventionally, to enable the use of a peristaltic pump, the tubing is provided with a dedicated engagement portion, also known as a pump segment, which is configured to be engaged by compression element(s) of the peristaltic pump. In FIG. 5 A, pump segments 4a, 4b are configured to be engaged by pumps Pl, P2 (FIG. 1).

[0076] The disposable part la may be releasably engaged with a machine lb shown schematically in FIG. 5B. In the illustrated example, the machine lb comprises the pumps Pl, P2, which are accessible for engagement with the pump segments 4a, 4b of the disposable part la. The machine lb also comprises the valve arrangement 15, which is accessible for engagement with fluid lines in the disposable part la. In the illustrated example, the scales 2a, 2b are also included in the machine lb and configured to carry the respective container 3a, 3b. The machine lb also includes the control device 40. In the example of FIG. 5B, the machine lb also includes the CRP sensor 20', although alternative installations are possible (below). As indicated by dashed lines, the machine lb may include further scales 2c-2d, pumps P3-P6, and valve arrangement 15a. The machine lb may be a dialysis machine or a dedicated machine for generation of medical fluid for use in RRT that is performed by a separate dialysis machine.

[0077] It is realized that the system 1 is operated to generate the medical fluid on-line. Further, the medical fluid is generated within the disposable part la. This means that an existing machine, for example a dialysis machine, may be configured for on-line generation of dialysis fluid by attachment of a properly configured disposable part la and by re-configuring the control device 40, for example by updating its control program.

[0078] The system 1 may be configured to generate the medical fluid by mixing any number of constituent fluids. FIG. 6 shows an example system 1 that is configured to mix three constituent fluids Fl, F2 and F3. The following description will focus on differences over the system in FIG. 1. In some embodiments, the first fluid Fl is water, and the second and third fluids F2, F3 are different liquid concentrates. The third fluid F3 is held in a container 3c, which is arranged on a scale 2c. The scale 2c is configured to provide a weight signal S4. The system 1 in FIG. 6 comprises a connecting fluid line 14 that extends from the container 3c to a junction 14b on the main fluid line 12. The junction 14b may be similar to the junction 13b. The system 1 is configured to allow a flow of F3 to meet and form a mixture with a combined flow of Fl and F2 in the main fluid line 12, within and downstream of junction 14b. The pump arrangement 4 of the system includes pumps Pl, P2, and P3. The pump P3 is arranged in the connecting fluid line 14 to define the flow of F3. The pump P3 is operated in response to a control signal C5 generated by the control device 40 (FIG. 1). Thus, the pump P3 is operable to control the amount of F3 admixed into Fl and F2 within the main fluid line 12. A connector 14a is arranged on the end of line 14 for releasable connection to the container 3c. A further CRP sensor 20a is arranged in the main fluid line 12 intermediate the junctions 13b, 14b. The further CRP sensor 20a is configured to output a measurement signal SI a, which is indicative of a composition-related parameter of passing fluid. The measurement signal Sla is provided to the control device 40 (FIG. 1). The further CRP sensor 20a may be disposable. Thus, the connecting line 14 and the further sensor 20a may be included in the disposable part la of FIG. 5 A, and the pump P3 may be included in the machine lb of FIG. 5B.

[0079] When the system 1 in FIG. 6 is operated in the production phase, the signal SI of sensor 20 is used for controlling the pump P3, to achieve the target CRP value of the medical fluid ("final CRP target"), by analogy with FIG. 4. Further, the signal Sla of sensor 20a is used for controlling the pump P2, to achieve a target CRP value ("intermediate CRP value") of the intermediate mixture of Fl and F2, by analogy with FIG. 4. Further, as understood from the foregoing, the pump Pl may or may not be operated by feedback control to generate a target flow rate.

[0080] FIG. 7 is a flow chart of an example method 700 of operating the system 1 in FIG. 6. In relation to the method 200 in FIG. 2A, steps 701-707 correspond to step 201, steps 708-709 correspond to step 202, and steps 710-711 correspond to step 203. The method 700 is configured to minimize the waste of constituent fluids Fl, F2, F3, by performing the calibration phase while sequentially admixing the fluids in proportions matching their proportions in the medical fluid. In step 701, the valve arrangement 15 is operated to direct fluid from the main fluid line 12 into the diversion line 16, and thus to drain 17. No fluid is passed to the receiving device 30. In step 702, pump Pl is started and operated to generate a target flow rate, which is maintained throughout the calibration phase. Thereby, Fl is pumped through sensors 20a, 20, and 20' as a first or initial test fluid. The target flow rate may be identical to the target flow rate of the medical fluid in the subsequent production phase. This will ensure a smooth transition from the calibration phase to the production phase. The pump Pl may or may not be operated by feedback control in the calibration phase. In step 703, a respective CRP value is obtained from signals SI a, SI and SI', resulting in a first SDP for sensors 20a, 20', and a first SDP for sensors 20, 20'. As noted above, the respective CRP value may be obtained as an average of a plurality of signal values in the respective signal. Step 703 may be performed after verifying that the temporal variability in the signals SI a, SI, SI' is below a variability threshold, to avoid transient effects. In step 704, the pump P2 is started and operated, by feedback control based on signal SI', to achieve a first target CRP value. The first target CRP value is identical to the intermediate CRP value used in the production phase. Thereby, an intermediate mixture of FI and F2 is pumped through sensors 20a, 20, and 20' as a second test fluid. In step 705, by analogy with the step 703, a respective CRP value is obtained from signals SI a, SI and SI', resulting in a second SDP for sensors 20a, 20', and a second SDP for sensors 20, 20'. In step 706, the pump P3 is started and operated, by feedback control based on signal SI', to achieve a second target CRP value. The second target CRP value is identical to the final CRP target used in the production phase. The pump P2 is operated to generate the same flow rate in steps 704 and 706. Thereby, a final mixture of Fl, F2 and F3 is pumped through sensors 20 and 20' as a third test fluid in step 706. The final mixture has the same composition as the medical fluid to be generated. The speeds of the pumps Pl and P2 may be fixed when the method 700 transitions from step 704 to step 706. If the speed of the pump Pl is allowed to vary, the speed of the pump P2 may be controlled to maintain the same relation between the speeds of the pumps Pl, P2 in step 706 as in step 704. In another embodiment, the speed of the pump P2 is controlled based on a measured or estimated flow rate produced by the pump P2, for example based on the weight signal S3 or the output signal of a flow meter (not shown). In another embodiment, the speed of the pump P2 is controlled to maintain the first target CRP value in the signal Sla from sensor 21a. In step 707, a respective CRP value is obtained from signals SI and SI', resulting in a third SDP for sensors 20, 20'. In step 708, a first conversion function for sensor 20 is determined by use of the first, second and third SDPs for sensors 20, 20' obtained in steps 703, 705 and 707. With reference to FIG. 3, Ml -M3 may correspond to the first to third SDPs. In step 709, a second conversion function for sensor 20a is determined by use of the first and second SPDs for sensors 20a, 20' obtained in steps 703 and 705. With reference to FIG. 3, Ml and M2 may correspond to the first and second SDPs. In step 710, a flow control procedure for the production phase is started. Pump Pl is operated to generate the target flow rate of the medical fluid, pump P2 is operated by feedback control based on the signal Sla and by use of the second conversion function, and pump P3 is operated by feedback control based on the signal SI and by use of the first conversion function. In step 711, the valve arrangement 15 is operated to direct the medical fluid along the main fluid line 12 to the outlet 12a.

[0081] The skilled person understands that the method 700 may be expanded to a larger number of constituent fluids. Such a system may include a correspondingly increased number of disposable CRP sensors. The method 700 is equally applicable to mixing of two constituent fluids Fl, F2, for example in the system 1 of FIG. 1.

[0082] It may be noted that the further CRP sensor 20a may be omitted in the system 1 of FIG. 6, for example if the pump Pl and one of the pumps P2, P3 are operated with a fixed pumping speed during the production phase. The further sensor 20a may also be omitted if one of the pumps P2, P3 is controlled based on another measurement signal in the calibration phase and / or the production phase. In some embodiments, P2 or P3 is controlled, by feedback control, based on a momentary weight change of the respective container 3b, 3c in relation to a momentary weight change of the container 3a. For example, the operation of the pump P2 may be controlled to achieve a target relation between the momentary weight change of the container 3b and the container 3 a. Such feedback control is thus performed based on the weight signals S3 and S2. The target relation may be determined as part of the calibration phase. In the example of FIG. 7, the target relation may be determined in step 705, when pump P2 has been controlled to yield the first target CRP value at the sensor 21', by determining a weight change per unit time in signal S2 and a weight change per unit time in signal S3. The weight change per unit time may be determined by operating any conventional differentiation algorithm on the respective signal S2, S3. The weight-based feedback control presumes provision of scales in the machine lb (FIG. 5B). Even if scales are available, it may be difficult or undesirable to implement the weight-based feedback control, for example to control the dosing of a liquid concentrate that is generated on-line by the system 1 from a dry concentrate. FIG. 12 shows an example installation of a container 3b that contains a dry concentrate F2'. The dry concentrate F2' is dissolvable in water and may be in the form of powder or granules. In the illustrated example, the container 3b is installed similar to the container 3b in the system 1 of FIG. 1 or FIG. 6. The container 3b is releasably connected to the connector 13a on the fluid line 13 and to a connector 18a on a water supply line 18. The water supply line 18 may extend to the container 3a or to the water supply device 10. The pump P2 is arranged on the fluid line 13 to draw liquid concentrate F2 from the container 3b, optionally via a conditioning unit 19. The conditioning unit 19 may be configured to ensure that the liquid concentrate F2 is supplied with a proper composition. The conditioning unit 19 may comprise conventional equipment for mixing, adding further water, recirculation, etc. It is realized that it may be difficult to implement weight-based control in the installation of FIG. 12, at least if the liquid concentrate F2 is generated on-demand.

[0083] In some embodiments, the system 1 is configured to perform weight-based control of pump(s) for dosing of liquid concentrate from prefilled container(s), and to perform CRP -based control of pump(s) for dosing of liquid concentrate that is formed by dilution of dry concentrate. The CRP -based control may be performed in accordance with the method in FIG. 2 A or FIG. 6.

[0084] FIG. 8 is a flow chart of an example method 800 of configuring and operating a system to generate medical fluid. The method 800 may be performed by a control device in any system described herein. In step 801, a user (operator) is caused to mount the disposable part on the machine, in proper engagement with scales, pumps, valve arrangement, etc. The machine may be a dialysis machine or any other appropriately equipped machine. In step 802, the user is caused to connect the diversion line 16 in fluid communication with the re-usable CRP sensor 20'. Then, the method 200 of FIG. 2A is executed to generate the medical fluid. At a certain time point, the method 200 is terminated and step 803 is performed to initiate a procedure for securing re-use of the CRP sensor 20'. Examples of step 803 are described below. When step 803 is completed, step 804 is performed to cause the user to remove the disposable part from the machine and discard the disposable part. Steps 801-804 may comprise providing user instructions on a UI device (not shown) to cause the user to perform one or more actions. Thus, in the context of the present disclosure, causing a user to perform an action is equivalent to outputting an instruction to the user to perform the action. Step 803 may differ depending on location and degree of integration of the reusable CRP sensor 20' within the system.

[0085] In some embodiments, the re-usable CRP sensor 20' is integrated in the water supply device 10. An example of such a supply device 10 is shown in FIG. 9. The operation of the supply device 10 is controlled by an internal controller (not shown). The device 10 comprises a water processing unit 90, which is operable to process incoming water to produce purified water for use in the medical fluid. The water processing unit 90 may be configured to purify the incoming water by any available technique, such as sediment filter, carbon filter, resin bed, ultrafiltration (UF), reverse osmosis (RO), nanofiltration, electrodeionization (EDI), capacitive deionization (CDI), or any combination thereof. The device 10 comprises a water supply line 91 that extends from an inlet connector 91a to an outlet connector 91b. In operation, a source of tap water may be connected to the inlet connector 91a, and the terminal connector I la of the disposable part (FIGS 1 and 6) may be connected to the outlet connector 91b. The device 10 further comprises an auxiliary fluid line 92, which extends from an inlet connector 92a to an outlet connector 92b via the re-usable sensor 20'. In operation, the terminal connector 16a of the disposable part (FIGS 1, 5 A and 6) may be connected to the inlet connector 92a, and a fluid line (not shown) extending to the drain 17 may be connected to the outlet connector 92b. The device 10 further comprises a cleaning unit 93, which is operable to perform a cleaning operation on the re-usable sensor 20' and optionally the water processing unit 90. The cleaning operation may include rinsing and / or disinfection. As used herein, rinsing involves flushing the sensor 20' by a fluid to remove deposits, particles, etc. The fluid may be any liquid, including water, and may or may not comprise a cleaning agent, such as a detergent, a descaling agent, etc. As used herein, disinfecting refers to a process of preventing growth of microorganisms in the sensor 20' and may involve heat treatment, flushing with a disinfectant or sterilant, etc. It is to be understood that not only the sensor 20' is treated in the cleaning operation but also connecting fluid paths. The device 10 further comprises an VO unit 94, which is operable to receive the control signal C4 (FIGS 1 and 6). In operation, the VO unit 94 is connected to the control device 40, by wire or wirelessly. In one implementation of step 803, the control device 40 transmits the control signal C4 to the supply device 10 to initiate the cleaning operation. In another implementation of step 803, the control device 40 causes, via its UI device, the user to initiate the cleaning operation, for example by pushing a dedicated button (not shown) on the device 10.

[0086] If the re-usable CRP sensor 20' is well-spaced from the main fluid line 12 (FIGS 1 and 6), growth of microorganisms in the sensor 20' is less of a risk factor. The need for disinfection is thereby reduced, or even eliminated. Nevertheless, since the sensor 20' is re-used in plural sessions, periodic cleaning may be performed to ensure proper functioning of the sensor 20' over time. For example, rinsing may be performed to mitigate fouling, for example by scaling, deposits, etc. Disinfection to mitigate growth of microorganisms in the sensor 20' may be relevant whenever there is a risk of microorganisms moving along the diversion line 16 into the main fluid line 12 (FIGS 1 and 6). It is realized that the cleaning operation may involve rinsing and / or disinfection and that rinsing and disinfection may be performed at different time intervals. Further, it is conceivable to perform the cleaning operation less frequently than after every session.

[0087] In some embodiments, the re-usable CRP sensor 20' is integrated in the machine lb (cf. FIG. 5B). If the machine lb comprises an integrated cleaning unit for cleaning the sensor 20', the control device 40 may autonomously initiate the cleaning operation in step 803.

[0088] In some embodiments, the re-usable CRP sensor 20' is included in a separate device (not shown), which is separate from the machine lb and the water supply device 10. Such a re-usable CRP sensor 20' may but need not be connected to the control device 40 for electronic transfer of the output signal SI' (cf. FIG. 1). Instead, measurement data generated by the sensor 20' may be manually entered into the control device 40 by an operator through a data entry interface, or be electronically transferred to the control device 40 by use of a scanner. For example, the scanner may be operated to scan a printed or displayed test result from the sensor 20', for example in the form of plain text or a machine-readable code.

[0089] FIGS 10A-10B show an example of a re-usable CRP sensor 20', which is arranged inside a device 1000, which may be the machine lb, the water supply device 10 or the above-mentioned separate device. Here, it is assumed that the device 1000 lacks functionality for rinsing or disinfecting the sensor 20'. The sensor 20' defines an internal channel 20" and is configured to measure CRP values for fluid in the channel 20". The device 1000 defines an inlet port 21a and an outlet port 21b, which are in fluid communication with the channel 20" on a flow path 21. Although not shown, the device 1000 comprises an VO unit for transfer of measurement data to the control device 40. FIG. 10A shows a first connection state, which is attained in step 802 of FIG. 8. In the first connection state, the sensor 20' is fluid communication with the diversion line 16. In the illustrated example, the diversion line 16 is connected to the inlet port 21a via a line segment 16'. Specifically, line segment 16' comprises terminal connector 16al, which is configured for connection to terminal connector 16a on diversion line 16, and terminal connector 16a2, which is configured for connection to inlet port 21a. Further, a line segment 16" is connected by terminal connector 16a3 to outlet port 21b and extends to drain 17. FIG. 10B shows a second connection state, which is attained in step 803 of FIG. 8. In the second connection state, the sensor 20' is encapsulated in a closed loop and is filled with a dedicated fluid, which is configured to prolong the operative life of the sensor 20'. For example, the dedicated fluid may be a bacteriostatic fluid. A bacteriostatic fluid comprises a bacteriostatic agent, which is a biological or chemical agent that stops bacterial growth, or even kills bacteria (also known as bactericidal agent). Thus, in the second connection state, the sensor 20' is kept in an environment that prevents bacterial growth. To attain the second connection state, step 803 may comprise operating the system 1 to convey the dedicated fluid from a supply into the diversion line 16 and through the sensor 20'. When the sensor channel 20" is deemed to contain the dedicated fluid, step 803 comprises instructing the user to disconnect line 16' from line 16, disconnect line 16" from port 21b, and attach terminal connector 16al to port 21b. By this manipulation, the dedicated fluid is retained within the sensor 20'. In some embodiments, the filling of the sensor channel 20" is monitored based on the output signal of the sensor 20', i.e. SI'. The manipulation in FIGS 10A-10B involve reusing a component of the disposable part to fluidly connect the ports 21a, 21b. When the method 800 is to be performed at a later time, at which the device 1000 is in the second connection state, step 802 may comprise instructing the user to disconnect and discard line segment 16' before connecting a new disposable part to the device 1000 in accordance with the first connection state (FIG. 10 A).

[0090] The dedicated fluid may be distinct from the fluids Fl, F2, F3 and may be conveyed into the diversion line 16 from a separate source by a dedicated pump. However, in some embodiments, the dedicated fluid is made up of at least one liquid concentrate that is included in the medical fluid.

[0091] FIGS 10A-10B only show one example of how the sensor 20' may be manipulated to retain the dedicated fluid within the sensor 20'. For example, the ports 21a, 21b may be sealed in other ways to retain the dedicated fluid. Further, the technique of retaining a dedicated fluid within the sensor 20' in step 803 is also applicable if the sensor 20' is integrated within the machine lb or the water supply device 10.

[0092] FIG. 11 is a flow chart of an example method 1100 which may be performed during generation of the medical fluid in the system 1. The method 1110 will be described with reference to the system 1 in FIG. 1 and is equally applicable to the system 1 in FIG. 6. When an interruption in the operation of the receiving device 30 is detected (step 1101), the valve arrangement 15 is operated to direct the medical fluid to drain 17 (step 1102). Here, it is presumed that the interruption prevents the device 30 from receiving the medical fluid. The control device 40 may detect the interruption based on an output signal from the receiving device 30 or from a sensor, for example a pressure sensor (not shown) in line 12. In conjunction with step 1102, to minimize the waste of liquid concentrate F2, the speed of at least pump P2 is reduced but not stopped (step 1103). Thus, both pumps Pl, P2 are still operative. When a resumed operation of the receiving device 30 is detected (step 1104), the speeds of pumps Pl, P2 are controlled to meet the target flow rate and to achieve the final CRP target at the sensor 20 (step 1105). In conjunction with step 1104, the valve arrangement 15 is operated to direct the medical fluid towards the receiving device 30 (step 1106). It is conceivable to implement step 1104 with a timeout function, which causes the system 1 to be shut down if resumed operation is not detected within a predefined time from step 1101.

[0093] By the method 1100, pumps Pl, P2 are kept operating during the interruption of the receiving device 30. If pumps Pl, P2 were to be stopped, hysteresis effects may require the control device 40 to enter the calibration phase. It is conceivable that both pumps Pl, P2 are operated to reduce their speeds in step 1103. Further, when operated at the reduced speeds, pumps Pl, P2 may be controlled to maintain the target composition of the medical fluid, based on the signal SI of the signal SI'. Thereby, the medical fluid is still generated in step 1103, albeit at a reduced flow rate.

[0094] In some embodiments, both pumps Pl, P2 are stopped when the operation of the receiving device 30 is interrupted and then re-started at their previous speeds when the operation of the receiving device 30 is resumed. Such embodiments may be possible for pumps that do not exhibit the above-mentioned hysteresis effect.

[0095] The present disclosure is not limited to the examples given hereinabove. For example, the container 3a for holding the first fluid Fl, typically water, is optional. Instead, water may be supplied directly to the main fluid line 12 from the water supply device 10. Further, the provision and use of scales is optional. Further, the scales may be used for other purposes, such as monitoring and / or controlling ultrafiltration. In some implementations, Fl does not only contain water.

[0096] In some embodiments, some or all of the fluid lines in the disposable part are configured as passageways in a unitary cassette. The pumps and / or the valve arrangement may or may not be integrated in the cassette. If integrated, the pumps may, for example, be implemented as membrane pumps or roller pumps.

[0097] In further alternatives, the containers 3b, 3c may be refillable, by being fluidly connected to a respective source of liquid concentrate.

[0098] In the systems 1 shown in the drawings, the pump Pl is located in the main fluid line 12 downstream of junction 13b (and junction 14b, if present). Thereby, the first pump Pl not only draws fluid Fl from container 3a but also defines the flow rate of the medical fluid ("main flow rate"). This gives the technical advantage of simplifying adjustment of the main flow rate. However, in some embodiments, the pump Pl may instead be located upstream of junction(s) 13b, 14b. Any commercially available concentrate(s) may be used in the system 1 as described herein.

[0099] In some embodiments, dialysis fluid for CRRT treatment of AKI patients is generated by mixing at least one concentrate with water. In a non-limiting example, such a dialysis fluid comprises bicarbonate, sodium, potassium, calcium, magnesium, phosphate, glucose, acetate and chloride. In one example, a base concentrate and an electrolyte concentrate may be mixed with water to form the dialysis fluid. For example, the base concentrate may be an alkaline bicarbonate solution, and the electrolyte concentrate may be an acidic glucose-based electrolyte solution.

[0100] In some embodiments, dialysis fluid for use in peritoneal dialysis (PD) is generated by mixing at least one concentrate with water. Example compositions of PD concentrates, to be mixed with water individually or in combination, are disclosed in US2018 / 0021501 and WO2017 / 193069, which are incorporated herein by reference.

[0101] In some embodiments, dialysis fluid for treatment of CKD patients by hemodialysis, hemofiltration or hemodiafiltration is generated by mixing a single concentrate with water at a dilution ration of 10-50 by volume. In a non-limiting example, the single concentrate comprises lactate, sodium, potassium, calcium, magnesium, glucose and chloride. Such a concentrate is, for example, commercially available for the PureFlow SL system from NxStage. Alternatively, the dialysis fluid may be generated by mixing two concentrates with water. For example, a bicarbonate concentrate and an acid concentrate may be mixed with water at a dilution ratio of 10- 50. Such concentrates are commercially available and well-known in the art. In a nonlimiting example, the bicarbonate concentrate comprises bicarbonate, and the acid concentrate comprises sodium, potassium, calcium, magnesium, glucose, acetate and chloride. In some acid concentrates, acetate is replaced or supplemented by another acid, for example citric acid or hydrochloric acid.

[0102] While the subject of the present disclosure has been described in connection with what is presently considered to be the most practical embodiments, it is to be understood that the subject of the present disclosure is not to be limited to the disclosed embodiments, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and the scope of the appended claims.

[0103] Further, while operations are depicted in the drawings in a particular order, this should not be understood as requiring that such operations be performed in the particular order shown or in sequential order, or that all illustrated operations be performed, to achieve desirable results. In the following, clauses are recited to summarize some aspects and embodiments as disclosed in the foregoing.

[0104] Cl. A system for generating a medical fluid for renal replacement therapy, said system comprising: a first flow path (12) for receiving and mixing at least two fluids to form the medical fluid; a pump arrangement (4) for pumping the at least two fluids through the first flow path (12); a first sensor (20, 20a), which is arranged in the first flow path (12) to provide a first signal (SI, Sla) indicative of a composition-related parameter; a valve arrangement (15) operable to selectively open a passage from the first flow path (12) to a second flow path (16); a second sensor (20'), which is arranged in the second flow path (16) to provide a second signal (SI1) indicative of the composition-related parameter; and a control device (40) configured to: operate, in a calibration phase (CP), the valve arrangement (15) and the pump arrangement (4) to convey at least one of the at least two fluids to the first and second sensors (20, 20a; 20'); determine, based on the first and second signals (SI, Sla; SI') during the calibration phase, a conversion function for converting measurement values in the first signal (SI, Sla) into measurement values in the second signal (SI'); and operate, in a production phase (PP), the valve arrangement (15) and the pump arrangement (4) to pump the at least two fluids through the first flow path (12) to provide the medical fluid at an outlet (12a), wherein at least one pump (P2; P3) in the pump arrangement (4) is controlled based on converted measurement values given by operating the conversion function on the measurement values in the first signal (SI; Sla) from the first sensor (20; 20a) during the production phase (PP).

[0105] C2. The system of Cl, wherein the first sensor (20, 20a) is a disposable component and the second sensor (20') is a re-usable component.

[0106] C3. The system of Cl or C2, wherein the second sensor (20') is configured to be retained in the system and used in a repetition of the calibration phase when the first sensor (20, 20a) has been discarded and replaced for a new first sensor (20, 20a), wherein the repetition of the calibration phase results in an updated conversion function for converting the measurement values in the first signal (SI, Sla) of the new first sensor (20, 20a) into the measurement values in the second signal (ST) of the second sensor (20').

[0107] C4. The system of any preceding clause, wherein the second sensor (20') has a higher accuracy than the first sensor (20, 20a).

[0108] C5. The system of any preceding clause, which comprises a machine (lb) and a disposable arrangement (la) releasably engaged with the machine (lb), wherein the machine (lb) includes the pump arrangement (4) and the valve arrangement (15), and wherein the disposable arrangement (la) defines the first flow path (12) and the second flow path (16), and wherein the first sensor (20, 20a) is included in the disposable arrangement (la).

[0109] C6. The system of any preceding clause, wherein the control device (40), in the calibration phase (CP), is configured to: operate the pump arrangement (4) to generate a set of test fluids from said at least two fluids; operate the pump arrangement (4) and the valve arrangement (15) to convey a respective test fluid in the set of test fluids to the first and second sensors (20, 20a; 20'); obtain a first measurement value for the respective test fluid from the first signal (SI, SI a); obtain a second measurement value for the respective test fluid from the second signal (ST); and determine the conversion function based on the first and second measurement values for the respective test fluid.

[0110] C7. The system of C6, wherein at least one test fluid in the set of test fluids comprises a mixture of the at least two fluids.

[0111] C8. The system of C7, wherein the control device (40), in the calibration phase (CP), is configured to operate the pump arrangement (4) to generate said at least one test fluid to achieve a target value in the second signal (ST) from the second sensor (20').

[0112] C9. The system of any one of C6-C8, wherein one test fluid in the set of test fluids is the medical fluid.

[0113] CIO. The system of any one of C6-C9, wherein control device (40), in the calibration phase (CP), is configured to operate the pump arrangement (4) to generate the set of test fluids by providing a first fluid (Fl) among the at least two fluids as an initial test fluid, and by sequentially adding another fluid among the at least two fluids to the initial test fluid, to generate a corresponding sequence of test fluids, until all fluids among the at least two fluids have been added to the initial test fluid.

[0114] Cl 1. The system of CIO, wherein the first fluid (Fl) is water, and wherein each of said another fluid is added in a proportion equal to its proportion in the medical fluid.

[0115] C12. The system of any one of C6-C11, wherein the control device (40) is configured to determine the conversion function by fitting a predefined function to the first and second measurement values for the set of test fluids.

[0116] C13. The system of any preceding clause, wherein the first sensor (20, 20a) is located upstream of the valve arrangement (15) in the first flow path (12), so that the first and second sensors (20, 20a; 20') are fluidly connected in series when the valve arrangement (15) is operated to open the passage from the first flow path (12) to the second flow path (16).

[0117] C14. The system of any preceding clause, wherein the control device (40), in the production phase, is configured to: intermittently operate the valve arrangement (15) to open the passage to the second flow path (16) and direct the medical fluid to the second sensor (20'); obtain a current first measurement value for the medical fluid from the first signal (SI, SI a); obtain a current second measurement value for the medical fluid from the second signal (SI1); evaluate the current first and second measurement values for detection of a deviation; and take dedicated action upon detection of the deviation.

[0118] C15. The system of C14, wherein the control device (40) is configured to: operate the conversion function on the current first measurement value to generate a current converted measurement value; and evaluate the current second measurement value and the current converted measurement value for detection of the deviation.

[0119] C16. The system of C14 or C15, wherein the dedicated action comprises at least one of generating an alarm, or performing the calibration phase (CP) to determine an updated conversion function.

[0120] Cl 7. The system of any preceding clause, wherein the control device (40), in the production phase (PP), is configured to monitor the speeds of pumps in the pump arrangement (4) for detection of changes indicative of operational error.

[0121] C18. The system of any preceding clause, said at least two fluids comprise a liquid concentrate.

[0122] Cl 9. The system of Cl 8, which is configured to generate the liquid concentrate from a dry concentrate.

[0123] C20. The system of any preceding clause, wherein the control device (40), in the production phase (PP), is configured to control the pump arrangement (4) to generate the medical fluid at a target flow rate, while maintaining the converted measurement values at a target value of the composition-related parameter.

[0124] C21. The system of any preceding clause, wherein the control device (40) is operable to initiate a procedure for securing re-use of the second sensor (20').

[0125] C22. The system of C21, wherein the procedure for securing re-use comprises at least one of a) operating a fluid supply device (10; lb; 1000), which comprises the second sensor (20'), to perform an operation of rinsing and / or disinfecting the second sensor (20'), or b) conveying a dedicated fluid through the second flow path (16) into the second sensor (20'), and causing a user to disconnect the second flow path (16) from the second sensor (20') and manipulate the second sensor (20') to retain the dedicated fluid within the second sensor (20').

[0126] C23. The system of C22, wherein the dedicated fluid is bacteriostatic.

[0127] C24. The system of C22 or C23, which is configured to provide the dedicated fluid based on at least one fluid among said at least two fluids.

[0128] C25. The system of any preceding clause, wherein said at least two fluids comprise a first fluid (Fl) provided by a first source (3a), and a second fluid (F2) provided by a second source (3b), wherein the pump arrangement (4) comprises a first pump (Pl), which is configured to convey the first fluid (Fl) from the first source (3a) into the first flow path (12), and a second pump (P2), which is configured to convey the second fluid (F2) from the second source (3b) into the first flow path (12) to generate a mixture of the first and second fluids (Fl, F2) in the first flow path (12).

[0129] C26. The system of C25, wherein the control device (40), in the production phase (PP), is configured to: operate the first and second pumps (Pl, P2) to pump the first and second fluids (Fl, F2) through the first flow path (12) to provide the mixture in the first flow path (12), wherein the second pump (P2) is controlled based on the converted measurement values.

[0130] C27. The system of C25 or C26, wherein a connecting line (13) extends from the second source (3b) to a junction (13b) on the first flow path (12), wherein the second pump (P2) is arranged in or on the connecting line (13) to convey the second fluid (F2) from the second source (3b) into the first flow path (12), and wherein the first pump (Pl) is arranged in or on the first flow path (12) between the junction (13b) and the outlet (12a) for the medical fluid.

[0131] C28. The system of C27, wherein the control device (40), in the production phase (PP), is configured to control the first pump (Pl) to generate a target flow rate of the medical fluid.

[0132] C29. The system of any one of C25-C28, further comprising a first scale (2a) and a second scale (2b), wherein the first source is a first container (3a) arranged on the first scale (2a), wherein the second source is a second container (3b) arranged on the second scale (2b), wherein the control device (40), in the calibration phase (CP) and / or the production phase (PP), is configured to partly control the pump arrangement (4) based on a change in weight of the first and second containers (3 a, 3b) given by a first output signal (S2) of the first scale (2a) and a second output signal (S3) of the second scale (2b).

[0133] C30. The system of C29, wherein the control device (40), in the production phase (PP), is configured to monitor the first and second output signals (S2, S3) for detection of changes indicative of operational error.

[0134] C31. The system of any preceding clause, wherein the outlet (12a) is connected to a receiving device (30), wherein the control device (40), in the production phase (PP), is configured to: detect, while the medical fluid is directed along the first flow path (12) to the outlet (12a), an interrupted operation of the receiving device (30); and, upon detecting the interrupted operation, operate the valve arrangement (15) to close the first flow path (12) and open the passage to the second flow path (16) and reduce a pumping speed of said at least one pump in the pump arrangement (4). C32. The system of C31, wherein the control device (40) is further configured to, upon detecting the interrupted operation, operate the pump arrangement (4) to generate the medical fluid.

[0135] C33. The system of any preceding clause, wherein the composition-related parameter represents conductivity, resistivity, concentration of one or more solutes, or pH.

[0136] C34. The system of any preceding clause, wherein the medical fluid is a treatment fluid for use in extracorporeal blood therapy or peritoneal dialysis therapy.

[0137] C35. A control method for operating the system of any preceding clause, said method comprising: operating (201), in the calibration phase, the valve arrangement and the pump arrangement to convey at least one of the at least two fluids to the first and second sensors; determining (202), based on the first and second signals during the calibration phase, a conversion function for converting measurement values in the first signal into measurement values in the second signal; and operating (203), in the production phase, the valve arrangement and the pump arrangement to pump the at least two fluids through the first flow path to provide the medical fluid at the outlet; wherein said operating (203) in the production phase comprises controlling (203c) at least one pump in the pump arrangement based on converted measurement values, which are given by operating the conversion function on the measurement values in the first signal from the first sensor during the production phase.

[0138] C36. A computer-readable medium comprising computer instructions which, when executed by a processor (41), cause the processor (41) to perform the method of C35.

[0139] C37. A disposable arrangement for use in the system of any one of C1-C34, said disposable arrangement comprising: the first flow path (12), the first sensor (20), and the second flow path (16), which extends from the first flow path (12) to a releasable fluid connector (16a) for connection in fluid communication with the second sensor (20').

Claims

CLAIMS1. A system for generating a medical fluid for renal replacement therapy, said system comprising: a first flow path (12) for receiving and mixing at least two fluids to form the medical fluid; a pump arrangement (4) for pumping the at least two fluids through the first flow path (12); a first sensor (20, 20a), which is arranged in the first flow path (12) to provide a first signal (SI, SI a) indicative of a composition-related parameter; a valve arrangement (15) operable to selectively open a passage from the first flow path (12) to a second flow path (16); a second sensor (20'), which is arranged in the second flow path (16) to provide a second signal (SI1) indicative of the composition-related parameter; and a control device (40) configured to: operate, in a calibration phase (CP), the valve arrangement (15) and the pump arrangement (4) to convey at least one of the at least two fluids to the first and second sensors (20, 20a; 20'); determine, based on the first and second signals (SI, SI a; SI') during the calibration phase, a conversion function for converting measurement values in the first signal (SI, SI a) into measurement values in the second signal (SI'); and operate, in a production phase (PP), the valve arrangement (15) and the pump arrangement (4) to pump the at least two fluids through the first flow path (12) to provide the medical fluid at an outlet (12a), wherein at least one pump (P2; P3) in the pump arrangement (4) is controlled based on converted measurement values given by operating the conversion function on the measurement values in the first signal (SI; Sla) from the first sensor (20; 20a) during the production phase (PP).

2. The system of claim 1, wherein the first sensor (20, 20a) is a disposable component and the second sensor (20') is a re-usable component.

3. The system of claim 1 or 2, wherein the second sensor (20') is configured to be retained in the system and used in a repetition of the calibration phase when the first sensor (20, 20a) has been discarded and replaced for a new first sensor (20, 20a), wherein the repetition of the calibration phase results in an updated conversion function for converting the measurement values in the first signal (SI, Sla) of the new firstsensor (20, 20a) into the measurement values in the second signal (SI1) of the second sensor (20').

4. The system of any preceding claim, wherein the second sensor (20') has a higher accuracy than the first sensor (20, 20a).

5. The system of any preceding claim, which comprises a machine (lb) and a disposable arrangement (la) releasably engaged with the machine (lb), wherein the machine (lb) includes the pump arrangement (4) and the valve arrangement (15), and wherein the disposable arrangement (la) defines the first flow path (12) and the second flow path (16), and wherein the first sensor (20, 20a) is included in the disposable arrangement (la).

6. The system of any preceding claim, wherein the control device (40), in the calibration phase (CP), is configured to: operate the pump arrangement (4) to generate a set of test fluids from said at least two fluids; operate the pump arrangement (4) and the valve arrangement (15) to convey a respective test fluid in the set of test fluids to the first and second sensors (20, 20a; 20'); obtain a first measurement value for the respective test fluid from the first signal (SI, SI a); obtain a second measurement value for the respective test fluid from the second signal (ST); and determine the conversion function based on the first and second measurement values for the respective test fluid.

7. The system of claim 6, wherein at least one test fluid in the set of test fluids comprises a mixture of the at least two fluids.

8. The system of claim 7, wherein the control device (40), in the calibration phase (CP), is configured to operate the pump arrangement (4) to generate said at least one test fluid to achieve a target value in the second signal (ST) from the second sensor (20').

9. The system of any one of claims 6-8, wherein one test fluid in the set of test fluids is the medical fluid.

10. The system of any one of claims 6-9, wherein control device (40), in the calibration phase (CP), is configured to operate the pump arrangement (4) to generate the set of test fluids by providing a first fluid (Fl) among the at least two fluids as an initial test fluid, and by sequentially adding another fluid among the at least two fluidsto the initial test fluid, to generate a corresponding sequence of test fluids, until all fluids among the at least two fluids have been added to the initial test fluid.

11. The system of claim 10, wherein the first fluid (Fl) is water, and wherein each of said another fluid is added in a proportion equal to its proportion in the medical fluid.

12. The system of any one of claims 6-11, wherein the control device (40) is configured to determine the conversion function by fitting a predefined function to the first and second measurement values for the set of test fluids.

13. The system of any preceding claim, wherein the first sensor (20, 20a) is located upstream of the valve arrangement (15) in the first flow path (12), so that the first and second sensors (20, 20a; 20') are fluidly connected in series when the valve arrangement (15) is operated to open the passage from the first flow path (12) to the second flow path (16).

14. The system of any preceding claim, wherein the control device (40), in the production phase, is configured to: intermittently operate the valve arrangement (15) to open the passage to the second flow path (16) and direct the medical fluid to the second sensor (20'); obtain a current first measurement value for the medical fluid from the first signal (SI, SI a); obtain a current second measurement value for the medical fluid from the second signal (SI'); evaluate the current first and second measurement values for detection of a deviation; and take dedicated action upon detection of the deviation.

15. The system of claim 14, wherein the control device (40) is configured to: operate the conversion function on the current first measurement value to generate a current converted measurement value; and evaluate the current second measurement value and the current converted measurement value for detection of the deviation.

16. The system of claim 14 or 15, wherein the dedicated action comprises at least one of generating an alarm, or performing the calibration phase (CP) to determine an updated conversion function.

17. The system of any preceding claim, wherein the control device (40), in the production phase (PP), is configured to monitor the speeds of pumps in the pump arrangement (4) for detection of changes indicative of operational error.

18. The system of any preceding claim, said at least two fluids comprise a liquid concentrate.

19. The system of claim 18, which is configured to generate the liquid concentrate from a dry concentrate.

20. The system of any preceding claim, wherein the control device (40), in the production phase (PP), is configured to control the pump arrangement (4) to generate the medical fluid at a target flow rate, while maintaining the converted measurement values at a target value of the composition-related parameter.

21. The system of any preceding claim, wherein the control device (40) is operable to initiate a procedure for securing re-use of the second sensor (20').

22. The system of claim 21, wherein the procedure for securing re-use comprises at least one of: a) operating a fluid supply device (10; lb; 1000), which comprises the second sensor (20'), to perform an operation of rinsing and / or disinfecting the second sensor (20'), or b) conveying a dedicated fluid through the second flow path (16) into the second sensor (20'), and causing a user to disconnect the second flow path (16) from the second sensor (20') and manipulate the second sensor (20') to retain the dedicated fluid within the second sensor (20').

23. The system of claim 22, wherein the dedicated fluid is bacteriostatic.

24. The system of claim 22 or 23, which is configured to provide the dedicated fluid based on at least one fluid among said at least two fluids.

25. The system of any preceding claim, wherein said at least two fluids comprise a first fluid (Fl) provided by a first source (3a), and a second fluid (F2) provided by a second source (3b), wherein the pump arrangement (4) comprises a first pump (Pl), which is configured to convey the first fluid (Fl) from the first source (3a) into the first flow path (12), and a second pump (P2), which is configured to convey the second fluid (F2) from the second source (3b) into the first flow path (12) to generate a mixture of the first and second fluids (Fl, F2) in the first flow path (12).

26. The system of claim 25, wherein the control device (40), in the production phase (PP), is configured to: operate the first and second pumps (Pl, P2) to pump thefirst and second fluids (Fl, F2) through the first flow path (12) to provide the mixture in the first flow path (12), wherein the second pump (P2) is controlled based on the converted measurement values.

27. The system of claim 25 or 26, wherein a connecting line (13) extends from the second source (3b) to a junction (13b) on the first flow path (12), wherein the second pump (P2) is arranged in or on the connecting line (13) to convey the second fluid (F2) from the second source (3b) into the first flow path (12), and wherein the first pump (Pl) is arranged in or on the first flow path (12) between the junction (13b) and the outlet (12a) for the medical fluid.

28. The system of claim 27, wherein the control device (40), in the production phase (PP), is configured to control the first pump (Pl) to generate a target flow rate of the medical fluid.

29. The system of any one of claims 25-28, further comprising a first scale (2a) and a second scale (2b), wherein the first source is a first container (3a) arranged on the first scale (2a), wherein the second source is a second container (3b) arranged on the second scale (2b), wherein the control device (40), in the calibration phase (CP) and / or the production phase (PP), is configured to partly control the pump arrangement (4) based on a change in weight of the first and second containers (3 a, 3b) given by a first output signal (S2) of the first scale (2a) and a second output signal (S3) of the second scale (2b).

30. The system of claim 29, wherein the control device (40), in the production phase (PP), is configured to monitor the first and second output signals (S2, S3) for detection of changes indicative of operational error.

31. The system of any preceding claim, wherein the outlet (12a) is connected to a receiving device (30), wherein the control device (40), in the production phase (PP), is configured to: detect, while the medical fluid is directed along the first flow path (12) to the outlet (12a), an interrupted operation of the receiving device (30); and, upon detecting the interrupted operation, operate the valve arrangement (15) to close the first flow path (12) and open the passage to the second flow path (16) and reduce a pumping speed of said at least one pump in the pump arrangement (4).

32. The system of claim 31, wherein the control device (40) is further configured to, upon detecting the interrupted operation, operate the pump arrangement (4) to generate the medical fluid.

33. The system of any preceding claim, wherein the composition-related parameter represents conductivity, resistivity, concentration of one or more solutes, or pH.

34. The system of any preceding claim, wherein the medical fluid is a treatment fluid for use in extracorporeal blood therapy or peritoneal dialysis therapy.

35. A control method for operating the system of any preceding claim, said method comprising: operating (201), in the calibration phase, the valve arrangement and the pump arrangement to convey at least one of the at least two fluids to the first and second sensors; determining (202), based on the first and second signals during the calibration phase, a conversion function for converting measurement values in the first signal into measurement values in the second signal; and operating (203), in the production phase, the valve arrangement and the pump arrangement to pump the at least two fluids through the first flow path to provide the medical fluid at the outlet; wherein said operating (203) in the production phase comprises controlling (203c) at least one pump in the pump arrangement based on converted measurement values, which are given by operating the conversion function on the measurement values in the first signal from the first sensor during the production phase.

36. A computer-readable medium comprising computer instructions which, when executed by a processor (41), cause the processor (41) to perform the method of claim 35.

37. A disposable arrangement for use in the system of any one of claims 1-34, said disposable arrangement comprising: the first flow path (12), the first sensor (20), and the second flow path (16), which extends from the first flow path (12) to a releasable fluid connector (16a) for connection in fluid communication with the second sensor (20').

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