Dialysis system with reservoir for treatment fluid and method of operation

Abstract

A dialysis system is operable in different operating states and comprises a supply sub-system (4) for supplying a treatment fluid, a reservoir (50) for receiving the treatment fluid from the supply sub-system (4), and a treatment sub-system (6) for performing a dialysis treatment by use of the treatment fluid. The reservoir (50) holds a supply of the treatment fluid during operation of the dialysis system, and the treatment sub-system (6) obtains the treatment fluid from the reservoir (50). The supply sub-system (4) is operated to perform a sequence of intermittent replenishment operations, in which a respective refill amount (V1, V2) of the treatment fluid is conveyed from the supply sub-system (4) to the reservoir (50). The respective refill amount for the respective intermittent replenishment operation is determined based on an intended operating state of dialysis system subsequent to the respective intermittent replenishment operation.

Description

[0001] DIALYSIS SYSTEM WITH RESERVOIR FOR TREATMENT FLUID AND METHOD OF OPERATION

[0002] Technical Field

[0003] The present disclosure relates to the field of dialysis and in particular to a technique of operating a dialysis system in which treatment fluid is held in a reservoir and supplied from the reservoir for use in dialysis treatment.

[0004] Background Art

[0005] In treating renal failure, various methods of purification and treatment of blood with machinery are used to replace the function of a healthy kidney. Such methods include extracorporeal (EC) blood treatment and aim at withdrawing fluid and removing substances from the blood, and they may also involve adding fluid and substances to the blood. In EC blood treatment, dialysis fluid and blood may be pumped through a blood filtration unit, commonly denoted dialyzer, on opposite sides of a semi-permeable membrane. Alternatively or additionally, a replacement fluid may be added to the blood upstream or downstream of the dialyzer. Common modalities of EC blood treatment include hemodialysis, hemodiafiltration, and hemofiltration.

[0006] Machines for EC blood treatment may be separated into machines for treatment of patients with chronic kidney disease (CKD), commonly known as "chronic dialysis", and machines for treatment of patients with acute kidney injury (AKI), commonly known as "acute dialysis". Acute dialysis is typically performed continuously or semi- continuously. Continuous therapy is a 24-hour treatment, whereas semi-continuous therapy may be performed daily with a duration of 6-12 hours or more. Continuous dialysis therapy is commonly denoted CRRT ("Continuous Renal Replacement Therapy"). An example of a semi-continuous therapy is SLEDD (Sustained Low Efficiency Daily Dialysis").

[0007] Machines for acute dialysis commonly comprise scales, on which containers or "fluid bags" are releasably arranged. The operation of the machine is controlled based on the weight of the fluid bags, given by the readings of the scales. Commonly, at least one fluid bag is arranged to hold a fresh dialysis fluid ("dialysis fluid bag"), which is used in the dialysis treatment, and at least one fluid bag is arranged to receive spent dialysis fluid ("effluent bag"). As is well-known to the skilled person, EC blood treatment involves extracting excess fluid from the patient, commonly known as "ultrafiltration". The excess fluid is included in the spent dialysis fluid. The ultrafiltration is controlled by a supply pump and an effluent pump in the machine. The amount of excess fluid extracted from the patient and the rate of extraction are important treatment parameters during dialysis. In operation, the machine calculates and monitors these treatment parameters based on the readings of the scales and controls the supply and effluent pumps to achieve corresponding set values.

[0008] During EC blood treatment, the dialysis fluid bag will eventually be depleted of fresh dialysis fluid and the effluent bag will be full of spent dialysis fluid. To avoid frequent changes of fluid bags, it has been proposed to configure the machine to intermittently pump fresh dialysis fluid into the dialysis fluid bag from a source, to raise the level of fresh dialysis fluid, and to intermittently pump spent dialysis fluid out of the effluent bag, to lower the level of spent dialysis fluid. Dialysis systems with such level adjustment are disclosed in JPH09-239024 and EP3238761.

[0009] In machines for EC blood treatment, a cleaning procedure is recommended every 24 hours to maintain the technical function of the machine and the quality of the dialysis fluid that is supplied to the patient. The cleaning procedure may involve a disinfection. Typically, the duration of the cleaning procedure is 30-60 minutes. This is difficult to accommodate in a machine for acute treatment that is operated to perform continuous therapy, which may extend well beyond 24 hours, for example 72 hours or longer.

[0010] During EC blood therapy, it may be desirable to change the composition of the dialysis fluid that is supplied to the dialyzer. In conventional machines for acute dialysis, the caretaker will remove the dialysis fluid bag and install a new dialysis fluid bag with the required composition. In the above-mentioned dialysis systems with level adjustment, the operator may replace the dialysis fluid bag for an empty bag and enter a new desired prescription of the dialysis fluid to be generated by the machine. This requires the caretaker to lift and handle a potentially quite heavy bag of fluid, with risk for spillage of dialysis fluid and the caretaker experiencing strain injuries.

[0011] These problems may be relevant to dialysis systems outside the field of acute dialysis, depending on the requirements and configuration of the respective dialysis system.

[0012] Summary

[0013] It is an objective to at least partly overcome one or more limitations of the prior art.

[0014] A further objective is to improve the utility of a dialysis system with a reservoir for holding a supply of treatment fluid.

[0015] Another objective is to facilitate change of composition of the treatment fluid during on-going therapy in such a dialysis system. Yet another objective is to ensure proper technical function of such a dialysis system even when it is operated to perform the dialysis treatment for an extended time period, for example beyond 24 hours.

[0016] 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 dialysis system, a method of operating a dialysis system, and a computer-readable medium according to the independent claim, embodiments thereof being defined by the dependent claims.

[0017] A first aspect of the present disclosure is a dialysis system. This dialysis system comprises: a supply sub-system comprising a fluid circuit, which is operable to supply a treatment fluid; a storage sub-system comprising a reservoir, which is fluidly connected to receive the treatment fluid from the supply sub-system and configured to hold a supply of the treatment fluid during operation of the dialysis system; and a treatment sub-system, which is configured to obtain the treatment fluid from the storage subsystem and perform a dialysis treatment by use of the treatment fluid. A control device is configured to operate the treatment sub-system to perform the dialysis treatment. The control device is further configured to operate the supply sub-system to perform a sequence of intermittent replenishment operations during the dialysis treatment, with a respective refill amount of the treatment fluid being conveyed from the supply subsystem to the reservoir during a respective intermittent replenishment operation. The control device is further configured to operate the dialysis system in a plurality of different operating states, and to determine the respective refill amount for the respective intermittent replenishment operation based on an intended operating state of the dialysis system subsequent to the respective intermittent replenishment operation, the intended operating state being an operating state among the plurality of different operating states.

[0018] The first aspect is based on the insight that, in a dialysis system that supplies treatment fluid from an intermittently refillable reservoir, it may be beneficial to dynamically adjust the amount of treatment fluid in the reservoir depending on how the dialysis system is intended to be operated during dialysis treatment. This dynamic adjustment may be achieved by adjusting the timing and / or the refill amount of the respective replenishment operation. For example, the Applicant has realized that above- mentioned difficulty of performing a cleaning procedure during on-going dialysis treatment may be overcome by cleaning the supply sub-system between replenishment operations, while the treatment sub-system receives treatment fluid from the reservoir. This is possible since the supply sub-system is likely to be idle between replenishment operations. With a larger refill amount, the time to the next replenishment operation will be extended and thereby also the time in which the supply sub-system is idle. Thus, by adjusting the timing and / or the refill amount of a replenishment operation, it is possible for the dialysis system to perform a cleaning procedure of a given duration at a selected time point. This allows the dialysis system to be operated to perform dialysis therapy for an extended period of time without compromising patient safety. The Applicant has also realized that an adjustment of the refill amount may enable well-controlled and automated change of composition of the treatment fluid during on-going dialysis treatment. Here, automated change implies that the dialysis system achieves the change of composition without manual intervention. An automated change of composition improves the utility of the dialysis system significantly. The automated change may be achieved by operating the supply sub-system to add new treatment fluid to the reservoir to achieve a desired composition of the treatment fluid in the reservoir. Irrespective of how this is done, the amount of existing treatment fluid in the reservoir when the composition change is initiated will affect how fast the dialysis system can be switched to provide treatment fluid of the new composition from the reservoir. This may be seen as a "response time" for composition change. Thus, if the dialysis system is expected to change the composition of the treatment fluid used in on-going dialysis treatment, the amount of treatment fluid in the reservoir may be adjusted to ensure that the response time for composition change is below a limit value.

[0019] The technique of the first aspect is simple to implement on any existing or future dialysis system that is operable in a plurality of different operating states and that is configured to supply treatment fluid from a reservoir and to intermittently replenish the reservoir.

[0020] In the following, various embodiments of the first aspect are defined. These embodiments provide at least some of the technical effects and advantages described in the foregoing, as well as additional technical effects and advantages as readily understood by the skilled person, for example in view of the following detailed description.

[0021] In some embodiments, the plurality of different operating states comprises at least two of a cleaning state; in which the supply sub-system is operated to perform a cleaning procedure of at least part of the fluid circuit; a fixed composition state, in which the dialysis system is operated to prevent a change in composition of the treatment fluid that is supplied by the supply sub-system; or a variable composition state, in which the dialysis system is operated to admit the change in composition of the treatment fluid that is supplied by the supply sub-system.

[0022] In some embodiments, the control device is configured to vary, as a function of the intended operating state and by way of the respective refill amount, an amount of available treatment fluid in the reservoir resulting from the respective intermittent replenishment operation.

[0023] In some embodiments, the control device is configured to, for at least one operating state among the plurality of operating states, achieve a predefined amount of treatment fluid in the reservoir at a designated time point.

[0024] In some embodiments, the designated time point is a calendar time.

[0025] In some embodiments, the sequence of intermittent replenishment operations comprises a first replenishment operation followed by a second replenishment operation, and the control device is configured to, for at least one of the operating states, determine the refill amount for the first replenishment operation as a function of an expected flow rate of the treatment fluid from the reservoir to the treatment sub-system during a calculation time period from a start of the first replenishment operation to a start of the second replenishment operation.

[0026] In some embodiments, by said function, the refill amount of the first replenishment operation increases with the expected flow rate.

[0027] In some embodiments, the calculation time period is predefined.

[0028] In some embodiments, at least two operating states are associated with a respective calculation time period, and wherein the respective calculation time period differs between said at least two operating states.

[0029] In some embodiments, the control device is configured to, for the at least one of the operating states, determine the refill amount of the first replenishment operation to achieve a predefined amount of treatment fluid in the reservoir such that a time for the treatment sub-system to consume the predefined amount of treatment fluid, at the expected flow rate, exceeds the calculation time period.

[0030] In some embodiments, the plurality of operating states comprises at least one cleaning state, in which the supply sub-system is operated to perform a cleaning procedure of at least part of the fluid circuit while stopping the supply of treatment fluid to the reservoir.

[0031] In some embodiments, the plurality of operating states comprises two or more cleaning states which differ at least by a duration of the cleaning procedure.

[0032] In some embodiments, the control device is configured to perform the cleaning procedure within a time period between two consecutive replenishment operations in said sequence.

[0033] In some embodiments, the control device is configured to operate the supply subsystem to repeatedly perform, at a cleaning time interval, the cleaning procedure between respective replenishment operations in said sequence, wherein the cleaning time interval is set to not exceed a predefined maximum value. In some embodiments, the predefined maximum value of the cleaning time interval is 72, 48 or 24 hours.

[0034] In some embodiments, the control device is configured to operate the supply subsystem to start the cleaning procedure at a predefined time point, wherein the control device is further configured to perform one of the replenishment operations in relation to the predefined time point, and determine the refill amount of said one of the replenishment operations so that an expected time for the treatment sub-system to consume the treatment fluid present in the reservoir at the start of the cleaning procedure exceeds a predefined maximum duration of the cleaning procedure.

[0035] In some embodiments, the control device is configured to perform said one of the replenishment operations so that it is completed at the start of the cleaning procedure.

[0036] In some embodiments, the plurality of operating states comprises a fixed composition state, in which the dialysis system is operated to prevent a change in composition of the treatment fluid that is supplied by the supply sub-system.

[0037] In some embodiments, the plurality of operating states comprises a variable composition state, in which the dialysis system is operated to admit a change in composition of the treatment fluid that is supplied by the supply sub-system.

[0038] In some embodiments, the control device, when the intended operating state is the variable composition state, is configured to determine the refill amount of the respective intermittent replenishment operation as a function of a predefined maximum value of a response time of the dialysis system, the response time being a required time to achieve a desired change in composition of the treatment fluid that is supplied from the reservoir to the treatment sub-system.

[0039] In some embodiments, the control device, when operating the dialysis system in the variable composition state and upon receipt of a request signal indicative of a requested composition change of the treatment fluid that is supplied from the reservoir to the treatment sub-system from a current composition to a new composition, is configured to perform an additional replenishment operation, in which the supply subsystem is operated to supply an additional refill amount of treatment fluid of a target composition to the reservoir, wherein control device is configured to determine the target composition based on the new composition.

[0040] In some embodiments, the target composition is equal to the new composition, and wherein the control device, before performing the additional replenishment operation, is configured to determine a current amount of treatment fluid in the reservoir, and operate the storage sub-system and / or the treatment sub-system to effectively remove the current amount of treatment fluid from the reservoir. In some embodiments, the target composition is equal to the new composition, and wherein the storage sub-system is operable, during the additional replenishment operation, to arrange the additional refill amount substantially above a current amount of treatment fluid that is located in the reservoir at start of the additional replenishment operation.

[0041] In some embodiments, the control device, before performing the additional replenishment operation, is configured to determine the current composition and a current amount of treatment fluid in the reservoir, and to determine the target composition and the additional refill amount, based on the current composition and the current amount, so that a mixture of the current amount and the additional refill amount attains the new composition.

[0042] In some embodiments, the control device is configured to calculate an actual response time based on the current amount, supply the actual response time for presentation to the user, and perform the additional replenishment operation subject to receipt of a user approval of the actual response time.

[0043] In some embodiments, the control device is configured to initiate a respective replenishment operation in the sequence of replenishment operations when a measured or estimated amount of treatment fluid in the reservoir falls below a predefined limit.

[0044] In some embodiments, the control device is configured to temporarily replace the predefined limit for a second predefined limit, which is lower than the predefined limit, when a command to change a composition of the treatment fluid is anticipated.

[0045] In some embodiments, at least part of the fluid circuit is permanently installed in the supply sub -system.

[0046] In some embodiments, the supply sub-system is configured to prepare the treatment fluid by mixing at least one concentrate with purified water in the fluid circuit.

[0047] In some embodiments, the supply sub-system is configured to receive incoming water and process the water into said purified water in the fluid circuit.

[0048] In some embodiments, the reservoir is a disposable part.

[0049] In some embodiments, the treatment sub-system is configured for CRRT.

[0050] A second aspect of the present disclosure is a computer-implemented method of operating a dialysis system. The dialysis system comprises: a supply sub-system comprising a fluid circuit, which is operable to supply a treatment fluid; a storage subsystem comprising a reservoir, which is fluidly connected to receive the treatment fluid from the supply sub-system and configured to hold a supply of the treatment fluid during operation of the dialysis system; and a treatment sub-system, which is configured to obtain the treatment fluid from the storage sub-system and perform a dialysis treatment by use of the treatment fluid, wherein the dialysis system is operable in a plurality of different operating states. The method comprises: operating the treatment sub-system to perform the dialysis treatment; and operating the supply sub-system to perform a sequence of intermittent replenishment operations during the dialysis treatment, by conveying a respective refill amount of the treatment fluid from the supply sub-system to the reservoir in the storage sub-system during a respective intermittent replenishment operation. The method further comprises: determining a respective refill amount for the respective intermittent replenishment operation based on an intended operating state of the dialysis system subsequent to the respective intermittent replenishment operation, the intended operating state being an operating state among the plurality of different operating states.

[0051] Any embodiment of the first aspect may be adapted as an embodiment of the second aspect.

[0052] A third aspect of the present disclosure is a computer-readable medium comprising computer instructions which, when executed by processing circuitry, cause the processing circuitry to perform the method of the second aspect or any of its embodiments.

[0053] Still other objectives, aspects and embodiments, as well as features and technical advantages, may appear from the following detailed description, from the attached claims as well as from the drawings.

[0054] Brief Description of the Drawings

[0055] FIG. 1 A is a diagrammatic view of an example dialysis system, and FIG. IB is a high-level representation of the operation of the dialysis system in FIG. 1 A.

[0056] FIG. 2 is diagram of example operating states of the dialysis system in FIG. 1 A.

[0057] FIGS 3 A-3B are flow charts of an example method of operating a supply subsystem in FIG. 1A.

[0058] FIGS 4A-4B show example time profiles of fluid volume in a treatment fluid reservoir in the dialysis system of FIG. 1 A when operated in accordance with the method of FIGS 3A-3B.

[0059] FIGS 5 A-5B are example timing diagrams for refill operations and cleaning procedures of the dialysis system in FIG. 1 A.

[0060] FIG. 6 is a flow chart of an example method of operating the supply sub-system in FIG. 1 A with variable treatment fluid composition.

[0061] FIGS 7A-7B show fill level and composition in the treatment fluid reservoir for a first implementation of the method in FIG. 6. FIGS 8A-8B show fill level and composition in the treatment fluid reservoir for a second implementation of the method in FIG. 6.

[0062] FIGS 9A-9B show fill level and composition in the treatment fluid reservoir for a third implementation of the method in FIG. 6.

[0063] FIG. 10 show fill level and composition in the treatment fluid reservoir for a fourth implementation of the method in FIG. 6.

[0064] FIG. 11 is a flow chart of an example verification method that may be part of the method in FIG. 6.

[0065] FIG. 12A is a flow chart of an example method of operating the supply subsystem in FIG. 1 A with variable treatment fluid composition, and FIG. 12B is a graph of fill level in a treatment fluid reservoir as a function of time by use of the method in FIG. 12 A.

[0066] FIG. 13 is a diagrammatic view of a dialysis system for hemodialysis by CRRT.

[0067] Detailed Description of Example Embodiments

[0068] 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.

[0069] 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.

[0070] 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. The term "and / or" includes any and all combinations of one or more of the associated listed elements.

[0071] 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.

[0072] The present disclosure relates to a technique for controlling the amount of treatment fluid in a reservoir of a dialysis system. The technique is applicable to any dialysis system that has such a reservoir and is configured to supply treatment fluid from the reservoir 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 includes extracorporeal (EC) blood treatment, in any modality, as well as peritoneal dialysis (PD). RRT may involve removal of water from the blood of the patient, as well as exchange of solutes with the blood. RRT is also denoted "dialysis therapy" or "dialysis treatment" herein. The proposed technique is, for example, applicable to dialysis systems for EC blood treatment of acute patients, as discussed in the Background section.

[0073] The treatment fluid may be any fluid that is consumed as part of RRT and is abbreviated TF herein. In the context of EC blood therapy, the medical fluid may be dialysis fluid, which is interfaced with blood in a filtration unit, commonly known as a "dialyzer". Alternatively or additionally, the medical fluid may be 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 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.

[0074] Various embodiments will now be described with reference to FIG. 1 A, which schematically illustrates an example dialysis system 1. The dialysis system 1 is fluidly connected to a patient 2 and operable to perform renal replacement therapy (RRT) on the patient 2. A water source 3 is arranged to provide water for use in producing treatment fluid (TF) for the RRT. Depending on implementation, the water source 3 may provide tap water or purified water. The purified water may be so-called "water for dialysis" or "water for injection". The dialysis system 1 comprises a plurality of subsystems: a supply sub-system (SUSS) 4, a storage sub-system (STSS) 5, and a dialysis treatment sub-system (DTSS) 6. The water source 3 may or may not be part of the dialysis system 1. A fluid path 3' extends from the source 3 to convey water to the SUSS 4.

[0075] In some embodiments, the SUSS 4 is operable to generate treatment fluid (TF) by mixing purified water with one or more treatment fluid concentrates (TFCs) in a fluid circuit 41. For example, as described, the purified water may be obtained from the water source 3. In an alternative, the SUSS 4 comprises a water purification device (not shown) within the fluid circuit 41 and is thus configured to receive water from the water source 3 and process the water into purified water. The fluid circuit 41 defines a coherent fluid manifold that may include fluid lines, mixing chamber(s), reservoirs, etc. The respective TFC may be in liquid form or solid form, for example a powder. Any number of TFCs may be used. In the example of FIG. 1A, a single TFC is held in a container 42. The container 42 is arranged for fluid communication with the fluid circuit 41 through a connecting line 3". A dosing device 43 is arranged to control, based on a control signal Cl, the amount of TFC that is admitted into the fluid circuit 41. The dosing device 43 may be a pump or a valve. The SUSS 4 further includes a sensor arrangement 44, which is arranged to sense one or more properties of the TFC, the TF or any intermediate fluid formed during operation. The sensor arrangement 44 is configured to output one or more corresponding sensor signals, collectively represented by SI in FIG. 1A. For example, the sensor arrangement 44 may include one or more of a flow meter, a conductivity sensor, a temperature sensor, a pressure sensor, etc. A supply device 45 is operable to supply TF from the SUSS 4 to the STSS 5 on a connecting path 4'. The supply device 45 may be a pump and is operated based on a control signal C2. The flow rate of TF to the STSS 5 is represented by a replenishment flow rate Qr in FIG. 1 A. In a non-limiting example, Qr is in the range of 100-500 mL / min.

[0076] It is to be understood that the SUSS 4 may include other parts than those shown in FIG. 1 A, for example a heater, valves, pumps, etc.

[0077] In a variant, not shown, the SUSS 4 is fluidly connected to a plurality of containers holding ready-made TFs of different compositions. The SUSS 4 is operable to supply TF to the STSS 5 by admitting one of the ready-made TFs into the fluid circuit 41. It is also conceivable that the SUSS 4 is operable to generate and supply TFs of other compositions by mixing ready-made TFs in different proportions.

[0078] In the illustrated example, the SUSS 4 includes a cleaning arrangement 46, which is operable to perform a cleaning procedure of the fluid circuit 41. The cleaning procedure may aim at removing deposits in the fluid circuit 41 and / or to disinfect the fluid circuit 41. The cleaning procedure may involve flushing the fluid circuit 41 with a cleaning fluid. The cleaning fluid may be water, which may or may not be heated. Additionally or alternatively, the water may include a cleaning agent, for example an acid such as citric acid. The cleaning fluid may reside in the fluid circuit 41 for a predefined time to ensure sufficient cleaning. The cleaning procedure is performed to ensure the operability of the fluid circuit 41 and the quality of the treatment fluid over time. As noted in the background section, it may be desirable to perform the cleaning procedure at least once every 24 hours. The cleaning procedure is particularly important when at least part of the fluid circuit 41 is permanently installed in the dialysis system. As used herein, a component that is permanently installed is not intended to be replaced at regular intervals and typically has a useful life of up to several years. The cleaning procedure may be sub-divided into sub-procedures, each for cleaning a respective subset of the fluid circuit 41. It is to be understood that the cleaning procedure may also affect other parts than the fluid circuit 41, such as the dosing device 42, the sensor arrangement 44, the supply pump 45, as well as parts not shown in FIG. 1 A.

[0079] The present disclosure is not limited to any particular structure of the SUSS 4. The skilled person is aware of numerous different types of SUSS 4 that are either commercially available or suggested in the literature.

[0080] The STSS 5 comprises a reservoir 50 for TF, and a fill level sensor 52. The reservoir 50 is configured receive the TF on path 4' and hold an intermediate supply of TF during operation of the dialysis system 1. The reservoir 50 may be a permanent component or a disposable component. By using a disposable reservoir 50, the need for cleaning of the reservoir 50 is obviated. As used herein, a disposable device (or component / part / arrangement, etc.) is a means that is intended to be used only for a limited time, after which the used disposable 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. In one example, the reservoir 50 is a disposable bag.

[0081] The fill level sensor 52 is arranged to measure the momentary amount of TF in the reservoir 50 and output a corresponding sensor signal S2. The fill level sensor 52 may represent the momentary amount in terms of weight, fluid volume, fluid level, etc. In some embodiments, the fill level sensor 52 is a weight scale, which is arranged to measure the weight of the reservoir 50. Other examples of available fill level sensors 52 comprise electrode-based sensors, ultrasonic sensors, capacitance sensors, float sensors, or optical sensors. A connecting path 5' extends between the sub-systems 5, 6 to convey TF from the reservoir 50 to the DTSS 6. The DTSS 6 is configured to obtain TF from the STSS 5 and perform dialysis therapy by use of the TF, in accordance with conventional practice. The flow rate of TF from the reservoir 50 is represented by a consumption flow rate Qc in FIG. 1 A. The DTSS 6 comprises a flow control arrangement 60, which is configured to obtain and distribute the TF in accordance with the RRT that is performed. In the example of EC blood therapy, the flow control arrangement 60 defines an extracorporeal blood circuit which is connected to receive blood from the patient 2, on path 6', and to return treated blood to the patient 2, on path 6". In the example of PD, path 6" may be omitted, and the flow control arrangement 6 may be configured to both supply TF to the peritoneal cavity in the patient 2 and receive spent TF from the peritoneal cavity on path 6'.

[0082] The dialysis system 1 may be implemented by one or more machine units and a disposable arrangement, in accordance with conventional practice. The disposable arrangement may comprise fluid lines and, in the example of extracorporeal blood therapy, a blood filtration unit ("dialyzer"). The disposable arrangement may be mechanically interfaced with the one or more machine units to form the dialysis system 1. The machine unit(s) may, for example, expose mechanical interfaces of pumps, clamps, sensors, etc.

[0083] As shown in FIG. 1 A, a control device 7 is configured to control the operation of dialysis system 1. The control device 7 may be a controller in a machine unit or a separate controller. The control device 7 need not be a unitary device but may be distributed among plural controllers in the system 1. The control device 7 is configured to receive sensor signals, represented as Si, and output control signals, represented as Cj.

[0084] FIG. IB is flow chart of a method 100 performed by the control device 7 to operate the dialysis system in FIG. 1A. The method 100 comprises a procedure or method 200 of operating the DTSS 6 to perform the RRT on the patient 2. While the dialysis system 1 is operated to perform the RRT, TF is drawn by the DTSS 6 from the reservoir 50. The procedure 200 is implemented in accordance with conventional practice and will not be described in detail. Although not shown in FIG. 1 A, part of the signals Si, Cj are used in the procedure 200 for controlling the DTSS 6.

[0085] The method 100 also comprises a procedure or method 300 of controlling the SUSS 4. The procedure 300 operates the SUSS 4 to generate and supply TF, by providing at least the control signal Cl to the dosing device 43 and the control signal C2 to the supply device 45, based at least on the sensor signals SI, S2. Specifically, the procedure operates the SUSS 4 to intermittently replenish the reservoir 50. Thus, during on-going RRT, the SUSS 4 is operated to perform a sequence of intermittent replenishment operations, ROPs. In each such ROP, a batch of TF is conveyed from the SUSS 4 to the reservoir 50. The procedure 300 may also operate the SUSS 4 to perform the above-mentioned cleaning procedure, by providing the control signal C3 to the cleaning arrangement 46.

[0086] The control device 7 may be configured to generate the control signals Cj in accordance with a control program comprising computer instructions. The control program is also configured to operate based on the sensor signals Si. The control device 7 comprises processing circuitry 71 and computer memory 72. The control program is stored in the memory 72 and executed by the circuitry 71. The circuitry 71 may, for example, include one or more of a CPU ("Central Processing Unit"), a DSP ("Digital Signal Processor"), a GPU ("Graphics Processing Unit"), a microprocessor, a microcontroller, an ASIC ("Application-Specific Integrated Circuit"), a combination of discrete analog and / or digital components, or some other programmable logical device, such as an FPGA ("Field Programmable Gate Array"). The control program may be supplied to the control device 7 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. In the illustrated example, the control device 7 comprises a signal interface 73a for providing control signals Cj and receiving sensor signals Si. The control device 7 also comprises a signal interface 73b for connection to a user interface (UI) device 74 which enables user interaction, for example input of control settings and / or output of instructions and feedback. For example, the UI device 74 may comprise one or more of a keyboard, keypad, computer mouse, control button, printer, microphone, display device, indicator lamp, alarm device, speaker, touch screen, camera, voice control system, gesture control system, etc.

[0087] The control device 7 is configured to set the dialysis system 1 in an operating state among a plurality of predefined operating states. Different operating states provide different functionality to the dialysis system 1. FIG. 2 schematically depicts a dialysis system 1 with five different operating states, as shown by dashed circles. State OS1 is a complete cleaning state in which the SUSS 4 is operated to perform a cleaning procedure (CP) for the entire fluid circuit 41. State OS2 is a variable composition (VC) state in which the control device 7 allows the operator to change the composition of the TF that is used by the DTSS 6 to perform the RRT. State OS3 is a fixed composition (FC) state in which the control device 7 operates the dialysis system to perform the RRT by use of a TF with a fixed composition, which may be predefined or entered by an operator. In other words, in state OS3, the dialysis system is operated to prevent a change in composition of the TF. States OS4 and OS5 are partial cleaning states in which the SUSS 4 is operated to subject different subsets of the fluid circuit 41 to the cleaning procedure (CP).

[0088] It should be noted that the SUSS 4 will be unable to supply TF during the cleaning procedure, since the fluid circuit 41 may, at least partly, be in a heat cleaning state, and / or possibly filled with a cleaning fluid. Thus, the replenishment flow rate Qr to the STSS 5 is zero for the duration of the cleaning procedure.

[0089] FIG. 2 is merely an example. In some embodiments, the operating states include at least one cleaning state, in which SUSS 4 is at least partially cleaned and no TF is supplied from the SUSS 4, and at least one production state, in which TF is supplied from the SUSS 4. However, the present disclosure is equally applicable to other situations in which the SUSS 4 is intermittently prevented from supplying TF. Thus, on a general level, any cleaning state mentioned herein may be replaced for any other operating state of the SUSS 4 that prevents the SUSS 4 from supplying TF.

[0090] The control device 7 may be configured to associate the respective cleaning state OS1, OS4, OS5 with a predefined duration, which corresponds to a maximum duration of the cleaning procedure in the respective cleaning state. It is realized that the predefined duration may differ between cleaning states. For example, the partial cleaning states OS4, OS5 typically have a shorter duration than the complete cleaning state OS1.

[0091] FIG. 3A is a flowchart of the method 300 in accordance with an example. The method 300 will be described with reference to the dialysis system 1 in FIG. 1 A.

[0092] The method 300 is based on the insight that the SUSS 4 is idle ("inactive") between replenishment operations, ROPs, and that it is possible to operate the SUSS 4 to perform a cleaning procedure, CP, during this time of inactivity. Based on this insight, the Applicant has found it advantageous to control at least some of the ROPs, with respect to refill amount, to ensure that a CP is accommodated within the available time between ROPs. Further, ROPs may be controlled to achieve a required fill level in the reservoir 50 at a given time point, so as to be able to perform a CP at a desired time point. As used herein, "fill level" designates the amount of TF in the reservoir 50 and may be given as volume, mass, level, or any other suitable quantity. The Applicant has further realized that the fill level in the reservoir 50 will affect how fast the dialysis system 1 is capable of performing a desired change in the composition of the TF that is supplied to the DTSS 6. It may thus be beneficial to control a ROP to result in a fill level in the reservoir 5 that allows a sufficiently fast composition change. In summary, the method 300 is designed to perform batch-wise replenishments of the reservoir 50 while adjusting the refill amount for each replenishment to an intended operating state of the dialysis system. In step 301, an intended operating state of dialysis system is determined. The intended operating state may be any of the available operating states of the dialysis system, for example any one of OS1-OS5 in FIG. 2. The intended operating state is an "upcoming" or "next" operating state, in relation to a current or future time point. The intended operating state may be given deterministically by the control program of the control device 7. For example, the control device 7 may be configured to set a specific cleaning state (OS1, OS3 or OS4) at predefined time intervals or at predefined time points. Likewise, the control device 7 may be configured to operate the dialysis system in the fixed composition state (OS3) or the variable composition state (OS4) between cleaning states. It is also conceivable that the control device 7 comprises logic that is operable to dynamically schedule CPs. For example, if a CP is warranted, for example based on elapsed time since the last CP, a new CP may be scheduled to be performed as soon as the SUSS 4 is deemed to be inactive for a sufficient time period. For example, a new CP may be scheduled when the RRT is suspended for some reason. For example, disposable blood lines (cf. 6', 6") in the DTSS 6 may need to be changed at least every 72 hours, and the control device 7 may schedule a CP to be performed during the change of blood lines since RRT is then suspended. In a further example, the intended state is given by user input via the UI device 74. For example, the user may enter a time period during which the RRT will be suspended, causing the control device 7 to schedule a CP. In another example, the user may enter a request to change the TF composition. Such a request may be designated to be applied as soon as possible or at a selected future time point. The request, if accepted by the control device 7, causes the control device 7 to set the dialysis system in the variable composition state (OS2) at an appropriate time point. In another example, the user may enter a request to enter the fixed composition state (OS3) or to start a specific cleaning procedure (OS1, OS4, OS5).

[0093] In step 302, the amount of TF to be supplied to the reservoir 50 during the next ROP is determined. This amount is denoted "refill amount" herein. The refill amount is determined to achieve a predefined property of the intended operating state. Thus, in some embodiments, at least part of the available operating states of the SUSS 4 are associated with a respective property for use in determining the refill amount. In the examples given herein, this property is the duration of the intended operating state, or a maximum response time for TF composition change.

[0094] In step 303, a ROP is performed. In the example of FIG. 1 A, the SUSS 4 is operated by control signals Cl, C2 to generate TF with a target composition and to pump the refill amount of TF into the reservoir 50. After step 303, the control device 7 switches to the intended operating state. For example, if the intended operating state is OS1, OS4 or OS5, the cleaning arrangement 46 may be operated by control signal C3 to perform a corresponding cleaning procedure. If the intended state is OS3, the control device 7 prevents changes to the composition of the TF that is made available to the DTSS 6. If the intended state is OS2, the control device 7 allows changes to the composition of the TF that is made available to the DTSS 6.

[0095] After step 303, the control device 7 may wait for a time period before performing step 301 anew, as indicated by steps 304A-304B. Step 301 is performed well before the reservoir 5 is depleted of TF. The duration of the time period may be projected by the control device 7 after step 303 based on a current fill level of the reservoir 50 and an estimation of the future consumption rate of TF by the DTSS 6 (cf. Qc in FIG. 1A). Alternatively, step 301 may be triggered by the fill level sensor 52 and / or based on a scheduled time point when the dialysis system should enter an operating state.

[0096] It is realized that the control device 7, by the method 300, is operated, as a function of the intended operating state, to vary the amount of fluid in the reservoir 50 upon completion of the respective ROP, by way of the respective refill amount. This functionality is illustrated in FIG. 4A, which shows the amount ("fill level") VR in the reservoir 50 over time while the dialysis system 1 is operated to perform RRT. Consecutive ROPs are enumerated to facilitate the discussion. FIG. 4A also indicates a maximum fill level ("maximum capacity") of the reservoir 50, Vmax. In advance of operating state OS1, a first ROP (ROP1) is performed to add a refill amount VI to the reservoir. ROP1 is completed at time tl. The dialysis treatment by DTSS 6 consumes TF from the reservoir, causing the amount in the reservoir to decrease over time. At time t2, in advance of operating state OS2, a second ROP (ROP2) is performed to add a refill amount V2 to the reservoir. ROP2 is completed at time t3. Again, DTSS 6 consumes TF from the reservoir and the amount in the reservoir decreases. At time t4, a third ROP (ROP) is performed. In accordance with the method 300, the respective refill amount VI, V2 is adapted to the intended operating state OS1, OS2. In the illustrated example, the dialysis treatment is stopped during the ROPs, and the increase in VR is equal to the refill amount. This is not necessary or even desirable. In practice, the dialysis treatment may be performed continuously, thus also during the ROPs, to optimize the efficiency of the dialysis treatment.

[0097] From FIG. 4A, it is realized that the method 300 allows the control device 7 to achieve a predefined fill level (VR) in the reservoir 50 at any designated or selected time point. Thereby, it is possible to control when the dialysis system is to be switched to a specific operating state. Thus, by associating an operating state with a designated time point, the control device will automatically perform an ROP to ensure that a predefined amount of TF, specific to the operating state, is available in the reservoir at the designated time point. This functionality is especially powerful when the designated time point is a calendar time, since this allows for scheduling an operating state of the dialysis system. As used herein, "calendar time" is given in terms of date and / or time of day ("clock time"). The scheduling functionality will be further exemplified below with reference to FIG. 5 A.

[0098] FIG. 3B is a flow chart of an example procedure corresponding to step 302 in FIG. 3A. The procedure comprises step 302A, which is performed when the intended operating state is a cleaning state, such as OS1, OS4 or OS5 in FIG. 2. In step 302A, the refill amount for the ROP to be performed is determined as a function of an expected flow rate of TF from the reservoir 50 to the DTSS 6 (cf. Qc in FIG. 1A) during a calculation time period, which extends from the start of this ROP to the start of the next ROP in sequence. The expected flow rate Qc is typically known to the control device 7. For example, Qc may be given by the sensor signal S2 from the fill level sensor 52, a flow meter, volumetric pumping, or settings entered by a caretaker. The expected flow rate Qc may be fixed or variable over time. In the example of FIG. 4A, the refill amount VI for ROP1 is determined in accordance with step 302A, since OS1 is a cleaning state. The calculation time period is designated by AT and extends from start of ROP1 to start of ROP2. The calculation time period AT may be predefined for the cleaning state and set to be at least equal to the expected duration of the cleaning procedure that is performed in the cleaning state. It is realized that the calculation time period AT may differ between cleaning states. The rationale for step 302A is to ensure that the reservoir 50 holds a sufficient amount of TF to sustain dialysis treatment throughout the duration of the cleaning procedure. In some embodiments of step 302A, the refill amount VI of ROP I is determined to achieve a predefined amount of TF in the reservoir 50 such that the time for the DTSS 6 to consume the predefined amount, at the expected flow rate Qc, exceeds the calculation time period AT. This may be expressed as: with Vresbeing the remaining (residual) amount of TF in the reservoir 50 at start of ROP 1, as indicated in FIG. 4 A. The remaining amount Vresat any time point may be determined from the sensor signal S2 of the fill level sensor 52 (FIG. 1 A). It is realized that VI may but need not be a linear function of Qc. In any event, VI increases with increasing Qc.

[0099] The procedure in FIG. 3B also comprises step 302B, which is performed when the intended state is a variable composition state, such as OS2 in FIG. 2. In step 302B, the refill amount for the next ROP is determined as a function of a predefined maximum value (RTm) of the response time (RT) of the dialysis system 1. In this context, the "response time" is the required time to achieve a desired change in the composition of the TF that is supplied from the reservoir 50 to the DTSS 6. Generally, RT increases with fill level of the reservoir 50. This means that the largest RT is obtained at the time point when the ROP is completed, since the fill level gradually decreases after the ROP (cf. FIG. 4A). Thus, the fill level at completion of the ROP constitutes the worst case in terms of RT. Therefore, in some embodiments of step 302B, the refill amount is determined so as to result in a predefined fill level of the reservoir at the end of the ROP. This presumes that the predefined fill level has been determined to result in RT < RTm. The determination of the refill amount may also account for the consumption of TF during the ROP. This may be expressed as:

[0100] AROP

[0101] VFL=Kes + V2 — Qc■ dt o with V2 being the refill amount, AROP being the duration of the ROP, and VFLbeing the predefined fill level at the end of the ROP.

[0102] In the example of FIG. 4A, the refill amount V2 for ROP2 is determined in accordance with step 302B, since OS2 is a variable composition state.

[0103] FIG. 4B shows another example of how the fill level VR in the reservoir 50 may be adjusted over time while the dialysis system 1 is operated to perform RRT. Like in FIG. 4A, consecutive ROPs are enumerated to facilitate the discussion. In the illustrated example, ROP1 and ROP5 are followed by a cleaning state, and the refill amount VI is determined in accordance with step 302 A in FIG. 3B. In the time interval IT between ROP1 and ROP2, the control device 7 operates the SUSS 4 to perform a cleaning procedure CP. Thereby, CP is completed before the reservoir 50 is depleted of TF and before ROP2 is started to replenish the reservoir 50. Likewise, a cleaning procedure CP is performed in the time interval IT between ROP5 and ROP6. As shown, the time interval IT may be larger than the duration of CP to accommodate unforeseen delays during cleaning, as well as to allow for start-up of the SUSS 4 to generate TF with a required composition. Between the cleaning procedures, the dialysis system may be operated in a variable composition state. Here, the refill amount V2 of ROP2, ROP3, ROP4 and ROP6 is determined in accordance with step 302B in FIG. 3B. It may be noted that no composition change is actually initiated in the example of FIG. 4B. The dialysis system is nevertheless prepared for a request to change TF composition, by ensuring that the fill level in the reservoir 50 is adjusted to yield a response time that is less than the predefined maximum value, RTm.

[0104] In a variant, the dialysis system may be operated in a fixed composition state (cf. OS3 in FIG. 2) between the cleaning procedures. In the fixed composition state, the response time of the dialysis system is not relevant. In some embodiments, the refill amount of a ROP before a fixed composition state is determined by analogy with step 302 A. However, the calculation time period, AT, need not be predefined but may be determined dynamically based on a future operating state of the dialysis system. For example, AT may be determined based on the timing of a future cleaning procedure, to ensure that that the reservoir 50 is not depleted of TF before the next ROP is started.

[0105] FIG. 5 A shows a time sequence of cleaning procedures, CPs, performed by a dialysis system in accordance with an example. Each CP is preceded by a dedicated ROP. The CPs are separated by a cleaning time interval, CI, which may or may not be fixed. The cleaning time interval CI may be limited to ensure the functionality of the dialysis system and the quality of the treatment fluid. Thus, generally, the cleaning time interval CI should not exceed a predefined maximum CI value, which may be set individually for each dialysis system. In some embodiments, the maximum CI value may be set to 24 hours. In less conservative setups, the maximum CI value may be set to 36 hours, 48 hours, 60 hours, or 72 hours. In some embodiments, a fixed cleaning time interval CI is used so that the CPs are performed periodically.

[0106] The skilled person realizes that the dialysis system will be operated in a fixed or variable composition state between CPs and thus that one or more additional ROPs, not shown, are performed between consecutive CPs in FIG. 5 A.

[0107] As discussed above, it may be desirable to schedule the start of the respective CP to a specific time point. In FIG. 5A, the dialysis system is configured to perform the respective CP at a scheduled time ST. For example, ST may be a specific clock time, for example in the morning or during nighttime, for example daily or every second day. This will result in a fixed cleaning time interval CI between CPs.

[0108] When the control device 7 is configured to operate the SUSS 4 to start a respective CP at a predefined time point, for example at ST in FIG. 5A, the control device 7 is operable to perform a ROP in relation to the predefined time point (step 303), after having determined the refill amount of the ROP to achieve a sufficient fill level in the reservoir 50 (step 302). The fill level is sufficient in that the expected time for the DTSS 6 to consume the TF that is present in the reservoir 50 at the start of the CP exceeds a predefined maximum duration of the CP. The predefined maximum duration may correspond to the calculation time period AT (step 302 A).

[0109] When the dialysis system is first started, it may be desirable to perform an initial cleaning procedure of the fluid circuit 41 before the SUSS 4 is operated to generate TF. In FIG. 5A, an initial cleaning procedure CPi is started at time CT. The dialysis system may be started at any time, with a time difference x to the first ST. It is quite likely that x differs from CI. However, since the first ST is known, the control device 7 is operable by the method 300 to timely perform a ROP to ensure that the reservoir 50 has a sufficient fill level at the first ST.

[0110] FIG. 5B shows a time sequence of cleaning procedures performed by a dialysis system in accordance with an example. In this example, the control device switches between different cleaning procedures, resulting in different operating states. During OS1, a complete cleaning procedure CP0 is performed. During OS4, a first-type partial cleaning procedure CPI is performed. During OS5, a second-type partial cleaning procedure CP2 is performed. For example, CPI and CP2 may clean different subsets of the fluid circuit 41. The partial cleaning procedures CPI and CP2 typically have shorter durations than the complete cleaning procedure CP0. Thus, the calculation time periods AT are typically smaller for OS4 and OS5 than for OS1. A smaller AT results in a smaller refill amount and a shorter duration of the ROP, as seen in FIG 5B. By including one or more partial cleaning procedures CPI, CP2 in the sequence of cleaning procedures, it is possible to increase the time between complete cleaning procedures or even eliminate these. Further, the maximum CI value may be dictated by a critical subset of the fluid circuit 41. By tailoring a partial cleaning procedure to clean the critical subset, is it possible to reduce the total cleaning time during operation of the dialysis system.

[0111] It is also conceivable that the maximum capacity (Vmax) of the reservoir is insufficient to achieve the AT for a complete cleaning procedure. This may occur when the consumption flow rate Qc is high in relation to the maximum capacity. In CRRT, Qc may be in the range of 5-100 mL / min. In SLEDD, Qc may be in the range of 100-300 mL / min. Assuming that a complete cleaning of the fluid circuit 41 takes 30 minutes (AT) and that the reservoir is empty (Vres=0) at the start of a ROP, the refill amount will be at least 0.15-3 L in CRRT, and at least 6-9 L in SLEDD. It is envisioned that the maximum capacity of the reservoir will be in the range of 1-5 L. Thus, it may not be possible to perform a complete CP for some values of Qc, and the control device may then switch to using only partial CPs. In some embodiments, the control device 7 monitors and evaluates the fill level in the reservoir 50 during the CP, to verify that the TF in the reservoir 50 is sufficient to sustain dialysis treatment throughout the CP. If a potential shortage of TF is detected, the control device 7 may compensate for the shortage by operating the DTSS 6 to reduce Qc (FIG. 1) for the remainder of the CP. When the CP is completed, the control device 7 may compensate for the loss of dialysis dose by operating the DTSS 6 to use an increased Qc for a time period.

[0112] In some embodiments, the dialysis system may be in more than one of the available operating states at the same time. For example, while the dialysis system is in the fixed composition state (OS3), the control device 7 may be operable to also set the dialysis system in one of the available cleaning states (OS1, OS4, OS5). It is to be noted that the SUSS 4 is idle while the dialysis system is in OS3. Thus, if the expected duration of OS3 is larger than the duration of an available cleaning state, the control device may choose to perform a cleaning procedure so that at least part of the SUSS 4 is cleaned during OS3. It is less uncomplicated to perform a cleaning procedure while the dialysis system is in the variable composition state (OS2), since the SUSS 4 needs to be activated whenever the TF composition is to be changed. In one potential solution, the control device may prematurely terminate an on-going cleaning procedure whenever a request for composition change is received in OS2. In another potential solution, the control device may instead, when receiving a request for composition change, decide to complete the on-going cleaning procedure and inform the operator that the composition change will be postponed. Here, the control device may also estimate the remaining time of the cleaning procedure, use the remaining time to determine when the composition change will be completed, and inform the operator accordingly.

[0113] In accordance with the foregoing, the control device 7 may be configured to perform an opportunistic evaluation when the dialysis system is in a current operating state not associated with a cleaning procedure, to determine if a cleaning procedure fits within the duration of the current operating state. If a fit is determined, the control device may operate the SUSS 4 to perform the cleaning procedure. In the opportunistic evaluation, the control device may choose between cleaning procedures of different durations (cf. CPO, CPI, CP2 in FIG. 5B). The control device may also account for the elapsed time since previous cleaning procedures when determining if a cleaning procedure is warranted.

[0114] FIG. 6 is a flowchart of an example method 600 for changing the composition of TF in the reservoir. The method 600 will be described with reference to the dialysis system 1 in FIG. 1 A and is performed by the control device 7. The method 600 changes the TF composition by performing an additional replenishment operation ROPa, in which a metered amount of TF with a selected composition is supplied to the reservoir 50.

[0115] The method is performed when the dialysis system is in the variable composition state (OS2 in FIG. 2), as shown by step 601. By step 602, the control device 7 is ready to receive a request signal indicative of a request to change the TF composition. For example, the operator may input a change request on the UI device 74, causing the request signal to be generated. Alternatively, the request signal may be internally generated by the control device 7 in accordance with a treatment schedule that defines the TF composition over time during the dialysis treatment.

[0116] Upon receipt of the request signal in step 602, the method proceeds to step 603, in which a desired composition Cd is obtained. The desired composition Cd is the new TF composition to be attained in the reservoir 50 and supplied to the DTSS 6. The desired composition Cd may be included in the request signal or provided separately. The desired composition Cd may be given in any suitable format, for example as a concentration of one or more substances, a proportion (mixing ratio) between one or more TF concentrates and water (cf. TFC in FIG. 1 A), a conductivity, etc.

[0117] Depending on implementation, the method 600 may include step 604 and / or step 605. Steps 604 and 605 are performed at a current time, for example when the request signal is received in step 602 or when the ROPa is started (step 608, below). In step 604, a current composition Cc of the TF presently in the reservoir 50 is determined. Since the control device 7 operates the SUSS 4, the current composition Cc may be known to the control device 7. Thus, step 604 may involve retrieving Cc from memory 72. Alternatively, Cc may be given by a sensor (not shown) in the STSS5, the connecting line 5' or the DTSS 6. In step 605, a current amount Vc of TF in the reservoir 50 is determined. The control device 7 may determine Vc from the sensor signal S2 of the fill level sensor 52.

[0118] In step 606, an additional refill amount Va is determined. The refill amount Va is the above-mentioned metered amount of TF to be supplied to the reservoir 50 in the additional replenishment operation, ROPa. In some embodiments, Va is a predefined value. In some embodiments, Va is set as a function of Vc from step 605. For example, Va may be determined by analogy with step 302B, i.e., to meet a maximum response time after ROPa. In another example, Va may be set to a predefined fraction of Vc.

[0119] In step 607, the target composition Ct of the TF to be generated by the SUSS 4 during ROPa is determined. The target composition Ct is thus the composition of the TF that is added to the reservoir during ROPa. The target composition Ct is determined as a function of the desired composition Cd from step 603. The target composition Ct will be determined differently depending on how the existing TF in the reservoir 50 is handled. This is further explained below with reference to FIGS 7-10. In some implementations, Ct is set to Cd. In other implementations, Ct is determined as a function of Vc at the start of the ROPa.

[0120] In step 608, by analogy with step 303 (FIG. 3 A), the ROPa is performed. In the example of FIG. 1A, the SUSS 4 is operated by control signals Cl, C2 to generate TF with the target composition Ct from step 607 and to pump the additional refill amount Va of TF into the reservoir 50.

[0121] FIGS 7-9 illustrate example embodiments of the method 600. FIGS 7A, 8A and 9A depict the reservoir 50 at different time points before and after the ROPa. FIGS 7B, 8B and 9B depict graphs of fill level (VR) and composition (CR) in the reservoir 50 over time. Here, the composition is given by the concentration of a substance in the TF.

[0122] In the first embodiment of FIGS 7A-7B, the dialysis system is operated to empty the reservoir 50 more or less completely before the ROPa is performed. In the illustrated example, the reservoir 50 contains a current amount Vc of treatment fluid Fl when the request signal is received. The fluid Fl has composition Cc. The current amount Vc is determined (step 605), and a step 609 is performed to consume the current amount Vc of fluid Fl. In one example of step 609, the DTSS 6 is operated to obtain the fluid Fl from the reservoir 50 for regular use in the dialysis treatment. In another example of step 609, the fluid Fl is discarded, by the STSS 5 being operated to pump the fluid Fl from the reservoir 50 to a drain or a dedicated vessel (not shown). The latter may shorten the duration of step 609 if a higher flow rate is used to discard the fluid Fl compared to the consumption flow rate Qc of the DTSS 6 (FIG. 1 A). After completion of step 609, the reservoir 50 is effectively empty. At this time, the ROPa is performed (step 608) to add a refill amount Va (step 606) of a treatment fluid F2 to the reservoir 50. The fluid F2 has the desired composition Cd. Thus, in step 607 (FIG. 6), the target composition Ct is set equal to Cd. Thereby, as seen from FIG. 7B, treatment fluid of the desired composition Cd is made available to the DTSS 6 when the ROPa is started. Thus, the response time RT extends to the start of the ROPa, or shortly thereafter (step 608). As indicated, a small amount AV of the fluid Fl may remain in the reservoir 50 after step 609. As used herein, "effectively empty" implies that any remaining amount AV causes the concentration (by volume) of a substance in the fluid F2 at the end of the ROPa to deviate by less than about 5%, or preferably less than about 2.5%, from the corresponding concentration given by desired composition Cd.

[0123] In the second embodiment of FIGS 8A-8B, the dialysis system is operated to perform the ROPa so as to add the new TF on top of the existing TF in reservoir 50. Thus, ROPa results in a stratification of TF in the reservoir 50. In the illustrated example, the reservoir 50 contains a current amount Vc of treatment fluid Fl when the request signal is received. The fluid Fl has composition Cc. The ROPa is performed (step 608) to add a refill amount Va (step 606) of treatment fluid F2 to the reservoir 50. The fluid F2 has the desired composition Cd. Thus, in step 607 (FIG. 6), the target composition Ct is set equal to Cd. As indicated by FIG. 8A, the STSS 5 is operable to arrange the fluid F2 substantially above the existing fluid Fl in the reservoir 50. As used herein, "substantially above" implies that at least 90% or at least 95% of the fluid F2 is located on top of the fluid at the end of the ROPa. The stratification may be achieved by admitting F2 via a fluid inlet at the top of the reservoir 50. Such a fluid inlet may be configured to reduce the speed of the incoming fluid, for example by use of a spray nozzle. Alternatively, the fluid inlet may be arranged at the bottom of the reservoir 50 and configured to form a jet of fluid towards the top of the reservoir 50. Alternatively or additionally, stratification may be promoted by ensuring that the fluid F2 has a higher temperature than the fluid Fl. After or during the ROPa, a step 609 is performed to consume the fluid Fl, by analogy with step 609 in FIGS 7A-7B. When the fluid F2 has been consumed, treatment fluid of the desired composition Cd is made available to the DTSS 6. Thus, the response time RT extends to the end of the consumption step 609.

[0124] The first and second embodiments yield approximately the same response time RT. A technical advantage of the first embodiment is that a simple reservoir 50 can be used since fluid is pumped into and out of the reservoir in sequence. A potential technical challenge of the first embodiment is to timely start the ROPa so as to enable a continuous supply of TF for the DTSS 6 and to avoid that the DTSS 6 draws air from the reservoir 5. A technical advantage of the second embodiment is that it inherently ensures a continuous supply of TF to the DTSS 6. A potential technical challenge of the second embodiment is to achieve and maintain the stratification.

[0125] In the third embodiment of FIGS 9A-9B, the dialysis system is operated to change the composition by mixing a new TF with the existing TF in the reservoir 50. In the illustrated example, the reservoir 50 contains a current amount Vc of treatment fluid Fl when the request signal is received. The fluid Fl has composition Cc. The ROPa is performed (step 608) to add a refill amount Va (step 606) of a new treatment fluid to the reservoir 50. As indicated by FIG. 9A, the STSS 5 is operable to mix the new treatment fluid with the existing fluid Fl to yield a mixture F2' in the reservoir 50. The refill amount Va and the composition of the new TF are selected (steps 606-607) so that the composition of the mixture F2' is between Cc and Cd. Then, a step 609 is performed to consume the mixture F2', suitably by operating the DTSS 6 to obtain the mixture F2' from the reservoir 50 for regular use in the dialysis treatment. After completion of step 609, the reservoir 50 is effectively empty. At this time, a second ROPa is performed (step 608) to add a second refill amount Va' (step 606) of a treatment fluid F3 to the reservoir 50. In FIG. 9B, Va' is determined to result in fill level Vc, but this merely an example. The fluid F3 has the desired composition Cd. Thereby, as seen from FIG. 9B, treatment fluid of the desired composition Cd is made available to the DTSS 6 when second ROPa is started. Thus, the response time RT extends to the start of the second ROPa. In a variant of the third embodiment, the composition of the treatment fluid in the reservoir 50 is changed in further steps, by performing at least one further ROPa during the consumption step 609 to generate another mixture in the reservoir 50 with a composition closer to Cd than the mixture F2'. The third embodiment may be seen as a variant of the first embodiment.

[0126] The dialysis system may be configured in many different ways to promote mixing of fluids in the reservoir 50 in the third embodiment. In one example, the fluid inlet of the reservoir is provided with a dedicated nozzle to promote mixing within the reservoir 50. In another example, the STSS 5 comprises a recirculation circuit in fluid communication with the reservoir 50 and is operable to circulate the existing and the new TF through the recirculation circuit to promote mixing. In yet another example, the supply pump 45 in the SUSS 4 is operated to repeatedly reverse the flow of fluid in the fluid line 4' during the ROPa so as to cause a back-and-forth motion of the fluid entering the reservoir 50.

[0127] FIG. 10 show graphs of fill level (VR) and composition (CR) in the reservoir 50 over time for a fourth embodiment of the method 600, which is designed to minimize the response time RT. In FIG. 10, a ROP is started at time tl in advance of a variable composition state, in accordance with step 303, resulting in a fill level Vf in the reservoir 50 at time t2. At time t3, a request for a change of TF composition to Cd is received (steps 602-603), whereupon the current composition Cc and current amount Vc in the reservoir 50 are determined (steps 604-605). Based on Cc and Vc, the additional refill amount Va and the target composition Ct are determined so that a mixture of Vc and Va attains the desired composition Cd (steps 606-607). In one implementation, Va is first determined, based on any suitable criterion, and Ct is then determined to achieve Cd in the mixture of Vc and Va. In another implementation, Ct is first determined, based on any suitable criterion, and Va is then determined to achieve Cd in the mixture of Vc and Va. Alternatively, Va and Ct may be jointly determined to achieve Cd. Then, shortly after time t3, the ROPa is performed (step 608) to add the refill amount Va of a new TF with the target composition Ct to the reservoir 50. At the end of the ROPa, at time t4, treatment fluid of the desired composition Cd is made available to the DTSS 6. As seen, the RT is short and extends between times t3 and t4. Like in the third embodiment, the dialysis system may be configured to promote mixing of fluids in the reservoir 50.

[0128] FIG. 11 is a flow chart of an example verification procedure 700 that allows an operator to verify the response time before the ROPa is started in step 608 (FIG. 6). The procedure 700 is performed by the control device 7. In step 701, an actual response time RTa to achieve a desired composition change is calculated based on the current amount Vc in the reservoir (step 605). The skilled person understands that the estimated response time may be estimated when Vc and Va are known, given that the flow rates Qr and Qc (FIG. 1A) are known or estimated. The estimation in step 701 may also account for delays associated with the preparation of treatment fluid by the SUSS 4. In step 702, the actual response time RTa is supplied for presentation to the operator, for example via the UI device 74. In step 703, the control device waits for operator approval of the RTa, for example via the UI device 74. If approval is received, the ROPa is performed in step 704, which corresponds to step 608 in FIG. 6. Otherwise, if the operator declines RTa, step 705 may be performed to allow the operator to either cancel the request for composition change or enter a new request. If a new request is entered in step 705, the control device returns to step 701. If the request is cancelled, the control device may return to step 601 in FIG. 6. In one example, the new request defines a future time point for the composition change. In step 701, based on the new request, Vc and Qc at the future time point may be estimated and used for estimating an RTa at the future time point. In another example, the new request may include an acceptance that existing fluid in the reservoir is discarded (cf. step 609 in FIGS 7A, 8A, 9A), causing a re-estimation of RTa in step 701. In yet another example, the new request may cause step 701 to reduce Va used in the estimation.

[0129] The control device may perform another verification procedure, as an alternative or supplement to the procedure 700, to allow an operator to verify the TF composition to be provided to the DTSS 6, before the ROPa is started in step 608 (FIG. 6). It may be that the control device 7 is unable to achieve the desired composition Cd, or for some other reason decides to deviate from the desired composition Cd. The TF composition in the reservoir 50 resulting from the up-coming ROPa may be presented to the operator, by analogy with step 702. The TF composition may or may not be presented together with the RTa. It is conceivable to present an estimated TF composition over time, for example similar to the CR graphs in FIGS 7-10. The operator may then be given the option to accept or decline, by analogy with step 703.

[0130] FIG. 12A is a flow chart of an example procedure 800, which may be performed by the control device 7 to determine when to start a ROP in accordance with step 303 in FIG. 3. During the procedure 800, the control device monitors the fill level in the reservoir 50, based on the sensor signal S2 from the fill level sensor 52 (FIG. 1 A). In step 801, a limit variable LIM is set to a value VL1, which designates a predefined fill level in the reservoir 50. In step 802, the current fill level is evaluated in relation to LIM. If the current fill level is below LIM, a ROP is performed in step 805, which corresponds to step 303. Thus, by steps 801-802, a ROP is automatically triggered by the fill level in the reservoir 50. If the current fill level is not below LIM, step 803 is performed to evaluate if a command to change the TF composition is anticipated. In some embodiments, such a command is anticipated whenever the dialysis system is set in the variable composition mode (OS2 in FIG. 2). In other embodiments, the command is anticipated when an up-coming composition change is indicated by a treatment schedule that defines the TF composition over time. If no composition change is anticipated in step 803, the procedure 800 returns to step 802. If a composition change is anticipated, LIM is set to a value VL2, which is smaller than VL1, and the procedure 800 returns to step 802. The effect of the procedure 800 is illustrated in FIG. 12B, which shows fill level VR in the reservoir 50 over time. The fill level VR decreases monotonically, until the ROP is initiated, since the DTSS 6 continuously obtains TF from the reservoir 50 during dialysis treatment. Curves 810, 811 represent the fill level with no anticipated composition change and with an anticipated composition change, respectively. As seen, the start of the ROP is postponed when a composition change is anticipated, and the fill level is allowed to decrease beyond VL1. This will increase the likelihood that the fill level in the reservoir 50 is small when a composition change is requested. It should be realized from the examples in FIGS 7-9 that the response time RT increases with increasing fill level in the reservoir 50 when the composition change is requested. Thus, by selectively changing LIM in accordance with FIG. 12 A, the RT will decrease on average. Further, a smaller fill level may facilitate both stratification (FIGS 8A-8B) and complete mixing (FIGS 9A-9B, 10).

[0131] FIG. 13 is a schematic illustration of a dialysis system 1 for extracorporeal blood therapy by hemodialysis (HD), in a configuration that may be used for treatment of acute kidney injury (AKI), for example by CRRT. As explained in the following, the system 1 includes the sub-systems of FIG. 1 A. Like in FIG. 1 A, a water source 3 is fluidly connected, on path 3', to a supply sub-system (SUSS) 4, which is fluidly connected to a reservoir 50, on path 4'. The reservoir 50 is part of the storage subsystem (STSS) 5 of FIG. 1A. The reservoir 50 is arranged on a scale 52. Instead of being hung from the scale 52, as shown, the reservoir 50 may be placed to rest on the scale 52. The reservoir 50 may be a rigid or flexible container of any suitable medicalgrade material, for example plastics. The reservoir 50 is arranged to hold an intermediate supply of treatment fluid, TF. The remaining components of the system 1 in FIG. 13 are part of the treatment sub-system (DTSS) 6 of FIG. 1A, as indicated by a dashed line in FIG. 13. Thus, in the example of FIG. 13, the DTSS 6 is fluidly connected to the reservoir 50 on path 5'. A fluid pump Pl is arranged in path 5' to pump TF from the reservoir 50 through a dialyzer 10. The dialyzer 10 is a conventional blood filter, in which a semipermeable membrane 10' is arranged to define a first chamber for TF and a second chamber for blood. One end of the first chamber is connected to receive TF on path 5'. The TF flows through the first chamber and leaves the dialyzer 10 at the opposite end. The TF that leaves the dialyzer 10 is "spent". To distinguish fresh TF from spent TF, the latter is denoted "effluent" herein and designated by EF. An effluent path 11 extends from the first chamber of the dialyzer 10 to an effluent reservoir 12. A fluid pump P2 is arranged in path 11 to pump EF into the reservoir 12. The reservoir 12 may be configured in correspondence with the reservoir 50 and is arranged on a scale 13. A drain path 14 extends from the reservoir 12 to a drain 15. A fluid pump P3 is arranged in path 14 to pump EF from the reservoir 12 to drain 15. The second chamber of the dialyzer 10 is arranged to receive blood from a withdrawal path 6', which is connected by a connector 6a to the patient 2. The second chamber of the dialyzer 10 is also in fluid communication with a return path 6", which extends to a connector 6b, which is connected to the patient 2. The connectors 6a, 6b are access devices (catheter, needle, etc.) in fluid communication with the circulatory system of the patient 2. A fluid pump P4 is arranged to pump blood from the patient 2 on the withdrawal path 6', through the second chamber of the dialyzer 10, and on the return path 6" back to the patient 2. When passing the second chamber, the blood is interfaced with the TF through the membrane 10' and thereby treated by hemodialysis. The principle of hemodialysis is well-known to the skilled person and will not be further explained herein. It should be appreciated that the example in FIG. 13 is simplified and that further conventional components may be included, such as clamps, pressure sensors, air detector, etc.

[0132] To perform HD therapy, the control device 7 (FIG. 1 A) operates the dialysis system 1 to pump TF from reservoir 50 to the dialyzer 10 by pump Pl (by control signal C4) and to pump EF from the dialyzer by pump P2 (by control signal C5), and to pump blood through the dialyzer 10 by pump P4 (by control signal C6). During HD therapy, fluid is removed from the blood in correspondence to the difference in flow rates generated by the pumps Pl, P2. The process of fluid removal is known in the art as ultrafiltration. In the illustrated example, and in accordance with conventional practice, the control device 7 precisely monitors the amount of ultrafiltration based on the weights of the reservoirs 50, 12, as given by the scales 52, 13 (by sensor signals S2, S3). However, flow metering or a volumetric pumping mechanism may instead be used to monitor the amount of treatment fluid supplied to the dialyzer 10 and the amount of effluent drawn from the dialyzer 10, respectively. During therapy, TF reservoir 50 is intermittently replenished, by the SUSS 4 being operated to supply TF in accordance with the method 300 in FIG. 3. Further, the EF reservoir 12 may be intermittently drained in any suitable way. In the illustrated example, the pump P3 is operated (by control signal C7) to pump EF from the EF reservoir 12 to drain 15. In another example, the EF reservoir 12 is removed when full and replaced for an empty EF reservoir. In a further example, the dialysis system 1 comprises two EF reservoirs and is operated to direct the flow of EF into one EF container while the other EF container is being drained.

[0133] 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.

[0134] 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.

Claims

CLAIMS1. A dialysis system, comprising: a supply sub-system (4) comprising a fluid circuit (41), which is operable to supply a treatment fluid, a storage sub-system (5) comprising a reservoir (50), which is fluidly connected to receive the treatment fluid from the supply sub-system (4) and configured to hold a supply of the treatment fluid during operation of the dialysis system, a treatment sub-system (6), which is configured to obtain the treatment fluid from the storage sub-system (5) and perform a dialysis treatment by use of the treatment fluid, and a control device (7) which is configured to operate the treatment sub-system (6) to perform the dialysis treatment, wherein the control device (7) is further configured to operate the supply subsystem (4) to perform a sequence of intermittent replenishment operations (ROP) during the dialysis treatment, wherein a respective refill amount (VI, V2) of the treatment fluid is conveyed from the supply sub-system (4) to the reservoir (50) during a respective intermittent replenishment operation (ROP), wherein the control device (7) is configured to operate the dialysis system in a plurality of different operating states (OS1-OS5), and wherein the control device (7) is configured to determine the respective refill amount for the respective intermittent replenishment operation (ROP) based on an intended operating state of dialysis system subsequent to the respective intermittent replenishment operation (ROP), the intended operating state being an operating state among the plurality of different operating states.

2. The dialysis system of claim 1, wherein the control device (7) is configured to vary, as a function of the intended operating state and by way of the respective refill amount (VI, V2), an amount of available treatment fluid in the reservoir (50) resulting from the respective intermittent replenishment operation (ROP).

3. The dialysis system of claim 1 or 2, wherein the control device (7) is configured to, for at least one operating state among the plurality of different operating states (0S1-0S5), achieve a predefined amount of treatment fluid in the reservoir (50) at a designated time point.

4. The dialysis system of claim 3, wherein the designated time point is a calendar time.

5. The dialysis system of any preceding claim, wherein the sequence of intermittent replenishment operations comprises a first replenishment operation (ROP1) followed by a second replenishment operation (ROP2), wherein the control device (7) is configured to, for at least one of the operating states (0S1-0S5), determine the refill amount for the first replenishment operation (ROP1) as a function of an expected flow rate (Qc) of the treatment fluid from the reservoir (50) to the treatment sub-system (6) during a calculation time period (AT) from a start of the first replenishment operation (ROP1) to a start of the second replenishment operation (ROP2).

6. The dialysis system of claim 5, wherein, by said function, the refill amount of the first replenishment operation (ROP1) increases with the expected flow rate (Qc).

7. The dialysis system of claim 5 or 6, wherein the calculation time period (AT) is predefined.

8. The dialysis system of any one of claims 5-7, wherein at least two operating states (0S1-0S5) are associated with a respective calculation time period (AT), and wherein the respective calculation time period (AT) differs between said at least two operating states.

9. The dialysis system of any one of claims 5-8, wherein the control device (7) is configured to, for the at least one of the operating states (0S1-0S5), determine the refill amount of the first replenishment operation (ROP1) to achieve a predefined amount of treatment fluid in the reservoir (50) such that a time for the treatment sub-system (6) to consume the predefined amount of treatment fluid, at the expected flow rate (Qc), exceeds the calculation time period (AT).

10. The dialysis system of any preceding claim, wherein the plurality of different operating states comprises at least one cleaning state (OS1, OS4, OS5), in which the supply sub-system (4) is operated to perform a cleaning procedure (CP) of at least part of the fluid circuit (41) while stopping the supply of treatment fluid to the reservoir (50).

11. The dialysis system of claim 10, wherein the plurality of different operating states comprises two or more cleaning states (OS1, OS4, OS5) which differ at least by a duration of the cleaning procedure (CP).

12. The dialysis system of claim 10 or 11, wherein the control device (7) is configured to perform the cleaning procedure (CP) within a time period (IT) between two consecutive replenishment operations (ROP) in said sequence.

13. The dialysis system of any one of claims 10-12, wherein the control device (7) is configured to operate the supply sub-system (4) to repeatedly perform, at a cleaning time interval (CI), the cleaning procedure (CP) between respective replenishment operations (ROP) in said sequence, wherein the cleaning time interval (CI) is set to not exceed a predefined maximum value.

14. The dialysis system of claim 13, wherein the predefined maximum value of the cleaning time interval (CI) is 72, 48 or 24 hours.

15. The dialysis system of any one of claims 10-12, wherein the control device (7) is configured to operate the supply sub-system (4) to start the cleaning procedure (CP) at a predefined time point, wherein the control device (7) is further configured to perform one of the replenishment operations in relation to the predefined time point, and determine the refill amount (VI) of said one of the replenishment operations so that an expected time for the treatment sub-system (6) to consume the treatment fluid present in the reservoir (50) at the start of the cleaning procedure (CP) exceeds a predefined maximum duration of the cleaning procedure (CP).

16. The dialysis system of claim 15, wherein the control device (7) is configured to perform said one of the replenishment operations so that it is completed at the start of the cleaning procedure (CP).

17. The dialysis system of any preceding claim, wherein the plurality of different operating states comprises a fixed composition state (OS3), in which the dialysis system is operated to prevent a change in composition of the treatment fluid that is supplied by the supply sub-system (4).

18. The dialysis system of any preceding claim, wherein the plurality of different operating states comprises a variable composition state (OS2), in which the dialysissystem is operated to admit a change in composition of the treatment fluid that is supplied by the supply sub-system (4).

19. The dialysis system of claim 18, wherein the control device (7), when the intended operating state is the variable composition state (OS2), is configured to determine the refill amount of the respective intermittent replenishment operation as a function of a predefined maximum value (RTm) of a response time (RT) of the dialysis system, the response time (RT) being a required time to achieve a desired change in composition of the treatment fluid that is supplied from the reservoir (50) to the treatment sub-system (6).

20. The dialysis system of claim 18 or 19, wherein the control device (7), when operating the dialysis system in the variable composition state (OS2) and upon receipt of a request signal indicative of a requested composition change of the treatment fluid that is supplied from the reservoir (50) to the treatment sub-system (6) from a current composition (Cc) to a new composition (Cd), is configured to perform an additional replenishment operation (ROPa), in which the supply sub-system (4) is operated to supply an additional refill amount (Va) of treatment fluid of a target composition to the reservoir (50), wherein control device (7) is configured to determine the target composition based on the new composition (Cd).

21. The dialysis system of claim 20, wherein the target composition is equal to the new composition, and wherein the control device (7), before performing the additional replenishment operation (ROPa), is configured to determine a current amount (Vc) of treatment fluid in the reservoir (50), and operate the storage sub-system (5) and / or the treatment sub-system (6) to effectively remove the current amount (Vc) of treatment fluid from the reservoir (50).

22. The dialysis system of claim 20, wherein the target composition is equal to the new composition, and wherein the storage sub-system (5) is operable, during the additional replenishment operation (ROPa), to arrange the additional refill amount (Va) substantially above a current amount of treatment fluid that is located in the reservoir (50) at start of the additional replenishment operation (ROPa).

23. The dialysis system of claim 20, wherein the control device (7), before performing the additional replenishment operation (ROPa), is configured to determine the current composition (Cc) and a current amount (Vc) of treatment fluid in thereservoir (50), and to determine the target composition and the additional refill amount (Va), based on the current composition (Cc) and the current amount (Vc), so that a mixture of the current amount (Vc) and the additional refill amount (Va) attains the new composition (Cd).

24. The dialysis system of any one of claims 21-23, wherein the control device (7) is configured to calculate an actual response time (RTa) based on the current amount (Vc), supply the actual response time (RTa) for presentation to the user, and perform the additional replenishment operation (ROPa) subject to receipt of a user approval of the actual response time (RTa).

25. The dialysis system of any one of claims 1-9, wherein the plurality of different operating states comprises at least two of a cleaning state (OS1, OS4, OS5) in which the supply sub-system (4) is operated to perform a cleaning procedure (CP) of at least part of the fluid circuit (41), a fixed composition state (OS3) in which the dialysis system is operated to prevent a change in composition of the treatment fluid that is supplied by the supply sub-system (4), or a variable composition state (OS2) in which the dialysis system is operated to admit the change in composition of the treatment fluid that is supplied by the supply sub-system (4).

26. The dialysis system of any preceding claim, wherein the control device (7) is configured to initiate a respective replenishment operation in the sequence of replenishment operations when a measured or estimated amount of treatment fluid in the reservoir (50) falls below a predefined limit (VL1).

27. The dialysis system of claim 26, wherein the control device (7) is configured to temporarily replace the predefined limit (VL1) for a second predefined limit (VL2), which is lower than the predefined limit, when a command to change a composition of the treatment fluid is anticipated.

28. The dialysis system of any preceding claim, wherein at least part of the fluid circuit (41) is permanently installed in the supply sub-system (4).

29. The dialysis system of any preceding claim, wherein the supply sub-system (4) is configured to prepare the treatment fluid by mixing at least one concentrate with purified water in the fluid circuit (41).

30. The dialysis system of claim 29, wherein the supply sub-system (4) is configured to receive incoming water and process the water into said purified water in the fluid circuit (41).

31. The dialysis system of any preceding claim, wherein the reservoir (50) is a disposable part.

32. The dialysis system of any preceding claim, wherein the treatment sub-system (6) is configured for CRRT.

33. A computer-implemented method of operating a dialysis system comprising: a supply sub-system comprising a fluid circuit, which is operable to supply a treatment fluid; a storage sub-system comprising a reservoir, which is fluidly connected to receive the treatment fluid from the supply sub-system and configured to hold a supply of the treatment fluid during operation of the dialysis system; and a treatment sub-system, which is configured to obtain the treatment fluid from the storage sub-system and perform a dialysis treatment by use of the treatment fluid, wherein the dialysis system is operable in a plurality of different operating states, said method comprising: operating (200) the treatment sub-system to perform the dialysis treatment, and operating (303) the supply sub-system to perform a sequence of intermittent replenishment operations during the dialysis treatment, by conveying a respective refill amount of the treatment fluid from the supply sub-system to the reservoir in the storage sub-system during a respective intermittent replenishment operation, said method further comprising: determining (302) a respective refill amount for the respective intermittent replenishment operation based on an intended operating state of the dialysis system subsequent to the respective intermittent replenishment operation, the intended operating state being an operating state among the plurality of different operating states.

34. A computer-readable medium comprising program instructions, which when executed by processing circuitry causes the processing circuitry to perform the method according to claim 33.

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