Handling leakage currents in dialysis therapy

Abstract

An apparatus is provided for handling waste fluid, WF, generated in connection with dialysis therapy, to mitigate the risk that a patient undergoing dialysis therapy is exposed to harmful leakage currents. The apparatus includes a fluid disposal arrangement, FDA (40), which is configured to receive WF and define a fluid flow path (41) for directing WF to a drain. The FDA (40) is operable to combine WF with a dilution fluid, DF, at a supply region (44) in the fluid flow path (41). A control device (50) is configured to operate one or more flow controllers (42, 45) in the FDA (40) to relatively control a first fluid flow of DF and a second fluid flow of WF into the supply region (44) so that a hypothetical homogeneous mixture of DF and WF at the supply region (44) has an electrical conductivity below a first limit value.

Description

[0001] HANDLING LEAKAGE CURRENTS IN DIALYSIS THERAPY

[0002] Technical Field

[0003] The present disclosure relates generally to dialysis therapy, and in particular to a technique of handling leakage currents in connection with dialysis therapy.

[0004] Background Art

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

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

[0007] Dialysis therapy may be automated by use of machines, i.e. electrical equipment. Such electrical equipment produces leakage currents. There are standards for safety and performance of medical electrical equipment. One such standard is IEC60601, which defines maximum leakage currents allowed in electrical medical equipment to reduce the risk of electrical shock based on type of applied part (AP) and based on type of leakage current. The AP is a component of the medical equipment that comes into contact with the patient.

[0008] Some types of medical electrical equipment that come into connect with a patient are required to have a floating patient ground. This means that the equipment needs to ensure that the patient is not electrically connected to protective Earth via the equipment.

[0009] For dialysis therapy, IEC60601-2-39:2018 applies to the basic safety and essential performance of medical electrical equipment for PD. It defines that PD equipment needs to be Class II BF (Body Floating). Class II BF require a floating patient ground and has a maximum allowed patient leakage current of I OOp A for NC and 500p A for SFC. Here, NC (Normal Condition) refers to the situation when leakage current flows from the patient via the AP to Earth, and SFC (Single Fault Condition) refers to the situation when a component or isolation barrier breaks, causing the patient to be exposed to a potentially increased leakage current. Electrical equipment for extracorporeal blood therapy that is not connected to protective Earth needs to be Class II CF (Cardiac Floating). Class II CF requires a floating patient ground and has a maximum allowed patient leakage current of I Op A for NC and 5 Op A for SFC.

[0010] Dialysis therapy produces used ("spent") treatment fluid that needs to be handled. Often, spent treatment fluid is pumped from the patient along a flow path that extends to a drain, such as a toilet, bathtub or sink. The toilet, bathtub or sink may establish an Earth ground relative to the patient and the dialysis machine. Treatment fluid, and thus spent treatment fluid, is electrically conductive. The flow path is accordingly an applied part (AP) and creates a conductive path from the patient to the drain.

[0011] It has been suggested to measure the leakage current in an electrically conductive fluid that flows on a fluid path from a patient to a drain and to actively break the flow when the leakage current exceeds a threshold, to thereby protect the patient from electrical shock. A rudimentary technique for measuring the leakage current is disclosed in US9636454, the leakage current is monitored via a voltage drop created by the leakage current across an impedance coupling. This technique is

[0012] Summary

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

[0014] One objective is to provide a simple technique of handling leakage currents through the drain line during dialysis therapy.

[0015] A further objective is to provide such a technique that is robust.

[0016] Another objective is to provide such a technique that can be implemented in existing dialysis systems.

[0017] One or more of these objectives, as well as further objectives that may appear from the description below, are at least partly achieved by an apparatus for handling waste fluid generated in connection with dialysis therapy, a system for performing dialysis therapy, and a method of handling waste fluid according to the independent claims, embodiments thereof being defined by the dependent claims.

[0018] A first aspect is an apparatus for handling waste fluid generated in connection with dialysis therapy. The apparatus comprises a fluid disposal arrangement, which is configured to receive the waste fluid and define a fluid flow path for directing the waste fluid to a drain. The fluid disposal arrangement is operable to combine the waste fluid with a dilution fluid at a supply region in the fluid flow path. The apparatus further comprises a control device, which is configured to operate one or more flow controllers in the fluid disposal arrangement to relatively control a first fluid flow of the waste fluid and a second fluid flow of the dilution fluid into the supply region so that a hypothetical homogeneous mixture of the dilution fluid and the waste fluid at the supply region has an electrical conductivity below a first limit value.

[0019] A second aspect is a system for performing dialysis therapy. The system comprises a therapy sub-system configured to supply treatment fluid to a patient as part of the dialysis therapy, said therapy sub-system being further configured to produce waste fluid before, during or after the dialysis therapy, and an apparatus for handling the waste fluid according the first aspect.

[0020] A third aspect is a method of handling waste fluid generated in connection with dialysis therapy. The method comprises: receiving and directing the waste fluid on a fluid flow path to a drain by a fluid disposal arrangement, which is operable to combine the waste fluid with a dilution fluid at a supply region in the fluid flow path, and operating one or more flow controllers in the fluid disposal arrangement to relatively control a first fluid flow of the waste fluid and a second fluid flow of the dilution fluid into the supply region so that a hypothetical homogeneous mixture of the dilution fluid and the waste fluid at the supply region has an electrical conductivity below a first limit value.

[0021] As used herein, "relatively control" implies that the relation or ratio between the flow rates of waste fluid (first fluid flow) and dilution fluid (second fluid flow) into the supply region is controlled. Thus, relatively control may include any of: adjusting only the flow rate of the waste fluid, adjusting only the flow rate of the dilution fluid, or by adjusting both of these flow rates such that a ratio between them is changed. Stated differently, relatively control may include adjusting the flow rate of the waste fluid in relation to the flow rate of the dilution fluid, adjusting the flow rate of the dilution fluid in relation to the flow rate of the waste fluid, or adjusting both the flow rate of the waste fluid and the flow rate of the dilution fluid in relation to each other.

[0022] The expression "so that a hypothetical homogenous mixture of the dilution fluid and the waste fluid at the supply region has an electrical conductivity below a first limit value" may be equivalently worded, and replaced by, "so that a homogeneous mixture of the dilution fluid and the waste fluid at the supply region would have an electrical conductivity below a first limit value" or "so that a homogeneous mixture of the dilution fluid and the waste fluid, if formed at the supply region, has an electrical conductivity below a first limit value". These expressions do not imply that a homogeneous mixture is actually formed at the supply region, but that the first fluid flow and the second fluid flow are relatively controlled to account for the scenario that a homogeneous mixture is formed at the supply region, with respect to the electrical conductivity of such a homogeneous mixture. Thus, the hypothetical homogeneous mixture is a theoretical fluid that is formed as a homogeneous mixture of the dilution fluid and the waste fluid. Worded differently, the electrical conductivity of a hypothetical homogenous mixture of the dilution fluid and the waste fluid is the same as the electrical conductivity of a homogenous mixture of an equivalent dilution fluid and an equivalent waste fluid.

[0023] The foregoing aspects provide a technique of mitigating the risk that the patient is connected to Earth ground via the fluid flow path to drain during on-going dialysis therapy and thereby is exposed to harmful leakage currents. Simply stated, the technique involves accounting for a worst case scenario while relatively dosing waste fluid and dilution fluid into the fluid flow path that directs the waste fluid to the drain. The lowest electrical resistance in the fluid flow path will be achieved for a complete ("homogeneous") mixing of the waste fluid and the dilution fluid in the supply region, whereas incomplete mixing or complete separation of the waste fluid and the dilution fluid into alternating fluid segments along the fluid flow path results in a higher electrical resistance. Thus, the worst case scenario in terms of leakage currents occurs for a complete mixing between the waste fluid and the dilution fluid. By operating the apparatus to ensure that the leakage currents through the fluid flow path to the drain are not harmful to the patient for the scenario with the lowest resistance, it inherently takes care of all other scenarios. Thus, a simple and effective technique is provided to limit leakage currents during dialysis therapy. The technique is inherently robust and simple to implement in existing dialysis systems by installation of the apparatus of the first aspect.

[0024] Below, some embodiments of the apparatus of the first aspect are recited.

[0025] In some embodiments, the control device is configured to operate said one or more flow controllers based on estimated values of the electrical conductivity of the dilution fluid and the waste fluid.

[0026] In some embodiments, the fluid disposal arrangement comprises a conductivity sensor in the fluid flow path downstream of the supply region, and the control device is configured to operate the fluid disposal arrangement based on a sensor signal from the conductivity sensor.

[0027] In some embodiments, the control device is configured to monitor the sensor signal and generate an alert signal when the sensor signal exceeds a second limit value. In some embodiments, the control device is configured to operate said one or more flow controllers to adjust at least one of the first fluid flow or the second fluid flow to attain a target conductivity value in the sensor signal.

[0028] In some embodiments, the supply region comprises a tank, which is configured to receive the first fluid flow and the second fluid flow and form a mixture of the waste fluid and the dilution fluid.

[0029] In some embodiments, the tank is arranged to receive the first flow of the waste fluid through at least one first inlet of the tank, to receive the second flow of dilution fluid through at least one second inlet in a top portion of the tank, and to provide the mixture of the waste fluid and the dilution fluid through at least one outlet at a bottom portion of the tank.

[0030] In some embodiments, the tank is configured to, at least by a spatial separation of the at least one second inlet from the at least one first inlet, and by a spatial separation of the at least one second inlet from a fluid level of the mixture in the tank, mitigate propagation of microorganisms from the fluid flow path into at least one supply line for the dilution fluid, said at least one supply line being connected to the at least one second inlet.

[0031] In some embodiments, the supply region is in fluid communication with an outlet connector for releasable connection to an inlet connector on a fluid line for directing the mixture of waste fluid and the dilution fluid to the drain.

[0032] In some embodiments, the fluid disposal arrangement is configured to receive at least two types of dilution fluids, which differ at least by their electrical conductivity, and the control device is configured to operate a flow controller among the one or more flow controllers to provide different combinations of the at least two types of dilution fluids to the supply region in dependence of at least one of a flow rate, a type or an electrical conductivity of the waste fluid.

[0033] In some embodiments, the control device is configured to operate the fluid disposal arrangement to direct at least one of source water, purified water, or reject water, to the supply region for use as the dilution fluid, wherein the purified water is generated from the source water by a water purification device, and the reject water is generated by a reverse osmosis unit in the water purification device when processing the source water into the purified water for use in connection with the dialysis therapy.

[0034] In some embodiments, the waste fluid comprises one or more of a spent treatment fluid generated by the dialysis therapy, or a discarded fluid from a mixing device configured to produce a treatment fluid for use in the dialysis therapy.

[0035] In some embodiments, the control device is configured to set the first limit value based on size data for the fluid flow path downstream of the supply region. In some embodiments, the control device is configured to set the first limit value to achieve a required electrical resistance in the fluid flow path downstream of the supply region.

[0036] In some embodiments, the fluid disposal arrangement comprises a measurement device for measuring an electrical resistance between two separated locations along the fluid flow path downstream of the supply region, and the control device is configured to evaluate the electrical resistance between the two separated locations in relation to a resistance limit.

[0037] In some embodiments, the control device is further configured to modify, based on the electrical resistance between the two separated locations, a relation between the first and second fluid flows into the supply region to account for buildup of conductive deposits inside the fluid flow path over time.

[0038] In some embodiments, the measurement device comprises a current source, a resistor, which is connected in series with the current source between the two separate locations, and a voltage detector, which is connected to measure an electrical voltage over the current source and generate an output signal indicative of said electrical resistance between the two separated locations, wherein the resistor has an electrical resistance that is at least a factor of 10 larger than a limit electrical resistance, and wherein the limit electrical resistance is a minimum allowed electrical resistance between the two separated locations.

[0039] In some embodiments, the measurement device further comprises an isolated DC / DC converter, which is connected to receive the output signal from the voltage detector and provide an isolated output signal, and wherein the voltage detector is connected to an isolated ground.

[0040] In some embodiments, in the control device is configured to perform a validation process comprising: operating the fluid disposal arrangement to fill the fluid flow path between the two separated locations with a reference fluid; establish, when the fluid flow path between the two separated locations is filled with the reference fluid, an electrical connection of the measurement device to the two separated locations; and operate the measurement device to measure the electrical resistance between the two separated locations.

[0041] In some embodiments, the control device is configured to, if the electrical resistance between the two separated locations is below the resistance limit, instruct a user to replace at least part of the fluid flow path.

[0042] The foregoing embodiments are also applicable to the second and third aspects. Some further embodiments of the system of the second aspect are recited below. In some embodiments, the therapy sub-system comprises a mixing device, which is configured to generate the treatment fluid by mixing purified water with one or more concentrates.

[0043] In some embodiments, the therapy sub-system further comprises a water purification device, which is configured to generate the purified water from source water.

[0044] In some embodiments, the control device is configured to perform a validation process according to one or more embodiments of the first aspect when the therapy subsystem is fluidly disconnected from the patient.

[0045] In some embodiments, the system is configured with a floating ground of each part that comes into direct conductive contact with the patient's body.

[0046] In some embodiments, the system is classified as body floating or cardiac floating under IEC 60601.

[0047] Still other objectives, aspects, embodiments, and technical effects, as well as features and advantages may appear from the following detailed description, from the attached claims as well as from the drawings.

[0048] Brief Description of the Drawings

[0049] FIGS 1A-1B are schematic views of example dialysis systems connected to a patient.

[0050] FIG. 2 is a block diagram of a combination of an example therapy sub-system of a dialysis system, and an example fluid disposal arrangement for disposal of waste fluid generated by the therapy sub-system.

[0051] FIGS 3A-3B are flow charts of example methods of operating a fluid disposal arrangement.

[0052] FIGS 4A-4B are side views of an example tank included in a fluid disposal arrangement.

[0053] FIG. 5A is a schematic view of an example fluid disposal arrangement with a replaceable drain line portion, FIG. 5B is a schematic view of a replaceable drain line portion connected to a resistance measurement device, FIG. 5C is a flow chart of an example validation procedure performed by use of a resistance measurement device, and FIG. 5D is a block diagram of an example resistance measurement device.

[0054] FIG. 6 is a block diagram of an example fluid disposal arrangement combined with a dialysis system.

[0055] Detailed Description of Example Embodiments 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.

[0056] 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.

[0057] 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.

[0058] 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.

[0059] Well-known functions or constructions 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.

[0060] As used herein, "dialysis therapy" refers to any therapy that replaces or supplements the renal function of a patient by use of a medical fluid. Dialysis therapy includes, without limitation, extracorporeal (EC) blood therapy and peritoneal dialysis (PD) therapy.

[0061] As used herein, "treatment fluid" refers to any fluid that is consumed as a result of dialysis therapy. Treatment fluid includes, without limitation, dialysis fluid for infusion into the peritoneal cavity during PD therapy, dialysis fluid for supply to a dialyzer during EC blood therapy, and replacement fluid and substitution fluid for infusion into blood during EC blood therapy.

[0062] Like reference signs refer to like elements throughout.

[0063] The present disclosure relates to a technique of handling leakage currents in relation to dialysis therapy performed by one or more machines. The technique is applicable to both peritoneal dialysis (PD) therapy and extracorporeal (EC) blood therapy. For context only, systems for PD therapy and EC blood therapy will be briefly discussed with reference to FIGS 1A-1B.

[0064] FIG. 1A is a generic overview of a dialysis system 10 for PD therapy. The dialysis system 10 is fluidly connected to the peritoneal cavity PC of a patient P. As indicated by a double-ended arrow, the dialysis system 10 is operable to convey fresh dialysis fluid into PC and to receive spent dialysis fluid from PC on a fluid path 11. The fluid path 11 may be defined by tubing that connects to an implanted catheter (not shown) in fluid communication with the peritoneal cavity PC. A drain line 13 is connected to the dialysis system 10 for conveying the spent dialysis fluid to a drain 25. In the illustrated example, the dialysis system 10 comprises an automated therapy sub-system 30 that performs the PD therapy. PD therapy is typically implemented as daily treatment sessions, each comprising a number of fluid exchange cycles. The respective fluid exchange cycle may include a fill phase, a dwell phase and a drain phase, performed in sequence. In the fill phase, the fresh dialysis fluid is supplied to PC on fluid path 11. In the dwell phase, the dialysis fluid resides in PC. In the drain phase, the spent dialysis fluid is extracted from PC on fluid path 11.

[0065] The therapy sub-system 30 may comprise one or more electrically controlled machines and may be implemented to provide different levels of functionality. In a first implementation, the therapy sub-system 30 includes a therapy device which is operable to control the flow of dialysis fluid to and from the PC, and the sub-system 30 receives pre-made dialysis fluid from a source 20 on a supply path 12. In PD therapy, the therapy device is commonly known as a "cycler". In a second implementation, the therapy subsystem 30 includes the cycler and a mixing device that is configured to generate the dialysis fluid for the cycler by mixing one or more concentrates with purified water, which is received from the source 20. In a third implementation, the therapy sub-system 30 includes the cycler, the mixing device and a water purification device that is configured to generate the purified water based on source water, which is received from the source 20.

[0066] FIG. IB is a generic overview of a dialysis system 10 for EC blood therapy. The dialysis system 10 is fluidly connected to the vascular system of a patient P on a fluid path. In the illustrated example, the fluid path is defined by tubing 11 A for blood extraction and tubing 1 IB for blood return. As indicated by arrows, the dialysis system 10 is operable to draw blood from the patient P through tubing 11 A, process the blood, and return the processed blood to the patient through tubing 1 IB. The tubing 11A, 1 IB is connected to an access device (for example a catheter, graph or fistula, not shown) in fluid communication with the vascular system of the patient P. The dialysis system 10 may be configured to process the blood by any form of EC blood therapy, such as HD, HF or HDF. In HD and HDF, dialysis fluid is interfaced with the blood of the patient in a filtration unit ("dialyzer"), resulting in spent dialysis fluid. A drain line 13 is connected to the dialysis system 10 for conveying the spent dialysis fluid to a drain 25. In the illustrated example, the dialysis system 10 comprises an automated therapy subsystem 30 that performs the EC blood therapy. Eike in FIG. 1A, the therapy sub-system 30 may comprise one or more electrically controlled machines and may be implemented to provide different levels of functionality. The first, second and third implementation examples are equally applicable to the therapy sub-system 30 in the dialysis system 10 for EC blood therapy.

[0067] In FIGS 1A-1B, a flow of spent treatment fluid will be guided through the drain line 13 to the drain 25 during on-going dialysis therapy while the dialysis system 10 is in is direct conductive contact with the patient P. As noted in the Background section, the drain 25 may form an Earth ground relative to the patient P and the dialysis system 10. Since the spent treatment fluid is electrically conductive, there is thus a risk that the patient P is subjected to a potentially harmful leakage current that is conducted to the drain 25 through the spent treatment fluid that flows in the drain line 13. This risk persists even if the outlet of the drain line 3 is spaced from with the drain 25, since any continuous stream of fluid from the outlet of the drain line 13 to the drain 25 will form an electrically conductive path.

[0068] FIG. 2 is a block diagram of an apparatus that is fluidly connected to a therapy sub- system 30 to mitigate the risk of harmful leakage currents being conducted from the patient (not shown) to drain 25. The apparatus comprises a fluid disposal arrangement 40 and a control device 50, which is configured to control the fluid disposal arrangement 40. In the following, the fluid disposal arrangement is abbreviated FDA.

[0069] The therapy sub-system 30 is part of a dialysis system 10 for PD therapy or EC blood therapy, for example as shown in FIGS 1A-1B. The therapy sub-system 30 is operated by a main control device (not shown) in conventional manner to perform dialysis therapy in accordance with a treatment schedule, which may be predefined or entered into the main control device by a caretaker. In the illustrated example, the therapy sub-system 30 comprises a therapy device 30A, a mixing device 30B and a water purification device 30C. The devices 30A-30B may be implemented by separate machines or be combined into one or two separate machines.

[0070] The therapy device 30A is configured to perform the dialysis therapy by supplying fresh treatment fluid TF on a supply line 31A and obtaining spent treatment fluid STF on a return line 3 IB in accordance with the treatment schedule. The supply line 31A may be fluidly connected to the tubing 11 in FIG. 1A or the tubing 11A in FIG. IB. The return line 3 IB may be fluidly connected to the tubing 11 in FIG. 1A or the tubing 1 IB in FIG. IB. The therapy device 30A is arranged to receive TF on a transfer line 31C, and to output STP on a drain line 32A. Therapy devices are well- known in the art and need no further description.

[0071] The mixing device 30B is configured to generate TF by mixing product water PW with one or more concentrates Cx. The respective concentrate may be in liquid form or in the form of a powder or granules. The mixing device 30B is arranged to receive the product water PW on a transfer line 3 ID and to provide TF to the therapy device 30A on the transfer line 31C. In the illustrated example, the mixing device 30B is also operable to output excess fluid EF on a drain line 32B. The excess fluid EF is discarded fluid that may be output by the mixing device 30B whenever the composition of the generated TF deviates from a target composition, for example during start-up of the mixing device 30B, when a concentrate is replaced, when there is a malfunction in the mixing device 30A, etc. The electrical conductivity of EF may thus be comparable to the electrical conductivity of TF, or even higher. A mixing device 30B is conventionally integrated into dialysis machines for treatment of chronic kidney disease (CKD) by EC blood therapy. The skilled person is also well aware of numerous mixing devices, integrated or stand-alone, that have been proposed in both scientific literature and patent literature, for use in PD therapy and EC blood therapy.

[0072] The water purification device 30C is configured to generate product water PW from source water SW, which may be tap water or any other water of insufficient (or at least unverified) purity and / or sterility for use in dialysis therapy. The water purification device 30C is arranged to receive SW on a transfer line 3 IE and to provide PW to the mixing device 30B on the transfer line 3 ID. The transfer line 3 IE may be fluidly connected to the supply path 12 in FIGS 1A-1B. The product water PW is purified water that may be generated to meet criteria of so-called "water for dialysis", "water for injection", or "ultrapure water". As used herein, the term "water purification" refers to a process of removing undesirable chemicals, biological contaminants, suspended solids, and gases from the water. Water purification devices are well-known in the art and may involve, in any combination, active carbon filtration, ultrafiltration, membrane filtration, ion exchange, electrodeionization, dechlorination, disinfection, softening, etc. One commonly used membrane filtration technique for water purification is reverse osmosis (RO), in which an RO membrane is used to separate ions, molecules and larger particles from water. Reverse osmosis inherently generates a flow of so-called reject water, which has a lower purity than the product water. In some implementations, the reject water, or part thereof, is discarded. As indicated by dashed lines in FIG. 2, the water purification device 30C may include an RO unit 34 for use in processing the source water SW into product water PW. During operation, the RO unit 34 produces reject water RW, which is output on a supply line 33B. Water purification devices and RO units are well-known in the art and need no further description.

[0073] In the example of FIG. 2, the fluid disposal arrangement, FDA, 40 comprises a first flow controller 42, which is connected to receive STF from the therapy device 30A on drain line 32A and to receive EF from the mixing device 30B on drain line 32B. The FDA 40 defines a drain path 41 from the fluid controller 42 to a drain 25. The FDA 40 further comprises a second flow controller 45, which is arranged to receive product water PW, reject water RW and source water SW on the respective supply line 33A, 33B, 33C. A dilution line 43 extends from the second flow controller 45 to a supply region 44 in the drain path 41.

[0074] As indicated in FIG. 2, the first flow controller 42 is operable to provide a flow of waste fluid WF into the drain path 41 towards the supply region 44. The waste fluid WF includes STF, EF, or a combination of STF and EF. The first flow controller 42 may be operable to vary the flow rate of waste fluid WF. In some embodiments, the first flow controller 42 is operable to change the proportion of STF and EF in the waste fluid WF. The first flow controller 42 may be configured to provide the desired functionality in a multitude of different ways, by use of one of more on / off valves, one or more pumping devices, one or more flow restrictors, etc., as readily understood by the skilled person. In some embodiments, the first flow controller 42 includes one or more reservoirs for intermediate storage of incoming STF and / or EF.

[0075] As seen in FIG. 2, the second flow controller 45 is operable to provide a flow of dilution fluid DF into the dilution path 43 towards the supply region 44. Generally, the dilution fluid DF is any available fluid that has a lower electrical conductivity than WF In the illustrated example, DF includes SW, RW, PW, or any combination thereof. In some embodiments, the mixing device 30B may be operable to generate a low- conductivity fluid, which may be supplied to the FDA 40 for use as DF. In one example, such a low-conductivity fluid may be generated from a glucose concentrate that is available to the mixing device (cf. Cx). The low-conductivity fluid may, for example, be a mixture of glucose concentrate and PW. The second flow controller 45 may be operable to vary the flow rate of dilution fluid DF. The second flow controller 45 may be configured to provide the desired functionality in a multitude of different ways, by use of one of more on / off valves, one or more pumping devices, one or more flow restrictors, etc., as readily understood by the skilled person. In some embodiments, the second flow controller 45 includes one or more reservoirs for intermediate storage of one or more of incoming SW, RW, PW.

[0076] The supply region 44 is a portion of the drain path 41 where the dilution fluid DF is allowed to interface with the waste fluid WF, for the purpose of achieving a combined flow of WF and DF in the drain path 41 towards the drain 25. This combined flow is denoted "diluted waste fluid" and designated by WF'. As will be described below with reference to FIG. 3A, the FDA 40 is operated such that the patient is protected from harmful leakage currents irrespective of the actual degree of mixing between WF and DF in WF' along the drain path 41. The supply region 40 may be designed to achieve anything from a complete mixing of WF and DF to a complete separation of WF and DF. As used herein, "complete separation" implies that WF and DF form alternating fluid segments along the drain line from the supply region 40 to the drain 25. In some embodiments, the supply region 44 is a simple juncture between fluid lines, for example a three-way connector. In some embodiments, the supply region 44 comprises a device that causes a more or less complete mixing of WF and DF. As will be described below with reference to FIGS 4A-4B, the mixing may be a secondary effect and the device may be installed in the supply region 44 for another purpose, for example to mitigate propagation of microorganisms into the dilution line 43.

[0077] In the illustrated example, a conductivity sensor 46 is arranged in the drain path 41 downstream of the supply region 44. In other words, the conductivity sensor 46 is arranged intermediate the supply region 44 and the drain 25. The conductivity sensor 46 is configured to provide a sensor signal SI, which indicative of electrical conductivity. Thus, the conductivity sensor 46 is operable to measure a parameter indicative of the electrical conductivity of WF'. The parameter may be electrical conductivity or electrical resistance. In a variant, the parameter is a concentration of a substance that is indicative of electrical conductivity, such as sodium. Such concentration may be measured by an ion- selective electrode.

[0078] As noted above, WF' may not be a homogeneous mixture of WF and DF. In some embodiments, it may be desirable to estimate the parameter value for a homogeneous mixture even if WF' comprises a more or less inhomogeneous mixture of WF and DF. This may be achieved by averaging, by the control device 50, the sensor signal SI over a predefined time period. The predefined time period may be determined by testing or simulations to yield a measured value of the parameter that is representative of a homogeneous mixture. In some embodiments, when the flow rate of WF' is known or estimated, the predefined time period may be modified as a function of the flow rate of WF' along the drain path 41.

[0079] The control device 50 is configured to control the operation of the FDA 40. The control device 50 may or may not be part of the main control device for operating the dialysis system, including the therapy sub-system 30. Generally, the control device 50 is configured to operate on one or more input signals to generate one or more control signals for the FDA 40. As shown, the input signal(s) may include the sensor signal SI and / or an additional signal S2, which may be received for the above-mentioned main control device to indicate one or more operating parameters of the therapy sub-system 30. In the illustrated example, the control signals include a first control signal Cl for operating the first flow controller 41, and a second control signal C2 for operating the second flow controller 45. The control signals Cl, C2 may be generated in accordance with logic that is implemented by the control device 50. The predefined logic may be implemented by hardware, or a combination of hardware and software. In the example of FIG. 2, the control device 50 comprises processor circuitry 51 and computer memory 52. The processor circuitry 51 may comprise one or more processors, such as a CPU, DSP, ASIC, FPGA, etc. A control program may be stored in the memory 52 and executed by the processor circuitry 51 to perform any of the methods, procedures, or functions as described herein. The control program may be supplied to the control device 50 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.

[0080] Although not shown in FIG. 2, the control device 30 may comprise one or more I / O interfaces for input of SI, S2 and output of Cl, C2, and optionally for connection to a user interface. The term "user interface" is intended to include any and all devices that are capable of performing guided human-machine interaction comprising presentation of information and receipt of user input. The I / O interface(s) may be configured for wired or wireless data communication.

[0081] FIG. 3A is a flow chart of an example method 300 of operating the FDA 40 in FIG. 2. The method 300 comprises steps 301-304, which may be performed by the control device 50. By the method 300, the control device 50 operates the first flow controller 42 and / or the second flow controller 45 in the FDA 40 to relatively control a first fluid flow of DF and a second fluid flow of WF into the supply region 44 so that a hypothetical homogeneous mixture of DF and WF at the supply region 44 has an electrical conductivity below a first limit value. The first limit value may be set to ensure that the patient is not exposed to harmful leakage currents via the drain path 41. The method 300 thereby enables the dialysis system 10, including the therapy sub- system 30, to be configured with a floating ground of each part that comes into direct conductive contact with the patient's body. For example, the first limit value may be set so that the dialysis system can be classified as body floating or cardiac floating under IEC 60601.

[0082] The method 300 is based on the insight that a homogeneous (complete) mixing of DF and WF is a worst case in terms of the magnitude of any leakage currents in the drain path 41 between the supply region 44 and the drain 25. In practice, the total electrical resistance between the supply region 44 and the drain 25 will be the lowest for a complete mixing of DF and WF and increase with a more incomplete mixing. The highest total electrical resistance is achieved with a complete separation of DF and WF into alternating fluid segments along the drain path 41. This effect can be understood by assuming that fluid segments of varying electrical conductivity are formed along the drain path 41. The difference in conductivity between adjacent fluid segments is the largest when these fluid segments consist of DF and WF, respectively. Each fluid segment contributes to the total electrical resistance by Rs= LS / (AS■ <JS), with Lsbeing the length of the fluid segment, Asbeing the cross-sectional area of the fluid segment, and asbeing the conductivity of the fluid segment. Here, it is assumed that oDP< os< (TWP, with aDPbeing the conductivity of DF, and awpbeing the conductivity of WF. Assuming that the fluid segments are staggered along the drain path 41, with each fluid segment having the cross-sectional area of the drain path 41, the total electrical resistance is given by s=i with N being the number of fluid segments. Since Rsis inversely proportional to <JS, it is realized that the total electrical resistance will increase monotonically with decreasing difference in asbetween the fluid segments.

[0083] By the method 300, the FDA 40 is designed for the worst case, thereby protecting the patient from harmful leakage currents irrespective of the actual mixing between DF and WF in the drain path 41. The method 300 provides a simple and effective technique of limiting leakage currents while a dialysis system is operating to provide dialysis therapy. It is also realized that the technique is robust, in that it is unaffected by any change in the degree of mixing over time. It is also simple to implement the technique in existing dialysis systems. In the examples of FIGS 1A-1B, the drain line 13 may be replaced for or fitted with the FDA 40.

[0084] Turning to the example in FIG. 3 A, step 301 involves obtaining a current flow rate of waste fluid WF into the drain path 41. In some embodiments, the FDA 40 is configured to process incoming WF in real time, without any intermediate storage. This means that the current flow rate of WF is governed by the operation of the therapy subsystem 30. In other embodiments, the FDA 40 may be operable to store WF and is thereby capable of controlling the current flow rate of WF into the drain path 41. Depending on implementation, the current flow rate of WF may be known to the control device 50, measured by a flow meter (not shown) in the FDA 40, or given by a signal from the therapy sub-system 30 or its main control device (cf. S2 in FIG. 2).

[0085] In step 302, a first limit value of electrical conductivity, LV1, is obtained. The first limit value corresponds to the minimum electrical resistance in the drain path 21 between the supply region 44 and the drain 25 to achieve an adequate protection of the patient from leakage currents. The first limit value may be predefined for the FDA 40 or calculated dynamically based on characteristic data for the FDA 40. A predefined LV 1 may be retrieved from the memory 52 of the control device 50 or entered via the above- mentioned user interface.

[0086] An example of a dynamic calculation of LV 1 is represented by steps 302A-302C in FIG. 3A. In step 302A, a required electrical resistance R1 in the drain path 41 downstream of the supply region 44 is determined. The resistance R1 corresponds to the above-mentioned minimum electrical resistance and may be predefined or entered by the operator. In step 302B, size data SD for the drain path 41 downstream of the supply region 44 is obtained. If the drain path 41 is defined by tubing, SD may include a length (cf. L in FIG. 2) and an inner dimension of the tubing. The size data may be entered by the operator, for example as explicit values or as an indicator representing the tubing (model designation, serial number, or the like). In step 302C, LV1 is calculated based on R1 and SD. In the example of a cylindrical tubing, LV1 may be given by L / (R1*A), with A being the inner cross-sectional area of the tubing. If the drain path 41 has a more complex shape, more advanced calculations may be applied by step 302C, or the drain path 41 may be approximated by a cylinder with an effective diameter.

[0087] In step 303, a target flow rate or target amount of DF is determined, based on the current flow rate of WF from step 301, so that a hypothetical homogenous mixture with WF in the drain path 41 would have a conductivity below LV1. Thus, in accordance with the insight described above, step 303 is performed under the assumption of complete mixing between WF and DF in the drain path 41 downstream of the supply region 44.

[0088] A target flow rate may be determined when the supply region 44 is configured to allow incoming streams of DF and WF to be continuously combined into WF' and flow along the drain path 41 to the drain 25. A target amount may be determined when the supply region 44 is configured for intermediate storage of the incoming streams of DF and WF, so that the average flow rate rather than the momentary flow rate affects the conductivity of WF'.

[0089] For a continuous combination of DF and WF in the storage region 44, the following relation may be used for calculating the target flow rate: with QWFbeing the current flow rate of WF from step 301, QDFbeing the target flow rate of DF to be determined, and owpand oDPbeing the electrical conductivity of WF and DF, respectively.

[0090] The following relation may be used for calculating the target amount when the supply region 44 involves an intermediate storage of WF and DF : with VWFbeing a volume of WF, VDFbeing the target amount of DF to be determined. Vwpmay be given for a predefined time period, At, and may be determined by aggregation of QWPfrom step 301 over At:

[0091] The foregoing calculations involve the conductivity of WF and DF, respectively. A conductivity value of DF may be estimated in different ways. In one example, the estimated conductivity value is a predefined value, for example a worst-case value among SW, RW, PW (FIG. 2). In another example, the estimated conductivity value may be based on conductivity measurement, for example by a conductivity sensor in the FDA 40. In yet another example, the estimated conductivity may be given by an operating state of the therapy sub-system 30, which may be indicated by the signal S2 (FIG. 2). A conductivity value of WF may be estimated by analogy with these examples.

[0092] In some embodiments, step 303 involves determining the target flow rate or target amount of DF based on the sensor signal S 1 from the conductivity sensor 46 in the drain path 41, representing the conductivity of WF'. The target flow rate or target amount of DF may be determined to maintain the measured conductivity at a target conductivity, which is set in relation to LV1. In some embodiments, the target conductivity is below LV 1. The determination of step 303 may be done by a conventional feedback controller, for example a P, PI, PD or PID controller. By the sensor signal SI, the determination may be made without knowledge about the conductivity of WF and DF. The sensor signal S 1 may be used in step 303 when WF and DF are known to be reasonably well- mixed at the location of the sensor 46, for example through the provision of a tank in the supply region 44 (cf. FIGS 4A-4B).

[0093] In step 304, the FDA 40 is operated to achieve the target flow rate or target amount of DF, as determined in step 303. In the example of FIG. 2, step 304 may involve generating a control signal C2 for the second flow controller 45 to produce the target flow rate or target amount.

[0094] The skilled person understands that the control device 50 may perform steps 301- 304 at startup and then repeatedly perform steps 301, 303, 304.

[0095] The method 300 is only given as an example. In FIG. 3A, the FDA 40 is operated to adjust the flow of DF in relation to the flow of WF. In a variant, not shown, the FDA 40 is instead operated to adjust the flow of WF in relation to the flow of DF. In this variant, control device 50 may obtain a current flow rate of DF (step 301), determine a target flow rate or target amount of WF (step 303), and operate the first flow controller 42 to achieve the target flow rate or target amount of WF (step 304). In another variant, the FDA 40 is instead operated to adjust, through the first and second flow controllers 42, 45, both the flow of WF and the flow of DF so that a hypothetical homogenous mixture of WF and DF in the drain path 41 would have a conductivity below LV 1.

[0096] When fluids of different conductivity are available for use as DF, for example as shown in FIG. 2, step 304 may involve operating the second flow controller 45 to provide different combinations of the available fluids to the supply region 44 in dependence of one or more characteristics of WF. In the example of FIG. 2, the control device 50 may supply DF formed by only SW, only RW, or only PW, or as a mixture of two or more of SW, RW and PW in any suitable proportion. The characteristics of WF may include one or more of the momentary flow rate of WF, the type of WF, or the estimated conductivity of WF. In this context, "type" indicates the origin of the WF, for example if WF is STF or EF, or a mixture of STF and EF. This means that the control device 50 is operable to actively adjust the content of DF to WF to ascertain that the hypothetical mixture of DF and WF has a conductivity below LV 1. This may expand the utility of the FDA 40.

[0097] Reverting to FIG. 2, it may be noted that various components may be omitted depending on implementation. For example, the first flow controller 42 may be omitted if the FDA 40 is operated to only adjust the flow of DF via the second flow controller 45. Correspondingly, the second flow controller 45 may be omitted if the FDA 40 is operated to only adjust the flow of WF via the first flow controller 42. It is also realized that the conductivity sensor 21 is an optional component.

[0098] The sensor signal S 1 may also be used for supervision of the operation of the FDA 40. FIG. 3B illustrates two uses of the sensor signal SI as part of a method 310. The method 310 comprises a step 311 of repeatedly obtaining the sensor signal SI from the conductivity sensor 46. In step 312, which corresponds to the method 300 when operating by feedback control, the FDA 40 is operated to achieve the above-mentioned target conductivity in the signal SI. In step 313, the signal SI is evaluated in relation to a second limit value of conductivity, LV2, which may be set to indicate a risk that the patient can be exposed to harmful leakage currents via the drain path 41. LV2 may be equal to or higher than LV1. If the signal SI exceeds LV2, an alert signal is generated in step 314. The alert signal may cause the dialysis system, or part thereof, to be automatically shut down. In some embodiments, the alert signal causes the dialysis system and / or the FDA 40 to stop the flow of WF into the FDA 40. Alternatively or additionally, the alert signal may be presented to the user, for example on the user interface.

[0099] The feedback control by step 312 and the supervision by steps 313-314 may be performed in parallel by the control device 50. Alternatively, only one of the feedback control and the supervision may be implemented by the control device 50. For example, supervision may be desirable when the FDA 40 is operated based on estimated conductivity values of WF and DF (feed-forward control), to timely detect fault conditions that may pose a danger to the patient.

[0100] FIG. 4A is a section view of an example supply region 44 in an FDA 40. The supply region 44 comprises a tank 44', which is arranged to receive DF from the dilution line 43 and WF from a first drain line segment 41 A, and to output diluted waste fluid WF' on a second drain line segment 4 IB. The first and second drain line segments 41 A, 4 IB are part of the drain path 41. The first drain line segment 41 A may extend to the first flow controller 42 in FIG. 2, and the second drain line segment 4 IB may extend to the drain 25. The tank 44' defines at least one inlet 47 (one shown) for WF and at least one inlet 48 (one shown) for DF, and at least one outlet 49 (one shown) for WF'. One purpose of having the tank 44' in the drain path 41 is to prevent or mitigate propagation of microorganisms from the drain path 41 into the dilution line 43, and from there into one or more of the supply lines 33A-33C. The waste fluid WF, and in particular the spent treatment fluid STF, may contain microorganisms. If these microorganisms are allowed to spread into the dilution line 43 and ultimately enter the therapy sub-system 30, the quality of the treatment fluid may be compromised and the patient may be harmed. The tank 44' mitigates this risk by spatially separating the DF inlet(s) 48 from both the WF inlet(s) 47 and the fluid level in the tank. The fluid level in the tank 44' may be controlled by the control device 50, based on knowledge of the flow rates of DF and WF into the tank 44' and / or based on a signal from a level sensor (not shown) associated with the tank 44'. When there is no flow of DF into the tank 44', there is an air gap between the inlet 48 and the fluid in the tank 44' that prevents migration of microorganisms. In the presence of a flow of DF, migration of microorganisms is prevented by the directional flow itself. It is realized that the tank 44' also has the side effect of causing DF to mix with WF.

[0101] As an alternative to installing a tank 44' to form a barrier to migration of microorganisms, it is conceivable to operate the therapy sub-system 30 or a dedicated device to intermittently perform a cleaning operation of the fluid paths in the FDA 40. However, this will increase complexity.

[0102] FIG. 4B is a section view of another example of a supply region 44 that includes a tank 44'. The only difference from FIG. 4A is that the tank 44' comprises one or more inlets 48A for SW, one or more inlets 48B for RW, and one or more inlets 48C for PW. The inlets 48 A, 48B, 48C are connected to a respective fluid line 43 A, 43B, 43C which may extend to the flow controller 45 (FIG. 2). In a further variant, not shown, the tank 44' comprises spatially separated inlets for different types of WF, for example one inlet for STF and one inlet for EF (cf. FIG. 2).

[0103] FIG. 5 A is a side view of the drain path 41 in an FDA 40 in accordance with an embodiment. The drain path 41 includes a first drain line segment 41 A, a supply region 44, and a second drain line segment 4 IB. The supply region 44 is fluidly connected to the dilution line 43 and may or may not include a tank. The second drain line segment 4 IB comprises a terminal connector 401, which is configured for releasable engagement with a terminal connector 402 of a disposable unit 41'. The disposable unit 41' comprises a fluid line 4 IBB that extends from the terminal connector 402. When installed in the FDA 40, the disposable unit 41' is arranged to direct fluid (WF') from the supply region 44 to the drain 25. The disposable unit 41' is thus a terminal portion of the drain path 41. The installation of the disposable unit 41' provides technical advantages. One advantage is to prevent that conductive deposits on the inside of the fluid line 4 IBB form an additional conductive path for leakage currents along the drain path 41. Such conductive deposits may build up over time during operation of the dialysis system. By replacing the disposable unit 41' for a new disposable unit 41', uncontrolled accumulation of deposits is prevented. For example, the disposable unit 41' may be replaced whenever the tubing 11 in FIG. 1A or the tubing 11 A- 1 IB in FIG. IB is replaced. Another advantage is that the extent L (FIG. 2) of the drain path 41 may be changed, by switching between disposable units 41' with different lengths of the fluid line 41BB. The conductivity of the drain path 41 decreases with increasing length for a given conductivity of the fluid in the drain path 41. Thus, for a longer drain path 41, less dilution of the waste fluid is required. For example, the FDA 40 may be adapted to a specific therapy sub-system 30 by installation of a disposable unit 41' with a selected length. Further, if the feedback control (step 312 in FIG. 3B) is unable to attain the target conductivity, or if the supervision (steps 313-314 in FIG. 3B) generates the alert signal, the user may be instructed by the control device 50 to install a disposable unit 41' with a longer fluid line 4 IBB.

[0104] FIG. 5B is a side view of a variant of the disposable unit 41'. Here, connectors 61, 62 are arranged at two spaced apart locations on the fluid line 4 IBB. The respective connector 61, 62 is arranged to be in electrical contact with the fluid in the fluid line 4 IBB. When the unit 41' is installed in the FDA 40, a measurement device 60 may be connected to the connectors 61, 62. The measurement device 60 may be part of the FDA and configured to measure electrical resistance (or equivalently, conductivity). The control device 50 may be operable to cause the measurement device 60 to measure the resistance between the connectors 61, 62, for example by closing a switch 63 arranged in series with the measurement device 60. The measured resistance may be evaluated by the control device 50 to determine the degree of deposit build up in the fluid line 41BB.

[0105] FIG. 5C is a flow chart of a validation procedure 500 that may be performed by the control device 50 by use of the measurement device 60 to evaluate the effect of deposits in the drain path 41. Depending on measurement device 60, it may or may not be possible to perform the validation procedure 500 during on-going dialysis therapy, for example if the measurement device 60 is electrically isolated from Earth ground or not. In some embodiments, represented by step 501 in FIG. 5C, the validation procedure 500 is only performed when the patient is fluidly disconnected from the dialysis system. In the examples of FIGS 1A-1B, this means that the tubing 11, HA-l lB is disconnected from the patient P. In step 501, the control device may output a request for the operator to confirm if the patient is fluidly disconnected, for example via the user interface. Alternatively, the control device 50 may detect the disconnection based on status information received from the therapy sub-system 30 (cf. signal S2 in FIG. 2). In step 502, the FDA 40 is operated to fill a reference fluid into the fluid flow path between the measurement locations on the drain path 41, between the connectors 61, 62 in the example of FIG. 5B. The reference fluid may be any fluid with a known conductivity, for example any one of SW, RW, PW. In step 503, after step 502, the measurement device 60 is operated to measure the electrical resistance R, for example by closing the switch 63. In step 504, the measured resistance R is compared to a limit value, which may be predefined for the reference fluid. If R is not below the limit value, the validation procedure 500 proceeds to step 506 and is terminated. On the other hand, if R is below the limit value, the alert signal may be generated. As indicated by step 505 in FIG. 5C, the alert signal may prompt the operator to replace the disposable unit 41'. Alternatively or additionally, the alert signal may cause the dialysis system, or part thereof, to be automatically shut down.

[0106] The validation procedure 500 may also be performed when the drain path 41 does not include a disposable unit 41'. Here, the alert signal may trigger a full or partial shutdown of the dialysis system and / or trigger a cleaning procedure of the FDA 40.

[0107] In further variant, the measurement device 60 is operated to measure the resistance in the drain path 41 during on-going therapy, with WF' in the drain path 41. The control device 50 may evaluate a trend of the measured resistance to detect a need to replace the disposable unit 41' (if present) or initiate the cleaning procedure.

[0108] In some embodiments, a conductivity contribution from the deposits inside the drain path 41 may be estimated based on the measured resistance R. The conductivity contribution may be used to update LV1 (step 302). Generally, LV1 will be decreased with increasing conductivity contribution from deposits inside the drain path 41 so as to maintain a required electrical resistance in the drain path 41 downstream of the supply region 40 (cf. R1 in step 302A). Thus, in some embodiments, the control device 50 is configured to modify the relation (proportion) between the flow of WF and the flow of DF into the supply region 44 based on resistance measurements in the drain path 41, to account for buildup of conductive deposits inside the drain path 41 over time. The relation between the flows of DF and WF may be modified via at least one of the flow controllers 42, 45 (FIG. 2).

[0109] FIG. 5D is a block diagram of an example measurement device 60 that may be used to measure resistance during on-going dialysis therapy. The measurement device 60 comprises a current source 64, which is electrically connected to connection points for the connectors 61, 62. A resistor 65 is arranged in series with the current source 64 between the connection points. A voltage detector 66 is connected to measure an electrical voltage over the current source 64. The voltage detector 66 is thus connected in parallel with the current source 64. The voltage detector 66 is configured to provide an output signal indicative of electrical resistance (or equivalently, conductivity) between the connection points. The resistor 65 is provided to limit leakage currents through the measurement device 60, including the leakage current that will bypass the fluid line 41BB by entering at connector 61 and exiting at connector 62. In some embodiments, the resistor 65 has a resistance that is at least a factor of 10 larger than a minimum allowed electrical resistance between the connectors 61, 62 in the fluid line 4 IBB during the resistance measurements. For example, the minimum allowable resistance may correspond to LV1 in FIG. 3A or LV2 in FIG. 3B. For example, the resistor may have a resistance of at least 1 MQ, 5 MQ or 10 MQ. The example in FIG. 5D is configured to further reduce the risk of leakage currents passing the measurement device 60. This is achieved by connecting an isolated DC / DC converter 67 to receive the output signal from the voltage detector 66, and by connecting the voltage detector 66 to an isolated ground 69. It is understood that the isolated ground 69 only exists on the isolated measuring side of the DC / DC converter 67. Thereby, the isolated DC / DC converter 67 provides an isolated output signal for use by the control device 50. In other words, the DC / DC converter 67 isolates the measurement device 60 from other resistive paths and guarantees that only the resistance in the fluid line 4 IBB is measured.

[0110] Reverting to FIG. 2, the FDA 40 need not be fluidly connected to both the therapy device 30A and the mixing device 30B. Thus, in some embodiments, the FDA 40 receives only one of STF and EF. Likewise, in some embodiments, the FDA 40 is arranged to receive only one or two of SW, RW or PW.

[0111] Further, the therapy sub-system 30 may have reduced functionality compared to the one in FIG. 2. In a first embodiment, the therapy sub-system 30 includes only the therapy device 30A, and the FDA 40 processes WF consisting of STF. In a second embodiment, the therapy sub-system 30 includes the therapy device 30A and the mixing device 30B, but no water purification device 30C, and WF may include both STF and EF, or only STF or only EF. In the second embodiment, the mixing device 30B may receive PW from a water purification center, a container, etc. Alternatively, the mixing device 30B may be configured to generate TF by mixing two or more ready-made fluids, which may be provided to the mixing device 30B similar to the concentrate(s) Cx in FIG. 2. In the first and second embodiments, the FDA 40 may use SW as DF. If PW is made available at the point of care, for example from a water purification center, DF may include PW, optionally in combination with SW.

[0112] It should be understood that the FDA 40 need not receive and process all waste fluid produced by the therapy sub-system 30. For example, any other waste fluid than STF may be handled by a separate sub-system, for example by being stored in a container for later disposal.

[0113] FIG. 6 shows an example of a dialysis system 10 with a therapy device 30A and a mixing device 30B. The dialysis system 10 is connected to a source (not shown) of product water PW on a transfer line 3 ID. Like in FIG. 2, the mixing device 30B receives PW and generates TF, and the therapy device 30A supplies TF to the patient (not shown) on supply line 31 A. The dialysis system 10 receives STF on return line 3 IB and outputs WF on the drain path 41. In this example, WF includes STF. Depending on implementation, WF may also include EF from the mixing system 30B. A supply line 33A is connected to the transfer line 3 ID to supply PW as DF to the FDA 40. The FDA 40 includes a flow regulator, which implements the second flow controller 45 and is connected to receive PW from the supply line 33A. A drain line 43 extends between the flow regulator 45 and the supply region 44 in the drain path 41. The FDA 40 in FIG. 6 may be operated, via the control signal Cl and in accordance with the methods described herein, to provide a flow of WF' downstream of the supply region 44 on the drain path 41 to the drain 25, so as to protect the patient from harmful leakage currents.

[0114] 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.

[0115] 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 parti- cular order shown or in sequential order, or that all illustrated operations be performed, to achieve desirable results.

Claims

CLAIMS1. An apparatus for handling waste fluid generated in connection with dialysis therapy, said apparatus comprising: a fluid disposal arrangement (40), which is configured to receive the waste fluid and define a fluid flow path (41) for directing the waste fluid to a drain (25), said fluid disposal arrangement (40) being operable to combine the waste fluid with a dilution fluid at a supply region (44) in the fluid flow path (41), and a control device (50), which is configured to operate one or more flow controllers (42, 45) in the fluid disposal arrangement (40) to relatively control a first fluid flow of the waste fluid and a second fluid flow of the dilution fluid into the supply region (44) so that a hypothetical homogeneous mixture of the dilution fluid and the waste fluid at the supply region (44) has an electrical conductivity below a first limit value.

2. The apparatus of claim 1, wherein the control device (50) is configured to operate said one or more flow controllers (42, 45) based on estimated values of the electrical conductivity of the dilution fluid and the waste fluid.

3. The apparatus of claim 1 or 2, wherein the fluid disposal arrangement (40) comprises a conductivity sensor (46) in the fluid flow path (41) downstream of the supply region (44), and wherein the control device (50) is configured to operate the fluid disposal arrangement (40) based on a sensor signal (SI) from the conductivity sensor (46).

4. The apparatus of claim 3, wherein the control device (50) is configured to monitor the sensor signal (SI) and generate an alert signal when the sensor signal (SI) exceeds a second limit value.

5. The apparatus of claim 3 or 4, wherein the control device (50) is configured to operate said one or more flow controllers (42, 45) to adjust at least one of the first fluid flow or the second fluid flow to attain a target conductivity value in the sensor signal (SI).

6. The apparatus of any preceding claim, wherein the supply region (44) comprises a tank (44'), which is configured to receive the first fluid flow and the second fluid flow and form a mixture of the waste fluid and the dilution fluid.

7. The apparatus of claim 6, wherein the tank (44') is arranged to receive the first flow of the waste fluid through at least one first inlet (47) of the tank (44'), to receive the second flow of dilution fluid through at least one second inlet (48; 48 A, 48B, 48C) in a top portion of the tank (44'), and to provide the mixture of the waste fluid and the dilution fluid through at least one outlet (49) at a bottom portion of the tank (44').

8. The apparatus of claim 7, wherein the tank (44') is configured to, at least by a spatial separation of the at least one second inlet (48; 48 A, 48B, 48C) from the at least one first inlet (47), and by a spatial separation of the at least one second inlet (48; 48 A, 48B, 48C) from a fluid level of the mixture in the tank (44'), mitigate propagation of microorganisms from the fluid flow path (41) into at least one supply line (43; 43 A, 43B, 43C) for the dilution fluid, said at least one supply line (43; 43 A, 43B, 43C) being connected to the at least one second inlet (48; 48 A, 48B, 48C).

9. The apparatus of any preceding claim, wherein the supply region (44) is in fluid communication with an outlet connector (402) for releasable connection to an inlet connector (403) on a fluid line (41BB) for directing the mixture of waste fluid and the dilution fluid to the drain (25).

10. The apparatus of any preceding claim, wherein the fluid disposal arrangement (40) is configured to receive at least two types of dilution fluids, which differ at least by their electrical conductivity, and wherein the control device (50) is configured to operate a flow controller (45) among the one or more flow controllers (42, 45) to provide different combinations of the at least two types of dilution fluids to the supply region (44) in dependence of at least one of a flow rate, a type or an electrical conductivity of the waste fluid.

11. The apparatus of any preceding claim, wherein the control device (50) is configured to operate the fluid disposal arrangement (40) to direct at least one of source water, purified water, or reject water, to the supply region (44) for use as the dilution fluid, wherein the purified water is generated from the source water by a water purification device (30C), and wherein the reject water is generated by a reverse osmosis unit (34) in the water purification device (30C) when processing the source water into the purified water for use in connection with the dialysis therapy.

12. The apparatus of claim 11, wherein the waste fluid comprises one or more of a spent treatment fluid generated by the dialysis therapy, or a discarded fluid from amixing device (30B) configured to produce a treatment fluid for use in the dialysis therapy.

13. The apparatus of any preceding claim, wherein the control device (50) is configured to set the first limit value based on size data for the fluid flow path (41) downstream of the supply region (44).

14. The apparatus of any preceding claim, wherein the control device (50) is configured to set the first limit value to achieve a required electrical resistance in the fluid flow path (41) downstream of the supply region (44).

15. The apparatus of any preceding claim, wherein the fluid disposal arrangement (40) comprises a measurement device (60) for measuring an electrical resistance between two separated locations (61, 62) along the fluid flow path (41) downstream of the supply region (44), and wherein the control device (50) is configured to evaluate the electrical resistance between the two separated locations (61, 62) in relation to a resistance limit.

16. The apparatus of claim 15, wherein the control device (50) is further configured to modify, based on the electrical resistance between the two separated locations (61, 62), a relation between the first and second fluid flows into the supply region (44) to account for buildup of conductive deposits inside the fluid flow path (41) over time.

17. The apparatus of claim 15 or 16, wherein the measurement device (60) comprises a current source (64), a resistor (65), which is connected in series with the current source (64) between the two separate locations (61, 62), and a voltage detector (68), which is connected to measure an electrical voltage over the current source (64) and generate an output signal indicative of said electrical resistance between the two separated locations (61, 62), wherein the resistor (65) has an electrical resistance that is at least a factor of 10 larger than a limit electrical resistance, and wherein the limit electrical resistance is a minimum allowed electrical resistance between the two separated locations (61, 62).

18. The apparatus of claim 17, wherein the measurement device (60) further comprises an isolated DC / DC converter (67), which is connected to receive the outputsignal from the voltage detector (66) and provide an isolated output signal, and wherein the voltage detector (66) is connected to an isolated ground (69).

19. The apparatus of any one of claims 15-18, wherein the control device (50) is configured to perform a validation process (500) comprising: operating the fluid disposal arrangement (40) to fill the fluid flow path (41) between the two separated locations with a reference fluid; establish, when the fluid flow path (41) between the two separated locations is filled with the reference fluid, an electrical connection of the measurement device (60) to the two separated locations (61, 62); and operate the measurement device (60) to measure the electrical resistance between the two separated locations (61, 62).

20. The apparatus of any one of claims 15-19, wherein the control device (50) is configured to, if the electrical resistance between the two separated locations (61, 62) is below the resistance limit, instruct a user to replace at least part of the fluid flow path (41).

21. A system for performing dialysis therapy, said system comprising: a therapy sub-system (30) configured to supply treatment fluid to a patient (P) as part of the dialysis therapy, said therapy sub-system (30) being further configured to produce waste fluid before, during or after the dialysis therapy, and an apparatus for handling the waste fluid according to any one of claims 1-20.

22. The system of claim 21, wherein the therapy sub-system (30) comprises a mixing device (30B), which is configured to generate the treatment fluid by mixing purified water with one or more concentrates.

23. The system of claim 22, wherein the therapy sub-system (30) further comprises a water purification device (30C), which is configured to generate the purified water from source water.

24. The system of any one of claims 21-23, wherein the apparatus for handling the waste fluid is configured according to claim 19, and wherein the control device (50) is configured to perform the validation process (500) when the therapy sub-system (30) is fluidly disconnected from the patient (P).

25. The system of any one of claims 21-24, which is configured with a floating ground of each part that comes into direct conductive contact with the patient's body.

26. The system of any one of claims 21-25, which is classified as body floating or cardiac floating under IEC 60601.

27. A method of handling waste fluid generated in connection with dialysis therapy, said method comprising: receiving and directing the waste fluid on a fluid flow path (41) to a drain (25) by a fluid disposal arrangement (40), which is operable to combine the waste fluid with a dilution fluid at a supply region (44) in the fluid flow path (41), and operating one or more flow controllers (42, 45) in the fluid disposal arrangement (40) to relatively control a first fluid flow of the waste fluid and a second fluid flow of the dilution fluid into the supply region (44) so that a hypothetical homogeneous mixture of the dilution fluid and the waste fluid at the supply region (44) has an electrical conductivity below a first limit value.

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