Patent Publication Number: US-2022211928-A1

Title: Emptying a blood circuit after extracorporeal blood treatment

Description:
TECHNICAL FIELD 
     The present invention relates to operating an extracorporeal blood treatment apparatus, e.g. a dialysis machine, and in particular to a technique of emptying a blood circuit subsequent to blood treatment. 
     BACKGROUND ART 
     Extracorporeal blood treatment, such as hemodialysis, is performed by an apparatus that is configured to supply one or more fluids for use in the treatment. Equipment that is exposed to blood during treatment is typically replaced after each treatment. Such disposable equipment may include a dialyzer and a line set with tubing for defining an extracorporeal blood circuit for conducting blood from a patient, through the dialyzer and back to the patient. During a treatment session, the extracorporeal circuit is connected to the patient at a withdrawal end and a return end, respectively, and a blood pump of the apparatus is operated to pump the patient&#39;s blood through the blood circuit while one or more pressure sensors of the apparatus are connected in fluid communication with the line set to monitor the pressure in the blood circuit. 
     Conventionally, at the end of a blood treatment session, the blood pump is stopped and a so-called rinseback procedure is initiated. Attending staff disconnects the withdrawal end from the patient and connects it to a bag containing a physiological saline solution, whereupon the blood pump is operated so that the saline solution pushes most of the blood present in the blood circuit back into the patient. Then, when the blood pump is stopped, attending staff may disconnect the return end from the patient and place the disposable equipment in a special container for contaminated waste. To reduce weight, the staff may first carry the dialyzer, the line set and the bag to a nearby sink or container for draining of remaining fluid. Alternatively, the attending staff may start a draining procedure on the apparatus, whereby the apparatus operates the blood pump to pump remaining fluid through the return connector into the nearby sink or container. 
     This conventional procedure involves a considerable risk of blood and blood-containing saline solution being spilled on the apparatus and its surroundings. 
     The prior art comprises US2003/0100857 which proposes to procedure for draining the blood circuit via the dialyzer by use of a specialized line set. In contrast to conventional line sets, the specialized line set includes a dedicated branch tube which is terminated by a connector that is specifically configured for interconnection with a connector on the return end of the line set. After rinseback and while the withdrawal end is connected to a flexible bag of saline solution, the caretaker connects the connector on the branch tube to the connector on the return end so as to form a closed loop. The apparatus then operates the blood pump to circulate the remaining fluid in the closed loop and controls one or more of its dialysis fluid pumps to create a pressure gradient over the membrane of the dialyzer, so as to drive the remaining liquid through the membrane into the apparatus for safe disposal. To benefit from the technique proposed in US2003/0100857, dialysis clinics are required to acquire and keep in stock the specialized line set. This is undesirable from a logistic point of view and increases operating cost and internal handling and storage at the dialysis clinics. Further, it is currently believed that it may be difficult to ensure a sufficient drainage of the blood circuit by use of the proposed line set and the associated draining procedure. 
     SUMMARY 
     It is an objective of the invention to at least partly overcome one or more limitations of the prior art. 
     A further objective is to provide a technique that enables draining of the blood circuit after completed blood treatment by use of a conventional line set. 
     Another objective is to facilitate or improve automated draining of the blood circuit. 
     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 control system, a blood treatment apparatus, a method and a computer readable medium in accordance with first and second inventive concepts as defined by the independent claims, embodiments thereof being defined by dependent claims. 
     A first aspect is a control system for a blood treatment apparatus. The blood treatment apparatus comprises a fluid supply unit and is configured for installation of a dialyzer and a line set to define a first flow circuit for conducting a fluid provided by the fluid supply unit through the dialyzer and back to the fluid supply unit, and to define a second flow circuit which is separated from the first flow circuit by a semi-permeable membrane of the dialyzer and comprises return and withdrawal lines for connection to a vascular system of a subject during a blood treatment session. The control system is configured to, subsequent to a termination of the blood treatment session: instruct an operator to connect the second flow circuit to a first port of a container that holds a human-compatible fluid; operate the blood treatment apparatus to push remaining blood in the second flow circuit into the vascular system of the subject through the return line while admitting the human-compatible fluid from the container into the second flow circuit; instruct the operator to disconnect the return line from the vascular system of the subject and re-arrange the second flow circuit to define a closed loop; and operate, in a draining phase, the blood treatment apparatus to draw residual liquid from the closed loop into the first flow circuit through the semi-permeable membrane of the dialyzer. 
     In accordance with the first inventive concept, the control system is further configured to instruct the operator to re-arrange the second flow circuit by connecting the second flow circuit to a second port of the container so that the container is included in the closed loop. 
     Generally, the first inventive concept enables the second flow circuit and the container to be substantially drained of residual fluid in the draining phase by a combination of automated control and operator instructions. According to the first inventive concept, the second flow circuit is connected in fluid communication with two separate ports of the container in the draining phase. Such use of a container that has more than one port enables the closed loop to be formed by a simple and conventional line set. For example, the ports on the container may be configured for connection, directly or indirectly, to any two suitable existing connectors of such a conventional line set, e.g. terminal connectors on the ends of the withdrawal and return lines. Further, by arranging the container within the closed loop, the residual fluid is circulated through the container in the draining phase, which serves to counteract the formation of obstructions to the flow within the container or at the ports. Thereby, the first inventive concept also improves the ability of the blood treatment apparatus to perform an automated draining of the second flow circuit. 
     In some embodiments of the control system of the first inventive concept, in the closed loop, the withdrawal line is connected in fluid communication with the first port of the container and the return line is connected in fluid communication with the second port of the container. 
     In some embodiments of the control system of the first inventive concept, in the closed loop, terminating connectors on the withdrawal and return lines are connected, directly or indirectly, to the first and second ports, respectively, of the container. 
     In some embodiments of the control system of the first inventive concept, the control system is further configured to, in the draining phase, operate the blood treatment apparatus to circulate the residual liquid in the closed loop, and thus through the container. 
     In accordance with the second inventive concept, the control system further is configured to instruct the operator to re-arrange the second flow circuit by connecting the return and withdrawal lines in fluid communication with the first port of the container through a three-way manifold coupling unit. 
     Generally, the second inventive concept enables the closed loop to be formed by a simple and conventional line set since the three-way manifold coupling unit, when connected to the first port of the container, provides two ports for connection, directly or indirectly, to any two existing connectors of a conventional line set, e.g. terminal connectors on the ends of the withdrawal and return lines. 
     In some embodiments of the control system of the second inventive concept, in the closed loop, a first port of the three-way manifold coupling unit is connected in fluid communication with the first port of the container, a second port of the three-way manifold coupling unit is connected in fluid communication with the withdrawal line, and a third port of the three-way manifold coupling unit is connected in fluid communication with the return line. 
     In some embodiments of the control system of the second inventive concept, the control system is further configured to, in the draining phase, operate the blood treatment apparatus to circulate the residual liquid in the closed loop. 
     In the following, further embodiments of the control system are defined and are applicable to both of the first and second inventive concepts. 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 in view of the following detailed description. 
     In some embodiments, the control system is further configured to, in the draining phase, operate a clamp of the blood treatment apparatus to selectively open a branch line, which is included in the line set and is arranged in fluid communication with the second flow circuit, so as to ventilate the closed loop. 
     In some embodiments, the control system is configured to, during the draining phase, operate the clamp to keep the branch line open and only intermittently close the branch line. 
     In some embodiments, the control system is configured to, in the draining phase, operate the clamp to repeatedly close the branch line, e.g. for 0.1-10 seconds, and preferably for 0.4-5 seconds. 
     In some embodiments, the control system is configured to, when terminating the draining phase, operate the clamp to close the branch line, operate the blood treatment apparatus to generate a sub-atmospheric pressure in the thus-closed branch line, and operate the clamp to open the branch line to release the sub-atmospheric pressure. 
     In some embodiments, one of the return and withdrawal lines is arranged in the clamp during the blood treatment session, and the control system is further configured to, before the draining phase, instruct the operator to remove said one of the return and withdrawal lines from the clamp and install the branch line in the clamp. 
     In some embodiments, the branch line is branched from the withdrawal line. 
     In some embodiments, the control system is further configured to, before the draining phase, instruct the operator to disconnect the branch line from a sensor port of the blood treatment apparatus. 
     In some embodiment, the return line is arranged in the clamp and the withdrawal line is arranged in a further clamp of the blood treatment apparatus during the blood treatment session, the branch line is branched from the withdrawal line downstream of the further clamp, and the control system is further configured to, before the draining phase, instruct the operator to remove the return line from the clamp, install the branch line in the clamp, and instruct the operator to disconnect the branch line from a sensor port of the blood treatment apparatus, wherein the control system is further configured to, before instructing the operator to disconnect the branch line, close the further clamp and operate the blood treatment apparatus to generate a sub-atmospheric pressure in the withdrawal line downstream of the further clamp and in the branch line. 
     In some embodiments, the fluid supply unit defines a drain flow path which extends from an inlet port for connection to the first flow circuit to a drain pump, wherein the drain flow path comprises a set of sensors and an inlet valve intermediate the inlet port and the set of sensors, wherein the fluid supply unit further defines a supply flow path, which comprises an outlet valve and extends from a supply pump to an outlet port for connection to the first flow circuit, and wherein the control system is further configured to, in the draining phase: close the outlet and inlet valves; open a valve located in a connecting line, which extends between a first location in the drain flow path intermediate the inlet port and the inlet valve and a second location in the drain flow path intermediate the drain pump and the set of sensors; and operate the drain pump to draw the residual liquid from the closed loop into the first flow circuit through the semi-permeable membrane of the dialyzer and from the first flow circuit into the drain flow path via the inlet port. 
     In some embodiments, the connecting line extends from a degassing device in the drain flow path, and wherein the control system is further configured to, during the blood treatment session, open the valve in the connecting line to expel gases from the degassing device through the connecting line. 
     In some embodiments, the control system is further configured to, in the draining phase: open a bypass valve in a bypass line, which extends between a third location in the drain flow path intermediate the inlet valve and the second location, and a fourth location in the supply flow path intermediate the supply pump and the outlet valve, so as to establish fluid communication between the inlet port and a pressure sensor in the supply flow path; and control the drain pump based on a pressure signal from the pressure sensor. 
     A second aspect is a blood treatment machine comprising a fluid supply unit configured to supply a fluid to a first flow circuit, a pump operable to engage with a second flow circuit, and the control system in accordance with the first or second inventive concept or any embodiment thereof. 
     A third aspect is a method of operating a blood treatment apparatus that comprises a fluid supply unit and is configured for installation of a dialyzer and a line set to define a first flow circuit for conducting a fluid provided by the fluid supply unit through the dialyzer and back to the fluid supply unit, and to define a second flow circuit which is separated from the first flow circuit by a semi-permeable membrane of the dialyzer and comprises return and withdrawal lines for connection to a vascular system of a subject during a blood treatment session. The method comprises, subsequent to a rinseback procedure and while the withdrawal line is connected to a first port of a container and when the return line has been disconnected from the vascular system of the subject: causing a re-arrangement of the second flow circuit to define a closed loop; and operating, in a draining phase, the blood treatment apparatus to draw residual liquid from the closed loop into the first flow circuit through the semi-permeable membrane of the dialyzer. 
     In the method of the first inventive concept, the re-arrangement comprises connecting the second flow circuit to a second port of the container so that the container is included in the closed loop. 
     In some embodiments of the method of the first inventive concept, the re-arrangement comprises connecting the withdrawal line in fluid communication with the first port of the container and connecting the return line in fluid communication with the second port of the container. 
     In some embodiments of the method of the first inventive concept, the re-arrangement comprises connecting terminating connectors on the withdrawal and return lines, directly or indirectly, to the first and second ports, respectively, of the container. 
     In some embodiments, the method of the first inventive concept further comprises: operating, in the draining phase, the blood treatment apparatus to circulate the residual liquid in the closed loop, and thus through the container. 
     In the method of the second inventive concept, the re-arrangement comprises connecting the return and withdrawal lines in fluid communication with the first port of the container through a three-way manifold coupling unit. 
     In some embodiments of the method of the second inventive concept, the re-arrangement results in a first port of the three-way manifold coupling unit being connected in fluid communication with the first port of the container, a second port of the three-way manifold coupling unit being connected in fluid communication with the withdrawal line, and a third port of the three-way manifold coupling unit being connected in fluid communication with the return line. 
     In some embodiments, the method of the second inventive concept further comprises, in the draining phase, operating the blood treatment apparatus to circulate the residual liquid in the closed loop. 
     In the following, further embodiments of the method are defined and are applicable to both of the first and second inventive concepts. 
     In some embodiments, the method further comprises, in the draining phase, operating a clamp to selectively open a branch line, which is included in the line set and is arranged in fluid communication with the second flow circuit, so as to ventilate the closed loop. 
     In some embodiments, the method comprises, during the draining phase, operating the clamp to keep the branch line open and only intermittently closing the branch line. 
     In some embodiments, the method further comprises, in the draining phase, operating the clamp to repeatedly close the branch line, e.g. for 0.1-10 seconds, and preferably for 0.4-5 seconds. 
     In some embodiments, the method further comprises, when terminating the draining phase: operating the clamp to close the branch line; operating the blood treatment apparatus to generate a sub-atmospheric pressure in the thus-closed branch line; operating the clamp to open the branch line to release the sub-atmospheric pressure. 
     In some embodiments of the method, one of the return and withdrawal lines is arranged in the clamp during the blood treatment session, and the method further comprises, before the draining phase, removing said one of the return and withdrawal lines from the clamp and installing the branch line in the clamp. 
     In some embodiment of the method, the branch line is branched from the withdrawal line. 
     In some embodiments, the method further comprises, before the draining phase, disconnecting the branch line from a sensor port of the blood treatment apparatus. 
     In some embodiments, the return line is arranged in the clamp and the withdrawal line is arranged in a further clamp of the blood treatment apparatus during the blood treatment session, and the branch line is branched from the withdrawal line downstream of the further clamp, wherein the method further comprises, before the draining phase, removing the return line from the clamp, installing the branch line in the clamp, and disconnecting the branch line from a sensor port of the blood treatment apparatus, and wherein the method further comprises, before said disconnecting the branch line, closing the further clamp and operating the blood treatment apparatus to generate a sub-atmospheric pressure in the withdrawal line downstream of the further clamp and in the branch line. 
     In some embodiments of the method, the fluid supply unit is configured to define a drain flow path, which extends from an inlet port for connection to the first flow circuit to a drain pump and which comprises a set of sensors and an inlet valve intermediate the inlet port and the set of sensors, and a supply flow path, which comprises an outlet valve and extends from a supply pump to an outlet port for connection to the first flow circuit, and the method further comprises, in the draining phase: closing the outlet and inlet valves; opening a valve located in a connecting line, which extends between a first location in the drain flow path intermediate the inlet port and inlet valve and a second location in the drain flow path intermediate the drain pump and the set of sensors; and operating the drain pump to draw the residual liquid from the closed loop into the first flow circuit through the semi-permeable membrane of the dialyzer and from the first flow circuit into the drain flow path via the inlet port. 
     In some embodiments of the method, the connecting line extends from a degassing device in the drain flow path, and the method further comprises, during the blood treatment session, opening the valve in the connecting line to expel gases from the degassing device through the connecting line. 
     In some embodiments, the method further comprises, in the draining phase: opening a bypass valve in a bypass line, which extends between a third location in the drain flow path intermediate the inlet valve and the second location and a fourth location in the supply flow path intermediate the supply pump and the outlet valve, so as to establish fluid communication between the inlet port and a pressure sensor in the supply flow path; and controlling the drain pump based on a pressure signal from the pressure sensor. 
     A fourth aspect is a computer-readable medium comprising computer instructions which, when executed by a processor, cause the processor to perform the method in accordance with the first or second inventive concept or any embodiment thereof. 
     Still other objectives, features, embodiments, aspects and advantages of the present invention may appear from the following detailed description, from the attached claims as well as from the drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments of the invention will now be described in more detail with reference to the accompanying drawings. 
         FIG. 1  is a schematic front view of a dialysis machine. 
         FIG. 2  is a schematic diagram of a dialysis machine connected and operated for blood treatment. 
         FIGS. 3A-3B  are flow charts of methods of operating a dialysis machine in accordance with a first and a second inventive concept, respectively. 
         FIGS. 4A-4B  are schematic diagrams of a dialysis machine connected and operated in accordance with the first inventive concept. 
         FIG. 5  is a flow chart of a method of operating a dialysis machine in accordance with the first or second inventive concepts. 
         FIGS. 6A-6C  are schematic diagrams of a dialysis machine connected and operated in accordance with the first inventive concept. 
         FIG. 7  is a schematic diagram of a dialysis machine connected and operated in accordance with the second inventive concept. 
         FIG. 8  is a flow chart of a method of operating a fluid supply unit of a dialysis machine in accordance with an embodiment. 
         FIGS. 9A-9B  are schematic diagrams of a fluid supply unit operated in accordance with  FIG. 8 . 
     
    
    
     DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS 
     Embodiments of the present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which some, but not all, embodiments of the invention are shown. Indeed, the invention 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. 
     Also, it will be understood that, where possible, any of the advantages, features, functions, devices, and/or operational aspects of any of the embodiments of the present invention described and/or contemplated herein may be included in any of the other embodiments of the present invention 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 of the invention. 
     In the following, embodiments of the invention will be exemplified with reference to an apparatus configured for treatment of renal failure, denoted “dialysis machine” below. 
       FIG. 1  shows an example of such a dialysis machine  1 , which is operable to perform a dialysis treatment when combined with a set of disposable products or “disposables” to be described below with reference to  FIG. 2 . The dialysis machine  1  in  FIG. 1  is also known as “monitor” and defines a machine chassis that exposes holders for mounting the disposable(s) in operative engagement with components such as connectors, pumps, sensors, clamps, etc. The disposables are exposed to circulating blood and are typically for single-use, i.e. they are discarded after each treatment session. 
     In the illustrated example, a control system or controller  2  in the machine  1  is configured to synchronize and control the operation of the components of the machine  1 , e.g. by electric control signals. The operation of the control system  2  may be at least partly controlled by software instructions that are supplied on a computer-readable medium for execution by a processor  2 A in conjunction with a memory  2 B in the control system  2 . A display unit  3  is operable to provide information and instructions for an operator, such as a nurse, a physician or a patient. The machine  1  may also enable the operator to enter data into the machine, e.g. via mechanical buttons (not shown) or virtual buttons on a touch panel, e.g. in the display unit  3 . A fluid supply unit  4  is configured to supply one or more suitable fluids during operation of the machine  1 . Such fluids may include one of more of a treatment fluid (dialysis fluid) for use during blood treatment, a disinfectant for use in disinfection of the machine between treatments, a saline solution, and purified water. The fluids may be supplied from replaceable containers attached to the machine  1  or may be generated on demand by the machine  1  or another apparatus in fluid communication with the machine  1 . In the illustrated example, the machine comprises machine ports  5 ,  6 ,  5 ′,  6 ′ in fluid connection to the supply unit  4 . The machine ports  5 ,  6  are input and output ports, respectively, for a human-compatible fluid such as a treatment fluid, saline solution or water, whereas the machine ports  5 ′,  6 ′ are input and output ports, respectively, for a disinfectant. The machine  1  further comprises a holder  7  for a dialyzer ( 20  in  FIG. 2 ), a machine-controlled peristaltic pump (“blood pump”)  8  for engagement with a withdrawal line ( 24 ″ in  FIG. 2 ), and a holder  9  for a drip chamber ( 25  in  FIG. 2 ), and two machine-controlled clamps  10 ,  11 . Further, a holder  12  is provided for a container ( 30  in  FIGS. 4A-4B ). The machine  1  also comprises sensor ports  13 ,  14  in fluid communication with pressure sensors (not shown) within the machine  1 . The skilled person realizes that the machine  1  may comprise further components that are not shown in  FIG. 1A , e.g. a blood detector, an injection system for anticoagulant, etc. 
       FIG. 2  illustrates a dialysis machine  1 , e.g. as shown in  FIG. 1 , which is connected to a set of disposables and operated for hemodialysis treatment of a subject S, in this example a human patient. The set of disposables includes a dialyzer  20 , which is a blood filtration unit configured for fluid connection to a line set (below) and for fluid connection to the machine ports  5 ,  6 . A semi-permeable membrane  21  (“dialyzer membrane”) is arranged inside the housing of the dialyzer  20  to separate a first chamber (“dialysis fluid side compartment”)  22  from a second chamber (“blood side compartment”)  23 . The first and second chambers  22 ,  23  are configured to be perfused by blood and dialysis fluid, respectively, during blood treatment. The set of disposables further includes fluid-conducting devices in the form of first and second line arrangements  24 A,  24 B, which are collectively known as a “line set” in the art. The first line arrangement  24 A comprises a drip chamber  25  and flexible tubing that defines a flow path extending from a first end with a dialyzer connector to a second end having a terminal connector  26 . In the following, the tubing  24 ′ that extends to the terminal connector  26  is denoted “return line”. The second line arrangement  24 B comprises flexible tubing that defines a flow path from a first end with a terminal connector  27  to a second end with a dialyzer connector. In the following, the tubing  24 ″ that extends to the terminal connector  27  is denoted “withdrawal line”. The line arrangements  24 A,  24 B and the dialyzer  20  may be provided as separate components that are interconnected before use, or they may be delivered as a preassembled unit. Although not shown in  FIG. 2 , each of the line arrangements  24 A,  24 B may include further components, such as one or more manual clamps, one or more branch lines for dedicated use such as connection to a pressure sensor (cf. sensor ports  13 ,  14  in  FIG. 1 ), infusion of anticoagulant, replacement fluid, etc. 
     As understood from  FIG. 2 , the disposables have been mounted to the machine  1  by attaching the dialyzer  20  to holder  7  ( FIG. 1 ) and the drip chamber  25  to holder  9  ( FIG. 1 ), by arranging the withdrawal line  24 ″ for engagement with pump  8  and clamp  11  (“withdrawal clamp”), and by arranging the return line  24 ′ for engagement with clamp  10  (“return clamp”). The set of disposables is connected for fluid communication with the dialysis machine  1  so as to define a first flow circuit Cl (“dialysis fluid circuit”) for dialysis fluid supplied by the dialysis machine  1  and a second flow circuit C 2  (“extracorporeal blood circuit”) which is connected to the vascular system of the subject S. Specifically, the dialyzer  20  is connected by a supply line  20 ′ and a drain line  20 ″ to establish fluid communication between the first chamber  22  and the ports  5 ,  6 , thereby forming the first flow circuit C 1 . Further, the dialyzer  20  is connected for establishing fluid communication between the second chamber  23  and the line arrangements  24 A,  24 B, thereby forming the second flow circuit C 2 . During blood treatment, the terminal connectors  26 ,  27  are connected to a blood vessel access of the subject S. As is well-known in the art, the blood vessel access (also known as “vascular access”) may be a fistula, graft or catheter, and the terminal connectors  26 ,  27  may be connected to the blood vessel access by any conventional device, including needles or catheters. 
       FIG. 2  also illustrates fluid lines  16 ,  17  that extend inside the machine  1  from the fluid supply unit  4  ( FIG. 1 ) to the ports  5 ,  6 , via machine-operated outlet and inlet valves  18 ,  19  for selectively opening and closing the ports  5 ,  6 . In the following, filled and non-filled valve symbols indicate that a valve is open and closed, respectively. 
     In  FIG. 2 , the machine  1  is operated by the control system  2  ( FIG. 1 ) to open the valves  18 ,  19  and establish a flow of dialysis fluid through the first chamber  22  of the dialyzer  20 , as indicated by arrows. The machine  1  is also operated by the control system  2  to open clamps  10 ,  11  and run pump  8  so that blood is drawn from the vascular system of the subject S along line arrangement  24 B, pushed through the second chamber  23  of the dialyzer  20  and back to the vascular subject S along line arrangement  24 A, as indicated by arrows, while the blood is being subjected to dialysis treatment in the dialyzer  20 . Dialysis treatment as such is well-known to the person skilled in the art and will not be described in detail herein. 
     When dialysis treatment is completed, it is common practice to return all or most of the blood remaining in the second flow circuit C 2  to the vascular system of the subject S. This process is known as “rinseback” or “reinfusion” and involves pushing at least a portion of the remaining blood into the subject S while introducing a rinseback fluid into the second flow circuit C 2 . After rinseback, the second flow circuit C 2  contains a residual fluid in the form of a mixture of rinseback fluid and blood. Embodiments of the invention aim at facilitating disposal of the residual fluid. 
     In the following, an embodiment of a first inventive concept will be described with reference to the flow chart in  FIG. 3A  in combination with system diagrams in  FIGS. 4A-4B , which illustrate a dialysis machine  1  when arranged and operated for rinseback and drainage of residual fluid, respectively. The flow chart in  FIG. 3A  represents a post-treatment procedure  300  that includes rinseback, a draining phase and removal of disposables. Each of the steps  301 - 305  of the method  300  may be controlled by the control system  2  of the dialysis machine  1 . To the extent that a step involves a manual operation, the control system  2  may generate and present corresponding instructions for the operator, e.g. on the display  3 , and may also require the operator to confirm when the manual operation has been completed, e.g. by pressing or touching a button on the machine  1 . However, it also conceivable that one or more of the steps are independently performed by the operator based on written instructions, e.g. from an operations manual or work guide, without involvement of the control system  2 . 
     The procedure  300  is initiated after termination of the dialysis treatment in  FIG. 2 . The dialysis treatment may be terminated by the machine  1  stopping the blood pump  8 , closing the clamps  10 ,  11 , and closing the valves  18 ,  19 . In a rinseback step  301 , the operator connects a container  30 , which contains a human-compatible fluid (“rinseback fluid”), to the second flow circuit C 2  and the machine  1  is operated to perform the above-mentioned rinseback. The rinseback fluid may be any fluid, which by its composition is compatible with the human body if administered to its circulatory system in relevant amounts, including but not limited to a saline solution, a treatment fluid, and water. 
     As shown in  FIG. 4A , the rinseback fluid is held within an internal space  31  of the container  30 , which comprises an outlet port  32  and an inlet port  33  in fluid communication with the internal space  31 . The container  30  may be made of rigid or flexible material, preferably a transparent or translucent material that allows for ocular inspection of the contents in the container  30 . In the illustrated example, the container  30  further defines a suspension hole  36 . 
     In the example of  FIG. 4A , step  301  involves instructing the operator to disconnect the terminal connector  27  from the vascular access of the subject S and connect the terminal connector  27  to the outlet port  32  of the container  30 . The dialysis machine  1  then opens clamps  10 ,  11  and operates pump  8  to push the remaining in the second flow circuit C 2  into the subject S while drawing rinseback fluid from the container  30  into the withdrawal line  24 ″, as indicated by arrows in  FIG. 4A , until all or a majority of the remaining blood in the second flow circuit C 2  has been returned to the subject S. The machine  1  then stops pump  8  and closes clamps  10 ,  11 . The rinseback may be terminated manually by the operator or automatically by the machine  1  based on input from a dedicated sensor (not shown). 
     In a re-arrangement step  302 , which is performed after termination of the rinseback step  301 , the operator is instructed to re-arrange the second flow circuit C 2  to form a closed loop that includes the container  30 . In the example of  FIG. 4B , the closed loop is formed by connecting the terminal connector  26  on the return line  24 ′ to the inlet port  33  of the container  30 . 
     After step  302 , the machine  1  enters a draining phase that includes a circulation step  303  and a filtration step  304 . 
     In the circulation step  303 , the machine  1  is operated to open clamps  10 ,  11  and start pump  8  to circulate the residual fluid in (along) the closed loop, as indicated by arrows in  FIG. 4B . The residual fluid is composed of remaining rinseback fluid in the container  30  and a mixture of rinseback fluid and blood residues in the line arrangements  24 A,  24 B and in the second chamber  23  of the dialyzer  20 . 
     In the filtration step  304 , the machine  1  is operated to draw residual fluid from the second flow circuit C 2  into the first flow circuit C 1  through the membrane  21 , and from the first flow circuit C 1  into the drain line  17  of the machine  1 , as indicated by arrows in  FIG. 4B . This process, denoted “filtration” herein, may be achieved by controlling the machine  1  to generate a lower pressure in the first chamber  22  compared to the second chamber  23 . In the illustrated example, inlet valve  19  is opened, outlet valve  18  is closed and the fluid supply unit  4  is operated to generate suction on drain line  17 , to thereby reduce the pressure in the first chamber  22  and draw residual fluid across the membrane  21 . In an alternative, both valves  18 ,  19  are opened and the fluid supply unit  4  is operated to supply a fluid, e.g. a dialysis fluid, to the supply line  16  and to establish a higher flow rate in the drain line  17  than in the supply line  16 . The filtration of step  304  may be at least partly concurrent with the circulation of step  303 . It is conceivable that the machine  1  is operated to alternate between filtration and circulation. Steps  303  and  304  are terminated when the second flow circuit C 2  is deemed to be sufficiently drained of residual fluid. Steps  303  and  304  may be terminated by the operator, e.g. by pressing a button on the machine, or automatically by the machine  1 , e.g. based on dead-reckoning of the volume pumped into the patient by the pump  8  and/or based on input from a sensor, such as a pressure sensor in fluid communication with the closed loop (cf. P 1 , P 2  in  FIGS. 6A-6B ) and/or a pressure sensor in the fluid supply unit (cf. P 3  in  FIGS. 9A-9B ). 
     Finally, in step  305 , clamps  10 ,  11  are opened and the operator is instructed to strip the machine  1  of the set of disposables by disconnecting the dialyzer  20 , the line arrangements  24 A,  24 B and the container  30 , preferably as a unit. The operator may then discard the set of disposables. Subsequently, the machine  1  may perform a conventional disinfection procedure, e.g. after instructing the operator to connect tubing  20 ′,  20 ″ to ports  5 ′,  6 ′ ( FIG. 1 ). 
     The procedure  300  enables the closed loop, including the container  30 , to be substantially drained of residual fluid during the draining phase. This reduces the weight of the set of disposables to be discarded and also reduces the risk that residual fluid is spilled on and around the machine  1 . As understood from  FIGS. 4A-4B , by enabling the second fluid circuit C 2  to be connected to two separate ports  32 ,  33  on the container  30 , the procedure  300  may be implemented by use of a simple and conventional line set and by use of a conventional dialysis machine  1 . Further, it is currently believed that the circulation of residual fluid through the container  30  serves to facilitate draining of the closed loop. For example, the inflow of residual fluid through the inlet port  33  may serve to reduce the risk of the outlet port  32  becoming obstructed before the container  30  is completely drained. Such obstruction may occur, e.g., if the container is compliant (flexible) and gradually collapses as the amount of residual fluid in the container  30  diminishes. 
     By experimentation, the inventors have found that the draining of the closed loop may be facilitated if the closed loop is vented to the atmosphere during the filtration and/or between periods of filtration (step  304 ). Such venting will counteract formation of negative (sub-atmospheric) pressure in the closed loop by the filtration, and thereby ensure a sufficient pressure difference between the chambers  23 ,  22  as well as counteract flow resistance caused by negative pressure, e.g. a collapsing of the container  30  (if flexible). For automated draining, the venting is preferably machine-controlled. 
     An embodiment that enables such machine-controlled venting by use of a simple and conventional line set will now be described with reference to a flow chart in  FIG. 5  in combination with system diagrams in  FIGS. 6A-6B , which illustrate a dialysis machine  1  when arranged and operated for blood treatment and drainage of residual fluid, respectively. In the illustrated example, the line arrangement  24 A includes a branch line  28  in fluid communication with the drip chamber  25  and extending to a connector for connection to sensor port  13 , which is in fluid communication with a first pressure sensor P 1  in the machine  1 . The line arrangement  24 B includes a branch line  29  in fluid communication with the withdrawal line  24 ″ and extending to a connector for connection to sensor port  14 , which is in fluid communication with a second pressure sensor P 2  in the machine  1 . As is well-known to the skilled person and shown in  FIG. 6A , the branch lines  28 ,  29  are connected to the ports  13 ,  14  during blood treatment, thereby enabling the machine  1  to monitor pressure (aka “arterial pressure”) on the withdrawal side of the second flow circuit C 2  upstream of the pump  8 , and pressure (aka “venous pressure”) on the return side of the second flow circuit C 2 . 
     The procedure  500  is performed when the blood treatment in  FIG. 6A  has been terminated and includes an initial rinseback step  501 , which may be identical to step  301 , and a re-arrangement step  502 , which may be identical to step  302  and results in connectors  26 ,  27  being connected to ports  33 ,  32  of container  30 , as seen in  FIG. 6B . After step  502 , the operator is instructed to remove the withdrawal line  24 ″ from the clamp  11 , which is opened (step  503 ), disconnect branch line  29  from sensor port  14  so that the terminal end of branch line  29  is open to the environment (step  504 ), and install branch line  29  in clamp  11  so that clamp  11  is operable to selectively open and close branch line  29  (step  505 ). The procedure  500  then proceeds to the draining phase, by performing a circulation step  506  and a filtration step  507  in correspondence with steps  303  and  304  as described above, as well as a ventilation step  508 , in which clamp  11  is opened to vent the closed loop, for reasons explained above. 
     The ventilation in step  508  may differ depending on implementation. In one embodiment, steps  506  and  507  are performed with open clamps  10 ,  11  to ensure proper filtration and circulation, as illustrated in  FIG. 6B , in which a dashed arrow designates air that enters the opened branch line  29 . However, the inventors have found that the draining of the closed loop may be facilitated, particularly at end of the draining phase when small amounts of residual fluid remain in the container  30 , if clamp  11  is intermittently closed during circulation and/or filtration. In one example, the clamp  11  is closed during a fraction of the duration of the draining phase, e.g. less than 20%, 15%, 10% or 5%. Thus, the branch line is kept open during the draining phase except for one or more short time periods in which the branch line is closed. In fact, the inventors have found that draining may be improved by toggling the clamp  11 , particularly towards the end of the draining phase. In such toggling, the clamp  11  is repeatedly ( 2  or more times) switched to close and then re-open the branch line  29 . In one embodiment, the clamp  11  is intermittently closed for 0.1-10 seconds, and preferably 0.4-5 seconds, during the toggling. In step  509 , when the second flow circuit C 2  is deemed, by operator input or based on sensor data, to be sufficiently drained of residual fluid the clamps  10 ,  11  are closed. After a predefined wait time AT (step  510 ), the pump  8  is stopped and filtration is terminated (step  511 ). Optionally, the filtration may be stopped already at step  509  or step  510 . By operating the pump  8  during the wait time ΔT, a negative pressure is established in branch line  29 . This will reduce risk of residual fluid leaking out of the branch line  29  when the clamps  10 ,  11  are subsequently opened for disconnection of the disposables (cf. step  305 ). In an alternative, only clamp  10  is closed in step  509 , and clamp  11  is subsequently closed in step  511 . This may further reduce the risk of liquid leaking from the branch line  29  when disconnected after completed draining phase. 
     The procedure  500  may be implemented by use of a simple and conventional line set and by use of a conventional dialysis machine  1  and enables facilitated draining of the second flow circuit C 2  by machine-controlled venting of the closed loop. 
     It is to be realized that corresponding effects may be achieved if steps  503 ,  505  are modified to instruct the operator to replace the return line  24 ′ by the branch line  29  in clamp  10 , resulting in the configuration shown in  FIG. 6C . All other steps of the procedure  500  may be implemented as described with reference to  FIG. 6B . However, to facilitate draining in step  508 , clamp  10  is operated for ventilation/toggling. Further, only clamp  11  may be closed in step  509 , whereas clamp  10  may be subsequently closed in step  511 . The installation of the branch line  29  in clamp  10  enables a dedicated leakage prevention procedure to be performed between steps  502  and  504 . In this procedure, the control system  2  closes clamp  11  and then operates pump  8  to generate negative pressure in the withdrawal line  24 ″ downstream of the clamp  11  and in the branch line  29 . The control system  2  may stop the blood pump  8  after a predefined time or when a predefined pressure is attained in the branch line  29 , e.g. indicated by the pressure sensor P 2 . The negative pressure reduces the risk of blood leakage when the branch line  29  is disconnected from the sensor port  14  in step  504 . 
     The installation of the branch line  29  in clamp  11  as shown in  FIG. 6B , or in clamp  10  as shown in  FIG. 6C , has the advantage of enabling the blood pump  8  to generate a negative pressure in the branch line  29  by steps  509 - 511 . 
     In further alternatives, not shown, steps  503 - 505  are modified to instruct the operator to disconnect branch line  28  from sensor port  13  and install branch line  28  in either of clamps  10 ,  11 . 
     The implementation of the procedure  500  may depend on the particular combination of dialysis machine and line set, e.g. which branch line  28 ,  29  is long enough to be arranged in which clamp  10 ,  11 . 
     In all embodiments herein, the above-mentioned negative pressure may be generated by operation of the blood pump  8  and/or by performing filtration through the dialyzer membrane. 
     There may be situations when it is not possible or desirable to use a two-port container  30  as described hereinabove. Instead, a single-port container may be preferred. For example, a dialysis clinic may want to keep an existing supply chain of single-port containers, may want to avoid stock-keeping of different container types, etc. When using a single-port container, it is equally important to avoid the need for a specialized line set to perform machine-controlled draining of the blood circuit after completed blood treatment. 
     This objective may be achieved in accordance with a second inventive concept by use of a three-way manifold coupling unit, which defines three ports and an internal manifold that fluidly connects the ports. Such a coupling unit may also be denoted “T coupling” or “Y coupling” in the art. One port of the coupling unit is connected to the port of the single-port container to provide two ports for connection to the return and withdrawal lines of a line set. By such an arrangement, a closed loop may be formed by use of a conventional line set, where the container is fluidly connected to the closed loop by the coupling unit, but is located outside of the closed loop. Experiments show that the closed loop and the container may be substantially drained of residual fluid by performing the above-described filtration to draw the residual fluid into the dialysis machine through the dialyzer membrane. 
     In the following, an embodiment of the second inventive concept will be described with reference to the flow chart in  FIG. 3B  in combination with the system diagram in  FIG. 7 , which includes a container  30  with a single port  32 ′ and otherwise corresponds to  FIG. 6C . The flow chart in  FIG. 3B  corresponds to  FIG. 3A  and represents a post-treatment procedure  300 ′ that includes rinseback, a draining phase and removal of disposables. Unless otherwise stated, the description of  FIG. 3A  is equally applicable to  FIG. 3B . The procedure  300 ′ differs from the procedure  300  by the re-arrangement step  302 ′, in which the operator is instructed to connect a first port of a 3-way manifold coupling unit  38  to the container port  32 ′ and to connect the terminal connectors  26 ,  27  to second and third ports of the coupling unit  38 . It is realized from  FIG. 7  that the provision of the coupling unit  38  enables the use of a conventional line set and that steps  301 ,  303 - 305  may be performed as described for  FIG. 3A . As indicated by an arrow in  FIG. 7 , fluid is drawn from the container  30  into the closed loop by the filtration (step  304 ). In a variant, the coupling unit  38  is connected to the container port  32 ′ already in step  301 , i.e. in preparation for the rinseback procedure. For example, step  301  may involve connecting the first port of the coupling unit  38  to the container port  32 ′ and connecting the connector  27  on the withdrawal line  24 ″ to the second port of the coupling unit  38 , while ensuring that the third port of the coupling unit  38  is closed. The dialysis machine then performs rinseback. Then, in step  302 , the operator may be instructed to form the closed loop by connecting the connector  26  on the return line  24 ′ to the third port of the coupling  28 . 
     The description of the procedure  500  in  FIG. 5  is also applicable to the second inventive concept, given that step  502  is modified in correspondence with step  302 ′. As noted, the coupling unit  38  may optionally be connected to the container port  32 ′ already in step  501 . All embodiments described with reference to  FIGS. 6A-6C  are equally applicable to the second inventive concept. 
     Experiments conducted by the inventors indicate that the venting step  508 , and in particular the toggling of the branch line during the venting step  508 , results in a significant reduction in the time required for draining the second flow circuit C 2  in accordance with the second inventive concept. The toggling will provide a motive force that actively pulls fluid from the container into the closed loop and thereby reduces the time required for draining the container  30 . 
     As a non-limiting example, the first and second inventive concepts may be implemented to substantially drain the second fluid circuit C 2  and the container  30  of residual fluid in 1-3 minutes, assuming that the total volume of residual fluid to be drained is less than approx. 0.5-0.8 L and that the dialyzer  20  has a high-flux or high-permeability membrane (having an ultrafiltration capacity of more than 20 mL/h/mmHg). As used herein, “substantially drain” may indicate that the total remaining amount of residual fluid after the draining phase is no more than 0.1 L, and preferably no more than 0.05 L. 
     By insightful reasoning, the inventors have found that it might be advantageous to avoid exposing sensitive components in the fluid supply unit  4  to the residual fluid, which may include blood residues. For example, exposing sensors to the residual fluid might lead to fouling that causes the machine  1  to malfunction. Thus, in one embodiment, a drain flow path within the fluid supply unit  4  is modified during filtration compared to blood treatment to avoid such exposure. Furthermore, the flow paths within the fluid supply unit  4  may be modified such that the output signal of a pressure sensor in the fluid supply unit  4  represents pressure in the first chamber  22  of the dialyzer  20 , allowing the control system  2  to at least partly control the filtration based on the output signal. 
     These principles will now be exemplified with reference to a conventional fluid supply unit  4  which is depicted in  FIGS. 9A-9B . The fluid supply unit  4  defines a supply flow path  40  that extends from a dialysis fluid supply  41  to the outlet port  5  and includes a supply valve  42 , a supply pump  43 , a degassing device  44 , a conductivity sensor  45 , a pressure sensor P 3 , a flow sensor  47 , and an outlet valve  48 . The fluid supply system  4  also defines a drain flow path  50  that extends from the inlet port  6  to a drain  57  and includes a degassing device  51 , an inlet valve  52 , a flow sensor  53 , a conductivity sensor  54 , a blood detector  55 , and a drain pump  56 . A gas evacuation line  80  connects the degassing chamber  51  to the drain flow path  50  upstream of the drain pump  56  and includes an evacuation valve  81 . In the illustrated example, fluid communication may be established between the first and second flow paths  40 ,  50 , via either of a first and a second bypass line  60 ,  70  with a respective bypass valve  61 ,  71 . The first bypass line  60  extends between an upstream end of flow sensor  53  and a downstream end of flow sensor  47 , and the second bypass line  70  extends between a downstream end of flow sensor  53  and an upstream end of flow sensor  47 . Although not shown in  FIGS. 9A-9B , further sensors may be included in the inlet and outlet flow paths  40 ,  50 , e.g. sensors included in a protective system of the machine  1 . 
     The fluid supply unit  4  may be operated during blood treatment, by the control system  2  ( FIG. 1 ), to generate a flow of fresh dialysis fluid through the outlet port  5  and a flow of spent dialysis fluid through the inlet port  6 , as indicated by solid arrows in  FIG. 9A . In the illustrated example, valves  42 ,  48  are open, supply  43  pump is active, bypass valves  61 ,  71  are closed, valve  52  is open and drain pump  56  is active. Further, evacuation valve  81  is opened, at least intermittently, to allow gases to be drawn from degassing device  51  along gas evacuation line  80  by drain pump  56 , as indicated by a dashed arrow. 
       FIG. 8  illustrates a method  800  of operating the fluid supply unit  4  for achieving the above-mentioned filtration during the draining phase. The control system  2  may execute the method  800  by generating suitable control signals for the valves and the pumps in the fluid supply unit  4 . The resulting configuration of the fluid supply unit  4  is shown in  FIG. 9B . In step  801 , supply pump  43  is stopped and outlet valve  48  is closed. In the example of  FIG. 9B , supply valve  42  may also be closed. In step  802 , inlet valve  52  is closed. In step  803 , evacuation valve  81  is opened to establish a flow path between drain port  6  and drain pump  56 . In step  804 , bypass valve  71  is opened to establish fluid communication between drain flow path  50  and the pressure sensor P 3  in the supply flow path  40 . In step  805 , drain pump  56  is started to thereby draw residual fluid from dialyzer  20  into inlet port  6 , via degassing device  51 , evacuation line  81 , and drain pump  56  into drain  57 , as indicated by solid arrows in  FIG. 9B . Thus, this unconventional use of the gas evacuation line  80  makes it possible to avoid exposing the sensors  53 - 55  in the drain flow path  50  to residual fluid. Further, by opening the bypass valve  71 , the pressure sensor P 3  will be responsive to pressure changes in the second chamber  22  of the dialyzer  20 . Thus, in step  805 , the drain pump  56  and thus the filtration may be controlled based on the output signal of the pressure sensor P 3 . 
     The method  800  may be implemented in any fluid supply unit  4  that defines a supply flow path (cf  40 ) and a drain flow path (cf  50 ) comprising a set of sensors (cf. 
       53 - 55 ), wherein step  803  generally involves opening a valve (cf.  81 ) located in a connecting line (cf.  80 ), which extends between a first location in the drain flow path intermediate an inlet port (cf  6 ) and an inlet valve (cf.  52 ) and a second location in the drain flow path intermediate a drain pump (cf.  56 ) and the set of sensors. Further, step  804  may generally involve opening a bypass valve (cf.  61 ,  71 ) in a bypass line (cf  60 ,  70 ), which extends between a third location in the drain flow path intermediate the inlet valve (cf.  52 ) and the second location, and a fourth location in the supply flow path intermediate a supply pump (cf.  43 ) and an outlet valve (cf  48 ), so as to establish fluid communication between the inlet port (cf.  6 ) and a pressure sensor (cf. P 3 ) in the supply flow path. 
     While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiments, it is to be understood that the invention 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. 
     For example, the foregoing description is equally applicable to any machine or apparatus which is configured to perform extracorporeal blood treatment by use of a dialyzer or an equivalent filtration unit, including but not limited to hemodialysis, hemofiltration, hemodiafiltration, plasmapheresis, extracorporeal blood oxygenation, extracorporeal liver support/dialysis, ultrafiltration, etc. 
     Further, it is conceivable to arrange another existing branch line of the line set in one of the machine-controlled clamps. For example, conventional line sets may include a branch line for infusion of anticoagulant and/or a branch line for infusion of substitution fluid. 
     In a further variant, the branch line may be installed in any other machine-controlled clamp than the withdrawal and return clamps that may be present on the dialysis machine. For example, dialysis machines may comprise a venting clamp for engagement with a branch line (“venting line”) connected to the drip chamber  25 . It is also conceivable to omit steps  503 - 505  and perform step  508  by controlling the venting clamp in engagement with the venting line. 
     In a further variant, steps  503  and  505  are omitted, which means that the branch line is disconnected to be open to the atmosphere during steps  506 - 508 . 
     Further, the above-mentioned toggling during step  508  may be achieved by instructing the operator to intermittently and manually pinch the branch line, e.g. by use of a manual clamp. 
     Still further, steps  509 - 511  may involve instructing the operator to manually pinch the return or withdrawal line  24 ′,  24 ″ and the branch line to create the desired negative pressure in the branch line at step  511 .