Patent Publication Number: US-2021170090-A1

Title: Syringe Warmer

Description:
TECHNICAL FIELD 
     This disclosure relates to dialysis systems and methods. 
     BACKGROUND 
     Dialysis is a treatment used to support a patient with insufficient renal function. The two principal dialysis methods are hemodialysis and peritoneal dialysis. 
     During hemodialysis (“HD”), the patient&#39;s blood is passed through a dialyzer of a dialysis machine while also passing a dialysis solution or dialysate through the dialyzer. A semi-permeable membrane in the dialyzer separates the blood from the dialysate within the dialyzer and allows diffusion and osmosis exchanges to take place between the dialysate and the blood stream. These exchanges across the membrane result in the removal of waste products, including solutes like urea and creatinine, from the blood. These exchanges also regulate the levels of other substances, such as sodium and water, in the blood. In this way, the dialysis machine acts as an artificial kidney for cleansing the blood. 
     A venous access line and an arterial access line can be connected to the patient to enable the blood to be drawn from the patient and to be returned to the patient after the blood flows through the filter. At the end of the hemodialysis treatment, some residual blood that has not been returned to the patient during the treatment may remain within the access lines. 
     SUMMARY 
     In one aspect, a method includes, after an extracorporeal blood treatment, connecting a fluid source to an access line that is connected to a patient, and delivering a fluid from the fluid source to the access line to infuse blood from the access line to the patient, wherein the fluid delivered to the access line has a temperature from about 30 degrees Celsius to about 38 degrees Celsius. 
     Embodiments can include one or more of the following features. 
     In some embodiments, the fluid includes saline. 
     In certain embodiments, the fluid source includes a fluid receptacle. 
     In some embodiments, the fluid receptacle includes one or more syringes containing the fluid. 
     In certain embodiments, connecting the fluid source to the access line includes connecting the fluid receptacle to an end of the access line. 
     In some embodiments, the method further includes heating the fluid contained in the fluid receptacle. 
     In certain embodiments, heating the fluid contained in the fluid receptacle includes positioning the fluid receptacle proximate a heating element 
     In some embodiments, heating the fluid contained in the fluid receptacle includes activating the heating element prior to performing extracorporeal treatment 
     In certain embodiments, heating the fluid contained in the fluid receptacle includes positioning the fluid receptacle in a housing coupled to an extracorporeal blood treatment apparatus, wherein the housing includes the heating element. 
     In some embodiments, heating the fluid contained in the fluid receptacle includes positioning the fluid receptacle proximate a dialyzer of an extracorporeal blood treatment system. 
     In certain embodiments, heating the fluid contained in the fluid receptacle includes positioning the fluid receptacle proximate a fluid line of an extracorporeal blood treatment system. 
     In some embodiments, the fluid line is a dialysate line carrying dialysate fluid to a dialyzer of the extracorporeal blood treatment system. 
     In certain embodiments, the method further includes filling the fluid receptacle with a fluid. 
     In some embodiments, filling the fluid receptacle includes connecting the fluid receptacle to a fluid line of an extracorporeal blood treatment system 
     In certain embodiments, the fluid line is a saline line coupled to a saline bag of the extracorporeal blood treatment system, and the fluid includes saline. 
     In some embodiments, the fluid line is a substitution line coupled to a dialysate filter of the extracorporeal blood treatment system, and the fluid includes substitution fluid. 
     In certain embodiments, the fluid receptacle includes a syringe, and filling the fluid receptacle includes connecting the syringe to a fluid line of an extracorporeal blood treatment system, and actuating a plunger of the syringe to draw fluid from the fluid line into the syringe. 
     In some embodiments, the fluid source includes a fluid line of an extracorporeal blood treatment system. 
     In certain embodiments, the fluid line includes a substitution fluid line of the extracorporeal blood treatment system, and the fluid includes substitution fluid. 
     In some embodiments, connecting the fluid source to the access line includes connecting an end of the access line to the substitution fluid line. 
     In a further aspect, an extracorporeal blood treatment system includes an extracorporeal blood treatment apparatus that includes a warming chamber configured to receive a fluid receptacle, and a blood component set coupled to the extracorporeal blood treatment apparatus and configured to convey fluid from a patient, through a dialyzer, and back to the patient during extracorporeal blood treatment, the blood component set including an access line, wherein the fluid receptacle is configured to be coupled to the access line to infuse blood to the patient following treatment. 
     Embodiments can include one or more of the following features. 
     In some embodiments, the fluid receptacle is coupled to a saline line of the blood component set, and the fluid receptacle is filled with saline from the saline line. 
     In certain embodiments, the fluid receptacle includes a syringe, and filling the fluid receptacle includes actuating a plunger of the syringe to draw saline from the saline line into the syringe. 
     In some embodiments, the fluid receptacle is coupled to a substitution line of the extracorporeal blood treatment apparatus, and the fluid receptacle is filled with substitution fluid from the substitution line. 
     In certain embodiments, the fluid receptacle includes a syringe, and filling the fluid receptacle includes actuating a plunger of the syringe to draw substitution fluid from the substitution line into the syringe. 
     In a further aspect, an extracorporeal blood treatment apparatus includes a housing configured to receive a fluid receptacle, and a heating element coupled to the housing and configured to heat a fluid in the fluid receptacle, wherein the fluid receptacle is configured to be coupled to an access line to infuse blood to a patient following hemodialysis treatment. 
     Embodiments can include one or more of the following features. 
     In some embodiments, the heating element is coupled to a door of the housing, and the housing is configured to position the fluid receptacle proximate the heating element when the door of the housing is in a closed position. 
     In certain embodiments, the heating element is positioned proximate the bottom of the housing, and the housing is configured to position the fluid receptacle above the heating element. 
     In some embodiments, the heating element is positioned along a wall of the housing, and the housing is configured to position the fluid receptacle proximate the heating element. 
     In certain embodiments, the heating element is spaced apart from the fluid receptacle when the fluid receptacle is positioned within the housing. 
     In some embodiments, the heating element includes an infrared heater 
     In certain embodiments, the heating element includes a photonic heater. 
     In some embodiments, the housing includes one or more mechanical attachment devices configured to position of the pair of syringes within the housing. 
     In another aspect, an extracorporeal blood treatment system includes an extracorporeal blood treatment apparatus, a blood component set configured to be coupled to the extracorporeal blood treatment apparatus to convey fluid from a patient, through a dialyzer, and back to the patient during extracorporeal blood treatment, the blood component set including an access line configured to be coupled to the patient, a fluid receptacle configured to be connected to the access line, and a holder configured to position the fluid receptacle adjacent a fluid line set to warm fluid in the fluid receptacle. 
     Embodiments can include one or more of the following features. 
     In some embodiments, the fluid line set includes a dialysate line configured to provide dialysate to a dialyzer of the extracorporeal blood treatment system. 
     In certain embodiments, the extracorporeal blood treatment system further includes an insulated door coupled to the holder and configured to cover the fluid receptacle coupled to the holder. 
     In some embodiments, the fluid receptacle is coupled to a saline line of the blood component set, and the fluid receptacle is filled with saline from the saline line. 
     In certain embodiments, the fluid receptacle includes a syringe, and filling the fluid receptacle with saline includes actuating a plunger of the syringe to draw saline from the saline line into the syringe. 
     In some embodiments, the fluid receptacle is coupled to a substitution line of the extracorporeal blood treatment apparatus, and the fluid receptacle is filled with substitution fluid from the substitution line. 
     In certain embodiments, the fluid receptacle includes a syringe, and filling the syringe with substitution fluid includes actuating a plunger of the syringe to draw substitution fluid from the substitution line into the syringe. 
     Advantages of the systems, devices, and methods described herein include reduced discomfort to the patient during reinfusion and flushing of the arterial access and venous access of the patient. The amount of blood that needs to be disposed of after a treatment can also be reduced. In addition, the systems, devices, and methods described herein may provide added convenience to performing dialysis treatment by providing a device for storing fluid receptacles used for flushing the arterial access and venous access of the patient during hemodialysis treatment. 
     Other aspects, features, and advantages will be apparent from the description and drawings, and from the claims. 
    
    
     
       DESCRIPTION OF DRAWINGS 
         FIGS. 1 and 2  illustrate a hemodialysis system that includes a fluid warming chamber. 
         FIG. 3  is a schematic of a blood circuit of the hemodialysis system of  FIG. 1 . 
         FIG. 4  is a schematic of a dialysate circuit of the hemodialysis system of  FIG. 1 . 
         FIGS. 5-11  illustrate extracorporeal hemodialysis systems. 
     
    
    
     DETAILED DESCRIPTION 
     Referring to  FIG. 1 , a hemodialysis system  100  includes a hemodialysis machine  102 , a disposable blood component set  104 , a dialyzer  110 , a blood pump  128 , a saline bag  138 , a saline delivery line  126 , and a warming chamber  170 . The disposable blood component set  104  includes an arterial line  106 , a venous line  108 , an arterial access line  116 , and a venous access line  118 . During treatment, the arterial access line  116  and venous access line  118  are coupled to the arterial line  106  and venous line  108 , respectively, using connectors  120 ,  122 . The blood pump  128  of the hemodialysis machine  102  is operable to draw blood from the patient into and through the blood component set  104  and dialyzer  110 . 
     During hemodialysis, the arterial access line  116  and venous access line  118  are coupled at a first end to the arterial line  106  and venous line  108 , respectively, and are fluidly coupled to a patient at a second end, and blood is circulated through various blood lines and components, including a dialyzer  110 , of the blood component set  104 . At the same time, dialysate is circulated through a dialysate circuit (shown in  FIG. 4 ) formed by the dialyzer  110  and various other dialysate components and fluid lines connected to the hemodialysis machine  102 . Many of these dialysate components and fluid lines are located inside the housing of the hemodialysis machine  102 , and are thus not visible in  FIG. 1 . The dialysate passes through the dialyzer  110  along with the blood. The blood and dialysate passing through the dialyzer  110  are separated from one another by a semi-permeable structure (e.g., a semi-permeable membrane and/or semi-permeable microtubes) of the dialyzer  110 . As a result of this arrangement, toxins are removed from the patient&#39;s blood and collected in the dialysate. The filtered blood exiting the dialyzer  110  is returned to the patient. The dialysate that exits the dialyzer  110  includes toxins removed from the blood and is commonly referred to as “spent dialysate.” The spent dialysate is routed from the dialyzer  110  to a drain. 
     Still referring to  FIG. 1 , the dialysate circuit of the hemodialysis machine  102  is formed by multiple dialysate components and fluid lines positioned inside the housing of the hemodialysis machine  102  as well as the dialyzer  110 , a dialyzer inlet line  134 , and a dialyzer outlet line  136  that are positioned outside of the housing of the hemodialysis machine  102 . The dialyzer inlet line  134  includes a connector adapted to connect to one end region of the dialyzer  110 , and the dialyzer outlet line  136  includes a connector adapted to connect to another end region of the dialyzer  110 . 
     Still referring to  FIG. 1 , the hemodialysis machine  102  includes a user interface system  150  that is operable to monitor and to control operations of the machine  102 . The user interface system  150  includes a touchscreen  151  and a display  152 . An operator can manually operate the touchscreen  151  to control operations of the machine  102 , and the display  152  can provide visual indications to the operator. The user interface system  150  is integral to the machine  102 . 
     The blood component set  104  of the hemodialysis system is secured to a module  114  attached to the front of the hemodialysis machine  102 . The module  114  includes a blood pump  128  capable of driving blood through the blood circuit. The module  114  also includes various other instruments capable of monitoring the blood flowing through the blood circuit. The module  114  includes a door that when closed cooperates with the front face of the module  114  to form a compartment sized and shaped to receive the blood component set  104 . In the closed position, the door presses certain blood components of the blood component set  104  against corresponding instruments exposed on the front face of the module  114 . This arrangement facilitates control of the flow of blood through the blood circuit and monitoring of the blood flowing through the blood circuit. 
     After the end of the extracorporeal treatment, blood component set  104  and the dialyzer  110  may contain residual blood drawn from the patient during the hemodialysis treatment. This blood can be returned to the patient to reduce patient blood loss using the blood reinfusion process described herein. However, even after performing a reinfusion process, the arterial access line  116  and the venous access line  118  may still contain blood drawn from the patient during the hemodialysis treatment. The remaining blood in the arterial access line  116  and the venous access line  118  may be flushed to prevent clotting at the patient&#39;s access sites. 
     A pair of saline-filled syringes  160 ,  162  is provided to flush any remaining blood in the access lines  116 ,  118  back to the patient following dialysis treatment and reinfusion. For example, as described in further detail herein, following treatment and reinfusion, the access lines  116 ,  118  can be disconnected from the arterial and venous lines  106 ,  108 , and a first syringe  160  can be coupled to the arterial access line  116  and a second syringe  162  can be coupled to the venous access line  118 . The saline contained in the syringes  160 ,  162  can be injected into the access lines  116 ,  118  to flush any remaining blood in the access lines  116 ,  118  back to the patient. 
     As described in further detail herein, the saline contained in the syringe  116 ,  118  can be heated in the warming chamber  170  of the hemodialysis machine  102  prior to injection of the saline into the access lines  116 ,  118 . Heating the saline contained in the syringes  160 ,  162  prior to flushing the access lines  116 ,  118  with the saline in the syringes  160 ,  162  can reduce the discomfort experienced by the patient during reinfusion. 
     As depicted in  FIG. 1 , the warming chamber  170  includes a housing  172  coupled to the hemodialysis machine  102 . The housing  172  is configured to hold the two saline-filled syringes  160 ,  162 . The housing  172  includes an insulating material, such as plastic, fiberglass, aerogel, cellulose, or polyurethane, to retain heat within the warming chamber  170 . For example, the interior surfaces of the housing  172  can include the insulating material. The housing can be made of any of a variety of suitable materials, such as metal or plastic materials. 
     The housing  172  includes a door  174  that can be opened to provide access to the syringes  160 ,  162  positioned in the warming chamber  170  and closed the retain heat within the warming chamber  170 . The door  174  is coupled to the housing  172  with a hinge  176 . The door  174  includes an insulating material, such plastic, fiberglass, aerogel, cellulose, polyurethane, or fabric with infrared reflecting surface (e.g., aluminum foil). For example, the interior surface of the door  174  can include the insulating material to help retain heat within the warming chamber when the door  174  of the housing  172  is in a closed position (as depicted in  FIG. 1 ). 
       FIG. 2  depicts the hemodialysis machine  102  of  FIG. 1  with the door  174  of the warming chamber  170  in an open position. As depicted in  FIG. 2 , the interior of the housing  172  of the warming chamber  170  includes clips  180 ,  182 ,  184 ,  186 . The clips  180 ,  182 ,  184 ,  186  are configured to couple the syringes  160 ,  162  to the warming chamber  170  and maintain the position of the syringes  160 ,  162  within the warming chamber  170 . For example, the syringes  160 ,  162  can be positioned in the warming chamber  170  during hemodialysis treatment by attaching the syringes  160 ,  162  to the clips  180 ,  182 ,  184 ,  186  and closing the door  174  of the warming chamber  170 . 
     As depicted in  FIG. 2 , the warming chamber  170  also includes a heating element  178  coupled to the interior of the door  174  of the warming chamber  170 . The heating element  178  is coupled to the door  174  such that the heating element  178  is positioned between each of the syringes  160 ,  162  when the syringes  160 ,  162  are coupled to the clips  180 ,  182 ,  184 ,  186  of the warming chamber  170 . Further, the heating element  178  is positioned such that when the syringes  160 ,  162  are coupled to the warming chamber with the clips  180 ,  182 ,  184 ,  186  and the door  174  of the warming chamber  170  is closed, the heating element  178  is positioned close to each of the syringes  160 ,  162  without touching the syringes  160 ,  162 . The heating element  178  provides radiated heat to the warming chamber  170 . As described in further detail herein, the heating element  178  can be turned on to heat the saline contained in the syringes  160 ,  162  in the warming chamber  170 . Any of various suitable photic or infrared heating elements can be used, such as metal resistance wire, ceramic, semiconducting materials, or a point-wise self-regulating polymer PTC resistive heater. The heating element  178  is configured to provide radiated heat to the warming chamber  170  in order to heat the interior of the warming chamber  170  to a temperature ranging from about 30 degrees Celsius to about 38 degrees Celsius. 
     Still referring to  FIG. 2 , the warming chamber  170  also includes temperature sensors  188 ,  190  positioned on an interior wall of the housing  172  of the warming chamber  170 . The temperature sensors  188 ,  190  are configured to measure the temperature of the interior of the warming chamber  170 . For example, as depicted in FIG.  2 , the temperature sensors  188 ,  190  are positioned on the interior wall of the housing  172  such that when the syringe  160 ,  162  are positioned in the warming chamber  170  with clips  180 ,  182 ,  184 ,  186 , the temperature sensors  188 ,  190  are proximate the syringes  160 ,  162  and measure the temperature of the warming chamber  170  near the syringes  160 ,  162 . The temperature sensors  188 ,  190  can be electronically coupled to a computing device to monitor and display the temperature inside the warming chamber  170 . 
     Based on the temperature of the warming chamber  170  measured by the temperature sensors  188 ,  190 , the temperature of the saline contained in the syringes  160 ,  162  in the warming chamber  170  can be determined. For example, an algorithm correlating the temperature of the interior of the warming chamber  170  with the temperature of the saline in syringes  160 ,  162  positioned within the warming chamber  170  can be used to determine the temperature of the saline in the syringes  160 ,  162 . By using the readings from the temperature sensors  188 ,  190  to determine and monitor the temperature of the saline in the syringes  160 ,  162 , a user can determine when the temperature of the saline in the syringes  160 ,  162  is in a range of about 30 degrees Celsius to about 38 degrees Celsius (e.g., 36.5 degrees Celsius to 37.5 degrees Celsius), which provides improved comfort when injecting the saline to flush the access lines  116 ,  118 . Any of various suitable temperature sensors can be used, such as bi-metallic thermostat, thermistors, thermocouples, semiconductor sensors, or infrared sensors. 
       FIG. 3  is a schematic showing the flow paths of fluids into, through, and out of the blood circuit  300  of the hemodialysis system  100 . As depicted in  FIG. 3 , the blood component set  104  includes an arterial line set  304  and a venous line set  308 . 
     The arterial line set  304  includes the arterial access line  116 , the arterial line  106 , and an arterial drip chamber  324 . The arterial line  106  extends at a first end from the arterial access line  116  to a port  319 , which connects the arterial line  106  to the saline line  126 . The arterial line  106  is connected at a second end to the arterial drip chamber  324 . A pressure transducer  325   a  is connected to the arterial drip chamber  324  via a pigtail line  323  extending from the arterial drip chamber  324  and is configured to detect a fluid pressure within the arterial drip chamber  324 . A U-shaped pump line  318  extends from the bottom of the arterial drip chamber  324  and is connected to a dialyzer inlet line  334 . The dialyzer inlet line  134  is connected via a tube adaptor to a blood entry port of the dialyzer  110 . 
     A manually operable connector  120   a  at the end of the arterial line  106  is configured to connect to a manually operable connector  120   b  at the end of the arterial access line  116 . During hemodialysis treatment, the arterial line  106  is connected to the arterial access line  116 , and the arterial access line  116  is connected to an arterial needle assembly  326 . The arterial needle assembly  326  includes a needle  327  that is insertable into the arterial access  346  of the patient  302 . During hemodialysis treatment, the arterial needle assembly  326  is connected to the arterial access line  116  and the needle  327  of the arterial needle assembly  326  is inserted into the patient  302  to enable blood to be drawn from the patient  302  into the arterial line set  304 . For example, the blood pump  128  pumps blood from the artery of the patient  302  through the arterial needle assembly  326 , the arterial access line  116 , and the arterial line  106  to the dialyzer  110 . 
     The venous line set  308  includes the venous access line  118 , the venous line  108 , and a venous drip chamber  332 . A dialyzer outlet line  336  extends from the dialyzer  110  to the venous drip chamber  332 . A pressure transducer  325   b  is connected to the venous drip chamber  332  via a pigtail line  331  extending from the venous drip chamber  332  and is configured to detect a fluid pressure within the venous drip chamber  332 . 
     One end of the venous line  108  is connected to a bottom of the venous drip chamber  332 , and the other end of the venous access line  118  is connected to the venous access line  118 . A manually operable connector  122   b  at the end of the venous access line  118  is configured to connect to a manually operable connector  122   a  at the end of the venous line  108 . During hemodialysis treatment, the venous line  108  is connected to the venous access line  118 , and the venous access line  118  is connected to the venous needle assembly  334 . The venous needle assembly  334  includes a needle  335  that is insertable into the patient  302  to enable filtered blood, e.g., blood that has traveled through the dialyzer  110 , to be returned to the patient  302  through the venous line  108  and venous access line  118 . 
     The arterial line set  304  and the venous line set  308  form an extracorporeal blood circuit through which the blood of the patient  302  circulates. The blood pump  128 , when operated during the extracorporeal treatment, causes blood to flow from the patient  302 , through the extracorporeal blood circuit  300  and the dialyzer  110 , and then back into the patient  302  after filtration has occurred in the dialyzer  110 . 
     The blood circuit  300  further includes one or more flow regulators engageable with the arterial line set  304 , the venous line set  308 , and the saline line  126 . The flow regulators can be manually operable, electronically addressable, or both. In the embodiment illustrated in  FIG. 3 , for example, the blood circuit  300  includes a set of manually operable clamps  338   a - 338   e.  Clamp  338   a  is positioned to engage the arterial access line  116 . Clamp  338   b  is positioned to engage the arterial line  106 . Clamp  338   c  is positioned to engage the saline line  126 . Clamp  338   d  is positioned to engage the venous line  108 . Clamp  338   e  is positioned to engage the venous access line  118 . The clamps  338   a - 338   e  can be independently actuated to control fluid flow through the arterial line set  304 , the venous line set  308 , and the saline line  126 . 
     The blood circuit  300  also includes a set of automatic clamps  338   f  and  338   g,  which function to clamp the lines extending from the arterial drip chamber  324  and the venous drip chamber  332 , respectively. As described in further detail herein, a controller of the hemodialysis machine is used to control the position of clamps  338   f  and  338   g  to allow for filling of the drip chambers  324 ,  332 . 
     In some implementations, the blood circuit  300  includes one or more fluid flow sensors. In the embodiment shown in  FIG. 3 , a fluid flow sensor  340   a  is positioned to detect fluid flow through the arterial drip chamber  324 , and a fluid flow sensor  340   b  is positioned to detect fluid flow through the venous drip chamber  332 . The fluid flow sensors  340   a,    340   b  can be optical sensors responsive to drops of fluid through the arterial drip chamber  324  and the venous drip chamber  332 , respectively. The fluid flow sensors  340   a,    340   b  can detect flow rates of fluid flowing through the arterial drip chamber  324  and the venous drip chamber  332 , respectively. In addition, the fluid flow sensors  340   a,    340   b  can distinguish between fluids having different opacities, such as blood and saline. For example, during operation of the blood pump  128 , the type of fluid flowing through the arterial drip chamber  324  and the venous drip chamber  332  may vary depending on the stage of the hemodialysis treatment or the blood reinfusion process. The fluid flow sensors  340   a,    340   b  can distinguish between the different types of fluid and provide a signal indicative of a current stage of the extracorporeal treatment or the blood reinfusion process. 
     In addition to the blood lines forming the main blood circuit  300 , a saline delivery line  126  can be connected to the blood circuit  300  for the introduction of saline into the blood circuit  300  (e.g., during priming and reinfusion). As depicted in  FIG. 3 , the saline delivery line  126  is connected at a first end to a saline bag  338  and at a second end to the port  319 . The port  319  fluidly couples the saline delivery line  126  to the arterial line  106  upstream of the arterial drip chamber  324 . 
     The various blood lines, access lines, and the saline delivery line  126  can be formed of any of various different medical grade materials. Examples of such materials include PVC, polyethylene, polypropylene, silicone, polyurethane, high density polyethylene, nylon, ABS, acrylic, isoplast, polyisoprene, and polycarbonate. 
     The various blood lines and the saline delivery line  126  are typically retained within the module  114  (as depicted in  FIG. 1 ). Various techniques can be used to secure the lines to the module  114 . For example, a carrier body with a series of apertures and recesses for capturing and retaining the various blood lines and components can be secured to the module  114  of the hemodialysis machine  102 . In some examples, mechanical attachment devices (e.g., clips or clamps) can be attached to a carrier body and used to retain the lines, and the carrier body can be attached to the module  114  of the hemodialysis machine  102 . As another example, the lines can be adhered to or thermally bonded to a carrier body, and the carrier body can be attached to the module  114  of the hemodialysis machine. 
       FIG. 4  is a schematic showing the flow paths of fluids into, through, and out of the dialysate circuit  400 . The dialysate circuit  400  includes a number of dialysate components that are fluidly connected to one another via a series of fluid lines. 
     Still referring to  FIG. 4 , the flow pump  495  of the dialysate circuit  400  is configured to draw water into the dialysate circuit  400  from a water inlet port (not shown). The water drawn into the dialysate circuit  400  by the flow pump  495  is provided to a heat exchanger of the dialysate circuit  400  (not shown) in order to warm the water received by the dialysate circuit  400 . After exiting the heat exchanger, the warmed water flows to a deaeration and heating chamber (not shown) configured to heat and deaerate water received by the dialysate circuit  400 . 
     The warmed and deaerated water flows to a mixing chamber (not shown) where the water is mixed with acid concentrate and bicarbonate concentrate to form warmed dialysate. In some examples the dialysate circuit  400  includes an acid concentrate pump coupled to a source of acid concentrate and a bicarbonate pump coupled to a source of bicarbonate to provide acid concentrate and bicarbonate concentrate, respectively, to the mixing chamber of the dialysate circuit  400  to mix with water and form dialysate. 
     The warm dialysate is drawn into a balancing device  454  connected to a fluid line downstream of the mixing chambers. The balancing device  454  is divided by a flexible membrane  460  into a first chamber half  456  and a second chamber half  458 . As fluid flows into the first chamber half  456 , fluid is forced out of the second chamber half  458 , and vice versa. For example, as fresh dialysate flows into first chamber half  456  of the balancing device  454 , spent dialysate is forced to flow out of the second chamber half  458  of the balancing device  454  towards the drain. In contrast, as spent dialysate flows into the second chamber half  458  of the balancing device  454 , fresh dialysate is forced out of first chamber half  456  of the balancing device  454  towards the dialyzer  110 . This balancing device construction and alternating flow of fresh and spent dialysate helps ensure that the volume of fresh dialysate entering the dialysate circuit is equal to the volume of spent dialysate exiting the dialysate circuit, when desired, during treatment. 
     During hemodialysis, fresh dialysate passing through the first chamber half  456  of the balancing device  454  is directed to the dialyzer  110  through a dialysate filter  474 . The fresh dialysate flowing out of balancing device  454  flows along a fluid line through the dialysate filter  474 , which is configured to filter the fresh dialysate received from the balancing device  454 . One example of such a dialysate filter  474  is the DIASAFE® plus dialysis fluid filter available from Fresenius Medical Care. During hemodialysis, a bypass valve  475  is closed in order to direct the flow of dialysate from the dialysis filter  474  towards dialyzer  110 . 
     After filtration by dialysate filter  474 , the fresh dialysate flows through a conductivity cell  470  and a temperature monitor thermistor  472  downstream of the of the dialysate filter  474 . The conductivity cell  470  and temperature monitor thermistor  472  regulate the temperature of the filtered dialysate exiting the dialysate filter  474 . 
     After flowing through the conductivity cell  470  and temperature monitor thermistor  472 , the filtered dialysate flows through a second filter  480 . The second filter  480  further filters the dialysate to generate substitution fluid. 
     When a dialyzer inlet valve  476  is in a closed position and a substitution valve  482  is in an open position, the substitution fluid exits the second filter  480  and flows through a substitution port  484  and along a substitution fluid line  486 . As depicted in  FIG. 4 , a substitution pump  488  is provided along the substitution fluid line  486  to draw the substitution fluid through the substitution port  484  to the substitution line  486 . 
     In contrast, when the dialyzer inlet valve  476  is in an open position and the substitution valve  482  is in a closed position, the substitution fluid exits the second filter  480  and flows along a dialysate inlet line  450  towards the dialyzer  110 . Before entering the dialyzer  110 , the substitution fluid flows through a pressure sensor  490  positioned along the dialysate inlet line  450 . The pressure sensor  490  is configured to measure the pressure of the fluid entering the dialyzer  110 . Any of various different types of pressure sensors capable of measuring the pressure of the substitution fluid entering the dialyzer  110  can be used, such as ultrasonic sensors, piezoresistive strain gauges, capacitive sensors, electromagnetic sensors, or piezoelectric sensors. 
     After flowing through the dialyzer  110 , spent substitution fluid exits the dialyzer  110  through the dialyzer outlet valve  492  along a dialysate outlet line  452  of the dialysate circuit  400 . A pressure sensor  494  located along the dialysate outlet line  452  is adapted to measure the pressure of the spent substitution fluid exiting the dialyzer  110 . Any of various different types of pressure sensors capable of measuring the pressure of the spent substitution fluid passing from the dialyzer  110  can be used, such as ultrasonic sensors, piezoresistive strain gauges, capacitive sensors, electromagnetic sensors, or piezoelectric sensors. 
     A dialysate flow pump  495  is configured to pump the spent substitution fluid from the dialyzer  110  to the second chamber half  458  of the balancing device  454 . As the second chamber half  458  of the balancing device  454  fills with the spent substitution fluid, fresh dialysate within the first chamber half  456  of the balancing device  454  is expelled towards the dialyzer  110 . Subsequently, as the first chamber half  456  of the balancing device  454  is refilled with fresh dialysate, the spent substitution fluid is forced out the second chamber half  458  of the balancing device  454  along the drain line  412  to the drain. 
     As shown in  FIG. 4 , an ultrafiltration line  491  is connected the drain line  412  and fluidly coupled to the dialyzer  110 . An ultrafiltration pump  497  is operatively connected to the ultrafiltration line  491  such that when the ultrafiltration pump  497  is operated, spent substitution fluid can be directed to the drain via the ultrafiltration line  491 . Operation of the ultrafiltration pump  497  while simultaneously operating the dialysate flow pump  495  causes increased vacuum pressure within the dialysate outlet line  452  and ultrafiltration line  491 , and thus creates increased vacuum pressure within the dialyzer  110 . As a result of the increased vacuum pressure, additional fluid is pulled from the blood circuit  300  into the dialysate circuit  400  across the semi-permeable structure (e.g., semi-permeable membrane or semi-permeable microtubes) of the dialyzer  110 . Thus, the ultrafiltration pump  497  can be operated to remove excess fluid from the patient. 
     The various fluid lines and drain line  112  of the dialysate circuit  400  can be formed of any of various different medical grade materials. Examples of such materials include PVC, polyethylene, polypropylene, silicone, polyurethane, high density polyethylene, nylon, ABS, acrylic, isoplast, polyisoprene, and polycarbonate. 
     An example process of hemodialysis treatment and blood reinfusion are described with respect to  FIGS. 2-5 . 
     Before the hemodialysis treatment is initiated, a human operator, e.g., a patient, a clinician, a nurse, or other clinical personnel, positions the arterial line set  304 , the venous line set  308 , the saline line  126 , and the saline bag  338  in preparation for the hemodialysis treatment. The operator also mounts the arterial drip chamber  324  and the venous drip chamber  332  adjacent the fluid flow sensors  340   a,    340   b  to enable the fluid flow sensors  340   a,    340   b  to detect fluid flow through the arterial drip chamber  324  and the venous drip chamber  332 , respectively. The operator mounts the dialyzer  110  to the hemodialysis machine  102  and connects the blood component set  104  to the dialyzer  110 . The operator also connects the saline line  126  to the port  319  coupled to the arterial line  106  to place the saline bag  138  in fluid communication with the blood circuit  300 . 
     Before performing the hemodialysis treatment, the operator primes the blood circuit  300 . Referring to  FIGS. 3 and 4 , a method of priming the blood circuit  300  for hemodialysis treatment will now be described. During priming, clamp  338   c  to allow saline flow through the saline line  126  into the blood circuit  300 . Clamp  338   b  is in a closed position to prevent fluid from flowing out the patient end of the arterial line  106 . Claim  338   d  is in an open position to allow fluid to flow out the patient end of the venous line  108  and the patient end of the venous line  108  is attached to a drain bucket (not shown). During the priming process, the arterial line  106  and the venous line  108  are not connected to the patient (as depicted in  FIG. 3 ). Rather, during the priming process, a first end of the arterial line  106  and a first end of the venous line  108  are coupled to the blood circuit  300 , and a second end the arterial line  106  and a second end of the venous line  108  are coupled to a drain or a drain bucket (not pictured). 
     To begin priming the system  300 , saline is introduced from the saline bag  138  into the blood circuit  300  via the arterial line  106 . To draw the saline from the saline bag  138  through the arterial line  106  and into the blood circuit  300 , the blood pump  128  is turned on. The blood pump  128  draws the saline from the saline bag  138 , through saline line  126  and the arterial line  106 , through the pressure transducer  325   a,  through fluid flow sensor  340   a,  into and fills the arterial drip chamber  324 . Once the arterial drip chamber  324  is filled (as detected by pressure transducer  325   a ), clamp  338   f  is automatically opened and the blood pump  128  draws saline through the pump line  318  towards the dialyzer  110 . The saline flows into the dialyzer  110  via the dialyzer inlet line  334  and exits the dialyzer  110  via the dialyzer outlet line  336 . 
     As the saline flows through the dialyzer outlet line  336  towards the venous drip chamber  332 , the saline passes through the pressure transducer  325   b  and fluid flow sensor  340   b.  The saline flows into and fills the venous drip chamber  332 . Once the venous drip chamber  332  is filled with saline (as detected by pressure transducer  325   b ), clamp  338   g  is automatically opened and saline flows through the venous line  108  towards the patient end of the venous line  108 . Once the entire blood circuit  300  is filled with saline, any additional (e.g., excess) saline pumped through the blood component set  104  exits the patient end of the venous line  108  and is captured by a drain bucket. Once all air is out of the arterial and venous lines  106 ,  108  and the blood circuit  300  is filled with saline, clamps  338   c  and  338   d  are closed, and the arterial line  106  and the venous line  108  are connected together via a sterile recirculation connector, and the saline contained within the blood circuit  300  is recirculated through the blood circuit  300  until the patient  302  is ready for treatment. 
     Before performing the hemodialysis treatment, the operator opens the door  174  of the warming chamber  170  and couples the saline-filled syringes  160 ,  162  to the warming chamber  170  by attaching the syringes  160 ,  162  to the clips  180 ,  182 ,  184 ,  186  of the warming chamber  170 , as depicted in  FIG. 2 . Once the syringes  160 ,  162  are positioned in the warming chamber  170  using the clips  180 ,  182 ,  184 ,  186 , the operator closes the door  174  of the warming chamber  170  (as depicted in  FIG. 1 ). The heating element  178  is automatically turned on once the door  174  of the warming chamber  170  is in the closed position (as depicted in  FIG. 1 ). For example, the machine  102  can include a switch that is triggered when closing the door to activate the heating element  178 . Once the heating element  178  has been turned on, the heating element begins to warm the interior of the warming chamber  170 , which warms the saline contained in the syringes  160 ,  162 . 
     The operator then connects the arterial access line  116  to the arterial needle assembly  326  and connects the venous access line  118  to the venous needle assembly  334 . Once the access lines  116 ,  118  are connected to the needle assemblies  326 ,  334 , the operator inserts the arterial needle  327  into an arterial access  346  of the patient  302 , and inserts the venous needle  335  into a venous access  348  of the patient  302 . The operator then removes any air contained in the access lines  116 ,  118 . In some implementations, air contained in the access lines is removed by connecting an empty syringe (not shown) to the end of each of the access lines  116 ,  118  opposite the needle assemblies  326 ,  334 , and actuating the plunger of each empty syringe to draw blood into the access lines  116 ,  118  to displace any air contained in the access lines  116 ,  118 . In some implementations, the blood pressure of the patient  302  is used to draw blood into the access lines  116 ,  118  to displace any air contained in the access lines  116 ,  118 . In some implementations, the access lines  116  are filled with saline using a syringe prior to inserting the needle assemblies  326 ,  334  into the patient  302  in order to remove air from the access lines  116 ,  118 . Once the access lines  116 ,  118  are filled with fluid (e.g., blood or saline), the access lines  116 ,  118  are clamped using clamps  338   a  and  338   e,  respectively. 
     Once the blood circuit  300  has been primed and the access lines  116 ,  118  have been fluidly coupled to the patient and clamped, the arterial access line  116  is coupled to the arterial line  106  via connectors  120   a,    120   b,  and the venous access line  118  is coupled to the venous line  108  via connectors  122   a,    122   b.  Connectors  120   a,    120   b,    122   a,  and  122   b  can include any suitable type of connector, such as luer-lock connectors. Once the access lines  116 ,  118  have been attached to the arterial line  106  and venous line  108 , hemodialysis is initiated. 
     Referring to  FIGS. 3 and 4 , a method of performing dialysis treatment using the hemodialysis system  100  will now be described. The operator initiates the hemodialysis treatment using a control on touchscreen  151 . During the hemodialysis treatment, the blood pump  128  is operated to circulate blood through the dialyzer  110 . A controller of the hemodialysis machine  102  can be used to control the blood pump  128  through feedback control based on pressures detected by the pressure transducers  325 ,  325   b  or based on flow rates detected by the fluid flow sensors  340   a,    340   b.  The blood pump  128  is driven such that blood in the arterial line set  104  is drawn from the patient  302  and directed toward the dialyzer  110 , and through the venous line set  108  back into the patient  302 . 
     Referring to  FIG. 4 , the dialysis flow pump  495  is operated to circulate dialysis fluid through the dialyzer  110  during hemodialysis treatment. Waste substances from the blood diffuse into the dialysis fluid. In addition, in some implementations, the ultrafiltration pump  497  is operated to draw excess fluid from the extracorporeal blood circuit  300  into the dialysate circuit  400  and to the drain. 
     After the end of the extracorporeal treatment, an operation to deactivate the blood pump  128 , the dialysis fluid pump  495 , and the ultrafiltration pump  497  is initiated. For example, a controller of the hemodialysis machine  102  can automatically stop the extracorporeal treatment after predetermined criteria are fulfilled, e.g., a certain amount of time has elapsed or a certain amount of ultrafiltrate has been removed from the blood. 
     After the operation of the pumps  128 ,  495 ,  497  has been stopped, blood drawn from the patient  302  during the hemodialysis treatment may be present in the arterial line set  304  and the venous line set  308 . A blood reinfusion process is used to return the blood contained in the arterial line  106  and the venous line  108  is to the patient  302  through the venous access  348  of the patient  302 . Before the blood reinfusion process is initiated, each of the clamps  138   a  and  338   b  is closed to inhibit flow through the arterial needle assembly  326 , and the arterial access line  116  is disconnected from the arterial line  106 . Clamp  338   c  is opened to fluidly connect the arterial line  106  to the saline line  126  and allow saline to flow from the saline bag  138  into and through the blood circuit  300 . 
     Once the saline line  126  is fluidly connected to the blood circuit  300 , the blood pump  128  is operated to draw the saline from the saline bag  138  and circulate the saline throughout all components of the blood circuit  300  to push any blood remaining in the blood circuit  300  back to the patient  302  and fill the blood circuit  300  with saline. The blood contained in the blood circuit  300  is returned to the patient  302  through the venous needle assembly  334  and enters the patient  302  through the venous access  348 . Once the majority of the blood contained in the blood circuit  300  has been reinfused back to the patient  302 , clamps  338   d  and  338   e  are closed to clamp the venous line  108  and venous access line  118 , respectively. Once clamped, the venous access line  118  is disconnected from the venous line  108 . 
     While the reinfusion process described above flushes the majority of the blood contained within the venous access line  118  and the venous needle assembly  334  back to the patient  302 , a small amount of blood is still typically contained in the venous access line  118  and venous needle assembly  334 . In addition, as the arterial access line  116  and arterial needle assembly  326  were disconnected from the blood circuit  300  prior to reinfusion, the arterial access line  116  and arterial needle assembly  326  still typically contain blood. In order to flush and care for the patient&#39;s arterial access  346  and venous access  348 , an additional flushing process using syringes  160 ,  162  is performed. 
     The access line flushing process will now be described with reference to  FIGS. 2 and 3 . With the arterial access line  116  clamped via clamp  338   a,  one of the syringes  160  is removed from the warming chamber  170  and attached to the end of the arterial access line  116 . As previously discussed, the heating element  178  of the warming chamber  170  is turned on before beginning the hemodialysis treatment. As a result, the saline contained within the syringes  160 ,  162  in the warming chamber  170  is at a temperature ranging between about 30 degrees Celsius to about 38 degrees Celsius (e.g., 36.5 degrees Celsius to 37.5 degrees Celsius) by the end of the hemodialysis treatment. 
     Once the syringe  160  containing the warm saline is attached to the arterial access line  116 , the plunger of the syringe  160  is depressed to flow the warm saline contained in the syringe  162  through the arterial access line  116 , through the arterial needle assembly  326 , and into the arterial access  346  of the patient  302 . The warm saline provided by the syringe  160  flushes any remaining blood in the arterial access line  116 , arterial needle assembly  326 , and arterial access  346  (e.g., arterial port) back to the patient  302 , which reduces the risk of clotting or infection at the arterial access  346 . After flushing the arterial access line  116 , the arterial needle assembly  326  can be disconnected from the patient  302 . 
     With the venous access line  118  clamped using clamp  338 e, the remaining syringe  162  is removed from the warming chamber  170  and attached to the end of the venous access line  118 . As previously discussed, the saline contained within the syringe  162  is heated throughout the hemodialysis treatment by the heating element  178  to a temperature ranging between about 30 degrees Celsius to about 38 degrees Celsius (e.g., 36.5 degrees Celsius to 37.5 degrees Celsius). 
     Once the syringe  162  containing the warm saline is attached to the venous access line  118 , the plunger of the syringe  162  is depressed to flow the warm saline contained in the syringe  162  through the venous access line  118 , through the venous needle assembly  334 , and into the venous access  348  of the patient  302 . The warm saline provided by the syringe  162  flushes any remaining blood in the venous access line  118 , venous needle assembly  334 , and venous access  348  (e.g., venous port) back to the patient  302 , which prevents clotting or infection at the venous access  348 . After flushing the venous access line  118 , the venous needle assembly  334  can be disconnected from the patient  302 . 
     While certain embodiments have been described above, other embodiments are possible. 
     For example, while the heating element  178  of the warming chamber  170  illustrated in  FIGS. 1 and 2  has been described as being coupled to the interior of the door  174  of the warming chamber  170 , alternatively, the heating element  178  may be positioned at the bottom of the warming chamber  170  such that the heating element  178  is below the syringes  160 ,  162  positioned in the warming chamber  170  via clips  180 ,  182 ,  184 ,  186 . In some implementations, the heating element  178  is positioned on a wall of the housing  172  of the warming chamber  170 . For example, in some implementations, the heating element  178  is coupled to a rear wall of the housing  172  of the warming chamber  170  such that the heating element  178  is behind the syringes  160 ,  162  positioned in the warming chamber  170  via clips  180 ,  182 ,  184 ,  186 . For example, the heating element  178  can be positioned on the rear wall of the housing  172  of the warming chamber  170  between clips  182  and  184 . 
     Further, while the method for warming the fluid in the syringes has been described as automatically turning on the heating element  178  in response to closing the door  174  of the warming chamber before starting hemodialysis treatment, alternatively, the heating element  178  may be turned at other times during the treatment and reinfusion process, such as after completing hemodialysis treatment and at the start of reinfusion process. In addition, in some examples, an operator of the dialysis machine turns on the heating element  178  of the warming chamber  170  using a control provided on the touchscreen  151  of the hemodialysis machine. 
     While the temperature of the fluid used to flush the access lines  116 ,  118  has been described as being 30 degrees Celsius or more, it should be understood that the fluid could be warmed to lesser temperatures. Any temperature greater than room temperature can, for example, have a positive impact on the comfort of the patient. 
     In addition, while the dialysate circuit  400  has been described as including two dialysate filters  474 ,  480 , in some examples, the dialysate circuit may only include a single dialysate filter. 
     While the warming chamber  170  has been described as including clips  180 ,  182 ,  184 ,  186  to position and retain the syringes  160 ,  162  in the warming chamber  170 , other mechanical attachment devices, such as clamps, ties, straps, hooks, latches, etc., can alternatively or additionally be used to couple the syringes  160 ,  162  to the warming chamber  170 . For example, in some implementations, rubber elements are used to couple the syringes  160 ,  162  to the warming chamber  170 . 
     While the temperature sensors  188 ,  190  have been described as being positioned on the interior wall of the housing  172  of the warming chamber  170  proximate the syringes  160 ,  162  to measure the temperature of the warming chamber  170 , alternatively the temperature sensors  188 ,  190  can be positioned to directly contact the exterior of the syringes  160 ,  162  in order to measure the temperature of the surface of the syringes  160 ,  162 . An algorithm correlating the temperature of the surface of the syringes  160 ,  162  with the temperature of saline contained within the syringes  160 ,  162  can be used to determine the temperature of the saline in the syringes  160 ,  162 . 
       FIG. 5  is a schematic showing an alternate arrangement of the warming chamber of the hemodialysis machine  102 . As shown in  FIG. 5 , the warming chamber  570  includes a door  574  that can be opened to provide access to saline-filled syringes  160 ,  162  positioned in the warming chamber  570 . The door  574  is coupled to the dialyzer  110  of the hemodialysis machine  102  with a hinge  576 . Door  574  includes an insulating material, such as plastic, fiberglass, aerogel, cellulose, or polyurethane. For example, the interior surface of the door  574  can include an insulating material to help retain heat within the warming chamber when the door  574  is in a closed position (as depicted in  FIG. 5 ). 
       FIG. 6  depicts the door  574  of the warming chamber  570  in an open position. As depicted in  FIG. 6 , the warming chamber  570  includes a holder  570  with a set of clips  580 ,  582 ,  584 ,  586 . The syringes  160 ,  162  are positioned adjacent to the dialyzer  110  through attachment to the clips  580 ,  582 ,  584 ,  586  of the holder  572 . The clips  580 ,  582 ,  584 ,  586  of the warming chamber  570  are each coupled to the housing of the dialyzer  110  and configured to couple and position the syringes  160 ,  162  against the dialyzer  110 . In some examples, the dialyzer machine includes a grip configured to couple and position the dialyzer  110  relative to the hemodialysis machine  102 , and the grip can include receptacles for receiving the syringes  160 ,  162  and positioning the syringes  160 ,  162  adjacent the housing of the dialyzer  110 . In some examples, the syringes  160 ,  162  may be positioned adjacent the housing  110  of the dialyzer using a strap. The strap for positioning the syringes  160 ,  162  adjacent the housing of the dialyzer  110  may be made of any suitable material, such as metal, fabric, or rubber, and may include any suitable fastening device, such as magnets, hook and loop fasteners, or snaps. In some examples, the straps used to position the syringes  160 ,  162  adjacent the housing of the dialyzer  110  can include slots for inserting the syringes  160 ,  162  through the strap. 
     As previously discussed with reference to  FIG. 4 , the water used to generate substitution fluid is heated by a heat exchanger of the dialysate circuit  400  prior to entering the dialyzer  110 . In addition, the blood entering the dialyzer  110  from the blood circuit  300  is approximately body temperature. Thus, the fluid flowing through the dialyzer  101  is warm (about 35 degrees Celsius to about 39 degrees Celsius). The heat radiated from the fluids flowing through the dialyzer  110  is transferred to the surface of the dialyzer  110 . As a result, when the syringes  160 ,  162  are positioned against the surface of the dialyzer  110  via clips  580 ,  582 ,  584 ,  586 , the heat radiating from the fluid passing through the dialyzer  110  serves to warm the saline contained within the syringe  160 ,  162 . The insulated door  574  of the warming chamber  570  covers the syringes  160 ,  162  and helps retain the heat transferred from the dialyzer  110  to the syringes  160 ,  162  within the warming chamber  570 . Therefore, by positioning the syringes  160 ,  162  against the dialyzer  110  during hemodialysis and covering the syringes  160 ,  162  with the door  574  of the warming chamber  570 , the saline contained in the syringes  160 ,  162  is heated by the heat radiated from the dialyzer  110 . In some examples, the saline in the syringes  160 ,  162  is heated to a temperature ranging from about 30 degrees Celsius to about 38 degrees Celsius. By utilizing the heat radiated from the dialyzer  110  during hemodialysis, the warming chamber  570  warms the saline in the syringes  160 ,  162  without requiring an extra heat source, and, thus, uses less energy to heat the saline used for flushing the access lines  116 ,  118 . 
     While the door  574  of the warming chamber  570  is depicted as being coupled to the dialyzer  110  via a hinge  576 , other arrangements are possible. For example, the door  574  can be coupled to the dialyzer  100  using a pair of clips attached to the dialyzer  110  configured to couple to the sides of the door  574 . In some implementations, the door  574  can be positioned over the syringes  160 ,  162  and a strap can be used to wrap around the door  574  and dialyzer  110  to hold the door  574  against the syringes  160 ,  162 . In some implementations, the warming chamber  570  is provided as a thermal pod with a flap that may be opened to access syringes  160 ,  162  contained in the thermal pod and closed to retain heat within the thermal pod. 
       FIG. 7  is a schematic showing an alternate arrangement of the warming chamber of the hemodialysis machine  102 . As shown in  FIG. 7 , the warming chamber  770  includes a door  774  that can be opened to provide access to saline-filled syringes  160 ,  162  positioned in the warming chamber  770 . The door  774  is coupled to the side of the hemodialysis machine  102  via hinge  776 . As depicted in  FIG. 7 , a portion of the dialysate inlet line  450  of the dialysate circuit  400  is positioned along a side  708  of the hemodialysis machine  102 . The door  774  of the warming chamber  770  is attached to the hemodialysis machine  102  such that the door  774  is positionable to cover a portion of the dialysate inlet line  450 . Door  774  includes an insulating material, such as plastic, fiberglass, aerogel, cellulose, polyurethane, or fabric with infrared reflecting surface (e.g., aluminum foil). For example, the interior surface of the door  774  can be covered with an insulating material to help retain heat within the warming chamber  770  when the door  774  is in a closed position (as depicted in  FIG. 7 ). 
       FIG. 8  depicts the warming chamber  770  with the door  774  of the warming chamber  770  in an open position. As depicted in  FIG. 8 , the warming chamber  770  includes holder  772  a set of clips  780 ,  782 ,  784 ,  786 , and the syringes  160 ,  162  are positioned against the dialysate inlet line  450  through attachment to the clips  780 ,  782 ,  784 ,  786 . The clips  780 ,  782 ,  784 ,  786  of the warming chamber  770  are each coupled to the dialysate inlet line  450  and configured to couple and position the syringes  160 ,  162  against the dialysate inlet line  450 . In some examples, the syringes  160 ,  162  may be positioned adjacent the dialysate inlet line  450  using a strap. The strap for positioning the syringes  160 ,  162  adjacent the dialysate inlet line  450  may be made of any suitable material, such as metal, fabric, or rubber, and may include any suitable fastening device, such as magnets, hook and loop fasteners, or snaps. In some examples, the straps used to position the syringes  160 ,  162  against the dialysate inlet line  450  can include slots for inserting the syringes  160 ,  162  through the strap. 
     As previously discussed with reference to  FIG. 4 , water used the generate substitution fluid is heated by a heat exchanger of the dialysate circuit  400  prior to entering the dialyzer  110  through the dialysate inlet line  450 . Thus, the substitution fluid flowing through the dialysate inlet line  450  is warm (about 35 degrees Celsius to about 39 degrees Celsius). The heat from the substitution fluid flowing through the dialysate inlet line  450  is transferred to the surface of the dialysate inlet line  450 . As a result, when the syringes  160 ,  162  are positioned against the dialysate inlet line  450  via clips  780 ,  782 ,  784 ,  786 , the heat radiating from the substitution fluid passing through the dialysate inlet line  450  serves to warm the saline contained within the syringe  160 ,  162 . The insulated door  774  of the warming chamber  770  helps retain the heat transferred from the dialysate inlet line  450  to the syringes  160 ,  162  in the warming chamber  770 . As a result, by positioning the syringes  160 ,  162  against the dialysate inlet line  450  during hemodialysis and covering the syringes  160 ,  162  with the door  774  of the warming chamber  770 , the saline contained in the syringes  160 ,  162  is heated by the heat radiated from the dialysate inlet line  450 . In some examples, the saline in the syringes  160 ,  162  is heated to a temperature ranging from about 30 degrees Celsius to about 38 degrees Celsius. By utilizing the heat radiated from the dialysate inlet line  450  during hemodialysis, the warming chamber  770  warms the saline in the syringes  160 ,  162  without requiring an extra heat source, and, thus, uses less energy to heat the saline used for flushing the access lines  116 ,  118 . 
     While the door  774  of the warming chamber  770  is depicted as being coupled to the side of the hemodialysis machine  102  via a hinge  776 , other arrangements are possible. For example, the door  774  can be coupled to the hemodialysis machine  102  using a pair of clips attached to the side of the hemodialysis machine  102  proximate the dialysate inlet line  450 , with the clips being configured to couple to the sides of the door  774 . In some implementations, the door  774  can be positioned along dialysate inlet line  450  and a strap can be used to wrap around the door  774  and dialysate inlet line  450  to hold the door  774  against the syringes  160 ,  162 . 
     Further, while the warming chamber  770  is depicted as being coupled to the dialysate inlet line  450 , in some implementations, the warming chamber  770  is coupled to the dialysate outlet line  452 . As depicted in  FIG. 7 , a portion of the dialysate outlet line  452  is positioned along a side  708  of the hemodialysis machine. In some examples, the clips  780 ,  782 ,  784 ,  786  of the warming chamber  770  can be coupled to the dialysate outlet line  452  and configured to couple and position the syringes  160 ,  162  against the dialysate outlet line  452 . Further, the door  774  of the warming chamber  770  can be attached to the hemodialysis machine  102  such that the door  774  is positionable to cover a portion of the dialysate outlet line  452 . As with the dialysate inlet line  450 , the substitution fluid flowing through the dialysate outlet line  452  has heated by a heat exchanger of the dialysate circuit  400 . Therefore, by utilizing the heat radiated from the dialysate outlet line  452  during hemodialysis, the warming chamber  770  positioned along the dialyzer outlet line  452  warms the saline in the syringes  160 ,  162  without requiring an extra heat source, and, thus, uses less energy to heat the saline used for flushing the access lines  116 ,  118 . 
     While the syringes  160 ,  162  have been described as being pre-filled with saline prior to placement in the warming chamber  170  of the hemodialysis machine  102 , the syringes can alternatively be filled with saline after being positioned in the warming chamber. 
     For example,  FIG. 9  depicts an arrangement in which the syringes  960 ,  962  are fluidly coupled to the saline line  126  of the hemodialysis machine  102  for filling the syringes  960 ,  962  with saline. As depicted in  FIG. 9 , the syringes  960 ,  962  are positioned in the warming chamber  770  and a fluid line  902  connects each of the syringes  960 ,  962  to the saline line  126 . 
     A method of filling the syringes  970 ,  972  with saline from the saline line  126  will now be described with reference to  FIG. 9 . After priming the hemodialysis machine  102 , the syringes  960 ,  962  are positioned within the warming chamber  170  using clips  180 ,  182 ,  184 ,  186 , and an end of each syringe is coupled to the fluid line  902 . A connector  904  is attached to an end of the fluid line  902  to fluidly couple the fluid line  902  to the saline line  126  of the hemodialysis machine  102 . Once the syringes  960 ,  962  are positioned within the warming chamber  170  and fluidly coupled to the saline line  126  via fluid line  902 , the motor of the blood pump  128  of the hemodialysis machine is run in reverse, causing increased pressure in the saline line  126  and thus filling the syringes  960 ,  962  with saline from the saline line  126 . Once the syringes  960 ,  962  have been filled with saline from the saline line  126 , the heating element  178  can be turned on to warm the saline in the syringes  960 ,  962 , and the hemodialysis treatment and reinfusion can proceed as described above. 
       FIG. 10  depicts an arrangement in which syringes  1060 ,  1062  are fluidly coupled to the substitution line  486  of the hemodialysis machine  102  for filling the syringes  1060 ,  1062  with saline. As depicted in  FIG. 9 , the syringes  1060 ,  1062  are positioned in the warming chamber  770  and a fluid line  1002  connects each of the syringes  960 ,  962  to the substitution fluid line  486 . 
     A method of filling the syringes  1060 ,  1062  with saline from the substitution fluid line  485  will now be described with reference to  FIGS. 4 and 10 . After priming the hemodialysis machine  102 , the syringes  1060 ,  1062  are positioned within the warming chamber  170  using clips  180 ,  182 ,  184 ,  186  and an end of each syringe is coupled to the fluid line  1002 . A connector  1004  is attached to an end of the fluid line  1002  to fluidly couple the fluid line  1002  to the substitution fluid line  486  of the hemodialysis machine  102 . Once the syringes  1060 ,  1062  are positioned within the warming chamber  170  and fluidly coupled to the substitution fluid line  486  via fluid line  1002 , the substitution pump  488  of the hemodialysis machine  102  is run to draw substitution fluid generated by the dialysate circuit  400  through the substitution fluid line  486  and the fluid line  1002 , causing increased pressure in the substitution fluid line  486  and thus filling the syringes  1060 ,  1062  with substitution fluid. In some examples, the plungers of the syringes  1060 ,  1062  can be withdrawn manually by an operator of the hemodialysis machine  102  to fill the syringes  1060 ,  1062  with substitution fluid from the substitution fluid line  486 . Once the syringes  1060 ,  1062  have been filled with substitution fluid from the substitution fluid line  486 , the substitution pump  488  is turned off and the heating element  178  is turned on to warm the substitution fluid contained in the syringes  1060 ,  1062 , and hemodialysis treatment and reinfusion can proceed as described above. 
     Further, while  FIG. 10  depicts the syringe  1060 ,  1062  being positioned in a warming chamber  170  and the fluid in the syringes  1060 ,  1062  being warmed by a heating element  178  of the warming chamber  170 , alternatively, the syringes  1060 ,  1062  can be filled with warm substitution fluid directly from the hemodialysis machine  102  without requiring additional heating from a warming chamber. For example, following hemodialysis treatment, the syringes  1060 ,  1062  can be fluidly coupled to the substitution fluid line  486  via a fluid line  1002  and the substitution pump  486  of the dialysate circuit  400  can be run to deliver warm substitution fluid from the dialysate circuit  400  to the syringes  1060 ,  1062  via the substitution fluid line  486  and the fluid line  1002 . As previously discussed, the water used to generate substitution fluid is warmed by a heat exchanger of the dialysate circuit  400  before being provided to the substitution fluid line  486 . Therefore, the substitution fluid provided by the substitution fluid line  486  is already warm (e.g., about 34 degrees Celsius to about 39 degrees Celsius). Since the process of reinfusion and flushing the access lines  116 ,  118  is performed immediately following hemodialysis treatment, the substitution fluid provided to the syringes  1060 ,  1062  via the substitution fluid line  486  following treatment would still be warm during reinfusion and flushing of the access lines. Therefore, a warming chamber to warm the fluid in the syringes  1060 ,  1062  is not necessary when the syringes  1060 ,  1062  are filled with substitution fluid directly from the substitution line  486  following hemodialysis treatment. 
     While the hemodialysis system  100  has been described as including a pair of syringes  160 ,  162  to store fluid for flushing the access lines  116 , other fluid receptacles, can alternatively or additionally be used to store fluid for flushing the access lines  116 ,  118 . In some implementations, one or more fluid-filled bags are used to store the fluid for flushing the access lines  116 ,  118 , and the warming chamber  170  is configured to couple to the one or more bags and warm the fluid contained in the bags. In some examples, a single fluid-filled syringe is used to flush both of the access lines  116 ,  118 . In some implementations, three or more fluid-filled syringes are used to flush the access lines  116 ,  118 . 
     Further, in some implementations, rather than flushing the access lines  116 ,  118  with fluid contained in a fluid receptacle, such as a syringe, the access lines  116 ,  118  are connected to the substitution fluid line  486  and flushed with substitution fluid provided by the substitution fluid line  486 . For example, as depicted in  FIG. 11 , following hemodialysis treatment and reinfusion, the arterial access line  116  and the venous access line  118  can be coupled to the substitution fluid line  486  via a connector  1102 . Once the access lines  116 ,  118  are fluidly coupled to the substitution fluid line  486  via the connector  1102 , the substitution pump  488  of the dialysate circuit  400  is run to draw warm substitution fluid from the dialysate circuit  400  through the substitution fluid line  486  and connector  1102 , and into the access lines  116 ,  118 . As previously discussed with reference to  FIG. 4 , the water used to generate the substitution fluid is heated by a heat exchanger of the dialysate circuit  400  prior to the substitution fluid entering the substitution fluid line  486 . Therefore, the substitution fluid provided to the access lines  116 ,  118  via the substitution fluid line  486  is already warm (e.g., about 34 degrees Celsius to about 39 degrees Celsius). 
     While  FIG. 11  depicts the access lines  116 ,  118  being connected to the substitution line simultaneously using a connector  1102 , alternatively, the arterial access line  116  and the venous access line  118  can each be individually connected to the substitution fluid line  486  and flushed with substitution fluid individually. For example, following hemodialysis treatment, clamps  338   a  and  338   e  are closed to clamp the arterial access line  116  and venous access line  118 , respectively, and the end of the arterial access line  116  can be fluidly coupled to the substitution fluid line  486 . Once the arterial access line  116  is fluidly coupled to the substitution fluid line  486 , clamp  338   a  is opened to allow flow through the arterial access line  116 , and the substitution pump  488  of the dialysate circuit  400  is turned on to draw warm substitution fluid from the dialysate circuit  400  through the substitution fluid line  486  into the arterial access line  116  to flush the arterial access line  116  and arterial needle assembly  326 . After flushing the arterial access line  116  and arterial needle assembly  326  of any remaining blood, the substitution pump  488  is turned off, the arterial access line  116  is detached from the substitution fluid line  486 , and the arterial needle assembly  326  is removed to patient  302 . 
     The venous access line  118  is then fluidly coupled to the substitution fluid line  486  and clamp  338   e  is opened to allow fluid to flow through the venous access line  118 . The substitution pump  488  of the dialysate circuit  400  is turned on to draw warm substitution fluid from the dialysate circuit  400  through the substitution fluid line  486  into the venous access line  118  to flush the venous access line  118  and venous needle assembly  334 . After flushing the venous access line  118  and venous needle assembly  334  of any remaining blood, the substitution pump  488  is turned off, the venous access line  118  is detached from the substitution fluid line  486 , and the venous needle assembly  334  is removed to patient  302 . 
     While the process of flushing the access line  116 ,  118  via direct connection of the access lines  116 ,  118  to the substitution fluid line  486  is described as flushing the arterial access line  116  before flushing the venous access line  118 , alternatively, the venous access line  118  can be flushed prior to flushing the arterial access line  116 . 
     A number of embodiments have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the disclosure. Accordingly, other embodiments are within the scope of the following claims.