PATENT DOCUMENT

Abstract:
A regenerative peritoneal dialysis system includes a dialysis fluid loop; a filter located in the dialysis fluid loop, a first portion of the dialysis fluid sent to the filter rejected by the filter and returned upstream of the filter, a second portion of the dialysis fluid sent to the filter forming permeate, the permeate being rich in urea; and a urea removing apparatus located in the dialysis fluid loop downstream from the filter to receive the permeate and absorb urea from the permeate.

Full Description:
PRIORITY CLAIM 
     This application claims priority to and the benefit of U.S. patent application Ser. No. 10/623,316, filed Jul. 17, 2003, entitled “Systems And Methods For Performing Peritoneal Dialysis”, which claims priority to and the benefit of U.S. Provisional Patent Application Ser. No. 60/397,131, filed Jul. 19, 2002, entitled “Systems And Methods For Performing Peritoneal Dialysis,” the entire contents of which are hereby incorporated by reference and relied upon. 
    
    
     BACKGROUND 
     The present invention generally relates to dialysis systems. More specifically, the present invention relates to regeneration dialysis systems and continuous flow dialysis systems. The present invention also relates to methods of performing dialysis therapies. 
     Due to disease, insult or other causes, a person&#39;s renal system can fail. In renal failure of any cause, there are several physiological derangements. The balance of water, minerals and the excretion of daily metabolic load is no longer possible in renal failure. During renal failure, toxic end products of nitrogen metabolism (urea, creatinine, uric acid, and others) can accumulate in blood and tissues. 
     Kidney failure and reduced kidney function have been treated with dialysis. Dialysis removes waste, toxins and excess water from the body that would otherwise have been removed by normal functioning kidneys. Dialysis treatment for replacement of kidney functions is critical to many people because the treatment is life saving. One who has failed kidneys could not continue to live without replacing at least the filtration functions of the kidneys. 
     Hemodialysis and peritoneal dialysis are two types of dialysis therapies commonly used to treat loss of kidney function. Hemodialysis treatment utilizes the patient&#39;s blood to remove waste, toxins and excess water from the patient. The patient is connected to a hemodialysis machine and the patient&#39;s blood is pumped through the machine. Catheters are inserted into the patient&#39;s veins and arteries to connect the blood flow to and from the hemodialysis machine. As blood passes through a dialyzer in the hemodialysis machine, the dialyzer removes the waste, toxins and excess water from the patient&#39;s blood and returns the blood to infuse back into the patient. A large amount of dialysate, for example about 120 liters, is used to dialyze the blood during a single hemodialysis therapy. The spent dialysate is then discarded. Hemodialysis treatment lasts several hours and is generally performed in a treatment center about three or four times per week. 
     One type of hemodialysis therapy is regenerative hemodialysis. This therapy uses a hemodialysis system, which includes a cartridge for dialysate regeneration. One such cartridge is manufactured under the name REDY™ by Sorb Technology, Oklahoma City, Okla. In this system, the dialysate fluid flow path must be properly cleaned before the hemodialysis machine can be used on another patient. Also, the dialysate fluid flow path is not a closed system, i.e., the dialysate fluid flow path is open to the atmosphere, such that oxygen from the atmosphere can contact fluid in the system and foster the growth of bacteria in same. Consequently, contamination of such a dialysis system can be a concern. Further, the dialysate fluid exiting the REDY™ cartridge is not suitable for peritoneal dialysis because the fluid is relatively acidic and not, therefore, physiologic. Moreover, this system requires the attention of medical personnel during therapy. 
     Peritoneal dialysis utilizes a sterile, pyrogen free dialysis solution or “dialysate”, which is infused into a patient&#39;s peritoneal cavity. The dialysate contacts the patient&#39;s peritoneal membrane in the peritoneal cavity. Waste, toxins and excess water pass from the patient&#39;s bloodstream through the peritoneal membrane and into the dialysate. The transfer of waste, toxins, and water from the bloodstream into the dialysate occurs due to diffusion and osmosis, i.e., an osmotic gradient occurs across the membrane. The spent dialysate drains from the patient&#39;s peritoneal cavity and removes the waste, toxins and excess water from the patient. This cycle is repeated on a semi-continuous or continuous basis. 
     There are various types of peritoneal dialysis therapies, including continuous ambulatory peritoneal dialysis (“CAPD”) and automated peritoneal dialysis. CAPD is a manual dialysis treatment, in which the patient connects an implanted catheter to a drain and allows a spent dialysate fluid to drain from the peritoneal cavity. The patient then connects the catheter to a bag of fresh dialysate and manually infuses fresh dialysate through the catheter and into the patient&#39;s peritoneal cavity. The patient disconnects the catheter from the fresh dialysate bag and allows the dialysate to dwell within the cavity to transfer waste, toxins and excess water from the patient&#39;s bloodstream to the dialysate solution. After a dwell period, the patient repeats the manual dialysis procedure. 
     In CAPD the patient performs several drain, fill, and dwell cycles during the day, for example, about four times per day. Each exchange or treatment cycle, which includes a drain, fill and dwell, takes about four hours. Manual peritoneal dialysis performed by the patient requires a significant amount of time and effort from the patient. This inconvenient procedure leaves ample room for improvement and therapy enhancements to improve patient quality of life. 
     Automated peritoneal dialysis is similar to continuous peritoneal dialysis in that the dialysis treatment includes a drain, fill, and dwell cycle. However, a dialysis machine automatically performs three to four cycles of peritoneal dialysis treatment, typically overnight while the patient sleeps. 
     With automated peritoneal dialysis, an automated dialysis machine fluidly connects to an implanted catheter. The automated dialysis machine also fluidly connects to a source or bag of fresh dialysate and to a fluid drain. The dialysis machine pumps spent dialysate from the peritoneal cavity, though the catheter, to the drain. The dialysis machine then pumps fresh dialysate from the dialysate source, through the catheter, and into the patient&#39;s peritoneal cavity. The automated machine allows the dialysate to dwell within the cavity so that the transfer of waste, toxins and excess water from the patient&#39;s bloodstream to the dialysate solution can take place. A computer controls the automated dialysis machine so that the dialysis treatment occurs automatically when the patient is connected to the dialysis machine, for example, when the patient sleeps. That is, the dialysis system automatically and sequentially pumps fluid into the peritoneal cavity, allows for dwell, pumps fluid out of the peritoneal cavity, and repeats the procedure. 
     Several drain, fill, and dwell cycles will occur during the treatment. Also, a “last fill” is often used at the end of the automated dialysis treatment, which remains in the peritoneal cavity of the patient when the patient disconnects from the dialysis machine for the day. Automated peritoneal dialysis frees the patient from having to manually performing the drain, dwell, and fill steps. Automated dialysis can improve the patient&#39;s dialysis treatment and undoubtedly improves the patient&#39;s quality of life. 
     So-called “continuous flow” peritoneal dialysis (“CFPD”) systems that purport to provide continuous dialysate flow exist. However, these systems typically have a single pass fluid flow. That is, the dialysate flows into, through, and out of the peritoneal cavity one time before being sent to a drain. The “spent” dialysate (waste laden dialysate) from the patient collects in a drain bag, which is discarded, or runs into a household drain or other drain. Known CFPD systems, therefore, typically use a volume of disalysate one time and then discard it. That is, the systems have no ability to regenerate or reuse a quantity of dialysate. 
     The effectiveness of existing peritoneal dialysis therapies, and existing systems which perform the therapies, depends upon the amount of dialysis fluid used. For example, typical peritoneal dialysis therapy requires about 4 to 6 exchanges of dialysate (drain, fill, dwell) with about 2 to 3 liters of dialysate for each exchange. Peritoneal dialysis is a daily therapy performed 7 days per week. As a consequence, 240 to 540 liters of fresh dialysate must be delivered to and stored at a patient&#39;s home each month. Increasing dialysate dosage to increase therapy effectiveness will necessitate even more dialysate. 
     Therefore, needs exist to provide improved dialysis systems and methods of performing dialysis. Particularly, needs exist to provide closed loop peritoneal dialysis systems and methods that regenerate or reuse spent dialysate. There are needs for such systems and methods to be compatible with CFPD treatment so that patients can perform the procedure at home without the need for storing an inordinate amount of fresh dialysate bags. There are further needs for such systems and methods to be automated so that the procedure can be largely performed at night while the patient sleeps. 
     SUMMARY 
     Generally, the present invention provides improved dialysis systems and improved methods of performing dialysis. More particularly, the present invention provides systems and methods for continuous flow dialysis (“CFD”) and regenerative dialysis, and in combination, continuous flow regenerative dialysis (“CFRD”). This invention also includes improved systems and methods for performing hemodialysis. 
     The dialysis system of the present invention automatically performs dialysis therapy on a patient, for example, during nighttime while the patient sleeps. The present invention automatically regenerates spent dialysate into fresh dialysate that is reintroduced into the patient to be used again for dialysis treatment. Further, the dialysis system provides continuous fluid flow simultaneously to and from the patient. 
     To this end, in one embodiment of the present invention a system for providing dialysis is provided. The system includes a patient fluid loop having a first pump and multiple patient lumens. The system includes a second fluid loop including a second pump and a medical fluid regenerator. A membrane device is placed in fluid contact with and separates the patient and the second fluid loops. The membrane device allows at least one selected component of the fluid in the patient fluid loop to transfer to the second fluid loop. The second loop is otherwise closed except for the transfer of the selected component via the membrane device. A controller is also provided that operates the first and second pumps to recirculate fluid in the patient loop and the second loop. 
     The system is adaptable to be used with various different types of components and to be arranged in a variety of ways. 
     For example, in an embodiment, the membrane device is a dialyzer. 
     In an embodiment, a pressure gradient exists across the membrane device. 
     In an embodiment, the patient loop is also closed except for the transfer of the selected component via the membrane device and the venting of air/gas. 
     In an embodiment, the membrane device includes a nanofilter which allows urea to pass from the patient fluid loop to the second fluid loop. 
     In an embodiment, the medical fluid regenerator includes a uremic toxin sorbent. 
     In an embodiment, the medical fluid regenerator can include any or all of the following materials: urease, zirconium phosphate, zirconium oxide, and carbon. 
     In an embodiment, the system includes a gas separator that removes gas from one or both of the patient and second fluid loops. 
     In an embodiment, the gas separator and the medical fluid regenerator are provided in a single device. 
     In an embodiment, the system includes a gas vent that vents gases from the patient and second fluid loops. 
     In an embodiment, the second fluid loop includes a multi-analyte sensor that monitors a concentration of electrolytes in the medical fluid. 
     In an embodiment, peritoneal dialysis fluid is circulated through the patient fluid loop. 
     In an embodiment, blood is circulated through the patient fluid loop. 
     In an embodiment, at least parts of the patient fluid loop and the second fluid loop are provided in a disposable device. 
     In an embodiment, the second fluid loop includes a balance chamber that balances flow within the second fluid loop. 
     In an embodiment, the controller enables fluid to flow in opposite directions through the multiple patient. 
     In an embodiment, the system includes a dual lumen catheter that defines the multiple patient lumens. 
     In an embodiment, one or both of the patient fluid loop and the second fluid loop includes an in-line fluid heater. 
     In an embodiment, the in-line fluid heater includes a radiant heater and a plate heater. 
     In an embodiment, the system includes a medical fluid sensor which senses one or more indicators including: ammonia, ammonium and pH. 
     In an embodiment, the system includes a fluid volume sensor in or both of the patient and second fluid loops. 
     In an embodiment, the fluid volume sensor includes a capacitance fluid volume sensor that uses a chamber in fluid communication with one or both of the fluid loops. 
     In an embodiment, the chamber is a pump chamber. 
     In an embodiment, the system includes an ultrafiltrate container in fluid communication with at least one of the patient and second fluid loops. 
     In an embodiment, the system includes a fluid concentrate container in fluid communication with one or both of the patient and second fluid loops. 
     The system as described herein uses, in one embodiment, a disposable dialysis cassette. The cassette includes a flexible membrane covering a patient pump chamber and a regeneration pump chamber. The cassette includes an apparatus for fluidly connecting the patient pump chamber to a closed loop patient fluid path. The cassette further includes an apparatus for fluidly connecting the regeneration pump chamber to a closed loop regeneration fluid path. The patient path and the regeneration path each fluidly communicates with a dialyzer. 
     The cassette is adaptable to be used with various different types of components and to be arranged in a variety of ways. 
     For example, in an embodiment, the disposable cassette defines a fluid path leading to a port that fluidly communicates with a dialysate sorbent cartridge. 
     In an embodiment, the disposable cassette defines a fluid path leading to a port that fluidly communicates with a gas separator. 
     In an embodiment, the disposable cassette defines a fluid path leading to a port that fluidly communicates with a dialysis concentrate container. 
     In an embodiment, the disposable cassette defines a fluid path leading to a port that fluidly communicates with a dialysate last bag. 
     In an embodiment, the disposable cassette defines a fluid path leading to a port that fluidly communicates with a dialysate bag. 
     In an embodiment, the disposable cassette defines a fluid path leading to a port that fluidly communicates with a drain container. 
     In an embodiment, the disposable cassette defines a fluid path leading to a port that fluidly communicates with a patient fluid connector. 
     Further, the disposable cassette can define a fluid path for a twenty-four hour collection and/or a remote analyte sensor. 
     The disposable cassette operates with a dialysis therapy device. The therapy device includes a housing having a portion that receives the disposable cassette. The housing houses a patient pump actuator that pumps fluid through a patient path defined at least in part by the disposable cassette. The housing also houses a regeneration pump actuator that pumps fluid through a regeneration path defined at least in part by the disposable cassette. 
     The dialysis therapy device is also adaptable to be used with various different types of components and to be arranged in a variety of ways. 
     For example, in an embodiment, the dialysis therapy device includes at least one fluid volume measurement sensor component that cooperates with the patient pump actuator and the regeneration pump actuator. 
     In an embodiment, the housing houses a fluid heater. 
     In an embodiment, the housing houses at least one sensor, such as an ammonia sensor, an ammonium sensor and a pH sensor. 
     In an embodiment, the housing houses at least one valve actuator that operates with the disposable cassette. 
     The present invention includes a plurality of different methods for operating the systems and apparatuses described herein. In one embodiment, a method is provided for moving fluid in a dialysis system. The method includes continuously recirculating a first fluid through a patient loop. The method includes continuously recirculating a second fluid through a regeneration loop. At least one waste component is simultaneously transferred from the patient loop to the regeneration loop through a device shared by both loops. The loops are otherwise closed except for the fluid transfer through the device. The method also includes removing the at least one waste component from the regeneration loop. 
     The first and second fluids can both include dialysate. Alternatively, the first fluid includes blood and the second fluid includes dialysate. 
     In an embodiment, the method includes flowing the second fluid in the regeneration loop through a waste sorbent and absorbing at least some of the waste component. 
     In an embodiment, the method includes the step of heating the at least one of the first and second fluids. 
     In an embodiment, the method includes the step of removing ultrafiltrate from at least one of the first and second fluids. 
     In an embodiment, the method includes the step of adding dialysate to at least one of the first and second fluids. 
     In an embodiment, the method includes the step of adding concentrate to at least one of the first and second fluids. 
     In an embodiment, the method includes the step of removing gas from at least one of the first and second fluids. 
     In an embodiment, the method includes the step of balancing the flow of fluid in at least one of the patient loop and the regeneration loop. 
     In an embodiment, the method includes the step of sensing a volume of flow of fluid in at least one of the patient loop and the regeneration loop. 
     In an embodiment of any of the methods described herein, recirculating dialysate fluid through the patient loop includes passing the fluid through a portion of a patient. 
     In an embodiment, the method is for continuous flow peritoneal dialysis and includes passing the dialysate fluid and the regeneration fluid past opposite sides of a dialyzer membrane and regenerating the regeneration fluid after the regeneration fluid exits the dialyzer. 
     In an embodiment of the continuous flow peritoneal dialysis method, recirculating dialysate fluid through the closed patient loop includes passing the fluid through a sleeping patient. 
     In an embodiment of the continuous flow peritoneal dialysis method, recirculating dialysate fluid through the closed patient loop includes passing the fluid through a patient at nighttime. 
     In another embodiment, a method of moving fluid in a peritoneal dialysis system is provided. The peritoneal dialysis method includes the steps of: (i) continuously recirculating dialysate through a container in a patient loop; (ii) continuously recirculating dialysate through the container in a regeneration loop; and (iii) continuously moving at least one waste component from the patient loop to the regeneration loop through the container shared by both loops, the loops being closed except for said transfer through said container. 
     In an embodiment, the peritoneal dialysis method includes the step of recirculating dialysate through the regeneration loop at a different rate than a rate at which dialysate is recirculated through the patient loop. 
     In a further method of the present invention, performing continuous flow dialysis includes multiple dialysis disciplines. The method includes performing continuous flow peritoneal dialysis with a closed loop dialysis device at a first point in time and performing continuous flow hemodialysis via the same closed loop dialysis device at a second point in time. 
     In an embodiment, the continuous flow peritoneal dialysis and the continuous flow hemodialysis are performed on the same patient. 
     In an embodiment, the method includes an intermediate step of removing a disposable cassette used with the device and coupling a new disposable cassette to the device. 
     In an embodiment, the method includes an intermediate step of removing a dual lumen peritoneal dialysis catheter and replacing the catheter with a hemodialysis needle. 
     In an embodiment, the method includes an intermediate step of removing a hemodialysis needle and replacing the needle with a dual lumen peritoneal dialysis catheter. 
     One advantage of the present invention is to provide improved systems and methods for performing dialysis. 
     Another advantage of the present invention is to provide improved systems and methods for performing automated continuous flow dialysis systems and methods. 
     A further advantage of the present invention is to provide regenerative dialysis systems and methods of operating same. 
     Still another advantage of the present invention is to provide a regenerative dialysis system that has clinical advantages. 
     Still a further advantage of the present invention is to provide a regenerative dialysis system that has economic advantages. 
     Yet another advantage of the present invention is to provide a regenerative dialysis system that has quality of life advantages. 
     Still further, an advantage of the present invention is to provide a regenerative dialysis system that reduces the amount of dialysis fluid need to perform dialysis. 
     Another advantage of the present invention is to provide a closed loop dialysis system. 
     Other advantages of the present invention are to provide systems and methods for performing both peritoneal dialysis and hemodialysis. 
     Additional features and advantages of the present invention are described in, and will be apparent from, the following Detailed Description of the Invention and the figures. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         FIG. 1  schematically illustrates an embodiment of a dialysis system according to the principles of the present invention. 
         FIG. 2  shows a multi-lumen patient fluid connector according to the principles of the present invention. 
         FIG. 3  schematically illustrates another embodiment of a dialysis system according to the principles of the present invention. 
         FIG. 4  schematically illustrates a further embodiment of a dialysis system according to the principles of the present invention. 
         FIG. 5  illustrates an embodiment of a disposable cassette according to the present invention. 
         FIG. 6  illustrates another embodiment of a disposable cassette according to the present invention. 
         FIG. 7  illustrates a disposable cassette of the present invention connected to various fluid containers. 
         FIG. 8  schematically illustrates yet another embodiment of a dialysis system according to the principles of the present invention. 
         FIG. 9  schematically illustrates an embodiment of a dialysis system according to the principles of the present invention that provides hemodialysis. 
         FIG. 10  illustrates a combination container providing various components used in the dialysis systems of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     Generally, the present invention relates to dialysis systems and methods of performing dialysis. In an embodiment, the present invention pertains to continuous flow regeneration peritoneal dialysis systems and methods. In other embodiments the present invention pertains to non-continuous flow regeneration peritoneal dialysis, and regeneration hemodialysis, both continuous and non-continuous flow. 
     The dialysis system automatically performs dialysis therapy on a patient, for example during nighttime while the patient sleeps. The present invention can provide true continuous flow dialysis therapy (fluid simultaneously flowing into and out of the patient), and automatically regenerate spent dialysate into fresh dialysate that is again used for the dialysis treatment. Continuous flow of dialysate tends to increase the efficacy of treatment by maximizing or maintaining a maximum osmotic gradient across the peritoneal membrane. Regeneration of dialysate by the present invention significantly reduces the amount of dialysate required for a treatment. For example, the amount of dialysate fluid can be reduced from about fifty liters for CFPD therapy if performed by an existing cycler to about six to eight liters of same for therapy with the present invention. 
     In a peritoneal dialysis embodiment of the present invention, the spent dialysate from the patient&#39;s peritoneal cavity passes through a regeneration unit and is regenerated into a useable dialysate. The regenerated dialysate in a patient fluid loop is returned to the patient&#39;s peritoneal cavity to further dialyze the patient. The regeneration unit removes undesirable components in the dialysate that were removed from the patient, for example, excess water (ultrafiltrate or UF), toxins, and metabolic wastes, so that the dialysate can be used for further dialysis. Desirable components can be added to the dialysate by the system, such as glucose and electrolytes, for example. The additives assist in maintaining the proper osmotic gradients in the patient to perform dialysis and provide the necessary compounds to the patient. 
     Continuous flow peritoneal dialysis according to the present invention means that when the patient is being dialyzed (e.g., dialysate is being pumped to and removed from the peritoneal cavity), the dialysate is constantly and simultaneously flowing into and out of the patient. The dialysis system pumps fresh dialysate into the patient&#39;s peritoneal cavity while simultaneously pumping spent dialysate out of the peritoneal cavity. Accordingly, the dialysis system can eliminate the dwell period inside the peritoneal cavity that is typical for existing dialysis systems. The flow rate of the continuous dialysate flow can be constant or varied as desired, and is generally about 100-300 ml/min. 
     The dialysis system of the present invention can be controlled to provide various dialysis therapies, as desired. Accordingly, even though the dialysis system can provide continuous flow, the present invention also supports non-continuous flow or batch systems and methods. Also, the continuous flow into and out of the peritoneal cavity occurs during the main therapy treatment, so that a dwell during a last bag, for example, does not detract from the continuous flow feature. Furthermore, the fluid pumping mechanisms of the present invention may provide for brief intermittent fluid flow, such as the filling of a pump chamber, for example. The continuous fluid flow of the present invention is considered to include such brief intermittent fluid flow. 
     The dialysis systems and methods of the present invention provide advantages compared to other dialysis systems and therapies, such as clinical advantages, economic advantages, and quality of life advantages, for example. It is believed that the present invention has clinical advantages, such as, improved blood pressure (“BP”) control, improved hematocrit (“HCT”) control, improved fluid volume control, improved preservation of residual renal function (“RRF”), improved adequacy vs. the National Kidney Foundation&#39;s DOQI standard, higher efficiency (clearances/time), lower glucose absorption, glucose profiling and ultrafiltrate management, and reduced catheter channeling. 
     It is also believed that the present invention has economic advantages, such as, reduced therapy cost and reduced Epogen (“EPO”) usage. Further, it is believed that present invention has quality of life advantages, such as, increased awake time free from dialysis devices, improved patient access, reduced complexity, reduced self-administration of drugs, reduced therapy training, elimination of the need for having a home water infrastructure, a reduced amount of fluid that the patient must handle and manage, simpler prescriptions and elimination of patient transportation to dialysis centers. 
     The dialysis systems and methods of the present invention more closely simulate and replace continuous kidney functioning as compared to intermittent dialysis therapies. This, in turn, can contribute to improved clinical outcomes (RRF, HCT, BP, for example) while minimally impacting the patient&#39;s lifestyle. The efficiency and convenience of the present invention provides patients with a renal replacement therapy that is relatively unrestrictive. This allows patients to have greater freedom from limitations experienced by dialysis devices and therapies. The present invention can provide easier entrance into early dialysis therapy because the system can enable the physician to retain a patient&#39;s RRF. while minimally impacting the patient&#39;s lifestyle. 
     Dual Loop System 
     Referring now to the drawings and in particular to  FIG. 1 , a system  10  for providing dialysis treatment to a patient needing same is illustrated. As illustrated in  FIG. 1 , two loops are provided: a patient loop (a recirculating patient fluid flow path)  12  and a regeneration loop  14  (a recirculating dialysate fluid flow path). However, it should be noted that the present invention can be used in a system including only one loop or more than two loops. The patient loop  12  is used to dialyze the patient  16  with dialysate in a peritoneal dialysis embodiment. The regeneration loop  14  also contains dialysate and is used to regenerate the dialysate in the patient loop  12 . In a hemodialysis embodiment, the patient loop  12  carries the patient&#39;s blood, and the regeneration loop  14  dialyzes the blood and regenerates the dialysate in the loop  14 . 
     As illustrated generally in  FIG. 1 , the patient loop  12  and the regeneration loop  14  are initially filled or primed with dialysate fluid from a bag  18  by pumping the dialysate through a pump, such as an ultrafiltrate pump  19 .  FIG. 1  shows a single dialysate bag  18  for both the patient and regeneration loops  12  and  14 ; however, separate dialysate bags and/or fluid pumps could be individually used for the patient loop  12  and the regeneration loop  14 . In a hemodialysis embodiment, the patient loop  12  can be primed with a suitable priming solution, such as a saline solution, and then connected to the patient&#39;s blood circulatory system. 
     The patient loop  12  is fluidly connected to the patient  16  by a multi-lumen patient fluid connector  20  and catheter. Referring to  FIGS. 1 and 2 , the multi-lumen patient fluid connector  20  can have, for example, a single housing  70  having more than one separate lumen  72  (to patient lumen) and  74  (from patient lumen), or separate housings each having one of the lumens  72  and  74 . In a peritoneal dialysis embodiment, the multi-lumen patient fluid connector  20  can be connected to a dual lumen catheter  22  (illustrated in  FIG. 1 ), such as a catheter disclosed in co-pending U.S. patent application Ser. No. 09/689,508, titled “Peritoneal Dialysis Catheters,” incorporated by reference or other multi-fluid path patient access. 
     The dual lumen catheter  22  is implanted in the patient  16  and provides fluid flow access to the patient&#39;s peritoneal cavity. Two separate lumens  72  and  74  of the multi-lumen patient connector  20  are fluidly connected to separate lumens (not illustrated) of the dual lumen catheter  22 . Fluid in the patient loop  12  can continuously flow through the patient fluid connector  20  simultaneously and continuously in multiple directions, e.g. two different directions, into and out of the catheter  22  and the patient  16 . The multi-lumen patient fluid connector  20  is described in further detail below in  FIG. 2 . 
     In a continuous flow embodiment, the patient loop  12  can be fluidly connected to the patient by any device or devices that provides for fluid to simultaneously flow into and out of the patient. For example, the patient loop  12  can be connected to the dual lumen catheter to two single lumen catheters. 
     In  FIG. 1 , the patient loop  12  has a patient fluid pump  24  that pumps fluid through the patient loop  12 . The fluid in the patient loop  12  is pumped from the patient  16  (the patient&#39;s peritoneal cavity in a peritoneal dialysis embodiment) through the patient fluid connector  20 , through a dialyzer  26 , back through the patient fluid connector  20 , and is returned to the patient  16 . In a peritoneal dialysis embodiment, the spent dialysate (laden with waste and excess water) in the patient loop  12  exiting from the patient  16  is cleansed or regenerated by passing through the dialyzer  26 . The waste, such as urea, creatinine and excess water passes from the patient loop  12  across a dialyzer membrane  28  to the regeneration loop  14  to produce fresh dialysate exiting the dialyzer in the patient loop  12 . The fresh dialysate is returned to the patient  16  for further dialysis treatment. In an embodiment, the fluid in the patient loop  12  is continuously recirculated through the patient loop  12  by the patient pump  24 . Also, the dialyzer  26  provides a sterile independent barrier between the patient loop  12  and the regeneration loop  14 . Existing dialyzers used for dialysis is therapy are suitable for use with the present invention, for example. Also, the membrane  28  referred to in the dialyzer  26  includes any suitable filter material, such as hollow dialyzer fibers. 
     In a hemodialysis embodiment, the patient loop  12  is connected to the patient&#39;s blood circuit rather than the peritoneal cavity. The patient pump  24  continuously recirculates the blood, as the dialyzer  26  removes waste and excess from the blood. 
     The regeneration loop  14  removes the waste and excess water from the patient loop  12 . In the embodiment illustrated in  FIG. 1 , a fluid pump  30 , pumps dialysate fluid in the regeneration loop  14  continuously to recirculate the dialysate through the loop  14 . The dialysate fluid pump  30  pumps the dialysate from the dialyzer  26 , through a sorbent cartridge  32 , and back to the dialyzer  26 . The fluid in the regeneration loop  14  flows past a side of the dialyzer membrane  28  opposite the side of the membrane  28  having the fluid in the patient loop  12 . In an embodiment, the regeneration loop  14  provides for balanced fluid flow through the dialyzer  26 , for example, by providing equal flow dialysate fluid pumps  30 , and/or balance chambers. 
     As mentioned above, waste and excess water passes from the fluid in the patient loop  12 , across the dialyzer membrane  28 , to the fluid in the regeneration loop  14 . The transfer across the dialyzer membrane  28  occurs at least in part due to diffusion and concentration gradients across the membrane  28 . Also, the system  10  in an embodiment maintains a lower fluid pressure in the regeneration loop  14  relative to the patient loop  12 . That is, there is a transmembrane pressure (“TMP”) across the dialyzer membrane  28 . The fluid pressure differential draws fluid from the patient loop  12 , across the dialyzer membrane  28 , to the regeneration loop  14 . This fluid pressure differential can be maintained by removing fluid from the regeneration loop  14 , for instance, by using the ultrafiltrate pump  19  to drain some of the fluid in the regeneration loop  14 . The amount or rate of fluid removed from the regeneration loop  14  by the ultrafiltrate pump  19  determines the amount or rate of fluid transferring from the patient loop  12 , across the dialyzer membrane  28 , to the regeneration loop  14 . This amount or rate equals the amount or rate of fluid removed from the patient  16  to the patient loop  12 . 
     A sorbent cartridge or container  32  includes materials that absorb particular compounds from the dialysate. For example, certain sorbents within the sorbent cartridge  32  may absorb uremic toxins, such as urea, creatinine, uric acid, and other metabolism by-products. By removing these undesirable waste materials, the sorbent cartridge  32  at least partially regenerates the dialysate. The sorbent cartridge  32  includes a body having a fluid inlet  34  and a fluid outlet  36 . One sorbent cartridge  32  according to the invention contains four layers of materials, including a first layer of urease, a second layer of zirconium phosphate, a third layer of zirconium oxide and a fourth layer of carbon. The interior of the cartridge  32  is constructed and arranged so that the fluid entering the interior from the inlet  34  flows (preferably upward and uniformly) through the first layer, the second layer, the third layer, the fourth layer and finally through the outlet  36 . 
     The sorbent cartridge  32  can also use materials that selectively remove certain solutes from the dialysate. The selective materials can include a binder or reactive sorbent material capable of selectively removing urea, a binder or reactive sorbent material capable of selectively removing phosphate and/or the like. The use of materials capable of selective removal of solutes, particularly urea, enhances the cleaning efficiency of the system of the present invention such that the amount of dialysate necessary for effective treatment can be minimized. 
     The materials that can selectively remove solutes from solution, such as binder materials, can include a variety of suitable and different materials including, for example, polymeric materials that are capable of removing nitrogen-containing compounds, such as urea, creatinine, other like metabolic waste and/or the like in solution. In general, these types of materials contain a functional group(s) that chemically binds with urea or other like solutes. 
     For example, U.S. Pat. Nos. 3,933,753 and 4,012,317, each incorporated herein by reference, disclose alkenylaromatic polymers containing phenylglyoxal that can function to chemically bind urea. In general, the phenylglyoxal polymeric material is made via acetylation performed in, for example, nitrobenzene followed by halogenation of the acetyl group and treatment with dimethylsulfoxide as disclosed in U.S. Pat. Nos. 3,933,753 and 4,012,317. Another example of a polymeric material that is capable of selectively removing solutes, such as urea, from solution includes polymeric materials that contain a tricarbonyl functionality commonly known as ninhydrin as disclosed in U.S. Pat. No. 4,897,200, incorporated herein by reference. However, it should be appreciated that the present invention can include any suitable type of material or combinations thereof to selectively remove solutes, such as urea, from solution as previously discussed. 
     In addition to absorbing certain materials from the dialysate, the sorbent cartridge  32  may also modify the dialysate in the regeneration loop  14  in other ways. For example, the materials in the sorbent cartridge  32  mentioned above or additional materials added to the cartridge  32  may modify the pH of the fluid passing through the cartridge  32 . In an embodiment, the pH of the dialysate in the regeneration loop  14  is modified as needed to maintain a physiologic level. One sorbent cartridge  32  is described in further detail in a U.S. patent application titled “Method and Composition for Removing Uremic Toxins in Dialysis Processes,” Ser. No. 09/990,673, incorporated herein by reference. 
     The sorbent cartridge  32  can also include a number of components in addition to the sorbent materials capable of removing solutes from the dialysate. For example, the cleaning cartridge may have the capability to remove all or a portion of electrolytes, such as sodium, potassium, or the like, from the dialysate solution. In this case, an additional source of electrolytes in solution may be needed to replenish the dialysate after it has been cleaned. The cartridge may also be configured to release bicarbonate or the like into the system depending on the type of sorbent material used. This can facilitate pH regulation of the dialysate. As necessary, the cartridge may be filtered to prevent proteins, particulate matter or like constituents from leaching or exiting from the cartridge and into the dialysate. 
     Ultrafiltrate (excess water) removed from the patient  16  can be removed from the dialysis system  10  by draining the ultrafiltrate to a drain bag  38  or other drain means. In one embodiment, the ultrafiltrate pump  19  removes fluid from the regeneration loop  14  at the exit end of the dialyzer  26  through valves  40  and  42  to the drain bag  38 , wherein the fluid contains the waste and excess water removed from the patient loop  12  by the dialyzer  26 . The drain pump  19  can remove fluid from the regeneration loop  14  continuously or intermittently (e.g., batch operation), as desired. 
     The dialysis solution in the regeneration loop  14  is removed from the system along with the ultrafiltrate. Accordingly, a dialysate concentrate is provided in a concentrate container  44  to supply necessary compounds to the regeneration loop  14 . The concentrate from the container  44  mixes with the dialysate in the regeneration loop  14  and adds the compounds to the dialysate. The concentrate in an embodiment also includes other components that are provided to the patient  16 , for example, electrolytes. A concentrate pump  46  and a valve  48  are provided to selectively pump the concentrate from the concentrate container  44  to the regeneration loop  14 . The concentrate contributes to the regeneration of the dialysis solution in the regeneration loop  14 . 
     Although the fluids in both the patient loop  12  and the regeneration loop  14  are, in an embodiment, recirculated continuously through their respective loops, the various fluid pumps can be controlled by a computer, processor, or microprocessor, collectively referred to herein as a “controller”  200 , to pump their respective fluids intermittently, if desired. 
     The dialysis system  10  in an embodiment is a closed, sterile system. Air, moisture and fluids from the environment around the dialysis system  10  cannot enter into the patient loop  12  or the regeneration loop  14 . The dialysis system  10  does permit fluids (such as ultrafiltrate) and air to exit the fluid loops  12 ,  14  and fluids (such as concentrate) to be added to the fluid loops  12 ,  14  under controlled circumstances. The dialysis system  10  is designed to prevent uncontrolled contact of the patient and the regeneration loops  12  and  14  with the surrounding environment. 
       FIG. 1  schematically shows an example of an gas separator  50  in the dialysis system  10 . The term “gas” is used herein to include gasses in general, including air, carbon dioxide (“CO2”) and any other type of gas that can become entrained in fluid loops  12  and  14 . The regeneration fluid loops  12  and  14  can accumulate air for various reasons. For example, the fluid loops  12  and  14  may contain air prior to priming the system  10  with fluid or the storage containers may introduce air into the fluid loops  12  and  14 . The sorbent cartridge  32  may produce CO2 and introduce the CO2 gas into the loops  12  and  14 . The patient  16  can also produce certain gasses, which become entrained in the dialysate and enter the loops  12  and  14 . 
     It is desirable to remove gas from the fluid loops  12  and  14 . The gas separator  50  removes entrained gas from the fluid in the regeneration loop  14  and vents the gas to outside of the dialysis system  10 . In this manner, gas is purged from the regeneration loop  14 . The gas separator  50  includes a one-way vent, i.e., it permits gas to vent from the fluid loops  12  and  14  to the atmosphere but prevents gas outside of the fluid loops  12  and  14  from entering into the loops. 
     In one embodiment illustrated in  FIG. 3 , the gas separator  50  and the sorbent cartridge  32  of  FIG. 1  are combined into a single device  102 . One example of an gas separator  50 /sorbant cartridge  32  combination is shown in the patent application titled “Method and Composition for Removing Uremic Toxins in Dialysis Processes,” Ser. No. 09/990,673, mentioned above. As illustrated in  FIG. 1 , however, the gas separator  50  can be a separate system component or incorporated into system components other than the sorbent cartridge  32 . 
     It is also desirable to purge gas from the patient loop  12 . In an embodiment, an additional gas separator (not illustrated) can be provided in the patient loop  12 , which vents to the atmosphere. In another embodiment, the gas can be removed from the patient loop  12 , fed to the gas separator  50  in the regeneration loop  14 , e.g., via line  51 , and vented to the atmosphere. 
     In an embodiment, one or more gas sensor(s)  52  are provided at desired locations along the patient loop and/or the regeneration loop  14  to detect gas in the system  10 . In an embodiment, gas sensors  52  electrically connect or are otherwise in communication with the system controller, which monitors gas content in the loops  12  and  14 . The controller can control the system to perform any desired function in response to the gas, such as, stopping fluid flow, changing the direction of fluid flow, or removing the gas. The gas separator  50  can be any suitable device, which separates gas from fluid known to those of skill in the art. Gas separators, such as the separator  50 , can be used which separate and vent the gas without being controlled by the system controller. In an embodiment, the gas separator  50  absorbs the gas rather than venting it to the atmosphere as illustrated. 
     In an embodiment, the dialysis system  10  contains a fluid heater  54 , shown schematically in  FIG. 1 . The fluid heater  54  heats the fluid in the patient loop  12  to a desired temperature for supplying the fluid to the patient  16 . The fluid heater  54  is an in-line heater (continuous flow heater) that heats the fluid to the desired temperature as the fluid flows continuously past the heater  54 . In other embodiments, heaters other than in-line heaters can be used, for example, bulk heaters. The fluid heater  54  is shown in  FIG. 1  in the patient loop  12  at the fluid supply to the patient  16 . However, the fluid heater  54  can be positioned at other locations in the patient loop  12  and the regeneration loop  14 , if desired. In another embodiment, one or both of the loops  12  and  14  include one or multiple heaters  54 . 
     In an embodiment, the fluid heater  54  is a dual heater, including an infrared heater  56  and a plate heater  58 . An example of such a dual heater  54  is disclosed in a patent application entitled, “Medical Fluid Heater Using Radiant Energy,” Ser. No. 10/051,609, incorporated herein by reference. Both the infrared heater  56  and the plate heater  58  are in-line heaters that heat the medical fluid that flows continuously past the heaters  56 ,  58 . The radiant energy or infrared heater  56  emits infrared energy that is directed to and absorbed by the fluid in the patient loop  12 , thereby heating the fluid. The radiant energy or infrared heater  56  is a primary or high capacity heater which can heat a relatively large volume of cold fluid to a desired temperature in a short period of time. 
     The plate heater  58  is a secondary or maintenance heater which has a relatively lower heating capacity relative to the infrared heater  56 . The plate heater  58  uses electrical resistance to increase the temperature of a plate that in turn heats the fluid flowing near the plate. 
     The heater  54 , which includes both high and low capacity heaters, provides an efficient heater design that accommodates various fluid heating requirements. For example, the radiant or infrared heater  56  is particularly useful for quickly heating cool dialysate (high heat energy demand) that is supplied to the dialysis system  10 , such as at the initial system fill or if there is severe heat loss during dialysis treatment. The temperature of the dialysate at initial system fill can be quite low, such as 5° C. to 10° C. if the fluid is stored in cold ambient temperature. 
     The plate heater  58  is particularly useful to maintain a desired temperature (lower heat energy demand) of the fluid being supplied to the patient, e.g., due to a normal amount of heat loss during dialysis treatment. The infrared heater  56  provides for the high heat demand in a small amount of fluid exposure space, while the plate heater  58  provides for maintenance heat demand and requires a lesser amount of input energy compared to the infrared or radiant heater  56 . Furthermore, the heating capacity of the heater  54  is increased if both the infrared and plate heaters  56  and  58  are used together to heat the fluid. 
     The infrared heater  56  and the plate heater  58  can be arranged in various configurations relative to each other. The heaters  56  and  58  in an embodiment are arranged so that the fluid passes by the heaters sequentially (e.g., first the radiant or infrared heater and then the plate heater). In another embodiment, the fluid passes by the heaters simultaneously (both heaters at the same time) or in the reverse order. The fluid flow path past the heaters  56  and  58  can be a common flow path for both heaters  56  and  58  or include independent flow paths for each heater  56  and  58 . Besides radiant or infrared electrical resistance heating, other types of heating such as convective, inductive, microwave and radio frequency (“RF”) heating may be used. 
     In an embodiment, temperature sensors are provided at desired locations along one or both of the patient loop  12  and the regeneration loop  14 . The temperature sensors monitor various fluid temperatures and are connected to the system controller to control the fluid temperatures with the heater  54 . When two or more heaters, such as the infrared heater  56  and the plate heater  58 , are provided in the dialysis system  10 , the system  10 , in an embodiment, can include separate temperature sensors for each heater so that each heater can be controlled individually. 
     The dialysis system  10  in an embodiment also includes various other sensors to monitor various parameters. For example, fluid pressure sensors  60  and  62  are provided in the patient loop  12  of  FIG. 1 . The fluid pressure sensors  60  and  62  electrically couple to or otherwise communicate with the controller to provide a signal that indicates the respective fluid pressure at that location. Based on the signals from the pressure sensors  60  and  62 , the controller operates the fluid pumps and valves to obtain and maintain desired fluid pressures in the loop  12  running to and from the patient  16 . 
     In an embodiment, the pressure sensors  60  and  62  are non-invasive pressure sensors. That is, the pressure sensors  60  and  62  do not physically contact (and possibly contaminate) the medical fluid or dialysate. The pressure sensors  60  and  62  measure the medical fluid pressure and help to maintain a steady flow within the closed fluid system. Of course, other fluid devices, such as flow rate sensors, pressure gauges, flowmeters, or pressure regulators, which are not illustrated  FIG. 1 , may be provided in any suitable quantity and at any desired location within either or both of the patient loop  12  and the regeneration loop  14 . 
     In the illustrated embodiment, the system  10  includes an ammonia sensor  64 . The ammonia sensor  64  measures the concentration of ammonia (NH3) and/or ammonium (NH4) in the fluid. Ammonia and ammonium are produced by the regeneration sorbent cartridge  32  as a by-product of the urea catalysis urease. The ammonia and ammonium are normally removed by a cation exchanger in the sorbent cartridge  32 . However, the dialysis system  10  monitors the fluid for ammonia/ammonium concentrations with the sensor  64  to confirm that the ammonia and ammonium are being removed and remain below safe threshold levels for the patient  16 . The total ammonia and ammonium in solution is primarily determined by three parameters: ammonia or ammonium, pH, and solution temperature. By measuring these parameters (or adjusting a parameter, such as adjusting the pH to a desired level), the total amount of ammonia and/or ammonium in the dialysate can be determined. 
     One sensor  64  according to the present invention is described in a patent application entitled, “Ammonia and Ammonium Sensors,” Ser. No. 10/024,170, incorporated herein by reference. The sensor  64  determines the total ammonia and ammonium content of an aqueous solution. The sensor  64  includes a hydrophobic ammonia sensing membrane, a pH indicator or conditioner, a temperature sensor and an optical sensor. An algorithm stored in the controller calculates the combined ammonia and ammonium content from the three parameters (e.g., NH3, pH and temperature). The ammonia gas, which is highly soluble in water, is quantified by the hydrophobic sensing membrane that changes color based on the quantity of ammonia gas diffused into it. A multi-wavelength optical sensor continuously measures the membrane color through a transparent window. The sensor  64  achieves a non-intrusive measurement by the using the optical sensor to monitor color changes in the disposable membrane placed inside the fluid path. 
     In the illustrated embodiment of  FIG. 1 , the dialysis system  10  also includes one or more fluid flow measurement devices or volume sensors  66  that measure the volume of the medical fluid pumped either intermittently or cumulatively through one or both of the loops  12  and  14 . In an embodiment, the fluid flow measurement device  66  measures the amount of fluid supplied to the patient  16  by the patient loop  12 . Additionally or alternatively, the regeneration loop  14  and/or the ultrafiltrate drain line employ one or more fluid flow measurement devices  66  to measure the amount of ultrafiltrate removed from the patient  16 . Various types of fluid volume measurement or flowrate devices can be used with the dialysis system  10 , such as orifice plates, mass flow meters or other flow measuring devices known to those of skill in the art. 
       FIG. 1  schematically illustrates one embodiment of a flow measurement device or volume sensing device  66 , which includes a capacitance sensor that measures the volume of fluid pumped through a chamber, such as a pump chamber (dotted lines designating the device  66  shown encircling the pumps  19 ,  24  and  30 ). The capacitive fluid sensor  66  is disclosed in greater detail in the patent application entitled, “Capacitance Fluid Volume Measurement,” Ser. No. 10/054,487, incorporated herein by reference. 
     The capacitance C between two capacitor plates changes according to the function C=k×(S/d), wherein k is the dielectric constant, S is the surface area of the individual plates and d is the distance between the plates. The capacitance between the plates changes proportionally according to the function 1/(R×V), wherein R is a known resistance and V is the voltage measured across the capacitor plates. 
     In one embodiment of the capacitance sensor  66 , the sensor cooperates with the pump chamber. The pump chamber in an embodiment includes shells or walls defining a fixed and known volume and a pair of flexible membranes operating between the shells, which expand to fill with fluid and contract to discharge fluid. The capacitance sensor  66  includes capacitor plates disposed on opposite sides of the pump chamber. As the volume of fluid in the chamber or fluid pump changes (i.e., the pump chamber fills or empties), the dielectric property of the varying fluids between the capacitance plates changes. For example, the combined dielectric constant of dialysate and air changes as dialysate replaces air (or air replaces dialysate) within shells of the constant volume chamber. This change in the overall dielectric constant affects a change in the capacitance between the two plates, which causes a change in voltage across the capacitance plates, wherein the change in voltage can be sensed by a voltage sensing device. The controller monitors the change in voltage by the voltage sensing device and correlates (after a calibration of the sensor) the capacitance change to an amount of fluid pumped through the chamber. 
     In another embodiment, the volume of the chamber or the pump chamber can vary, e.g., by movement of one or both the shells of the chamber. In this embodiment, the capacitance between the capacitor plates changes due to a changing distance d between the plates and/or a changing surface area S of one or more of the plates, wherein the dielectric constant k is static because only one fluid resides at all times between the capacitor plates. In a further alternative embodiment of the measurement device  66 , the capacitance C between the capacitor plates changes based on any combination or all three of a change in dielectric constant k, distance d and surface area S. 
     The controller collects a multitude of voltage signals from capacitance changes from sensor  66  due to a plurality of chamber fill and drain cycles, wherein the controller calculates a total volume of medical fluid pumped over a length of time or number of pump cycles. The capacitance sensor  66  monitors the medical fluid, e.g., dialysate, flow into or from the pump chamber on a real time basis, and in a non-invasive manner. 
     The capacitance sensor  66  enables the dialysis system  10  to maintain the volume of fluid that is provided to the patient  16  at desirable amounts and flow rates. Maintaining the fluid flow to the patient  16  within desired levels is particularly advantageous for peritoneal dialysis therapies. 
     Also, it is desirable to maintain the fluid provided to the patient at physiologic levels. Physiologic control, such as sensing and/or adjusting parameters of the fluids, can take place at various locations in the dialysis system  10 , including the patient loop  12  and the regeneration loop  14 . For example, as mentioned above, the sorbent cartridge  32  may include a pH sensor that adjusts the fluid in the regeneration loop  14 , which then adjusts the fluid in the patient loop  12  via the dialyzer to be at a desired physiologic level. 
     Dual Lumen Connector 
     Referring now to  FIG. 2 , one embodiment of a dual lumen patient fluid connector  20  of the present invention is described in further detail. As described above, the dual lumen connector  20  includes a housing  70  having a lumen  72  for providing fluid to the patient lumen and a separate lumen  74  to remove fluid from the patient. Separate housings each having one of the lumens  72  and  74  may be provided. The patient inflow lumen  72  connects to a patient inflow tube  76  of the patient loop  12 . Similarly, the patient outflow lumen  74  connects to a patient outflow tube  78  of the patient loop  12 . A removable end cap  80  is provided to seal a cavity  82  defined by the housing  70 . The cavity  82  surrounds or abuts the lumens  72  and  74  and provides a connection area for the dual lumen catheter  22  ( FIG. 1 ) to insert into the cavity  82  and mate with the lumens  72  and  74 . 
     The housing  70 , lumens  72  and  74  and the end cap  80 , in an embodiment, are made of any material suitable for medical applications, such as plastic for example. In an embodiment, one of the lumens, e.g., the patient inflow lumen  72  extends further into the cavity  82  than the other lumen, which helps facilitate mating of the connector  20  to the catheter  22 . In another embodiment both lumens  72  and  74  extend into the cavity  82  the same or different distance. 
     The dialysis system  10 , particularly the patient loop  12 , can be primed, e.g., filled, with the end cap  80  in sealing engagement with the housing  70 . The arrows  84  and  86  figuratively illustrate the recirculating fluid flow through the dual lumen connector  20 . The system  10  can therefore run without a fluid connection to the patient. Also, the system  10  may include a patient by-pass line between the patient inflow and outflow tubes  76 ,  78  to allow fluid flow through the patient loop  12  while by-passing the patient  16 . The end cap  80  is removed, e.g., pulled off or unscrewed, to expose the cavity  82  and the patient inflow and outflow lumens  72  and  74 , respectively, for connection to the dual lumen catheter  22 . 
     In an alternative embodiment, the patient fluid loop  12  directly connects to the dual lumen catheter  22  or to two separate single lumen catheters. In a further alternative embodiment, the connector  20  is adapted to connect to two separate single lumen catheters. In yet another alternative embodiment, two separate connectors link single lumen catheters to incoming and outgoing lines of the patient fluid loop  12 . Other configurations are also contemplated by the present invention. 
     Alternative Dual Loop System with Balanced Flow 
     Referring now to  FIG. 3 , a system  100  for providing dialysis treatment to a patient is illustrated. The system  100  of  FIG. 3  includes many of the same components as the system  10  of  FIG. 1 . For example, the system  100  includes two loops, a patient loop  12  and a regeneration loop  14 . The patient loop  12  passes a medical fluid, dialysate or blood, to and from a patient  16 . In a peritoneal dialysis embodiment, the patient loop  12  and regeneration loop  14  are initially filled and primed with dialysate from a dialysate bag  18 . The patient loop  12  fluidly connects to the patient  16  by the multi-lumen patient fluid connector  20  described above in connection with  FIG. 2 . In a peritoneal dialysis embodiment, the multi-lumen connector  20  connects to a dual lumen catheter  22 . In a hemodialysis embodiment, the patient loop  12  fluidly connects to a multi-lumen hemodialysis needle or other patient blood access device. 
     The system  100  includes multiple patient fluid pumps  24   a  and  24   b . It has been found that using multiple pumps, such as the patient fluid pumps  24   a  and  24   b , creates a steadier flow of fluid to and from the patient  16  within the patient loop  12 . For example, fluid may be exiting the fluid pump  24   a  while the fluid pump  24   b  is filling with fluid. Balance chambers can be provided, in an embodiment, to balance fluid flow. 
     The system  100  includes the dialyzer  26  having the dialyzer membrane  28 . The spent dialysate (or blood in a hemodialysis embodiment) laden with waste and excess water in the patient fluid loop  12  is cleaned or regenerated when recirculated through the dialyzer  26 . The waste passes from the patient loop  12  across the dialyzer membrane  28  to the regeneration loop  14 . In the regeneration loop  14 , the fluid pumps  30 ,  30  continuously pump the regenerating dialysate through the combination device  102 , which includes the absorbent cartridge  32  and the gas separator  50 . The system  100  includes dual dialysate fluid pumps  30  to provide balanced flow within the regeneration loop  14 . That is, one of the fluid pumps  30  is being emptied of fluid while the other pump  30  is being filled with fluid. In an embodiment, balance chambers can be provided for balancing fluid flow. 
     The system  100  can drain ultrafiltrate and other fluids into the drain bag  38 . An ultrafiltrate pump  19  pumps the ultrafiltrate and fluids from the patient loop  12  or the regeneration loop  14 , for example through valves  40  and  42 , into the drain  38 . The system  100  also provides the ability to collect fluid in a twenty-four hour collection bag  39  for evaluation of the dialysis therapy. 
     In an embodiment, one of the patient fluid pumps  24   a  or  24   b  pulls dialysate fluid from either the dialysate bag or container  18  or the last bag  21 . The last bag  21  includes a volume of fluid that is placed in the patient&#39;s peritoneal cavity just prior to the end of the dialysis treatment. The patient with the dialysate from the last bag  21  in the peritoneal cavity disconnects from the system  100  and is able to perform daily activities. The next dialysis therapy begins with draining the last bag from the patient. 
     The system  100  includes a concentrate container  44 , a concentrate pump  46  and valves  48 . The concentrate pump  46  provides concentrate from the concentrate container  44  to the regeneration loop  14 , for example into the fluid line exiting from the outlet  36  of the combination absorbent cartridge and vent  102 . The concentrate container  44  supplies necessary compounds, such as electrolytes and osmotic agents, to the regeneration loop  14  of the system  100  to maintain the desired concentrations of those components. 
     Besides the concentrate that is contained in the concentrate container  44 , the system  100  regenerates dialysate through the regeneration loop  14  and does not require fluids from an outside source. Hence the system  100 , as are each of the systems described herein, is completely closed to the outside. The systems of the present invention are thus “closed loop systems”. The closed loop nature of the patient loop  12  and the regeneration loop  14  enables the loops to run continuously without absorbing or gathering outside contaminants. The closed loop systems of the present invention also maintain sterility by preventing contamination from the environment. 
     The system  100 , like the system  10 , may generate gases over time, such as air and CO2. The system  100  provides a plurality of gas sensors  52  that detect the various gases that may be in the system  100 . In the system  100 , the gas sensors  52  are provided at an air separator which separates gas from the fluid in the patient loop  12 . A gas separation line  51  feeds the separated gas from the patient loop  12  to the inlet side  34  of the combination absorbent cartridge and gas separator device  102 . The gas is then purged out of the system  100  by the gas separator  50 . The gas separator  50  maintains the closed loop structure of the system  100  by preventing contaminants from entering the system  100 . For example, the gas separator  50  can include a microbial filter which allows gas to exit the system  100 , but prevents contaminants from entering the system  100 . In another embodiment, the gas from the patient loop  12  may be purged from the system  100  by a separate gas purge device at the patient loop  12 . The gas sensors  52 , in an embodiment, can send an electronic signal to the controller (not illustrated). When the controller detects gas, the controller causes one or more valves to open, wherein the gas from the loop  12  is fed to a one-way vent and purged from the system  100 . 
     The system  100  further includes the inline heater  54 , which, in an embodiment, includes an infrared or radiant heater  56  and a plate heater  58  as described above. In an embodiment, the heater  54  has an air separator which allows air to exit port  59  on be purged from the system. 
     The system  100  further includes an orifice device  61  that stabilizes the differential pressure in the dialyzer  26  across the membrane  28 . That is, the orifice device  61  can restrict the flow in the patient loop  12  to create a pressure differential between the patient side and regeneration side of the dialyzer  26 . The pressure gradient or differential occurs across the membrane  28  in which the patient loop  12  having a higher fluid pressure than the regeneration loop  14 . The orifice device can be a fixed or variable flow restriction and can provide a fixed or variable pressure differential. Also, the orifice device  61  can be electrically coupled to and operated by the controller, which can activate, e.g., open or close the orifice device as necessary. 
     The pressure differential across the membrane  28  (higher pressure in the patient loop  12  and lower pressure in the regeneration loop  14 ) created by the orifice  61  assists in maintaining a greater pressure in the regeneration loop  14  relative to atmosphere pressure external to the system  100 . The positive pressure in the regeneration loop  14  relative to the external atmosphere pressure aids in ensuring that external air is not pulled from the surrounding environment through the air vent  50  into the regeneration loop  14 , i.e., air can only exit the system  100  and not enter into the system  100 . Accordingly, the orifice  61  contributes to the closed loop nature of the system  100 . 
     The system  100  provides a number of temperature sensors, such as sensors  63 ,  65  and  67 , which monitor temperatures at various points within the patient loop  12 . The controller uses the sensed temperatures to maintain a desired temperature within the patient loop  12 . As illustrated, the temperature sensor  63  is located at or on the heater  54 , which enables the system  100  to sense a temperature at a point very close to the constituent heaters  56  and  58 , and to control the heaters  56 ,  58 . 
     The system  100  further includes one or more pressure sensors  60  and  62 , which reside at various points along the patient fluid loop  12 . The pressure sensors  60  and  62  can be used to prevent excessive positive or negative pressures from being applied to the patient. The pressure within the system can be controlled by, e.g., activation of the patient fluid pumps  24   a ,  24   b.    
     The system  100  also monitors the absorbent cartridge  32  with an ammonia/ammonium sensor. Sample fluid exiting the absorbent cartridge  32  can be directed through a pH adjuster  71  to force the ammonia/ammonium equilibrium balance to a particular level. The amount of ammonia and/or ammonium in the sample fluid is measured by a sensor  73 . Accordingly, the effectiveness of the cartridge  32  to remove ammonia/ammonium after conversion from urea can be monitored. When the concentration of ammonia and/or ammonium reaches a threshold level, the system can produce a signal, or take other action such as shutting down, that indicates the cartridge  32  needs to be replaced. 
     Of course, the system  100  can monitor other fluid parameters and take appropriate action, as desired. Also, sample fluid can be taken at any desired location in the system  100 . Further, fluids in the patient and regeneration loops  12 ,  14  can be tested or monitored directly rather than taking samples. 
     The system  100  also includes fluid volume sensors  66  which in an embodiment are capacitance sensors that sense a change in capacitance occurring between two capacitor plates. The capacitor plates surround the pumps  24  of the patient loop  12 , the pumps  30  of the regeneration loop  14  and the pumps leading to the fluid containers. Each of the pumps  24   a ,  24   b , pump  30 , pump  19  and pump  46  can be provided with the capacitance volume sensor  66  of the present invention. Each of the sensors  66  sends a discrete signal to the controller (not illustrated), which measures and monitors the volume of fluid flowing through the pump chambers of the respective pumps. In other embodiments, any suitable fluid volume measurement device can be used. 
     Alternative Dual Loop System with Gas Separation 
     Referring now to  FIG. 4 , a system  110  of the present invention is illustrated. The system  110  of  FIG. 4  is similar to the system  100  of the  FIG. 3  and is a closed loop system. The system  110  includes various components of the system  100  described previously. The system  110  has a regeneration loop  14  which has a pair of balanced dialysate fluid pumps created by a pair of chambers  75  that operate with the pumps  30 . Each balance chamber  75  includes a pair of chambers separated by a membrane. When one of the pumps  30  fills one side of the chambers of the balance chambers  75  fills with medical fluid, the membrane is forced toward the other chamber, which forces fluid out of that chamber. In this way, the membrane acts to balance the flow of the dialysate fluid within the regeneration loop  14 , so that there is no net flow of fluid across the dialyzer membrane except for the flow needed to replace the fluid removed by the ultrafiltrate pump  19 . 
     Another difference of the system  110  of  FIG. 4  compared to the system  100  of  FIG. 3  is the gas separator  50 . The gas separator  50  in the illustrated embodiment of the system  110  is independent of the sorbent cartridge  32 . The gas separator  50  accepts gas through a vent line  51  that runs from the exit port  59  of the heater  54  in the patient fluid loop  12 . One or more gas sensors  52  monitor gas in the vent line  51  as illustrated. 
     Disposable Cassettes 
     Referring now to  FIG. 5 , a dialysis system having a disposable cassette  120  according to the present invention is illustrated. In this variation of the system  100  of  FIG. 3 , the pumps  30  of system  120  draw fluid from accumulators A 4  and A 6  and discharge into accumulators A 3  and A 5 . Accumulators A 3  to A 6  smoothen the dialysate flow by dampening pressure fluctuations during pumping. In an embodiment, much of the flow logic and at least parts of the flow devices described above are provided in the disposable cassette  120 . The cassette  120 , in an embodiment, has a rigid plastic body  122  with various fluid flow channels and fluid chambers defined in the body  122 . A flexible membrane is bonded to the front side of the cassette body  122  shown in  FIG. 5 . The membrane covers the fluid channels and chambers and is sealed to the body  122  around the channels and chambers. Accordingly, the membrane forms a wall of the fluid flow paths and fluid chambers. Similarly, the back side of the cassette body  122  may also be covered with a membrane. 
     The body  122 , in an embodiment, is approximately 12 inches high, eight inches wide, and one inch deep. The flow components and flow lines defined by the body  122  fluidly connect to other system components. Also, pump actuators, valve actuators, sensors and other system components may interface with the cassette  120 . 
     Specifically, the body  122  provides a portion of the closed patient the regeneration loops  12  and  14 . The dual lumen catheter  22  that inserts into the peritoneal cavity of the patient  16  connects to the dual lumen connector  20  outside of the body  122  of the disposable cassette  120 . The patient loop  12  extends from an exit port  124  of the dialyzer  26  to a valve chamber  126  defined by the body  122 . The patient fluid loop  12  includes a series of manifolds and fluid flow paths that fluidly connect to the patient fluid pump(s)  24 . The patient fluid pump  24  pumps the dialysate through the patient  16  and into an inlet  128  of the dialyzer  26 . 
     The patient fluid loop  12  also connects via pathways defined by the body  122  of the disposable cassette  120  to various medical fluid bags. For instance, the dialysate fluid bag  18 , which is maintained outside of the disposable cassette  120 , fluidly connects to a line  130  leading to the patient fluid loop  12 . Similarly, the last bag  21  also connects via a line defined by the body  122  to the line  130  that fluidly communicates with the patient fluid loop  12 . The line  130  defined by the body  122  also fluidly communicates with the ultrafiltrate drain  38 . 
     The body  122  of the disposable cassette  120  also defines chambers for the concentrate pump  46  and the ultrafiltrate pump  19 . The concentrate pump  46  fluidly connects to an external concentrate bag  44 . The twenty-four hour collection bag  39  described above fluidly connects along with the drain  38  to a fluid line defined by the body  122  that runs to the ultrafiltrate pump  19 . 
     The disposable cassette  120  provides fluid flow paths and defines chambers and other types of fluid orifices for the fluid flow components described above. Specifically, the body  122  of the disposable cassette  120  defines a patient fluid pump chamber  24  and dialysate fluid pump chambers  30 . The disposable cassette  120  mounts to a separate non-disposable housing that includes the mechanical workings of the flow components, such as the pumps. The pump chambers are bounded on one side by a flexible membrane (not illustrated) that is positioned adjacent to and driven by the pump plungers of the non-disposable housing. 
     At least one side of the cassette  120  is covered with the flexible, e.g., plastic membrane (not illustrated). The disposable cassette  120  plugs into a cavity or portion of the non-disposable housing (not illustrated). The housing provides the actuators for each of the pumps herein described, e.g., the patient pumps  24 , the dialysate pumps  30 , the ultrafiltrate pump  19  and the concentrate pump  46 . The housing also provides the actuators for the various valve chambers defined by the body  122  of the cassette  120 , e.g., valve chamber  126 . The more expensive mechanical and electromechanical pieces of the flow components, e.g., the pump actuators and valve actuators, are kept and reused in the housing. 
     The disposable cassette  120  provides sterile, disposable fluid pathways, such as the pump chambers and the valve chambers. The actuators of the non-disposable housing press against the flexible plastic membrane at the pump chambers and valve chambers to force or allow fluid through the system. When the pump actuator pulls back from pressing against the membrane, the membrane returns to its normal shape and no longer exerts a force on the fluid within the pump chamber. The pump chamber fills with fluid as the membrane is drawn back. Also, the membrane can be positively drawn back by, for example, the pump actuator or vacuum pressure. The pump has thus made a cycle. 
     The body  122  of the disposable cassette  120  also defines at least a portion of a mounting area for housing the ammonia, ammonium or pH sensors or adjustors. In the illustrated embodiment, the disposable cassette  120  defines an area for housing the pH adjustor  71  and a disposable colormetric membrane (which changes color based on the ammonia/ammonium concentration) of the ammonia/ammonium sensor  73 , wherein the fluid within the body  122  of the cassette  120  can fluidly communicate with the sensor. The optical color reader of the ammonia/ammonium sensor  64  is disposed in the non-disposable housing (not illustrated), wherein the sensor can receive electrical power as needed. If a pH sensor is used instead of the pH adjustor  71 , a reusable portion of the pH sensor can also be located in the housing. 
     The housing also provides the in-line heater  54  and in an embodiment provides one of either the radiant heater  56  and the plate heater  58 , which is described in detail in the patent application entitled, “Medical Fluid Heater Using Radiant Energy,” Ser. No. 10/051,609, mentioned above. Further, the housing provides one of the capacitor plates of the fluid volume sensor  66  beneath one or more of the pump actuators, as described in detail in the patent application entitled, “Capacitance Fluid Volume Measurement,” Ser. No. 10/054,487, mention above. 
     Referring back to the cassette  120  of  FIG. 5 , the cassette  120  has an in-line heating fluid heating path  123  for heating the fluid. The fluid in the heating path  123  is heated by a heater external to the cassette. 
     The cassette  120  also has one or more gas separators  125  which separate gas from fluid in the cassette  120 . The gas separators  125  feed the separated gas through a line  127  to a vent  129 . 
     The closed loop system of the present invention enables at least one waste component to pass through the membrane  28  of the dialyzer  26  from the patient fluid loop  12  to the regeneration loop  14 . The patient loop  12  extending outside of the body  122  fluidly connects to a valve chamber  132  defined by the body  122 . The regeneration loop  14  includes manifold sections defined by the body  122  and leads to pump chambers  30 . The closed loop system prevents air or other fluids from entering the system. 
     The pump chambers  30  fluidly communicate with the sorbent chemical cartridge  32  and the gas separator  50  of the combined device  102 . The regeneration loop  14  extends from the outlet  36  of the combined device  102  and returns to the body  122  of the disposable cassette  120  through the valve chamber  134 . From the valve chamber  134 , the regenerated dialysate is pumped through the pump chambers  30  and into the manifold system defined by the body  122 . 
     Referring now to  FIG. 6 , another closed loop system having another disposable cassette  140  is illustrated. This embodiment of the disposable cassette  140  of the present invention includes many of the same flow components and flow chambers as the cassette  120  of  FIG. 5 . The cassette  140 , however, only includes a single regeneration pump body  30 . The cassette  140  in general, is less complicated than the cassette  120  and illustrates that the disposable cassettes of the present invention may be adapted for different embodiments of the closed loop dialysate regeneration systems described herein. 
     Like the cassette  120  of  FIG. 5 , at least one side of the cassette  140  is covered with a flexible, e.g., plastic membrane (not illustrated). The disposable cassette  140  plugs into a non-disposable housing (not illustrated) that provides the actuators for the various pumps, e.g., the patient pump  24 , the dialysate pump  30 , the ultrafiltrate pump  19  and the concentrate pump  46 . The housing also provides the actuators for the various valve chambers defined by the body  122  of the cassette  140 . The more expensive mechanical and electromechanical pieces of the flow components, e.g., the pump actuators, are again kept and reused in the housing. As described above, the actuators press against the flexible plastic membrane at the pump chambers to force fluid through the system. 
     As illustrated in both  FIGS. 5 and 6 , the disposable cassette  120  or  140 , in combination with certain external devices such as the dialyzer  26 , sorbent cartridge and gas separator device  102  and the fill and drain bags, provides completely closed loop systems. The only make-up or additional fluid that the regeneration system uses is that of the concentrate from the concentrate bag  44 , which seals to a device within the body  122  of the cassettes  120  and  140 . Also, other than the systems being connected to a patient, fluids and air cannot enter the closed loop system. 
     Referring now to  FIG. 7 , a schematic diagram illustrates the different physical components of a disposable set of the regeneration systems of the present invention. The disposable set is intended to be used for a single dialysis therapy and then discarded. Another disposable set is used for the next dialysis therapy. Each of the above-described systems  10 ,  100  and  110  in an embodiment includes a disposable cassette, such as the cassette  120  or  140 . The disposable cassette  120  or  140  provides a port  141  that connects to the concentrate bag  44  via a line  147 . The cassette provides a port  142  that fluidly connects to the drain bag  38  via a line  148 . The cassette provides a port  143  that fluidly connects to the last bag  21  via a line  149 . The cassette defines a port  144  that fluidly connects to the dialysate bag  18  via a line  150 . The cassette provides ports  145  and  146  that run to and from the dual lumen connector  20  via patient lines  151  and  152 , respectively. 
     In an embodiment, each of the lines  147  to  152  are made of medical grade tubing, such as a flexible, sterile and inert plastic such as polyethylene, polystyrene, polypropylene or polyvinylchloride (“PVC”). In an embodiment, the bags and the lines are clear so that the patient or operator can see fluids traveling from the bags and through the lines to a cassette  120  or  140 . The lines  147  to  152  connect to the ports  141  to  146  via any type of medical fluid connection known to those of skill in the art. In an embodiment, the connections are quick-type connections that enable the patient or operator to easily remove the line from its mating port. 
     The disposable cassette  120  or  140  includes at least one port  153  that fluidly connects to at least one outlet port  154  of the gas separator  50  or combination device  102 . The disposable cassette  120  or  140  includes at least one port  155  that fluidly connects to at least one inlet port  156  of the sorbent cartridge  32  or combination device  102 . The lines connecting the disposable cassette  120  or  140  to the sorbent cartridge  32 , gas separator  50  or combination device  102  including same are made of medical grade tubing, such as a flexible, sterile and inert plastic such as polyethylene, polystyrene, polypropylene or polyvinyl chloride. 
     Alternative Dual Loop System 
     Referring now to  FIG. 8 , an alternative closed loop regenerative system  160  is illustrated. The system  160  is shown schematically, however, the system  160  may employ the disposable set described above such as the disposable cassette, the fluid pumps, the various sensors, valves and controller. The system  160  includes a patient fluid loop  12  and a regeneration loop  14 . 
     When dialysate is removed from the peritoneal cavity of the patient  16 , the solution passes through an activated charcoal and anion exchanger  162 . The activated charcoal of the filter or exchanger  162  removes uric acid, creatinine, small molecular weight organics and middle molecules. The anion exchange column of the exchanger  162  removes phosphate. The solution exiting the filter or exchanger  162  enters a solution or dialysate bag  18 . The dialysate entering the solution bag  18  has two possible places to exit. One possibility includes exiting the solution bag  18  from a port  163 , entering a filter  166  and returning to the peritoneal cavity of the patient  16 . Another possibility includes exiting the solution bag  18  at a port  165  and entering a nanofilter  164 . The system  160  splits the dialysate fluid exiting the solution bag or container  18 . 
     The nanofilter  164  operates similar to the dialyzer  26  described above. The nanofilter  164  includes a membrane. The membrane of the nanofilter  164  rejects most electrolytes, i.e., allows most of the electrolytes to return to the solution bag. The nanofilter  164 , however, filters most all of the urea and a small amount of sodium through the membrane and into a sorbent system cartridge  32 , which is similar to the sorbent cartridges described above. The sorbent cartridge  32  as described above absorbs and the urea from the fluid that is able to permeate through the membrane of the nanofilter  164 . 
     A plurality of pumps (not illustrated) are provided to individually circulate medical fluid or dialysate through the patient loop  12  and the regeneration loop  14 . The pump or pumps that control the recirculation through the regeneration loop  14  are adapted to circulate the regenerating fluid at a different flow rate, i.e., much faster, than the flow rate of fluid pumped through the patient loop  12 . It is believed that by using this method, the need for a concentration bag such as the concentration bags  44  described above would not be needed. Thus, it should be appreciated that the system  160  is a closed loop system that does not require any sort of make-up materials or any continuous source of outside fluid. The system  160  is therefore very adept at keeping air and other contaminants from entering the system. 
     In an alternative embodiment, the a reverse osmosis membrane or an electrooxidation system replaces the sorbent cartridge  32 . In this alternative embodiment, a reconstitution or concentration bag, such as the concentration bag  44 , is likely to be necessary. 
     The regeneration loop  14  removes urea at a rate of approximately 50 to 80%. The dialysate returns to the peritoneal cavity of the patient  16  substantially free from uric acid, creatinine, small molecular weight organics and middle molecules. Further, the nanofilter  164  can reject calcium magnesium at a rate of approximately 98% and glucose at a rate of approximately 80%. The permeate stream exiting the nanofilter  164  includes urea, approximately 70% sodium chloride and approximately 20% glucose. It should be appreciated that the system  160  is useful for performing continuous flow peritoneal dialysis. 
     Dual Loop System for Hemodialysis 
     Referring now to  FIG. 9 , a system  170  is illustrated. Each of the previous systems  10 ,  100  and  110  of  FIGS. 1 ,  3  and  4 , respectively, can be used for peritoneal dialysis or hemodialysis. However, each of the systems described above has been primarily described and illustrated using peritoneal dialysis, that is, the patient loop has been illustrated using a dialysis solution. The system  170  illustrates that the dual lumen catheter or two single lumen catheters can be replaced by a hemodialysis needle  171 , which connects to the arm (or other suitable portion) of the patient  16  to withdraw blood through the hemodialysis needle  171 . 
     The system  170  illustrates that the patient&#39;s blood flows through the patient loop  12  while dialysate flows through the regeneration loop  14 . The patient&#39;s blood flows along one side of the membrane  28  of the dialyzer  26 , while the dialysate flows along the outside or other side of the membrane  28  of the dialyzer  26 . The waste components and ultrafiltrate transfer from the patient&#39;s blood in the patient loop  12 , through the membrane  28 , into the dialysate in the regeneration loop  14 . 
     The system  170  includes a fixed volume recirculating regeneration loop  14  that dialyzes the patient fluid loop  12 . A single pump  172  operates to remove the ultrafiltrate from the patient  16  to the ultrafiltrate container  38 . The pump  172  adds dialysis fluid from the dialysis bag  18  or concentrate from the concentrate bag  44  to the regeneration loop  14 . In an alternative embodiment, the concentrate can be metered into the dialysate of the regeneration loop  14  as a solid prior to or during therapy. 
     As an alternative to the capacitance volume sensing described above, the volume of dialysate fluid flowing through the regeneration loop  14  can be determined using an electronic balance  174  illustrated below the dialysate bags. The electronic balance  174  keeps track of the amount of dialysate that is supplied to the system during a priming of the system. The electronic balance  174  also monitors any additional dialysate added to the patient loop  12  during dialysis treatment. The electronic balance  174  measures the amount of ultrafiltrate that is withdrawn from the system and the amount of the concentrate that is added from the concentrate bag  44 . In other alternative embodiments, any of the systems described herein can be sensed using other types of flowmeters or devices employing Boyle&#39;s Law known to those of skill in the art. 
     The system  170  removes ultrafiltrate by opening a valve chamber and transferring a known volume of the fluid into the ultrafiltrate bag  38 . The removal of fluid creates a pressure differential across the membrane  28  of the dialyzer  26 , which causes fluid to filter through the dialyzer membrane  28  and into the regeneration circuit  14 . Sterile dialysate from a supply bag  18  is infused into the patient circuit  12  as required. Concentrate from the concentrate. bag  44  can also be infused into the regenerating circuit  14  as needed. Pressure sensors  176  monitor and control the rate at which the system  170  draws ultrafiltrate into the container  38 . 
     Gas sensors  52  are used to prevent air from being delivered to the patient  16 . In an embodiment, a multi-analyte sensor  178  is employed to monitor the concentration of electrolytes in the regenerated dialysate as well as the efficiency of the regeneration system in removing uremic toxins. The output of the multi-analyte sensor  178  controls the rate of reconstitution from the concentrate bag  44 , the efficiency of the regeneration system and can detect the presence of a leak in the dialyzer. A vent  180  vents air that becomes trapped in the system or CO2 that is generated by the absorbent cartridge  32 . In an alternative embodiment, an automated valve that is provided integrally with the adsorbent cartridge  32  replaces the mechanical vent  180 . 
     Although the system  170  is illustrated as a hemodialysis system, the system  170  is easily converted to a peritoneal dialysis system by placing the catheter into the patient&#39;s peritoneal cavity and by running dialysate through the patient loop  12  as opposed to the patient&#39;s blood. The ultrafiltrate bag  38 , the dialysate container  18  and the concentrate container  44  each fluidly connect to the regeneration loop  14  and the patient circuit is kept relatively simple. The system  170  is especially conducive for continuous flow of peritoneal dialysis, however, standard APD and TIDAL therapies could be performed in the system  170 . 
     Multi-Purpose Container 
     Referring now to  FIG. 10 , a combined absorbent cartridge, pump and valve system is placed into a single container, e.g., a canister, cartridge or cassette  190 . The combination container  190  is illustrated as housing the components specifically described in the system  170  of  FIG. 9 . However, the combination container  190  is adaptable to house the components of any of the above-described systems, namely, the systems  10 ,  100  and  110 . The canister, cartridge or cassette is adaptable to be made of any material such as plastic or metal. The container  190  includes the adsorbent cartridge  32 , which is configured as described above. Alternatively, the container includes the combination device  102  that provides the adsorbent cartridge  32  and the gas separator  50 . 
     The container  190  includes the pumps illustrated in  FIG. 9  including the pump  172  that enables dialysate to be drawn from the dialysate bag  18  or concentrate to be drawn from the concentrate bag  44 . Additionally, the pump  172  enables ultrafiltrate to be drained into the bag  38 . In an embodiment, the container  190  includes the multi-analyte sensor  178  and the gas sensor  52 , as described in the system  170  of  FIG. 9 . The container  190  also includes the mechanical or automated vent  180  described in the system  170 . Thus, the only devices external to the container  190  are the dialysate bags and the hemodialysis needle  171  that is inserted in the patient&#39;s arm or other extremity to perform hemodialysis. Obviously, by the multi-lumen connector  20  and catheter  22  can replace the needle  171  to perform peritoneal dialysis. 
     When the container  190  is provided in the form of a disposable cassette, the cassette  190 , like the cassettes  120  and  140  of  FIGS. 5 and 6 , is covered on at least one side with a flexible, e.g., plastic membrane (not illustrated). The disposable cassette  190  plugs into a non-disposable housing that provides the actuators for the various pumps, e.g., the patient pumps  24 , the dialysate pumps  30 , the ultrafiltrate pump  19  and the concentrate pump  46 . The more expensive mechanical and electromechanical pieces of the flow components, e.g., the pump actuators, are again kept and reused in the housing. The sorbent cartridge  32  and the gas vent  180  can be disposable. 
     The above specification has been broken down into headings for purposes of readability, clarification and to promote the enablement of the present invention. The headings are in no way intended to limit the combined teachings of the present invention. The features taught under any given heading are not limited to the embodiments disclosed under the heading. The present invention includes any combination of features from the disclosures under the different headings provided herein. Further, while the presently preferred embodiments have been illustrated and described, numerous changes and modifications can be made without significantly departing from the spirit and scope of this invention. Therefore, the inventors intend that such changes and modifications are covered by the appended claims.