PERITONEAL DIALYSIS SYSTEM HAVING CARBON DIOXIDE INJECTION TO INHIBIT/REMOVE CALCIUM CARBONATE

Abstract

A peritoneal dialysis (“PD”) system includes a PD fluid pump; a disinfection loop including the PD fluid pump, the disinfection loop including PD fluid used for disinfecting the disinfection loop; and a carbon dioxide (CO.sub.2), source positioned and arranged to supply CO.sub.2 to the disinfection loop to inhibit and/or remove the production of calcium carbonate (CaCO.sub.3) during a disinfection sequence. The PD system includes a control unit configured to open a valve to allow CO.sub.2 to be supplied, wherein the control unit may use a lookup table or algorithm to determine the desired pressure or pressure increase.

Claims

1. A peritoneal dialysis (“PD”) system comprising: a PD fluid pump; a disinfection loop including the PD fluid pump, the disinfection loop including PD fluid used for disinfecting the disinfection loop; and a carbon dioxide (CO.sub.2), source positioned and arranged to supply CO.sub.2 to the disinfection loop to inhibit and/or remove the production of calcium carbonate (CaCO.sub.3) during a disinfection sequence.

2. The PD system of claim 1, which includes a CO.sub.2 valve located between the disinfection loop and the CO.sub.2 source, the CO.sub.2 valve opened to allow the CO.sub.2 to be supplied to the disinfection loop.

3. The PD system of claim 2, which includes a control unit configured to cause the CO.sub.2 valve to open to allow the CO.sub.2 to pressurize the PD fluid to a desired pressure or pressure increase to inhibit and/or remove the production of calcium carbonate during the disinfection sequence.

4. The PD system of claim 3, which includes at least one pressure sensor outputting to the control unit, the control unit configured to monitor the at least one pressure sensor output to detect the desired pressure or pressure increase.

5. The PD system of claim 3, wherein the control unit is configured to use a lookup table to determine the desired pressure or pressure increase.

6. The PD system of claim 5, wherein the control unit stores a disinfection temperature to which the PD fluid is heated for the disinfection sequence, and wherein the desired pressure or pressure increase in the lookup table corresponds to the disinfection temperature.

7. The PD system of claim 6, which includes at least one temperature sensor outputting to the control unit, the control unit configured to monitor the at least one temperature sensor output to detect the disinfection temperature.

8. The PD system of claim 5, wherein the lookup table is specific to the type of PD fluid used for disinfection.

9. The PD system of claim 5, wherein the control unit knows a bicarbonate level for the PD fluid used for disinfection, and wherein the desired pressure or pressure increase in the lookup table corresponds to the bicarbonate level.

10. The PD system of claim 5, wherein the control unit is configured to take initial pressure and temperature readings prior to supplying CO.sub.2 to the disinfection loop, the control unit further configured to determine the initial amount of CO.sub.2 contained in the disinfection loop using the lookup table and the initial pressure and temperature readings.

11. The PD system of claim 3, wherein the control unit is configured to use an algorithm to determine the desired pressure or pressure increase.

12. The PD system of claim 3, wherein the control unit is configured to cause the CO.sub.2 valve to open to allow the CO.sub.2 to pressurize the PD fluid to the desired pressure or pressure increase prior to causing the PD fluid pump to run during the disinfection sequence.

13. The PD system of claim 3, wherein the control unit is configured to cause the CO.sub.2 valve to open to allow the CO.sub.2 to pressurize the PD fluid to the desired pressure or pressure increase while causing the PD fluid pump to run during the disinfection sequence.

14. The PD system of claim 3, which includes a PD fluid heater, and wherein the control unit is configured to cause the CO.sub.2 valve to open to allow the CO.sub.2 to pressurize the PD fluid to the desired pressure or pressure increase prior to causing the PD fluid heater to heat the PD fluid during the disinfection sequence.

15. The PD system of claim 3, which includes a PD fluid heater, and wherein the control unit is configured to cause the CO.sub.2 valve to open to allow the CO.sub.2 to pressurize the PD fluid to the desired pressure or pressure while causing the PD fluid heater to heat the PD fluid during the disinfection sequence.

16. The PD system of claim 3, wherein the control unit is configured to cause the CO.sub.2 valve to open to allow the CO.sub.2 to pressurize the PD fluid during a cool down period if a loss of pressure is detected by the control unit.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0052] FIG. 1 is a schematic view of one embodiment of an automated peritoneal dialysis (“APD”) machine or cycler and associated system of the present disclosure.

[0053] FIG. 2 is a simplified schematic view of one embodiment of an automated peritoneal dialysis (“APD”) machine or cycler of the present disclosure after treatment and prior to disinfection.

[0054] FIG. 3 is a simplified schematic view of one embodiment of an automated peritoneal dialysis (“APD”) machine or cycler of the present disclosure delivering CO.sub.2 to a disinfection loop.

[0055] FIG. 4 is a simplified schematic view of one embodiment of an automated peritoneal dialysis (“APD”) machine or cycler of the present disclosure pumping heated PD disinfection fluid containing delivered CO.sub.2 during disinfection.

[0056] FIG. 5 is a simplified schematic view of one embodiment of an automated peritoneal dialysis (“APD”) machine or cycler of the present disclosure optionally delivering CO.sub.2 to the disinfection loop during a cool down period.

[0057] FIG. 6 is an example lookup table stored in a control unit of an automated peritoneal dialysis (“APD”) machine or cycler of the present disclosure, the lookup table providing a pressure to achieve, or a pressure increase, due to CO.sub.2 injection, wherein the pressure is based on at least one of an amount of bicarbonate in the PD disinfection fluid and/or a disinfection fluid temperature.

[0058] FIG. 7 is an example alternative lookup table stored in a control unit of an automated peritoneal dialysis (“APD”) machine or cycler of the present disclosure, the lookup table providing a pressure to achieve, or a pressure increase, due to CO.sub.2 injection, wherein the pressure is based on a mole fraction of CO.sub.2.

DETAILED DESCRIPTION

System Generally

[0059] Referring now to the drawings and in particular to FIG. 1, automated peritoneal dialysis (“APD”) system 10 and associated methodology of the present disclosure includes an APD machine or cycler 20. System 10 and cycler 20 attempt to eliminate disposable items as much as possible and instead provide the majority of its fluid carrying portions as reusable components, which are disinfected after treatment. Fluid lines within the machine or cycler are reused. In particular, FIG. 1 illustrates that cycler 20 includes a housing 22 from which reusable PD fluid supply lines 24a to 24d extend. FIG. 1 further illustrates that a reusable patient line 26 also extends from housing 22 of machine or cycler 20. Reusable patient line 26, which is typically longer than reusable PD fluid supply lines 24a to 24d, may be coiled or rolled up within the housing via a spool or hose reel 28 when reusable patient line 26 is not connected to a patient for treatment.

[0060] When not connected to PD fluid containers or bags, the reusable PD fluid supply lines 24a to 24d and patient line 26 can be connected to dedicated connectors supported and provided by housing 22. The reusable PD fluid supply and patient lines may for example extend from a front of housing 22 and connect to connectors also provided at the front of the housing for ready access to the PD fluid and patient lines. In the illustrated embodiment, distal ends 24e of reusable PD fluid supply lines 24a to 24d releasably attach in a fluid-tight manner to disinfection connectors 30a to 30d, respectively, provided at housing 22. Distal end 26d of reusable patient line 26 releasably attaches in a fluid-tight manner to patient line connector 32 provided at housing 22. Disinfection connectors 30a to 30d and patient line connector 32 are configured in one embodiment to close or shut automatically when reusable PD fluid supply lines 24a to 24d and reusable patient line 26, respectively, are removed or not connected to the connectors.

[0061] FIG. 1 also illustrates that housing 22 provides a drain line connector 34, which may be releasably covered by a moveable, e.g., rotatable or slideable cover 34c. Drain line connector 34 receives a disposable drain line 36 for treatment, which may run to a drain container or bag or to a house drain. Disposable drain line 36 is disconnected from drain line connector 34 during disinfection.

[0062] Disposable PD fluid or solution containers or bags (not illustrated because system 10 is in a disinfection configuration with the containers or bags removed) are connected respectively to reusable PD fluid supply lines 24a to 24d. Distal ends 24e of reusable PD fluid supply lines 24a to 24d may be color coded and/or keyed to match a colored or keyed connector of a dedicated PD fluid container or bag. The containers or bags may hold the same or different dextrose or glucose level PD fluids, such as 1.36% glucose PD fluid, 2.27% glucose PD fluid, 3.86% glucose PD fluid and/or a last bag of a different formulation of PD fluid, such as icodextrin.

[0063] It should be appreciated that any number of reusable PD fluid supply lines 24a to 24d and PD fluid containers or bags may be provided, including a single reusable PD fluid line and PD fluid container or more than one reusable PD fluid lines and PD fluid containers. In a further alternative embodiment, the PD fluid containers or bags are replaced by an online PD fluid generation source, which connects to and communicates fluidly with a single reusable PD fluid supply line.

[0064] Besides disposable drain line 36 (and associated container if used) and the disposable PD fluid containers or bags, it is contemplated that in one embodiment, the only other disposable component of system 10 is a disposable filter set (not illustrated) removably connected by the patient at the distal end 26d of reusable patient line 26 to provide a final stage of PD fluid filtration prior to delivery to the patient. In an embodiment, the disposable filter set is spliced between the distal end 26d of reusable patient line 26 and the patient's transfer set, which leads to an indwelling PD catheter inserted into the patient.

[0065] It is contemplated that any one, or more, or all of reusable PD fluid supply lines 24a to 24d, reusable patient line 26, disinfection connectors 30a to 30d, patient line connector 32, drain line connector 34, drain line 36, the PD fluid containers or bags and the patient line filter set be made of any one or more plastic, e.g., polyvinylchloride (“PVC”) or a non-PVC material, such as polyethylene (“PE”), polyurethane (“PU”), polypropylene (“PP”) or polycarbonate (“PC”).

[0066] FIG. 1 further illustrates that reusable supply tube 52a runs from each reusable PD fluid supply line 24a to 24d, via a PD fluid supply valve 54a to 54d, respectively, to a PD fluid inline heater 56. In an embodiment, each of the valves of APD cycler 20, including PD fluid supply valves 54a to 54d, is an electrically actuated valve having a reusable valve body that occludes (e.g., when unpowered for fail safe operation) or allows (e.g., when powered) PD fluid to flow through the body. In the illustrated embodiment, valve 54d is a three-way valve having a normally open port for receiving PD fluid from reusable PD fluid supply line 24b or 24c and a normally closed port for receiving PD fluid from reusable PD fluid supply line 24d. PD fluid inline heater 56 is also electrically actuated in one embodiment and is, for example, a resistive heater having a reusable heater body that accepts PD fluid for treatment and for disinfection heating. Inline heater 56 in an embodiment is able to heat PD fluid from room temperature or colder (e.g., if the PD fluid is stored in a cold environment) to body temperature, e.g., 37° C., at a flowrate of up to at least 200 milliliters (“ml”)/minute.

[0067] A first temperature sensor 58a is located adjacent to inline heater 56, e.g., downstream from the heater to provide feedback for temperature control. If desired, a second temperature sensor (not illustrated) may be provided upstream from PD fluid heater 56 to enable the incoming temperature of fresh PD fluid to be taken into account for the heating algorithm. A second temperature sensor 58b is illustrated just downstream from PD fluid pump 70, which is provided for example as a second check that fresh PD fluid exiting PD fluid pump 70 is at a desired temperature for treatment, e.g., body temperature or 37° C.

[0068] In the illustrated embodiment, a flow switch 68 is located just upstream from PD fluid inline heater 56. An output from flow switch 68 is used to make sure there is PD fluid flow through inline heater 56. If the output (or lack thereof) from flow switch 68 indicates no or little PD fluid flow, which could be harmful to inline heater 56 if powered, causes system 10 to halt power to inline heater 56 and to stop treatment or disinfection if needed while (i) attempting to find a remedy to the no or low flow situation or (ii) causing an audio, visual or audiovisual alarm or alert at user interface 108. Alternative ways for ensuring flow to the inline heater 56 in order to power the heater may be used alternatively.

[0069] Reusable tube 52b runs from the outlet of PD fluid inline heater 56 to an airtrap 60 in the illustrated embodiment of FIG. 1. Any of the reusable tubing inside the housing of cycler 20, including reusable tubes 52a and 52b, may be made of metal, e.g., stainless steel or plastic, e.g., polyvinylchloride (“PVC”) or a non-PVC material, such as polyethylene (“PE”), polyurethane (“PU”), polypropylene (“PP”), polyether ether ketone (“PEEK”), or polycarbonate (“PC”). In an embodiment, one or more level sensor 62a and 62b is located adjacent airtrap 60, so that a desired level or range of levels of PD fluid is/are maintained in the airtrap. A fluid line valve 54e is located downstream from airtrap 60 in the illustrated embodiment and receives fresh, heated PD fluid from the airtrap. A gas line valve 54g is located along a gas line 52g extending from a top of airtrap 60. Airtrap 60 may be closed upstream by PD fluid supply valves 54a to 54d to drain the airtrap when dictated by the output of level sensor 62a or 62b.

[0070] A reusable fluid line 52c and gas line 52g run between fluid line valve 54e and gas line valve 54g, respectively, and a PD fluid pump 70 located within housing 22 of cycler 20. PD fluid pump 70 includes a reusable pump body that accepts PD fluid for pumping. That is, pump 70 does not require the PD fluid to flow within a disposable item, such as a tube or cassette. The reusable pump body of pump 70 itself accepts the PD fluid. PD fluid pump 70 may be of a type, e.g., piston pump, which is inherently accurate so that a separate PD fluid volume measurement apparatus, such as a balance chamber or flowmeter, is not needed. PD fluid pump 70 may alternatively be a less accurate gear or centrifugal pump that does operate with a PD fluid volume measurement apparatus. PD fluid pump 70 is controllable to pump to and from the patient at or below a pressure limit by controlling a level of current to the PD fluid pump. A positive patient pressure limit may for example be one to five psig (e.g., two psig (14 kPa)). A negative patient pressure limit may for example be −1.0 psig to −3.0 psig (e.g., −1.3 psig (−9 kPa)). PD fluid pump 70 is also capable of supplying lower pressures if needed, e.g., for small children or babies. PD fluid pump 70 is bidirectional and continuous in one embodiment, such that a single pump may be provided.

[0071] FIG. 1 further illustrates that a fresh PD fluid patient line valve 54f is located in an embodiment along reusable fresh PD fluid patient tube or line 52f between downstream temperature sensor 58b and spool or hose reel 28. Fresh PD fluid patient tube or line 52f communicates fluidly with a fresh PD fluid lumen of dual lumen reusable patient line 26 in one embodiment. A used PD fluid patient line valve 54u is located in an embodiment along reusable used PD fluid patient tube or line 52u between PD fluid pump 70 (via cross 64a) and spool or hose reel 28. Used PD fluid patient tube or line 52u communicates fluidly with a used PD fluid lumen of dual lumen reusable patient line 26 in one embodiment. A drain line valve 54h is located along reusable drain tube or line 52h that extends from a tee 66 to drain line connector 34.

[0072] A first patient pressure sensor 72a is located along fresh PD fluid patient tube or line 52f between PD fluid pump 70 and spool or hose reel 28 to measure positive patient PD fluid pressure. A second patient pressure sensor 72b is located along gas line 52g to measure negative patient PD fluid pressure during a patient drain (gas is at same negative pressure as used PD fluid via fluid communication at cross 64a). Third and fourth pressures sensor 72c and 72d are located along reusable disinfection tube or line 52d.

[0073] As discussed above, patient line connector 32 is located at APD cycler housing 22 and accepts dual lumen reusable patient line 26 during disinfection and generally while the patient is not undergoing treatment. Patient line connector 32 in one embodiment includes a sealed fluidic U-turn or 180 degree turn that allows disinfection fluid, e.g., heated PD fluid, to flow from one lumen of the dual lumen patient line to another lumen of the dual lumen patient line. Dual lumen reusable patient line 26 is therefore included in the disinfection loop.

[0074] As further discussed above, drain line 36 is flexible and disposable in one embodiment and connects to drain line connector 34 extending from housing 22 of APD cycler 20 during treatment. After treatment, drain line 36 may be removed during the disinfection sequence. Drain line connector 34 receives an internal, reusable drain tube or line 52h for delivering used PD fluid to drain line 36 during a patient drain. Drain line connector 34 also receives vent tube or line 52v for delivering gas, such as air or carbon dioxide (CO.sub.2), to drain line 36 during treatment. A vent valve 54v is located along vent tube or line 52v.

[0075] A reusable disinfection tube or line 52d as illustrated in FIG. 1 extends to a second cross 64b along with vent tube or line 52v and used PD fluid patient tube or line 52u. Reusable disinfection tube or line 52d includes a disinfection valve 54s. Disinfection tube or line 52d handles disinfection fluid, e.g., fresh, heated PD fluid, vent tube or line 52v handles vented gas, e.g., air, while used PD fluid patient tube or line 52u handles used PD fluid during treatment.

[0076] A bypass line 52y as illustrated in FIG. 1 is located between disinfection connectors 30c and 30d for use during disinfection. A similar bypass line 52z is provided between disinfection connectors 30a and 30b. During disinfection, heated disinfection fluid, such as PD fluid, is directed through bypass lines 52y and 52z to fully disinfect disinfection connectors 30a to 30d.

[0077] FIG. 1 also illustrates that system 10 includes a carbon dioxide (CO.sub.2) source 80, which may be connected fluidly to the disinfection loop for example between PD fluid pump 70 and pressure sensor 72a, e.g., via CO.sub.2 line 52o. A CO.sub.2 valve 54o is located along CO.sub.2 line 52o. As discussed in detail below, system 10 causes a desired and efficient amount of CO.sub.2 gas to be metered from CO.sub.2 source 80 into the disinfection fluid, e.g., PD fluid, just prior to disinfection to prevent and/or remove any build-up of calcium carbonate (CaCO.sub.3) as the PD fluid is heated. CO.sub.2 source 80 may for example be initially pressurized to 70 kPa (10 psig) to provide ample pressure over multiple disinfection sequences according to the pressurization scheme discussed herein.

[0078] FIG. 1 further illustrates that a gas or CO.sub.2 pressure regulator 74 and a CO.sub.2 pressure sensor 76 may optionally be located along CO.sub.2 line 52o upstream from CO.sub.2 valve 54o. CO.sub.2 pressure regulator 74 enables CO.sub.2 source 80 to be pressurized to a higher level so that is lasts longer. Regulator 74 then regulates the high incoming pressure from CO.sub.2 source 80 down to a smoothly outputted desired output pressure. The desired operating pressure for example may be slightly above the pressures (or pressure increases) to be achieved, which are obtained from table 110 or table 120 as discussed below in connection with FIGS. 6 and 7, respectively. CO.sub.2 pressure sensor 76 reads and outputs a pressure corresponding to the CO.sub.2 pressure remaining within CO.sub.2 source 80. A one-way or check valve 78 may also be provided and oriented so as to prevent fresh or used PD fluid from entering CO.sub.2 line 52o.

[0079] FIG. 1 still further illustrates that APD cycler 20 of system 10 of the present disclosure includes a control unit 100 having one or more processor 102 and one or more memory 104 that receive, store and process signals or outputs from the pressure sensors 72a to 72d, CO.sub.2 pressure sensor 76 if provided, temperature sensors 58a and 58b, flow switch 68 and possibly a conductivity sensor (not illustrated). Control unit 100 uses pressure feedback from pressure sensors 72a and 72b to control PD fluid pump 70 to pump fresh and used PD at safe patient and system pressure limits. Control unit 100 uses temperature feedback from temperature sensor 58a to control inline PD fluid heater 56 to heat the fresh PD fluid to, e.g., body temperature or 37° C. for treatment, and to 85° C. for disinfection. Control unit 100 uses flow switch feedback from flow switch 68 to determine whether to power PD fluid inline heater 56. Control unit 100 as discussed herein further uses feedback from pressure sensor 72a (and perhaps pressure sensor 72b) to determine how much CO.sub.2 has been delivered to a disinfection loop via CO.sub.2 line 52o.

[0080] Control unit 100 as illustrated in FIG. 1 also includes a video controller 106 that interfaces with a user interface 108, which may include a display screen operating with a touchscreen and/or one or more electromechanical button, such as a membrane switch. User interface 108 may also include one or more speaker for outputting alarms, alerts and/or voice guidance commands. User interface 108 may be provided with cycler 20 as illustrated in FIG. 1 and/or be a remote user interface operating with control unit 100. Control unit 100 may also include a transceiver (not illustrated) and a wired or wireless connection to a network, e.g., the internet, for sending treatment data to and receiving prescription instructions from a doctor's or clinician's server interfacing with a doctor's or clinician's computer.

[0081] Control unit 100 opens and closes PD fluid valves 54a to 54h, 54o, 54s, 54u and 54v in combination with the operation of PD fluid pump 70 and inline heater 56 to run a priming sequence, multiple patient fill sequences, multiple patient drain sequences, and a disinfection sequence after a PD treatment. The disinfection sequence readies APD cycler 20 for the next treatment. In an embodiment, remaining fresh PD fluid is heated after the final patient drain and is used as the disinfection fluid for disinfection.

[0082] To form a disinfection loop 90 for the disinfection sequence, each reusable PD fluid supply line 24a to 24d is connected to a respective disinfection connector 30a to 30d, reusable patient line 26 is connected to reusable patient line connector 32, and drain line 36 is removed in one embodiment, so that drain line connector 34 may close shut. As illustrated in FIG. 1, disinfection loop 90 includes patient line connector 32 (including its U-turn or 180 degree turn), both lumens of reusable dual lumen patient line 26, used PD fluid patient tube or line 52u, reusable disinfection tube or line 52d, reusable drain tube or line 52h, vent tube or line 52v, drain line connector 34, reusable PD fluid supply lines 24a to 24d, bypass lines 52y, 52z, and reusable tubes or lines 52a to 52c and 52f. Disinfection loop 90 also includes the insides of all flow components and fluid-contacting sensors located along the above-listed lines.

[0083] Control unit 100 may sequence certain of the valves along disinfection loop 90 during disinfection. For example, PD fluid supply valve 54a may be sequenced open and closed during disinfection to allow disinfection fluid to flow through supply valve 54a or be forced completely through reusable PD fluid supply line 24a. Control unit 100 may also cause PD fluid pump 70 to run sequentially in forward and reverse states during disinfection, so that the disinfection fluid may flow clockwise and counterclockwise through disinfection loop 90. Control unit 100 also causes inline heater 56 to heat the disinfection fluid, e.g., fresh PD fluid, to a desired disinfection temperature, such as 70° C. to 95° C.

[0084] The use of PD fluid containing bicarbonate as a disinfection fluid likely leads to the formation of calcium carbonate (CaCO.sub.3) in the disinfected flowpaths and flow components of disinfection loop 90 of PD machine or cycler 20. Carbon dioxide (CO.sub.2) from source 80 is provided accordingly just prior to disinfection to prevent and/or to remove the formation of calcium carbonate. FIGS. 2 to 5 illustrate a simplified version of disinfection loop 90, showing important components to the CO.sub.2 injection from source 80, including PD fluid inline heater 56, first temperature sensor 58a, PD fluid pump 70, fresh PD fluid patient pressure sensor 72a, CO.sub.2 source 80, CO.sub.2 line 52o, CO.sub.2 valve 54o and control unit 100. It should be appreciated however that the sequences described in connection with FIGS. 2 to 5 are equally applicable to the full disinfection loop 90 of PD machine or cycler 20 of system 10 in FIG. 1.

Lookup Table Based on Bicarbonate Level and/or Disinfection Temperature

[0085] Referring now to FIG. 6, the sequences of FIGS. 2 to 5 in an embodiment rely on a table 110 (or corresponding algorithm) stored in one or more memory 104 of control unit 100, which sets a pressure to achieve, or a pressure increase, due to the injection of CO.sub.2 based on at least one of a bicarbonate level in the PD disinfection fluid or a disinfection fluid temperature. As illustrated in FIG. 6, table 100 sets a pressure increase due to the CO.sub.2 injection or an overall pressure to be achieved (P.sub.11 to P.sub.46) by the CO.sub.2 injection as a function of at least one of solution bicarbonate composition (b.sub.1 to b.sub.4) and disinfection fluid temperature setting (T.sub.1 to T.sub.6). FIG. 6 accordingly illustrates the pressure (or pressure increase) to achieve as a function of both bicarbonate level and disinfection fluid temperature setting in a two dimensional array. FIG. 6 could alternatively however base the pressure (or pressure increase) to achieve as a function of only one of bicarbonate level or disinfection fluid temperature

[0086] Generally, the more bicarbonate present in the fresh PD fluid, the higher the pressure in table 110 needed due to the injected CO.sub.2 gas. And generally, the higher the disinfection PD fluid temperature, the higher the pressure in table 110 needed due to the injected CO.sub.2 gas. To populate table 110, experiments and/or calculations are performed varying bicarbonate levels against varied disinfection fluid temperatures to determine how much CO.sub.2 gas pressure is needed to effectively block the formation of calcium carbonate precipitation, while efficiently using CO.sub.2 gas, so as not to waste CO.sub.2, and so that the CO.sub.2 source 80 may be of a reasonable size, while still providing many disinfection sequence's worth of CO.sub.2.

[0087] Control unit 100 at the beginning of each disinfection sequence knows the bicarbonate level from the prescribed PD fluid used for the just-ended treatment. Control unit 100 also knows and sets the disinfection fluid temperature, which may be the same or be different for different disinfection sequences. Control unit 100 accesses table 110 (or corresponding algorithm) and finds the operating pressure (or pressure increase) to achieve based on the known bicarbonate level and the known disinfection fluid temperature. It should be appreciated that table 110 could alternatively compare disinfection fluid temperature against the type of bicarbonate-based PD fluid used, which is basically the same as comparing disinfection fluid temperature against bicarbonate level. It should also be appreciated that PD fluids not containing bicarbonate do not have the precipitation issues discussed herein. So when using a PD fluid for disinfection that does not contain bicarbonate, control unit 100 does not access table 110 and does not inject CO.sub.2 gas from CO.sub.2 source 80.

Lookup Table Based on Mole Fraction

[0088] Referring now to FIG. 7, the sequences of FIGS. 2 to 5 in an alternative embodiment rely on a table 120 (or corresponding algorithm) stored in one or more memory 104 of control unit 100, which uses a mole fraction of CO.sub.2. Table 120 of FIG. 7 represents the mole fraction of CO.sub.2, which depends on the type of disinfection fluid, e.g., type of PD fluid, PD fluid temperature (left-hand column, ° C.) and PD fluid pressure (upper row, kPA), wherein the mole fraction values populate the spaces corresponding to a given temperature and pressure. In an embodiment, a separate table (like table 120) is stored and is accessible by control unit 100 for each possible disinfection fluid or PD fluid, e.g., one for 1.36% glucose PD fluid, another for 2.27% glucose PD fluid and a third for 3.86% glucose PD fluid.

[0089] In one example for using a table 120 in FIG. 7, the following information is taken as being known and may be stored (or a portion thereof) in control unit 100: [0090] disinfection loop 90 volume is 200 ml [0091] CO.sub.2 source 80 holds 18 g of CO.sub.2 [0092] CO.sub.2 molar mass is 44.01 g/mol [0093] CaCO.sub.3 molar mass is 100.0869 g/mol [0094] disinfection fluid molar mass (assume that of H.sub.2O) is 18.02 g/mol [0095] disinfection fluid H.sub.2O density (assume that of H.sub.2O) is 0.96859 g/ml [0096] calcium content (Ca)′ of disinfection fluid is 1.25 mmol/L)

[0097] On a per disinfection sequence basis using the following chemical reaction for eliminating calcium carbonate, where H.sub.2CO.sub.3 is carbonic acid and HCO.sub.3 is bicarbonate, and wherein H.sub.2O is obtained from the PD fluid used for disinfection:

##STR00001## [0098] max CaCO.sub.3=1.25×0.2 mmol=0.25 mmol.fwdarw.0.25e.sup.−3×100.0869 g=0.025021725 g CaCO3 [0099] 1 mmol Ca.sup.2+.fwdarw.2 mmol H.sup.+ [0100] needed CO.sub.2=2×mmol CaCO.sub.3=0.5 mmol CO.sub.2.fwdarw.0.5e.sup.−3×44.01 g=0.022005 g CO.sub.2 [0101] one tank of 18 g CO.sub.2 with an effective use of 45%.fwdarw.18/0.022005×0.45=368 cycles of CO.sub.2

[0102] A goal of the CO.sub.2 injection is to increase the pressure measured by pressure sensor 72a, so that dissolved CO.sub.2 is maintained during the heated disinfection sequence at a predetermined amount calculated above to be 0.5 mmol. An assumption that the source of PD fluid used for disinfection, e.g., a bag of such fluid, is in equilibrium with the ambient surroundings regarding temperature and pressure is made, such that the initial partial pressure of CO.sub.2 may be assumed to be roughly 0.04 kPa (partial pressure of CO.sub.2 at ambient). Using table 120 of FIG. 7, and extrapolating from the 0.031 molar fraction valve at 5 kPa and 25° C. yields about 0.00031 molar fraction of CO.sub.2 at normal ambient conditions ((0.04 kPa/5 kPa) is roughly 1/10 of 0.031, which equals 0.00031 molar fraction).

[0103] In the example it is also assumed (and would be known in a commercial implementation) that the volume of disinfection or PD fluid circulated in disinfection loop 90 is 200 milliliters (“ml”). Knowing the density of the PD disinfection fluid (using density of water in the example), 200 ml of PD fluid equals 193.72 grams or 10.75 mols of the fluid in disinfection loop 90. At normal ambient conditions (5 kPa and 25° C.) 10.75 mols×0.00031 molar fraction yields 0.0033 mmols of CO.sub.2, which drops to 0.0012 mmols CO.sub.2 at 85° C. (0.00011 molar fraction×10.75 mols) as extrapolated from table 120 of FIG. 7 for 0.04 kPa at 85° C., which is a typical disinfection temperature. The drop dictates that 0.5012 (0.0012+0.5) mmols of CO.sub.2 needs to be injected into the heated PD fluid. 0.5012 (0.0012+0.5) mmols of CO.sub.2 in turn yields a needed molar fraction of 0.5012/10.75=0.0466, which in turn yields a partial pressure increase of about 21 kPa (3 psig) at 85° C. according to table 120 of FIG. 7.

[0104] Using the table 120 of FIG. 7 and the above knowns based on solid assumptions, which are programmed into control unit 100, control unit 100 can thereby calculate for a given PD fluid to be used as a disinfecting fluid, and a given disinfection temperature (each of which may be programmed into control unit 100 at the time of treatment, or be known from a patient's prescription), the pressure at which the disinfecting PD fluid needs to be increased via CO.sub.2 pressure from source 80, wherein the pressure is set in one embodiment by downstream CO.sub.2 pressure regulator 74.

CO.SUB.2 .Injection Steps

[0105] FIG. 2 illustrates a first step in which a PD treatment has been completed and it is time for control unit 100 to perform disinfection. Prior to beginning the disinfection sequence, control unit 100 in one embodiment, with CO.sub.2 valve 54o closed (not shaded), PD fluid pump 70 not actuated and inline heater 56 unenergized, finds the pressure (or pressure increase) to be achieved from table 110 of FIG. 6 based on a known bicarbonate level and/or disinfection temperature. Control unit 100 in an alternative embodiment, with CO.sub.2 valve 54o closed, PD fluid pump 70 not actuated and inline heater 56 unenergized, takes initial pressure and temperature measurements via pressure sensor 72a and temperature sensor 58a, respectively, to obtain an initial CO.sub.2 mole fraction value from the table 120 of FIG. 7. An optional pH sensor or CO.sub.2 sensor (not illustrated) may be provided and used alternatively or additionally to determine the initial CO.sub.2 mole fraction, however, the table 120 of FIG. 7 for the disinfection fluid will suffice and eliminates the need for extra sensors.

[0106] FIG. 3 illustrates a second step in which control unit 100, with PD fluid pump 70 not actuated and inline heater 56 unenergized, causes CO.sub.2 valve 54o to open (valve shaded), allowing CO.sub.2 to be injected into the PD fluid within disinfection loop 90. Control unit 100 may pulse CO.sub.2 or inject the CO.sub.2 continuously, but in either case control unit 100 monitors the output of pressure sensor 72a and stops injecting CO.sub.2 when the pressure achieves the needed pressure (or pressure increase (e.g., about 21 kPa (3 psig) at 85° C.)) from table 110 of FIG. 6 or table 120 of FIG. 7.

[0107] FIG. 4 illustrates a third step in which control unit 100 causes inline heater 56 to be energized and PD fluid pump 70 to circulate heated, disinfection fluid (PD fluid) about disinfection loop 90 in any of the alternative manners described above and at the elevated pressure obtained in FIG. 3. Heated disinfection fluid circulation takes place for a designated amount of time. During this time, the presence of the designated amount of CO.sub.2 at the elevated pressure prevents or removes calcium carbonate (CaCO.sub.3) according to the chemical reaction shown above. It should be appreciated that while CO.sub.2 valve 54o is shown as being closed (not shaded) in FIG. 4, in an alternative embodiment, control unit 10 may cause CO.sub.2 valve 54o to be opened so as to allow CO.sub.2 gas to be injected into disinfection loop 90 during a part or all of the heat disinfection.

[0108] FIG. 5 illustrates a fourth and perhaps optional step in which control unit 100 causes inline heater 56 to de-energize but continues to allow fluid pump 70 to circulate cooled-down PD fluid. During a cool down period, control unit 100 monitors the output of pressure sensor 72a to see if the output returns to the pressure level prior to heating in FIG. 4. If perhaps some leakage of CO.sub.2 has occurred and the pressure falls below the CO.sub.2 injected pressure at the end of FIG. 3, then control unit 100 may cause CO.sub.2 valve 54o to open (valve shaded) to allow additional CO.sub.2 to be injected, e.g., so as to re-reach the needed pressure increase (e.g., about 21 kPa (3 psig)) above the initial, starting pressure. The ammonia and/or CO.sub.2 sensor if provided may be used additionally or alternatively here. Note that the cooled-down PD fluid will have a higher mole fraction of CO.sub.2, such that the CO.sub.2 pressure will not need to be increased to the earlier level, e.g., to 21 kPa.

[0109] Control unit 100 in one embodiment causes valves 54e, 54f, 54g, 54h and 54u to be closed and CO.sub.2 valve 54o to open, so that PD fluid patient tube or line 52f is pressurized with CO.sub.2 gas to whatever pressure remains within CO.sub.2 source 80. Here, first patient pressure sensor 72a reads the pressure remaining within CO.sub.2 source 80 and sends a corresponding signal to control unit 100. In an alternative embodiment illustrated in FIG. 1, CO.sub.2 pressure sensor 76 is provided upstream from pressure regulator 74 so as to be able to read the pressure remaining within CO.sub.2 source 80 and send a corresponding signal to control unit 100. In either situation, control unit 100 in an embodiment is configured to send a message to a central location when it determines that the pressure level within CO.sub.2 source 80 is running low, so that a new CO.sub.2 source 80 may be ordered and delivered to the patient. User interface 108 may also provide an audio, visual or audiovisual message to the patient that CO.sub.2 source 80 is running low but that a new supply is on the way. Upon the patient receiving the new CO.sub.2 source 80, user interface 108 may also provide an audio, visual or audiovisual instructions to the patient as to how to replace the existing CO.sub.2 source 80 with a new CO.sub.2 source 80.

[0110] It should be understood that various changes and modifications to the presently preferred embodiments described herein will be apparent to those skilled in the art. It is therefore intended that such changes and modifications be covered by the appended claims. For example, while FIGS. 2 to 5 illustrate readings being taken from a single pressure sensor and temperature sensor, control unit 100 may alternatively analyze pressure and temperature outputs from multiple pressure and temperature sensors located at different locations along disinfection loop 90. As noted herein, the pressures listed in tables 110 and 120 of FIGS. 6 and 7, respectively, may be absolute pressure values or pressure increase or pressure delta values.