Patent Description:
Complex medical fluids are often administered to a patient through a variety of different medication delivery systems. For example, a medication delivery system such as a dialysis machine for performing peritoneal dialysis on a patient having decreased or total loss of kidney function uses a dialysis solution or dialysate that removes waste from the patient's bloodstream. In another example, infusion pumps for medication delivery deliver liquid drugs or medical fluids, such as morphine or the like to a patient based upon parameters entered into the medication delivery system. The above fluids can be a homogenous liquid, a mixed solution or a solution that includes particulates in a buffer liquid. Infusion pumps can for example be rotary, linear or roller type peristaltic pumps or piezoelectric pumps.

The concentration or presence of the medication in the solution being delivered to a patient is important because an improper dose or the administration of the wrong drug can cause serious problems. A problem associated with peritoneal dialysis, for example, is an improperly mixed or non-mixed solution being delivered to a patient. Certain types of dialysate are packaged in dual-chamber bags, in which one chamber includes a buffer solution and the other chamber includes a concentrated glucose solution. The chambers of the bag are separated by a peelable or frangible seal that the patient or caregiver ruptures to open. The pH value of either the buffer solution and the glucose solution is such that the liquids alone are potentially harmful to the patient. The resulting pH value of the two fluids properly mixed however is suitable for injection into the patient's peritoneum. With peritoneal dialysis, therefore, it is desirable to make sure that the peelable or frangible seal is ruptured so that the resulting solution is mixed properly.

Certain dialysates, such as those used in hemodialysis, are bicarbonatebased. Bicarbonate is unstable in the presence of magnesium and calcium and forms a precipitate after a period of time. Accordingly, bicarbonate based dialysate needs to be packaged in a dual chamber supply container or bag. Here, premature mixing of the bicarbonate and contents of adjacent chambers may have deleterious effects on the resulting combination or render the combination of contents useless after an extended time. Bicarbonate alone can also be physiologically unsafe for the patient. Accordingly, it is necessary to properly mix the bicarbonate and other solution to form a final solution before contacting any solution with the patient's blood. With hemodialysis, therefore, it is desirable to make sure that solution has been mixed timely and properly.

<CIT> discloses a peritoneal dialysis system comprising a conductivity cell arranged to contact concentrates for making dialysis fluid.

Again, with any medical fluid injection, it is important to know that the proper type and dose of a drug or medical fluid is being infused into a patient.

According to the present invention there is provided a peritoneal dialysis system according to claim <NUM>. Also according to the present invention there is provided a method for preparing a peritoneal dialysis fluid according to claim <NUM>. The disclosure is described generally for a dialysis or renal failure therapy system having a need to know fluid conductivity.

Generally, the systems involve the use of one or a pair of metal or conductive contacts placed in a fluid pathway, such as a disposable fluid pathway. Fluid pathways described herein include tubes, such as medical fluid supply tubes, drug infusion tubes, drain tubes, patient tubes, fluid heater tubes, etc. Other pathways include pathways defined by and occurring within a disposable fluid pumping/valving cassette. While the fluid pathways discussed herein are for the most part disposable (e.g., for handling sterile fluids), the pathways do not have to be disposable and, e.g., can be cleaned or sterilized between treatments.

The electrical contacts are used to sense a variety of fluid properties including conductivity sensing, needle or catheter access disconnection, temperature sensing, and valve leak detection. For conductivity sensing, a pair of electrodes is provided and a signal (e.g., current signal) is injected through the contacts and a fluid or hydraulic pathway in communication with the contacts. A resistance sensor measures a resistance of the fluid in the pathway between the contacts. A processor using one or more algorithm compensates for fluid temperature and calculates a conductivity using the sensed resistance. Solution conductivity sensitivity to temperature is approximately <NUM>% per °c.

Different fluids produce different sensed resistances, yielding different conductivities. With dialysate, for example. the inventors have found that conductivity can be used to sense between a dialysate buffer concentrate, a dialysate glucose concentrate and a mixed dialysate of buffer and glucose Using the same apparatus and method, concentration can be used to detect whether a proper drug is about to be administered to the patient or whether a proper dose of the drug is about to be administered. Other detectable fluids include but are not limited to a parenteral compounding fluid, an intravenous infusion fluid and a chemotherapeutic compounding fluid.

The above sensing can be done using an absolute analysis, e.g., comparing the measured conductivity to an acceptable range of conductivities. Certain types of sensing can be done alternatively on a relative basis, for example, sensing whether multiple chamber bags have been opened properly. For example, multiple chamber supply bags can have integral tubing connectors as shown below. The connectors are filled initially with solution concentrate from the side of the container where the connector is attached. Mixing of solution from the other chamber into the connector chamber does not immediately affect the solution in the integral tube connector. Thus the sensed conductivity signal of fluid flowing from a properly mixed container will have a characteristic step change from that of the unmixed fluid in the tube connector to that of the mixed solution in the opened bag or container. Thus an unmixed or improperly mixed solution can be detected as the absence of detecting this step change in measured conductivity of the solution initially flowing from the container. This approach is advantageous in one respect because it does not necessitate an absolute concentration calibration and use of a lookup table, Instead, the approach looks for a change in conductivity.

Disclosed herein are various conductivity cells employing a pair of electrodes having varying geometrics and surface areas with respect to the fluid path being sensed. The electrodes can be made of different materials and are integrated into a fluid tube or pumping cassette in a variety of ways. For example, the electrodes can be metal or of a conductive plastic. The electrodes are solvent bonded to the fluid pathway in one embodiment. In other embodiments, the electrodes are molded into the fluid pathway or sealed mechanically, e.g., via a retainer ring or threads. The surface area contact of the fluid and the electrodes can be controlled tightly by extending the electrodes entirely across the hydraulic pathway as opposed to partial insertion. However, an accurate apparatus for partial insertion is shown below.

The present disclosure also sets forth apparatus and associated electronics for interfacing with the conductivity cells, either integrated with tubing or a cassette.

It is another advantage of the present disclosure to provide an economical and efficient apparatus and method for incorporating conductive components into a tube or pumping cassette.

It is a further advantage of the present disclosure to provide an accurate apparatus and method for determining medical fluid constituents.

It is yet a further advantage of the present disclosure to provide a system and method for measuring conductivity.

It is yet another advantage of the present disclosure to provide apparatus and method for more accurately and safely controlling a renal failure therapy system.

Additional features and advantages are described herein, and will be apparent from, the following Detailed Description and the figures.

Referring now to the drawings and in particular to <FIG>, <FIG>, <FIG> and <FIG>, a renal failure therapy system <NUM> is provided. System <NUM> is applicable generally to include any type of renal failure therapy system, such as peritoneal dialysis ('PD"), hemodialysis ("HD"), hemofiltration ("HF"), hemodiafiltration ("HDF"), colorectal dialysis and continuous renal replacement therapy ("CRRT").

System <NUM> in the illustrated embodiment includes a dialysis instrument <NUM>. Dialysis instrument <NUM> is configured for whichever type of renal failure therapy system is used. Dialysis instrument <NUM> as seen in <FIG> includes a central processing unit ("CPU") <NUM> and a plurality of controllers <NUM> operable with central processing unit <NUM>. Central processing unit <NUM> also operates with a graphical user-machine interface ("GUI") <NUM>, e.g., via a video controller <NUM>, which includes a video monitor <NUM> and one or more type of input device <NUM>, such as a touch screen or electromechanical input device (e.g., membrane switch see also <FIG>).

As seen in <FIG>, dialysis instrument <NUM> accepts and operates with a disposable apparatus <NUM>. Disposable apparatus <NUM> can include any one or more of supply bags 32a to 32c (referred to herein collectively as supply bags <NUM> or individually, generally as supply bag <NUM>) shown here as dual or multi-chamber supply bags separating two fluids via a peel or frangible seal <NUM>, drain bag (not illustrated), a warmer bag <NUM>, bag tubes 38a to 38d (referred to herein collectively as tubing or tubes <NUM> or individually, generally as tube <NUM>) and a disposable pumping/valve cassette <NUM> (<FIG>). Depending on the type and structure of the renal failure therapy system <NUM>, one or more of the items of disposable apparatus <NUM> may not be needed. For example, any system can pump spent fluid to a house drain, such as a toilet or sink, instead of to drain bag. System <NUM> can also include an inline heater, in which case warmer bag <NUM> is not needed.

While three supply bags <NUM> are shown, system <NUM> can employ any suitable number of supply bags. Supply bags <NUM> are shown having multiple chambers 42a and 42b, separated by frangible seal <NUM>, which hold different solutions depending on the type of therapy employed. For example, chambers 42a and 42b can hold buffer and glucose for PD or acetate and bicarbonate solution for HD Supply bags <NUM> are alternatively single chamber bags, which hold a single solution, such as lactate or acetate. Alternatively, multiple chamber bags with more than two chambers may be employed to deliver parenteral nutrition solutions for example.

One embodiment of a disposable cassette <NUM> is shown in more detail below in connection with <FIG>. As seen in <FIG> and <FIG>, cassette <NUM> connects to supply bags <NUM>$ drain bag and warmer bag <NUM> via tubes 38a, 38b and 38c, respectively. Tube 38d runs to a patient connection <NUM>. As shown in detail below, suitable places to place the conductivity cells of system <NUM> include different areas of tubing <NUM>, e.g., in each of supply tubes 38a, in warmer bag tube 38c or patient tube 38d (could be two patient tubes, e.g., arterial and venous line, for hemodialysis). A conductivity cell can also be placed in cassette <NUM> as seen in <FIG>.

One primary reason for the conductivity cells described herein is to make sure that system <NUM> is delivering a proper solution or properly mixed solution to the patient, which in such case would make placing a conductivity cell in drain line 38b unlikely. However, an additional conductivity cell could be placed in drain line 38b, e.g., for diagnostic or therapy effectiveness purposes.

Placing the conductivity cell in solution lines 38a enables each supply bag <NUM> to be tested individually. Placing the conductivity cell in warmer bag tube 38c or patient tube 38d allows a single conductivity cell to ensure that proper fluid or properly mixed fluid is delivered to the patient, Likewise, placing the conductivity cell in the disposable cassette <NUM> enables a single conductivity cell to be used. Placement in cassette <NUM> has the added benefit that the cassette is already placed into operable contact with dialysis instrument <NUM> for operation. Placing the conductivity cell in tubing <NUM> in one arrangement requires that section of the tubing to be coupled operably to dialysis instrument It is contemplated however to provide a separate instrument or hardware device (see, e.g., hardware unit <NUM> of <FIG>), which operates with a conductivity cell located in one of tubes <NUM>.

Referring now to <FIG>, an electrical scheme <NUM> for a conductivity cell <NUM> (and other functions) is illustrated. The circuitry and processing for the electrical schematic <NUM> in one embodiment is placed on a printed circuit board ("PCB"), e.g., on one of controllers <NUM> or CPU <NUM>. The electronics includes a voltage or current source <NUM>, which for example is placed on safety controller <NUM>. Source <NUM> generates an electrical signal, which travels along lead or trace 74a, to one electrode 102a of cell <NUM> through a hydraulic or liquid pathway <NUM> of cell <NUM>, through a return electrode 102b, return lead or trace 74b, returning to source <NUM>. Frequency of the generated electrical signal is maintained at a desired level as seen below in connection with <FIG>.

Liquid pathway <NUM> interacts with a plurality of sensors, such as an electrical, e.g., voltage or resistance sensor <NUM> and/or a temperature sensor <NUM>. Electrical or resistance sensor <NUM> can be a current or voltage sensor, which in combination with a known driving voltage or current, respectively, allows for a calculation of resistance and conductivity. Resistance sensor <NUM> is used in a conductivity calculation as described in detail below. Temperature sensor <NUM> can be of a type such as a diode, thermistor, integrated circuit sensor, infrared sensor, or resistance temperature device ("RTD").

Electrical sensor <NUM> can also be used to detect a patient access disconnections One suitable access disconnection system ("ADS") is disclosed in copending patent application entitled, "Enhanced Signal Detection For Access Disconnection Systems", filed <CIT> assigned to the eventual assignee of the present disclosure ("The ' <NUM> application"). The referenced application discloses at least one system that looks for a change in impedance occurring in the dialysate path. Hydraulic or liquid pathway <NUM> can thus be part of the dialysate path. The referenced application also discloses at least one system that looks for a change in impedance occurring in a blood path. Hydraulic or liquid circuit <NUM> can also therefore be part of the blood path.

Temperature sensor <NUM> senses a temperature of the medical fluid, e.g., dialysate, and takes advantage of the invasive metal electrodes 102a and 102b (referred to herein collectively as electrodes <NUM> or individually, generally as electrode <NUM>). Knowing the temperature of the fluid is useful for fluid heating, patient safety, and perhaps pumping accuracy, e.g., for a volumetric system based on Boyle's Law. As seen, electrodes <NUM> can be multifunctional, which is true in any of the embodiments or configurations described below.

The signals from sensors <NUM> and <NUM> can be sent through a series of components (not illustrated), e.g., located on one of the controllers <NUM>, such as: (i) a filter or filters, which can act to filter noise from the signal, e.g., noise derived from the rotation from a blood pump to minimize a false negative and/or positive detection of needle dislodgment; (ii) a rectifier; (iii) a peak detector; and/or (iv) an analog to digital converter ("ADC") to digitize the signal. Controller <NUM> (referring to one of the controllers of <FIG>) or CPU <NUM> includes a memory that stores the digital signal, e.g., in a buffer, for processing by a processor, such as a digital signal processor ("DSP"), which can be located at controller <NUM> or CPU <NUM>.

Controller <NUM> or CPU <NUM> continuously measures the electrical, e.g., voltage signal and processes the signal over time. The processor in one embodiment compares the digitized signals to look for changes over time and/or to compare the signals with a baseline or set point. For ADS, for example, signals are compared to an expected or baseline signal. Controller <NUM> or CPU <NUM> continually performs a calculation to determine whether a difference in the sensed signal compared to an expected or baseline signal is large enough to constitute a needle dislodgement. Variations in treatment can cause the expected or baseline signal to drift. System <NUM> can account for this.

For conductivity sensing, the signals in one embodiment are compared to an absolute norm, e.g., a range of values stored in a database or lookup table in the memory of controller <NUM> or CPU <NUM>. If the conductivity falls within a safe range of conductivities, the dialysate is assumed to be mixed properly. Otherwise an alarm condition is reached as discussed below.

If electrical scheme <NUM> of system <NUM> senses an access disconnection or a conductivity of medical fluid or dialysate that is out of range, system <NUM> takes evasive action to ensure the safety of the patient. With ADS, the goal is to minimize blood loss from the patient. In an embodiment, safety controller <NUM> receiving the signals from sensors <NUM> and <NUM> sends an error message to CPU <NUM>, which in turn sends a command to an instrument controller <NUM> to cause instrument <NUM> to take one or more evasive action, such as to shut down a pump, occlude a line <NUM> or close a valve (and corresponding fluid pathway) of cassette <NUM>.

In an alarm state, CPU <NUM> in one embodiment also sends a command to GUI controller <NUM>. GUI controller causes GUI <NUM> to display a message, such as an error and/or instructional message, on video monitor <NUM>. Although not illustrated, instrument <NUM> can be equipped with speakers and sound or voice activation to sound an alarm or verbalize an alarm and/or corrective action. The visual or audible alarm alerts the patient, a medical care provider (e.g., doctor or registered nurse) or a non-medical care provider (e.g., family member or friend) of the conductivity error or needle dislodgment.

For ADS, the alarm function is particularly useful during dialysis therapy in a non-medical facility, such as in a home setting or self-care setting in which dialysis therapy is administered typically by the patient and/or a non-medical care provider in a non-medical setting or environment. The ADS alarms the patient or caregiver to ensure that the dialysis therapy has been terminated by, for example, checking that the blood pump has been automatically shut off to minimize blood loss to the patient.

For a conductivity error, the alarm can alert the patient or caregiver to check that peel seals <NUM> of dual chamber bags <NUM> have been opened. Instrument <NUM> of system <NUM> halts pumping and/or occludes one or more appropriate tubes <NUM> or fluid paths of cassette <NUM> and also causes any improperly mixed fluid to be dumped to drain. Once fluid of the correct conductivity is sensed, treatment can continue.

For a conductivity error in an infusion pump setting, the alarm can tell the hospital nurse or machine operator to check that the correct solution or solution having the correct dose of a medicament has been connected to the instrument <NUM>.

The communication between electrical scheme <NUM> and instrument <NUM> can be either hard-wired, for example if electrical scheme <NUM> is provided with instrument <NUM>. Alternatively, the communication is a wireless communication (e.g., wireless RF interface). For example if electrical scheme <NUM> is provided in a separate unit or housing (see, e.g., unit <NUM> of <FIG>), the separate unit can communicate wirelessly with instrument <NUM>. With a wireless interface, the separate unit can implement scheme <NUM> and have its own controller with memory, processing, power supply, etc., mentioned above. Additionally, the unit can include a transceiver for two-way communication with a transceiver located within instrument <NUM>.

Referring still to <FIG>, the operation of cell <NUM> as a conductivity sensor is described. Here, system <NUM> uses an electrical signal, e.g., current, between spaced-apart electrodes 102a and 102b to test the quality of a medical fluid to be delivered to a patient, e.g., in a renal failure therapy setting or drug infusion setting. Electrodes <NUM> are disposed within the flow path <NUM> of the medical fluid so as to contact the medical fluid.

Assuming flow path <NUM> to have a length L and cross-sectional hydraulic area Ah, assuming the dialysate or drug to be an isotropic, homogeneous material, and assuming that signal source applies a signal having a current i at a voltage V, then the conductivity of the isotropic, homogeneous material can be expressed as: <MAT> which can be expressed in units of mS/cm. The geometry of cell <NUM> of <FIG>, in which the entire cross-sectional hydraulic area Ah contacts or is contacted by an electrode <NUM>, simplifies conductivity measuring but is problematic to a flow-through system. Some of the hydraulic area Ah needs to be uncovered or not contacted by an electrode <NUM> to allow fluid to flow past the electrode. In such a case, a cell constant k is added to the equation to account for the specific geometry of: (i) hydraulic area Ah, (ii) the contact area and shape of the electrode <NUM>, and (iii) the relation of (i) to (ii). The conductivity of the isotropic, homogeneous material in the flow-through system is now expressed as: <MAT>.

<FIG> and <FIG> illustrate alternative electrical systems <NUM> and <NUM>, respectively. Systems <NUM> and <NUM> include CPU <NUM>, controllers <NUM>, GUI <NUM>, monitor <NUM> and input devices <NUM> as shown and described above with system <NUM> of <FIG>. Accordingly these apparatuses are not shown in these additional figures. The primary difference with systems <NUM> and <NUM> versus system <NUM> involves the addition of redundant contacts and sensing, which ensure proper performance regardless of or provides a detection of a faulty or improperly made electrical contact between at least electrodes <NUM> and the instrument or machine <NUM>. Systems <NUM> and <NUM> mitigate a contact failure mode that may not be detectable with system <NUM>.

System <NUM> shows dual contacts on each electrode 102a and 102b that compensate for a poor electrical connection between the instrument <NUM> (<FIG> and <FIG>) and either electrode <NUM>. As shown, system <NUM> includes a signal source <NUM> applying a known signal, e.g., voltage signal, to contacts 102a and 102b. Sensor <NUM> is shown here as a current meter, which measures the current flowing from signal source <NUM> to conductivity cell <NUM>. The secondary contact at each electrode 102a and 102b communicates with a voltage meter <NUM>, which measures the actual voltage applied to the electrodes <NUM>. The ratio of the measured current to measured voltage, and other system constants, are used to determine the conductivity of the fluid between the electrodes.

All of the current measured through electrodes <NUM> supplied from signal source <NUM> must be applied through the fluid because there is no other path that the current can take between the electrodes. If there is a relatively poor electrical contact between the signal source and the electrode, however, the voltage applied to electrodes <NUM> decreases, while the current supplied through electrodes <NUM> remains within normal specifications. If voltage meter <NUM> measures a voltage at the electrodes <NUM> that is outside a normal operating voltage due to an inadequate electrical contact between signal source <NUM> and electrodes <NUM>, the electronics within instrument <NUM> detects the voltage as being out of specification and signals a faulty cassette or cell loading alarm. Instrument <NUM> can confirm such condition by detecting a large difference between the voltage that signal source <NUM> applies versus the voltage that voltage meter <NUM> measures.

System <NUM> shows another alternative embodiment in <FIG>. System <NUM> includes signal source <NUM>, current meter <NUM> (for conductivity determination) and voltage meter <NUM> discussed above with system <NUM>. System <NUM> additionally measures a contact resistance between conductivity cell <NUM> and instrument <NUM>.

Switches S1 and S2 connect an ohmmeter <NUM> to electrodes 102a and 102b, respectively, for example in a multiplexed fashion at the beginning of therapy to interrogate the electrical connection at each electrode 102a and 102b separately. Ohmmeter <NUM> measures a total resistance between electrodes <NUM> and the electronic circuits contained within instrument <NUM>. After the resistance is determined to be within an allowable tolerance, switches S1 and S2 connect the electrodes <NUM> to signal source <NUM> and voltage meter <NUM>. It should be noted that system <NUM> can connect signal source <NUM> and voltage meter <NUM> to each other within instrument <NUM> so that the signal source and voltage meter do not need to be connected separately at electrodes <NUM> as shown in <FIG>.

Referring now to <FIG>, cell 100a illustrates one suitable flow-through conductivity cell. The electrodes of cell 100a can be used alternatively or additionally for any of the types of sensing discussed herein, e.g., needle/catheter access disconnection, valve leak detection, and temperature sensing. For ease of illustration, the tube or conduit of cell 100a is labeled conduit <NUM>, <NUM>, which signifies that cell 100a can be part of different fluid flow structures, such as cassette <NUM>, one of tubes <NUM> as discussed above, a supply bag <NUM> or other container, a tube of an infusion pump or any type of relatively non-conductive fluid conduit, be it disposable or non-disposable. Cell 100a can interface directly with instrument <NUM> or with a separate hardware unit <NUM> shown in <FIG>.

Cell 100a transmits a current through a medical fluid, e.g., dialysate, flowing within conduit <NUM>, <NUM> between a pair of opposing electrodes 102a and 102b. Instrument <NUM> or separate hardware unit <NUM> includes circuitry <NUM> shown in <FIG>, which controls the transmission of the electrical current between the electrodes <NUM> and measures the resistance of the medical fluid.

In one embodiment, conduit <NUM>, <NUM> is injection molded plastic. Here, conduit <NUM>, <NUM> is injection molded around and sealed to electrodes <NUM>. In another embodiment, conduit <NUM>, <NUM> is extruded plastic. In still a further embodiment, electrodes <NUM> are bonded adhesively to conduit <NUM>, <NUM>. In yet another embodiment, electrodes <NUM> are inserted into conduit <NUM>, <NUM> via an insert molding process. Conduit <NUM>, <NUM> can accordingly be made of moldable material, which is chemically and biologically inert with respect to the medical fluids, e.g., dialysate or drugs, and is electrically insulative in an embodiment. Suitable materials for conduit <NUM>, <NUM> include acrylonitrile butadiene styrene ("ABS"), polyvinyl chloride ("PVC"), silicone rubber, polyolefin, cyclic olefin and cyclic olefin copolymers ("COC"), polycarbonates, synthetic and natural rubber, thermoplastic elastomers, glass, silicone and other semiconductors used in micro electro-mechanical ("MEMS") fabrication processes.

Electrodes <NUM> are stainless steel in one embodiment, which is generally considered as a safe metal for contacting a medical fluid. Electrodes 102a and 102b can alternatively be formed of different materials, perhaps for better electrical or thermal properties, so to provide a thermocouple effect for measuring the temperature of the medical fluid, and/or in a non-sterile situation or for example, sensing effluent or spent fluid (that has already contacted the patient) electrodes can alternatively be made of a conductive plastic described in more detail below, Suitable conductive plastics are described in the '<NUM> application referenced above.

Electrodes 102a and 102b of cell 100a are illustrated as being cylindrical but could alternatively be square, rectangular or of an arbitrary crosssection. Electrodes <NUM> extend into or through fluid pathway <NUM> in an at least substantially perpendicular orientation relative to the flow axis through the pathway. Alternatively, electrodes may extend along the fluid pathway, e.g., as surface-printed electrodes (discussed below) having a controlled separation distance. It is important to know the amount of surface area of electrodes <NUM> that the medical fluid contacts accurately so that the conductivity can be calculated accurately. Accordingly, conduit <NUM>, <NUM> includes or provides pockets 114a and 114b (referred to herein collectively as pockets <NUM> or generally, individually as pocket <NUM>) that receive electrodes 102a and 102b, respectively. In this relatively easily controlled way, it is assured that electrodes <NUM> extend all the way across fluid pathway <NUM>. Conduit <NUM>, <NUM> also includes or provides posts 116a and 116b (refe1Ted to herein collectively as posts <NUM> or generally, individually as post <NUM>), which hold electrodes 102a and 102b, respectively, firmly and in the proper at least substantially perpendicular orientation with respect to the flow of medical fluid through pathway <NUM>. Extensions <NUM> also provide additional contact area for electrodes <NUM> to be sealed within conduit <NUM>, <NUM> of cell <NUM>.

As discussed above, electrodes <NUM> can be adhesively joined to cell <NUM> Here, the adhesive can be applied within posts <NUM>, such that an adequate amount of adhesive is applied, but wherein the adhesive is kept safely away from fluid pathway <NUM>. The plastic to metal adhesive process is readily amenable to high-volume production. The process can include forming molded, e.g., insert molded posts <NUM>, inserting, e.g., stainless steel, electrodes or cannula needles <NUM>, applying a metered adhesive (e.g., Loctite™ adhesive) and cross-linking the adhesive and material of plastic post <NUM> (e.g., ABS) for example with ultraviolet ("UV") light.

Parameters needing to be tightly controlled during high-volume manufacturing include fluid path length L, electrode size and surface characteristics, and hydraulic area Ah. An alternating current ("AC") signal, as either a driving current (i) or driving voltage (V), is used in one embodiment to preclude anodic loss of the electrodes. A direct current is not ideal because it would result in anodic erosion of one electrode, altered sensor calibration and create contaminates in the medical fluid. Resistance as has been discussed is determined by controlling the driving current (i) or voltage (V), measuring the other and calculating resistance.

As alluded to above, cell constant k for full contact electrodes <NUM> of <FIG> is unity. For an, e.g., circular fluid path <NUM> (of conduit <NUM>, <NUM>) of hydraulic diameter Dh that the cylindrical and non-full contact area electrodes <NUM> of diameter De of cell 100a of <FIG> traverses, the electrode to solution contact area can be expressed as: <MAT> The cell constant k for cell 100a is then derived using the value of Ae and hydraulic area Ah diameter Dh of electrode <NUM> of cell 100a. Assuming manufacturing variances A'e , A'h , and L' associated with parameters Ae , Ah , and L, respectively, the effects of the variances can be mitigated via making cell 100a with path length L relatively long so that resistance is high and the variance L' is a small percentage of L and at the same time imposing that the relative variance, L'/L, is the dominant variance, and <MAT>.

Controlling L'/L ensures measurement accuracy and minimizes uncertainty without requiring overly stringent manufacturing controls of cross-sectional flow path area or electrode area. The electrode variance may be minimized by making the electrode surface area, Ae, larger than the hydraulic area, Ah.

In one experiment cells 100a as shown in <FIG> were made having electrodes of stainless steel and having a diameter De of <NUM> and a fluid pathway <NUM> of area Ah = <NUM><NUM>. Electrodes 102a and 102b were spaced apart a hydraulic pathway distance (center to center) of <NUM>. Mixed dialysate solution was measured to have a resistance of about <NUM>,<NUM> ohms. Cell 100a and associated electronics <NUM> were able to distinguish mixed solution from unmixed solution. In particular, unmixed buffer was detected with a resistance of about <NUM>,<NUM> ohms, while glucose concentrate was detected with a resistance of about <NUM>,<NUM> ohms. Thus, circuitry <NUM> and cell 100a have a sensitivity of about <NUM> ohms or less when expecting to see a mixture of about <NUM>,<NUM> ohm resistance. For a solution which is expected to have a conductivity of about <NUM>/cm, this corresponds to a sensitivity of about <NUM>/cm.

Results from testing have been tabulated in <FIG>. <FIG> shows a linear relationship of conductivity with varying volume fraction of bicarbonate buffer in a dialysis solution. Here, conductivity is a function of mix ratio. As the percentage of buffer, fB increases, so does conductivity. Diamonds in <FIG> represent <NUM> percent glucose dialysate. Squares in <FIG> represent <NUM> percent glucose dialysate. The dialysate of <FIG> is for a two-part dialysis solution, a buffered concentrate and a glucose concentrate. When mixed properly (e.g., fB = <NUM>) the components combine to form a therapeutic solution with physiologic balance of pH, osmolarity, Na, for example. <FIG> shows cell calibration with different conductivity standards. Here, squares and diamonds represent replicated trials. In five cells of the same type, a coefficient of variation of about <NUM>% in conductivities was measured. Thus, cell 100a and circuitry <NUM> were found to be relatively repeatable.

Modulating frequency provides an alternative method for distinguishing solution mix concentration. <FIG> illustrates the dependence of resistance (more generally impedance) or conductivity on signal frequency. As seen, the resistances are more distinct at lower signal frequencies (glucose concentrate in triangles, bicarbonate concentrate in diamonds and mixed solution in squares). When a certain signal frequency is reached, measured resistances begin to decrease. Therefore, in one embodiment signal frequency is maintained at a suitably low level, such as between about <NUM> to <NUM>,<NUM>, e.g., at about <NUM> and solutions may be distinguished as differences in resistance measured. Alternatively, solutions may be distinguished by the frequency at which the resistance decreases, e.g., about <NUM>,<NUM> for the glucose concentrate, about <NUM>,<NUM> for the mixed solution and about <NUM>,<NUM> for the buffer solution.

Once the resistance of the medical fluid is measured, a processor (e.g., located at CPU <NUM> or controller <NUM>) applies an algorithm to the measured resistance, which compensates for temperature to calculate the conductivity of the medical fluid. The processor performs a matching check to compare the calculated conductivity of the medical fluid with, e.g., a look-up table in a database for the particular pharmaceutical substance to determine if the concentration of the pharmaceutical substance within the medical fluid is within an acceptable range. Detectable conditions for dialysis include, for example: (i) no disposable cell loaded (alarm); (ii) disposable cell loaded (no alarm); (iii) only glucose concentration detected (alarm); (iv) only bicarbonate concentration detected (alarm); and (v) mixed solution detected (no alarm).

If the measured concentration of the pharmaceutical substance is outside an acceptable range, the processor outputs a signal (e.g., from safety controller <NUM> to CPU <NUM> of the dialysis, infusion or other medication delivery system <NUM>) to provide an alarm to the user and/or prevent the medication delivery system from delivering the medical fluid (e.g., by shutting down a pump, tube <NUM> or pathway of cassette <NUM>). If the measured concentration of the pharmaceutical substance is within an acceptable range, the processor outputs a signal to proceed with the delivery of the medical fluid. In the case of APD, fluid mixing quality can be tested once (for each bag <NUM>) before the start of therapy or during therapy to ensure proper mixing. Other detectable fluids include but are not limited to a parenteral compounding fluid, an intravenous infusion fluid and a chemotherapeutic compounding fluid.

In an alternative embodiment, detection is performed on a relative rather than an absolute basis. Here, instead of comparing a measured value to an acceptable range, cell <NUM> looks for a step change or relative change in conductivity. Here, a lookup table or absolute comparison is not needed. One example of this embodiment is possible in connection with dual chamber bag <NUM> having chambers 42a and 42b separated by a frangible seal <NUM>. Dual chamber bags <NUM> in the illustrated embodiment have integral tubing/connectors <NUM> in communication with chambers 42b. While tubing <NUM> is shown as being a relatively short run in <FIG>, integral tubing <NUM> can alternatively be longer and in one embodiment extend all the way to and connect directly to cassette <NUM>. Tubing/connectors <NUM> are filled initially with solution concentrate from chamber 42b. Mixing of solution from the other chamber 42a into the connector chamber 42b once seal <NUM> is broken does not immediately affect the solution conductivity in tubing/connector <NUM>, especially in longer lengths of tubing <NUM>. Electrodes <NUM> positioned here along each of tubes <NUM> will therefore initially sense pure (or near pure) solution of chamber 42b flowing from bag <NUM>, after which properly mixed fluid flows past electrodes <NUM> and causes a characteristic step change in conductivity. If solutions from chambers 42a and 42b are not mixed properly, the expected step change in conductivity does not occur, indicating that the chambers have not been mixed. This relative approach is advantageous in one respect because it does not necessitate an absolute calibration and use of a lookup table.

Referring again to <FIG>, hardware unit <NUM> illustrates an embodiment of a separate testing mechanism or hardware unit including circuitry <NUM> which is, configured to apply an electrical signal and to measure the resistance of a medical fluid through a cell such as cell <NUM> While separate hardware unit <NUM> is shown in operation with cell 100a, it should be appreciated that the hardware unit is alternatively operable with any of the cells discussed herein. Hardware unit <NUM> maintains the cell in a secured position and includes leads or contacts that contact each of the electrodes <NUM> of the cell to enable the cell to communicate electrically with the rest of circuit <NUM>. A snap-fit is provided in one embodiment to provide enough force to minimize contact resistance but still allow the cell to be loaded and unloaded in an efficient and ergonomic manner. Hardware unit <NUM> can include a processor and hard-wired or wireless communication equipment as discussed herein.

Referring now to <FIG>, cell 100b illustrates another conductivity, ADS, leak detection and/or heat sensor. Cell 100b again includes a pair of electrodes 102a and 102b, which in one arrangement are overmolded around a section of conduit <NUM>, <NUM> defining hydraulic pathway <NUM> of hydraulic diameter Dh having hydraulic Area Ah and length L as described above. In one arrangement, cell 100b is formed using various sections of conduit <NUM>, <NUM>, which are inserted into a mold such that adjacent ends of the conduits are spaced apart. Then, an electrically conductive material, such as an electrically conductive plastic referenced above, is overmolded around adjacent ends of the conduit <NUM>, <NUM>. The space between the adjacent ends of the tubes <NUM> is filled with the conductive material, such that the conductive plastic forms a portion of the surface of the fluid passageway <NUM> of the cell 100b as seen best in <FIG>, The exposed portions of the conductive material within the passageway <NUM> form the electrodes <NUM> that are in fluid communication with the medical fluid that flows through the passageway <NUM>. The exposed portions can have a flat, cylindrical surface defining an annular surface area Ae = π * De * length le of contact ring. Alternatively, exposed portions of conductive electrodes <NUM> can include inwardly facing surface area increasing apparatuses or members. In any case, the overmolding process connects adjacent tubes and provides a seal therebetween to form a continuous passageway <NUM>.

In an alternative arrangement, conductive polymer electrodes <NUM> are press-fit into conduit <NUM>, In another alternative arrangement, conductive polymer electrodes <NUM> are solvent bonded and UV cured and cross-linked to conduit <NUM>, <NUM>.

In a further alternative arrangement, electrodes (not shown) are printed or deposited on the inner surface of conduit <NUM>, <NUM>, e.g., via a conductive ink in a screening or photolithographic process. For example, the ink can be applied in such a manner to a flexible membrane of disposable cassette <NUM> or other disposable plastic component of a medication delivery system.

Referring now to <FIG> and <FIG>, two disposable cassette-based electrical cells are illustrated by cells 100c and 100d. Cassette <NUM> generally models a Homechoice@ APD system cassette marketed by the eventual assignee of the present disclosure. Cassette <NUM> in general includes a rigid structure having rigid outer walls 52a to 52d (referred to herein collectively as walls <NUM> or generally, individually as wall <NUM>), rigid inner walls <NUM> (defining inner pump chambers PI and P2 and inner fluid pathways such as pathway <NUM>), rigid fluid ports <NUM> (connectable sealingly to tubing <NUM>) and a pair of flexible membranes <NUM> sealed to outer rigid walls <NUM> and inner rigid walls <NUM>. Suitable materials for the rigid portion of cassette <NUM> include medical grade engineered thermoplastics, ego, polycarbonate, acrylic, cyclic olefins and their copolymers, thermoplastic elastomers, and their blends and alloys. Suitable materials for flexible membrane <NUM> include polyvinyl chloride, olefin, coextruded multi-layer films and micro-layer coextruded films (e.g., <NUM> to <NUM> layers typically). It should be appreciated that the Homechoice® APD system cassette serves merely as an example and that other fluid pumping/valving cassette made of different materials can employ cells 100c and 100d.

Cell 100c is similar to cell 100a in that it employs cylindrical electrodes 102a and 102b that extend all the way across fluid pathway <NUM> and penetrate through slightly into inner wall 54a for the process control and accuracy reasons discussed above in connection with cell 100a. Upper, outer wall 52a can be molded sealingly around electrodes <NUM> or electrodes <NUM> can be sealed adhesively to upper, outer wall 52a of cassette <NUM>. Press-fitting or other types of mechanical bonding can be used additionally or alternatively. Upper wall 52c can include or define ports or extensions 60a and 60b that provide additional surface area for cassette <NUM> to be sealed and crosslinked to the adhesive to seal to electrodes <NUM>.

Electrodes <NUM> in cell 100c are again spared apart a distance L, have a contact length l, have a diameter De and a contact surface area expressed as follows: <MAT> Hydraulic area Ah of hydraulic pathway <NUM> in the illustrated embodiment is square or rectangular and can be expressed as follows: <MAT> where w is the width of cassette <NUM> (see <FIG>).

As seen in <FIG>, when cassette <NUM> is loaded into cycler <NUM> of system <NUM>, a door <NUM> is closed such that cassette <NUM> resides between door <NUM> and an inflexible bladder <NUM> of instrument <NUM>. At this point, electrodes 102a and 102b may be loosely in contact with electrical leads or contacts 74a and 74b, respectively, mounted to the door <NUM> and shown in <FIG> in electrical communication with signal source <NUM>. When inflatable bladder <NUM> is inflated, cassette <NUM> is pushed against door <NUM> causing electrodes 102a and 102b to make intimate contact with contacts 74a and 74b.

<FIG> and <FIG>, illustrate an alternative cassette-based electrical cell arrangement 100d. Cell 100d employs a layer of conductive ink stencil printed, screen printed or applied via a photolithographic process in a continuous manner onto inner and outer surfaces of flexible membrane <NUM> to form electrodes 102a and 102b. Suitable conductive inks are provided for example by carbon, conductive polymers, metalized inks, metal particle filled polymers, and nanoparticle filled conductive inks.

As before, electrodes 102a and 102b of cell 100d are separated by a hydraulic path length L. The contact area Ae of electrodes <NUM> of cell 100d is the length l that the inked electrodes extend downwardly on the inner surface of membrane <NUM> multiplied by the width w of electrodes <NUM> on the inner surface of the membrane as seen in <FIG>.

For cell 100d, when cassette <NUM> is loaded into cycler <NUM>, door <NUM> is closed and inflatable bladder <NUM> is inflated, electrodes 102a and 102b, extending to the outer surface of membrane <NUM> are placed in intimate contact with leads or contacts 74a and 74b, respectively, mounted to pressure plate <NUM> shown in <FIG>, and communicating electrically with signal source <NUM>.

It is contemplated that the inked electrodes <NUM> of cell 100d are applied thinly enough that a standard flexible plastic membrane to rigid plastic piece bonding procedure, such as a heat seal, ultrasonic seal, solvent or adhesive bond is sufficient to seal the electrode areas of membrane <NUM> to upper, rigid plastic wall 52a. It may be necessary however to apply a local application of a sealant to the electrode areas to ensure a proper seal. The inked electrodes <NUM> of cell 100d are applied in a sufficient length l and width w to provide a sufficient amount conductive mass to carry the signal of source <NUM>, which can be on the order of micro- or milli-Watts.

It should be appreciated that electrodes <NUM> of cell 100c and cell 100d can be placed in any suitable position, on any suitable wall <NUM> or membrane of cassette <NUM>.

Referring now to <FIG>, one preferred electrode <NUM> is illustrated. Electrode <NUM> of <FIG> is advantageous from a number of respects including, size, ease of manufacture and ease of installation with a fluid conduit, e.g., in communication with one of tubes <NUM> (<FIG>) or fluid cassette <NUM>. For ease of illustration, electrode <NUM> of <FIG> is shown as being inserted into one of the walls <NUM> or <NUM> of cassette <NUM>.

Electrode <NUM> includes a fluid contact interface <NUM> extending to an annular sidewall <NUM>, which extends upwardly to a retainer ring portion <NUM> of the electrode. Retainer <NUM> is bent and configured so as to be somewhat pliable and capable of being press-fit or frictionally engaged with a stepped or tapered aperture <NUM> formed in wall <NUM> and <NUM> of cassette <NUM>. Stepped or tapered aperture <NUM> can provide or define an annular receiving groove <NUM>, which is sized and shaped to snap-fittingly receive the upper edge <NUM> of retainer ring portion <NUM> of electrode <NUM>. Thus when electrode <NUM> is pushed into stepped aperture <NUM>, the sidewall of aperture <NUM> causes upper edge <NUM> of retainer ring <NUM> to bend inward until reaching receiving groove <NUM> of aperture <NUM>. At this point, upper edge <NUM> snaps into groove <NUM>, which holds electrode <NUM> sealingly in place. It should be appreciated however that in an alternative embodiment groove <NUM> is not provided, and wherein the seal instead relies on a press or interference fit between the wall of aperture <NUM> and upper edge <NUM> of electrode <NUM>.

It may be that the apparatus and mechanical installation procedure of electrode <NUM> just described is enough to prevent (i) medical fluid or dialysate from escaping through the interface between retainer ring portion <NUM> and stepped aperture <NUM> of cassette <NUM> and (ii) air from outside cassette <NUM> from reaching sterile fluid in hydraulic pathway <NUM> without an additional sealing apparatus. Alternatively, a sterile sealing barrier <NUM>, e.g., of an o-ring nature, is provided to prevent fluid or air from leaking out of or into, respectively, cassette <NUM>. Still further alternatively, a suitably bondable adhesive or overmolding procedure discussed above can be employed.

Sealing ring <NUM> is made of a suitable medical grade compressible material, such as silicon, thermoplastic elastomer or isoprene. Flange portion <NUM> of electrode <NUM> compresses sealing ring <NUM> against stepped surface <NUM> of stepped or tapered aperture <NUM>. It is also possible that sidewall <NUM> of electrode <NUM> can press sealing ring <NUM> outwardly against side surface <NUM> of stepped or tapered aperture <NUM>.

Electrode <NUM> is made of stainless steel in one embodiment, e.g., for contacting fresh, sterile dialysate or other medicament. It is contemplated however to make electrode <NUM> and any of electrodes <NUM> described above from a different conductive material, such as a conductive polymer. Further, different metals could be used, such as copper or aluminum, for electrical or thermal sampling of a waste fluid, for example, such as fluid delivered from cassette <NUM>, through drain line 38b to drain as shown in <FIG>.

For conductivity sensing, contact <NUM> will have a contact area Ae, which is generally defined by the diameter De of contact portion <NUM>. Fluid flows through pathway <NUM> and contacts portion <NUM>. Electrode <NUM> (e.g., pair of electrodes <NUM>) is in turn connected electrically via a contact <NUM> (referring generally to one of contacts 74a and 74b), directly or indirectly, to signal source <NUM> located within instrument <NUM>. Alternatively, the pair of electrodes interfaces with a stand-alone hardware unit, such as cell holder <NUM> of <FIG>.

As discussed above, it is contemplated to use any of electrodes <NUM> or electrodes <NUM> for multiple purposes, such as for a needle or catheter access disconnection system ("ADS"), temperature sensing, valve leak detection in addition to conductivity measurement. To this end, it is contemplated to use a single one or a single pair of electrodes <NUM> or <NUM> for multiple purposes or to dedicate an electrode <NUM> or <NUM> or electrode pair to a single use.

In a multi-use example, a pair of electrodes <NUM> or <NUM> can be used to detect conductivity at the beginning of each bagged dialysis cycle (e.g. peritoneal dialysis or bagged hemodialysis solution) to ensure that the dialysate through a hydraulic pathway <NUM> (e.g., from dual chamber bags <NUM>) has been mixed properly. After this determination has been made, contacts <NUM> can then be used to sense an impedance of the dialysate through hydraulic pathway <NUM> as disclosed in the '<NUM> application referenced above for ADS purposes. Conductivity sensing and ADS sensing in one embodiment both require that at least one signal be injected through electrodes <NUM> to the dialysate. The same signal source <NUM> may be used, however, a different and/or additional signal source could be provided. The different sensing requires different signal processing, e.g., software.

At the same time or in a different application, a separate dedicated pair of electrodes <NUM> can be provided, e.g., at the to- and from- heater bag ports <NUM> for temperature sensing and heater control. Alternatively, the temperature sensing and heating sensing system could use a single electrode <NUM> at, e.g., from-heater port <NUM>. The Homechoice® APD system and associated disposable cassette illustrated throughout this application uses a batch heating system via a warmer bag <NUM> shown in <FIG>. Electrodes <NUM> and <NUM> can be used alternatively with an in-line heating system, for example by placing electrodes <NUM> and <NUM> upstream and downstream of an in-line fluid heating pathway.

Referring now to <FIG>, an alternative configuration for installing electrodes <NUM> into a disposable cassette is illustrated. Here, alternative cassette <NUM> includes rigid sidewalls <NUM> having or providing a plurality of fluid ports <NUM> and a top wall <NUM> defining or including various apertures and fluid pathways. Two of ports <NUM> shown in <FIG> are shown in Detail XV in <FIG> as including bulkheads <NUM>. Bulkheads <NUM> include or define stepped or tapered electrode receiving apertures <NUM>, described above, which receive electrodes <NUM>.

Ports <NUM> having bulkhead <NUM> receiving electrodes <NUM> can be, for example, to- and from- patient ports <NUM>, at which system <NUM> tests for an access disconnection. Alternatively, the bulkhead ports <NUM> are any that are any downstream of one or more valve seat of cassette <NUM>, wherein system <NUM> uses those electrodes <NUM> to determine if any valve seat or corresponding valve actuator is not functioning properly. Or, bulkhead ports <NUM> can be supply ports upstream of the cassette valves for conductivity sensing, wherein the valves can virtually immediately be closed to stop flow of improperly mixed fluid through cassette <NUM> (or improper dose or type of drug in a drug infusion machine) when such a situation is sensed.

Referring now to <FIG>, an embodiment for installing electrode <NUM> into a tube or conduit <NUM> is illustrated. Here, tube or conduit defines or includes an alternative aperture <NUM>, which has an at least substantially uniform inner diameter. In an alternative embodiment, tube or conduit <NUM> includes or defines tapered aperture <NUM>. Electrode <NUM> is press-fit, overmolded into and/or solvent bonded to aperture <NUM> as has been described herein.

Electrode <NUM> in conduit <NUM> can be used alone or in a pair of electrodes <NUM> for any one or more of the functions described herein. Electrode <NUM> is made of any of the materials discussed herein.

Electrode <NUM> is different than that of <FIG>. As before, electrode <NUM> includes a fluid contact interface <NUM>, an annular sidewall <NUM> and a flange portion <NUM>. Here, however, retention ring portion <NUM> discussed above is not provided. Instead, flange portion <NUM> is sized to be slightly wider than the inner diameter of aperture <NUM>. Aperture <NUM> can define a groove, similar to groove <NUM> of <FIG>, into which the outer edge of flange portion <NUM> snap-fits for permanent or semi-permanent installation into tube or conduit <NUM>.

Tube or conduit <NUM> can be formed integrally with an elongated section of tubing or conduit. Alternatively, tube or conduit <NUM> in <FIG> is configured to seal, semi-permanently or permanently with one or more section of elongated tubing or conduit.

Referring now to <FIG>, electrode <NUM> illustrates a further alternative electrode configuration. Here tube <NUM> is formed with or connected to a T-extension <NUM>. T-extension <NUM> defines an aperture <NUM> into which electrode <NUM> is placed. Electrode <NUM> includes a stem <NUM> and a head <NUM>. Head <NUM> bottoms out against a seat <NUM> of T-extension <NUM>. Seat <NUM> defines a cylindrical aperture <NUM> through which stem <NUM> of electrode <NUM> is inserted. In an embodiment, a diameter of aperture <NUM> is smaller than that of stem <NUM>, such that a compression seal is formed. Further sealing can be provided via overmolding and/or bonding as has been described herein.

The length of stem <NUM> and aperture <NUM> are controlled such that stem <NUM> extends into pathway <NUM> a precise, controlled and repeatable distance. Electrode <NUM> is used alternatively with a disposable cassette, such as cassette <NUM> or <NUM>. Electrode <NUM> can be any of the materials described herein and operate alone or in a pair (e.g., as a cell).

Claim 1:
A peritoneal dialysis system (<NUM>) comprising:
a dialysis instrument (<NUM>);
a disposable cassette (<NUM>, <NUM>) operable with the dialysis instrument;
a plurality of fluid lines (<NUM>) in fluid communication with the disposable cassette (<NUM>, <NUM>);
a supply of dialysis fluid buffer concentrate (42a);
a supply of dialysis fluid glucose concentrate (42b) that is separate from the supply of dialysis fluid buffer concentrate;
a conductivity cell (<NUM>) including a pair of electrodes (102a, 102b);
electronics (<NUM>, <NUM>, <NUM>) including an electrical sensor (<NUM>) operable with the conductivity cell (<NUM>) to measure a conductivity of the fluid flowing within the disposable cassette (<NUM>, <NUM>) using the pair of electrodes (102a, 102b); and
a processor (<NUM>, <NUM>) operable with the electronics (<NUM>, <NUM>, <NUM>),
characterized in that the processor (<NUM>, <NUM>) is configured to discern a conductivity difference between (i) a sensed fluid containing one of the dialysis fluid buffer concentrate or the dialysis fluid glucose concentrate and (ii) a sensed fluid including mixed dialysis fluid having buffer concentrate and glucose concentrate,
wherein the processor (<NUM>, <NUM>) is configured to use the sensed conductivities for properly mixing the mixed dialysis fluid, and
wherein the conductivity cell (<NUM>) is positioned and arranged to contact fluid flowing within the disposable cassette (<NUM>, <NUM>).