Apparatus for extracorporeal blood treatment

Abstract

An extracorporeal blood treatment apparatus is provided comprising a filtration unit (2) connected to a blood circuit (17) and to a dialysate circuit (32), a preparation device (9) for preparing and regulating the composition of the dialysis fluid; a control unit (12) is configured for receiving a conductivity or sodium concentration set point for the dialysis fluid and for calculating a mass transport of a substance at an instant t of a treatment session based on said set value of the parameter for the dialysis fluid in the dialysis supply line (8).

Claims

1. An apparatus for extracorporeal blood treatment comprising: a filtration unit including a primary chamber and a secondary chamber separated by a semi-permeable membrane; a blood withdrawal line connected to an inlet of the primary chamber; a blood return line connected to an outlet of the primary chamber, said blood lines being configured for connection to a patient cardiovascular system; a dialysis supply line; a dialysis effluent line connected to an outlet of the secondary chamber; a preparation device for preparing a dialysis fluid connected to said supply line and including a regulator for regulating the composition of the dialysis fluid; and a control unit connected to the regulator and configured to receive a set value of a parameter for the dialysis fluid in the dialysis supply line, said parameter of the dialysis fluid being at least one parameter selected from the group consisting of a conductivity of the dialysis fluid, a conductivity-related parameter of the dialysis fluid, a concentration of the substance in the dialysis fluid, and a concentration-related parameter of the substance in the dialysis fluid, and wherein the control unit is further configured to calculate a mass transport of a substance at an instant t of a treatment session based on said set value of the parameter for the dialysis fluid in the dialysis supply line, wherein the mass transport includes an amount of the substance that has been transported over the dialyzer membrane over a period of time.

2. The apparatus according to claim 1, wherein the control unit is further configured to: receive or calculate a value of a first parameter, the first parameter being chosen from a group consisting of a plasma conductivity, a plasma conductivity-related parameter, a concentration of the substance in the blood, a concentration-related parameter of the substance in the blood, and a dialysis fluid concentration of the substance at a dialysis treatment in which the substance concentration of the dialysis fluid does not change pre-filtration unit versus post-filtration unit; and calculate a mass transport of the substance at the instant t of the treatment session based on both said value of the first parameter and said set value of the parameter for the dialysis fluid in the dialysis supply line.

3. The apparatus according to claim 2, wherein the control unit is configured to calculate the mass transport of the substance as a function of a difference between the value of the first parameter and the set value of the parameter for the dialysis fluid in the dialysis supply line.

4. The apparatus according to claim 2, wherein the first parameter is a dialysis fluid concentration of sodium at an isonatric dialysis.

5. The apparatus according to claim 1, wherein the parameter for the dialysis fluid is a dialysis fluid concentration.

6. The apparatus according to claim 1, wherein the control unit is configured to calculate the mass transport of the substance as a function of a difference between a dialysis fluid concentration of sodium to provide isonatric dialysis and a dialysis fluid concentration set point.

7. The apparatus according to claim 1, wherein the control unit is configured to calculate the mass transport of the substance as a function of an efficiency parameter of the filtration unit for the substance.

8. The apparatus according to claim 1, wherein the control unit is configured to calculate the mass transport of the substance as a function of a respective adjusting factor taking account of the Donnan effect.

9. The apparatus according to claim 1, wherein the control unit is configured to calculate the mass transport of the substance as a function of a distribution volume of the substance.

10. The apparatus according to claim 1, wherein the control unit is configured to calculate an accumulated mass transport of the substance as a function of an elapsed treatment time.

11. The apparatus according to claim 1, wherein the control unit is configured to calculate the mass transport of the substance as a function of an ultrafiltration flow rate.

12. The apparatus according to claim 1, wherein the control unit is configured to calculate the mass transfer as a function of one or more of the following: an efficiency parameter of the filtration unit for the substance, the efficiency parameter being the clearance of the substance, a distribution volume of the substance, an ultrafiltration flow rate, a treatment time, and a respective adjusting factor taking account of the Donnan effect.

13. The apparatus according to claim 1, wherein the first parameter is either the plasma conductivity or a dialysis fluid concentration of a substance at a dialysis treatment in which the substance concentration of the dialysis fluid does not change pre-filtration unit versus post-filtration unit, and the parameter of the dialysis fluid is the concentration of the substance in the dialysis fluid.

14. The apparatus according to claim 1, wherein the substance is sodium.

15. The apparatus according to claim 1, wherein the first parameter is a dialysis fluid concentration of sodium at an isonatric dialysis and the parameter of the dialysis fluid is the concentration of the substance in the dialysis fluid.

16. The apparatus according to claim 1, wherein the control unit is programmed for calculating a total mass transport value or a diffusive mass transport value according to the respective one of the following relationships: total mass transport achieved at the instant t, defined as: $M\left(t\right)=\left(Q_u.Math.c_{d,\mathrm{set}}+{\delta }_d.Math.K_u\right).Math.t+\frac{V_0}{\alpha }.Math.\left({\delta }_0-{\delta }_d\right).Math.\left(1-{\left(1-\frac{Q_u}{V_0}.Math.t\right)}^{\frac{\alpha .Math.K_u}{Q_u}}\right),$ or diffusive mass transport achieved at the instant t, defined as: $M_d\left(t\right)=\left(Q_u.Math.\left(c_{d,\mathrm{set}}-\frac{c_{d,\mathrm{isoNa}}}{\alpha }\right)+{\delta }_d.Math.K_u\right).Math.t+\frac{V_0}{\alpha }.Math.\left({\delta }_0-{\delta }_d\right).Math.\left(1-{\left(1-\frac{Q_u}{V_0}.Math.t\right)}^{\frac{\alpha .Math.K_u}{Q_u}}\right)$ wherein: ${\delta }_d=\frac{\left(1-\alpha \right).Math.Q_u}{\alpha .Math.K_u-Q_u}.Math.c_{d,\mathrm{set}}$
δ.sub.0=c.sub.d,isoNa−c.sub.d,set, and wherein: M(t) is the total mass transport of sodium at the instant t, M.sub.d(t) is the diffusive mass transport of sodium at the instant t, c.sub.d,set is a dialysis fluid sodium concentration set point, c.sub.d,isoNa is a dialysis fluid concentration of sodium at an isonatric dialysis, Q.sub.u is a ultrafiltration rate, V.sub.0 is a distribution volume of sodium, t is the instant of calculating the total mass transport value or the diffusive mass transport, K.sub.u is a filtration unit clearance for sodium, and α is a Donnan factor.

17. An apparatus for extracorporeal blood treatment comprising: a filtration unit including a primary chamber and a secondary chamber separated by a semi-permeable membrane; a blood withdrawal line connected to an inlet of the primary chamber; a blood return line connected to an outlet of the primary chamber, said blood lines being configured for connection to a patient cardiovascular system; a dialysis supply line; a dialysis effluent line connected to an outlet of the secondary chamber; a preparation device for preparing a dialysis fluid connected to said supply line and including a regulator for regulating the composition of the dialysis fluid; and a control unit connected to the regulator and configured to receive a set value of a parameter for the dialysis fluid in the dialysis supply line, said parameter of the dialysis fluid being at least one parameter selected from the group consisting of a conductivity of the dialysis fluid, a conductivity-related parameter of the dialysis fluid, a concentration of the substance in the dialysis fluid, and a concentration-related parameter of the substance in the dialysis fluid, and wherein the control unit is further configured to calculate a mass transport of a substance at an instant t of a treatment session based on said set value of the parameter for the dialysis fluid in the dialysis supply line, and wherein the control unit is programmed for calculating a total mass transport value or a diffusive mass transport value according to the respective one of the following relationships: total mass transport achieved at the instant t, defined as: $M\left(t\right)=\left(Q_u.Math.c_{d,\mathrm{set}}+{\delta }_d.Math.K_u\right).Math.t+\frac{V_0}{\alpha }.Math.\left({\delta }_0-{\delta }_d\right).Math.\left(1-{\left(1-\frac{Q_u}{V_0}.Math.t\right)}^{\frac{\alpha .Math.K_u}{Q_u}}\right),\mathrm{or}$ diffusive mass transport achieved at the instant t, defined as: $M_d\left(t\right)=\left(Q_u.Math.\left(c_{d,\mathrm{set}}-\frac{c_{d,\mathrm{isoNa}}}{\alpha }\right)+{\delta }_d.Math.K_u\right).Math.t+\frac{V_0}{\alpha }.Math.\left({\delta }_0-{\delta }_d\right).Math.\left(1-{\left(1-\frac{Q_u}{V_0}.Math.t\right)}^{\frac{\alpha .Math.K_u}{Q_u}}\right)$ wherein: ${\delta }_d=\frac{\left(1-\alpha \right).Math.Q_u}{\alpha .Math.K_u-Q_u}.Math.c_{d,\mathrm{set}}$
δ.sub.0=c.sub.d,isoNa−c.sub.d,set, and wherein: M(t) is the total mass transport of sodium at the instant t, M.sub.d(t) is the diffusive mass transport of sodium at the instant t, c.sub.d,set is a dialysis fluid sodium concentration set point, c.sub.d,isoNa is a dialysis fluid concentration of sodium at an isonatric dialysis, Q.sub.u is a ultrafiltration rate, V.sub.0 is a distribution volume of sodium, t is the instant of calculating the total mass transport value or the diffusive mass transport, K.sub.u is a filtration unit clearance for sodium, and α is a Donnan factor.

18. An apparatus for extracorporeal blood treatment comprising: a filtration unit including a primary chamber and a secondary chamber separated by a semi-permeable membrane; a blood withdrawal line connected to an inlet of the primary chamber; a blood return line connected to an outlet of the primary chamber, said blood lines being configured for connection to a patient cardiovascular system; a dialysis supply line; a dialysis effluent line connected to an outlet of the secondary chamber; a preparation device for preparing a dialysis fluid connected to said supply line and including a regulator for regulating the composition of the dialysis fluid; and a control unit connected to the regulator and configured to receive a set value of a parameter for the dialysis fluid in the dialysis supply line, said parameter of the dialysis fluid being at least one parameter selected from the group consisting of a conductivity of the dialysis fluid, a conductivity-related parameter of the dialysis fluid, a concentration of the substance in the dialysis fluid, and a concentration-related parameter of the substance in the dialysis fluid, and wherein the control unit is further configured to: receive or calculate a value of a first parameter, the first parameter being chosen from a group consisting of a plasma conductivity, a plasma conductivity-related parameter, a concentration of the substance in the blood, a concentration-related parameter of the substance in the blood, and a dialysis fluid concentration of the substance at a dialysis treatment in which the substance concentration of the dialysis fluid does not change pre-filtration unit versus post-filtration unit; and calculate a mass transport of a substance at an instant t of a treatment session as a function of said set value of the parameter for the dialysis fluid in the dialysis supply line, an elapsed treatment time, an ultrafiltration flowrate, and a difference between the value of the first parameter and the set value of the parameter for the dialysis fluid in the dialysis supply line, wherein the mass transport includes an amount of the substance that has been transported over the dialyzer membrane over a period of time.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The description will now follow, with reference to the appended FIGURE, provided by way of non-limiting example, in which:

(2) FIG. 1 schematically represents an extracorporeal blood treatment apparatus made according to an illustrating embodiment.

DETAILED DESCRIPTION

(3) Blood Treatment Apparatus

(4) FIG. 1 illustrates an extracorporeal blood treatment apparatus 1 in an embodiment of the invention.

(5) An example of a hydraulic circuit 100 is schematically illustrated, but it is to be noted that the specific structure of the hydraulic circuit 100 is not relevant for the purposes of the present invention and therefore other and different circuits to those specifically shown in FIG. 1 might be used in consequence of the functional and design needs of each single medical apparatus.

(6) The hydraulic circuit 100 exhibits a dialysis fluid circuit 32 presenting at least one dialysis supply line 8. Depending on the specific apparatus treatment mode, the dialysis supply line 8 may or, may not, assume different hydraulic circuit line configurations.

(7) In a hemodialysis (HD) treatment mode, the supply line 8 is destined to transport a dialysis fluid from at least one source 14 towards a treatment station 15 where one or more filtration units 2, or dialyzers, operate. Dialysis fluid and blood exchange through the semipermeable membrane in the filtration unit 15 mainly by diffusion process.

(8) In a hemofiltration (HF) treatment mode, the supply line 8 comprises an infusion line 39, which is destined to transport an infusion fluid from at least one source 14 to the blood circuit. The infusion line 39 may include an ultrafilter 44 to additionally filter the received fluid upstream the injection point into the blood circuit. The removal of waste products from the blood is achieved by using large amounts of ultrafiltration with simultaneous reinfusion of sterile replacement fluid in the blood circuit.

(9) In a hemodiafiltration (HDF) treatment mode, the supply line 8 is destined to transport the dialysis fluid from the source 14 towards the treatment station 15 and also comprises the infusion line 39 to transport the infusion fluid from the source 14 to the blood circuit 17. HDF is a combination of hemodialysis and hemofiltration.

(10) In general, though not essential, the source 14 for the supply line 8 and the infusion line 39 is the same (i.e. a dialysis fluid preparation devices 9). Of course, different sources may be used.

(11) Additionally, the supply line 8 normally branches into the infusion line 39, infusing fluid in the blood circuit 17, and into an inlet line 45 directing the fluid to the treatment station 15. Referring to FIG. 1, a branch point is indicated with reference numeral 46.

(12) Notwithstanding the fact that different hydraulic circuits 100 may be used to deliver HF, HD and HDF treatments having exclusively the relevant lines for the specific treatment (e.g. no infusion line 39 for HD, no inlet line 45 for HF), generally the hydraulic circuit 100 is of the kind shown in FIG. 1 and includes both infusion line 39 and inlet line 45, the apparatus control unit 12 may then control the passage of fluid trough said lines, depending on the selected treatment, by means e.g. proper valves or clamps.

(13) The dialysis fluid circuit 32 further comprises at least one dialysis effluent line 13, destined for the transport of a dialysate liquid (spent dialysate and liquid ultrafiltered from the blood through a semipermeable membrane 5) from the treatment station 15 towards an evacuation zone, schematically denoted by 16 in FIG. 1.

(14) The hydraulic circuit cooperates with a blood circuit 17, also schematically represented in FIG. 1 in its basic component parts. The specific structure of the blood circuit is also not fundamental, with reference to the present invention. Thus, with reference to FIG. 1, a brief description of a possible embodiment of a blood circuit is made, which is however provided purely by way of non-limiting example.

(15) The blood circuit 17 of FIG. 1 comprises a blood withdrawal line 6 designed to remove blood from a vascular access 18 and a blood return line 7 designed to return the treated blood to the vascular access 18.

(16) The blood circuit 17 of FIG. 1 further comprises a primary chamber 3, or blood chamber, of the blood filtration unit 2, the secondary chamber 4 of which is connected to the hydraulic circuit 100.

(17) In greater detail, the blood withdrawal line 6 is connected at the inlet of the primary chamber 3, while the blood return line 7 is connected at the outlet of the primary chamber 3.

(18) In turn, the dialysis supply line 8 is connected at the inlet of the secondary chamber 4, while the dialysis effluent line 13 is connected at the outlet of the secondary chamber 4.

(19) The filtration unit 2, for example a dialyzer or a plasma filter or a hemofilter or a hemodiafilter, comprises, as mentioned, the two chambers 3 and 4 which are separated by a semipermeable membrane 5, for example of the hollow-fibre type or plate type.

(20) The blood circuit 17 may also comprise one or more air separators 19: in the example of FIG. 1 a separator 19 is included at the blood return line 7, upstream of a safety valve 20.

(21) Of course other air separators may be present in the blood circuit, such as positioned along the blood withdrawal line 6.

(22) The safety valve 20 may be activated to close the blood return line 7 when, for example, for security reasons the blood return to the vascular access 18 has to be halted.

(23) The extracorporeal blood treatment apparatus 1 may also comprise one or more blood pumps 21, for example positive displacement pumps such as peristaltic pumps; in the example of FIG. 1, a blood pump 21 is included on the blood withdrawal line 6.

(24) The apparatus of above-described embodiment may also comprise a user interface 22 (e.g. a graphic user interface or GUI) and a control unit 12, i.e. a programmed/programmable control unit, connected to the user interface.

(25) The control unit 12 may, for example, comprise one or more digital microprocessor units or one or more analog units or other combinations of analog units and digital units. Relating by way of example to a microprocessor unit, once the unit has performed a special program (for example a program coming from outside or directly integrated on the microprocessor card), the unit is programmed, defining a plurality of functional blocks which constitute means each designed to perform respective operations as better described in the following description.

(26) In combination with one or more of the above characteristics, the medical apparatus may also comprise a closing device operating, for example, in the blood circuit 17 and/or in the dialysis fluid circuit 32 and commandable between one first operating condition, in which the closing device allows a liquid to flow towards the filtration unit 2, and a second operative position, in which the closing device blocks the passage of liquid towards the filtration unit 2.

(27) In this case, the control unit 12 may be connected to the closing device and programmed to drive the closing device to pass from the first to the second operative condition, should an alarm condition have been detected.

(28) In FIG. 1 the closing device includes the safety valve 20 (e.g. a solenoid valve) controlled by the unit 12 as described above. Obviously a valve of another nature, either an occlusive pump or a further member configured to selectively prevent and enable fluid passage may be used.

(29) Alternatively or additionally to the safety valve 20, the closing device may also comprise a bypass line 23 which connects the dialysis fluid supply line 8 and the dialysate effluent line 13 bypassing the dialyzer, and one or more fluid check members 24 connected to the control unit 12 for selectively opening and closing the bypass line 23. The components (bypass line 23 and fluid check members 24), which may be alternative or additional to the presence of the safety valve 20 are represented by a broken line in FIG. 1.

(30) The check members 24 on command of the control unit close the fluid passage towards the treatment zone and connect the source 14 directly with the dialysis effluent line 13 through the bypass line 23.

(31) Again with the aim of controlling the fluid passage towards the filtration unit 2, a dialysis fluid pump 25 and a dialysate pump 26 may be included, located respectively on the dialysis fluid supply line 8 and on the dialysate effluent line 13 and also operatively connected to the control unit 12.

(32) The apparatus also comprises a dialysis fluid preparation device 9 which may be of any known type, for example including one or more concentrate sources 27, 28 and respective concentrate pumps 29, 30 for the delivery, as well as at least a conductivity sensor 35.

(33) Of course other kinds of dialysis fluid preparation devices 9 might be equivalently used, having a single or further concentrate sources and/or a single or more pumps.

(34) Since the dialysis apparatus may comprise various liquid sources 14 (for example one or more water sources, one or more concentrate sources 27, 28, one or more sources 33 of disinfectant liquids) connected to the dialysis supply line 8 with respective delivery lines 36, 37 and 38, the apparatus may exhibit, at each delivery line, a respective check member (not all are shown) and, for example, comprising a valve member 31 and 34 and/or an occlusive pump.

(35) The preparation device 9 may be any known system configured for on-line preparing dialysis fluid from water and concentrates.

(36) The dialysis supply line 8 fluidly connects the preparation device 9 for preparing dialysis fluid to the filtration unit 2 and/or to the blood circuit 17. The preparation device 9 may be, for example, the one described in the U.S. Pat. No. 6,123,847 the content of which is herein incorporated by reference.

(37) As shown, the dialysis supply line 8 connects the preparation device 9 for preparing dialysis fluid to the filtration unit 2 and comprises a main line 40 whose upstream end is intended to be connected to a source 14 of running water.

(38) Delivery line/s 36/37 is/are connected to this main line 40, the free end of which delivery line/s is/are intended to be in fluid communication (for example immersed) in a container/s 27, 28 for a concentrated saline solution each containing sodium chloride and/or calcium chloride and/or magnesium chloride and/or potassium chloride.

(39) Concentrate pump/s 29, 30 is/are arranged in the delivery line/s 36/37 in order to allow the metered mixing of water and concentrated solution in the main line 40. The concentrate pump/s 29, 30 is/are driven on the basis of the comparison between 1) a target conductivity value for the mixture of liquids formed where the main line 40 joins the delivery line/s 36/37, and 2) the value of the conductivity of this mixture measured by means of a conductivity sensor 35 arranged in the main line 40 immediately downstream of the junction between the main line 40 and the delivery line/s 36/37.

(40) Therefore, as mentioned, the dialysis fluid may contain, for example, ions of sodium, calcium, magnesium, and potassium and the preparation device 9 may be configured to prepare the dialysis fluid on the basis of a comparison between a target conductivity value and an actual conductivity value of the dialysis fluid measured by the conductivity sensor 35 of the device 9.

(41) The preparation device 9 comprises regulating means 10, of a known type (i.e. concentrate pump/s 29, 30), which is configured to regulate the concentration of a specific substance, in particular an ionic substance, in the dialysis liquid. Generally it is advantageous to control the sodium concentration of the dialysis fluid.

(42) The dialysis supply line 8 forms an extension of the main line 40 of the preparation device 9 for preparing dialysis fluid. Arranged in this dialysis supply line, in the direction in which the liquid circulates, there are the first flow meter 41 and the dialysis fluid pump 25.

(43) The supply line 8 branches (at branch point 46) into the infusion line 39, which, in the example of FIG. 1, is shown directly connected to the blood return line 7, in particular to the air separator 19 (solid line) via post infusion tract 47b.

(44) Alternatively, the infusion line 39 may infuse infusion fluid in the blood withdrawal line 6 via pre-infusion tract 47a, in particular downstream the blood pump 21 (dotted line) at pre-infusion point 48.

(45) It is also in the scope of the present description an embodiment including an infusion line 39 branching into a pre-infusion branch 47a and in a post infusion branch 47b directing infusion fluid, respectively, in the blood withdrawal line 6 and in the blood return line 7.

(46) One or more infusion pumps 43 may be used to pump the desired flow of infusion fluid into the blood circuit. The infusion pump 43 may be a positive displacement pump (e.g. a peristaltic pump as shown) or any other pump adapted to displace infusion fluid (e.g. a volumetric pump).

(47) The dialysis effluent line 13 may be provided with a dialysate pump 26 and a second flow meter 42. The first and second flow meters 41, 42 may be used to control (in a known manner) the fluid balance of a patient connected to the blood circuit 17 during a dialysis session.

(48) A sensor 11 is provided on the dialysis effluent line 13, immediately downstream the filtration unit 2, to measure a parameter value of the dialysate in the dialysate effluent line.

(49) In detail, the parameter of the dialysate, which is measured by the sensor 11 is at least one chosen in the group consisting of conductivity of the dialysate, a conductivity-related parameter of the dialysate, concentration of at least a substance in the dialysate and a concentration-related parameter of at least a substance in the dialysate.

(50) In detail the sensor 11 is a conductivity sensor, which is connected to the dialysis effluent line 13, and is configured to detect conductivity values of the dialysate downstream of the filtration unit 2.

(51) Alternatively (or in combination) sensor 11 may include a concentration sensor configured for measuring the concentration of at least one substance in the dialysate, such as sodium concentration.

(52) Correspondingly, sensor 35 on the dialysis fluid supply line may differently include a concentration sensor configured for measuring the concentration of at least one substance in the dialysis fluid, such as sodium concentration.

(53) The control unit 12 of the dialysis apparatus represented in FIG. 1 may be connected to a (graphic) user interface 22 through which it may receive instructions, for example target values, such as blood flow rate Q.sub.b, dialysis fluid flow rate Q.sub.di, infusion liquid flow rate Q.sub.inf (pre infusion and/or post infusion), patient weight loss WL. The control unit 12 furthermore may receive detected values by the sensors of the apparatus, such as the aforementioned flow meters 41, 42, the (e.g. conductivity) sensor 35 of the preparation device 9 and the (e.g. conductivity) sensor 11 in the dialysis effluent line 13. On the basis of the instructions received and the operating modes and algorithms which have been programmed, the control unit 12 drives the actuators of the apparatus, such as the blood pump 21, the aforementioned dialysis fluid and dialysate pumps 25, 26, and the preparation device 9, and the infusion pump 43.

(54) As already mentioned, the described embodiments are intended to be non-limiting examples. In particular the circuits of FIG. 1 should not be interpreted as defining or limiting, as an apparatus such as in the invention may comprise other additional or alternative components to those described.

(55) For example an ultrafiltration line may be included, with at least one respective pump connected to the dialysis effluent line 13.

(56) The blood circuit of FIG. 1 is intended for double needle treatments; however, this is a non-limiting example of the blood set.

(57) Indeed, the apparatus may be configured to perform single needle treatments, i.e. the patient is connected to the extracorporeal blood circuit by way of a single needle and the extracorporeal line from the patient is then split into a withdrawal line and a return line, using, for example, an ‘Y’ connector. During single needle treatment, a blood withdrawal phase removing blood from patient is alternated to a blood return phase in which blood is restituted to the patient.

(58) Furthermore one or more devices for measuring specific substance concentrations might be implemented either (or both) in the dialysis fluid side or (and) in the blood side of the hydraulic circuit. Concentration of calcium, potassium, magnesium, bicarbonate, and/or sodium might be desired to be known.

(59) Finally, the above-cited one or more pumps and all the other necessary temperature, pressure, and concentration sensors may operate either on the dialysis supply line 8 and/or on the dialysis effluent line 13, in order to adequately monitor the preparation and movement of the liquid in the hydraulic circuit.

(60) Given the above description of a possible embodiment of extracorporeal blood treatment apparatus, thereafter the specific working of the apparatus and the algorithm programming the control unit are described.

Definitions

(61) We define the “dialysis fluid” as the fluid prepared and, when appropriate based on the selected treatment, introduced to the second chamber (4) of the filtration unit (2)—e.g. HD and HDF—. The dialysis fluid may also be denoted “fresh dialysis fluid”.

(62) We define the “dialysate” as the fluid from the outlet from the second chamber (4) of the filtration unit (2). Dialysate is the spent dialysis fluid, comprising the uremic toxins removed from the blood.

(63) We define “infusion fluid” as the fluid prepared and infused in the blood circuit (17), either in the blood withdrawal line (6) or in the blood return line (7) or in both blood lines (6, 7).

(64) We define “isonatric dialysis” as a treatment where the sodium concentration of the dialysis fluid does not change pre- to post-filtration unit 2. It is then assumed that the sodium concentration of the dialysis fluid matches the sodium concentration of the plasma, and thus the diffusive sodium mass transfer is zero.

(65) We define “isotonic dialysis”, as a treatment where the tonicity of the dialysis fluid does not change pre- to post-filtration unit 2. It is then assumed that the tonicity of the dialysis fluid matches the tonicity of the plasma.

(66) We define “isoconductive dialysis”, as a dialysis treatment where the conductivity of the dialysis fluid does not change pre- to post-filtration unit 2, κ.sub.di=κ.sub.do.

(67) We define “plasma conductivity” (PC, κ.sub.p) as the conductivity of the dialysis fluid in an isoconductive dialysis.

(68) We define “mass transport”, as the amount of a substance, usually given with the units grams or millimols, that is transported over the dialyzer membrane during a given time, usually the total treatment time.

(69) We define “convective mass transport”, as the amount of a substance in a thought volume where the volume is the total ultrafiltered volume (the patient volume loss and approximately mass loss) with a concentration identical to the matching blood concentration.

(70) We define “diffusive mass transport”, as the difference between total mass transport and convective mass transport.

(71) In the present text, the term “desired mass transport” denotes the mass transport prescribed by the physician, taking in account the condition of the patient.

(72) In this application the term “citrate” means that the component is in form of a salt of citric acid, such as sodium, magnesium, calcium, or potassium salt thereof. The citric acid (denoted C.sub.6H.sub.8O.sub.7) is deprotonated stepwise, therefore the “citrate” include all the different forms, citrate (denoted C.sub.6H.sub.5O.sub.7.sup.3−), hydrogen citrate (denoted C.sub.6H.sub.6O.sub.7.sup.2−), and dihydrogen citrate (denoted C.sub.6H.sub.7O.sup.7−).

(73) The term “citrate” or “total citrate” means that the total amount of citric acid and any salts thereof, such as its sodium, magnesium, calcium, or potassium salt thereof. In other terms, “total citrate” is the sum of free citrate ions and citrate containing complexes and ion pairs.

Glossary

(74) The following terms are consistently used throughout the equations provided in the following description of the detailed working of the extracorporeal blood treatment apparatus.

(75) TABLE-US-00011 c.sub.d,M.sub.d Dialysis fluid sodium concentration to achieve a desired diffusive sodium mass transfer at the treatment time T; c.sub.d,M Dialysis fluid sodium concentration to achieve a desired total sodium mass transfer at the treatment time T; c.sub.d,isoNa Dialysis fluid concentration of sodium at an isonatric dialysis; c.sub.d,set Dialysis fluid concentration set point of sodium set by the operator; c.sub.d,isoNa,adj Sodium set point adjustment (relative to isoconductive state) required to provide isonatric dialysis; c.sub.d,Na,κ.sub.p,pre Sodium concentration in the dialysis fluid to run an isoconductive dialysis; c.sub.d,Na,actual,i Actual dialysis fluid sodium concentration set point used during the treatment; c.sub.d,M.sub.d,.sub.compensated Dialysis fluid sodium concentration new set point to compensate for unwanted substance transfer; κ.sub.p Plasma conductivity; PC κ.sub.p,1 Plasma conductivity first estimate; κ.sub.p,2 Plasma conductivity second estimate; κ.sub.p,pre Plasma conductivity at the beginning of the treatment; κ.sub.di Dialysis fluid conductivity at the filtration unit inlet; κ.sub.do Dialysis fluid conductivity at the filtration unit outlet; κ.sub.0,di Dialysis fluid conductivity at the filtration unit inlet for a pure electrolyte solution; κ.sub.0,do Dialysis fluid conductivity at the filtration unit outlet for a pure electrolyte solution; Q.sub.b Real blood flow rate; Q.sub.u Ultrafiltration rate; Q.sub.di Dialysis fluid flow rate (set); Q.sub.do Dialysate flow rate at the filtration unit outlet; Q.sub.bw Blood water flow rate; f.sub.bw Apparent blood water fraction for urea; WL Total weight loss; V.sub.u Expected total ultrafiltered volume; M Desired total mass transport of sodium (convective + diffusive); M.sub.c Desired convective mass transport of sodium; M.sub.d Desired diffusive mass transport of sodium; V.sub.0 Total distribution volume (initial value); V.sub.Na.sub.+ Distribution volume of sodium; V.sub.HCO.sub.3.sub.− Distribution volume of bicarbonate; V.sub.Ac.sub.− Distribution volume of acetate; V.sub.K.sub.+ Distribution volume of potassium; V.sub.rest,mean Mean distribution volume of the substances in the rest term; T Total treatment time (set); t Elapsed treatment time; K.sub.u Filtration unit clearance for urea; K.sub.b,Cit Filtration unit clearance for citrate; K.sub.u,Na.sub.+ Filtration unit clearance for sodium; K.sub.u,HCO.sub.3.sub.− Filtration unit clearance for bicarbonate; K.sub.Ac.sub.− Filtration unit clearance for acetate; K.sub.u,K.sub.+ Filtration unit clearance for potassium; K.sub.u,rest,mean Mean clearance of the substances in the rest term; K.sub.0A Mass transfer coefficient of the filtration unit; M.sub.κ,NaHCO.sub.3 Molar conductivity of sodium bicarbonate (NaHCO.sub.3) at ionic strength 150 mM; M.sub.κ,NaCl Molar conductivity of sodium chloride (NaCl) at ionic strength 150 mM; M.sub.κ,NaAc Molar conductivity of sodium acetate (NaCH.sub.3COO) at ionic strength 150 mM; M.sub.κ,KCl Molar conductivity of potassium chloride (KCl) at ionic strength 150 mM; M.sub.κ,Na.sub.3.sub.Cit Molar conductivity of trisodium citrate (Na.sub.3C.sub.6H.sub.5O.sub.7) at ionic strength 150 mM; κ.sub.rest3 Conductivity contribution from lesser solutes 3; c.sub.pw,Na Estimated or measured pre-dialysis concentration of sodium ions (Na.sup.+) in plasma water; c.sub.pw,HCO.sub.3 Estimated or measured pre-dialysis concentration of bicarbonate anions (HCO.sub.3.sup.−) in plasma water; c.sub.pw,Ac Estimated or measured pre-dialysis concentration of acetate anions (CH.sub.3COO.sup.−) in plasma water; c.sub.pw,K Estimated or measured pre-dialysis concentration of potassium ions (K.sup.+) in plasma water; c.sub.pw,Na.sub.3.sub.Cit Estimated or measured or known pre-dialysis concentration of total citrate in plasma water; c.sub.di,HCO.sub.3 Dialysis fluid concentration of bicarbonate as set by the operator; c.sub.di,Na Dialysis fluid concentration of sodium ions (Na.sup.+) as set by the operator or by the control unit; c.sub.di,K Dialysis fluid concentration of potassium ions (K.sup.+) as determined by the used concentrate; c.sub.di,Ac Dialysis fluid concentration of acetate as determined by the used concentrate; c.sub.di,Na.sub.3.sub.Cit Dialysis fluid concentration of total citrate as determined by the used concentrate; δ.sub.Na.sub.+(0) Sodium driving gradient over filtration unit at instant t = 0; δ.sub.HCO.sub.3.sub.−(0) Bicarbonate driving gradient over filtration unit at instant t = 0; δ.sub.Ac.sub.−(0) Acetate driving gradient over filtration unit at instant t = 0; δ.sub.K.sub.+(0) Potassium driving gradient over filtration unit at instant t = 0; α Donnan factor;

(76) The Donnan factor indicates a value of electroneutrality to be kept over the membrane. For estimating the Donnan factor reference is made to Trans Am Soc Artif Intern Organs, 1983; 29; 684-7, “Sodium Fluxes during hemodialysis”, Lauer A., Belledonne M., Saccaggi A., Glabman S., Bosch J.

(77) Solution Proposal

(78) The technical solution here described consists of three main parts: Estimating/calculating or receiving either PC (i.e., κ.sub.p, κ.sub.p,pre) or dialysis fluid concentration of sodium to provide isonatric dialysis (i.e. c.sub.d,isoNa) at the beginning of the treatment; Setting the dialysis fluid sodium concentration such that a desired mass transport (M; M.sub.d) is achieved at the end of the treatment session; Maintaining the dialysis fluid composition throughout the treatment.

(79) The various steps of the proposed method described below are intended to be performed by the control unit 12 of the extracorporeal blood treatment device 1, even if not explicitly stated.

(80) In particular a treatment session is started, preferably, but not necessarily, as a double needle hemodialysis treatment.

(81) The user shall input the prescription values through the user interface 22. For example the set values for total weight loss WL and total treatment time T are provided, as well as the blood flow rate Q.sub.b and the fresh dialysis flow rate Q.sub.di.

(82) The user may input either the desired total (diffusive+convective) sodium mass transport M or the desired sodium diffusive mass transport M.sub.d over the treatment. Alternatively, desired mass transport might also be denoted personalized, or individualized, mass transport.

(83) Other parameters may be entered through the user interface, such as bag type, sodium user limits, etc.

(84) The operator has to further input the ‘bicarbonate’ set before starting the treatment.

(85) The First Parameter Value (e.g. Plasma Conductivity or c.sub.d,isoNa)

(86) According the above discussed approach, the control unit 12 receives either a dialysis fluid concentration of sodium to provide isonatric dialysis (i.e. c.sub.d,isoNa) or a value representative of a parameter of the blood in said blood lines 6, 7. The blood related parameter may be concentration of a substance in the blood plasma (e.g. sodium), a concentration-related parameter of said substance in the blood, the plasma conductivity or a plasma conductivity-related parameter.

(87) In a first embodiment, the control unit 12 receives the dialysis fluid concentration of sodium to provide isonatric dialysis (i.e. c.sub.d,isoNa). This value may be know from previous calculations or estimated e.g. based on previous treatments on the same patient. In case the apparatus directly receives or determines the above sodium concentration, the control unit is configured to apply the procedure described in the following paragraph named “Adjustment term to achieve the desired sodium balance”.

(88) In another embodiment, the control unit 12 directly receives as an input the plasma conductivity or the plasma sodium concentration. For example, the physician or the nurse may receive a lab analysis and may provide the datum to the machine through the user interface of the dialysis monitor; the control unit 12 is programmed for storing in a memory the plasma conductivity/plasma sodium concentration to be used for the following dialysis fluid parameter regulation.

(89) The plasma conductivity (or sodium concentration) may be directly measured in vivo by the monitor before starting the treatment session using a proper plasma conductivity/concentration sensor. In case the apparatus directly receives the above plasma conductivity/plasma sodium concentration, the control unit is configured to apply the procedure described in the following paragraph named “Determining isonatric dialysis set point”.

(90) Alternatively, the control unit 12 may be programmed for calculating the plasma conductivity, for example using known methods such as those described in EP 2377563.

(91) In an additional embodiment which here in after briefly presented and disclosed, the plasma conductivity may be calculated by the machine according to the following procedure which starts with a proper initial set of the dialysis fluid and determines the plasma conductivity with a specific algorithm.

(92) The control unit 12 is generally configured for setting a parameter value for the dialysis fluid in the dialysis supply line 8 at an initial set point.

(93) The parameter of the dialysis fluid is chosen between a conductivity of the dialysis fluid, a conductivity-related parameter of the dialysis fluid, a concentration of a substance in the dialysis fluid and a concentration-related parameter of a substance in the dialysis fluid.

(94) Depending on the specific dialysis monitor, the sodium content (or the content of more than one electrolyte) may be regulated in the dialysis line. Alternatively, the control parameter may be the overall conductivity of the dialysis fluid.

(95) The setting of the parameter value in the dialysis fluid (which is hereinafter identified as sodium concentration set point in the dialysis fluid with no limiting effect) includes the sub-step of calculating the sodium concentration initial set point.

(96) The control unit 12 calculates either the initial dialysis liquid conductivity or the initial concentration of at least one solute, e.g. sodium, in the dialysis liquid in order to start with a dialysis fluid conductivity as close as possible to the expected patient pre-dialytic plasma conductivity.

(97) In order to not disturb the tonicity of the patient, it is necessary to set the fluid composition as quickly as possible so that the patient initial plasma conductivity is not inadvertently changed. Thus, estimating of the plasma conductivity has to be done as rapidly as possible when treatment starts; moreover, since the estimation is preferably performed only once, this measure should be as reliable as possible.

(98) Reference is made to regulating means controlling concentration of an ionic substance, in detail sodium concentration, in the preparation of the dialysis fluid so as to obtain a desired conductivity of the dialysis fluid.

(99) However, regulating means directly regulating the overall dialysis fluid conductivity is also included in the spirit of the present description or, alternatively, regulating means modifying the concentration of a different ionic substance is included in the present description, too.

(100) In detail, the control unit 12 is configured to set the parameter value for the dialysis fluid at the initial set point so that a dialysis fluid conductivity matches a first estimate of the plasma conductivity of the blood.

(101) In the specific, the control unit 12 calculates the initial set point of the substance concentration and drives the regulating means 10 acting on the sodium concentration in the dialysis liquid.

(102) The set point is calculated before starting the blood circulation (i.e. before starting the treatment).

(103) In order to calculate the dialysis composition initial set point alternative ways might be used, e.g. determine a certain sodium concentration (see below), or using an average plasma conductivity from a large population, or using an average plasma conductivity from a large population corrected for the composition of the dialysis fluid, or calculate based on historic patient data.

(104) In any case, the initial set point for the dialysis liquid is calculated by the control unit 12 so that the expected plasma conductivity is the best guess of plasma conductivity that may be calculated, without prior knowledge of the individual patient.

(105) Once the sodium initial set point has been calculated and a corresponding dialysis fluid has been prepared by the control unit 12 driving the regulating means 10, the treatment may start.

(106) The dialysis fluid is circulated through the dialysis fluid circuit 32 so as to exchange with and/or to be infused into blood.

(107) Correspondingly, blood is withdrawn from the patient and circulated in the extracorporeal blood circuit 17 and particularly is circulated through the primary chamber 3 of the filtration unit 2.

(108) At least one, and in general a plurality, of consecutive initial values of the parameter (in the specific example, the conductivity) of the dialysate downstream of the secondary chamber 4 are measured at the beginning of the treatment through sensor 11. The control unit 12 is configured to validate and further process the measurement of an initial value of the conductivity of the dialysate as soon as the diffusion process in the filtration unit 2 reaches stable conditions. Indeed, a transient exists when dialysis fluid and blood start exchanging during which the dialyzer outlet conductivity is not stable; during the transient period the measured outlet conductivity values should be disregarded.

(109) Glucose and urea, the main electrically neutral substances in dialysis fluid, reduce the conductivity of the dialysis fluid. Hence, a compensation for urea and glucose contribution may also be applied to the measured conductivities κ.sub.di and κ.sub.do: the resulting conductivities for pure ion solutions (κ.sub.0,di and κ.sub.0,do) may alternatively be used in all the calculations using conductivities reported below.

(110) It is worth to note that the initial conductivity of the fresh dialysis fluid upstream the secondary chamber 4, namely κ.sub.di, may be either measured or taken as the set value for dialysis conductivity.

(111) In general, it is preferred to measure the initial conductivity of the dialysis fluid through the sensor 35, too.

(112) The initial setting of the sodium concentration calculated or determined as above stated to be as close as possible to the expected plasma conductivity may be optional, meaning that the method for estimating the initial plasma conductivity may be performed even if the sodium content of the dialysis conductivity is initially simply set by the operator. Also correction based on main electrically neutral substances is optional and may be used or not to increase accuracy.

(113) Vice versa, it is relevant to measure at least the conductivity downstream the filtration unit (and preferably also the conductivity upstream the filtration unit) as soon as possible, i.e. as soon as stable conditions are reached or as soon as an estimate of such conductivity in stable conditions may be performed.

(114) In order to make a first estimate of the plasma conductivity based on measured values, firstly, the control unit 12 calculates the value of the initial plasma conductivity, based on the measured initial parameter value of the dialysate (i.e. based on conductivity or concentration measurement of dialysate on the filtration unit outlet) and on the corresponding parameter value of the dialysis fluid in the dialysis fluid supply line 8 e.g. conductivity or concentration). During the start of the treatment and particularly during circulating the dialysis fluid through the secondary chamber 4 up to measuring the initial value of the parameter of the dialysate downstream of the secondary chamber used for the calculating of the initial plasma conductivity, the dialysis fluid conductivity (or concentration) is kept substantially constant.

(115) In this respect the term ‘substantially constant’ means that the conductivity of the dialysis fluid is not changed by the machine or by the operator, but it may not be exactly constant due to small oscillations on the measured value caused by noise, tolerances in the concentrate dosing system or tolerances in the conductivity measurements. Generally these small variations around the set value are less than 0.2 mS/cm.

(116) Just a single reliable measurement at the inlet and at the outlet of the dialyzer may be sufficient to have a preliminary (to be made more accurate) or an already final estimation of the PC.

(117) From a general point of view, the control unit 12 is configured to calculate the plasma conductivity as a function of at least one or more of the following parameters: one flow rate, namely the dialysate flow rate at the outlet of the secondary chamber 4; an efficiency parameter of the filtration unit 2, in particular a clearance of the filtration unit 2 (e.g. the urea clearance). Of course, a nominal clearance and/or a calculated clearance may be used and the calculated clearance may be both an estimated clearance as well as a compensated clearance; an (possibly compensated) initial conductivity of the dialysate and a (possibly compensated) conductivity of the dialysis fluid in the dialysis supply line 8.

(118) In more detail, the control unit 12 is programmed to calculate the initial plasma conductivity based on the sum of at least the initial conductivity of the fresh dialysis fluid plus a difference between inlet and outlet conductivity at the dialyzer weighted by a factor of the dialysate flow rate. The difference between inlet and outlet conductivity at the filtration unit, or dialyzer, is weighted by a factor of the dialyzer clearance too.

(119) Specifically, the control unit 12 is configured to calculate the plasma conductivity using the following formula:

(120) 0$\begin{array}{cc}{\kappa }_{p,1}={\kappa }_{0,\mathrm{di}}+\frac{Q_{\mathrm{do}}}{K_u}\left({\kappa }_{0,\mathrm{do}}-{\kappa }_{0,\mathrm{di}}\right)& \left(1\right)\end{array}$

(121) The significance of the denotations and constants above is given in the Glossary.

(122) It is worth to underline that during the above described calculation of the initial plasma conductivity (formula (1)), the dialysis fluid circulates through the secondary chamber 4 maintaining the dialysis fluid parameter value substantially constant.

(123) In more detail, in the formulas above: k.sub.0,di is the set/measured-by-sensor 35 value for conductivity of the dialysis fluid, optionally corrected for glucose; k.sub.0,do is the mean value of outlet conductivity in stable conditions, corrected for glucose and urea; Q.sub.di is the set value for dialysis fluid flow rate; Q.sub.do is the mean value of dialysate flow rate at the filtration unit, or dialyzer, outlet, in stable conditions; K.sub.u is the dialyzer diffusive clearance for urea. Since K.sub.u may not be known, different estimates may be used.

(124) K.sub.u may be approximated as Q.sub.di/2.

(125) Alternatively, K.sub.u may be calculated as follows:

(126) $\begin{array}{cc}{K}_u=Q_{\mathrm{bw}}{Q}_{\mathrm{di}}\frac{1-e^{\mathrm{KoA}\left(\frac{1}{Q_{\mathrm{di}}}\frac{1}{Q_{\mathrm{bw}}}\right)}}{Q_{\mathrm{di}}-Q_{\mathrm{bw}}{e}^{\mathrm{KoA}\left(\frac{1}{Q_{\mathrm{di}}}\frac{1}{Q_{\mathrm{bw}}}\right)}}& \left(2\right)\end{array}$
where KoA is either a known value if the control unit has information about the dialyzer used. In case the control unit has no information on the used dialyzer, a standard dialyzer value with a KoA=1100 ml/min as a fixed value may be used. Q.sub.bw is the blood water flow, for example, calculated as:
Q.sub.bw=f.sub.bw.Math.Q.sub.b=0.89.Math.Q.sub.b   (3)

(127) where Q.sub.b is real blood flow rate and f.sub.bw is the apparent blood water fraction for urea, where a hematocrit of 30% has been assumed.

(128) Of course, formula (1) for estimation of plasma conductivity may be iteratively applied, meaning that the newly calculated estimate of PC (k.sub.p,1) is imposed to the dialysis fluid and a new estimate again calculated after taking measures of the conductivity at the inlet and outlet of the filter as soon as stable conditions are reached.

(129) Of course, in case of iteration, after the first plasma conductivity estimation, the dialysis fluid parameter value is changed since the newly calculated estimate of PC (k.sub.p,1) is imposed to the dialysis fluid, meaning that the conductivity of the dialysis fluid is changed. This however does not impact on the fact that the first calculation according to formula (1) is made without a change in the conductivity of the dialysis fluid.

(130) The dialysis fluid sodium concentration correspondent to k.sub.p,pre is then determined. The resulting dialysis fluid sodium concentration applied, c.sub.d,Na,kp,pre, would correspond to implement an isoconductive dialysis.

(131) Determining Isonatric Dialysis Set Point

(132) Since a sodium set value for an isonatric dialysis is to be determined, the sodium concentration, c.sub.d,Na,kp,pre, (corresponding to implement an isoconductive dialysis) is to be adjusted with a proper adjustment factor.

(133) The adjustment contribution term is the sodium concentration set point adjustment relative to an isoconductive state to provide an isonatric dialysis.

(134) In order to obtain a dialysis fluid sodium implementing isonatric dialysis, i.e. c.sub.d,isoNa, an adjustment factor c.sub.d,isoNa,adj needs to be applied to make the sodium concentration of dialysate out from the dialyzer matching the sodium concentration of dialysis fluid at the inlet of the dialyzer:
c.sub.d,isoNa=c.sub.d,Na,kp,pre+c.sub.d,isoNa,adj   (4)

(135) In case of an isonatric treatment is to be performed, the mentioned adjustment factor may be calculated based on molar conductivities, dialysis fluid composition and the best estimate of plasma water composition.

(136) In particular:

(137) $\begin{array}{cc}{c}_{d,\mathrm{isoNa},\mathrm{adj}}=-\frac{1}{M_{{\kappa }_{\mathrm{NaCl}}}}\left(\left(M_{{\kappa }_{{\mathrm{NaHCO}}_3}}-M_{{\kappa }_{\mathrm{NaCl}}}\right)\left(\frac{1}{\alpha }*c_{\mathrm{pw},{\mathrm{HCO}}_3}-c_{\mathrm{di},{\mathrm{HCO}}_3}\right)+\left(M_{{\kappa }_{\mathrm{NaAc}}}-M_{{\kappa }_{\mathrm{NaCl}}}\right)\left(\frac{1}{\alpha }*c_{\mathrm{pw},\mathrm{Ac}}-c_{\mathrm{di},\mathrm{Ac}}\right)+\frac{K_{b_{\mathrm{Cit}}}}{K_u}\left(M_{k_{{\mathrm{Na}}_3\mathrm{Cit}}}-3M_{{\kappa }_{\mathrm{NaCl}}}\right)\text{⁠}\left(\left(0.167{\alpha }^{-3}+0.125{\alpha }^{-2}+0.706{\alpha }^{-1}\right)*c_{\mathrm{pw},{\mathrm{Na}}_3\mathrm{Cit}}-c_{\mathrm{di},{\mathrm{Na}}_3\mathrm{Cit}}\right)+M_{{\kappa }_{\mathrm{KCl}}}\left(\alpha *c_{\mathrm{pw},K}-c_{\mathrm{di},K}\right)+\frac{Q_{\mathrm{do}}}{K_u}{\kappa }_{\mathrm{rest}3}\right)& \left(5\right)\end{array}$

(138) K.sub.b.sub.Cit is the approximated clearance value for citrate. This clearance is calculated for the actual flow rates using a mass transfer value of K.sub.0A.sub.Cit=0.212*K.sub.0A.sub.Urea in the corresponding K.sub.u formula.

(139) Factor k (namely, k.sub.rest3) defines the effect on the conductivity due to other components in the dialysis fluid different from the components already treated and included in the respective formula. Thus, the effect of salts containing calcium, magnesium, lactate, phosphate, and sulphate may have upon the conductivity. The effect created by these components is most often small, and does not vary considerably between the dialysis treatments.

(140) Adjustment Term to Achieve the Desired Sodium Balance

(141) Once the sodium set point for running an isonatric treatment is determined (e.g. calculated or received), the control unit 12 is configured to adapt the dialysis fluid set point in order to match a desired mass transport at the end of the treatment session. In particular, the following embodiments refer to sodium; in other term, the sodium set point is calculated in order to match the desired total sodium mass transport M (diffusive+convective−M=M.sub.d+M.sub.c) or the desired diffusive sodium mass transport M.sub.d.

(142) However, the following equations for the quantification of sodium balance may be used for other substances that are distributed in one distribution volume.

(143) The equation system may work with e.g. urea, bicarbonate and chloride. An issue may be to determine the ‘isoX’ value for substance X corresponding to ‘isoNa’ value for sodium. Urea cannot be determined by a conductivity method; however, a measured value of the plasma concentration could be used. Of course, the corresponding parameters for the other substance (e.g. urea) should be entered into the here-below detailed equations.

(144) If the sodium set point for running an isonatric treatment is applied at the beginning of the treatment session, a zero diffusive mass transport of sodium is obtained. Therefore, the physician, who requires a net mass transport, shall input either the desired total mass transport M of sodium or the desired diffusive mass transport M.sub.d of sodium, e.g. with the prescription, and the apparatus calculates the adjustment contribution term to be imposed to adjust the previously determined sodium set point. The updated set point is determined so that the desired mass transport M; M.sub.d of sodium is achieved at the end of the treatment session, i.e. at the end of the total treatment time T.

(145) Clearly, the setting of the second parameter value (conductivity/concentration of sodium) in the dialysis fluid is a function of the desired mass transport received as an input.

(146) In more detail, the control unit 12 is configured to calculate the second parameter value (i.e. sodium concentration for the dialysis fluid) as a function of a main contribution term and as a function of an adjustment contribution term based on the desired mass transport (being it the total mass transport M or the diffusive mass transport M.sub.d). In particular, the sodium concentration for the dialysis fluid is calculated as a sum of the main contribution term and of the adjustment contribution term. The main contribution term is a dialysis fluid concentration of sodium at an isonatric dialysis (c.sub.d,isoNa); the adjustment contribution term is the sodium concentration set point adjustment relative to an isonatric dialysis to provide a treatment configured to achieve the desired total or diffusive mass transport over the treatment time.

(147) The control unit is programmed to calculate the adjustment contribution term as a function of one or more (and in particular all) of the following parameters: an efficiency parameter of the filtration unit 2 for the substance, in particular the clearance of the filtration unit for the substance; a distribution volume of the substance; the ultrafiltration rate and/or the total ultrafiltered volume; a treatment time, in particular the total treatment time; and a respective adjusting factor which takes into account the Donnan effect.

(148) The second parameter value, which is here a concentration, may be determined taking into account the ultrafiltration or disregarding the ultrafiltration.

(149) In case ultrafiltration is disregarded, the second parameter value may be calculated according to the following formula:

(150) $\begin{array}{cc}{c}_{d,M_d}=c_{d,\mathrm{isoNa}}+\frac{\alpha .Math.M_d}{V.Math.\left(e^{\frac{\alpha .Math.K_b}{V}.Math.T}-1\right)}& \left(6A\right)\end{array}$

(151) wherein the used symbols meaning is clarified in the glossary section.

(152) Notably, the ultrafiltration causes a volume loss in the patient during the treatment, thereby changing the considered concentrations. In a more precise determination of the dialysis fluid concentration to achieve the desired mass transport, ultrafiltration rate and its effects are considered.

(153) In this latter case, the second parameter value may be determined in accordance with the following mathematical relationships: to achieve a desired total mass transport: eq. 6B—

(154) $\begin{array}{cc}{c}_{d,M}=c_{d,\mathrm{isoNa}}+\frac{M-\left(V_2-f_{\mathrm{cd}}.Math.V_1\right).Math.c_{d,\mathrm{isoNa}}}{V_2-\left(1+f_{\mathrm{cd}}\right).Math.V_1}& \left(6B\right)\end{array}$ to achieve a desired diffusive mass transport: eq. 6C—

(155) $\begin{array}{cc}{c}_{d,M_d}=c_{d,\mathrm{isoNa}}+\frac{M_d-\left(V_2-f_{\mathrm{cd}}.Math.V_1-\frac{V_u}{\alpha }\right).Math.c_{d,\mathrm{isoNa}}}{V_2-\left(1+f_{\mathrm{cd}}\right).Math.V_1}& \left(6C\right)\end{array}$
wherein f.sub.cd, V.sub.1, V.sub.2 and V.sub.u are:

(156) $\begin{array}{cc}{f}_{\mathrm{cd}}=\frac{\left(1-\alpha \right).Math.Q_u}{\alpha .Math.K_u-Q_u}& \left(7\right)\end{array}$$\begin{array}{cc}{V}_1=\frac{V_0}{\alpha }.Math.\left(1-{\left(1-\frac{V_u}{V_0}\right)}^{\frac{\alpha .Math.K_u}{Q_u}}\right)& \left(8\right)\end{array}$$\begin{array}{cc}{V}_2=f_{\mathrm{cd}}.Math.K_u.Math.T.Math.V_u& \left(8\right)\end{array}$$\begin{array}{cc}{V}_u=Q_u.Math.T& \left(10\right)\end{array}$
and wherein the used symbols meaning is clarified in the glossary section.

(157) As mentioned, the second term is the adjustment contribution term which added to the dialysis fluid concentration of sodium at an isonatric dialysis allows to achieve the wanted sodium balance.

(158) With these formulas the dialysis fluid sodium concentration can be set to get a predetermined sodium mass balance over the treatment based on estimations of parameters that are fairly good known as the initial sodium distribution volume (V.sub.0—total body water), clearance (K.sub.u), duration of treatment (T), the ultrafiltration flow rate (Q.sub.u) and the Donnan factor (α).

(159) Once the set point for sodium c.sub.d,M; c.sub.d,M.sub.d is calculated, the control unit 12 drives the regulating means 10 for regulating the conductivity or the concentration of the substance in the fresh dialysis fluid and sets the parameter value for the dialysis fluid in the dialysis fluid supply line 8 at the calculated set point.

(160) Determination of the Sodium Mass Transport

(161) There are two fundamental ways to evaluate the physiological effects of substance transport from or to the patient during a dialysis treatment. The first way is the idea of an ideal plasma concentration of a substance that represents a homeostatic state. To achieve that plasma concentration a corresponding dialysis fluid setting is selected and the dialysis process drives the plasma concentration towards the desired concentration. The second way to quantify the effect is to study the mass balance or dose the treatment causes. This will in the long run match the net intake by food for the substance. Regarding sodium it is more beneficial to know the mass balance than its concentration as it is the total mass of sodium that distributes water between extracellular and intracellular space. A homeostatic volume of the extracellular space is crucial for heart function and blood pressure control.

(162) In the spirit of the present description, the apparatus for extracorporeal blood treatment may also be configured to determine the (total or diffusive) mass transport of the substance (e.g. sodium).

(163) The mass transport is the amount of a substance, usually given with the units grams or millimols, that is transported over the dialyzer membrane during a given time (usually the total treatment time). If the mass transport are from the blood to the dialysis fluid and thus leaving the patient it is by convention given a positive sign. If the mass transport is from the dialysis fluid to the blood it is given a negative sign. Other names used in the literature are mass transfer and mass balance. For a momentary effect the common term is mass transfer rate.

(164) Further, mass transport can be divided in two parts, the convective part and the diffusive part. The convective part is the mass in a thought volume where the volume is the total ultrafiltered volume (the patient volume loss and approximately mass loss) with a concentration identical to the matching blood concentration. A dialysis with a total mass transport identical to convective mass transport will not change the concentration in blood. The diffusive mass transport is the difference between total mass transport and convective mass transport.

(165) Based on the knowledge of the patient, regarding food and intake of salt, a desired mass transport can be prescribed. If the patient has a history of hypotensive episodes one may prescribe a certain amount of sodium to be added during the treatment. If the patient has a tendency to hypertension an amount of sodium may be removed. These prescriptions can be calculated on total mass transport or diffusive mass transport.

(166) In this respect the physician may set a desired target of plasma conductivity to be reached at the end of the treatment (e.g. by properly setting the dialysis fluid conductivity) and the apparatus perform the extracorporeal blood treatment so as to change the plasma conductivity of the patient towards the target.

(167) During the course of the treatment, the control unit may monitor and display the substance mass transport achieved at the treatment time t. Anyone or all of the diffusive, convective or total mass transport may be monitored.

(168) Knowing the total sodium balance (or the diffusive sodium balance or the convective sodium balance) at a certain treatment time t may help the physician to adapt the treatment to the patient by e.g. modifying treatment parameters (for example the dialysis fluid conductivity) during the treatment itself; in any case a relevant information is provided in terms of total sodium transport.

(169) To calculate the achieved mass transport, the control unit 12 receives/calculates the dialysis fluid sodium concentration set point, c.sub.d,set; the operator may indeed input such concentration or the dialysis fluid conductivity set point at the start of the treatment.

(170) Moreover, the control unit 12 should receive as input or determine as above described, the dialysis fluid concentration of sodium to provide isonatric dialysis, i.e. c.sub.d,isoNa.

(171) The mass transport achieved at instant t of the extracorporeal blood treatment (M(t); M.sub.d(t); M.sub.c(t)) is function of at least: the dialysis fluid concentration of sodium to provide isonatric dialysis, i.e. c.sub.d,isoNa; the ultrafiltration flow rate Q.sub.u; the elapsed treatment time t; and the Donnan factor α.

(172) In case the convective mass transport is of interest, the same may be calculated as follows:

(173) $\begin{array}{cc}{M}_c\left(t\right)=Q_u.Math.\frac{c_{d,\mathrm{isoNa}}}{\alpha }.Math.t& \left(11\right)\end{array}$

(174) wherein the used symbols meaning is clarified in the glossary section.

(175) The total mass transport and the diffusive mass transport achieved at instant t of the extracorporeal blood treatment are both function of the above listed parameters and of the dialysis fluid sodium concentration set point, c.sub.d,set, and in more detail of the difference in concentration between the dialysis fluid sodium concentration set point and the dialysis fluid concentration of sodium to provide isonatric dialysis, i.e. δ.sub.0=c.sub.d,isoNa−c.sub.d,set. Furthermore, the achieved total mass transport and the diffusive mass transport are a function of the efficiency parameter K.sub.u of the filtration unit 2 for the substance, in particular the clearance of the substance, the elapsed treatment time t, the Donnan factor α and the initial distribution volume V.sub.0.

(176) The total mass transport is the sum of two different terms, a first term based on the ultrafiltration flow rate, the efficiency parameter of the filtration unit, the elapsed time, the Donnan factor and the set conductivity in the dialysis fluid. The second term being function of the distribution volume, the Donnan factor, the efficiency parameter of the filtration unit, the elapsed time, the ultrafiltration flow rate, as well as the dialysis fluid concentration of sodium to provide isonatric dialysis.

(177) The specific mathematical relation to be used for determination of the total mass transport is the following:

(178) $\begin{array}{cc}M\left(t\right)=\left(Q_u.Math.c_{d,\mathrm{set}}+{\delta }_d.Math.K_u\right).Math.t+\frac{V_0}{\alpha }.Math.\left({\delta }_0-{\delta }_d\right).Math.\left(1-{\left(1-\frac{Q_u}{V_0}.Math.t\right)}^{\frac{\alpha .Math.K_u}{Q_u}}\right)& \left(12\right)\end{array}$$\begin{array}{cc}{\delta }_d=\frac{\left(1-\alpha \right).Math.Q_u}{\alpha .Math.K_u-Q_u}.Math.c_{d,\mathrm{set}}& \left(13\right)\end{array}$$\begin{array}{cc}{\delta }_0=c_{d,\mathrm{isoNa}}-c_{d,\mathrm{set}}& \left(14\right)\end{array}$

(179) wherein the used symbols meaning is clarified in the glossary section.

(180) If the diffusive mass transport is to be determined, the difference between total and convective mass transport may be used.

(181) The equation for deriving the diffusive mass transport is the following:

(182) $\begin{array}{cc}{M}_d\left(t\right)=\left(Q_u.Math.\left(c_{d,\mathrm{set}}-\frac{c_{d,\mathrm{isoNa}}}{\alpha }\right)+{\delta }_d.Math.K_u\right).Math.t+\frac{V_0}{\alpha }.Math.\left({\delta }_0-{\delta }_d\right).Math.\left(1-{\left(1-\frac{Q_u}{V_0}.Math.t\right)}^{\frac{\alpha .Math.K_u}{Q_u}}\right)& \left(15\right)\end{array}$

(183) With the aid of the above formulas, the physician may determine the sodium mass transfer (total, convective and diffusive) at any time t during the treatment. Of course, substituting t with the total treatment time T, the operator may know the total diffusive mass transport of sodium of the entire treatment.

(184) The control unit 12 may also be configured to change a prescription value e.g. the sodium set point for the dialysis fluid based on the determined mass transport so that, in case of abnormal or undesired transport, the remaining part of the treatment may compensate the sodium transport.

(185) Online Validation of Electrolyte Transport

(186) In case the apparatus is configured to achieve a set mass transport, once the treatment session is started using the calculated set point for the dialysis fluid, e.g. c.sub.d,M; c.sub.d,M.sub.d, the conductivity of the dialysate post the filtration unit 2 can be measured and analyzed. The individual values of K.sub.u for the substances are used. The dialysis fluid concentration of the different substances are assumed fixed and the plasma water concentrations may alternatively be modeled individually, using the best available models known from literature.

(187) During the treatment at any time t, the modeled κ.sub.do(t) may be calculated according to the formula here below reported:

(188) 0$\begin{array}{cc}{\kappa }_{\mathrm{do}}\left(t\right)={\kappa }_{\mathrm{di}}+\frac{K_{u,{\mathrm{Na}}^{+}}}{Q_{\mathrm{do}}}.Math.M_{{\kappa }_{\mathrm{NaCl}}}.Math.\left({\delta }_{d,{\mathrm{Na}}^{+}}+\left({\delta }_{0,{\mathrm{Na}}^{+}}-{\delta }_{d,{\mathrm{Na}}^{+}}\right).Math.{\left(1-\frac{Q_u}{V_{0,{\mathrm{Na}}^{+}}}.Math.t\right)}^{\frac{\alpha .Math.K_{u,{\mathrm{Na}}^{+}}}{Q_u}-1}\right)+\frac{K_{u,{\mathrm{HCO}}_3^{-}}}{Q_{\mathrm{do}}}.Math.\left(M_{{\kappa }_{{\mathrm{NaHCO}}_3}}-M_{{\kappa }_{\mathrm{NaCl}}}\right).Math.\left({\delta }_{d,{\mathrm{HCO}}_3^{-}}+\left({\delta }_{0,{\mathrm{HCO}}_3^{-}}-{\delta }_{d,{\mathrm{HCO}}_3^{-}}\right).Math.{\left(1-\frac{Q_u}{V_{0,{\mathrm{HCO}}_3^{-}}}.Math.t\right)}^{\frac{{\alpha }^{-1}.Math.K_{u,{\mathrm{HCO}}_3^{-}}}{Q_u}-1}\right)+\frac{K_{u,{\mathrm{Ac}}^{-}}}{Q_{\mathrm{do}}}.Math.\left(M_{{\kappa }_{\mathrm{NaAc}}}-M_{{\kappa }_{\mathrm{NaCl}}}\right).Math.\left({\delta }_{d,{\mathrm{Ac}}^{-}}+\left({\delta }_{0,{\mathrm{Ac}}^{-}}-{\delta }_{d,{\mathrm{Ac}}^{-}}\right).Math.{\left(1-\frac{Q_u}{V_{0,{\mathrm{Ac}}^{-}}}.Math.t\right)}^{\frac{{\alpha }^{-1}.Math.K_{u,{\mathrm{Ac}}^{-}}+\frac{V_{\max }}{K_M}}{Q_u}-1}\right)+\frac{K_{u,K^{+}}}{Q_{\mathrm{do}}}.Math.M_{{\kappa }_{\mathrm{KCl}}}.Math.\left({\delta }_{d,K^{+}}+\left({\delta }_{0,K^{+}}-{\delta }_{d,K^{+}}\right).Math.{\left(1-\frac{Q_u}{V_{0,K^{+}}}.Math.t\right)}^{\frac{\alpha .Math.K_{u,K^{+}}}{Q_u}-1}\right)+{\kappa }_{\mathrm{rest}3}.Math.e^{\frac{K_{u,\mathrm{rest},\mathrm{mean}}}{V_{\mathrm{rest},\mathrm{mean}}}.Math.t}& \left(16\right)\end{array}$

(189) wherein the time variable gradients are denoted:

(190) ${\delta }_{d,{\mathrm{Na}}^{+}}=\alpha .Math.c_{\mathrm{pw},\mathrm{Na}}\left(t\right)-c_{\mathrm{di},\mathrm{Na}}{\delta }_{d,{\mathrm{HCO}}_3^{-}}=\frac{1}{\alpha }.Math.c_{\mathrm{pw},{\mathrm{HCO}}_3}\left(t\right)-c_{\mathrm{di},{\mathrm{HCO}}_3}{\delta }_{d,{\mathrm{Ac}}^{-}=}\frac{1}{\alpha }.Math.c_{\mathrm{pw},\mathrm{Ac}}\left(t\right)-c_{\mathrm{di},\mathrm{Ac}}{\delta }_{d,K^{+}}=\alpha .Math.c_{\mathrm{pw},K}\left(t\right)-c_{\mathrm{di},K}$

(191) and wherein the other used symbols meaning is clarified in the glossary section.

(192) The modeled conductivity is then compared with the measured conductivity to check that the dialysis progresses as expected with the used estimations of sodium, bicarbonate and potassium.

(193) Compensation for Unwanted Sodium Transfer

(194) After the application of sodium adjustments above described, the inlet conductivity correspondent to the fresh dialysis fluid sodium concentration determined with Eq. 6 shall then be kept constant throughout the remainder of the treatment.

(195) After the setting of the sodium set point for achieving the desired mass transfer, the plasma conductivity may be further calculated/monitored using common procedures, such as those described in patents EP 547025 or in EP 920877 to monitor PC throughout the treatment.

(196) During the identification phase (i.e. plasma conductivity initial estimate), the sodium setting is likely to be too high, leading to unwanted sodium load. The time for this estimation may slightly vary, but as an average is about 15 minutes; accordingly, the magnitude of the error is in the range of 5 mmol/l (of course varying with how well the expected plasma conductivity matches the actual plasma conductivity, as well as the magnitude of the isotonic adjustment).

(197) To maintain the patient's sodium balance during the dialysis treatment, the calculated sodium set value must be adjusted to compensate for any additional unwanted sodium load to the patient.

(198) Moreover, if common procedures such as those described in patents EP 547025 or in EP 920877 to monitor plasma conductivity throughout the treatment are used (e.g. Diascan measurements), a sodium transfer will result from the conductivity steps (10 mmol/L for 120 s for example). This sodium transfer can be either in the positive or negative direction.

(199) Such unwanted transfers may need to be compensated for in order to maintain the desired sodium balance during the treatment.

(200) In order to manage multiple deviations e.g. from Diascan measurements, the compensation may be implemented by integrating some, or possibly any deviation from the intended sodium set point (i.e. the sodium concentration that is set after calculation, c.sub.d,M.sub.d) and then compensate for this over the remaining time of treatment (T−t, where T is the total treatment time and t is the elapsed treatment time).

(201) The applied compensated sodium concentration set point may be calculated according to the following formula:

(202) $\begin{array}{cc}{c}_{d,M_d,\mathrm{compensated}}=c_{d,M_d}+\underset{i}{.Math.}\frac{1}{T-t_i}{\int }_{t_i}^{t_i+\Delta t_i}\left(c_{d,M_d}-c_{d,\mathrm{Na},\mathrm{actual},i}\right)\mathrm{dt}& \left(17\right)\end{array}$
where c.sub.d,M.sub.d is the sodium set point calculated by the described algorithm (sodium set point which correspond to dialysis fluid concentration of sodium ions (Na.sup.+) to provide the desired sodium mass transport M.sub.d, cf. formula 6), c.sub.d,Na,actual,i is the actual dialysis fluid sodium concentration set point used during the treatment at the time an additional compensation is to be applied for (note that c.sub.di,Na,actual may deviate from c.sub.d,M.sub.d due to both the initial estimation of isoconductivity and/or the plasma conductivity monitoring procedures, e.g. Diascan steps).

(203) The compensation may be or may be not activated once c.sub.d,M.sub.d has been calculated (for example about 15 minutes after treatment start, i.e. at the end of the identification phase), and may (or may not) take the past history into account so that any sodium transfer during the isoconductivity identification phase is also compensated.

(204) The compensation may be applied after every sodium i-th deviation, i.e., when sodium is equal to c.sub.d,Na,actual,i for a duration of Δt.sub.i. Hence, also aborted Diascan measures may be taken into account (in this case, Δt may be lower than the forecast conductivity step).

(205) Instead of applying a single compensation factor for each deviation, a potential alternative is to apply an integral controller, which, on the basis of the current error on applied sodium set vs. isotonic/isonatric/isonatrikalemic set found and on the time still available, applies automatically a corrected set.