FLUID WARMING DEVICE FOR AN EXTRACORPOREAL BLOOD TREATMENT APPARATUS AND METHOD FOR DETECTING A FLUID TEMPERATURE AT AN OUTLET OF A FLUID WARMING DEVICE FOR AN EXTRACORPOREAL BLOOD TREATMENT APPARATUS

Abstract

A fluid warming device for an extracorporeal blood treatment apparatus, comprises: an outlet temperature sensor (31) operatively active at an outlet (22) of a fluid warming path (23) to detect a measured outlet temperature (To) of a fluid leaving the fluid warming device (18); an electronic control unit (29) operatively connected to the outlet temperature sensor (31). The electronic control unit (29) is configured to perform the following procedure: receiving, from the outlet temperature sensor (31) a signal correlated to a measured outlet temperature (To); correcting the measured outlet temperature (To) through a correction model to obtain an actual fluid outlet temperature (Tout); adjusting a heating power (Ph) of heating elements to keep the actual fluid outlet temperature (Tout) at a set reference temperature value (Tset). The correction model is an empirical model of a measurement error (E) derived from a plurality of experimental data sets, the measurement error (E) being a difference between the measured outlet temperature (To) and the actual fluid outlet temperature (Tout).

Claims

1-15. (canceled)

16. Fluid warming device for an extracorporeal blood treatment apparatus, comprising: a casing defining a heating zone configured to accommodate a fluid warming path, wherein the fluid warming path comprises an inlet and an outlet for fluid connection to an extracorporeal blood treatment apparatus; heating elements operatively active in the heating zone, the heating elements configured to heat the fluid warming path; an outlet temperature sensor operatively active at the outlet of the fluid warming path and configured to convey a measured outlet temperature of a fluid leaving the fluid warming device; and an electronic control unit operatively connected to the outlet temperature sensor, wherein the electronic control unit is configured to: receive, from the outlet temperature sensor a signal correlated to the measured outlet temperature; correct the measured outlet temperature using a correction model to obtain an actual fluid outlet temperature; adjust a heating power of the heating elements to keep the actual fluid outlet temperature at a set reference temperature; wherein the correction model is based at least in part on a measurement error, the measurement error being a difference between the measured outlet temperature and the actual fluid outlet temperature.

17. The fluid warming device of claim 16, wherein the correction model is an empirical model of the measurement error derived from a plurality of experimental data sets.

18. The fluid warming device of claim 16, wherein the fluid warming device is a blood warming device configured to be coupled to a blood return line of an extracorporeal blood circuit of the extracorporeal blood treatment apparatus to heat blood.

19. The fluid warming device of claim 17, wherein the correction model is derived from a regression analysis of the measurement error, collected through said plurality of experimental data sets, versus a plurality of parameters, wherein said parameters comprise the measured outlet temperature and at least one further working parameter of the fluid warming device or of the extracorporeal blood treatment apparatus.

20. The fluid warming device of claim 19, wherein the at least one further working parameter comprises at least one of: a temperature of a heating element of the fluid warming device, a heating power of the fluid warming device, a measured inlet temperature of the fluid entering the fluid warming device, a measured compensation temperature, an ambient temperature, a power supply a fluid flow rate, a ratio between the heating power of the fluid warming device, and a difference between the measured outlet temperature and the measured inlet temperature.

21. The fluid warming device of claim 17, wherein the plurality of experimental data sets substantially covers a full intended operating range of the fluid warming device, wherein the full intended operating range is defined by one or more of the following ranges: operating range of the actual fluid site temperature; operating range of the measured site temperature; operating range of a fluid flow rate through the fluid warming path; operating range of a temperature of the heating elements; operating range of the heating power; operating range of an actual or measured inlet temperature at the inlet of the fluid warming path; operating range of at least one measured compensation temperature; operating range of ambient temperature; operating range of power supply voltage for the heating elements.

22. The fluid warming device of claim 16, comprising: an inlet temperature sensor operatively active at the inlet of the fluid warming path and configured to detect a measured inlet temperature of the fluid entering the fluid warming device; a heating element temperature sensor coupled to a heating element of the heating elements of the fluid warming device and configured to detect a measured temperature of the heating element; a compensation temperature sensor located between the outlet temperature sensor and the heating element and configured to detect a measured temperature of a part of the fluid warming device; wherein the electronic control unit is further configured to: receive from the inlet temperature sensor a signal correlated to the measured inlet temperature; receive from the heating element temperature sensor a signal correlated to the measured temperature of the heating element; receive from the compensation temperature sensor a signal correlated to the measured temperature of the part of the fluid warming device; calculate the actual fluid outlet temperature from the measured outlet temperature and from at least one of: the measured inlet temperature, the measured temperature of the heating element, and the measured temperature of the part of the fluid warming device.

23. The fluid warming device of claim 16, wherein the outlet temperature sensor is a contact type outlet temperature sensor, wherein the contact type outlet temperature sensor is configured to be placed in contact with an outlet of the fluid warming path.

24. The fluid warming device of claim 16, comprising a plurality of heating plate temperature sensors coupled to the heating elements, the plurality of heating plate temperature sensors configured to detect a measured temperature of the heating elements, each of the heating elements being provided with one or more heating plate temperature sensors which are placed along the fluid warming path.

25. The fluid warming device of claim 16, wherein the casing defines a heating seat configured to accommodate a fluid warming bag, wherein the fluid warming bag defines the fluid warming path and comprises the inlet and the outlet, the heating elements comprising two opposite heating plates defining the heating seat, to heat the fluid warming bag, wherein the outlet temperature sensor is mounted in the casing and is in contact with the outlet of the fluid warming bag, the inlet temperature sensor is mounted in the casing and is in contact with the inlet of the fluid warming bag, and a plurality of heating element temperature sensors are coupled to the heating elements.

26. The fluid warming device of claim 22, wherein the compensation temperature sensor is configured to sense the temperature of the casing and is close to a location of a circuit board assembly operatively connected to the outlet temperature sensor.

27. The fluid warming device of claim 16, wherein the casing comprises a holder housing the outlet temperature sensor, the holder and the outlet temperature sensor being housed in a seat of the casing, wherein a heat conducting element is mounted in the holder and the outlet temperature sensor rests against the heat conducting element and is configured to detect a temperature of the heat conducting element.

28. The fluid warming device of claim 27, wherein the heat conducting element opens on a bottom surface of the casing and is flush with said bottom surface, the heat conducting element being in contact with the outlet of the fluid warming path, the outlet temperature sensor configured to detect a temperature of the heat conducting element and indirectly of the outlet of the fluid warming path.

29. Fluid warming device for an extracorporeal blood treatment apparatus, comprising: a casing defining a heating zone configured to accommodate a fluid warming path, wherein the fluid warming path has an inlet and an outlet for fluid connection to an extracorporeal blood treatment apparatus; heating elements operatively active in the heating zone, the heating elements configured to heat the fluid warming path; an outlet temperature sensor operatively active at the outlet of the fluid warming path and configured to convey a measured outlet temperature of a fluid leaving the fluid warming device; at least one heating element temperature sensor coupled to one of the heating elements of the fluid warming device and configured to detect a measured temperature of the heating element; an electronic control unit operatively connected to the outlet temperature sensor and to the heating element temperature sensor, wherein the electronic control unit is configured to: receive, from the outlet temperature sensor, a signal correlated to the measured outlet temperature; receive, from the at least one heating element temperature sensor, a signal correlated to the measured temperature of the heating element; correct the measured outlet temperature using a correction model to obtain an actual fluid outlet temperature; control the heating elements to keep the actual fluid outlet temperature at a set reference temperature; wherein the electronic control unit is configured to obtain the actual fluid outlet temperature as a function of a difference between the measured outlet temperature and the measured temperature of the heating element.

30. The fluid warming device of claim 29, wherein the electronic control unit is configured to obtain the actual fluid outlet temperature as a linear function of the difference between the measured outlet temperature and the measured temperature of the heating element.

31. The fluid warming device of claim 29, wherein the electronic control unit is configured to obtain the actual fluid outlet temperature as follows:
T.sub.out=α.Math.(T.sub.o−T.sub.plate)−T.sub.a+b wherein T.sub.out is the actual fluid outlet temperature; T.sub.o is the measured outlet temperature; T.sub.place is the measured temperature of the heating element; and a, b are constants.

32. A fluid warming device for an extracorporeal blood treatment apparatus, comprising: a casing defining a heating zone configured to accommodate a fluid warming path, wherein the fluid warming path has an inlet and an outlet for fluid connection to an extracorporeal blood treatment apparatus; heating elements operatively active in the heating zone and configured to heat the fluid warming path; at least one site temperature sensor operatively active on a site along the fluid warming path to detect a measured site temperature of a fluid in the fluid warming device; an electronic control unit operatively connected to the site temperature sensor, wherein the electronic control unit is configured to: receive, from the at least one site temperature sensor, a signal correlated to the measured site temperature; correct the measured site temperature using a correction model to obtain an actual fluid site temperature; adjusting the heating elements based on the actual fluid site temperature to keep an actual fluid temperature in a further site along the fluid warming path at a set reference temperature value.

33. The fluid warming device of claim 32, wherein the at least one site temperature sensor is one among an inlet temperature sensor, an outlet temperature sensor, and a temperature sensor placed between the inlet and the outlet.

34. The fluid warming device of claim 32, wherein the at least one site temperature sensor is other than an outlet temperature sensor and the electronic control unit is configured to: determine an actual fluid outlet temperature from the actual fluid site temperature; adjust a heating power of the heating elements to keep the actual fluid outlet temperature at a set reference temperature value.

35. The fluid warming device of claim 32, wherein the correction model is based at least in part on a measurement error, the measurement error being a difference between the measured site temperature and the actual fluid site temperature.

Description

DESCRIPTION OF DRAWINGS

[0116] The following drawings relating to aspects of the invention are provided by way of non-limiting example:

[0117] FIG. 1 shows a schematic representation of an extracorporeal blood treatment apparatus provided with a fluid warming device according to the present invention;

[0118] FIG. 2 shows a schematic perspective view of the fluid warming device of FIG. 1;

[0119] FIG. 3 shows the fluid warming device of FIG. 1 in an open configuration;

[0120] FIG. 4 is a disposable fluid warming bag to be used with the fluid warming device of FIGS. 2 and 3;

[0121] FIG. 5 shows a sectioned and enlarged view of a portion of the fluid warming device of FIG. 3;

[0122] FIG. 6 shows a sectioned and enlarged view of another portion of the fluid warming device of FIG. 3;

[0123] FIG. 7 is a flowchart showing steps for a building a correction model according to a method of the present invention;

[0124] FIG. 8 shows a cumulative plot of results used to build the correction model;

[0125] FIG. 9 is a flowchart showing a method for controlling the fluid warming device according to the present invention.

DETAILED DESCRIPTION

[0126] With reference to the appended drawings, FIG. 1 shows a schematic representation of an extracorporeal blood treatment apparatus 1. The apparatus 1 comprises one blood treatment device 2, for example a hemofilter, a hemodiafilter, a plasmafilter, a dialysis filter, an absorber or other unit suitable for processing the blood taken from a patient P.

[0127] The blood treatment device 2 has a first compartment or blood chamber 3 and a second compartment or fluid chamber 4 separated from one another by a semipermeable membrane 5. A blood withdrawal line 6 is connected to an inlet port 3a of the blood chamber 3 and is configured, in an operative condition of connection to the patient P, to remove blood from a vascular access device inserted, for example in a fistula on the patient P. A blood return line 7 connected to an outlet port 3b of the blood chamber 3 is configured to receive treated blood from the treatment unit 2 and to return the treated blood, e.g. to a further vascular access also connected to the fistula of the patient P. Note that various configurations for the vascular access device may be envisaged: for example, typical access devices include a needle or catheter inserted into a vascular access which may be a fistula, a graft or a central (e.g. jugular vein) or peripheral vein (femoral vein) and so on. The blood withdrawal line 6 and the blood return line 7 are part of an extracorporeal blood circuit of the apparatus 1.

[0128] The extracorporeal blood circuit 6, 7 and the treatment unit 2 are usually disposable parts which are loaded onto a frame of a blood treatment machine, not shown.

[0129] As shown in FIG. 1, the apparatus 1 comprises at least a first actuator, in the present example a blood pump 8, which is part of said machine and operates at the blood withdrawal line 6, to cause movement of the blood removed from the patient P from a first end of the withdrawal line 6 connected to the patient P to the blood chamber 3. The blood pump 8 is, for example, a peristaltic pump, as shown in FIG. 1, which acts on a respective pump section of the withdrawal line 6.

[0130] It should be noted that for the purposes of the present description and the appended claims, the terms “upstream” and “downstream” may be used with reference to the relative positions taken by components belonging to or operating on the extracorporeal blood circuit. These terms are to be understood with reference to a blood flow direction from the first end of the blood withdrawal line 6 connected to the patient P towards the blood chamber 3 and then from the blood chamber 3 towards a second end of the blood return line 7 connected to the vascular access of the patient P.

[0131] The apparatus 1 may further comprise an air trapping device 9 operating on the blood return line 7 (the air trapping device 9 may be a venous deaeration chamber). The air trapping device 9 is placed online in the blood return line 7.

[0132] A first section of the blood return line 7 puts in fluid communication the outlet port 3b of the blood chamber 3 with the air trapping device 9 and a second section of the blood return line 7 puts in fluid communication the air trapping device 9 with the patient P. The blood coming from the blood chamber 3 of the treatment device 2 enters and exits the air trapping device 9 before reaching the patient P.

[0133] The apparatus 1 of FIG. 1 further comprises one fluid evacuation line 10 connected with an outlet port 4b of the fluid chamber 4 such as to receive the filtered waste fluid through the semipermeable membrane 5. The fluid evacuation line 10 receives such filtered waste fluid coming from the fluid chamber 4 of the treatment device 2, for example, comprising used dialysis liquid and/or liquid ultra-filtered through the membrane 5. The fluid evacuation line 10 leads to a receiving element, not shown, for example having a collection bag or a drainage pipe for the waste fluid. One or more dialysate pumps, not shown, may operate on the fluid evacuation line 10.

[0134] In the example of FIG. 1, a dialysis line 11 is also present for supplying a fresh treatment fluid into the inlet port 4a of the fluid chamber 4. The presence of this dialysis line 11 is not strictly necessary since, in the absence of the dialysis line 11, the apparatus 1 is still able to perform treatments such as ultrafiltration, hemofiltration or plasma-filtration. In case the dialysis line 11 is present, a fluid flow intercept device may be used, not shown, to selectively allow or inhibit fluid passage through the dialysis line 11, depending on whether or not a purification by diffusive effect is to be performed inside the treatment device 2.

[0135] The dialysis line 11, if present, is typically equipped with a dialysis pump and is able to receive a fresh fluid from a module, not shown, for example a bag or on-line preparation section of dialysis fluid, and to send such a fluid to the inlet port 4a of the fluid chamber 4.

[0136] The fluid evacuation line 10, the dialysis line 11 and the fluid chamber 4 are part of a treatment fluid circuit 12.

[0137] The apparatus 1 as shown in FIG. 1 further comprises an infusion circuit comprising one or more infusion lines of a replacement fluid. According to the embodiment of FIG. 1, a pre-infusion line 13 is connected to the blood withdrawal line 6 between the blood pump 8 and the inlet port 3a of the blood chamber 3. A pre pump infusion line 14 is connected to the blood withdrawal line 6 upstream of the blood pump 8, between said blood pump 8 and the vascular access device inserted in the fistula on the patient P. A post-infusion line 15, 16 is connected to the blood return line 7 for performing HF or HDF treatments. Usually one or two post-infusion lines are used connected upstream of or to the air trapping device 9. FIG. 1 shows that the post-infusion line comprises a first and a second branch 15, 16. Each of the pre- and/or post-infusion line 13, 14, 15, 16 is provided with a respective pump, not shown. The pre- and/or post-infusion lines 13, 14, 15, 16 may be supplied by fluid coming from bags or directly by infusion fluid prepared on-line. Each of the pre- and/or post-infusion lines 13, 14, 15, 16 are part of the treatment fluid circuit 12. The specific configuration of the pre- and post-infusion circuits may of course differ from those shown in FIG. 1.

[0138] The blood return line 7 presents a heating zone, for example interposed between the first and second branches 15, 16 of the post-infusion line. In said heating zone blood is warmed before flowing into the blood circulation system of the patient P. In the embodiment shown in the attached figures, the heated portion is part of a disposable blood warming bag 17 which is inserted into a blood warming device 18. The blood warming device 18 is connected to or is part of the extracorporeal blood treatment apparatus 1.

[0139] The blood warming bag 17 shown in the attached figures is a substantially flat and soft bag insertable through a slot 19 in a heating seat 20 provided in the blood warming device 18 (FIGS. 2 and 3).

[0140] The blood warming bag 17 presents an inlet 21 and an outlet 22 connected to the extracorporeal blood circuit. For instance, the blood warming bag 17 comprises two sheets of plastic (e.g. polyurethane or polyvinylchloride) superposed and welded to form the bag and to form, inside the bag, a fluid warming path 23 delimited by said two sheets and by lines of welding.

[0141] The inlet 21 and the outlet 22 are tube sections placed at opposite ends of the fluid warming path 23. These tube sections of the inlet 21 and the outlet 22 protrude from a side of the blood warming bag 17 and are substantially parallel to each other.

[0142] The blood warming device 18 comprises a casing 24 delimiting the heating seat 20 configured to accommodate the blood warming bag 17. The casing 24 comprises an upper part 25 and a lower part 26 which may be linked and movable between a working configuration (shown in FIG. 2) and a maintenance configuration (shown in FIG. 3). The upper part 25 and lower part 26 of FIGS. 2 and 3 are hinged to move between the mentioned configurations. When the casing 24 is in the working configuration of FIG. 2, the upper part 25 and the lower part 26 are juxtaposed and delimit inside the casing 24 the heating seat 20 which opens outside through the slot 19.

[0143] When the blood warming bag 17 is inserted in the seat through the slot 19, the inlet 21 and the outlet 22 of the blood warming bag 17 are disposed close to the slot 19 or protrude from said slot 19 to allow tubing of blood withdrawal line 6 and blood return line 7 to be connected to the other elements of the extracorporeal blood treatment apparatus 1.

[0144] An upper face of the lower part 26 has a hollow delimiting a lower part of the heating seat 20 and shaped to accommodate the blood warming bag 17. The hollow presents a first heating plate 27 heated by a first heating device, not shown, placed underneath said first heating plate 27.

[0145] A lower face of the upper part 25 has a second heating plate 28 heated by a second heating device, not shown, placed underneath said second heating plate 28. The second heating plate 28 delimits an upper part of the heating seat 20. The first heating plate 27 and the second heating plate 28 are opposite and parallel surfaces delimiting the heating seat 20.

[0146] The first and second heating plates 27, 28 define heating elements for the blood warming bag 17. The first and second heating devices may be or may be connected to electrical resistors powered by a power control unit and controlled by an electronic control unit 29 in order to heat the blood warming path 23 in the blood warming bag 17.

[0147] In an embodiment, not shown, the heating zone comprises a plurality of subzones configured to be heated independently. By way of example, each of the first and second heating plates 27, 28 is divided into a plurality of parts each heated independently form the other part/s.

[0148] The blood warming device 18 comprises an inlet temperature sensor 30 and an outlet temperature sensor 31 embedded in a bottom surface 32 of the casing 24 close to the slot 19 (FIG. 3). The inlet temperature sensor 30 is operatively active at the inlet 21 of the blood warming path 23 to detect a measured inlet temperature of blood entering the blood warming device 18. The outlet temperature sensor 31 is operatively active at the outlet 22 of the blood warming path 23 to detect a measured outlet temperature of blood leaving the blood warming device 18.

[0149] The inlet temperature sensor 30 is a contact type temperature sensor, e.g. a temperature sensor integrated circuit (IC) with a thermistor or a thermocouple, housed in a plastic holder 33 (FIG. 5). The plastic holder 33 and the inlet temperature sensor 30 are housed in a seat fashioned in the bottom surface 32 of the casing 24. A heat conducting element, like an aluminum platelet 100, is mounted in the plastic holder 33. The aluminum platelet 100 opens on the bottom surface 32 and it is flush with said bottom surface 32. The inlet temperature sensor 30 is placed inside the plastic holder 33 and rests against the aluminum platelet 100 (FIG. 5).

[0150] When the blood warming bag 17 is correctly inserted in the seat, the inlet 21 of the blood warming bag 17 is in contact with the aluminum platelet 100 (FIG. 6). The inlet temperature sensor 30 detects the temperature Ti of the aluminum platelet 100 and of the inlet 21 through which the blood flows.

[0151] The outlet temperature sensor 31 is a contact type temperature sensor, e.g. a temperature sensor integrated circuit (IC) with a thermistor or a thermocouple, housed in a plastic holder 34 (FIG. 5). The plastic holder 34 and the outlet temperature sensor 31 are housed in a seat fashioned in the bottom surface 32 of the casing 24. The outlet temperature sensor 31 rests against a respective aluminum platelet 101 which opens on the bottom surface 32 and it is flush with said bottom surface 32 (FIG. 5).

[0152] When the blood warming bag 17 is correctly inserted in the seat, the outlet 22 of the blood warming bag 17 is in contact with the aluminum platelet 101. The outlet temperature sensor 31 detects the temperature of the aluminum platelet 101 and of the outlet 22 through which the warmed blood flows.

[0153] A holder compensation temperature sensor 35, e.g. a thermistor, is embedded in the plastic holder 34 of the outlet temperature sensor 31 to measure the temperature Tcomp1 of said plastic holder 34.

[0154] The blood warming device 18 comprises a further compensation temperature sensor 36, e.g. a temperature sensor integrated circuit (IC) with a thermistor or a thermocouple, placed in the casing 24 to sense the temperature of the casing 24.

[0155] Ambient temperature Ta may also be used as compensation temperature. The ambient temperature Ta may be measured through a respective sensor of the extracorporeal blood treatment apparatus 1 or through an independent device and entered manually by an operator in the control unit 29.

[0156] A printed circuit board assembly (PCBA) 37 is mounted inside the casing 24 and, together with other printed circuit board assemblies, forms part of the electronic control unit 29 of the blood warming device 18.

[0157] In the illustrated embodiment, the further compensation temperature sensor 36, e.g. a thermocouple, is placed at or close to a location of the printed circuit board assembly 37 to sense the temperature Tcomp2 of said printed circuit board assembly 37.

[0158] The blood warming device 18 comprises a plurality of heating plate temperature sensors 38 coupled to the first and second heating plates 27, 28 to detect a measured temperature of the heating plates 27, 28. In the illustrated embodiment, each of the first and second heating plates 27, 28 is provided with three heating plate temperature sensors 38 which, when the blood warming bag 17 is accommodated inside the heating seat 20, are placed along the fluid warming path 23.

[0159] The temperature sensors (inlet temperature sensor 30, outlet temperature sensor 31, compensation temperature sensor 35, further compensation temperature sensor 36, heating plate temperature sensors 38) are operatively connected to the printed circuit board assembly 37 and to the electronic control unit 29.

[0160] The electronic control unit 29 may be part of the blood warming device 18 and connected to an electronic control unit of the apparatus 1 or may be the electronic control unit of the apparatus 1 itself.

[0161] The electronic control unit 29 may comprise a digital processor (CPU) and memory (or memories), an analog circuit, or a combination thereof, and input/output interfaces. Said control unit 29 may be the control unit which is configured to control the apparatus 1 during patient blood treatment through a software stored in the control unit 29. In the embodiment of FIG. 1, the electronic control unit 29 is connected at least to the blood pump 8 and to the power control unit, not shown, of the blood warming device 18.

[0162] The electronic control unit 29 is configured to control the actual fluid temperature Tout of treated blood leaving the blood warming device 18 and flowing back into the patient P through a heat controller algorithm. To this aim, the electronic control unit 29 receives the measured outlet temperature To from the outlet temperature sensor 31, performs a correction of the measured outlet temperature To according to the steps disclosed in the following (to improve accuracy of the measurement and to obtain a value very close to an actual blood outlet temperature Tout) and adjusts the heating power Ph of the power control unit to keep the actual outlet temperature Tout at a set reference temperature value Tset (set point). The electronic control unit 29 uses a closed-loop control to maintain desirable temperature at its outlet.

[0163] In order to correct the measured outlet temperature To, a correction mathematical model or algorithm is previously developed and stored in a memory of the electronic control unit 29 or connected to the electronic control unit 29. The correction mathematical model or algorithm may be embedded in the heat controller algorithm.

[0164] The correction model is an empirical model of a measurement error E derived from a plurality of experimental data sets gathered during development testing. The measurement error E is a difference between the measured outlet temperature To and the actual outlet temperature Tout.

[0165] The empirical correction model is built by carrying out a plurality of test treatments k. An experimental data set is collected for each test treatment k. Each experimental data set comprises a plurality of measured parameters, wherein said parameters comprise the measured outlet temperature To.sub.k and at least one further working parameter of the blood warming device 18 and/or of the extracorporeal blood treatment apparatus 1 for that test treatment k.

[0166] The measured parameters for each test treatment k may the following: [0167] To.sub.k measured outlet temperature (through the outlet temperature sensor 31); [0168] Ti.sub.k measured inlet temperature (through the inlet temperature sensor 32); [0169] Tplate.sub.k measured heating plate/s temperature/s (through the heating plate temperature sensor/s 38); [0170] Ph.sub.k heating power of the fluid warming device (through a signal from the power control unit); [0171] Tcomp1.sub.k measured compensation temperature (through the compensation temperature sensor 35); [0172] Tcomp2.sub.k measured further compensation temperature (through the further compensation temperature sensor 36); [0173] Q.sub.k blood flow rate (through a signal from the blood pump 8 or communicated from a system controlling the blood flow); [0174] Tout.sub.k measured actual fluid outlet temperature (measured during test treatments through an independent and very accurate sensor); [0175] Tin.sub.k measured actual fluid inlet temperature (measured during test treatments through an independent and a very accurate non-contact sensor); [0176] Ta.sub.k ambient temperature; [0177] Pw.sub.k power supply voltage of the fluid warming device.

[0178] The blood flow rate Q may be replaced by a ratio Ph/(To−Ti) between the heating power Ph and a difference between the measured outlet temperature To and the measured inlet temperature Ti. Indeed, heating power transferred to the blood may be expressed by Ph=ρ×Cp×Q×(Tout−Tin) where Tin is the actual fluid inlet temperature. This relationship indicates that Ph/(To−Ti) should be proportional to the actual fluid flow rate.

[0179] Measured compensation temperature and measured further compensation temperature Tcomp1, Tcomp2 may be used in combination with measured heating plate/s temperature/s Tplate or in lieu of measured heating plate/s temperature/s Tplate.

[0180] The correction model may be derived from a regression analysis of the measurement error E.sub.k collected through said plurality of experimental data sets versus the mentioned parameters collected through said plurality of experimental data sets. The model will be as reliable as the experimental data set collection is large and covers the full intended operating range of the blood warming device 18 and it is built using several fluid warming devices 18 and several warmer bags/cassettes 17.

[0181] A number of the experimental data sets k may be thirty or more. The full intended operating range may be defined by ranges of the above mentioned parameters (ΔTo, ΔTi, ΔTplate, ΔPh, ΔTcomp1, ΔTcomp2, ΔQ, ΔTout, ΔTa, ΔPw). Several general regression models may be used according to the operating range/s of the blood warming device 18.

[0182] The empirical model may include: 1st and 2nd order terms of each of the parameters and/or crossed terms and/or other combinations of terms.

[0183] Once the empirical correction model is ready and stored in the memory of the electronic control unit 29, the electronic control unit 29 is configured to perform the following procedure during an extracorporeal blood treatment session performed on a patient P through the apparatus 1: receiving, from the outlet temperature sensor 31 a signal correlated to the measured outlet temperature To and correcting the measured outlet temperature To through the correction model to obtain the actual fluid outlet temperature Tout.

[0184] In addition to the measured outlet temperature To, the electronic control unit 29 receives as input at least one of the following measured parameters: [0185] To measured outlet temperature (through the outlet temperature sensor 31); [0186] Ti measured inlet temperature (through the inlet temperature sensor 32); [0187] Tplate measured heating plate/s temperature/s (through the heating plate temperature sensor/s 38); [0188] Ph heating power of the fluid warming device (through a signal from the power control unit); [0189] Tcomp1 measured compensation temperature (through the compensation temperature sensor 35); [0190] Tcomp2 measured further compensation temperature (through the further compensation temperature sensor 36); [0191] Q blood flow rate (through a signal from the blood pump 8 or communicated from a system controlling the blood flow); [0192] Ta ambient temperature; [0193] Pw Power supply voltage.

[0194] Therefore, the actual fluid outlet temperature Tout is calculated from the measured outlet temperature and from at least one of To, Ti, Tplate, Ph, Tcomp1, Tcomp2, Q, Ta, Pw and through the corrective model/algorithm, which works as a transfer function.

[0195] Example of Empirical Modeling

[0196] An empirical model/algorithm was developed based on empirical data gathered during developmental testing. The test setup was comprised of a simulated patient (warm water reservoir), an extracorporeal CRRT apparatus, and a blood warming device. The blood warming device outlet was instrumented with independent temperature sensors at the inlet and outlet in order to read the actual fluid temperatures at those points.

[0197] Outlet measurement error E was defined as the measured outlet temperature To minus the actual fluid temperature Tout at the outlet. In equation form: E=To−Tout.

[0198] Three metrics were used to compare against the outlet error E. Each metric was the difference between a specific secondary sensor and the measured outlet temperature.

[0199] In equation form:

DTcomp1=To−Tcomp1

DTcomp2=To−Tcomp2

DTplate=To−Tplate

[0200] where Tcomp1, Tcomp2 and Tplate were the measured temperatures at outlet temperature sensor 31, further compensation temperature sensor 36 and the heating plate temperature sensor 38 of the first heating plate 27 closest to the outlet temperature sensor 31, respectively.

[0201] To examine if there was a correlation between outlet error and any of these metrics, data was gathered from numerous test treatments. Treatments were performed using a hot water bath connected to a filter set on a blood treatment apparatus 1 with a blood warming device 18 attached. In order to calculate each metric once per treatment, the metrics were averaged over the time period at which the blood warming device 18 was at steady state. In other words, each treatment had a mean steady state outlet error DTcomp1, DTcomp2 and DTplate. A flow chart related to DTplate is shown in FIG. 7 and a cumulative plot of the results related to DTplate is shown in FIG. 8.

[0202] This plot shows a strong linear correlation between outlet error and DTplate. From this correlation, a correction equation may be derived:

E=−a×DTplate−b

To−Tout=−a×(To−Tplate)−b

Tout=a×(To−Tplate)+b−To

[0203] where Tout is the estimated fluid temperature at the outlet.

[0204] Example of Closed Loop Correction

[0205] This equation was implemented in the electronic control unit 29 with the constants a and b shown in in the last block of FIG. 7. This implementation is illustrated in block diagram form in FIG. 9. As shown in this figure, the outlet correction is part of the feedback loop within the electronic control unit 29.

[0206] The warming device 18 according to the invention herewith disclosed may also be designed to be coupled or configured to be coupled to the treatment fluid circuit to heat treatment fluid/s.

[0207] In lieu of the blood warming device or in combination with said blood warming device, one or more treatment fluid warming device/s 18 may be coupled to one or more of the pre- and/or post-infusion lines 13, 14, 15, 16 or the dialysis line 11.

[0208] In these embodiments, blood is warmed by the treatment fluids.

[0209] The correction model above disclosed may be applied to temperature sensor or sensors other than the outlet temperature sensor, e.g. to a generic site of the flow path in the fluid warming device 18. The correction model may be applied to the measured inlet temperature to calculate the actual fluid inlet temperature Tin. Actual fluid inlet temperature Tin may be used to perform, e.g., internal consistency checks of the fluid warming device, malfunction, diagnostic, etc.

[0210] While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not to be limited to the disclosed embodiment, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and the scope of the appended claims.