Patent Description:
The present invention relates to a fluid warming device coupled or configured to be coupled to an extracorporeal blood circuit of the extracorporeal blood treatment apparatus to heat blood (blood warming device) and/or to a fluid warming device coupled or configured to be coupled to a treatment fluid circuit of the extracorporeal blood treatment apparatus to heat treatment fluid (treatment fluid warming device).

The present invention relates to a method for detecting a fluid temperature at an outlet of the fluid warming device.

In particular, the present invention relates to the correction of temperature measurement provided by contact temperature sensors, like thermistors or thermocouples, at the outlet of the fluid warming device.

Extracorporeal blood treatment involves removing blood from a patient, treating the blood externally to the patient, and returning the treated blood to the patient. Extracorporeal blood treatment is typically used to extract undesirable matter or molecules from the patient's blood and add desirable matter or molecules to the blood. Extracorporeal blood treatment is used with patients unable to effectively remove matter from their blood, such as when a patient has suffered temporary or permanent kidney failure. These patients and other patients may undergo extracorporeal blood treatment to add or remove matter to their blood, to maintain an acid/base balance or to remove excess body fluids, or to perform extracorporeal gas exchange processes, for example.

Extracorporeal blood treatment is typically accomplished by removing the blood from the patient in e.g. a continuous flow, introducing the blood into a primary chamber, also referred to as blood chamber, of a treatment unit (such as a dialyzer or an hemofilter) where the blood is allowed to flow past a semipermeable membrane. The semipermeable membrane selectively allows matter in the blood to cross the membrane from the primary chamber into a secondary chamber and also selectively allows matter in the secondary chamber to cross the membrane into the blood in the primary chamber, depending on the type of treatment.

During extracorporeal blood treatment therapies, the patient may lose significant amount of heat due to fluid exchange by diffusion or convection, and due to heat lost to the atmosphere. As extracorporeal blood treatments may last from several hours up to several days, the patient is put at risk of hypothermia in case no preventive measures are taken. This risk is, for example, present both in the case of relatively short treatments with high volume exchange, like chronic haemodialysis (HD), and in the case of low volume but continuous therapies like continuous renal replacement therapy (CRRT). Furthermore, the risk of hypothermia is even more problematic in case of treatments applied to low body weight patients, such as children. Blood cooling due to fluid exchange (dialysate, infusion or both) or due to water evaporation during gas exchange processes is usually more important than heat losses to atmosphere in the complete extracorporeal blood circuit.

In order to prevent hypothermia during extracorporeal blood treatment, blood warmers acting on the bloodline and capable of directly warming blood and treatment fluid warmers acting on the treatment fluid circuit to heat treatment fluid/s prior to their infusion in the blood circuit or treatment unit have been used.

Measurement of the blood/fluid temperature at an outlet of blood/fluid warmer is known and it is used to control the blood/fluid warming device, in order to adjust the temperature of the treated blood returning to the patient and to drive the patient temperature on the long run.

Document <CIT> relates to an intravenous fluid warming system with a removable heat exchanger. The system includes a warming unit for warming the fluid and an inlet slot for receiving a heat exchanger which is embodied as a cassette. An exit temperature of the warmed fluid at an exit port is monitored by a temperature sensor located near a fluid outlet port. The fluid outlet port may have an infrared thermometer, integral heat sensor, or thermocouple for sensing the fluid temperature.

Document <CIT> discloses an extracorporeal blood treatment apparatus comprising a recirculation loop and a warming device. A temperature sensor is configured to sense a blood temperature. A control unit, connected to the warming device and to the temperature sensor, is configured to execute the following procedure: receiving from the temperature sensor a signal correlated to the blood temperature; adjusting the blood temperature by controlling the warming device and/or a recirculation pump.

Document <CIT> discloses a dialysis fluid heating system includes a dialysis fluid heater and a logic implementer configured to control the heater using a heater input, determined from a dialysis fluid temperature delta and a dialysis fluid flowrate, and a potential adjustment of the temperature delta using a measured dialysis fluid outlet temperature. Document <CIT> discloses an extracorporeal blood treatment apparatus comprising a control unit connected to a blood warming device and configured to calculate a set point value of an operating parameter to be imposed on the warming device configured to heat a blood heating zone of the extracorporeal blood circuit in order to maintain the desired blood temperature at the end of a blood return line.

Disadvantages of most of known solutions are related to lack of accuracy of the temperature measurements at the outlet of the blood/fluid warmers, in particular of the measurements performed through contact temperature sensors, like thermistors and thermocouples.

These types of temperature sensor are required to be in physical contact with the object being sensed and use conduction to monitor changes in temperature. In blood/fluid warmers these types of temperature sensor are placed in contact with bag, cassette or tubing in which blood/fluid flows.

In view of the above, it is an object of embodiments according to the present invention to improve the reliability of the fluid warming devices for extracorporeal blood treatment apparatuses and to improve the reliability of the extracorporeal blood treatment apparatuses employing said fluid warming devices.

It is an object of embodiments according to the present invention to improve controlling the temperature of the treated blood returning to the patient and driving the patient temperature on the long run.

In particular, it is an object to provide a fluid warming device wherein the reliability and accuracy of the fluid temperature measurement at the outlet of the fluid warming device is improved.

It is a further object to provide for optimized fluid temperature accuracy for a given design of a fluid warming device and/or of an extracorporeal blood treatment apparatus.

It is a further object to provide a fluid warming device and/or an extracorporeal blood treatment apparatus with the mentioned improved accuracy which, at the same time, is/are structurally simple, reliable and cost effective.

It is a further object to provide said reliability and accuracy avoiding development of complex and cumbersome insulation of the sensor/s.

It is a further object to provide said reliability and accuracy without impacting costs of the device and/or apparatus.

At least one of the above objects is substantially achieved by correcting a temperature measurement performed by a contact temperature sensor at the outlet of the fluid warming device through an empirical model of a measurement error derived from other available parameters.

In particular, at least one of the above objects is substantially achieved by a fluid warming device and a method for detecting a fluid temperature at an outlet of a fluid warming device according to one or more of the appended claims.

In a <NUM>st independent aspect, the invention relates to a fluid warming device for an extracorporeal blood treatment apparatus according to claim <NUM>.

In a <NUM>nd aspect, the invention concerns an extracorporeal blood treatment apparatus according to claim <NUM>.

In a <NUM>rd independent aspect, the invention relates to a method for detecting a fluid temperature at a site of a fluid warming device for an extracorporeal blood treatment apparatus according to claim <NUM>.

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

With reference to the appended drawings, <FIG> shows a schematic representation of an extracorporeal blood treatment apparatus <NUM>. The apparatus <NUM> comprises one blood treatment device <NUM>, 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.

The blood treatment device <NUM> has a first compartment or blood chamber <NUM> and a second compartment or fluid chamber <NUM> separated from one another by a semipermeable membrane <NUM>. A blood withdrawal line <NUM> is connected to an inlet port 3a of the blood chamber <NUM> 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 <NUM> connected to an outlet port 3b of the blood chamber <NUM> is configured to receive treated blood from the treatment unit <NUM> 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 <NUM> and the blood return line <NUM> are part of an extracorporeal blood circuit of the apparatus <NUM>.

The extracorporeal blood circuit <NUM>, <NUM> and the treatment unit <NUM> are usually disposable parts which are loaded onto a frame of a blood treatment machine, not shown.

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

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 <NUM> connected to the patient P towards the blood chamber <NUM> and then from the blood chamber <NUM> towards a second end of the blood return line <NUM> connected to the vascular access of the patient P.

The apparatus <NUM> may further comprise an air trapping device <NUM> operating on the blood return line <NUM> (the air trapping device <NUM> may be a venous deaeration chamber). The air trapping device <NUM> is placed online in the blood return line <NUM>.

A first section of the blood return line <NUM> puts in fluid communication the outlet port 3b of the blood chamber <NUM> with the air trapping device <NUM> and a second section of the blood return line <NUM> puts in fluid communication the air trapping device <NUM> with the patient P. The blood coming from the blood chamber <NUM> of the treatment device <NUM> enters and exits the air trapping device <NUM> before reaching the patient P.

The apparatus <NUM> of <FIG> further comprises one fluid evacuation line <NUM> connected with an outlet port 4b of the fluid chamber <NUM> such as to receive the filtered waste fluid through the semipermeable membrane <NUM>. The fluid evacuation line <NUM> receives such filtered waste fluid coming from the fluid chamber <NUM> of the treatment device <NUM>, for example, comprising used dialysis liquid and/or liquid ultra-filtered through the membrane <NUM>. The fluid evacuation line <NUM> 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 <NUM>.

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

The dialysis line <NUM>, 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 <NUM>.

The fluid evacuation line <NUM>, the dialysis line <NUM> and the fluid chamber <NUM> are part of a treatment fluid circuit <NUM>.

The apparatus <NUM> as shown in <FIG> further comprises an infusion circuit comprising one or more infusion lines of a replacement fluid. According to the embodiment of <FIG>, a pre-infusion line <NUM> is connected to the blood withdrawal line <NUM> between the blood pump <NUM> and the inlet port 3a of the blood chamber <NUM>. A pre pump infusion line <NUM> is connected to the blood withdrawal line <NUM> upstream of the blood pump <NUM>, between said blood pump <NUM> and the vascular access device inserted in the fistula on the patient P.

A post-infusion line <NUM>, <NUM> is connected to the blood return line <NUM> for performing HF or HDF treatments. Usually one or two post-infusion lines are used connected upstream of or to the air trapping device <NUM>. <FIG> shows that the post-infusion line comprises a first and a second branch <NUM>, <NUM>. Each of the pre- and/or post-infusion line <NUM>, <NUM>, <NUM>, <NUM> is provided with a respective pump, not shown. The pre- and/or post-infusion lines <NUM>, <NUM>, <NUM>, <NUM> 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 <NUM>, <NUM>, <NUM>, <NUM> are part of the treatment fluid circuit <NUM>. The specific configuration of the pre- and post- infusion circuits may of course differ from those shown in <FIG>.

The blood return line <NUM> presents a heating zone, for example interposed between the first and second branches <NUM>, <NUM> 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 <NUM> which is inserted into a blood warming device <NUM>. The blood warming device <NUM> is connected to or is part of the extracorporeal blood treatment apparatus <NUM>.

The blood warming bag <NUM> shown in the attached figures is a substantially flat and soft bag insertable through a slot <NUM> in a heating seat <NUM> provided in the blood warming device <NUM> (<FIG> and <FIG>).

The blood warming bag <NUM> presents an inlet <NUM> and an outlet <NUM> connected to the extracorporeal blood circuit. For instance, the blood warming bag <NUM> 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 <NUM> delimited by said two sheets and by lines of welding.

The inlet <NUM> and the outlet <NUM> are tube sections placed at opposite ends of the fluid warming path <NUM>. These tube sections of the inlet <NUM> and the outlet <NUM> protrude from a side of the blood warming bag <NUM> and are substantially parallel to each other.

The blood warming device <NUM> comprises a casing <NUM> delimiting the heating seat <NUM> configured to accommodate the blood warming bag <NUM>. The casing <NUM> comprises an upper part <NUM> and a lower part <NUM> which may be linked and movable between a working configuration (shown in <FIG>) and a maintenance configuration (shown in <FIG>). The upper part <NUM> and lower part <NUM> of <FIG> and <FIG> are hinged to move between the mentioned configurations.

When the casing <NUM> is in the working configuration of <FIG>, the upper part <NUM> and the lower part <NUM> are juxtaposed and delimit inside the casing <NUM> the heating seat <NUM> which opens outside through the slot <NUM>.

When the blood warming bag <NUM> is inserted in the seat through the slot <NUM>, the inlet <NUM> and the outlet <NUM> of the blood warming bag <NUM> are disposed close to the slot <NUM> or protrude from said slot <NUM> to allow tubing of blood withdrawal line <NUM> and blood return line <NUM> to be connected to the other elements of the extracorporeal blood treatment apparatus <NUM>.

An upper face of the lower part <NUM> has a hollow delimiting a lower part of the heating seat <NUM> and shaped to accommodate the blood warming bag <NUM>. The hollow presents a first heating plate <NUM> heated by a first heating device, not shown, placed underneath said first heating plate <NUM>.

A lower face of the upper part <NUM> has a second heating plate <NUM> heated by a second heating device, not shown, placed underneath said second heating plate <NUM>. The second heating plate <NUM> delimits an upper part of the heating seat <NUM>. The first heating plate <NUM> and the second heating plate <NUM> are opposite and parallel surfaces delimiting the heating seat <NUM>.

The first and second heating plates <NUM>, <NUM> define heating elements for the blood warming bag <NUM>. 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 <NUM> in order to heat the blood warming path <NUM> in the blood warming bag <NUM>.

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 <NUM>, <NUM> is divided into a plurality of parts each heated independently form the other part/s.

The blood warming device <NUM> comprises an inlet temperature sensor <NUM> and an outlet temperature sensor <NUM> embedded in a bottom surface <NUM> of the casing <NUM> close to the slot <NUM> (<FIG>). The inlet temperature sensor <NUM> is operatively active at the inlet <NUM> of the blood warming path <NUM> to detect a measured inlet temperature of blood entering the blood warming device <NUM>. The outlet temperature sensor <NUM> is operatively active at the outlet <NUM> of the blood warming path <NUM> to detect a measured outlet temperature of blood leaving the blood warming device <NUM>.

The inlet temperature sensor <NUM> 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 <NUM> (<FIG>). The plastic holder <NUM> and the inlet temperature sensor <NUM> are housed in a seat fashioned in the bottom surface <NUM> of the casing <NUM>. A heat conducting element, like an aluminum platelet <NUM>, is mounted in the plastic holder <NUM>. The aluminum platelet <NUM> opens on the bottom surface <NUM> and it is flush with said bottom surface <NUM>. The inlet temperature sensor <NUM> is placed inside the plastic holder <NUM> and rests against the aluminum platelet <NUM> (<FIG>).

When the blood warming bag <NUM> is correctly inserted in the seat, the inlet <NUM> of the blood warming bag <NUM> is in contact with the aluminum platelet <NUM> (<FIG>). The inlet temperature sensor <NUM> detects the temperature Ti of the aluminum platelet <NUM> and of the inlet <NUM> through which the blood flows.

The outlet temperature sensor <NUM> 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 <NUM> (<FIG>). The plastic holder <NUM> and the outlet temperature sensor <NUM> are housed in a seat fashioned in the bottom surface <NUM> of the casing <NUM>. The outlet temperature sensor <NUM> rests against a respective aluminum platelet <NUM> which opens on the bottom surface <NUM> and it is flush with said bottom surface <NUM> (<FIG>).

When the blood warming bag <NUM> is correctly inserted in the seat, the outlet <NUM> of the blood warming bag <NUM> is in contact with the aluminum platelet <NUM>. The outlet temperature sensor <NUM> detects the temperature of the aluminum platelet <NUM> and of the outlet <NUM> through which the warmed blood flows.

A holder compensation temperature sensor <NUM>, e.g. a thermistor, is embedded in the plastic holder <NUM> of the outlet temperature sensor <NUM> to measure the temperature Tcomp1 of said plastic holder <NUM>.

The blood warming device <NUM> comprises a further compensation temperature sensor <NUM>, e.g. a temperature sensor integrated circuit (IC) with a thermistor or a thermocouple, placed in the casing <NUM> to sense the temperature of the casing <NUM>.

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 <NUM> or through an independent device and entered manually by an operator in the control unit <NUM>.

A printed circuit board assembly (PCBA) <NUM> is mounted inside the casing <NUM> and, together with other printed circuit board assemblies, forms part of the electronic control unit <NUM> of the blood warming device <NUM>.

In the illustrated embodiment, the further compensation temperature sensor <NUM>, e.g. a thermocouple, is placed at or close to a location of the printed circuit board assembly <NUM> to sense the temperature Tcomp2 of said printed circuit board assembly <NUM>.

The blood warming device <NUM> comprises a plurality of heating plate temperature sensors <NUM> coupled to the first and second heating plates <NUM>, <NUM> to detect a measured temperature of the heating plates <NUM>, <NUM>. In the illustrated embodiment, each of the first and second heating plates <NUM>, <NUM> is provided with three heating plate temperature sensors <NUM> which, when the blood warming bag <NUM> is accommodated inside the heating seat <NUM>, are placed along the fluid warming path <NUM>.

The temperature sensors (inlet temperature sensor <NUM>, outlet temperature sensor <NUM>, compensation temperature sensor <NUM>, further compensation temperature sensor <NUM>, heating plate temperature sensors <NUM>) are operatively connected to the printed circuit board assembly <NUM> and to the electronic control unit <NUM>.

The electronic control unit <NUM> may be part of the blood warming device <NUM> and connected to an electronic control unit of the apparatus <NUM> or may be the electronic control unit of the apparatus <NUM> itself.

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

The electronic control unit <NUM> is configured to control the actual fluid temperature Tout of treated blood leaving the blood warming device <NUM> and flowing back into the patient P through a heat controller algorithm. To this aim, the electronic control unit <NUM> receives the measured outlet temperature To from the outlet temperature sensor <NUM>, 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 <NUM> uses a closed-loop control to maintain desirable temperature at its outlet.

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 <NUM> or connected to the electronic control unit <NUM>. The correction mathematical model or algorithm may be embedded in the heat controller algorithm.

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.

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 Tok and at least one further working parameter of the blood warming device <NUM> and/or of the extracorporeal blood treatment apparatus <NUM> for that test treatment k.

The measured parameters for each test treatment k may the following:.

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 x Cp x Q x (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.

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.

The correction model is derived from a regression analysis of the measurement error Ek 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 <NUM> and it is built using several fluid warming devices <NUM> and several warmer bags/cassettes <NUM>.

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 <NUM>.

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.

Once the empirical correction model is ready and stored in the memory of the electronic control unit <NUM>, the electronic control unit <NUM> is configured to perform the following procedure during an extracorporeal blood treatment session performed on a patient P through the apparatus <NUM>: receiving, from the outlet temperature sensor <NUM> 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.

In addition to the measured outlet temperature To, the electronic control unit <NUM> receives as input at least one of the following measured parameters:.

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.

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.

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.

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.

In equation form: <MAT> <MAT> <MAT> where Tcomp1, Tcomp2 and Tplate were the measured temperatures at outlet temperature sensor <NUM>, further compensation temperature sensor <NUM> and the heating plate temperature sensor <NUM> of the first heating plate <NUM> closest to the outlet temperature sensor <NUM>, respectively.

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 <NUM> with a blood warming device <NUM> attached. In order to calculate each metric once per treatment, the metrics were averaged over the time period at which the blood warming device <NUM> 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> and a cumulative plot of the results related to DTplate is shown in <FIG>.

This plot shows a strong linear correlation between outlet error and DTplate. From this correlation, a correction equation may be derived: <MAT> <MAT> <MAT> where Tout is the estimated fluid temperature at the outlet.

This equation was implemented in the electronic control unit <NUM> with the constants a and b shown in in the last block of <FIG>. This implementation is illustrated in block diagram form in <FIG>. As shown in this figure, the outlet correction is part of the feedback loop within the electronic control unit <NUM>.

The warming device <NUM> 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.

In lieu of the blood warming device or in combination with said blood warming device, one or more treatment fluid warming device/s <NUM> may be coupled to one or more of the pre- and/or post-infusion lines <NUM>, <NUM>, <NUM>, <NUM> or the dialysis line <NUM>.

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

Claim 1:
Fluid warming device for an extracorporeal blood treatment apparatus, comprising:
a casing (<NUM>) delimiting a heating zone accommodating or configured to accommodate a fluid warming path (<NUM>), wherein the fluid warming path (<NUM>) has an inlet (<NUM>) and an outlet (<NUM>) connected or connectable to an extracorporeal blood treatment apparatus (<NUM>);
heating elements operatively active in the heating zone to heat the fluid warming path (<NUM>);
at least an outlet temperature sensor (<NUM>) operatively active at the outlet (<NUM>) of the fluid warming path (<NUM>) to convey a measured outlet temperature (To) of a fluid leaving the fluid warming device (<NUM>);
an electronic control unit (<NUM>) operatively connected at least to the outlet temperature sensor (<NUM>);
wherein the electronic control unit (<NUM>) is configured to perform at least the following procedure:
- receiving, from the outlet temperature sensor (<NUM>) a signal correlated to the 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 the heating elements to keep the actual fluid outlet temperature (Tout) at a set reference temperature (Tset);
wherein the correction model is a mathematical model of a measurement error, wherein the correction model is an empirical model of the 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);
characterized in that the correction model is derived from a regression analysis of the measurement error (E) collected through the plurality of experimental data sets versus a plurality of parameters (To, Tplate, Ph, Ti, Tcomp1, Tcomp2, Q, P/(To-Ti), Pw, Ta) collected through said plurality of experimental data sets, wherein said parameters (To, Tplate, P, Ti, Tcomp1, Tcomp2, Q, P/(To-Ti), Pw, Ta) comprise the measured outlet temperature (To) and one further working parameter (Tplate, P, Ti, Tcomp1, Tcomp2, Q, P/(To-Ti), Pw, Ta) of the fluid warming device (<NUM>) and/or of the extracorporeal blood treatment apparatus (<NUM>).