APPARATUS FOR EXTRACORPOREAL TREATMENT OF BLOOD

Abstract

An extracorporeal blood treatment apparatus comprises a blood treatment device (2), an extracorporeal blood circuit, a blood pump (8) configured to be coupled to a blood withdrawal line (6) of the extracorporeal blood circuit. A closed fluid line (10) is connected to an inlet port (4a) and to an outlet port (4b) of a fluid chamber (4) of the blood treatment device (2), wherein the closed fluid line (10) together with the fluid chamber (4) forms a recirculation loop. An evacuation line (15) departs from the closed fluid line (10). A warming device (13) and a recirculation pump (17) are coupled or configured to be coupled to the closed fluid line (10). At least one temperature sensor (22) is operative on the extracorporeal blood circuit and it is configured to sense a blood temperature (Tb). A control unit (25), connected to the warming device (13), to the recirculation pump (17) and to the temperature sensor (22), is configured to execute the following procedure: receiving from the temperature sensor (22) at least a signal correlated to the blood temperature (Tb); adjusting the blood temperature (Tb) by controlling at least one of the warming device (13) and the recirculation pump (17).

Claims

1. An extracorporeal blood treatment apparatus, comprising: a blood treatment device comprising a blood chamber and a fluid chamber separated by a semipermeable membrane; an extracorporeal blood circuit comprising a blood withdrawal line connected to an inlet port of the blood chamber and a blood return line connected to an outlet port of the blood chamber; a blood pump operable with the blood withdrawal line; a closed fluid line connected to an inlet port of the fluid chamber and to an outlet port of the fluid chamber, wherein the closed fluid line together with the fluid chamber form a recirculation loop; an evacuation line departing from the closed fluid line; a warming device coupled to the closed fluid line; a recirculation pump operable with the closed fluid line; at least one temperature sensor operable with the extracorporeal blood circuit to sense a blood temperature; and a control unit operably connected to the warming device, to the recirculation pump and to the at least one temperature sensor, the control unit configured to: (i) receive from the temperature sensor a signal correlated to the blood temperature, and (ii) adjust said blood temperature by controlling the fluid warming device to regulate a fluid temperature in the recirculation loop.

2. The apparatus of claim 1, wherein adjusting the blood temperature comprises: bringing and maintaining the blood temperature to a preset blood temperature.

3. The apparatus of claim 1, wherein adjusting the blood temperature comprises further controlling the recirculation pump and regulating a fluid flow rate in the recirculation loop by controlling the recirculation pump.

4. The apparatus of claim 1, wherein the temperature sensor is placed adjacent to the outlet port of the blood chamber to sense a blood outlet temperature.

5. The apparatus of claim 1, wherein adjusting the blood temperature includes regulating a power of the fluid warming device.

6. The apparatus of claim 3, wherein the recirculation pump is controlled to set the fluid flow rate in the recirculation loop to a preset fluid flow rate.

7. The apparatus of claim 1, wherein the warming device is controlled to set the fluid temperature in the recirculation loop to a preset fluid temperature, and wherein adjusting the blood temperature further includes regulating a recirculation pump flow rate.

8. The apparatus of claim 1, wherein adjusting the blood temperature comprises: setting the fluid flow rate in a recirculation pump section of the recirculation loop to zero; and regulating the fluid temperature, wherein if said fluid temperature is at a maximum and the preset blood temperature is not reached, maintaining the fluid temperature at the maximum and increasing the fluid flow rate in the recirculation loop until the preset blood temperature is reached.

9. The apparatus of claim 1, wherein the warming device is located downstream of the recirculation pump along the closed fluid line.

10. The apparatus of claim 1, comprising a dialysis line connected to the closed fluid line for supplying a fresh treatment fluid to the inlet port of the fluid chamber, wherein the dialysis line is connected between the recirculation pump and the warming device.

11. The apparatus of claim 1, comprising at least one of: (i) a pre-infusion line connected to the blood withdrawal line, (ii) a post-infusion line connected to the blood return line, (iii) a pre-pump infusion line connected to the blood withdrawal line upstream of the blood pump, and wherein the post-infusion line is connected between the outlet port of the blood chamber and the blood temperature sensor.

12. The apparatus of claim 11, wherein the at least one of (i) the post-infusion line, (ii) the pre-infusion line, and (iii) the pre-pump infusion line passes through the fluid warming device to heat the infusion fluid before reaching the blood circuit.

13. The apparatus of claim 11, further comprising a heat exchanger located along the closed fluid line, and wherein the at least one of (i) the post-infusion line, (ii) the pre-infusion line, and (iii) the pre-pump infusion line passes through said heat exchanger to exchange heat with the fluid in the closed fluid line before reaching the blood circuit.

14. The apparatus of claim 13, wherein the heat exchanger is located downstream of the fluid warming device.

15. The apparatus of claim 1, comprising an air trap operable with the closed fluid line and located between the fluid warming device and the inlet port of the fluid chamber.

16. The apparatus of claim 1, comprising an air trap operable with the closed fluid line and located between the recirculation pump and the outlet port of the fluid chamber, wherein the evacuation line departs from said air trap.

17. The apparatus of claim 1, wherein the control unit is further configured to ultrafilter blood by causing (i) plasma water to be removed from blood in the extracorporeal blood circuit through the blood treatment device and (ii) excess fluid to be discharged through the evacuation line.

18. The apparatus of claim 1, wherein the control unit is further configured to ultrafilter blood by causing (i) plasma water to be removed from blood in the extracorporeal blood circuit through the blood treatment device, (ii) excess fluid to be discharged through the evacuation line, and (iii) fluid to be re-circulated contemporaneously in the recirculation loop.

19. An extracorporeal blood treatment apparatus, comprising: a blood treatment device comprising a blood chamber and a fluid chamber separated by a semipermeable membrane; an extracorporeal blood circuit comprising a blood withdrawal line connected to an inlet port of the blood chamber and a blood return line connected to an outlet port of the blood chamber; a blood pump operable with the blood withdrawal line; a closed fluid line connected to an inlet port of the fluid chamber and to an outlet port of the fluid chamber, wherein the closed fluid line together with the fluid chamber form a recirculation loop; an evacuation line departing from the closed fluid line; a warming device coupled to the closed fluid line; a recirculation pump operable with the closed fluid line; at least one temperature sensor operable with the extracorporeal blood circuit to sense a blood temperature; and a control unit operably connected to the warming device, to the recirculation pump and to the at least one temperature sensor, the control unit configured to: (i) receive from the temperature sensor a signal correlated to the blood temperature, (ii) adjust said blood temperature by controlling the fluid warming device to regulate a fluid temperature in the recirculation loop, (iii) ultrafilter blood by causing plasma water to be removed from blood in the extracorporeal blood circuit through the blood treatment device, and (iv) cause excess fluid to be discharged through the evacuation line.

20. An extracorporeal blood treatment apparatus, comprising: a blood treatment device comprising a blood chamber and a fluid chamber separated by a semipermeable membrane; an extracorporeal blood circuit comprising a blood withdrawal line connected to an inlet port of the blood chamber and a blood return line connected to an outlet port of the blood chamber; a blood pump operable with the blood withdrawal line; a closed fluid line connected to an inlet port of the fluid chamber and to an outlet port of the fluid chamber, wherein the closed fluid line together with the fluid chamber form a recirculation loop; a warming device coupled to the closed fluid line; a recirculation pump operable with the closed fluid line; an evacuation line connected to the closed fluid line for removing spent treatment fluid departing from the closed fluid line, wherein the evacuation line is interposed between the outlet port of the fluid chamber and the recirculation pump; a dialysis line connected to the closed fluid line for supplying a fresh treatment fluid to the inlet port of the fluid chamber, wherein the dialysis line is interposed between the recirculation pump and the inlet port of the fluid chamber; at least one temperature sensor operable with the extracorporeal blood circuit to sense a blood temperature; wherein the recirculation pump is operable with the closed fluid line at a first circuit portion located between the evacuation line and the dialysis line, and wherein the fluid chamber is connected to the closed fluid line between the dialysis line and the evacuation line at a second circuit portion opposed to the first circuit portion; and a control unit operably connected to the warming device, to the recirculation pump and to said at least one temperature sensor, the control unit configured to: (i) receive from the temperature sensor a signal correlated to the blood temperature; (ii) adjust said blood temperature by controlling the fluid warming device to regulate a fluid temperature in the recirculation loop; (iii) ultrafilter blood by causing plasma water to be removed from blood in the extracorporeal blood circuit through the blood treatment device; and (iv) cause excess fluid to be discharged through the evacuation line.

Description

DESCRIPTION OF THE DRAWINGS

[0098] The following drawings relating to aspects of the invention are provided by way of non-limiting example:

[0099] FIG. 1 shows a schematic representation of an extracorporeal blood treatment apparatus provided with a recirculation loop according to the invention;

[0100] FIG. 2 shows a portion of a variant of the extracorporeal blood treatment apparatus of FIG. 1;

[0101] FIG. 3 shows the portion of FIG. 2 according to another variant;

[0102] FIG. 4 shows the portion of FIG. 2 according to another variant;

[0103] FIG. 5 shows a flow chart of a procedure for blood warming control;

[0104] FIG. 6 shows a flow chart of another procedure for blood warming control;

[0105] FIG. 7 shows a flow chart of another procedure for blood warming control.

DETAILED DESCRIPTION

[0106] With reference to the appended drawings, FIG. 1 shows a schematic representation of an extracorporeal blood treatment apparatus 1.

[0107] The apparatus 1 comprises one blood treatment device 2, for example a hemofilter, a hemodiafilter, a plasmafilter, a dialysis filter or other unit suitable for processing the blood taken from a patient P.

[0108] 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.

[0109] 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.

[0110] 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. When rotated, e.g., clockwise, the blood pump 8 causes a flow of blood along the blood withdrawal line 6 towards the blood chamber 3 (see the arrows in FIG. 1 indicative of the blood flow along the blood withdrawal line 6).

[0111] 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.

[0112] The apparatus 1 may further comprise an air trapping device 9 operating on the blood return line 7 (the air trapping device 9 is a venous deaeration chamber). The air trapping device 9 is placed online in the blood return line 7.

[0113] 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.

[0114] The apparatus 1 further comprises a closed fluid line 10 connected to an inlet port 4a of the fluid chamber 4 and to an outlet port 4b of said fluid chamber 4. In other words, the closed fluid line 10 comprises a first section 11 connected to the outlet port 4b and departing from the fluid chamber 4 and a second section 12 connected to the inlet port 4a and joined to said fluid chamber 4. The second section 11 develops uninterrupted from the first section 11 and, in the attached non limiting figures, the closed fluid line 10 is “U” shaped. The closed fluid line 10 together with the fluid chamber 4 forms a recirculation loop for at least part of the fluid flowing through the fluid chamber 4.

[0115] A fluid warming device 13 is coupled to the closed fluid line 10. The fluid warming device 13 is schematically represented in the annexed figures. The fluid warming device 13 is associated with the apparatus 1 to form an assembly which is structured to treat fluid and keep fluid within predetermined desired temperature boundaries. The fluid warming device 13 may comprise a warmer provided with a heating unit which cooperates with a heated section 14 of the closed fluid line 10. This heated section 14 may be a tube or a bag or a cassette part of the closed fluid line 10 or part of the warmer itself. The fluid warming device 13 may be an independent device (e.g. a stand alone unit physically separated from the apparatus 1) cooperating with the apparatus 1 and—in particular—warming the heated section 14 of the closed fluid line 10. Alternatively, the fluid warming device 13 may be a component of the apparatus 1. In this case the fluid warming device 13 is not an independent stand alone unit, but rather part of the apparatus 1. In practice the heating unit has heating elements (e.g. electric impedances, infrared emitters or other types of heating elements) configured to heat the corresponding heated section 14 of the closed fluid line 10.

[0116] The apparatus 1 of FIG. 1 further comprises one fluid evacuation line 15 connected with an outlet port 4b of the fluid chamber 4 through the first section 11 of the closed fluid line 10 such as to receive at least part of a filtered waste fluid through the semipermeable membrane 5. The fluid evacuation line 15 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 15 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 evacuation line 15.

[0117] In the example of FIG. 1, a dialysis line 16 is also present, for supplying a fresh treatment fluid into the closed fluid line 10 and then into the inlet port 4a of the fluid chamber 4. The presence of this dialysis line 16 is not strictly necessary since, in the absence of the dialysis line 16, the apparatus 1 is still able to perform treatments such as ultrafiltration, hemofiltration or plasma-filtration. In case the dialysis line 16 is present, a fluid flow intercept device may be used, not shown, to selectively allow or inhibit fluid passage through the dialysis line 16, depending on whether or not a purification by diffusive effect is to be performed inside the treatment device 2.

[0118] The dialysis line 16, if present, is typically equipped with a dialysis pump, not shown, and is able to receive a fresh fluid from a module, 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. The fluid evacuation line 10, the dialysis line 16, the closed fluid line 10 and the fluid chamber 4 are part of a treatment fluid circuit.

[0119] A recirculation pump 17 is coupled to the closed fluid line 10 and operates to cause movement of the fluid in said closed fluid line 10 from the outlet port 4b of the fluid chamber 4 through the first section 11 and through the second section 12 of the closed fluid line 10 to the inlet port 4a of the fluid chamber 4 and, inside said fluid chamber 4, from the inlet port 4a towards the outlet port 4b. The recirculation pump 17 is, for example, a peristaltic pump which acts on a respective pump section of the closed fluid line 10. When rotated, e.g., clockwise, the recirculation pump 17 causes a flow of fluid counterclockwise in recirculation loop (see arrows in FIG. 1). The recirculation loop on the fluid circuit allows to constantly maintain a significant fluid flow rate in the fluid chamber 4 of the blood treatment device 2.

[0120] The fluid evacuation line 15 is connected to the closed fluid line 10 between the outlet port 4b and said recirculation pump 17. The fluid warming device 13 is placed between the recirculation pump 17 and the inlet port 4a. The dialysis line 16 is connected to the closed fluid line 10 between the fluid warming device 13 and the recirculation pump 17.

[0121] Downstream of the fluid warming device 13 (with respect to the counterclockwise flow of fluid in the recirculation loop), between the warming device 13 and the inlet port 4a, an air trap 18 is placed on the closed fluid line 10 to manage air generated by degassing due to fluid warming.

[0122] The apparatus 1 as shown 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 19 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 20 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 21 is connected to the blood return line 7 upstream of the air trapping device 9. Infusion pump or pumps, not shown, equips the infusion circuit. Each of the pre- and/or post-infusion lines 19, 20, 21 may be provided with a respective pump. The pre- and/or post-infusion lines 19, 20, 21 may be supplied by fluid coming from bags or directly by infusion fluid prepared on-line.

[0123] The apparatus 1 comprises a blood temperature sensor 22 operative on the extracorporeal blood circuit and configured to sense a blood temperature. The blood temperature sensor 22 is placed on the blood return line 7. The blood temperature sensor 22 is placed so close to the outlet port 3b of the blood chamber 3 to sense the temperature of the blood coming out of the blood chamber 3. The blood temperature sensor 22 is placed downstream of the post-infusion line 21, between said post-infusion line 21 and the air trapping device 9. The post-infusion line 21 is connected between the outlet port 3b of the blood chamber 3 and the blood temperature sensor 22.

[0124] The apparatus 1 comprises an auxiliary blood temperature sensor 23 operative on the withdrawal line 6 close to the patient P to sense the temperature of the blood withdrawn from the patient P. The pre-infusion line 19 is connected downstream of the auxiliary blood temperature sensor 23.

[0125] The apparatus 1 comprises a fluid temperature sensor 24 operative on the closed fluid line 10 and configured to sense a fluid temperature in the closed fluid line 10. The fluid temperature sensor 24 of FIG. 1 is placed so close to an outlet of the fluid warming device 13 to sense the temperature of the fluid coming out of said fluid warming device 13. According to an embodiment not shown, said fluid temperature sensor 24 may also be part of the fluid warming device 13, embedded in a frame or casing of the fluid warming device 13. The apparatus 1 comprises a control unit 25 which may comprise a digital processor (CPU) and memory (or memories), an analog circuit, or a combination thereof. The control unit 25 is connected to the blood pump 8 and may be configured to control the blood pump 8 based, by way of example, on a set blood flow rate. The control unit 25 of the apparatus 1 may also be configured to control the flow rate of dialysis fluid through the dialysis line 16, of evacuation fluid through the evacuation line 15, of infusion fluid/s through pre-infusion line 19, the pre-pump infusion line 20 and post-infusion line 21.

[0126] The control unit 25 is also connected to the recirculation pump 17 and to the fluid warming device 13 and it is configured to control said recirculation pump 17 and said fluid warming device 13 in order to adjust the temperature of blood in the blood circuit.

[0127] To this aim, the control unit 25 is also connected to the blood temperature sensor 22, to the auxiliary blood temperature sensor 23 and to the fluid temperature sensor 24. In use and according to the procedure and method of the invention, warming of blood is performed through warming of fluid in the recirculation loop.

[0128] A preset/target blood temperature Tbp at the outlet 3a of the blood chamber 3 is entered into the control unit 25 or previously saved in the memory of the control unit 25. Said preset blood temperature Tbp may be the body temperature or close to the body temperature. Said preset blood temperature Tbp may of about 37° C. In order to take into account the heat losses downstream of the blood temperature sensor 22, said preset blood temperature Tbp may be higher than the body temperature, for example of about 38° C.

[0129] Fluid flow rate Qr in the recirculation loop as well as fluid temperature Tf at the outlet of the warming device are modulated to reach and keep the preset/target blood temperature Tbp at the outlet 3a of the blood chamber 3. During treatment, the control unit 25 continuously receives from the blood temperature sensor 22 a signal correlated to the blood temperature Tb at the outlet 3b of the blood chamber 3. The control unit 25 controls at least one of the fluid warming device 13 and the recirculation pump 17 to bring and keep the measured blood temperature Tb equal to or close to the preset blood temperature Tbp.

Example 1

[0130] According to one example of the procedure performed by the apparatus of FIG. 1, the fluid flow rate Qr in the recirculation loop 10 is fixed to a preset fluid flow rate Qrp, by maintaining a fixed rotational speed of the recirculation pump 17, and the fluid temperature Tf at the outlet of the warming device 13 is regulated in order to bring and keep the measured blood temperature Tb at the outlet 3a of the blood chamber 3 equal to or at least close to the preset blood temperature Tbp (flow chart of FIG. 5). The control unit 25 may regulate a power of the fluid warming device 13 to bring and keep the measured blood temperature Tb equal to or at least close to the preset blood temperature Tbp.

[0131] The control unit 25 receives from the fluid temperature sensor 24 a signal correlated to the fluid temperature Tf at the outlet of the warming device 13.

[0132] A maximum fluid temperature Tfmax at the outlet of the warming device 13 is set (by way of example to 42° C.) The control unit 25 controls the power of the fluid warming device 13 so that the fluid temperature Tf does not exceed said maximum fluid temperature Tfmax.

[0133] The following table 1 shows the outcome in the case of the recirculation loop of FIG. 1 is operated at a fixed fluid flow rate Qr and the fluid temperature Tf at the outlet of the warming device 13 is adjusted as to deliver the desired/preset outlet blood temperature Tbp. The 66 ml/min fixed fluid flow rate Qr is chosen as the minimum flow allowing to deliver the preset 38° C. outlet blood temperature Tbp in the worst case of the selected conditions (Qb=200 ml/min, Qd=0). Qb (ml/min) is the blood flow rate in the blood circuit. Qd (ml/min) is the flow rate of dialysate in the dialysis line 16.

[0134] For the sake of simplicity, the following additional assumptions are used: [0135] temperature of the blood flowing into the blood chamber (Tbi) is taken as 36° C., [0136] blood treatment device (Hemodialyzer) surface area (S) is taken as 1.5 m.sup.2, [0137] preset blood temperature (Tbp) is taken as 38° C., as to anticipate cooling effects present in the return line 7, [0138] maximum fluid temperature (Tfmax) is set to 42° C., in accordance with IEC 60601-2-16 standard default recommendations.

TABLE-US-00001 TABLE 1 Qr = 66 ml/min Qb (ml/min) 100 200 Qd (ml/min) 0 25 50 75 0 25 50 75 Tf ° C. 39.0 39.5 38.2 38.1 42.0 40.4 39.5 39.0 Tb ° C. 38.0 38.0 38.0 38.0 38.0 38.0 38.0 38.0

Example 2

[0139] According to another example of the procedure performed by the apparatus of FIG. 1, a fluid temperature Tf at the outlet of the warming device 13 is fixed to a preset fluid temperature Tfp, which may be the maximum fluid temperature Tfmax, by controlling the power of the warming device 13.

[0140] The fluid flow rate Qr in the recirculation loop is regulated in order to bring and keep the measured blood temperature Tb at the outlet 3b of the blood chamber 3 equal to or at least close to the preset blood temperature Tbp (flow chart of FIG. 6). The control unit 25 may regulate the rotational speed of the recirculation pump 17 to bring and keep the measured blood temperature Tb equal to or at least close to the preset blood temperature Tbp.

[0141] Table 2 shows that the fluid flow rate Qr is minimized by having the warming device 13 operating at its maximum set point when non-zero fluid flow rate Qr is used to get the desired preset blood temperature Tbp. In these conditions, much lower fluid flow rates Qr than the 66 ml/min of table 1 may be used as soon as dialysate flow is not zero.

TABLE-US-00002 TABLE 2 Qb (ml/min) 100 200 Qd (ml/min) 0 25 50 75 0 25 50 75 Qr (ml/min) 33 8.5 0 0 66 42 17 0 Tfmax ° C. 42.0 42.0 40.0 38.7 42.0 42.0 42.0 41.3 Tb ° C. 38.0 38.0 38.0 38.0 38.0 38.0 38.0 38.0

Example 3

[0142] According to another example of the procedure performed by the apparatus of FIG. 1, the control unit 25 may operate as follows (flow chart of FIG. 7): [0143] starting patient blood treatment with no recirculation (setting the fluid flow rate Qr in the recirculation loop 10 to zero, recirculation pump 17 stopped) and adjusting the fluid temperature Tf at the outlet of the warming device 13 according to the desired/preset blood temperature Tbp; [0144] if the preset blood temperature Tbp is reached with the fluid temperature Tf lower than or equal to the maximum Tfmax, the recirculation pump 17 is not activated; [0145] if the preset blood temperature Tbp cannot be reached with the fluid temperature Tf at the maximum Tfmax and with no recirculation, keeping the fluid temperature Tf at the maximum Tfmax and increasing step by step the fluid flow rate Qr in the recirculation loop 10 (the recirculation pump 17 is activated) till the preset blood temperature Tbp is reached.

[0146] This procedure allows to minimize performance loss in term of dialyzer clearance (with no measurable performance loss for small solutes like urea and about 10% losses for large solutes like inulin) with respect to a conventional apparatus with no recirculation loop. For sake of clarity, the system dialyzer clearance is defined as the volume of plasma or blood from which a given substance has been removed completely in a given time period. The dialyzer clearance of a substance depends on four factors: 1. Surface area of the dialyzer. 2. Blood flow rate. 3. Dialysate flow rate. 4. Permeability of that substance with respect to the dialyzer membrane.

[0147] The extracorporeal blood treatment apparatus of FIG. 1 may also be configured to perform a degassing procedure of the membrane 5 (filter) of the blood treatment device 2 to allow for periodical removal of air bubbles generated or trapped inside said membrane 5.

[0148] During the degassing procedure, the control unit 25 controls the recirculation pump 17 to reverse the fluid flow in the recirculation loop. Instead of being moved, in the closed fluid line 10, from the outlet port 4b to the inlet port 4a of the fluid chamber 4, the fluid is moved from the inlet port 4a towards the outlet port 4b with a maximum fluid flow rate of about 300 ml/min and for a time period of about 1 min. In this way, air bubbles from the membrane 5 are moved into the air trap 18 and then air accumulated in the air trap 18 may be removed through a service line, not shown. The removal through the service line may be fully automatic, if the air trap 18 is equipped with a level sensor and the service line is connected to a pump, or manually under the supervision of the operator. Alternatively, air trapped in the air trap 18 may be vented ‘passively’ through a hydrophobic membrane, provided that the absolute pressure is kept positive in the recirculation loop. This may require the addition of a pressure drop in the recirculation loop.

[0149] The extracorporeal blood treatment apparatus of FIG. 2 differs from the apparatus of FIG. 1 in that the post-infusion line 21 is operatively coupled to the warming device 13, so that said infusion fluid is heated before reaching the return line 7 of the blood circuit. FIG. 2 shows that the post-infusion line 21 passes through the fluid warming device 13 and then is connected to the blood circuit. Please note that in other not shown embodiments also the pre-infusion line 19 and the pre-pump infusion line 20 may be heated by the fluid warming device 13. The fluid warming device 13 comprises a first portion operative on the closed fluid line 10 and at least a second portion operative on said at least one among the post-infusion line 21, the pre-infusion line 19 and the pre-pump infusion line 20. Each portion of the warming device 13 may comprise a respective heating unit which cooperates with a heated section 26 of the respective infusion line 19, 20, 21. Each heating unit may be controlled separately by the control unit 25 in order to heat in different manner the closed fluid line 10 and each of the infusion line 19, 20, 21. This configuration allows for both cheaper and easier operation of the system. The combined warming device 13 may combine both hardware components (display, user interface commands, power supply, etc.) in one single device, as well as the disposable circuit components in one single article.

[0150] The extracorporeal blood treatment apparatus of FIG. 3 differs from the apparatus of FIG. 1 in that a heat exchanger 27 is placed on the closed fluid line 10 between the fluid warming device 13 and the inlet port 4b of the fluid chamber 4. A heating section 28 of the closed fluid line 10 passes through the heat exchanger 27. A heated section 26 of the post-infusion line 21 passes through the heat exchanger 27 and then it is connected to the blood circuit. In said heat exchanger 27 the flow of fluid in the heating section 28 of the closed fluid line 10 and the flow of infusion fluid in the heated section 26 of the post-infusion line 21 flows in opposite directions (the heat exchanger is of counter-current type). The fluid in the heating section 28 of the closed fluid line 10 has just been heated in the warming device 13 and supplies heat to the infusion fluid in the heated section 26. Please note that in other not shown embodiments also the pre-infusion line 19 and the pre-pump infusion line 20 may be heated in the heat exchanger 27.

[0151] In both the embodiments of FIG. 1 and FIG. 2, the infusion fluid/s are heated exploiting the same warming device 13 which heats the recirculation loop.

[0152] The extracorporeal blood treatment apparatus of FIG. 4 differs from the apparatus of FIG. 1 in that the air trap 18′ is placed between the recirculation pump 17 and the outlet 4b of the fluid chamber 4 instead of between the warming device 13 and the inlet 4a of the fluid chamber 4. Furthermore, the evacuation line 15 departs from said air trap 18′. The air trap 18′ is located at the outlet port 4b of the fluid chamber 4 and the evacuation line 15 is used as to remove air bubbles simultaneously to the ‘waste’ fluid. In this configuration, the degassing procedure simply consists in running maximum recirculation flow rate (300 ml/min) for a short time period (typically less than 1 min).

[0153] In other not shown embodiments, dialysis line 16 may be connected to the recirculation loop between the evacuation line 15 and the recirculation pump 17. In this case, a fluid flow rate in the recirculation loop is equal to or greater than a dialysate flow rate in the dialysis line 16.

[0154] In other not shown embodiments, the dialysis line 16 is connected downstream of the warming device 13.

[0155] In other not shown embodiments, the dialysis line 16 is not present. With respect to FIG. 1 the dialysis line 16 simply disappears.

[0156] 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.