Apparatus for extracorporeal treatment of blood and method of priming an extracorporeal blood circuit

Abstract

An extracorporeal blood treatment apparatus comprises: a blood treatment device (2); an extracorporeal blood circuit comprising a blood withdrawal line (6) and a blood return line (7) coupled to the extracorporeal blood treatment device (2), wherein the blood return line (7) presents a heating zone (14) coupled or configured to be coupled to a blood warmer (15); a blood pump (6) configured to be coupled to a pump section of the blood withdrawal line (6); at least a post-infusion line (13, 13′) connected to the blood return line (7) upstream of the heating zone (14); an air trapping device (9) placed on the blood return line (7) upstream of the heating zone (14).

Claims

1. A method for priming an extracorporeal blood circuit of an extracorporeal blood treatment apparatus, before starting patient treatment, the extracorporeal blood treatment apparatus including: (a) a blood treatment device; and (b) a blood warmer, and the extracorporeal blood circuit including: (i) a blood withdrawal line and a blood return line coupled to the blood treatment device, wherein the blood return line includes a heating zone coupled to the blood warmer; (ii) a blood pump configured to be coupled to a pump section either of the blood withdrawal line or of the blood return line; (iii) at least a post-infusion line connected to the blood return line upstream of the heating zone; and (iv) an air trapping device located along the blood return line upstream of the heating zone, the method comprising: filling the extracorporeal blood circuit of the extracorporeal blood treatment apparatus with a priming fluid, wherein the priming fluid flows at least through the extracorporeal blood treatment device and through at least the blood return line towards the heating zone of said blood return line; diverting, during an initial time interval, the priming fluid into a secondary post-infusion line to bypass a blood warmer operatively active on said heating zone, wherein the secondary post-infusion line is in fluid communication with the blood return line upstream of the heating zone and is in fluid communication with the blood return line downstream of the heating zone; and directing, after said initial time interval, the priming fluid to flow through an air trapping device placed on the blood return line upstream of the heating zone and then through said heating zone towards a terminal end of the blood return line.

2. The method of claim 1, wherein the extracorporeal blood treatment apparatus includes the secondary post-infusion line in fluid communication with the blood return line upstream of the heating zone and in fluid communication with said blood return line downstream of the heating zone, to bypass the blood warmer.

3. The method of claim 1, wherein during the initial time interval, the priming fluid flows through the post-infusion line connected to the blood return line upstream of the heating zone.

4. The method of claim 1, wherein after the initial time interval, the priming fluid flows through the post-infusion line in fluid communication with the blood return line upstream of the heating zone.

5. The method of claim 1, wherein during the initial time interval, the priming fluid flows through the air trapping device.

6. The method of claim 1, wherein during the initial time interval, the priming fluid flows from the blood return line placed upstream of the heating zone, through the air trapping device and into the secondary post-infusion line.

7. The method of claim 1, wherein after the initial time interval, the priming fluid flows from the post-infusion line in fluid communication with the blood return line upstream of the heating zone, through the air trapping device and into the blood return line downstream of the air trapping device.

8. The method of claim 1, wherein during the initial time interval, a warmer clamp placed on the blood return line between the air trapping device and the heating zone is closed, thus allowing the priming fluid flowing from the post-infusion line, and the priming fluid flowing from the blood return line and through the air trapping device, to flow through the secondary post-infusion line.

9. The method of claim 1, wherein after said initial time interval, the priming fluid, flowing through the post-infusion line in fluid communication with the blood return line upstream of the heating zone, is split into the air trapping device and into the secondary post-infusion line.

10. The method of claim 1, wherein after the initial time interval, the warmer clamp is opened, thus allowing the priming fluid flowing from the post-infusion line to flow through at least one of the secondary post-infusion line and the air trapping device, and allowing the priming fluid flowing from the blood treatment device to flow through the air trapping device and through the heating zone.

11. The method of claim 1, wherein after the initial time interval, the warmer clamp is opened, thus allowing the priming fluid flowing from the post-infusion line to flow through at least one of the secondary post-infusion line and the air trapping device, and allowing the priming fluid flowing from the blood treatment device to flow through the air trapping device and through the heating zone.

12. The method of claim 1, wherein during the initial time interval a post-infusion clamp, placed on the post-infusion line downstream of a branching off point of the secondary post-infusion line, is open so that the air trapping device is in fluid communication with the secondary post-infusion line.

Description

DESCRIPTION OF THE DRAWINGS

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

(2) FIG. 1 shows a schematic representation of an extracorporeal blood treatment apparatus provided with an air trapping device and of a blood warmer according to the invention;

(3) FIG. 2 shows another embodiment of the apparatus of FIG. 1;

(4) FIG. 3 shows a portion of the apparatus of FIG. 1 in a first operative configuration;

(5) FIG. 4 shows the portion of FIG. 3 in a second operative configuration;

(6) FIG. 5 shows a variant of the portion of FIG. 3 and FIG. 4;

(7) FIG. 6 shows another variant of the portion of FIG. 3 and FIG. 4;

(8) FIG. 7 shows another variant of the portion of FIG. 3 and FIG. 4;

(9) FIG. 8 shows another variant of the portion of FIG. 3 and FIG. 4;

(10) FIG. 9 shows another variant of the portion of FIG. 3 and FIG. 4;

(11) FIG. 10 shows another embodiment of the portion of FIG. 3 and FIG. 4;

(12) FIG. 11 is a flow chart of a priming procedure of the apparatus of FIG. 3 according to a method of the invention.

DETAILED DESCRIPTION

(13) With reference to the appended drawings, FIG. 1 shows a schematic representation of an extracorporeal blood treatment apparatus 1.

(14) The apparatus 1 comprises one blood treatment device 2, for example a hemofilter, a hemodiafilter, a plasmafilter, a dialysis filter, a membrane oxygenator, an adsorption device or other unit suitable for processing the blood taken from a patient P. 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.

(15) 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.

(16) 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 6a 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).

(17) 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.

(18) The apparatus 1 further comprises 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.

(19) 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 trap 9 and a second section of the blood return line 7 puts in fluid communication the air trap 9 with the patient P.

(20) The blood coming from the blood chamber 3 of the treatment device 2 enters and exits the air trap 9 before reaching the patient P.

(21) The apparatus 1 further comprises one fluid evacuation line 11 connected with an outlet port 4b of the fluid chamber 4 such as to receive at least a filtered fluid through the semipermeable membrane 5. The evacuation line 11 receives the 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 evacuation line 11 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 11.

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

(23) The dialysis line 10, 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 11, the dialysis line 10, and the fluid chamber 4 are part of a treatment fluid circuit.

(24) Finally, the apparatus 1 as shown comprises an infusion circuit comprising one or more infusion lines 12, 13 of a replacement fluid: for example a pre-infusion line 12 may be connected to the blood withdrawal line 6 and/or a post-infusion line 13 may be connected to the blood return line 7. Infusion pump or pumps, not shown, equips typically the infusion circuit. The pre- and/or post-infusion lines 12, 13 may be supplied by fluid coming from bags or directly by infusion fluid prepared on-line.

(25) The post-infusion line 13 is connected to the blood return line 7 through the air trapping device 9 to supply fluid to the blood at said air trapping device 9. According to a different embodiment, not shown, the post-infusion line 13 is connected to the blood return line 7 upstream the air trapping device 9.

(26) Downstream of the air trapping device 9, the blood return line 7 presents a heating zone 14 coupled or configured to be coupled to a blood warmer 15. It follows that the post-infusion line 13 is connected to the blood return line 7 upstream of the heating zone 14 and that the air trapping device 9 is placed on the blood return line 7 upstream of the heating zone 14.

(27) The blood warmer 15 is associated with the apparatus 1 to form an assembly which is structured to treat blood and keep blood within predetermined desired temperature boundaries. The blood warmer 15 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 heating zone 14. Alternatively, the blood warmer 15 may be a component of the apparatus 1. In this case the blood warmer 15 is not an independent stand alone unit, but rather part of the apparatus 1.

(28) In both cases, the blood warmer 15 has a heating unit, not shown, configured for receiving and heating the heating zone of the blood return line 7. For instance, the heating zone 14 of the blood return line 7 may be in the form of a substantially flat bag insertable in a heating seat provided in the heating unit of the blood warmer. The flat bag presents an inlet and an outlet connected to the extracorporeal blood circuit. Alternatively, the heating zone 14 may include a section of the tubing or a rigid cassette inserted into the heating unit of the blood warmer 15, which heating unit for instance may comprise a heating sleeve or a heating coil wound around the heating zone 14. 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 heating zone 14 of the blood return line 7.

(29) In the embodiment shown in FIG. 1, an air bubble detector 16 is placed downstream of the heating zone 14, between a terminal end with access device of the blood return line 7, connected to the patient P, and said heating zone 14.

(30) In order to make possible troubleshooting of air bubble detector 16 alarms, the blood return line 7 may also include a puncture site, not shown, upstream the air bubble detector 16 and clamp for the air removal procedure.

(31) A return pressure sensor 17 is placed on the blood return line 7, between the heating zone 14 and the air bubble detector 16, to monitor pressure downstream of the blood warmer 15. Pressure upstream the blood warmer 15 may be monitored in the air trapping device 9 through a pressure monitor 17′ which is operatively active in said air trapping device 9, by way of example through an air filled service line required for a level adjustment in the air trapping device 9.

(32) The apparatus shown in FIG. 1 further comprises a withdrawal clamp 18 placed close to a terminal end of the blood withdrawal line 6 and a return clamp 19 placed close to the terminal end of the blood return line 7.

(33) The air bubble detector 16 is connected to a control unit 100 of the apparatus 1 and sends to the control unit 100 signals for the control unit 100 to cause closure of the return clamp 19 in case one or more bubbles above predetermined safety thresholds are detected.

(34) The control unit 100, during treatment, may be configured to control the blood pump 8 based, by way of example, on a set blood flow rate. The control unit 100 of the apparatus 1 may also be configured to control the flow rate of dialysis fluid through the dialysis line 10, of evacuation fluid through the evacuation line 11, of infusion fluid/s through pre-infusion line 12 and post-infusion line 13.

(35) The control unit 100 of the apparatus 1 may also be configured to control the blood warmer 15, during treatment, to keep blood within said desired temperature boundaries. The control unit 100 may comprise a digital processor (CPU) and memory (or memories), an analog circuit, or a combination thereof.

(36) In use, during patient P treatment, the blood coming from the extracorporeal blood treatment device 2 and the infusion fluid flowing in the post-infusion line 13 enter the air trapping device 9 before flowing through the heating zone 14. This allows to prevent air intake at the blood warmer 15 inlet.

(37) In addition, the air trapping device 9 may have at least a low level liquid sensor, not shown in figures, alerting the operator for adjusting the chamber level of said air trapping device 9 before air bubbles are moved to the blood warmer and to the air bubble detector 16. Alternatively, the circuit may include a second air bubble detector 16′ (dashed line in FIG. 1) located immediately downstream of the air trapping device 9. The apparatus 1 of FIG. 1 is fully robust to the presence of some air bubbles in the post-infusion fluid.

(38) With respect to the apparatus of FIG. 1, the apparatus 1 shown in FIG. 2 further comprises a secondary post-infusion line 20. Said secondary post-infusion line 20 is connected to the post-infusion line 13 at a branching off point 21 located upstream of the air trapping device 9. The post-infusion line 13 of the apparatus of FIG. 2 has a line segment 13′ comprised between the branching off point 21 and the air trapping device 9. In another embodiment, not shown, the secondary post-infusion line 20 is connected to the air trapping device 9 (the branching off point 21 is located on the air trapping device 9). Said secondary post-infusion line 20 is connected to the blood return line 7 at a connection point 22 placed downstream of the heating zone 14 and upstream of the air bubble detector 16. In this way, the secondary post-infusion line 20 by-passes the heating zone 14 and the blood warmer 15.

(39) A by-pass pump 23 is placed on the secondary post-infusion line 20. The return pressure sensor 17 is placed on the secondary post-infusion line 20 too (instead of on the blood return line 7 like in FIG. 1). A warmer clamp 24 is placed on the blood return line 7 between the air trapping device 9 and the heating zone 14. The by-pass pump 23 and the warmer clamp 24 are connected to the control unit 100, not shown in FIG. 2. The by-pass pump 23 is a control device operatively active on the secondary post-infusion line 20, for controlling a flow through said secondary post-infusion line 20.

(40) In use, during patient P treatment (FIG. 2) the warmer clamp 24 is open, the return clamp 19 is open and the heating zone 14 is placed in the blood warmer 15. The blood coming from the extracorporeal blood treatment device 2 and all or part of the infusion fluid flowing in the post-infusion line 13 enter the air trapping device 9 before flowing through the heating zone 14. This allows to prevent air intake at the blood warmer 15 inlet. Through the by-pass pump 23, it is also possible to control the post-infusion flow which is split between the air trapping device and the return circuit downstream of the blood warmer 15. The post-infusion flow rate may be in the range of 50 ml/h to 6000 ml/h. The by-pass pump 23 may operate in continuous or in periodic mode. The blood warmer 15 may slightly overheat blood as to balance for the cooling effect of the secondary post-infusion, depending on the flow rates.

(41) The presence of the secondary post-infusion line 20 during treatment may require additional means in case the post-infusion contains some air bubbles. As infusion of such air bubbles downstream the blood warmer 15 will create difficult troubleshooting situations, it may be of interest to prevent these events by: stopping temporarily flow in the secondary post-infusion line 20 when presence of air bubbles is suspected (e.g. after a bag change); adding an air detector on the post-infusion 13 upstream the post-infusion line split (an optical detection may be suitable for this purpose); having preventing means in the post-infusion 13, such as a self-venting chamber using an hydrophobic membrane, and taking advantage of the positive pressure present in the post-infusion 13 upstream the air trapping device 9.

(42) According to a method of the invention, the apparatus detailed above and shown in FIG. 2 allows to control the flow of a priming fluid through the heating zone 14, through the infusion line 13 and through the secondary post-infusion line 20 when priming of the apparatus before patient P treatment is performed.

(43) To this aim, the extracorporeal blood circuit of the extracorporeal blood treatment apparatus 1 is loaded and filled with the priming fluid so that the priming fluid flows at least through the blood withdrawal line 6, through the blood treatment device 2 and through the blood return line 7 towards the heating zone 14 of said blood return line 7. FIG. 11 shows a flow chart of one example of the priming procedure.

(44) FIG. 3 shows the configuration of the apparatus 1 of FIG. 2 during an initial time interval ΔT1 of the priming procedure. The initial time interval ΔT1 may last for about the time required to flow a priming fluid volume matching with the total blood circuit volume. Priming may be done using the prescribed solutions for the patient treatment.

(45) During said initial time interval ΔT1 the warmer clamp 24 is closed, the return clamp 19 is open. The by-pass pump 23 rotates clockwise to pump fluid from the branching off point 21 towards the connection point 22 or the by-pass pump 23 is not present and not active on the secondary post-infusion line 20 (a pump segment of the secondary post-infusion line 20 is unloaded).

(46) The priming fluid coming from the blood treatment device 2 and flowing through the section of the blood return line 7 placed upstream of the warmer clamp 24 enters the air trapping device 9 but is prevented from entering the heating zone 14.

(47) Therefore, the priming fluid coming from the blood treatment device 2, once in the air trapping device 9, is compelled to flow into the line segment 13′ of the post-infusion line 13 (comprised between the air trapping device 9 and the branching off point 21) and then into the secondary post-infusion line 20. Also the priming fluid coming from a source of priming fluid and flowing in a section of the post-infusion line 13 upstream of the branching off point 21 flows into the secondary post-infusion line 20. All the priming fluid by-passes the heating zone 14 and the blood warmer 15 and enters again the blood return line 7 at the connection point 22.

(48) Downstream of the connection point 22, the priming fluid flows towards the terminal end of the blood return line 7.

(49) FIG. 4 shows the configuration of the apparatus 1 after the initial time interval ΔT1, during the remaining priming step. During said remaining priming step, the warmer clamp 24 is open, the return clamp 19 is open, the pump segment of the secondary post-infusion line 20 is loaded onto the by-pass pump 23 and the by-pass pump 23 rotates clockwise to pump fluid from the branching off point 21 towards the connection point 22. The by-pass pump 23 is compatible with the priming by-pass phase with relatively high flow rates and air-water mixture. Such a by-pass pump 23 may be a peristaltic pump which pump segment is loaded after the by-pass phase (initial time interval ΔT1). A diaphragm pump or a finger pump may also be considered.

(50) The priming fluid coming from the blood treatment device 2 and flowing through the section of the blood return line 7 placed upstream of the warmer clamp 24 enters and exits the air trapping device 9, flows through a section of the blood return line 7 comprised between the air trapping device 9 and the heating zone 14, then through said heating zone 14 towards the connection point 22. The priming fluid coming from the source of priming fluid and flowing in a section of the post-infusion line 13 upstream of the branching off point 21 is split into the line segment 13′ (and then into the air trapping device 9) and into the secondary post-infusion line 20. Indeed, said priming fluid flows in part into the air trapping device 9 and then through the heating zone 14 and in part through the secondary post-infusion line 20 towards the connection point 22. Downstream of the connection point 22, all the priming fluid flows towards the terminal end of the blood return line 7.

(51) FIG. 5 shows a variant of the apparatus of FIG. 2, in which the by-pass pump 23 is not present and a 3-way pinch valve 25 is placed between the post-infusion line 13 and the secondary post-infusion line 20 at the branching off point 21. Said pinch valve 25 is a control device operatively active on the post-infusion line 13 and on the secondary post-infusion line 20, for controlling a flow through the line segment 13′ of said post-infusion line 13 and through said secondary post-infusion line 20.

(52) In use, during patient P treatment the warmer clamp 24 is open. The pinch valve 25 is periodically switched between a first and a second position. In the first position, the pinch valve 25 closes the secondary post-infusion line 20 and let the infusion fluid to flow into the line segment 13′ and into the air trapping device 9. In the second position, the pinch valve 25 closes the post-infusion line 13 and let the infusion fluid to flow through the secondary post-infusion line 20 and into the blood return line 7 downstream of the blood warmer 15. The pinch valve design shall be such that, when switching during patient P treatment, no direct communication is present between the air trapping device 9 and the blood return line 7 as to prevent blood flow by-pass through the secondary post-infusion line 20.

(53) When priming, during (warmer clamp 24 closed) and after (warmer clamp 24 open) the initial time interval ΔT1, the pinch valve 25 is set in a neutral position so that the air trapping device 9 is in fluid communication with the secondary post-infusion line 20.

(54) The variant of FIG. 6 differs from the apparatus of FIG. 5 in that the pinch valve 25 is substituted by a flow resistor 26 placed on the secondary post-infusion line 20 in combination with a post-infusion clamp 27 placed on the line segment 13′ of the post-infusion line 13 downstream of the branching off point 21. During treatment, this prevents blood flow in the secondary post-infusion line 20 when post-infusion is stopped. The flow resistor 26 may be designed in order to prevent blood flow by-pass in the secondary post-infusion line 20 as soon the post-infusion flow rate is large enough. The post-infusion clamp 27 on the line segment 13′ of the post-infusion line 13 is required for preventing blood flow by-pass when post-infusion is stopped.

(55) The variant of FIG. 7 differs from the apparatus of FIG. 5 in that the pinch valve 25 is substituted by a secondary post-infusion clamp 28 placed on the secondary post-infusion line 20 in combination with a non-return valve 29 placed on the line segment 13′ of the post-infusion line 13 downstream of the branching off point 21

(56) The variant of FIG. 8 differs from the variant of FIG. 7 in that the secondary post-infusion clamp 28 is substituted by a secondary flow resistor 30.

(57) The embodiment of FIG. 9 differs from the apparatus of FIG. 5 in that FIG. 9 further comprises another auxiliary air trapping device 31 and in that no warmer clamp 24 is present. Said auxiliary air trapping device 31 is placed on the blood return line 7 downstream of the heating zone 14 and of the blood warmer 15. Downstream of the heating zone 14, the secondary post-infusion line 20 is connected to the blood return line 7 at the auxiliary air trapping device 31.

(58) Moreover, the return pressure sensor 17 is not on the secondary post-infusion clamp 28 but it is operatively active in the auxiliary air trapping device 31. Optionally, fluid level is automatically monitored in the chambers of both the air trapping devices 9, 31.

(59) Other variants, not shown, of the embodiment of FIG. 9 (in which air trapping devices 9, 31 are present both upstream and downstream of the blood warmer 15) may comprise the control devices (operatively active on the post-infusion lines) shown in FIGS. 2-4 (post-infusion pump 23), 6 (post-infusion clamp 27 and flow resistor 26), 7 (non-return valve 29 and secondary post-infusion clamp 28), 8 (non-return valve 29 and secondary flow resistor 30).

(60) In other variants, not shown, of the embodiment of FIG. 9 (in which air trapping devices 9, 31 are present both upstream and downstream of the blood warmer 15) no post infusion in the auxiliary air trapping device 31 is present. In the case, like in the embodiment of FIG. 1, the blood warmer 15 has not to compensate for any post-infusion cooling effect.

(61) Furthermore, the air trapping device 9 and the auxiliary air trapping device 31 may be each other identical, as in FIG. 9, or the auxiliary air trapping device 31′ may be a filled air trap including a soft diaphragm for return pressure measurement.

(62) FIG. 10 shows the filled air trap 31′ and an auxiliary blood line 32 with an auxiliary blood pump 33 connecting the top of the filled air trap 31′ to the air trapping device 9.

(63) The auxiliary blood pump 33 may be a peristaltic pump. Pump flow rate might be settled in a wide range from a few ml/min to 100 ml/min and more. This auxiliary blood pump 33 does not need to be stopped in case of alarm and system safe state with stop of the blood pump 8 and return clamp 19 closure. The main purpose of this blood circuit loop is to flow air bubbles back to the air trapping device 9, which should provide for means to remove this air.

(64) In a variant of FIG. 10, not shown, the auxiliary blood pump 33 on the auxiliary blood line 32 is substituted by an additional clamp. This variant plays with the position of two air trapping chamber for making possible the transfer of air bubbles from the filled air trap 31′ to the air trapping device 9, when stopping the blood flow and opening the additional clamp.

(65) In another variant of FIG. 10, not shown, the auxiliary blood line 32 is not present.

(66) 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.