Abstract:
A device and method for monitoring an access to a patient, an extracorporeal blood circuit and/or a dialysing fluid system includes a centrifugal pump for conveying blood or dialysing fluid instead of an occluding pump. Centrifugal pumps bring about a large change in flow rate by even a small change in pressure difference across the pump. The device includes a measuring unit for measuring the flow rate of blood or dialysing fluid conveyed by the centrifugal pump, and a control and computing unit configured to determine an incorrect vascular access or malfunction if a change in measured flow rate Q is more than a predetermined amount. For example, a small drop in pressure in the venous blood line leads to a marked increase in the flow rate of the centrifugal pump, which is used as a basis for the detection of an incorrect vascular access.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present application is the national stage entry of International Patent Application No. PCT/EP2010/007948, filed on Dec. 27, 2010, and claims priority to Application No. DE 10 2009 060 668.8, filed in the Federal Republic of Germany on Dec. 28, 2009. 
     
    
     FIELD OF INVENTION 
       [0002]    The present invention relates to a device for monitoring an access to a patient for an extracorporeal blood treatment apparatus with an extracorporeal blood circuit. Moreover, the present invention relates to a device for monitoring an extracorporeal blood circuit of an extracorporeal blood treatment apparatus. Furthermore, the present invention relates to a method for monitoring a patient access and an extracorporeal blood circuit in an extracorporeal blood treatment. The present invention also relates to an extracorporeal blood treatment apparatus with a monitoring device. 
       BACKGROUND INFORMATION 
       [0003]    In the field of medical technology, various extracorporeal blood treatment apparatuses comprising an extracorporeal blood circuit are known. The known extracorporeal blood treatment apparatuses include for example haemodialysis apparatuses and cell separators, which necessitate an access to the patient&#39;s vascular system. In extracorporeal blood treatment, blood is removed from the patient with an arterial puncture cannula via an arterial hose line, the blood being fed back to the patient with a venous puncture cannula via a venous hose line. 
         [0004]    In order to convey the blood in the extracorporeal blood circuit, the extracorporeal blood treatment apparatuses generally comprise an occluding hose pump, in particular a roller pump. Occluding hose pumps are also generally provided in the dialysing fluid system of extracorporeal blood treatment apparatuses. From other specialist medical fields, for example in heart bypass operations, other blood pumps are known for the operation of an extracorporeal blood circuit, in particular special centrifugal pumps designed for blood, which are characterised by causing relatively little damage to the blood. 
         [0005]    Despite regular monitoring of the vascular access by hospital staff during extracorporeal blood treatment, there is in principle the risk of the venous puncture cannula slipping out of the patient&#39;s blood vessel unnoticed. Whereas slipping-out of the arterial cannula is associated with the sucking-in of air into the arterial hose line, the slipping-out of the venous cannula leads to the feared free flow of blood into the surroundings. If the slipping-out of the venous cannula is not detected immediately, therefore, there is the risk of the patient bleeding to death. 
         [0006]    Various devices of differing design are known for the monitoring of the vascular access. The known monitoring devices generally rely on the safety devices which are present as standard in blood treatment apparatuses and which, in the event of an incorrect vascular access, trigger an immediate interruption to the blood flow in the extracorporeal blood circuit. 
         [0007]    A monitoring device for a vascular access is described in International Patent Publication No. WO 99/29356 A1, wherein the strength of an electric current flowing through the fluid in the hose line is measured. U.S. Patent Publication No. 2004/0254513 describes a monitoring device, wherein the impedance between two electrodes disposed on the arterial and venous hose line is measured. A drawback is that the known devices require the creation of an electrical connection to the fluid flowing in the hose lines. 
         [0008]    Monitoring systems are also known for monitoring both the arterial and the venous vascular access, said systems being based on a measurement of the pressure in the extracorporeal blood circuit. A drop in pressure of 20 mmHG can be assumed in practice in the event of the venous puncture cannula slipping out. Since the nominal value of the measurement value resolution lies in practice in the region of 2 mmHG with a maximum total error between 15 and 20 mmHG, the detection of a venous disconnection proves to be difficult. A monitoring system with pressure monitoring is described for example in U.S. Pat. No. 6,221,040. The known pressure monitoring makes use of a special evaluation procedure. 
         [0009]    Monitoring devices which can detect the outflow of blood at the puncture point are described in International Patent Publication No. WO 2006/008866 A1 and U.S. Patent Publication No. 2005/0038325. These devices comprise a moisture sensor. 
       SUMMARY 
       [0010]    A problem underlying the present invention is to monitor, with particularly high reliability, a vascular access and/or an extracorporeal blood circuit and/or a dialysing fluid system of an extracorporeal blood treatment apparatus without substantial changes to the blood treatment apparatus and without the use of separate components. 
         [0011]    A solution to this problem takes place according to the present invention and advantageous embodiments described herein. 
         [0012]    The device according to the present invention and the method according to the present invention are based on the use of a centrifugal pump for conveying blood in the extracorporeal blood circuit or dialysing fluid in the dialysing fluid system instead of an occluding pump. The centrifugal pump, which is also known by the term rotary pump, comprises a rotating pump impeller for conveying fluids. The fluid, which enters into the centrifugal pump via the suction pipe, is conveyed by the rotating pump impeller and forced to the exterior on a circuit. The kinetic energy of the fluid thereby absorbed increases the pressure inside the pump and pushes the fluid into the pressure pipe. 
         [0013]    The present invention makes use of the special properties of the known centrifugal pumps when they are used to convey blood and/or dialysing fluid. These centrifugal pumps are characterised in that a large change in the flow rate is brought about by even a small change in the pressure difference across the pump. When mention is made below of the flow rate, this is also understood to mean any other variable correlating with the flow rate which, as it were, increases with the increase in the flow rate. 
         [0014]    The device according to the present invention comprises a measuring unit for measuring the flow rate of the blood conveyed by the centrifugal pump in the extracorporeal blood circuit and/or of the dialysing fluid in the dialysing fluid system as well as a control and computing unit, which is constituted such that, in the event of a change in the measured flow rate of more than a predetermined amount, it is concluded that there is an incorrect vascular access or a malfunction in the extracorporeal blood circuit or dialysing fluid system. If, for example, there is a small drop in pressure in the venous blood line during the extracorporeal blood treatment, this leads to a marked increase in the flow rate of the centrifugal pump. This significant and sudden increase in the flow rate, which results from the characteristic flat delivery curve of the centrifugal pump, is used according to the present invention as a basis for the detection of an incorrect venous vascular access. With the monitoring of the flow rate of the centrifugal pump, it is possible to detect not only the slipping out of one of the two puncture cannulas from the patient&#39;s vascular system, but also nipping or kinking of the blood lines or dialysing fluid lines and a leakage of the hose lines. The flow rate can in principle be measured at any point in the extracorporeal blood circuit or dialysing fluid system. 
         [0015]    It is advantageous that the device according to the present invention and the method according to the present invention do not make use of external components which require additional manipulations and unnecessarily restrict the patient&#39;s freedom of movement. 
         [0016]    In a preferred embodiment of the present invention, the control and computing unit comprises a comparison unit for comparing the measured flow rate with a preset flow rate and a signal generation unit for generating a control signal when the difference between the measured flow rate and the preset flow rate is greater than a specific threshold value. This threshold value is dependent upon various factors. For example, the threshold value is dependent on the condition of the hose lines. Different threshold values can be preset depending on the various factors. A preferred embodiment provides for the imputting of data records on an input unit, said data records being characteristic of the various factors, for example of the hose set used. These data records are compared with stored data records to which specific threshold values are assigned, in order to be able to select the threshold value which corresponds to the inputted data record. 
         [0017]    The monitoring device preferably comprises an alarm unit, which emits an acoustic and/or optical and/or tactile alarm when the control and computing unit generates the control signal. 
         [0018]    The measuring unit for measuring the flow rate preferably comprise a flow sensor for the non-invasive measurement of the blood flow rate. The flow sensor is preferably an ultrasound flow sensor which works according to the known ultrasound Doppler method or propagation time difference method. Such ultrasound flow sensors are known to the person skilled in the art. Any other methods of measuring the flow rate known to the person skilled in the art can also be used, for example the evaluation of the motor data of the centrifugal pump, a magnetic induction flow measurement or an optical flow measurement with a laser. On the other hand, the measurement of the flow rate can also take place invasively for measurements of the flow rate in the dialysing fluid system. All flow meters known to the person skilled in the art can be used for this purpose. 
         [0019]    The flow sensor can in principle be disposed at any point in the extracorporeal blood circuit or the dialysing fluid system, in particular on the arterial or venous blood line or the dialysing fluid supply and discharge line. In particular, the flow sensor can be integrated into the device for arterial air bubble detection which is present as standard in blood treatment apparatuses. 
         [0020]    The apparatus for extracorporeal blood treatment according to the present invention comprises the monitoring device according to the present invention. A preferred embodiment of the blood treatment apparatus according to the present invention makes provision such that the control unit of the blood treatment apparatus intervenes in the machine control when the control and computing unit of the monitoring device generates a control signal. The control unit is preferably constituted such that the centrifugal pump disposed in the extracorporeal blood circuit is stopped as an intervention into the machine control. Moreover, at least one shut-off element disposed in or on the venous blood line is preferably closed. Both the arterial and the venous hose clamp are preferably closed. In the event of an incorrect vascular access, for example when the venous puncture cannula has slipped out or a leakage is present in the hose system, the free flow of blood into the surroundings is thus immediately stopped. 
         [0021]    An exemplary embodiment of the present invention is described in detail below by reference to the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0022]      FIG. 1  shows the main components of an exemplary extracorporeal blood treatment apparatus according to the present invention, with a device according to the present invention for monitoring a vascular access or the extracorporeal blood circuit or dialysing fluid system. 
           [0023]      FIG. 2  shows the basic course of the pressure difference across the exemplary centrifugal pump present in the extracorporeal blood circuit as a function of the blood flow. 
       
    
    
     DETAILED DESCRIPTION 
       [0024]    The device according to the present invention for monitoring a vascular access or the extracorporeal blood circuit or dialysing fluid system can form a separate unit or can also be a component of the extracorporeal blood treatment apparatus. If the monitoring device according to the present invention is a component of the blood treatment apparatus, the monitoring device according to the present invention can make use of specific subassemblies or components which are in any case present in the blood treatment apparatus. 
         [0025]    An extracorporeal blood treatment apparatus A is described below, which comprises a device for monitoring the vascular access and the extracorporeal blood circuit and the dialysing fluid system. A monitoring device solely for monitoring the vascular access or the extracorporeal blood circuit or the dialysing fluid system can however also be provided. 
         [0026]      FIG. 1  shows only the main components of an exemplary blood treatment apparatus in a schematic representation, since blood treatment apparatuses as such are known to the person skilled in the art. 
         [0027]    The blood treatment apparatus is a known haemodialysis apparatus, which comprises a dialyser  1  which is divided by a semi-permeable membrane  2  into a blood chamber  3  and a dialysing fluid chamber  4 . Connected by an arterial puncture cannula  5  to the shunt or a fistula of the patient is arterial hose line  6  which leads to the inlet of blood chamber  3  of the dialyser. Leading away from the outlet of blood chamber  3  of the dialyser is a venous hose line  7 , which is connected by a venous puncture cannula  8  to the shunt or the fistula. The blood is conveyed in extracorporeal blood circuit I by a centrifugal pump  9 , which is provided on arterial hose line  6 . The centrifugal pump is a pump specially designed for blood, which is characterised by causing little damage to the blood. 
         [0028]    Dialysing fluid system II of the haemodialysis apparatus comprises a dialysing fluid source  10 , to which a dialysing fluid supply line  11  is connected, which leads to the inlet of dialysing fluid chamber  4  of the dialyser. Leading away from the outlet of dialysing fluid chamber  4  of the dialyser is a dialysing fluid discharge line  12  which leads to an outlet  13 . The dialysing fluid is conveyed in the dialysing fluid circuit by a dialysing fluid pump  14 , which is disposed on dialysing fluid discharge line  12 . In the present example embodiment, the monitoring device is also used to monitor the dialysing fluid system. Dialysing fluid pump  14  is therefore also a centrifugal pump. This is not necessary, however, if the monitoring device is used solely to monitor the vascular access or the extracorporeal blood circuit. 
         [0029]    The control of the dialysis apparatus is assumed by a central control unit  15 , which controls blood pump and dialysing-fluid pump  9 ,  14  via control lines  16 ,  17 . Located downstream of blood chamber  3  of the dialyser on venous hose line  7  is an electromagnetically operated hose clamp  18 , which can be opened or closed by central control unit  15  via a further control line  19 . When venous hose clamp  18  is closed, the fluid flow in extracorporeal blood circuit I is interrupted, so that blood cannot pass into the surroundings. 
         [0030]    Monitoring device B comprises a control and computing unit  20 , which is represented in  FIG. 1  as a separate unit. Control and computing unit  20  can however also be a component of central control unit  15  of the blood treatment apparatus. 
         [0031]    Moreover, monitoring device B comprises a measuring unit for measuring the flow rate of the blood conveyed in extracorporeal blood circuit I by centrifugal pump  9  and a measuring unit for measuring the flow rate of the dialysing fluid conveyed in a dialysing fluid system II by centrifugal pump  14 . The measuring unit for measuring the flow rate in extracorporeal blood circuit I comprises a flow sensor  21 A, which in the present example embodiment is disposed downstream of dialysing fluid chamber  3  of dialyser  1  and upstream of hose clamp  18  on venous blood line  7 , whilst the measuring unit for measuring the flow rate of the conveyed dialysing fluid comprises a flow sensor  21 B, which is disposed downstream of dialysing fluid pump  14 . In the present example embodiment, flow sensors  21 A and  21 B are ultrasound flow sensors for the non-invasive measurement of the flow rate of the blood and the dialysing fluid respectively. The measured values of ultrasound flow sensors  21 A and  21 B are received by control and computing unit  20  via data lines  22 A and  22 B. 
         [0032]    Control and computing unit  20  comprises a comparison unit  20 A for comparing the measured flow rate with a preset flow rate. Moreover, control and computing unit  20  comprises a signal generation unit  20 B for generating a control signal which is received by central control unit  15  via a data line  23 . 
         [0033]    A specific blood flow rate is set for the extracorporeal blood treatment by the doctor in charge. Central control unit  15  of the blood treatment apparatus sets speed n of centrifugal pump  9  such that the blood in extracorporeal blood circuit I is conveyed at a preset flow rate. The preset flow rate is measured by flow sensor  21 A. This flow rate corresponds to the flow rate of centrifugal pump  9 , which is preset as a reference value in control and computing unit  20 . This flow rate is therefore referred to as the preset flow rate. The flow rate of the blood is now continuously monitored during the extracorporeal blood treatment. The flow rate measured by flow sensor  21 A is constantly compared with the flow rate previously preset as a reference value. The difference between the measured flow rate and the preset flow rate is worked out. If the difference is greater than a specific threshold value, control and computing unit  20  generates a control signal, which is received by central control unit  15  via data line  23 . 
         [0034]      FIG. 2  shows the pressure difference between inlet  9   a  and outlet  9   b  of an exemplary centrifugal pump  9  as a function of flow rate Q. The slipping-out of venous puncture cannula  8  leads to a change in pressure ΔP of 20 mmHG across centrifugal pump  9  in extracorporeal blood circuit I.  FIG. 2  shows that, with a speed n of 3000 revs/min, blood flow rate Q of 300 ml/min increases by 133 ml/min. At 4500 revs/min, a volume flow increase of 235 ml/min can be seen. The two characteristic curves (characteristic curve A 4500 revs/min and characteristic curve B  3000  revs/min) show that even a small change in pressure ΔP of 20 mmHG leads to a significant increase in flow rate Q. 
         [0035]    Control and computing unit  20  compares the difference between the measured flow rate and the preset flow rate with a specific threshold value. If the difference is greater than the threshold value, i.e. a significant increase in the flow rate is recorded, an incorrect vascular access is assumed and the control signal is generated. 
         [0036]    Monitoring device B comprises an alarm unit  24 , which receives the control signal of control and computing unit  20  via a data line  25 . Alarm unit  24  then emits an acoustic and/or optical and/or tactile alarm. The alarm unit can however also be a component of the blood treatment apparatus. When central control unit  15  of the blood treatment apparatus receives the control signal of control and computing unit  20 , central control unit  15  stops centrifugal pump  9  immediately and immediately closes hose clamp  18 , so that the free flow of blood into the surroundings is immediately stopped. 
         [0037]    Monitoring device B also comprises an input unit  26 , which is connected via a data line  27  to control and computing unit  20 . Input unit  26  can also be a component of the blood treatment apparatus. 
         [0038]    Various parameters can be inputted on input unit  26  of monitoring device B, said parameters including for example the data describing employed hose system  6 ,  7 , which indicate for example the internal diameter, the wall thickness or the material of the hose lines. The data input can take place manually or automatically, for example by means of a barcode, matrix code, RFID etc. Control and computing unit  20  comprises a memory  20 C, in which specific threshold values for the monitoring of the vascular access are assigned to various data records. Control and computing unit  20  compares the data records inputted on input unit  26  with the assigned data records and selects the threshold value that corresponds to the inputted data record. This ensures that different threshold values for the monitoring of the vascular access can be made available for different hose lines. 
         [0039]    The threshold value can in principle also be dynamically variable. On the one hand, the threshold value can be preselected as fixed by the user, for example before the start of the treatment. On the other hand, the threshold value can also be adapted during the treatment. The adaptation can also take place automatically. For example, slow changes in the flow can occur due to viscosity changes in the blood or also a change in the filter properties. In order not to trigger an alarm in such cases, the threshold value can be automatically adapted accordingly. The alarm limits for abrupt changes in the flow rate can also be “carried along” until a preset limit is reached. “Preset” is understood in this connection to mean that the threshold value is present or made available in the evaluation unit before its use. 
         [0040]    The monitoring of the flow rate of the dialysing fluid in order to detect a malfunction in dialysing fluid system II takes place in a similar manner to the monitoring of the blood flow rate, wherein the dialysing fluid rate measured by flow sensor  21 B is compared with a preset flow rate. If the difference between the measured and preset flow rate is greater than a specific threshold value, it is concluded that there is a malfunction in the dialysing fluid system. This malfunction may again lie in a kinked or nipped hose line or a leakage. 
         [0041]    In a preferred embodiment, the rate of change of the flow rates in the hose lines is monitored, wherein the hose lines may be arterial and venous blood line  6 ,  7  or dialysing fluid supply or discharge line  11 ,  12 . The rate of change of the flow rate is compared with a preset threshold value. It is concluded that there is a malfunction especially in the case of a sudden change in the flow rate. In addition to the monitoring of the flow rates, the pressure characteristics in the hose lines can also be monitored. It is thus possible to distinguish between specific malfunctions, for example between a disconnection of a cannula or a leakage or the clogging up of dialyser  1 . In a preferred embodiment, pressure sensors for measuring the pressure in the hose lines are provided for this purpose. 
         [0042]      FIG. 1  shows a pressure sensor  28 A for measuring the pressure in arterial blood line  6  upstream of blood pump  9  and a pressure sensor  28 B for measuring the pressure in arterial blood line  6  downstream of blood pump  9  as well as a pressure sensor  28 C for measuring the pressure in venous blood line  7 . Pressure sensor  28 A is connected via a data line  29 A, pressure sensor  28 B is connected via a data line  29 B and pressure sensor  28 C is connected via a data line  29 C to control and computing unit  20 . 
         [0043]    In the preferred embodiment, control and computing unit  20  is constituted such that a distinction can be made between the cases stated below. 
         [0044]    If the blood flow rate in extracorporeal blood circuit I measured by flow sensor  21 A falls at a rate which is greater than a preset first threshold value, and the pressure measured by pressure sensor  28 A upstream of blood pump  9  falls below a preset threshold value, control and computing unit  20  concludes that the blood line is kinked or nipped. 
         [0045]    If the blood flow rate in extracorporeal blood circuit I measured by flow sensor  21 A falls at a rate which is greater than a preset second threshold value, and the pressure measured by pressure sensor  28 B downstream of blood pump  9  increases above a preset threshold value, control and computing unit  20  concludes that the blood line is kinked or nipped. 
         [0046]    If the blood flow rate in extracorporeal blood circuit I measured by flow sensor  21 A falls at a rate which is greater than a preset third threshold value which is less than the aforementioned first threshold value, i.e. the flow rate falls more slowly, and the pressure measured by pressure sensor  28 B downstream of blood pump  9  increases above a preset threshold value, control and computing unit  20  concludes that dialyser  1  is clogged up. 
         [0047]    If the blood flow rate in extracorporeal blood circuit I measured by flow sensor  21 A increases at a rate which is greater than a preset fourth threshold value, i.e. the flow rate increases rapidly, and the pressure measured by pressure sensor  28 C in venous blood line  7  remains constant or falls, control and computing unit  20  concludes that a disconnection of venous cannula  8  is present.