Device for blood treatment in single-needle operating mode

Device for the treatment of blood to work with a single needle

The invention relates to a device for the treatment of blood for operation with a single needle, which has an extracorporeal blood circuit, which has a blood inlet tube leading to the entrance of a treatment unit for blood and a blood return tube that starts at the outlet of the blood treatment unit, leading the blood inlet tube and the blood return tube to a common needle (cannula) and starting from a common needle.

Devices for the treatment of blood with a unit for the treatment of blood that is pierced by the blood of a patient, are generally known. Among them are, for example, the known devices of hemodialysis, hemofiltration or hemodiafiltration. Known blood treatment devices can operate in operation with a single needle or with two needles.

In the technique of two needles the blood is extracted by a first needle from a patient's blood vessel, it is taken to the blood treatment unit of the blood treatment device and it is carried back through a second needle to a patient's blood vessel. For the collection and return of blood, replaceable flexible tube systems with a blood inlet tube and a blood return tube are used, to which both needles are connected. These disposable hose systems are also called "disposable."

In the technique of a single needle, the blood is taken and returned through a single needle. The blood taken from the patient is stored during an arterial phase in a reservoir and then, in a venous phase, it is carried back from the reservoir to the patient's blood circuit through the same needle.

A device for the treatment of blood for operation by a single needle is known from EPA-0 472 480 B1. In a constructive form of the apparatus for the treatment of known blood, two blood expansion chambers are provided for temporary storage of blood, arranged upstream and downstream of the blood treatment unit. The blood treatment apparatus has a regulating device, which essentially keeps the pressure in the expansion chambers constant. Level sensors are provided to detect the level of liquid in the expansion chambers.

Document DE 10 2005 001 779 A1 describes a set for disposable equipment for operating a device for the treatment of blood in operation with a single needle or with two needles. The disposable includes, in addition to the blood inlet and blood outlet tube for connection to a blood treatment unit, an expansion unit, which can be coupled for operation with a single needle to the blood separator unit. air, to increase the volume. During operation with a single needle, blood is transported in the arterial phase through the blood inlet tube to the blood treatment unit and from the blood treatment unit to the air separation and expansion unit , the blood supply to the patient being interrupted. A predetermined pressure is then created in the air separation and expansion unit, which is monitored by a pressure measurement unit. With a pressurized air unit, it can be adjusted by operating an air pump, connected between a tank and the expansion unit, a predetermined pressure in the expansion and air separation unit. In addition, it is proposed to calculate the volume of blood in the air expansion and separation unit with the help of the measured values ​​of three pressure sensors and the known system volumes. In addition, it is proposed to use the air pump to regulate the pressure in the venous phase, so that the flow of blood transported can be optimally adapted.

EP 0 405 094 A2 describes a device for the treatment of blood operating with a single needle, which has a plasma separator. Single needle operation includes two stages. In a first stage the patient's blood is collected in a blood collection bag. In the second stage, the accumulated blood is conducted from the blood collection bag to the plasma separator, the blood plasma is conducted from the plasma separator to a plasma collection bag and the remaining blood components are returned to the patient. The extracorporeal blood circuit includes a blood inlet tube and a blood return tube, which lead to a common needle. The blood collection bag and the plasma collection bag are in collection units, in which the bags may be subject to overpressure or depression.

The invention has as a basic task to achieve a device for the treatment of blood for operation with a single needle in which the volume of blood in the blood tank can be determined without level sensors and the behavior in case of failure can be improved.

The solution to these tasks is carried out within the framework of the invention with the features of claim 1. Advantageous constructive forms of the invention are subject to the dependent claims.

The device corresponding to the invention for the treatment of blood has an extracorporeal blood circuit, which has a blood inlet tube leading to the entrance of a blood treatment unit and a return tube of blood. the blood that starts from the exit of the unit for the treatment of blood. This extracorporeal blood circuit with the blood treatment unit does not need to be part of the blood treatment device, but it can be a disposable (disposable) element intended for a single use, which is inserted for Blood treatment in the treatment unit.

It also presents the device for the treatment of blood means for collecting blood and means for accumulating gas, especially air. The means for collecting blood and the means for accumulating gas are respective deposits, which constitute a closed volume, for example a blood or air chamber with a predetermined volume.

The means to collect blood are connected to the means to accumulate gas, so that in the arterial phase when filling the means to collect blood can reach from the means to collect blood displaced air to the means to accumulate gas and in the venous phase air from the means to accumulate gas to the means to collect blood, whereby the blood previously accumulated in the arterial phase can be displaced from the means to collect blood. In this way it is achieved that in the arterial phase blood is taken from the patient and in the venous phase the blood treated with the blood treatment unit is brought back to the patient.

The union between the means for collecting blood and the means for accumulating gas has a first and second connection route. The first connection route joins the means to collect blood and to accumulate gas such that in the arterial phase air displaced from the means to collect blood is transferred to the means to accumulate gas, means being provided in the first joining route means to interrupt the Union. The second route of connection connects the means to collect blood and accumulate gas such that in the venous phase the air accumulated in the means to accumulate gas is conducted to the means to collect blood. The second junction route contains means for compressing gas, whereby the air accumulated in the means for accumulating gas can be transferred to the means for collecting blood. With the means to compress the air, a predetermined pressure can be established in the means to collect blood both during the arterial phase and also during the venous phase. The means for compressing gas can be configured for example as a conventional compressor.

The means for collecting blood and accumulating gas together with the first and second joining route form a closed volume, in which no gas can enter or any gas can escape. Only for closed system initialization the closed volume is aerated / purged of air. The first joining route and the second joining route may be formed by separate tubes. The first and second junction path may, however, also include a section of common tube.

An infusion of air into the patient can be excluded with great certainty because in the means to accumulate gas a pressure results that in no case of service is greater than the pressure that results in the means to collect blood. In this way it is achieved that only air can reach with the means to compress gas from the means to accumulate gas to the means to collect blood. When the means for compressing gas fail, for example in a compressor leak, on the other hand air cannot reach the means for collecting blood. In this way it is excluded that the means to collect blood function in a vacuum inadvertently, with which air could reach the patient.

In practice, it is intended that the return pressure with which blood is displaced from the means to collect blood be adjusted as low as possible, while the volume per beat is as large as possible. In order to fulfill the condition that in a compressor failure air cannot reach the means to accumulate gas to the means to collect blood, for a reduced return pressure and large volume per beat, the system is distended to initialize the consecutive phases arterial and venous at the time of switching from the arterial phase to the venous phase, that is, at the instant of the upper switching point, at which the means for collecting blood are full, up to a predetermined pressure, preferably the ambient pressure. The pressure in the means for accumulating gas is thus found in the successive arterial and venous phases always below the predetermined pressure, in particular of the surrounding pressure, to which the closed system has distended.

The means to accumulate gas in direct contact with the patient are no longer found during the arterial phase, since the extracorporeal blood circuit is separated on the venous side, for example with a hose clamp. With this, the evolution of the pressure in the means to accumulate gas during the arterial phase for the safety of the patient is of little importance. However, it is crucial that towards the end of the arterial phase, that is, at the beginning of the venous phase, there is the desired return pressure in the means for collecting blood. This is preferably achieved by dividing the arterial phase into two time intervals. In a first predetermined interval of time a union is established between the means to collect blood and the means to accumulate gas, whereby the air displaced when filling the means to collect blood reaches the means to accumulate gas, thereby generating there a certain pressure. In a second predetermined interval, however, the connection between the means for collecting blood and the means for accumulating gas is interrupted. In this way, the pressure in the means to accumulate gas remains constant, while the pressure in the means to collect blood continues to increase, since blood is continuously supplied to the means to collect blood. This results in two separate volumes of air.

In a preferred constructive form of the device for the treatment of blood corresponding to the invention, it presents the second route of connection between the means for accumulating gas and collecting blood a tube for providing gas, which joins the means for accumulating gas with the means for collect blood The means for compressing gas, for example a compressor, are arranged in this tube. The first connection route has a bypass tube that bridges the means for compressing gas, in which a bypass valve is arranged. When the means for compressing gas do not operate and when the bypass valve is closed, the closed volume of the means for collecting blood is separated from the closed volume of the means for accumulating gas. When the bypass valve on the other hand is open, both volumes form a closed common volume.

In another preferred constructive form, the tube for supplying gas has a first section of tube that joins the means for collecting blood with the pressure side of the means for compressing gas, and a second section of tube that joins the suction side of the means for compressing gas with means for accumulating gas.

In order to dispense the closed volume to the surrounding pressure when initializing the system, means for aerating or purging the air are preferably provided in the first tube section.

Preferably, the means for collecting blood are configured as a container with a predetermined volume, which has an inlet and an outlet and is arranged in the blood return tube of the extracorporeal circuit. Also the means for accumulating gas are preferably configured as a container with a predetermined volume.

The blood in the extracorporeal circuit is preferably supplied with a blood pump, arranged in the blood inlet tube.

A special advantage of the device for the treatment of blood corresponding to the invention is that the level of filling of the means for collecting blood with great accuracy can be ascertained without level sensors only based on pressure measurements. A preferred constructive form of the blood treatment device corresponding to the invention presents means for measuring the pressure in the closed volume of the means for collecting blood, the closed volume in the junction routes between the means for collecting blood on one side. and the means for compressing gas on the other hand and the closed volume of the means for accumulating gas, the volume of blood being calculated from the measured pressure values.

In order to determine the pressure in the joining routes between the means for collecting blood on one side and the means for compressing gas on the other hand, the pressure can be measured in a tube section of the first joining route and / or in a section of tube of the second route of connection, the sections of tube extending between the means for collecting blood on one side and the means for compressing gas or the means for interrupting the union on the other side. When the first and second joining routes have a common pipe section, it is also possible to measure the pressure in the common pipe section of both joining routes with a pressure sensor.

An exemplary embodiment of the invention will be described in more detail below with reference to the drawings.

It is shown in:

1 shows an example of the device for treating blood corresponding to the invention for

operation with a single needle, in simplified schematic representation, figure 2 the evolution of the filling level and the pressure during initialization and the operation of the device for

the treatment of the blood corresponding to the invention, and figure 3 the evolution of the pressure during the successive arterial and venous phases after initialization.

Figure 1 shows the essential components of a device for the treatment of blood, in particular of a dialysis device for operation with a single needle, in schematic representation.

The dialysis device has an extracorporeal blood circuit 1 during the blood treatment, which includes a blood treatment unit 2 configured as "disposable", for example a dialyzer. The dialyzer 2 is divided by a semipermeable membrane 3 into a blood chamber 4 and a dialyzer fluid chamber 5.

In the extracorporeal blood circuit, blood is supplied by a blood pump 6, which is part of the dialysis device. The dialysis fluid circuit is not shown in Figure 1.

A set of flexible tubes 7 is inserted into the dialysis device, which is discarded after treatment. The disposable 7 has a blood inlet tube 8 that leads to the inlet 4A of the blood chamber 4 of the dialyzer 2, which is inserted in the roller pump 6 of the dialyzer device, and a blood return tube 9 that part of the 4B outlet of the blood chamber. The blood inlet and return tubes 8, 9 are connected to a common cannula 10 (needle).

Blood collection means 11, arranged as a container with a predetermined volume, are arranged in the blood return tube 9 of the disposable. Means for accumulating blood collection vessel or blood deposit are referred to below. Flow down the blood collection container 11, means 9 are arranged in the blood return tube 9 means 12 to interrupt the blood return tube, for example a venous hose clamp.

The blood collection vessel 11 has an inlet 13, to which a first section 9A of the blood return tube 9 leads, and an outlet 14, from which a second section 9B of the blood return tube 9 starts To detect a certain level of filling in the container for collecting blood 11, the dialysis device has a filling level transmitter 15, which detects when the level of filling in the container reaches a predetermined value. In addition, a pressure transmitter 16 is provided, which measures the pressure in the blood collection vessel 11.

When the blood collection vessel 11 is full of blood, a certain volume of air remains in the blood reservoir above the level of the liquid 17. The blood reservoir is in flow junction with means 18 for accumulating gas, in particular air, configured as a container with closed volume. The means 18 for accumulating gas tank air accumulator or air accumulator are referred to below.

So that the blood reservoir and the air accumulator can communicate with each other, part of the upper side of the blood reservoir 11 a tube 19, which leads to the air accumulator 18. In the tube 19 there are arranged means 20 to compress gas, which they can be constituted for example as a conventional compressor. When the compressor is not running, the compressor interrupts the flow junction between the blood reservoir and the air accumulator. When the compressor works, the air in the air accumulator is transferred to the blood tank. Since the air is compressed, a predetermined pressure is set in the blood reservoir.

The tube 19 has two sections of tube 19A, 19B, of which one section of tube 19A connects the blood reservoir 11 with the outlet of the pressure side 20A of the compressor 20 and the other section of tube 19B joins the connection of the side of suction 20B of the compressor 20 with the air accumulator 18. These sections of tube 19A, 19B form a junction path for transporting gas from the air accumulator to the blood reservoir.

In order to be able to transfer air from the blood reservoir to the air accumulator when the compressor is not running, a bypass pipe 21 is provided, which starts from the first section 19A of the tube 19 and leads to the second section 19B of the tube 19. In the bypass tube 21 is connected a bypass valve 22. Together with the corresponding tube sections 19, the bypass tube 21 constitutes a connection route for supplying gas from the blood tank to the air accumulator.

To prevent liquid from reaching the blood tank to the air accumulator, a filter 23 is provided in the first section 19A of the tube 19, which contains a hydrophobic membrane, that is, permeable to the air, but impervious to the liquid. . Since the blood reservoir is only filled to a maximum filling level, however, liquid can reach the tube 19 only in the event of a breakdown.

To aerate / purge the closed volume, which includes the blood reservoir and the air accumulator, as well as the tube 19, means 24 are provided for aerating / purging air, which for example have an aeration / purge line. air 24A connected to the first section 19A of the tube 19 with an aeration / air purge valve 24B. The aeration / air purge tube 24A can basically start from any point of the volume to be aerated or purged of air. In particular, aeration / air purging must be carried out on the side of the machine.

In addition to the pressure transmitter 16 for measuring the pressure in the blood reservoir, a pressure transmitter 25 is provided to measure the pressure in the first section 19A of the tube 19 between the filter 23 and the compressor 20 and another pressure transmitter 26 for measure the pressure in the air accumulator 18. In the air accumulator 18 a temperature sensor T is provided to measure the temperature of the air in the air accumulator.

The dialysis device has a central control and calculation unit 27, which is connected by power lines not shown with the blood pump 6, the venous hose clamp 12, the bypass valve 22, the aeration / purge valve of air 24B, the filling level transmitter 15, the compressor 20, as well as the pressure transmitters 16, 25 and 26. The central control and calculation unit is in turn connected to an input unit not shown, which performs an interface between the user and the machine.

The operation of the dialysis device is described below with reference to Figures 2 and 3 in detail. The control and calculation unit 27 controls the dialysis machine as follows.

At the beginning of the dialysis treatment itself, the system is initialized with the following procedure steps.

Figure 2 shows the level of filling in the blood tank as a function of time during the different phases of initialization. In addition, Figure 2 shows the evolution of the pressure in the blood tank, which is called the pressure chamber, of the pressure in the air accumulator, which is called the pressure of the accumulator, and of the pressure in the first section 19A of the tube 19, which is called tube pressure. In addition, Figure 2 shows the evolution in time of the total mass of air housed in the blood tank and in the air accumulator, as well as in the corresponding sections of the tubes 19, 22.

In the first stage of initialization, the blood level in the blood reservoir is lowered below a certain level, which is between the upper switching point, at which during the operation of the dialysis device it must be switched from the arterial phase to the venous phase, and the lower switching point, at which it must be switched from the venous phase to the arterial phase. To do this, open the control and calculation unit 27, with the blood pump 6 stopped, the venous clamp of the flexible tube and put the compressor 20 into operation until the desired liquid level has been reached, which is detected by the transmitter of the filling level Figure 2 shows that the filling level drops, while the total mass of air in the system remains constant. This stage can be skipped when the blood level is already below the desired level.

In the second stage the blood level is adjusted to the desired level, which is detected by the filling level transmitter. For this purpose, the bypass valve 22 and the aeration / air purge valve 24B are opened and the blood pump 6 operates, with the venous clamp of the flexible tube closed, until the desired level has been reached. Figure 2 shows that the fill level rises to the desired level, while the mass of air in the system drops.

When the desired level has been reached, wait until the pressures in the chamber and in the tank, as well as the pressure in the tube, have been adjusted to the surrounding pressure. In this regard, the filling level remains constant, while the air mass continues to decrease slightly (step 3). Only then is the aeration / air purge valve 24B closed again (step 4).

Then continue filling the blood tank with blood. With the bypass valve open, the blood pump 6 operates until the fill level in the blood reservoir has reached the level of the upper connection point (step 5). Then the mass of air remains in the constant system. Since both the pressure in the chamber and in the reservoir as well as the pressure in the tube are measured with the pressure transmitters, the level of filling in the blood reservoir can be calculated continuously. The control and calculation unit calculates the level of filling in the blood tank and stops the blood pump when the level of filling has reached the level of the upper switching point. This will be described later in detail.

Once the control and calculation unit has stopped the blood pump 6, the aeration / air purge valve 24B is opened again, whereby the pressure created in the system is distended to the surrounding pressure (stage 6). Figure 2 shows that the filling level remains constant, while the pressure of the chamber and the tank, as well as the pressure in the tube, decrease to the surrounding pressure. Since the volume covered by the system, that is, the volume of the blood reservoir and the air accumulator, as well as the tubes, and also the pressures in the system are known, the mass of air contained in the system can be calculated . This will be described later in detail.

As the last stage of the initialization, the aeration / air purge valve 24B is closed, the filling level and the pressures not being modified, as well as the mass of air in the system (step 7). The aeration / air purge valve remains closed during the whole blood treatment, if a new initialization is not necessary, for example after an air leak is detected. With this the initialization is finished and the blood treatment begins with the first venous phase.

In the first venous phase the compressor 20 operates with the bypass valve 22 closed, the venous clamp of the flexible tube 12 is open and the blood pump 6 is stopped. During operation of the compressor, air from the air accumulator 18 is compressed and leads to the blood tank 11. Because of this the pressure in the chamber and the tube increases, while the pressure in the tank drops. At the same time, the level of filling in the blood tank decreases continuously, until the level of the lower switching point is reached. In this regard it is decisive that the tank pressure is below the chamber pressure and consequently also below the tube pressure, in case of a failure to prevent the penetration of gas from the air accumulator to the tank of blood. Additionally, it is intended that the tank pressure is even below the ambient pressure.

Then the arterial phase begins, in which the blood reservoir is filled again with the blood taken from the patient, following what follows again the venous phase, in which the blood is conducted from the blood reservoir of Again to the patient.

The air accumulator is sized so large that there is also enough air in the system at the end of the venous phase to maintain the desired return pressure in the blood reservoir. In order to be able to adjust all operating points with a return pressure of 0 to 500 mmHg relative to a volume per beat of up to 60 ml with the same initialization, an air accumulator with a tank volume of about 300 is required in practice ml.

The evolution in time of the pressure in the chamber and in the reservoir, as well as of the pressure in the tube during the arterial and venous phases proper after the initialization of the system, is represented in Figure 3, which shows a detail of Figure 2

The blood pump 6 operates throughout the arterial phase, the compressor 20 being stopped. The venous clamp of the flexible tube 12 remains closed during the entire arterial phase.

At the beginning of the arterial phase, the control and calculation unit 27 opens the bypass valve 22, whereby the air displaced from the blood reservoir 11 arrives through the bypass line 21 to the air accumulator 18. Consequently, the tank pressure, while the pressure in the chamber and in the tube first drops, to then also increase approximately as the pressure in the accumulator. The mass of air contained in the blood reservoir and in the corresponding volume of the tube decreases with it continuously.

As soon as the mass of air contained in the blood reservoir and in the volume of tubes has reached a predetermined amount, resulting from the desired beat volume and the desired return pressure, the control and calculation unit closes the valve bypass Consequently, two separate air volumes result, that is, the volume of air in the blood tank with the corresponding sections of the tube and the volume of the air accumulator with the corresponding sections of the tube. The blood pump is then activated with the bypass valve closed, so that the pressure in the tank remains constant, while the air in the blood tank and in the corresponding volume of tubes is compressed until the volume reaches desired beat, the desired return pressure has also been reached. Figure 3 shows that towards the end of the arterial phase the pressure in the chamber and in the tube has increased to the desired return pressure, the reservoir pressure being found throughout the arterial phase always below the chamber pressure and of the tube, in particular below the ambient pressure. Thus it is excluded that even in a case of disturbance in the system, for example when there is a leak in the compressor, air arrives from the air accumulator to the blood reservoir.

Instead of dividing the arterial phase into a first and a second time interval, other embodiments are also possible, with which the advantages corresponding to the invention can also be achieved. An alternative embodiment provides, instead of the bypass valve 22, to use a pressure-controlled valve, which opens upon reaching a limit pressure corresponding to the return pressure, whereby a pressure reigns in a certain time interval constant in the blood tank.

Then the control and calculation unit is switched to the venous phase, the bypass valve is closed, the blood pump is stopped and the compressor is started, also opening the venous clamp of the flexible tube. The compressor works throughout the venous phase, the blood pump being stopped. The venous clamp of the flexible tube remains open during the venous phase and the bypass valve is closed.

The compressor supplies air from the air accumulator to the blood tank, to create an overpressure, thereby transporting the blood from the blood tank. The compressor then operates such that the desired return pressure results in the blood reservoir. Since air from the air accumulator is continuously carried to the blood tank, the pressure in the tank continuously decreases. Again, it is decisive that the tank pressure is always below the chamber and tube pressure, preferably also below the ambient pressure, thereby excluding an infusion of air from the air accumulator to the patient in case of failure. The venous phase ends when the blood level in the blood reservoir has again fallen to the level of the lower switching point. Then follow the next arterial phase.

The following describes the calculation of the volume of VBlut blood in the blood reservoir, which is performed by the control and calculation unit during the operation of the dialysis device, continuously or at predetermined time intervals. When the volume of blood is known, it can be used for comparison with the switching points of the arterial phase to the venous phase or vice versa.

To calculate the volume of VBlut blood found in the blood reservoir, it is basically necessary to determine the mass of air in the blood reservoir. Once the balance of pressures is performed, it turns out

with p = pressure (absolute), V = volume, m = mass, Mm = molar mass, R = general gas constant and T = temperature. Since MM and R are constant and for the mass of air no absolute value is needed, they do not need to be taken into

Count them explicitly. Consequently, the determination has only to be done with To determine the total air mass, the sum of all partial air masses must be formed, that is, the mass of air in the blood tank, in the corresponding tubes and in the accumulator of air. For this, all volumes filled with air must be multiplied by the corresponding prevailing pressure and divided by temperature.

is at the height H of the level detected by the transmitter of the filling level 15, then it corresponds

the volume of air in the blood tank at the lower switching point UT and the difference in volumes between the lower switching point UT and the height of the filling level 15 detected in the blood tank by the filling level transmitter 15 .

At the end of the initialization at the upper switching point OT, blood is additionally found with the volume per total beat

in the blood tank, which results

The remaining volumes remain constant. Then the temperatures with a good approximation have to be considered as constants, when no temperature compensation is made. However, preferably a temperature sensor is provided to measure the temperature at least in the air accumulator, with

25 that temperature compensation can be performed. However, temperature sensors may also be provided for the other pressure values.

The volume of blood transported

in the blood tank it is calculated throughout the cycle for each loop of the program. Then the volume of air included in the blood tank is calculated based on the measured pressures

30 and the difference between the volume of air in the blood tank at the lower switching point UT and the volume of air in the blood tank is formed.

35 The total mass of air remains unchanged after the initialization of the system, because the purge valve remains closed Since the calculation of blood volume

it is performed when the blood pump circulates and when the compressor is running, a smoothing of the pressure signals and blood volume is performed

calculated

The switching from the arterial phase to the venous phase (OT) is performed when the difference between the volume of blood

calculated and volume per beat adjusted

it is equal to zero and the switching from the venous phase to the arterial phase is performed when the calculated blood volume is equal to zero.

The following describes how the control and calculation unit calculates the moment in which within the arterial phase it is switched between the first and the second time interval of the arterial phase.

As already described, it is possible to calculate the switching point from arterial phase to venous phase and vice versa by a simple comparison of blood volume with volume per beat or zero. The arterial phase is divided, as already mentioned, into a first and a second time interval. In the first arterial phase, the blood pump carries blood through the dialyzer with the bypass valve open to the blood tank. In this way the depression that has been established in the venous phase previously in the air accumulator is used to support the pump. In the second arterial phase, the air accumulator is disengaged by closing the bypass valve of the rest of the system and the pressure in the blood tank increases strongly due to the volume of blood supplied. At the end of the second arterial phase, the desired setpoint pressure must be taken in the blood vessel. The switching point between the first and second arterial phase must therefore be chosen such that the volume of blood remaining establishes the set pressure up to the upper switching point OT in the blood reservoir and in the tube.

Accordingly, the mass of air that, during compression, sets the set pressure on the volume of air available in the blood tank and in the tube at the upper switching point OT must be calculated. The mass of air in the blood reservoir and in the tube is

At the switching point of the first to the second time interval of the arterial phase the mass of air that is in the blood reservoir and in the tube must be equal to the mass of air that is in the upper switching point OT in the air accumulator.

Then it is

the volume of air in the blood reservoir at the upper switching point OT.

The control and calculation unit checks during the arterial phase if the above equation has been fulfilled. As soon as the equation has been fulfilled, the second time interval of the arterial phase begins, closing the bypass valve. The blood pump operates controlled by the control and calculation unit in the second time interval with the same flow rate, until the desired beat volume has been achieved and with this the upper switching point OT has been reached.

A leak in the closed volume can result in a variation in the amount of gas included in the system. When the leak is in the overpressure zone of the system, that is, in the area of ​​the blood reservoir or the adjacent tube sections, then the leak results in a reduction of the amount of air included, whereby the Blood filling level in the blood tank increases. Then there is a danger that the blood reservoir is filled to the brim and the blood level rises to the hydrophobic membrane, so that the arterial phase can no longer be properly terminated. Conversely, when there is a leak in the area of ​​depression, that is, in the gas accumulator, or due to the entry of air from the blood system, the amount of air lodged increases, bringing the level of blood in the blood tank it descends. This can result in the level of blood in the venous phase falling too quickly, which can lead to unwanted foaming, and in extreme cases even to the air alarm. However, this can be monitored by observing the amount of air included in the system. Such monitoring of the amount of air can be provided in the device corresponding to the invention.

The monitoring of the amount of air to detect a leak is carried out by detecting the instant at which the transmitter of the filling level 15 detects in the blood tank 11 the filling level, that is, the blood reaches the predetermined level. With this, the level of effective blood filling is known at this time. This value is compared with the filling level calculated at that time from the pressure values. When the difference between the measured and calculated fill level is greater than a predetermined limit value, then the amount of air included in the system has varied significantly, which can be attributed to a leak in the system. In this case the system is initialized again. If the fault occurs too frequently, interrupt the central control and calculation unit 27 the treatment.

An alternative evaluation foresees not finishing based on the level of filling measured and calculated, but comparing the moment

5 in which the filling level transmitter 15 detects the predetermined filling level with the calculated time at which the predetermined filling level should be reached. If there is a significant time difference, it follows that there is a leak in the system.

Another constructive form further provides for detecting a leak in the system opposite the blood reservoir.

10 11 behind the filter 23 after increasing the level of filling beyond the level detected by the transmitter of the level of filling in the arterial phase, detecting with the pressure sensor 16 in the blood tank 11 a pressure that increases too quickly, when the pressure and / or the pressure increase per unit of time exceeds a predetermined limit value. In this case, the blood that reaches the filter results in an increase in pressure, which drastically reduces compliance in this part of the system. This is especially true in the case where a sensor is used

fifteen of pressure that measures the pressure in direct contact, that is, without intermediate space that can be compressed.