Device and method for detecting the recirculation during an extracorporeal blood treatment

Abstract

A device and method for detecting recirculation for an extracorporeal blood treatment apparatus and an apparatus with a device for detecting recirculation are based on targeted haemodilution by administration of a substituate bolus, causing a pressure change in venous and arterial branches of the extracorporeal circuit due to a viscosity change of flowing fluid. Recirculation is detected based on detection of the pressure change. The device includes a control unit cooperating with a device for conveying blood and a device for supplying substituate. The control unit provides an operating mode for detecting recirculation, in which blood flow rate is reduced during administration of a substituate bolus. With simultaneous substituate bolus administration and reduction of blood flow rate, the composition of fluid flow is optimized for detection of recirculation, so that fairly large pressure changes result in venous and arterial branches, thereby improving sensitivity and reliability of the measurement method.

Claims

1. A device for detecting recirculation for an extracorporeal blood treatment apparatus, the extracorporeal blood treatment apparatus comprising an extracorporeal blood circuit with an arterial blood line, which leads to a first chamber of a dialyser or filter divided by a membrane into the first chamber and a second chamber, and a venous blood line, which leads away from the first chamber of the dialyser or filter, a fluid system, which comprises the second chamber of the dialyser or filter, a device for conveying blood at a preset blood flow rate Q.sub.b through the arterial blood line into the first chamber of the dialyser or filter and through the venous blood line from the first chamber of the dialyser or filter, and a device for supplying substituate to the blood at a preset substituate rate Q.sub.s in the arterial blood line upstream of the dialyser or filter, the device for detecting the recirculation comprising: a measuring unit adapted for measuring pressure in the extracorporeal circuit in the arterial and/or venous blood line; an evaluation unit adapted for detecting the recirculation based on the pressure measurement; and a control unit cooperating with the device for conveying blood and the device for supplying substituate, the control unit being adapted, in an operating mode for detecting the recirculation, to control the device for conveying blood such that in a preset time interval, a preset first blood flow rate Q.sub.b1 is reduced to a preset second blood flow rate Q.sub.b2, and to control the device for supplying substituate such that in the preset time interval, substituate is fed at the preset substituate rate Q.sub.s to the blood in the arterial blood line upstream of the dialyser or filter, wherein the evaluation unit is adapted to monitor the pressure measured by the measuring unit in the arterial and/or venous blood line for a change in the pressure and to calculate a ratio between an amount of the change in the pressure measured by the measuring unit in the arterial blood line and an amount of the change in the pressure measured in the venous blood line.

2. The device according to claim 1, wherein the evaluation unit is adapted to generate a control signal signalling a presence of the recirculation when a pressure increase is detected in the arterial blood line.

3. The device according to claim 1, wherein the evaluation unit is adapted to generate a control signal signalling a presence of the recirculation when a pressure reduction is detected in the venous blood line.

4. The device according to claim 1, further comprising: an optical and/or acoustic signal unit adapted to receive a control signal of the evaluation unit, said signal unit being adapted to generate an acoustic and/or optical signal when the signal unit receives the control signal from the evaluation unit.

5. The device according to claim 1, wherein the control unit is adapted to control the device for supplying substituate in the preset time interval in the operating mode for detecting the recirculation such that a difference between the preset substituate rate Q.sub.s and a difference between the first blood flow rate Q.sub.b1 and the second blood flow rate Q.sub.b2 corresponds to a specific value.

6. The device according to claim 5, wherein the specific value is zero.

7. The device according to claim 1, further comprising: an actuation unit provided for the control unit, the actuation unit being adapted such that, after actuation of an actuation element, the control unit selects the operating mode for detecting the recirculation, in which the device for conveying blood and the device for supplying substituate are controlled.

8. An extracorporeal blood treatment apparatus, comprising: an extracorporeal blood circuit with an arterial blood line, which leads to a first chamber of a dialyser or filter divided by a membrane into the first chamber and a second chamber, and a venous blood line, which leads away from the first chamber of the dialyser or filter, a fluid system, which comprises the second chamber of the dialyser or filter, a device for conveying blood at a preset blood flow rate Q.sub.b through the arterial blood line into the first chamber of the dialyser or filter and through the venous blood line from the first chamber of the dialyser or filter, a device for supplying substituate to the blood at a preset substituate rate Q.sub.s in the arterial blood line upstream of the dialyser or filter, and the device for detecting the recirculation according to claim 1.

9. A method for detecting recirculation for an extracorporeal blood treatment apparatus, the extracorporeal blood treatment apparatus comprising an extracorporeal blood circuit with an arterial blood line, which leads to a first chamber of a dialyser or filter divided by a membrane into the first chamber and a second chamber, and a venous blood line which leads away from the first chamber of the dialyser or filter, a fluid system, which comprises the second chamber of the dialyser or filter, a device for conveying blood at a preset blood flow rate Q.sub.b through the arterial blood line into the first chamber of the dialyser or filter and through the venous blood line from the first chamber of the dialyser or filter, a device for supplying substituate to the blood at a preset substituate rate Q.sub.s in the arterial blood line upstream of the dialyser or filter, wherein pressure in the extracorporeal blood circuit is measured in the arterial and/or venous blood line and detection of the recirculation takes place based on the pressure measurement, the method comprising: in an operating mode for detecting the recirculation, reducing a preset first blood flow rate Q.sub.b1 to a preset second blood flow rate Q.sub.b2 in a preset time interval, supplying substituate at the preset substituate rate Q.sub.s to the blood in the arterial blood line upstream of the dialyser or filter in the preset time interval, monitoring the pressure measured by a measuring unit in the arterial and/or venous blood line for a change in the pressure, and detecting a presence of the recirculation by calculating a ratio between an amount of the change in the pressure measured by the measuring unit in the arterial blood line and an amount of the change in the pressure measured in the venous blood line.

10. The method according to claim 9, wherein the pressure measured by the measuring unit in the arterial blood line is monitored for an increase in the pressure, wherein the presence of the recirculation is detected when there is an increase in pressure.

11. The method according to claim 9, wherein the pressure measured by the measuring unit in the venous blood line is monitored for a reduction in the pressure, wherein the presence of the recirculation is detected when there is a reduction in pressure.

12. The method according to claim 9, further comprising: generating an acoustic and/or optical signal when there is a change in pressure.

13. The method according to claim 9, further comprising: in the operating mode for detecting the recirculation, the substituate rate Q.sub.s is selected, at which a difference between the preset substituate rate Q.sub.s and a difference between the first blood flow rate Q.sub.b1 and the second blood flow rate Q.sub.b2 corresponds to a specific value.

14. The method according to claim 13, wherein the specific value is zero.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 shows an extracorporeal blood treatment apparatus with a device for detecting the recirculation in a very simplified diagrammatic representation.

(2) FIG. 2 shows a diagram to illustrate the flow rates in the extracorporeal blood circuit during the bolus administration.

(3) FIG. 3 shows a first exemplary embodiment of the time-related course of the pressure in the arterial and venous branch of the extracorporeal blood circuit during the bolus administration in the presence of a recirculation.

(4) FIG. 4 shows a second exemplary embodiment of the time-related course of the pressure in the arterial and venous branch of the extracorporeal blood circuit during the bolus administration in the presence of a recirculation.

(5) FIG. 5 shows the time-related course of the pressure in the arterial and venous branch of the extracorporeal blood circuit during the bolus administration when no recirculation is taking place.

DETAILED DESCRIPTION

(6) FIG. 1 shows in a simplified diagrammatic representation only the main components of an extracorporeal blood treatment apparatus, which comprises a device for detecting the recirculation.

(7) The present blood treatment apparatus is a haemo(dia)filtration apparatus, which comprises a dialyser 1, which is separated by a semipermeable membrane 2 into a first chamber 3 through which blood flows, which is referred to in the following as a blood chamber, and a second chamber 4 through which dialysing fluid flows, which is referred to as a dialyser fluid chamber. First chamber 3 is incorporated into an extracorporeal blood circuit 5A, whilst second chamber 4 is incorporated into dialysing fluid system 5B of the haemo(dia)filtration apparatus.

(8) Extracorporeal blood circuit 5A comprises an arterial blood line 6, which leads from an arterial cannula 6a to inlet 3a of blood chamber 3, and a venous blood line 7, which leads away from outlet 3b of blood chamber 3 of dialyser 1 and leads to a venous cannula 7a. The arterial and venous cannulas are connected to the fistula (shunt) of the patient, said fistula not being represented. The patient's blood is delivered through blood chamber 3 of dialyser 1 by an arterial blood pump 8, which is disposed on arterial blood line 6. Blood pump 8 feeds blood at a preset blood flow rate Q.sub.b, referred to as the first blood flow rate, to blood chamber 3 of the dialyser. The first blood flow rate can be changed during the blood treatment. Blood lines 6, 7 and dialyser 1 form a disposable intended for one-off use, which is inserted into the dialysis apparatus for the dialysis treatment. In order to eliminate air bubbles, air separators (drip chambers) can be incorporated into the arterial and venous blood line.

(9) The fresh dialysing fluid is prepared in a dialysing fluid source 9. From dialysing fluid source 9, a dialysing fluid supply line 10 leads to inlet 4a of dialysing fluid chamber 4 of dialyser 1. A dialysing fluid discharge line 11 leads from outlet 4b of dialysing fluid chamber 4 to a drain 12. A dialysing fluid pump 13 is incorporated into dialysing fluid discharge line 11.

(10) During the dialysis treatment, substitution fluid (substituate) can be fed from a substituate source 15 via a substituate line 14 to extracorporeal blood circuit 5A. Substitution line 14 is connected to a line segment of arterial blood line 6 downstream of blood pump 8 and upstream of blood chamber 3 of dialyser 1. The substituate is conveyed with a substituate pump 16, which feeds substituate at a preset substituate rate Q.sub.s to arterial blood line 6. The substituate can be a fluid prepared from the dialysing fluid during the treatment. The substituate can however also be a fluid prepared in the substituate source, for example a cooking salt solution.

(11) The device for detecting a recirculation comprises a control unit 17, which can be a component of the central control and computing unit of the blood treatment apparatus. Blood pump 8 and substituate pump 16 are connected via control lines 8, 16 to control unit 17 of the device for detecting the recirculation. The control unit switches pumps 8, 16 on and off and presets specific flow rates for the pumps.

(12) Moreover, the device for detecting the recirculation comprises a measuring unit 18 with an arterial pressure sensor 18A for measuring the pressure in arterial blood line 6 upstream of blood pump 8 and a venous pressure sensor 18B for measuring the pressure in venous blood line 7 downstream of the blood chamber of the dialyser. Arterial and venous pressure sensors 18A, 18B are connected via data lines 18A, 18B to measuring unit 18, and measuring unit 18 is connected via a data line 18 to an evaluation unit 19 of the device for detecting a recirculation, said evaluation unit being connected via a data line 19 again to control unit 17.

(13) Furthermore, the device for detecting the recirculation comprises an actuation unit 20 with an actuation element 20A, for example a pushbutton, and a signal unit 21, which comprises an optical and/or acoustic signal transmitter 21A. Actuation unit 20 and signal unit 21, which can also be a component of the blood treatment apparatus, are connected via control and data lines 20, 21 to control unit 17.

(14) Control unit 17 can be a data processing unit (microprocessor), on which a data processing program runs in order to execute the steps required for the performance of the method according to the present invention. The mode of functioning of the control unit is described in detail below. The control unit is configured (programmed) such that the individual components of the blood treatment apparatus are controlled as follows.

(15) During the blood treatment, blood pump 8 conveys the blood at a preset first blood flow rate Q.sub.b1, which can vary during the blood treatment. To initiate the recirculation test, actuation element 20A is actuated, for example the pushbutton is pressed. After pressing of the pushbutton, control unit 17 selects the operating mode for detecting the recirculation, so that blood pump 8 and substituate pump 16 are controlled for the administration of a substituate bolus with a reduced blood flow. Control unit 17 is configured (programmed) such that blood pump 8 conveys the blood within a preset time interval T at a reduced second blood flow rate Q.sub.b2. Control unit 17 calculates the difference between first blood flow rate Q.sub.b1 and second blood flow rate Q.sub.b2 and presets a rate for substituate rate Q.sub.s which corresponds to the difference between first and second blood flow rates Q.sub.b1, Q.sub.b2.

(16) FIG. 2 illustrates the selection of substituate rate Q.sub.s during the bolus administration for different flow rates. The blood flow rate is reduced from a value Q.sub.b1 to a minimum value Q.sub.b2=Q.sub.min, for example 50 ml/min. For a blood flow rate Q.sub.b1 before the bolus administration of 400 ml/min, a value of 350 ml/min results for example for substituate rate Q.sub.s during the bolus administration, from which the value of 400 ml again results as the sum Q.sub.G=Q.sub.s+Q.sub.b2.

(17) In the operating mode for recirculation detection, arterial and venous pressure sensor 18A, 18B of measuring unit 18 measures the pressure in arterial and venous blood line 6, 7, wherein evaluation unit 19 evaluates the pressure signals.

(18) FIG. 3 shows the measured time-related course of venous and arterial pressure p.sub.v (mbar) and p.sub.a (mbar). After the substituate bolus with a reduced blood flow, a pressure drop I by a specific amount is detected in venous blood line 7 and a pressure rise II is detected in arterial blood line 6 on account of the haemodilution, the latter being denoted by the symbols I and II. In this exemplary embodiment, the recirculation amounts to 20%. For comparison, FIG. 4 shows the time-related course of venous and arterial pressure p.sub.v (mbar) and p.sub.a (mbar) with a recirculation of 40%, whilst FIG. 5 shows the time-related course of venous and arterial pressure p.sub.v (mbar) and p.sub.a (mbar) when no recirculation is present. It can clearly be seen that an arterial pressure rise can be noted only in the case of the recirculation.

(19) The characteristic course of the pressure signal shown in FIGS. 3 to 5 is due to the changed viscosity of the blood. On account of the bolus administration, the viscosity of the blood in venous blood line 7 downstream of the blood chamber is increased on account of the supply of substituate. Consequently, a smaller pressure drop occurs at venous cannula 7a. The venous pressure thus drops. After the bolus administration, the viscosity of the blood in venous blood line 7 is reduced again, so that the venous pressure increases again. On account of the fistula recirculation, a part of the diluted blood passes via the fistula directly into arterial blood line 6, which leads to a reduction in viscosity, for which reason the pressure in the arterial blood line increases. Evaluation unit 19 concludes from the arterial pressure rise or venous pressure drop that a fistula recirculation is present. In this regard, evaluation unit 19 determines the amount of the pressure rise in arterial blood line 6 and compares the amount with a preset threshold value. Alternatively, evaluation unit 19 can also determine the amount of the pressure drop in venous blood line 7 and compares the amount with a preset threshold value. If the threshold value is exceeded with a significant change in the pressure, evaluation unit 19 generates a control signal which signals a recirculation. Signal unit 21 receives the control signal of evaluation unit 19 via control unit 17, so that signal transmitter 21A generates an acoustic and/or optical alarm. The doctor performing treatment can then take the necessary measures.

(20) The device according to the present invention also permits the determination of the recirculation. The ratio between the amount of the maximum change in the arterial pressure signal of the arterial pressure sensor and the amount of the maximum change in the venous pressure signal of the venous pressure sensor serves as a measure for the recirculation. The recirculation Rez [%] is calculated by the evaluation unit according to the following equation.

(21) The relationship between the obtained haematocrit change Hkt and the measured pressure change (p.sub.a and p.sub.v) on the venous and arterial side is however not linear. Moreover, there is a dependence on blood flow Q.sub.b, the geometry of the cannula, in particular its diameter, and the absolute haematocrit value. The device according to the present invention therefore preferably provides for a measurement under defined conditions, wherein Q.sub.b and Q.sub.s are constant, so that the recirculation Rez [%] can be determined according to the above equation with sufficient accuracy.

(22) In contrast with a measurement on the basis of a thickening instead of a thinning of the blood, the problem does not arise that the dialyser may become clogged up or blood clots may form in the hose system. Moreover, no effects from the cardiopulmonary recirculation on the measurement result appear with the measurement method according to the present invention due to the detection of the pressure change immediately after the haemodilution.