Device for extracorporeal blood treatment having an evaluation and control unit

Abstract

The invention relates to a blood treatment device having an extracorporeal blood circuit which comprises an arterial line, a blood pump, a blood treatment unit and a venous line, wherein the arterial and venous lines can be connected to a blood vessel of a patient, and wherein the blood treatment device has an evaluation and control unit, wherein the evaluation and control unit is configured to carry out the following steps: (a1) determining the blood recirculation in a blood vessel of the patient connected to the extracorporeal blood circuit; and (b) calculating the blood flow in the blood vessel using the blood recirculation determined in accordance with (a1) and using a provided value or a value likewise previously determined for the cardiac output of the patient.

Claims

1. A blood treatment device comprising: an extracorporeal blood circuit, which includes an arterial line, a blood pump, a blood treatment unit, and a venous line, the arterial and venous lines being connectable to a blood vessel of a patient, and an evaluation and control unit, the evaluation and control unit being configured to carry out the following steps: (a1) determining a blood recirculation in a blood vessel of the patient connected to the extracorporeal blood circuit; (b) calculating a blood flow in the blood vessel using the blood recirculation determined in accordance with (a1) and using a provided value or a value likewise previously determined for a cardiac output of the patient; and accounting for an extracorporeal blood flow and an outflow of fluid in the blood treatment device, in addition to the blood recirculation and the cardiac output, when determining the blood flow in step (b) for controlling operation of the blood treatment device.

2. The blood treatment device in accordance with claim 1, further comprising a blood pressure sensor; wherein the evaluation and control unit is configured to carry out the following step: (a2) determining the cardiac output of the patient by evaluating a time progression of a pressure pulse measured using the blood pressure sensor.

3. The blood treatment device in accordance with claim 1, further comprising a bolus sensor arranged in the arterial line of the extracorporeal blood circuit; wherein the evaluation and control unit is configured to carry out step (a1) in the following manner: (a1) determining the blood recirculation in a blood vessel of the patient connected to the extracorporeal blood circuit using a signal of the bolus sensor.

4. The blood treatment device in accordance with claim 1, wherein the evaluation and control unit is configured to define critical values for the recirculation for a normal and/or inverse connection of the arterial and venous lines to the blood vessel under an assumption that the blood flow in a corresponding vessel can achieve a specific portion of the cardiac output as a maximum.

5. The blood treatment device in accordance with claim 4, wherein the evaluation and control unit is configured to compare the determined recirculation with the critical values and to group the recirculation values based on the comparison.

6. The blood treatment device in accordance with claim 5, further comprising an output unit which communicates with the evaluation and control unit, wherein the output unit and the evaluation and control unit are configured to output a different signal to a user depending on the group association of the determined recirculation.

7. The blood treatment device in accordance with claim 5, wherein three groups are distinguished: (1) the determined recirculation is below the critical values for a normal connection; (2) the determined recirculation is above the critical value for a normal connection, but below the critical value for an inverse connection; and (3) the determined recirculation is above the critical value for an inverse connection.

8. The blood treatment device in accordance with claim 7, wherein the evaluation and control unit is configured such that, when the determined recirculation has been associated with group (2), a conveying performance of the blood pump is reduced and the carrying out of steps (a1) and (b) is repeated.

9. The blood treatment device in accordance with claim 1, wherein the evaluation and control unit is configured to output a warning signal when the calculated blood flow in a respective vessel exceeds an upper threshold value or falls below a lower threshold value.

Description

(1) Further details and advantages of the invention result from the following embodiment shown with reference to the Figures. There are shown in the Figures:

(2) FIG. 1: a schematic representation of an embodiment of a dialysis device in accordance with the invention;

(3) FIG. 2: a plot of critical values determined in accordance with the invention for the portion of recirculations R.sub.n and R.sub.x in a normal and inverse needle position in dependence on the cardiac output CO for extracorporeal blood flows of 200, 300 and 400 ml/min;

(4) FIG. 3: a plot of the relative error on the determination in accordance with the invention of the shunt flow Q.sub.a at a blood flow of 300 ml/min for values of Q.sub.a of 400 to 2000 ml/min;

(5) FIG. 4: a plot of the shunt flow Q.sub.a in dependence on CO at different values of the recirculation R.sub.x in an inverse needle position at an extracorporeal blood flow of 300 ml/min; and

(6) FIG. 5: a plot of the relative error on the determination of the shunt flow Q.sub.a with swapped over needles and with an extracorporeal blood flow of 300 ml/min.

THEORETICAL BACKGROUND

(7) The algorithm stored in the control unit of the dialysis device in accordance with the invention in accordance with the embodiment is based on the theoretical background explained below.

(8) The cardiopulmonary recirculation in hemodialysis patients with a cardiac output CO who are treated via a vessel access with a shunt flow Q.sub.a is defined as

(9) $\begin{matrix} CPR = \frac{Q_{a}}{CO} & Formula 1 \end{matrix}$

(10) According to Schneditz (1998), the shunt flow Q.sub.a can be determined with a known extracorporeal blood flow Q.sub.b and a UF rate O.sub.f by measuring the portion of recirculations R.sub.n and R.sub.x in a normal and inverse needle position. The following parameters are defined for this.

(11) $\begin{matrix} f_{n} = \frac{R_{n}}{1 - R_{n}}, f_{x} = \frac{R_{x}}{1 - R_{x}}, \tilde{Q} = Q_{b} - Q_{f} & Formula 2 \end{matrix}$

(12) The formula given by Schneditz (1998) herewith reads:

(13) $\begin{matrix} Q_{a} = \frac{1}{f_{x}} \frac{\tilde{Q}}{1 - CPR} mit CPR = \frac{f_{n}}{f_{X}} \frac{\tilde{Q}}{Q_{b}} & Formula 3 \end{matrix}$

(14) If the cardiac output is known Q.sub.a can be calculated with knowledge of only one of the values R.sub.n or R.sub.x.

(15) $\begin{matrix} Q_{a} = CO - \frac{\tilde{Q}}{f_{n}} & Formula 4 \\ Q_{a} = \frac{CO}{2} - \sqrt{{(\frac{CO}{2})}^{2} - \frac{{\tilde{Q}}^{2}}{Q_{b}} \frac{CO}{f_{x}}} & Formula 5 \end{matrix}$

(16) The error of the determination of Q.sub.a from CO and R.sub.n can be estimated as follows according to the law of error propagation.

(17) $\begin{matrix} σ_{Q_{a}} = \sqrt{σ_{CO}^{2} + \frac{{(1 - R_{n})}^{2}}{R_{n}^{2}} σ_{\tilde{Q}}^{2} + {(\frac{\tilde{Q}}{R_{n}^{2}})}^{2} σ_{R_{n}}^{2}} & Formula 6 \\ σ_{Q_{a}} = \frac{1}{2} \sqrt{\begin{matrix} {(1 - \frac{\frac{1}{2} CO - \frac{(1 - R_{x}) \tilde{Q}}{R_{x}}}{W})}^{2} σ_{CO}^{2} + \\ {(\frac{(1 - R_{x}) CO}{R_{x} W})}^{2} σ_{\tilde{Q}}^{2} + {(\frac{\tilde{Q} CO}{R_{x}^{2} W})}^{2} σ_{R_{x}}^{2} \end{matrix}} mit W = \sqrt{{(\frac{CO}{2})}^{2} - \frac{\tilde{Q} CO}{f_{x}}} & Formula 7 \end{matrix}$

(18) It follows from formula 4 or formula 5.

(19) $\begin{matrix} R_{n} = \frac{\tilde{Q}}{\tilde{Q} + CO - Q_{a}}, R_{x} = \frac{\frac{{\tilde{Q}}^{2}}{Q_{b}}}{\frac{{\tilde{Q}}^{2}}{Q_{b}} + Q_{a} - \frac{Q_{a}^{2}}{CO}} & Formula 8 \end{matrix}$

(20) Under the physiologically founded assumption that the shunt flow Q.sub.a can reach as a maximum 50% of the cardiac output CO, critical values result for R.sub.n and R.sub.x which cannot be exceeded or fallen below in a measurement of the recirculation.

(21) $\begin{matrix} R_{n, crit} = \frac{1}{1 + \frac{1}{2} \frac{CO}{\tilde{Q}}}, R_{x, crit} = \frac{1}{1 + \frac{1}{4} \frac{Q_{b}}{{\tilde{Q}}^{2}} CO} & Formula 9 \end{matrix}$

(22) The measurement of the shunt flow is desired for various reasons. It is also important to recognize dangerously high shunt flows (steal syndrome) in addition to low shunt flows. In accordance with the present idea, the shunt flow Q.sub.a is therefore calculated as Q.sub.a=CO−Q.sub.b/f.sub.n, where f.sub.n=R.sub.n/1−R.sub.n. R is the recirculation fraction here and Q.sub.b the extracorporeal blood flow. The cardiac output CO and the recirculation are determined experimentally. Dangerously high shunt flows can thus be recognized without disposable and without any intervention of the user. The concept also manages without the introduction of a bolus in one embodiment. With swapped over needles, a more accurate determination is also conceivable with low shunt flows due to the higher recirculation.

(23) The determination of the cardiac output can, for example, take place using the formula
CO=(MAP−CVP)/R.sub.P,

(24) where MAP is the mean arterial blood pressure, CVP is the central venous pressure and R.sub.P is the peripheral resistance. This method, which works according to the principle of “flow=pressure/resistance”, is used, for example, in the commercial available Vicorder devices of the company SMT medical GmbH. The central venous pressure can in this respect, for example, be measured or estimated using a central venous catheter and can be input manually and the peripheral resistance can be determined from the falling flank of a pulse curve.

EMBODIMENT

(25) A schematic representation of an embodiment of a dialysis device in accordance with the invention is shown in FIG. 1.

(26) The dialysis device is generally marked by the reference numeral 1 in the Figure. It has an extracorporeal blood circuit 2 which comprises in a known manner an arterial line 3 having a blood pump 4, a dialyzer 5 and a venous line 6. The arterial line 3 and the venous line 6 are connected to a vessel 9 of a patient 10 by an arterial needle 7 or by a venous needle 8.

(27) A semipermeable membrane 11 which separates the blood chamber 12 from the dialyzing fluid chamber 13 within the dialyzer 5 is arranged within the dialyzer 5. The arterial and venous lines 3 and 6 of the extracorporeal blood circuit 2 are connected to the blood chamber 12. A dialyzing fluid system 14 is connected to the dialyzing fluid chamber 13 and comprises an apparatus 15 for preparing a dialyzing fluid, a feed line 16 to the dialyzer 5 and an out line 17 from the dialyzer 5. An ultrafiltration pump, not shown in the Figure, can be arranged in the out line 17.

(28) The directions of flow of the blood in the extracorporeal blood circuit 2 and of the dialyzing fluid in the dialyzing fluid system 14 are shown by arrows in the Figure.

(29) The dialysis device 1 furthermore comprises an evaluation and control unit 18 and an output unit 19.

(30) Temperature sensors 20 and 21 respectively are arranged close to the respective needles both at the arterial line 3 and at the venous line 6.

(31) The device 1 furthermore comprises means, not shown in the Figure, for varying the blood temperature in the venous blood line. These means can, for example, comprise the temperature of the dialyzing fluid produced in the apparatus 15 being varied according to the demand of the evaluation and control unit 18 with the aim of a change in the blood temperature. Alternatively, the change in the blood temperature can e.g. also take place by Peltier elements attached to the blood hose system.

(32) Finally, the device 1 comprises a sensor 22 to measure a pulse pressure curve progression of the patient which is suitable to determine CO, e.g. by a cuff on the upper arm. The sensor is connected to the control and evaluation unit 18 in a manner not shown in the Figure.

(33) In operation of the apparatus, the blood pump 4 sucks in blood from the vessel 9 of the patient via the arterial needle 7 into the arterial line 3 of the extracorporeal blood circuit 2 and subsequently pumps the blood through the dialyzer 5, the venous line 6 and the venous needle 8 back into the vessel 9 of the patient 10. After administering a temperature bolus, the temporal temperature progression of the removed and returned blood is measured at the sensors 20 and 21 and the measured values are transferred to the evaluation and control unit 18. The recirculation R is then determined in the evaluation and control unit 18 as described in Schneditz (2003). Furthermore, the cardiac output is determined by means of oscillometric blood pressure measurements at the blood pressure sensor.

(34) Alternatively, the cardiac output can be estimated with a known stroke volume V.sub.co originating, for example, from echocardiogram examinations or estimated as a typical value of 70 ml, by measuring the heart rate v, by means of CO=v.Math.V.sub.co.

(35) After determining R and CO and with a known conveying rate of the blood pump 4 and ultrafiltration rate, the calculations presented above in more detail are now carried out in the evaluation and control unit 18 for determining the blood flow in the vessel 9 of the patient 10. The results can, for example, be output at the output unit 19, can be transferred via any desired manner of communication such as via a network, and/are can be used automatically for the control of the device 1.

(36) Interpretation and Use of the Results:

(37) The results can be interpreted or used in the manner described in the following.

(38) If the cardiac output CO is measured or estimated close in time to the measurement of the recirculation R, critical values R.sub.n,crit and R.sub.x,crit for the recirculations R.sub.n and R.sub.x can be calculated in accordance with formula 9 in normal and inverse needle positions together with the known values for the extracorporeal blood flow and the UF rate, and R can be compared with these values. FIG. 2 shows the critical values for R.sub.n and R.sub.x calculated according to formula 9 in dependence on the cardiac output CO for extracorporeal blood flows of 200, 300 and 400 ml/min.

(39) The critical values can, however, also be determined or predefined in another manner in a further embodiment of the invention.

(40) Different cases can be distinguished which allow different conclusions.

(41) If R<R.sub.n,crit, only cardiopulmonary recirculation is present. The shunt flow is therefore larger than the extracorporeal blood flow; the arterial and venous needles are correctly punctured and connected to the hose system. The user can be informed of this in any desired manner by means of the output unit 19.

(42) The shunt flow Q.sub.a can furthermore be estimated using formula 4. FIG. 3 shows the relative error in the determination of Q.sub.a calculated according to formula 6 with a blood flow of 300 ml/min under the assumption of an error in the recirculation measurement of ±1% and the determination of CO and of Q.sub.b of ±10% for values of Q.sub.a of 400 to 2000 ml/min. It becomes clear from this that the measurement accuracy is very restricted with low Q.sub.a values. It is nevertheless ensured that Q.sub.a>Q.sub.b in every case. Since the relative error for high shunt flows falls, the determination of Q.sub.a can be used to be able to recognize dangerously high shunt flows. Shunt flows>2000 ml/min put a strain on the heart of the patient, which results in increased mortality. At the same time, they result in a lack of circulation of the limbs distal of the vessel access (typically close to the wrist), i.e. in particular of the hand and fingers, which can result in damage to them and in impairments of the patient. A warning of too high a shunt flow can therefore be generated on the basis of a shunt flow determined from R.sub.n and CO. If too low a shunt flow of <600 ml/min or too high a shunt flow is detected using the described method, the user can be prompted now to swap over the needles for a more accurate determination of the shunt flow, which is advantageously then easily possible if a disposable is already present for this purpose. Q.sub.a can then be determined more accurately in accordance with formula 3 from the determination of R.sub.x; the determination of R.sub.n and CO would then only serve as pre-screening.

(43) If R>R.sub.x,crit, the vessel recirculation is so high that a swapping over of the arterial and venous needles is likely with a high probability. The user can also be informed of this in any desired manner by means of the output unit 19.

(44) FIG. 4 shows a plot of the shunt flow Q.sub.a in dependence on CO at different values of R.sub.x in accordance with formula 5 with an extracorporeal blood flow of 300 ml/min. It can be recognized from this that the shunt flow can be determined solely from the measured recirculation R.sub.x with swapped over needles, in particular at low shunt flows (<800 ml/min) and that the value of the CO only slightly influences the value of the shunt flow when Q.sub.a<¼ CO. This can also be recognized in FIG. 5 where the relative error in the determination of Q.sub.a in accordance with formula 7 was plotted with an extracorporeal blood flow of 300 ml/min. The shunt flow can thus be determined solely by measurement of the recirculation with swapped over needles with only an imprecise knowledge of CO without requiring a recirculation measurement in a normal needle orientation. The time required for determining the shunt flow can thus be considerably reduced. The needle swapping generally has to take place manually by the user while using a corresponding disposable. In the event of an already incorrectly present needle swapping, the shunt flow can immediately be given by means of formula 5 once a needle swap has been recognized from the measurement of the recirculation and of the CO.

(45) If R.sub.n,crit<R<R.sub.x,crit, there is a partial recirculation between the arterial and the venous needle, which can arise due to an unfavorable positioning of the needles (e.g. too close to one another). Alternatively, the extracorporeal blood flow can exceed the shunt flow. Provision can be made that the evaluation and control unit 18 is configured for distinguishing these two scenarios such that a recirculation measurement is carried out automatically with a reduced blood flow Q.sub.b′ and the values are determined again. If the value R′ then determined is below R′.sub.n,crit, Q.sub.a is between Q.sub.b′ and Q.sub.b.

(46) It results in summary that the present invention provides a possibility of recognizing a shunt flow which is above all excessively high. A very high shunt flow is medically undesirable. In accordance with the invention, the recirculation is determined, for example, by administering a temperature bolus and the cardiac output is determined, for example, by an oscillometric blood pressure measurement. The shunt flow is calculated from both using formula 4. Said shunt flow can above all be determined with a relatively small error at very high flows. The invention furthermore allows the determination of two limit values of the recirculation and the derivation of corresponding conclusions. A further aspect of the invention in particular deals with the comparison of the recirculation with limit values and with the derivation of conclusions in isolation from how the limit values are determined.

Device for extracorporeal blood treatment having an evaluation and control unit

Assignee

Inventors

Cpc classification

Classification Explorer

A61M2205/3382

HUMAN NECESSITIES

Classification Explorer

A61M2230/30

HUMAN NECESSITIES

Classification Explorer

A61M1/3658

HUMAN NECESSITIES

Classification Explorer

A61M1/3623

HUMAN NECESSITIES

Classification Explorer

A61M2230/50

HUMAN NECESSITIES

Classification Explorer

A61M2205/3334

HUMAN NECESSITIES

Classification Explorer

A61M2205/3386

HUMAN NECESSITIES

International classification

Classification Explorer

A61M1/36

HUMAN NECESSITIES

Abstract

Claims

Description