Dialysis machine and method of correcting the blood flow value

Abstract

The invention relates to a dialysis machine having an extracorporeal blood circuit in which a dialyzer, a blood pump, and an arterial pressure sensor are arranged, wherein the dialysis machine furthermore has a compensation device by means of which the set value for the blood flow through the extracorporeal circuit can be corrected to a compensated value using the arterial blood pressure; wherein the dialysis machine furthermore has recognition means which are configured to recognize whether the arterial pressure sensor is connected to the extracorporeal blood circuit or not; and wherein the dialysis machine has an estimator unit which is configured to estimate a value for the arterial blood pressure if it is recognized by the recognition means that the arterial pressure sensor is not connected to the extracorporeal blood circuit.

Claims

1. A dialysis machine having an extracorporeal blood circuit (1) in which a dialyzer (6), a blood pump (3) and an arterial pressure sensor (1a) are arranged, wherein the dialysis machine furthermore has a compensation device by means of which the value set for the blood flow (Q.sub.b,set) can be corrected to a compensated value (Q.sub.b) by the extracorporeal circuit (1) using the arterial blood pressure (P.sub.a), characterized in that the dialysis machine furthermore has detection means which are configured to recognize whether the arterial pressure sensor (1a) is connected to the extracorporeal blood circuit (1) or not; and in that the dialysis machine has an estimator unit which is configured to estimate a value for the arterial blood pressure (P.sub.a) if it is recognized by the recognition means that the arterial pressure sensor (1a) is not connected to the extracorporeal blood circuit (1).

2. A dialysis machine in accordance with claim 1, characterized in that the dialysis machine is configured such that a pressure return line (1c) can be connected which connects the arterial pressure sensor (1a) to the extracorporeal blood circuit (1) in the connected state; and in that the recognition means are configured to recognize whether the pressure return line (1c) is connected or not.

3. A dialysis machine in accordance with claim 1, characterized in that the compensation device is configured to determine the value for the compensated blood flow (Q.sub.b) in [ml/min] in accordance with equation (1):
Q.sub.b=Q.sub.b,set(α+β*P.sub.a)  (1), where α adopts the value 1.0 and β adopts the value 0.00057 and P.sub.a is used as a value in [mmHg].

4. A dialysis machine in accordance with claim 1, characterized in that the estimator unit is configured to estimate the arterial blood pressure (P.sub.a) to a constant value, preferably to the value −200 mmHg; and/or in that the estimator unit is configured to estimate the arterial blood pressure (P.sub.a) in dependence on the blood flow (Q.sub.b,set) set by the user, with a memory or a calculation unit being provided in which a relationship is stored between the arterial blood pressure (P.sub.a) and the blood flow (Q.sub.b,set) set by the user, with provision preferably being made that the estimator unit is configured such that a property of the used dialysis cannula and/or the hematocrit value (HKT) of the blood is taken into the named relationship as a further parameter.

5. A dialysis machine in accordance with claim 1, characterized in that the estimator unit is configured to estimate the arterial blood pressure (P.sub.a) in dependence on the venous blood pressure (P.sub.v) in the extracorporeal blood circuit, with provision preferably being made that the estimator unit is configured to determine the arterial blood pressure (P.sub.a) in [mmHg] in accordance with one of the relationships (P.sub.v: venous blood pressure in the extracorporeal circuit; MAP: mean blood pressure; P.sub.f,v, fistula pressure/shunt pressure at the point of the venous dialysis needle)
P.sub.a=0.35*MAP−P.sub.v  (2)
P.sub.a=2.33*P.sub.f,v−P.sub.v  (3)
P.sub.a=0.90*MAP−P.sub.v  (4)
P.sub.a=2.57*P.sub.f,v−P.sub.v  (5), with equations (2) and (3) being applied for the use of a fistula and equations (4) and (5) being applied for the use of a shunt.

6. A dialysis machine in accordance with claim 5, characterized in that the dialysis machine has a computation unit for determining P.sub.f,v; and in that this computation unit is configured to open a venous pressure clamp (12) after the introduction of blood into the extracorporeal circuit up to the venous pressure sensor and then to measure the venous blood pressure (P.sub.v0) with an idling blood pump; and in that the computation unit is configured to determine the value for P.sub.f,v in [mmHg] as follows:
P.sub.f,v=P.sub.v0+14.72  (6).

7. A dialysis machine in accordance with claim 1, characterized in that the recognition means are configured to determine the pressure signal detected by means of the arterial pressure sensor (1a), to carry out an ongoing mean value formation and variance calculation over a specific period in time and to draw a conclusion on the presence or absence of the connection of the arterial pressure sensor (1a) to the extracorporeal blood circuit (1) with reference to the evaluation of the mean value and the variance value.

8. A dialysis machine in accordance with claim 1, characterized in that the recognition means are configured to determine the pressure signal detected by means of the arterial pressure sensor (1a), to start the blood pump and to stop it again, to determine the change of the arterial blood pressure (P.sub.a) and, based on this, to draw a conclusion on the presence or absence of the connection of the arterial pressure sensor (1a) to the extracorporeal blood circuit (1).

9. A method of correcting a set value for the blood flow (Q.sub.b,set) using the arterial blood pressure (P.sub.a) to a compensated value (Q.sub.b) in a dialysis machine having an extracorporeal blood circuit (1) in which a dialyzer (6), a blood pump (3) and an arterial pressure sensor (11) are arranged, characterized in that a detection is made whether the arterial pressure sensor (11) is connected to the extracorporeal circuit (1) or not; and in that a value is estimated for the arterial blood pressure (P.sub.a) if it is found that the arterial pressure sensor (11) is not connected to the extracorporeal circuit (1).

10. A method in accordance with claim 9, characterized in that the value for the compensated blood flow (Q.sub.b) is determined in [ml/min] in accordance with equation (1):
Q.sub.b=Q.sub.b,set(α+β*P.sub.a)  (1), where α adopts the value 1.0 and β adopts the value 0.00057 and P.sub.a is used as a value in [mmHg].

11. A method in accordance with claim 9, characterized in that the arterial blood pressure (P.sub.a) is estimated to a constant value, preferably to the value −200 mmHg; and/or in that the arterial blood pressure (P.sub.a) is estimated in dependence on the blood flow (Q.sub.b,set) set by the user, with a relationship between the arterial blood pressure (P.sub.a) and the blood flow (Q.sub.b,set) set by the user being retrievably stored, with provision preferably being made that a property of the dialysis cannula used and/or the hematocrit value (HKT) of the blood is taken into the named relationship as a further parameter.

12. A method in accordance with claim 9, characterized in that the arterial blood pressure (P.sub.a) is estimated in dependence on the venous blood pressure (P.sub.v) in the extracorporeal circuit, with provision preferably being made that the arterial blood pressure (P.sub.a) is determined in [mmHg] in accordance with one of the relationships (P.sub.v: venous blood pressure in the extracorporeal circuit; MAP: mean blood pressure; P.sub.f,v: fistula pressure/shunt pressure at the point of the venous dialysis needle)
P.sub.a=0.35*MAP−P.sub.v  (2)
P.sub.a=2.33*P.sub.f,v−P.sub.v  (3)
P.sub.a=0.90*MAP−P.sub.v  (4)
P.sub.a=2.57*P.sub.f,v−P.sub.v  (5), with equations (2) and (3) being applied for the use of a fistula and equations (4) and (5) being applied for the use of a shunt.

13. A method in accordance with claim 12, characterized in that P.sub.f,v is determined, with a venous pressure clamp (12) being opened after the introduction of blood into the extracorporeal circuit up to the venous pressure sensor and the venous blood pressure (P.sub.v0) the being measured with an idling blood pump; and in that the value for P.sub.f,v is then determined in [mmHg] as follows:
P.sub.f,v=P.sub.v0+14.72  (6).

14. A method in accordance with claim 9, characterized in that, for the recognition of the present or absent connection of the arterial pressure sensor (1a) at the extracorporeal circuit (1), the pressure signal detected by the arterial pressure sensor (1a) is determined, an ongoing mean value formation and variance calculation is carried out over a specific time period, and a conclusion is drawn on the presence or absence of the connection of the arterial pressure sensor (1a) at the extracorporeal circuit (1) with reference to the evaluation of the mean value and the variance value.

15. A method in accordance with claim 9, characterized in that, for recognizing the presence or absence of the arterial pressure sensor (1a) at the extracorporeal circuit (1), the pressure signal detected by the arterial pressure sensor (1a) is determined, the blood pump is started and stopped again, the change of the arterial blood pressure (P.sub.a) is determined and, based on this, a conclusion is drawn on the presence or absence of the arterial pressure sensor (1a) at the extracorporeal circuit (1); and/or in that a pressure return line (1c) can be connected which connects the arterial pressure sensor (1a) to the extracorporeal blood circuit (1) in the connected state; and in that the recognition of the presence or absence of the connection of the arterial sensor (1a) at the extracorporeal circuit comprises a recognition being made whether the pressure return line (1c) is connected or not.

Description

(1) This embodiment of the invention will be explained in more detail with reference to the single FIGURE which represents an extracorporeal blood circuit of a hemodialysis machine in accordance with the invention.

(2) In this respect, the reference numeral 16 designates the blood port which can be configured as a fistula or as a shunt and reference numerals 15a and 15b designate the arterial needle and the venous needle.

(3) The blood moves from the arterial needle 15a through the blood hose 14 over the arterial pressure return line 1c to the arterial TP having the reference numeral 1b to which the arterial pressure sensor 1a is connected for measuring the arterial pressure P.sub.a. The blood pump 3 is located downstream thereof and the heparin pump 4 is located downstream of the blood pump. The arterial bubble trap 5 is located between the heparin pump 4 and the dialyzer.

(4) The dashed line in 1b represents the transition from the hose system to the dialysis machine. The pressure return line is connected to the pressure sensor there, e.g. by a Luer lock connection.

(5) The dialyzer is designated by the reference numeral 6 and is divided by a semipermeable membrane 7, preferably by a hollow fiber bundle, into a dialyzate chamber and a blood chamber, wherein the dialyzate infeed 8 and the dialyzate outfeed 9 are connected to the dialyzate chamber.

(6) The venous drip chamber 10 having a level detector 11 is located downstream of the dialyzer 6. The venous pressure return line 2c, which is in communication with the venous pressure sensor having the reference numeral 2a for measuring the venous blood pressure P.sub.v is connected to the venous drip chamber 10. The venous TP having the reference numeral 2b is introduced into the venous pressure return line.

(7) A venous clamp 12, by means of which the blood hose can be blocked and the optical detector 13 for recognizing air bubbles in the blood are located downstream of the venous drip chamber 10.

(8) The blood moves back into the fistula or into the shunt 16 via the venous needle 15b.

(9) It will now be shown in the following how a conclusion can be drawn on the arterial blood pressure P.sub.a with reference to the venous blood pressure P.sub.v which can e.g. be measured in or at the venous drip chamber 10.

(10) Q.sub.b=(P.sub.f,a−P.sub.a)/R.sub.a applies to the arterial side of the extracorporeal blood circuit analogously to Ohm's law. If this equation is resolved for P.sub.a,
P.sub.a=P.sub.f,a−Q.sub.b*R.sub.a  (2′)
results. Q.sub.b−Q.sub.UF=(P.sub.v−P.sub.f,v)/R.sub.v results at the venous side of the extracorporeal blood circuit.

(11) If this equation is resolved for the venous pressure:
P.sub.v=(Q.sub.b−Q.sub.UF)*R.sub.v+P.sub.f,v  (3′)
results. If equations (2′) and (3′) are added:
P.sub.a+P.sub.v=Q.sub.b*(R.sub.v−R.sub.a)+(P.sub.f,a+P.sub.f,v)−Q.sub.UF*R.sub.v  (4′)
results. Within the framework of the present invention: P.sub.f is the fistula pressure, P.sub.f,a is the fistula pressure at the point of the arterial dialysis needle, P.sub.f,v is the fistula pressure at the point of the venous dialysis needle, P.sub.a is the arterial pressure before the blood pump, P.sub.v is the venous pressure at the venous drip chamber, P.sub.v,0 is the measured venous pressure on a stop of the blood pump and with an open venous clamp, Q.sub.b,set is the set blood flow, Q.sub.b is the compensated blood flow, Q.sub.UF is the ultrafiltration rate, R.sub.a is the flow resistance between the arterial pressure return line 1c and the tip of the arterial needle, R.sub.v is the flow resistance between the venous drip chamber and the tip of the venous needle, and MAP is the mean measured arterial blood pressure of the dialysis patient.

(12) The length of the arterial hose section between the arterial pressure return line and the arterial needle connector is almost identical to the length of the venous hose section between the venous drip chamber and the venous needle connector. This length can amount to approximately 190 cm, for example. When taking account of the fact that arterial and venous needles of the same type are used in a routine analysis, e.g. 16 G, the flow resistances of the above-named hose sections are also almost identical, that is R.sub.a=R.sub.v applies in equation (4′). It results from this:
P.sub.a=(P.sub.f,a+P.sub.f,v)−Q.sub.UF*R.sub.v−P.sub.v  (5′)

(13) The ultrafiltration rate Q.sub.UF is relatively small in the dialysis. If this value is neglected or if P.sub.a is measured with a switched-off ultrafiltration, the following relationship results from equation (5′):
P.sub.a=(P.sub.f,a+P.sub.f,v)−P.sub.v  (6′)

(14) The pressures in the shunt or in the fistula can be estimated as follows:

(15) It applies to the case of the fistula:
P.sub.f,a=0.20*MAP
P.sub.f,v=0.15*MAP
P.sub.f,a=1.33*P.sub.f,v

(16) The following relationships apply to the shunt:
P.sub.f,a=0.55*MAP
P.sub.f,v=0.35*MAP
P.sub.f,a=1.57*P.sub.f,v

(17) It results from this from equation (6′) in the fistula case
P.sub.a=0.35*MAP−P.sub.v  (7′)
and
P.sub.a=2.33*P.sub.f,v−P.sub.v  (8′)

(18) It results from equation (6′) in the shunt case
P.sub.a=0.90*MAP−P.sub.v  (9′)
and
P.sub.a=2.57*P.sub.f,v−P.sub.v  (10′)

(19) It is obligatory in hemodialysis to measure the blood pressure of a patient. The mean arterial blood pressure MAP in equations (7′) and (9′) is therefore known. This MAP value can either be determined automatically by a blood pressure monitor (BPM) integrated into the dialysis machine or can be input manually via the user interface. In these cases, the sought value P.sub.a can be determined with a measured P.sub.v in accordance with equation (7′) or in accordance with equation (9′).

(20) As can be seen from the equations (8′) and (10′), the value P.sub.f,v is required for determining P.sub.a in these cases and P.sub.f,v can be determined in a further preferred embodiment by the relationship P.sub.f,v=P.sub.v0+14.72.

(21) This relationship results as follows:

(22) After the connection of the patient to the extracorporeal blood circuit, the blood pump is started and the patient blood is conveyed into the extracorporeal blood circuit. As soon as the optical detector recognizes the blood at the venous drip chamber, the blood pump is stopped and the venous clamp 12 is closed. The user is subsequently asked whether the dialysis treatment should be started. If the venous clamp is briefly opened in this case, the venous pressure is measured as P.sub.v0.

(23) While taking account of the hydrostatic pressure between the fistula port at the patient's arm and the venous pressure return line 2c, the value for P.sub.f,v is calculated in accordance with
P.sub.f,v=P.sub.v0+r*g*H  (11)

(24) Here, r is the water density and amounts to 1000 kg/m.sup.3, H is the height difference between the fistula port and the venous pressure return line 2c, e.g. 20 cm, and g is the acceleration due to gravity (9.81 m/s.sup.2). It results for the fistula from equations (8′), (10′) and (11′)
P.sub.a=2.33*(P.sub.v0+r*g*H)−P.sub.v  (12′)
and for the shunt
Pa=2.57*(P.sub.v0+r*g*H)−P.sub.v  (13′)

(25) With a height difference of 0.2 m, it results therefrom:
r*g*H=1000*9.81*0.2=14.72mmHg.

(26) If this value is used in equation (11′), the named relationship results, that is
P.sub.f,v=P.sub.v0+14.72[mmHg]  (14′)

(27) With knowledge of this value and of the venous blood pressure, the value P.sub.a can be determined from equations (8′) and (10′).

(28) Provision is made in a further embodiment of the invention that the recognition means are configured to determine the signal detected by means of the arterial pressure sensor, to carry out an ongoing mean value formation and variance calculation over a specific time period, e.g. over a minute, and to draw a conclusion on the presence or absence of a connected arterial pressure sensor with reference to the evaluation of the mean value and the variance value. The lack of this connection can be due to the fact, for example, that the arterial pressure return line (having the TP located therein) is not inserted so that the arterial pressure sensor cannot measure the pressure in the extracorporeal blood circuit.

(29) Provision is made in an alternative or additionally usable embodiment that the recognition means are configured to determine the pressure signal detected by means of the arterial pressure sensor, to start and to stop the blood pump while the blood hose system is filled, to determine and to evaluate the signal change of the arterial blood pressure and, based on this, to draw a conclusion on the absence or presence of the arterial pressure return line or of the connection of the arterial pressure sensor.

(30) If no connected pressure sensor is recognized, the blood flow compensation is carried out with the aid of the above-described method, wherein equation (1) is preferably used, where a value estimated in accordance with the invention is used for P.sub.a.

(31) Otherwise, the measured value is used for P.sub.a.

(32) The present invention furthermore relates to a method of correcting a set value for the blood flow using the arterial blood pressure to a compensated value in a dialysis machine having an extracorporeal blood circuit in which a dialyzer, a blood pump and an arterial pressure sensor are arranged, with it being detected whether the pressure sensor is connected to the extracorporeal circuit or not and with a value for the arterial blood pressure being estimated if it is found that this is not the case. In this respect, the value for the compensated blood flow can be determined in accordance with the above equation (1).

(33) The arterial blood pressure can be estimated to a constant value such as to the value −200 mmHg. It is also possible to estimate the arterial blood pressure in dependence on the blood flow set by the user, with a corresponding relationship between the arterial blood pressure and the set blood flow being stored by software or in a memory or by a computation unit. In this respect, further parameters can play a role, in particular the kind of dialysis cannula used and in particular its outer diameter and/or the measured or entered hematocrit value of the blood.

(34) It is also conceivable, as stated above, that the arterial blood pressure is estimated in dependence on the venous blood pressure in the extracorporeal circuit.

(35) It is conceivable in this respect that the following relationships are used:
P.sub.a=0.35*MAP−P.sub.v,
P.sub.a=2.33*P.sub.f,v−P.sub.v
or
P.sub.a=0.90*MAP−P.sub.v,
P.sub.a=2.57*P.sub.f,v−P.sub.v

(36) We refer to the above statements with respect to the derivation of these relationships. Provision is made in a further embodiment of the method that the value P.sub.f,v is calculated after blood has been introduced into the extracorporeal circuit up to the venous pressure sensor, that the venous pressure clamp is then opened, and the venous blood pressure P.sub.v0 is then measured with an idling blood pump. The value of P.sub.f,v then results from the relationship P.sub.f,v=P.sub.v0+14.72. We likewise refer to the above statements for the determination of this equation.

(37) Provision is made in a further embodiment of the method that the pressure signal detected by the arterial pressure sensor is determined for the recognition of the presence or absence of the connection of the arterial pressure sensor and a check is made with reference to an ongoing mean value formation and variance calculation over a certain time period whether the pressure sensor is connected or not. It is also conceivable to determine the pressure signal detected by the arterial pressure sensor while the blood pump is being started and stopped again. The pressure signal provides conclusions on the presence or absence of the connection of the arterial pressure sensor or of the arterial pressure return line.

(38) It is generally conceivable that the recognition whether the pressure sensor is connected is based on the fact that the pressure sensor does not measure any pressure fluctuations although the blood pump is running or that a pressure pulse is output by the blood pump which is not measured at the pressure sensor.

(39) Further details and advantages of the invention will be explained in more detail with reference to an embodiment described in the drawing and in the following.

(40) The only FIGURE shows an extracorporeal blood circuit which is connected via a venous needle and via an arterial needle to a fistula or to a shunt of the patient.

(41) An input is first made via a user interface of the dialysis machine which is not shown in the drawing and in which the extracorporeal blood circuit in accordance with the FIGURE is inserted whether the blood port is a fistula or a shunt. The input of the measured MAP, that is of the mean blood pressure of the patient, then takes place.

(42) From the time of the blood recognition by the optical detector 13 onward the values for P.sub.a and P.sub.v are evaluated in segments, e.g. every two minutes, to recognize a non-connected pressure sensor or pressure return line. If it is recognized that both pressure sensors or pressure return lines are connected, that is the arterial and the venous pressure sensors or return lines, the blood flow is compensated in accordance with equation (1), where the measured arterial blood pressure is used for P.sub.a.

(43) If it is found that neither of the pressure sensors, that is neither the venous pressure sensor nor the arterial pressure sensor, is connected, a warning is output which prompts the user to connect both pressure sensors. If it is found that the venous pressure sensor is connected, but not the arterial pressure sensor, a warning is output which prompts the user also to connect the arterial pressure sensor. If this is not done, the method continues as follows.

(44) The venous pressure of the blood in the extracorporeal circuit, that is P.sub.v, is measured with a running blood pump during the normal dialysis treatment. The formation of an ongoing mean value of P.sub.v then takes place.

(45) In accordance with equation (7′) or in accordance with equation (9′), the calculation, that is the estimation of P.sub.a, takes place for the fistula or for the shunt. Based on these values, the value for the compensated blood flow, that is Q.sub.b, can then be determined by means of equation (1).

(46) It is conceivable in this respect that this value is restricted to the range
0.85Q.sub.b,set≤Q.sub.b≤Q.sub.b,set

(47) The compensation process is preferably only carried out for the active dialysis phase, that is when blood is recognized in the system, the blood pump is running and the dialysis is alarm-free. A compensation in the phase of preparation and of reinfusion is admittedly conceivable, but not necessary in principle.

(48) It is finally pointed out that the term “one” used within the framework of the invention covers a single one of the respective elements, but also a plurality of these elements, i.e. is not necessarily to be equated as “one/one single”.