Method and system for monitoring the operation of a medical device for extracorporeal blood treatment

Description

[0001] The invention relates to a method for monitoring the operation of a medical device for extracorporeal blood treatment, a monitoring system for a medical device for extracorporeal blood treatment and a medical device for extracorporeal blood treatment with such a monitoring system.

[0002] Extracorporeal blood treatments usually take place as part of renal replacement therapy, for example in the form of hemodialysis, hemofiltration or hemodiafiltration.

[0003] Typical devices for extracorporeal blood treatment comprise a blood treatment unit with a blood chamber, a treatment chamber, and a semipermeable membrane arranged between the two chambers. During operation, the patient's blood flows through the blood chamber. A treatment fluid flows through the treatment chamber. Urinary fluid is removed from the blood flowing through the blood chamber via the semipermeable membrane and transported away with the treatment fluid. The amount of fluid removed from the blood per unit of time is referred to as the ultrafiltration rate or filtration volume flow. The filtration volume flow can be adjusted on the medical device, for example, by controlling a filtration pump that conveys the treatment fluid.To transport blood between the patient and the blood treatment unit, conventional medical devices have an arterial fluid line and a venous fluid line. The arterial fluid line is connected at one end to an inlet of the blood chamber and the other end to a patient's arterial vascular access. The venous fluid line is connected at one end to an outlet of the blood chamber and the other end to a fluid-conducting connection to a patient's venous vascular access. The blood-carrying components of the medical device, in particular the blood chamber and the aforementioned fluid lines, are also referred to as the extracorporeal blood circuit. Conventional medical devices have a pump for conveying blood along the extracorporeal blood circuit. The pump's pumping volume flow is adjustable and typically ranges from several hundred milliliters per minute.The connection of the extracorporeal blood circuit with the patient's blood circuit is usually made via corresponding cannulas or catheters, which are / can be attached to the other end of the said fluid lines and with which an arteriovenous fistula or a vascular implant of the patient can be punctured.

[0004] Disturbances or even interruptions of blood flow in the extracorporeal blood circuit and / or its connection to the bloodstream can endanger the patient.

[0005] Methods and systems for monitoring the operation of medical devices for extracorporeal blood treatment are therefore known from the state of the art.

[0006] EP 2 913 072 A1 discloses a system and a method for monitoring a dialysis machine, in which a venous needle disconnection is to be detected by evaluating the fluid pressures prevailing in the fluid lines.

[0007] Furthermore, EP 1 938 847 A2 discloses a method for monitoring the operation of a dialysis machine, in which the electrical conductivity of the treatment fluid is evaluated.

[0008] The object of the invention is to provide a method, a monitoring system and a medical device of the type mentioned above, each of which offers advantages over the prior art.

[0009] This object is achieved by providing a method having the features of claim 1, a monitoring system having the features of claim 10, and a medical device having the features of claim 14. Advantageous embodiments are the subject of the subclaims.

[0010] The method according to the invention is provided for monitoring the operation of a medical device for extracorporeal blood treatment. The medical device to be monitored has a blood treatment unit, an arterial fluid line, a venous fluid line, and a blood pump. The blood treatment unit has a blood chamber through which blood flows during operation, and a treatment chamber through which a blood treatment fluid flows during operation and which is separated from the blood chamber by a semipermeable membrane. The arterial fluid line is fluidically connected at one end to an inlet of the blood chamber and at the other end to an arterial vascular access of a patient, and through which an arterial volume flow flows. The venous fluid line is fluidically connected at one end to an outlet of the blood chamber and at the other end to a venous vascular access of the patient, and through which a venous volume flow flows.The blood pump is designed to deliver a pumped volume flow through an extracorporeal blood circuit of the medical device. The extracorporeal blood circuit includes the blood chamber, the arterial fluid line, and the venous fluid line.

[0011] The method comprises the steps of: determining a control parameter representing a relationship between the venous volume flow through the venous fluid line and the arterial volume flow through the arterial fluid line; monitoring the operation depending on the determined control parameter.

[0012] The method according to the invention allows operational monitoring based on a mathematical comparison between the venous volume flow in the venous fluid line and the arterial volume flow in the arterial fluid line. The said mathematical comparison is formed by the ratio, i.e. a quotient, between the two volume flows and thus the control parameters. The control parameter represents a quantitative comparison value between the venous volume flow and the arterial volume flow. The control parameter as such, a temporal change in the control parameter and / or a comparison of the control parameter with a reference parameter allow a conclusion to be drawn about a disturbance in the blood flow in the extracorporeal blood circuit and / or its connection to the patient's blood circuit. The control parameter is determined in different ways in different embodiments.In one embodiment, the two volume flows are directly measured using suitable sensors. In a preferred embodiment, the volume flows and / or their ratio are calculated, preferably approximately. The approximate calculation is preferably carried out on the basis of determining equations that depict a model and / or approximate functional relationship between operating parameters of the medical device and / or measured variables determined on the medical device and the volume flows or their ratio. Monitoring depending on the determined control parameter is carried out in different ways in different embodiments. In one embodiment, the monitoring comprises a graphical, text-based and / or character-based display of the control parameter for perception by medical personnel.Depending on the display, medical personnel can take measures to control or shut down the medical device. In a further embodiment, monitoring includes determining a monitoring signal depending on the control parameter. The monitoring signal can be output acoustically and / or visually for perception by medical personnel. Alternatively or additionally, the monitoring signal can serve as a control signal for the medical device, for example, to continue and / or terminate operation of the medical device with modified operating parameters.

[0013] In an embodiment of the invention, the method comprises the steps of: detecting a change in the control parameter over time; monitoring operation as a function of the detected change in the control parameter over time. In this embodiment, the control parameter is preferably detected continuously or quasi-continuously over time. Monitoring as a function of the change in the control parameter over time allows for early detection of whether and to what extent the ratio of the volume flows is changing. The change over time allows conclusions to be drawn about an emerging disturbance in the blood flow in the extracorporeal blood circuit and / or its connection to the patient's blood circuit. For example, by monitoring the change in the control parameter over time, a change in the properties of the vascular accesses can be detected. Furthermore, a needle disconnection can be detected, i.e.Disconnecting the fluid lines from the relevant vascular access. Assuming that the control parameter is in accordance with . K = Q v Q a is formed, where K denotes the control parameter, Q v denotes the venous volume flow, and Q a denotes the arterial volume flow, monitoring the temporal change in the control parameter can provide the following information: If the control parameter increases over time, this can be an indicator that the venous fluid line is impaired, for example, because a venous needle arranged at the other end of the venous fluid line has become blocked. If the control parameter decreases over time, this can be an indicator that the arterial fluid line is impaired, for example, because an arterial needle has become blocked. A decrease in the control parameter over time can also be an indicator that the venous fluid line is separated from the venous vascular access ("venous needle disconnection"). In a similar way, a detachment of the arterial fluid line or a change in the arteriovenous fistula can be detected.

[0014] In a further embodiment of the invention, the method comprises the steps of: determining a theoretical control parameter which represents a theoretical relationship between the venous volume flow and the arterial volume flow, wherein the theoretical control parameter is determined as a function of the pump volume flow and a filtration volume flow which is discharged from the blood chamber via the semipermeable membrane; comparing the determined control parameter with the determined theoretical control parameter; monitoring operation as a function of the comparison. Ideally, the control parameter does not undergo any significant change during the course of operation of the medical device, i.e. during extracorporeal blood treatment. However, a change inevitably occurs when the ultrafiltration rate discharged from the bloodstream via the semipermeable membrane, i.e. the filtration volume flow, is changed.A change in the filtration volume flow can be made by adjusting the medical device. To take such a change in device settings into account during monitoring, this embodiment of the invention provides for a comparison of the determined control parameter with the aforementioned theoretical control parameter. The theoretical control parameter is preferably calculated according to the equation. K t = Q p − Q F Q p formed. Here, K t denotes the theoretical control parameter, Q p the pump flow rate, and QF the filtration flow rate. Both flow rates are adjustable operating parameters of the medical device. By comparing the control parameter with the theoretical control parameter, it is possible to prevent a change in the filtration flow rate setting from influencing the monitoring.

[0015] In a further embodiment of the invention, the arterial volume flow and the venous volume flow are each directly measured. The measurement is carried out using suitable sensors.

[0016] In a further embodiment of the invention, the arterial volume flow and the venous volume flow are determined approximately based on the Hagen-Poiseuille equation. This is a particularly preferred embodiment of the invention. The Hagen-Poiseuille equation describes, in simplified form, the volume flow of a laminar, steady-state flow of a homogeneous Newtonian fluid through a tube (capillary) with a radius r and a length I. The approximate volume flow Q is obtained according to the equation Q = π ∗ r 4 ∗ Δ P 8 ∗ η ∗ l where η is the dynamic viscosity and Δ P denotes the pressure loss over the length l. Consequently, the arterial volume flow is: Q a = π ∗ r a 4 ∗ Δ P a 8 ∗ η a ∗ l a

[0017] The following applies to the venous volume flow: Q v = π ∗ r v 4 ∗ Δ P v 8 ∗ η v ∗ l v

[0018] The control parameter is therefore calculated according to K = Q v / Q a = η a ∗ Δ P v η v ∗ Δ P a where it is assumed for simplicity that l v = l a and r v = r a . It becomes clear that by determining the control parameter, i.e., by forming the quotient of the volume flows, the radius and length in particular can be removed from the determination equation. The inventors recognized that the length and radius are subject to manufacturing tolerances. Therefore, directly using these variables to approximate the two volume flows could potentially lead to inaccuracies. This is all the more so since the radius is exponentially included in the Hagen-Poiseuille equation. If the ratio of the volume flows (the control parameter) is used as the monitoring variable instead of the volume flows, these inaccuracies can be avoided.

[0019] In a further embodiment of the method, the approximate determination comprises: determining a venous differential pressure between the venous fluid line and the venous vascular access and an arterial differential pressure between the arterial fluid line and the arterial vascular access; determining an arterial viscosity of the arterial volume flow and a venous viscosity of the venous volume flow; calculating the control parameter as a function of the detected differential pressures and the detected viscosities. The said differential pressures and viscosities form the basis for the approximate determination of the volume flow ratio based on the Hagen-Poiseuille equation. The differential pressures are determined in different ways in different embodiments. The same applies analogously to the determination of the viscosities. In one embodiment, the viscosities are measured directly using suitable sensors.In a further embodiment, the viscosities are calculated based on physical model equations, preferably approximated. Operating parameters set on the medical device and / or recorded measured values ​​can be used for the calculation.

[0020] In a further embodiment of the invention, determining the differential pressures comprises: measuring a venous fluid pressure in the venous fluid line and an arterial fluid pressure in the arterial fluid line; detecting, in particular non-invasively measuring, a mean arterial pressure of the patient. The venous fluid pressure and the arterial fluid pressure are preferably each determined using a suitable sensor. Said sensors are preferably arranged on the respective fluid line. The mean arterial pressure, often abbreviated to MAD or MAP (Mean Arterial Pressure), describes the mean value of the blood pressure curve over time. The mean arterial pressure can be approximately assumed to be the fluid pressure prevailing in the vascular accesses. The mean arterial pressure can be determined according to P m = 2 3 ∗ P sys + 1 3 ∗ P dias where P m the mean arterial pressure, P sys the systolic and P dias The diastolic blood pressure. The mean arterial pressure is preferably determined via a non-invasive blood pressure measurement on the patient. Alternatively, the mean arterial pressure can be recorded as part of the procedure without prior measurement based on empirical values, database values, or the like. Therefore, a measurement directly on the patient is not absolutely necessary as part of the procedure. The venous differential pressure can therefore be determined based on the measured venous fluid pressure and the recorded mean arterial pressure of the patient as follows: Δ P v = P v − P m

[0021] The same applies to the arterial differential pressure, where Δ P a = P m − P a

[0022] In a further embodiment of the invention, determining the viscosities comprises: measuring an arterial hematocrit value of the blood in the arterial fluid line and / or a venous hematocrit value of the blood in the venous fluid line; determining the arterial viscosity as a function of the measured arterial hematocrit value and / or the venous viscosity as a function of the measured venous hematocrit value. This embodiment of the invention is based on the consideration that direct measurement of the viscosities is comparatively complex and may, in particular, require modifications to the medical device. Determining the viscosities based on a measurement of the hematocrit values, in contrast, offers particular advantages. This is because conventional medical devices for extracorporeal blood treatment are often already equipped to measure the arterial and / or venous hematocrit value.Appropriate sensors may be present for this purpose. Furthermore, this embodiment of the invention is based on the consideration that the viscosity of blood has an approximately functional relationship with the hematocrit value. When the hematocrit value is measured, the viscosity can therefore be easily determined based on the known correlation / function. The relationship is approximately linear and based on empirical data. In one embodiment, both the arterial and the venous hematocrit values ​​are measured. In another embodiment, only one of the two hematocrit values ​​is measured, and the other hematocrit value is determined approximately.

[0023] In a further embodiment of the invention, the arterial hematocrit value is measured, and the venous viscosity is approximately determined as a function of the pump volume flow, the filtration volume flow, and the measured arterial hematocrit value. This embodiment of the invention eliminates the need for measurement technology to determine both hematocrit values. Only one of the two hematocrit values, namely the arterial one, is measured. The other, venous hematocrit value is calculated. Of course, a reverse procedure is also conceivable and possible. In this embodiment, two variants for the calculated determination of the venous hematocrit value can be provided.

[0024] In a first variant, the set filtration volume flow and a plasma value P 0 of the blood are taken into account. To calculate the venous hematocrit value H v, a total volume of blood in the patient's body is also required. This total volume can be determined using the Kaplan-Hakim formula. The venous hematocrit value can be calculated using this information as follows: H v = 100 ∗ Q p − Plasma 0 − Q F Q p

[0025] The parameters required for this are usually already available directly or at least indirectly on the medical device to be monitored.

[0026] A second variant involves considering the blood plasma flow rate in a time-resolved manner by using the known parameters of the set pump flow rate and the set filtration flow rate. The filtration flow rate can naturally only be derived from the plasma portion of the blood, since the hematocrit itself cannot pass through the semipermeable membrane. A plasma flow upstream of the blood chamber can be calculated from the set pump flow rate and the measured arterial hematocrit value. The (venous) plasma flow downstream of the blood treatment unit is therefore the difference between the arterial plasma flow rate and the filtration flow rate. These relationships result in: H v = 100 − Q p ∗ 100 − H a − Q F Q p − Q F

[0027] In a further embodiment of the method, the operation of the device is monitored during several consecutive extracorporeal blood treatments of the patient, and the control parameters determined in each case are compared with one another, with operation being monitored as a function of the comparison. This embodiment of the method makes it possible, in particular, to detect changes in the vascular access and / or the arteriovenous fistula. If their condition changes over time, i.e. across individual extracorporeal blood treatments, this can be detected based on the change in the control parameter over the number of treatments. This is a particularly advantageous embodiment of the invention. The control parameter determined in each case can be stored in a database. In order to compare the control parameters determined in each case, they can be retrieved from the said database and evaluated accordingly.

[0028] The monitoring system according to the invention is provided for a medical device for extracorporeal blood treatment, wherein the device comprises a blood treatment unit with a blood chamber configured for blood to flow through, and with a treatment chamber configured for a treatment fluid to flow through and separated from the blood chamber by a semipermeable membrane, an arterial fluid line, which is fluidically connected at one end to an inlet of the blood chamber and which is fluidically connectable at the other end to an arterial vascular access of a patient and which is configured for an arterial volume flow to flow through, a venous fluid line, which is fluidically connected at one end to an outlet of the blood chamber and which is fluidically connectable at the other end to a venous vascular access of the patient and which is configured for a venous volume flow to flow through, and a blood pump,which is configured to pump a set pump volume flow through an extracorporeal blood circuit comprising the blood chamber, the arterial fluid line, and the venous fluid line, wherein the monitoring system comprises: a determination device configured to determine a control parameter representing a relationship between the venous volume flow through the venous fluid line and the arterial volume flow through the arterial fluid line, and a monitoring device configured to monitor the operation of the medical device as a function of the determined control parameter. The determination device is configured to determine the control parameter in accordance with the preceding description of the method according to the invention and / or its embodiments. The same applies, mutatis mutandis,for the monitoring device. In one embodiment, the monitoring system is a separate system from the medical device. In a preferred embodiment, the monitoring system is an integral part of the medical device. In other words, in this preferred embodiment, the monitoring system is formed by components of the medical device.

[0029] In a further embodiment of the invention, the monitoring system comprises a detection device. The detection device comprises a venous pressure sensor, an arterial pressure sensor, a blood pressure measuring device, and at least one hematocrit sensor. The venous pressure sensor is configured to detect a venous fluid pressure in the venous fluid line. The arterial pressure sensor is configured to detect an arterial fluid pressure in the arterial fluid line. The blood pressure measuring device is configured to detect a mean arterial pressure of the patient. The at least one hematocrit sensor is configured to detect an arterial or venous hematocrit value in the respective fluid line. Furthermore, in this embodiment of the invention, the determination device is configured to determine the control parameter as a function of the variables determined by the detection device.This configuration of the monitoring system enables an approximate calculation of the control parameter based on the Hagen-Poiseuille equation. To avoid repetition, reference is made to the relevant disclosure in connection with the method according to the invention.

[0030] In a further embodiment of the invention, the monitoring device is configured for the acoustic, optical, and / or data-based output of at least one monitoring signal. The at least one monitoring signal can be perceived by medical personnel when acoustic and / or optically output. The medical personnel can initiate measures based on the acoustic and / or optical monitoring signal. In the case of data-based output, the at least one monitoring signal can, in particular, serve to control the medical device. Operating parameters of the medical device can be changed and / or operation of the medical device can be terminated by means of the control.

[0031] In a further embodiment of the invention, the monitoring system is formed by components of the medical device. This is a preferred embodiment of the invention.

[0032] The medical device according to the invention is designed for extracorporeal blood treatment and comprises: a blood treatment unit with a blood chamber through which blood flows, and with a treatment chamber through which a treatment fluid flows and is separated from the blood chamber by a semipermeable membrane, an arterial fluid line, which is fluidically connected at one end to an inlet of the blood chamber, which is fluidically connectable at the other end to an arterial vascular access of a patient and which is designed for an arterial volume flow to flow through, a venous fluid line, which is fluidically connected at one end to an outlet of the blood chamber, which is fluidically connectable at the other end to a venous vascular access of the patient and which is designed for a venous volume flow to flow through, a blood pump,which is configured to pump a set pump volume flow through an extracorporeal blood circuit comprising the blood chamber, the arterial fluid line, and the venous fluid line, and a monitoring system according to the preceding description. The medical device is preferably a dialysis machine. The blood treatment unit in this case can also be referred to as a dialyzer. The treatment chamber in this case is a dialysate chamber, and the treatment fluid is a dialysate.

[0033] Further advantages and features of the invention will become apparent from the description of preferred embodiments of the invention, which are illustrated with reference to the drawings. Fig. 1 shows a schematically simplified block diagram of an embodiment of a medical device according to the invention with an embodiment of a monitoring system according to the invention, which is set up to carry out an embodiment of a method according to the invention for monitoring the operation of the medical device, Fig. 2 shows a schematically simplified and enlarged detailed view of end sections of two fluid lines of the medical device in the area of ​​patient-side vascular accesses, Fig. 3 shows a diagram to illustrate different volume flow profiles over the duration of an extracorporeal blood treatment, as well as the profile of a mean arterial pressure of the treated patient, Fig. 4 shows a diagram to illustrate the time profile of a control parameter and a theoretical control parameter over the duration of an extracorporeal blood treatment, Fig.Fig. 5 is a diagram illustrating a relationship between a dynamic viscosity and a hematocrit value based on empirical values, and Fig. 6 is a diagram illustrating the change in the control parameter over several consecutive extracorporeal blood treatments.

[0034] According to Fig. 1 a medical device 1 is provided for extracorporeal blood treatment and comprises a blood treatment unit 10, an arterial fluid line 20, a venous fluid line 30 and a blood pump 40.

[0035] The medical device 1 is designed in the form of a dialysis machine. The treatment unit 10 can therefore also be referred to as a dialyzer.

[0036] The blood treatment unit 10 has a blood chamber 11 and a treatment chamber 12. The treatment chamber 12 can also be referred to here as a dialysate chamber. The blood chamber 11 and the treatment chamber 12 are separated from each other by a semipermeable membrane 13.

[0037] The arterial fluid line 20 is elongated between a first end 21 and a second end 22. The first end 21 of the arterial fluid line 20 is fluidly connected to an inlet 14 of the blood chamber 11. The second end 22 of the arterial fluid line 20 is fluidly connectable to an arterial vascular access Z a of a patient.

[0038] The venous fluid line 30 is elongated between a first end 31 and a second end 32. The first end 31 of the venous fluid line 30 is fluidly connected to an outlet 15 of the blood chamber 11. The second end 32 of the venous fluid line 30 is fluidly connectable to a venous vascular access Z v of the patient.

[0039] The blood chamber 11 is located upstream of the arterial fluid line 20. The venous fluid line 30 is located upstream of the blood chamber 11.

[0040] During operation of the medical device 1, the two said second ends 22, 32 of the fluid lines 20, 30 are fluidically connected to the respective vascular access Z a , Z v by means of a needle N and, if necessary, further hose sections (without reference symbol) (see Fig. 2 ). The needles N can also be referred to as cannulas or hollow needles.

[0041] How to proceed based on Fig. 2 As illustrated, the vascular accesses Z a , Z v are located on an arteriovenous fistula F of the patient. In the exemplary situation shown, the arteriovenous fistula is located on a forearm of the patient (see Fig. 1 ) and is surgically created in a manner known to those skilled in the art. The arteriovenous fistula F creates a fluidic short circuit between a patient's vein and artery.

[0042] During extracorporeal blood treatment, the patient's blood to be treated enters the arterial fluid line 20 via the arterial vascular access Z a and from its first end 21 via the inlet 14 into the blood chamber 11. From there, the blood enters the venous fluid line 30 via the outlet 15 and via its second end 32 and the venous vascular access Z v back into the patient's bloodstream.

[0043] The arterial fluid line 20, the blood chamber 11, and the venous fluid line 30 form the extracorporeal blood circuit of the medical device 1. The blood pump 40 serves to pump the blood within the extracorporeal blood circuit. The pumping rate, or more precisely, the pumping volume flow PQ of the blood pump 40, is adjustable.

[0044] During operation of the medical device 1, a treatment fluid, which can be referred to here as dialysate, flows through the treatment chamber 12. The flow occurs countercurrently to the blood flow in the blood chamber 11.

[0045] When flowing through the blood chamber 11, urinary fluid from the bloodstream is transferred via the semipermeable membrane 13 into the treatment chamber 12 and transported away with the fluid flow there.

[0046] The amount of fluid to be removed from the blood stream per unit of time can be adjusted on the medical device 1 and is referred to as the filtration volume flow QF.

[0047] In this case, the filtration volume flow QF is adjusted via a filtration pump 41. The filtration pump 41 pumps the treatment fluid through the treatment chamber 12. A volume flow Q d1 is present at an inlet (no reference symbol) of the treatment chamber 12. A volume flow Q d2 is present at an outlet (no reference symbol) of the treatment chamber 12. The volume flow Q d2 present at the outlet is the sum of the volume flow Q d1 introduced at the inlet and the filtration volume flow QF .

[0048] As a result of the derivation of the filtration volume flow QF from the extracorporeal blood circuit, there is consequently also a (calculated) difference between the volume flows within the fluid lines 20, 30, where Q v = Q a − Q F

[0049] Here, Q a indicates an arterial volume flow in the arterial fluid line 20. Q v indicates a venous volume flow in the venous fluid line 30.

[0050] The medical device 1 also has a monitoring system 50. The monitoring system 50 serves to monitor the operation of the medical device 1. In particular, the monitoring system 50 can be used to monitor whether there is any impairment of the blood flow within the extracorporeal blood circuit. Furthermore, it can be monitored whether the connection between the extracorporeal blood circuit and the patient's blood circuit via the vascular accesses Z a , Z v is present. Furthermore, changes in the arteriovenous fistula F can be detected.

[0051] In the embodiment shown, the monitoring system 50 is an integral part of the medical device 1. In other words, the monitoring system 50 is formed by components of the medical device 1. In an embodiment not shown in the figures, the monitoring system is not integrated into the medical device.

[0052] The monitoring system 50 has a detection device 60 and a monitoring device 70.

[0053] The determination device 60 is configured to determine a control parameter K. The control parameter K represents a ratio between the venous volume flow Q v and the arterial volume flow Q a , where K = Q v Q a

[0054] The monitoring device 70 is configured to monitor the operation of the medical device 1 as a function of the determined control parameter K.

[0055] In the embodiment shown, the monitoring device 70 is configured to output a monitoring signal S. The monitoring signal S can be output acoustically, optically, and / or data-based.

[0056] Based on the optically and / or acoustically emitted control signal S, medical personnel can detect whether there is an impairment or malfunction, so that operating parameters of the medical device 1 can be changed manually.

[0057] A data-based output of the control signal S can be used as a basis for automatic control of the medical device 1. For example, the blood pump 40 and / or the filtration pump 41 can be controlled depending on the control signal S.

[0058] In different embodiments, the determination device 60 is configured in different ways to determine the control parameter K. For example, the control parameter K can be determined based on a direct metrological recording of the arterial volume flow Q a and the venous volume flow Q v . In the present case, the control parameter K is instead determined / calculated approximately. This approximate determination / calculation is carried out on the basis of operating parameters set on the medical device 1 and / or recorded measured variables that have an indirect, approximate physical relationship to the volume flows Q a and Q v .

[0059] In the embodiment shown, the monitoring system 50 has a detection device 80 for measuring the measured variables. The detection device 80 has a venous pressure sensor 81, an arterial pressure sensor 82, a blood pressure measuring device 83, and a hematocrit sensor 84.

[0060] The venous pressure sensor 81 is configured to detect a venous fluid pressure P v in the venous fluid line 30. The arterial pressure sensor 82 is configured to detect an arterial fluid pressure P a in the arterial fluid line 20. The blood pressure measuring device is configured to detect a mean arterial pressure P m . The hematocrit sensor 84 is configured to detect an arterial hematocrit value H a of the blood flow in the arterial fluid line 20.

[0061] The control parameter K is determined here using the measured variables P v , P a , P m , H a acquired by the acquisition device 80 and based on the Hagen-Poiseuille equation. The Hagen-Poiseuille equation, often referred to as the Hagen-Poiseuille law, describes the volume flow for a laminar, steady-state flow of a Newtonian fluid in a pipe with a radius r and a length l. Consequently, the following approximately applies to the two volume flows in the fluid lines 20, 30: Q a = π ∗ r a 4 ∗ Δ P a 8 ∗ η a ∗ l a Q v = π ∗ r v 4 ∗ Δ P v 8 ∗ η v ∗ l v

[0062] The control parameter K is therefore K = Q v / Q a = η a ∗ Δ P v η v ∗ Δ P a By forming the ratio / quotient, the length and radius can be reduced from the determining equation. These two parameters are subject to manufacturing tolerances. Since the radius r also enters the determining equation exponentially, deviations have a significant impact on the result. Determining the control parameter as the quotient of the two volume flows Q a , Q v avoids the associated inaccuracies.

[0063] In view of the above equation, it can be stated that for the approximate determination of the volume flow ratio, i.e., the control parameter K, differential pressures, more precisely a venous differential pressure P v -P m and an arterial differential pressure P m -P a , are determined. The said pressure values ​​are determined by means of the venous pressure sensor 81, the arterial pressure sensor 82, and the blood pressure measuring device 83. The mean arterial pressure P m is determined non-invasively and in a manner generally known to those skilled in the art.

[0064] Furthermore, an arterial viscosity η a and a venous viscosity η v are determined. Both viscosities are determined approximately. Alternatively, direct measurement of the viscosities is also conceivable and possible.

[0065] In the embodiment shown, the arterial viscosity η a is determined as a function of the measured arterial hematocrit value H a. The determination device 60 is configured accordingly. The determination is carried out on the basis of the Fig. 5 The relationship between the variables illustrated by way of example is based on empirical values ​​and allows the arterial viscosity η a to be determined as a function of the measured arterial hematocrit value H a. The arterial viscosity η a can be determined, for example, on the basis of a linear function that approximately reflects the empirical relationship illustrated. Alternatively or additionally, the empirical values ​​can be stored and retrieved in a storage unit of the medical device 1 configured for this purpose, which can in particular be assigned to the determination device 60.

[0066] The venous viscosity η v is determined approximately. Different approximations are conceivable and possible: In one variant, the venous viscosity η v is determined as a function of the pump volume flow Q p set on the medical device 1, the set filtration volume flow QF and the measured arterial hematocrit value H a. The determination equation resulting from this variant follows as H v = 100 − Q p ∗ 100 − H a − Q F Q p − Q F

[0067] According to a further variant, the venous hematocrit value H v is first calculated downstream of the blood chamber 11 and thus in the venous fluid line 30. This calculation is based on operating parameters set on the medical device, namely the pump volume flow Q p and the filtration volume flow QF , as well as the plasma value Plasma 0 of the blood. The plasma value Plasma 0 is usually available on the medical device 1 as a measured value and can be recorded, for example, by means of the recording device 80 and a suitable sensor or the like. The relevant equation for the mathematical determination of the venous hematocrit value H v is as follows: H v = 100 ∗ Q p − Plasma 0 − Q F Q p

[0068] Based on the venous hematocrit value H v calculated in this way, the venous viscosity η v can be calculated on the basis of the Fig. 5 reproduced empirical relationship and thus analogous to the arterial viscosity η a.

[0069] The control parameter K determined in this way represents a comparison between the approximated volume flows Q a , Q v . Monitoring the control parameter K therefore allows conclusions to be drawn about excessive deviations between the volume flows Q a , Q v . The causes of such deviations can be impairments or changes to the fluid lines 20, 30, the vascular accesses Z a , Z v and / or the arteriovenous fistula F.

[0070] For monitoring purposes, in one embodiment only the control parameter K is determined and used as the basis for monitoring, i.e. the output of the monitoring signal S.

[0071] In the embodiment shown, the change in the control parameter K over time is also recorded. Monitoring is performed depending on the recorded temporal change in the control parameter K.

[0072] Fig. 4 shows an exemplary curve of the control parameter K over time t, which in the example shown extends over the duration of an extracorporeal blood treatment. The example shows an increase in the control parameter K in the period between approximately 2,000 s and 4,000 s. This increase can have various causes: For example, the venous fluid line 30, the needle N connected to the venous fluid line 30, and / or the venous vascular access Z v may be impaired. As a result, the venous differential pressure increases, and the control parameter K increases over time t.

[0073] A decrease in the control parameter K over time t can have the following causes in particular: Due to an impairment of the arterial fluid line 20, the needle N connected at the end and / or the arterial vascular access Z a, a larger arterial differential pressure results, the control parameter K decreases.

[0074] Detaching the venous fluid line 30 from the venous vascular access Z v , for example by disconnecting the respective needle N, results in the measured venous fluid pressure P v decreasing. Consequently, the control parameter K also decreases. The same applies analogously to detaching the arterial fluid line 20 and / or disconnecting the respective needle N. As a result, the arterial fluid pressure P a increases, which consequently causes the control parameter K to decrease.

[0075] In contrast to prior art monitoring methods, which only provide monitoring based on measured arterial and venous fluid pressures, the present monitoring method / system also allows for consideration of any changes in blood viscosity and changes in the patient's blood pressure. This allows for more reliable and therefore safer monitoring for the patient.

[0076] Furthermore, a change in the arteriovenous fistula F can be detected. A change in the Fig. 2 The schematically indicated narrowing between the arterial vascular access Z a and the venous vascular access Z v is accompanied by a change in the prevailing blood pressures there. Due to the aforementioned change in pressure, the control parameter K also changes.

[0077] In the embodiment shown, the determined control parameter K is also compared with a comparison parameter, which is referred to here as the theoretical control parameter K t . The theoretical control parameter represents a theoretical volume flow ratio and is determined as a function of the set pump volume flow Q p and the set filtration volume flow QF . K t = Q p − Q F Q p

[0078] By comparing the control parameter K with the theoretical control parameter K t, the influence of a change in the set filtration volume flow QF can be taken into account.

[0079] The course of the theoretical control parameter K t over time t is shown as an example in the diagram according to Fig. 4 Based on the theoretical control parameter K t, an upper limit value K L1 and a lower limit value K L2 can be determined for the control parameter K. If the control parameter K exceeds the upper limit value K L1 or falls below the lower limit value K L2 , this indicates an impairment of the operation of the medical device 1. In addition, an excessive deviation between the control parameter K and the theoretical control parameter K t indicates a possible change in the arteriovenous fistula F.

[0080] The present monitoring method also provides for monitoring the operation of the medical device 1 during several consecutive extracorporeal blood treatments of the patient. The control parameters determined in this process are compared with each other. Such monitoring is based on Fig. 6 There, the relationship between the control parameter K and the theoretical control parameter K t is plotted against a number B of extracorporeal blood treatments for one and the same patient. The change in this relationship allows a conclusion to be drawn about a temporal change in the arteriovenous fistula F. In particular, the Fig. 6 The course of the ratio K / Kt illustrated may indicate excessive narrowing or occlusion of the arteriovenous fistula F between the two vascular accesses Z a , Z v .

Claims

1. Method for monitoring the operation of a medical device (1) for extracorporeal blood treatment, the device (1) comprising a blood treatment unit (10) having a blood chamber (11) that is traversed by blood and a treatment chamber (12) that is traversed by a blood treatment fluid and separated from the blood chamber (11) by way of a semipermeable membrane (13), an arterial fluid line (20) that is connected in fluid-conveying fashion at one end to an inlet (14) in the blood chamber (11) and at the other end to an arterial vessel access (Za) of a patient and that is traversed by an arterial volume flow (Qa), a venous fluid line (30) that is connected in fluid-conveying fashion at one end to an outlet (15) from the blood chamber (11) and at the other end to a venous vessel access (Zv) of the patient and that is traversed by a venous volume flow (Qv), and a blood pump (40) that is configured to convey a pump volume flow (Qp) through an extracorporeal blood circuit comprising the blood chamber (11), the arterial fluid line (20) and the venous fluid line (30), wherein the method includes the steps of: ascertaining a control parameter (K) that represents a relationship between the venous volume flow (Qv) through the venous fluid line (30) and the arterial volume flow (Qa) through the arterial fluid line (20); ascertaining a theoretical control parameter (Kt) that represents a theoretical relationship between the venous volume flow (Qv) and the arterial volume flow (Qa), the theoretical control parameter (Kt) being ascertained as a function of the pump volume flow (Qp) and a filtration volume flow (QF), which is led away from the blood chamber (11) via the semipermeable membrane (13); comparing the ascertained control parameter (K) to the ascertained theoretical control parameter (Kt); monitoring the operation on the basis of the comparison.

2. Method according to Claim 1, comprising the steps of: recording a change in the control parameter (K) over time (t); monitoring the operation on the basis of the recorded change of the control parameter (K) over time.

3. Method according to either of the preceding claims, wherein the arterial volume flow (Qa) and the venous volume flow (Qv) are each detected directly by measurement.

4. Method according to Claim 1 or 2, wherein the arterial volume flow (Qa) and the venous volume flow (Qv) are ascertained approximately on the basis of the Hagen-Poiseuille equation.

5. Method according to Claim 4, wherein the approximate ascertainment comprises: ascertaining a venous differential pressure (Pv-Pm) between the venous fluid line (30) and the venous vessel access (Zv) and an arterial differential pressure (Pm-Pa) between the arterial fluid line (20) and the arterial vessel access (Za); ascertaining an arterial viscosity (ηa) of arterial volume flow (Qa) and venous viscosity (ηv) of venous volume flow (Qv); calculating the control parameter (K) as a function of the recorded differential pressures (Pv-Pm, Pm-Pa) and the recorded viscosities (ηa, ηv).

6. Method according to Claim 5, wherein the ascertainment of the differential pressures (Pv-Pm, Pm-Pa) comprises: measuring a venous fluid pressure (Pv) in the venous fluid line (30) and an arterial fluid pressure (Pa) in the arterial fluid line (20); recording, especially non-invasively measuring, a mean arterial pressure (Pm) of the patient.

7. Method according to Claim 5 or 6, wherein the ascertainment of the viscosities (ηa, ηv) comprises: measuring an arterial haematocrit value (Ha) of the blood in the arterial fluid line (20) and / or a venous haematocrit value (Hv) of the blood in the venous fluid line (30); ascertaining the arterial viscosity (ηv) as a function of the measured arterial haematocrit value (Ha) and / or venous viscosity (ηv) as a function of the measured venous haematocrit value (Hv).

8. Method according to Claim 7, wherein the arterial haematocrit value (Ha) is recorded by measurement and the venous viscosity (ηv) is ascertained in approximated fashion as a function of the pump volume flow (Qp), the filtration volume flow (QF) and the arterial haematocrit value (Ha) recorded by measurement.

9. Method according to any of the preceding claims, wherein the operation of the device (1) is monitored over a plurality of temporally successive treatments of the patient, and control parameters ascertained in each case in the process are compared to one another, the operation being monitored in a manner dependent on the comparison.

10. Monitoring system (50) for a medical device (1) for extracorporeal blood treatment, the device (1) comprising a blood treatment unit (10) having a blood chamber (11) configured for traversal by blood and a treatment chamber (12) configured for traversal by a blood treatment fluid and separated from the blood chamber (11) by way of a semipermeable membrane (13), an arterial fluid line (20) that is connected in fluid-conveying fashion at one end to an inlet (14) in the blood chamber (11), connectable in fluid-conveying fashion at the other end to an arterial vessel access (Za) of a patient and configured for traversal by an arterial volume flow (Qa), a venous fluid line (30) that is connected in fluid-conveying fashion at one end to an outlet (15) from the blood chamber (11), connectable in fluid-conveying fashion at the other end to a venous vessel access (Zv) of the patient and configured for traversal by a venous volume flow (Qv), and a blood pump (40) that is configured to convey a pump volume flow (Qp) by pumping through an extracorporeal blood circuit comprising the blood chamber (11), the arterial fluid line (20) and the venous fluid line (30), wherein the monitoring system (50) comprises: an ascertainment means (60) that is configured for ascertaining a control parameter (K) that represents a relationship between the venous volume flow (Qv) through the venous fluid line (30) and the arterial volume flow (Qa) through the arterial fluid line (20); ascertaining a theoretical control parameter (Kt) that represents a theoretical relationship between the venous volume flow (Qv) and the arterial volume flow (Qa), the ascertainment means (60) being configured to ascertain the theoretical control parameter (Kt) as a function of the pump volume flow (Qp) and a filtration volume flow (QF), which is led away from the blood chamber (11) via the semipermeable membrane (13); comparing the ascertained control parameter (K) to the ascertained theoretical control parameter (Kt); a monitoring means (70) that is configured for monitoring the operation of the medical device (1) on the basis of the comparison between the ascertained control parameter (K) and the ascertained theoretical control parameter (Kt).

11. Monitoring system (50) according to Claim 10, characterized in that a recording means (80) is present and comprises a venous pressure sensor (81) that is configured for ascertaining a venous fluid pressure (Pv) in the venous fluid line (30), an arterial pressure sensor (82) that is configured for ascertaining an arterial fluid pressure (Pa) in the arterial fluid line (20), a blood pressure measuring apparatus (83) that is configured for recording a mean arterial pressure (Pm) of the patient and at least one haematocrit sensor (84) that is configured for recording an arterial or venous haematocrit value (Ha, Hv) in the respective fluid line (20, 30), wherein the ascertainment means (60) is configured for ascertaining the control parameter (K) as a function of the quantities recorded by means of the recording means (80).

12. Monitoring system (50) according to Claim 10 or 11, characterized in that the monitoring means (70) is configured for acoustic, optical and / or data-based output of at least one monitoring signal (S).

13. Monitoring system (50) according to any of Claims 10 to 12, wherein the monitoring system (50) is formed by components of the medical device (1).

14. Medical device (1) for extracorporeal blood treatment, comprising a blood treatment unit (10) having a blood chamber (11) configured for traversal by blood and a treatment chamber (12) configured for traversal by a blood treatment fluid and separated from the blood chamber (11) by way of a semipermeable membrane (13), an arterial fluid line (20) that is connected in fluid-conveying fashion at one end to an inlet (14) in the blood chamber (11), connectable in fluid-conveying fashion at the other end to an arterial vessel access (Za) of a patient and configured for traversal by an arterial volume flow (Qa), a venous fluid line (30) that is connected in fluid-conveying fashion at one end to an outlet (15) from the blood chamber (11), connectable in fluid-conveying fashion at the other end to a venous vessel access (Zv) of the patient and configured for traversal by a venous volume flow (Qv), and a blood pump (40) that is configured to convey a pump volume flow (Qp) by pumping through an extracorporeal blood circuit comprising the blood chamber (11), the arterial fluid line (20) and the venous fluid line (30), and comprising a monitoring system (50) according to any of Claims 10 to 13.