WO2015004009A1

WO2015004009A1 - Method and device for the detection of suction of a sampling needle

Info

Publication number: WO2015004009A1
Application number: PCT/EP2014/064277
Authority: WO
Inventors: Andre STOLLENWERK; Stefan KOWALEWSKI; Felix GATHMANN; Marian Walter
Original assignee: Rwth Aachen
Priority date: 2013-07-09
Filing date: 2014-07-04
Publication date: 2015-01-15
Also published as: DE102013213390A1

Abstract

The invention relates to a method and a device for the detection (1) of suction of a sampling needle (EK) in the vascular system of a mammal. In a first step, first measurement values are measured, wherein the first measurement values are chosen from the group comprising volumetric flow and pressure on the sampling needle (EK). The first measurement values are then evaluated with respect to frequency-specific energy components, and, when a limit value is reached or exceeded, the close proximity of the sampling needle (EK) is detected and is delivered as a signal for further processing or notification.

Description

Method and device for detecting an aspiration of a withdrawal cannula

RWTH Aachen, Germany

The invention relates to a method for detecting an aspiration of a withdrawal cannula and a device for detecting an aspiration of a withdrawal cannula.

Background of the invention

In many areas of human and veterinary medicine, fluids, in particular blood, are taken from the respective body (continuously) by means of removal cannulas and returned to the respective body again (continuously) after processing outside the body.

This can lead to problems with respect to aspiration of the withdrawal cannula, as will be explained in the following by way of example with reference to the extracorporeal lung support.

For extracorporeal circulation (ECC), e.g. in extracorporeal lung assist (ECLA), it may e.g. due to intravascular volume deficiency (hypovolemia) or a displacement of the withdrawal cannula come to a suction of this cannula on the vessel wall. The blood volume flow taken from the organism is so great that the vessel from which the blood is taken collapses, thereby covering at least part of the inlets of the withdrawal cannula. This in turn leads to an increase in the volume flow through the remaining inlets. In the worst case, all inlets are covered after a short time. As the blood pump continues to attempt to maintain extracorporeal flow, the vessel will not be able to disengage from the cannula without external intervention.

This scenario is a dangerous complication during an ECLA that needs to be prevented. Since the volume loss, which leads to hypovolemia, usually over a longer period arises, sometimes the first signs of a lack of volume can be detected.

Indications for an approaching suction of the sampling cannula are increased hemolysis indicators (eg increased plasma HB or LDH). To avoid the suction of the withdrawal cannula, either volume - z. In the form of saline or stored blood, which reduces extracorporeal blood flow or adjusts the location of both the retrieval cannula and the patient.

However, the early detection of an approaching aspiration of the withdrawal cannula with the aforementioned indicators is not possible because the measurements are relatively cumbersome and long.

It would therefore be desirable to provide a simple and inexpensive solution that can detect early detection of the aspiration of a sampling cannula so that there is sufficient time to initiate countermeasures.

The object is achieved by a method for detecting an aspiration of a withdrawal cannula and a device for detecting an aspiration of a withdrawal cannula according to the independent claims. Further advantageous embodiments are in particular subject of the dependent claims.

The invention will be explained in more detail with reference to the figures. In these shows:

1 shows an exemplary volume flow through an exemplary extracorporeal circuit with respect to a time course,

2 shows an exemplary pressure through an exemplary extracorporeal circuit with respect to a time course,

3 shows an exemplary spectrogram of a volumetric flow measuring signal,

4 shows an exemplary (unfiltered) volumetric flow measuring signal,

FIG. 5 shows a confidence measure determined by way of example, and FIG

6 shows an exemplary schematic arrangement according to an embodiment of the invention.

FIG. 1 shows an exemplary volume flow, in the present case a blood flow, through an exemplary extracorporeal circuit with respect to a time course on a withdrawal cannula. FIG. 1 shows, for better clarity, a low-pass filtered blood flow measurement value at 0.1 Hz. The volume flow is initially positive in a range of 3 l / min. In the time range of 0 s, the volume flow drops sharply, in the present case to about 0.5 l / min. That is, at the time 0 s, the withdrawal cannula is on and there is a risk, since now the extracorporeal circulation can not be maintained (sufficient). FIG. 2 shows an exemplary pressure through an exemplary extracorporeal circuit with respect to a time course on a withdrawal cannula. At first, the pressure at the sampling cannula is only slightly negative at about 60 mmHg. In the time range of 0 s, the pressure drops sharply, in this case to values below -100 mmHg. That is, at the time 0 s, the withdrawal cannula is on and there is a risk, since now the extracorporeal circulation can not be (sufficiently) maintained.

The inventors have recognized that the approaching abutment of the withdrawal cannula can be recognized from the measurement of the volume flow and / or the measurement of the pressure. That It is possible to react accordingly far before the impending concern of the withdrawal cannula. Thus, the risk decreases.

A more detailed analysis of the measurement of the blood flow in FIG. 1 and of the blood pressure in FIG. 2 shows a distinct pulsatility several seconds before the aspiration of the vessel to the cannula (t = 0 s). Furthermore, it can also be seen in FIG. 2 that the already negative removal pressure drops even further. In the illustrated case, the extraction pressure reaches the lower end of the measuring range of the pressure sensor, which is why the pressure values shown are limited.

The pulsatility can be understood as caused by the beating of the heart. Typically, an extracorporeal funded flow is continuously conveyed by a pump BP; the heart, however, promotes pulsatile. This results especially in the case of veno-venous extracorporeal circulation, e.g. ECLA, the vial begins to collapse at each heartbeat as the heart draws volume from the venous system of the systemic bloodstream.

Based on the pulsatility, a model can be developed to early detect volume depletion in general and aspiration of the sampling cannula.

For this purpose, the blood flow signal in the frequency domain is considered below by way of example, but without being limited to the volume signal. In the same way, the pressure signal could be considered.

A spectral analysis of the blood flow signal from FIG. 1 can be seen in FIG. Lighter areas indicate areas of high energy content, while darker areas have lower or no energy content.

In addition to a DC component of the signal, an increase in the energy in the frequency spectrum at about 1, 1 7 Hz or the harmonics of this frequency can be seen. This is due to the heart rate of the respective mammal of about 70 beats / minute in this example. In addition, more than a minute before aspiration of the vessel wall to the cannula, there is a large increase in the spectral energy in a very wide area Detect frequency range. This correlates directly with the observations from FIGS. 1 and 2. The fact that the increase in energy can be recognized not only at the current heart rate or the harmonics can be explained by the dynamic behavior of the overall structure. The excitation leads to an increase in the spectral power density in the entire low frequency range.

This property can be used.

On the one hand, an evaluation in the time domain can be made, on the other hand, however, an evaluation in the frequency domain can be made.

In a method according to the invention for detecting an aspiration of a withdrawal cannula in the vascular system of a mammal, first measurement of either the volume flow or the pressure at the withdrawal cannula can be measured.

Subsequently, these measured values are evaluated in relation to frequency-specific energy components, wherein when approaching or exceeding a limit value, the approaching abutment of the withdrawal cannula is recognized and supplied as a signal for further processing or reporting.

For example, in the time domain by means of a high-pass or a bandpass the measured value signal can be filtered and fed to a comparator. Exceeds the filtered measured value signal, for example, an empirically determined limit, the approaching concern of the sampling cannula is detected. In the frequency domain, by contrast, the measured value spectrum can be evaluated, for example, by transforming the measured values. If one or more frequency components have a high proportion, one or more frequency components exceed an empirically determined limit value, for example, then the approaching abutment of the withdrawal cannula is detected. For example, a (discrete) (fast) Fourier transformation can be provided in order to transform the measured values into the frequency domain in order to obtain a frequency spectrum of the measured values. Advantageously, in order to keep the computational effort low, the measured values for this purpose can be measured in predetermined - preferably the same - time intervals. In one embodiment of the invention, for example, both measured value signals, ie volume flow and pressure at the sampling cannula can be evaluated. Both signals can be evaluated either in the time domain or in the frequency domain, or one of the measured value signals can be evaluated in the frequency domain and the other measured value signal in the time domain. The result of the respective evaluation can then be combined or weighted combined.

In an advantageous embodiment, frequency components which correspond to the heart rate or to a harmonic of the heart rate of the mammal are excluded from the evaluation for the evaluation.

In this case, the heart rate of the mammal can be determined from the first and / or possibly existing second measured values. Alternatively or additionally, an external signal may also be supplied, e.g. from a corresponding patient monitor.

In an advantageous development of the invention, the evaluation effort can be minimized by signaling in the case of the measurement of a positive pressure at the withdrawal cannula that the withdrawal cannula can not be aspirated. In this respect, there is no need for further evaluation of the measured values, whereby the processing effort and thus the energy used can be minimized. In a further advantageous development of the invention, frequency components with a higher frequency are weighted more heavily in the evaluation than frequency components of a low frequency. It is advantageously exploited that at higher frequencies, the observed effect is more pronounced, i. that the difference of the change of the energy component in the higher frequencies is more pronounced than at lower frequencies. As a result, the security of recognizing the near concern can be increased.

Hereinafter, an exemplary arrangement according to an embodiment of the invention will be explained with reference to FIG.

Schematically, a withdrawal cannula EK is shown on the left half of the illustration, through which blood is taken from the vascular system of a mammal, for example a human. The withdrawal cannula EK opens into a lumen, which is shown as a downwardly directed arrow. An exemplary pressure sensor DS and an exemplary volumetric flow sensor VS are arranged on the removal cannula. The term "on the withdrawal cannula" is not necessarily to be understood spatially exactly, but it is sufficient if the pressure or the volume flow at the withdrawal cannula can be derived from the respective measured values of the sensors DS, VS.

The device according to the invention for detecting an aspiration of a withdrawal cannula 1 in the vascular system of a mammal has means for receiving first measured values I, for example a conventional interface, as in a plurality of medical devices is to be found, wherein the first measured values are selected from the group comprising the volume flow and pressure at the sampling cannula. The received measured values are fed to an evaluation unit CPU.

Depending on the implementation, an analog or a digital evaluation is carried out on the basis of the measured values by the evaluation unit CPU. Depending on the evaluation method, an analog circuit or a digital circuit may be provided. By way of example, when using an analysis in the frequency domain, the evaluation unit can be implemented as a digital signal processor, as a microcontroller, as an ASIC or as an FPGA. Furthermore, it can be provided that a memory MEM stores measured values or stores intermediate values of a processing by the evaluation unit CPU. In an analog evaluation, for example, a filtering by means of suitable high-pass and / or low-pass and / or band-pass filter or combination thereof and subsequent comparison with a threshold, for example with a comparator or alternatively an integrator, may be provided. During the evaluation, the first measured values are evaluated with respect to frequency-specific energy components, the approaching abutment of the sampling cannula being recognized upon reaching or exceeding a limit value, and the signal O being fed to a further processing or message SPK, LED, NET. For example, a warning signal can be output via an acoustic signal generator SPK, for example a loudspeaker. Alternatively or additionally, a warning signal via an optical signal transmitter LED, such as a light emitting diode, are output. Alternatively or additionally, an alarm in another room, eg via a network connection, can also be triggered by means of a remote warning. Without further ado it can also be provided that the blood pump BP is actuated differently, for example the volume flow is reduced, in order to counteract an approaching abutment of the withdrawal cannula EK. Alternatively or additionally, provision may also be made for a replacement volume EV, for example a NaCl solution or blood plasma, to be added in order to counteract an intravascular volume deficiency as a cause for a delivery of the withdrawal cannula. Without further processing, a separate processing can be provided for each measuring channel. However, processing within a device is advantageous, as shown in FIG. 6 for the measuring channel of the pressure sensor DS and the measuring channel of the volume flow sensor VS. In this respect, the device may further comprise means for receiving second measured values I, wherein the second measured values are selected from the group comprising volume flow and pressure at the sampling cannula, wherein the second measured values concern pressure, if the first measured values relate to volume flow or the second If the first measured values relate to pressure, the evaluation unit CPU is furthermore set up for evaluating the second measured values with respect to frequency-specific energy components, the approaching abutment of the sampling cannula being recognized or reaching a limit value as a signal for further processing or Message is supplied.

As already described above, frequency components which correspond to the heart rate or a harmonic of the heart rate of the mammal can be excluded from the evaluation for the evaluation, the heart rate of the mammal being determined from the first measured values and / or an external supplied signal. If a measurement of pressure values is available, it can also be provided that, in the case of the measurement of a pressure on the sampling cannula, a measured positive pressure signals that the sampling cannula can not be aspirated.

An exemplary evaluation will be outlined below. If there is a positive withdrawal pressure, the vessel wall can not be sucked to the cannula and it requires no further processing. If the withdrawal pressure is negative, first the measured values from the time domain are transformed into the frequency domain. In the frequency domain, the areas of the heart rate of the mammal and its harmonics are masked for further calculation. The energy in the remaining spectral ranges is summed up. The lower the pressure on the sampling cannula, the higher the likelihood that the vessel wall can be aspirated. Therefore, the removal pressure can be incorporated in an antiproportional measure of confidence.

FIG. 4 shows an unfiltered blood flow measurement. The corresponding calculated confidence measure is shown in FIG. In the blood flow, first oscillations can be seen approximately 90 seconds before the blood flow drops at 0 s. The confidence level exceeds the set threshold 87 seconds before aspirating the cannula.

Due to the established confidence level, cannulation can be detected early.

In addition, a permanent mild increase indicates hypovolemia.

Without going into detail here, of course, individual components of the device according to the invention may be provided by other devices, since they are already being used by other monitoring and / or control devices.

The device according to the invention is particularly advantageous if it is designed as part of a pump control, as this integration can be made meaningful, because typically pump controls already include a volume flow sensor VS, so that its measurements are already available. The device according to the invention can be used particularly advantageously in an extracorporeal lung assist device, in a heart-lung machine, in a hemodialysis device, in a hemodiafiltration device, in an extracorporeal circulation, or in an albumin dialysis device. As a result, it can be seen that the proposed arrangement according to the invention fulfills the requirements for a simple and cost-effective solution which can detect an early detection of the aspiration of a withdrawal cannula so that there is sufficient time to initiate countermeasures. Bezeichnunqsliste

Device 1

Withdrawal cannula EK

Pressure sensor DS

Volume flow sensor VS

Pump BP

Means for receiving the measured values I

Evaluation unit CPU

Memory MEM

Signal O

Acoustic signal transmitter SPK

Optical signal transmitter LED

Remote warning NET

Replacement volume EV

Claims

claims

A method of detecting aspiration of a sampling cannula in the vasculature of a mammal comprising the steps of:

Measuring first measured values, wherein the first measured values are selected from the group comprising volume flow and pressure at the withdrawal cannula (EK),

Evaluating the first measured values in relation to frequency-specific energy components, wherein when the limit value is reached or exceeded, the approaching abutment of the withdrawal cannula (EK) is recognized and is sent as a signal for further processing or reporting.

A method according to claim 1, characterized in that the method further comprises the steps of:

• Measuring second measured values, the second measured values being selected from the group comprising volume flow and pressure at the withdrawal cannula (EK), the second measured values relating to pressure, if the first measured values relate to volumetric flow or the second measured values relate to volumetric flow, if the first Measurements concern pressure,

Evaluating the second measured values with respect to frequency-specific energy components, wherein when the limit value is reached or exceeded, the approaching abutment of the withdrawal cannula (EK) is detected and is sent as a signal for further processing or reporting.

A method according to claim 1 or 2, characterized in that for the evaluation frequency components corresponding to the heart rate or a harmonic of the heart rate of the mammal are excluded from the evaluation, wherein the heart rate of the mammal of the first measured values and / or an external supplied signal is determined.

Method according to one of the preceding claims, characterized in that in the case of measuring a pressure at the withdrawal cannula (EK) a measured positive pressure signals that the withdrawal cannula (EK) can not be sucked. Method according to one of the preceding claims, characterized in that the method is carried out digitally and the measured values are measured at different times, wherein the method further comprises the step of performing a transformation of the first measured values in the frequency domain to obtain a first frequency spectrum of the first measured values ,

Method according to one of the preceding claims 1 to 4, characterized in that the measured values are evaluated analogously.

Method according to one of the preceding claims, characterized in that the evaluation frequency components with higher frequency weighted higher than frequency components of low frequency.

Device for detecting an aspiration of a withdrawal cannula (1) in the vascular system of a mammal comprising:

Means for receiving first measured values (I), the first measured values being selected from the group comprising volume flow and pressure at the withdrawal cannula (EK),

An evaluation unit (CPU), which is set up for evaluating the first measured values with respect to frequency-specific energy components, whereby when approaching or exceeding a limit value the approaching abutment of the withdrawal cannula (EK) is recognized and as signal (O) of further processing or message ( SPK; LED, NET) is supplied.

Device according to claim 8, characterized in that the device further comprises:

Means for receiving second measured values, wherein the second measured values are selected from the group comprising volume flow and pressure at the withdrawal cannula (EK), wherein the second measured values concern pressure, if the first measured values relate to volumetric flow or the second measured values relate to volumetric flow, if the first readings concern pressure,

• wherein the evaluation unit is further configured to evaluate the second measured values with respect to frequency-specific energy components, wherein when reaching or exceeding a limit, the approaching concerns of Removal cannula (EK) is detected and is supplied as a signal for further processing or message.

Apparatus according to claim 8 or 9, characterized in that for the evaluation frequency components corresponding to the heart rate or a harmonic of the heart rate of the mammal are excluded from the evaluation, wherein the heart rate of the mammal of the first measured values and / or an external supplied signal is determined.

Device according to one of the preceding claims 8 to 10, characterized in that in the case of measuring a pressure at the withdrawal cannula a measured positive pressure signals that the withdrawal cannula (EK) can not be sucked.

Device according to one of the preceding claims 6 to 1 1, characterized in that the evaluation unit is designed digitally and the measured values are measured at different times, wherein the evaluation unit is further configured to perform a transformation of the first measured values in the frequency domain to obtain a first frequency spectrum the first readings.

13. Device according to one of the preceding claims 8 to 1 1, characterized in that the evaluation unit is designed analogously.

Device according to one of the preceding claims 8 to 13, characterized in that the evaluation frequency components with higher frequency weighted higher than frequency components of low frequency.

Device according to one of the preceding claims 8 to 14, characterized in that the device is part of a pump control.

Use of the device according to one of the preceding claims 8 to 15 in an extracorporeal lung assist device, in a heart-lung machine, in a hemodialysis device, in a hemodiafiltration device, in an extracorporeal circulation, or in an albumin dialysis device.