WO2010130723A1

WO2010130723A1 - Central venous line insertion monitoring system

Info

Publication number: WO2010130723A1
Application number: PCT/EP2010/056434
Authority: WO
Inventors: Maurits Karel Konings
Original assignee: Umc Utrecht Participates B.V.
Priority date: 2009-05-11
Filing date: 2010-05-11
Publication date: 2010-11-18

Abstract

A catheter insertion monitor comprises a signal generator for generating a patient safe electrical signal at a first frequency higher than IkHz. This signal is fed into a human or animal body via a catheter and a return electrode. The catheter insertion monitor further has an amplifier for measuring electrical signals from the at least one signal generator by at least two sensor electrodes attached to the body. A processing unit generates a catheter position indicating signal by demodulating the signal from the amplifier of the first frequency and further generating an,,strength of cardiac modulation" (SCM) signal being the peak to peak value of this demodulated signal which has a low frequency modulation caused by the cardiac cycle. The SCM signal has a maximum when the catheter is close to the cavo-atrial junction.

Description

Central Venous Line Insertion Monitoring System

Field of the invention

The invention assists in placement of venous catheters such as central venous catheters CVCs and PICC (Peripherally Inserted Central Catheter) lines, feeding tubes and other catheters. More generally, the invention relates to the guidance, positioning and placement confirmation of tubes or elongated bodies such as catheters, guide wires, stylets to be inserted into bodies, especially the vasculature of human or animal bodies.

Description of the related art

Access of vasculature of humans and mammals has long performed for clinical purposes to administer medicines and provide therapy. Various procedures exist for venous or arterial access. Central venous lines, including PICC lines, are frequently used for short or long term access, for example, for infusions of concentrated solutions, monitoring of blood pressures (e.g., in central venous and pulmonary artery), for estimating cardiac or vascular parameters and to save frequent small injections or drips in arms, to reduce hospital stay and administer medicine at home.

While the optimal position of the catheter tip is still debated, there is general agreement that for a therapy over several days the catheter tip must be positioned outside of the right atrium in order to avoid damageing to the heart and to avoid thrombosis. If the access occurs via the superior vena cava, the catheter tip should be positioned approximately 2 cm before the opening into the right atrium or the cavo-atrial junction, although the ideal location is still under professional debate. Incorrect catheter tip position could lead to potentially lethal complications including cardiac (pericardial) tamponade caused by perforation and thrombus formation .

Various solutions exist to determine catheter tip placement (or equivalently catheter introduction depth).

The catheter can be introduced under angiographic control. This is expensive, time consuming and mostly disruptive to the process of care and therefore not frequently used.

Most commonly, the landmark method is used to provide a rough assessment of depth by measuring on external landmarks. These landmarks are external and the method is not precise, the method cannot account for irregular anatomies or detect false placement (e.g., in the jugular vein). This method implies frequent re-positioning after fluoroscopic control.

Fluoroscopic control (usually by thoracic x-ray/radiography of the chest) has become standard after the introduction, and is also used to assist introducing catheters under angiographic control. It uses an external irradiation source with ionizing radiation and imaging, and requires a separate step at point of care (damage already done when visible). It is also criticized for being difficult to read and giving inaccurate results.

Ultrasound assessment via the oesophagus: Transesophageal Echocardiograpic Evaluation. This is complicated and invasive, requires extra work , and is very patient unfriendly.

Electrocardiographic guidance ECG as disclosed in EP 0210340. The autologous ECG signal is recorded with the catheter tip functioning as one of the electrodes. If the catheter tip is situated in the right atrium the ECG will record an elevated P-wave. When the catheter is pulled back into the vena cava superior the atrial-P will assume a normal shape. The position of the catheter tip correlates with the morphology of the P-wave. An ECG recording performed during insertion of the catheter can be used to achieve correct positioning of the catheter to start with and thereby reduce the frequency of having to replace wrongly positioned catheters. Intraoperative^ the ECG recording is a practical method of achieving correct and extracardial placement of the catheter tip.

Magnetic positioning as disclosed in WO 2008/124234 makes use of the extracorporeal detection of electromagnetic fields resulting by magnets on the catheter. This requires special equipment and cannot detect the distance to the heart.

Alternatively, currents can be induced by sources connected to electrodes on the surface of the body and be used to determine the location of a catheter equipped with means to measure the potential at the end of the catheter EP 0775 466. This makes use of the effect that the strength of the signal varies significantly with the distance to the electrodes. Different current signals are applied to substantially orthogonally placed electrode pairs so as to distinguish them from each other. Again, they do not provide information about the location with respect to the heart and require expensive equipment.

In general, the use of bioelectric impedance measurements for the assessment of biologic information has a long history. It was discovered that movements such as those caused by respiration or heartbeat cause fluctuations in the impedance, which can be measured to attempt to gain insight into biological processes. It is known to be preferable to separate current carrying and potential measuring electrodes to increase resolution. The electrodes are maintained at fixed positions to avoid rapid variations of the measured field that would occur especially when the current carrying electrodes are moved. Examples are known in impedance cardiography. The use of impedance measurements with intravascular catheters is known for diagnostic radiology, such as the detection of fatty lesions in arteries. Here it was noted that a displacement of the current source resulted in strong variances of the measurement electrodes. It uses only electrodes on the catheter; no external electrodes are used and modulations of the potential distribution by the heartbeat are not monitored. It was noted that differential measurements with three or more adjacent electrodes provides high sensitivity for the localization of secondary sources and allow the mapping of intravascular lesions.

Other concepts combine the use of several technologies to obtain more information especially about the location relative to the heart, notably ECG and related information with imaging ultrasound, non-imaging ultrasound, pressure signals, or catheters with magnets.

Summary of the invention

The problem to be solved by the invention is to improve a catheter insertion monitor, a catheter insertion monitoring system and a method to use such a monitoring system to simplify placement of catheters, in particular of PICC catheters. The monitoring system should be inexpensive and easy to use. It should not require any expensive equipment like x-ray apparatus. Placement of catheters should become so easy, that it can be done by nursing staff and no physician is required. The monitoring system shall provide a signal that indicates the relative distance of the PICC catheter tip with respect to the heart safely, easy, non- invasively, cost-effective, and with minimal discomfort to the patient, and without the need of knowing the exact location of the heart inside the thorax beforehand. Solutions of the problem are described in the independent claims. The dependent claims relate to further improvements of the invention.

The catheter insertion monitoring system comprises an insertion monitor being connected to a catheter and a return electrode. Furthermore the insertion monitor is connected to at least two sensor electrodes. The insertion monitor comprises at least one signal generator to generate an electrical signal of a first frequency/ preferably above 1 kHz, preferably below lMhz, most preferably in a range between 1OkHz and 20 kHz. It is preferably a patient safe signal preferably below 5V and lOOμA, most preferably at 3V and lOμA. This electrical signal is applied between the return electrode and the catheter. The return electrode may be any electrode attached to the body on the head or neck, or on the arm into which the catheter is inserted, but preferably on the head behind the ear closest to the arm into which the catheter is inserted. The signal is conducted by a conductor in the catheter preferably to the tip of the catheter, such as a metallic guide wire or stiffener, or simply a saline-filled lumen present inside the catheter for the entire length of the catheter. While the catheter has an isolated body, its end or a predetermined current exit location is without isolation to allow the signal to exit from the catheter. For sensing this signal at least two sensor electrodes are attached preferably on the thoracic skin. They feed a signal into an amplifier and an processing unit of the insertion monitor. By evaluating and comparing the signals measured at the sensor electrodes, the location of the catheter tip can be precisely identified.

Preferably the insertion monitor demodulates the signal from the amplifier to remove the first frequency. This may be done by RMS evaluation or rectifying and low pass filtering. This demodulated signal value has a further modulation according to the cardiac cycle. From the demodulated signal preferably ,,strength of cardiac modulation" values, further referenced as SCM values are calculated as the peak to peak values of individual cardiac cycles. This may be done by cal- culating the difference of the demodulated values of individual maximums and the demodulated values of their succeeding minimums. These SCM values vary with the position of the catheter tip in relation to the heart. They have a maximum near the cavo-atrial junction.

In a further embodiment compensation for individual factors like subcutaneous muscle and fat layers below the thoracic skin are made. In general SCM is proportional to the product of the transmission function G_c from catheter tip to heart and G_E from heart to a sensor electrode: SCM ~ G_c ^■ G_E .

For compensation of person specific factors in a first catheter-based raw SCM measurement of SCM ^ , a reference measurement is made. For this purpose an additional skin electrode preferably somewhere on the lower limbs of the body (leg, knee, or ankle) is connected to the signal generator for feeding an electrical signal into the body. Preferably the signal generator is disconnected from the catheter and re-connected to the additional skin electrode. For this purpose the signal generator may have an additional output and a switch to switch the signal between the outputs, so that only one output delivers a signal at one time, thus allowing time multiplexing of the measurements. Alternatively different signal generators may be provided for delivering different signals, for example, at different frequencies to the catheter and the additional skin electrode. In this case measurements using both signals may be made at the same time. In this embodiment the reference SCM value SCM ^ is determined by determining an SCM value from the amplifier signal as described above. It is proportional to the product of the transmission function G_s from additional skin electrode to heart and G_E from heart to a sensor electrode: SCM ^ ~ G_S G_E . Finally the compensated SCM value SCM _C0MP is obtained by dividing the uncompensated SCM _RAW value by the reference SCM ^ value: SCM _C0MP = ^- which is therefore independent from GE up to a first order

SCM ^ accuracy, as well as independent from the Stroke Volume of the heart beat.

When it cannot be assumed that the PICC nurse or PICC insertion operator will move the catheter at a more-or-less constant speed inside the body. The catheter will have various traveling speeds, including standstill and even moving backwards from time to time. Therefore, one cannot simply use a "spatial derivative" in the SCM function to indicate the catheter position, because the relation between catheter displacement and time is essentially unknown. Accordingly in another preferred embodiment a non-spatiotemporal algorithm is used that does not depend on assumptions concerning catheter travel speeds. It does however depend on the direction of the motion (i.e., pushing the catheter further into the body, or pulling the catheter a bit out of the body). The direction of motion is evaluated by an additional measurement like a position sensor. In this way, reaching of the correct positioning of the catheter can be signaled to the operator by simply comparing the value of the compensated SCM function SCM _C0MP by at least one predetermined threshold values. Preferably this can be done by detecting that the SCM _C0MP reaches a maximum that has a value within a range of predetermined values.

In one embodiment, the device instructs the user to insert the catheter at essentially constant speed and direction or to provide user input about the nature of the speed and direction of introduction. This enables the correlation of elapsed time to spatial displacement and thus the calculation of spatial derivatives and the straightforward determination of maxima.

In a further embodiment audio and/or visual indications may be triggered when a predetermined value of the SCM function is reached or when the SCM function reaches a maximum that has a value within a range of predetermined values. In another preferred embodiment the device translates SCM_C0MP , SCM ^w and/or SCM ^ and/or a related variable into analog user feedback such as audible or visible signals of varying parameters like intensity or frequency to allow the user to determine the correct position based on experience and a maximum detected by the processing unit.

In a further embodiment, some or all of the sensing electrodes may be used as current feeding electrodes using yet another frequency, which, in combination with the normal operation described above, and invoking the reciprocity principle from (bio-)electromagnetism, provides extra information about the different contributions to the signal of the various moving parts inside the heart, and provides extra spatial resolution. Preferably at least one additional current source operating at frequencies different from the first frequency are provided to perform reciprocal stimulation to at least one sensor electrode, and that at least one sensor electrode, as well as the catheter lead, are connected to amplifiers to measure the vol-tages at the frequencies different from the first frequency.

In a further embodiment at least one additional sensor electrode is placed on the central vertical line on the thoracic skin above the heart, and another electrode is placed on the thoracic ribs a few cm below the heart, and slightly to the left (in patient's own coordinates).

In another embodiment two additional electrodes are provided on the central vertical line on the thoracic skin above the heart, but very near to the other measuring electrode above the heart, thus forming a triplet of measuring electrodes above the heart.

The monitoring system may use these measurement electrodes to determine additional SCM values. If these values exceed predetermined threshold values the monitoring system can issue warnings. For example a thorax warning may be issued if the catheter tip passes below the middle electrode of a triplet inside the thorax.

In a further embodiment a warning may be issued for an erroneous entry into the jugular vein by using a triplet of measuring electrodes in the neck.

A further aspect of the invention relates to a method for detecting the position of a venous catheter close to the heart. This method comprises the following steps:

a) supplying an electrical signal of a first frequency into an catheter and a return electrode,

b) amplifying the electrical signal of at least two sensor electrodes placed close to the heart,

c) demodulating the electrical signal,

d) generating a SCM signal by evaluating the peak to peak value of the demodulated signal,

e) evaluating a maximum of the SCM signal to detect the position of the catheter essentially in the cavo-atrial junction.

In a further embodiment the following steps take place before evaluating a maximum of the SCM signal in step e):

f) supplying an electrical signal into an additional skin electrode and a return electrode,

g) amplifying the electrical signal of at least two sensor electrodes placed close to the heart,

h) demodulating the electrical signal, i) generating a reference SCM signal by evaluating the peak to peak value of the demodulated signal,

j) dividing the SCM signal from step d) by the reference SCM signal to obtain a corrected SCM signal.

k) evaluating a maximum of the corrected SCM signal to detect the position of the catheter essentially in the cavo-atrial junction.

Here step k) replaces previous step e).

This method preferably uses the above described catheter monitor and/or catheter monitoring system.

Another aspect of the invention relates to a method for using such a monitoring system by inserting a catheter into a vein until the monitoring system signals the correct positioning of the catheter tip. After the catheter has reached the position signalled by the insertion monitor it may be necessary to insert or remove the catheter for a predetermined distance, preferably in the range of lcm to 2cm to achieve optimum placement of the catheter.

As is obvious to one skilled in the art, the invention can be used in a number of generalizations, even with different systems or tubes. Such generalization could include for example, a catheter being essentially any tube of with a cladding of low conductivity (electrically isolating). The end of the catheter where the current exits, could be an open point in the isolating cladding anywhere along the catheter. The catheter may have a conducting core where at least part of the core of the tube is electrically conducting and part is isolated until the position to be detected. The catheter may be filled with a conducting liquid or may contain a wire. Preferably it has a conductive tip. Instead of looking at the variance of the voltage, one could record it at different times that mark the same position in different heart cycles while the catheter is moved towards the heart and con- elude the proximity to the heart from a rapid increase from one heart cycle to the next. The body can be a human or an animal body or a part thereof. The sensor electrodes can be any points of electric contact comprising any electrically conducting material, but are preferably classic ECG like electrodes.

Description of Drawings

In the following the invention will be described by way of example, without limitation of the general inventive concept, on examples of embodiment with reference to the drawings.

Figure 1 shows the insertion monitoring system connected to a patient.

Figure 2 shows an exemplary embodiment using two sensor electrodes.

Figure 3 shows an exemplary embodiment using six sensor electrodes.

Figure 4 shows a measured signal at the output of amplifier 41.

Figure 5 shows the strength of the cardiac modulation over the position of the catheter.

Figure 6 shows the electrical transfer functions.

In figure 1 a preferred embodiment is shown. The insertion monitor 40 comprises a signal generator 43 for generating a catheter signal, an amplifier 41 for measuring sensor electrode signals, and processing unit 42 for evaluating these signals and a control unit 44. Preferably all these individual parts are contained in a common housing, but they may also be distributed into separate units. The sig- nal generator 43 is connected to a return electrode by the return electrode line 22 and to the catheter 30 via catheter signal line 21. Here a return electrode in form of an arm strap 31 attached to the arm 12 of patient 10 is shown. The catheter is preferably an isolated tube having an inner conductor leading to an un- isolated tip 39. Furthermore at least two sensor electrodes 32, 33 are attached to the patient's body close to the heart 11. The first sensor electrode 32 is connected via first sensor line 23 to amplifier 41, while the second sensor electrode 33 is connected via second sensor line 24 to amplifier 41. The amplifier is preferably a difference amplifier, amplifying the difference of the signals of the sensor electrodes. The amplified signal from amplifier 41 is fed to processing unit 42 for further processing and generating a signal indicating the position of the catheter tip 39.

The output signal of amplifier 41 shows a slow variation in strength that follows the heart rhythm in time, because the very pumping action of the heart represents a displacement of the well-conducting blood volumes within the atria and ventricles in the heart, and hence an oscillating conductivity distribution within the thorax, oscillating with the frequency (typically a few Hz) of the heart.

In figure 2 a patient is shown with a first sensor electrode 32 above the heart and a second sensor electrode 33 below the heart.

Preferably, sensor electrode 32 is placed on the central vertical sternal line, about 8 cm below the incisura iugularis of the manibrium, and sensor elec-trode 33 is placed on the skin above the end-points of the ribs, at about 5 cm below the apex of the heart. Preferably the sensor electrode 33 may be placed slightly to the right.

In figure 3 a more complex configuration comprising six additional sensor electrodes 33 - 37 at different locations is shown. Electrode 34 is positioned at the bone directly behind the ear, and serves as an alternative current feeding electrode, replacing current feeding electrode 31. Additional sensor electrodes 35 and 36 are both placed on the central vertical sternal line; the heart-to-heart distance between 32 and 35, as well as between 35 and 36, does preferably not exceed 3cm. Electrode 37 is the same as electrode 38.

Figure 4 shows a measured signal at the output of amplifier 41 which has further been demodulated. This signal is measured in Volt over time from 0 to 5s. As can be seen in the graph, a variation (oscillation) of the voltage in the rhythm of the heart is present. This low-frequency variation or oscillation will be referred to as the "cardiac modulation of the voltages". Simultaneously with the measurement of the AC voltage differences, an ECG is measured using the same electrodes. The time-points of the R-peaks of the ECG correlate with the peaks 60, 62, 64. During each cardiac cycle, (i.e., between two of the peaks 60, 62, 64) the cardiac modulation of the voltages causes a maximum (peak) 60, 62, 64, as well as a minimum 61, 63, 65 to be present in the graph within that cardiac cycle. The peak to peak values, e.g. the value of an individual maximum minus the value of the following minimum (60-61, 62-63, 64-65) is further referred as the "strength of cardiac modulation" (SCM) as will be shown in the next figure. The SCM is strongly dependent on the relative distance between catheter tip 39 and the heart 11. This distance happens to be the crucial parameter in optimal PICC catheter positioning.

Figure 5 shows the SCM over the position of the catheter tip in millimeters. At position "x=l", a maximum is reached. This position roughly corresponds to the cavo-atrial junction. The vertical axis scale is in Volt.

Figure 6 shows the compensated SCM _C0MP over the position of the catheter tip in millimeters. At position "x=l", a maximum is reached. This position roughly corresponds to the cavo-atrial junction. The vertical axis scale is in relative units. These units are independent of specific body properties. Therefore different SCM _C0MP curves can directly be compared with each other.

Figure 7 shows the signal path from catheter tip 39 to the sensor electrodes 32, 33. The signal transfer from catheter tip 39 to heart 11 is described by transmission function G_c 50. Signal from the heart is then coupled via transmission function G_E (51) to the sensor electrodes 32, 33. Signal from the additional skin electrode 38 is coupled via transmission function G_s (52) to the heart.

List of reference numerals

10 patient

11 heart

12 arm

21 catheter signal line

22 return line

23 first sensor line

24 second sensor line

30 catheter

31 arm strap with return electrode

32 first sensor electrode

33 second sensor electrode 34 - 37 additional sensor electrodes

38 additional skin electrode

39 catheter tip

40 catheter insertion monitor

41 amplifier

42 processing unit

43 signal generator

44 control unit

50 transmission function Gc

51 transmission function G_E

52 transmission function G₅

60.62.64 signal maximum

61.63.65 signal minimum

66 - 69 signal maximum in the SCM signal

Claims

1. Catheter insertion monitor comprising

- at least one signal generator (43) for generating an electrical signal at a first frequency to be fed into a human or animal body (10) via a catheter (30) and a return electrode (31), and

- an amplifier (41) for measuring electrical signals from the at least one signal generator by at least two sensor electrodes (32 - 37) attached to the body, and

an processing unit (42) generating a catheter position indicating signal by demodulating the signal from the amplifier of the first frequency and further generating an SCM signal being the peak to peak value of this demodulated signal having a low frequency modulation caused by the cardiac cycle, wherein the catheter position indicating signal has a maximum near the cavo-atrial junction.

2. Catheter insertion monitor according to claim 1 characterized in that the at least one signal generator (43) is provided for generating an electrical reference signal to be fed into a human or animal body (10) via an additional skin electrode and a return electrode (31), and the processing unit (42) is configured for generating a reference SCM signal being the peak to peak value of the demodulated signal from the amplifier and for further generating a compensated SCM signal by further dividing a catheter signal based SCM signal by the reference SCM signal.

3. Catheter insertion monitor according to claim 2 characterized in that the catheter position indicating signal is generated by comparing the compensated SCM signal with predetermined threshold values.

4. Catheter insertion monitoring system comprising a catheter insertion monitor (40) according to any one of claims 1 - 4, a catheter (30) having an isolated body and an inner conductor, at least one return electrode (31) and at least two sensor electrodes (32 - 37), the catheter and the at least one return electrodes being connected to the signal generator of the catheter insertion monitor (40), and the at least two sensor electrodes (32 - 37) being connected to the amplifier of the catheter insertion monitor (40).

5. Catheter insertion monitoring system according to claim 5, characterized in that the catheter has a conductive tip.

6. Catheter insertion monitoring system according to claim 5, characterized in that additional sensor electrodes (34 - 37) are provided and the monitoring system is enabled to calculate additional SCM values from the signals of these additional sensor electrodes to determine the catheter approaching at least one of these additional sensor electrodes.

7. Catheter insertion monitoring system according to claim 5, characterized in that at least one additional current source operating at frequencies different from the first frequency are provided to perform reciprocal stimulation to at least one sensor electrode, and that at least one sensor electrode, as well as the catheter lead, are connected to amplifiers to measure the voltages at the frequencies different from the first frequency.

8. Method for detecting the position of a venous catheter close to the heart of a human or animal body comprising the steps of:

c) demodulating the electrical signal,

e) evaluating a maximum of the SCM signal to detect the position of the catheter in the cavo-atrial junction.

9. Method according to claim 8 before evaluating a maximum of the SCM signal in step e) comprising the steps of:

h) demodulating the electrical signal,

i) generating a reference SCM signal by evaluating the peak to peak value of the demodulated signal, j) dividing the SCM signal from step d) by the reference SCM signal to obtain a corrected SCM signal.

k) evaluating a maximum of the corrected SCM signal to detect the position of the catheter in the cavo-atrial junction.