AU1050499A

AU1050499A - Method and device for monitoring a catheter unit

Info

Publication number: AU1050499A
Application number: AU10504/99A
Authority: AU
Inventors: Rudolf Dunki; Rudolf Fuchslin; Peter F. Meier; Michel Willemin
Original assignee: PETER F MEIER
Current assignee: PETER F MEIER
Priority date: 1997-12-05
Filing date: 1998-11-26
Publication date: 1999-06-28
Also published as: CA2312746A1; CH692570A5; JP2001525229A; EP1035885A1; WO1999029356A1

Description

3836AU METHOD AND DEVICE FOR MONITORING A CATHETER UNIT 5 TECHNICAL FIELD The invention relates to a method for monitoring a catheter unit as recited in the generic of claim 1, and a device for monitoring a catheter unit as defined in the ge 10 neric part of claim 4. STATE OF THE ART 15 As generally known, a catheter is a tube-shaped instrument meant to be introduced into hollow organs, for in stance for emptying, flushing them, or for introducing a foodstuff and/or medicaments into them. The catheter can be stiff or supple, single or multi-barrelled, it can bear dis 20 tance-marks and be opaque or not for x-rays. It is named ac cording to its intended use as a catheter for the bladder, the urine duct, the heart, blood-vessels, the trachea, the bronchia and so on. The catheter together with its ancillary equipment, such as means for an infusion, forms a functional 25 device for entering or removing a liquid. In the present con text the term catheter unit is meant to encompass all known devices comprising one or several catheters, together with the attached cannula, connectors, connecting conduits, meter ing valves etc. 30 - 1- DESCRIPTION OF THE INVENTION Thus, the invention relates to medical devices which transfer a liquid from a reservoir through a catheter 5 into the body of a patient, or which are used to remove a fluid from the body of a patient through the use of a cathe ter. Such catheter may also be either peripher or intended for the central vein system. Such catheters should be moni tored with regard to their functionality because different 10 incidents may impair or interrupt the correct transfer of liquid from a reservoir to the intended location, or the re moval of liquid from the same; the malfunction may be caused by torn, cut or kinked conduits between the reservoir and the patient, by air bubbles in a tube that serves as a conduit, 15 or by a tearing away of the tube or the catheter from the pa tient. Until now the necessary monitoring is ensured in the course of the usual nursing activity of the hospital person nel; however, in some situations malfunctions of a catheter may occur which are discovered too late. 20 Therefore, the invention aims at removing this drawback by enabling the nursing personnel to correct a mal function in time; in other words it aims at easing the burden of the personnel and at simplifying the check of the catheter units, particularly at night. 25 To this end the invention is defined as recited in the main claims. An automatic monitoring of the catheter function, specially for long time periods, makes it possible to warn the nursing personnel when the liquid supply is im paired. 30 -2- BRIEF DESCRIPTION OF THE DRAWINGS The invention shall now be explained in more de tail through the description of preferred embodiments and 5 with the help of the drawings. Figure 1 schematically shows a first embodiment of the invention, figure 2 shows a diagram for the circuit used for a measurement of resistance in figure 1, 10 figure 3 schematically sketches a second embodi ment of the -invention, figure 4 is a diagram of a circuit for measuring a resistance in figure 3, and figure 5 is a very schematic presentation of an 15 embodiment of a part of the conduit of a catheter unit. A PREFERRED WAY TO REALIZE THE INVENTION 20 Figure 1 schematically shows a device for moni toring a peripheral catheter identified by numeral 1, where the catheter in this case delivers a liquid to a patient. The catheter is fed through a conduit 4 with a liquid 3 stored in a recipient 2. As a rule the conduit 4 consists in an elec 25 trically insulating rubber or plastic tube which, for the commodity of the patient, is as thin and supple as possible and can therefore comparatively easily be kinked or torn, thus impairing or interrupting the liquid flow. The letters P, Q and R identify three electrical contact locations; the 30 first location P is situated near the entry into the body, and hence in the vicinity of one end of the conduit 4, the second location Q is situated near the reservoir and hence in the vicinity of the other end of the conduit, and the third - 3 contact point is formed by an electrode 10 placed anywhere, for instance as a skin surface electrode or within the body. In principle, it would be possible to detect an impairment of the liquid supply to the patient by way of a single resis 5 tance measurement between the locations Q and R. In general, however, and particularly when supplying a physiological salt solution, the resistance between P and Q differs very much from that between P and R. Moreover, the result of an ex pected disturbance is very different in both cases; if the 10 catheter 1 or its supply conduit is torn out, then the resis tance between P and R becomes practically infinite, whilst a kink in the conduit 4 or the presence of air bubbles in this conduit only results in a finite change of the resistance be tween P and Q. As actual trials have shown, it is therefore 15 preferable to separately monitor the resistances across the paths P-Q and P-R with two different circuits, each of which is adapted to the particular electrical parameters of one path. To this end the circuits 7 and 11 are provided. The first circuit is connected with an electrode 5 placed in the 20 vicinity of location Q and with an electrode 6 placed in the vicinity of the location P of this conduit. Both electrodes are in contact with the liquid contained in the conduit and the circuit 7 can induce in a known way a current between the electrodes 5 and 6 and monitor the tension which this re 25 quires, as described below in connection with figure 2. In order to avoid an electrolyse even during a long lasting time interval, one will preferably use an alternative current, and also preferably a constant current, i.e. an alternative cur rent with a constant amplitude; the circuit is constructed so 30 that an alarm signal occurs at its output 8 when the resis tance measured between the locations P and Q exceeds a prede termined value or lies outside a predetermined interval. The circuit 11 monitors in a similar way the resistance between - 4 the electrodes 6 and 10 placed at locations P and R, respec tively. The two circuits can be built or adjusted in a known way so that each is optimally adapted to the resistances and the changes it must monitor. A second catheter could also be 5 used as a contact point instead of the skin electrode 10. The output signals of the circuits 7 and 11 are transmitted through an OR gate 15 to an alarm system (not shown) in order to trigger an alarm signal as soon as the re sistance across one of the two paths P-Q and P-R takes for 10 bidden values. In order to avoid false alarms, one or both circuits can be built so as to only generate an output signal when the resistance, respectively the allowed resistance in terval, is exceeded, respectively not maintained, for longer than some adjustable, minimal time interval (lasting for in 15 stance several seconds). As an example figure 2 shows a circuit diagram for the circuits 7 and 11 that can be used when each of these comprises a source of constant current and a voltage detec tor. This circuit comprises an oscillator 30 which feeds a 20 stabilized alternative current source 31, the output of which is connected both with electrode 5 of the monitoring device (see figure 1) and with the input of the high resistance pre amplifier 32. The pre-amplifier is followed by a bandpass filter 33, the output signal of which is transmitted through 25 an amplifier 34 to a unit 35 which measures the peak-to-peak value of the signal and generates a corresponding direct voltage which is led to one input of a comparator 37. The other input of this comparator receives a threshold voltage from an adjustable voltage source 36 and delivers an output 30 signal when the direct voltage which it receives from the unit 35 exceeds the threshold voltage. This output signal is delivered to a clock and stop circuit 39 driven by an oscil lator 38 and which can be reset by a reset signal and deliv - 5 ers an alarm signal at its output when it receives from the comparator 37 a signal exceeding a predetermined minimal time span of for instance one second. The adjustable voltage source 36, thus, allows to adjust, respectively predetermine, 5 the detected voltage, respectively resistance, which indi cates a disfunction of the catheter unit and triggers an alarm. Figure 3 schematically shows a preferred embodi ment of an unit according to the invention for monitoring the 10 flow of a catheter 21 for the central vein system; elements. with the same function as in figure 1 are identified by the same reference numbers. As in figure 1 liquid 3 from a re cipient 2 flows through a supple conduit 4 to the catheter, and the second and third contact points identified by the 15 letters Q and R are placed as in figure 1. However, because the catheter 21 intrudes deeply into the (only very sketchily indicated) body 22 of the patient, the first contact point can take any position between a location P 1 near the entry point of the catheter into the body of the patient and a lo 20 cation P 2 near the end of the catheter, provided the corre sponding electrode contacts the liquid flow. The position Px will depend on the intended use and in particular on whether it is more important to monitor the introduction of the catheter or its correct working during a long time stretch. 25 As a rule, the last part of the electrical connection of the electrode will consist either in an insulated conductor run ning inside the catheter, or the conductor will be placed in side an insulating wall of the catheter. In both cases the end of the conductor has a naked part which works as an elec 30 trode and protrudes into the liquid flow at the chosen loca tion. Either, another embodiment sketched in figure 3 may be used, where the contact points can be moved between the posi tion P 2 which lies near the end of the catheter and is pref - 6 erable during the introduction of the same, and the position

P

1 near the entry point of the catheter, which is preferable for a continuous monitoring. As sketched in figure 3, the electrode comprises for this purpose an insulated, suffi 5 ciently supple conductor which can glide forwards and back wards within the catheter and the rear extremity of which ex its laterally from the catheter or from the conductor that feeds it through a lateral, water-tight opening. Thus, the position Px of the electrode situated at the end of the insu 10 lating conductor can be chosen at will between the points P 1 and P 2 . As in the preceding example, two distinct circuits are provided for monitoring the resistances between the loca tions Px and Q, respectively Px and R. Whilst the circuit 7 is of the same type as the corresponding circuit 7 of figure 15 1, the circuit 11' comprises only one voltage detector, the details of which will now be briefly described with the help of figure 4. This has the advantage that no additional cur rents flow in the vicinity of the heart; further, one can use the electrical signal connected with the heart-beat. 20 Figure 4 shows the circuit diagram of a voltage detector of a type that may be used for the circuit 11'. The tension to be monitored is entered through an adapter, the output of which feeds an unit 44 through a bandpass filter 42 followed by an amplifier 43, and the unit 44 measures the 25 peak-to-peak values of the incoming signal and generates a corresponding direct voltage. The further part of the circuit is in principle the same as that described in connection with figure 2. Said direct voltage is fed into an input of a com parator 45 the other input of which receives a threshold 30 voltage from an adjustable tension source 46, and the com parator emits a signal when the direct voltage received from the unit 45 exceeds the threshold voltage. As in the preced ing example the timing and stopping circuit 49 which is -7driven by an oscillator 48 generates an alarm signal if it receives a signal from the comparator 47 during more than a predetermined time interval. Of course, the circuits 7 and 11, or 11', respec 5 tively, can be replaced by other devices known to one skilled in the art and which are able to adequately measure the re sistances in question. An unit with a drain catheter that removes fluids from the body can be monitored in basically the same manner. 10 The catheter monitoring according to the present invention can also be used for operations with a by-passed heart where the blood circulation is maintained through a pump situated outside the body and where the blood flow from the body to the pump and back occurs through a catheter unit. In this 15 case it is particularly useful to check for air bubbles in the flow of liquid or blood, respectively. When one uses conduits 4 with a comparatively large diameter of about 5 mm, and depending on the type of liquid, it can be useful for the detection of small air bub 20 bles to build the monitoring unit so that a part of the con duit 4 comprises a constriction with a smaller diameter of for instance 1-3 mm, where the conduit 4 can, for instance, be an infusion tube or a tube of the above-mentioned pump. Figure 5 shows a corresponding intermediate part 4' having a 25 smaller inner diameter than the conduit 4. This intermediate part is inserted into the conduit 4 with adapters 19 and cre ates a larger change of resistance in the conduit when there are air bubbles 17 in the liquid 18, which makes for a better detection of the air bubbles by the monitoring unit. Of 30 course, the example shown is only meant as an example for a possible embodiment, and the desired modification can also be obtained through other means, for instance by an appropriate shape or coating of the inner wall of the conduit 4, or else - 8 through an element that acts on this conduit from outside, for instance by a squeezing device. In figures 1 and 3 the device is schematically shown as a constriction 4'. The monitoring of the tube 4 and thereby of the 5 catheter unit can also be realized through other means in stead of the previously described, preferred electrical moni toring. Once can, for instance, use a plastic hose or the liquid itself as a light conductor, so that light entered at location Q can be detected at location P, or vice-versa. Ap 10 propriate devices for generating the light and for detecting it are commercially available. By analyzing the received light, one can thus detect an interruption, a kink or even a leak in the tubing and generate an alarm signal accordingly. The tubing and the liquid can also be used as a conductor of 15 sound, for instance of ultra-sound signals which may, for in stance, be entered at location Q and monitored at location P and which can also detect defects in the tubing. 20 -9-

Claims

1. Method for monitoring a catheter unit comprising at least a catheter (1) with at least one conduit (4) con nected with it, which method includes monitoring the trans mission of an optical, acoustical or electrical signal be tween a first location (Q) in or on the conduit and a second location (P; P 1 , Px, P 2 ) in or on the conduit and/or a loca tion (R) on the patient, in order to detect changes in the signal transmission due to a malfunction of the catheter unit and to trigger an alarm when a trouble arises.

2. Method according to claim 1, characterized in that one monitors the transmission of the signal along dif ferent paths, on one hand from the first to the second loca tion and on the other from there to a location situated on the patient.

3. Method according to claim 2, characterized in that one utilizes an electrical signal and generates an alarm signal when the electrical resistance across one or both paths exceeds a chosen value or gets out of a given range.

4. Device for monitoring a catheter unit with a fluid conduit (4), characterized in that it comprises at least monitoring means (5, 6, 7) able to detect a malfunction of the conduit, a disturbance in it, or a malfunction of the catheter, and to trigger an alarm signal.

5. Device according to claim 4 for implementing the method of claim 3, characterized in that it comprises a first circuit (7) for measuring the electrical resistance be tween an electrode (6) placed near or at the entry point of the catheter, and a second electrode (5) placed in the con duit or in a vessel which feeds it, this first circuit being - 10 - able to generate an alarm signal when said resistance exceeds a predetermined value or gets out of a given range.

6. Device according to claim 4 or 5, character ized in that it comprises a circuit (11, 11') for measuring the electrical resistance between a first electrode (6) placed near or at the entry point of the catheter and an electrode (10) placed in or on the skin of the patient, and for generating an alarm signal when this resistance exceeds a predetermined value or gets out of a given range.

7. Device according to claims 5 and 6, character ized by an OR gate (15) which receives the first and the sec ond alarm signal and the output of which is connected to an alarm device.

8. Device according to one of claims 4 to 7, characterized in that the first electrode (6) is movable lengthwise relative to the catheter.

9. Device according to one of claims 4 to 8, characterized by a constriction in the conduit or a modifica tion of its inner wall that acts on the liquid flow.

10. Device according to one of claims 4 to 9, characterized by an electrode which is situated in a wall of the catheter.

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