DE4014572A1 - Medical monitoring sensor for bleeding under bandage - responds to change in bandaging material i.e. dampness and/or colour to release alarm via evaluating circuit - Google Patents

Abstract

The sensor can be wound into the bandaging. A lead connection (42) conveys at least one signal dependent on the presence of blood to the outside as well as supplying power to the sensor arrangement (40). An evaluating circuit derives: an alarm signal from the measured value(s) in case of bleeding. The sensor (20) can be a moisture responsive type or an optical type responding to change of colour. The optical sensor can be additional to the dampness type. The latter can be based on change of electrical conductivity of the bandaging material and comprise two conductor paths (22,24) mounted on insulating, chemically inert surface, e.g. of plastics material. ADVANTAGE - Reliably self operating response to start of low blood loss, alerting medical personnel and avoiding need for more serious medical intervention arising from neglect.

Description

The invention relates to a bleeding sensor for monitoring Bleeding among bandages that are involved in the bandage can. In addition, a particularly advantageous method for Operation of such sensors specified.

The invention is based on the following problem:

In the course of medical catheter examinations and -Treatments in the area of arteries and under elevated Blood vessels under pressure (cardiac catheter, diagnostic arterial catheterization, cardiopulmonary bypass etc.) it often while arterial catheters are still positioned, or in the period after removing the catheter to situations with increased risk of bleeding. This is especially true if the arterial catheter over a long period of time (hours to days) the vessels, or if large-lumen catheters from arteries be removed. In such cases, pressure bandages are usually used created to minimize the risk of bleeding. It comes bleeding nevertheless, this can either be as bleeding in the surrounding tissue take place inside, or it comes to one Loss of blood to the outside along the puncture channel. In the former case it can also lead to major blood loss without being noticed the way of bleeding outwards, however, is the amount of lost blood not by the size of each Connective tissue spaces limited. There remains a bleeding to the outside unnoticed, it can easily lead to fatal blood loss. To prevent these blood losses, patients are treated according to the prior art after catheter examinations or -Therapies closely monitored, with strong arterial Bleeding, however, is enough for the frequently performed half-hourly Check no more, especially at night when the respective Patient sleep. Furthermore, it can e.g. B. during Heart operations using a heart-lung machine after Performing a cardiac catheter examination for undetected patients large blood losses come because of the potential exit point of the Blood does not routinely come under the sterile cover can be monitored. Heavy arterial bleeding can begin  a few minutes lead to blood loss that is not with life are more compatible.

It is therefore an object of the invention to provide an easy to use and to create the most reliable monitoring device possible, the already smaller bluish losses to the outside reliably automatically recognizes and alarms the medical staff. If possible, no significant changes to the best practice (dressing technique, catheter positioning and removal, etc.) become necessary. Furthermore, that should Device if possible in a reusable version be producible to avoid unnecessary costs through disposable material prevent.

This object is achieved in that a Sensor is integrated into the dressing, which is connected to one by the Bleeding-induced change in the dressing material responds and an alarm signal for such a change delivers.

For this purpose, for example, a sensor can be provided that points to the moisture content of the Dressing material responds (moisture sensor). Here can but due to moisture penetrating into the dressing, for example, if the patient is sweating, a false alarm to be triggered. A preferred sensor according to the present Invention therefore sees instead of the moisture sensor or in addition, an optical sensor in front of the by the bleeding caused a change in the color of the dressing material appeals.

In a preferred embodiment of the invention, both  Combined sensor concepts. Two become independent mutually working sensor principles applied, both as a prerequisite that the sensor lies directly on a gauze compress or similar used in the association need.

The first sensor (moisture sensor) preferably speaks the big difference in electrical conductivity between dry dressing material and soaked with blood Dressing material. By measuring the resistance between two Electrodes that rest firmly on the bandage, by means of a high impedance amplifier (no risk to the patient by currents) changes in the moisture content recognize the dressing material. Process the won Signal by means of a threshold switch, so this delivers Device already part of the particularly advantageous Double sensor.

The second method (optical sensor), the appearance of blood in Recognizing the pressure dressing mentioned above is based on the different reflection of colored light on different colored surfaces:

Since blood causes the dressing material to turn red, becomes at least one light source with non-red light, preferably a yellow or green light-emitting diode, and a light-sensitive receiver element (e.g. photodiode, Photo transistor, light sensitive resistor, photo element) used. Of course, a corresponding one must then be used electronic circuit for supplying the light source and Evaluation of the receiver signal be available. In a particularly preferred embodiment is the optical Sensor from two different colored light sources, e.g. B. LEDs (red and yellow or green) that the used illuminate white dressing material. The one from the illuminated Surface reflected light falls on an appropriately mounted photosensitive component (e.g. phototransistor) where the Intensity of the incident (reflected) light in one analog electrical signal is implemented. The spectrum of Sensitivity of the light detector must be used on the Light sources must be matched. When switching on alternately  each only one of the two light sources and measuring the respective intensity of a diffuse-white surface reflected light should be approximately the same electrical Intensity signals result (possibly adjustment by Front filter in front of the light detector or control of the Intensity of the individual light sources). Now the changes Color of the reflective surface, so you can find changes of the electrical light intensity signal that is used for the two different light sources turn out differently. At a red reflection surface will change the intensity of the reflected red light - compared to the white surface - change little, whereas the yellow or green light changes one shows significantly less reflection on the red surface. On this way, by comparing the two serially obtained signals statements about the color of the Meet the reflection surface.

The presence of the color of the reflection surface can thus be bleeding can be detected.

Further features and advantages of the invention result from the following, described with reference to the drawing Design example:

Show it:

Fig. 1 shows the structure of an optical bleeding sensor according to the invention.

Fig. 2 shows the structure of a combined (optical and moisture) sensor according to the invention.

FIGS. 3 and 4 an inventive electronic circuit for evaluating the sensor signals and for triggering the alarm.

The bleeding sensor 10 , which corresponds to a particularly preferred embodiment of the invention, comprises two independent sensor elements 20 ; 30 :

The moisture sensor 20 , which is based on the electrical conductivity, comprises two interconnected conductor tracks 22 , 24 which are applied to an insulating, chemically inert plastic surface. In order to prevent changes in the contact resistance due to corrosion and to ensure a long service life, the conductor tracks 22 , 24 should preferably consist of a noble metal (for example Au, Ag) or be coated with such a metal. The distances between the two mutually insulated, toothed conductor tracks 22 , 24 can be matched to the intended task, so that on the one hand they react sensitively enough, but on the other hand they are insensitive to disturbances caused by small impurities.

The optical sensor 30 can be easily integrated into the sensor surface of the conductivity sensor 20 . In order to ensure easy cleaning with great mechanical stability and reliability, the sensitive surface of the optical sensor 30 is cast with a highly transparent, chemically inert and physiologically harmless synthetic resin. The structure is as shown in FIG. 1. The two differently colored light sources 31 and 32 , like the light-sensitive element 33, are embedded in a dark-colored plastic 36 . The two light sources protrude into the space encapsulated with a highly transparent synthetic resin 35 , the optical connection of the light-sensitive element 33 to the reflective surface 34 is formed by a constricting channel 37 which protects the light-sensitive element 33 from direct scattered light from the two light sources 31 , 32 . The two light sources 31 , 32 are aligned at an acute angle to the reflecting surface 34 , so that light which is reflected at the interface between the highly transparent potting compound and the air (between the sensor and the reflecting surface) does not fall directly into the light-sensitive element 33 . This ensures that only light diffusely reflected on the reflecting surface 34 reaches and detects the photosensitive element. Because of the dark coloring of the carrier material 36 , multiple reflections cannot falsify the measurement result.

Fig. 2 shows the arrangement of the optical sensor 30 within the humidity sensor 20, the two toothed conductor tracks 22, 24 comprises.

The sensor signal is preferably evaluated by the electronic circuit shown in FIGS. 3 and 4:

This is preferably carried out in two parts: the circuit part 40 , which processes high-resistance analog signals, is attached directly in the assembly and is connected to the evaluation circuit 50 via a (preferably shielded) cable 42 . This can be operated at a distance from the patient. The electrical circuit diagram of the circuit part 40 is shown here in FIG. 3:

The electrical output signal of the photosensitive element 33 is fed to an operational amplifier 43 , which is configured as a threshold switch. The switching threshold is set such that when each of the two light sources 31 , 32 is switched on, the light reflected by a white, diffusely reflecting surface (e.g. dressing material, compresses, etc.) is safely above the response threshold. If a red colored material (e.g. blood-soaked dressing material) is used as the reflecting surface, the light emitted by the red light source must be reflected with such a high intensity that the reflected light is still safely above the response threshold that of the yellow one However, light (or green) light source no longer responds due to the lower reflection on the red surface. The intensities of the two light sources 31 , 32 and the response threshold of the light-sensitive element 33 are matched to one another in such a way that this behavior is reliably present in all discolorations of the dressing material caused by bleeding.

The conductivity sensor 20 is also connected to an operational amplifier 44 with a high input resistance, which is configured as a threshold switch. The response threshold is set in such a way (depending on the shape and distance of the conductor tracks of the sensor) that a reliable output signal is obtained when the dressing material is saturated with blood.

Of the evaluation circuit 50 , only the logical block diagram in FIG. 4 is given:

In the present exemplary embodiment, it consists of a ring counter 51 which is driven by an oscillator 52 . The ring counter controls a demultiplexer 53 and the two light sources 31 and 32 . The demultiplexer 53 receives the output signal P of the light-sensitive element 33 digitized by the operational amplifier 43 and generates three output signals:

• - Light reception when no light source is in operation.
• - Light reception when the light source is red in operation.
• - Light reception when light source is yellow / green in operation.

These three signals are fed together with the digitized by the operational amplifier 44 output signal L of the humidity sensor 20 to a controlled also by the ring counter 51 latch 54, from which it is also controlled by the ring counter 51 are passed to the memory 55. This memory combination 54 , 55 ensures that the signals measured sequentially one after the other are constantly and in parallel at a decoder 56 . According to the evaluation instruction described below, this controls the displays "Ok" 57 , "Bleeding" 58 , "Error" 59 and "External light" 60 as well as the alarm buzzer 61 and the relay for the remote alarm 62 .

The measuring process is advantageously divided into several phases, during which the individual sensor parts are activated one after the other and be queried. This measurement procedure is repeated cyclically. This ensures optimal operational reliability. The individual measurement phases are:

• 1. Query the light sensor without switching on one Light source to check for incident external light.
• 2. Switch on one of the two light sources (red) and Query the light sensor.
• 3. Switch off the first (red) light source and Switching on the second (e.g. yellow) light source, then the light sensor is queried again.
• 4. Switch off the second light source and query the Conductivity sensor.
• 5. Transfer the cached query Results from 1-4 as well as checking the results with possible triggering of an alarm.

If the query in the first phase gives a positive result (light present), an alarm with an error message is issued in all cases, since the bleeding detector device is not adequately positioned and extraneous light is incident. The evaluation circuit 50 indicates "extraneous light".

If the query results of the measurement phases two and three are positive (reflected light available), there is no alarm as long as no other measurement phase is found to be faulty, since there is apparently no red-colored material as the reflecting surface. The evaluation circuit 50 shows "Ok".

If the query of the light sensor only gives a positive signal when the red light source is switched on, but not while the yellow (or green) light source is switched on, an alarm is given in any case, since there is obviously a red discoloration. The evaluation circuit 50 indicates "bleeding".

If the query of the light sensor shows a positive result only when the yellow light source is switched on and not with red light, an alarm is triggered in any case, since there is a non-red discoloration which may mask the detection of bleeding. The evaluation circuit 50 indicates "errors".

If the query of the light sensor in the measurement phases two and three both results in a negative result (no reflected light), an alarm is triggered in any case, since the bleeding detector is obviously not adequately positioned (reflecting surface not in the focus of the measuring device) or an incorrect (non-white) reflective surface is used. The evaluation circuit 50 indicates "errors".

If the fourth phase is queried, the result is positive (Conductivity present = <moisture present), this is done an alarm, but which can be switched off manually in order to long lying pressure bandages the function of bleeding Sweat moisture does not impede the detector. display the evaluation circuit "bleeding".

This particularly preferred embodiment of the described above Invention and the described particularly advantageous Operation have the following particular advantages:  

The serial query of the individual sensors was chosen because this can greatly reduce the expenditure on components, and the sensor can be kept smaller by its construction.

Furthermore, there is a serial optical problem Measurement at one point of the association with two different ones Light sources more reliable than the simultaneous measurement of the different reflection intensities at two different Places.

By dividing the measurement into individual phases, the power consumption by the light sources is drastically reduced, which considerably simplifies the use of such a bleeding sensor as a small battery device with a long operating time. The use of only a single light-sensitive element is advantageous from a safety point of view, since only in this way can the function of the light-sensitive element and the components connected downstream of it be checked for their function (red light must lead to a positive result in measurement phase 2 , otherwise alarm).

The optical and the conductivity sensor advantageously in the value of their results valued differently. One by the unspecific Conductivity sensor triggered alarm can be switched off become the work of the more specific optical blood Detection does not interfere when the dressing used after longer time z. B. is soaked with sweat. A Error message of a sensor part or one by the optical Sensor triggered alarms cannot be switched off selectively because thereby questioning the general function of the bleeding detector would be asked.

When an alarm is triggered, the evaluation circuit 50 can emit a loud intermittent warning tone, for example. With an additional built-in relay 62 , the bleeding detector can also be connected to a central warning system in a potential-free manner. The triggering of the warning tone on the device itself is not affected.

The bleeding sensor is preferably waterproof in plastic shed so that an intensive cleaning, as well as a Low temperature sterilization (formaldehyde, ethylene oxide etc.) is easily possible and the sensor as a reusable component too can be used in sterile fields.

Claims (23)

1. bleeding sensor for monitoring bleeding among dressings, which can be integrated into the dressing, characterized by a sensor device ( 40 ) which responds to a bleeding-related change in the dressing material ( 34 ), a line connection ( 42 ) for transmitting at least one of the presence a bleeding-dependent signal to the outside as well as for supplying energy to the sensor device ( 40 ) and an evaluation circuit ( 50 ) which, in the event of bleeding, obtains an alarm signal from at least one measured value obtained from the sensor device ( 40 ). 2. Bleeding sensor according to claim 1, characterized in that the sensor device comprises at least one sensor ( 20 ) which responds to a bleeding-related change in the moisture content of the dressing material ( 34 ) (moisture sensor). 3. Bleeding sensor according to claim 1, characterized in that the sensor device ( 40 ) comprises at least one sensor ( 30 ) which responds to a bleeding-related change in the color of the dressing material ( 34 ) (optical sensor). 4. Bleeding sensor according to claim 1, characterized in that in addition to the moisture sensor ( 20 ) at least one optical sensor ( 30 ) is provided according to claim 3. 5. bleeding sensor according to at least one of claims 2 or 4, characterized in that the moisture sensor ( 20 ) responds to the moisture-related change in the electrical resistance of the dressing material ( 34 ). 6. Bleeding sensor according to claim 5, characterized in that the moisture sensor ( 20 ) comprises two conductor tracks ( 22 , 24 ) which are attached to an electrically insulating, chemically inert surface. 7. bleeding sensor according to claim 7, characterized, that the surface is made of plastic. 8. bleeding sensor according to claim 6 or 7, characterized in that the two conductor tracks ( 22 , 24 ) are interlocked. 9. bleeding sensor according to at least one of claims 6, 7 or 8, characterized in that at least the surface of the conductor tracks ( 22 , 24 ) facing the dressing material consists of a noble metal. 10. bleeding sensor according to at least one of claims 3 or 4, characterized in that the optical sensor ( 30 ) contains at least one light-emitting ( 32 ) and at least one light-receiving component ( 33 ). 11. Bleeding sensor according to claim 10, characterized in that the light-emitting component ( 31 ) or one of the light-emitting components ( 31 , 32 ) can emit light of a color other than red. 12. Bleeding sensor according to one of claims 10 or 11, characterized in that light-emitting diodes are used as light-emitting components ( 31 , 32 ). 13. Bleeding sensor according to one of claims 10, 11 or 12, characterized in that phototransistors are used as light-receiving components ( 33 ). 14. Bleeding sensor according to one of claims 10 to 14, characterized in that the one or more light-emitting components ( 31 , 32 ) and the one or more light-receiving components ( 33 ) are arranged such that only the light of the dressing material ( 34 ) diffusely scattered or the light-emitting components ( 31 , 32 ) can be received. 15. Bleeding sensor according to claim 14, characterized in that the or the light-emitting and the or the light-receiving components ( 31 , 32 , 33 ) are arranged close together so that the directions of their maximum light radiation or light sensitivity in parallel or at most at an acute angle lie perpendicular to the surface of the dressing material ( 34 ). 16. Bleeding sensor according to at least one of claims 10 to 15, characterized in that at least one of the light-emitting components ( 32 ) emits red light and at least one further light-emitting component ( 31 ) is provided, which emits yellow or green light and the different light colors individually can be adjusted. 17. Bleeding sensor according to one of claims 10 to 15, characterized in that one or more light-emitting components ( 31 , 32 ) are provided, the light color of which can be switched between red and green or yellow. 18. Bleeding sensor according to claim 16, characterized in that only one between two or more light-emitting components ( 31 , 32 ) arranged light-receiving component ( 33 ) is provided and that the axis of the highest light sensitivity of the light-receiving component ( 33 ) on a certain section of Association surface (34) is perpendicular, while the light emission axes of the light-emitting components (31, 32) enclose an acute angle with this axis, so that the light-emitting components (31, 32) illuminate the given portion alike. 19. Bleeding sensor according to claim 18, characterized in that it has a curved recess filled with translucent material ( 35 ), in the middle of which the light-receiving component ( 33 ) is attached, while the light-emitting components ( 31 , 32 ) approximately halfway between the middle and the edge of the recess are attached. 20. Bleeding sensor according to claim 19, characterized in that the recess is surrounded by black colored, opaque and electrically insulating material ( 36 ). 21. Bleeding sensor according to claim 20, characterized in that the light-receiving component ( 33 ) is sunk in the material ( 36 ) and is only connected to the recess by a thin, translucent channel ( 37 ) running perpendicular to the sensor surface. 22. A method for operating a bleeding sensor according to at least one of claims 16 to 21, characterized by at least the following method steps in any order:

• 1) Check whether the light-receiving component (s) respond if none of the light-emitting components is working;
• 2) Check whether the light-receiving component (s) respond if only the red light-emitting component (s) are working;
• 3) checking whether the component or components receiving light respond if only the component or components emitting yellow or green light are working;

whereby an alarm is only triggered if the (1) or do not respond to the light-receiving components, while responding to both (2) and (3).