Abstract:
A high-frequency surgical testing device for testing a neutral electrode during treatment, particularly during monopolar coagulation of biological tissue using a high-frequency current. The neutral electrode includes at least one first electrically conductive electrode segment having a first cable for connecting to a high-frequency generator, and a second electrically conductive electrode segment having a second cable for connecting to a high-frequency generator, the first and second electrode segments contacting the tissue. The test device includes an encoding element having a code for describing the neutral electrode and a measurement device for capturing the code describing the neutral electrode. The test device allows an identification of the neutral electrode to ensure safety.

Description:
FIELD OF THE INVENTION 
       [0001]    The disclosed embodiments relate to a high-frequency surgical testing device for testing a neutral electrode during treatment, particularly monopolar coagulation of biological tissue by means of a high-frequency current. 
       BACKGROUND 
       [0002]    High-frequency surgery has been used for many years in both human and veterinary medicine in order to coagulate and/or cut biological tissue. With the aid of suitable electrosurgical instruments, high-frequency current is conducted through the tissue to be treated, so that said tissue changes due to protein coagulation and dehydration. In the process, the tissue contracts such that the vessels become closed and bleeding is stopped. A subsequent increase in the current density brings about explosive evaporation of the tissue fluid and tearing open of the cell membranes, so that the tissue is fully parted. 
         [0003]    Both bipolar and monopolar techniques are used for the thermal treatment of biological tissue. In the case of monopolar arrangements, the high-frequency current fed from the high-frequency generator to the electrosurgical instrument is applied to the tissue to be treated via a ‘different’ electrode, wherein the current path runs through the body of a patient to an ‘indifferent’ neutral electrode and from there back to the high-frequency generator. A high current density per unit area is provided at the ‘different’ electrode for the treatment, whereas at the ‘indifferent’ electrode, the current density per unit area is significantly less compared with the ‘different’ electrode. This can be achieved with a suitably large area configuration of the neutral electrode. This arrangement ensures that no injuries, such as burns, occur in the tissue at the interface between the tissue and the neutral electrode. 
         [0004]    In order to perform a coagulation, a high-frequency surgical apparatus is used which comprises an high-frequency surgical device with an high-frequency generator to create a high-frequency voltage or a high-frequency alternating current, as well as switching equipment and/or control and regulating equipment for activating or deactivating, or more generally for controlling the high-frequency generator. 
         [0005]    For the safety of the patient, provision should be made, during a procedure, for constantly checking whether the neutral electrode is operating correctly and, for example, is properly placed on the patient. Any detachment of the electrode leads to a dangerous increase in the current density at the regions which still adhere, so that the injuries mentioned above could possibly occur. In order to ensure a high degree of safety for the patient, monitoring circuits are used which, for example, test the adhesion of the neutral electrode on the patient. Neutral electrode monitoring circuits of this type in a high-frequency surgical apparatus typically determine the transition resistance and/or the current distribution between the two conductive segments of the neutral electrode. Conclusions are often drawn concerning possible heating of the electrodes from these measured values. However, these conclusions are only relevant if electrode-specific parameters, such as area, geometry and structure of the electrodes are known. Particularly problematic in this context is the evaluation of very small neutral electrodes such as those sold for use with babies and small children. These can only be operated with a reduced high-frequency current strength since otherwise the heating can reach unacceptably high values. Also problematic herein is assessing neutral electrodes for their ‘operating behavior’. 
         [0006]    It is therefore an object of the disclosed embodiments to provide a high-frequency surgical testing device which not only enables this evaluation and assures a high level of safety both for the patient and the surgeon when using a neutral electrode and but also is as easy to use as possible. 
       SUMMARY 
       [0007]    Disclosed embodiments include a high-frequency surgical testing device for testing a neutral electrode during treatment, in particular monopolar coagulation of biological tissue by means of a high-frequency current, wherein the neutral electrode comprises at least one first electrically conductive electrode segment which can be brought into contact with the tissue and has a first cable for connecting to a high-frequency generator and a second electrically conductive electrode segment which can be brought into contact with the tissue and has a second cable for connecting to the high-frequency generator and wherein the testing device comprises an encoding element with a coding characterizing the neutral electrode between the first and second electrode segments, and a measurement device which is configured so that the coding can be detected in order to identify the neutral electrode. 
         [0008]    In the disclosed embodiments, electrode identification can be carried out with divided neutral electrodes, allowing the treatment process to be designed more readily plannable. Through identification of the neutral electrode, i.e. by identifying the type of the neutral electrode, the course of the treatment can be optimized and a high degree of safety for the patient can be assured. For example, depending on the identified neutral electrode, particular current and/or voltage values can be specifically set. 
         [0009]    Preferably, the testing device or measurement device comprises a source for direct current or low frequency alternating current as a testing current, in order to detect the coding of the encoding element. Electrical and/or electronic decoding can be carried out without great difficulty. In the process, a property of the hydrogel used to fasten the neutral electrode to the patient is utilized. The hydrogel in question has a chemical composition such that it has very low electrical conductivity for direct currents and alternating currents of very low frequency (up to ca. 100 Hz), i.e. it has high ohmic resistance. If an encoding element is now installed on the divided neutral electrode between the two partial surfaces, said encoding element can be measured with the direct current signal or the alternating current signal of very low frequency. Since the gel has a high resistance in this condition, it is irrelevant whether the neutral electrode is placed on the patient, i.e. whether a low value parallel resistance through the tissue is present or not. 
         [0010]    According to one disclosed embodiment, the testing device, or at least portions of the testing device, is/are arranged between the first cable and the second cable such that the test current can be conducted via the first and second cable. Since the test current—as distinct from the working current—is a direct current or a low frequency alternating current, it is possible to detect the characterizing coding without providing a special conductor for this purpose. The existing cable system therefore simultaneously serves as a cable system for the measurement device and thus for detecting the coding. An additional test line or measuring line is therefore not necessary. This means that a significant advantage with regard to compatibility results therefrom that, despite the extended functional scope of the neutral electrode identification, only the two existing neutral electrode connections are used for measuring. Thus the electrodes, the connecting cables and the plug connectors remain compatible with the components available on the market. No additional cables or electrical contacts are needed. 
         [0011]    In another disclosed embodiment, the encoding element includes a resistor element having a resistance value which characterizes the neutral electrode, wherein the testing device is configured such that the resistance value can be detected to identify the neutral electrode. Encoding via a resistor element can be carried out easily and is also easily identified by means of the test current. 
         [0012]    The resistor element is preferably configured as an ohmic resistor or a complex resistor with inductive behavior. The resistors used (encoding resistors) must have resistance values that are significantly smaller than the resistance of the gel at the measuring frequency. However, the values must be large enough such that no appreciable high-frequency currents can flow via the resistance between the two electrode segments. Typical values lie in the range of 1 kΩ&lt;R K &lt;100 kΩ. For direct current and alternating current of low frequency, the relation R Gel &gt;R K &gt;R P  applies. 
         [0013]    In another disclosed embodiment, the resistor element is provided as a resistor film or resistor wire integrated into the neutral electrode. It is herein possible to equip even electrodes without fixed cables which are contacted via a suitable cable to a terminal with this functionality. The resistor element is therefore installed, for example, in the divided neutral electrode between the two electrode segments. 
         [0014]    In the case of electrodes that are equipped with suitable cables, the encoding element or the resistor element, or possibly resistor elements, can be arranged between the first cable and the second cable. The application of a resistor, for example, to the cable segments, can be very easily realized. 
         [0015]    Decoupling the test current from the (high-frequency) working current can be undertaken, for example, by connecting in an inductor as a filter element into the measuring system. 
         [0016]    In another disclosed embodiment, the testing device or the measurement device comprises a voltage measurement device for measuring a voltage across the encoding element or resistor element (e.g. arising from the test current). The resistance value can therefore be easily determined for the respective neutral electrode. It is also possible to measure the coding or the resistance value by means of a current measurement device for measuring the direct current or the low-frequency current. This type of indirect measurement can be carried out without difficulty. 
         [0017]    In another disclosed embodiment of the testing device, the testing device or at least parts of the testing device are configured to be integrated in the high-frequency generator to generate a high-frequency voltage. This means that the high-frequency generator is configured such that when the neutral electrode is plugged into the generator, an identification procedure can be performed, without a separate apparatus being necessary to do so. In other words, the testing device can be integrated in a high-frequency surgical apparatus. 
         [0018]    In another disclosed embodiment, the testing device is configured such that it controls the high-frequency generator to the relevant setting, depending on the coding detected, for example, based on the resistance value detected. This means that all the values to be set at the high-frequency generator, such as current strength, would be automatically set depending on the neutral electrode that is identified. This is particularly advantageous when neutral electrodes are used which would cause burning of the patient upon exceeding a particular current strength. Therefore, a suitable current limitation could be automatically implemented, particularly with neutral electrodes for babies and small children. 
         [0019]    It is also possible for a control device to be assigned to the testing device, the control device (which is possibly also integrated into the testing device) being configured to control the high-frequency generator to the setting thereof depending on the detected coding or the detected resistance value. A distinct control device could also be configured programmable for this purpose and could thus take over the control or regulation of the high-frequency generator. 
         [0020]    It is also possible to carry out the relevant settings based on the detected resistance value by hand. As soon as the surgeon receives the feedback from the system concerning the detected neutral electrode, he can make the required settings, particularly on the high-frequency generator. 
         [0021]    A storage device is preferably assigned to the testing device, in which the encodings, for example, the resistance values of resistor elements, of different neutral electrodes, can be stored as comparison values for neutral electrode identification. Thus, details concerning the neutral electrodes used can be output in simple manner which simplifies assignment for the user and enables planning of the progress of the intervention. The surgeon can therefore make suitable settings on the high-frequency generator which are adapted to the neutral electrode used. 
         [0022]    Information concerning the neutral electrode identified can, quite generally, be output via a display on the high-frequency generator or on the high-frequency surgical apparatus. Sounds, light signals or the like can also be used for this purpose. 
         [0023]    Preferably, the testing device is assigned to an input unit which is configured such that a user can, for example, input the comparative values into the storage device. Any other communication with the high-frequency surgical apparatus is also possible via the input unit, for example, a keyboard. The storage device can also be configured so that encodings that are not yet stored, or the values of any resistors of neutral electrodes, are detected and stored as soon as they are detected by the measurement device. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0024]    The disclosed embodiments will now be described by reference to example embodiments which will be explained in greater detail with reference to the enclosed drawings. 
           [0025]      FIG. 1  illustrates a testing device according to a disclosed embodiment. 
           [0026]      FIG. 2   illustrates  a further representation of the embodiment of  FIG. 1 . 
           [0027]      FIG. 3   illustrates  a further representation of the embodiment of  FIG. 1 . 
       
    
    
     DETAILED DESCRIPTION 
       [0028]    In the following description, the same reference signs are used for the same and similarly acting parts. 
         [0029]      FIG. 1  illustrates one disclosed embodiment of a testing device  20 . As shown in  FIG. 1 , a two-part neutral electrode  40  is connected to a high-frequency generator  30  of a high-frequency surgical apparatus  10 , said high-frequency generator  30  supplying a high-frequency current. The neutral electrode  40  has a first electrically conductive electrode segment  41  and a second electrically conductive electrode segment  42 , wherein the first electrode segment  41  is connected to the high-frequency generator  30  via a first cable  50  and the second electrode segment  42  is connected thereto via a second cable  51 . The electrode segments are arranged on a common support element  43 . 
         [0030]    The neutral electrode  40  can be applied as an indifferent electrode, particularly in monopolar treatment methods, to a tissue section of a patient and serves finally to conduct away current over a relatively large area. The flat configuration of the electrode segments  41 ,  42  ensures good current distribution, so that high current peaks do not occur at points across the transition between the tissue and the neutral electrode  40 . In this way, burns and similar injuries to the patient can be avoided. 
         [0031]    It is advantageous if the neutral electrode  40  can be identified for use thereof. This means that essential parameters of the neutral electrode  40  are identifiable to the surgeon, so that all settings regarding current strength, etc. can be specifically matched on the high-frequency generator  30  to the particular neutral electrode  40 . The setting can be carried out by hand, for example, by the surgeon, or the testing device  20  is configured or is connected to a control device  100  such that necessary settings are carried out automatically. Identification of the neutral electrode  40  and the associated matching of setting parameters are especially important, for example, for electrodes to be used with babies and small children. With these electrodes, depending on the identification thereof, a suitable current limit can be set automatically (or by hand). 
         [0032]    In this example embodiment, a resistor element  90  is provided for identification of the neutral electrode  40  as an encoding element between the two electrode segments  41 ,  42 . The resistor element  90  has a particular resistance value as the coding which is characteristic of the corresponding neutral electrode  40 , so that the precise type of neutral electrode used can be determined. The resistor element  90  is connected between the two conductive electrode segments  41 ,  42 . 
         [0033]    In order to detect the resistance value, components of the testing device  20  are connected between the generator  30  and the neutral electrode  40 . Aside from the resistor element, the testing device  20  also comprises a direct current source as the measuring current source  71 , a voltage measurement device  70  for indirect detection of the resistance value of the resistor element  90  and an inductor (e.g., a coil as the filter element  80 ) which enables decoupling of the working current and the test current or measuring current. These components of the testing device  20  constitute a measurement device  60  and are arranged such that the measuring current can be conducted via the already existing cables for connecting the neutral electrode  40  to the high-frequency generator  30 . The testing device therefore includes the encoding element  90  and the measurement device  60 . 
         [0034]    The measuring current can be decoupled as direct current or as low frequency alternating current from the high-frequency working current in that, for example, the coil is provided as a filter, the reactive impedance of which is greater the higher the frequency is. 
         [0035]    The direct current is supplied from the direct current source  71 ; measurement of the resistance value takes place, for example, indirectly via the voltage measurement device  70  with subsequent resistance calculation. It is also possible to use, for example, measuring bridges for resistance determination. 
         [0036]    The resistance can be measured using the direct current or a low frequency alternating current (measuring current) without the measuring current flowing through the body of the patient. The body of the patient is essentially only capacitively coupled to the electrode. It is not necessary to provide a special connecting cable for signal transmission. A current is thus applied which, for lack of coupling into the body of the patient, cannot be used as a working current and thus enables electrode identification without the need for a special transmission line therefor. A hydrogel  44 ,  44 ′ applied to the electrodes  41 ,  42  for contacting the neutral electrode  40  to the tissue  130  of the patient has a chemical composition for this purpose such that said hydrogel represents a high value resistance R Gel  and R′ Gel  for direct current or alternating current at low frequencies (up to ca. 100 Hz). Since the gel has a high resistance in the region of the measuring current, it is unimportant whether the neutral electrode is placed on the patient, i.e. a low value parallel resistance due to the tissue  130  is present or not. With a type of filter which is in any event present (capacitive coupling of the neutral electrode to the patient) and the use of an “unsuitable” measuring current, additional cables are not necessary for data transmission in the context of neutral electrode recognition. 
         [0037]    As described above, a control device  100  can optionally be provided, by means of which the high-frequency generator  30  is controllable depending on the detected coding value, e.g. depending on the detected resistance value. The high-frequency generator  30  can then be set to a particular current value or a current limit is preset. This is advantageous particularly in the case of neutral electrodes for children, in order to avoid overheating. 
         [0038]    The control device  100  can be configured integrally with at least parts of the testing device  20  and the testing device  20  and/or control device  100  can also be configured integrally with the high-frequency generator  30 . In one example embodiment, a storage device  110  (which could also be assigned directly to the testing device  20 ) is also assigned to the control device  100 . Thus a particular resistance value can be assigned as the coding for each type of neutral electrode. By means of a table (e.g., type of neutral electrode vs. associated setting parameters) stored in the storage device  110 , the high-frequency generator  30 , in particular, can be automatically adjusted in the context of an instrument (or electrode)-oriented system configuration to the circumstances at the identified neutral electrode. 
         [0039]    Furthermore, an input unit  120  is assigned to the testing device  20  via which input device a user can communicate with the system and, for example, input information which is to be stored. 
         [0040]      FIGS. 2 and 3  show a different representation of the arrangement shown in  FIG. 1 .  FIG. 2  shows the neutral electrode  40  applied on a tissue section  130  of a patient by means of hydrogel  44 ,  44 ′. The two conductive electrode segments  41 ,  42  are separated from one another by means of a gap. The two electrode segments  41 ,  42  are connected via the encoding element, the resistor element  90  which has the resistance value that is characteristic of the neutral electrode  40 . The measuring current can be applied via the connecting cables of the electrode segments (cables)  50 ,  51  for connecting the electrode segments  41 ,  42  to the high-frequency generator  30  and via the measurement device  60  such that the resistance value can be detected (e.g., measured). The first electrode segment  41  and the second electrode segment  42  lie on top of the gel  44 ,  44 ′ on the tissue  130  of the patient. The neutral electrode monitoring system, which is integrated, for example, in the high-frequency generator  30  or in a high-frequency surgical device of a high-frequency surgical apparatus  10 , is shown in a simplified form. The divided active contact surface (electrode segments  41 ,  42 ) is made, for example, from aluminium. 
         [0041]      FIG. 3  shows, in the form of an equivalent circuit, the connection between the individual resistors. The encoding element  90 , i.e. the resistor element with the resistance R K  is connected in parallel to a patient resistance R P . The two resistors R Gel  and R′ Gel  of the gel layers  44  and  44 ′ under the respective electrode segments behave as if they had high resistance values, as described above. 
         [0042]    It is therefore clear that, in order to detect a coding which is characteristic for the neutral electrode, the cables with which the neutral electrode is connected to the high-frequency generator can be used. Using a suitable measuring current, the parameters of the measuring circuit can be predetermined such that a neutral electrode identification can be carried out with the least possible effort. 
         [0043]    It should be pointed out here that all the above described parts and in particular the details illustrated in the drawings are essential for the disclosed embodiments alone and in combination. Adaptations thereof are the common practice of persons skilled in the art.