DE102018114482A1 - Electrosurgical device - Google Patents

Abstract

The invention relates to an electrosurgical device (10) comprising an HF generator for generating a high - frequency alternating current for the electrosurgical treatment of biological tissue, which by means of an active electrode (12) of an electrode instrument (14) that can be connected to the device (10) into a body (16) of a patient can be introduced or can be applied to a body of a patient, and can be discharged from the patient's body by means of a neutral electrode (18) which can be connected to the device (10) and can be brought into contact with the patient's skin, and wherein the device (10) has a control device (20) which is set up and designed to switch the device (10) into a first functional state assigned to a first neutral electrode type and into a second functional state assigned to a second neutral electrode type, which is characterized in that the Control device (20) issued is formed and set up by means of an impedance measurement to detect an impedance (ZPT) of a neutral electrode (18) connected to the device (10) and contacting the patient's skin, and wherein the control device (20) is further designed and set up the connected one Assign neutral electrode (18) as a function of one or more detected impedance values (ZPT) to the first neutral electrode type or the second neutral electrode type, and the control device (20), when assigning the connected neutral electrode (18) to the first neutral electrode type, assigns the device (10) in the first Functional state switches, and the control device (20) switches the device (10) into the second functional state when the connected neutral electrode (18) is assigned to the second neutral electrode type.

Description

The invention relates to an electrosurgical device according to the preamble of claim 1.

In the medical treatment of body tissue with high-frequency alternating current, a distinction is usually made between a monopolar or a bipolar application. In a bipolar application, the active electrode delivering the high-frequency current to the body tissue and the neutral electrode returning the high-frequency current are usually arranged at a fixed distance from one another on an instrument shaft. The active electrode and neutral electrode are moved by the instrument to the treatment site. The high-frequency current is emitted from the active electrode to the tissue to be treated and returned via the neutral electrode.

In the case of monopolar use, the instrument intended for the treatment usually only carries the active electrode. The neutral electrode provided to derive the high-frequency current from the patient's body is usually placed on the patient's skin surface and fastened there. The neutral electrode formed with flat contact areas conducts the high-frequency current introduced into the tissue with the active electrode back out of the patient's body via the skin surface. The neutral electrode is connected to the generator, which closes the circuit between the active electrode and the neutral electrode.

With the monopolar application of high-frequency current, it is problematic if the contacting of the neutral electrode on the skin surface deteriorates during the electrosurgical treatment. If, for example, the neutral electrode unintentionally detaches from the skin, the contact area between the neutral electrode and the skin is reduced, the current density at the transition between the neutral electrode and the skin surface increases, which can lead to excessive heating and even burns to the patient's skin surface.

The neutral electrodes designed for monopolar applications are essentially divided into two different types of neutral electrodes. The undivided neutral electrodes and the divided neutral electrodes. Undivided neutral electrodes are equipped with a single, contiguous metallic contact surface, and divided neutral electrodes have at least two separate metallic contact surfaces. The contact surfaces, also called contact pads, are brought into contact with the skin surface of the patient. For this purpose, the contact pads are usually arranged on a carrier material provided in its edge regions with an adhesive layer, so that the neutral electrode can be attached to the patient's skin in the manner of a plaster.

Split neutral electrodes were especially developed to reduce the described risk of burns to the skin surface due to excessive current densities. For this purpose, the divided neutral electrode can (before and / or during the electrosurgical treatment) be subjected to a measuring current which is conducted from a first contact pad over the contacted skin to the second contact surface. The electrical resistance between the contact surfaces can be detected by means of the measuring current. A deterioration in contact quality, for example due to the unintentional detachment of the neutral electrode from the skin, can be recognized by an increasing ohmic resistance. The electrosurgical device can then give an acoustic and / or visual warning to the operator and / or completely interrupt the flow of current in order to avoid burning the skin. It can be provided that the power supply is interrupted until a sufficiently good contact quality is restored.

This continuous monitoring of the resistance values between two contact surfaces contacting the skin is usually only possible in the case of divided neutral electrodes. Such monitoring functions are currently not used for undivided neutral electrodes.

Since new generation electrosurgical devices typically support the use of both types of neutral electrodes, the device must be adjusted either manually or automatically to the type of neutral electrode connected to match the monitoring to the connected neutral electrode.

For automatic adjustment of the device, it is known from the prior art, for example, to use special connecting cables for connecting the neutral electrode, which allow a distinction to be made between a divided or an undivided neutral electrode. For the differentiation, for example, a mechanical switch can be provided on the plug contact between the electrosurgical device and the cable or on the plug contact between the cable and the neutral electrode, which closes or opens an electrical contact when an undivided or divided neutral electrode is connected and thus provides information what type of neutral electrode is used on the device.

For manual adjustment of the device it is known from the prior art to equip the electrosurgical device with operating elements which enable the surgeon or medical personnel to switch the device into the functional state provided for undivided or divided neutral electrodes, depending on the type of electrode connected.

A third possibility known from the prior art for differentiating the connected neutral electrode type consists in detecting and evaluating the ohmic resistance of the neutral electrode contacting the skin surface of the patient. The ohmic resistance of an undivided neutral electrode is usually in the lower resistance range, since only the cable resistance is measured and no tissue resistance of the patient is recorded. A split neutral electrode applied to the skin has a higher total resistance due to the additional tissue resistance between the contact pads, which increases when the neutral electrode detaches and decreases when, for example, sweat forms a conductive transition between the two contact surfaces of the split neutral electrode. If an ohmic resistance that is small compared to a reference value is detected, an undivided neutral electrode can be concluded. When a resistance that is greater than a reference value is detected, a divided neutral electrode can be concluded.

The detection of the neutral electrode type connected to the device is usually carried out via a resistance measurement in the lower frequency range (approx. 70 kHz). With this resistance measurement, however, due to different factors such as the electrical conductivity of the skin, which differs from patient to patient, or different electrical properties of neutral electrodes from different manufacturers, measurement values can be obtained which cannot be clearly assigned to one or the other neutral electrode type.

The poor interpretability of resistance values when using different neutral electrodes and the differing electrical conductivities of the skin make it difficult to identify contact errors in the first place. When detecting a particularly small resistance value, for example, either an undivided neutral electrode can be connected or there can be a short circuit in a divided neutral electrode. Particularly small resistances can also occur with split neutral electrodes that are applied to a skin with a very low skin resistance.

The poor interpretability of resistance values makes automatic detection of the connected electrode type difficult. Split neutral electrodes of a newer type usually have a very low ohmic resistance in their state in contact with the skin, which reduces the heating of the skin surface when the high-frequency current is applied. These improved neutral electrodes sometimes have resistances so small that they are recognized by a conventional high-frequency generator as undivided neutral electrodes and the high-frequency generator is thereby switched to a functional state assigned to the undivided neutral electrodes, in which the continuous monitoring of the resistance values between the two contact pads contacting the skin is not carried out becomes.

The object of the invention is to provide an electrosurgical device of the generic type which enables improved automatic detection of the connected neutral electrode type.

This object is achieved by a device having the features of claim 1. Advantageous refinements are specified in the subclaims.

Electrosurgical device, comprising an HF generator for generating a high-frequency alternating current for the electrosurgical treatment of biological tissue, which can be introduced into a body of a patient or can be used on a body of a patient by means of an active electrode of an electrode instrument which can be connected to the device, and which can be used by means of a the neutral electrode can be connected to the device and can be brought into conductive contact with the patient's skin, and the device has a control device, which is designed and configured, the device in a first functional state assigned to a first type of neutral electrode and in a to switch a second functional state assigned to a second type of neutral electrode, the control device being designed and set up, by means of an impedance measurement, an impedance of a device connected to the device, to detect the neutral electrode contacting the patient's skin, and wherein the control device is further configured and configured to assign the connected neutral electrode to the first neutral electrode type or the second neutral electrode type depending on one or more detected impedance values, and wherein the control device when the connected neutral electrode is assigned to the the first neutral electrode type switches the device into the first functional state, and the control device when assigned the connected neutral electrode to the second neutral electrode type switches the device into the second functional state.

The first functional state is assigned to the first neutral electrode type, which comprises at least some neutral electrodes from the group of divided surface electrodes. The second functional state is assigned to the second neutral electrode type, which comprises at least some neutral electrodes from the group of undivided surface electrodes. A further functional state can also be provided, into which the device is switched by means of the control device if it is recognized that no neutral electrode has yet been connected. This third functional state can be assumed, for example, if none of the detected resistance is higher than a certain threshold value, the threshold value being chosen to be very high for neutral electrodes that are not connected.

The first and the second functional state can each activate a function of the device specified for the respective neutral electrode type. In particular, it is contemplated that the respective functional state contains a monitoring function of the contact quality between the neutral electrode and the patient's skin, which is designed for the corresponding type of neutral electrode.

For the impedance detection, the device can have an impedance detection device integrated in particular into the control device. When recording the impedance, it is intended to measure the real part and the imaginary part in each case by measuring technology and to store it in a memory as a further processable data.

The control device is in particular set up to detect the real part and the imaginary part of the impedance of the neutral electrode. Incidentally, impedance is understood to mean the impedance that can be measured above the neutral electrode, that is to say in particular on the one hand the impedance components influenced by the electrical properties of the contact surfaces of the neutral electrode and on the other hand further impedance components such as the impedance components influenced by the electrical properties of the patient's skin. The impedance of the neutral electrodes thus also includes the contact resistances from the contact surfaces to the skin and possibly also the impedance components influenced by the electrical connecting lines between the device and the neutral electrode.

In a first embodiment, it is contemplated that the control device is set up and designed to detect the impedance of the neutral electrode at at least two different frequencies.

In the first regard, it is contemplated that the first type of neutral electrode comprises divided neutral electrodes with two separate contact surfaces that are electrically separated from one another, the separate contact surfaces of which can be connected to the device with an electrical connecting line in each case. The connecting lines can be designed as separate lines of a connecting cable.

In addition, it is contemplated that the second type of neutral electrode comprises undivided neutral electrodes with a single undivided contact area, the undisconnected contact area of which can be connected to the device with two connecting lines that electrically contact the undivided contact area.

For the assignment of the recorded impedance values to one of the neutral electrode types, comparisons should be made between the recorded values and reference values. To do this, an impedance pattern should first be formed from the recorded impedance values. Correspondingly, it is contemplated that the control device is set up and designed to form an impedance pattern from at least two detected impedances. The impedance pattern can, for example, be an ordered sequence of function values that correspond to a specific course in a Nyquist diagram.

With the acquisition of the real part and the imaginary part, there are two parameters per acquisition, that is, with the impedance acquisition at two different frequencies, there are four parameters. These parameters result in a specific pattern in the Nyquist diagram, which can be used to classify the connected neutral electrode. As explained further below, equivalent circuit diagram parameters can be calculated with the aid of the recorded impedance values, which parameters can be used to identify the connected neutral electrode.

Furthermore, it can be provided that the control device is set up and designed to compare the impedance pattern with a first reference pattern that is characteristic of the first neutral electrode type and / or with a second reference pattern that is characteristic of the second neutral electrode type. The reference pattern used for the comparison can be formed, for example, from calculated reference values or from reference values stored in a memory.

An evaluation of a comparison between detected impedance values and reference values can take place to decide which functional state is to be switched. Accordingly, it is thought that the control device at sufficient correspondence of the impedance pattern with the first reference pattern assigns the connected neutral electrode to the first neutral electrode type and switches the device into the first functional state. Adequate agreement can exist if the difference between the reference pattern and the impedance pattern, which is determined, for example, by means of an integral calculation, lies below a certain threshold value. The threshold value can be fixed or can be set by the user. A comparison between the impedance pattern and the reference pattern and thus the evaluation of the correspondence can also be carried out using a correlation calculation.

In one embodiment, it is contemplated that the first reference pattern is formed from impedance values that result from an estimate representing a polarization effect of a divided neutral electrode, in particular according to the calculation rule: $$Z_{R1}=R_e+\frac{\text{cos}\left(\frac{\pi }{2}\cdot {\alpha }_P\right)}{Q_P\cdot {\omega }^{{\alpha }_P}}-i\frac{\text{sin}\left(\frac{\pi }{2}\cdot {\alpha }_P\right)}{Q_P\cdot {\omega }^{{\alpha }_P}}$$

The reference pattern, which results from an estimation of the expected impedance values of a certain type of neutral electrode, such as a split neutral electrode, is compared with an impedance pattern formed from the detected impedance values in order to determine the connected neutral electrode. For example, by means of a correlation, an integration calculation or other comparison methods. The reference values used for the reference pattern are an approximation or an estimate of the impedance values that can actually be expected, on the basis of an equivalent circuit diagram. The calculation rule that can be used for the estimation describes the course of a polarization effect of a split neutral electrode lying on the skin surface of a patient.

In a further embodiment, it is contemplated that the control device is set up and designed to evaluate the real part and the imaginary part of the detected impedance of the connected neutral electrode in order to generate a data item that characterizes the electrical properties of the connected neutral electrode.

Equivalent circuit diagram parameters are preferably calculated with the aid of the detected impedance values, it being possible for the control device to be set up and designed to generate a date from the real parts and the imaginary parts of two impedances detected at different frequencies, in particular according to the calculation rule: $${\alpha }_P=\frac{2}{\pi }*\text{arctan}\left(\frac{Im\left\{Z_{PT}\left({\omega }_2\right)\right\}-Im\left\{Z_{PT}\left({\omega }_1\right)\right\}}{Re\left\{Z_{PT}\left({\omega }_2\right)\right\}-Re\left\{Z_{PT}\left({\omega }_1\right)\right\}}\right)$$

To utilize further equivalent circuit diagram parameters, it is contemplated that the control device is set up and designed to generate a date from the real parts and the imaginary parts of two impedances detected at different frequencies, in particular according to the calculation rule: $$Q_p=\frac{\text{sin}\left(\frac{\pi }{2}*{\alpha }_p\right)}{Im\left\{Z_{PT}\left({\omega }_1\right)\right\}*{\omega }_1{}^{{\alpha }_p}}$$

For the use of a further equivalent circuit diagram parameter, it is contemplated that the control device is set up and designed to generate a date from the real parts and the imaginary parts of two impedances detected at different frequencies, in particular according to the calculation rule: $$R_e=Re\left\{Z_p\left({\omega }_1\right)\right\}+\frac{Im\left\{Z_P\left({\omega }_1\right)\right\}}{\text{tan}\left(\frac{\pi }{2}*{\alpha }_p\right)}$$

In a preferred embodiment, it is contemplated that the control device is set up and constructed, a datum formed from the real parts and imaginary parts of one or more detected impedances of the connected neutral electrode with a first reference datum characteristic of the first neutral electrode type and / or with one for the second neutral electrode type to compare the characteristic second reference date.

In this embodiment, the first thought is to compare determined equivalent circuit parameters such as α _p , Q _p or R _e with first reference data which characterize the polarization effect of a divided neutral electrode glued to the skin. Furthermore, it is contemplated to compare recorded impedance values with second reference data, which are characteristic of a short circuit of the measuring lines on an undivided neutral electrode. The absolute values of one or more of the calculated parameter values are preferably used for the comparison with the reference values.

In the case of an undivided neutral electrode, that is to say with a connected neutral electrode of the second neutral electrode type, essentially the ohmic resistance of the neutral electrode itself and a small capacitive part of the cable are measured when the impedance of the neutral electrode is detected. The polarization effect does not appear, which can be seen in the calculated data α _p , Q _p or R _e . In such cases, the date α _p has a low value, which means a slight slope of the curve in the Nyquist diagram.

In such cases, the date Q _p has a small value, which means a short length in the Nyquist diagram. The date R _e has also a small value in such cases; the real resistance is therefore very small. In addition, both measurements are close together in the Nyquist diagram.

In the case of a split neutral electrode, that is to say when a neutral electrode of the first neutral electrode type is connected, the impedance between two contact pads and the patient's skin is measured. This results in specific values for the data α _p , Q _p or R _e which, when a predetermined limit value is exceeded or undershot, indicate the connection of a divided neutral electrode. When a divided neutral electrode is connected, the data α _p can have an absolute value of approx. 0.5, for example, which corresponds to a slope of the curve of approx. 45 °. In such cases, the date Q _p usually has a medium value, which means a medium length in the Nyquist diagram. The real ohmic resistance is usually greater than a predetermined threshold.

It is intended to use the polarization effect in the lower frequency range to determine the contact quality of the neutral electrode. The parameters α _p , Q _p or R _{e of} the equivalent circuit diagram can be used for this.

For the assignment of the connected neutral electrode to one of the neutral and electrode types belonging to the first and second functional state, it is initially thought that the control device, if there is sufficient agreement of one or more data formed from the real parts and imaginary parts of one or more detected impedances of the connected neutral electrode with the first reference data connects the connected neutral electrode of the first neutral electrode type and switches the device into the first functional state. Sufficient correspondence can be achieved if a preset and / or adjustable threshold value - depending on the reference method - is undershot or exceeded.

Furthermore, it is contemplated that if one or more data formed from the real parts and imaginary parts of one or more detected impedances of the connected neutral electrode match the second reference data, the control device assigns the connected neutral electrode to the second neutral electrode type and switches the device to the second functional state.

It is also conceivable that if the control device does not sufficiently match one or more data formed from the real parts and imaginary parts of one or more detected impedances of the connected neutral electrode with the first or second reference data, the device switches a third functional state. The third functional state can be provided, for example, in the event that no neutral electrode is connected. A third functional state can also be a fault state in which the device provides the user with an acoustic or visual information signal to indicate a fault.

According to a further embodiment, it can be provided that the control device is set up and designed to monitor the electrical resistance and / or the impedance of the neutral electrode connected to the device in the first functional state of the device.

Furthermore, it can be provided that the control device controls the device in such a way that when the monitored electrical resistance or the monitored impedance or a parameter of the neutral electrode connected to the device calculated on the basis of the detected resistance or impedance values, the output of the high-frequency alternating current is output via a specific reference value to an electrode instrument connected to the device is prevented at least temporarily.

• 1 eine schematische Darstellung einer erfindungsgemäßen Vorrichtung mit einem angeschlossenen Elektrodeninstrument und einer angeschlossenen Neutralelektrode,
• 2 eine geteilte Neutralelektrode in schematischer Darstellung,
• 3 eine ungeteilte Neutralelektrode in schematischer Darstellung,
• 4 eine schaltungstechnische Repräsentation eines erweiterten Gewebe-Modells,
• 5 ein erstes Beispiel von gemessenen Impedanzwerten einer auf die Haut eines Patienten aufgeklebten geteilten Neutralelektrode dargestellt im Nyquist Diagramm,
• 6 eine schaltungstechnische Repräsentation eines Ersatzschaltbildes eines Gewebe-Modells für den niederfrequenten Impedanzbereich,
• 7 eine gemeinsame Darstellung von gemessenen Impedanzwerten einer auf die Haut eines Patienten aufgeklebten geteilten Neutralelektrode und des berechneten Kurvenverlaufes des Ersatzschaltbildes aus 6 im Nyquistdiagramm

Further advantages, features and details of the invention also result from the exemplary embodiments described below with reference to schematic drawings. Show it:

• 1 1 shows a schematic representation of a device according to the invention with a connected electrode instrument and a connected neutral electrode,
• 2 a divided neutral electrode in a schematic representation,
• 3 an undivided neutral electrode in a schematic representation,
• 4 a circuit-technical representation of an extended tissue model,
• 5 a first example of measured impedance values of a divided neutral electrode glued to the skin of a patient shown in the Nyquist diagram,
• 6 a circuit-technical representation of an equivalent circuit diagram of a tissue model for the low-frequency impedance range,
• 7 a common representation of measured impedance values of a divided neutral electrode glued to the skin of a patient and the calculated curve of the equivalent circuit diagram 6 in the Nyquist diagram

1 shows a device according to the invention 10 to the one for electrosurgical treatment of a patient's body 16 established electrode instrument 14 connected. The electrode instrument 14 carries an active electrode 12 with the one via a connection cable 46 from the device 10 to the electrode instrument 14 high-frequency current transmitted to the patient's body 16 is applied.

The one on the patient's body 16 High-frequency current acting on the skin surface of the patient's body 16 applied neutral electrode 18 by means of a further connection cable 44 to the device 10 returned. The circuit is thus closed.

By means of one of the devices 10 control device 20 can the device 10 can be switched to different functional states. The control device 20 can also be set up the current flow between the active electrode 12 and neutral electrode 18 to control. For the control of the current flow it is thought that the control device 20 Impedance values on the skin of the patient's body 16 applied neutral electrode 18 recorded and evaluated.

As the 2 and 3 show by way of example, it can be provided that a neutral electrode 26 . 27 by means of at least two measuring or connecting lines 32 . 34 respectively 40 . 42 with the device 20 are electrically connected. 2 shows a split neutral electrode 26 with two contact surfaces 28 . 30 , This split neutral electrode 26 is assigned to the first neutral electrode type. 3 shows an undivided neutral electrode 36 with an undivided contact surface 38 , The contact areas 28 . 30 are each by means of a connecting line 32 . 34 electrically with the device 10 connectable. The contact areas 28 . 30 are electrically separated from each other. Only a skin contact creates an electrically conductive connection between the contact surfaces 28 . 30 ago. In the case of the undivided neutral electrode 36 becomes the common undivided contact area 38 also with two connecting lines 40 . 42 contacted. The connecting lines 40 . 42 are thus over the contact area 38 electrically connected to each other.

The connecting lines 32 . 34 and 40 . 42 are each - as indicated - preferably in a common cable 44 up to the device 10 guided. A connector is usually provided on neutral electrodes with which the cable 44 to the neutral electrodes 26 . 36 can be connected. Thus, a single cable 44 can be used for various neutral electrodes.

The contact areas 28 . 30 . 38 the neutral electrodes are - as indicated - usually on a carrier material 48 . 50 arranged, which holds the contact surfaces in position. The carrier material can have an adhesive layer by means of which the neutral electrodes 26 . 36 on the skin surface of the patient's body 16 are attachable.

A basic consideration of the invention is to use detected impedance values to recognize whether the connected neutral electrode is a split neutral electrode. For this, an extended tissue model is used, as in 4 shown. In addition to the tissue itself, this model also models the transition of the electrodes to the tissue and the cable capacity. The transition from electrodes to tissue creates the so-called polarization effect, which can be used to improve the detection of the electrode type as well as to monitor the contact quality between the electrode surfaces and the skin.

5 shows a real course of the impedance of a split neutral electrode lying on the skin in the Nyquist diagram. This characteristic curve profile shows in particular the impedance profile during the transition from tissue to the metallic electrode surfaces of the divided neutral electrode over a frequency range from 10 kHz to 10 MHz. In the lower frequency range (approx. 10 kHz to 100 kHz), the so-called polarization effect is particularly pronounced and can be recognized by a linear rise.

Since the polarization effect only occurs during the transition from metal to skin, it can be used to distinguish between divided and undivided neutral electrodes. With undivided neutral electrodes 36 , as in 3 , both connecting lines 40 . 42 over the undivided contact area 38 short-circuited and the contact resistance to the skin is not measured. Using split neutral electrodes 26 , as in 2 , however, the resistance or impedance between two contact surfaces 28 . 30 be determined on the skin. With split neutral electrodes, a polarization effect would thus be detectable.

For the detection and detection of the polarization effect, it is preferably provided to measure the impedance of the connected neutral electrode at two or more than two low frequencies, preferably in the range 1 kHz to 80 kHz. By adopting an equivalent circuit diagram, the polarization effect can be described mathematically.

Since the polarization effect is decisive for the course of the impedance curve in the low-frequency range, the extended tissue model can be used 4 be simplified. It results in 6 schematically represented equivalent circuit diagram.

If the cable capacitance C _{p is} known, it can be subtracted from the measured impedance. The result is Z _PT with two measuring points each at the frequencies ω ₁ and ω ₂ .

$$Q_p=\frac{\text{sin}\left(\frac{\pi }{2}*{\alpha }_p\right)}{Im\left\{Z_{PT}\left({\omega }_1\right)\right\}*{\omega }_1{}^{{\alpha }_p}}$$

$$R_e=Re\left\{Z_p\left({\omega }_1\right)\right\}+\frac{Im\left\{Z_P\left({\omega }_1\right)\right\}}{\text{tan}\left(\frac{\pi }{2}*{\alpha }_p\right)}$$

The following formulas can be used to describe the polarization effect: $${\alpha }_p=\frac{2}{\pi }*\text{arctan}\left(\frac{Im\left\{Z_{PT}\left({\omega }_2\right)\right\}-Im\left\{Z_{PT}\left({\omega }_1\right)\right\}}{Re\left\{Z_{PT}\left({\omega }_2\right)\right\}-Re\left\{Z_{PT}\left({\omega }_1\right)\right\}}\right)$$

$$Q_p=\frac{\text{sin}\left(\frac{\pi }{2}*{\alpha }_p\right)}{Im\left\{Z_{PT}\left({\omega }_1\right)\right\}*{\omega }_1{}^{{\alpha }_p}}$$

$$R_e=Re\left\{Z_p\left({\omega }_1\right)\right\}+\frac{Im\left\{Z_P\left({\omega }_1\right)\right\}}{\text{tan}\left(\frac{\pi }{2}*{\alpha }_p\right)}$$

The course of the curve of the equivalent circuit diagram is made up 6 with the calculated values of the components in a Nyquist diagram, the result is in 7 shown course.

In 7 is easy to see that the curves 22 . 24 are almost congruent in the low frequency range. The curves soften with increasing frequency> 100 kHz 22 . 24 more and more different from each other. This deviation is due to the non-modeled tissue and is not important for the use of the polarization effect to determine the type of neutral electrode connected. The curve 24 shows the course of the impedance according to the equivalent circuit diagram 6 , Curve 22 shows a real course of the impedance of a divided neutral electrode. The curve 24 can be used as a reference pattern, with the one from the real course 22 formed impedance pattern can be compared to recognize the polarization effect. The polarization effect can be seen in the curve area designated 52. For the comparison of the curves 22 and 24 different methods are conceivable. For example, the comparison can be carried out by means of integral formation. Among other things, the slope of the curves and their distance from one another can also be evaluated.

LIST OF REFERENCE NUMBERS

10

Electrosurgical device

12

active electrode

14

electrodes instrument

16

patient's body

18

neutral electrode

20

control device

22

Impedance curve according to the equivalent circuit diagram

24

Impedance curve of a split neutral electrode

26

Split neutral electrode

28

First separate contact area

30

Second separate contact area

32

connecting line

34

connecting line

36

Undivided neutral electrode

38

Unseparated contact area

40

connecting line

42

connecting line

44

connection cable

46

connection cable

48

support structure

50

support structure

52

polarization effect

Claims (17)

Electrosurgical device (10) comprising an HF generator for generating a high-frequency alternating current for the electrosurgical treatment of biological tissue, which by means of an active electrode (12) of an electrode instrument (14) connectable to the device (10) into a body (16) Patients can be introduced or applied to a patient's body, and by means of a neutral electrode (18) that can be connected to the device (10) and can be brought into conductive contact with the patient's skin, can be led out of the patient's body, and the device (10) has a control device (20) that is set up and configured, to switch the device (10) into a first functional state assigned to a first neutral electrode type and into a second functional state assigned to a second neutral electrode type, characterized in that the control device (20) is designed and set up by means of an impedance measurement to an impedance (Z _PT ) of an the device (10) connected to detect the neutral electrode (18) contacting the patient's skin, and wherein the control device (20) is further configured and set up to connect the connected neutral electrode (18) as a function of one or more detected impedance values (Z _PT ) the first neutral electrode type or the second assign the neutral electrode type, and the control device (20) switches the device (10) into the first functional state when the connected neutral electrode (18) is assigned to the first neutral electrode type, and the control device (20) switches when the connected neutral electrode (18) is assigned the second neutral electrode type switches the device (10) into the second functional state. Device after Claim 1 , characterized in that the control device (20) is set up and designed to detect the impedance (Z _PT ) of the neutral electrode (18) at at least two different frequencies (ω ₁ , ω ₂ ). Device according to one of the Claims 1 or 2 , characterized in that the first type of neutral electrode comprises divided neutral electrodes (26) with two separate electrically separate contact surfaces (28, 30), the separate contact surfaces (28, 30) of which each have an electrical connecting line (32, 34) to the device (10 ) can be connected. Device according to one of the preceding claims, characterized in that the second type of neutral electrode comprises undivided neutral electrodes (36) with a single undivided contact area (38), the undivided contact area (38) of which each has two connecting lines (40, electrically contacting the undivided contact area (38)) 42) can be connected to the device (10). Device according to one of the preceding claims, characterized in that the control device (20) is set up and designed to form an impedance pattern (22) from at least two detected impedances (Z _PT ). Device after Claim 5 , characterized in that the control device (20) is set up and designed to compare the impedance pattern (22) with a first reference pattern (24) characteristic of the first neutral electrode type and / or with a second reference pattern characteristic of the second neutral electrode type. Device after Claim 6 , characterized in that the control device (20) assigns the connected neutral electrode (18) to the first neutral electrode type and the device (10) switches to the first functional state if the impedance pattern (22) matches the first reference pattern (24). Device according to one of the Claims 6 or 7 , characterized in that the first reference pattern (24) is formed from impedance values (Z _R1 ) which result from an estimate representing a polarization effect of a divided neutral electrode (26), in particular according to the calculation rule: $$Z_{R1}=R_e+\frac{\text{cos}\left(\frac{\pi }{2}\cdot {\alpha }_P\right)}{Q_P\cdot {\omega }^{{\alpha }_P}}-i\frac{\text{sin}\left(\frac{\pi }{2}\cdot {\alpha }_P\right)}{Q_P\cdot {\omega }^{{\alpha }_P}}$$

Device according to one of the preceding claims, characterized in that the control device (20) is set up and designed, the real part (Re {Z _PT }) and the imaginary part (Im {Z _PT }) of the detected impedance (Z _PT ) of the connected neutral electrode (18) in order to generate a data characterizing the electrical properties of the connected neutral electrode (18). Device after Claim 9 , characterized in that the control device (20) is set up and constructed from the real parts (Re {Z _PT (ω ₁ )}, Re {Z _PT (ω ₂ )}) and the imaginary parts (I _m {Z _PT (ω ₂ )}, Im {Z _PT (ω ₂ )}) of two impedances detected at different frequencies (ω ₁ , ω ₂ ) (Z _PT (ω ₁ ), Z _PT (ω ₂ )) to generate a date (α _p ), in particular according to the calculation rule: $${\alpha }_p=\frac{2}{\pi }*\text{arctan}\left(\frac{Im\left\{Z_{PT}\left({\omega }_2\right)\right\}-Im\left\{Z_{PT}\left({\omega }_1\right)\right\}}{Re\left\{Z_{PT}\left({\omega }_2\right)\right\}-Re\left\{Z_{PT}\left({\omega }_1\right)\right\}}\right)$$

Device after Claim 10 , characterized in that the control device (20) is set up and constructed from the real parts (Re {Z _PT (ω ₁ )}, Re {Z _PT (ω ₂ )}) and the imaginary parts (I _m {Z _PT (ω _2)} I _m {Z _PT (ω _2)}) of two at different frequencies (ω _1, ω ₂₎ impedances detected (Z _PT (ω _1), Z _PT (ω ₂₎₎ a date (Q _p) generate, especially according to the calculation rule: $$Q_p=\frac{\text{sin}\left(\frac{\pi }{2}*{\alpha }_P\right)}{Im\left\{Z_{PT}\left({\omega }_1\right)\right\}*{\omega }_1{}^{{\alpha }_P}}$$

Device according to one of the Claims 10 or 11 , characterized in that the control device (20) is set up and constructed from the real parts (Re {Z _PT (ω ₁ )}, Re {Z _PT (ω ₂ )}) and the imaginary parts (I _m {Z _PT (ω ₂ )}, I _m {Z _PT (ω ₂ )}) of two impedances (Z _PT (ω ₁ ), Z _PT (ω ₂ )) detected at different frequencies (ω ₁ , ω ₂ ) to a date (R _e ) generate, especially according to the calculation rule: $$R_e=Re\left\{Z_p\left({\omega }_1\right)\right\}+\frac{Im\left\{Z_p\left({\omega }_1\right)\right\}}{\text{tan}\left(\frac{\pi }{2}*{\alpha }_p\right)}$$

Device according to one of the preceding claims, characterized in that the control device (20) is set up and designed, a date formed from the real parts and imaginary parts of one or more detected impedances of the connected neutral electrode (18) with a for the first neutral electrode type for the first neutral electrode type to compare characteristic first reference data and / or with a second reference data characteristic of the second neutral electrode type. Device after Claim 13 , characterized in that the control device (20) with sufficient correspondence of one or more data formed from the real parts and imaginary parts of one or more detected impedances of the connected neutral electrode (18) with the first reference data, assigns the connected neutral electrode (18) to the first neutral electrode type and the device (10) switches to the first functional state. Device according to one of the Claims 13 or 14 , characterized in that the control device (20) with sufficient correspondence of one or more data formed from the real parts and imaginary parts of one or more detected impedances of the connected neutral electrode (18) with the second reference data assigns the connected neutral electrode (18) to the second type of neutral electrode and that Device (10) switches to the second functional state. Device according to one of the preceding claims, characterized in that the control device (20) is set up and designed to increase the electrical resistance and / or the impedance of the neutral electrode (18) connected to the device (10) in the first functional state of the device (10) monitor. Device after Claim 16 , characterized in that the control device (20) controls the device such that when the monitored electrical resistance or the monitored impedance or a parameter calculated on the basis of the detected resistance or impedance values is exceeded, the neutral electrode (18) connected to the device (10) a specific reference value prevents the delivery of the high-frequency alternating current to an electrode instrument (14) connected to the device (10), at least temporarily.

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