Abstract:
An electrosurgical high frequency (HF) generator comprising a generator circuit that produces an HF current between an active electrode and at least one neutral electrode. During the cutting or coagulating of biological tissue, unwanted tissue heating due to the HF current can be reduced because the electrosurgical HF generator comprises at least one further auxiliary neutral electrode connected in parallel to the neutral electrode.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is the U.S. national stage of International Application No. PCT/EP2009/005856, filed Aug. 12, 2009. 
     FIELD OF THE INVENTION 
     Embodiments of the invention relate to an electrosurgical high frequency (HF) generator for treating biological tissue. 
     BACKGROUND 
     Electrosurgical HF generators are used for treating biological tissue, particularly for cutting or coagulating biological tissue. For this purpose, a generator circuit is provided for generating an HF current, which flows between an active electrode and at least one neutral electrode, via a first current path through the tissue. Accordingly, the generator circuit comprises an active output and a neutral output. 
     In HF surgery, a distinction is made between the known monopolar and bipolar uses. In monopolar use, the active electrode is configured as an insulated hand-piece, which, for example, has an electrode tip guided by a surgeon to the tissue regions to be treated. An HF current flows through the tissue to a neutral electrode, which contacts the tissue over a large area and is applied, for example, to the thigh of a patient. Such neutral electrodes usually have a contact area of approximately 1 dm 2  to 3 dm 2 . Monopolar applications have the advantage of using a compact hand-piece, the electrode tip of which can also be applied to tissue sites that are difficult to reach. A disadvantage is that the HF current also flows to the neutral electrode through tissue not being treated. Particularly, if the cross-sectional area of the tissue along the current path is small, overheating and damage to regions of the tissue not being treated can occur. This can be counteracted with bipolar instruments. For bipolar instruments, the HF current flows between two closely adjacent electrodes e.g., bipolar coagulation forceps, and therefore exclusively through tissue situated between the clamping surfaces. With these instruments, however, poorly accessible tissue sites can often only be reached and treated with difficulty, or not at all. 
     SUMMARY 
     It is an object of the embodiments of the invention to provide an electrosurgical HF generator that enables treatment without the risk of damaging tissue not being treated, even for tissue sites that are difficult to reach. 
     This object is solved by an HF generator for treating (e.g., cutting or coagulating) biological tissue that generates an HF current by means of a generator circuit, said current flowing via a first current path between a first active electrode and at least one neutral electrode. Accordingly, the electrosurgical HF generator has an active output and a neutral output. The HF generator also has at least one auxiliary neutral electrode connected in parallel to the neutral electrode, so that part of the HF current flows through the tissue in a targeted way via at least one second current path. Because the entire HF current is distributed between at least two current paths, the current density in the current paths is reduced accordingly. As a consequence, the tissue along the current paths is only slightly heated, if at all. The risk of damage from overheating is correspondingly reduced. 
     Preferably, the electrosurgical HF generator comprises a measuring circuit that measures the ratio of the currents flowing through the neutral electrode and auxiliary neutral electrode. Alternatively or optionally, the measuring circuit can measure the HF current flowing through the neutral electrode and/or the auxiliary neutral electrode. The measuring circuit allows the determination of whether the HF current is distributed between the two current paths such that undesirable tissue damage is prevented. If the risk of undesirable tissue damage exists, an indication can be provided and/or the HF generator can switch off automatically. In most cases, the risk can be eliminated by repositioning e.g., the auxiliary neutral electrode. 
     The auxiliary neutral electrode can comprise, for example, at least one clamping surface of a preferably self-locking pair of grasping forceps. This is particularly advantageous if a part of the tissue is to be separated. The tissue part can be grasped with the grasping forceps so that the additional current path leads from the active electrode, through the tissue part to be separated, and to the clamping surface of the grasping forceps. In this way, damage to the tissue to be preserved is prevented due to the additional current path. If the part of the tissue to be separated is to be histologically examined, then said part of the tissue to be separated must not be damaged. This can be monitored by a measuring circuit, particularly one of the measuring circuits described herein. 
     Preferably, the two clamping surfaces of the grasping forceps are connected to the generator circuit. If both the clamping surfaces of the grasping forceps are connected in parallel to the neutral electrode, the contact surface of the auxiliary electrode is doubled; thus, reducing the loading on the tissue region contacted by the clamping surfaces. 
     The grasping forceps can be configured as bipolar grasping forceps. The electrosurgical HF generator can then comprise a measuring circuit for determining the resistance between the two clamping surfaces of the grasping forceps. With this measuring circuit, determining whether the clamping surfaces of the grasping forceps contact the tissue sufficiently can be achieved. 
     If the electrosurgical HF generator comprises a selector switch for connecting one clamping surface of the bipolar grasping forceps to the active output and for connecting the other clamping surface of the bipolar grasping forceps to the neutral output, then the operating mode of the HF generator can be switched by actuating the selecting switch from monopolar use to bipolar use; thereby increasing the range of applications for the HF generator. Preferably, the HF generator has a selector switch for separating the remaining electrodes i.e., the active electrode and the neutral electrode, from the generator circuit. This helps prevent accidents. 
     Preferably, the electrosurgical HF generator has a switch for separating the auxiliary neutral electrode from the generator circuit because not every operating situation requires an auxiliary neutral electrode to be applied to the tissue. 
     If the electrosurgical HF generator comprises a measuring circuit for determining the electric resistance between the neutral electrode and the auxiliary neutral electrode, then, before the actual treatment (i.e., before a surgeon cuts or coagulates the tissue to be treated), a determination as to whether both the neutral electrode and the auxiliary neutral electrode have been correctly applied to the tissue (i.e., they make sufficient contact therewith) can be made. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Exemplary embodiments of the invention will now be described in greater detail with reference to the drawings, in which: 
         FIG. 1  shows a first embodiment of an electrosurgical HF generator disclosed herein; 
         FIG. 2  shows a second embodiment of an electrosurgical HF generator; 
         FIG. 3  shows a further embodiment of an electrosurgical HF generator; and 
         FIG. 4  shows an electrosurgical HF generator for monopolar and bipolar use. 
     
    
    
     DETAILED DESCRIPTION 
     In the following description, the same reference signs are used for identical parts and parts acting in an identical manner. 
     The HF generator  10  in  FIG. 1  comprises a generator circuit  12  with a neutral output  13  and an active output  14 . The neutral output  13  is connected, via a line  83 , to a neutral electrode  40  contacting tissue  60  over a large area. In addition, the neutral output  13  is connected, via lines  81 ,  82 , to two clamping surfaces  51 ,  52  of a pair of bipolar grasping forceps  50 , which serve as auxiliary neutral electrodes that contact a part  61  of the tissue  60  that is to be separated. The active output  14  is connected, via a line  84 , to an active electrode  30  that is configured as a hand-piece and comprises an electrode tip  31 . Using a switch (not shown), which can be configured as a foot switch or as a hand switch on the active electrode  30 , a surgeon can close the circuit so that an HF current flows between the active output  14  and the neutral output  13  of the generator circuit  12 . This HF current divides between two current paths  71 ,  72  through the tissue  60 . The first current path  71  runs from the electrode tip  31  to the neutral electrode  40 . The second current path  72  runs from the electrode tip  31  to the auxiliary neutral electrode, i.e. to the clamping surfaces  51 ,  52  of the bipolar grasping forceps  50 . The current density along the first current path  71 , via a tissue region  62  of narrowed cross-section, is reduced accordingly compared with monopolar electrosurgical treatment with an HF generator according to the prior art (i.e. a prior art generator without the clamping surfaces  51 ,  52  of the grasping forceps  50 , which in the disclosed embodiments function as auxiliary neutral electrodes). The tissue regions that are not to be treated are accordingly heated less along the first current path  71 , particularly in tissue region  62 . 
     The electrosurgical HF generator  10  according to  FIG. 2  is similarly constructed to the generator of  FIG. 1  except that it can be operated either in monopolar mode or in bipolar mode. For monopolar mode, switches S 4  and S 5  are closed (switches S 2  and S 3  remain in the open position), so that one neutral electrode  40  is connected to the neutral output  13  and one active electrode  30  is connected to the active output  14 . Alternatively, switches S 2  and S 3  can be closed (S 4  and S 5  remain in the open position), so that one clamping surface  52  of a pair of bipolar grasping forceps  50  is connected, via a line  82 , to the neutral output  13  and the other clamping surface  51  of the bipolar grasping forceps  50  is connected, via a line  81 , to the active output  14 . Consequently, the HF generator can be used with bipolar instruments when switches S 2 , S 3  are closed. 
     The HF generator  10  according to  FIG. 3  essentially corresponds to the HF generator of  FIG. 1 , with the following noted differences. With the switches S 2 , S 3  and S 5 , the neutral electrode  40  and the clamping surfaces serving as auxiliary neutral electrodes  51 ,  52  of the bipolar grasping forceps  50  can be connected to the neutral output  13  of the generator circuit  12 . The corresponding lines  81 ,  82 ,  83  from the neutral output  13  to the clamping surfaces  51 ,  52  and to the neutral electrode  40  are routed via a measuring circuit C 1 . The measuring circuit C 1  determines the currents through the clamping surfaces  51 ,  52  and the current through the neutral electrode  40 , as well as the ratio of said currents. If a measured value lies outside the corresponding previously set value range, then this is signalled to the surgeon, for example, with an indicator (not shown). The circuit C 1  preferably measures the resistance between the neutral electrode  40  and the two clamping surfaces  51 ,  52  of the auxiliary neutral electrode before the actual electrosurgical treatment. If this resistance is above a previously determined limit value, then the switch S 4  between the active electrode  30  and the active output  14  can be locked in an open position and/or a corresponding warning signal can be given to the surgeon (e.g., with an LED) to indicate that he should check the seating of the neutral electrode  40  and the auxiliary neutral electrode(s). If an auxiliary neutral electrode cannot be applied during an operation, the switches S 2  and S 3  remain open. 
     The electrosurgical HF generator  10  in  FIG. 4  comprises, like the electrosurgical generator in  FIG. 3 , a generator circuit  12  with a neutral output  13  and an active output  14 , which can be connected, via a series of switches S 1  to S 6 , to an active electrode  30  configured as a hand-piece or to a neutral electrode  40  and/or the clamping surfaces  51 ,  52  of a pair of bipolar grasping forceps  50 . Switches S 1  to S 6  enable the electrodes to be connected to the active and neutral outputs  13 ,  14  so that both monopolar (with and without the auxiliary electrode(s)) and bipolar electrosurgical treatments can be carried out with the electrosurgical generator  10 . For conventional monopolar electrosurgical treatment, only switches S 4  and S 5  are closed. The active electrode  30  is then connected to the active output  14  and the neutral electrode  40  is connected to the neutral output  13  of the generator circuit  12 . If switches S 2 , S 3  and S 6  are also closed, the clamping surfaces  51 ,  52  of the bipolar grasping forceps  50  are also connected to the neutral output  13  of the generator circuit  12  and serve as an auxiliary neutral electrode. In this operating mode, using the measuring circuit C 1  described above with reference to  FIG. 3 , the correct seating of the neutral electrode  40  and of the auxiliary neutral electrodes  51 ,  52  is monitored. If switches S 4 , S 5  and S 6  are opened and switches S 1 , S 2  and S 3  are closed, a clamping surface  52  of the bipolar grasping forceps  50  is connected to the neutral output  13  of the generator circuit  12  and the other clamping surface  51  is connected to the active output  14  of the generator circuit  12 . With the selection switches Si to S 6  in this setting, bipolar electrosurgical treatment can be carried out with the bipolar instrument  50  as usual. With the selection switches S 1  to S 6 , the electrosurgical HF generator  10  according to  FIG. 4  offers the possibility of carrying out monopolar electrosurgical treatment with the active electrode  30  and with the neutral electrode  40 . In addition, clamping surfaces  51 ,  52  of a pair of bipolar grasping forceps  50  can be connected as auxiliary neutral electrodes. Alternatively, the electrosurgical HF generator  10  also enables bipolar electrosurgical treatment using the bipolar instrument  50 . In this case, switches S 1  to S 6  are shown only symbolically. In order to prevent faulty operation, the switches S 1  to S 6  are preferably controlled via an operating mode selection element that is to be controlled by a surgeon.