Abstract:
Electrosurgical instruments that transmit electrical energy from an electrosurgical generator via an electrode and a current path of ionized gas into biological tissue. In order to obtained a defined, low treatment depth in the target tissue, the electrosurgical instrument contains a resistive element with a predetermined impedance between the distal end of the connection line and the electrode, installed in such a way that treatment current is limited after ionizing of the gas.

Description:
FIELD OF THE INVENTION 
       [0001]    The disclosed embodiments relate to plasma applicators for the use of plasma surgery in open surgery or in rigid endoscopy and plasma probes for the use of plasma-surgical methods in flexible endoscopy. 
       BACKGROUND 
       [0002]    Generally in plasma surgery (shown schematically in  FIG. 6 ), ionized and consequently electrically conductive gas (plasma), i.e. argon plasma, is used to direct high-frequency electrical AC current (HF current, I HF ) onto or into biological tissue (target tissue, A, B, C, D) in order to generate medically beneficial thermal effects on or in the target tissue, in particular devitalization (D), coagulation (C), desiccation (B) and/or shrinkage (A) without damaging collateral tissue (G) any more than is unavoidable and tolerable. The ionization of the gas between an ionization electrode (E) and the target tissue occurs with a sufficiently high electrical field strength (F e ) corresponding to the function F e =U HF :d. Ionization of argon at atmospheric pressure requires approximately 500 V/mm. 
         [0003]    Plasma-surgical methods and plasma applicators are not new. One such plasma-surgical method, fulguration or spray coagulation, has been used for more than 50 years for thermal haemostasis in surgical operations. Fulguration or spray coagulation employs primarily oxygen and nitrogen plasmas which are generated in air. These plasmas are chemically reactive and give rise to carbonization effects, pyrolysis effects and consequently vaporization of tissue and smoke on the surface of the tissue. Such side effects disrupt and can even prevent the use of fulguration or spray coagulation, especially for endoscopic operations. 
         [0004]    U.S. Pat. No. 4,060,088 describes limiting the above-described side effects of fulguration or spray coagulation by replacing the air between the active electrode and tissue being treated with a chemically inert or noble gas, such as helium or argon and mixtures thereof. Nowadays, argon is mainly used due to its relatively low cost. This method, known as argon plasma coagulation (APC), has been in use almost 20 years. An early example of a clinically applicable device for APC is described in U.S. Pat. No. 4,781,175, but that device is only for use in open surgery and rigid endoscopy for thermal haemostasis. 
         [0005]    Use of APC for flexible endoscopy was first described in 1994 by Farin and Grund (G. Farin, K. E. Grund: Technology of Argon Plasma Coagulation with Particular Regard to Endoscopic Applications. Endoscopic Surgery and Allied Technologies, No. 1 Volume 2, 1994: 71-77; and K. E. Grund, D. Storek, G. Farin: Endoscopic Argon Plasma Coagulation (APC): First Clinical Experiences in Flexible Endoscopy. Endoscopic Surgery and Allied Technologies, No. 1 Volume 2, 1994: 42-46). The range of applications of APC in flexible endoscopy was later described by Grund, Zindel and Farin (K. E. Grund, C. Zindel, G. Farin: Argon Plasma Coagulation in Flexible Endoscopy: Evaluation of a New Therapeutic after 1606 Uses. Deutsche Medical Wochenschrift 122, 1977: 432-438). 
         [0006]    APC is not used only for the coagulation of biological tissue. APC is also used for thermal devitalization of pathological tissue and desiccation and shrinking of blood vessels and their collateral tissue for purposes of haemostasis. This use of APC is becoming increasingly important for the thermal devitalization of relatively thin layers of tissue such as the mucosa of the gastrointestinal tracts or tracheobronchial system. APC is also becoming increasingly important for the thermal sterilization of the surface of tissue during transmural operations, for example in transgastral operations, in order to avoid the dissemination of germs from the stomach into the abdominal cavity. Because such uses are not adequately defined by the term argon plasma coagulation (APC), and the subject matter to be discussed in this application is not solely restricted to the coagulation of biological tissue only or the use of argon gas, we will use the broader and more comprehensive term “plasma surgery.” 
         [0007]    The broad range of applications for plasma surgery places different requirements on the properties of the devices used, in particular the reproducibility of the intended thermal effects on or in target tissue and the avoidance of the side effects common to air-based fulguration or spray coagulation described above. This is especially the case when plasma surgery is used on or in thin-walled hollow organs in the gastrointestinal tract or the tracheobronchial system (As described in G. Farin, K. E. Grund: Principles of Electrosurgery, Laser, and Argon Plasma Coagulation with Particular Regard to Colonoscopy. In: Colonoscopy; Principles and Practice, Edited by J. D. Waye, D. K. Rex and C. B. Williams, Blackwell Publishing 2003: 393-409). 
         [0008]    In fact, the range of different plasma applicators for medical applications, in particular plasma surgery and endoscopically controlled interventions, is very broad. As far as access to the respective target organ or target tissue, known plasma applicators may be differentiated between those used for open surgery, those used for rigid endoscopy and those used for flexible endoscopy. The basic structure and function of such plasma applicators can be seen in G. Farin and K. E. Grund: Technology of Argon Plasma Coagulation with Particular Regard to Endoscopic Applications, Endoscopic Surgery and Allied Technologies, Thieme Verlag, Stuttgart, No. 1, Volume 2, 1994: 71-77. 
         [0009]    An arrangement for endoscopic plasma surgery is shown in  FIG. 7 . Generally, endoscopic plasma surgery requires a surgical high-frequency (HF) generator  1 , which is connected to a neutral electrode  2  and a surgical instrument or probe  10  (or its discharge electrode, which is not shown). The probe  10  is inserted in one of the working channels  6  of an endoscope  5 . Argon (or another noble gas) is fed from a noble gas source  7  to a lumen of the probe  10 . The neutral electrode  2  is placed in contact with the patient&#39;s biological tissue  3 . In this way, the operator can treat target tissue  4  with argon plasma. 
         [0010]    HF generators available for plasma surgery may be differentiated with respect to their internal resistance. HF generators with a high internal resistance are in particular suitable for treating superficial lesions, with which a low penetration depth of the thermal effects is expedient. HF generators with a low internal resistance are in particular suitable for treating massive lesions, where a high penetration depth of the thermal effects is expedient. DE 19839826 describes an HF generator in which the internal resistance is adjustable between high and low, but such HF generators are not yet available. 
         [0011]    For treatment of superficial lesions, low penetration depth of thermal effects is desired and often necessary. As such, it can be problematic to employ low internal resistance HF generators because penetration depth is primarily controlled by duration of application, i.e., by the operator. Since the rate of penetration of the thermal effects at the start of the plasma application with low internal resistance HF generators is relatively quick and becomes progressively slower over time until the maximum achievable penetration depth is achieved, the achievement of a low and uniform penetration depth of the thermal effects with surface lesions is extremely difficult, if not impossible. Although the rate of penetration of the thermal effects can be influenced by varying the power or HF current flowing through the plasma, the pulse modulation can interfere with video signals from video endoscopes and give rise to neuromuscular stimuli, the latter in particular at modulation frequencies of less than 1 kHz. With known HF generators, this is done by considering the high HF voltage required to ionize the gas by pulse modulation. A further problem with the use of HF generators with low internal resistance to treat superficial lesions is the very high temperature of the plasma due to the high HF voltage required for the ionization and of the low electrical resistance of the plasma path, which results in a very high HF current density in the plasma path and may result in a high enough temperature to cause carbonization and pyrolysis effects. 
         [0012]    However, HF generators with high internal resistance are essentially unusable for endoscopic operations or interventions because of stray capacitance between the active HF lines and neutral HF line. As such, the transmission of high HF voltage between the ionization electrode and target tissue required for the ionization of the gas from the HF generator to the ionization electrode is inadequate or worse, impossible. This is particularly well documented with respect to flexible endoscopy. 
         [0013]    EP 1 148 770 A2 describes a plasma applicator where none of the neutral electrodes normally provided are used. The HF generator provided there is supposedly a resonance transmitter, wherein the HF current flows as a “dielectric displacement current from the surface of the patient to earth”. This is supposed to induce scabbing with a surgical cold plasma jet apparatus that can take place without carbonization or combustion products caused by oxygen inclusion. 
       SUMMARY 
       [0014]    The disclosed embodiments include an electrosurgical instrument having a resistive element in a hand piece of the instrument in series connection with the electric circuit. This resistive element has a fixed position, and remains in the hand piece even when the electrode is connected separately. Such an electrosurgical instrument is both inexpensive and safe, and adequately addresses the problems noted above with respect to controlling penetration depth of thermal effects. 
         [0015]    Another embodiment comprises an electrosurgical instrument for the transmission of electrical energy from an electrosurgical HF generator via a connection line and an electrode connected to a distal end thereof and further via a current path of ionized gas into a biological target tissue. Disposed between the distal end of the connection line and the electrode is a resistive element having predetermined impedance. The element is selected in such a way that ensures limitation of treatment current after gas ionization. 
         [0016]    An important point is that because the entire arrangement including the generator and all leads is considered to be the “entire generator,” the internal resistance of the entire generator can be determined by the resistive element. The resistive element can thus be selected to meet requirements for a desired penetration depth, and it is therefore possible to provide different instruments for different penetration depths. Obviously, treatment time is still significant, but there is significant added control during the critical phase (the brief moment following the “ignition” of the arc during which a high current flow is possible). 
         [0017]    The resistive element can be an ohmic resistance which ensures the desired current limitation. However, the resistive element is preferably capacitive in nature, i.e., a capacitive element with necessary dielectric strength. When a capacitive element is used, it forms a high-pass filter so that low-frequency portions of the current are dampened. This in turn leads to a significant reduction in interference to video systems (such as those commonly used in endoscopes) and avoidance of neuromuscular stimuli that can occur with lower frequency current. 
         [0018]    In the case of sufficiently large plasma applicators, the capacitive element can be implemented by commercially available components, for example, a ceramic capacitor capable of resisting high voltage. But in rigid or flexible endoscopes (as described in connection with  FIG. 7 ), such as, for example, argon-plasma coagulation probes (APC probes) such as those described in DE 19820240 or DE 10129699 or EP 1397082, the instrument channels are quite narrow, often times with an external diameter of only 2 to 3.5 mm. As such, the capacitive element itself has to be specially developed (to fit in the small space) or the distal end of the APC probe must be altered. 
         [0019]    Since, as mentioned above, APC probes can be used with other gases or gas mixtures, for other thermal effects and optionally also in other specialist fields, in the following, plasma applicators such as those described herein will be called general plasma probes (“P probes”). 
         [0020]    In a preferred embodiment, the resistive element comprises a segment of the connection line and/or the electrode, i.e. segments of these components are used either for the formation of an ohmic resistance or (optionally) for the formation of a capacitance. The resistive element can be formed from parallel-guided or twisted or coaxially-arranged segments of the connection line, which are electrically insulated from each other and/or a supply line to the electrode and/or the electrode itself. In this case, it should be ensured that no inductances form, for instance, because of the use of bifilar line arrangements. 
         [0021]    Generally, the resistive element has a capacitance of 10 pF to approximately 1,000 pF. These are capacitance ranges that result in currents at the frequencies usually used in high-frequency surgery, thus ensuring the desired (relatively low) penetration depth. 
         [0022]    The dielectric used to create the capacitive element should have the highest possible dielectric constant. Plastics can be used, but ceramic materials are generally preferred. The material used can be rigid ceramic material or even (if greater flexibility is required) powdery ceramic material. 
         [0023]    All the above features can also be used in electrosurgical arrangements in which no “protective gas” is used, though it is preferable to work with a protective gas (in particular argon). Generally, the electrode is in or close to a tube, a hose or a probe and is positioned in such a way that the gas to be ionized can be supplied to a chamber between the electrode and the target tissue. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0024]    The following describes an exemplary embodiment of the invention in more detail with reference to the attached diagrams: 
           [0025]      FIG. 1  shows a schematic representation of an embodiment of the disclosed electrosurgical instruments, 
           [0026]      FIGS. 2-5  show schematic representations of resistance elements embodied as capacitive elements and the associated electrodes, 
           [0027]      FIG. 6  shows the representation described in the introduction to explain the processes during argon plasma coagulation and 
           [0028]      FIG. 7  shows an overall arrangement for the endoscopic treatment of tissue by means of APC. 
       
    
    
     DETAILED DESCRIPTION 
       [0029]    In the following description, the same reference numerals denote the same objects or objects having similar functions. 
         [0030]      FIG. 1  shows a schematised arrangement of an embodiment of the electrosurgical instrument disclosed herein that corresponds to the plasma surgical instrument shown in  FIG. 7 . The endoscope shown in  FIG. 7  is not seen in this arrangement. However, as mentioned above, arrangements of this kind can also be used for open surgery which does not require an endoscope. 
         [0031]    As shown  FIG. 1 , a high-frequency generator is provided having a voltage source with a voltage U 0  and an internal resistance  8  with a resistance value R i . Thus, where there is an output current I HF1  at the output from the generator  1 , there is a voltage U 1    
         [0000]    
       
      
       U 
       1 
       =U 
       0 
       −R 
       i 
       *I 
       HF1  
      
     
         [0000]    at the output terminals of the generator  1 . The generator is connected via a supply line  11  to a probe supply line  12  arranged within a hose of the probe  10 . The probe line  12  is connected at its distal end via a resistive element  20  and an electrode supply line  24  to an electrode  13 . Argon gas is conducted through the hose of the probe  10  so a chamber between the distal end of the probe  10  and the biological tissue  3  is filled with argon gas and the air normally found there is forced out. When the voltage between the tip of the electrode  13  and the biological tissue  3  is high enough, the gas (argon) in this chamber between the electrode  13  and the biological tissue  3  is ionized, and an arc  14  forms. Then, a current I HF4  flows through the target area  4  and surrounding biological tissue  3  to the neutral electrode  2 . 
         [0032]    The supply line  11  is usually a monopole line. In addition, the neutral electrode  2  is kept at the surrounding potential (as is an optionally provided endoscope) so that there is a relatively high stray capacitance  15  between the supply line  11  and a stray capacitance  16  between the probe line  12  and the surroundings. Currents I HF2  or I HF3  flow through these stray capacitances  15  and  16 . This stray capacitance causes a drop in the voltage (U Z ) used between the electrode  13  and the target area  4  for the ignition of plasma before the ignition of an arc  14 : 
         [0000]        U   Z   =U   0   −R   I  ( I   HF2   +I   HF3 ) 
         [0033]    In order to ensure the ignition of the plasma  14  at the greatest possible distance from target area  4 , it is advantageous for the value R I  of the internal resistance  8  to be low. On the other hand, when arc  14  is ignited it has a very low resistance, and due to the fact that the resistance between the target area  4  and the neutral electrode  2  is also relatively small, there will be a very high current I HF4 . As such, only a short time will pass before target area  4  is affected at a relatively deep depth. 
         [0034]    Resistive element  20  is thus disposed between the distal end of the (high-loss) line  11 ,  12  and the electrode  13 , so that even with a high ignition voltage available at the electrode  13  following the ignition of the arc  14 , a high voltage drop is generated to limit current I HF4 . This limiting is made possible by having the resistive element  20  at this position. However, it should be stressed that the resistive element  20  does not have to locally limit the current. The resistor element  20  can in fact extend over the length of the (high-loss) line  11 ,  12  up to the tip of the electrode  13 . 
         [0035]    The following describes different embodiments of the resistive element  20  with reference to  FIGS. 2-5 . 
         [0036]    In the embodiment shown in  FIG. 2 , a distal end of the probe line  12  is shown comprising a probe conducting wire  21  insulated by insulating material  22 . Disposed parallel to this distal end of the probe line  12  is the electrode supply line  24 , which is connected to the electrode  13  and provided with insulation  22 ′. Parallel guidance of the two lines  12 / 24  results in the formation of a capacitance which functions as resistive element  20 . 
         [0037]    The embodiment shown in  FIG. 3  differs from the  FIG. 2  embodiment in that both the distal end of the probe conducting wire  21  and the end of the electrode supply line  24  are embedded in a common insulating material  22 . In addition, the electrode supply line  24  is bifilar so that any line inductances are compensated. In such a case, ceramic material can be used as insulating material (solid or powder form) to achieve the highest possible capacitance in the smallest space. 
         [0038]    In the embodiment shown in  FIG. 4 , the capacitance is increased by winding the electrode supply line  24  around the end of the probe supply line  12 . The electrode supply line  24  can be bifilar here as well to compensate for line inductances. 
         [0039]    In the embodiment shown in  FIG. 5 , the electrode supply line  24  is embodied as a sleeve surrounding the distal end of the probe line  12  and forming a capacitance with said probe line. In this case, the electrode is in an electrically conductive connection via a connecting point  25  with the sleeve-shaped electrode supply line  24 . The dimensions can also be similar to those in  FIG. 4 , so the supply of argon gas no longer flows through the sleeve-shaped electrode supply line  24 , but past it into the hose  9  of the probe  10 . 
         [0040]    No matter the embodiment, it is important to provide suitable insulation so that there is no disruptive discharge between elements formed by lines  12 / 24 . It is also possible to embed the lines  12 / 24  in a wall of the hose  9  that forms the gas line for the probe  10 . The working channel  6  of the endoscope  5  can also be used as a gas line, as described in EP 0954246 A1. 
         [0041]    The physical parameters that determine the capacitance between the lines can be found in technical literature. Further, the arrangement and shape of the gas outlet opening can obviously be embodied not only, as shown in the exemplary embodiments, in the axial direction, they can also be arranged differently, such as shown for example in DE 19820240 A1 or DE 10129699 A1. 
         [0042]    In sum, limiting the amplitude of the HF current flowing through the plasma, as the above described embodiments do, provides not only control of the penetration depth of thermal effects in target tissue, but several other advantages, including: avoidance of excessively high plasma temperatures and hence avoidance of carbonization or even pyrolysis of the target tissue; avoidance of thermal overloading of the distal end of the plasma probe, i.e., when the plasma comes into direct contact with plastic (such as with the plasma probes of DE 10129699); avoidance of interference with video systems; and avoidance of neuromuscular stimuli, which are both prevented by the capacitive resistance&#39;s mitigation of low-frequency currents. 
         [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.