Abstract:
An electrosurgical stapling instrument includes an end effector capable of applying bipolar RF energy into tissue. The end effector has a first pole electrode and a second pole electrode for forming an RF contact circuit with tissue. At least one of the electrodes may have a dielectric coating thereon to create a RF circuit with tissue. The dielectric coating can cover one of the electrodes to create a capacitive coupling circuit with tissue, or can have at least one open passageway extending through the dielectric coating to enable tissue contact with the electrode and the passage of RF energy therethrough. The dielectric coating on the electrode can be masked to create passageways through the dielectric, or the dielectric coating can be locally removed with a variety of techniques to form passageways. The dielectric coating may provide a barrier to prevent shorting between the dielectrically coated electrode and a conductive fastener embedded within tissue. Alternately, a cartridge coating can be used to reduce an electric surface sheet charge on the cartridge thermoplastic that can occur during the application of RF energy to tissue.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates, in general, to an electrosurgical instrument and, more particularly, to coatings for an electrosurgical instrument which uses thermogenic energy for cauterization, coagulation and tissue joining/welding in combination with staples to form a hemostatic staple/coagulation/cut line in tissue. 
       BACKGROUND OF THE INVENTION 
       [0002]    Surgical procedures frequently require cutting of tissue which can cause bleeding at the operative or surgical site. Hemostasis, or the arrest of bleeding, is important to surgeons to reduce blood loss and reduce surgical complications. A variety of hemostatic control techniques are available to the surgeon such as suturing, stapling, the application of surgical clips, the application of ultrasonic energy, the application of laser energy, as well as the application of monopolar or bipolar electrical energy. Surgeons frequently use a combination of these means to induce hemostasis during surgery. For open procedures, the surgical site is readily accessible through the large incision and the application of devices or techniques to reduce bleeding are readily applied. Endoscopic surgery is done through small access ports inserted into small incisions. Endoscopic surgeries are more challenging as the surgeon does not have the large incision to work through, visibility of the site is more difficult, and access to the surgical site is limited to the number of small access ports or trocars. Electrocautery instruments are commonly used when accessing a patient during surgery. These instruments apply monopolar or bipolar Radio Frequency (RF) energy to cauterize the local “bleeders” in tissue incisions. Monopolar instruments have one electrode that is associated with a cutting or cauterizing instrument and a return or ground electrode is attached to a remote portion of the patient. Energy is applied to the bleeder by delivering energy from a tip of the device to the patient at the site of the bleeder. 
         [0003]    Bipolar instruments normally apply a cauterizing current to a pair of electrodes on moveable opposed jaw members of the instrument. Tissue is cauterized by clamping the open jaw members upon tissue to bring the electrodes into tissue contact, and then applying RF bipolar energy to the compressed tissue within the jaw members. The current conducts between the electrodes and cauterizes, coagulates, or tissue welds the tissue compressed therebetween. 
         [0004]    Additionally, mechanical devices such as surgical staplers and linear cutters, both open and endoscopic, have been utilized as a means of excising tissue and controlling hemostasis. Staples are used to provide hemostasis in vascular structures, and when applied to lung tissue, were found to provide a good degree of pneumostasis as well. Surgical cutters have a plurality of staples held in multiple staggered rows in a replaceable cartridge. The cutters compress the tissue, and the staples are formed or fired into the compressed tissue in close proximity to the diseased tissue portion that is to be excised. A cutting blade passes longitudinally between the innermost rows of formed staples, transecting the tissue. The cutter is removed from the surgical site, reloaded with another unfired stapling cartridge, and the procedure is repeated until the desired section of the lung is resected and removed. 
         [0005]    One known problem which can arise with using surgical staplers in this fashion has been the formation of small “bleeders” in the cut and stapled tissue. To ensure peace of mind, surgeons can suture or use other techniques to staunch the small bleeders. RF energy devices and/or ultrasonic energy devices are frequently used to cut and coagulate tissue during endoscopic surgery. However, energy delivery to tissue next to a metallic staple line can require care and technique. With bipolar RF devices, a staple can cause a short and prevent the RF generator from firing and coagulating tissue. With ultrasonic and/or monopolar devices, contact with staples can conduct energy away from the initial application site. 
         [0006]    U.S. Pat. No. 5,735,848, U.S. Pat. No. 5,688,270, and U.S. Pat. No. 5,709,680 by Yates et al. disclose surgical instruments that combine a staple applying endocutter with an electrosurgical bipolar RF device to improve hemostasis, reduce surgical complexity, and operating room time. With these improved bipolar cutting and stapling devices, activation of the clamping trigger puts tissue in contact with a first and second electrode, and activation of the electrosurgical generator, typically with a foot pedal, produces a narrow stripe of coagulated tissue with the application of RF energy. The first electrode, the clamped tissue, and the second electrode form a conductive circuit. The moisture and ions within the tissue chemistry conducts the RF energy, and the tissue begins to desiccate or coagulate. As the tissue desiccates, it becomes less and less conductive. When the tissue is fully desiccated, it is nearly an insulator and only a small amount of current flows between the first and second electrodes. Activation of a second firing trigger on the surgical instrument fires rows of staples from a single shot staple cartridge on either side of the coagulation stripe, and places a cut line along the center of the coagulated tissue. When the surgical instrument is opened, the tissue cut line is cauterized along the edge for hemostasis, and has multiple parallel rows of staple lines placed in the un-cauterized tissue flanking the cauterized cut edge for additional security. 
         [0007]    If a longer cut line is needed, the surgeon reloads a second staple cartridge into the electrosurgical stapling instrument, and reinserts it into the patient at the desired location. The instrument is then re-clamped, and the generator is again activated to produce a second coagulation stripe. In some cases, it is desirable to place the second coagulation stripe and staple line over the first staple line. This can occur when the second cut line is at an angle to the first. Placing and clamping the end effector over the first staple line can create a “short” condition by shorting the first and second electrodes of the electrosurgical stapler through one or more staples. The metal staples are far more conductive to RF energy than tissue in any condition. When the electrodes are shorted, the RF current preferentially flows through the staple and not through the tissue. For a short, the surgeon must unclamp the instrument and reposition and reclamp the end effector at another location. If the instrument shorts again, the instrument must again be repositioned until shorting is eliminated. What is needed is an improved electrosurgical stapling device that decreases operating room time by reducing the ability to cause shorts. 
         [0008]    Additionally, in electrosurgical devices that combine staples with RF energy delivery, the application of RF energy can create a surface charge with the plastic cartridge. Cartridge materials are commonly plastics chosen for strength, moldability, thin walls, and dimensional accuracy or repeatability. What is needed is a cost effective way to reduce the surface charge of the cartridge. 
         [0009]    Alternately, it may be desirable to use capacitive coupling of RF energy to coagulate the tissue. Classical bipolar RF electrosurgical devices form a conductive resistance network to coagulate tissue. Conductive coupling devices also use RF bipolar energy, but transfer energy from one circuit to another by means of the mutual capacitance between the circuits. A capacitive coupling RF bipolar electrosurgical device places a non-conductive material or dielectric between the tissue and at least one of the electrodes. The transfer of energy from the shielded electrode to the unshielded electrode is by means of the mutual capacitance between the first pole electrode dielectric, tissue and second pole electrode circuit. 
         [0010]    At present, there are no known electrosurgical instruments that can meet all of the needs outlined above. These and other advantages will become more apparent from the following detailed description and drawings. 
       SUMMARY OF THE INVENTION 
       [0011]    In accordance with the present invention, there is provided an electrosurgical instrument having an end effector capable of receiving RF bipolar energy therein. The end effector has a first pole electrode and a second pole electrode. A dielectric coating can be placed on at least one of the first and second pole electrodes, the dielectric having least one open channel through the dielectric coating. The at least one open channel in the dielectric coating may provide passage of radio frequency energy between the first and second pole electrodes 
         [0012]    Also in accordance with the present invention, there is provided an electrosurgical instrument having an end effector capable for clamping and coagulating tissue. The end effector can have a first pole electrode and a second pole electrode. A dielectric coating may be placed on at least one of the first and second pole electrodes where the dielectric coating can prevent direct tissue contact with at least one of the electrically active electrodes. 
         [0013]    Yet another embodiment in accordance with the present invention is an electrosurgical instrument having an end effector capable of receiving bipolar energy and placing at least one staple into tissue. The end effector may have a first pole electrode, a second pole electrode; and a staple cartridge having said at least one staple therein. The staple cartridge can have a coating to reduce formation of a surface charge thereon during the application of bipolar energy to tissue. 
     
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]    The novel features of the invention are set forth with particularity in the appended claims. The invention itself, however, both as to organization and methods of operation, together with further objects and advantages thereof, may best be understood by reference to the following description, taken in conjunction with the accompanying drawings in which: 
           [0015]      FIG. 1  is an isometric view of an electrosurgical instrument of the present invention, showing an electrosurgical generator operably coupled to an actuation foot switch and to an electrosurgical instrument having a distal end effector with an angularly open anvil. 
           [0016]      FIG. 2  is a side view, in cross section, of the end effector of the electrosurgical instrument of  FIG. 1  showing a first unfired staple cartridge located below the angularly open anvil, and a coating on the anvil. 
           [0017]      FIG. 3  is a cross sectional end view of the end effector of  FIG. 1  with the anvil in a closed position, the cross section taken along lines A-A ( FIG. 2 ) and showing the anvil and cartridge coatings. 
           [0018]      FIG. 4  is a cross sectional end view of a prior art end effector clamped on tissue and showing the path of RF energy between the electrodes. 
           [0019]      FIG. 5  is a cross sectional view of an end effector with a coated anvil clamped on tissue and showing the RF energy paths into uncoated staple pockets and channel. 
           [0020]      FIG. 6  is an isometric view showing the prior art end effector of  FIG. 4  being placed on a portion of severed tissue containing a plurality of formed staples, the prior art end effector of  FIG. 4  being positioned for a second clamp, coagulation, staple and cutline on top of the prior staple lines. 
           [0021]      FIG. 7  is a cross sectional view of the prior art end effector of  FIG. 6  clamped on the portion of tissue containing a plurality of formed staples and showing how a staple formed in tissue can induce shorting between the first pole electrode and the anvil. 
           [0022]      FIG. 8  is a cross sectional view of the end effector of  FIG. 5  clamped on the portion of tissue containing a plurality of formed staples and showing how an anvil coating can eliminate shorting with a formed staple; 
           [0023]      FIG. 9  is an alternate embodiment of the coatings of the present invention with a portion of the coating removed from an upper surface of the anvil. 
           [0024]      FIG. 10  shows a second alternate anvil coating of the present invention placed on the anvil wherein the anvil coating has no openings along the tissue contact areas. 
           [0025]      FIG. 11  shows an alternate E-beam electrosurgical instrument  120  of the present invention. 
           [0026]      FIG. 12  is a cross sectional view of the E-beam end effector of  FIG. 11  clamped on tissue containing one formed staple and showing how an anvil coating prevents shorting between a first pole electrode and anvil. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0027]    As best shown in  FIG. 1 , the present invention includes an electrosurgical instrument, generally designated  20 , used for the cauterization, coagulation and/or tissue welding in the performance of surgical procedures. Electrosurgical instrument  20  clamps on tissue, can apply RF energy for tissue coagulation, and can be fired to place a plurality of parallel rows of staples and cut tissue between the innermost rows of staples. Electrosurgical instruments of this type are described in the U.S. Pat. No. 5,735,848, U.S. Pat. No. 5,688,270 and U.S. Pat. No. 5,709,680 by Yates et al. which are incorporated herein by reference. However, the electrosurgical instrument  20  can have coating improvements to an end effector  45  that will be described in detail below. 
         [0028]    The electrosurgical instrument  20  has a handle  30  and a shaft  40  extending distally from the handle  30 . End effector  45  extends distally from a distal end of the shaft  40 . Rotation knob  35  is located between the handle  30  and shaft  40  for simultaneous rotation of the shaft  40  and the end effector  45  about a longitudinal axis LL. End effector  45  extends distally from shaft  40  and has a moveable anvil  55  and a fixed lower channel  47 . Anvil  55  is moveable from a first open position  FIG. 1 ) angled away from the channel  47  to a second clamped or closed position parallel to and spaced away from channel  47  ( FIG. 3 ). A cartridge  50  containing a plurality of staples  53  ( FIG. 3 ) is removably mounted within the channel  47 . A closure trigger  32  and a firing trigger  34  are rotatably mounted within the handle  30  near a grip  31 . Actuation of closure trigger  32  rotates the trigger adjacent to grip  31 , closes of the anvil  55 , and unlocks of the firing trigger  34 . Actuation of the firing trigger  34  ejects the plurality of staples  53  and moves a knife  66  between the inner most rows of staples  53  (not shown). Release button  36  is located at the proximal end of the handle  30  for opening the anvil  55  from its closed position. 
         [0029]    RF energy is supplied to the electrosurgical instrument  20  from an electrosurgical generator  21  when the surgeon activates a foot switch  22 . A first pole wire  38  and a second pole wire  39  electrically connect the generator  21  to the electrosurgical instrument  20  for delivery of RF energy to a first and second pole electrode. The first and second pole wires  38  and  39  respectively extend from the generator, into a strain relief  37  and to the first and second pole electrodes in end effector  45 . 
         [0030]    As best shown in  FIG. 2 , shaft  40  has a longitudinally moveable hollow closure tube  4  and a longitudinally fixed to a nonconductive retainer  42  made from a suitable material such as glass reinforced polycarbonate. Retainer  42  is rotatably restrained within handle  30  and is prevented from moving longitudinally but allowed to rotate about the longitudinal axis LL Channel  47  is fixed to a distal end of retainer  42 , extends distally from closure tube  41 , and has anvil  55  moveably mounted within. Anvil  55  can be formed from a conductive material such as stainless steel, and is shown in the open position angularly spaced away from channel  47  and cartridge  50 . Anvil  55  contains a plurality of staple forming pockets  58  that are brought into alignment above the staples  53  in the cartridge  50  when anvil  55  is closed (see  FIG. 3 ). A “C” shaped insulator  62  is fixedly attached within groove  59  ( FIG. 3 ) of anvil  55 , and a first pole electrode  60  having a tissue contact surface and mounted within the inner portion of the “C”. Insulator  62  electrically isolates the first pole electrode  60  from the electrically conductive anvil  55 . A distal end of first pole wire  38  forms an electrical connection with first pole electrode  60  and a proximal end is electrically connected to generator  21  ( FIG. 1 ). First pole wire  38  is electrically isolated from all elements of electrosurgical instrument  20  therebetween. Staple forming anvil  55  also acts as the return path or second pole electrode  56  for the electrosurgical device  20  of the present invention. Anvil  55  is closed by activating the closure trigger  32 . Closure trigger  32  is operably coupled to closure tube  41  of shaft  40  and moves closure tube  41  distally from a proximal position shown in  FIG. 2 . This motion brings closure tube  41  into contact with a ramp  57  of anvil  55  and through wedging action, moves anvil  55  to the closed position of  FIG. 3 . Closure tube  41  is also in sliding and electrical contact with channel  47 . The anvil  55  of the present invention is covered in a dielectric or non-conducting coating  75  in selected areas. As shown in  FIG. 2 , the ramp  57  of the anvil  55  is not coated to ensure an electrically conducting path with the closure tube  41 . Closure tube  41  is brought into electrical contact with the second pole wire  39  when the closure trigger  32  is activated to form a second pole electrical circuit extending from the generator  21  to the second pole anvil  55 . 
         [0031]    Actuation of the firing trigger  34  ejects the staples  53  from the cartridge  50 , forms staples  53  against the anvil  55 , and move a knife  66  along a knife slot  54  to sever tissue between the inner most rows of staples  53  (action not shown). Firing trigger  34  moves wedge block  51  and knife  66  distally through the cartridge  50  to form the staples  53  against the anvil  55 . Knife  66  attaches to the wedge block  51  and moves longitudinally through knife slot  54  within cartridge  50  and first electrode  60  (see  FIG. 3 ) in response to movement of firing trigger  34 . Knife  66  trails the formation of the staples  53  so tissue is stapled first and cut second.  FIG. 3  is a cross sectional end view AA of the end effector  45  of the present invention when the anvil  55  is in the closed position spaced away from and generally parallel to cartridge  50  and channel  47 . See  FIG. 2  for the longitudinal location of cross section AA on end effector  45 . In  FIG. 3 , the cross section of the anvil is taken across staple pockets  58 , and electrode groove  59 . The electrosurgical instrument of the present invention includes a non-conducting or dielectric anvil coating  75  on anvil  55 . By way of example, the dielectric coating  75  could be but is not limited to a PTFE (polytetrafluroethylene), Paralene™ or Parylene™, titanium dioxide, or an epoxy. Paralene™ or Parylene™ are generic names for a series of polymers based on paraxylene and are available from Advance Coating, 10723 Edison Court, Rancho Cucamonga, Calif. 91730. The Parylenes are formed by the pyrolysis of a di-p-xylene (dimer) in a vacuum environment which is then deposited on a cooler (i.e. room temperature) substrate under continuous vacuum. Paralene exhibits excellent dielectric strength, exceptionally high surface and volume resistivities; and electrical properties that are essentially independent of temperature. It provides a conformal, pinhole-free coating that is unexcelled for corrosion resistance and dielectric protection. If desired, coating  75  can be selectively coated onto desired areas of the anvil, or the anvil can be entirely coated. If desired, selected areas of coating  75  may be removed by laser etching, sandblasting, water jet, grinding and the like. As shown in  FIG. 2 , the anvil coating  75  has been selectively excluded or removed from the ramp  57  to ensure electrical conductivity of the anvil  55  to the closure tube  41 . Closure tube  41  is electrically connected to the second pole wire  39  extending from the strain relief  37  to the generator  21  to complete the second pole ground circuit. Anvil  55  and channel  47  are both electrically connected to the second pole wire  39  by contact with closure tube  41 . In  FIG. 3 , anvil coating  75  generally extends around the anvil  55  but does not extend into the plurality of uncoated staple pockets  58  extending upwardly into anvil  55 . Additionally, the coating  75  has variable thickness near the staple pockets  58 . Insulator  62  is constrained in groove  59  and holds first pole electrode  60 . 
         [0032]    Cartridge  50  is constructed from an engineering thermoplastic such as the liquid crystal polymer (LCP) Vectra™. Drivers  52  move vertically in cartridge  50  when pushed upwards by wedge block  51  to form staples  53  in anvil pockets  58 . Drivers  52  are also constructed from an engineering thermoplastic such as polycarbonate or a liquid crystal polymer (LCP) such as Vectra™. When exposed to RF energy, some engineering thermoplastics can exhibit a strong sheet surface charge which can expose the plastics to high heat and possibly arcing. It is an object of the present invention to provide cartridge coating  80  on the cartridge  50  and/or drivers  52 . Cartridge coating  80  can be a dielectric coating, reduce the surface charge effect on the cartridge  50 , and prevent potential damage to the cartridge thermoplastics. Additionally, the cartridge coating  80  can provide some degree of thermal protection and/or add lubricity to the cartridge  50  and drivers  52  and, if desired, selectively excluded by masking or removed by laser etching, sandblasting, water jet, grinding and the like. Cartridge coatings  80  can be PTFE (polytetrafluroethylene), a Parlene™ or Parylene™, titanium dioxide, or an epoxy. 
         [0033]      FIG. 4  is a cross sectional view of a prior art end effector  90  as disclosed in a U.S. Pat. No. 5,833,690 by Yates et al. which is hereby incorporated by reference. In  FIG. 4 , the prior art end effector  90  is clamped on tissue  70  and current paths from a first pole electrode  94  to a second pole electrode  95  are shown. In this invention, both a prior art anvil  91  and a prior art channel  92  form a prior art second pole electrode  95  (prior art anvil  91 ) by contact with a prior art closure tube  93  (not shown). Prior art cartridge  96  has staples  53 , prior art drivers  97  and prior art wedges  98 . 
         [0034]      FIG. 5  is a cross sectional view of the end effector  45  of the present invention clamped on tissue  70  with RF energy being applied to the tissue. As shown, the anvil coating  75  of the preferred invention redirects current flow to the second pole electrode  56  formed from uncoated staple pockets  58  and uncoated channel  47 . 
         [0035]      FIG. 6  shows the open prior art end effector  90  being placed on top of a previously placed staple line in tissue just prior to placement of a second clamp, coagulation staple and cut line. The first firing of the prior art instrument has formed staples  71  shown extending along the cut line and directly below the first and second electrodes  94  and  95  respectively within anvil  91 . A new cartridge  50  containing staples  53  has been loaded for this firing. 
         [0036]      FIG. 7 , shows the prior art end effector  90  of  FIG. 6  after the prior art anvil  91  is clamped on tissue containing one formed staple  71 . The formed staple  71  is in direct contact with the prior art first pole electrode  94 , and with the second pole electrode  95  creating an electrical short. The prior art second pole electrode  92  can easily contact the staple  71  and can cause a short condition between the prior art first and second pole electrodes  94 ,  95  respectively. The short means the surgeon must unclamp the instrument, reposition it, and clamp it again. 
         [0037]      FIG. 8  is a cross sectional view of the end effector  45  of the present invention clamped on tissue  70  containing one formed staple  71 . As shown, the anvil coating  75  prevents the formed staple  71  from contacting the exposed areas of second pole electrode  56  located in staple pockets  58  and “U” shaped channel  47  (extending below cartridge  50 —see  FIG. 1 ) and creating an electrical short. Thus, anvil coating  75  of the preferred invention allows current flow through tissue to the staple pockets  58  and channel  47 , but prevents the formed staple  71  from easily contacting the second pole electrode  56  and shorting within the end effector  45 . Current paths can be to the staple pockets  58  or to the channel  47 , or a combination of both. In the presence of staples  71 , current paths can also be from first pole electrode  60 , to the staple  71 , and then to the pockets  58  and channel  47 . Electrical energy flows mostly through the path of least resistance though some portion also flows through higher resistance portions of the circuit as well. The current through any individual element of the circuit can be calculated using Ohm&#39;s Law (V=IR where V is voltage, I is current and R is the resistance). In the case of the formed staple  71 , the least resistive current path (and therefore the path of greatest current flow) is from the first pole electrode  60 , through the staple  71 , through tissue  70  and into pockets  58 . This path coagulates and desiccates tissue  70  adjacent to the formed staple  71 . As the tissue  70  near staple  71  desiccates, it becomes more resistive and less current flows to staple pocket  58 . With the conductive path through staple  71  and pocket  58  is in contact with more resistive coagulated tissue, the uncoagulated tissue  70  adjacent to the next least resistive path begins to coagulate. 
         [0038]      FIG. 9  is an alternate embodiment of the coatings of the present invention. In this embodiment, alternate anvil coating  76  is masked from or removed from an upper anvil surface  55   a , from the staple pockets  58  of the anvil  55 , and from the ramp  57  (see  FIG. 2 ) of the anvil  55 . This alternate embodiment reduces the area of the alternate anvil coating  76  and the material cost of the coating  76  without reducing effectiveness. 
         [0039]      FIG. 10  shows anvil  55  with an alternate capacitive coupling coating  100  or dielectric coating that can be placed across the entire surface of the anvil  55  with the exception of the electrical contact area at ramp  57  (see  FIG. 2 ). As a consequence, the contact network from the first pole electrode  60 , through the tissue  70  and to a second pole electrode  85  (anvil  55  for this example) is blocked by the capacitive coupling anvil coating  100  on the anvil  55  and the tissue coagulation method shifts to capacitive coupling. Whereas the second pole electrode  56  is shown fully coated, a partial coating may suffice provided it creates capacitive coupling circuit with tissue. A rule of capacitance is that the impedance presented by the capacitor is inversely proportional to the frequency. In other words, capacitive coupling favors transfer of the higher frequency components of a signal, and has been found to work well at RF electrosurgical generator frequencies from about 300 kHz to about 3 MHz, and between about 500 kHz and about 700 kHz. Capacitive coupling works well over short distances such as that found between the electrodes of an electrosurgical device. Capacitive coupling coating  100  can be a dielectric such as but not limited to PTFE (polytetrafluroethylene), a Parlene™ or Parylene™, titanium dioxide or an epoxy. 
         [0040]    In  FIG. 10 , tissue  70  contains a formed staple  71  in direct contact with first pole electrode  56  but contact with second pole electrode  56  is prevented by capacitive coupling coating  100 . The anvil  55  and second pole electrode  56  can have a large generally flat portion which is prevented from creating a direct contact circuit with the tissue  70  by capacitive coupling coating  100 . The surface area of the second pole electrode  56  is much larger than the surface area of the first pole electrode  60 . Capacitive coupling circuits with at least one large surface area electrode (second pole electrode  56 ) and one small surface area electrode (first pole electrode  60 ) can exhibit a subtle but different effect. This effect works as follows. There is a threshold of electrosurgical energy density in tissue that must be met before tissue effects can occur. When the energy density is below the threshold, the tissue is unaffected by the application of energy. When the energy density rises above the threshold, the tissue is affected by the energy and begins to heat or cook. With the second alternate anvil coating  100  of the present invention, the energy density is spread between the first and second pole electrodes  60 ,  56 , somewhat analogous to magnetic lines of force between two magnets. This concentrates the energy density at the first pole electrode  60  and spreads or dilutes the field lines across the horizontal surface of second pole electrode  56 . When a small metallic object, such as formed staple  71  is present in tissue  70  of the above capacitive circuit, the capacitive coupled RF energy can ignore the small area of the conductive staple  71  as a path of least resistance. This means capacitive coupling coagulation can occur near the first pole electrode and not around the formed staple  71 , unlike contact RF circuits. 
         [0041]      FIG. 11  shows an alternate E-beam electrosurgical instrument  120 . The E-beam electrosurgical instrument  120  is similar in operation to that of the previously described electrosurgical instrument  20 . That is, both electrosurgical instruments clamp, apply RF energy, form rows of staples in the tissue, and cut the tissue between the innermost rows of staples. E-beam electrosurgical instrument  120  has first and second pole E-beam wires  138 ,  139  respectively. These e-beam wires  138 ,  139  are attachable to generator  21  and foot switch  22  (See  FIG. 1 ) by connector  140  to deliver RF energy to an E-beam end effector  145 . The E-beam end effector  145  of the alternate electrosurgical instrument  120  has some mechanical improvements over the original electrosurgical instrument  20 . 
         [0042]    As best shown in  FIG. 12 , the alternate electrosurgical instrument has an E-beam  165  that travels through the end effector  145  during firing to maintain a uniform tissue gap between an E-beam anvil  155  and an E-beam channel  147 . E-beam  165  has upper supports  167  that travel within an anvil slot (in anvil  155  about upper supports  167 ), lower supports  169  that travel below a channel slot  148  and middle supports  168  that run along an inner surface of E-beam channel  147 . E-beam upper supports  167  and E-beam lower supports  169  tie the E-beam anvil  155  and an E-beam channel  147  together in the vertical direction prevent spreading of the end effector  145  from thick tissue. E-beam upper supports  167  and E-beam middle supports  168  prevent the E-beam end effector  145  from coming together when clamped on thin tissue. Since E-beam cartridge  150  mounts within E-beam channel  147 , the tissue gap between E-beam cartridge  150  and E-beam anvil  155  is also maintained. E-beam electrosurgical instruments such as E-beam electrosurgical instrument  120  are well known in the art such as that found in US. Patent Publication number 20040232196 by Shelton et al. and filed on May 20, 2003 which is incorporated herein in its entirety by reference. 
         [0043]    The E-beam mechanism has necessitated some changes in the design of the first pole electrode  60 , insulator  62  and second pole electrode  56  of the electrosurgical instrument  20 . As shown in  FIG. 11 , the electrode design of -beam electrosurgical instrument  120  has a pair of E-beam first pole electrodes  160  mounted on E-beam insulators  162 . E-beam anvil  155  acts as E-beam second pole electrode  156 . Tissue  70  is shown clamped within The E-beam end effector  145  and a formed staple  71  is in contact with one of the E-beam first pole electrodes  160  and in contact with E-beam anvil coating  175 . E-beam anvil coating  175  prevents contact of the formed staple  71  with E-beam second pole electrode  156 . E-beam cartridge coating  180  prevents the formation of a surface charge on the E-beam cartridge  150 . 
         [0044]    Whereas the above stapling devices are straight, it would be obvious to one skilled in the art to apply the coatings to anvils and cartridges of any stapling device of any shape, including but not limited to actuator circular. Alternately, staples or other conductive fasteners used in the body could also be coated in dielectric coatings, the dielectric coatings making the staples nonconductive when subjected to electrosurgical energy. Dielectric staple coatings could be but are not limited to PTFE (polytetrafluroethylene), a Parlene™ or Parylene™, titanium dioxide or an epoxy. 
         [0045]    It will be recognized that equivalent structures may be substituted for the structures illustrated and described herein and that the described embodiment of the invention is not the only structure which may be employed to implement the claimed invention. As one example of an equivalent structure which may be used to implement the present invention, a coating such as PTFE can be used as a dielectric coating in a bipolar electrosurgical device. As a further example of an equivalent structure which may be used to implement the present invention, an alternate coating such as a coating having polymers based on paraxylene can be used as a dielectric coating in a bipolar electrosurgical device. 
         [0046]    While preferred embodiments of the present invention have been shown and described herein, it will be obvious to those skilled in the art that such embodiments are provided by way of example only. Numerous variations, changes, and substitutions will now occur to those skilled in the art without departing from the invention. Accordingly, it is intended that the invention be limited only by the spirit and scope of the appended claims.