Abstract:
A surgical system and associated method for sealing the passageway of a fluid-carrying vessel with a diameter up to 5 millimeters comprises an electrosurgical generator capable of delivering electrosurgical power, a surgical instrument electrically connected to the electrosurgical generator and adapted to transfer electrosurgical power from the electrosurgical generator to a pair of end effectors disposed at a distal end of the surgical instrument. The system also includes a power control circuit for controlling the delivery of radio frequency energy to the vessel through the end effectors, wherein the delivery of the radio frequency energy to the vessel comprises, raising the output current to a range below 1.75 Amperes RMS and the output voltage to a range below 135 Volts RMS. Radio frequency energy is applied to the vessel for a period of time while the power is held approximately constant. The flow of radio frequency energy is terminated when the impedance of the vessel being sealed reaches a predetermined level.

Description:
PRIORITY AND RELATED APPLICATIONS 
       [0001]    This application claims the benefit of Provisional U.S. Application No. 61/352,114 filed on Jun. 7, 2010. The details of Application No. 61/352,114 are incorporated by reference into the present application in its entirety and for all proper purposes. 
     
    
     FIELD OF THE INVENTION 
       [0002]    Aspects of the present invention relate to electrosurgical procedures, techniques, and devices that utilize radiofrequency energy to seal blood vessels during surgical procedures. In particular, and by no means of limitation, aspects of the present invention relate to devices and techniques for sealing precisely placed or otherwise sensitive or difficult to access blood vessels often found in micro-surgical procedures, difficult to access anatomy or general surgery in pediatric patients. 
       BACKGROUND 
       [0003]    The use of electrosurgical energy in vessel sealing surgical procedures is common and has been used in conjunction with a variety of surgical techniques for many years. In general, electrosurgical devices used in vessel sealing rely on a combination of pressure and high frequency electric energy applied to biological tissue as a way to cut, coagulate, desiccate or seal tissue, for example, blood vessels. In the case of vessel sealing, the electrosurgical energy acts to create collagen melting and tissue fusion. Most RF surgical devices on the market today and described in the prior art have power delivery systems and end effectors that are sized to accommodate a wide range of situations, tissue thicknesses, tissue volume, and end effector bite sizes. In particular, vessel sealing technology has always relied upon the use of relatively high current settings and large end effector sizes to create a seal in varying surgical situations. No one has been able to produce a reliable vessel sealing instrument that operates at currents below 2 Amps. 
         [0004]    For coagulation or blood vessel sealing with known devices, the average power density delivered by the end effector is typically reduced below the threshold of cutting. In some cases (e.g. a monopolar coagulation instrument) a modulated sine wave is used with the overall effect being a slower heating process which causes tissue to coagulate rather than burn and/or char to the point of cutting. In some simple dual function coagulation/cutting devices, a lower duty cycle is used for a coagulation mode and a higher duty cycle is used for a cutting mode with the same equipment. Coagulation and in particular vessel sealing techniques present unique challenges in electrosurgery 
         [0005]    While some modern electrosurgical generators provide modulated waveforms with power adjusted in real time based on changes of the tissue characteristics (e.g. impedance), none have been able to address the complexities and sensitivities that arise when dealing with blood vessels located in delicate surgical sites or other difficult to reach blood vessels. None of the prior art or products currently offered combine aspects of applied pressure, low-power energy delivery, waveform modulation, and instrument size/configuration to safely and effectively seal the blood vessels that are often presented in micro-surgical procedures, difficult to access anatomy or pediatric general surgery. 
         [0006]    Recent advances in vessel sealing technology have specifically abandoned an attempt to address this specialized market and instead focus on larger devices and techniques for sealing larger vessels more commonly found in general surgery or on “one-size-fits all” devices. U.S. Pat. No. 5,827,271 describes how earlier attempts to seal vessels with electrosurgery were unsuccessful in part because they attempted to apply relatively low currents to the vessels. As a solution, the advances described in U.S. Pat. No. 5,827,271 relate to increasing the current applied to the blood vessel above a certain threshold. The prior art in this field is consistent in its recognition that a high current and high generator power output is required to seal vessels. None of the prior art addresses the unique circumstances presented with small caliber blood vessels that present during micro-surgical procedures, difficult to access anatomy or general surgery in pediatric patients. None of the art accounts for a technique or device that effectively and safely seals blood vessels with an instrument that is smaller in size (both in the shaft and entry point features) and configured to be more effective which working in smaller spaces and with smaller vessel calibers. None of the prior art recognizes the role of the surgical instrument size and end effector surface area in the development of effective vessel sealing techniques and energy delivery sequencing. 
       SUMMARY OF THE INVENTION 
       [0007]    In accordance with one aspect, a electrosurgical vessel sealing system can produce controlled RF vessel sealing with as little as 7 Watts of power applied. 
         [0008]    In accordance with another aspect, an electrosurgical vessel sealing system can produce controlled RF vessel sealing with as little as 15 Watts of power applied with an upper limit of 75 volts and a range of between 1.3 and 1.8 amps, and can be utilized in sealing vessels of all sizes as well as tissue bundles and mesentery tissue. In a further embodiment, an electrosurgical vessel sealing system can produce controlled RF vessel sealing with between 7 Watts and 15 Watts of constant power applied with an upper limit of 75 volts and a range of between 0.8 and 1.2 amps. 
         [0009]    In accordance with another aspect, a control algorithm is adapted to utilize a fast rise in current to a set power and with a limit on the maximum applied voltage. In accordance with aspects of this embodiment arcing is eliminated due to the voltage limit. 
         [0010]    In accordance with another aspect, an electrosurgical vessel sealing system incorporates an end effector with a sealing jaw surface area between 0.23 in 2  and 0.30 in 2  and produces a maximum current density between 0.052 amps/mm 2  and 0.068 amps/mm 2 . 
         [0011]    In accordance with another aspect, an electrosurgical vessel sealing system incorporates a generator that is limited to 30 Watts and provides adequate sealing power with better control. 
         [0012]    In accordance with another aspect, an electrosurgical vessel sealing system incorporates a generator that delivers a constant power and is current limited and/or voltage limited. 
         [0013]    In accordance with another aspect a surgical system for sealing the passageway of a fluid-carrying vessel with a diameter up to 5 millimeters comprises an electrosurgical generator capable of delivering electrosurgical power, a surgical instrument electrically connected to the electrosurgical generator and adapted to transfer electrosurgical power from the electrosurgical generator to a pair of end effectors disposed at a distal end of the surgical instrument, wherein the surgical instrument end effectors are adapted to close the passageway of the vessel, a power control circuit for controlling the delivery of radio frequency energy to the vessel through the end effectors. The delivery of the radio frequency energy to the vessel comprises raising the output current to a value between 0.2 and 1.75 Amperes RMS and the output voltage to between 5 and 135 Volts RMS, applying the radio frequency energy to the vessel for a period of time, monitoring the impedance of the vessel being sealed, and terminating the flow of radio frequency energy when the impedance of the vessel being sealed reaches a predetermined level. 
         [0014]    In accordance with another aspect, a power control system for delivering radio frequency energy to a vessel sealing surgical instrument including an end effector comprises a power supply for delivering an output voltage and an output current to the end effector, an impedance sensing circuit for detecting the impedance of the vessel being sealed, a power sequencing module for automatically sequencing the electrosurgical power delivered to the surgical instrument. The power sequencing module is adapted to raise the output current of the power supply to between 0.5 and 1.75 Amperes RMS and the output voltage of the power supply to between 5 and 135 Volts RMS, apply power to the vessel being sealed for a period of time, monitor the impedance of the vessel being sealed through the impedance sensing circuit, and terminate the flow of power to the vessel being sealed when the impedance of the vessel being sealed reaches a predetermined level. 
         [0015]    In accordance with yet another aspect, a method for sealing the interior passageways of a fluid carrying vessel in a patient comprises applying a force about a vessel with an end effector instrument, the end effector coupled to a source of radio frequency energy, applying electrosurgical power to the fluid carrying vessel, wherein an output current of the electrosurgical power is between 0.5 and 1.75 Amperes RMS and an output voltage of the electrosurgical power is between 5 and 135 Volts RMS, maintaining the applied electrosurgical power to the fluid carrying vessel for no more than five seconds, and terminating the delivery of electrosurgical power to the fluid carrying vessel. 
         [0016]    Other aspects will become apparent to one of skill in the art upon a review of the following drawings and detailed description. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0017]    Various aspects, objects and advantages, and a more complete understanding of the present invention are apparent and more readily appreciated by reference to the following Detailed Description and to the appended claims when taken in conjunction with the accompanying Drawings, wherein: 
           [0018]      FIG. 1  is a side view of an electrosurgical instrument in accordance with aspects of the present invention; 
           [0019]      FIG. 2  is a perspective view of the electrosurgical instrument in  FIG. 1 ; 
           [0020]      FIGS. 3A-3B  are various views of an end effector constructed in accordance with aspects of the present invention; 
           [0021]      FIG. 4  is a close up of the mechanical and electrical engagement mechanisms of the electrosurgical instrument shown in  FIG. 1 ; 
           [0022]      FIG. 5  is an exploded perspective view of the mechanisms shown in  FIG. 4 ; 
           [0023]      FIGS. 6A-6C  show several views of an electrical cable and associated connection devices in accordance with aspects of the present invention; 
           [0024]      FIG. 7  is a block diagram of an RF power generator system in accordance with aspects of the present invention; 
           [0025]      FIG. 8  is a prior art vessel sealing impedance curve; 
           [0026]      FIG. 9  is an end effector constructed in accordance with aspects of the present invention; and 
           [0027]      FIGS. 10-14  are oscilloscope traces of various vessel sealing procedures in accordance with aspects of the present invention. 
       
    
    
       [0028]    Other aspects of devices and methods in accordance with the present invention will become known to those of skill in the art when read in conjunction with the following disclosure. 
       DETAILED DESCRIPTION 
       [0029]    Throughout this specification references are made to the use of various materials, combinations, mechanical configurations, ranges and other aspects that may be used in various combinations to form one or more devices and methods in accordance with aspects of the present invention. It should be understood, both to one of skill in the art as well as the examining divisions in the United States Patent Office and Patent Offices throughout the world, that each of the lists of materials, examples, and other embodiments are included herein in order to teach one of skill in the art that they may be combined into various alternative embodiments, without requiring specific claim permutations of these individual features, and without departing from the spirit and scope of the invention. The claims as presented herein, as well as any potential future amendments to those claims, may include one or more combinations of these materials, ranges and other alternatives without departing from the spirit and scope of the invention described herein. In particular it is contemplated that one of skill in the art would recognize and find adequate support in the written description for any combination of the features disclosed herein, whether described in a single example or embodiment, or described in multiple and disjointed sections of the written description. The description of these various example and options is specifically drafted to comply with 35 U.S.C. §112 of the United States Patent Laws, Article 123(2) of the European Patent Laws as well as other similar national country laws relating to the adequacy of the written description. 
         [0030]    Aspects of a device constructed in accordance with the present invention generally pertain to a low-power vessel sealing system. Application of such devices have particular applicability in pediatric surgery and other situations where small caliber blood vessels may be encountered such as micro-surgery, difficult to access anatomy and all aspects of pediatric surgery. In addition, devices constructed in accordance with aspects of the present invention allow smaller profile instruments which in turn allow smaller incisions to be made during the associated surgical procedure. A system constructed in accordance with aspects of the present invention has as its major components an RF generator and a bipolar grasper/dissector/sealer instrument hand piece that plugs into the generator. Various power sequencing and control systems are incorporated into the generator and system logic that enable effective and safe vessel sealing capabilities at lower power outputs than is currently available or otherwise known in the art. 
         [0031]    Features of an instrument and vessel sealing system constructed in accordance with aspects of the present invention may include one or more of the following, each of which is described in greater detail below. 
       Orientation and Operation of End Effectors 
       [0032]    Aspects of a device constructed in accordance with the present invention include opposing electrically isolated end effector jaw members that provide energy delivery to tissue, such as a blood vessel, undergoing a surgical procedure. The jaws preferably open in a simultaneous dual action fashion, although other jaw movement dynamics are contemplated. The jaws are located on the distal end of a shaft that serves to maximize surgical site visibility in either open, endoscopic or laparoscopic procedures. The length of the instrument shaft may vary from 10 cm to 30 cm depending on the designed use. In one embodiment the instrument shaft may vary from 15 cm to 20 cm long. Furthermore, aspects of the present invention can be used in connection with both rigid shaft instruments and flexible shaft instruments such as might be found in steerable surgical systems or robotic surgical systems. 
         [0033]    The size of the jaws may range from 1.0-3.5 mm in width and from 8.0-12.0 mm in length. The surfaces of the jaws may include one or more non-conductive elements that function to maintain electrical isolation between the jaw surfaces and keep the electrodes from shorting out. Preferably the jaws are designed to close in a parallel fashion, i.e. both jaw surfaces move in coordination with each other upon activation by a user. The instrument or end effector itself may or may not be built with a cutting instrument that serves to divide the tissue after sealing is accomplished. 
         [0034]    In accordance with one aspect, an instrument end effector constructed in accordance with the present invention applies pressure to the tissue to be sealed in the range of 75-110 psi so that the tissue is adequately compressed prior to the sealing action taking place. 
         [0035]    There is preferably limited play in the motion of the instrument handle. In one embodiment the ring handle design enables a close to 1-1 opening and closing of the jaws. A ratchet point may be incorporated into the handle assembly so that full jaw closure and the required pressure is applied prior to the sealing function. 
       Generator Capabilities and Function 
       [0036]    With respect to the generator and electrical aspects of the present invention, features of a device constructed in accordance with aspects of the present invention include one or more of the following, each of which is described in greater detail below. 
         [0037]    Energy is preferably applied to the tissue undergoing a surgical procedure at a constant power. The power delivery cycle may terminate when one or more of the following occurs: a) voltage reaches a maximum level not to exceed a set level such as 80 Volts RMS or 100 Volts RMS; b) impedance reaches a final value of between 180-350 ohms; and c) a maximum seal time of between 2 and 5 seconds is reached. In addition, voltage or current limits may be put in place that further confine the operational parameters of the power delivery system. 
         [0038]    The generator has a power capability in the range of 25-35 Watts total power, but typical operation is preferably in the range of 8-15 Watts in order to control resolution and accuracy of the power output and to minimize the possibility of tissue charring and other damaging effects. A voltage limit incorporated into the generator operation minimizes the potential for tissue damage during a sealing procedure. 
         [0039]    Maximum current delivery is under 2 Amps, and typical operation is in the range of 0.75-1.5 Amps. Maximum voltage of the system is 100 Volts RMS. The typical maximum voltage is in the range of 70-85 Volts RMS. 
         [0040]    The above summary should be considered as one set of overall design parameters and not as any type of exclusive requirements for how a system or particular instrument is required to be designed in accordance with aspects of the present invention. In addition, any examples given throughout this specification, and any data or test results given throughout this specification, should not be used as evidence during prosecution of the claims herein of any intention by the applicant to limit the scope of any claims to those particular embodiments or examples. For example, maximum current delivery may be limited to under 1.5 Amps in one embodiment, under 1.0 amps in another embodiment and under 0.5 amps in yet another embodiment. In addition to the above, operation of the system may be in the range of 1.0-1.25 Amps. In another embodiment operation of the system may be in the range of 0.5 to 2 Amps. In other embodiments, maximum voltage of the system is 75 Volts RMS. In yet other embodiments maximum voltage of the system is 50 Volts RMS. In another embodiment the typical maximum voltage is in the range of 50-100 Volts RMS. 
         [0041]    One of skill in the art would know to utilize various permutations of the described examples to arrive at the claim scope submitted below. 
         [0042]    With reference to  FIGS. 1-6 , various drawings are shown that depict one example of a surgical instrument  100  that may be used in connection with aspects of the present invention. As shown in  FIGS. 1-6 , surgical instrument  100  is depicted as a forceps for use with a variety of laparoscopic and open procedures. As such, instrument  100  includes an elongated shaft  102  with an end effector  104  located at a distal end of the shaft  102 . The shaft  102  and end effector  104  are coupled with a rotational element  114  that allows a user to rotate the shaft  102  and end effector  104  about the longitudinal axis of the shaft  102  thereby enabling various presentations of the end effector  104  within a surgical site. 
         [0043]    A handle assembly  106  generally includes a stationary handle portion  108  and a thumb lever portion  110  that operate in conjunction with an actuation mechanism  119  to control the movement, physical engagement of and electrical engagement of the end effector  104 . Each of the handle portion  108  and thumb lever portion  110  define an area for a user&#39;s fingers to engage the instrument and operate the handle assembly  106  in a scissor-like movement. As such, movement of the thumb lever portion  110  with respect to the handle portion  108  facilitates movement of the end effector from an open position to a closed position. In one embodiment the handle portion  108  and the thumb level portion  110  enable a single action movement of the end effector  104 . A ratchet mechanism  112  is included for selectively locking the handle assembly  106  at a selected position during movement. In another embodiment, several ratchet stops are include so that a user can select a closure position and/or pressure applied by the end effector around a tissue sample. Electrical cable assembly  116  extends from a position in an electro-mechanical sub-assembly  118  and serves generally to connect the surgical instrument  100  to a power source, such as a radio frequency generator described below. Further details of the electrical cable assembly  116  are described below.  FIG. 2  shows the surgical instrument  100  in a perspective view but generally illustrates the same features as those described in conjunction with  FIG. 1  and that description is not repeated here. 
         [0044]      FIGS. 3A-3B  show details of the end effector  104  of the surgical instrument  100 . With continuing reference to  FIGS. 3A-3B , the end effector  104  is shown in various perspectives and with varying detail. In the example of  FIGS. 3A-3B , the end effector  104  is shown as a grasper/dissector, sealer combination. However, it is contemplated that various other instrument configurations may be employed without departing from the spirit and scope of the invention. For example, various alternate configurations of the grasper itself may be employed as well as different instruments, such as a dissector or cutter may be used in connection with the sealing aspects disclosed herein. The size and overall shape of the end effector may also be varied in accordance with other aspects of a device constructed in accordance with aspects of the present invention. 
         [0045]    With respect to the grasper/dissector, sealer end effector  104  depicted in  FIGS. 3A-3C , the end effector  104  includes opposing grasper portions  130  and  132  that are adapted to open and close as a result of the action of the handle assembly  108 . Cables  122  and  124  engage with each of the grasper portions  130  and  132  and extend through the shaft  102  back to the handle assembly  108  where they engage with an electrical connection and linkage system  118 . A tension block  126  secures the cables  122  and  124  at the distal end of the shaft  102  and provide a mechanism to couple each of the cables  122  and  124  with the grasper portions  130  and  132 . In combination, this mechanical arrangement allows the grasper portions  130  and  132  to open and close when the thumb lever portion  110  is engaged by a user. As shown, the embodiment of the grasper/sealer  100  provides for both grasper portions  130  and  132  to move simultaneously in a single action motion when actuated by thumb lever portion  110 . 
         [0046]    With reference to  FIGS. 4-6E , details of the electrical connection and linkage system  118  are shown. Overall, the electrical connection and linkage system  118  provides both a mechanical interface between the handle assembly  106  and the effected movement of the grasper portions  130  and  132 , as well as an electrical interface between the cable assembly  116 , which is connected to an electrosurgical power source, and the grasper portions  130  and  132 . Actuation cables  151   a  and  151   b  extend from the jaw portions  130  and  132 , are routed to the handle assembly  106  and are crimped and constrained to the cable collar  150 . Electrical connections are made to the proximal ends of the actuation cables  151   a  and  151   b.  In some embodiments, the actuation cables  151   a  and  151   b  also conduct the current to the end effector  104  and to the tissue undergoing a procedure. 
         [0047]    Actuation cables  151   a  and  151   b  route through the cable collar  150 . Joined to each cable is a mechanically fastened ferrule crimp  200   a  and  200   b  near the proximal end of both cables, which allows the actuation cables to be pulled (to clamp/close the jaw portions  130  and  132 ) and pushed (to open the jaw portions  130  and  132 ). In the short section of actuation cables proximal to the ferrule crimp (shown as  151   a ), each of the two cables are electrically connected to the two poles of the electrosurgical power wires ( 182  and  184 ). This connection can be done with an additional electrical ferrule (crimped) or soldered. This is not a load bearing connection; simply electrical. The electrosurgical power wires wrap around the cable collar  150  to provide enough path length to allow the cable collar to rotate approximately one full rotation without causing undue strain on the power wires or electrical connections. The two poles of the electrosurgical trigger switch ( 188  and  186 ) form a closed loop in the flex circuit  142  (See  FIG. 6B ) when the dome contact is depressed by the trigger  152 . The dome switch circuit activates the electrosurgical connection to actuation cables  151   a  and  151   b,  thereby conducting current down the length of the shaft to grasper portions  130  and  132 . The rest state is an open loop when the trigger  152  is not depressed and there is no electrosurgical connection. 
         [0048]    In accordance with proper functioning of the instrument and system is that the two poles remain electrically isolated at all times. Power wires  182  and  184 , solder/crimp connections  182   a  and  182   b  (not shown),  151   a  and  151   b,  and jaw portions  130  and  132  have to remain isolated from each other.  FIG. 6D  shows how along the length of the Shaft  102  the actuation cables are isolated by an extrusion  210 , and encapsulated on the outside by electrically isolating heat-shrink jacket  212 . 
         [0049]      FIGS. 6C and 6E  shows how actuator cables  151   a  and  151   b  are separated by insulator  220 , and how jaw portions  130  and  132  are separated by insulator  222 . Extrusion  210  and insulator  220  (with jacket  212  enclosing the tracks on the outside) guide the actuator cables to allow them to be pushed as well as pulled. The constrained track allows the assembly to push a flexible cable in order to open the jaw portions  130  and  132 . 
         [0050]    Located on an interior surface of grasper portion  130  are a series of non-conductive raised elements  134   a,    134   b,  and  134   c  that ensure that the interior conductive surfaces of grasper portions  130  and  132  do not physically touch and are maintained at a constant and predictable separation distance from each other when the grasper portions  130  and  132  are in a closed position. Raised elements  134   a,    134   b  and  134   c  may be on either of the interior surfaces of grasper portions  130  or  132 . 
         [0051]    In other embodiments, non-conductive elements  134   a ,  134   b  and  134   c  may be made of a variety of non-conductive material. For example the non-conductive elements may be made of a ceramic material, nylon, polystryenes, Nylons, Syndiotacticpolystryrene (SPS), Polybutylene Terephthalate (PBT), Polycarbonate (PC), Acrylonitrile Butadiene Styrene (ABS), Polyphthalamide (PPA), Polymide, Polyethylene Terephthalate (PET), Polyamide-imide (PAI), Acrylic (PMMA), Polystyrene (PS and HIPS), Polyether Sulfone (PES), Aliphatic Polyketone, Acetal (POM) Copolymer, Polyurethane (PU and TPU), Nylon with Polyphenylene-oxide dispersion and Acrylonitrile Styrene Acrylate. 
         [0052]    Handle portion  108  includes an exterior shell portion  144  that forms part of a casing that surrounds several of the components within electrical connection and linkage system  118 . A second portion of the casing is indicated as reference number  146 . Casing portion  146  connects to thumb lever  110 . Enclosed in a top portion of casing portion  146  are a shaft collar  148 , a cable collar  150 , and a ring cable collar  154  that serve to actively engage the shaft assembly  102  with the overall handle assembly  118 . Cable assembly  116  is coupled with a flex circuit  142 . A length of cable  140  extends from the cable assembly  116  and is coiled about cable collar  150  in order to allow the shaft assembly  102  to rotate freely without undue resistance to the user. Rotational element  114  couples to the housing portions  144  and  146  and allow a user to rotate the shaft assembly  102  and alter the presentation of the end effector  104  during a procedure. 
         [0053]    Various fastening devices secure the components of the handle assembly together such as screws  158 ,  160 ,  162 , and  164  as well as pin  156 . Alternatively, sonic welding or other connection techniques may be utilized to secure the components together. Switch  152  engages with the thumb lever  110  and is adapted to engage the power delivery through cable assembly  116  as delivered from an electrosurgical generator. 
         [0054]      FIGS. 6A-6C  show the components that form the electrical connection between a power source, such as a radio frequency electrosurgical generator, and the device  100 , eventually delivering the electrosurgical energy to the end effector  104 . The connector  170  is keyed for insertion into the output of an electrosurgical generator (See e.g.  FIG. 7 ). The connector  170  is coupled to the cable assembly  116 . The length of the cable assembly  116  is determined by the particular application but is preferably long enough to allow operation of the instrument at a position remote from the electrosurgical generator. At an end of the cable assembly  116  opposite the connector  170 , a strain relief device  180  is intermediate with an exit portion  190  of the cable assembly  116 . 
         [0055]    The cable assembly  116  houses four conductors,  182 ,  184 ,  186 , and  188 . In general the four conductors provide the RF power  182  and  184  to the end effector  104  a common/ground conductor  186  and a switch conductor  188  that couples with an identification resistor that signals the general as to what type of device is plugged in to the power source. 
         [0056]    With reference to  FIG. 7 , a schematic of an RF generator  300  is shown. The use of an RF generator in connection with the delivery of electrosurgical energy is generally known in the art. However, aspects described herein that relate to the functioning and sequencing of low-power and energy delivery has not been described before. 
         [0057]    Generator  300  inputs AC power from a wall outlet  302  and delivers that AC power to a power module  304  such as an IEC power entry module. Power module  304  may include such components as a DPDT switch  306  and 2 replaceable fuses  308 . Power is transferred from power module  304  to a power supply unit  310 . Preferably in connection with medical applications the power supply unit  310  is a medical grade power supply such as a CSS65-24 from Lambda. DC to DC converters  312  and  314  convert a 24 volt output of the power supply  310  into a pair of 12 volt outputs that are used to power control circuits. Power supply  310  then serves as the inputs  320  and  330  to a Buck-Boost Converter  340 . The output of the converter  340  is passed to an H-Bridge circuit  345  which then passes that signal to a resonant LC transformer circuit  350 . The transformer circuit  350  includes capacitor  352 , inductor  354  and transformer  356 . In one embodiment, transformer  356  is a 1:9 transformer. From the transformer  356 , power is delivered to a load  400 . In one embodiment, load  400  is a grasper/sealer instrument  100  as described above in connection with  FIGS. 1-6  and the power delivered to instrument  100  is no more than 25 Watts, no more than 80 Volts RMS, and less than 2 Amps RMS. 
         [0058]    Controller  360 , in conjunction with the components described below, is used to sense various aspects of the energy applied to load  400 , and adjust one or more of the energy characteristics in response to the vessel sealing process. Coupled to the load  400  (e.g. an electrosurgical instrument) are a current sensor circuit  390  and a voltage sensor circuit  395 . Based on the sensed current and voltage, op-amps  392  and  394  pass these values to conversion circuits  380  that includes voltage RMS-DC Converter  382  and a current RMS-DC Converter  384 . A multiplier  386  and a divider  388  derive power and impedance respectively from the sensed voltage and current. Each of the circuits  382 ,  384 ,  386  and  388  provide input data to the controller  360  which can then process and analyze the various input to indicate the state of the vessel sealing process. These circuits  382 ,  384 ,  386  and  388  also may be used as direct feedback signals to the Buck-Boost converter controller. 
         [0059]    In some embodiment a user input panel  368  may be included that allows operator interaction with the controller and may include a display and some form of input device (such as a keyboard, mouse, pointer, dials or buttons). Data from the controller  360  may be output via analog or digital means such as an RS-232 connector  362 , programming port  364  or memory chip  366 . 
         [0060]      FIG. 8 , shows a known impedance curve as applied to RF vessel sealing and shows the changing impedance of a vessel and the various phases the vessel impedance goes through during an RF electrosurgical sealing process. In  FIG. 8 , the impedance is responding to changes in the power applied to the jaws of the surgical device. The tissue being sealed goes through several stages of change in order to achieve a complete seal. Prior systems effected vessel sealing by adjusting the power through the sealing cycle by pulsing the current and voltage applied to the tissue according to observing the rate of change of impedance during the rising section of the curve from the minimum value through the denaturation and desiccation and adjusting the power to the vessel in order to control that change. However, these systems cannot apply a uniform power delivery scheme that would apply to vessels of varying sizes. 
       Power Delivery Sequencing 
       [0061]    Throughout the sealing process, the impedance of the vessel is calculated in real-time by measuring the voltage and current to the jaws. (Z=V/I). Since it is known that the impedance will follow the prescribed format, impedance thresholds can be set which act as trip points to cause the power profile curve to advance to the next phase of its settings. However, if the impedance limit is not met before the time has elapsed, the curve advances to the next phase. Each phase of the curve advances to the next phase according to an “OR” logic. If any one of the parameters is met according to impedance or time, the power profile is advanced. 
         [0062]    In accordance with one aspect of the present invention it is desirable to achieve a single set of parameters that would be effective at sealing blood vessels with a diameter under 6 mm, typical in micro-surgery applications, pediatric patients, and surgical sites that are often difficult to reach and/or visualize. 
       EXAMPLES 
       [0063]    The following examples are illustrative of aspects of the present invention but are not meant to be limiting under 35 U.S.C. §112 of the United States Patent Laws, Article 123(2) of the European Patent Laws or any corresponding national country patent laws concerning the adequacy of the written description. By giving these examples, it is submitted that variations in the scope of the test results and corresponding implementations and claim scope are clearly and unambiguously disclosed to one of skill in the art. 
       Vessel Sealing Results 
       [0064]    Table 1 shows the electrical characteristics associated with various seals performed according to aspects of the present invention. 
         [0000]    
       
         
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
               
                   
                 Vessel 
                   
                 Peak 
                 Peak 
                 Seal 
                 Burst 
               
               
                 Seal 
                 Size 
                 Power 
                 Current 
                 Voltage 
                 time 
                 Pressure (mm 
               
               
                 Number 
                 (mm) 
                 (W) 
                 (A) 
                 (Vrms) 
                 (sec) 
                 Hg) 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 41-3 
                 5 
                 10 
                   
                 80 
                 1.3 
                 687 
               
               
                 41-4 
                 5 
                 10 
                   
                 78 
                 1.5 
                 687 
               
               
                 41-5 
                 4 
                 10 
                 1.1 
                 84 
                 1.1 
                 1034+ 
               
               
                 41-6 
                 4 
                 10 
                 0.9 
                 80 
                 1.1 
                 1034+ 
               
               
                 42-3 
                 3.5 
                 10 
                 0.8 
                 81 
                 1.6 
                 899 
               
               
                 42-4 
                 3.5 
                 8 
                 1.05 
                 82 
                 1.4 
                 899 
               
               
                 43-1 
                 5 
                 8 
                 1 
                 80 
                 2.3 
                 786 
               
               
                 43-2 
                 5 
                 10 
                 0.95 
                 82 
                 2.2 
                 786 
               
               
                 43-3 
                 5 
                 15 
                 1 
                 80 
                 2.2 
                 889 
               
               
                 43-4 
                 5 
                 10 
                 1 
                 83 
                 2.6 
                 889 
               
               
                 43-5 
                 5 
                 15 
                 1 
                 83 
                 2.5 
                 682 
               
               
                 43-6 
                 5 
                 10 
                 1 
                 76 
                 2.1 
                 682 
               
               
                 44-1 
                 1.5 
                 15 
                 1 
                 80 
                 1.5 
                 1034+ 
               
               
                 44-2 
                 1.5 
                 15 
                 1 
                 84 
                 0.8 
                 1034+ 
               
               
                 44-3 
                 3 
                 10 
                 1 
                 81 
                 1.1 
                 889 
               
               
                 44-4 
                 3 
                 10 
                 1.15 
                 78 
                 2.1 
                 424 
               
               
                 45-3 
                 2 
                 8 
                   
                 78 
                 1.5 
                 584 
               
               
                 45-4 
                 2 
                 15 
                   
                 82 
                 1.5 
                 584 
               
               
                 45-5 
                 4 
                 10 
                   
                   
                 2 
                 734 
               
               
                 45-6 
                 4 
                 10 
                 1.19 
                 81 
                 2.4 
                 734 
               
               
                 46-1 
                 5 
                 15 
                   
                 78 
                 1.25 
                 780 
               
               
                 46-2 
                 5 
                 15 
                   
                 80 
                 1.25 
                 780 
               
               
                 46-5 
                 3.5 
                 15 
                   
                 78 
                 3.5 
                 682 
               
               
                 46-6 
                 3.5 
                 15 
                   
                 78 
                 1.25 
                 682 
               
               
                 47-1 
                 5 
                 15 
                 0.82 
                 38 
                 3 
                 698 
               
               
                 47-2 
                 5 
                 15 
                 0.84 
                 34 
                 3 
                 698 
               
               
                 47-3 
                 2.5 
                 15 
                   
                 81 
                 1.5 
                 589 
               
               
                 47-4 
                 2 
                 15 
                   
                 77 
                 0.8 
                 589 
               
               
                 47-5 
                 4.5 
                 15 
                 0.94 
                 42 
                 1.7 
                 1034+ 
               
               
                 47-6 
                 4.5 
                 15 
                   
                 78 
                 1.7 
                 1034+ 
               
               
                 48-1 
                 2.5 
                 10 
                 0.9 
                 80 
                 0.5 
                 424 
               
               
                 48-2 
                 2.5 
                 10 
                 1 
                 80 
                 1.2 
                 424 
               
               
                 48-3 
                 3 
                 10 
                   
                 77 
                 1.3 
                 693 
               
               
                 48-4 
                 3 
                 10 
                 1.15 
                 82 
                 1.1 
                 693 
               
               
                 49-3 
                 4 
                 10 
                 0.8 
                 81 
                 0.4 
                 801 
               
               
                 49-4 
                 4 
                 10 
                 0.78 
                 84 
                 0.35 
                 801 
               
               
                 49-5 
                 6 
                 10 
                 0.84 
                 81 
                 3 
                 526 
               
               
                 49-6 
                 6 
                 10 
                 0.86 
                 82 
                 2.1 
                 526 
               
               
                 50-1 
                 6 
                 15 
                 0.82 
                 82 
                 1.8 
                 729 
               
               
                 50-2 
                 6 
                 15 
                 0.84 
                 80 
                 1.95 
                 729 
               
               
                 50-3 
                 4 
                 15 
                 0.76 
                 81 
                 0.6 
                 536 
               
               
                 50-4 
                 4 
                 15 
                 0.8 
                 82 
                 0.7 
                 536 
               
               
                 50-5 
                 3 
                 15 
                 0.78 
                 81 
                 0.6 
                 623 
               
               
                 50-6 
                 3 
                 15 
                 0.84 
                 84 
                 0.85 
                 623 
               
               
                 51-1 
                 6 
                 15 
                   
                   
                   
                 708 
               
               
                 51-2 
                 6 
                 15 
                 0.72 
                 79 
                 1.3 
                 708 
               
               
                 51-3 
                 3 
                 15 
                 0.86 
                 82 
                 1.2 
                 1034+ 
               
               
                 51-4 
                 3 
                 15 
                 0.84 
                 81 
                 0.8 
                 1034+ 
               
               
                 51-5 
                 2 
                 15 
                   
                   
                   
                 478 
               
               
                 51-6 
                 2 
                 15 
                 0.8 
                 82 
                 0.55 
                 478 
               
               
                 52-3 
                 3 
                 10 
                 0.8 
                   
                 1.25 
                 1034+ 
               
               
                 52-4 
                 3 
                 10 
                 0.78 
                 81 
                 0.4 
                 1034+ 
               
               
                 52-5 
                 2 
                 15 
                 0.88 
                 80 
                 0.85 
                 532 
               
               
                 52-6 
                 2 
                 10 
                 0.92 
                 81 
                 0.9 
                 532 
               
               
                   
               
             
          
         
       
     
         [0065]    With respect to the test results described in Table 1, the examples were completed by the power being held constant while current and voltage were allowed to float to the maximum values. The power was disengaged when Vmax reached 80 Volts RMS or Impedance reached 200 ohms. An initial cycle was established with a one (1) second ramp to maximum power followed by a two (2) second hold and then a one (1) second hold at a minimum power of 5 watts. If the power is left on too long, the additional power applied to the vessel will rapidly increase the impedance. In one embodiment it is envisioned that the power is deactivated within 100 msec. Complete and translucent seals were obtained at as low as 7 watts maximum power. 
         [0066]    The time to Pmax for the series was 1 second. The observations were that 5 W did not provide an adequate seal and both 10 W and 15 W began to show charring of the vessel. It was found that translucency wasn&#39;t necessarily a good indication of a good seal. Burst tests of some clear seals did not achieve the desired 500 mm Hg (˜10 psi level). It was found that some charring of the seals seemed to produce stronger seals that reach a 500 mm Hg burst strength. A series of 30 tests were then run where the time to Pmax was reduced to 0.5 seconds in order to reduce the total time of the seal and to get more energy into the vessel more quickly. 
         [0067]    The time to Pmax was fixed at 0.5 seconds and the time to Pmin was fixed at 0.2 seconds. Pmax and Pmin were then incrementally adjusted to optimize the seal results. This testing established Pmax at 12 W and Pmin at 5 W, with Pmin being as low as 0 Watts as providing reasonable and consistent seals. Subsequent testing attempted to bracket the range for which good seals could be achieved. This ranged from 10 W to 14 W. In other embodiments the range for Pmax and Pmin is between 5 W to 10 W, alternatively between 2 W to 15 W. 
         [0068]    In a second example, the goal was to enable seal times under 3 seconds. In this embodiment, power delivery of 12 watts for 1.1 seconds followed, by 5 watts for 1.5 seconds gave good results. These settings were initially set based on observations that seals at 7 W took about 3 seconds. If shorter sealing times were desired, it was understood that a higher power setting would be required since the seals are the result of the total energy delivered to the vessel. 
         [0069]    Approximately 100 seals (See Table 1) were performed with varying results. The primary problem with obtaining repeatable seals at a constant power setting was that there was often arcing between the jaws and a subsequent burn-through of the vessel. In particular, tests performed using the parameters that worked on large vessels when applied to smaller vessels often had arcing at the end of the seal cycle. Experimentation realized that settings were not simply power and time dependent. Further testing incorporated the impedance threshold and voltage and current limits described below. 
         [0070]    In another example seals were effected based on real-time measurements of the impedance. Examples of viable seals were created at 7 W peak power for 2.9 sec followed by 2 W of sustained minimum power.  FIGS. 10 and 11  show the power output on an oscilloscope for these seals. The maximum output scale for the impedance on the user interface is 200 ohms. When the impedance reaches 200 ohms, the programmed input power curve switches to the next phase of the profile. 
         [0071]    During the seals shown in  FIG. 10 , the maximum impedance was set to 175 ohms. This seal was following the typical bathtub shaped curve of impedance changes. The tissue begins to desiccate and the impedance drops. As it continues to dry out, the impedance begins a rapid rise. In this case, the impedance threshold was attained and the power was turned off. 
       Conclusions 
       [0072]    Testing confirmed that controlled RF sealing of blood vessels can be achieved with as little as 7 Watts of power applied. Voltage and current applied during these seals were less than 50 volts and 0.6 A, respectively. The square area of the jaws used is 0.023 in 2 /14.84 mm 2 . The maximum current density applied by the system and as represented by I/A=0.6 Amps/14.84 mm 2  or 0.040 A/mm 2 . 
         [0073]    These tests and examples demonstrated that vessels up to 6 mm in size can be sealed with a low power RF energy output that utilizes a small bipolar grasper jaw end effector. Parameters of such a system include applied pressure, current density, low voltage, impedance monitor and midpoint. Steps for sealing may include one or more of the following:
       a. Apply pressure to the tissue sufficient to compress the instrument jaws to less than or equal to 0.005″. This pressure must also be high enough so that as the tissue contracts during heating, the jaws do not deflect and the gap between the jaws remains constant. Experimental data indicates that this pressure requirement is between 65-110 lb/in 2 . In another embodiment the pressure requirement may be up to approximately 125 lb/in 2 .   b. Radio frequency current is then applied to the tissue such that the current density is in the range of 0.034-0.1 Amps/mm 2 . This current is sufficient to heat the tissue quickly so that the internal elastic laminae will fuse. A temperature of about 140° C. is required for this to occur.   c. Power delivery from the generator is generally less than 20 Watts to deliver this current density but may be as high as 35 Watts. Higher power may shorten the sealing time.   d. After the tissue begins to desiccate, the power may be reduced by 60-80% and heating is continued for a period of time before shutting off. The power can be reduced either when the tissue impedance reaches a level of 150-250 ohms or at a set time interval.   e. The voltage of the system is limited to less than 100 Volts RMS and peak voltage is typically in the range of 85 Volts RMS.   f. One or more wait states may also be interposed between the above steps.       
 
         [0080]    As demonstrated, vessel sealing is possible using a low power system by limiting jaw size and applying high pressure. A jaw of approximately 3 mm in width and 10-12 mm in length with a cross-sectional area of approximately 15-22 mm 2  is preferred but other geometries are contemplated.  FIG. 9  shows one embodiment of an end effector jaw geometry, such as a Maryland style jaw, as used in connection with aspects of the present invention. When describing the surface area of the jaws in  FIG. 9 , reference is made to the surface area of the jaws that actually align with each other and grasp around the tissue being sealed. In some embodiments, there may be curved surfaces or tapered edges to the jaw surface that does not actually perform the bulk of the sealing function. When describing jaw surface area, it is not intended to encompass these portions of the jaw that are outside the normal boundaries of the sealing surface. In combination with the power delivery schemes described herein, the system results in a significantly reduced power requirement over standard bipolar sealing systems. Power requirements in some embodiments are in the range of 10-35 Watts. 
         [0081]    In accordance with other testing aspects, non-conductive spacers, such as ceramic beads, were incorporated into the instruments to stop the jaws before they touch and prevent short circuits in the electrical systems. The ceramic beads also provided a means of keeping the jaws parallel since the moving jaw will land on the top of the beads. 
         [0082]    In the testing environment, a silk suture material (0.006″ diameter) that is non-conductive and will not melt during sealing was utilized to maintain the separation between jaw surfaces and prevent arcing. In the examples described in Table 1, two wraps of the suture were placed around the upper jaw so that the jaws would be separated by 0.006″ when they were closed by the spring. 
         [0083]    In accordance with another example, and with the non-conductive sutures in place, the power was set at 12 W as a nominal starting point and bracketed from 10 W to 14 W. When full jaw bites were sealed (100% filling of jaws with tissue), there were high quality seals, excellent translucency, with minimal sticking and charring. However, attempts to perform seals using these settings on smaller vessels that fill less (50-75%) of the jaw still resulted in arcing. Additional testing bracketed Pmax between 7 W and 15 W. Pmin was set at 5 W and bracketed between 4 W and 7 W. Since there was no control limit on parameters other than power and time, the lower power settings were used to produce reasonable seals on smaller vessels in the range of 50-80% jaw tissue fill. When the vessels filled 100% of the jaws, the 7 W was not sufficient to seal and a higher power near 12 W was necessary to adequately seal these larger vessels. 
         [0084]    In accordance with other examples, further seals were provided by setting impedance thresholds in the user interface. It was then possible to set break points in the power curve that could limit the power delivered to the jaws by watching the real-time rise in impedance. Additional seals were performed with power and time as the sole modifiers of the power curve. An impedance trigger point added to the sequence and control of power delivery enabled the generator to quickly respond to changes in impedance and make the necessary adjustments. 
       Current and Voltage Clamping 
       [0085]    In another aspect of testing the device, current and voltage limits were implemented. Based on observation, by limiting the voltage to 100 V arcing was eliminated in vessels ranging from 2 to 7 mm in width. These parameters made it possible to seal vessels that filled any percentage of the jaws thus the process and device were not limited to fully filling the jaws with tissue material. As an experimental validation, raising the voltage limit to 150 volts again caused arcing. This confirmed that the voltage limit is correctly stopping the arcing from occurring. The voltage maximum was set at between 75 and 100 volts for the next series of seals performed. 
         [0086]    As another method to determine a maximum current for sealing, a system energy check was performed to see what current level is required to boil off saline that is placed between the jaws. It was found that 1.8 A was needed to cause the saline to begin to steam and boil away when RF power is applied to the jaws and this was used as the maximum current for sealing. 
         [0087]    In another example, it was determined that a fast application of energy with a high influx of current creates good seals. Examples included following the high current energy with a one (1) second burst of low energy with Pmin set at 5 W. 
         [0088]    In another example, a set of jaws 0.409 inches in length were installed in the system. The old jaws were removed and found to have experienced significant pitting due to the arcing incurred while there was no voltage limit in place. In addition to being longer than the original jaws, the top edges of the jaws were eased to reduce any sharp corner effects and high current concentrations that can occur with sharp edges. 
         [0089]    In another example, seals were made with Vmax set to 75 volts and Imax set to 1.8 A. There were never any incidents of arcing observed in subsequent seals. Seals were created with the following set of parameters: 
         [0090]    Pmax=15 W 
         [0091]    Time at Pmax=2.5 sec 
         [0092]    Pmin=5 W 
         [0093]    Time at Pmin=1 sec 
         [0094]    Vmax=75V 
         [0095]    Imax=1.8 A 
         [0096]    Time to Pmax=0.01 
         [0097]    Time from Pmax to Pmin=0.01 sec 
         [0098]    A series of thirty-two (32) seals were performed on two animals. Vessels ranged from 2 mm to 6 mm wide. Twenty (20) of the 32 seals from the series were burst tested. All seals successfully withstood a minimum of 360 mm Hg. Seals were also successfully performed on mesentery tissue using the same settings. 
         [0099]      FIGS. 10-14  show reproductions of oscilloscope traces captured for three different seals demonstrating three different sizes of vessels. All were sealed using the above settings. All were set with the impedance threshold at 200 ohms. Seal time was determined by observing when the power was triggered to switch off.  FIG. 11  shows the results for a 3.5 mm Vessel with a 1.5 second seal time.  FIG. 12  shows the results for a 5 mm vessel with a 2.3 second seal time.  FIG. 13  shows the results for a 1.5 mm Vessel with a 0.75 second seal time. 
         [0100]      FIG. 14  shows a reproduction of an oscilloscope trace captured for additional sealing example where the maximum impedance was set to 175 ohms. This impedance of the seal followed the typical curve of impedance changes. Through the sealing process, the tissue begins to desiccate and the impedance drops. As it continues to dry out, the impedance begins a rapid rise. In this case, the impedance threshold was attained and the Pmax was switched to Pmin for the duration of the run. 
         [0101]    Those skilled in the art can readily recognize that numerous variations and substitutions may be made in the invention, its use and its configuration to achieve substantially the same results as achieved by the embodiments described herein. Accordingly, there is no intention to limit the invention to the disclosed exemplary forms. Many variations, modifications and alternative constructions fall within the scope and spirit of the disclosed invention as expressed in the claims.