Patent Publication Number: US-7909820-B2

Title: Electrosurgical generator and bipolar electrosurgical device adaptors

Description:
This application is being filed on 3 Mar. 2004, as a PCT international patent application in the name of TissueLink Medical, Inc. (a U.S. national corporation), and David E. Lipson and David J. Flanagan (both U.S. citizens. 
     FIELD 
     This invention relates generally to the field of medical devices and methods for use upon a body during surgery. More particularly, the invention relates to electrosurgical devices, systems and methods for use upon tissues of a human body during surgery, particularly open surgery and minimally invasive surgery such as laparoscopic surgery. 
     BACKGROUND 
     Electrosurgical devices configured for use with a dry tip use electrical energy, often radio frequency (RF) energy, to cut tissue or to cauterize blood vessels. During use, a voltage gradient is created at the tip of the device, thereby inducing current flow and related heat generation in the tissue. With sufficiently high levels of electrical power, the heat generated is sufficient to cut the tissue and, advantageously, to stop the bleeding from severed blood vessels. 
     Current dry tip electrosurgical devices can cause the temperature of tissue being treated to rise significantly higher than 100° C., resulting in tissue desiccation, tissue sticking to the electrodes, tissue perforation, char formation and smoke generation. Desiccation occurs when tissue temperature exceeds 100° C. and all of the intracellular water boils away, leaving the tissue extremely dry and much less electrically conductive. Peak temperatures of target tissue as a result of dry RF treatment can be as high as 320° C., and such high temperatures can be transmitted to adjacent tissue via thermal diffusion. Consequently, this may result in undesirable desiccation and thermal damage to the adjacent tissue. 
     The use of saline inhibits undesirable effects such as tissue desiccation, electrode sticking, smoke production and char formation. However, an uncontrolled or abundant flow rate of saline can provide too much electrical dispersion and cooling at the electrode/tissue interface. This reduces the temperature of the target tissue being treated, and, in turn, can result in longer treatment time to achieve the desired tissue temperature for treatment of the tissue. Long treatment times are undesirable for surgeons since it is in the best interest of the patient, physician and hospital, to perform surgical procedures as quickly as possible. 
     RF power delivered to tissue can be less than optimal when using general-purpose generators. Most general-purpose RE generators have modes for different waveforms (e.g., cut, coagulation, or blend) and device types (e.g., monopolar, bipolar), as well as power levels that can be set in watts. However, once these settings are chosen, the actual power delivered to tissue and associated heat generated can vary dramatically over time as tissue impedance changes during the course of RF treatment. This is because the power delivered by most generators is a function of tissue impedance, with the power ramping down as impedance either decreases toward zero or increases significantly to several thousand ohms. Current dry tip electrosurgical devices are not configured to address a change in power provided by the generator as tissue impedance changes or the associated effect on tissue, and rely on the surgeon&#39;s expertise to overcome this limitation. 
     SUMMARY OF THE INVENTION 
     The invention is directed to various embodiments of electrosurgical devices, systems and methods. In one preferred embodiment, an electrosurgical device has a handle, a shaft extending from the handle having a distal end, and an electrode tip having an electrode surface with at least a portion of the electrode tip extending distally beyond the distal end of the shaft. In one embodiment, preferably the portion of the electrode tip extending distally beyond the distal end of the shaft comprises a cone shaped portion. The device also has a fluid passage being connectable to a fluid source and at least one fluid outlet opening in fluid communication with the fluid passage. 
     In another preferred embodiment, the electrode tip extending distally beyond the distal end of the shaft has a neck portion and an enlarged end portion with the enlarged end portion located distal to the neck portion and comprising the cone shaped portion. 
     In another preferred embodiment, the fluid outlet opening is arranged to provide a fluid from the fluid source to the neck portion of the electrode tip. 
     In yet another preferred embodiment, the fluid outlet opening is arranged to provide a fluid from the fluid source towards the enlarged end portion of the electrode tip. 
     In another preferred embodiment, an electrosurgical device has a handle, and an electrode tip having an electrode surface with the electrode surface and comprising a cone shaped portion. The device also has a fluid passage being connectable to a fluid source and at least one fluid outlet opening in fluid communication with the fluid passage and arranged to provide a fluid from the fluid source to the cone shaped portion of the electrode tip. 
     The invention is also directed to a surgical method for treating tissue. The method includes providing tissue having a tissue surface, providing radio frequency power at a power level, providing an electrically conductive fluid at a fluid flow rate, providing an surgical device configured to simultaneously provide the radio frequency electrical power and the electrically conductive fluid to tissue, providing the electrically conductive fluid to the tissue at the tissue surface, forming a fluid coupling comprising the electrically conductive fluid which couples the tissue and the surgical device, providing the radio frequency power to the tissue at the tissue surface and below the tissue surface into the tissue through the fluid coupling, coagulating the tissue without cutting the tissue, and dissecting the tissue after coagulating the tissue. Preferably, the device comprises an electrode tip having an electrode surface, and comprising a cone shaped portion and a distal end. Also preferably, coagulating the tissue is performed with the cone shaped portion and dissecting is performed with the distal end of the device. In various embodiments, the dissection may be blunt as where the distal end of the device is blunt, or sharp as where the distal end of the device is pointed. 
     The invention is also directed to various embodiments of an adaptor for electrically coupling between an electrosurgical generator and a bipolar electrosurgical device. In one preferred embodiment, the adaptor comprises a power input connector for coupling the adaptor with a monopolar mode power output connector of the electrosurgical generator, a ground connector for coupling the adaptor with a ground connector of the electrosurgical generator, a first and a second power output connector, each for coupling the adaptor with a first and a second bipolar mode power input connector of the bipolar electrosurgical device, respectively, a transformer coupled between the power input connector and the first and second power output connectors, a monopolar hand switch connector for coupling the adaptor with a monopolar mode hand switch connector of the electrosurgical generator, and at least one bipolar mode hand switch connector for coupling the adaptor with a bipolar mode hand switch connector of the electrosurgical device. 
     The invention is also directed to various embodiments of a bipolar electrosurgical device. In one preferred embodiment, the device comprises a first electrode tip and a second electrode tip with the electrode tips coupled to an impedance transformer provided with the electrosurgical device, at least one fluid delivery passage being connectable to a fluid source, at least one fluid outlet opening in fluid communication with the at least one fluid delivery passage, the electrode tips configured to paint along a tissue surface in the presence of fluid from the fluid outlet opening as the tips are moved along the tissue surface whereby the tissue surface can be coagulated without cutting upon the application of radio frequency energy from the electrodes simultaneously with fluid from the fluid outlet opening while the tips are coupled with the fluid adjacent the tissue surface and moved along the tissue surface. 
     The invention is also directed to various embodiments of medical kits. In one preferred embodiment, the kit has an electrosurgical device configured to provide radio frequency power and a fluid to a tissue treatment site, and a transformer. In various embodiments, the electrosurgical device and transformer may be provided as separate connectable components, or integrally as a single piece. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram showing one embodiment of a control system of the invention, and an electrosurgical device; 
         FIG. 2  is a schematic graph that describes a relationship between RF power to tissue (P, in watts), flow rate of saline (Q, in cc/sec.), and tissue temperature (T, in ° C.) when heat conduction to adjacent tissue is considered; 
         FIG. 3  is schematic graph that describes a relationship between RF power to tissue (P, in watts), flow rate of saline (Q, in cc/sec.), and tissue temperature (T, in ° C.) when heat conduction to adjacent tissue is neglected; 
         FIG. 4  is a schematic graph that describes a relationship between RF power to tissue (P, in watts), flow rate of saline (Q, in cc/sec.), and tissue temperature (T, in ° C.) when the heat required to warm the tissue to the peak temperature (T) is considered; 
         FIG. 5  is a graph that describes a relationship between percentage saline boiling (%) and saline flow rate (Q, in cc/min) for an exemplary RF generator output setting of 75 watts; 
         FIG. 6  is a schematic graph that describes a relationship between load impedance (Z, in ohms) and generator output power (P, in watts), for an exemplary RF generator output setting of 75 watts in a bipolar mode; 
         FIG. 7  is a schematic graph that describes a relationship between time (t, in seconds) and tissue impedance (Z, in ohms) after RF activation; 
         FIG. 8  is a schematic perspective view of a cannula which may be used with an electrosurgical device according to the present invention; 
         FIG. 9  is a schematic exploded perspective view of an assembly of an electrosurgical device according to the present invention; 
         FIG. 10  is a schematic longitudinal cross-sectional side view of the tip and shaft of the device of  FIG. 9  taken along line  10 - 10  of  FIG. 12 ; 
         FIG. 11  is a schematic close-up longitudinal cross-sectional side view of the tip portion of the device bounded by circle  45  shown in  FIG. 10  taken along line  10 - 10  of  FIG. 12 ; 
         FIG. 12  is a schematic distal end view of the tip portion of the device bounded by circle  45  shown in  FIG. 10 ; 
         FIG. 13  is a schematic side view of the of the tip and shaft of the device of  FIG. 9  with a fluid coupling to a tissue surface of tissue; 
         FIG. 14  is a schematic close-up side view of an alternative tip portion; 
         FIG. 15  is a schematic close-up cross-sectional side view of the tip portion of  FIG. 14  taken along line  15 - 15  of  FIG. 14 ; 
         FIG. 16  is a schematic close-up cross-sectional side view of the tip portion of  FIG. 14  disposed in a tissue crevice; 
         FIG. 17  is a schematic graph that describes a relationship between time (t, in seconds) and changes in impedance (Z, in ohms) represented by impedance spikes; 
         FIG. 18  is a schematic graph that describes a relationship between percentage saline boiling (%) and impedance (Z, in ohms); 
         FIG. 19  is schematic close-up cross-sectional view of a sleeve taken along line  19 - 19  of  FIG. 15 ; 
         FIG. 20  is a schematic close-up perspective view of an alternative tip portion; 
         FIG. 21  is a schematic close-up cross-sectional side view of the tip portion of  FIG. 20  taken along line  21 - 21  of  FIG. 20 ; 
         FIG. 22  is a schematic close-up cross-sectional side view of the tip portion of  FIG. 20  disposed in a tissue crevice; 
         FIG. 23  is a schematic close-up front perspective view of the electrode for the tip portion of  FIG. 20 ; 
         FIG. 24  is a schematic close-up rear perspective view of the electrode for the tip portion of  FIG. 20 ; 
         FIG. 25  is a schematic close up cross-sectional view of a porous electrode with recesses; 
         FIG. 26  is schematic close up cross-sectional view of an electrode with semi-circular recesses; 
         FIG. 27  is schematic close up cross-sectional view of an electrode with V-shaped recesses; 
         FIG. 28  is schematic close up cross-sectional view of an electrode with U-shaped recesses; 
         FIG. 29  is a schematic close-up perspective view of an alternative tip portion; 
         FIG. 30  is a schematic close-up cross-sectional side view of the tip portion of  FIG. 29  taken along line  30 - 30  of  FIG. 29 ; 
         FIG. 31  is a schematic close-up perspective view of an alternative tip portion; 
         FIG. 32  is a schematic close-up cross-sectional side view of the tip portion of  FIG. 31  taken along line  32 - 32  of  FIG. 31 ; 
         FIG. 33  is a schematic close-up perspective view of an alternative tip portion; 
         FIG. 34  is a schematic close-up cross-sectional side view of the tip portion of  FIG. 33  taken along line  34 - 34  of  FIG. 33 ; 
         FIG. 35  is a schematic close-up perspective view of an alternative tip portion; 
         FIG. 36  is a schematic close-up cross-sectional side view of the tip portion of  FIG. 35  taken along line  36 - 36  of  FIG. 35 ; 
         FIG. 37  is a schematic close up side view of an alternative cone shape portion of an electrode; 
         FIG. 38  is a schematic close up side view of an alternative cone shape portion of an electrode; 
         FIG. 39  is a schematic close up side view of an alternative cone shape portion of an electrode; 
         FIG. 40  is a schematic close up side view of an alternative cone shape portion of an electrode; 
         FIG. 41  is a schematic exploded perspective view of an assembly of an alternative electrosurgical device according to the present invention; 
         FIG. 42  is a schematic close-up cross-sectional side view of the tip portions of  FIG. 41  assembled with a fluid coupling to a tissue surface of tissue; 
         FIG. 43  is a schematic close-up cross-sectional side view of the tip portions of  FIG. 41  assembled with an alternative fluid coupling to a tissue surface of tissue; 
         FIG. 44  is a block diagram showing another embodiment of a control system of the invention, and an electrosurgical device; 
         FIG. 45  is a block diagram of an electrical configuration for a generator and a bipolar device without a hand switch; 
         FIG. 46  is a block diagram of an electrical configuration for a generator and a monopolar device with a hand switch; 
         FIG. 47  is a block diagram of an electrical configuration for a generator and a bipolar device with a hand switch and a transformer; 
         FIG. 48  is a block diagram of an electrical configuration for a generator and a bipolar device without a handswitch and with a transformer; 
         FIG. 49  is a block diagram of an electrical configuration for a generator, a bipolar device without a hand switch, and an adaptor with a transformer therebetween; 
         FIG. 50  is a block diagram of an electrical configuration for a generator and a bipolar device with a hand switch; 
         FIG. 51A  is a block diagram of an electrical configuration for a generator, a bipolar device with a hand switch, and an adaptor with a transformer therebetween; 
         FIG. 51B  is a block diagram of an electrical configuration for a generator, a bipolar device with a hand switch, and an adaptor with a transformer therebetween; 
         FIG. 52  is a schematic perspective view of an alternative electrosurgical device according to the present invention; 
         FIG. 53  is a schematic perspective view of a handle portion of the device of  FIG. 52  assembled with various components; 
         FIG. 54  is a schematic side view of a handle portion of the device of  FIG. 52  assembled with various components; 
         FIG. 55  is a schematic side view of a handle portion of the device of  FIG. 52  assembled with various components; 
         FIG. 56  is a schematic side view of a handle portion of the device of  FIG. 52  assembled with various components; 
         FIG. 57  is a schematic perspective view of an alternative electrosurgical device according to the present invention; 
         FIG. 58  is a schematic perspective view of a handle portion of the device of  FIG. 57  assembled with various components; and 
         FIG. 59  is a schematic side view of a handle portion of the device of  FIG. 52  assembled with various components. 
     
    
    
     DETAILED DESCRIPTION 
     Throughout the description, like reference numerals and letters indicate corresponding structure throughout the several views, and such corresponding structure need not be separately discussed. Furthermore, any particular feature(s) of a particular exemplary embodiment may be equally applied to any other exemplary embodiment(s) of this specification as suitable. In other words, features between the various exemplary embodiments described herein are interchangeable as suitable, and not exclusive. 
     The invention provides devices, systems and methods that control tissue temperature at a tissue treatment site during a medical procedure. This is particularly useful during surgical procedures upon tissues of the body, where it is desirable to seal, coagulate and shrink tissue, to occlude lumens of blood vessels (e.g., arteries, veins), airways (e.g., bronchi, bronchioles), bile ducts and lymphatic ducts. 
     The invention includes electrosurgical procedures, which preferably utilize RF power and electrically conductive fluid, to treat tissue. Preferably, a desired tissue temperature range is achieved by adjusting parameters, such as fluid flow rate, to affect the temperature at the tissue/electrode interface. 
     In one embodiment, the invention provides a control device, the device comprising a flow rate controller that receives a signal indicating power applied to the system, and adjusts the flow rate of fluid from a fluid source to the electrosurgical device. The invention also provides a control system comprising a flow rate controller, a measurement device that measures power applied to the system, and a pump that provides fluid at a selected flow rate. 
     The invention will be discussed generally with reference to  FIG. 1 , which shows a block diagram of one exemplary embodiment of a system of the invention. Preferably, an electrically conductive fluid  24  is provided from a fluid source  1  through a fluid line  2  to a pump  3 , which has an outlet fluid line  4   a  that is connected as an input fluid line  4   b  to electrosurgical device  5 . In a preferred embodiment, outlet fluid line  4   a  and input fluid line  4   b  are flexible and are made from a polymeric material, such as polyvinylchloride (PVC) or polyolefin (e.g., polypropylene, polyethylene) and the conductive fluid comprises a saline solution. More preferably, the saline comprises sterile, and even more preferably, normal saline. Although the description herein will specifically describe the use of saline as the fluid  24 , other electrically conductive fluids, as well as non-conductive fluids, can be used in accordance with the invention. 
     For example, in addition to the conductive fluid comprising physiologic saline (also known as “normal” saline, isotonic saline or 0.9% sodium chloride (NaCl) solution), the conductive fluid may comprise hypertonic saline solution, hypotonic saline solution, Ringers solution (a physiologic solution of distilled water containing specified amounts of sodium chloride, calcium chloride, and potassium chloride), lactated Ringer&#39;s solution (a crystalloid electrolyte sterile solution of distilled water containing specified amounts of calcium chloride, potassium chloride, sodium chloride, and sodium lactate), Locke-Ringer&#39;s solution (a buffered isotonic solution of distilled water containing specified amounts of sodium chloride, potassium chloride, calcium chloride, sodium bicarbonate, magnesium chloride, and dextrose), or any other electrolyte solution. 
     While a conductive fluid is preferred, as will become more apparent with further reading of this specification, fluid  24  may also comprise an electrically non-conductive fluid. The use of a non-conductive fluid is less preferred than a conductive fluid, however, the use of a non-conductive fluid still provides certain advantages over the use of a dry electrode including, for example, reduced occurrence of tissue sticking to the electrode of device  5  and cooling of the electrode and/or tissue. Therefore, it is also within the scope of the invention to include the use of a non-conducting fluid, such as, for example, deionized water. 
     Returning to  FIG. 1 , energy to heat tissue is provided from an energy source, such as an electrical generator  6  which preferably provides RF alternating current via a cable  7  to an energy source output measurement device, such as a power measurement device  8  that measures the RF alternating current electrical power. In one exemplary embodiment, preferably the power measurement device  8  does not turn the power off or on, or alter the power in any way. A power switch  15  connected to generator  6  is preferably provided by the generator manufacturer and is used to turn generator  6  on and off. The power switch  15  can comprise any switch to turn the power on and off, and is commonly provided in the form of a footswitch or other easily operated switch, such as a switch  15   a  mounted on electrosurgical device  5 . The power switch  15  or  15   a  may also function as a manually activated device for increasing or decreasing the power provided from device  5 . Alternatively, internal circuitry and other components of generator  6  may be used for automatically increasing or decreasing the power provided from device  5 . A cable  9  preferably provides RF power from power measurement device  8  to electrosurgical device  5 . Power, or any other energy source output, is preferably measured before it reaches electrosurgical device  5 . 
     When capacitation and induction effects are negligibly small, from Ohm&#39;s law, power P, or the rate of energy delivery (e.g., joules/sec), may be expressed by the product of current times voltage (i.e., I×V), the current squared times resistance (i.e., I 2 ×R), or the voltage squared divided by the resistance (i.e., V 2 /R); where the current I may be measured in amperes, the voltage V may be measured in volts, the electrical resistance R may be measured in ohms, and the power P may be measured in watts (joules/sec). Given that power P is a function of current I, voltage V, and resistance R as indicated above, it should be understood, that a change in power P is reflective of a change in at least one of the input variables. Thus, one may alternatively measure changes in such input variables themselves, rather than power P directly, with such changes in the input variables mathematically corresponding to a changes in power P as indicated above. 
     Heating of the tissue is preferably performed by electrical resistance heating. That is, the temperature of the tissue increases as a result of electric current flow through the tissue, with the electrical energy being absorbed from the voltage and transformed into thermal energy (i.e., heat) via accelerated movement of ions as a function of the tissue&#39;s electrical resistance. 
     Referring again to  FIG. 1 , a flow rate controller  11  preferably includes a selection switch  12  that can be set to achieve desired levels of percentage fluid boiling (for example, 100%, 98%, 80% boiling). Preferably, flow rate controller  11  receives an input signal  10  from power measurement device  3  and calculates an appropriate mathematically predetermined fluid flow rate based on percentage boiling indicated by the selection switch  12 . In a preferred embodiment, a fluid switch  13  is provided so that the fluid system can be primed (e.g., air eliminated) before turning on generator  6 . The output signal  16  of flow rate controller  11  is preferably sent to pump  3  motor to regulate the flow rate of fluid, and thereby provide an appropriate fluid flow rate which corresponds to the amount of power being delivered. 
     In one embodiment, flow rate controller  11  is configured and arranged to be connected to a source of RF power (e.g., generator  6 ), and a source of fluid (e.g., fluid source  1 ), for example, a source of conductive fluid. The device of the invention receives information about the level of RF power applied to electrosurgical device  5 , and adjusts the flow rate of fluid  24  to electrosurgical device  5 , thereby controlling temperature at the tissue treatment site. 
     In another embodiment, elements of the system are physically included together in one electronic enclosure. One such embodiment is shown by enclosure within the outline box  14  of  FIG. 1 . In the illustrated embodiment, pump  3 , flow rate controller  11 , and power measurement device  8  are enclosed within an enclosure, and these elements are connected through electrical connections to allow signal  10  to pass from power measurement device  8  to flow rate controller  11 , and signal  16  to pass from flow rate controller  11  to pump  3 . Other elements of a system can also be included within one enclosure, depending upon such factors as the desired application of the system, and the requirements of the user. 
     Pump  3  can be any suitable pump to provide saline or other fluid at a desired flow rate. Preferably, pump  3  is a peristaltic pump. With a rotary peristaltic pump, typically a fluid  24  is conveyed within the confines of a flexible tube (e.g.,  4   a ) by waves of contraction placed externally on the tube which are produced mechanically, typically by rotating rollers which intermittently squeeze the flexible tubing against a support with a linear peristaltic pump, typically a fluid  24  is conveyed within the confines of a flexible tube by waves of contraction placed externally on the tube which are produced mechanically, typically by a series of compression fingers or pads which sequentially squeeze the flexible tubing against a support. Peristaltic pumps are generally preferred, as the electromechanical force mechanism (e.g., rollers driven by electric motor) does not make contact the fluid  24 , thus reducing the likelihood of inadvertent contamination. 
     Similar pumps can be used in connection with the invention, and the illustrated embodiments are exemplary only. The precise configuration of pump  3  is not critical to the invention. For example, pump  3  may include other types of infusion and withdrawal pumps. Furthermore, pump  3  may comprise pumps which may be categorized as syringe pumps, piston pumps, rotary vane pumps (e.g., axial impeller, centrifugal impeller), cartridge pumps and diaphragm pumps. In some embodiments, pump  3  can be substituted with any type of flow controller, such as a manual roller clamp used in conjunction with an IV bag, or combined with the flow controller to allow the user to control the flow rate of conductive fluid to the device. Alternatively, a valve configuration can be substituted for pump  3 . 
     Fluid  24 , such as conductive fluid, is preferably provided from an intravenous (IV) bag full of saline (e.g., fluid source  1 ) that flows by gravity. Fluid  24  may flow directly to electrosurgical device  5 , or first to pump  3  located there between. Alternatively, fluid  24  from a fluid source  1  such as an IV bag can be provided through an IV flow controller that may provide a desired flow rate by adjusting the cross sectional area of a flow orifice (e.g., lumen of the connective tubing with the electrosurgical device  5 ) while sensing the flow rate with a sensor such as an optical drop counter. Furthermore, fluid  24  from a fluid source  1  such as an IV bag can be provided through a manually or automatically activated device such as a flow controller, such as a roller clamp, which also adjusts the cross sectional area of a flow orifice and may be adjusted manually by, for example, the user of the device in response to their visual observation (e.g., fluid boiling) at the tissue treatment site or a pump. 
     Similar configurations of the system can be used in connection with the invention, and the illustrated embodiments are exemplary only. For example, the fluid source  1 , pump  3 , generator  6 , power measurement device  8  or flow rate controller  11 , or any other components of the system not expressly recited above, may be present as a part of the electrosurgical device  5 . For example, fluid source  1  may be a compartment of the electrosurgical device  5  which contains fluid  24 , as indicated at reference character  1   a  . In another exemplary embodiment, the compartment may be detachably connected to electrosurgical device  5 , such as a canister which may be attached via threaded engagement with device  5 . In yet another embodiment, the compartment may be configured to hold a pre-filled cartridge of fluid  24 , rather than the fluid directly. 
     Also for example, with regards to alternatives for the generator  6 , an energy source, such as a direct current (DC) battery used in conjunction with inverter circuitry and a transformer to produce alternating current at a particular frequency, may comprise a portion of the electrosurgical device  5 , as indicated at reference character  6   a . In one embodiment the battery element of the energy source may comprise a rechargeable battery. In yet another exemplary embodiment, the battery element may be detachably connected to the electrosurgical device  5 , such as for recharging. 
     Use of the components of the system will now be described in further detail. From the specification, it should be clear that any use of the terms “distal” and “proximal” are made in reference from the user of the device, and not the patient. 
     Flow rate controller  11  controls the rate of flow from the fluid source  1 . Preferably, the rate of fluid flow from fluid source  1  is based upon the amount of RF power provided from generator  6  to electrosurgical device  5 . Referring to  FIG. 2 , there is illustrated a relationship between the rate of fluid flow Q and the RF power P. More precisely, as shown in  FIG. 2 , the relationship between the rate of fluid flow Q and RF power P may be expressed as a direct, linear relationship. The flow rate Q of conductive fluid  24 , such as saline, interacts with the RF power P and various modes of heat transfer to transfer heat away from the target tissue, as described herein. 
     Throughout this disclosure, when the terms “boiling point of saline”, “vaporization point of saline”, and variations thereof are used, what is actually referenced for explanation purposes, is the boiling point of the water (i.e., 100° C.) in the saline solution given that the difference between the boiling point of normal saline (about 100.16° C.) and the boiling point of water is negligible. 
       FIG. 2  shows the relationship between the flow rate of saline, RF power to tissue, and regimes of boiling as detailed below. Based on a simple, one-dimensional, lumped parameter model of the heat transfer, the peak tissue temperature can be estimated, and once tissue temperature is estimated, it follows directly whether it is hot enough to boil saline. The total RF electrical power P that is converted into heat can be defined as:
 
 P=ΔT/R+ρc   ρ   Q   1   ΔT+ρQ   b   h   v    (1)
 
where P=the total RF electrical power that is converted into heat.
 
     Conduction. The first term [ΔT/R] in equation (1) is heat conducted to adjacent tissue, represented as  70  in  FIG. 2 , where:
         ΔT=(T−T ∞ ) the difference in temperature (° C.) between the peak tissue temperature (T) and the normal temperature (T ∞ ) of the body tissue; normal temperature of the body tissue is generally 37° C.; and   R=Thermal resistance of surrounding tissue, the ratio of the temperature difference to the heat flow (° C./watt).       

     This thermal resistance can be estimated from published data gathered in experiments on human tissue (see for example, Phipps, J. H., “Thermometry studies with bipolar diathermy during hysterectomy,”  Gynaecological Endoscopy,  3:5-7 (1994)). As described by Phipps, Kleppinger bipolar forceps were used with an RF power of 50 watts, and the peak tissue temperature reached 320° C. For example, using the energy balance of equation (1), and assuming all the RF heat put into tissue is conducted away, then R can be estimated:
 
 R=ΔT/P =(320-37)/50=5.7≈6° C./watt
 
     However, it is undesirable to allow the tissue temperature to reach 320° C., since tissue will become desiccated. At a temperature of 320° C., the fluid contained in the tissue is typically boiled away, resulting in the undesirable tissue effects described herein. Rather, it is preferred to keep the peak tissue temperature at no more than about 100° C. to inhibit desiccation of the tissue. Assuming that saline boils at about 100° C., the first term in equation (1) (ΔT/R) is equal to (100−37)/6=10.5 watts. Thus, based on this example, the maximum amount of heat conducted to adjacent tissue without any significant risk of tissue desiccation is 10.5 watts. 
     Referring again to  FIG. 2 , RF power to tissue is represented on the X-axis as P (watts) and flow rate of saline (cc/min) is represented on the Y-axis as Q. When the flow rate of saline equals zero (Q=0), there is an “offset” RF power that shifts the origin of the sloped lines  76 ,  78 , and  80  to the right. This offset is the heat conducted to adjacent tissue. For example, using the calculation above for bipolar forceps, this offset RF power is about 10.5 watts. If the power is increased above this level with no saline flow, the peak tissue temperature can rise well above 100° C., resulting in tissue desiccation from the boiling off of water in the cells of the tissue. 
     Convection. The second term [ρc ρ Q 1 ΔT] in equation (1) is heat used to warm up the saline without boiling the saline, represented as  72  in  FIG. 2 , where:
         ρ=Density of the saline fluid that gets hot but does not boil (approximately 1.0 gm/cm 3 );   c ρ =Specific heat of the saline (approximately 4.1 watt-sec/gm-° C.);   Q 1 =Flow rate of the saline that is heated (cm 3 /sec); and   ΔT=Temperature rise of the saline. Assuming that the saline is heated to body temperature before it reaches the electrode, and that the peak saline temperature is similar to the peak tissue temperature, this is the same ΔT as for the conduction calculation above.       

     The onset of boiling can be predicted using equation (1) with the last term on the right set to zero (no boiling), i.e. ρQ b h v =0, and solving equation (1) for Q 1  leads to:
 
 Q   1   =[P−ΔT/R]/ρc   ρ   ΔT    (2)
 
     This equation defines the line shown in  FIG. 2  as the line of onset of boiling  76 . 
     Boiling. The third term [ρQ b h v ] in equation (1) relates to heat that goes into converting the water in liquid saline to water vapor, and is represented as  74  in  FIG. 2 , where:
         Q b =Flow rate of saline that boils (cm 3 /sec); and   h v =Heat of vaporization of saline (approximately 2,000 watt-sec/gm).       

     A flow rate of only 1 cc/min will absorb a significant amount of heat if it is completely boiled, or about ρQ b h v =(1) (1/60) (2,000)=33.3 watts. The heat needed to warm this flow rate from body temperature to 100° C. is much less, or ρc ρ Q 1 ΔT=(1) (4.1) (1/60) (100−37)=4.3 watts. In other words, the most significant factor contributing to heat transfer from a wet electrode device can be fractional boiling. The present invention recognizes this fact and exploits it. 
     Fractional boiling can be described by equation (3) below: 
     
       
         
           
             
               
                 
                   
                     Q 
                     1 
                   
                   = 
                   
                     
                       { 
                       
                         P 
                         - 
                         
                           Δ 
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           
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                       } 
                     
                     
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     If the ratio of Q b /Q 1  is 0.50 this is the 50% boiling line  78  shown in  FIG. 2 . If the ratio is 1.0 this is the 100% boiling line  80  shown in  FIG. 2 . 
     As indicated previously in the specification, use of a fluid to couple energy to tissue inhibits undesirable effects such as tissue desiccation, electrode sticking, char formation and smoke production. Tissue desiccation, which occurs if the tissue temperature exceeds 100° C. and all the intracellular water boils away, is particularly undesirable as it leaves the tissue extremely dry and much less electrically conductive. 
     As shown in  FIG. 2 , one control strategy or mechanism which can be employed for the electrosurgical device  5  is to adjust the power P and flow rate Q such that the power P used at a corresponding flow rate Q is equal to or less than the power P required to boil 100% of the fluid, and does not exceed the power P required to boil 100% of the fluid. This control strategy targets using the electrosurgical device  5  in the regions of  FIG. 2  identified as T&lt;100° C. and T=100° C., and includes the 100% boiling line  80 . That is, this control strategy targets not using the electrosurgical device  5  only in the region of  FIG. 2  identified as T&gt;&gt;100° C. 
     Another control strategy that can be used for the electrosurgical device  5  is to operate device  5  in the region T&lt;100° C., but at high enough temperature to shrink tissue containing Type I collagen (e.g., walls of blood vessels, bronchi, bile ducts, etc.), which shrinks when exposed to about 85° C. for an exposure time of 0.01 seconds, or when exposed to about 65° C. for an exposure time of 15 minutes. An exemplary target temperature/time for tissue shrinkage is about 75° C. with an exposure time of about 1 second. A determination of the high end of the scale (i.e., when the fluid reaches 100° C.) can be made by the phase change in the fluid from liquid to vapor. However, a determination at the low end of the scale (e.g., when the fluid reaches, for example, 75° C. for 1 second) requires a different mechanism as the temperature of the fluid is below the boiling temperature and no such phase change is apparent. 
     In order to determine when the fluid reaches a temperature that will facilitate tissue shrinkage, for example 75° C., a thermochromic material, such as a thermochromic dye (e.g., leuco dye), may be added to the fluid. The dye can be formulated to provide a first predetermined color to the fluid at temperatures below a threshold temperature, such as 75° C., then, upon heating above 75° C., the dye provides a second color, such as clear, thus turning the fluid clear (i.e., no color or reduction in color). This color change may be gradual, incremental, or instant. Thus, a change in the color of the fluid, from a first color to a second color (or lack thereof) provides a visual indication to the user of the electrosurgical device  5  as to when a threshold fluid temperature below boiling has been achieved. Thermochromic dyes are available, for example, from Color Change Corporation, 1740 Cortland Court, Unit A, Addison, Ill. 60101. 
     It is also noted that the above mechanism (i.e., a change in the color of the fluid due to a dye) may also be used to detect when the fluid reaches a temperature which will facilitate tissue necrosis; this generally varies from about 60° C. for an exposure time of 0.01 seconds and decreasing to about 45° C. for an exposure time of 15 minutes. An exemplary target temperature/time for tissue necrosis is about 55° C. for an exposure time of about 1 second. 
     In order to reduce time, use of the electrosurgical device  5  in the region T=100° C. of  FIG. 2  is preferable to use of the electrosurgical device  5  in the region T&lt;100° C. Consequently, as shown in  FIG. 2 , another control strategy which may be employed for the electrosurgical device  5  is to adjust the power P and flow rate Q such that the power P used at a corresponding flow rate Q is equal to or more than the power P required to initiate boiling of the fluid, but still less than the power P required to boil 100% of the fluid. This control strategy targets using the electrosurgical device  5  in the region of  FIG. 2  identified as T=100° C., and includes the lines of the onset of boiling  76  and 100% boiling line  80 . That is, this control strategy targets using the electrosurgical device  5  on or between the lines of the onset of boiling  76  and 100% boiling line  80 , and not using the electrosurgical device  5  in the regions of  FIG. 2  identified as T&lt;100° C. and T&gt;&gt;100° C. 
     For consistent tissue effect, it is desirable to control the saline flow rate so that it is always on a “line of constant % boiling” as, for example, the line of the onset of boiling  76  or the 100% boiling line  80  or any line of constant % boiling located in between (e.g., 50% boiling line  78 ) as shown in  FIG. 2 . Consequently, another control strategy that can be used for the electrosurgical device  5  is to adjust power P and flow rate Q such that the power P used at a corresponding flow rate Q targets a line of constant % boiling. 
     It should be noted, from the preceding equations, that the slope of any line of constant % boiling is known. For example, for the line of the onset of boiling  76 , the slope of the line is given by (ρc p ΔT), while the slope of the 100% boiling line  80  is given by 1/(ρc p ΔT+ρh v ). As for the 50% boiling line  78 , for example, the slope is given by 1/(ρc p ΔT+ρh v 0.5). 
     If, upon application of the electrosurgical device  5  to the tissue, boiling of the fluid is not detected, such indicates that the temperature is less than 100° C. as shown by the area T&lt;100° C. of  FIG. 2 , and the flow rate Q must be decreased to initiate boiling if the power remains unchanged. The flow rate Q may be decreased until boiling of the fluid is first detected, at which time the line of the onset of boiling  76  is transgressed and the point of transgression on the line  76  is determined. From the determination of a point on the line of the onset of boiling  76  for a particular power P and flow rate Q, and the known slope of the line  76  as outlined above (i.e., 1/ρc p ΔT), it is also possible to determine the heat conducted to adjacent tissue  70 . 
     Conversely, if upon application of the electrosurgical device  5  to the tissue, boiling of the fluid is detected, such indicates that the temperature is approximately equal to 100° C. as shown by the area T=100° C. of  FIG. 2 , and the flow rate Q must be increased to reduce boiling until boiling stops, at which time the line of the onset of boiling  76  is transgressed and the point of transgression on the line  76  determined. As with above, from the determination of a point on the line of the onset of boiling  76  for a particular power P and flow rate Q, and the known slope of the line  76 , it is also possible to determine the heat conducted to adjacent tissue  70 . 
     With regards to the detection of boiling of the fluid, preferably such is physically detected by the user (e.g., visually by the naked eye) in the form of either bubbles or steam evolving from the fluid coupling at the electrode/tissue interface. Alternatively, such a phase change (i.e., from liquid to vapor or vice-versa) may be measured by a sensor which preferably senses either an absolute change (e.g., existence or non-existence of boiling with binary response such as yes or no) or a change in a physical quantity or intensity and converts the change into a useful input signal for an information-gathering system. For example, the phase change associated with the onset of boiling may be detected by a pressure sensor, such as a pressure transducer, located on the electrosurgical device  5 . Alternatively, the phase change associated with the onset of boiling may be detected by a temperature sensor, such as a thermistor or thermocouple, located on the electrosurgical device  5 , such as adjacent to the electrode. Also alternatively, the phase change associated with the onset of boiling may be detected by a change in the electric properties of the fluid itself. For example, a change in the electrical resistance of the fluid may be detected by an ohm meter; a change in the amperage may be measured by an amp meter; a change in the voltage may be detected by a volt meter; and a change in the power may be determined by a power meter. 
     Yet another control strategy which may be employed for the electrosurgical device  5  is to eliminate the heat conduction term  70  of equation (1) (i.e., ΔT/R). Since the amount of heat conducted away to adjacent tissue can be difficult to precisely predict, as it may vary, for example, by tissue type, it may be preferable, from a control point of view, to assume the worst case situation of zero heat conduction, and provide enough saline so that if necessary, all the RF power could be used to heat up and boil the saline, thus providing that the peak tissue temperature will not go over 100° C. significantly. This is shown in the schematic graph of  FIG. 3 . 
     Stated another way, if the heat conducted to adjacent tissue  70  is overestimated, the power P required to intersect the 100% boiling line  80  will, in turn, be overestimated and the 100% boiling line  80  will be transgressed into the T &gt;&gt;100° C. region of  FIG. 2 , which is undesirable as established above. Thus, assuming the worse case situation of zero heat conduction provides a “safety factor” to avoid transgressing the 100% boiling line  80 . Assuming heat conduction to adjacent tissue  70  to be zero also provides the advantage of eliminating the only term from equation (1) which is tissue dependent, i.e., depends on tissue type. Thus, provided ρ, c p , ΔT, and h v  are known as indicated above, the equation of the line for any line of constant % boiling is known. Thus, for example, the 98% boiling line, 80% boiling line, etc. can be determined in response to a corresponding input from selection switch  12 . In order to promote flexibility, it should be understood that the input from the selection switch preferably may comprise any percentage of boiling. Preferably the percentage of boiling can be selected in single percent increments (i.e., 100%, 99%, 98%, etc.). 
     Upon determination of the line of the onset of boiling  76 , the 100% boiling line  80  or any line of constant % boiling there between, it is generally desirable to control the flow rate Q so that it is always on a particular line of constant % boiling for consistent tissue effect. In such a situation, flow rate controller  11  will adjust the flow rate Q of the fluid  24  to reflect changes in power P provided by the generator  6 , as discussed in greater detail below. For such a use flow rate controller  11  may be set in a line of constant boiling mode, upon which the % boiling is then correspondingly selected. 
     As indicated above, it is desirable to control the saline flow rate Q so that it is always on a line of constant % boiling for consistent tissue effect. However, the preferred line of constant % boiling may vary based on the type of electrosurgical device  5 . For example, if with use of the device  5 , shunting through saline is not an issue, then it can be preferable to operate close to or directly on, but not over the line of the onset of boiling, such as  76   a  in  FIG. 3 . This preferably keeps tissue as hot as possible without causing desiccation. Alternatively, if with use of the device  5  shunting of electrical energy through excess saline is an issue, then it can be preferable to operate along a line of constant boiling, such as line  78   a  in  FIG. 3 , the 50% line. This simple proportional control will have the flow rate determined by equation (4), where K is the proportionality constant:
 
 Q   1   =K×P    (4)
 
     In essence, when power P goes up, the flow rate Q will be proportionately increased. Conversely, when power P goes down, the flow rate Q will be proportionately decreased. 
     The proportionality constant K is primarily dependent on the fraction of saline that boils, as shown in equation (5), which is equation (3) solved for K after eliminating P using equation (4), and neglecting the conduction term (ΔT/R): 
     
       
         
           
             
               
                 
                   K 
                   = 
                   
                     1 
                     
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                   ( 
                   5 
                   ) 
                 
               
             
           
         
       
     
     Thus, the present invention provides a method of controlling boiling of fluid, such as a conductive fluid, at the tissue/electrode interface. In a preferred embodiment, this provides a method of treating tissue without use of tissue sensors, such as temperature or impedance sensors. Preferably, the invention can control boiling of conductive fluid at the tissue/electrode interface and thereby control tissue temperature without the use of feedback loops. 
     In describing the control strategy of the present invention described thus far, focus has been drawn to a steady state condition. However, the heat required to warm the tissue to the peak temperature (T) may be incorporated into equation (1) as follows:
 
 P=ΔT/R+ρc   ρ   Q   1   ΔT+ρQ   b   h   v   +ρc   ρ   VΔT/Δt    (6)
 
     where ρc ρ VΔT/Δt represents the heat required to warm the tissue to the peak temperature (T)  68  and where:
         ρ=Density of the saline fluid that gets hot but does not boil (approximately 1.0 gm/cm 3 );   c ρ =Specific heat of the saline (approximately 4.1 watt-sec/gm-° C.);   V=Volume of treated tissue;   ΔT=(T−T ∞ ) the difference in temperature (° C.) between the peak tissue temperature (T) and the normal temperature (T ∞ ) of the body tissue; normal temperature of the body tissue is generally 37° C.; and   Δt=(t−t ∞ ) the difference in time to achieve peak tissue temperature (T) and the normal temperature (T ∞ ) of the body tissue (° C.).       

     The inclusion of the heat required to warm the tissue to the peak temperature (T) in the control strategy is graphically represented at  68  in  FIG. 4 . With respect to the control strategy, the effects of the heat required to warm the tissue to the peak temperature (T)  68  should be taken into account before flow rate Q adjustment being undertaken to detect the location of the line of onset of boiling  76 . In other words, the flow rate Q should not be decreased in response to a lack of boiling before at least a quasi-steady state has been achieved as the location of the line of onset of boiling  76  will continue to move during the transitory period. Otherwise, if the flow rate Q is decreased during the transitory period, it may be possible to decrease the flow Q to a point past the line of onset of boiling  76  and continue past the 100% boiling line  80  which is undesirable. In other words, as temperature (T) is approached the heat  68  diminishes towards zero such that the lines of constant boiling shift to the left towards the Y-axis. 
       FIG. 5  is an exemplary graph of flow rate Q versus % boiling for a situation where the RF power P is 75 watts. The percent boiling % is represented on the X-axis, and the saline flow rate Q (cc/min) is represented on the Y-axis. According to this example, at 100 % boiling the most desirable predetermined saline flow rate Q is 2 cc/min. Also according to this example, flow rate Q versus % boiling at the remaining points of the graft illustrates a non-linear relationship as follows: 
     
       
         
           
               
             
               
                 TABLE 1 
               
               
                   
               
               
                 % Boiling and Flow Rate Q (cc/min) at RF Power P of 75 watts 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
            
               
                   
                  0% 
                 17.4 
               
               
                   
                 10% 
                 9.8 
               
               
                   
                 20% 
                 6.8 
               
               
                   
                 30% 
                 5.2 
               
               
                   
                 40% 
                 4.3 
               
               
                   
                 50% 
                 3.6 
               
               
                   
                 60% 
                 3.1 
               
               
                   
                 70% 
                 2.7 
               
               
                   
                 80% 
                 2.4 
               
               
                   
                 90% 
                 2.2 
               
               
                   
                 100%  
                 2.0 
               
               
                   
                   
               
            
           
         
       
     
     Typical RF generators used in the field have a monopolar power selector switch to 300 watts of power, and on occasion some have been found to be selectable up to 400 watts of power. In conformance with the above methodology, at 0% boiling with a corresponding power of 300 watts, the calculated flow rate Q is 69.7 cc/min and with a corresponding power of 400 watts the calculated flow rate Q is 92.9 cc/min. Thus, when used with typical RF generators in the field, a fluid flow rate Q of about 100 cc/min or less with the present invention is expected to suffice for the vast majority of applications. 
     As discussed herein, RF power delivery to tissue can be unpredictable and vary with time, even though the generator has been “set” to a fixed wattage. The schematic graph of  FIG. 6  shows the general trends of the output curve of a typical general-purpose generator, with the output power changing as load impedance Z changes. Load impedance Z (in ohms) is represented on the X-axis, and generator output power P (in watts) is represented on the Y-axis. In the illustrated embodiment, the electrosurgical power (RF) is set to 75 watts in a bipolar mode. As shown in the figure, the power will remain constant as it was set as long as the impedance Z stays between two cut-offs, low and high, of impedance, that is, for example, between 50 ohms and 300 ohms in the illustrated embodiment. Below load impedance Z of 50 ohms, the power P will decrease, as shown by the low impedance ramp  28   a . Above load impedance Z of 300 ohms, the power P will decrease, as shown by the high impedance ramp  28   b . This change in output is invisible to the user of the generator and not evident when the generator is in use, such as in an operating room. 
       FIG. 7  shows the general trend of how tissue impedance generally changes with time for saline-enhanced electrosurgery. As tissue heats up, the temperature coefficient of the tissue and saline in the cells is such that the tissue impedance decreases until a steady-state temperature is reached upon which time the impedance remains constant. Thus, as tissue heats up, the load impedance Z decreases, potentially approaching the impedance Z cut-off of 50 ohms. If tissue is sufficiently heated, such that the low impedance cut-off is passed, the power P decreases along the lines of the low impedance ramp  28   a  of  FIG. 6 . 
     Combining the effects shown in  FIG. 6  and  FIG. 7 , it becomes clear that when using a general-purpose generator set to a “fixed” power, the actual power delivered can change dramatically over time as tissue heats up and impedance drops. Looking at  FIG. 6 , if the impedance Z drops from 100 to 75 ohms over time, the power output would not change because the curve is “flat” in that region of impedances. If, however, the impedance Z drops from 75 to 30 ohms one would transgress the low impedance cut-off and “turn the corner” onto the low impedance ramp  28   a  portion of the curve and the power output would decrease dramatically. 
     According to one exemplary embodiment of the invention, the control device, such as flow rate controller  11 , receives a signal indicating the drop in actual power delivered to the tissue and adjusts the flow rate Q of saline to maintain the tissue/electrode interface at a desired temperature. In a preferred embodiment, the drop in actual power P delivered is sensed by the power measurement device  8  (shown in  FIG. 1 ), and the flow rate Q of saline is decreased by flow rate controller  11  (also shown in  FIG. 1 ). Preferably, this reduction in saline flow rate Q allows the tissue temperature to stay as hot as possible without desiccation. If the control device was not in operation and the flow rate Q allowed to remain higher, the tissue would be over-cooled at the lower power input. This would result in decreasing the temperature of the tissue at the treatment site and lead to longer treatment time. 
     Flow rate controller  11  of  FIG. 1  can include a delay mechanism, such as a timer, to automatically keep the saline flow on for several seconds after the RF is turned off to provide a post-coagulation cooling of the tissue or “quench,” which can increase the strength of the tissue seal. Flow rate controller  11  can also include a delay mechanism, such as a timer, to automatically turn on the saline flow several seconds before the RF is turned on to inhibit the possibility of undesirable effects as tissue desiccation, electrode sticking, char formation and smoke production. Optionally, flow rate controller  11  can include a low level flow standby mechanism, such as a valve, which continues the saline flow at a standby flow level (which prevents the flow rate from going to zero when the RF power is turned off) below the surgical flow level ordinarily encountered during use of the electrosurgical device  5 . 
     An exemplary electrosurgical device of the present invention which may be used in conjunction with the system of the present invention is shown at reference character  5   a  in  FIG. 9 , and more particularly in  FIGS. 9-13 . While various electrosurgical devices of the present invention are described with reference to use with the remainder of the system of the invention, it should be understood that the description of the combination is for purposes of illustrating the remainder of the system of the invention only. Consequently, it should be understood that the electrosurgical devices of the present invention can be used alone, or in conjunction with the remainder of the system of the invention, or that a wide variety of electrosurgical devices can be used in connection with the remainder of the system of the invention. The electrosurgical devices disclosed herein are preferably further configured for both open and minimally invasive surgery, such as laparoscopic surgery. For laparoscopic surgery, the devices are preferably configured to fit through either a 5 mm or 12 mm trocar cannula. 
     As shown in  FIG. 8 , electrosurgical device  5   a  may be used in conjunction with a cannula as illustrated at reference character  19 , during laparoscopic surgery such as, for example, a laparoscopic cholecystectomy. Cannula  19  comprises a proximal portion  19   a  separated from a distal portion  19   b  by an elongated rigid shaft portion  19   c . Proximal portion  19   a  of cannula  19  preferably comprises a head portion  19   d  connected to rigid shaft portion  19   c , preferably by threaded engagement. Most importantly, cannula  19  has a working channel  19   e  which extends through head portion  19   d  and shaft portion  19   c  from proximal portion  19   a  to distal portion  19   b  of cannula  19 . In one particular embodiment, during insertion into cannula  19 , electrosurgical device  5   a  is configured to enter the proximal end of working channel  19   e , move along the channel  19   e  distally, and then be extended from the distal end of the working channel  19   e . In the same embodiment, during retraction from cannula  19 , electrosurgical device  5   a  is configured to enter the distal end of working channel  19   e , move along the channel  19   e  proximally, and then be removed from the proximal end of working channel  19   e.    
     Referring back to  FIG. 9 , as shown electrosurgical device  5   a  is a monopolar electrosurgical device. Electrosurgical device  5   a  preferably includes a rigid, self -supporting, hollow shaft  17 , a proximal handle comprising mating handle portions  20   a ,  20   b  and a tip portion as shown by circle  45 . Handle  20   a ,  20   b  is preferably made of a sterilizable, rigid, non-conductive material, such as a polymer (e.g., polycarbonate). As shown in  FIGS. 10 and 11 , tip portion  45  includes a contact element preferably comprising an electrode  25  which, as shown, comprises a solid ball having a smooth, uninterrupted surface. Tip portion  45  also comprises a sleeve  82  having a uniform diameter along its longitudinal length, a spring  88  and a distal portion of shaft  17 . As shown in  FIG. 10 , the longitudinal axis  31  of the tip portion  45  may be configured at an angle A relative to the longitudinal axis  29  of the proximal remainder of shaft  17 . Preferably, angle A is about 5 degrees to 90 degrees, and more preferably, angle A is about 8 degrees to 45 degrees. 
     As shown in  FIGS. 10 and 11 , for electrosurgical device  5   a , electrode  25  generally has a spherical shape with a corresponding spherical surface, a portion  42  of which is exposed to tissue  32  at the distal end of device  5   a . When electrode  25  is in the form of a sphere, the sphere may have any suitable diameter. Typically, the sphere has a diameter in the range between and including about 1 mm to about 7 mm, although it has been found that when a sphere is larger than about 4 mm or less than about 2 mm tissue treatment can be adversely effected (particularly tissue treatment time) due to an electrode surface that is respectively either to large or to small. Thus, preferably the sphere has a diameter in the range between and including about 2.5 mm to about 3.5 mm, more preferably, about 3 mm. 
     It is understood that shapes other than a sphere can be used for the contact element. Examples of such shapes include oblong or elongated shapes. However, as shown in  FIGS. 10 and 11 , preferably a distal end surface of electrosurgical device  5   a  provides a blunt, rounded surface which is non-pointed and non-sharp as shown by electrode  25 . 
     As shown in  FIGS. 10 and 11 , electrode  25 , is preferably located in a cavity  81  of a cylindrical sleeve  82  providing a receptacle for electrode  25 . Among other things, sleeve  82  guides movement of electrode  25 . Among other things, sleeve  82  also functions as a housing for retaining electrode  25 . 
     Also as shown in  FIG. 11 , a portion  44  of electrode  25 , is retained within cavity  81  while another portion  43  extends distally through the fluid outlet opening provided by circular fluid exit hole  26 . Also as shown, sleeve  82  is connected, preferably via welding with silver solder, to the distal end  53  of shaft  17 . For device  5   a , electrode  25 , sleeve  82  and shaft  17  preferably include, and more preferably are made at least almost essentially of, an electrically conductive metal, which is also preferably non-corrosive. A preferred material is stainless steel. Other suitable metals include titanium, gold, silver and platinum. Shaft  17  preferably is stainless steel hypo-tubing. 
     As for cavity  81 , the internal diameter of cavity  81  surrounding electrode  25  is preferably slightly larger than the diameter of the sphere, typically by about 0.25 mm. This permits the sphere to freely rotate within cavity  81 . Consequently, cavity  81  of sleeve  82  also preferably has a diameter in the range of about 1 mm to about 7 mm. 
     As best shown in  FIGS. 11 and 12 , in order to retain electrode  25 , within the cavity  81  of sleeve  82 , preferably the fluid exit hole  26 , which ultimately provides a fluid outlet opening, of cavity  81  at its distal end  83  comprises a distal pinched region  86  which is reduced to a size smaller than the diameter of electrode  25 , to inhibit escape of electrode  25  from sleeve  82 . More preferably, the fluid exit hole  26  has a diameter smaller than the diameter of electrode  25 . 
     As best shown in  FIG. 12 , fluid exit hole  26  preferably has a diameter smaller than the diameter of electrode  25 , which can be accomplished by at least one crimp  84  located at the distal end  83  of sleeve  82  which is directed towards the interior of sleeve  82  and distal to the portion  44  of electrode  25  confined in cavity  81 . Where one crimp  84  is employed, crimp  84  may comprise a single continuous circular rim pattern. In this manner, the contact element portion extending distally through the fluid outlet opening (i.e., electrode portion  43 ) provided by fluid exit hole  26  has a complementary shape to the fluid outlet opening provided by fluid exit hole  26 , here both circular. 
     As shown in  FIG. 12 , crimp  84  may have a discontinuous circular rim pattern where crimp  84  is interrupted by at least one rectangular hole slot  85  formed at the distal end  83  of sleeve  82 . Thus, the fluid outlet opening located at the distal end of the device  5   a  may comprise a first portion (e.g., the circular fluid exit hole portion  26 ) and a second portion (e.g., the slot fluid exit hole portion  85 ). As shown in  FIG. 12 , preferably, crimp  84  comprises at least four crimp sections forming a circular rim pattern separated by four discrete slots  85  radially located there between at 90 degrees relative to one another and equally positioned around the fluid outlet opening first portion. Slots  85  are preferably used to provide a fluid outlet opening or exit adjacent electrode  25 , when electrode  25  is fully seated (as discussed below) and/or when electrode  25  is not in use (i.e., not electrically charged) to keep surface portion  42  of the electrode surface of electrode  25  wet. Preferably, slots  85  have a width in the range between and including about 0.1 mm to 1 mm, and more preferably about 0.2 mm to 0.3 mm. As for length, slots  85  preferably have a length in the range between and including about 0.1 mm to 1 mm, and more preferably bout 0.4 mm to 0.6 mm. 
     As shown in  FIG. 12 , the contact element portion extending distally through the fluid outlet opening (i.e., electrode portion  43 ) extends distally through the fluid outlet opening first portion (e.g., the circular fluid exit hole portion  26 ) and does not extend distally through the fluid outlet opening second portion (e.g., the slot fluid exit hole portion  85 ). In this manner an edge  91  of slot  85  remains exposed to tissue  32  to provide a tissue separating edge as discussed below. 
     It should be understood that the particular geometry of fluid outlet opening provided by the fluid exit hole located at the distal end of device  5   a  to the electrode is not critical to the invention, and all that is required is the presence of a fluid exit hole which provides fluid  24  as required. For example, fluid exit hole  26  may have an oval shape while electrode  25  has a different shape, such as a round shape. 
     As shown in  FIG. 12 , in addition to slot  85  providing a fluid exit, at least one edge  91  of slot  85  may provide a tissue separating edge adjacent a blunt surface (e.g., surface portion  42  of electrode  25 ) which may be used for blunt dissection when the electrosurgical device  5   a  is manipulated, particularly by rotating (e.g., twirling), abrading or impacting. When edge  91  is used in such regard, it is preferred that the edge comprise a sharp edge with a sharp angle which has not been rounded by, for example, a fillet. 
     Turning to the proximal end of the tip (comprising electrode  25 , spring  88  and sleeve  82 ) of the device  5   a , as shown in  FIG. 11 , preferably the portion of sleeve  82  proximal to electrode  25 , also has a proximal pinched region  87  which retains electrode  25  in the cavity  81  of sleeve  82  and inhibits escape of electrode  25  from the cavity  81  of sleeve  82 , such as a diameter smaller than the diameter of electrode  25 . 
     While distal pinched region  86  and proximal pinched region  87  may be used solely to support electrode  25 , in its position of use, the electrode may be further supported by a compression spring  88  as shown in  FIG. 11 . The use of spring  88  is preferred to provide a variable length support within the working length of the spring  88  for overcoming manufacturing tolerances (e.g., length) between the fixed supports (i.e., pinched regions  86  and  87 ) of sleeve  82 . As for maintaining proper location of the spring  88 , sleeve  82  also comprises a lumen  89  as shown in  FIG. 11 , which, in addition to providing a direct passage for fluid, provides a guide tube for spring  88 . Furthermore, the surface portion  60  of electrode  25 , which contacts spring  88  may have a flat surface rather than a curvilinear surface to better seat the spring against electrode  25 . 
     In addition to the above, spring  88  provides a multitude of functions and advantages. For example, the configuration of the distal pinched region  86 , proximal pinched region  87  and spring  88  offers the ability to move electrode  25  distally and proximally within sleeve  82 . As shown in  FIG. 11 , spring  88  is located proximal to electrode  25  between a first load bearing surface comprising the electrode surface  60  and a second load bearing surface comprising the distal end  53  of shaft  17 . In this manner, spring  88  can be configured to provide a decompression force to seat electrode  25  against the distal pinched region  86 , in this case the perimeter edge  92  of crimp  84 , prior to use of electrosurgical device  5   a.    
     Conversely, upon application of electrode  25  against surface  22  of tissue  32  with sufficient force to overcome the compression force of the spring  88 , spring  88  compresses and electrode  25  retracts proximally away from distal pinched region  86 , in this case perimeter edge  92  of crimp  84 , changing the position thereof. In the above manner, the contact element comprising electrode  25  is retractable into the cavity  81  of the housing provided by sleeve  82  upon the application of a proximally directed force against surface  42  of the portion  43  of electrode  25  extending distally beyond the distal opening  26  located at the distal end  83  of the housing and spring  88  functions as a retraction biasing member. 
     By making electrode  25  positionable in the above manner via spring  88 , electrosurgical device  5   a  can be provided with a damper mechanism which dampens the force of electrode  25  on tissue  32  being treated. 
     Furthermore, electrode  25  which can be positioned as outlined above can comprise a fluid flow rate adjustment mechanism which incrementally increases the area of fluid exit hole  26  and the corresponding fluid flow rate in response to the incremental proximal retraction of electrode  25 . In such an instance, electrode  25  functions as a valve by regulating flow of fluid  24  through fluid exit hole  26 . 
     In various embodiments, spring  88  may be used in conjunction with the distal pinched region  86  (e.g., crimp  84  comprising a single continuous circular pattern) to provide a fluid seal between electrode  25  and the distal pinched region  86  which stops fluid flow from the electrosurgical device  5   a . In this manner, the electrosurgical device  5   a  may be used to provide both a wet electrode and dry electrode (i.e., when the fluid flow is on and off, respectively) with the energy and fluid provided sequentially as opposed to simultaneously. 
     Furthermore, in various embodiments of electrosurgical device  5   a , an electrode  25  which can be positioned as outlined above can include a declogging mechanism. Such a mechanism can retract to provide access for unclogging fluid exit holes (e.g.,  26  and  85 ), which may become flow restricted as a result of loose debris (e.g., tissue, blood, coagula) becoming lodged therein. For example, when a biasing force, such as from a handheld cleaning device (e.g., brush) or from pushing the distal tip against a hard surface such as a retractor, is applied to surface  42  of electrode  25  which overcomes the compression force of the spring  88  causing the spring  88  to compress and electrode  25  to retract, the tip of the handheld cleaning device may by extended into the fluid exit hole  26  for cleaning the fluid exit hole  26 , perimeter edge  92 , slot  85  and edge  91 . Stated another way, electrode  25 , which can be positioned as outlined, provides a methodology for declogging a fluid exit hole by increasing the cross-sectional area of the fluid exit hole to provide access thereto. 
     Additionally, in various embodiments of device  5   a , spring  88  comprises an electrical conductor, particularly when electrode  25 , is retracted to a non-contact position (i.e., not in contact) with sleeve  82 . 
     In other embodiments, proximal pinched region  87  may comprise one or more crimps similar to distal pinched region  86 , such that electrode  25  is retained in sleeve  82  both distally and proximally by the crimps. Also, in other embodiments, sleeve  82  may be disposed within shaft  17  rather than being connected to the distal end  53  of shaft  17 . Also, in still other embodiments, sleeve  82  may be formed unitarily (i.e., as a single piece or unit) with shaft  17  as a unitary piece. 
     As best shown in  FIGS. 10 and 11 , electrode  25  is retained in sleeve  82  with a portion  43  of electrode  25  extending distally beyond distal end  83  of sleeve  82 . As shown, preferably the surface  42  of this exposed portion  43  of electrode  25  is blunt and does not have any sharp corners. Also, the portion  43  of electrode  25  which extends distally beyond the distal end  83  of sleeve  82  is controlled by the shape of the fluid exit hole  26  in sleeve  82  in relation to the shape of electrode  25 . In other words, the portion  43  of electrode  25  that extends distally beyond distal end  83  of sleeve  82  is controlled by the contact of the electrode surface with the edge  92 . 
     In locations where shaft  17  and sleeve  82  are electrically conductive (for device  5   a , preferably shaft  17  and sleeve  82  are completely electrically conductive and do not comprise non-conductive portions) an electrical insulator  90  (i.e., comprising non-conductive or insulating material) preferably surrounds shaft  17  and sleeve  82  along substantially its entire exposed length (e.g., the portion outside the confines of the handle  20 ), terminating a short distance (e.g., at the proximal onset of crimp  84  or less than about 3 mm) from distal end  83  of sleeve  82 . Insulator  90  preferably comprises a shrink wrap polymer tubing. 
     As with the other electrosurgical devices described within, a input fluid line  4   b  and a power source, preferably comprising generator  6  preferably providing RF power via cable  9 , are preferably fluidly and electrically coupled, respectively, to the tip portion  45  of the electrosurgical device  5   a.    
     As indicated above, device  5   a  comprises a monopolar device. For electrosurgical device  5   a , electrode  25  provides an active electrode, while a ground pad dispersive electrode  125  (shown in  FIG. 45 ) located on the patient, typically on the back or other suitable anatomical location, provides a return electrode. Preferably, both electrodes are electrically coupled to generator  6  to form an isolated electrical circuit. Preferably the active electrode is coupled to generator  6  via a wire conductor from insulated wire cable  9  to the outer surface  18  of shaft  17  within the confines of handle  20   a ,  20   b , typically through a switch such as  15   a.    
     Switch  15   a  preferably comprises a dome switch having two electrical contacts. The contacts preferably comprise upper and lower contacts disposed on a platform in overlying relationship. Preferably the upper contact comprises a dome shaped configuration overlying and spaced from the lower contact which is flat. Preferably the contacts are spaced from one another by virtue of the domed configuration of the upper contact when the switch  15   a  is in an undepressed position, thus creating an open control circuit relative to switch  15   a . However, when the upper contact is pressed into a depressed position, the upper contact comes into contact with the lower contact thus closing the hand switch control circuit. The presence of the closed control circuit is then sensed by generator  6  which then provides power to the electrode  25 . 
     When a depression force is removed from the upper contact, the contact returns to its undepressed domed position as a result of its resiliency or elastic memory, thus returning switch  15   a  to its undepressed position and reopening the hand control circuit. The presence of the open control circuit is then sensed by the generator which then stops providing power to electrode  25 . 
     In some embodiments, shaft  17  may be made of an electrical non-conducting material except for a portion at its distal end  53  that comes in contact with sleeve  82 . This portion of shaft  17  that contacts sleeve  82  should be electrically conducting. In this embodiment, the wire conductor from insulated wire cable  9  extends to this electrically conducting portion of shaft  17 . In still other embodiments, shaft  17  may completely comprise a non-conducting material as where the wire conductor from insulated wire cable  9  extends directly to sleeve  32 . 
     With respect to the fluid coupling, fluid  24  from the fluid source  1  preferably is communicated from fluid source  1  through a flexible, polyvinylchloride (PVC) outlet fluid line  4   a  to a flexible, polyvinylchloride (PVC) inlet fluid line  4   b  connected to electrosurgical device  5   a . Outlet fluid line  4   a  and inlet fluid line  4   b  are preferably connected via a male and female mechanical fastener configuration; a preferred such connection is a Luer-Lok® connection from Becton, Dickinson and Company. The lumen of the inlet line is then preferably interference fit over the outside diameter of shaft  17  to provide a press fit seal there between. An adhesive may be used there between to strengthen the seal. Fluid  24  is then communicated down lumen  23  of shaft  17  through lumen  89  and cavity  81  of sleeve  82  where it is expelled from around and on the exposed surface  42  of electrode  25 . This provides a wet electrode for performing electrosurgery. 
     As shown in  FIG. 13 , during use of electrosurgical device  5   a , typically a fluid coupling  30  preferably comprising a discrete, localized web and more preferably comprising a triangular shaped web or bead portion providing a film of fluid  24  is provided between surface  22  of tissue  32  and electrode  25 . When the user of electrosurgical device  5   a  places electrode  25  at a tissue treatment site and moves electrode  25  across the surface  22  of the tissue  32 , fluid  24  is expelled around and on surface  42  of electrode  25  at the distal end  83  of sleeve  82  and onto the surface  22  of the tissue  32  via coupling  30 . The fluid  24 , in addition to providing an electrical coupling between electrosurgical device  5   a  and tissue  32 , lubricates surface  22  of tissue  32  and facilitates the movement of electrode  25  across surface  22  of tissue  32 . During movement of electrode  25 , electrode  25  typically slides across surface  22  of tissue  32 , but also may rotate as electrode  25  moves across surface  22  of tissue  32 . Typically the user of the electrosurgical device  5   a  slides the electrode across surface  22  of tissue  32  back and forth with a painting motion while using fluid  24  as, among other things, a lubricating coating. Preferably the thickness of the fluid  24  between the distal end surface of electrode  25  and surface  22  of tissue  32  at the outer edge of the coupling  30  is in the range between and including about 0.05 mm to 1.5 mm, more preferably in the range between and including about 0.1 mm to 0.3 mm. Also preferably, in certain embodiments, the distal end tip of electrode  25  contacts surface  22  of tissue  32  without any fluid  24  in between. 
     Another exemplary electrosurgical device is shown at reference character  5   b  in  FIGS. 14-16 . In this embodiment, electrical insulator  90  preferably terminates proximally to sleeve  82  where sleeve  82  is connected to the distal end  53  of shaft  17 . In certain embodiments where sleeve  82  is formed unitary shaft  17 , electrical insulator  90  preferably terminates proximally to proximal pinched region  87 . In this manner, in addition to the spherical surface portion  42  of electrode  25  and the narrowing surface portion  41 , here conical, of sleeve  82  being used for treating tissue  32  when exposed thereto, a cylindrical surface  40  of a cylindrical portion  39  of sleeve  82  and a broadening surface portion  47  of broadening portion  54 , here both conical, of sleeve  82  also function as electrode surfaces for treating tissue. Thus, the electrode exposed to tissue  32  now comprises a cylindrical surface portion  40  and a broadening surface portion  47  in addition to the spherical surface portion  42  and the narrowing surface portion  41 , with the cylindrical surface portion  40  substantially increasing the surface area of the electrode. As a result, electrode  25  has surfaces which are parallel and perpendicular to the longitudinal axis  31  of tip portion  45 , and more particularly, sleeve  82  of electrosurgical device  5   b . In the above manner, front end use (e.g., surfaces  41  and  42 ), sideways use (e.g., surface  40  and  47 ), or oblique use (e.g., surfaces  40 ,  41  and  42 ) of electrosurgical device  5   b  is facilitated. 
     In the above manner, tip portion  45  now includes a first tissue treating surface (e.g., distal end spherical surface  42 ) and a second tissue treating surface (e.g., side surface  40 ). As discussed above, preferably the first tissue treating surface is configured for blunt dissection while the second tissue treating surface is configured for coagulation. Additionally, tip portion  45  also has a third tissue treating surface (e.g., surface  41 ) located between the first tissue treating surface (e.g., surface  42 ) and a second tissue treating surface (e.g., surface  40 ). Furthermore, tip portion  45  also has a fourth tissue treating surface (e.g., surface  47 ) located proximal and adjacent to surface  40 . 
     With device  5   a , when electrode  25  is placed directly in contact with surface  22  of tissue  32 , tissue  32  may occlude fluid flow from fluid exit holes  26 ,  85  located at the distal end of device  5   a . Consequently, for device  5   b  fluid exit holes  93 ,  94  may be located in the cylindrical side portion  39  of sleeve  82 , either proximal or adjacent to electrode  25 , and either in addition to or as an alternative to fluid exit holes  26 ,  85 . 
     As shown in  FIGS. 14 and 15 , at least one fluid exit hole  93  is preferably formed in the cylindrical longitudinal side surface  40  and through the wall of side portion  39  of sleeve  82  adjacent to electrode  25  when electrode  25  is fully seated. Furthermore, preferably at least one fluid exit hole  94  is formed in the cylindrical side portion  39  of sleeve  82  proximal to electrode  25  when electrode  25  is fully seated. 
     Preferably, holes  93 ,  94  each has more than one hole which are equally spaced radially in a circular pattern around the longitudinal axis  31  of tip portion  45 , and more particularly sleeve  82 . More preferably, holes  93 ,  94  each comprise four discrete holes equally spaced 90 degrees around the cylindrical side portion  39  of sleeve  82 . Preferably holes  93 ,  94  have a diameter in the range between and including about 0.1 mm to 1.0 mm, and more preferably have a length in the range between and including about 0.2 mm to 0.6 mm. 
     Electrode  25 , which can be positioned as outlined above, can comprise not only a valve for regulating fluid flow from the fluid exit holes, such as fluid exit hole  26 , but also comprise a valve which, while opening one fluid flow exit, simultaneously closes another fluid flow exit. For example, as electrode  25  retracts proximally, fluid exit hole  26  is opened while fluid exit hole  93  is closed. Stated another way, an electrode  25  which can be positioned as outlined above can provide a mechanism for altering the size and/or location of the fluid exit holes during use of electrosurgical device  5   b  which may be necessary, for example, to direct fluid to a particular tissue location or balance fluid flow among the fluid exit outlets. 
     Thus, as shown in  FIGS. 14 and 15 , surfaces  40 ,  41  and  47  of sleeve  82 , and surface  42  of electrode  25  are all active electrode surfaces and can provide electrical energy to tissue  32 . Portions of this combined electrode surface can be wet by fluid flow from holes  26 ,  94  or  93 , as well as from the hole slots  85  in crimp  84  adjacent electrode  25 . 
     The holes  94 ,  93  in the cylindrical sleeve  82  of the overall electrode surface are intended to assure that fluid  24  is provided to the smooth, less rough, atraumatic sides of the electrode that may be predominately used for tissue coagulation and hemostasis (e.g., surfaces  40  and  47 ) rather than blunt dissection (e.g., surfaces  41  and  42 ). The most distal portion of the device may have a more rough, but also wetted, electrode surface that can blunt dissect as well as coagulate tissue. 
     The electrode configuration shown in  FIGS. 14 and 15  is particularly useful to a surgeon performing a liver resection. Once the outer capsule of the liver is scored with a dry bovie blade along the planned line of resection the distal tip of tip portion  45  is painted back and forth along the line, resulting in coagulation of the liver parenchyma beneath the scored capsule. As the tissue is coagulated under and around the electrode surfaces  40 ,  41  and  42 , the electrode is used to blunt dissect into the coagulated parenchyma, with edge  91  of slots  85  around crimp  84  providing roughness elements that aid in disrupting the tissue  32  and enabling the parting of tissue  32 . 
     As shown in  FIG. 16 , the device  5   b  can be used in a crevice  97  of tissue  32  to blunt dissect tissue  32  and coagulate it at the same time. Blunt dissection is preferred over sharp dissection, such as with a blade or scissors, since blunt dissection is less likely to tear or damage the larger blood vessels or other vessels. Once identified by blunt dissection, very large vessels can be safely clipped, tied with suture or sealed with some other device. If the larger vessels are not thus first “skeletonized” without being damaged by blunt dissection, they may bleed profusely and require much more time to stop the bleeding. The device can also be used to coagulate first without simultaneous blunt dissection, and then blunt dissect in a separate step. 
     This technique can also be used on other parenchymal organs such as the pancreas, the kidney, and the lung. In addition, it may also be useful on muscle tissue and subcutaneous fat. Its use can also extend to benign tumors, cysts or other tissue masses found in the urological or gynecological areas. It would also enable the removal of highly vascularized tumors such as hemangiomas. 
     In  FIG. 16  the zone  99  identifies the part of the electrode that has the ability to blunt dissect and coagulate, and the zone  98  identifies the part that is intended primarily for coagulation and hemostasis. The line  100  indicates the depth of the zone of tissue that is coagulated, typically from 3 mm to 5 mm deep. 
     For the devices disclosed herein, the presence of various fractions of boiling can be visually estimated by the naked eye, or by detecting changes in electrical impedance.  FIG. 17  shows a graph of electrical impedance Z versus time t. The impedance spikes  101  shown in  FIG. 17  occur at a frequency of about 1 cycle per second and with an amplitude that is on the same order as the baseline impedance. This frequency is shown in  FIG. 17  as the interval  102  between successive impedance spikes. Impedance is directly measurable by dividing the voltage by the current as previously described. The use of electrical impedance to detect the onset of tissue dessication when impedance rises dramatically as a result of being heated to the point of smoking and charring, but not to detect the presence of boiling, is described above. 
     Shown in  FIG. 18  is the qualitative nature of the boiling as the % boiling increases, indicated by the small figures for each of five exemplary “regimes” of boiling. In each small figure a portion of the tip of the tip portion  45  of device  5   a  is shown in close proximity to tissue  32 . As boiling begins in regime  104 , there are few small bubbles  37  of vapor in the conductive fluid  24 , here saline, of coupling  30 . As the percentage of boiling increases at regime  106  there are a larger number of small bubbles  37 . As the percentage boiling increases further at regime  107 , the bubbles  37  become much larger. At even higher percentage boiling at regime  108  intermittent threads of saline form and are quickly boiled off. Finally, at the highest level of regime  109 , drops  36  of saline are instantly boiled upon contacting the hot surface  22  of tissue  32  and arcing occurs from the metal to tissue  32 . 
     Returning to  FIGS. 14 and 15 , fluid outlet openings are provided by substantially linear through holes  93 ,  94  which provide conductive fluid  24  to the treatment site. However, in an alternative embodiment, as shown in  FIG. 19 , fluid outlet openings in sleeve  82  may be provided by holes in the form of tortuous and interconnected pathways  59 , which are formed in a material pervious to the passage of fluid  24 , therethrough, such as a porous material. The discrete, linear through holes  93 ,  94  may be either supplemented with or replaced by a plurality of tortuous, interconnected pathways  59  formed in the porous material which, among other things, provides porous surfaces  40 ,  41  and  47  to more evenly distribute fluid flow and provide the conductive fluid  24  to tissue  32  at the treatment site. According to the invention, all or a portion of sleeve  82  may comprise a material pervious to the passage of fluid  24  therethrough as disclosed herein. 
     In certain embodiments, the contact element, here electrode  25  may also comprise a material pervious to the passage of fluid  24 , therethrough, such as a porous material (e.g., metal, polymer or ceramic) to provide the tortuous pathways  59 . In these embodiments, the porous structure of electrode  25  allows fluid  24  to not only pass around electrode  25  on the outer porous surface  42  to be expelled, but also allows fluid  24  to pass through electrode  25 , to be expelled. According to the invention, all or a portion of the electrodes or any particular electrodes for treating tissue  32  may comprise a material pervious to the passage of fluid  24  therethrough as disclosed herein. 
     Where the contact element and sleeve provide electrodes for treating tissue and compromise a porous material, preferably the porous material further comprises porous metal. Porous sintered metal is available in many materials (such as, for example, 316L stainless steel, titanium, Ni-Chrome) and shapes (such as cylinders, discs, plugs) from companies such as Porvair, located in Henderson, N.C. 
     While the electrode provided by contact element and/or sleeve preferably comprises an electrically conductive material such as metal, a non-electrically conductive porous contact element and/or sleeve, such as porous polymers and ceramics, can be used to replace an electrically conductive contact element and/or sleeve. While the porous polymers and ceramics are generally non-conductive, they may also be used to conduct the RF energy through the porous polymer and ceramic thickness and porous surface to the tissue to be treated by virtue of conductive fluid  24  contained within the plurality of interconnected tortuous pathways  59 . 
     Preferably the porous material provides for the wicking (i.e., drawing in of fluid by capillary action or capillarity) of the fluid  24  into the pores of the porous material. In order to promote wicking of the fluid  24  into the pores of the porous material, preferably the porous material, and in particular the surface of the tortuous pathways, is hydrophilic. The porous material may be hydrophilic with or without post treating (e.g., plasma surface treatment such as hypercleaning, etching or micro-roughening, plasma surface modification of the molecular structure, surface chemical activation or crosslinking), or made hydrophilic by a coating provided thereto, such as a surfactant. 
     Though not preferable, it is not necessary that fluid coupling  30  of fluid  24  be present in between the metal electrode surfaces (e.g.,  40 ,  41 ,  42 ) and tissue  32  at all locations of tissue treatment and there may be points of direct tissue contact by the electrode surfaces without any fluid coupling  30  therebetween. In such an instance, the convective cooling of the metal electrode by flowing saline is often sufficient to keep the metal electrode and tissue contacting the metal electrode at or below a temperature of 100° C. In other words, heat may be also first dissipated from tissue  32  to the electrodes by conduction, then dissipated from the electrodes to the fluid  24  by convection. 
     Preferably the relationship between the material for electrodes particularly their surfaces (e.g.,  40 ,  41 ,  42 ,  47 ), and fluid  24  throughout the various embodiments should be such that the fluid  24  wets the surface of the electrodes to form a continuous thin film coating thereon (for example, see  FIG. 21 ) and does not form isolated rivulets or circular beads (e.g., with a contact angle, θ greater than 90 degrees) which freely run off the surface of the electrode. Contact angle, θ, is a quantitative measure of the wetting of a solid by a liquid. It is defined geometrically as the angle formed by a liquid at the three phase boundary where a liquid, gas and solid intersect. In terms of the thermodynamics of the materials involved, contact angle θ involves the interfacial free energies between the three phases given by the equation γ LV  cos θ=γ SV   −γ   SL  where γ LV , γ SV  and γ SL  refer to the interfacial energies of the liquid/vapor, solid/vapor and solid/liquid interfaces, respectively. If the contact angle θ is less than 90 degrees the liquid is said to wet the solid. If the contact angle is greater than 90 degrees the liquid is non-wetting. A zero contact angle θ represents complete wetting. Thus, preferably the contact angle is less than 90 degrees. 
     For clarification, while it is known that the contact angle θ may be defined by the preceding equation, in reality, contact angle θ is determined by various models, to an approximation. According to the publication entitled “Surface Energy Calculations” (dated Sep. 13, 2001) from First Ten Angstroms (465 Dinwiddie Street, Portsmouth, Va. 23704), there are five models which are widely used to approximate contact angle θ and a number of others which have small followings. The five predominate models and their synonyms are: (1) Zisman critical wetting tension; (2) Girifalco, Good, Fowkes, Young combining rule; (3) Owens, Wendt geometric mean; (4) Wu harmonic mean; and (5) Lewis acid/base theory. Also according to the First Ten Angstroms publication, for well-known, well characterized surfaces, there can be a 25% difference in the answers provided for the contact angle θ by the models. Also for clarification, any one of the five predominate models above which calculates a contact angle θ within a particular range of contact angles θ or the contact angle θ required of a particular embodiment of the invention should be considered as fulfilling the requirements of the embodiment, even if the remaining four models calculate a contact angle θ which does not fulfill the requirements of the embodiment. 
     The effects of gravity and surface tension tend to wick the fluid  24 , here saline, around the circumference of the cylindrical sleeve  82  to preferably cover the entire active electrode surface. More specifically, the effects of gravity and surface tension on fluid  24  which is located on the electrode surfaces may be modeled by the Bond number N BO . Bond number N BO  measures the relationship of gravitational forces to surface tension forces and may be expressed as:
 
 N   BO   =ρL   2   g/σ   (7)
 
where:
         ρ=Density of the saline fluid (approximately 1.0 gm/cm 3 );   L=Droplet diameter (cm);   g=Gravitational acceleration (980 cm/s 2 ); and   ν=Surface tension (approximately 72.8 dynes/cm @20° C.)       

     For a Bond number N BO =1, the droplet diameter is equal to about 0.273 cm or about 2.7 mm, which is in the same order of magnitude as the preferred size of the electrode. For the purposes of the present invention, preferably Bond number N BO  for a droplet of fluid  24  on a surface of electrode  25  is preferably less than 1. 
     Another tip portion of an exemplary electrosurgical device  5   c  of the present invention which may be used in conjunction with the system of the present invention is shown at reference character  45  in  FIGS. 20-24 . As best shown in  FIGS. 20 and 21 , the separate sleeve  82  of embodiments  5   a  and  5   b  has been eliminated from tip portion  45  of device  5   c . Consequently, the contact element, still preferably comprising an electrode  25 , is assembled directly with the shaft  17 . Electrode  25  is preferably assembled (e.g., mechanically connected via press fit, mechanical connector, threaded, welded, adhesively bonded) adjacent the distal end  53  of shaft  17 . In certain embodiments, electrode  25  preferably is detachably assembled to the shaft  17  such that it may be removed from the shaft  17 , preferably manually by human hand, so that the shaft  17  may be used with multiple different contact elements/electrodes, or the shaft  17  may be reuseable and used with disposable contact elements/electrodes. 
     As shown in  FIGS. 20-24 , electrode  25  preferably comprises an enlarged head portion comprising a spherical portion  43  and a corresponding spherical surface portion  42  located at the distal end of the device  5   c  which provide a smooth, blunt contour outer surface. More specifically, as shown, the spherical portion  43  and spherical surface portion  42  further provide a domed, hemisphere (i.e., less than a full sphere) and hemispherical surface portion comprising preferably about 180 degrees. 
     Also as shown in  FIGS. 20-24 , the enlarged head portion of electrode  25  preferably also comprises a cylindrical portion  39  and a corresponding cylindrical surface portion  40  located proximal and adjacent to the spherical portion  43  and spherical surface portion  42 , respectively. 
     Further continuing with  FIGS. 20-24 , electrode  25  preferably comprises a connector portion, preferably comprising a shank  46 , which connects the remainder of electrode  25  to the shaft  17 . Among other things, the connector portion of electrode  25  is preferably configured to form a connection with a mating connector portion of the shaft  17 . As shown, preferably the shank portion  46  is configured to extend into cavity  50  of shaft  17  which comprises a cylindrical receptacle and provides the mating connector portion for shank  46 . More preferably, surface  48  of the shank portion  46  is configured to mate against and form an interference fit with surface  52  of cavity  50  to provide the connection. 
     Continuing with  FIGS. 20-24 , shank portion  46  is preferably cylindrical and located proximal and adjacent to a neck portion  56 . As shown, neck portion  56  comprises a cylindrical portion  57  (having a corresponding cylindrical surface portion  58 ) and a broadening portion  54  (having a corresponding broadening surface portion  47 ). Here broadening portion  54  and corresponding broadening surface portion  47  are both spherical, and more specifically comprise a domed, hemisphere and hemispherical surface portion comprising preferably about 180 degrees, located proximal and adjacent to the cylindrical portion  39  and cylindrical surface portion  40 . 
     Preferably, cylindrical portion  39  has a diameter in the range between and including about 1 mm to about 7 mm, although it has been found that when cylindrical portion  39  is larger than about 4 mm or less than about 2 mm, tissue treatment can be adversely effected (particularly tissue treatment time) due to an electrode surface that is respectively either to large or to small. Thus, preferably the cylindrical portion  39  has a diameter in the range between and including about 2.5 mm to about 3.5 mm, and more preferably, about 3 mm. 
     With respect to length, preferably cylindrical portion  39  has a length in the range between and including about 2 mm to about 8 mm, and more preferably has a length in the range between and including about 3 mm to about 5 mm. Even more preferably, cylindrical portion  39  has a length of about 4.5 mm. 
     As shown in  FIGS. 20-24 , the cylindrical portion  57  of neck portion  56  preferably has a cross-sectional dimension, here diameter, greater than the cross-sectional dimension, here also diameter, of the shank  46 . In this manner, in certain embodiments, the proximal end of the neck portion  56  may be located adjacent and in contact with the distal end  53  of shaft  17 . Preferably, cylindrical portion  57  has a diameter in the range between and including about 2 mm to about 2.5 mm and the shank  46  has a diameter in the range between and including about 1.4 mm to about 1.9 mm. More preferably, cylindrical portion  57  has a diameter of about 2.2 mm and the shank  46  has a diameter of about 1.6 mm. 
     With respect to length, preferably cylindrical portion  57  has a length in the range between and including about 1 mm to about 8 mm, and more preferably has a length in the range between and including about 3 mm to about 5 mm. Even more preferably, cylindrical portion  57  has a length of about 4 mm. Shank  46  preferably has a length in the range between and including about 2 mm to about 6 mm, and more preferably has a length in the range between and including about 2.5 mm to about 5 mm. Even more preferably, shank  46  has a length of about 3 mm. 
     Also as shown in  FIGS. 20-24 , electrode  25  comprises at least one recess  64  which provides an elongated fluid flow channel for the distribution of fluid  24 . The use of device  5   c , and in particular recesses  64 , for the distribution of fluid  24  is generally preferred to the fluid exit holes  93 ,  94  of device  5   b  in particularly deep tissue crevices  97 . 
     As shown, electrode  25  preferably comprises a plurality of longitudinally directed recesses  64  and, more specifically, four recesses  64  equally spaced 90 degrees around the shank  46  and/or neck portion  56 , both proximal of cylindrical portion  39 . As best shown in  FIG. 24 , in certain embodiments, the recess  64  may comprise a first side wall  64   a , a second opposing side wall  64   b , and a bottom wall  64   c . Preferably, recess  64  has a width in the range between and including about 0.1 mm to about 0.6 mm, and more preferably has a width of about 0.4 mm. 
     In use, when tissue  32  overlies and occludes the fluid outlet opening  55  of recess  64  for a portion of its longitudinal length, thus inhibiting fluid  24  from exiting therefrom, fluid  24  from recess  64  may still be expelled from the electrosurgical device  5   c  after flowing longitudinally in the channel  64  to a remote location where the channel  64  is unoccluded and uninhibited to fluid flow exiting therefrom. 
     On very rare occasion, it may be possible that the recess  64  may be occluded by tissue  32  completely along its longitudinal length, thus completely inhibiting fluid flow from exiting through opening  55 . In order to overcome this problem, at least a portion of electrode  25  may comprise a material pervious to the passage of fluid  24 , therethrough, such as a porous material described above. 
     Of the monopolar devices disclosed herein, device  5   c  has been found to be particularly useful to a surgeon performing a liver resection. Once the outer capsule of the liver is scored with a dry bovie blade along the planned line of resection, the distal tip of tip portion  45  is painted back and forth along the line, with radio frequency power and the flow of fluid  24  on, resulting in coagulation of the liver parenchyma. Once the tissue is coagulated under and around the electrode surface  42  and, as the device  5   c  enters crevice  97  as shown in  FIG. 22 , surfaces  40  and  42  of electrode  25  are used to blunt dissect the coagulated parenchyma. Blunt dissection of the coagulated parenchyma is performed by continuous abrading or splitting apart of the parenchyma with the substantially the same back and forth motion as coagulation and with the device  5   c  being held substantially in the same orientation as for coagulation of the liver parenchyma. However, with blunt dissection, the surgeon typically applies more force to the tissue. In various embodiments, once the liver parenchyma is coagulated, blunt dissection may be performed with or without the radio frequency power (i.e., on or off) and/or with or without the presence of fluid  24 . 
     As shown in  FIG. 25 , in another embodiment of the electrosurgical device of the present invention, as shown at reference character  5   d  in  FIG. 25 , the walls  64   a ,  64   b  of recess  64 , surface  48  of the shank portion  46 , and/or the surfaces of the neck portion  56  of electrode  25  may be porous and connected by a plurality of tortuous pathways  59  in the porous material. Consequently, rather than flowing out of recess  64  from a direct fluid outlet opening  55 , which may be occluded by tissue  32 , the fluid  24  may exit indirectly from recess  64  by first flowing through tortuous pathways  59  of electrode  25  from side walls  64   a ,  64   b  of the recess  64  and then exit electrode  25  from surface  58 , which may be in unoccluded by tissue  32 . Alternatively, if adjacent surface  58  of electrode  25  is also occluded by tissue  32 , the fluid  24  may continue to flow through tortuous pathways  59  of electrode  25  and exit electrode  25  from a surface  64   a ,  64   b  of a recess  64  or surface such as  40 ,  42 ,  47  or  58  which may be in unoccluded by tissue  32 . 
     Where electrode  25  comprises a porous material, recess  64  may be either supplemented with or replaced by the plurality of tortuous, interconnected passages  59  formed in the porous material as shown in  FIG. 25 . All or a portion of the electrodes can be porous according to the invention. 
     In other embodiments of the invention, recess  64  may comprise cross-sectional shapes other than rectangular shapes. For example, as shown in  FIGS. 26-28  recess  64  comprises a semi-circular shape, a V-shape, or a U-shape respectively, or any combination thereof. 
     Returning to  FIG. 21 , in order to facilitate direct fluid communication of recess  64  with lumen  23  of shaft  17 , preferably recesses  64  of device  5   c  are initiated within the confines of shaft  17 . In other words, within the cavity  50  of shaft  17  proximal to distal end  53 . As indicated above, the use of device  5   c , and in particular recesses  64 , for the distribution of fluid  24  is generally preferred to the fluid exit holes  93 ,  94  of device  5   b  in deep tissue crevices  97  where tissue  32  can occlude fluid flow from the fluid exit holes  93 ,  94  located in the cylindrical portion  39  of electrode  25 . Also, since holes  93 ,  94  are not presented with a declogging mechanism, such as provided for such as fluid exit holes  26  and  85 , holes such as  93 ,  94  that can be simply occluded by ordinary tissue/electrode contact will sooner or later become irreversibly clogged. 
     As shown in  FIG. 21 , with device  5   c  fluid outlet openings  73  are provided by the structure of electrode  25  (i.e., recesses  64 ) at the distal end  53  of the shaft  17  which are protected and sheltered from contact and occlusion from surface  22  of tissue  32 . Fluid outlet openings  73  of device  5   c  are protected from occlusion from surface  22  of tissue  32  as the structure of device  5   c  defining the openings  26  is at least partially configured for non-contact with surface  22  of tissue  32 . More specifically, here the structure of the device defining the openings  73  is completely configured for non-contact with surface  22  of tissue  32 . Stated another way, the openings  73  are provided on the device  5   c  at a location removed from the tissue surface  22 . Also, as shown, openings  26  are particularly sheltered from occlusion from surface by  22  of tissue  32  by a portion of the shaft  17 . Also as shown, openings  73  are formed substantially perpendicular to the surface  22  of tissue  32  and thus turned away from direct contact with surface  22  of tissue  32 . 
     Another tip portion of an exemplary electrosurgical device  5   e  of the present invention which may be used in conjunction with the system of the present invention is shown at reference character  45  in  FIGS. 29-30 . As shown, the broadening portion  54  has been eliminated and the cylindrical portion  39  has an equal cross-sectional dimension, here diameter, with the neck portion  56 . Conversely, for device  5   c , the cylindrical portion  39  has a cross-sectional dimension, there also diameter, greater than the cross-sectional dimension, there also diameter, of the neck portion  56 . 
     Also as shown, the cylindrical portion  39  further comprises a rectilinear cylindrical portion  39   a  having a rectilinear cylindrical surface portion  40   a  and a curvilinear cylindrical portion  39   b  having a curvilinear cylindrical surface portion  40   b . As shown, device  5   e  comprises the shape of a hockey stick. The cylindrical portion  39  for device  5   c  may be similarly arranged. 
     Another tip portion of an exemplary electrosurgical device  5   f  of the present invention which may be used in conjunction with the system of the present invention is shown at reference character  45  in  FIGS. 31-32 . As shown, the cylindrical portion  39  has a cross-sectional dimension, here diameter, less than the cross-sectional dimension, here also diameter, of the neck portion  56 . As shown the neck portion  56  includes a narrowing portion  49  with a corresponding narrowing surface portion  51 , here both conical. 
     Also as shown, the cylindrical portion  39  further comprises a rectilinear cylindrical portion  39   a  having a rectilinear cylindrical surface portion  40   a  and a curvilinear cylindrical portion  39   b  having a curvilinear cylindrical surface portion  40   b . Furthermore, as shown, the cylindrical portion  39 , and more specifically at least one of the rectilinear cylindrical portion  39   a  and the curvilinear cylindrical portion  39   b , comprises a portion of a hook. Preferably, as shown both the rectilinear cylindrical portion  39   a  and the curvilinear cylindrical portion  39   b  comprise portions of a hook. As shown, the hook further comprises an L-hook. 
     Another tip portion of an exemplary electrosurgical device  5   g  of the present invention which may be used in conjunction with the system of the present invention is shown at reference character  45  in  FIGS. 33-34 . Similar to devices  5   c - 5   f , the separate sleeve  82  of embodiments  5   a  and  5   b  has been eliminated from tip portion  45  of device  5   g . Consequently, the contact element, still preferably comprising an electrode  25 , is assembled directly with the shaft  17 . Electrode  25  is preferably assembled (e.g., mechanically connected via a press fit, or interference fit, adjacent the distal end  53  of shaft  17 . 
     As shown in  FIGS. 33-34 , electrode  25  preferably comprises a spherical portion  43  and a corresponding spherical surface portion  42  located at the distal end of the device  5   g , which provided a smooth, blunt contour outer surface. More specifically, as shown, the spherical portion  43  and spherical surface portion  42  further provide a domed, hemisphere (i.e., less than a full sphere) and hemispherical surface portion comprising preferably about 180 degrees. 
     Also as shown in  FIGS. 33-34 , electrode  25  preferably also comprises a narrowing portion  49  and a corresponding narrowing surface portion  51 , here both conical, located proximal and adjacent to the spherical portion  43  and spherical surface portion  42 , respectively. More preferably, as shown narrowing portion  49  and corresponding narrowing surface portion  51  comprise a conical portion in the form of a concentric cone shape, as opposed to device  5   f  where the conical portion provided by narrowing portion  49  and a corresponding narrowing surface portion  51  comprises an eccentric cone shape. Thus, in the above manner, spherical portion  43  and spherical surface portion  42  may provide a blunt apex to narrowing portion  49  and a corresponding narrowing surface portion  51 , respectively. 
     Continuing with  FIGS. 33-34 , electrode  25  preferably also comprises a cylindrical portion  39  and a corresponding cylindrical surface portion  40  located proximal and adjacent to the narrowing portion  49  and narrowing surface portion  51 , respectively. 
     Similar to devices  5   c - 5   f , electrode  25  preferably comprises a connector portion, preferably comprising a shank  46 , which connects the remainder of electrode  25  to the shaft  17 . Among other things, the connector portion of electrode  25  is preferably configured to form a connection with a mating connector portion of the shaft  17 . As shown, preferably the shank portion  46  is configured to extend into cavity  50  of shaft  17  which comprises a cylindrical receptacle and provides the mating connector portion for shank  46 . More preferably, surface  48  of the shank portion  46  is configured to mate against and form an interference fit with surface  52  of cavity  50  to provide the connection. Also similar to devices  5   c - 5   f , shank portion  46  is preferably cylindrical and located proximal and adjacent to a neck portion  56 . 
     As shown, similar to device  5   c , neck portion  56  comprises a cylindrical portion  57  (having a corresponding cylindrical surface portion  58 ) and a broadening portion  54  (having a corresponding broadening surface portion  47 ). Here broadening portion  54  and corresponding broadening surface portion  47  are both spherical, and more specifically comprise a domed, hemisphere and hemispherical surface portion comprising preferably about 180 degrees, located proximal and adjacent to the cylindrical portion  39  and cylindrical surface portion  40 . 
     Similar to devices  5   c - 5   f , the cylindrical portion  57  of neck portion  56  of device  5   g  preferably has a cross-sectional dimension, here diameter, greater than the cross-sectional dimension, here also diameter, of the shank  46 . In this manner, in certain embodiments, the proximal end of the neck portion  56  may be located adjacent and in contact with the distal end  53  of shaft  17 . 
     Also similar to devices  5   c - 5   f , preferably electrode  25  comprises at least one recess  64  which provides an elongated fluid flow channel for the distribution of fluid  24 . As shown, electrode  25  preferably comprises a plurality of longitudinally directed recesses  64  and, more specifically, four recesses  64  equally spaced 90 degrees around the shank  46  and/or neck portion  56 , both proximal of cylindrical portion  39 . 
     Another tip portion of an exemplary electrosurgical device  5   h  of the present invention which may be used in conjunction with the system of the present invention is shown at reference character  45  in  FIGS. 35-36 . Device  5   h  is similar to device  5   g  in all respects except that spherical portion  43  and spherical surface portion  42  have been eliminated and replaced with a distal end sharp point  71 . 
     As shown in  FIG. 36 , the electrode  25  of device  5   h  comprises a simple cone. In other embodiments, electrode  25  may comprise other cone shapes. For example, as shown in  FIGS. 37-40 , the cone shape may comprise an give cone shape, an elliptical (prolate hemispheroid) cone shape, a bi-conic cone shape and parabolic series cone shapes, respectively, which all may be defined by mathematical equations as known in the art. Still other cone shapes may include power series cone shapes, Haake series cone shapes, Sears-Haake and Von Karman, which all may be defined by mathematical equations as known in the art. 
     Certain embodiments of the invention may be particularly configured for bipolar devices. For example, an exemplary bipolar electrosurgical device of the present invention which may be used in conjunction with the system of the present invention is shown at reference character  5   i  in  FIGS. 41-43 . With a bipolar device, the ground pad electrode located on the patient is eliminated and replaced with a second electrical pole as part of the device. An alternating current electrical circuit is then created between the first and second electrical poles of the device. Consequently, alternating current no longer flows through the patient&#39;s body to the ground pad electrode, but rather through a localized portion of tissue preferably between the poles of the bipolar device. 
     In certain embodiments, an exemplary bipolar surgical device of the present invention may comprise, among other things, multiple, substantially parallel, arms. As shown in  FIG. 41 , electrosurgical device  5   i  preferably includes two arms comprising rigid, self-supporting, hollow shafts  17   a ,  17   b , a proximal handle comprising mating handle portions  20   a ,  20   b  and arm tip portions as shown by circles  45   a ,  45   b . In this embodiment, shafts  17   a ,  17   b  preferably comprise thick walled hypo-tubing. In this manner, the shafts  17   a ,  17   b  have sufficient rigidity to maintain their form during use of the device without kinking or significant bending. 
     Preferably the arms of device  5   i  (comprising shafts  17   a ,  17   b ) are retained in position relative to each other by a mechanical coupling device comprising a collar  95  and inhibited from separating relative to each other. Collar  95  preferably comprises a polymer (e.g., acrylonitrile-butadiene-styrene or polycarbonate) and is preferably located on the distal portion of the arms. More preferably, the collar  95  is located proximal the distal ends  53   a ,  53   b  of the shafts  17   a ,  17   b . Preferably the collar  95  comprises two apertures  96   a ,  96   b , preferably comprising opposing C-shapes, configured to receive a portion of the shafts  17   a ,  17   b  which are preferably snap-fit therein. Once the collar  95  is connected to the shafts  17   a ,  17   b , preferably by a snap-fit connection, the collar  95  may be configured to slide along the length of the shafts  17   a ,  17   b  as to adjust or vary the location of the collar  95  on the shafts  17   a ,  17   b . Alternatively, the location of the collar  95  may be fixed relative to the shafts  17   a ,  17   b  by welding, for example. 
     Device  5   i  comprises a first arm tip portion  45   a  and a second arm tip portion  45   b . As shown, preferably both first arm tip portion  45   a  and second arm tip portion  45   b  are each individually configured identical to tip portion  45  of device  5   a . As a result, device  5   i  has two separate, spatially separated (by empty space) contact elements preferably comprising electrodes  25   a ,  25   b.    
     As shown in  FIG. 42 , when device  5   i  is in use electrodes  25   a ,  25   b  are laterally spaced adjacent tissue surface  22  of tissue  32 . Electrodes  25   a ,  25   b  are connected to a source of alternating electrical current and alternating current electrical field is created between electrodes  25   a  and  25   b . In the presence of alternating current, the electrodes alternate polarity between positive and negative charges with current flow from the positive to negative charge. 
     Similar to device  5   a , for device  5   i  fluid  24  is communicated from a fluid source  1  within the lumens  23   a ,  23   b  of the shafts  17   a ,  17   b  through the lumens  89   a ,  89   b  and cavities  81   a ,  81   b  of the sleeves  82   a ,  82   b  where it is expelled from around and on the surface  42   a ,  42   b  of the electrodes  25   a ,  25   b.    
     As with use of device  5   a , with use of device  5   i  fluid couplings  30   a ,  30   b  preferably comprising discrete, localized webs and more preferably comprising a triangular shaped web or bead portion providing a film of fluid  24  between surface  22  of tissue  32  and electrodes  25   a ,  25   a . When the user of electrosurgical device  5   i  places electrodes  25   a ,  25   b  at a tissue treatment site and moves electrodes  25   a ,  25   b  across surface  22  of tissue  32 , fluid  24  is expelled around and on surfaces  42   a ,  42   b  of electrodes  25   a ,  25   b  at the distal ends  83   a ,  83   b  of sleeves  82   a ,  82   b  and onto surface  22  of tissue  32  via couplings  30   a ,  30   b . At the same time, RF electrical energy, shown by electrical field lines  130 , is provided to tissue  32  at tissue surface  22  and below tissue surface  22  into tissue  32  through fluid couplings  25   a ,  25   b.    
     As with device  5   a , the fluid  24 , in addition to providing an electrical coupling between the electrosurgical device  5   i  and tissue  32 , lubricates surface  22  of tissue  32  and facilitates the movement of electrodes  25   a ,  25   b  across surface  22  of tissue  32 . During movement of electrodes  25   a ,  25   b , electrodes  25   a ,  25   b  typically slide across the surface  22  of tissue  32 , but also may rotate as electrodes  25   a ,  25   b  move across surface  22  of the tissue  32 . Typically the user of electrosurgical device  5   i  slides electrodes  25   a ,  25   b  across surface  22  of tissue  32  back and forth with a painting motion while using fluid  24  as, among other things, a lubricating coating. Preferably the thickness of the fluid  24  between the distal end surface of electrodes  25   a ,  25   b  and surface  22  of tissue  32  at the outer edge of couplings  30   a ,  30   b  is in the range between and including about 0.05 mm to 1.5 mm. More preferably, fluid  24  between the distal end surface of electrodes  25   a ,  25   b  and surface  22  of tissue  32  at the outer edge of coupling  30   a ,  30   b  is in the range between and including about 0.1 mm to 0.3 mm. Also preferably, in certain embodiments, the distal end tip of electrode  25  contacts surface  22  of tissue  32  without any fluid  24  in between. 
     As shown in  FIG. 43 , the fluid coupling for device  5   i  may comprise a conductive fluid bridge  27  between electrodes  25   a ,  25   b  which rests on surface  22  of tissue  32  and forms a shunt between electrodes  25   a ,  25   b . Given this scenario, a certain amount of RF energy may be diverted from going into tissue  32  and actually pass between electrodes  25   a ,  25   b  via the conductive fluid bridge  27 . This loss of RF energy may slow down the process of coagulating tissue and producing the desired hemostasis or aerostasis of the tissue. 
     In order to counteract the loss of energy through bridge  27 , once enough energy has entered bridge  27  to boil fluid  24  of bridge  27 , the loss of RF energy correspondingly decreases with the loss of bridge  27 . Preferably energy is provided into fluid  24  of bridge  27  by means of heat dissipating from tissue  32 . 
     Thus, where a high % boiling of conductive fluid  24  of bridge  24  is created, the loss of RF energy through bridge  27  may either be reduced or eliminated because all the fluid  24  of bridge  27  boils off or a large fraction of boiling creates enough disruption in the continuity of bridge  27  to disrupt the electrical circuit through bridge  27 . Thus, one control strategy of the present invention is to reduce the presence of a conductive fluid shunt by increasing the % boiling of the conductive fluid. 
     Bipolar device  5   i  is particularly useful as non-coaptive tissue sealer and coagulator given it does not grasp tissue. Device  5   i  is particularly useful to surgeons to achieve hemostasis after dissecting through soft tissue as part of hip or knee arthroplasty. The tissue treating portions can be painted over the raw, oozing surface  22  of tissue  32  to seal the tissue  32  against bleeding, or focused on individual larger bleeding vessels to stop vessel bleeding. 
     Bipolar device  5   i  is also useful to stop bleeding from the surface of cut bone tissue as part of any orthopaedic procedure that requires bone to be cut. Device  5   i  is particularly useful for these applications over monopolar device  5   a  as a much greater surface area  22  of tissue  32  may be treated in an equivalent period of time and with better controlled depth of the treatment. 
     As is well known, bone, or osseous tissue, is a particular form of dense connective tissue consisting of bone cells (osteocytes) embedded in a matrix of calcified intercellular substance. Bone matrix mainly contains collagen fibers and the minerals calcium carbonate, calcium phosphate and hydroxyapatite. Among the many types of bone within the human body are compact bone and cancellous bone. Compact bone is hard, dense bone that forms the surface layers of bones and also the shafts of long bones. It is primarily made of haversian systems which are covered by the periosteum. Compact bone contains discrete nutrient canals through which blood vessels gain access to the haversian systems and the marrow cavity of long bones. For example, Volkmann&#39;s canals which are small canals found in compact bone through which blood vessels pass from the periosteum and connect with the blood vessels of haversian canals or the marrow cavity. Bipolar device  5   i  disclosed herein may be particularly useful to treat compact bone and to provide hemostasis and seal bleeding vessels (e.g. by shrinking to complete close) and other structures associated with Volkmann&#39;s canals and Haversian systems. 
     In contrast to compact bone, cancellous bone is spongy bone and forms the bulk of the short, flat, and irregular bones and the ends of long bones. The network of osseous tissue that makes up the cancellous bone structure comprises many small trabeculae, partially enclosing many intercommunicating spaces filled with bone marrow. Consequently, due to their trabecular structure, cancellous bones are more amorphous than compact bones, and have many more channels with various blood cell precursors mixed with capillaries, venules and arterioles. Bipolar device  5   i  disclosed herein may be particularly useful to treat cancellous bone and to provide hemostasis and seal bleeding structures such as the above micro-vessels (i.e. capillaries, venules and arterioles) in addition to veins and arteries. Device  5   i  may be particularly useful for use during orthopedic knee, hip, shoulder and spine procedures (e.g. arthroplasty). 
     During a knee replacement procedure, the condyle at the distal epiphysis of the femur and the tibial plateau at the proximal epiphysis of the tibia are often cut and made more planer with saw devices to ultimately provide a more suitable support structure for the femoral condylar prosthesis and tibial prosthesis attached thereto, respectively. The cutting of these long bones results in bleeding from the cancellous bone at each location. In order to seal and arrest the bleeding from the cancellous bone which has been exposed with the cutting of epiphysis of each long bone, bipolar device  5   i  may be utilized. Thereafter, the respective prostheses may be attached. 
     Turning to a hip replacement procedure, the head and neck of the femur at the proximal epiphysis of the femur is removed, typically by cutting with a saw device, and the intertrochantic region of the femur is made more planer to provide a more suitable support structure for the femoral stem prosthesis subsequently attached thereto. With respect to the hip, a ball reamer is often used to ream and enlarge the acetabulum of the innominate (hip) bone to accommodate the insertion of an acetabular cup prosthesis therein, which will provide the socket into which the head of the femoral stem prosthesis fits. The cutting of the femur and reaming of the hip bone results in bleeding from the cancellous bone at each location. In order to seal and arrest the bleeding from the cancellous bone which has been cut and exposed, bipolar device  5   i  may be utilized. Thereafter, as with the knee replacement, the respective prostheses may be attached. 
     Bipolar device  5   i  may be utilized for treatment of connective tissues, such as for shrinking intervertebral discs during spine surgery. Intervertebral discs are flexible pads of fibrocartilaginous tissue tightly fixed between the vertebrae of the spine. The discs comprise a flat, circular capsule roughly an inch in diameter and about 0.25 inch thick, made of a tough, fibrous outer membrane called the annulus fibrosus, surrounding an elastic core called the nucleus pulposus. 
     Under stress, it is possible for the nucleus pulposus to swell and herniate, pushing through a weak spot in the annulus fibrosus membrane of the disc and into the spinal canal. Consequently, all or part of the nucleus pulposus material may protrude through the weak spot, causing pressure against surrounding nerves which results in pain and immobility. 
     Bipolar device  5   i  may be utilized to shrink protruding and herniated intervertebral discs which, upon shrinking towards normal size, reduces the pressure on the surrounding nerves and relieves the pain and immobility. Device  5   i  may be applied via posterior spinal access under surgeon control for either focal shrinking of the annulus fibrosus membrane. 
     Where a intervertebral disc cannot be repaired and must be removed as part of a discectomy, device  5   i  may be particularly useful to seal and arrest bleeding from the cancellous bone of opposing upper and lower vertebra surfaces (e.g. the cephalad surface of the vertebral body of a superior vertebra and the caudad surface of an inferior vertebra). Where the disc is removed from the front of the patient, for example, as part of an anterior, thoracic spine procedure, device  5 i may also be particularly useful to seal and arrest bleeding from segmental vessels over the vertebral body. 
     Bipolar device  5   i  may be utilized to seal and arrest bleeding of epidural veins, which bleed as a result of the removal of tissue around the dural membrane during, for example, a laminectomy or other neurosurgical surgery. The epidural veins may start bleeding when the dura is retracted off of them as part of a decompression. Also during a laminectomy, device  5   i  may be used to seal and arrest bleeding from the vertebral arch and, in particular the lamina of the vertebral arch. 
     As already discuss with respect to  FIG. 6 , even when general-purpose generator  6  is set to a predetermined “fixed” power output, the actual power delivered from generator  6  may be significantly different if the impedance is outside the range defined by of the generator&#39;s low and high impedance cut-off limits. 
     Also with respect to  FIG. 6 , the output power is identified as being set to 75 watts in the generator&#39;s bipolar mode of operation. With respect to general-purpose generators  6  currently used in the electrosurgical industry, it has been found that a significant portion of the generators only provide an output power of 50 watts in their bipolar mode, with only a few providing an output power of 70-75 watts in bipolar mode. Above 75 watts, a very small number of generators may provide power in their bipolar mode of 100 watts. 
     As is well known, the maximum output power of a general-purpose generator  6  in its bipolar mode of operation is lower than the maximum output power of the generator in its monopolar mode of operation. One reason for this is that the electrodes commonly associated with a bipolar device are generally in much closer in proximity as compared to the active and return electrodes of a monopolar device, thus reducing the need for greater power. Furthermore, with additional power, use of many prior art dry tip electrosurgical devices only leads to more tissue desiccation, electrode sticking, char formation and smoke generation, thus further obviating the need for additional power. 
     However, as established above, bipolar device  5   i  of the present invention inhibits such undesirable effects of tissue desiccation, electrode sticking, char formation and smoke generation, and thus do not suffer from the same drawbacks as prior art dry tip electrosurgical devices. 
     It has been found that bipolar device  5   i  is, in certain instances, able to use significantly greater power than the output power current general-purpose generators offer in their accorded bipolar modes. For example, bipolar device  5   i  may use greater power to treat bone in knee, hip, shoulder and spine surgeries where blood loss would traditionally be particularly high thus necessitating a blood transfusion. 
     General-purpose generators may offer significantly greater output power than 75 watts when set in their monopolar modes. For example, in monopolar “cut mode”, the maximum power output of the generator is typically in the range of 300 watts. However, in monopolar cut mode the voltage and preferred impedance ranges are much greater than in bipolar mode. For example, with respect to impedance, an exemplary low impedance cut-off for a monopolar cut mode is about 200 ohms while an exemplary low impedance cut-off for bipolar mode is about 25-50 ohms. 
     In order to reduce monopolar voltage and impedance ranges to desirable levels for bipolar use, a transformer may be placed in series circuit configuration between the electrodes of bipolar device  5   i  and the monopolar mode power output of the generator  6 . 
     As shown in  FIG. 41 , without a transformer, cable  9  of bipolar device  5   i  may ordinarily comprise two insulated wires  21   a ,  21   b  connectable to generator  6  via two banana (male) plug connectors  77   a ,  77   b  connecting directly to (female) plug receptacles  79   a ,  79   b  of the generator  6  (shown in  FIG. 45 ). As shown in  FIG. 41 , the banana plug connectors  77   a ,  77   b  are each assembled with wires  21   a ,  21   b  within individual housings  129   a ,  129   b  which are not connected relative to one another and may be referred to as “loose leads”. Consequently, in this embodiment, the banana plug connectors  77   a ,  77   b  are independently movable relative to one another. An exemplary electrical configuration established between banana plug connectors  77   a ,  77   b  of device  5   i  and banana plug receptacle connectors  79   a ,  79   b  of generator  6  is further illustrated in  FIG. 45 . From the above, it should be understood that the use of plug connectors and receptacle connectors, is merely exemplary, and that other types of mating connector configurations may be employed. 
     However, with the introduction of a transformer  310  to convert monopolar output power to voltage and impedance ranges associated with bipolar output power, preferably the wires  21   a ,  21   b , plug connectors  77   a ,  77   b  and transformer  310  are all assembled and provided in a single, common housing similar to housing  129  shown in  FIG. 9 , and better shown in  FIG. 57 . In contrast to the previous embodiment, in this embodiment the plug connectors are held in a fixed, predetermined position relative to one another. In this manner, the plug connectors can be tailored to fit only those generators  6  with receptacle connectors positioned to coincide or match up with the predetermined positions of the plug connectors. 
     To further illustrate the above,  FIG. 46  illustrates an exemplary electrical configuration which may be associated between monopolar device  5   a  and generator  6 . As shown in  FIG. 46 , in this embodiment the wiring within plug housing  129  of device  5   a  is configured such that hand switch  15   a  may be electrically coupled to the “coagulation mode” hand switching circuitry of generator  6 . More specifically, as shown hand switch  15   a  is electrically coupled to generator  6  upon the insertion of hand switch plug connector  77   d  of device  5   a  into hand switch receptacle connector  79   d  of generator  6 . 
     In addition to plug connector  77   d , plug housing  129  also contains power plug connector  77   c  which may be electrically coupled to the monopolar power receptacle connector  79   c  of generator  6 . As shown, upon insertion of power plug connector  77   c  into power receptacle connector  79   c , electrode  25  is now coupled to the power output of generator  6 . 
     As shown, the finally connection of device  5   a  to generator  6  comprises ground pad receptacle connector  177  of ground pad  125  being inserted over ground pad plug connector  179  of generator  6 . 
     Plug connectors  77   c ,  77   d  are provided in a single common housing  129  to better and more easily direct the plug connectors  77   c ,  77   d  to their predetermined targeted plug receptacle connectors  79   c ,  79   d  by virtue of being held in a fixed, predetermined position relative to one another by plug housing  129  such that they can only coincide with receptacle connectors  79   c ,  79   d , respectively. 
     In other embodiments, as indicated by the dotted lines, the wiring within plug housing  129  of device  5   a  may be configured such that hand switch  15   a  is coupled to plug connector  77   e  and plug receptacle  79   e , in which case hand switch  15   a  is now electrically coupled to the monopolar “cut mode” of generator  6  rather than the coagulation mode. 
     Now, with use of a bipolar device  5   i , as shown in  FIG. 47 , housing  129  now includes transformer  310  and monopolar device  5   a  has been replaced with bipolar device  5   i , now also including hand switch  15   a . Furthermore, as shown, hand switch  15   a  is coupled to the monopolar cut mode of generator  6  by use of plug connector  77   e  and plug receptacle  79   e . In other embodiments, the hand switch  15   a  may be eliminated as shown in  FIG. 48  and foot switch  15  may be used alone. 
     The option between monoploar “coagulation mode” hand switching and monopolar “cut mode” hand switching is driven by a number of factors. However, an overriding consideration is often output power. In monopolar coagulation mode, the maximum output power of a general purpose generator is typically about 120 watts, while in monopolar cut mode the maximum output power of the same general purpose generator is typically about 300 watts. For use of the monopolar devices disclosed herein (e.g.  5   a ,  5   c ), 120 watts maximum output power associated with coagulation mode has been found to be generally sufficient, thus precluding the need for higher powers associated with cut mode. However, for the bipolar device  5   i , when using power provided from the generator&#39;s monopolar output, the higher power associated with monopolar cut mode is generally more desirable than the lower power associated with monopolar coagulation mode. 
     In other embodiments, the transformer  310  may be provided as part of an in-line adaptor  312 , as shown in  FIGS. 44 and 49 . In this embodiment, preferably the adapter  312  includes its own receptacle connectors  314   a ,  314   b  on one side which are configured to receive plug connectors  77   a ,  77   b  of device  5   i , and on the opposing side has its own plug connector  316   c  and ground pad receptacle connector  177  which are configured to connect to receptacle connector  79   c  and ground pad plug connector  179  of generator  6 , respectively. To further illustrate the above,  FIG. 49  illustrates an exemplary electrical configuration which may be associated between bipolar device  5   i , adapter  312  and generator  6 . 
     The adaptor  312  may also be configured to accommodate a bipolar device with a hand switch. Without adaptor  312 ,  FIG. 50  shows an exemplary electrical configuration established between plug connectors  77   a ,  77   b  of device  5   i  and receptacle connectors  79   a ,  79   b  of generator  6 . In addition,  FIG. 50  shows hand switch  15   a  coupled to the hand switching circuitry of generator  6 . More specifically, as shown hand switch  15   a  is electrically coupled to generator  6  upon the insertion of bipolar hand switch plug connector  77   f  of device  5   i  into bipolar hand switch receptacle connector  79   f  of generator  6 . 
     With adaptor  312 , as shown in  FIG. 51A  and as with the earlier embodiment, preferably the adaptor  312  includes its own receptacle connectors  314   a ,  314   b  on one side which are configured to receive plug connectors  77   a ,  77   b  of device  5   i , and on the opposing side has its own plug connector  316   c  and ground pad receptacle connector  177  which are configured to connect to receptacle connector  79   a  and ground pad plug connector  179  of generator  6 , respectively. Furthermore, adaptor  312  has its own bipolar hand switch receptacle connector  314   f  on one side configured to mate with the bipolar hand switch plug connector  77   f  of device  5   i , and on the opposing side has its own monopolar hand switch plug connector  316   e  configured to connect to monopolar “cut mode” hand switch receptacle connector  79   e  of generator  6 . Finally, in order to establish the remaining link between the hand switch circuitry and the monopolar power output, the adaptor  312  has a hand switch plug connector  314   g  configured to mate with hand switch receptacle connector  77   g  of device  5   i.    
     As shown in  FIG. 51A , bipolar device  5   i  now includes four connectors (i.e.  77   a ,  77   b ,  77   f ,  77   g ) when adaptor  312  is used rather than just the three connectors (i.e.  77   a ,  77   b ,  77   f ) associated with  FIG. 50 . Connector  77   g  is added to provide a connection, when mated with connector  314   g  of adaptor  312 , to plug connector  316   c  which bypasses transformer  310 . This is required as the hand switch circuitry of generator  6  typically utilizes direct current (DC) rather than the alternating current (AC) associated with the power circuitry. Consequently, since continuous DC will not cross between the primary coil  318  and secondary coil  320  of transformer  310 , this fourth connection is required. 
     In other embodiments, bipolar device  5   i  may return to the use of only three connectors with a modification of the electrical wiring within adaptor  312 . As shown in  FIG. 51B , rather than bipolar hand switch receptacle connector  314   f  being electrically wired to connect to monopolar hand switch plug connector  316   e  as in  FIG. 51A , bipolar hand switch receptacle connector  314   f  is electrically wired to connect to monopolar power plug connector  316   c , which ultimately connects to monopolar power receptacle connector  79   c  of generator  6 . Furthermore, in addition to bipolar power receptacle connector  314   a  being electrically wired to connect to the secondary coil  320  of transformer  310 , it is also electrically wired to connect to monopolar hand switch plug connector  316   e , which ultimately connects to monopolar “cut mode” hand switch receptacle connector  79   e  of generator  6 . In this manner, where direct current is utilized as part of the hand switch circuitry of generator  6 , the direct current is still provided a return electrical path to the generator  6 . 
     For the embodiment shown in  FIG. 51B , the primary and secondary coils  318 ,  320  are wound and/or wired (preferably both) such that the secondary voltage V s  is electrically in-phase with the primary voltage V p . In other words, the secondary voltage V s  associated with secondary coil  320  rises and falls simultaneously with the primary voltage V p  associated with the primary coil  318 . The black “dots” accompanying the primary and secondary coils  318 ,  320  are commonly used to indicate points on a transformer schematic that have the same instantaneous polarity and are in-phase. On an oscilloscope, an “in-phase” relationship between the primary voltage V p  and the secondary voltage V s  may be shown by the corresponding sine waves having the same frequency and their positive and negative peaks occurring at the same time. 
     Turning to the specifics of transformer  310 , preferably the transformer  310  comprises primary and secondary coils  318 ,  320  comprising # 18  magnet wire wound on a toroidal shaped, magnetic core  322 . More preferably the core  322  comprises a ferromagnetic core and even more preferably a ferrite core. Preferably the ferrite has an amplitude permeability in the range of 500μ to 5,000μ and more preferably of about 2,000μ. More preferably, the ferrite comprises ferrite material no.  77 . Preferably the core has a 1.4 inch outside diameter, a 0.9 inch inside diameter and a 0.5 inch thickness which is available from Coil Winding Specialists. 
     For a perfect transformer, that is, a transformer with a coefficient of coupling (k) equal to 1, the impedances can be described as follows:
 
 Z   p   =Z   s ( N   p   /N   s ) 2    (8)
 
where:
         Z p =Impedance looking into the primary terminals from the power source;   Z s =Impedance of load connected to secondary;   N p =Number of turns (windings) for primary coil; and       

     N s =Number of turns (windings) for secondary coil 
     Based a primary impedance Z p =200 ohms and a secondary impedance of 25-50 ohms, the transformer  310  should be a step-down transformer with a turns ratio, N p /N s , in the range between and including about 3:1-2:1, respectively, and preferably about 2.5:1. This will result in power being provided to the tissue in monopolar mode at much lower impedances (i.e. 25-50 ohms) than typically required for use of the generator&#39;s monopolar mode (i.e. 200 ohms). 
     Turning to voltage, the high impedance cut-off for bipolar mode at 75 watts occurs at about 300 ohms, with the power remaining substantially unchanged between 25 ohms and 300 ohms. Thus, based on Ohm&#39;s law, for 75 watts ohms and 300 ohms, the voltage before power begins to drop in bipolar mode is about 150 RMS volts. This now becomes the targeted voltage from the monopolar mode with use of the transformer  310 . 
     The high impedance cut-off for monopolar mode at 150 watts occurs at about 1000 ohms. At 150 watts and 1000 ohms, the voltage in monopolar mode is about 387 RMS volts. With the transformer above, secondary voltage may be described as follows:
 
 V   s   =V   p ( N   s   /N   p )   (9)
 
where:
         V s =Secondary voltage;   V p =Primary voltage;   N p =Number of turns (windings) for primary coil; and   N s =Number of turns (windings) for secondary coil       

     Based on a primary voltage of 387 RMS volts, and a turns ratio N p /N s  of 2.5:1, the secondary voltage is 155 RMS volts, which is only slightly greater than the targeted 150 RMS volts. With respect to the number of windings, in one embodiment preferably, the primary coil  318  comprises  40  windings while the secondary coil  320  comprises  16  windings resulting in the turns ratio of 2.5. 
     In yet another embodiment, as shown in  FIGS. 52-56 , electrosurgical device  5   i  may include a fluid flow control mechanism for turning fluid flow on and off to the tissue treating portion of the device, such as a roller pinch clamp assembly. As best shown in  FIGS. 54-56 , device  5   i  includes a roller pinch clamp assembly  242  and, more specifically, an inclined ramp roller pinch clamp assembly (as opposed to a parallel acting clamp). 
     As best shown in  FIGS. 54-55 , the clamp assembly  242  includes a housing provided by handles  20   a ,  20   b , a roller wheel  244  having a wheel center axis  246  and a guide pin hub. As shown, the guide pin hub is provided by pair of opposing, integrally formed, cylindrical trunnions  248   a ,  248   b , but may also be provided by a separately formed pin. Trunnions  248   a ,  248   b  are contained within and move along a track  250  preferably provided and defined by opposing trunnion channels  252   a ,  252   b  formed between wheel upper guide surfaces  254   a ,  254   b  and wheel lower guide surfaces  256   a ,  256   b  extending longitudinally and parallel inward from the side wall portions of the handles  20   a ,  20   b . As shown, wheel upper guide surfaces  254   a ,  254   b  are provided by a lip portion of the handles  20   a ,  20   b  which partially define aperture  258  through which roller wheel partially extends while wheel lower guide surfaces  256   a ,  256   b  are provided by ribs  260   a ,  260   b.    
     Handles  20   a ,  20   b  also preferably provide tubing guide surfaces  272   a ,  272   b  which at least a portion of which provide a clamping surface against which plastic tubing  4   b  is clamped by roller  244 . As best shown in  FIGS. 54-55 , tubing guide surfaces  272   a ,  272   b  are provided by ribs  270   a ,  270   b . In use, fluid line  4   b  is externally squeezed and compressed between the outer perimeter surface  262  of roller wheel  244  and at least a portion of tubing guide surfaces  272   a ,  272   b . In this embodiment, preferably surface  262  is serrated. 
     Trunnions  248   a ,  248   b  support the movement of roller wheel  244  in two opposing directions, here proximally and distally, along track  250 . As best shown in  FIGS. 55-56 , the separation distance between the outer perimeter surface  262  of roller wheel  244  and tubing guide surfaces  272   a ,  272   b  changes throughout the proximal and distal travel of roller wheel  244  along track  250 . More specifically, the separation distance between the outer perimeter surface  262  of roller wheel  244  and tubing guide surfaces  272   a ,  272   b  is greater between the outer perimeter surface  262  of roller wheel  244  and distal end portions  274   a ,  274   b  of tubing guide surfaces  272   a ,  272   b  provided by distal end portions  264   a ,  264   b  of ribs  270   a ,  270   b  than between the outer perimeter surface  262  of roller wheel  244  and proximal end portions  276   a ,  276   b  of tubing guide surfaces  272   a ,  272   b  provided by proximal end portions  266   a ,  266   b  of ribs  270   a ,  270   b.    
     As shown in  FIGS. 54-55 , when axis  246  of roller wheel  244  is opposing distal end portions  274   a ,  274   b  of tubing guide surfaces  272   a ,  272   b , preferably the separation distance is configured such that the tubing  4   b  may be uncompressed and the lumen of tubing  4   b  completely open for full flow therethrough. Conversely, as shown in  FIG. 56 , when axis  246  of roller wheel  244  is opposing proximal end portions  276   a ,  276   b  of tubing guide surfaces  272   a ,  272   b  preferably the separation distance is configured such that the tubing  4   b  is compressed and the lumen of tubing  4   b  is completely blocked so that the flow of fluid through tubing  4   b  is prevented. 
     Distal end portions  274   a ,  274   b  of tubing guide surfaces  272   a ,  272   b  are separated from proximal end portions  276   a ,  276   b  of tubing guide surfaces  272   a ,  272   b  by transition surfaces  278   a ,  278   b  which are provided by transition rib portion  268   a ,  268   b  of ribs  270   a ,  270   b . Preferably compression of tubing initially begins between transition surfaces  278   a ,  278   b  and the outer perimeter surface  262  of roller wheel  244  and increases as wheel  244  moves proximally along proximal end portions  276   a ,  276   b  of tubing guide surfaces  272   a ,  272   b . With this configuration, consideration may be given to eliminating at least that portion of distal end portions  274   a ,  274   b  of tubing guide surfaces  272   a ,  272   b  that do not contribute to compression of the tubing  4   b . However, given that of distal end portions  274   a ,  274   b  of tubing guide surfaces  272   a ,  272   b  guide tubing  4   b  to splitter  240 , such may not be desirable. 
     As shown in  FIGS. 54-56 , both transition surfaces  278   a ,  278   b  and proximal end portions  276   a ,  276   b  of tubing guide surfaces  272   a ,  272   b  provide sloped inclining surfaces proximally along their respective lengths which decreases the separation distance between the outer perimeter surface  262  of roller wheel  244  and the tubing guide surfaces  272   a ,  272   b  as the wheel  244  moves proximally. As shown, preferably the transition surfaces  278   a ,  278   b  and proximal end portions  276   a ,  276   b  of tubing guide surfaces  272   a ,  272   b  have different slopes such that the separation distance decreases at a faster rate along transition surfaces  278   a ,  278   b  as compared to proximal end portions  276   a ,  276   b  of tubing guide surfaces  272   a ,  272   b . In this manner, compression of tubing  4   b  is non-linear along the length of travel of wheel  244  with a majority of the compression occurring between roller wheel  244  and transition surfaces  278   a ,  278   b . More preferably, the lumen of tubing  4   b  is completely blocked when roller wheel  244  is compressing the tubing  4   b  against the proximal portion of transition surfaces  278   a ,  278   b , and the added compression of the tubing  4   b  along proximal end portions  276   a ,  276   b  of tubing guide surfaces  272   a ,  272   b  provides an additional safety to assure complete blocking of the lumen even where there are variations in the tubing, such as the size of the lumen. 
     It should be realized that, due to the slope of the transition rib portion  268   a ,  268   b , as the roller wheel  244  moves proximally relative to transition surfaces  278   a ,  278   b  the lumen of tubing  4   b  is blocked incrementally. Thus, in addition to providing an on/off mechanism, the roller pinch clamp assembly  242  can also be used to regulate the fluid flow rate between two non-zero flow values. It should also be realized that the roller pinch clamp assembly  242  of the device may be used in series conjunction with another roller pinch clamp assembly which is typically provided as part of an IV set (i.e. IV bag, IV bag spike, drip chamber, connecting tubing, roller clamp, slide clamp, luer connector). When used in this manner, the roller pinch clamp assembly of the IV set may be used to achieve a primary (major) adjustment for fluid flow rate, while the roller pinch clamp assembly  242  of the device may be used to achieve a secondary (more precise minor) adjustment for the fluid flow rate. 
     In another embodiment, as shown in  FIGS. 57-59  for device  5   i , roller wheel  244  of roller pinch clamp assembly  242  may be concealed from view to reduce the possibility of foreign objects (e.g. practitioner&#39;s rubber gloves) from entering into the confines of handle  20   a ,  20   b  through aperture  258  and getting snagged, for example, between the trunnions  248   a ,  248   b  and track  250 . 
     As shown in  FIG. 57 , roller wheel  244  is concealed from view by handle portions  20   a ,  20   b . As shown, switch button  192  protrudes through an aperture  194  formed in handle portions  20   a ,  20   b . Button  192  is preferably integrally connected via a single piece polymer molding to a proximally extending switch arm  196  which provides a receptacle  306  which contains and holds roller wheel  244 . 
     With use of the fluid flow control mechanism of  FIGS. 57-59 , in response to button  192  being moved proximally and distally in switch button aperture  194 , switch arm  196  moves proximally and distally along track  250 , which correspondingly moves roller wheel  244  to compress tubing  4   b  as discussed above. 
     As best shown in  FIG. 59 , preferably the fluid flow control mechanism further comprises a mechanism which may hold the arm  196  in a fixed position while compressing and occluding fluid line  4   b . As shown, preferably the locking mechanism comprises detents  308   a ,  308   b  (308 b  not shown) formed in handle portions  20   a ,  20   b  which partially receive trunnions  248   a ,  248   b  therein to hold arm  196  in a fixed position. 
     The devices of the present invention may provide treatment of tissue without using a temperature sensor built into the device or a custom special-purpose generator. In a preferred embodiment, there is no built-in temperature sensor or other type of tissue sensor, nor is there any custom generator. Preferably, the invention provides a means for controlling the flow rate to the device such that the device and flow rate controller can be used with a wide variety of general-purpose generators. Any general-purpose generator is useable in connection with the fluid delivery system and flow rate controller to provide the desired power; the flow rate controller will accept the power and constantly adjust the saline flow rate according to the control strategy. Preferably, the generator is not actively controlled by the invention, so that standard generators are useable according to the invention. Preferably, there is no active feedback from the device and the control of the saline flow rate is “open loop.” Thus, in this embodiment, the control of saline flow rate is not dependent on feedback, but rather the measurement of the RF power going out to the device. 
     The use of the disclosed devices can result in significantly lower blood loss during surgical procedures such as liver resections. Typical blood loss for a right hepatectomy can be in the range of 500-1,000 cubic centimeters. Use of the devices disclosed herein to perform pre-transection coagulation of the liver can result in blood loss in the range of 50-300 cubic centimeters. Such a reduction in blood loss can reduce or eliminate the need for blood transfusions, and thus the cost and negative clinical consequences associated with blood transfusions, such as prolonged hospitalization and a greater likelihood of cancer recurrence. Use of the device can also provide improved sealing of bile ducts, and reduce the incidence of post-operative bile leakage, which is considered a major surgical complication. 
     For purposes of the appended claims, the term “tissue” includes, but is not limited to, organs (e.g. liver, lung, spleen, gallbladder), highly vascular tissues (e.g. liver, spleen), soft and hard tissues (connective, bone, cancellous) and tissue masses (e.g. tumors). 
     While a preferred embodiment of the present invention has been described, it should be understood that various changes, adaptations and modifications can be made therein without departing from the spirit of the invention and the scope of the appended claims. The scope of the invention should, therefore, be determined not with reference to the above description, but instead should be determined with reference to the appended claims along with their fall scope of equivalents. Furthermore, it should be understood that the appended claims do not necessarily comprise the broadest scope of the invention which the Applicant is entitled to claim, or the only manner(s) in which the invention may be claimed, or that all recited features are necessary.