Abstract:
A bipolar electrosurgical instrument includes first and second shafts each having a jaw member extending from its distal end. Each jaw member is adapted to connect to a source of electrosurgical energy such that the jaw members are capable of selectively conducting energy through tissue held therebetween. A knife channel is configured to reciprocate a cutting mechanism therealong. An actuator selectively advances the cutting mechanism. A switch is disposed on the first shaft and is configured to be depressed between a first position and at least one subsequent position upon biasing engagement with a mechanical interface disposed on the second shaft. The first position of the switch relays information to the user corresponding to a desired pressure on tissue and the at least one subsequent position is configured to activate the source of electrosurgical energy to supply electrosurgical energy to the jaw members.

Description:
BACKGROUND 
       [0001]    1. Background of Related Art 
         [0002]    The present disclosure relates to forceps used for open surgical procedures. More particularly, the present disclosure relates to a forceps that applies electrosurgical current to seal tissue. 
         [0003]    2. Technical Field 
         [0004]    A hemostat or forceps is a simple plier-like tool which uses mechanical action between its jaws to constrict vessels and is commonly used in open surgical procedures to grasp, dissect and/or clamp tissue. Electrosurgical forceps utilize both mechanical clamping action and electrical energy to effect hemostasis by heating the tissue and blood vessels to coagulate, cauterize and/or seal tissue. 
         [0005]    Certain surgical procedures require sealing and cutting blood vessels or vascular tissue. Several journal articles have disclosed methods for sealing small blood vessels using electrosurgery. An article entitled Studies on Coagulation and the Development of an Automatic Computerized Bipolar Coagulator, J. Neurosurg., Volume 75, July 1991, describes a bipolar coagulator which is used to seal small blood vessels. The article states that it is not possible to safely coagulate arteries with a diameter larger than 2 to 2.5 mm. A second article is entitled Automatically Controlled Bipolar Electrocoagulation—“COA-COMP”, Neurosurg. Rev. (1984), pp. 187-190, describes a method for terminating electrosurgical power to the vessel so that charring of the vessel walls can be avoided. 
         [0006]    By utilizing an electrosurgical forceps, a surgeon can either cauterize, coagulate/desiccate, reduce or slow bleeding and/or seal vessels by controlling the intensity, frequency and duration of the electrosurgical energy applied to the tissue. Generally, the electrical configuration of electrosurgical forceps can be categorized in two classifications: 1) monopolar electrosurgical forceps; and 2) bipolar electrosurgical forceps. 
         [0007]    Monopolar forceps utilize one active electrode associated with the clamping end effector and a remote patient return electrode or pad which is typically attached externally to the patient. When the electrosurgical energy is applied, the energy travels from the active electrode, to the surgical site, through the patient and to the return electrode. 
         [0008]    Bipolar electrosurgical forceps utilize two generally opposing electrodes which are disposed on the inner opposing surfaces of the end effectors and which are both electrically coupled to an electrosurgical generator. Each electrode is charged to a different electric potential. Since tissue is a conductor of electrical energy, when the effectors are utilized to grasp tissue therebetween, the electrical energy can be selectively transferred through the tissue. 
         [0009]    In order to effect a proper seal with larger vessels, two predominant mechanical parameters must be accurately controlled—the pressure applied to the vessel and the gap between the electrodes both of which affect thickness of the sealed vessel. More particularly, accurate application of the pressure is important to oppose the walls of the vessel, to reduce the tissue impedance to a low enough value that allows enough electrosurgical energy through the tissue, to overcome the forces of expansion during tissue heating and to contribute to the end tissue thickness which is an indication of a good seal. It has been determined that a fused vessel wall is optimum between 0.001 and 0.006 inches. Below this range, the seal may shred or tear and above this range the lumens may not be properly or effectively sealed. 
         [0010]    With respect to smaller vessel, the pressure applied to the tissue tends to become less relevant whereas the gap distance between the electrically conductive surfaces becomes more significant for effective sealing. In other words, the chances of the two electrically conductive surfaces touching during activation increases as the vessels become smaller. 
         [0011]    Electrosurgical methods may be able to seal larger vessels using an appropriate electrosurgical power curve, coupled with an instrument capable of applying a large closure force to the vessel walls. It is thought that the process of coagulating small vessels is fundamentally different than electrosurgical vessel sealing. For the purposes herein, “coagulation” is defined as a process of desiccating tissue wherein the tissue cells are ruptured and dried and vessel sealing is defined as the process of liquefying the collagen in the tissue so that it reforms into a fused mass. Thus, coagulation of small vessels is sufficient to permanently close them. Larger vessels need to be sealed to assure permanent closure. 
         [0012]    Numerous bipolar electrosurgical forceps have been proposed in the past for various open surgical procedures. However, some of these designs may not provide uniformly reproducible pressure to the blood vessel and may result in an ineffective or non-uniform seal. For example, U.S. Pat. No. 2,176,479 to Willis, U.S. Pat. Nos. 4,005,714 and 4,031,898 to Hiltebrandt, U.S. Pat. Nos. 5,827,274, 5,290,287 and 5,312,433 to Boebel et al., U.S. Pat. Nos. 4,370,980, 4,552,143, 5,026,370 and 5,116,332 to Lottick, U.S. Pat. No. 5,443,463 to Stern et al., U.S. Pat. No. 5,484,436 to Eggers et al. and U.S. Pat. No. 5,951,549 to Richardson et al., all relate to electrosurgical instruments for coagulating, cutting and/or sealing vessels or tissue. 
         [0013]    Many of these instruments include blade members or shearing members which simply cut tissue in a mechanical and/or electromechanical manner and are relatively ineffective for vessel sealing purposes. Other instruments rely on clamping pressure alone to procure proper sealing thickness and are not designed to take into account gap tolerances and/or parallelism and flatness requirements which are parameters which, if properly controlled, can assure a consistent and effective tissue seal. For example, it is known that it is difficult to adequately control thickness of the resulting sealed tissue by controlling clamping pressure alone for either of two reasons: 1) if too much force is applied, there is a possibility that the two poles will touch and energy will not be transferred through the tissue resulting in an ineffective seal; or 2) if too low a force is applied, a thicker less reliable seal is created. 
       SUMMARY 
       [0014]    According to an embodiment of the present disclosure, a bipolar electrosurgical instrument includes first and second shafts each having a jaw member extending from its distal end and a handle disposed at its proximal end for effecting movement of the jaw members relative to one another about a pivot from a first position wherein the jaw members are disposed in spaced relation relative to one another to a second position wherein the jaw members cooperate to grasp tissue. Each jaw member is adapted to connect to a source of electrosurgical energy such that the jaw members are capable of selectively conducting energy through tissue held therebetween to effect a tissue seal. At least one of the jaw members includes a knife channel defined along its length. The knife channel is configured to reciprocate a cutting mechanism therealong to cut tissue grasped between the jaw members. The instrument also includes an actuator for selectively advancing the cutting mechanism from a first position wherein the cutting mechanism is disposed proximal to tissue grasped between the jaw members to at least one subsequent position wherein the cutting mechanism is disposed distal to tissue grasped between the jaw members. The instrument also includes a switch disposed on the first shaft. The switch is configured to be depressed between a first position and at least one subsequent position upon biasing engagement with a mechanical interface disposed on the second shaft upon movement of the jaw members from the first position to the second position. The first position of the switch relays information to the user corresponding to a desired pressure on tissue grasped between the jaw members and the at least one subsequent position is configured to activate the source of electrosurgical energy to supply electrosurgical energy to the jaw members. 
         [0015]    According to another embodiment of the present disclosure, a bipolar electrosurgical instrument includes first and second shafts each having a jaw member extending from its distal end and a handle disposed at its proximal end for effecting movement of the jaw members relative to one another about a pivot from a first position wherein the jaw members are disposed in spaced relation relative to one another to a second position wherein the jaw members cooperate to grasp tissue. Each jaw member is adapted to connect to a source of electrosurgical energy such that the jaw members are capable of selectively conducting energy through tissue held therebetween to effect a tissue seal. A knife channel is defined along a length of one or both of the jaw members. The knife channel is configured to reciprocate a cutting mechanism therealong to cut tissue grasped between the jaw members. The instrument also includes an actuator for selectively advancing the cutting mechanism from a first position wherein the cutting mechanism is disposed proximal to tissue grasped between the jaw members to at least one subsequent position wherein the cutting mechanism is disposed distal to tissue grasped between the jaw members. The instrument also includes a switch disposed on the first shaft. The switch is configured to be depressed between at least two positions upon biasing engagement with the second shaft upon movement of the jaw members from the first position to the second position. The switch generates a first tactile response upon movement to the first position of the switch and a subsequent tactile response upon movement to the at least one subsequent position of the switch. The first tactile response relays information to the user corresponding to a predetermined pressure on tissue grasped between the jaw members and the subsequent tactile response is configured to activate the source of electrosurgical energy to supply electrosurgical energy to the jaw members. 
         [0016]    According to another embodiment of the present disclosure, a method of performing an electrosurgical procedure includes the step of approximating first and second shafts of a bipolar forceps to grasp tissue between first and second jaw members associated with the first and second shafts. The method also includes the steps of depressing a switch upon approximation of the first and second shafts to a first position to relay information to the user corresponding to a predetermined grasping pressure applied to tissue grasped between the jaw members and depressing the switch to at least one subsequent position to activate a source of electrosurgical energy to supply electrosurgical energy to the jaw members. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0017]    Various embodiments of the subject instrument are described herein with reference to the drawings wherein: 
           [0018]      FIG. 1  is a right, perspective view of a forceps according to one embodiment of the present disclosure; 
           [0019]      FIG. 2  is an exploded view of the forceps of  FIG. 1 ; 
           [0020]      FIG. 3A  is an exploded view of an end effector assembly of the forceps of  FIG. 1 ; 
           [0021]      FIG. 3B  is a cross-sectional view of the end effector assembly of the forceps of  FIG. 1 ; 
           [0022]      FIG. 4A  is a side view of the forceps of  FIG. 1  with parts partially removed to show the electrical connection between a switch and the end effector assembly; 
           [0023]      FIG. 4B  is a left, perspective view of a jaw member of the end effector assembly of  FIG. 1 ; 
           [0024]      FIG. 4C  is a left, perspective view of a jaw member of the end effector assembly of  FIG. 1 ; and 
           [0025]      FIGS. 5A-5C  are side views of the forceps of  FIG. 1  illustrating actuation thereof between open and closed positions; and 
           [0026]      FIG. 6  is a side view of a knife for use with the forceps of  FIG. 1  according to one embodiment of the present disclosure. 
       
    
    
     DETAILED DESCRIPTION 
       [0027]    Referring initially to  FIGS. 1 and 2 , a forceps  10  for use with open surgical procedures includes elongated shaft portions  12   a  and  12   b  each having a proximal end  14   a,    14   b  and a distal end  16   a  and  16   b,  respectively. In the drawings and in the description that follows, the term “proximal”, as is traditional, will refer to the end of the forceps  10  that is closer to the user, while the term “distal” will refer to the end that is further from the user. 
         [0028]    The forceps  10  includes an end effector assembly  100  that attaches to the distal ends  16   a  and  16   b  of shafts  12   a  and  12   b,  respectively. The end effector assembly  100  includes pair of opposing jaw members  110  and  120  that are pivotably connected and movable relative to one another about a pivot  65  ( FIG. 2 ) to grasp tissue. Pivot  65  is disposed on a proximal end of jaw member  120  and includes opposing halves  65   a  and  65   b  disposed on opposing sides of a channel  126  ( FIG. 4C ) that is configured to facilitate reciprocation of a cutting mechanism or knife  85  therethrough ( FIG. 2 ), as discussed in detail below. 
         [0029]    Each shaft  12   a  and  12   b  includes a handle  15  and  17 , respectively, disposed at the proximal end  14   a  and  14   b  thereof. Each handle  15  and  17  defines a finger hole  15   a  and  17   a,  respectively, therethrough for receiving a finger of the user. Handles  15  and  17  facilitate movement of the shafts  12   a  and  12   b  relative to one another which, in turn, pivot the jaw members  110  and  120  from an open position wherein the jaw members  110  and  120  are disposed in spaced relation relative to one another to a clamping or closed position wherein the jaw members  110  and  120  cooperate to grasp tissue therebetween. 
         [0030]    As best seen in  FIG. 2 , shaft  12   a  is constructed from two components, namely,  12   a   1  and  12   a   2 , that are coupled together to form shaft  12   a.  Likewise, shaft  12   b  is constructed from two components, namely,  12   b   1  and  12   b   2 , that are coupled together to form shaft  12   b.  In some embodiments, component halves  12   a   1  and  12   a   2  and component halves  12   b   1  and  12   b   2  are ultrasonically welded together at a plurality of different weld points and/or may be mechanically coupled together by any suitable method including snap-fitting, adhesive, fastened, etc. 
         [0031]    The arrangement of shaft  12   b  is slightly different from shaft  12   a.  More particularly, shaft  12   a  is generally hollow to house the knife  85  and an actuating mechanism  40 . The actuating mechanism  40  is operatively associated with a trigger  45  having handle members  45   a  and  45   b  disposed on opposing sides of shaft  12   a  to facilitate left-handed and right-handed operation of trigger  45 . Trigger  45  is operatively associated with a series of suitable inter-cooperating elements (e.g.,  FIG. 2  shows a trigger link  43 , a knife pushing link  41 , a spring  49 , and an anti-deployment link  47 ) configured to mechanically cooperate (not explicitly shown) to actuate the knife  85  through tissue grasped between jaw members  110  and  120  upon actuation of trigger  45 . Handle members  45   a  and  45   b  operate in identical fashion such that use of either of handle members  45   a  and  45   b  operates the trigger  45  to reciprocate the knife  85  through the knife channel  115  ( FIG. 5C ). Further, the proximal end  14   b  of shaft  12   b  includes a switch cavity  13  protruding from an inner facing surface  23   b  of shaft  12   b  and configured to seat a depressible switch  50  therein (and the electrical components associated therewith). Switch  50  aligns with an opposing inner facing surface  23   a  of the proximal end  14   a  of shaft  12   a  such that upon approximation of shafts  12   a  and  12   b  toward one another, the switch  50  is depressed into biasing engagement with the opposing inner facing surface  23   a  of the proximal end  14   a  of shaft  12   a.    
         [0032]    As shown in  FIG. 1 , an electrosurgical cable  210  having a plug  200  at its proximal end connects the forceps  10  to an electrosurgical generator (not shown). More specifically, the distal end of the cable  210  is securely held to the shaft  12   b  by a proximal shaft connector  19  and the proximal end of the cable  210  includes a plug  200  having prongs  202   a,    202   b,  and  202   c  that are configured to electrically and mechanically engage the electrosurgical generator. 
         [0033]    The tissue grasping portions of the jaw members  110  and  120  are generally symmetrical and include similar component features that cooperate to permit facile rotation about pivot  65  to effect the grasping and sealing of tissue. As a result, and unless otherwise noted, jaw member  110  and the operative features associated therewith are initially described herein in detail and the similar component features with respect to jaw member  120  will be briefly summarized thereafter. 
         [0034]    With reference to  FIGS. 3A and 3B , jaw member  110  includes an outer housing  116   a,  first and second non-conductive plastic insulators  108   a  and  114   a,  and an electrically conductive sealing surface  112   a.  The first and second insulators  108   a  and  114   a  are overmolded about jaw housing  116   a  in a two-shot overmolding process. More specifically, the first insulator  108   a  is overmolded about jaw housing  116   a  to electrically insulate the jaw housing  116   a  from sealing surface  112   a  and the second insulator  114   a  is overmolded about jaw housing  116   a  to secure the electrically conductive sealing surface  112   a  thereto. This may be accomplished by stamping, by overmolding, by overmolding a stamped sealing surface, and/or by overmolding a metal injection molded sealing surface. The jaw members  110  and  120  are made from a conductive material. In some embodiments, the jaw members  110  and  120  are powder coated with an insulative coating to reduce stray current concentrations during sealing. 
         [0035]    As best shown by the cross-sectional view of  FIG. 3B , electrically conductive sealing surface  112   a  of jaw member  110  is pronounced from the jaw housing  116   a  and the second insulator  114   a  such that tissue is grasped by the opposing electrically conductive sealing surfaces  112   a  and  112   b  when jaw members  110  and  120  are in the closed position. 
         [0036]    Likewise, jaw member  120  includes similar elements that correspond to jaw member  110  including: an outer housing  116   b,  first and second plastic insulators  108   b  and  114   b,  and an electrically conductive sealing surface  112   b  that is pronounced from the jaw housing  116   b  and second insulator  114   b.  As described above with respect to jaw member  110 , the first insulator  108   b  electrically insulates the jaw housing  116   b  from the sealing surface  112   b  and the second insulator  114   b  secures the sealing surface  112   b  to the jaw housing  116   b.  Insulators  114   a  and  114   b  extend along the entire length of jaw members  110  and  120 , respectively, to reduce alternate or stray current paths during sealing. In some embodiments, each of sealing surfaces  112   a  and  112   b  may include an outer peripheral edge that has a radius such that each insulator  114   a  and  114   b  meets the respective sealing surface  112   a  and  112   b  along an adjoining edge that is generally tangential to the radius and/or meets along the radius. 
         [0037]    As shown in  FIGS. 3A and 3B , at least one of the jaw members, e.g., jaw member  120 , includes at least one stop member  750  disposed on the inner facing surfaces of the electrically conductive sealing surface  112   b  and/or  112   a.  Alternatively or in addition, the stop member(s)  750  may be disposed adjacent to the electrically conductive sealing surfaces  112   a,    112   b  or proximate the pivot  65 . The stop member(s)  750  facilitate gripping and manipulation of tissue and to define a gap between opposing jaw members  110  and  120  during sealing and cutting of tissue. In some embodiments, the stop member(s)  750  maintain a gap distance between opposing jaw members  110  and  120  within a range of about 0.001 inches (˜0.03 millimeters) to about 0.006 inches (˜0.015 millimeters). 
         [0038]    As shown in  FIG. 2 , shaft  12   b  includes a beam  57  disposed therein and extending between handle  15  and jaw member  110 . In some embodiments, the beam  57  is constructed of flexible steel to allow the user to generate additional sealing pressure on tissue grasped between the jaw members  110  and  120 . More specifically, once end effector assembly  100  is closed about tissue, the shafts  12   a  and  12   b  may be squeezed toward each other to utilize the flexibility of the beam  57  to generate the necessary closure pressure between jaw members  110  and  120 . In this scenario, the mechanical advantage realized by the compressive force associated with the beam  57  facilitates and assures consistent, uniform, and accurate closure pressure about tissue grasped between jaw members  110  and  120  (e.g., within a working pressure range of about 3 kg/cm 2  to about 16 kg/cm 2 ). By controlling the intensity, frequency, and duration of the electrosurgical energy applied to the tissue, the user can seal tissue. In some embodiments, the gap distance between opposing sealing surfaces  112   a  and  112   b  during sealing ranges from about 0.001 inches to about 0.005 inches. 
         [0039]    In some embodiments, the sealing surfaces  112   a  and  112   b  are relatively flat to avoid current concentrations at sharp edges and to avoid arcing between high points. In addition, and due to the reaction force of the tissue when engaged, each of jaw members  110  and  120  may be manufactured to resist bending, e.g., tapered along its length to provide a constant pressure for a constant tissue thickness at parallel and the thicker proximal portion of the jaw members  110  and  120  will resist bending due to the reaction force of the tissue. 
         [0040]    As shown in  FIGS. 3A ,  3 B,  4 B, and  4 C, at least one of jaw members  110  and  120  includes a knife channel  115   a  and/or  115   b,  respectively, disposed therebetween that is configured to allow reciprocation of a knife  85  therethrough. In the illustrated embodiment, a complete knife channel  115  is formed when two opposing channel halves  115   a  and  115   b  associated with respective jaw members  110  and  120  come together upon grasping of the tissue. Each plastic insulator  108   a  and  108   b  includes a trough  121   a  and  121   b,  respectively, that aligns in vertical registration with an opposing knife channel half  115   a  and  115   b,  respectively, such that knife  85  does not contact or cut through plastic insulators  108   a  and  108   b  upon reciprocation through knife channel  115 . In some embodiments, the width of knife channels  115   a  and  115   b  and their respective troughs  121   a  and  121   b  may be equal along an entire length thereof. 
         [0041]    As best shown in  FIG. 4A , the interior of cable  210  houses leads  71   a,    71   b  and  71   c.  Leads  71   a,    71   b,  and  71   c  extend from the plug  200  through cable  210  and exit the distal end of the cable  210  within the proximal connector  19  of shaft  12   b.  More specifically, lead  71   a  is interconnected between prong  202   b  and a first terminal  75   a  of the switch  50 . Lead  71   b  is interconnected between prong  202   c  and a solder sleeve  73   a  which, in turn, connects lead  71   b  to an RF lead  71   d  and to a second terminal  75   b  of the switch  50  via a connector lead  71   f.  RF lead  71   d  carries a first electrical potential of electrosurgical energy from lead  71   b  to sealing surface  112   a.  Lead  71   e  is interconnected between prong  202   a  and a solder sleeve  73   b  which, in turn, connects lead  71   c  to an RF lead  71   e.  RF lead  71   e  carries a second electrical potential of electrosurgical energy from lead  71   c  to sealing surface  112   b.    
         [0042]    With reference to  FIG. 4B , a lead channel  77  is defined in the proximal end of jaw member  110  to provide a pathway for lead  71   d  to connect to a junction  311   a  ( FIG. 3A ) extending from a proximal end of sealing surface  112   a.  A proximal end of lead channel  77  opens into a raceway  70  that includes a generally elongated configuration with a narrowed proximal end  72  and a broadened distal end  74  that defines an arcuate sidewall  68 . Lead  71   d  is routed to follow a path through the proximal end  72  of raceway  70  and, further, through lead channel  77  for connection to junction  311   a.    
         [0043]    With reference to  FIG. 4C , pivot halves  65   a  and  65   b  are disposed on opposing sides of channel  126  to facilitate translation of the knife  85  therethrough ( FIGS. 5A-5C ). Pivot halves  65   a  and  65   b  are disposed in a split spherical configuration and each include a respective base portion  165   a  and  165   b  that support an extension portion  166   a  and  166   b  thereon, respectively. Extension portions  166   a  and  166   b  are configured to engage correspondingly-dimensioned apertures  67   a  and  67   b,  respectively, disposed through pivot plate  66  to pivotably secure jaw member  110  to jaw member  120 . A lead channel  109  is defined in the proximal end of jaw member  120  to provide a pathway for lead  71   e  to connect to a junction  311   b  extending from a proximal end of sealing surface  112   b.  Lead  71   e  is routed to follow a path through raceway  70  and, further between opposing pivot halves  65   a  and  65   b  and through lead channel  109  for connection to junction  311   b.    
         [0044]    With reference to  FIGS. 5A-5C , as the user applies closure pressure on shafts  12   a  and  12   b  to depress switch  50  ( FIG. 5B ), a first threshold is met corresponding to the closure force applied to switch  50  as a function of displacement of switch  50  that causes switch  50  to generate a first tactile response that corresponds to a complete grasping of tissue disposed between jaw members  110  and  120 . Following the first tactile response, as the user applies additional closure pressure on shafts  12   a  and  12   b  ( FIG. 5C ), a second threshold is met corresponding the closure force applied to switch  50  as a function of displacement of switch  50  that causes the switch  50  to generate a second tactile response that corresponds to a signal being generated to the electrosurgical generator to supply electrosurgical energy to the sealing surfaces  112   a  and  112   b.  More specifically, the second tactile response indicates closing of a normally open circuit between switch terminals  75   a  and  75   b  and, in turn, establishment of an electrical connection between leads  71   a  and  71   b.  As a result of the electrical connection between leads  71   a  and  71   b,  the electrosurgical generator senses a voltage drop between prongs  202   b  and  202   c  and, in response thereto, supplies electrosurgical energy to sealing surfaces  112   a  and  112   b  via leads  71   d  and  71   e,  respectively. 
         [0045]    In one embodiment, the first tactile response indicates to the user that the maximum grasping pressure has been reached before end effector  100  is energized where the user is free to approximate, manipulate, and grasp tissue as needed. In this scenario, the second tactile response indicates to the user the electrosurgical activation of the end effector  100 . The switch  50  may include a plurality of other tactile responses between the above discussed first and second tactile responses and/or subsequent to the second tactile response that correspond to particular functions of the forceps  10  such as, for example, operation of the knife  85  and/or the actuation assembly  40 , operation of a safety lockout mechanism associated with the actuation assembly  40 , as discussed in detail below. 
         [0046]    As shown in  FIG. 4A , forceps  10  may include a gauge or sensor element  87  disposed within one or both of shafts  12   a,    12   b  such that the clamping or grasping forces being applied to target tissue by end effector  100  may be measured and/or detected. For example, in some embodiments, sensor element  87  may be a strain gauge  87  operably associated with one or both jaw members  110 ,  120 . Sensor element  87  may be one or more Hall effect sensors or strain gauges such as, for example, metallic strain gauges, piezoresistive strain gauges, that may be disposed within one or both of shafts  12   a  and  12   b  and/or within one or both of jaw members  110  and  120  to detect tissue pressure. Metallic strain gauges operate on the principle that as the geometry (e.g., length, width, thickness, etc.) of the conductive material changes due to mechanical stress, the resistance of the conductive material changes as a function thereof. This change in resistance is utilized to detect strain or applied mechanical stress such as, for example, the mechanical stress applied to tissue by jaw members  110  and  120 . Piezoresistive strain gauges operate based on the changing resistivity of a semiconductor due to the application of mechanical stress. 
         [0047]    Hall effect sensors may be incorporated to determine the gap between jaw members  110  and  120  based on a detected relationship between the magnetic field strength between jaw members  110  and  120  and the distance between jaw members  110  and  120 . 
         [0048]    In some embodiments, one or more reed switches  81   a,    81   b  may be incorporated within shafts  12   a  and  12   b  to determine the proximity thereof relative to one another, as shown in  FIG. 4A . More specifically, the reed switch(s) may be comprised of a switch  81   a  disposed within one of the shafts (e.g., shaft  12   a ) and a magnetic element  81   b  (e.g., electromagnet, permanent magnet, coil, etc.) disposed within the opposing shaft (e.g., shaft  12   a ) such that upon approximation of shafts  12   a  and  12   b,  the reed switch  81   a  is activated or closed by the magnetic field of the magnetic element  81   b  and, likewise, as shafts  12   a  and  12   b  are moved away from each other, the lack of magnetic field operates to deactivate or open the reed switch  81   a.  In this manner, the proximity of shafts  12   a  and  12   b  and thus, jaw members  110  and  120 , may be determined based on the reaction of the reed switch  81   a  to the magnetic element  81   b.    
         [0049]    Any of the above discussed sensors, switches, and/or strain gauge(s) may be incorporated within an electrical circuit such that the strain detected by the strain gauge changes the electrical signal through the circuit. With this purpose in mind, an electrical circuit between the strain gauge and the switch  50  and/or an electrosurgical generator (not shown) allows communication of information such as desired tissue pressure thereto. This information may be tied to the activation of switch  50  such that the switch is not activated until a desired and/or predetermined pressure on tissue grasped between jaw members  110  and  120  is achieved as detected by the strain gauge. Accordingly, the strain gauge may be disposed strategically on the forceps  10 , e.g., on one or more of jaw members  110 ,  120 , such that pressure applied to tissue grasped between jaw members  110  and  120  affects the strain gauge. 
         [0050]    In use, forceps  10  may be calibrated such that particular tactile responses (e.g., the first tactile response) of switch  50  corresponds to a predetermined grasping pressure on tissue as determined through use of one or more of the above discussed sensors, switches, and/or strain gauge(s). The predetermined grasping pressure about tissue is within the range of about 3 kg/cm 2  to about 16 kg/cm 2  in one embodiment and, in another embodiment, about 7 kg/cm 2  to about 13 kg/cm 2 . In some embodiments, switch  50  may generate multiple tactile responses, each of which corresponds to different predetermined grasping force. For a more detailed discussion of force sensing and/or measuring devices such as load cells, strain gauges, etc., reference is made to commonly-owned U.S. application Ser. No. 11/409,154, filed on Apr. 21, 2006. 
         [0051]    As shown in  FIGS. 2 ,  4 B, and  4 C, the pivot  65  connects through an aperture  125  defined through jaw member  120  and matingly engages a pivot plate  66  seated within a circumferential lip or flange  78  ( FIG. 4B ) defined around the periphery of aperture  125  such that the pivot  65  is rotatably movable within the aperture  125  to move jaw members  110  and  120  between open and closed positions. 
         [0052]    In some embodiments, actuation of the knife  85  is associated with activation of the switch  50 . For example, sensor  87  may be embodied as a position sensor configured to detect the position of knife  85  relative to jaw members  110  and  120  and/or relative to tissue held therebetween. Additionally or alternatively, sensor  87  may be configured to detect either of the first and second tactile responses of switch  50  and allow or prevent actuation of the knife  85  accordingly. For example, based on feedback from the sensor  87 , any one or more inter-cooperating elements or lockout mechanisms associated with the actuating mechanism  40  may be energized or de-energized to allow or prevent actuation of the knife  85 , as described in more detail below. 
         [0053]    As shown in  FIG. 7 , knife  85  includes a step  86  that reduces the profile of the knife  85  toward a distal end thereof. The distal end of the knife  85  has a step  88  that increases the profile of the knife  85  toward a sharpened distal cutting edge  89 . The knife  85  includes a chamfered portion  84  where the sharpened distal cutting edge  89  meets the step  88  to facilitate smooth retraction of knife  85  through the knife channel  15 . 
         [0054]    In some embodiments, the forceps  10  may include a safety lockout mechanism having a series of suitable inter-cooperating elements (e.g., anti-deployment link  47 , trigger link  47 ) that work together to prevent unintentional firing of the knife  85  when the jaw members  110  and  120  are disposed in the open position. Generally, the anti-deployment link  47  mechanically cooperates with the trigger link  43  to prevent advancement of the knife  85  until the jaw members  110  and  120  are closed about tissue. One such safety lockout mechanism for use with forceps  10  is described in commonly-owned U.S. application Ser. No. 12/896,100 entitled “Blade Deployment Mechanisms for Surgical Forceps”, filed on Oct. 1, 2010. 
         [0055]    In some embodiments, any one or more of the inter-cooperating elements of the safety lockout mechanism (e.g., anti-deployment link  47 ) may be electrically interconnected to the switch  50  and include suitable electro-mechanical components (e.g., springs, rods, solenoids, etc.) configured to be energized via activation of the switch  50  (e.g., via any one of leads  71   a,    71   b,    71   c,    71   d,    71   e ) to mechanically manipulate the safety lockout mechanism. For example, upon electrical conduction through leads  71   d  and  71   e  to energize the end effector  100 , the anti-deployment link  47  is energized to cause actuation thereof such that the safety lockout mechanism disengages to allow selective actuation of the knife  85 . In this scenario, by way of example, selective actuation of the knife  85  may be prevented until switch  50  has been depressed to generate at least the first tactile response. 
         [0056]    While several embodiments of the disclosure have been shown in the drawings, it is not intended that the disclosure be limited thereto, as it is intended that the disclosure be as broad in scope as the art will allow and that the specification be read likewise. Therefore, the above description should not be construed as limiting, but merely as exemplifications of particular embodiments. Those skilled in the art will envision other modifications within the scope and spirit of the claims appended hereto.