Abstract:
A bipolar electrosurgical instrument for vessel sealing comprises first and second members connected by a pivot. A pair of jaws have opposable seal surfaces that are designed to grasp vascular tissue and conduct bipolar electrosurgical current therethrough. Electrodes on the jaws, including the seal surfaces, are removable and disposable. The jaws of the instrument have mechanical interfaces designed to accept replacement electrodes. The instrument further comprises interlocking ratchets designed to hold a constant closure force between the seal surfaces. Wires extend from the electrodes along one of the members and are connectable to an electrosurgical generator.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application is a continuation of U.S. application Ser. No. 09/387,883 filed on Sep. 1, 1999 now abandoned, which is a continuation of U.S. application Ser. No. 08/968,496 filed on Nov. 12, 1997 now U.S. Pat. No. 6,080,996 both of which are hereby incorporated by reference in their entirety. 
    
    
     FIELD OF THE INVENTION 
     This invention relates to a bipolar electrosurgical instrument, and more particularly to a bipolar electrosurgical instrument having replaceable electrodes for sealing vessels and vascular tissue. 
     BACKGROUND OF THE DISCLOSURE 
     A hemostat is commonly used in surgical procedures to grasp, dissect and clamp tissue. It is typically a simple pliers-like tool that uses mechanical action between its jaws to constrict vessels without cutting them. It is also typical to have a interlocking ratchet between the handles so that the device can be clamped and locked in place. 
     Many hemostats are used in a typical open-surgical procedure. Once vascular tissue has been clamped with a hemostat, it is common for a surgeon to tie a suture around the tissue to close it off permanently prior to removing the hemostat. Several hemostats may be left in the surgical field until the surgeon has the opportunity to tie a suture around each section of clamped tissue. 
     Neurosurgeons have used bipolar instruments to coagulate vessels in the brain that are smaller than two millimeters in diameter. These bipolar instruments are typically tweezers-like devices with two arms that can be deflected toward each other to grasp tissue. However, it has been found that these instruments are not capable of sealing blood vessels with diameters larger than about two millimeters. There has been a long-felt need for an easy way to seal larger vessels and vascular tissue bundles without the need for sutures. 
     It is thought that the process of coagulating small vessels is fundamentally different then vessel sealing. Coagulation is defined as a process of desiccating tissue wherein the tissue cells are ruptured and dried. Vessel sealing is defined as the process of liquefing the collagen in the tissue so that it crosslinks and 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. 
     A number of bipolar electrosurgical forceps and clamps are known in the field. However, these instruments are not designed to apply the correct pressure to a blood vessel to achieve a lasting seal. All of these instrument also suffer from the drawback that they do not combine the simplicity and familiarity of a hemostat with a bipolar electrosurgical circuit. 
     An example of a bipolar electrosurgical power curve for vessel sealing is disclosed in a U.S. Patent application entitled, “Energy Delivery System for Vessel Sealing,” Ser. No. 08/530,495, filed Sep. 19, 1995, and is hereby incorporated by reference and made a part of this disclosure. 
     A U.S. Patent application entitled, “Vascular Tissue Sealing Pressure Control and Method,” Ser. No. 08/530,450, filed on Sep. 19, 1995, discloses another surgical tool for sealing vessels, and is hereby incorporated by reference and made a part of this disclosure. 
     U.S. Pat. No. 371,664 discloses a pair of electric forceps with positive and negative electric poles located on the jaws. 
     U.S. Pat. No. 728,883 discloses an electrothermic instrument in which electricity is used to heat one of the jaws of the instrument. 
     U.S. Pat. No. 1,586,645 disclose; a bipolar instrument for coagulating tissue. 
     U.S. Pat. No. 2,002,594 discloses a bipolar laparoscopic instrument for treating tissue, whereby coagulation and cutting of tissue can be performed with the same instrument. 
     U.S. Pat. No. 2,176,479 discloses an instrument for finding and removing metal particles. The jaws of the instrument are designed to complete an electrical circuit when conductive material is placed therebetween. An insulated pivot and an insulated ratchet are used to prevent a short circuit. 
     U.S. Pat. No. 3,651,811 discloses a bipolar electrosurgical instrument for cutting and coagulating tissue. 
     U.S. Pat. No. 4,005,714 discloses bipolar coagulation forceps with jaws that open and close by way of an actuating sleeve. 
     U.S. Pat. Nos. 4,370,980 and 5,116,332 disclose an electrocautery hemostats wherein the hemostatic clamping function and the electrocautery function may be accomplished with a single instrument. Monopolar electrosurgical designs are shown and described. 
     U.S. Pat. No. 4,552,143 discloses a family of removable switch electrocautery instruments, including an electrocautery hemostat. Monopolar electrosurgical designs are shown and described. 
     U.S. Pat. No. 5,026,370 discloses an electrocautery forceps instrument having an enclosed electrical switching mechanism. Monopolar electrosurgical designs are shown and described. 
     U.S. Pat. No. 5,443,463 discloses coagulating forceps having a plurality of electrodes. 
     U.S. Pat. No. 5,484,436 discloses bipolar electrosurgical instruments for simultaneously cutting and coagulating tissue. 
     The article, “The Mechanism of Blood Vessel Closure by High Frequency Electrocoagulation” discloses experiments upon the blood vessels of dogs. The sentence starting on the last line of page 823 describes “an electrode forceps, each of the blades being insulated form the other and each connected to a terminal of the high frequency generator.” 
     The article, “Studies on coagulation and development of an automatic computerized bipolar coagulator” discloses on page 150 that, “It was not possible to coagulate safely arteries with a diameter larger than 2 to 2.5 mm.” On page 151, line 5, it is noted that “Veins can be coagulated safely up to a diameter of 3 to 4 mm.” 
     Russian Patent 401,367, translation enclosed, discloses a bipolar instrument with a linkage that brings the working jaws together in a parallel manner. 
     Prior disclosures have not provided a design for a bipolar electrosurgical instrument with removable electrodes capable of conveniently applying a constant pressure, from a calibrated spring-loaded source held by a ratchet, that is sufficient to seal vessels and vascular tissue. 
     SUMMARY OF THE INVENTION 
     It is the general object of this invention to provide a bipolar electrosurgical instrument or sealing vessels and vascular tissue. The instrument is designed to grasp and clamp vessels or vascular tissue between its jaws. The jaws have removable electrodes that are electrically connected to an electrosurgical generator. Electrosurgical current flows through the clamped tissue between the electrodes. The instrument is bipolar because electrosurgical current flows from one electrode, through the tissue, to another electrode, and both electrodes are located on the instrument. In contrast, a monopolar instrument requires a separate electrode (sometimes called an “neutral electrode”) that is located remote from the instrument. 
     One of the advantages of the instrument is that vessels and vascular tissue can be sealed without the use of sutures, staples, or other material that is foreign to the tissue. 
     Another advantage of the instrument is that the removable electrodes provide safety against electrical shocks and bums. Electrically insulative materials, such as plastics, can be damaged or compromised by repeated sterilization cycles. It is also possible for electrical insulation to be cut or nicked by sharp surgical tools. Removable electrodes provide a safety advantage because they can be replaced prior to each procedure. The electrodes can also be replaced at any tune if the surgeon suspects an electrical insulation failure. This advantage is particularly important for vessel sealing instruments because currents up to 4 amperes may be used. 
     The present invention is a bipolar electrosurgical instrument comprising first and second members having first and second jaws near a distal end, and having first and second handles near a proximal end. A pivot joint connects the first and second members to allow for arcuate motion of the first and second jaws toward each other. First and second mechanical interfaces are located respectively on the first and second jaws. The first and second mechanical interfaces are preferably shaped to removably mate with first and second electrodes. The mating portion of the electrodes are made from an insulative material to prevent electrical conduction to the members. Seal surfaces on the opposable electrodes are preferably designed to clamp vessels and vascular tissue and conduct electrosurgical current therethrough in a bipolar circuit. First and second interlocking ratchets are located on the proximal end of the members to provide a constant closure force between the seal surfaces. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of a bipolar electrosurgical instrument showing the electrodes mated together in parallel opposition. 
     FIG. 2 is a perspective view of a bipolar electrosurgical instrument, showing one electrode removed with the socket in view, and one electrode in place. 
     FIG. 3 is a perspective view of a bipolar electrosurgical instrument, showing one electrode in place and one electrode removed. 
     FIG. 4 is a bottom view of a replaceable electrode showing the electrically insulative substrate with a portion of a wire attached. 
     FIG. 5 is a side view of FIG.  4 . 
     FIG. 6 is a detail view of a forked snapfit extension. 
     FIG. 7 is a perspective view of a replaceable electrode. 
     FIG. 8 is side view of an electrode showing a forked snapfit extension. 
     FIG. 9 is a partial side view of a portion of a socket designed to receive the snapfit extension. 
     FIG. 10 is a partial side view of an electrode seated in a socket. 
     FIG. 11 is an enlarged view of a portion of a snap-fit extension seated in a socket. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to FIG. 1, a bipolar electrosurgical instrument  10  is shown with replaceable electrodes  11  and  12  for sealing vessels and vascular bundles. The instrument  10  comprises a first member  13  and a second member  14  that are connected at a pivot joint  15 . Handles  16  and  17  are located generally at the proximal end  18 . Jaws  19  and  20  are located generally at the distal end  21 . Sockets  22  and  23  are located on the jaws  19  and  20 . The sockets  22  and  23  each preferably comprise several features, as shown in FIG. 2 at the location where the electrode  11  is removed. In one embodiment, shown in FIG. 1, the jaws  19  and  20  are straight. In alternative embodiments, the jaws  19  and  20  may be curved to accept curved electrodes  11  and  12 , as shown in FIG.  4 . 
     The first and second electrodes  11  and  12  are removably mounted respectively in the first and second sockets  22  and  23 . While the term socket is used herein, it will be understood that either a male or female mechanical interface may be used on the jaws  19  and  20 , with a mating mechanical interface on the electrodes  11  and  12 . In FIG. 2, one of the sockets  22  is shown with the electrode  11  removed. FIG. 3 shows the socket  23  with an electrode  12  mated therein. 
     Each of the first and second electrodes  11  and  12  has an electrically conductive seal surface  24  and an electrically insulative substrate  25 , as shown in FIGS. 5 and 7. Each substrate  25  is shaped to engage one of the first or second sockets  22  or  23  with mating features that fit removably within the sockets  22  or  23 . In the preferred embodiment, the seal surfaces  24  are relatively flat to avoid current concentrations at sharp edges, and to avoid arcing between high points. 
     First and second wires  26  and  27  are connected to the first and second electrodes  11  and  12 , respectively, as shown in FIGS. 1,  4 ,  5 , and  7 . In the preferred embodiment, the wires  26  and  27  are bundled together along one of the members  13  or  14  from the proximal end  18  to the pivot  15 . Near the pivot  15 , the wires  26  and  27  are separated and connected each to its respective electrode  11  or  12 . This arrangement of wires  26  and  27  is designed to be convenient for the surgeon so that there is little interference with the manipulation of the instrument  10 . The wires  26  and  27  are preferably terminated in a connector  2  near the proximal end  18 , although in another embodiment the wires  26  and  27  may extend all the way to an electrosurgical generator. In an alternative embodiment, the wires  26  and  27  each extend along a separate handle  16  or  17 . 
     First and second ratchets,  29  and  30 , are located on the members  13  and  14  near the handles  16  and  17 , as shown in FIGS. 1,  2 , and  3 . The ratchets  29  and  30  interlock in at least one position, shown in FIG. 1 at  31 . In the preferred embodiment, there are several interlocking positions. The ratchet position  31  holds strain energy in the first and second members  13  and  14  to force the electrodes  11  and  12  against each other in opposition. 
     Each member  13  and  14  is preferably designed to deflect in a shank portion, defined as the section between the pivot  15  and the location of the ratchet. The jaws  19  and  20  are preferably more rigid than the shank portions. A lateral deflection of the shank portion causes strain due to bending that behaves like a spring. The strain energy that is stored in the shank provides a constant closure force between the electrodes  11  and  12 . A design without a ratchet requires the surgeon to hold the electrodes together by applying a constant squeeze to the handles. It has been found through experimentation that a constant force throughout the sealing process will yield a more predictable surgical outcome. It is difficult to hold a constant force by hand, therefore a ratchet in combination with a deflectable shank mill provide a better surgical outcome. 
     The electrically insulative substrate  25  on each of the electrodes  11  and  12  is preferably made from an injection moldable plastic. The substrate  25  is preferably overmolded to capture the electrically conductive seal surface  24 , as shown in FIG.  8 . Wires  26  and  27  are electrically connected to the seal surface  24  of each electrode  11  or  12 . There is preferably a strain relief feature  33  on the electrodes  11  and  12 , as shown in FIGS. 4 and 7. 
     The substrate  25  preferably comprises a forked snap fit extension  32  as shown in detail in FIG.  6 . Each jaw  19  and  20  has a socket  22  and  23  that comprises a recess  34 , shown in FIG. 9, shaped to capture the forked snap fit extension  32 . One of the advantages of this design is that manufacturing tolerances can be accommodated by the snap fit as shown in FIG.  11 . The preferred embodiment also comprises a pair of alignment pins  37  and  35  that fit into the sockets  22  and  23 . 
     In the preferred embodiment, the instrument  10  is designed so that the electrodes  11  and  12  meet in parallel opposition. Thus, opposing seal surfaces  24  meet each other in the same plane, as shown in FIG.  1 . In an alternative embodiment, the seal surfaces can be slightly biased to meet each other at the distal end, and further closure force at the handles will cause the seal surface  24  on each electrode  11  and  12  to deflect together in the same plane. In certain embodiments, there may be a stop to create a fixed gap, preferably about 0.3 millimeters, to prevent shorting of the electrodes. Other embodiments have an insulative element on each jaw that opposes the conductive seat surface  24  on the opposing jaw, such that the instrument  10  does not short circuit when the jaws  19  and  20  are closed together. 
     It has been determined experimentally that the closure force between the seal surfaces  24  is preferably sufficient to overcome a tendency of the tissue to expand during heating. The sealed tissue thickness must be less than the initial tissue thickness, under pressure, in order to create a fused vessel wall. The amount of pressure required depends on the type of tissue, and the dimensions of the seal surfaces  24 , and the size of the tissue that is grasped with the instrument  10 . The pressure is expressed herein as a formula depending on the width of the seal surface and the closure force between the seal surfaces. 
     For an instrument designed for abdominal vessels and vascular bundles, each seal surface  24  has a width that is preferably in the range of 2 to 5 millimeters, and a length in the range of 10 to 30 millimeters. For abdominal vessels and vascular bundles, experimental results indicate that good vessel sealing performance can be achieved when the instrument  10  is calibrated to have at least one ratchet position  31  set such that the closure force (in grams) divided by the width of the seed surface (in millimeters) is in the range of 400 to 650, and most preferably 525. For example, an instrument with a seal surface width of 4 millimeters would preferably have a closure force of 2100 grams. 
     For an instrument designed for thick connective tissues and ligaments, particularly a hysterectomy style Heaney device, the closure force (in grams) divided by the width of the seal surface (in millimeters) is in the range of 1000 to 2000. Such an instrument would also preferably have a cross hatched or knurled seal surfaces  24  to improve grasping capability, but the height of the roughness features should be minimized to avoid arcing. 
     While a particular preferred embodiment has been illustrated and deck the scope of protection sought is in the claims that follow.