Abstract:
Components for an endoscopic vessel harvesting system suitable for harvesting target vessels such as the saphenous vein or radial artery for cardiac artery bypass graft surgery. The main components of such systems include a vessel dissector and a vessel harvester, both of which work in conjunction with a separately provided endoscope. The vessel dissector is an elongated cannula having a blunt tip for separating layers of facial around vessels. The tip may be movable, and is typically transparent to permit viewing forward of the tip using the endoscope. Internal features of the tip may reduce glare back to the endoscope. Several devices improve visibility through the tip by reducing interference from tissue or fluid on the tip. The vessel harvester also has an elongated cannula for receiving the endoscope. Several tools within the harvester permit manipulation, severing, and sealing of vessels forward of the distal end. The tool for manipulating vessels may have a low-profile for increased visibility of operation, and may be coupled to the cannula with a damping mechanism to reduce the possibility of avulsion of the vessels. Various vessel cutting and sealing devices are provided that may accommodate various sizes of vessels and improve cutting and sealing efficacy.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to surgical devices and methods for dissection and removal of blood vessels from a patient&#39;s body and, in particular, to endoscopic vessel harvesting systems, components and methods. 
       BACKGROUND OF THE INVENTION 
       [0002]    Endoscopic harvesting of vessels is well known in the surgical field and has been the subject of a great deal of recent technological advancement. Typically, the harvested vessel is used for bypass or as a shunt around an artery that has diminished flow from stenosis or other anomaly, such as in a Coronary Artery Bypass Grafting (CABG) procedure. Often in CABG, a saphenous vein from the patient&#39;s leg is harvested for subsequent use in the surgery. Other vessels, such as the radial artery, can also be harvested and used in this manner. Vessel harvesting involves liberating the vessel from surrounding tissue and transecting smaller side branches, cauterizing, tying or ligating the vessel at a proximal site and a distal site, and then transecting the vessel at both sites before it is removed from the body. 
         [0003]    Known endoscopic methods and devices for performing vessel harvesting are discussed in detail in U.S. Pat. Nos. 6,176,825 to Chin, et al., Re 36,043 to Knighton, 6,406,425 to Chin, et al., and 6,471,638 to Chang, et al., all of which are expressly incorporated herein by reference. Furthermore, various devices and methods disclosed in U.S. Pat. Nos. 5,895,353 to Lunsford, et al., and 6,162,173 to Chin, et al., and pending patent application Ser. No. 10/602,490 entitled “Apparatus and Method for Integrated Vessel Ligator and Transector” are also expressly incorporated herein by reference. Also, commercial vessel harvesting systems sold under the tradename VASOVIEW® Uniport Plus, VASOVIEW® 5, VASOVIEW® 6, and VASOVIEW® 7 are available from Guidant Corporation of Santa Clara, Calif. 
         [0004]    Another version of an endoscopic vessel harvesting system is disclosed in U.S. Patent Publication No. 2003/0130674 to Kasahara, et al., filed on Dec. 24, 2002, or and later updated in U.S. Patent Publication No. 2005/0159764 also to Kasahara, et al., filed Oct. 27, 2004. In these systems, various devices are utilized to first dissect a vein from surrounding tissue and then harvest the vein. Each of the devices passes through a guide tube of a trocar inserted through a body surface, such as disclosed in U.S. Pat. No. 6,863,674 also to Kasahara, et al., filed Dec. 23, 2002. Certain elements of these and other related patent disclosures are evident in the VirtuoSaph™ endoscopic vein harvesting system (see, www.terumo-cvs.com/products) marketed by Terumo Cardiovascular Systems Corp. of Japan. 
         [0005]    Despite accepted endoscopic vessel harvesting systems and techniques, there remains a need for systems and components that both make the user&#39;s task less complicated and improve the surgical outcome. 
       SUMMARY OF THE INVENTION 
       [0006]    The present invention provides an endoscopic vessel harvesting system suitable for harvesting various target vessels that allows for simple and convenient operation in a limited space. The invention includes improvements to various components of vessel harvesting systems each of which can be used with any of the other component improvements. It should be understood, therefore, that even if a particular combination is not explicitly described, any one component can be used with any other component disclosed herein unless that combination is structurally impossible. 
         [0007]    In accordance with a first embodiment, the present invention provides a vessel dissector that is used in conjunction with an endoscope, comprising an elongated cannula including a lumen therein for receiving the endoscope, the elongated cannula further housing a passage for delivery of an insufflation gas therethrough. The vessel dissector has an input for connecting to a supply of insufflation gas, the input being in fluid communication with the passage. A port opens near the distal end of the elongated cannula in fluid communication with the passage and out of which insufflation gas is expelled. A fluid barrier covers the port that permits expulsion of insufflation gas from the passage within the elongated cannula and prevents ingress of fluid from outside the elongated cannula through the port to the passage. 
         [0008]    The port may be formed in the side of the elongated cannula. Desirably, the fluid barrier comprises a tubular member surrounding the distal end of the elongated cannula and covering the port. In one embodiment, the fluid barrier comprises a polymer shield that closes off the port from the outside but is flexible so that insufflation gas may escape from the passage therethrough. In another embodiment, the fluid barrier comprises a gas-permeable liquid-resistant membrane that permits escape of insufflation gas therethrough but prevents entrance of fluid to the passage. 
         [0009]    The vessel dissector may further include a transparent conical tip on a distal end of the elongated cannula that permits an operator of the dissector to dissect tissue while viewing internal body structures via an objective lens of the endoscope positioned close to the blunt tip. The insufflation gas port may be located at the apex of the conical tip. The vessel dissector may also have a coupling between the distal end of the elongated cannula and the transparent blunt tip and a control member extending through the elongated cannula to enable the user to angle the tip relative to the axis of the elongated cannula. For instance, the coupling may be an accordion-like flexible interface or sleeve, or a spherical bearing surface. 
         [0010]    In accordance with a second embodiment, the present invention provides a vessel dissector that is used in conjunction with an endoscope, comprising an elongated cannula including a lumen therein for receiving the endoscope. A hollow outwardly conical transparent dissecting tip on a distal end of the elongated cannula permits an operator of the dissector to dissect tissue while viewing internal body structures via an objective lens of the endoscope. The tip comprises a structure generally arranged about an axis and having an inner wall that terminates at a distal end in a shape that tends to reduce glare back to the objective lens of the endoscope in comparison to a conical inner wall that tapers symmetrically to an apex. For example, the shape of the distal end of the inner wall of the dissecting tip may be an inner tapering surface that terminates at its distal end in a line so as to form an elongated inner corner, an inner surface that tapers downward toward its distal end and terminates in a flat surface set at an angle from the axis of the tip, or a backward wedge. Desirably, the dissecting tip has a tip diameter and the elongated cannula has a diameter adjacent the dissecting tip that is between about 50-75% of the tip diameter. 
         [0011]    In a more robust system, the vessel dissector may also include a vessel holding tool extending through the elongated cannula and adapted for longitudinal movement therein, and a vessel severing tool such as a tissue welder extending through the elongated cannula and adapted for longitudinal movement therein. In this embodiment, the dissecting tip includes apertures for passage of the vessel holding tool and the vessel severing tool. Preferably, both the vessel holding tool and the vessel severing tool dock into recesses in the dissecting tip and have exterior shapes that conform to the conical exterior of the dissecting tip so as to match its shape. 
         [0012]    In accordance with a third embodiment, the present invention provides a vessel dissector that is used in conjunction with an endoscope. The vessel dissector is defined by an elongated cannula including a lumen therein for receiving the endoscope. A transparent blunt tip on a distal end of the elongated cannula permits an operator of the dissector to dissect tissue while viewing internal body structures via an objective lens of the endoscope. A wiper clears tissue from the exterior of the transparent blunt tip. The wiper may be arranged on the elongated cannula to pivot about an axis to alternately contact and disengage from the transparent blunt tip, and a mechanism for rotating the blunt tip. Alternatively, the wiper is arranged on the elongated cannula to contact the blunt tip and swivel about the axis of the device. Still further, the wiper may be an O-ring wiper fitted over the blunt tip and connected to an actuation rod that displaces the O-ring wiper longitudinally to wipe over the blunt tip. In one embodiment, the wiper is arranged on the elongated cannula to contact the blunt tip and has an energized cutting electrode thereon to remove tissue via ablation. Preferably, a handle disposed at a proximal end of the elongated cannula has a thumb lever thereon connected to an actuating rod for displacing the wiper relative to the transparent blunt tip and clearing tissue therefrom. 
         [0013]    In accordance with a fourth embodiment, a vessel harvester used in conjunction with an endoscope comprises an elongated cannula including a lumen therein for receiving the endoscope, and a vessel holding tool extending through the elongated cannula and adapted for longitudinal movement therein. A distal end of the vessel holding tool includes a vessel hook and a locking member used to capture a target vessel, wherein the hook is open on one side and extension of the locking member closes the open side so that the target vessel is completely surrounded and captured therein. A vessel severing tool extends through the elongated cannula for longitudinal movement therein, and has a distal operative end with structure for severing a target vessel. The vessel holding tool includes a support rod that extends through the elongated cannula and which is configured to angle laterally at a location close to the distal end of the tool to enable lateral vessel manipulation and improve positioning of the vessel severing tool relative to the target vessel. 
         [0014]    Desirably, the support rod is bent out of a plane in which the support rod lies at a location close to the distal end of the vessel holding tool such that the distal end angles either toward or away from the vessel severing tool. The support rod may be flexible such that the bend is retracted into the cannula and distal extension of the vessel holding tool from the end of the elongated cannula displaces its distal end laterally. A flexible support rod may be surrounded by a rigid hypotube also adapted for longitudinal movement with respect to the cannula, wherein extension of both the support rod and hypotube from the cannula and then retraction of the hypotube from around the support rod angles the vessel holding tool. Alternatively, the support rod is bent out of a plane in which the support rod lies at a location close to the distal end of the vessel holding tool using an active angling mechanism controlled from a proximal end of the elongated cannula. 
         [0015]    The vessel hook of the vessel holding tool may include a blunt tapered distal dissecting surface for blunt dissection of tissue. Further, the vessel hook of the vessel holding tool defines a space therein for receiving a target vessel, and the locking member may be shaped as a large wedge to reduce the space within the open vessel hook by about 50% and includes a tapered leading edge that helps prevent pinching of the target vessel as the locking member extends. 
         [0016]    In accordance with a fifth embodiment, the present invention provides a vessel harvester that is used in conjunction with an endoscope, comprising an elongated cannula including a lumen therein for receiving the endoscope. A vessel severing tool extends through the elongated cannula for longitudinal movement therein, the severing tool having a distal operative end with structure for severing a target vessel. A vessel holding tool also extends through the elongated cannula for longitudinal movement therein and has a single support rod that extends through the elongated cannula and a distal end with a vessel hook and a locking member used to capture a target vessel and manipulate it to present a side branch of the target vessel to the vessel severing tool. The hook is open on one side and extension of the locking member closes the open side so that the target vessel is completely surrounded and captured therein. The locking member extends concentrically from the single support rod on one lateral side of the vessel hook, the single support rod therefore reducing endoscopic viewing impediments relative to more than one support rod. 
         [0017]    The support rod may be configured to angle laterally at a location close to the distal end of the tool to enable lateral vessel manipulation and improved positioning of the vessel severing tool relative to the target vessel. Desirably, the vessel hook of the vessel holding tool includes a blunt tapered distal dissecting surface for blunt dissection of tissue. 
         [0018]    In accordance with a sixth embodiment, the present invention provides a vessel harvester that is used in conjunction with an endoscope, comprising an elongated cannula including a lumen therein for receiving the endoscope. A vessel severing tool extends through the elongated cannula for longitudinal movement therein, the severing tool having a distal operative end with structure for severing a target vessel. A vessel holding tool also extends through the elongated cannula for longitudinal movement therein. The vessel holding tool has a support rod that extends through the elongated cannula and a distal end with a vessel hook and a locking member used to capture a target vessel and manipulate it to present a side branch of the target vessel to the vessel severing tool. The hook is open on one side and extension of the locking member closes the open side so that the target vessel is completely surrounded and captured therein. The distal end of the vessel holding tool including the hook and locking member are constructed of a thin wireform for reduced impediment to endoscopic viewing. Preferably, the thin wireform is formed of metal or plastic wires having a thickness of between about 0.5 mm and 1.0 mm. Desirably, the support rod is configured to angle laterally at a location close to the distal end of the tool to enable lateral vessel manipulation and improved positioning of the vessel severing tool relative to the target vessel. 
         [0019]    In accordance with a seventh embodiment, the present invention provides a vessel harvester that is used in conjunction with an endoscope, comprising an elongated cannula including a lumen therein for receiving the endoscope. A vessel severing tool extends through the elongated cannula for longitudinal movement therein, the severing tool having a distal operative end with structure for severing a target vessel. A vessel holding tool also extends through the elongated cannula for longitudinal movement therein. The vessel holding tool has a support rod that extends through the elongated cannula and a distal end with a vessel holder used to capture a target vessel and manipulate it to present a side branch of the target vessel to the vessel severing tool. A damped slip mechanism provided around the support rod of the vessel holding tool permits relative movement between the cannula and the support rod if the vessel holder catches on any body structure and generates a reaction force in the support rod in opposition to movement of the cannula. For instance, the damped slip mechanism comprises a friction collar surrounding the support rod, or a piston/cylinder/spring arrangement that couples movement of the support rod and cannula. 
         [0020]    In a preferred embodiment wherein the vessel holder of the vessel holding tool is open on one side and defines a space therein for receiving a target vessel. A locking member moves to close the open side of the holder so that the target vessel is completely surrounded and captured therein. The locking member is shaped as a large wedge to reduce the space within the open vessel holder by about 50% and includes a tapered leading edge that helps prevent pinching of the target vessel as the locking member moves. Also, the vessel holding tool has improved visibility by virtue of a single support rod that extends through the elongated cannula, wherein the locking member extends concentrically from the single support rod on one lateral side of the vessel holder, the single support rod therefore reducing endoscopic viewing impediments relative to more than one support rod. Desirably, the distal end of the vessel holding tool including the holder and locking member are constructed of a thin wireform for reduced impediment to endoscopic viewing. 
         [0021]    In accordance with an eighth embodiment, the present invention provides a vessel harvester that is used in conjunction with an endoscope, comprising an elongated cannula including a lumen therein for receiving the endoscope. A vessel severing tool extends through the elongated cannula for longitudinal movement therein, the severing tool has a distal operative end with an open mouth for receiving a target vessel that automatically accommodates widely varying sizes of vessel, and a severing device associated with the mouth. A vessel holding tool extends through the elongated cannula for longitudinal movement therein, the vessel holding tool having structure used to capture a target vessel and manipulate it to relative to the vessel severing tool. The mouth of the vessel severing tool preferably accommodates vessels having diameters that range from between 0.5 and 1.0 mm. 
         [0022]    In one embodiment, the mouth has facing vessel contacts that flex apart upon receiving a vessel therebetween. The severing device may have bipolar electrodes disposed to contact a target vessel received within the mouth. For instance, the bipolar electrodes comprise wire electrodes arranged in a crossing pattern in the mouth. In another version, the mouth has a stepped shape with several progressively smaller intermediate gaps having generally parallel sides that provide regions of constant width surface contact with the vessel. The intermediate gaps may have widths in decreasing increments of 1.0 mm. The severing device may be a mechanical cutter disposed transverse to a target vessel received within the mouth. For efficacy, a fluid conduit terminates close to the distal operative end of the vessel severing tool and is adapted to deliver a fluid jet to knock away tissue that may stick to the distal operative end. 
         [0023]    The vessel severing tool may be connected to a control rod and located within an arcuate slot formed in the elongated cannula, the control rod being capable of translating the distal operative end laterally within the arcuate slot as well as longitudinally. The mouth of the vessel severing tool may open to one side of the distal operative end. The vessel holding tool may includes a support rod that extends through the elongated cannula and is bent out of a plane in which the support rod lies at a location close to the distal end of the vessel holding tool such that the distal end angles either toward or away from the vessel severing tool. 
         [0024]    In accordance with a ninth embodiment, the present invention provides a vessel harvester that is used in conjunction with an endoscope, comprising an elongated cannula including a lumen therein for receiving the endoscope. A pair of partial tubular vessel shields extend from the cannula and define a lumen sized to receive a target vessel, the partial tubular vessel shields defining gaps therebetween sized to receive a side branch extending from the target vessel. A tubular cutting element sized to surround the partial tubular vessel shields and axially displaceable from the cannula, advances to sever any side branch received within the gaps while the partial tubular vessel shields protect the target vessel from the severing operation. The vessel severing tool may be a tubular knife blade. A fluid conduit terminating close to the partial tubular vessel shields may be adapted to deliver a fluid jet to knock away tissue that may stick to the vessel shields. 
         [0025]    In accordance with a tenth embodiment, the present invention provides a vessel harvester that is used in conjunction with an endoscope, comprising an elongated cannula including a lumen therein for receiving the endoscope. A pair of fork-shaped vessel sealing electrodes having tines are spaced laterally apart so as to create a gap therebetween. A vessel capturing mandible moves within the gap between the electrodes to capture a target vessel positioned between the tines. A severing blade moves within the gap and sever the target vessel. Desirably, the vessel capturing mandible has a serrated distal finger to securely capture the target vessel within the tines. Both of the vessel capturing mandible and severing blade may have control rods and angled proximal surfaces that cam against a distal end of the elongated cannula and displace them toward one another upon proximal retraction of the control rods. A fluid conduit terminating close to the fork-shaped vessel sealing electrodes may deliver a fluid jet to knock away tissue that sticks to the sealing electrodes. 
         [0026]    A further understanding of the nature and advantages of the present invention are set forth in the following description and claims, particularly when considered in conjunction with the accompanying drawings in which like parts bear like reference numerals. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0027]    Features and advantages of the present invention will become appreciated as the same become better understood with reference to the specification, claims, and appended drawings wherein: 
           [0028]      FIG. 1A  is a perspective view of an endoscopic vessel dissector of the prior art; 
           [0029]      FIG. 1B  is a perspective view of an endoscopic vessel harvester of the prior art; 
           [0030]      FIG. 1C  is a perspective view of an access trocar of the prior art; 
           [0031]      FIGS. 2A and 2B  are side views of the distal end of alternative vessel dissectors of the present invention including articulated dissecting tips; 
           [0032]      FIG. 3  is a side view schematically illustrating the possible path of bodily fluids into the prior art endoscopic vessel dissector of  FIG. 1A ; 
           [0033]      FIGS. 4A and 4B  are side views of the distal end of alternative vessel dissectors of the present invention including structures for inhibiting ingress of bodily fluids into the dissector cannula; 
           [0034]      FIG. 5A  is a schematic side view of an endoscopic vessel dissector of the prior art passing through body tissue; 
           [0035]      FIG. 5B  is a schematic side view of an endoscopic vessel dissector of the present invention having a narrowed cannula for easier passage through body tissue; 
           [0036]      FIGS. 6A-6C  are longitudinal sectional views through alternative transparent conical tips for use with endoscopic vessel dissectors of the present invention; 
           [0037]      FIG. 7  is a schematic sectional view of the distal end of an alternative endoscopic vessel dissector of the present invention which incorporates tools for harvesting vessels; 
           [0038]      FIG. 8  is a perspective view of an endoscopic vessel dissector of the present invention having a wiper blade for clearing the distal tip; 
           [0039]      FIGS. 9 and 10  are perspective views of the distal tip of two alternative endoscopic vessel dissectors of the present invention both having tip wiping capabilities; 
           [0040]      FIGS. 11A and 11B  are schematic side views of an endoscopic vessel harvester of the prior art showing vessel holding and severing tools extended from the distal end of a cannula; 
           [0041]      FIGS. 12A and 12B  are schematic side views of an endoscopic vessel harvester of the present invention showing vessel holding and severing tools extended from the distal end of a cannula wherein the vessel holding tool translates laterally for better vessel retraction; 
           [0042]      FIG. 13  is a schematic side view of an alternative endoscopic vessel harvester of the present invention wherein a vessel holding tool includes a tip angled toward the vessel severing tool; 
           [0043]      FIGS. 14A-14C  are several views of the transverse displacement of an alternative vessel holding tool from an endoscopic vessel harvester of the present invention; 
           [0044]      FIGS. 15A-15B  are side and perspective views of an alternative vessel holding tool of the present invention having one connecting rod; 
           [0045]      FIGS. 16A-16B  are side and perspective views of a low profile vessel holding tool of the present invention formed of thin wire; 
           [0046]      FIGS. 17A-17B  are partial sectional views of alternative vessel holding tools of the present invention incorporating a mechanism for preventing vessel avulsion; 
           [0047]      FIG. 18  is a side view of the distal end of an alternative vessel holding tool of the present invention having an enlarged locking member for better positioning of the vessel; 
           [0048]      FIGS. 19A and 19B  are schematic views of an alternative vessel severing tool of the present invention having wire electrodes extending into an enlarged vessel-receiving gap; 
           [0049]      FIG. 20  is a schematic view of an alternative vessel severing tool of the present invention having a stepped vessel receiving gap; 
           [0050]      FIGS. 21A-21B  are two side views of a vessel severing tool of the present invention having movable jaws; 
           [0051]      FIG. 22  is a side view of a vessel severing tool of the present invention having rotary blades incorporated therein; 
           [0052]      FIGS. 23A-23B  are two side views of a vessel severing tool of the present invention having a movable blade; 
           [0053]      FIG. 24  is a schematic view of a vessel severing tool of the present invention having a system for clearing tissue therefrom using gas jets; 
           [0054]      FIGS. 25A-25B  are front and top section views, respectively, of an alternative vessel severing tool of the present invention capable of translating transversely as well as longitudinally; 
           [0055]      FIG. 26  is a schematic front view of an alternative vessel severing tool of the present invention having a tubular cutting element surrounding a tubular primary vessel shield; 
           [0056]      FIGS. 27A-27B  are side elevational and top plan views, respectively, of a further alternative vessel severing/sealing tool that incorporates a movable mandible for capturing a vessel and a mechanical blade for severing it; 
           [0057]      FIGS. 28A-28B  are two schematic views of a side-opening vessel severing/sealing tool; 
           [0058]      FIG. 29  is a longitudinal endoscopic view showing the use of the tool in  FIGS. 28A-28B ; and 
           [0059]      FIG. 30  is a top plan view of an alternative severing tool having a ring and concentric coil bipolar electrode structure. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0060]    The present application provides a number of improvements to prior art vessel harvesting systems. The disclosures herein of various component parts of vessel harvesting systems should be viewed with the presumption that each can work in combination with other components unless stated as being mutually exclusive. For example, the various endoscopic vessel dissectors described herein may be utilized in combination with any of the endoscopic vessel harvesters. Moreover, any single one component improvement described herein may be incorporated into any existing vessel harvesting system, again, unless the structures or functions are mutually exclusive. 
       Prior Endoscopic Vessel Harvesting System 
       [0061]    The three primary components of an exemplary prior art vessel harvesting system are seen in the separate views of  FIGS. 1A-1C . This particular system is representative of one type of prior art vessel harvesting systems, and many of the improvements described herein will be described with direct reference to it. However, as will be understood by one of skill in the art, any one single improvement to a subcomponent of the vessel harvesting system may, in most cases, be incorporated into other such systems. More important, if any single improvement(s) are independently claimed, the application should not be construed as being limited to the system shown in  FIGS. 1A-1C . That said, the exemplary prior art system includes an endoscopic dissector  20  in  FIG. 1A , an endoscopic vessel harvester  22  seen in  FIG. 1B , and an access trocar  24  seen in  FIG. 1C . 
         [0062]    The endoscopic dissector  20  includes an elongated tube or cannula  30  extending between a distal conical tip  32  and a proximal handle  34 . A bell-shaped port  36  on a proximal end of the handle  34  receives a conventional medical endoscope  38  which may be fitted with an optical connector  40 . Although not shown, the elongated shaft of the endoscope  38  extends through the entire length of the dissector  20  such that a viewing end terminates in proximity to the conical tip  32 , which is typically transparent. It should be understood that vessel harvesting systems are typically disposable and are packaged and sold separately from the endoscope which is typically reused. In all cases, however, these endoscopic vessel harvesting systems are designed to accommodate and function with a conventional endoscope, and are therefore claimed accordingly. 
         [0063]    Tubing  42  supplies insufflation gas into an input within the handle  34  that opens into an elongated passage within the cannula  30  in communication with a distal egress port  44 . In use, the user inserts the distal tip  32  and cannula  30  into the body through an access device such as the trocar  24  seen in  FIG. 1C , and into proximity with a target vessel, such as the saphenous vein in the leg. By pushing the conical tip  32  along the target vessel under endoscopic vision, the user is able to grossly dissect connecting tissue from around the vessel. Insufflation gas forced out of the distal port  44  pressurizes the dissected cavity and facilitates viewing and further dissection. After a desired length of target vessel has been separated from surrounding tissue, the dissector  20  is removed from the patient. 
         [0064]    Subsequent to vessel dissection, the vessel harvester  22  is inserted through the access trocar  24  and into the dissected cavity around the target vessel. The vessel harvester  22  also includes an elongated tube or cannula  50  extending between an open distal end  52  and a proximal handle  54 . Again, a conventional endoscope  38  snaps into a proximal bell-shaped port  56  that includes an axial slot  58  to receive the perpendicularly-extending optical connector  40 . As with the dissector  20 , the elongated shaft of the endoscope passes entirely through the cannula  50  and terminates at a viewing end or objective lens  60  close to the open distal end  52 . 
         [0065]    The harvester  22  further includes tools to sever side branches from the target vessel while simultaneously closing them off to prevent bleeding. For instance, a holding tool  62  may be used to manipulate the target vessel so that a severing and sealing tool  64  has clear access to the various side branches. Each of these tools may be manipulated by controls  66  provided in the handle  54 . One of the controls  66  is a thumb lever thumb lever that connects to a wiper blade at the distal end of the elongated cannula  50  for clearing the objective lens  60  of the endoscope. To facilitate the harvesting operation, an insufflation system including tubing  68  may be provided so that gas may be passed out the open distal end  52  of the cannula  50 . Also, electrical wires  70  connect to the handle  54  to provide energy for a coagulator incorporated into the severing and sealing tool  64 . It should be understood that as generally described so far, these components of the prior art vessel harvesting system are well known in the art, the present application dealing with improvements thereto. 
         [0066]    The third main component of the harvesting system is the access trocar  24  seen in  FIG. 1C . In this embodiment, the trocar includes a main access tube  70  having an angled distal tip  72  and a proximal housing  74 . Although not shown, an inner seal such as a diaphragm seal may be incorporated within the housing  74  to provide a gas-tight interface with the dissector  20  or harvester  22  that passes through the trocar  24 . The main access tube  70  extends through an incision in the body and a spring-biased clip  76  secures the trocar thereto. 
       Improvements to Dissection Function 
       [0067]      FIG. 2A  shows the distal end of an alternative vessel dissector  80  of the present invention including an articulated dissecting tip  82 . The tip  82  connects to an elongated cannula  84  via an accordion-like flexible interface or sleeve  86 . A pair of pull wires  88  extends through the cannula  84  and attaches to points on opposite sides of the dissecting tip  82 . By manipulating the pull wires  88 , the user can angle the generally conical tip  82  in either direction within a plane, relative to the axis of the elongated cannula. By rotating the entire cannula  84 , a full 360° range of tip movement is obtained. The flexible sleeve  86  acts like a compression spring and tends to revert the tip  82  back to an axial alignment when pull forces are released. 
         [0068]      FIG. 2B  is another alternative vessel dissector  90  having an articulated dissecting tip  92 . As with the dissector  80 , the tip  92  connects to the distal end of an elongated cannula  94  in a manner that enables it to be angled within a plane with respect to the cannula. In this embodiment, a spherical bearing surface  96  provides the interface between the tip  92  and cannula  94 . A pair of pull wires  98  connected to the tip  92  enables the user to angle the tip as desired. A flexible spine of sorts (not shown) may also be provided to provide a force that restores the axial alignment of the tip  92  when pull forces are released. 
         [0069]      FIG. 3  is a side view schematically illustrating the possible path of bodily fluids into an existing endoscopic vessel dissector  100  that includes one or more ports  102  near its distal end for insufflation of gas such as CO 2 . That is, a passage is provided within the cannula of the vessel dissector  100  to deliver gas from a proximal end thereof to the ports  112 . If fluid is permitted to enter the cannula through the insufflation ports  102 , it may eventually migrate to within the transparent distal tip and interfere with endoscopic viewing therefrom. 
         [0070]      FIG. 4A  illustrates the distal end of an alternative vessel dissector  110  of the present invention including a small fluid barrier  112  extending proximally from the distal tip  114  for inhibiting ingress of bodily fluids into insufflation ports  116  formed in the side of the dissector cannula. The fluid barrier  112  in this embodiment comprises a tubular shield which can be formed from relatively thin medical plastics. The fluid barrier  112  is desirably flexible enough to permit gas egress from the ports  116  while preventing liquid or solid ingress, much like a reed valve. 
         [0071]      FIG. 4B  shows an alternative vessel dissector  120  having an alternative fluid barrier  122  surrounding the distal end thereof near the distal tip  124 . The fluid barrier  122  in this embodiment comprises a tubular porous membrane that covers the gas insufflation ports  126  in the side of the dissector cannula so that liquid or solid is prevented from entering though gas can exit. The membrane  122  is any medically suitable gas-permeable liquid-resistant barrier such as ePTFE made by W.L. Gore. 
         [0072]    In a further embodiment, the port from which insufflation gas is expelled is located not on the cannula body, but on a dissecting tip secured to the distal end thereof. For example, the dissecting tips  82 ,  92  of  FIG. 2A / 2 B may feature a port from which gas escapes into the surrounding tissue cavity. Alternatively, a transparent conical tip  32  as in  FIG. 1A  may have a port formed at the distal apex. In each of these alternatives, a fluid barrier desirably fills or covers the port to prevent liquid or solid ingress, while permitting gas egress. Forming the port on the dissecting tip may be advantageous because the gas is expelled farther distally, and a selection of different tips as desired may be coupled to a generic cannula. 
         [0073]      FIG. 5A  is a schematic side view of an endoscopic vessel dissector  100  of the prior art passing through body tissue  104 . Insufflation assists in maintaining the dissected cavity or tunnel, though there may be friction between tissue and the following cannula  106  because of its equal size relative to the dissecting tip  108 . 
         [0074]    To help facilitate passage of the cannula through tissue, an endoscopic vessel dissector  130  of the present invention seen in  FIG. 5B  includes a narrowed cannula  132 , at least adjacent to a dissecting tip  134  and desirably along its entire length. The cannula  132  has a diameter that is smaller than the diameter of the dissecting tip  134 , and preferably between about 50-75% of the diameter of the dissecting tip  134 . A narrow cannula proximal to the dissecting tip improves maneuverability and reduces shaft friction within the dissected tunnel. 
         [0075]      FIGS. 6A-6C  are longitudinal sectional views through alternative transparent tips for use with endoscopic vessel dissectors of the present invention. Prior transparent dissection tips, such as seen in U.S. Pat. No. 5,980,549 to Chin, et al., include a hollow interior with a front wall tapering to a sharp point, or apex. The outer profile retains a more rounded, blunt configuration for atraumatic dissection. The sharp inner apex helps remove a spot of distortion in the center of the visual field. 
         [0076]    In addition to distortion, some conical blunt dissection tips made of clear materials reflect light from the light fibers back to the objective lens of the endoscope. To address this need, a generally conical dissection tip  140  in  FIG. 6A  includes an inner tapering surface  142  that terminates at its distal end in a line  144  so as to form an elongated inner corner, or reverse wedge shape. This configuration works to reduce glare back to the objective lens of the endoscope. In  FIG. 6B , a dissection tip  146  includes an inner surface that tapers downward toward its distal end and terminates in a flat surface  148  set at an angle from the axis of the tip  146 . In this case, incident light is reflected away from the objective lens, which is typically placed along or near the axis of the tip or dissector cannula. Finally,  FIG. 6C  illustrates a dissection tip  150  having an internal taper that ends at its distal-most extent in a backward wedge. This shape helps deflect light from the fibers outward as opposed to directly backward, thus reducing glare or reflection. All of these shapes have the effect of reducing incident glare from the light fibers back to the objective lens of the endoscope, thus improving the user&#39;s view. 
         [0077]    A common technique for vessel harvesting is to provide a separate vessel dissector and vessel harvester, with the devices being inserted one at a time in the body, typically through the access trocar. Such is the configuration of the system in  FIGS. 1A-1C . However, it is conceivable that the dissecting and harvesting functions can be combined into a single device to save time. For instance,  FIG. 7  schematically illustrates the distal end of an integrated endoscopic vessel dissector/harvester  160  of the present invention having a blunt dissecting tip  162  with apertures or recesses for the harvesting tools. More particularly, a vessel holding tool  164  includes a tapered outer surface to match the dissection tip  162  and is stationed within a recess therein. Likewise, a vessel severing tool  166  having an outer surface that conforms to the dissection tip  162  is retracted into a similar recess. Each of the vessel holding tool  164  and vessel severing tool  166  docks into recesses in the dissecting tip and has an exterior shape that conforms to the conical exterior of the dissecting tip so as to match its shape. The distal end of an endoscope  168  is seen extending within the clear dissection tip  162 . For dissection, the tools  164 ,  166  are retracted to conform to the conical tip  162 . Then, by manipulating the vessel holding tool  164  and vessel severing tool  166  (such as by axial and rotational movement), selected side branches or primary vessels may be severed and sealed immediately after a section of tunnel around the primary vessel has been dissected. The vessel dissector/harvester  160  is therefore advanced in stages along the primary vessel performing both dissection and side branch management. 
         [0078]    Another configuration that is contemplated to combine the functions of the tissue dissector and vessel harvester is to provide a dissection tip that can be detached from a cannula which contains harvesting tools. For example, any of the conical tips seen in  FIGS. 6A-6C  may be separable from a cannula that houses any of the harvesting tools described below. With such a system the user may alternate between dissection in ligation-transection as desired. Furthermore, such a detachable conical tip may include an opening therethrough to permit CO 2  insufflation. Following dissection, the cone is detached and insufflation may continue through the open end of the cannula. Another alternative is to provide a tether connecting the removable conical tip to the cannula. In this way, the tip can be detached the remains in close proximity to the distal end of the cannula for reattachment if desired. 
         [0079]    Occasionally, fatty or other tissue sticks to the outside of the conical dissecting tip and prevents clear visualization therethrough.  FIG. 8  is a perspective view of an endoscopic vessel dissector  170  of the present invention having a wiper blade or finger  172  for clearing the distal dissecting tip  174  of tissue. In this embodiment, the wiper blade  172  pivots about an axis  176  at the beginning of the dissecting tip  174 , or end of the cannula  178 . An actuating rod  180  controlled by a thumb lever  182  connects to the wiper blade  172  and permits the user to alternately retract and engage the blade with the exterior of the dissecting tip  174 . The tip  174  rotates about the axis of the cannula  178  when the user turns a knob  184  at the proximal end of the device. The wiper blade  172  may be rigid or include a resilient scraper much like a vehicle wiper blade. Various structural details of this arrangement are left out but are well within those skilled in the art of medical device design. Likewise, alternative arrangements are contemplated, such as those shown in  FIGS. 9 and 10 . 
         [0080]      FIGS. 9 and 10  are perspective views of the distal tip of two alternative endoscopic vessel dissectors of the present invention both having tip wiping capabilities. The dissector  190  in  FIG. 9  is similar to the dissector  170  of  FIG. 8  in that it includes a wiper blade or finger  192  for clearing tissue from the conical dissecting tip  194 . Instead of the tip rotating, however, the blade  192  swivels about the axis of the device, such as through its connection with a rotating outer sleeve or shaft  196  of the elongated device. Again, details of the actuation of the shaft  196  are not shown, but are easily borrowed or surmised from existing devices.  FIG. 10  illustrates a dissector  200  fitted with an O-ring wiper  202  over its conical dissecting tip. An actuation rod  204  displaces the O-ring wiper  202  longitudinally to wipe clean the dissecting tip. The O-ring wiper  202  may be formed as a loosely-wound metal or plastic spiral to facilitate expansion and contraction around the tip. Of course, there are numerous other configurations of wipers that may be displaced over the dissecting tip, the present application only illustrating an exemplary selection. 
         [0081]    A further alternative to the tip wiping devices in  FIGS. 8-10  is to add an energized cutting electrode to the wiper blade to remove tissue via ablation. That is, instead of or in addition to an inert rigid or resilient blade, a wire or bar electrode may be incorporated to enable clearing of more stubborn tissue via electrocautery. Although a specific structure is not shown, the reader will understand that any of the wiper elements shown in  FIGS. 8-10  may represent such an energized wiper. 
         [0082]    Still further, any of the conical tips illustrated herein, including the simple prior art tip seen in  FIG. 5A , may be fitted with a system for clearing adhered tissue using fluid expelled from the cannula. For example, an annular opening or a series of separate circumferentially-spaced openings may be provided between the conical tip and cannula, and streams of saline expelled from the openings to knock tissue off the tip. Saline is particularly suitable, although other fluids such as jets of CO 2  gas maybe used. The design intent would be to port the fluid so that it flowed distally along the surface of the cone using the Coanda effect in which a stream of fluid or gas will tend to hug a convex contour when directed at a tangent to that surface. 
       Improvements to Vessel Holding Function 
       [0083]    Once the target vessel has been exposed, such as with dissection along its length, endoscopic vessel harvesting involves passing an elongated device under visualization along the vessel to sever and seal side branches. As mentioned above, numerous such systems are currently available, including the system seen in  FIG. 1A-1C . In that system, a vessel holding tool manipulates the target vessel such that the side branches are positioned in front of a severing and sealing tool. It is important to present both the side branch and target vessel clearly so that the user does not accidentally cut the target vessel instead of the side branch. Also, it is desirable to retract the target vessel so that the side branch can be cauterized as far away from the target vessel as possible, to minimize risk of damage to the vessel from the cautery tool (thermal spread). 
         [0084]      FIGS. 11A and 11B  are schematic side views of an endoscopic vessel harvester of the prior art showing a vessel holding tool  210  and a complementary severing tool  212  axially extended from the distal end of a cannula  214 . The holding tool  210  typically has a hook or other capturing feature for holding a primary vessel  216 . As the device advances, side branches  218  are encountered and the system is manipulated to place them in line with the severing tool  212 . There are certain drawbacks to this arrangement, in particular the linear extension of the tools  210 ,  212 , rendering them somewhat awkward to maneuver for proper positioning of the side branches  218 . 
         [0085]      FIGS. 12A and 12B  are schematic side views of an endoscopic vessel harvester  220  of the present invention showing a vessel holding tool  222  and a severing tool  224  extended from the distal end of a cannula  226 . To more easily accomplish straightening of the side branches  218  in line with the severing tool  224 , the vessel holding tool  222  translates laterally. As seen in  FIG. 12B , the effect of angling the holding tool  222  radially outward is to facilitate advancement of the tool along the primary vessel  216  as well as to straighten the side branch  218  for more effective cutting with the severing tool  224 . A comparison of  FIGS. 11A and 12A  shows the increase in spacing between the holding and severing tools, which exposes a greater length of side branch. The holding tool  222  can be displaced laterally as shown by simply mounting it on a curved or bent actuation rod, or via an angling mechanism, not shown. In the case of a curved or bent support rod, the rod may be flexible so as to retract within the cannula, and the farther the tool  22  extends the greater the lateral displacement. In general, the vessel holding tool  222  includes a support rod that extends through the elongated cannula  226  and which is angled or is configured to angle laterally at a location close to the distal end of the tool. 
         [0086]      FIG. 13  is a schematic side view of an alternative endoscopic vessel harvester  230  of the present invention wherein a vessel holding tool  232  includes a tip angled toward the vessel severing tool  234 . In this way, the holding tool  232  can position the primary vessel  216  in line with the severing tool  234 . Ultimately, the primary vessel  216  will be severed at at least one end after having been separated from its connecting side branches. The holding tool  232  facilitates this step. It is conceivable that the harvesters  220  and  230  can be combined such that the vessel holding tool may alternately be angled away from the severing tool, as seen in  FIG. 12A , and toward the severing tool, as seen in  FIG. 13 . In other words, an articulating vessel holding tool may be provided that has a support rod extending through the cannula which is configured to articulate laterally at a location close to the distal end of the tool and enable different angulations depending on the situation. 
         [0087]      FIGS. 14A-14C  are several views of the transverse displacement of an alternative vessel holding tool  240  upon extension from the cannula  242  of an endoscopic vessel harvester of the present invention. In this embodiment, the holding tool  240  mounts on the end of an elastic wireform  244  having a bend  246 . When retracted, the wireform  244  straightens within the delivery channel  248 . As the tool is extended, the bend  246  eventually clears the end of the channel  248  causing lateral displacement of the holding tool  240 . 
         [0088]    Another way to enable angling of the distal end of the vessel holding tool is to provide a flexible support rod or wireform and surround it with a rigid hypotube. Both structures may longitudinally extend from the mouth of the cannula, and then retraction of the hypotube from around the wireform angles the vessel holding tool. In this embodiment, greater maneuverability of the vessel holding tube is provided as it may be angled at various axial locations rather than immediately as it exits the cannula. 
         [0089]    In a further advantageous feature, the vessel hook of the vessel holding tool may incorporate a tapered blunt distal dissecting surface for blunt dissection of tissue. The term “blunt” surface in this context means one without sharp points or corners and with some degree of taper to facilitate division or partition of tissue planes. For example, the conical tips described herein are considered blunt, and as a rule do not have sharp points. The more rectilinear tissue holders of the prior art, however, are too blunt and not well suited for tissue dissection. 
         [0090]    It is very important to minimize obstructions in the field of view - the more the device blocks the user&#39;s view of the tissue, the greater the risk of avulsions and cautery mistakes.  FIGS. 15A-15B  are side and perspective views of an alternative vessel holding tool  250  of the present invention that has a lower profile than previous tools and thus provides greater visibility of its operation. With reference back to  FIG. 1B , the holding tool  62  of the prior art includes two rods or supports that extend distally from the cannula  50 . These two rods present solid viewing obstacles interposed between the endoscope objective lens and the actual vessel holding operation. Desirably these obstacles are minimized. 
         [0091]    In one such lower profile holder, the vessel holding tool  250  has a single main rod or support  252  extending distally from the distal end of the cannula  254  that carries a vessel hook  256 . The hook  256  is shaped to partially surround the primary vessel and manipulate it to present a side branch to an associated vessel severing tool (not shown).  FIG. 15B  illustrates the extension of a locking member  258 , which can be, for example, a concentric or telescoping extension of the main rod  252 . The hook  256  may be substantially C-shaped so as to partially surround the vessel, and the extension of the locking member  258  closes the remaining open side so that the vessel is completely surrounded and captured therein. In this way, a vessel may be securely held by the holding tool  250  without risk of dislodgment yet the view from the objective lens is maximized by removal of one of the support rods. 
         [0092]      FIGS. 16A-16B  illustrate a further vessel holding tool  260  of the present invention formed of thin wire, also to reduce its profile, reduce impediments to endoscopic viewing, and thus increase visibility and accuracy of the operation. The tool  260  extends from the cannula  262  and includes a hook portion  264  formed of a single wire, and a translating locking member  266  formed of another wire or pin. Again, with the locking member  266  extended the holding tool  260  completely encloses the vessel for manipulation and severing. Although there are two support rods extending from the cannula, they are extremely thin and present a minimum viewing obstacle to the objective lens. Desirably, the holding tool  260  is formed of metal or plastic wires having a thickness of between about 0.5 mm and 1.0 mm. 
         [0093]      FIG. 17A  is a partial sectional view of a vessel holding tool  270  of the present invention incorporating a mechanism for preventing vessel avulsion. These types of vessel holding tools are used to hook the primary vessel and move down its length, occasionally stopping to sever side branches. If the tool is moved too fast or too hard when a side branch is reached, damage can occur. The tool  270  includes a hook portion  272  that is mounted on the end of a displacement rod  274  extending from the cannula  276 . Within the cannula  276 , the rod  274  passes through a friction collar  278  that acts as a damped slip mechanism between the hook portion  272  and the cannula  276 . That is, if the hook portion  272  experiences resistance as it travels down the length of the primary vessel, further movement of the cannula  276  will not further pull or push on the vessel, but instead will cause damped relative movement between the cannula and the hook portion. 
         [0094]    In a similar manner,  FIG. 17B  shows a vessel holding tool  280  with a hook portion  282  mounted on a displacement rod  284  extending from a cannula  286 . A slip mechanism  288 , in this case a piston/cylinder/spring arrangement, permits damped relative tool/cannula movement in case the hook portion catches on any body structure and generates a reaction force in the displacement rod  284  in opposition to movement of the cannula  286 . Of course, the two examples of  FIGS. 17A and 17B  are merely exemplary and other clutch mechanisms performing a similar function can be substituted. 
         [0095]    Finally,  FIG. 18  illustrates still another vessel holding tool  290  of the present invention having an enlarged locking member  292  for better positioning of the vessel  294 . That is, the vessel  294  is first retained within the hook portion  296  then a locking member  292  is axially extended to capture it. Earlier locking members were thin rods or pins that left a relatively large space within the mouth of the hook portion  296 , and thus especially smaller vessels could easily move around. In this embodiment, the locking member  292  is shaped as a large wedge that limits the space in which the vessel  294  is held and thus increases its stability prior to the side branch severing operation. In terms of relative size, the locking member  292  when extended desirably reduces the space within the mouth of the hook portion  296  by about 50%. The tapered leading edge helps prevent pinching of the vessel as the locking member  292  extends. 
       Improvements to Vessel Severing Function 
       [0096]    Numerous instruments are known which coagulate, seal, join, or cut tissue, and which are suitable, for example, for severing a target vessel from surrounding side branches and securing the separated ends to stanch bleeding. Such devices typically comprise a pair of tweezers, jaws or forceps that grasp onto and hold tissue therebetween. The devices may operate with a heating element in contact with the tissue, with an ultrasonic heater that employs frictional heating of the tissue, or with a mono- or bi-polar electrode heating system that passes current through the tissue such that the tissue is heated by virtue of its own electrical resistance. The devices heat the tissue to temperatures such that the tissue is either “cut” or “sealed”, as follows. When tissue is heated in excess of 100° Celsius, the tissue disposed between the tweezers, jaws or forceps will be broken down and is thus, “cut”. However, when the tissue is heated to temperatures between 50° to 90° Celsius, the tissue will instead simply “seal” or “weld” to adjacent tissue. Monopolar and bipolar probes, forceps or scissors use high frequency electrical current that passes through the tissue to be coagulated. The current passing through the tissue causes the tissue to be heated, resulting in coagulation of tissue proteins. In the monopolar variety of these instruments, the current leaves the electrode and after passing through the tissue, returns to the generator by means of a “ground plate” which is attached or connected to a distant part of the patient&#39;s body. In a bipolar version of such an electro-surgical instrument, the electric current passes between two electrodes with the tissue being placed or held between the two electrodes as in the “Kleppinger bipolar forceps” used for occlusion of Fallopian tubes. A new development in this area is the “Tripolar” instrument marketed by Cabot and Circon-ACMI which incorporates a mechanical cutting element in addition to monopolar coagulating electrodes. A similar combined sealing and mechanical cutting device may also be known as a tissue “bisector,” which merges the terms bipolar cautery and dissector. One tissue bisector is packaged for sale as an element of the VASOVIEW® 6 vessel harvesting systems by Guidant Corporation of Santa Clara, Calif. In ultrasonic tissue heaters, a very high frequency (ultrasonic) vibrating element or rod is held in contact with the tissue. The rapid vibrations generate heat causing the proteins in the tissue to become coagulated. Conductive tissue welders usually include jaws that clamp tissue therebetween, one or both of which are resistively heated. In this type of instrument, no electrical current passes through the tissue, as is the case for monopolar or bipolar cautery. 
         [0097]    It should be understood that any of these prior instruments for severing and/or sealing vessels, or those described below, may be combined with the various components of the vessel harvesting systems described herein. It should also be understood that various configurations of monopolar, bipolar, or other type of electrodes may be provided on the vessel severing/sealing tools described below. Those of skill in the art will understand that the particular shape and size of the electrodes, and their arrangement with respect to other electrodes, will dictate the power requirements and operational constraints. Further, some embodiments described herein may work better with one or other type of electrodes or heating elements, though such optimal permutations will not be exhaustively described. 
         [0098]    One important function of any severing tool is to manage vessels of different sizes without extra effort on the part of the user. This is particularly important for bipolar cautery tools which must realize good tissue contact with both electrodes for optimum performance. For fixed electrodes (such as the “bisector” described above), small vessels are more difficult to cauterize; users are taught to position the vessel between the bisector electrodes, and then to rotate the bisector to ensure good contact with both electrodes. Merely decreasing the distance between the electrodes for better contact may prevent use on larger vessels. Moveable electrodes, or jaws, are on solution but require some additional effort to avoid clamping too hard on the vessel, which may result in damage thereto. 
         [0099]      FIGS. 19A and 19B  are schematic views of an alternative vessel severing tool  300  of the present invention having two wire electrodes  302  overlapping across a large gap G defined by a mouth for receiving a vessel. In contrast with some earlier devices, the gap G is large enough to receive both the side branches and the primary vessel, preferably between about 4.0 mm and 6.0 mm, more preferably about 6.0 mm. The wire electrodes  302  that overlap in a crossing pattern across the gap G are resilient and flex to automatically accommodate widely varying sizes of vessel. In this context “accommodate” means to contact opposite sides of the vessel. This is especially important to ensure good contact with very small vessels. The vessel severing tool  300  desirably accommodates vessels having diameters that range from between 0.5 mm and 6.0 mm. In a variation of the embodiment of  FIGS. 19A and 19B , a vessel severing tool has a mouth defined by facing vessel contacts that flex apart upon receiving a vessel therebetween, though the contacts may not be electrodes. Any cutting tool may be combined with a variably-sized mouth to secure different sized vessels. 
         [0100]    Desirably, the wire electrodes are made of stainless steel and have a wire thickness of between about 0.5 mm and 1.0 mm so that they easily flex to permit a vessel to move farther into the gap than if they were more rigid and thus ensure good current contact with the vessel. Also, as seen in  FIG. 19B , the wire electrodes  302  are set at different radial distances from the central axis of the tool out of contact with each other, thus providing the separation needed for bipolar coagulation. One distinct advantage of the vessel severing tool  300  over prior designs is its ability to automatically accommodate varying sizes of vessel. That is tools having movable jaws, for example, can adapt to various vessel diameters but only upon careful user manipulation. The tool  300  thus speeds up the entire vessel harvesting operation, which may involve severance of numerous vessels. 
         [0101]      FIG. 20  is a side view of an alternative vessel severing tool  310  of the present invention having a stepped vessel-receiving mouth  312 . The stepped shape of the mouth  312  accommodates a wider range of vessel sizes while ensuring good contact with tissue cautery electrodes (not shown) provided, for example, on opposite sides of the mouth. In contrast to a fixed V-shaped gap, the stair-stepped shape of the mouth  312  presents several progressively smaller intermediate gaps with generally parallel sides that provide regions of constant width surface contact with the vessel. Also, the step to the next smaller intermediate gap contacts the vessel. This “bracketing” of the vessel helps ensure a good seal without the risk of excessive pinching. The vessel severing tool  300  desirably accommodates vessels having diameters that range from between 0.5 mm and 6.0 mm. In one embodiment, the mouth  312  of the vessel severing tool  300  defines intermediate gaps having widths in decreasing increments of 1.0 mm, for example 6-5-4 mm, or 5-4-3 mm. 
         [0102]    Although immovable severing/sealing tools may prove suitable in certain applications, often it is desirable to apply certain amount of pressure to the vessel with movable jaws, for example.  FIGS. 21A-21B  illustrate a vessel severing tool  320  of the present invention having jaws  322  that are resiliently biased away from one another and which can be partially closed. The jaws  322  may carry bipolar or monopolar electrodes. A pull wire or control rod  324  connects to a closure ring  326  and enables axial displacement thereof for closing the jaws  322 , as seen in  FIG. 21B . Visualization of the severing/sealing operation then enables the user to vary the extent of closure of the jaws  322 , and thus the magnitude of pressure applied. The jaws  322  cannot completely close and have a minimum gap therebetween as see in  FIG. 21B  of between about 0.5 mm and 1.0 mm. This minimum is calibrated so that the tool  320  accommodates even the smallest expected vessels, yet excessive clamping of even much larger vessels is reduced because there is no contact between the jaws  322 . 
         [0103]      FIG. 22  is a side view of a vessel severing tool  330  having stationery jaws  332  and rotary blades  334  incorporated thereon. The blades  334  may be connected to electric power and function as cutting electrodes, or may be inert knife blades, that work in conjunction with separate sealing electrodes (not shown) provided on the jaws  332 . This configuration removes the need for providing electrodes that perform dual severing and sealing functions, which frees the designer to optimize the sealing electrodes. 
         [0104]      FIGS. 23A-23B  are two side views of a vessel severing tool  340  having a movable blade  342  that desirably works in cooperation with electrodes (not shown) that seal the cut vessel. A control rod  344  connects to displace the blade  342  toward an anvil  346  provided on a hook portion  348  of the tool  340 . The blade  342  and cooperating anvil  346  are slightly angled as shown to sever the vessel with a shearing action. A mechanical cutter such as this may be desirable in contrast to electrocautery transection which can be time-consuming, may inflict thermal damage on the tissue, and may not be entirely effective. 
         [0105]      FIG. 24  schematically illustrates a vessel severing tool  350  having a system for clearing tissue therefrom using gas jets. Occasionally, the repeated application of heat or electricity to tissue creates sticking or burning of the tissue to the electrodes. One means to resolve this problem is to provide tubing  352  extending adjacent a severing/sealing tool  354 . The tubing  352  terminates close to the electrodes or cutting blades of the tool  354  and jets of gas such as CO 2  may be expelled from the open ends or from special nozzles to knock tissue off the tool. CO 2  is particularly suitable because it is already used for insufflation of the body cavity, although other fluids such as saline may also be used. 
         [0106]      FIGS. 25A-25B  are front and top section views, respectively, of an alternative vessel severing tool  360  capable of translating transversely as well as longitudinally. An electrode-carrying member  362  translates circumferentially within an arcuate slot  364 , and may be actuated by a control rod  366 . This arrangement greatly enhances the maneuverability of the tool and consequently the options for the user. 
         [0107]    In  FIG. 26 , a severing/sealing tool  370  shown from its front end within an insufflated tunnel  372  includes a cannula having a pair of partial tubular vessel shields  374  extending therefrom around a primary vessel  376 . The gaps between the shields  374  accommodate side branches  378  from the primary vessel  376 . A tubular cutting element  380  that may be axially displaced from the cannula surrounds the shields  374 . The user positions the shields around a vessel  376  with the side branches  378  as shown, and then advances the cutting element  380 . The shields  374  protect the vessel  376  and ensure adequate stump length of the transected branches  378 . The cutting element  380  may be a tubular knife blade or an electrode designed to cut. 
         [0108]      FIGS. 27A-27B  are side and top views of a vessel severing/sealing tool  400  that incorporates several moving parts. The tool  400  includes a pair of fork-shaped electrodes  402  spaced laterally apart so as to create a gap within which moves a severing blade  404 . A vessel capturing mandible  406  also moves within the gap between the electrodes  402 . In use, a vessel  408  is seen positioned within the tines of the fork-shaped electrodes  402  and prior to capture by the mandible  406 . The mandible  406  has a serrated distal finger to securely capture the target vessel within the tines. Upward movement of the mandible traps the vessel  408  at which time energy may be applied by the electrodes  402  to begin the coagulation process. Subsequently, the blade  404  actuates downward and severs the vessel  408 . Mechanisms for moving both the blade  404  and mandible  406  are not shown, although both have angled or arcuate proximal surfaces that can be utilized to cam against a delivery cannula and displace the elements toward one another upon their proximal retraction using a control rod, for example. 
         [0109]      FIGS. 28A-28B  are two schematic views of a vessel severing/sealing tool  420  incorporating a side-opening cutter/sealer  422 . In the enlarged view of  FIG. 28B , the cutter  422  comprises an upper electrode  424  and a lower electrode  426  separated across a slot  428 . The upper and lower electrodes  424 ,  426  may be bipolar, and the slot  428  may accommodate a knife blade or other such cutting device.  FIG. 29  is an endoscopic view showing the use of the tool  420  severing a side branch  430  from a primary vessel  432 . 
         [0110]    Finally,  FIG. 30  is a top plan view of an alternative severing tool  440  which has a first ring-shaped electrode  442  extending from a cannula structure  444 , and the second coil-shaped electrode  446  concentrically arranged around the first electrode. 
         [0111]    While the invention has been described in its preferred embodiments, it is to be understood that the words which have been used are words of description and not of limitation. Therefore, changes may be made within the appended claims without departing from the true scope of the invention.