Abstract:
A surgical instrument for performing an anastomosis includes a housing having proximal and distal ends and a shaft extending from the distal end of the housing. The instrument also includes an actuator attached to the housing and a disposable loading unit configured for selective attachment to the shaft. The disposable loading unit includes a fastener support member configured and dimensioned to support an array of surgical fasteners thereon and a fastener pusher member which is movable through a firing stroke in response to movement of the actuator to deform the surgical fasteners.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
       [0001]    This application is a continuation of U.S. application Ser. No. 09/875,411 filed on Jun. 6, 2001 by Nicholas et al. entitled “Anastomosis Instrument and Method” and a continuation of U.S. application Ser. No. 09/584,541 filed on Jun. 1, 2000 by Nicholas et al. entitled “Anastomosis Instrument and Method” which is a continuation of U.S. application Ser. No. 09/256,260 filed on Feb. 23, 1999 by Nicholas et al. entitled “Anastomosis Instrument and Method” which is a continuation-in-part of U.S. application Ser. No. 08/877,701, entitled “Singleshot Anastomosis Instrument With Detatchable Loading Unit and Method”, which was filed Jun. 17, 1997 by Manzo et al., which application is a continuation-in-part of U.S. application Ser. No. 08/685,385, entitled “Anastomosis Instrument and Method”, filed Jul. 23, 1996 by Hinchliffe et al., now U.S. Pat. No. 5,707,380, the entire contents of both of these disclosures are hereby incorporated by reference. 
     
    
     
       BACKGROUND  
         [0002]    1. Technical Field  
           [0003]    The present disclosure relates to a surgical instrument and method for performing anastomosis of tubular body structures, and more particularly to an instrument for performing vascular anastomoses.  
           [0004]    2. Background of Related Art  
           [0005]    Anastomoses of tubular body structures may be performed for a number of different procedures. One general example of an anastomosis is a vascular anastomosis wherein two blood vessels are joined together to permit blood flow therebetween. A specific example of vascular anastomosis is an arteriovenous fistula (“A-V fistula”) which is performed to facilitate hemodialysis for end stage kidney disease. The procedure usually consists of an end to side anastomosis joining an artery and a vein in the forearm, e.g., joining the radial artery end to side with the cephalic (radial) vein or the ulnar artery with the basilic (ulnar) vein. It can also be performed in the leg, but usually after all the arm sites have been exhausted. The A-V fistula allows a single puncture at the dialysis unit for blood cleansing. The fistula allows a greater flow and outflow rate through the dialyzer.  
           [0006]    Another specific example of a vascular anastomosis is a coronary artery bypass graft (“CABG”). Coronary artery disease is often characterized by lesions or occlusions in the coronary arteries which may result in inadequate blood flow to the myocardium, or myocardial ischemia, which is typically responsible for such complications as angina pectoris, necrosis of cardiac tissue (myocardial infarction), and sudden death. In some cases, coronary artery disease may be treated by the use of drugs and by modifications in behavior and diet. In other cases, dilatation of coronary arteries may be achieved by such procedures as angioplasty, laser ablation, atherectomy, catheterization, and intravascular stents.  
           [0007]    For certain patients, a CABG procedure is the preferred form of treatment to relieve symptoms and often increase life expectancy. A CABG procedure consists of direct anastomosis of a vessel segment to one or more of the coronary arteries. For example, a reversed segment of the saphenous vein may be grafted at one end to the ascending aorta as an arterial blood source and at the other end to a coronary artery at a point beyond the arterial occlusion. Alternatively, the internal mammary artery (IMA) is located in the thoracic cavity adjacent the sternum and is likewise suitable for grafting to a coronary artery, such as the left anterior descending artery (LAD).  
           [0008]    The performance of a CABG procedure typically requires access to the heart, blood vessels and associated tissue. Access to the patient&#39;s thoracic cavity may be achieved in an open procedure by making a large longitudinal incision in the chest. This procedure, referred to as a median sternotomy, requires a saw or other cutting instrument to cut the sternum and allow two opposing halves of the rib cages to be spread apart. U.S. Pat. No. 5,025,779 to Bugge discloses a retractor which is designed to grip opposite sternum halves and spread the thoracic cavity apart. The large opening which is created by this technique enables the surgeon to directly visualize the surgical site and perform procedures on the affected organs. However, such procedures that involve large incisions and substantial displacement of the rib cage are often traumatic to the patient with significant attendant risks. The recovery period may be extensive and is often painful. Furthermore, patients for whom coronary surgery is indicated may need to forego such surgery due to the risks involved with gaining access to the heart.  
           [0009]    U.S. Pat. No. 5,503,617 to Jako discloses a retractor configured to be held by the surgeon for use in vascular or cardiac surgery to retract and hold ribs apart to allow access to the heart or a lung through an operating “window”. The retractor includes a rigid frame and a translation frame slidably connected to the rigid frame. Lower and upper blades are rotatably mounted to the rigid frame and the translation frame respectively. The “window” approach enables the surgeon to gain access through a smaller incision and with less displacement of the ribs, and consequently, less trauma to the patient.  
           [0010]    Once access to the thoracic cavity has been achieved, surgery on the heart may be performed. Such procedures typically require that the heart beat be arrested while maintaining circulation throughout the rest of the body. Cardioplegic fluid, such as potassium chloride (KCI) is delivered to the blood vessels of the heart to paralyze the myocardium. As disclosed in WO 95/15715 to Sterman et al. for example, cardioplegic fluid is infused into the myocardium through the coronary arteries by a catheter inserted into the ascending aorta. Alternatively, cardioplegic fluid is infused through the coronary veins in a retrograde manner by a catheter positioned in the interior jugular vein accessed at the patient&#39;s neck. Such procedures require the introduction of multiple catheters into the blood vessels adjacent the heart, which is complicated procedure requiring that the desired vessels be properly located and accessed. The progression of the guide wires and catheters must be closely monitored to determine proper placement. Furthermore, the introduction of catheters forms punctures in the blood vessels that must be subsequently closed, and there is an increased risk of trauma to the interior walls of the vessels in which the catheters must pass.  
           [0011]    Alternatively, the CABG procedure may be performed while the heart is permitted to beat. Such a procedure is now commonly referred to as minimally invasive direct coronary artery bypass (MIDCAB). A surgical instrument is used to stabilize the heart and restrict blood flow through the coronary artery during the graft procedure. Special care must be given to procedures performed on a beating heart, e.g. synchronizing procedures to occur at certain stages in the cardiac cycle, such as between heartbeats.  
           [0012]    To perform a CABG procedure, the harvested vessel segment, such as the IMA, is grafted to the coronary artery by end-to-side anastomosis. Typically, sutures are used to graft the vessel segments. However, conventional suturing is complicated by the use of minimally invasive procedures, such as the window approach. Limited access and reduced visibility may impede the surgeon&#39;s ability to manually apply sutures to a graft. Additionally, it is difficult and time consuming to manually suture if the CABG procedure is being performed while the heart is beating as the suturing must be synchronized with the heart beat.  
           [0013]    The process of manually suturing the harvested vessel segment to a coronary artery is time consuming and requires a great deal of skill on the part of the surgeon. The resulting sutured anastomosis will also be dependent on the skills of the surgeon. In minimally invasive procedures such as in MIDCAB, the ability to suture is even more complicated due to limited maneuverability and reduced visibility. U.S. Pat. No. 5,707,380 to which issued on Jan. 3, 1998 to Hinchliffe et al., the entire contents of which are hereby incorporated by reference, discloses an apparatus and a procedure that enables the remote anastomosis without piercing of vessels during both conventional and minimally invasive procedures. A continuing need exists, however, for improved surgical instruments and methods for performing remote anastomoses during both conventional and minimally invasive procedures.  
         SUMMARY  
         [0014]    The present disclosure provides a surgical instrument for performing an anastomosis and includes a housing having proximal and distal ends with a shaft extending from the distal end of the housing. The surgical instrument also includes an actuator attached to the housing and a disposable loading unit configured for selective attachment to the shaft.  
           [0015]    The disposable loading unit includes a fastener support member configured and dimensioned to support an array of surgical fasteners and a fastener pusher member which is movable through a firing stroke in response to movement of the actuator to deform the surgical fasteners. Preferably, the disposable loading unit includes opposed split sections which are pivotable relative to one another between an open position and a close position after movement of the fastener pusher member through the firing stroke.  
           [0016]    In one embodiment, the opposed split sections of the disposable loading unit are locked in a closed, non-pivotable configuration prior to initiation of the firing stroke. In another embodiment, the return of the fastener pusher member unlocks the opposable split sections to allow pivotable movement thereof.  
           [0017]    In another embodiment according to the present disclosure, the fastener support member supports generally C-shaped surgical fasteners in a partially compressed configuration. Preferably, each of the surgical fasteners includes a proximal tip and a distal tip and at least one of the proximal and distal tips of at least one of the surgical fasteners is atraumatic.  
           [0018]    The present disclosure also relates to a method of performing a vascular anastomosis between first and second vessels and includes the steps of providing a surgical instrument which includes:  
           [0019]    a housing having proximal and distal ends with a shaft extending from the distal end of the housing;  
           [0020]    an actuator attached to the housing;  
           [0021]    a disposable loading unit configured for selective attachment to the shaft, the disposable loading unit having a passageway defined therethrough. The disposable loading unit includes a fastener support member configured and dimensioned to support an array of surgical fasteners at a distal end thereof and a fastener pusher member which is movable through a firing stroke in response to movement of the actuator to deform the surgical fasteners.  
           [0022]    The method further includes the step of inserting the first vessel through the passageway and everting an end of the first vessel over the distal end of the fastener support member adjacent the distal tips of the surgical fasteners. An additional step of the method include inserting the fastener support member and the everted end of the first vessel into an opening in a sidewall of the second vessel such that the proximal tips of the surgical fasteners are adjacent the opening. The method also includes the steps of connecting the disposable loading unit to the shaft and actuating the actuator to deform the surgical fasteners to secure the first and second vessels in fluid communication with one another. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0023]    An illustrative embodiment of the subject surgical instrument and method are described herein with reference to the drawings wherein:  
         [0024]    [0024]FIG. 1 is a perspective view of a surgical instrument constructed in accordance with a preferred embodiment of the present disclosure;  
         [0025]    [0025]FIG. 2 is a perspective view of a disposable loading unit constructed in accordance with a preferred embodiment of the present disclosure;  
         [0026]    [0026]FIG. 3 is a perspective view of the disposable loading unit of FIG. 2 as seen from a reverse angle;  
         [0027]    [0027]FIG. 4 is a perspective view the disposable loading unit embodiment of FIG. 2 shown with parts separated;  
         [0028]    [0028]FIG. 5 is a perspective view of a fastener pusher half-section and a hinge lock the embodiment of the disposable loading unit of FIG. 2;  
         [0029]    [0029]FIG. 6 is a side view of the disposable loading unit of the embodiment of FIG. 2;  
         [0030]    [0030]FIG. 7 is a perspective view of the disposable loading unit of the embodiment of FIG. 2 showing a hinge lock and a cover plate separated;  
         [0031]    [0031]FIG. 8 is a horizontal cross-sectional view of the disposable loading unit shown greatly enlarged for clarity;  
         [0032]    [0032]FIG. 9 is a perspective view of a handle/actuator assembly of the surgical instrument with parts separated;  
         [0033]    [0033]FIG. 10 is a perspective view of the handle/actuator assembly of FIG. 9 shown with parts separated;  
         [0034]    [0034]FIG. 11 is an enlarged view of the distal end of a disposable loading unit holding tube;  
         [0035]    [0035]FIG. 12 is a horizontal cross section of the handle/actuator assembly;  
         [0036]    [0036]FIG. 13 is a view showing an operating “window” with the patient&#39;s heart exposed;  
         [0037]    [0037]FIG. 14 is a perspective view of a disposable loading unit with a first vessel inserted therethrough;  
         [0038]    [0038]FIG. 15 is a perspective view of the disposable loading unit shown in reverse angle from that of FIG. 14, which shows the vascular tissue everted over a plurality of surgical fasteners;  
         [0039]    [0039]FIG. 16 is a horizontal cross-sectional view of the disposable loading unit of FIG. 15;  
         [0040]    [0040]FIG. 17 is a perspective view showing insertion of the disposable loading unit and everted vascular tissue through a second vessel;  
         [0041]    [0041]FIG. 18 is a view similar to FIG. 17, which shows full insertion of the distal end of the disposable loading unit with the everted vascular tissue through an incision formed in the second vessel;  
         [0042]    [0042]FIG. 19 is a horizontal cross-sectional view of the inserted disposable loading unit of FIG. 18;  
         [0043]    [0043]FIG. 20 is a horizontal cross-sectional view of the handle/actuator assembly;  
         [0044]    [0044]FIG. 21 is a partial horizontal cross-sectional view showing a locking mechanism to secure the disposable loading unit to the handle/actuator assembly;  
         [0045]    [0045]FIG. 22 is an enlarged view isolating on the safety firing lockout member of the handle/actuator assembly;  
         [0046]    [0046]FIG. 23 is a view similar to FIG. 22, which shows operation of the safety firing lockout;  
         [0047]    [0047]FIG. 24 is a horizontal cross-sectional view of the handle/actuator assembly, which shows the firing sequence of the handle/actuator assembly;  
         [0048]    [0048]FIG. 25 is an enlarged horizontal cross-sectional view of the distal end of the handle/actuator assembly and the disposable loading unit, which shows the deformation of the surgical fasteners;  
         [0049]    [0049]FIG. 26 is a side view showing operation of the disposable loading unit;  
         [0050]    [0050]FIG. 27 is a view similar to FIG. 26, which shows retraction of a pusher member of the disposable loading unit after deformation of the surgical fasteners;  
         [0051]    [0051]FIG. 28 is a horizontal cross-sectional view, which shows retraction of an actuator rod of the handle/actuator assembly and lockout of a hinge lock on the disposable loading unit;  
         [0052]    [0052]FIG. 29 is an enlarged view of the indicated area of detail of FIG. 28;  
         [0053]    [0053]FIG. 30 is a perspective view of the distal end of the surgical instrument showing the opening of the disposable loading unit;  
         [0054]    [0054]FIG. 31 is a view showing the completed anastomosis;  
         [0055]    [0055]FIG. 31A is a view showing an alternative anastomosis site for a procedure known as an A-V fistula;  
         [0056]    [0056]FIG. 32 is a perspective view of an alternative embodiment of a safety firing lockout member of the handle/actuator assembly;  
         [0057]    [0057]FIG. 33 is a perspective view of a safety release slide of the embodiment of FIG. 32;  
         [0058]    [0058]FIG. 33A is a perspective view showing the bottom of the safety release slide of FIG. 33;  
         [0059]    [0059]FIG. 34 is a perspective view of a lockout spring of the safety firing lockout of FIG. 32;  
         [0060]    [0060]FIG. 35 is a perspective view of an actuator rod of the embodiment of FIG. 32;  
         [0061]    [0061]FIG. 36 is a partial cross-sectional view illustrating the initial lockout configuration of the safety firing lock-out mechanism of FIG. 32;  
         [0062]    [0062]FIG. 37 is a view similar to FIG. 36, which illustrates an operational sequence of the safety firing lockout mechanism;  
         [0063]    [0063]FIG. 38 is a view similar to FIG. 36 which illustrates an operational sequence of the safety firing lockout mechanism; and  
         [0064]    [0064]FIG. 39 is a view similar to FIG. 36 which illustrates a further operational sequential view of the safety firing lockout mechanism.  
     
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0065]    Preferred embodiments of the surgical instrument and method disclosed herein will be described in terms of a minimally invasive direct coronary artery bypass (MIDCAB) procedure wherein a vascular anastomosis is created by joining a section of a harvested vessel, e.g., the internal memory artery (IMA) to bypass an occlusion in a coronary artery, e.g., the left anterior descending artery (LAD). However, the presently disclosed surgical anastomosis instrument may also be utilized in performing anastomosis of other tubular luminal body structures For example, the presently disclosed surgical anastomosis instrument may also be utilized to perform an A-V fistula to facilitate hemodialysis. This procedure consists of an end-to-side anastomosis joining an artery and a vein in the forearm or near the elbow. The A-V fistula allows a single puncture at the dialysis unit for blood cleansing.  
         [0066]    Referring now in detail to the drawing figures in which like reference numerals identify similar or identical elements, one embodiment of the present disclosure is illustrated generally in FIG. 1 and is designated therein as surgical instrument  100 . Briefly, surgical instrument  100  includes a handle/actuator assembly  110  having a disposable loading unit  112  which is removably and rotatably attached to the handle/actuator assembly  110  by way of intermediate section  114  which extends from a distal end of housing/actuator assembly  110 .  
         [0067]    Referring now to FIGS.  2 - 8 , disposable loading unit  112  includes a two-part fastener support member made up of split half-sections  116   a  and  116   b  which form a hinge and are connected to each other by hinge pin  118 . Split half-section  116   a  includes an actuator barrel  120  which forms a bore that opens at a proximal end. Actuator barrel  120  includes opposed longitudinal slots  122  and  124  to facilitate operation of an actuator member  126  which is slidably mounted in actuator barrel  120 . Actuation member  126  is spring biased to a proximal-most orientation by a coil spring  128 . Actuator  126  is further retained within actuator barrel  120  by a lock ring  130  which includes an annular groove  132  defined by proximal and distal flanges  134  and  136 , respectively. Each of the proximal and distal flanges  134  and  136  include a pair of opposed slotted portions which are aligned to facilitate locking of ring  130  anterior portion of a mounting hub  138 .  
         [0068]    For example, by way of passing lock ring  130  over opposed extended tabs  140  and  142 , as best seen in FIG. 8, at the rotating lock ring  130  one quarter turn such that the pairs of opposed slots formed in proximal flange and distal flange  134  and  136 , respectively, are rotated 90° with respect to tabs  140  and  142 . Lock ring  130  is biased against the distal facing surfaces of extended tabs  140  and  142  by the force of compressed coil spring  128  which is disposed in the bore formed longitudinally within actuator  126 . In particular, a shoulder portion  144  of actuator  126  is biased against an annular lip  146  (FIG. 4) which is formed on the distal facing surface of lock ring  130 . Actuator member  126  further includes a pair of opposed transversely extending slots  148  and  150  formed on the outer surface thereof which, as will be described in further detail herein, provide an engagement surface for a fastener pusher member.  
         [0069]    Split half-sections  116   a  and  116   b  of the fastener support member are provided with fastener retaining sections  152  and  154 . Each of fastener retaining sections  152  and  154  are provided with a plurality of longitudinal channels  156  which are configured and dimensioned to support a “C”-shaped surgical fastener or clip  158  therein by, for example, friction or partial compression of clips  158 . Fastener retaining sections  152  and  154  are preferably arranged such that longitudinal channels  156  form an eccentric array radially about the outer surface of fastener support member  116 . This arrangement facilitates the efficacious formation of an angled connection or fistula between the vessels to be joined. Such a connection facilitates better fluid flow through the anastomotic site.  
         [0070]    A fastener pusher member  160  is provided to facilitate deformation of clips  158  during firing of the instrument. Fastener pusher member  160  is made up of split half-sections  160   a  and  160   b  which are secured to split half-sections  116   a  and  116   b , respectively, by way of mounting plates  162  and  164  and screws  166  which are threaded into threaded holes formed in receiving posts  168 ,  170 ; and  172 ,  174  disposed on split half-sections  116   a  and  116   b , respectively. Mounting plates  162  and  164  are attached to split half-sections  116   a  and  116   b  in a manner to permit longitudinal sliding movement of split half-sections  160   a  and  160   b  of fastener pusher member  160  relative to fastener support member  116 . This sliding movement is facilitated by longitudinally aligned slots  176 ,  178 ; and  180 ,  182  which are provided on split half-sections  160   a  and  160   b , respectively.  
         [0071]    Split half-sections  160   a  and  160   b  are further provided with molded surfaces such as protrusions  184  and depressions  186  as shown on split half-section  160   a  which interfit with corresponding protrusions and depressions formed on split half-section  160   a  so as to prevent relative longitudinal movement of split half-sections  160   a  and  160   b . Stepped camming or pusher surfaces  188  are formed on the distal ends of each of split half-sections  160   a  and  160   b  and serve to cam a proximally oriented portion of clips  158  towards a distal oriented portion of clips  158 . This motion effects deformation of the clips upon firing of surgical instrument  100 .  
         [0072]    Finally, a hinge lock  190  is mounted between mounting plate  162  and split half-section  160   b . Hinge lock  190  is provided with latch portions  192  and  194  which extend transversely across one side of disposable loading unit  112  to latch onto raised correspondingly shaped surfaces  196  and  198 , respectively, formed on the outer surface of split half-section  160   a . Hinge lock  190  is further provided with a pair of longitudinally oriented slots  200  and  202  which are radially aligned with slots  180  and  182  of split half-section  160   b  to facilitate relative longitudinal movement of hinge lock  190  with respect to both split half-section  160   b  and split half-section  116   a.    
         [0073]    A flexible return lockout tab  204  extends proximally from the distal end of slot  202  and is cantilevered outwardly away from a plane defined by slots  202  and  204  such that it is positioned in a tab receiving recess  206  formed on the inner surface of mounting plate  162  when the DLU  112  is in a pre-fired condition. A lockout slot  208  is formed longitudinally aligned with tab receiving recess  206  and spaced distally therefrom such that upon distal movement of hinge lock  190  (when split half-section  160   b  is moved distally), return lockout tab will be deflected to a flattened condition and will extend into lockout slot  208  in order to prevent subsequent proximal movement of hinge lock upon proximal movement of split half-section  160   b  after firing of surgical instrument  100 .  
         [0074]    In this manner, after firing of surgical instrument  100 , latch portions  192  and  194  of hinge lock  190  will remain distal relative to raised surfaces  196  and  198  of split half-section of  160   a  by permitting the split half-sectioned DLU  112  to be opened by pivoting split half-sections  116   b  and  160   a  away from split half-sections  116   a  and  160   b  to facilitate removal of the vessel segment from within the vessel pathway formed through the distal end of DLU  112  and out through a lateral opening  210  formed by aligned molded recesses formed in each of split half-sections  116   a ,  116   b ; and  160   a  and  160   b  of fastener support member  116  and fastener pusher member  160 , respectively.  
         [0075]    Referring now to FIGS.  9 - 12 , the handle/actuator assembly  110  of surgical instrument  100  will now be described in detail. Handle/actuator assembly  110  includes a housing formed of half-sections  212   a  and  212   b  which are preferably molded to have recessed inner surfaces and contours formed therein to house the various components which are contained within handle/actuator assembly  110 . In particular, handle/actuator assembly  110  includes a DLU mounting assembly which facilitates detachable mounting of a DLU  112  to the distal end of handle/actuator assembly  110 . The DLU mounting assembly includes an elongated holding tube  214  which is held longitudinally and rotationally fixed relative to housing half-sections  212   a  and  212   b . This mounting arrangement may be accomplished for example, by way of an annular flange  216  formed adjacent the proximal end of holding tube  214  being held within an annular groove defined by partition wall segments  218  and  220  formed in each of housing half-sections  212   a  and  212   b.    
         [0076]    Holding tube  214  is further prevented from rotational movement by way of flattened sidewall portions  222  formed on opposing sides of holding tube  214  being retained within and abutting flat surfaces  224  and  226  formed long partition wall segments  218  and  220 , respectively, in each of housing half-sections  212   a  and  212   b . DLU locking tube  215  is secured within a collar  228  formed on slide  217 . Tube  215  may be secured in slide  217  by any suitable means, for example, friction fitting bonding, adhesives, or the like.  
         [0077]    Coil spring  219  is interposed in housing half-sections  212   a  and  212   b  between partitioned segments  218  and the proximal end surface of collar  228 . In this manner, locking tube  215  is biased in a distal-most position which corresponds to a locked position to retain DLU  112  on the distal end of surgical instrument  100 . The distal end of DLU holding tube  214  is provided with a semi-annular groove  230  which is dimensioned to receive mounting hub  138  formed at the proximal end of DLU  112 . Semi-annular groove  230  is dimensioned to permit DLU mounting hub  138  to rotate within the groove.  
         [0078]    Handle and actuator assembly  110  further includes a firing assembly which facilitates movement of actuator  126  housed within the actuator barrel  120 . In the embodiment illustrated in FIGS.  9 - 15 , the firing assembly is a linkage mechanism which imparts reciprocating longitudinal movement in an actuator rod by way of movement of an actuator lever. However, it is within the scope of the present disclosure that the actuator rod may be reciprocatingly moved by any suitable known methods. The firing assembly basically includes an actuator rod  232  which is connected to an actuator lever  234  by way of links  236  pivotally attached at either end to actuator rod  232  and actuator lever  234 , respectively.  
         [0079]    Actuator rod  232  is slidably disposed within a longitudinal bore formed through DLU holding tube  214 . Actuator rod  232  is biased in a proximal-most position by way of a torsion spring  238  being mounted on a post  240  formed near the proximal end of housing half-section  212   b . Extended legs  238   a  and  238   b  are provided on torsion spring  238  to bias actuator lever  234  upwardly away from housing half-sections  212   a  and  212   b  thereby pulling actuator rod  232  toward its proximal-most position as determined by the abutment of annular shoulder  242  against partition  244  formed in each of housing half-sections  212   a  and  212   b.    
         [0080]    To facilitate comfort and ease of operation for the user, a cover  246  is secured over actuator lever  234  and is independently pivotally mounted to housing half-sections  212   a  and  212   b . Cover  246  is provided with an ergonomic surface  248  which is contoured and configured to be comfortably actuated by the thumb of a user when handle and actuator assembly  210  is held in the palm of the user&#39;s hand.  
         [0081]    A firing safety mechanism is also provided to prevent premature firing of surgical instrument  100 . In the illustrated embodiment, the firing safety assembly includes an inverted leaf spring  250  having a cut-out portion  252  formed therein which biases against a shoulder  254  formed on actuator rod  232 . Spring  250  is further provided with a hook portion  256  formed at the proximal end thereof which latches onto a protruding surface  258  formed in housing half-sections  212   a  and  212   b . In this manner, spring  250  prevents distal movement of actuator rod  232  when the safety mechanism is armed.  
         [0082]    A safety release slide  260  which includes an upwardly extending contact surface is exposed from the upper surface of housing half-sections  212   a  and  212   b  to permit the user to operate the slide and forms a clevis on a lower portion thereof which receives a flattened section  266  of actuator rod  332 . Safety release slide  260  is further provided with a camming surface  268  along the lower edge thereof which cams the spring  250  out of contact with shoulder  254  upon proximal movement of safety release slide  260 .  
         [0083]    In use, as shown in FIGS.  13 - 31 , surgical instrument  100  facilitates the performance of a vascular anastomosis without the need for manual suturing of the vessels. The method and usage described herein will be addressed in terms of minimally invasive vascular anastomosis performed on a beating heart such as in a MIDCAB procedure. However, the presently disclosed surgical instrument may also be used in performing anastomoses of other tubular or luminal body structures without departing from the scope of the present disclosure. For example, surgical instrument  100  may be used in conventional open CABG procedures using a median sternotomy or other large incision without stopping the heart. Alternatively, the thoracic “window” procedure may be used to achieve access to the heart. The “window” approach involves a smaller incision and less displacement of the ribs, and therefore is less traumatic to the patient. For this approach, conventional surgical techniques are used to determine the location of the incision to access the chest cavity.  
         [0084]    In particular, a surgical retractor assembly may be used to separate the ribs at the site of the incision as shown in FIG. 13. Specifically, a base  270  is placed on the chest of the patient with the central opening defined by the base being positioned over the operative site. Retractor assemblies  272  are mounted to the base at various locations. Each of retractor assemblies  272  includes a blade having a hook to engage either a rib or the sternum therewith. The retractor assemblies are mounted and used to retract ribs until a sufficiently large opening in the chest cavity is defined to provide direct access to the heart. For example, the sternum and the fourth and fifth ribs can be split apart to create a window. Other configurations of spreading the ribs and/or selectively cutting individual ribs away from the sternum may also be utilized for a particular procedure.  
         [0085]    Once the desired access to the heart is achieved, the graft vessel, e.g., the internal memory artery (IMA) is dissected from the surrounding cartilage and muscle, in a free end of the vessel is exposed. The occluded coronary artery, e.g., the left anterior descending artery (LAD), is then prepared for receiving the IMA graft. The heart is positioned in the desired orientation either by traction sutures passing through the pericardium or by manipulation with heart manipulation instruments which are held by the surgical personnel or clamped in a fixed orientation to a base such as the retractor assembly base. One such heart manipulating instrument is available from United States Surgical Corporation of Norwalk, Conn. Blood flow through the LAD can be restricted by cardiopulmonary bypass and pericardial cooling. Alternatively, a damping instrument may be applied directly on the LAD to restrict blood flow and reduce movement of the heart near the LAD. Such a heart stabilizing instrument is also available from United States Surgical Corporation of Norwalk, Conn.  
         [0086]    Referring to FIG. 14, the free end of the IMA is inserted through lateral opening  210  of DLU  112  and passed out the distal end opening of the DLU. The free end of the IMA is then everted over the distal end of the DLU such that the end of the IMA is retained by the distal end oriented portions of clips  158  as best shown in FIG. 15 and FIG. 16. Everting of the tissue may be achieved by any suitable known techniques such as y using graspers. With the IMA loaded in DLU  112 , the DLU is manipulated preferably detached from the handle and actuator assembly  110  in approximation to an incision “I” formed in the LAD, as shown in FIG. 17. Referring to FIGS. 18 and 19, the DLU with the everted IMA is inserted into the incision “I” of the LAD such that the walls of the LAD surrounding the incision are retained between the everted end of the IMA and the proximal ends of clips  158 , as shown in FIG. 19.  
         [0087]    As previously noted, the distal end of DLU  112  is configured with an angle relative to a transverse plane of the DLU in order to optimize the anastomosis and to facilitate optimal blood flow across the graft site from the IMA to the LAD. This junction creates “heel” and “toe” portions in which an acute or obtuse angle between the vessels is defined.  
         [0088]    Once DLU  112  with the everted IMA has been successfully inserted through the incision of the LAD, the surgeon may then attach the handle/actuator assembly  110  to DLU  112  as shown in FIGS. 20 and 21. In particular, the DLU lock slide  217  is moved proximally as indicated by arrow “A” in order to retract locking tube  215  and thereby expose the distal end of DLU holding tube  214 , and in particular, semi-annular groove  230 . DLU  112  is inserted on the distal end of the handle and actuator assembly  110  by placing mounting hub  138  within semi-annular groove  230  and releasing the force applied on DLU lock slide  217  as indicated by arrow “B” in FIG. 21, to permit coil spring  219  to return lock slide  217  and locking tube  215  to their distal-most orientations thereby securing the DLU in place.  
         [0089]    Referring to FIGS. 22 and 23, when the surgeon is ready to complete the anastomosis, the safety release slide  260  is moved proximally as indicated by arrow “C” in FIG. 23 thereby causing camming surface  268  to cam spring  250  downwardly away from shoulder  254  as indicated by arrow “D”. Thereafter, the surgeon may depress cover  246  towards handle half-sections  212   a  and  212   b , as indicated by arrow “E” in FIG. 24, causing actuator rod  232  to drive actuator  126  of DLU  112  distally as indicated by arrow “F”, thereby moving pusher member split half-sections  160  and  160   b  distally to deform clips  158  as shown in FIGS. 25 and 26.  
         [0090]    As best illustrated in FIG. 24, one particularly advantageous feature of the presently disclosed surgical instrument is that upon actuation of handle/actuator assembly  110 , safety release slide  260  is urged back into its initial locked orientation by way of annular flange  216  of actuator rod  232  pushing the lower portion of safety release slide  260  during the distal movement of actuator rod  232 . In this manner, upon release of cover handle  246 , the potential energy created by the compression of torsion spring  238  will cause actuator rod  232  to be pulled back proximally thereby engaging shoulder  254  with cutout  252  of spring  250 . This will serve to prevent accidental re-firing action of surgical instrument  100 .  
         [0091]    Referring to FIGS.  26 - 30 , a further uniquely advantageous feature of surgical instrument  100  is hinge lock  190  and its operation. Upon firing of surgical instrument  100 , return lockout tab  204  of hinge lock  190 , which extended into lockout slot  208  during distal movement of hinge lock  190  with split half-sections  160  and  160   b , serves to retain hinge lock  190  distal of its original seated location in tab receiving recess  206 . By retaining hinge lock  190  at this position, latch portions  192  and  194  are released from raised surfaces  196  and  198  of split half-section  160   a  of the pusher member. In this manner, split half-section  116   b  and  160   a  may be pivoted away from split half-sections  116   a  and  160   b  as shown in FIG. 30 to permit the removal of the IMA from within the pathway of the DLU thereby completing the vascular anastomosis as shown in FIG. 31.  
         [0092]    Referring to FIG. 31A, a portion of the vascular anatomy of an arm which may be an alternative utilized anastomosis site as illustrated wherein instead of joining the IMA to the LAD in a bypass procedure, an A-V fistula is performed utilizing surgical instrument  100  to join the radial artery end-to-side with the cephalic vein (sometimes called the radial vein). Other A-V fistulas which may also be achieved utilizing surgical instrument  100  include joining the ulnar artery end-to-side with the basilic vein (sometimes called the ulnar vein). Such A-V fistulas are performed to facilitate hemodialysis for end stage kidney disease to allow a single puncture at the dialysis unit for blood cleansing. The fistula allows a greater flow rate through the dialyzer (not shown).  
         [0093]    Referring to FIGS.  32 - 39 , an alternative embodiment of the firing safety mechanism illustrated in FIGS.  22 - 24  is illustrated which also prevents the unintended firing of surgical instrument  100 . The firing safety mechanism includes a lock spring  350  and a safety release slide  360 . Referring to FIGS. 33 and 33A, safety release slide  360  includes a pair of camming surfaces  360   a  and  360   b  which interact with cam follower surfaces  350   d  and  350   e . Lock spring  350 , as best illustrated in FIG. 34, includes a body portion  350   a  that defines a yoke, a pair a leaf spring portions  350   b  and  350   c , and a pair of cam follower surfaces  350   d  and  350   e  formed along a top portion thereof. An actuator rod  332 , FIG. 35, is configured and dimensioned to pass through yoke portion  350   a  of lock spring  350 .  
         [0094]    In the initial (pre-fired) configuration, as shown in FIG. 36, safety release slide  360  is disposed above lock spring  350  such that camming surfaces  360   a  and  360   b  contact cam following surfaces  350   e  and  350   e , respectively, when safety release slide  360  is in the distal-most position. In this orientation, leaf spring portions  350   b  and  350   c  serve to bias lock spring  350  upwardly within the instrument housing so that a shoulder portion  332   a  of actuator rod  332  abuts against a proximal facing lower surface  350   f , as shown in FIG. 36, to prevent firing of the instrument.  
         [0095]    When the surgeon desires to fire the instrument, safety release slide  360  is moved proximally as indicated by arrow “G” in FIG. 37. In this manner, camming surfaces  360   a  and  360   b  travel over cam follower surfaces  350   e  and  350   d , respectively, thereby urging lock spring  350  downwardly in the direction of arrows “H” to overcome the spring force of leaf spring portions  350   b  and  350   c . This movement displaces proximal surface  350   f  below shoulder portion  332   a  thereby permitting actuator rod  332  to move distally.  
         [0096]    Upon distal movement of actuator rod  332  as indicated by arrow “I” in FIG. 38, a second shoulder portion  332   b  formed proximal of shoulder portion  332   a  on actuator rod  332  contacts a rear wall portion  360   c  of safety release slide  360  thereby urging safety release slide distally in a direction of arrow “I” as well. Upon release of actuator handle cover  246 , actuator rod  332  moves proximally as indicated by arrow “J” in FIG. 39 thereby permitting lock spring  350  to move upwardly as indicated by arrow “K” in FIG. 39 to reset the firing safety mechanism.  
         [0097]    It will be understood that various modifications may be made to the embodiment shown herein. For example, the instruments may be sized to perform an anastomosis for other vessels and luminal tissue. Therefore, the above description should not be construed as limiting, but merely as exemplifications of preferred embodiments. Those skilled in the art will envision other modifications within the scope and spirit of the claims appended hereto.