Abstract:
A transition device for placement at the opening of the tip of a cannula body for the purpose of controlling the shape of the cannula tip opening under various loads such as might be encountered during device placement.

Description:
BACKGROUND 
       [0001]    1. Field of the Invention 
         [0002]    This invention relates to the field of medical technology and medical devices and more particularly to the process of cannulation of the cardiovascular system to remove or return blood or other fluids through a cannula device. 
         [0003]    2. Related Art 
         [0004]    The process of cannulation of the cardiovascular system to remove or return blood or other fluids through a cannula device is known. One example, shown in  FIG. 1A , is a venous cannulation system  100 , including a cannula  102  and an introducer  104  designed to remove blood from the venous side of the circulatory system during a surgical procedure that requires cardiopulmonary bypass (CPB). 
         [0005]    Cannula  102  should preferably be deflectable at its distal end  106  to permit proper positioning of distal end  106  of cannula  102  including introducer  104  within the femoral vein. 
         [0006]    Frequently, the distal end or tip  106  of cannula  102  is made from a soft material, such as soft Polyurethane (PU) tubing, tipped to provide a smooth tapered profile for insertion into the femoral vein. Generally, insertion is done either through percutaneous access (Seldinger technique) or a standard cut-down access. 
         [0007]    The soft PU tubing is prone to deformation or compression under resistance, for example when pushing through connective tissue such as might be encountered during a Seldinger technique access to the femoral vein. Such deformation causes difficulty for the surgeon by increasing the drag force on cannula  102  during insertion. 
         [0008]    Additionally, as shown in  FIG. 1B , the junction  108  between cannula  102  and introducer  104  is prone to exposing an edge during cannulation if introducer  104  is bent. 
       SUMMARY 
       [0009]    In light of the foregoing background, an improved device and associated method for the process of cannulation of the cardiovascular system are provided according to the various embodiments of the present invention. 
         [0010]    This present invention relates to a transition device for placement at the opening of the tip of a cannula body for the purpose of controlling the shape of the cannula tip opening under various loads such as might be encountered during device placement. 
         [0011]    In one aspect, a cannulation system is provided including a cannula body having a distal end and a first lumen extending therein. The system also includes an introducer configured to be insertably received into the distal end of the cannula body; and a transition device including a first section having an attachment geometry, a second section having a variable external diameter and an inner lumen extending therein. The first section is inserted into the first lumen at the distal end of the cannula body to secure the transition device thereto. The second section extends outside of the cannula body and is configured to allow the introducer into the first lumen of the cannula body. The second section provides a transition between the outer surface of the cannula body and the outer surface of the introducer such that no gap is opened at the intersection of the outer surface of the cannula body and the outer surface of the introducer as the introducer is flexed relative to the cannula body. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]    Having thus described the invention in general terms reference will now be made to the accompanying drawings, which are not necessarily drawn to scale, and wherein: 
           [0013]      FIGS. 1A and 1B  are simplified views of a cannulation system; 
           [0014]      FIG. 2A  is a simplified perspective view of a transition device in accordance with an embodiment of the present invention; 
           [0015]      FIG. 2B  is a cross-sectional view of the transition device of  FIG. 2A , including detailed sections, in accordance with an embodiment of the present invention; 
           [0016]      FIG. 3  is a simplified cross-sectional view of a cannulation system including a transition device in accordance with an embodiment of the present invention; 
           [0017]      FIG. 4A  is a simplified perspective side view of a transition device in accordance with an embodiment of the present invention; 
           [0018]      FIG. 4B  is a cross-sectional view of the transition device of  FIG. 4A  in accordance with an embodiment of the present invention; 
           [0019]      FIG. 5  is a simplified perspective view of a cannulation system including a transition device in accordance with an embodiment of the present invention; and 
           [0020]      FIG. 6A  is a cross sectional view of a typical drainage hole defined through a cannula; and 
           [0021]      FIG. 6B  is a cross sectional view of a chamfered drainage hole defined through a cannula in accordance with an embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0022]    The disclosure is now described more fully hereinafter with reference to the accompanying drawings, in which some, but not all embodiments are shown. The disclosure may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Like numbers refer to like elements throughout. 
         [0023]      FIG. 2A  is a simplified perspective view of a transition device  200  in accordance with an embodiment of the present invention. As shown in  FIG. 2A , transition device  200  is a tubular structure formed as a combination of two external sections: a first section  204  having a first geometry, for example, a variable external diameter and a second section  206  having a second geometry, for example, a substantially constant external diameter. In one embodiment, the substantially constant external diameter is formed with a requisite length and diameter to facilitate attachment to cannula tubing, such as by interference fitting second section  206  into the lumen of the cannula tubing. Alternatively, second section  206  may include attachment structures formed thereon or attached thereto, for example, hooks, barbs, laser welding, adhesives or any of a number of possible equivalents well known in the art. Internally, transition device  200  is shown to define an internal lumen  208 . 
         [0024]    As shown in  FIG. 2B , first section  204  is designed such that leading edge  210  of first section  204  includes a tip portion  212  that includes a tip section  214 . In one embodiment, tip section  214  is further tapered or otherwise shaped to reduce trauma and to provide for easy insertion, especially through difficult tissue (connective tissue, skin, muscle) such as might be encountered during insertion into the femoral vein. 
         [0025]    Transition device  200  may be made of any suitable material that is rigid enough to withstand various loads such as might be encountered during device placement, such as plastic, metal, ceramic, and the like. 
         [0026]      FIG. 3  is a simplified cross sectional illustration of a cannulation system  300  in accordance with an embodiment of the present invention. In operation, second section  206  of transition device  200  is positioned within cannula  308 . 
         [0027]    When second section  206  is positioned within cannula  308 , external cannula surface  306  is made to abut against the large end of first section  204 . First section  204  creates a gradual and smooth transition between external cannula surface  306  and an object positioned within internal lumen  208  of transition device  200 , such as surface  302  of introducer  304 . In one embodiment, internal lumen  208  is configured to interface tightly, for example, with an interference fit, with introducer  304 . 
         [0028]    Tapered tip section  214  ( FIG. 2B ) on tip portion  212  of transition device  200  further provides and allows for a smooth transition between surface  302  of introducer  304  and cannula surface  306  of cannula  308 . 
         [0029]      FIGS. 4A and 4B  are perspective and cross-sectional views, respectively, of another embodiment of a transition device  400 . Externally, transition device  400  is similar to the embodiment of transition device  200  illustrated in  FIGS. 2A and 2B . For example, as shown in  FIG. 4A , transition device  400  is a tubular structure formed as a combination of a first section  402  having a variable external diameter, a second section  404  having a substantially constant external diameter, and tapered tip section  406  allowing for a smooth transition between the surface of an introducer and a cannula surface. 
         [0030]    Internally, as shown in  FIG. 4B , transition device  400  includes interior threads  408 . Interior threads  408  mate with corresponding threads placed on the exterior surface of an introducer (not shown). Interior threads  408  when mated to the threaded introducer provide a secure lock which helps to maintain the relative position of the cannula and introducer during penetration through difficult tissue, such as may be encountered in a patient with previous scar tissue, or someone with significant obesity. 
         [0031]    In one embodiment, interior threads  408  of transition device  400  include a three-start helical square thread with a predetermined height and pitch. Alternatively, interior threads  408  may be a rope thread, which is a thread with a smooth surface relative to typical square or triangular threads. 
         [0032]    The threaded transition device  400  acts as a fixation point to control the position of the distal end  502  ( FIG. 5 ) of cannula  308  relative to introducer  304  during cannulation. 
         [0033]    As shown in  FIG. 5 , cannulation system  300  is deflectable at its distal end  502  to permit proper positioning of distal end  502  of cannula  308  including introducer  304  within the femoral vein. However, junction  504  between cannula  308  and introducer  304  having transition device  200  or  400  is no longer prone to exposing an edge during cannulation. 
         [0034]    As shown in  FIG. 5  introducer  304  includes an elongated tube like structure  512  having a distal end including tip  514 . 
         [0035]    Elongated tube like structure  512  may be formed of any suitable, material having a sufficiently high durometer to impart substantial rigidity to introducer  304  to facilitate its placement. In one embodiment, tip  514  may be formed of a material, which is substantially softer, i.e., has a substantially lower durometer and molecular weight, than the material of the remainder of tube like structure  512 . Using a substantially softer material ensures that tip  514  does not traumatize any tissue with which it engages when introducer  304  is being positioned. 
         [0036]    In one embodiment, the high durometer material of tube like structure  512  may have a durometer, for example, in the range of 55 to 75 durometer (Shore D), such as a polyether based polyurethane. In one embodiment, the lower durometer material of tip  514  may have a durometer in the range of 75 to 85 durometer (Shore A), such as aliphatic polyurethane. One particularly effective polyurethane for tube like structure  512  is Pellethane 2363-65D commercially available from Dow Chemical Company of Midland Mich., which has a durometer of 65 (Shore D), while a particularly effective polyurethane for tip  514  is Tecoflex 80A-B20 commercially available from Thermedics, Inc. of Wooburn, Mass., which has a durometer of 80 (Shore A). 
         [0037]    In one specific embodiment, introducer  304  is made of polyurethane as the base material. Tube like structure  512  is a blend of HDPE (shore 75D) and LDPE (shore 45D). Tip  514  is made entirely of LDPE. Both tip  514  and tube like structure  512  include BaSO 4  and TiO 2 . 
         [0038]    Alternatively, other means to impart substantial rigidity to introducer  304  to facilitate its placement other than durometer shift include: the insertion of stiffening members in tube like structure  512 , the covering of tube like structure  512  with a stiffening sheath, and chemically treating tip  514  and tube like structure  512 . 
         [0039]    In one embodiment, the material of tip  514  may include a radiopaque material, such as barium sulfate or the equivalent. The inclusion of the radiopaque material in the material of tip  514 , helps to radiographically locate introducer  304  when it is in position, by producing a sharply defined, distinct radiographic image. 
         [0040]    Again referring to  FIG. 5 , in one embodiment of the present invention, cannula  308  includes at least one to a plurality of drainage holes  510  defined between external surface  306  and inner lumen  208  ( FIG. 3 ). 
         [0041]    As shown in  FIG. 6A , a typical drainage hole  510  includes a square edge  602  and exhibits perceptible roughness to the touch. Generally, hole  510  is punched through the wall  604  of cannula  308  in one stroke. When the punch exits the far side of cannula  308 , it may leave a slight-burr or raised edge on external surface  302  (tissue-contacting side of cannula  308 ) around drainage hole  510 . Since cannula  308  is to be inserted through skin, subcutaneous tissue, fat, and connective tissue; then pushed through the femoral vein up to the right atrium of the heart, there is a chance that some of the tissue may be scraped off by the square-edged drainage hole  510 . This problem is especially evident during percutaneous insertion, when the surgeon has to push cannula  308  through the most difficult tissue. 
         [0042]    As shown in  FIG. 6B , in accordance with an embodiment of the present invention, drainage hole  510 A may be smoothed, chamfered or given a radius at edge  602 A to reduce the possibility of traumatic tissue damage during insertion of cannula  308 . 
         [0043]    Various methods exist for smoothening edge  602 A of hole  510 A, including using abrasive material removal, melt profiling, or hot drilling. In an alternative method, the section of cannula  308  which includes drainage holes  510 A may be molded from rigid plastic or other similar material to provide a smooth profile. 
         [0044]    It is to be understood that the invention is not to be limited to the specific embodiments disclosed and that modifications and other embodiments are intended to be included within the scope of the appended claims. Although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation.