Abstract:
A blood vessel catheter includes a dual lumen catheter tube and a bolus insert attached to the distal end of the tube. First and second ports are formed between the nose section of the bolus and distal end openings of first and second lumens in the tube. The catheter is fabricated by insert molding a thermoplastic bolus onto the distal end of a thermoplastic tube.

Description:
RELATED APPLICATION  
       [0001]     This application is a continuation of International Application No. PCT US2004/037101 filed Nov. 5, 2004, which is related to Provisional U.S. Application Ser. No. 60/517,826, filed Nov. 6, 2003, and claims priority from that application. 
     
    
     FIELD OF THE INVENTION  
       [0002]     The invention relates generally to catheters for use in intravenous applications. It relates particularly to hemodialysis catheters and methods of manufacturing them.  
       BACKGROUND OF THE INVENTION  
       [0003]     Hemodialysis, as practiced today, normally employs one of two types of catheter to remove blood from the patient for processing and return processed blood to the patient. Most commonly, a catheter tube containing two lumens is used, each lumen having a generally semi-cylindrical or D-shape configuration. This type of catheter is frequently referred to as a dual lumen catheter. Alternatively, two tubes, each with a full cylindrical configuration, are used separately to remove blood for dialysis and return the processed blood.  
         [0004]     Flow rates possible with conventional dual lumen catheters are usually lower than those achievable where separate tubes are used to remove blood from a vein for dialysis and then return processed blood back to the vein. Thus, the use of two tubes has become more and more popular as the capacity (maximum flow rate) of hemodialysis membranes has increased. However catheters utilizing two separate lumens are more difficult to insert and also take up considerably more space in the vessel, thereby somewhat compromising blood flow in the vessel.  
         [0005]     Hemodialysis membranes are now able to process blood at over 500 ml of flow per minute. Even higher processing rates are foreseeable. However, problems occur with both the line introducing purified blood back into the vein (the venous or outflow line) and the line removing blood for purification (the arterial or intake line) at flow rates above 300 ml per minute. A high flow rate from the venous line may cause whipping or “fire-hosing” of the tip in the vein with consequent damage to the vein lining. A corresponding high flow rate into the arterial line may cause the port to be sucked into the vein wall, resulting in occlusion. It should be understood, of course, that both lines normally access the superior vena cava and the left atrium and the designations are used for differentiation purposes.  
         [0006]     Speed of flow through a catheter lumen, whether it be in a single lumen or a dual lumen catheter, is controlled by a number of factors including the smoothness of the wall surface, the internal diameter or cross-sectional area of the tube lumen, and the length of the tube lumen. The most important factor is the cross-sectional area of the tube lumen. The force or speed of the fluid flow in a tube lumen for a given cross-sectional area is controlled by the external pumping force, of course. This is a positive pressure pushing processed blood through the venous lumen and a negative (suction) pressure pulling unprocessed blood through the arterial lumen.  
         [0007]     Problems encountered in providing for a high flow rate through a catheter are magnified in a dual lumen catheter construction. Because each of the lumens in a dual lumen catheter normally has a D-shape, it has been assumed that flow rates are limited. Furthermore, such dual lumen catheters are, to a great extent, catheters with a main port that opens at the end of a lumen substantially on the axis of the lumen. Thus, “fire-hosing” frequently results. Fire-hosing may damage the vein wall, triggering the build-up of fibrin on the catheter tip. Fibrin build-up may result in port occlusion.  
         [0008]     There are dual lumen catheters described in the prior art which utilize side ports for both outflow and inflow. An example is the catheter disclosed in the Cruz et al. U.S. Pat. No. 5,571,093. Another example is the catheter disclosed in Quinn U.S. Pat. No. 6,461,321. Yet another example is the catheter disclosed in the DeCant, Jr. et al. U.S. Pat. No. 6,786,884. Each of these catheter designs combines a dual lumen catheter tube with a dual passage bolus, which is independently formed and then attached to the distal end of the tube. Each has unique shortcomings in performance and/or manufacturability which detract from its attractiveness as a commercial product, however.  
       SUMMARY OF THE INVENTION  
       [0009]     An object of the invention is to provide improved dual lumen hemodialysis catheters.  
         [0010]     Another object is to provide dual lumen hemodialysis catheters which accommodate flow rates as high as the latest separate dual cylindrical lumen tubes and combined dual “D” lumen catheters.  
         [0011]     Still another object is to provide dual lumen hemodialysis catheters which are capable of returning processed blood to the patient at high flow rates without harmful fire-hosing of the catheter tip.  
         [0012]     Yet another object is to provide dual lumen hemodialysis catheters which permit high flow rates while minimizing trauma and potential red cell damage so as to substantially avoid clotting.  
         [0013]     A further object is to provide dual lumen hemodialysis catheters in which occlusion of the return line port is substantially avoided regardless of the flow rate.  
         [0014]     Another object is to provide dual lumen dialysis hemodialysis catheters in which occlusion of the return line port is substantially avoided regardless of the position of the port in relation to the vessel wall.  
         [0015]     Still another object is to provide dual lumen hemodialysis catheters that facilitate reversal of the venous and arterial lines to relieve port occlusion without greatly increasing the potential for mixing of dialyzed blood with blood being removed for dialysis.  
         [0016]     Yet another object is to provide a dual lumen catheter having an arterial port configuration that, in the reverse flow mode, directs the blood flow upward and forward along a 21° ramp angle immediately upon its point of exit from the lumen so as to direct the flow away from the venous port.  
         [0017]     A further object is to provide an arterial port wherein, in the reverse flow mode, blood flows upward and forward along the 21° ramp angle immediately upon its point of exit from the lumen, which slows the flow and protects the blood components.  
         [0018]     Yet a further object is to provide a dual lumen catheter that has rounded bullet tip portion that is smaller than the outside diameter of the tube so as to assist in insertion and minimize vessel wall damager.  
         [0019]     Yet a further object is to provide a dual lumen hemodialysis catheter wherein a bolus tip is formed in place on a prepared distal end of a dual lumen catheter tube.  
         [0020]     Yet a further object is to provide a dual lumen catheter that has rounded bullet tip portion that can be inserted using a tunneler and then placed in its final location without the utilization of a guide wire.  
         [0021]     The foregoing and other objects are realized in accordance with the present invention by providing dual lumen catheters comprising a catheter tube having first and second lumens of different length. The venous lumen half of the tube extends to a distal end well beyond the distal end of the arterial lumen half of the tube, leaving the septum between the lumens substantially exposed between those distal ends. A bolus tip which, in itself, contains no fluid passages, is insert molded onto that exposed septum.  
         [0022]     The invention is embodied in two forms of hemodialysis catheter. In each the bolus tip includes a bullet nose section which extends forwardly of the distal end of the venous lumen and forms a flow direction ramp in front of the venous lumen opening, creating a venous port on one side of the catheter. The bolus tip also includes an attachment section which extends forwardly of the distal end of the arterial lumen and forms a flow direction ramp in front of the lumen opening, creating an arterial port on the opposite side of the catheter.  
         [0023]     In one form of the invention, the venous port ramp begins at the point where the blood exits an ovoid lumen opening and travels over an ascending arc that slows and directs the flow forward, but also diffuses it, thereby softening the mixing of the infused blood with the normal venous flow. In this normal flow mode, blood is immediately carried forward and away from the aspirating arterial lumen, so some diffusion is desired. The ramp is fed by the ovoid shaped outlet end of the lumen that is formed in the manufacturing process from the original extruded “D” shape of the tube. This ovoid port is slightly larger than the “D”, thereby slowing fluid flow. Its shape also raises the fluid outflow stream above the normal “D” septum, thereby assisting in the directional flow up and forward over the top of the bullet tip.  
         [0024]     In this one form of the invention, the ramp in the arterial port differs from that in the venous port in several ways. Overall, the arterial port ramp is longer and, where it begins at the surface of the septum and the opening of the lumen, is slightly convex in cross-sectional shape. The ramp becomes flat as it continues radially outward and then slightly convex where it blends into the top surface. In the normal flow mode the longer ramp provides a larger recessed area to allow the maintenance of flow in the reversed flow mode. For this design a straight 21° angle ramp profile is highly preferred. The ramp angle may vary between 18° and 24° and still produce good results, however. Ramps with much larger profile angles, such as 45°, present an abrupt surface direction change and result in excessive diffusion around the sides of the tip that causes mixing in the reverse flow mode. Angles much smaller than 21°, such as 12° to 16°, do not provide enough upward flow direction and, also, result in unwanted mixing in the reversed flow mode.  
         [0025]     In the normal aspiration mode, the rounded top distal end of the 21° angle ramp, in cooperation with the top of the inclined edge of the arterial lumen distal end, provide a protected area in the port which is created that assures the continuation of flow in the normal aspiration mode. Larger ramp angles reduce the size of the protected aspiration area. Smaller angles increase the length and size of the protected aspiration area but the additional length tends to allow the vessel wall to stretch and protrude into the protected area, thereby reducing its size and presenting the potential for port occlusion. The 21° angle presents the optimum ramp inclination for aspiration in normal flow, and in the reversed mode provides the maximum results for diffusion and flow direction.  
         [0026]     Between the bullet nose section and the distal end opening of the arterial lumen, short side walls are formed on the exposed septum. These side walls serve two purposes. They control fluid flow and they stiffen the catheter at that point so that any tendency of the catheter to fold there is counteracted. The 45° angle of the proximal edge of the arterial port assures that there is no cross-sectional area reduction that would result in increased flow speed as the blood exits the port. Fluid can flow forward and upward without restriction. To further assure that there is no restriction to flow, the 21° angle ramp begins to rise from the floor of the port at the exact point where the leading edge of the 45° angle arterial lumen opening meets the beginning of the ramp, hence preventing any increased resistance to flow except by the ramp. The top edges of the side walls meet the 45° inclined edge of the arterial lumen opening behind the junction of the ramp and the surface of the lumen, after the ramp has ascended from the septum surface. The side walls contain the lower level of the fluid outflow that first meets the resistance of the ramp. As has been explained, the ramp tends to push flow upward (radially outward), but also tends to diffuse it around the tube. The side walls reduce the tendency for diffusion at this initial, and most critical point. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0027]     The invention, including its construction and method of operation, is illustrated more or less diagrammatically in the drawings in which:  
         [0028]      FIG. 1  is a side elevational view of a portion of a hemodialysis catheter embodying features of a first form of the invention;  
         [0029]      FIG. 2  is a front end view of the catheter bolus of  FIG. 1 ;  
         [0030]      FIG. 3  is a bottom plan view of the bolus end of the catheter of  FIG. 1 ;  
         [0031]      FIG. 4  is a top plan view of the bolus for the catheter of  FIG. 1 ;  
         [0032]      FIG. 5  is a longitudinal sectional view taken through the bolus of the catheter of  FIG. 4 ;  
         [0033]      FIG. 6  is a cross-sectional view taken along line  6 - 6  of  FIG. 1 ;  
         [0034]      FIG. 7  is a cross-sectional view taken along line  7 - 7  of  FIG. 1 ;  
         [0035]      FIG. 8  is a side elevations view of the tube in the catheter of  FIG. 1 ;  
         [0036]      FIG. 9  is a top plan view of the tube seen in  FIG. 1 ;  
         [0037]      FIG. 10  is a side elevational view of the first form of catheter showing the compound curve slope of the ramp in front of the arterial lumen opening;  
         [0038]      FIG. 11  is a side elevational view of the catheter of  FIG. 10  illustrating fluid flow patterns;  
         [0039]      FIG. 12  is a side elevational view of a portion of a hemodialysis catheter embodying features of a second form of the invention;  
         [0040]      FIG. 13  is a bottom plan view of the catheter of  FIG. 12   
         [0041]      FIG. 14  is a top plan view of the catheter of  FIG. 11   
         [0042]      FIG. 15  is a longitudinal sectional view taken along line  15 - 15  of  FIG. 14 ;  
         [0043]      FIG. 16  is a cross-sectional view taken along line  16 - 16  of  FIG. 11 ;  
         [0044]      FIG. 17  is a cross-sectional view taken along line  17 - 17  of  FIG. 14 ;  
         [0045]      FIG. 18  is a cross-sectional view taken along line  16 - 16  of  FIG. 14 ;  
         [0046]      FIG. 19  is another top plan view of the catheter embodying features of the second form of the invention, showing the improved fluid flow patterns which are produced;  
         [0047]      FIG. 20  is a cross-sectional view taken along line  20 - 20  of  FIG. 19 ;  
         [0048]      FIG. 21  is a side elevational view of the catheter and fluid flow patterns seen in  FIG. 19 ;  
         [0049]      FIG. 22  is a top plan view of the distal end of the catheter tube for the second form of catheter;  
         [0050]      FIG. 23  is a bottom plan view to the tube portion seen in  FIG. 22 ;  
         [0051]      FIG. 24  is a longitudinal sectional view taken along line  24 - 24  of  FIG. 22 ;  
         [0052]      FIG. 25  is a cross-sectional view taken along line  25 - 25  of  FIG. 22 ;  
         [0053]      FIG. 26  is another top plan view of the second form of catheter;  
         [0054]      FIG. 27  is another side elevational view of the second form of catheter;  
         [0055]      FIG. 28  is a sectional view taken along line  28 - 28  of  FIGS. 26 and 27 ;  
         [0056]      FIG. 29  is a sectional view taken along line  29 - 29  of  FIGS. 26 and 27 ;  
         [0057]      FIG. 30  is a sectional view taken along line  30 - 30  of  FIGS. 26 and 27 ;  
         [0058]      FIG. 31  is a sectional view taken along line  31 - 31  of  FIGS. 26 and 27 ;  
         [0059]      FIG. 32  is a sectional view taken along line  32 - 32  of  FIGS. 26 and 27 ; and  
         [0060]      FIG. 33  is a longitudinal sectional view through a catheter embodying the second form of the invention as the bolus is insert molded onto the distal end of the tube. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0061]     Referring now to drawing  FIGS. 1-11 , a dual lumen catheter embodying features of a first form of the invention is shown generally at  10 , with parts removed. The catheter  10  illustrated here is a dual-lumen hemodialysis catheter but it should be understood that the invention might find advantageous application in other intravenous treatment. The catheter  10  comprises a polyurethane catheter tube  12  onto which a polyurethane bolus tip  14  is insert molded.  
         [0062]     The catheter tube  12  comprises a tube body  16  (see  FIGS. 8 and 9 ) which contains a venous lumen  20  and an arterial lumen  22  separated by a septum  24 . The lumens  20 ,  22  and the septum  24  are enclosed by a cylindrical body wall  26 .  
         [0063]     As best seen in  FIG. 8 , the venous lumen  20  has a distal end  30  which is cut off (skived) at a 45° angle to the septum  24  in the manner illustrated. The arterial lumen  22  has a distal end  32  which is displaced longitudinally from the end  30  of the venous lumen and is also cut off (skived) at a 45° angle to the septum  24 . The upper surface  34  of the septum  24  is then, effectively, the outer surface of the tube  12  between the 45° angle skived ends  30  and  32 .  
         [0064]     In this first form of the catheter  10  invention, however, there is a short section  40  of the body wall  26  which remains between the lumen ends  30  and  32 . As seen in  FIG. 5 , this wall section  40  overlies the bolus tip  14  after the tip is insert molded onto the tube  12 , in a manner hereinafter discussed.  
         [0065]     The bolus tip  14  is insert molded onto the tube  12  in a conventional manner. Referring to  FIG. 5 , the distal end of the tube  12  is placed in a suitably shaped die (not shown) with a gate where the end of the bullet nose on the bolus tip  14  is located. Molten plastic flows through the wall section  40  on the septum surface  34  and solidifies in the form illustrated. In doing so, it forms a bond with all complementary tube  12  surfaces.  
         [0066]     The bolus tip  14  formed includes a bullet nose section  42  extending forwardly of the distal end  30  of the lumen  20 . It also includes an attachment section  44  which is fastened to the lumen surface  34 . The section  44  has a ramp  60  on its trailing face. The ramp  60  faces the open end  32  of the arterial lumen  22 .  
         [0067]      FIGS. 10 and 11  show the catheter  10  and the ramp  60  which, with the skived end  32  of the arterial lumen  22  forms the arterial port  48 .  FIG. 10  illustrates ramp angles and  FIG. 11  illustrates fluid flow patterns.  
         [0068]     Turning now to  FIGS. 12-32 , a portion of a dual lumen catheter embodying features of a second form of the invention is shown generally at  110 . The catheter  110  comprises a catheter tube  112  onto which a bolus tip  114  is insert molded according to the invention.  
         [0069]     The catheter tube  112  comprises a tube body  116  (see  FIGS. 22-25 ) which contains a venous lumen  120  and an arterial lumen  122  separated by a septum  124 . The lumens  120 ,  122  and the septum  124  are enclosed by a cylindrical body wall  126 .  
         [0070]     As best seen in  FIG. 24 , the venous lumen  120  also has a distal end  130  which is cut off (skived) at 45° to the septum  124 , in the manner illustrated. The arterial lumen  122  has a distal end  132  which is displaced longitudinally from the end  130  of the venous lumen and is also cut off (skived) at 45° to the septum  124 . One surface  134  of the septum  124  then forms the outer surface of the tube  112  between the 45° angle cut-off lumen ends  130  and  132 . The tube  112  is formed with short side walls  136  which bracket the surface  134 .  
         [0071]     Referring now specifically to the  FIG. 33 , bolus tip  114  is insert molded onto the tube  112  in a conventional manner. Mold halves a form each side of the catheter. Before the mold is closed over tube  112 , insert pin B is placed in arterial lumen  122 . Insert pin C is inserted into the distal end of the venous lumen  120 . The pin C has bulbous center section that stretches the septum  124  upwardly and outwardly adjacent its free end, at  150 . Molten plastic is then introduced into the mold cavity through gate D.  
         [0072]     The molten plastic adheres to the surface  134  of the septum  124  and to the side walls  136 . Its temperature is effective to cause the bulge  150  formed in the thermoplastic septum  124  to retain this shape when the dies A and B and the pin C are removed.  
         [0073]     The bolus tip includes a bullet nose section  142  extending forwardly of the distal end  130  of the lumen  120 . It also includes an attachment section  144  which is fastened to the lumen surface  134  and the side walls  136 .  
         [0074]     Referring now specifically to  FIGS. 26-32 , the catheter  110  formed in this process has a ramp  160  facing the distal end  132  of the arterial lumen  122  and forming the arterial port  148 . The ramp  160  is inclined at an angle of 21° to the septum  124 . The ramp  160 , where it meets the septum  124  at the base of cut-off lumen end  132 , is slightly convex, as best seen in  FIG. 29 . The ramp  160  then becomes flat for a substantial (relative) distance, as best seen in  FIG. 30 . The ramp  160  then becomes increasingly concave, as best seen in  FIGS. 31 and 32 , to where it blends in with the tip surface. Adjacent the lumen end  132  the ramp  160  is bracketed by exposed portions  164  of the side walls  136 .  
         [0075]     Although both forms of the catheter invention which have been described provide substantial advantages over prior art dual lumen catheters, the second form is preferred. The side walls  136  in the arterial port reinforce the catheter at the port. Downward bending of the bolus tip is substantially prevented by the resistance of these side walls to stretching. Similarly, upward folding of the tip is substantially prevented by axial compression of the side walls.  
         [0076]     Also, as previously discussed, the arterial ramp configuration provides substantial advantages. Initially, the slightly concave ramp channels flow (in the reverse flow mode) toward the center of the ramp. Subsequently, the 21° angle, flat ramp section continues to direct flow upwardly (radially outwardly). Finally the slightly convex ramp section encourages flow around the tip as it proceeds forwardly over the end of the tip. The result is that there is no substantial mixing flow, i.e., flow directly back toward the venous port.  
         [0077]     While preferred embodiments of the invention have been described, it should be understood that the invention is not so limited, and modifications may be made without departing from the invention. The scope of the invention is defined by the appended claims, and all devices and methods that come within the meaning of the claims, either literally or by equivalence, are intended to be embraced therein.