Medical procedures for the treatment of chronic diseases often require repeated access to the vascular system for the injection of therapeutic compounds and the sampling of blood. Kidney dialysis, chemotherapy and other chronic treatments generally rely on catheters for both injection to and withdrawal of fluids from the vascular system. For example, during kidney dialysis, large amounts of blood are withdrawn from the patient, treated externally in a dialysis machine to remove impurities and add nutrients, medications and other therapeutic elements and returned to the patient.
Typically, a single catheter having two or more lumens is used for the removal and return of the blood with a first of the lumens being used to aspire impure blood from a blood vessel (usually a vein) and a second of the lumens being used to return the treated blood to the blood vessel. A single catheter tip including inlet and outlet orifices connected to the first and second lumens, respectively, is commonly used to perform both functions.
Since the inlet and outlet orifices are located on the same tip, a portion of the treated blood exiting the outlet orifice is recirculated directly through the inlet orifice to the dialysis machine. This delays treatment of portions of the venous blood displaced by the recirculated fluid, increasing the time required to achieve a desired amount of purification, as well as the cost of the procedure and patient discomfort.
In one aspect, the present invention is directed to a multi-lumen catheter comprising a first lumen extending through the catheter to a first distal opening, and a second lumen extending through the catheter to a second distal opening which is distal to the first distal opening so that an extending portion of a septum separating the lumens extends distally past the first distal opening. A tip is overmolded on the extending portion and includes a first ramp adjacent to the first distal opening and a second ramp adjacent to the second distal opening. The ramps direct fluids exiting the openings away from a longitudinal axis of the catheter.
The present invention is further directed to a method of forming a distal tip for a multi-lumen catheter whereby a catheter is provided with a first lumen extending through the catheter to a first distal opening and a second lumen extending through the catheter to a second distal opening which is distal to the first distal opening so that an extending portion of a septum separating the lumens extends past the first distal opening. A tip bonded to the extending portion includes a first ramp adjacent to the first distal opening and a second ramp adjacent to the second distal opening. The first and second ramps direct fluids exiting from the first and second distal openings at first and second angles relative to a longitudinal axis of the catheter.
The present invention may be further understood with reference to the following description and the appended drawings, wherein like elements are referred to with the same reference numerals. The present invention relates to devices for accessing the vascular system. Although the present invention is described in regard to a catheter used to withdraw and return blood during dialysis, those skilled in the art will understand that the invention is equally applicable to any treatment in which a single catheter to withdraw fluid from and provide fluid to a blood vessel or other lumen. More particularly, the invention relates to catheter tips that minimize recirculation during such treatments.
To reduce recirculation, the tips of conventional dialysis catheters are shaped, to a certain extent, to separate the inlet and outlet orifices. For example, conventional designs have staggered orifices, with the outlet orifice further downstream (in the direction of the flow of blood) than the inlet orifice. Typically, in this configuration, the outlet orifice is placed on the tip distally of the inlet orifice. However, at times it is necessary to reverse the direction of flow through the catheter so that the inlet orifice serves as an outlet and the outlet orifice serves as an inlet.
In this reverse mode, the outlet orifice is no longer downstream of the inlet, increasing recirculation. This effect is alleviated to a certain extent by the flow of blood which tends to entrain the injected blood away from the catheter tip. However, the flow of blood pulsates with the beating heart and, when the rate of flow is at its lowest, the purified blood exiting the conventional catheter is not entrained away from the tip and the inlet through which it may be recirculated.
To gain a quantitative understanding of the scope of the problem caused by recirculating blood, exemplary recirculation rates determined experimentally are described below. For an exemplary conventional staggered tip catheter with inlet and outlet orifices displaced longitudinally relative to one another, the recirculation rate in the normal more of operation is about 0.4% while for the reverse mode of operation the recirculation rate is about 20.9%. In contrast, exemplary embodiments of a catheter tip according to the present invention provide recirculation rates in the normal mode of between about 0.4% and 2.4%, with reverse mode recirculation rates of between about 6.3% and about 7.8%. As can be seen, the exemplary embodiments according to the present invention provide a substantial reduction in recirculation in the reverse mode of operation of the catheter, while maintaining normal mode recirculation comparable to that of the conventional catheters.
In addition to the amount of recirculation in both reverse and normal modes of operation, thrombogenicity of the design is of interest. This refers to the tendency of the catheter tip to facilitate coagulation of the blood flowing therethrough forming coagulated particles known as thrombi. As is understood by those skilled in the art, thrombi may be very dangerous if they become dislodged and travel through the body. The hemolysis of the catheter tip (i.e., the tendency of the tip to damage blood cells flowing therethrough) is also important.
The exemplary embodiments of the present invention thus provide improvements in the ability of the catheter to minimize recirculation in a reverse mode of operation, while at the same time retaining the ability to minimize recirculation in the normal mode of operation. Those skilled in the art will understand that this latter property is important as the catheter spends a majority of its operational life in the normal mode of operation with the reverse mode of operation being implemented less frequently. In addition, the embodiments of the catheter tip according to the present invention retain acceptable thrombogenicity and hemolysis properties.
In addition to
In greater detail, the flow control element 122 includes a ramp 118 near the first opening 108, as shown in
The flow control element 122 may also include lateral elements 126 designed to prevent flow from “wrapping” around the sides of the tip 100 toward the second opening 110. The first opening 108 includes an orifice 112 formed on a plane diagonal to a longitudinal axis of the first lumen 104. The specific angle and size of the orifice 112 is preferably selected to cooperate with the ramp 118 to obtain a selected flow rate out of the first opening 108. The length of the flow control element 122 in front of the ramp 118 may also be selected in part to reduce the tendency of blood to recirculate during the reverse mode. In addition, a contoured bolus 120 may be provided at a distal-most point of the tip 100 to facilitate insertion of the tip/catheter assembly into the vein and to assist in navigating the assembly therein. Preferably, the contoured bolus 120 forms an atraumatic tip for catheter tip 100 allowing the catheter tip 100 to penetrate and navigate within the blood vessels without causing injury thereto.
Another important consideration in the design of the catheter tip 100 is the stagger distance s between the first and second openings 108, 110. An increase in the stagger distance s generally reduces recirculation. However, an excessive increase in the stagger distance s may make the catheter tip 100 impractical for use in a blood vessel (i.e., the length of the tip 100 may make navigation difficult or impossible). Accordingly, an optimum stagger distance s may be determined for various applications. For example, the stagger distance s for a dialysis catheter of typical dimensions is preferably between about 1.5 cm to about 2.5 cm, while for applications in vessels of greater or lesser diameter and with longer or shorter radii of curvature, different optimum dimensions may be arrived at.
Additional control of the flow surrounding the tip 100 may be achieved by forming the flow control element 120 with a second ramp 124 designed to deflect flow exiting the second opening 110 in the normal mode. The second ramp 124 or a similar flow control device may be used to further reduce recirculation in the normal mode by directing the exiting flow away from the first opening 108. For example, the second ramp 124 preferably has a length and a ramp angle β designed to cooperate with the orifice 114 of the second opening 110. For example the orifice 114 may be formed on a plane inclined with respect to a longitudinal axis of the second lumen 106 to form a substantial mirror image of the orifice 112 of the first opening 108. Properly forming the contours of the second ramp 124 further reduces recirculation in the normal mode. However, the design of the second opening 110 and the second ramp 124 is generally less critical than that of the first opening 108 and the first ramp 118 as, in the normal mode of operation, flow exiting the second opening 110 is entrained away from the first opening 108 by the natural flow of blood and is less likely to be recirculated.
The flow control element 122 may also include features adapted to increase an exit plane cross sectional area of the second opening 110. For example, an upper expanded section 116 may be included in the design, as shown in
The tip structure may be formed in multiple steps. For example, in one embodiment the catheter shaft extends into a catheter tip 300, and is shaped to form a core of the tip 300. An overmolding process may then be used to form the contoured bolus defining the flow control elements of the tip, according to the invention. As shown in
A slit or web cut 310 may be formed in a subsequent step, along the distal end of an upper surface 324 for a length selected to allow upward expansion of the second lumen 308, to form an upper expanded section 330 in a subsequent forming step. As discussed above, the upper expanded section 330 lowers the velocity of the flow exiting the second orifice 308 in the normal mode, by providing a larger exit plane cross sectional area of the second lumen 304. By cutting the slit 310 in the upper surface 324, a molding core or other tool may be inserted in the distal portion of the second lumen 304 to expand the distal portion upward. The size of the slit 310 is preferably based, for example, on the material of which the catheter 290 is formed, on a desired maximum exit velocity of the flow leaving the second lumen 304 and a desired volume flow rate.
As shown in
Various other considerations may affect the details of the design and construction of the improved catheter tip according to embodiments of the invention. For example, the tip should not cause a sudden jump in the outer diameter of the catheter, which make the device unsuitable for certain applications. Accordingly, a maximum radial dimension of the tip is preferably substantially the same or smaller than the radius of the distal portion of the catheter to which the tip is attached. Similarly, the tip portion is designed so that it does not restrict the passage of the catheter through an introducer sheath. The tip also is designed to prevent obstructing the passage of a guidewire through the catheter. A guidewire that may be used with the base catheter is thus also usable with the catheter plus the distal tip. Embodiments of the distal tip also do not increase the pressure required to pass fluid therethrough. Thus, no changes are required to the supporting equipment. In addition, the improved tip has hemolysis and thrombogenesis characteristics comparable with those of conventional catheters.
Turning now to
The catheter tube 1112 comprises a tube body 1116 (see
As best seen in
Referring to
The molten plastic adheres to the surface 1134 of the septum 1124 and to the side walls 1136. The bulge 1150 formed in the thermoplastic septum 1124 retains this shape when the dies A and B and the pin C are removed.
Referring to
The side walls 1136 provide certain advantages for the catheter 1110. For example, the side walls 1136 reinforce the catheter 1110 at the arterial port 1148. Downward bending of the bolus tip 1114 is resisted by resistance of the side walls 1136 to stretching. Similarly, upward folding of the bolus tip 1114 is resisted by resistance to axial compression of the side walls 1136.
The ramp 1160, due to its concavity, channels flow (in the reverse flow mode) toward a center of the ramp. Subsequently, the angled section continues to direct flow upward (i.e., radially outward). Finally, the slightly convex ramp section urges flow around the bolus tip 1114 as it proceeds forward over the distal end of the tip. The result is that there is no substantial mixing of flows, i.e., flow directly back toward the venous port.
The present invention provides a dual lumen hemodialysis catheter which accommodates flow rates comparable to separate dual cylindrical lumen tubes and combined dual “D” lumen catheters. The present catheter also allows processed blood to be returned quickly but at a low velocity to avoid tissue damage.
According to the present invention, occlusion of a return line port is substantially avoided regardless of the flow rate and the position of the port in relation to a vessel wall (e.g., a vein wall). However, if port occlusion does occur, it may be relieved by reversing flow through the venous and arterial lumens without greatly increasing the potential for recirculating blood.
In a reverse mode, the arterial port configuration directs flow upward and forward along a ramp angled at approximately 210 relative to an axis of the lumen immediately upon its point of exit from the arterial lumen to direct flow away from the venous port, slow the flow and protect the components of the blood.
A bullet nose may be formed from a predetermined portion of the bolus tip 1114 which is smaller than the outside diameter of the tube to assist in insertion and minimize vessel wall damage. The bullet nose may be inserted using a tunneler and placed in its final location without the utilization of a guide wire. Alternatively, a bolus tip may be formed in place of a prepared distal end of the catheter.
As described above, the catheter tube includes first and second lumens of different lengths. For example, the venous lumen may extend distally beyond the distal end of the arterial lumen leaving the septum between the lumens substantially exposed between those distal ends. The bolus tip which, in itself, may not contain fluid passages, is insert molded onto that exposed septum. The bolus tip may include the bullet nose which extends forward of the distal end of the venous lumen and forms a venous port ramp in front of the venous port. The bolus tip further includes an attachment section which extends forward of the distal end of the arterial lumen and forms an arterial port ramp in front of the arterial port on a side of the catheter opposite the venous port.
The venous port ramp begins at a point where blood exits an ovoid lumen opening (e.g., the venous port) and travels over an ascending arc that slows and directs the flow forward, but also diffuses it, thereby softening the mixing of infused blood with the normal venous flow. In this normal mode, blood is carried forward and away from the aspirating arterial lumen. The ramp is fed by the ovoid lumen opening which is formed in the manufacturing process from the original extruded “D” shape of the tube. This ovoid lumen opening may be slightly larger than the “D”, thereby slowing fluid flow. Its shape, which may be any predetermined shape (e.g., circular, elliptical, square, rectangular, triangular, etc.), may also raise the fluid outflow stream above the normal “D” septum, thereby assisting in the directing the flow up and forward over the top of the bolus tip.
The arterial port ramp may differ from the venous port ramp in several ways. Overall, the arterial port ramp may be longer and, where it begins at the surface of the septum and the opening of the lumen, may be slightly convex in cross-sectional shape. The arterial port ramp may become flat as it continues radially outward and then become slightly convex as it blends into the top surface. In the normal flow mode, the arterial port ramp provides a larger recessed area to allow the maintenance of flow in the reverse mode. In one embodiment, the arterial port ramp has a straight 21° angle ramp profile. However, the ramp angle profile may vary between about 18° and 24°.
In the normal aspiration mode, the rounded top distal end of the arterial port ramp, in cooperation with the top of the inclined edge of the arterial lumen distal end, provides a protected area in the arterial port that assures the continuation of flow in the normal aspiration mode. Those of skill in the art will understand that larger ramp angles may reduce the size of the protected aspiration area, while smaller angles may increase the length and size of the protected aspiration area. However, the additional length increases the tendency of the vessel wall to stretch and protrude into the protected area, thereby reducing its size and presenting the potential for port occlusion. Thus, an angle of approximately 21° is the preferred ramp inclination for aspiration in normal flow, and, in the reverse mode, provides the maximum results for diffusion and flow direction.
Between the bullet nose and the distal end opening of the arterial lumen, short side walls 1136 are formed on the exposed septum. These side walls 1136 serve several purposes controlling fluid flow and stiffening the catheter so that any tendency of the catheter to fold/kink is counteracted. For example, the 45° angle of the proximal edge of the arterial port opens for flow therefrom so that the flow velocity is not increased as blood exits the port. That is, fluid can flow forward and upward without restriction. Similarly, the 21° angle ramp 1160 rises from the floor of the venous port at a point substantially even with a leading edge of the 45° angle arterial lumen opening preventing any increased resistance to flow except by the ramp. Top edges of the side walls 1136 meet the 45° inclined edge of the arterial lumen opening proximal to a junction of the ramp and the surface of the lumen, after the ramp has ascended from the septum surface by an amount equal to a height of the side walls 1136. The side walls 1136 may contain a lower level of the fluid outflow that first meets the resistance of the ramp. As has been explained, the ramp 1160 tends to push flow upward (radially outward), but also tends to diffuse it around the tube. The side walls 1136 reduce the tendency for diffusion at this initial point.
The present invention has been described with reference to specific embodiments, and more specifically to a dialysis catheter with dual lumens. However, other embodiments may be devised that are applicable to different medical devices, without departing from the scope of the invention. Accordingly, various modifications and changes may be made to the embodiments, without departing from the broadest spirit and scope of the present invention as set forth in the claims that follow. The specification and drawings are accordingly to be regarded in an illustrative rather than restrictive sense.
The present application claims priority to U.S. patent application Ser. No. 10/777,545 entitled “Dialysis Catheter Tip” naming as inventor Kristian DiMatteo which was filed Feb. 12, 2004. The entire disclosure of this application is expressly incorporated herein by reference.
Number | Date | Country | |
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Parent | 10777545 | Feb 2004 | US |
Child | 11266925 | Nov 2005 | US |