CATHETER

Abstract: The present invention provides a catheter assembly comprising a catheter 20 having first and second lumens 23,24 for concurrently withdrawing and returning blood to a venous segment 11. The catheter 20 has axially-displaced first and second lumen openings 25,26 in the distal end portion of said catheter 20, and external alignment means 52 mounted on said catheter 20 for aligning a veno-occlusive ligature 50 when the distal end portion of the catheter 20 is inserted into the venous segment 11 so that the ligature 50 occludes the venous segment 11 at a location between said first and second lumen openings 25,26. The invention also provides a method of extracorporeal treatment of human blood comprising insertion of a catheter 20 of the invention into a venous segment 11 and occluding the venous segment 11 between the first and second lumen openings 25,26.

Description: The present invention relates generally to extracorporeal treatments in which blood and its components are treated outside of the body and which require access to the circulatory system of the human body and, more particularly, to dual-lumen catheters and catheterization methods for use in such treatments. As used herein, the term "catheter" includes rigid metal devices such as needles as well as flexible or semi-rigid polymeric devices. The circulatory access for extracorporeal treatments such as hemodialysis, hemofiltration, plasmapheresis, cytopheresis, and component blood banking, poses special problems. Because of the quantitative nature of the extracorporeal processes, and due to the fact that clearance rates of selected substances from the blood are directly related to the rate at which blood flows to and from the system, high blood flow rates to the system are preferable. To achieve these high flow rates, e.g. in excess of 200 ml. per minute, large veins such as the subclavian or femoral veins are usually accessed by the catheters used to gain circulatory access for these treatments. These large veins are located deep, in close proximity to vital organs such as the heart, lungs, and viscera, and are difficult to puncture and lead to a higher incidence of complications due to the blind techniques that must be used. In order to obtain high blood flow rates from portions of the circulatory system closer to the surface, various surgical techniques are employed, usually in the arm. The blood supply to the arm begins in the brachial artery which divides into three arteries, i.e., the interosseous, radial and ulnar arteries. Arterial blood flow is under relatively high pressure and has a relatively high velocity. After supplying the oxygen and nutritional needs of the tissues, the blood returns via a large number of veins in the arm, including the basalic and cephalic veins. Since the blood brought to the arm by three arteries is returned through a multitude of venous channels, each venous channel carries a small fraction of the blood. This blood is under relatively low pressure and moves slowly, and the blood from the central veins cannot flow to the peripheral veins because of the one-way valves in the veins. Therefore, in their natural state the veins are not able to provide adequate blood flow for most extracorporeal treatments. Consequently, the surgical techniques referred to above are used to join one of the arteries in the arm with an adjacent vein, and diverting the arterial blood flow through the vein. Such a vein is known as a "fistula" and can be readily accessed to supply blood to the extracorporeal treatment system. A fistula is typically accessed by either two single-lumen catheters or a single double-lumen catheter in order to provide simultaneous flow into and out of the vein. The use of single-lumen catheters requiring two needle punctures is yet to be replaced by the use of a single double-lumen catheter requiring a single needle puncture, largely because of a disproportionate increase in pain and trauma resulting from the larger puncture for the double-lumen catheter. Double-lumen catheters and cannulas have employed both coaxial lumens and lumens adjacent to one another. It is now known, however, that the preferred lumen geometry includes two side-by-side semicircular lumens. Coaxial catheters and cannulas are described, for example, in McLaughlin U.S. Patent 4,096,860; Sorenson et al. U.S. Patent 4,099,528; Tursteegen et al. U.S. Patent 4,202,332; and Udall Canadian Patent 1,092,927. Dual-lumen catheters and cannulas having lumens adjacent to one another are described, for example, in Consalvo U.S. Patent 4,098,275; Mahurkar U.S. Patent 4,134,402; Belan Belguim Patent 8,342,211; Jacobson et al. U.S. Patent 4,180,068; Grimsrud U.S. Patent 4,203,436; Uthmann U.S. Patent 4,385,631; Mahurkar U.S. Design Patent D272,651; Edelman U.S. Patent 4,403,983; and Martin U.S. Patent 4,451,252. The present invention relates specifically to a catheter comprising an elongated polymeric tube having a centrally located septum which divides a proximal portion of the tube into first and second lumens, the first lumen extending from the proximal end of the tube to an intermediate location at a pre-determined distance from the distal end of the tube, the tube having at least one opening for the first lumen in its outer wall near the intermediate location, the second lumen extending from the proximal end of the tube to a second opening at the distal end of the tube. In a catheter of this kind disclosed in U.S. Patent 4 134 402, the portion of the tube extending from the intermediate location to the distal end has a constant semi-circular cross-section and is cut off at an angle at the distal end to form the second opening. The first lumen is terminated by an inclined cut-off at the intermediate location. This results in a catheter configuration which is not easy to insert into a blood vessel and which is rather difficult to manufacture. EP-A I-79 719 discloses a dual lumen catheter in which one lumen ends in a tapered tip filled with an inert substance, the other lumen terminating near the root of said tip in a surface extending perpendicularly to the longitudinal axis of the lumen and comprising a semi-circular opening. This catheter configuration results in a step near the distal tip of the catheter which again makes insertion of the catheter into a blood vessel rather difficult. Insertion of an inert substance into one of the lumens renders manufacture of the catheter complicated. EP-A-63859 discloses a single lumen catheter having a tapered distal end. US-A-4451252 discloses a dual lumen catheter wherein the walls of the lumens merge adjacent the distal end to strengthen this end. The task underlying the present invention is to provide a catheter of the type described above which can be easily inserted into a blood vessel with minimal insertion trauma and pain and which is economical to manufacture. The invention solves this task and is characterized in that the distal portion of the tube gradually tapers from the intermediate location to a distal tip comprising the second opening of circular cross-section, and that the first lumen is terminated at the intermediate location by merging the outer wall of the tube with the septum. The catheter according to the invention has a slim and easily insertable configuration not only at the distal tip but also at the location of termination of the first lumen. All thickness transitions are smooth and without any steps. Due to the absence of inclined cut-offs and of any inserted material or any other material build-up, the catheter according to the invention cannot only be inserted into a blood vessel with a minimum of pain and trauma, but is also economical to manufacture. For further ease of insertion, the distal tip of the tube can be bevelled. To render the catheter even more sleek in its portion to be inserted into the blood vessel, the wall thickness of the tube can reduce from the intermediate location to a minimum at the distal tip. To ensure smooth and unobstructed blood flow, it can be provided that the first and second lumens have semi-circular cross-sections from the proximal end of the tube to the intermediate location, and that the second lumen from the intermediate location to the distal tip gradually converts from the semi-circular cross-section to a circular cross-section. By making the radius of the circular cross-section of the second lumen at the distal tip substantially smaller than the semi-circular cross-section, a nozzle effect can be attained at the tip of the second lumen. This nozzle effect aids in re-inserting processed blood into a blood vessel. If a needle is provided traversing the second lumen and extending outwardly through the second opening, in order to initiate the puncturing of the blood vessel, as disclosed in US Patent 4 134 402,66, the puncturing trauma can be minimized by using a needle which is spaced from the internal walls of the second lumen and supported at its distal end in the second opening. FIGURE 1 is a diagrammatic illustration of the anatomy of a portion of the circulatory system of the arm containing various surgical alterations that are made in the arm to augment the blood flow through a vein when the vein is to be accessed for extracorporeal treatment of the blood; FIG.2 is a diagrammatic illustration of a portion of the anatomy of the circulatory system of the arm, with a veno-occlusive tourniquet or ligature applied to produce venous engorgement for phlebotomy; FIG.3 is a side elevation, partially in section, of a dual-lumen catheter for use in accordance with the present invention; FIG. 4 is an enlarged section taken generally along line 4-4 in FIG. 3; FIG. 5 is an enlarged section taken generally along line 5-5 in FIG. 3; FIG. 6 is an enlarged section taken generally along line 6-6 in FIG. 3; Although the invention will be described in connection with certain preferred embodiments, it is to be understood that there is no intention to limit the invention to these particular embodiments; to the contrary, various changes and modifications can be made therein without departing from the spirit and scope of the invention, and it is intended to cover all such changes and modifications that fall within the scope of the appended claims. Referring now to the drawings and turning first to FIGURE 1, a human arm includes arteries 10 for carrying blood from the heart to the capillaries extending throughout the arm and hand, and a larger number of veins 11 for returning the blood to the heart. As mentioned previously, the arterial blood flow is at a considerably higher pressure and velocity than the venous blood flow, and the arteries are located in deeper parts of the arm than the veins. In order to obtain adequate blood flow from portions of the circulatory system near the surface, the following surgical procedures, illustrated in FIGURE 1, are commonly performed: A. Shunt : Silastic (Trade Mark) tubes 12 and 13 are inserted into the ends of an artery 10a and an adjacent vein 11a while the distal ends of the artery and vein are cut off and ligated. The arterial tube 12 provides blood for processing in the extracorporeal equipment, while the venous tube 13 returns the processed blood. The silastic tubes protrude through the skin, and between treatments they are joined by a connector 14 which shunts arterial blood directly into the vein. B. Fistula : The end or side of an artery 10b is surgically connected to the end of an adjacent vein 11b. This admits the high-pressure, high-velocity arterial blood flow directly into the vein 11b, which in time dilates and can be repeatedly punctured to obtain adequate blood for extracorporeal treatments. C. Graft : In this procedure a synthetic or biologic tube 15 is surgically interposed between an artery 10c and a vein 11c. The high-pressure, high-velocity blood gushes into the low-resistance venous system via the graft, which can be repeatedly punctured or can have permanent ports for obtaining blood for extracorporeal treatments. D. Phlebotomy : Venous blood at low flow rates, e.g. 100 ml per minute, can be obtained for transfusions and blood banking via a conventional single-lumen needle (not shown) by impeding the venous return by a veno-occlusive tourniquet such as a pneumatic cuff or ligature 16 (FIG. 2) and pooling the blood. To return the blood to the veins, the occlusion is removed. A single puncture by a conventional single-lumen needle (not shown) can be used for intermittent withdrawal and return of the blood by sequentially applying and removing the occlusion. A pneumatic cuff (not shown) is preferred for this purpose since it is easily inflated and deflated to sequentially apply and remove the occlusion. This technique, however, requires complicated equipment and is not suitable for continuous extracorporeal operations utilizing membrane devices and centrifuges. In addition to being intermittent, it produces pressure and velocity oscillations and no-flow states. Initially shunts made chronic dialysis possible; femoral venipunctures made acute dialysis life-saving; and dual-lumen catheters placed surgically in a femoral vein permitted prolonged acute dialysis treatment. Currently acute dialysis is done via femoral or subclavian venipunctures; chronic dialysis is done via fistulas or grafts; and plasmapheresis or cytopheresis is done via peripheral venipunctures. All the access sites, i.e. the veins, fistulas and grafts, need two punctures, one for withdrawal and another for return of the processed blood. Having two punctures at different sites or in the same vessel is not only painful, but also causes additional trauma to the vessel and shortens the life of the vessel. Single puncture machines with cyclical bidirectional flow require special equipment, are complicated to operate and, as a result, are largely obsolete today. Dual-lumen needles which provide bidirectional flow through a single puncture have been proposed, but have not been adopted because of the penetration hole size, trauma, and accompanying pain. A dual-lumen catheter 20 for penetrating a vein 11 is shown in detail in FIGS. 3-6. The portion of the catheter 20 which extends into the vein is a polymeric tube 21 having a centrally located longitudinal septum 22 which divides the tube into two longitudinal lumens 23 and 24 of semicircular cross-section (see FIG. 5). The intake lumen 23 is terminated a predetermined distance away from the tip of the catheter and is accessed through a plurality of entrance openings 25. The return lumen 24 extends through the entire length of the tube 21 so that its exit opening 26 is located at the distal end of the catheter. This arrangement permits the externally processed blood to be returned to the vein via the lumen 24 at a point sufficiently far downstream from the entrance openings 25 to ensure that the processed blood returned to the vein is not mixed with the unprocessed blood being withdrawn from the vein. At the distal end of the catheter 20 the semicircular cross section of the return lumen 24 is gradually converted to a circular cross-section (see FIG. 4) with a beveled tip 27 to facilitate entry through the puncture initiated by a needle 28. As can be seen in FIGS. 3, 4 and 5, the circular cross-section has a much smaller radius than the semicircular cross-section, and is about the same as the radius of the needle 28 so that the catheter tip 27 fits tightly around the needle. The transition from a semicircular to circular cross-section in the return lumen 24 begins about where the intake lumen 23 is terminated. The termination of the intake lumen 23 is effected by merging the semicircular outer wall of the lumen 23 with the central septum 22, as can be seen in FIG. 3. Beyond this merger, the septum becomes part of the circular wall of the intake lumen 23. The semicircular of D-shaped cross-sections of the lumens 23 and 24 permit relatively high flow rates to be achieved in a tube having a relatively small diameter. This configuration is particularly advantageous as compared with, for example, a coaxial pair of lumens. For a given area and pressure difference, the flow in a single direction is only about 15% less in a dual-lumen catheter having semicircular lumens compared to a single lumen catheter, but it is 45% less for a dual-lumen catheter having a coaxial annular lumen. In order to connect the two lumens 23 and 24 with a pair of flexible tubes 32 and 33 leading to the desired extracorporeal treatment equipment, the catheter 20 is fastened to a Y-shaped connector 30 by means of a surrounding collar 31. More specifically, the central septum 22 of the catheter fits into a slot 34 in a corresponding central divider 35 within the connector 30, and the adjacent outside wall of the catheter 20 is flared outwardly, as at 36 in FIG. 3, to fit against a complementary tapered surface 37 on the end of the connector 30. This outwardly flared portion of the catheter 20 is pressed firmly against the connector surface 37 by the collar 31 which surrounds the adjacent portions of both the catheter 20 and the connector 30. The inside surface of the collar 31 is adhesively bonded to both the catheter 20 and the connector 30. This method of joining the catheter 20 to the Y-shaped connector 30 is especially advantageous since the catheter 20 has a small diameter and its septum 22 and side walls are particularly thin. Therefore, it is relatively difficult to joint the catheter and the Y-shaped connector by the conventional method of inserting the catheter into the Y-shaped connector. To initiate the puncture through which the catheter 20 is inserted into the desired vein 11, the needle 28 extends through the full length of the return lumen 24 and the mating portion of the connector 30. The end of this needle 28 is fastened to a luer 40 used to telescope the needle through the catheter and into the patient's arm. After the catheter has been inserted into the arm through the puncture initiated by the needle 28, the luer is used to withdraw the needle from the catheter. The return lumen 24 is then clear of any obstructions so that blood can flow smoothly therethrough. In accordance with an important aspect of the present invention, the venous segment into which the dual-lumen catheter is inserted is occluded between the entrance to the intake lumen and the exit from the return lumen so that the venous segment is engorged on the side of the occlusion where the entrance to the intake lumen is located, and is partially collapsed on the side of the occlusion where the exit from the return lumen is located. With this occlusion, the venous pool of blood in the engorged section of the vein provides a sufficient supply of blood to the intake lumen to permit blood to be withdrawn through that lumen at relatively high flow rates. (The suction to withdraw the blood is provided by the extracorporeal treatment equipment.) At the same time, blood can be returned to the collapsed section of the vein at similarly high flow rates; the flow rate of the returned blood is determined by the pressure produced by the extracorporeal treatment equipment, and the vein will accommodate whatever flow rate is produced by this equipment because the exit of the return lumen is located downstream of the occlusion. That is, the occlusion which produces the venous pool of blood to supply the intake lumen with blood at the desired high flow rate, does not impede the flow of blood through that portion of the vein which receives blood from the return lumen. Consequently, the desired high flow rates can be achieved in both lumens, even though the dual-lumen catheter is inserted in a peripheral vein by a single puncture and without surgical intervention. With care, a veno-occlusive tourniquet such as a ligature can be manually positioned to occlude the venous segment at a location between the entrance to the intake lumen and the exit from the return lumen of the dual-lumen catheter.

Claims: Catheter (20) comprising an elongated polymeric tube (21) having a centrally located septum (22) which divides a proximal portion of the tube (21) into first and second lumens (23,24), the first lumen (23) extending from the proximal end of the tube (21) to an intermediate location at a predetermined distance from the distal end of the tube (21), the tube (21) having at least one opening (25) for the first lumen (23) in its outer wall near the intermediate location, the second lumen (24) extending from the proximal end of the tube (21) to a second opening (26) at the distal end of the tube (21), characterized in that the distal portion of the tube gradually tapers from the intermediate location to a distal tip (27) comprising the second opening (26) of circular cross-section, and that the first lumen (23) is terminated at the intermediate location by merging the outer wall of the tube (21) with the septum (22). Catheter (20) in accordance with claim 1 , characterized in that the distal tip (27) of the tube (21) is bevelled. Catheter (20) in accordance with at least one of claims 1 to 2, characterized in that the first and second lumens (23,24) have semi-circular cross-sections from the proximal end of the tube (21) to the intermediate location, and that the second lumen (24) at the distal end gradually converts from the semi-circular cross-section to a circular cross-section. Catheter (20) in accordance with at least one of claims 1 to 3, characterized in that the circular cross-section of the second lumen (24) at the distal tip (27) has a much smaller radius than the semi-circular cross-section. Catheter (20) in accordance with at least one of claims 1 to 4, provided with a needle (28) traversing the second lumen (24) and extending outwardly through the second opening (26), characterized in that the radius of the circular cross-section of the second lumen (24) is about the same as the radius of the needle (28) so that the catheter tip (27) fits tightly around the needle.

Inventors: MAHURKAR, SAKHARAM DHUNDIRAJ
Applicants: MAHURKAR, SAKHARAM DHUNDIRAJ
Application year: 1986
Main classification: A61M5
IPC codes: A61M25, A61M5