Abstract:
A multi-lumen catheter and method for inserting same in a patient is disclosed. The catheter includes an elongated, central, multi-lumen tube portion having a proximal end and a distal end. The central tube portion has a substantially cylindrical outer shape and is internally segmented into a plurality of lumens. A distal branch portion includes a plurality of single-lumen distal extension tubes. Each distal extension tube has a proximal first end and a distal second end. The proximal first end of each distal extension tube is connected to the distal end of the central tube portion such that the single lumen of each distal extension tube is in fluid communication with one of the plurality of lumens of the central tube portion. A proximal branch portion includes a plurality of single-lumen proximal extension tubes. Each proximal extension tube has a distal first end and a proximal second end. The distal first end of each proximal extension tube is connected to the proximal end of the central tube portion such that the single lumen of each distal extension tube is in fluid communication with one of the plurality of lumens of the central tube portion. Each lumen of the central tube portion and the lumens of the distal and proximal extension tubes in fluid communication therewith define a flow path through the catheter. Selectively attachable hub connectors are provided for selective attachment to the distal extension tubes and connection of the catheter to a fluid exchange device.

Description:
RELATED APPLICATIONS  
       [0001]    This application is a continuation-in-part of pending U.S. patent application Ser. No. 10/086,033, filed Feb. 28, 2002, which is a continuation of pending U.S. patent Application Ser. No. 09/769,052, filed Jan. 24, 2001. 
     
    
     
       BACKGROUND  
         [0002]    1. Field of the Invention  
           [0003]    The present invention relates generally to medical instrumentation and more specifically to a multi-lumen catheter including y-shaped distal and proximal ends, and including selectively attachable hubs for selectively connecting the catheter to a fluid exchange device.  
           [0004]    2. Description of the Prior Art  
           [0005]    Catheters, generally, are hollow, flexible tubes for insertion into a body cavity, duct, or vessel to allow the passage of fluids or distend a passageway. Catheters are often used for temporary or long-term dialysis treatment. Dialysis treatment provides for blood to be withdrawn from the patient, purified, and then returned to the patient. Thus, in dialysis treatment, catheters are used to allow passage of a patient&#39;s blood into and out of the patient&#39;s body. For optimal performance during dialysis treatment, the catheter tips, both in-flow and out-flow, should be placed in close proximity to the heart. Typically, medical personnel use either a double lumen catheter or two single lumen catheters. Both types, however, present certain deficiencies.  
           [0006]    While double lumen catheters (e.g., U.S. Pat. No. 4,895,561) allow for a single insertion of the catheter into the desired vein, double lumen catheters typically do not permit optimal catheter tip placement. Due to differences among patients, optimal tip position varies from patient to patient. Non-optimal tip position may significantly lower flow values, resulting in less effective dialysis treatment. For current double lumen catheters, a physician must make an estimate regarding the appropriate catheter tube length prior to beginning the procedure of catheterization. Then, a subcutaneous tunnel is made from a first end, which is near the area to be catheterized, to a second end, which is the preferred end position of the hub assembly, namely, away from the neck of the patient, in order to allow for more convenient access to the dialysis treatment equipment. The catheter tube is then routed forwardly into the through the subcutaneous tunnel from the second end to the first end so that the catheter tips extend outwardly from the first end of the tunnel. Either before or after tunneling, a sheath is inserted trough the first end of the tunnel and into the area to be catheterized, and the catheter tips are inserted into the sheath and the area to be catheterized. The estimated catheter tube length and subsequent forward tunneling may result in less than optimal tip placement.  
           [0007]    With the use of two independent single lumen catheters (e.g., U.S. Pat. No. 5,776,111 to Tesio) the problem of tip placement is addressed. The hub assembly of each catheter is removable from the tube and tip portion of the catheter, thereby allowing the catheter tip to be placed directly into the vein and advanced into the desired position. Then, the proximal end of the catheter can be reversed tunneled and trimmed to a desired length. Thereafter, the hub assembly is attached. Deficiencies, however, exist in this method of catheterization as well. One problem associated with this method is that this method requires two separate venous insertions, namely, two tunnels and two of each accessory instrument used for the procedure. Therefore, there is increased surgical time required to place two catheters, there are two wound entry sites which doubles the risk of post-surgical infection, and the two catheters together are significantly larger in diameter than one double lumen catheter.  
           [0008]    Applicant&#39;s co-pending application Ser. No. 09/769,052, filed Jan. 24, 2001, and Ser. No. 10/086,033, filed Feb. 28, 2002, disclose a multi-lumen catheter apparatus and method for inserting the apparatus in a patient. The disclosures of these co-pending applications are hereby incorporated by reference. In the disclosed apparatus and method, a multi-lumen catheter includes a selectively attachable hub assembly that allows the catheter tip to be positioned accurately within a patient&#39;s vein prior to subcutaneous tunneling. The distal end of the catheter tube is selectively attachable to the hub assembly. Accordingly, after the tips of the catheter have been accurately positioned in a patient, the other end of the catheter may be reverse tunneled under the skin of a patient. Before or after tip placement, an incision is made in the skin adjacent to the point where the protruding distal end of the catheter exits the skin. A subcutaneous tunnel is then formed having a first end at the incision and a second end exiting the skin at a point remote from the first end of the tunnel, generally as the caudal direction. A sheath dilator is inserted into the tunnel, which is partially dilated so as to accommodate a tissue in-growth stabilizing cuff. The distal end of the catheter tube is routed through the subcutaneous tunnel and the cuff seated therein, thereby stabilizing the distal portion of the catheter tube in the patient. A selectively attachable hub assembly is connected to the lumens at the distal tip of the catheter tube for subsequent connection of the catheter to a fluid exchange device, such as a dialysis machine.  
           [0009]    While the selectively attachable hub assembly described above facilitates tunneling a multi-lumen catheter in a patient, the separable hub assembly creates the need to connect the hub to a distal end of a multi-lumen catheter tube, thereby adding an additional step to the catheter insertion/connection procedure, which increases surgical time and expense. Furthermore, the hub-catheter connection provides an additional connection which may leak or separate from the catheter tube due to external loads on the hub such as by pulling or snagging. In addition, the attachable hub assembly is a relatively complex part, which makes it difficult to manufacture and, therefore, use of the hub assembly increases the cost of the catheter itself.  
           [0010]    Therefore, there is a need for a multi-lumen catheter that can be inserted into a patient using a reverse tunneling technique, which permits accurate placement of the tips of the catheter into the area to be catheterized and that is selectively attachable to a fluid exchange device. The improved catheter should not required an extensive hub assembly, thus making it relatively inexpensive to manufacture and easy to insert into a patient.  
         SUMMARY OF THE INVENTION  
         [0011]    A multi-lumen catheter is provided for use in hemodialysis and the like. The multi-lumen catheter includes an elongated, central, multi-lumen tube portion having a distal end and a proximal end. The central tube portion has a substantially cylindrical outer shape and is internally segmented into a plurality of lumens. A distal branch portion includes a plurality of single-lumen distal extension tubes. Each distal extension tube has a proximal first end and a distal second end. The proximal first end of each distal extension tube is connected to the distal end of the central tube portion such that the single lumen of each distal extension tube is in fluid communication with one of the plurality of lumens of the central tube portion. A proximal branch portion includes a plurality of single-lumen proximal extension tubes. Each proximal extension tube has a distal first end and a proximal second end. The distal first end of each proximal extension tube is connected to the proximal end of the central tube portion such that the single lumen of each distal extension tube is in fluid communication with one of the plurality of lumens of the central tube portion. A plurality of selectively attachable connector hubs are provided, each connector hub being configured to be selectively attachable to the distal second end of one of the distal extension and being configured for selective connection to a fluid exchange device. Each lumen of the central tube portion and the lumens of the distal and proximal extension tubes in fluid communication therewith define a flow path through the catheter. An in-growth stabilizing cuff may be affixed to an outer portion of the central tube portion.  
           [0012]    The multi-lumen catheter may include a central tube portion having two lumens. In such a catheter, the distal branch portion includes two distal extension tubes, and the proximal branch portion includes two proximal extension tubes. The catheter may be arranged such that the plurality of single-lumen distal extension tubes of the distal branch portion converge to form a distal multi-lumen connecting portion which connects to the distal end of the central tube portion, and the plurality of single-lumen proximal extension tubes comprising the proximal branch portion converge to form a proximal multi-lumen connecting portion which connects to the proximal end of the central tube portion.  
           [0013]    The central tube portion, the distal extension tubes, and the proximal extension tubes may be comprised of a fusible material, and the distal extension tubes and proximal extension tubes may be respectively fused to the distal and proximal ends of the central tube portion. The distal extension tubes may have a substantially cylindrical outer shape near their distal second ends, and the proximal multi-lumen connecting portion may also have substantially cylindrical outer shape. The proximal extension tubes may have a substantially D-shaped cross-section over at least a portion of their length. Also, the proximal extension tubes may be substantially parallel to each other in a free state, and the proximal second ends of the distal extension tubes may be longitudinally spaced from each other.  
           [0014]    The multi-lumen catheter may further include a plurality of connector hubs for connecting the catheter to a fluid exchange device. Each connector hub may configured to be connected to the distal second end of one of the distal extension tubes, and configured for connection to a portion of a fluid exchange apparatus. Each of the proximal extension tubes may include a tube wall, and each of the proximal extension tubes may include at least one opening extending through its tube wall. Further, an external portion of at least one of the distal extension tubes may include indicia which indicates a discrete flow path through the catheter. In one arrangement, the two proximal extension tubes have longitudinal axes which intersect at an included angle in a free state, the included angle being in a range from about 10 degrees to about 30 degrees.  
           [0015]    A y-shaped catheter junction for a multi-lumen catheter is also provided. The y-shaped junction includes a dual-lumen trunk, having a substantially cylindrical outer wall, a first end, a second end, a first lumen, and a second lumen. A first single-lumen extension tube is connected to the first end of the trunk, such that the single lumen of the first single-lumen extension tube is in fluid communication with the first lumen of the trunk. A second single-lumen extension tube is connected to the first end of the trunk such that the single lumen of the second single-lumen extension tube is in fluid communication with the second lumen of the trunk. The y-shaped junction is arranged such that the first lumen of the trunk and the first extension tube define a first flow path, and the second lumen of the trunk and the second extension tube define a second flow path. The y-shaped catheter junction may also be arranged such that the first and second extension tubes have longitudinal axes which intersect at an included angle near the first end of the trunk in a free state, the included angle being in a range from about 10 degrees to about 30 degrees.  
           [0016]    A method of forming a multi-lumen catheter is also disclosed. The method includes attaching a first plurality of single-lumen extension tubes to a distal end of a length of multi-lumen tubing comprising a plurality of multiple lumens, and attaching a second plurality of single-lumen extension tubes to a distal end of the length of multi-lumen tubing. Each single lumen of each extension tube is in fluid communication with one of the lumens of the length of multi-lumen tubing. The length of multi-lumen tubing may include two lumens, and the first and second pluralities of extension tubes may form substantially y-shaped junctions on each end of the length of multi-lumen tubing.  
           [0017]    The method of forming a multi-lumen catheter may include first forming a y-shaped distal junction. The process may include providing a first length of single-lumen tubing to form a distal arterial extension tube, providing a second length of single-lumen tubing to form a distal venal extension tube, providing a first length of multi-lumen tubing comprising at least an arterial lumen and a venal lumen, and having a distal end and a proximal end, attaching an end of the distal arterial extension tube to the distal end of the first length of multi-lumen tubing such that the distal arterial extension tube is in fluid communication with the arterial lumen of the first length of multi-lumen tubing, and attaching an end of the distal venal extension tube to the distal end of the first length of multi-lumen tubing such that the distal venal extension tube is in fluid communication with the venal lumen of the first length of multi-lumen tubing. The proximal end of the first length of multi-lumen tubing forms a connecting end.  
           [0018]    A second length of multi-lumen tubing having a distal end and a proximal end is provided. The tubing includes an arterial lumen and a venal lumen. The connecting end of the first length of multi-lumen tubing is connected to the distal end of the second length of multi-lumen tubing, such that the arterial extension tube of the distal junction is in fluid communication with the arterial lumen of the second length of multi-lumen tubing, and the venal extension tube of the distal junction is in fluid communication with the venal lumen of the second length of multi-lumen tubing.  
           [0019]    A y-shaped proximal junction is also formed. This process includes providing a third length of single-lumen tubing to form a proximal arterial extension tube, and providing a fourth length of single-lumen tubing to form a proximal venal extension tube. A third length of multi-lumen tubing is also provided which includes at least an arterial lumen and a venal lumen, and has a distal end and a proximal end. An end of the proximal arterial extension tube is attached to the distal end of the third length of multi-lumen tubing such that the proximal arterial extension tube is in fluid communication with the arterial lumen of the third length of multi-lumen tubing. Also, an end of the proximal venal extension tube is attached to the distal end of the third length of multi-lumen tubing such that the proximal venal extension tube is in fluid communication with the venal lumen of the third length of multi-lumen tubing. The distal end of the third length of multi-lumen tubing forms an attachment end.  
           [0020]    The attachment end of the third length of multi-lumen tubing is attached to the proximal end of the second length of multi-lumen tubing, such that the arterial extension tube of the proximal junction is in fluid communication with the arterial lumen of the second length of multi-lumen tubing, and the venal extension tube of the proximal junction is in fluid communication with the venal lumen of the second length of multi-lumen tubing. The method may also include forming at least one opening in a wall of the proximal venal extension tube, and forming at least one opening in a wall of the arterial proximal extension tube. The steps of attaching extension tubes and lengths of multi-lumen tubing together or to each other may include heat welding or similar fusing techniques. The longitudinal axes of the distal arterial extension tube and distal venal extension tube may be arranged to intersect at an included angle in a free state in a range from about 10 degrees to about 30 degrees.  
           [0021]    A method for surgically implanting a double-y shaped multi-lumen catheter into a patient is also provided. The method is suited for implanting a multi-lumen catheter having a an elongated, central, multi-lumen tube portion, a proximal end portion including a single-lumen proximal venal extension tube and a single-lumen proximal arterial extension tube each having a proximal tip, and a distal end portion including a single-lumen distal venal extension tube and a single-lumen distal arterial extension tube each having a distal end. The method includes making an incision in the skin of the patient, and inserting the proximal tips of the proximal venal and arterial extension tubes through the incision and placing the proximal tips in the patient. A subcutaneous tunnel is formed having a first end proximate to the incision and a second end remote from the first end of the tunnel. The distal venal and arterial extension tubes and at least a portion of the central tube portion are guided through the subcutaneous tunnel such that at least the distal ends of the distal venal and arterial extension tubes extend outwardly from the tunnel through the second end of the tunnel. At least a portion of the distal end portion of the catheter is secured to the patient such as by sutures or any other suitable means.  
           [0022]    When the catheter includes a stabilizing cuff, the method may further include dilating at least a portion of the subcutaneous tunnel to receive the cuff. Dilation of the tunnel may be accomplished by sliding a sheath dilator along the shaft of a trocar longitudinally positioned within the tunnel. The distal end portion of the catheter is secured to the patient by seating the cuff in a dilated portion of the subcutaneous tunnel.  
           [0023]    The catheter implanting method may further include respectively connecting the distal arterial and venal extension tubes to arterial and venal legs of a fluid exchange device. Connecting the distal arterial and venal extension tubes may include connecting the distal arterial extension tube to the arterial leg with a first connector hub, and connecting the proximal venal extension tubes to the venal leg with a second connector hub. Inserting the proximal tips of the proximal venal and arterial extension tubes into a patient may include placing the proximal tip of the venal extension tube into a vein in the patient, and placing the proximal tip of the arterial extension tube into an artery in the patient.  
           [0024]    These and other aspects of the invention will be made clear from a reading the following detailed description together with the drawings. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0025]    [0025]FIG. 1 is a perspective view of a double y-shaped multi-lumen catheter;  
         [0026]    [0026]FIG. 2 is a cross-sectional view of a distal portion of the multi-lumen catheter of FIG. 1;  
         [0027]    [0027]FIG. 3 is a partially exploded detail perspective view of a distal portion of the multi-lumen catheter of FIG. 1;  
         [0028]    [0028]FIG. 4 is a partially exploded detail perspective view of a proximal portion of the multi-lumen catheter of FIG. 1;  
         [0029]    [0029]FIG. 5 is a cross-sectional view of a proximal portion of the multi-lumen catheter of FIG. 1;  
         [0030]    [0030]FIGS. 6A-6D illustrate a procedure for tunneling a multi-lumen catheter like that of FIG. 1 in a patient;  
         [0031]    [0031]FIG. 7 is a partial sectional view of a sheath dilator engaged along a trocar to dilate a portion of a subcutaneous tunnel in a patient;  
         [0032]    [0032]FIGS. 8A-8C are views of a connection between a distal end of the catheter and a trocar for guiding the catheter through a subcutaneous tunnel. 
     
    
     DETAILED DESCRIPTION  
       [0033]    For the purposes of the following description and the claims appended hereto, the relative term “proximal” refers to those portions of a catheter and those portions of components of the catheter which are nearest the insertion end of the catheter, that is, the end of the catheter that is inserted into an area of a patient&#39;s body being catheterized, such as a blood vessel. Conversely, the relative term “distal” refers to those portions of a catheter and those portions of components of the catheter which are farthest from the insertion end of the catheter.  
         [0034]    [0034]FIG. 1 shows a double-Y shaped multi-lumen catheter  10  according to the present invention. The catheter  10  includes a proximal end  34  for insertion into a patient, and a distal end  36  for connection to a fluid exchange device, such as a dialysis machine or the like. The catheter  10  includes an elongated, central, multi-lumen tube portion  12 , a plurality of proximal single-lumen extension tubes  14 ,  16 , and a plurality of distal single-lumen extension tubes  18 ,  20 . In the embodiment shown, the central tube portion  12  includes an arterial lumen  5  and a venal lumen  6 . In this arrangement, the catheter  10  includes a proximal venal extension tube  14  and a distal venal extension tube  18  in fluid communication with the venal lumen  6 , and a proximal arterial extension tube  16  and a distal arterial extension tube in fluid communication with the arterial lumen  5 . The catheter  10  may include a stabilizing cuff  15  affixed to an outer portion of the central tube portion  12  as shown in FIG. 1. Preferably, the cuff  15  is longitudinally positioned on the central tube portion  12  such that the cuff  15  will be finally positioned in a subcutaneous tunnel in a patient as described more fully below.  
         [0035]    A construction for the distal end  36  of the multi-lumen catheter  10  is shown in FIGS. 1-3. As shown in FIGS. 2 and 3, the proximal ends  18   p ,  20   p  of the distal extension tubes  18 ,  20  may be connected to a distal end  12   d  of the central tube portion  12  by a distal multi-lumen trunk  30 . The multiple lumens of the distal trunk  30  correspond in number to the multiple lumens of the central tube portion  12  and the number of distal extension tubes  18 ,  20 . In the illustrated embodiment, the distal trunk  30  includes a venal distal trunk lumen  48 , and an arterial distal trunk lumen  47  as shown in FIG. 2. As shown in FIG. 3, the proximal ends  18   p ,  20   p  of the distal extension tubes  18 ,  20  are connected to the distal end  30   d  of the distal trunk, thereby forming a substantially Y-shaped junction. The proximal end  30   p  of the distal trunk  30  is connected to the distal end  12   d  of the central tube portion  12  as shown in FIG. 2, thereby forming a Y-shaped distal end  36 . Preferably, the proximal end  30   p  of the distal trunk  30  is substantially cylindrical in shape, and is substantially equal in outer diameter to the outer diameter of the central tube portion  12 , thereby providing a smooth transition at the juncture between the distal trunk  30  and the central tube portion  12 .  
         [0036]    As shown in FIG. 2, the distal extension tubes are arranged such that an included angle “θ” exists between the longitudinal axes of the tubes  18 ,  20  in a free state. In a preferred arrangement, the angle “θ” ranges from about 10 degrees to about 30 degrees. The distal extension tubes  18 ,  20  can be arranged, however, so that the angle “θ” is any desired angle. The venal distal trunk lumen  48  is in fluid communication with the venal lumen  6  of the central tube portion  12  and the single lumen of the distal venal extension tube  18 . Similarly, the arterial distal trunk lumen  47  is in fluid communication with the arterial lumen  5  of the and the single lumen of the distal arterial extension tube  20 .  
         [0037]    In an alternative arrangement, the distal extension tubes  18 ,  20  may be connected directly to the distal end  12   d  of the central tube portion  12  rather than to an interconnected distal trunk  30  (not shown). In either arrangement, the mating end portions of the distal extension tubes  18 ,  20 , the distal end of the central tube portion  12   d , and/or the distal trunk  30  are sealably fused together by heat welding or the like such that the fluid communication between the interconnecting lumens of the components is established and maintained and no leakage occurs at the connections.  
         [0038]    As shown in FIGS. 1-3, the catheter  10  also includes selectively attachable connector hubs  72 ,  74  on the distal ends  18   d ,  20   d  of the distal extension tubes  18 ,  20 . As will be described in detail below, the connector hubs  72 ,  74  are selectively attachable so that the connector hubs  72 ,  74  can be attached to and removed from the distal end  36  of the catheter  10  after insertion of the proximal end  34  of the catheter  10  into a patient, and after reverse, subcutaneous tunneling of the distal end  36 . As shown in FIGS. 1 and 2, the connector hubs  72 ,  74  are configured for selective sealable attachment between the distal ends  18   d ,  20   d  of the distal extension tubes  18 ,  20  and legs of a fluid exchange device. The connector hubs. The venal connector hub  74  is selectively attachable to the distal portion  18   d  of the distal venal extension tube  18 , and the arterial connector hub  72  is selectively attachable to the distal portion  20   d  of the distal arterial extension tube  20 .  
         [0039]    In one embodient as shown in FIGS. 1-3, the selectively attachable hubs  72 ,  74  are connectable with mating compression fittings  58 ,  60 . The compression fittings may include cannulae  66 ,  68  and threaded male portions  62 ,  64  that matingly engage the distal extension tubes  18 ,  20  and the connector hubs  72 ,  74  as shown in FIG. 2. When fully engaged, the hubs  72 , 74  and compression fittings  58 ,  60  compress compression sleeves  70  about the distal portions  18   d ,  20   d  of the distal extension tubes  18 ,  20 , thereby forming sealed connections. The compression fittings  58 ,  60  may be further connected to luer-type fittings  50 ,  52  or the like by connector tubes  54 ,  56 . The luer-type fittings  50 ,  52  may then be connected to corresponding luer-type connection mechanisms on a fluid exchange device  200 . For example, the distal ends of the luer-type fittings  50 ,  52  may include quarter-turn type threads for leak-tight engagement with matching quarter-turn fittings on the venal and arterial legs of a fluid exchange device  200 . Other types of known leak-tight selectively attachable connection configurations may also be used.  
         [0040]    As shown in FIGS. 1 and 3, the connector hubs  72 ,  74  can be selectively attached to the distal ends  18   d ,  20   d  of the distal extension tubes  18 ,  20 . This arrangement permits the distal end  36  of the catheter  10  to be subcutaneously reverse tunneled in a patient as described more fully below without interference from the hubs  72 ,  74 . After the distal end of the catheter  10  is subcutaneously reverse tunneled in a patient such that the distal end  36  protrudes outwardly from the patient, the hubs  72 ,  74  can be backfit over the distal ends of distal extension tubes  18 ,  20  as shown for hub  72  in FIG. 3. The compression sleeves  70  can then be placed over the distal ends  18   d ,  20   d  of the extension tubes  18 ,  20 , and the sealed connections can be completed as shown in FIG. 2. The catheter  10  can then be connected to a fluid exchange device  200 .  
         [0041]    A construction for the proximal end  34  of the catheter  10  is shown in FIGS. 1, 4, and  5 . The distal ends  14   d ,  16   d  of the proximal extension tubes  14 , 16  may be connected to a proximal end  12   p  of the central tube portion  12  by a proximal multi-lumen trunk  32 . The lumens of the proximal trunk  32  correspond in number to the multiple lumens of the central tube portion  12  and to the number of proximal extension tubes  14 ,  16 . In the illustrated embodiment, the proximal trunk  32  includes a venal proximal trunk lumen  31 , and an arterial proximal trunk lumen  33  as shown in FIG. 5. As shown in FIG. 4, the distal ends  14   d ,  16   d  of the proximal extension tubes  14 ,  16  are connected to the proximal end  32   p  of the proximal trunk  32 , thereby forming a substantially Y-shaped junction. The distal end  32   d  of the proximal trunk  32  is connected to the proximal end  12   p  of the central tube portion  12  as shown in FIG. 5, thereby forming a substantially Y-shaped proximal end  34  on the catheter  10 . Preferably, the distal end  32   d  of the proximal trunk  32  is substantially cylindrical in shape, and is substantially equal in outer diameter to the outer diameter of the central tube portion  12 , thereby providing a smooth transition at the juncture between the proximal trunk  32  and the central tube portion  12 .  
         [0042]    As shown in FIG. 4, the proximal extension tubes are arranged such that an included angle “α” exists between the longitudinal axes of the tubes  14 ,  16  in a free state. In a preferred arrangement, the angle “α” is about 5 degrees in a rest position or free state. The distal extension tubes  18 ,  20  can be arranged, however, so that the angle “α” is any desired angle. The venal proximal trunk lumen  31  is in fluid communication with the venal lumen  6  of the central tube portion  12  and the single lumen of the proximal venal extension tube  14 . Similarly, the arterial proximal trunk lumen  33  is in fluid communication with the arterial lumen  5  of the central tube portion  12  and the single lumen of the proximal arterial extension tube  16 .  
         [0043]    In an alternative arrangement, the proximal extension tubes  14 ,  16  may be connected directly to the proximal end  12   p  of the central tube portion  12  rather than to an interconnecting proximal trunk  32  (not shown). In either arrangement, the mating end portions of the proximal extension tubes  14 ,  16 , the proximal end of the central tube portion  12   p , and/or the proximal trunk  32  are sealably fused together, such as by heat welding or the like, such that the fluid communication between the interconnected lumens of the components is established and maintained and no leakage occurs at the connections.  
         [0044]    As shown in FIGS. 1, 4, and  5 , the proximal arterial extension tube  16  is preferably shorter in length than the proximal venal extension tube  14 . For example, the proximal arterial extension tube  16  may be about 4 cm shorter in length than the proximal venal extension tube  14 . The resulting longitudinal spacing between the proximal tips  14   p  and  16   p  facilitates optimal proximal tip placement in a patient. As shown in FIG. 4, the proximal venal extension tube  14  may include an end opening  43  in or near its proximal tip  14   p . The proximal venal extension tube  14  may also include one or more transverse openings  42  in its tube wall  40 . Similarly, as also shown in FIG. 4, the proximal arterial extension tube  16  may include an end opening  47  in or near its proximal tip  16   p . The proximal arterial extension tube  16  may also include one or more transverse openings  46  in its tube wall  44 . The openings  42 ,  43 ,  46 , and  47  facilitate fluid flow into or out from the proximal extension tubes  14 ,  16 .  
         [0045]    The hubs  72  and  74  are selectively attachable and detachable from the distal end  36  of the catheter  10  to facilitate tunneling the catheter  10  in a patient. A method of installing a catheter  10  in a patient is illustrated in FIGS. 6A-6D. As shown in FIG. 6A, an incision  100  is made in the skin of a patient. The proximal tips  14   p ,  16   p  of catheter  10  are inserted through the incision  100  and are placed at desired locations within the patient using conventional techniques, such as the Seldinger technique.  
         [0046]    At this stage, the distal end  36  and distal portions of the catheter  10  extend outwardly from the incision  100 . A trocar  120  or other suitable instrument is used to form a subcutaneous tunnel  102  having a first end  104 , which is preferably coincident with the incision  100 , and an opposed second end  106 , which is remote from the first end  104 , as shown in FIG. 6A.  
         [0047]    As shown in FIG. 6B, the distal end  36  of the catheter  10  is inserted through the first end  104  of the tunnel  102 , and the distal end  36  is guided through the tunnel  102  such that the distal end  36  extends out from the tunnel  102  at its second end  106 . The distal extension tubes  18 ,  20  are sufficiently flexible that they may be bundled or clamped together by any suitable means to facilitate passing the Y-shaped distal end  36  of the catheter  10  through the tunnel  102 .  
         [0048]    In a preferred arrangement as shown in FIGS. 8A and 8B, the distal ends  18   d ,  20   d  of the distal extension tubes  18 ,  20  are attached to a connector  300 . The proximal end of the connector  300  may include a first tip  302  and a second tip  304  as shown. The tips  302 ,  304  are insertable into the lumens at the distal ends  18   d ,  20   d  of the distal extension tubes  18 ,  20 . The tips  302 ,  304  preferably include ribs  301  or the like to tightly engage within the distal ends  18   d ,  20   d  of the distal extension tubes  18 ,  20  such that the connector  300  is securely but removably attached to the extension tubes  18 ,  20 . When the tips  302 ,  304  are respectively engaged in the distal extension tubes  18 ,  20 , the connector  300  holds the distal extension tubes  18 ,  20  in close arrangement as shown so that the distal extension tubes  18 ,  20  can be simultaneously subcutaneously tunneled in a patient as described below. The distal end of the connector  300   d  preferably includes a bore  306  which is configured to attachably receive an insertion tip  308  of the trocar  120 . The bore  306  may include threads  310  which can be engaged with mating threads  312  on the insertion tip  308  of the trocar  120 . Alternatively, the bore  306  may include a collar portion  314  which snaps into a groove  309  on the insertion tip  308  of the trocar  120  as shown in FIG. 8C. In this way, the distal end  300   d  of the connector  300  can be engaged on the insertion tip  308  of the trocar  120  to route the attached distal extension tubes  18 ,  20  through the subcutaneous tunnel  102  with the trocar  120 . Once the distal end  36  of the catheter  10  has been drawn through the tunnel  102 , the connector  300  can be disengaged from the distal extension tubes  18 ,  20 .  
         [0049]    In order to provide the distal portions of the catheter  10  with a smooth and compact outer profile to facilitate passage of the distal end  36  of the catheter  10  through the tunnel  102 , a sheath  320  may be used as shown in FIG. 8B. The sheath  320  is placed over at least a portion of the connector  300  and the distal extension tubes  18 ,  20 . Preferably, the distal end  320   d  of the sheath  320  is tapered as shown. The sheath  320  and the distal portions of the catheter  10  can be drawn together through the tunnel  102  with the trocar  120 . The sheath  320  is removed from the catheter  10  once the distal portions of the catheter  10  have been drawn through the tunnel  102 .  
         [0050]    As shown in FIG. 6C, the distal end  36  of the catheter  10  is drawn from the second end  104  of the tunnel  102  such that the distal extension tubes  18 ,  20  and at least a portion of the central tube portion  12  extends from the second end  104  and the catheter  10  is fully tunneled in the patient. The incision  100  and the second end  104  of the tunnel are suitably treated and dressed.  
         [0051]    An outer portion of the central tube portion  12  may include a tissue in-growth stabilizing cuff  15 , as shown in FIG. 1, for stabilizing the inserted catheter  10  in the patient. Referring to FIGS. 6C and 7, when the catheter  10  includes a stabilizing cuff  15 , a portion  130  of tunnel  102  may be dilated to enlarge the width of the tunnel  102  to receive the cuff  15  as the catheter  10  is drawn through the tunnel  102 . As shown in FIG. 7, the dilated portion  130  of the tunnel is preferably dilated by sliding a sheath dilator  200  over an end  42  and shaft  41  of the trocar  120  when the trocar  120  is positioned in the subcutaneous tunnel  102  as shown in FIG. 6A. The sheath dilator  200  preferably includes a hollow bore  208 , a tapered leading end  206 , a substantially cylindrical portion  204 , and a handle  202 . The sheath dilator  200  is inserted through the first end  104  of the tunnel  102  and into the tunnel  102  until the tip  206  has been inserted proximate to a cuff seating point  140  in the tunnel  102  to form a dilated portion  130  of the tunnel  102 . Once the dilated portion  130  is sufficiently dilated, the sheath dilator  200  is removed from the tunnel  102  and the trocar  120 . The catheter  10  is finally positioned in the tunnel  102  when the cuff  15  is seated near an end  140  of the dilated portion  130  of the tunnel  102  as shown in FIG. 6C.  
         [0052]    As shown in FIG. 6D, the catheter  10  is connected to a fluid exchange device  200 . The distal end  18   d  of the distal venal extension tube  18  is selectively attached to a venal leg  224  of the fluid exchange device  200  by connector hub  74 . Similarly, the distal end  20   d  of the distal arterial extension tube  20  is selectively attached to an arterial leg  222  of the fluid exchange device  200  by connector hub  72 . As shown in FIG. 3, indicia  26  and  28  may be included on the distal extension tubes  18 ,  20  and/or the connector hubs  72 ,  74  to assist medical personnel in identifying the proper distal extension tube  18  or  20  for connection to a corresponding leg of the fluid exchange device  300 . The indicia  26 ,  28  may be markings, colors, or any other distinctive indicator.  
         [0053]    While this invention has been illustrated and described in accordance with a preferred embodiment, it is recognized that variations and changes may be made therein without departing from the invention as set forth in the claims. Certain modifications and improvements will occur to those skilled in the art upon a reading of the forgoing description. For example, while the multi-lumen catheter has been described with reference to a catheter with two lumens, the invention also includes multi-lumen catheters including three or more lumens as required. It should be understood that all such modifications are not contained herein for the sake of conciseness and readability, but are properly within the scope of the following claims.