Patent Publication Number: US-2022233809-A1

Title: Double-lumen catheter

Description:
TECHNICAL FIELD 
     The present disclosure relates to a double lumen catheter. 
     BACKGROUND ART 
     In the field of hemodialysis, blood is extracted from a blood vessel of a subject, treated outside the body, and then returned to the blood vessel. If urgent dialysis is performed or shunting is difficult, the blood is removed and returned using a catheter inserted into the blood vessel. 
     In such a case, a double lumen catheter is used which includes a blood removal passage and a blood return passage. The double lumen catheter is required to achieve high insertability, a decrease in poor blood removal and return, a decrease in recirculation, and other purposes. 
     In order to meet these requirements, displacing the positions of the end holes of the blood removal passage and the blood return passage to each other or providing side holes in the side wall of a catheter are considered (see, e.g., Patent Document 1). 
     CITATION LIST 
     Patent Document 
     PATENT DOCUMENT 1: Japanese Unexamined Patent Publication No. 2001-104486 
     SUMMARY OF THE DISCLOSURE 
     Technical Problems 
     In double lumen catheters, the blood removal and return passages are generally determined in advance. However, if a double lumen catheter is left in a blood vessel for a long time period, reverse connection of temporarily switching the blood removal and return passages may be performed to deal with occlusion or stenosis. An end hole displaced to reduce recirculation in forward connection may cause more recirculation in reverse connection. 
     Sticking of a catheter to a blood vessel wall causes blood removal failure. In addition, a thrombus may occur due to stagnation of blood. A catheter free from not only recirculation but also from these problems is required. 
     It is an objective of the present disclosure to achieve a double lumen catheter that hardly sticks to a blood vessel wall and causes less recirculation. 
     Solutions to the Problems 
     A double lumen catheter according to a first aspect of the present disclosure includes: a circumferential wall forming a lumen extending from a proximal end to a distal end; and a partition dividing the lumen into a first passage and a second passage extending in a longitudinal direction. Distal ends of the first passage and the second passage of the circumferential wall are aligned with each other. The partition includes a projection projecting beyond the distal end of the circumferential wall. The first passage has, at the distal end, a first passage slit formed by cutting out a part of the circumferential wall around a circumferential center of the circumferential wall. 
     The double lumen catheter according to the first aspect includes the projection, which reduces recirculation. The double lumen catheter further includes the first passage slit formed by cutting out a part of the circumferential wall, and thus hardly sticks to a blood vessel wall. 
     In the double lumen catheter according the first aspect, the second passage may have, at the distal end, a second passage slit formed by cutting out a part of the circumferential wall around the circumferential center of the circumferential wall. With this configuration, the double lumen catheter more hardly sticks to a blood vessel wall. 
     In this case, lengths of the first passage slit and the second passage slit are different from each other. In this configuration, the proximal ends of the slits are not aligned in the longitudinal direction, which causes less recirculation at the time of forward or reverse connection. This further reduces the recirculation. 
     In the double lumen catheter according the first aspect, the first passage may have the first passage through-hole being closer to the proximal end than the first passage slit is and penetrating the circumferential wall, and with this configuration, the double lumen catheter more hardly sticks to a blood vessel wall at the first passage slit. 
     In this case, the first passage through-hole may include a plurality of first passage through-holes in a zigzag pattern. With this configuration, the double lumen catheter more hardly sticks to a blood vessel wall at the first passage through-holes. Adjacent two of the first passage through-holes may be arranged on opposite sides of the first passage slit. 
     In the double lumen catheter according the first aspect, the second passage may have, at the distal end, a plurality of second passage through-holes penetrating the circumferential wall and arranged in a zigzag pattern. With this configuration, the double lumen catheter more hardly sticks to a blood vessel wall. Adjacent two of the second passage through-holes may be arranged on opposite sides of the first passage slit. This configuration further reduces the sticking at the time of reverse connection. 
     In this case, one of the second passage through-holes closest to the proximal end may be closer to the proximal end than the first passage slit is. This configuration further reduces the recirculation at the time of reverse connection. 
     In this case, the first passage may have the first passage through-hole being closer to the proximal end than the first passage slit is and penetrating the circumferential wall. One of the first passage through-holes closest to the distal end and one of the second passage through-holes closest to the proximal end may be arranged on opposite sides of the first passage slit. This configuration further reduces the recirculation. 
     A double lumen catheter according to a third aspect of the present disclosure may include: a circumferential wall forming a lumen extending from a proximal end to a distal end; and a partition dividing the lumen into a first passage and a second passage extending in a longitudinal direction. Distal ends of the first passage and the second passage of the circumferential wall may be aligned with each other. The first passage and the second passage may have, at the distal ends, a first passage slit and a second passage slit, respectively, each formed by cutting out a part of the circumferential wall from an end closer to the partition. Distal end surfaces of the circumferential wall and the partition may form a substantially S-shape as viewed from the distal end. This configuration reduces recirculation. 
     In the double lumen catheter according the third aspect, the first passage slit and the second passage slit may be arranged on opposite sides in a circumferential direction. This configuration further reduces the recirculation. 
     In the double lumen catheter according the third aspect, each of the first passage slit and the second passage slit may have a smaller slit width at the distal end than at the proximal end. With this configuration, the double lumen catheter reduces the removal blood pressure around the proximal end of each slit and more hardly sticks to a blood vessel wall. 
     A tunneler according to an aspect of the present disclosure includes: a shaft; and a connector at a proximal end of the shaft, the connector being connected to a double lumen catheter, the double lumen catheter including a partition dividing a lumen surrounded by a circumferential wall into two passages and having a projection projecting toward a distal end of the circumferential wall, the connector including: an insertion portion to be inserted and fitted into one of the two passages; and a non-insertion portion between the insertion portion and the shaft, and the non-insertion portion having an outer diameter smaller than an outer diameter of the proximal end of the shaft and larger than an outer diameter of the distal end of the insertion portion, and a length greater than or equal to a length of the projection. 
     With this configuration, the tunneler is easily connectable to a double lumen catheter having a projection. 
     In the tunneler according to an aspect, a difference between radii of the non-insertion portion and the insertion portion is smaller than or equal to a thickness of the partition of the double lumen catheter. This configuration reduces bending of the projection. 
     A tunneler according to another aspect of the present disclosure includes: a shaft; an insertion portion at a proximal end of the shaft so as to be inserted into one of passages of a double lumen catheter; and a curved portion connecting the shaft and the insertion portion, center axes of the shaft and the double lumen catheter coinciding with each other, when the insertion portion is inserted into the one of the passages of the double lumen catheter. This configuration facilitates the covering of the connector with the sheath. 
     A catheter complex according to an aspect of the present disclosure includes the double lumen catheter and tunneler according to the present disclosure. 
     The catheter complex according to the aspect may further include: a sheath covering the connector between the double lumen catheter and the tunneler. 
     Advantages of the Invention 
     The double lumen catheter according to the present disclosure hardly sticks and causes less recirculation. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of a double lumen catheter according to a first embodiment. 
         FIG. 2  is a top view of the double lumen catheter according to the first embodiment. 
         FIG. 3  is a side view of the double lumen catheter according to the first embodiment. 
         FIG. 4  is a bottom view of the double lumen catheter according to the first embodiment. 
         FIG. 5  is a front view of the double lumen catheter according to the first embodiment. 
         FIG. 6  is a top view of a double lumen catheter according to a first variation of the first embodiment. 
         FIG. 7  is a bottom view of the double lumen catheter according to the first variation of the first embodiment. 
         FIG. 8  is a top view of a double lumen catheter according to a second variation of the first embodiment. 
         FIG. 9  is a bottom view of the double lumen catheter according to the second variation of the first embodiment. 
         FIG. 10  is a top view of a double lumen catheter according to a third variation of the first embodiment. 
         FIG. 11  is a bottom view of the double lumen catheter according to the third variation of the first embodiment. 
         FIG. 12  is a perspective view of a double lumen catheter according to a second embodiment. 
         FIG. 13  is a side view of the double lumen catheter according to the second embodiment. 
         FIG. 14  is a side view of a tunneler according to an embodiment. 
         FIG. 15  is a side view of a tunneler according to a variation. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     As shown in  FIGS. 1 to 5 , a double lumen catheter according to a first embodiment is a tube made of resin or other materials, and includes a circumferential wall  101  and a partition  102 . The circumferential wall  101  forms a lumen extending from a proximal end to a distal end. The partition  102  divides the lumen into a first passage  110  and a second passage  120 . The distal ends of the first passage  110  and the second passage  120  of the circumferential wall  101  are aligned with each other. The positions of end holes in the first passage  110  and the second passage  120  are thus aligned with each other. The partition  102  has a projection  103  projecting beyond the distal end of the circumferential wall  101  and having a U-shaped plane. 
     In the double lumen catheter according to this embodiment, the distal ends of the first passage  110  and the second passage  120  of the circumferential wall  101  are aligned with each other, which reduces recirculation at the time of reverse connection. The projection  103  provides the advantage of further reducing the recirculation. 
     The double lumen catheter according to this embodiment includes a first passage slit  111  and a plurality of first passage through-holes  112  at the distal end of the first passage  110 , and a plurality of second passage through-holes  122  at the distal end of the second passage  120 . The distal end of the circumferential wall  101  has a first distal end circumferential wall  115  and a second distal end circumferential wall  116  with the first passage slit  111  interposed therebetween. The second passage through-holes  122  are interposed between the distal end of the first passage slit  111  and the first passage through-holes  112 . More specifically, the one of the second passage through-holes  122  closest to the proximal end is interposed between the proximal end of the first passage slit  111  and the one of the first passage through-holes closest to the distal end. 
     The double lumen catheter according to this embodiment has the first passage slit  111 . When the first passage  110  serves as a blood removal lumen, the flow of blood sucked into the first passage  110  is dispersed not to be concentrated in the end hole at the distal end. This configuration reduces the recirculation of the blood flowing out of the distal end of the second passage  120  to be directly sucked into the first passage  110 . In addition, the dispersed blood flow hardly causes the sticking of the catheter to a blood vessel wall. With an increase in the number of openings, less occlusion is caused by thrombus. 
     The double lumen catheter according to this embodiment includes the first and second distal end circumferential walls  115  and  116  with the first passage slit  111  interposed therebetween which is located around the circumferential center of the circumferential wall  101 . This configuration reduces a decrease in the rigidity of the first passage slit  111  and the occlusion or stenosis of the distal end of the circumferential wall  101  caused by the pressure from the blood vessel wall or other portions in the use of the catheter. 
     The first passage  110  has the first passage through-holes  112 . This configuration further disperses the flow of the blood sucked into the first passage  110 , which hardly causes the sticking of the catheter to a blood vessel wall. In view of reducing the sticking to a blood vessel wall, the first passage through-holes  112  are displaced from the first passage slit  111  as much as possible in one preferred embodiment. The sticking to a blood vessel wall is further reduced by arranging the first passage through-holes  112  in a zigzag pattern. If the first passage through-holes  112  are arranged in a zigzag pattern, adjacent two of the first passage through-holes  112  are displaced from each other as much as possible in one preferred embodiment. For example, the angle formed by the straight lines connecting the adjacent two of the first passage through-holes  112  and the center of the circle formed by the circumferential wall  101  ranges from 120° to 180° in one preferred embodiment. However, the first passage through-holes  112  may be arranged in series in the longitudinal direction. 
     When the first passage  110  serves as the blood return lumen, the first passage slit  111  disperses the outflowing blood. This configuration hardly causes the recirculation of the blood flowing out of the first passage  110  to be directly sucked into the end hole of the second passage  120 . The one of the second passage through-holes  122  at the distal end of the second passage  120  disperses the flow of blood sucked into the second passage  120  as well. This configuration further reduces the rate of recirculation at the time of reverse connection. In view of this, the one of the second passage through-holes closest to the proximal end is located closer to the proximal end than the first passage slit  111  is in one preferred embodiment. The second passage through-holes  122  reduce the sticking to a blood vessel wall at the time of reverse connection. In view of reducing the sticking to a blood vessel wall, the second passage through-holes  122  are also arranged in a zigzag pattern in one preferred embodiment. In this case, adjacent two of the second passage through-holes  122  are displaced from each other as much as possible in one preferred embodiment. For example, the angle formed by the straight lines connecting adjacent two of the second passage through-holes  122  and the center of the circle formed by the circumferential wall  101  ranges from 120° to 180° in one preferred embodiment. 
     Even if the distal end of the second passage  120  is closed by a thrombosis or other causes, the second passage through-holes  122  keep the second passage  120  open. 
     In view of reducing recirculation, the one of the second passage through-holes  122  closest to the proximal end is closer to the distal end than the one of the first passage through-holes  112  closest to the distal end is, and closer to the proximal end than the proximal end of the first passage slit  111  is in one preferred embodiment. Assume that both of the first and second passage through-holes  112  and  122  are arranged in a zigzag manner. In this case, in view of further reducing the recirculation, the one of the second passage through-holes  122  closest to the proximal end and the one of the first passage through-holes  112  closest to the distal end are arranged on opposite sides of the first passage slit  111  in one preferred embodiment. 
     The double lumen catheter according to this embodiment includes the first passage slit  111  around the circumferential center of the first passage  110  of the circumferential wall  101 . With this configuration, the first and second distal end circumferential walls  115  and  116  are formed on respective sides of the first passage slit  111 . The first passage slit  111  around the circumferential center reduces the rigidity of at least one of the first or second distal end circumferential wall  115  or  116 , which reduces the occlusion of the end hole of the first passage  110  when the catheter is left in a blood vessel. The width W 1  of the first passage slit  111  is not particularly limited, but may be about 15% to about 35% of the outer diameter ϕ 1  of the catheter in one preferred embodiment. The length L 1  of the first passage slit  111  is not particularly limited, but may be about 1.5 times to about 2.5 times the outer diameter ϕ 1  of the catheter in one preferred embodiment. In this embodiment, the outer diameter ϕ 1  of the catheter is 4.3 mm. The width W 1  and the length L 1  of the first passage slit  111  are 1 mm and 8 mm, respectively. In one preferred embodiment, the first passage slit  111  has a wall surface with rounded corners. 
     The first passage through-holes  112  are side holes penetrating the circumferential wall  101  and connecting the first passage  110  to the outside, and are arranged at intervals in the longitudinal direction. While an example will be described in this embodiment where two first passage through-holes  112  are provided, three or more first passage through-holes  112  may be provided. In this embodiment, adjacent two of the first passage through-holes  112  are arranged to be displaced from each other in the longitudinal and transverse directions of the first passage  110 , that is, arranged in a zigzag pattern, and further alternately arranged on opposite sides of the first passage slit  111 . The first passage through-holes  112  may be arranged at equal or unequal intervals in the longitudinal direction. 
     The second passage through-holes  122  are side holes penetrating the circumferential wall  101  and connecting the second passage  120  to the outside, and are arranged at intervals in the longitudinal direction. While an example will be described in this embodiment where two second passage through-holes  122  are provided, three or more second passage through-holes  122  may be provided. The second passage through-holes  122  are also arranged in a zigzag pattern. The one of the second passage through-holes  122  closest to the proximal end is located on the opposite side of the first passage slit  111  to the one of the first passage through-holes  112  closest to the distal end in one preferred embodiment. The first and second passage through-holes  112  and  122  are, as a whole, arranged in a zigzag pattern in one more preferred embodiment. 
     The one of the second passage through-holes  122  closest to the distal end is spaced apart from the distal end of the circumferential wall  101  to some extent in one preferred embodiment. Specifically, the distance from the distal end of the circumferential wall to the center of the one of the second passage through-holes  122  closest to the distal end may be about 0.8 times to about 1.5 times the outer diameter ϕ 1  of the catheter in one preferred embodiment. All the first and second passage through-holes  112  and  122  may be arranged at equal intervals in the longitudinal direction in one preferred embodiment. In this case, the distance between the centers of the adjacent through-holes may be about 3.5 times to about 5.5 times the diameter of the through-holes in one preferred embodiment. For example, if the outer diameter ϕ 1  of the catheter is 4.3 mm, the through-holes may be arranged at the intervals of 5 mm. Note that the intervals of the first and second passage through-holes  112  and  122  in the longitudinal direction may be different. All the first and second passage through-holes  112  and  122  may be arranged at unequal intervals. The diameter(s) of the first and second passage through-holes  112  and  122  is not particularly limited but may be about 15% to about 35% of the outer diameter ϕ 1  of the catheter in one preferred embodiment. 
     The diameters of the first and second passage through-holes  112  and  122  may be the same or different. Some of the diameters of the first and second passage through-holes  112  and  122  may be different. 
     There may be variations of the double lumen catheter according to this embodiment. For example, as in a first variation shown in  FIGS. 6 and 7 , no first passage through-holes  112  may be provided. In the first variation, the second passage through-holes  122  are arranged in series but may be arranged in a zigzag pattern. 
     As in a second variation shown in  FIGS. 8 and 9 , the second passage through-holes  122  may be replaced with a second passage slit  121 . When serving as a blood removal lumen, the second passage  120  with the slit less sticks to a blood vessel wall. The second passage slit  121  may have, in the longitudinal direction, a length L 2  that is shorter than the length L 1  of the first passage slit  111 . Specifically, L 2  may be about 80% to about 45% of L 1  in one preferred embodiment. Note that L 2  may be the same as L 1 . One of the first passage through-holes  112  or the second passage through-holes  122  may be provided. 
     The second passage may include neither the second passage through-holes nor the second passage slit. As in a third variation shown in  FIGS. 10 and 11 , the first passage slit  111  may be replaced with the first passage through-holes  112 . In this case as well, the second passage  120  may have at least one of the second passage through-holes  122  or the second passage slit  121 . 
     An example has been described in this embodiment and variations where the projection  103  has the U-shaped plane without any corner. The projection  103  is not necessarily in such the shape but may have a rectangular or trapezoidal plane with corners. 
       FIGS. 12 and 13  show a double lumen catheter according to a second embodiment. In the double lumen catheter according to the second embodiment, first and second passages  210  and  220  include first and second passage slits  211  and  221 , respectively. Each of the first and second passage slits  211  and  221  is formed by cutting out a part of a circumferential wall  201  from an end closer to a partition  202 . The first and second passage slits  211  and  221  are arranged on opposite sides in a circumferential direction. The distal end surfaces of the circumferential wall  201  and the partition  202  form a substantially S-shape when the lumen catheter according the second embodiment is viewed from the distal end of the double lumen catheter according to the second embodiment. 
     The first and second passage slits  211  and  221  include partition-side slit lines  212  and  222 , opposed slit lines  213  and  223 , and connecting slit lines  214  and  224 , respectively. Each of the connecting slit lines  214  and  224  is in a substantially U-shape. In this embodiment, the partition-side slit lines  212  and  222  substantially coincide with the surfaces of the partition  202 . The configuration is not limited to such the aspect. The circumferential wall may exist between each of the partition-side slit lines  212  and  222  and the associated one of the surfaces of the partition  202 . 
     The first and second passage slits  211  and  221  are arranged on opposite sides in the circumferential direction. This configuration separates the blood flows for removal and return and hardly causes recirculation when the first passage  210  serves as a blood removal lumen or a blood return lumen. 
     In this embodiment, each of the first and second passage slits  211  and  221  has a smaller width (i.e., slit width) at the distal end than at the proximal end of the circumferential wall  201 . Accordingly, the phenomenon hardly occurs that the distal end of the passages serving as the blood removal lumen is crushed largely and causes occlusion. Each slit with the greater slit width at the proximal end reduces the concentration of the removal blood pressure around the connecting slit line  214 ,  224 . Note that each of the first and second passage slits  211  and  221  may have a constant slit width or a greater slit width at the distal end than at the proximal end. 
     The maximum slit width of the first and second passage slits  211  and  221  is not particularly limited but may be about 15% to about 35% of the outer diameter ϕ 1  of the catheter in one preferred embodiment. The length of each slit is not particularly limited but may be about 1.5 times to about 2.5 times the outer diameter ϕ 1  of the catheter in one preferred embodiment. 
     The double lumen catheter according to the second embodiment may also have one of the first or second passage through-holes. The first and second passage through-holes may be arranged as in the first embodiment and its variations. In the double lumen catheter according to the second embodiment as well, the partition  202  may have a projection. 
     The double lumen catheter according to the embodiments and variations is left within a blood vessel to be used for removing and returning blood, if dialysis is performed without shunting. A hub, connector, or other items may be connected to the proximal end of the catheter as necessary. 
     The double lumen catheter according to the embodiments and variations may serves as a catheter complex including a tunneler, connected at the distal end, for tunneling under a skin. The tunneler at the distal end forms a subcutaneous tunnel. After introducing the double lumen catheter into the subcutaneous tunnel, the tunneler is removed so that the double lumen catheter extends through the subcutaneous tunnel into the blood vessel. The tunneler to be connected is not particularly limited but may be the one shown in  FIG. 14 , for example. 
     A tunneler  300  shown in  FIG. 14  includes a shaft  301  and a connector  302  at the proximal end of the shaft  301 . The shaft  301  includes a tapered distal end  311 , a body  312  with a constant diameter, and thinner parts  313 . The shaft  301  includes, at the proximal end, a tapered portion  314  as a stopper of a sheath. 
     The thinner parts  313  facilitate bending of the shaft  301 . Although two thinner parts  313  are shown in  FIG. 14 , one, three or more thinner parts  313  may be provided. Alternatively, no thinner part may be provided. 
     The connector  302  includes an insertion portion  321  to be inserted into the double lumen catheter, and a non-insertion portion  322  between the insertion portion  321  and the shaft  301 . 
     The insertion portion  321  has a smaller outer diameter than the non-insertion portion  322 , and has a maximum outer diameter to be inserted and fitted into the first or second passage of the double lumen catheter. In  FIG. 14 , the insertion portion  321  has, at the proximal end, a thicker part  324  with a larger diameter than other parts not to allow the inserted catheter to easily come out of the insertion portion  321 . As long as not coming out after being inserted into the double lumen catheter, the insertion portion  321  may be in the shape of a taper with the diameter gradually decreasing from the distal end toward the proximal end, in the shape of a bamboo shoot, or other shapes. 
     The insertion portion  321  has, at least at the proximal end, an outer diameter slightly smaller than the maximum heights of the first and second passages of the double lumen catheter in one preferred embodiment for the ease of inserting the insertion portion  321 . The insertion portion  321  (the thicker part  324 ) has the maximum outer diameter slightly larger than the maximum heights of the first and second passages of the double lumen catheter in one preferred embodiment not to allow the insertion portion  321  to come out of the catheter. The length of the insertion portion  321  is not particularly limited but may be preferably 5 mm or more not to allow the insertion portion  321  to come out, and preferably 25 mm or less for the ease of handling. The maximum height H max  of each passage is the maximum vertical distance from the surface of the partition to the inner surface of the circumferential wall as shown in  FIG. 5 . 
     The non-insertion portion  322  has a larger outer diameter than the end of the insertion portion  321  closer to the non-insertion portion  322 . There is a first step  322   a  between the insertion portion  321  and the non-insertion portion  322 . On the other hand, the non-insertion portion  322  has a smaller outer diameter than the proximal end of the tapered portion  314  located at the proximal end of the shaft  301 . There is a second step  322   b  between the non-insertion portion  322  and the shaft  301 . 
     When a catheter complex with a tunneler connected is used for forming a subcutaneous tunnel, the tunneler is generally used after being inserted into a sheath to cover the connector connecting the tunneler to the distal end of the catheter. It is thus important to connect the catheter and the tunneler as flat as possible (without any unevenness) to be inserted into the sheath. 
     A typical tunneler without any non-insertion portion  322  has a larger step between the connector and the shaft. If the typical tunneler is inserted into a double lumen catheter having a projection, the larger step between the connector and the shaft largely bends the projection largely outward. The projection thus comes out of the sheath and fails to cover the connector. 
     The tunneler  300  according to this embodiment has the smaller first step  322   a.  Even if the tunneler  300  is, until the root of the insertion portion  321 , inserted into the double lumen catheter, the projection neither is largely bent nor comes out of the sheath. The non-insertion portion  322  secures the space for the projection, and the distance from the distal end of the double lumen catheter to the shaft  301 , which facilitates radial movement at the time of covering with the sheath. The step  322   b  between the non-insertion portion  322  and the tapered portion  314  does not allow the projection and the sheath arranged along the non-insertion portion  322  to abut on each other along the end surface. Accordingly, the connector is smoothly inserted into the sheath. 
     The non-insertion portion  322  has an outer diameter larger than the maximum height or width of the first or second passage in one preferred embodiment not to allow the non-insertion portion  322  to enter the inside of the first or second passage of the double lumen catheter. On the other hand, in view of smooth insertion into the sheath, the distal end of the projection of the catheter bent by the first step  322   a  does not exceed the circumferential wall of the passage that is not connected to the tunneler in one preferred embodiment. The non-insertion portion  322  has a length equal to or longer than the length of the projection of the double lumen catheter in one preferred embodiment. The second step  322   b  has a size equal to or greater than the thickness of the projection in one preferred embodiment. 
     The maximum outer diameter of the insertion portion  321  and the outer diameter of the non-insertion portion are not particularly limited. In view of providing the advantages described above, the maximum outer diameter of the insertion portion  321  may be about 1.1 times to about 1.4 times the maximum height H max  of each passage, and the outer diameter of the non-insertion portion may be about 1.5 times to about 1.9 times the maximum height H max  of each passage in one preferred embodiment. 
     In a double lumen catheter where the first and second passages have the same maximum height and the distal ends of the first and second passages are aligned with each other, the insertion portion  321  may be inserted into any of the first and second passages. If one of the passages has a slit, the insertion portion may be inserted into the other passage without any slit in one preferred embodiment, because the insertion portion  321  hardly comes out. 
     Even when used in combination with a double lumen catheter with a projection, the tunneler  300  according to this embodiment is inserted into the sheath smoothly, which facilitates the placement of the catheter. The tunneler  300  according to this embodiment may be used in combination with a double lumen catheter without any projection. 
     The double lumen catheters according to the embodiments may be used in combination with a tunneler  300 A shown in  FIG. 15 . The tunneler  300 A includes: a shaft  301 ; an insertion portion  321  to be inserted into one of first and second passages  351  and  352  of a double lumen catheter  350 ; and a curved portion  331  curved in a substantially S-shape between the shaft  301  and the insertion portion  321 . The curved portion  331  is configured so that the center axes of the shaft  301  and the double lumen catheter  350  coincide with each other, when the insertion portion  321  is inserted into the one of the passages of the double lumen catheter  350 . This configuration causes no significant unevenness between the tunneler and the double lumen catheter, and easily covers the connector between the double lumen catheter and the tunneler using the sheath. The phase “the center axes . . . coincide with each other” here not only means that the center axes completely overlap each other but also includes the case where the center axes are displaced from each other by about several millimeters in any direction without hindering the insertion into the sheath. 
     INDUSTRIAL APPLICABILITY 
     The double lumen catheter according to the present disclosure hardly sticks to a blood vessel wall and causes less recirculation, and is thus useful as a hemodialysis catheter, for example. 
     DESCRIPTION OF REFERENCE CHARACTERS 
     
         
           101  Circumferential Wall 
           102  Partition 
           103  Projection 
           110  First Passage 
           111  First Passage Slit 
           112  First Passage Through-Hole 
           115  First Distal End Circumferential Wall 
           116  Second Distal End Circumferential Wall 
           120  Second Passage 
           121  Second Passage Slit 
           122  Second Passage Through-Hole 
           201  Circumferential Wall 
           202  Partition 
           210  First Passage 
           211  First Passage Slit 
           212  Partition-Side Slit Line 
           213  Opposed Slit Line 
           214  Connecting Slit Line 
           220  Second Passage 
           221  Second Passage Slit 
           222  Partition-Side Slit Line 
           223  Opposed Slit Line 
           224  Connecting Slit Line 
           300  Tunneler 
           301  Shaft 
           302  Connector 
           311  Distal End 
           312  Body 
           313  Thinner Part 
           314  Tapered Portion 
           321  Insertion Portion 
           322  Non-Insertion Portion 
           322   a  First Step 
           322   b  Second Step 
           324  Thicker Part 
           331  Curved Portion