Abstract:
A seal member and outer cylinder needle (OCN) tip part for blocking, in a fluid-tight state, both external peripheral space (EPS) end parts formed between the external-peripheral-surface of an inner needle (IN) and internal peripheral surface of an OCN, for slidably holding the IN in close contact; an opening part formed on the OCN external-peripheral-surface and for intravascular communication with the EPS; an OCN connection part for communicating between the EPS and blood circuit end; an IN connection part for communicating between the IN internal space and other blood circuit end. The movable IN positioned between the projecting position where the tip part protrudes from the OCN tip and the housed position housing the tip inside the OCN. The IN punctures the blood vessel interior while holding the projecting position, and moved to the housed position after puncture allowing blood to extracorporeally circulate via the OCN and IN connection part.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to an indwelling needle for extracorporeal circulation for use by being punctured into and dwelling in a blood vessel of a patient when conducting extracorporeal circulation of blood. 
       BACKGROUND ART 
       [0002]    In blood extracorporeal circulation (for example, blood extracorporeal circulation for blood purification treatment such as dialysis or the like), conventionally, an indwelling needle is punctured into to indwell in a blood vessel of a patient, and a blood circuit is connected to the indwelling needle. In general, one indwelling needle indwells in each of an artery and a vein, and these indwelling needles are connected to the respective ends of a blood circuit (see Patent Document 1, for example). 
         [0003]    However, it is painful for a patient to have two indwelling needles dwelling in his/her blood vessel throughout the entire period of blood extracorporeal circulation. In addition, when two indwelling needles are used, there is a problem that, should a needle for receiving blood (on the vein side) be removed, a large amount of blood will be poured to the outside. In view of the above, in order to avoid use of two indwelling needles, there has been known a single indwelling needle having a structure in which a unit for connection to a blood circuit is branched into two so that one branched connection portion is connected to an inlet end of the blood circuit and the other to a discharge end of the blood circuit (for example, see Patent Document 2). 
         [0004]    However, an indwelling needle having a connection portion simply branched into two requires provision of an inlet pump for introducing blood from the indwelling needle and a discharge pump for discharging blood to the indwelling needle. This results in a complicated structure of a, blood circuit. Moreover, as it is necessary to alternately conduct blood introducing operation and blood discharging operation, poor efficiency in blood extracorporeal circulation results. In order to address the above-described inconvenience, it is preferable to form an indwelling needle having a double lumen structure to ensure separate introducing and discharging passages (see Patent Document 3, for example). 
       CITATION LIST 
     Patent Literature 
       [0000]    
       
         Patent Document 1: JP 3073713 B 
         Patent Document 2: JP H4-26110 U 
         Patent Document 3: WO 2006/022025 A 
       
     
       SUMMARY OF INVENTION 
     Technical Problem 
       [0008]    However, an indwelling needle in a simple double lumen structure has a problem that the tip end portion thereof is inevitably finished thick, which increases pain for a patient punctured by the needle. Moreover, as the inner needle is removed while the needle is dwelling in a blood vessel, it is possible that the tip end of the removed inner needle erroneously pricks a person involved in operation (that is, a nurse or a patient on home dialysis). 
         [0009]    The present invention has been conceived in view of the above, and aims to achieve a double lumen structure without an excessively thick tip end portion of a needle to thereby provide an indwelling needle for extracorporeal circulation capable of reducing inconvenience due to severe pain caused when puncturing a needle into a blood vessel, and free from a possibility that the tip end portion of the inner needle removed erroneously pricks a person involved in operation. 
       Solution to Problem 
       [0010]    The present invention has been conceived in order to achieve the above-described object, and according to claim  1 , there is provided an indwelling needle for extracorporeal circulation having a double tube structure including an outer needle made of a tube member having an opening formed on a tip end thereof, and an inner needle made of a tube member having a puncture portion formed on a tip end thereof and inserted in the outer needle, including: a holding member for closing, in a liquid-tight state, respective ends of an outer circumferential space formed between an outer circumferential surface of the inner needle and an inner circumferential surface of the outer needle, and for closely holding the inner needle in a slidabale state; a hole formed on an outer circumferential surface of the outer needle on a tip end side thereof in a position further rearward than the holding member, for communicating between the interior of a blood vessel and the outer circumferential space when being punctured into the blood vessel; a first connection portion for communicating between the outer circumferential space and one end portion of a blood circuit; and a second connection portion for communicating between an inner space of the inner needle and another end portion of the blood circuit, wherein the inner needle is held by the holding member so as to move between a projecting position where an tip end portion thereof projects from a tip end of the outer needle and a housed position where the tip end portion thereof is housed in the outer needle, and the inner needle is punctured into the blood vessel while being held in the projecting position, and then moved to the housed position after being punctured so that blood extracorporeal circulation is able to be conducted via the first connection portion and the second connection portion. 
         [0011]    According to claim  2 , there is provided an indwelling needle for extracorporeal circulation according to claim  1 , wherein the holding member positioned on a tip end side of the outer needle may be a tip end portion of the outer needle attached to a tip end portion of a longitudinal tube-like outer needle main body. 
         [0012]    According to claim  3 , there is provided an indwelling needle for extracorporeal circulation according to claim  1 , wherein the holding member positioned on a tip end side of the outer needle may be a tip end portion of the outer needle that is formed by thinning a tip end portion of a longitudinal tube-like outer needle main body so as to have a reduced diameter. 
         [0013]    According to claim  4 , there is provided an indwelling needle for extracorporeal circulation according to claim  1 , wherein the hole may be an inlet through which to introduce blood from the blood vessel, and a tip end opening of the inner space of the inner needle may be a return opening through which to return into the blood vessel blood having circulated in the blood circuit. 
         [0014]    According to claim  5 , there is provided an indwelling needle for extracorporeal circulation according to claim  1 , wherein the first connection portion may have a movement guide portion for guiding the second connection portion along a movement direction of the inner needle. 
         [0015]    According to claim  6 , there is provided an indwelling needle for extracorporeal circulation according to claim  1 , wherein the second connection portion may have an inner needle movement operation unit projecting toward the outside of the second connection portion. 
         [0016]    According to claim  7 , there is provided an indwelling needle for extracorporeal circulation according to claim  1 , wherein one of the first connection portion and the second connection portion may have an engaged member, and the other has an engagement portion with which the engaged member is able to be engaged, and the engagement portion may include a projecting engagement portion with which the engaged member in the projecting position may be engaged and a housed engagement portion with which the engaged member in the housed position is engaged. 
         [0017]    According to claim  8 , there is provided an indwelling needle for extracorporeal circulation according to claim  7 , further including an engaged guide portion provided between the projecting engagement portion and the housed engagement portion, for guiding the engaged member along a movement direction of the inner needle. 
         [0018]    According to claim  9 , there is provided an indwelling needle for extracorporeal circulation according to claim  1 , further including an urging member provided between the first connection portion and the second connection portion, for urging the inner needle in a direction from the projecting position to the housed position, and when engagement between the engaged member and the projecting engagement portion is released, the second connection portion may be urged by an urging force of the urging member whereby the inner needle moves from the projecting position to the housed position. 
         [0019]    According to claim  10 , there is provided an indwelling needle for extracorporeal circulation according to claim  1 , wherein the outer diameter of the inner needle may be set smaller than an inner diameter of a longitudinal tube-like outer needle main body so that the outer circumferential space is formed to be cylindrical between the outer circumferential surface of the inner needle and an inner circumferential surface of the outer needle main body. 
       Advantageous Effect of Invention 
       [0020]    According to the present invention, advantageous effects described below are obtained. 
         [0021]    According to the invention defined in claim  1 , the inner needle punctured in the blood vessel can be utilized as a part of a blood circulation passage, rather than being pulled out. This can eliminate the need for preparing a member only for puncture into a blood vessel separately from a member constituting a blood circulation passage. This makes it possible to achieve an indwelling needle for extracorporeal circulation having a double lumen structure without an excessively thick tip end portion, which can reduce inconvenience with severe pain caused during puncture into a blood vessel. Further, as it is unnecessary to pull out the inner needle from the outer needle, there is no possibility that the puncture unit of the inner needle erroneously pricks a person involved in operation (a person preparing for blood extracorporeal circulation). Still further, as the inner needle is moved to the housed position, it is possible to prevent the puncture unit of the inner needle from being exposed in a blood vessel. This can avoid inconvenience that the puncture unit of the inner needle unintentially damages a blood vessel while the indwelling needle for extracorporeal circulation is dwelling in the blood vessel. 
         [0022]    According to the invention defined in claim  2 , as the holding member positioned on the tip end side of the outer needle is a tip end portion of the outer needle attached to the tip end portion of a longitudinal tube-like outer needle main body, it is easier to manufacture the tip end portion of the outer needle, using a harder material than that used for the outer needle main body. This makes it easier to implement an outer needle that can facilitate puncture. 
         [0023]    According to the invention defined in claim  3 , as the holding member positioned on the tip end side of the outer needle is a tip end portion of the outer needle that is made by thinning the tip end portion of a longitudinal tube-like outer needle main body so as to have a reduced diameter, it is unnecessary to form the tip end portion of the outer needle separately from the outer needle main body. This can reduce manufacturing cost. 
         [0024]    According to the invention defined in claim  4 , as the hole is an inlet through which to introduce blood from a blood vessel, and the tip end opening of the inner space of the inner needle is an outlet through which to return back to the blood vessel blood having circulated in the blood circuit, it is possible to avoid inconvenience that blood is poured from the hole even when the indwelling needle for extracorporeal circulation indwelling is unintentially partially removed from the blood vessel and the hole is thereby exposed to the outside. 
         [0025]    According to the invention defined in claim  5 , as the first connection portion has a movement guide portion for guiding the second connection portion along the movement direction of the inner needle, it is possible to smoothly move the inner needle, and thus to promptly execute an indwelling preparation operation for an indwelling needle for extracorporeal circulation. 
         [0026]    According to the invention defined in claim  6 , as the second connection portion has an inner needle movement operation unit projecting outward of the second connection portion, it is possible to more readily move the inner needle. 
         [0027]    According to the invention defined in claim  7 , as one of the first connection portion and the second connection portion has an engaged member and the other has an engagement portion with which the engaged member can be engaged, and the engagement portion includes a projecting engagement portion with which the engaged member in the projecting position is engaged and a housed engagement portion with which the engaged member in the housed position is engaged, it is possible to achieve proper positioning of the inner needle in the projecting position and the housed position. Therefore, it is possible to promptly execute a movement operation for moving the inner needle; in particular, a movement operation for movement from the projecting position to the housed position after puncture into a blood vessel, and thus to efficiently execute an indwelling preparation operation for an indwelling needle for extracorporeal circulation. Further, it is possible to prevent unintentional displacement of the inner needle having been positioned. With the above, it is possible to avoid inconvenience that the tip end portion of the inner needle moves to be housed in the outer needle when puncturing an indwelling needle for extracorporeal circulation into a blood vessel or that the tip end portion of the inner needle projects from the outer needle while the outer needle is dwelling in a blood vessel. 
         [0028]    According to the invention defined in claim  8 , as an engaged guide portion for guiding an engaged member along the movement direction of the inner needle is provided between the projecting engagement portion and the housed engagement portion, it is possible to more readily move the inner needle. 
         [0029]    According to the invention defined in claim  9 , as there is provided an urging member between the first connection portion and the second connection portion, for urging the inner needle in a direction from the projecting position to the housed position, and when engagement between the engaged member and the projecting engagement portion is released, the second connection portion is urged by an urging force of the urging member whereby the inner needle is caused to move from the projecting position to the housed position, it is possible to conduct a movement operation for moving the inner needle to the housed position simply by releasing the engaged member from the projecting engagement portion. This makes it possible to promptly execute an indwelling preparation operation for an indwelling needle for extracorporeal circulation. 
         [0030]    According to the invention defined in claim  10 , as the outer diameter of the inner needle is set smaller than the inner diameter of a longitudinal tube-like outer needle main body so that the outer circumferential space is formed to be cylindrical between the outer circumferential surface of the inner needle and the inner circumferential surface of the outer needle main body, it is possible to form the outer circumferential space between the outer circumferential surface of the inner needle and the inner circumferential surface of the outer needle, by means of a simple structure. Further, it is possible to ensure a large cross section of the outer circumferential space, and to achieve a structure for facilitating blood circulation without backset. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0031]      FIG. 1  shows the external appearance of an indwelling needle for extracorporeal circulation; 
           [0032]      FIG. 2   a  is a cross sectional view of an inner needle of an indwelling needle for extracorporeal circulation having moved to a projecting position; 
           [0033]      FIG. 2   b  is a cross sectional view of an inner needle of an indwelling needle for extracorporeal circulation having moved to a housed position; 
           [0034]      FIG. 3   a  is a diagram explaining an inner needle of an indwelling needle for extracorporeal circulation having moved to a projecting position, and showing cross sections at respective positions; 
           [0035]      FIG. 3   b  is a diagram explaining an inner needle of an indwelling needle for extracorporeal circulation having moved to a housed position; 
           [0036]      FIG. 4   a  shows external appearance of major members of an indwelling needle for extracorporeal circulation having a movement guide portion; 
           [0037]      FIG. 4   b  shows external appearance of major members of an indwelling needle for extracorporeal circulation having a movement guide portion; 
           [0038]      FIG. 5  is a diagram explaining major members of an indwelling needle for extracorporeal circulation having an urging member for urging a second connection portion; 
           [0039]      FIG. 6   a  is a diagram explaining an inner needle of an indwelling needle for extracorporeal circulation having moved to a projecting position and showing cross sections at respective positions, in which a holding member is formed by thinning the tip end portion of the outer needle main body so as to have a reduced diameter; and 
           [0040]      FIG. 6   b  is a diagram explaining an inner needle of an indwelling needle for extracorporeal circulation having moved to a housed position and showing cross sections at respective positions, in which a holding member is formed by thinning the tip end portion of the outer needle main body so as to have a reduced diameter. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0041]    In the following, embodiments of the present invention will be described by reference to the drawings. As shown in  FIGS. 1 and 2 , an indwelling needle for extracorporeal circulation  1  has an inner needle  2  and an outer needle  3 , each made of a tube. The inner needle  2  is inserted in the outer needle  3 , whereby a double-tube structure is formed. The tip end portion of the inner needle  2  and that of the outer needle  3  are sharpened so that these can be punctured into a blood vessel of a patient. A base end portion of the inner needle  2  and that of the outer needle  3  are connected to a blood circuit  4  for extracorporeal circulation of blood of a patient so that blood can circulate between a blood vessel and the blood circuit  4 . 
         [0042]    The inner needle  2  is made of a thin long metallic tube. An inner space  2   a  where blood can flow is formed inside the inner needle  2  so as to extend throughout the entire length of the inner needle  2 . A tip end opening  2   b  and a base end opening  2   c  are defined on respective both ends of the inner space  2   a  so that the inner space  2   a  is exposed outward through the holes  2   b,    2   c.  The tip end portion of the inner needle  2  with the tip end opening  2   b  defined therein (the left end portion in  FIG. 2   a ) has a puncture unit  2   d.    
         [0043]    Meanwhile, the base end portion of the inner needle  2  with the base end opening  2   c  defined therein (the right end portion in  FIG. 2   a ) has an inner needle connection portion  7  (corresponding to the second connection portion according to the present invention). The inner needle connection portion  7  is a plastic cylindrical member positioned coaxial to the inner needle  2 , and an inner needle communicating space  8  is formed inside the inner needle connection portion  7 . The end of the inner needle communicating space  8  on the inner needle  2  side (the left side in  FIG. 2   a ) communicates with the base end opening  2   c  of the inner needle  2 , while the other end on the opposite side from the inner needle  2  with the middle portion of the inner needle communicating space  8  in-between (the right side in  FIG. 2   a ) is exposed outward. An inner needle side male screw  9  is formed on the outer circumference of the inner needle connection portion  7  in a position on the released end side of the inner needle communicating space  8 , so that a lock ring  4   a  (see  FIG. 1 ) mounted on an end portion of the blood circuit  4  can be threaded into the inner needle side male thread  9 . When the end portion of the blood circuit  4  is set abutting on the released opening and the lock ring  4   a  is then screwed onto the inner needle side male thread  9 , the blood circuit  4  and the inner needle connection portion  7  are closely adhered to each other in a liquid-tight state, as a result of which the blood circuit  4  communicates with the inner space  2   a  through the inner needle communicating space  8  inside the inner needle connection portion  7 . 
         [0044]    The outer needle  3  can indwell in a blood vessel. The outer needle  3  includes an outer needle main body  13  and an outer needle tip end portion  14 . The inner needle  2  is inserted in the outer needle main body  13  so that the puncture portion  2   d  can project from the tip end of the outer needle main body  13 . The outer needle tip end portion  14  is attached to the tip end portion of the outer needle main body  13  as a tip end portion of the outer needle  3 . An outer needle connection portion  15  (corresponding to the first connection portion according to the present invention) is connected to the base end portion (the right end in  FIG. 2   a ) of the outer needle  3 . 
         [0045]    As shown in  FIGS. 2 and 3 , the outer needle main body  13  is a longitudinal cylindrical member made of flexible plastic (for example, polypropylene or polyethylene), whose outer diameter is set equal to that of the outer needle tip end portion  14  so as to avoid formation of a step between the outer needle main body  13  and the outer needle tip end portion  14 . Further, as shown in  FIG. 3   a , the inner diameter of the outer needle main body  13  is set larger than the outer diameter of the inner needle  2  (in other words, the outer diameter of the inner needle  2  is set smaller than the inner diameter of the outer needle main body  13 ), so that a part (a tip end side part)  16   a  of an outer circumferential space  16  where blood can flow is formed to be cylindrical between the outer circumferential surface of the inner needle  2  and the inner circumferential surface of the outer needle main body  13 . Further, two or more (four in this embodiment) holes  17  are formed on the outer circumferential surface of the outer needle main body  13  at positions closer to the outer needle tip end portion  14  so that the outer circumferential space  16  is exposed through these holes  17 . Specifically, the holes  17  are formed on the outer needle  3  on the tip end side thereof at positions further rearward than the outer needle tip end portion  14  (in other words, a position displaced toward the base end portion of the outer needle  3  in relation to the outer needle tip end portion  14 ). In this embodiment, two holes  17  are formed at positions closer to the outer needle tip end portion  14 , and another two holes  17  are formed at positions displaced toward the outer needle connection portion  15  side by a few mm from the former holes  17 . The two holes  17  closer to the outer needle tip end portion  14  are positioned displaced in phase by 180 degrees as viewed in the circumferential direction of the outer needle  3 , and the other two holes  17  closer to the outer needle connection portion  15  are positioned displaced in phase by 90 degrees relative to the respective holes  17  closer to the outer needle tip end portion  14  as viewed in the circumferential direction of the outer needle  3 . 
         [0046]    The outer needle tip end portion  14  attached to the tip end portion of the outer needle main body  13  is a short cylindrical component made of plastic harder than the outer needle main body  13 , and has a thinner tip end portion. The entire length of the outer needle tip end portion  14  is set to a length L 2  sufficiently longer than the length L 1  of the puncture portion  2   d  (see  FIG. 3   b ). That is, the outer needle  3  has a tapered thin tip end portion. A penetrating space  14   a  is formed inside the outer needle tip end portion  14 , and the puncture portion  2   d  of the inner needle  2  inserted in the outer needle  3  can be housed in the penetrating space  14   a . The inner diameter of the outer needle tip end portion  14  is set equal to or slightly smaller than the outer diameter of the inner needle  2 , so that the inner circumferential surface of the outer needle tip end portion  14  maintains close contact with the outer circumferential surface of the inner needle  2  in a slidable and liquid-tight state. With the above, the outer needle tip end portion  14  closes the end of the outer circumferential space  16  in a liquid-tight state such that the tip end opening  2   b  of the inner needle  2  does not communicate with the outer circumferential space  16 . Further, the outer needle tip end portion  14  functions as a part of a holding member in the present invention for closely holding the tip end portion of the inner needle  2  in a slidable state. Still further, in the base portion of the outer needle tip end portion  14  (an end portion positioned on the outer needle main body  13  side), a joint portion  14   b  having a reduced diameter is formed for insertion into the outer needle main body  13 . The outer circumferential surface of the joint portion  14   b  is held in close contact with the inner circumferential surface of the outer needle main body  13  in a liquid-tight state. 
         [0047]    The outer needle  3  including the outer needle tip end portion  14  and the outer needle main body  13  may be formed, for example, by means of insert molding by inserting the outer needle tip end portion  14  into an end portion of the outer needle main body  13  prepared in advance. Alternatively, the outer needle tip end portion  14  and the outer needle main body  13  may be separately molded in advance, and the outer needle main body  13  and the joint portion  14   b  inserted in the outer needle main body  13  are then adhered or welded to each other. 
         [0048]    The outer needle connection portion  15  connected to the base end portion (the right end portion in  FIG. 2   a ) of the outer needle main body  13  is a substantially y-shaped plastic member that is formed by integrally molding a connection portion main body  21  and a branched portion  22 , in which the connection portion main body  21  is positioned coaxially with the inner needle  2  and the outer needle  3 , and the branched portion  22  is branched from the connection portion main body  21 , as shown in  FIGS. 1 and 2 . The inner needle connection portion  7  can be housed in the connection portion main body  21 , with the inner needle  2  inserted in the outer needle  3 . One end portion of the blood circuit  4  can be connected to the branched portion  22 . Specifically, the connection portion main body  21  has a cylindrical shape positioned coaxially with the inner needle  2  and the outer needle  3 . The tip end portion  21   a  of the connection portion main body  21 , to which the outer needle  3  is connected, is formed having a smaller diameter than that of the base end portion  21   b  where the inner needle connection portion  7  can be housed. An insertion space  21   c  for inserting the inner needle  2  into the outer needle  3  is formed to penetrate the tip end portion  21   a  of the connection portion main body  21  along the central axis of the connection portion main body  21 . A part (a part within the base portion) of the outer circumferential space  16  is formed to be cylindrical between the inner circumferential surface of the insertion space  21   c  and the outer circumferential surface of the inner needle  2  so as to communicate with the tip end side portion  16   a  of the outer circumferential space  16  inside the outer needle  3 . The housing space  21   d  larger than the inner needle connection portion  7  is formed in the base end portion  21   b  of the connection portion main body  21  so as to communicate with the insertion space  21   c  (see  FIG. 2   b ). The end (the right side in  FIG. 2   a ) of the housing space  21   d  on the opposite side from the tip end portion  21   a  of the connection portion main body  21  with the middle portion of the housing space  21   d  in-between is released so that the inner needle connection portion  7  can be inserted into the housing space  21   d  with the inner needle side male thread  9  exposed outward from the released opening. 
         [0049]    At a position where the housing space  21   d  communicates with the insertion space  21   c;  in other words, in an insertion opening of the insertion space  21   c  through which the inner needle  2  is to be inserted, a seal member  23 , made of silicon rubber or the like, is attached to close the insertion opening of the insertion space  21   c.  A seal-penetrating hole  23   a  having a smaller diameter than that of the inner needle  2  is formed to penetrate the seal member  23  along the extension line of the insertion space  21   c.  The seal member  23  (in detail, the inner circumferential surface of the seal penetrating hole  23   a ) is kept in close contact with the outer circumferential surface of the inner needle  2  in a slidabe and liquid-light state. With the above, the seal member  23  closes the base end of the outer circumferential space  16  in a liquid-tight state so that the housing space  21   d  does not communicate with the outer circumferential space  16 . The seal member  23  functions also as a part of the holding member in the present invention for closely holding the base end portion of the inner needle  2  in a slidabale state. 
         [0050]    The branched portion  22  has a cylindrical shape branched from the lateral surface of the tip end portion  21   a  of the connection portion main body  21  and projecting toward the lateral side of the base end portion  21   b  of the connection portion main body  21 . Inside the branched portion  22 , a branched communicating space  22   a  is formed branched from the insertion space  21   c  and extending along the axial direction of the branched portion  22 . A part of the branched communicating space  22   a  positioned on the projecting end portion side of the branched portion  22  is formed having a larger diameter than that of a part of the same positioned on the insertion space  21   c  side, and exposed outward from the projecting end portion. A branch side male thread  24  is formed on the external circumference of the branched portion  22  in a position on the exposed opening side of the branched communicating space  22   a  so that a lock ring  4   b  mounted on an end portion of the blood circuit  4  can be screwed onto the branch side male thread  24  (see  FIG. 1 ). When an end portion of the blood circuit  4  is held abutting on the released opening and the lock ring  4   b  is then screwed onto the branch side male thread  24 , the blood circuit  4  and the branched portion  22  are kept in close contact with each other in a liquid-tight state, as a result of which the blood circuit  4  communicates with the outer circumferential space  16  via the insertion space  21   c  and the branched communicating space  22   a  inside the outer needle connection portion  15 . 
         [0051]    In the indwelling needle for extracorporeal circulation  1  having the above-described structure, when the inner needle connection portion  7  is sufficiently advanced toward the outer needle  3  side with the inner needle  2  inserted in the outer needle  3 , the inner needle  2  will move to the projecting position while being held on the respective ends thereof by the seal member  23  and the outer needle tip end portion  14 , as shown in  FIGS. 2   a  and  3   a.  As a result, the inner needle connection portion  7  abuts on the inner walls of the seal member  23  and the housing space  21   d,  and the puncture portion  2   d  projects from the outer needle  3 . With the above, the tip end portion of the indwelling needle for extracorporeal circulation  1  is ready to be punctured into a blood vessel. When the needle connection portion  7  is pulled out with the inner needle  2  held in the projecting position, the inner needle  2  will move to a housed position while being held on the respective ends thereof by the seal member  23  and the outer needle tip end portion  14 , as shown in  FIGS. 2   b  and  3   b,  and the puncture portion  2   d  is housed in the outer needle  3 . 
         [0052]    To conduct extracorporeal circulation of blood of a patient, using the indwelling needle for extracorporeal circulation  1 , initially, one end portion of the blood circuit  4  is set connected to the outer needle connection portion  15 , and the other end portion to the inner needle connection portion  7 . With the above, the one end portion of the blood circuit  4  communicates with the branched communicating space  22   a,  the outer circumferential space  16 , and the hole  17 , while the other end portion of the blood circuit  4  communicates with the inner needle communicating space  8  and the inner space  2   a.  After the blood circuit  4  is connected to the indwelling needle for extracorporeal circulation  1 , the tip end portion (specifically, the puncture portion  2   d  projecting from the outer needle tip end portion  14 ) of the indwelling needle for extracorporeal circulation  1  is punctured into a blood vessel of a patient, with the inner needle  2  held in the projecting position by the seal member  23  and the outer needle tip end portion  14 . Then, the indwelling needle  1  is inserted until the hole  17  formed on the lateral side of the outer needle main body  13  sufficiently enters the blood vessel, as a result of which the inside of the blood vessel communicates with the outer circumferential space  16  through the hole  17 . 
         [0053]    After the indwelling needle for extracorporeal circulation  1  is punctured into the blood vessel, the inner needle connection portion  7  is retreated (pulled out) to move the inner needle  2  from the projecting position to the housed position. As a result, the puncture portion  2   d  is housed in the outer needle tip end portion  14 . With the above, the blood vessel communicates with one end portion of the blood circuit  4  through the hole  17 , the outer circumferential space  16 , and the branched communicating space  22   a,  and also with the other end portion of the blood circuit  4  via the outer needle tip end portion  14 , the puncture portion  2   d  housed in the outer needle tip end portion  14 , the inner space  2   a,  and the inner needle communicating space  8 . That is, it is possible to utilize the inner needle  2  punctured into the blood vessel as a part of a blood circulation passage, rather than being pulled out. This can eliminate the need for preparing a member only for puncture into a blood vessel separately from a member constituting a blood circulation passage. This makes it possible to achieve an indwelling needle for extracorporeal circulation  1  having a double lumen structure without an excessively thick tip end portion, which in turn can reduce inconvenience with severe pain caused in puncture into a blood vessel. Further, as it is unnecessary to pull out the inner needle  2  from the outer needle  3 , there is no possibility that the puncture portion  2   d  erroneously pricks a person involved in operation (a person preparing for blood extracorporeal circulation). Still further, as the inner needle  2  is moved to the housed position, it is possible to prevent the puncture portion  2   d  from being exposed in a blood vessel. This can avoid inconvenience that the puncture portion  2   d  of the indwelling needle for extracorporeal circulation  1  unintentionally damages a blood vessel while the indwelling needle for extracorporeal circulation  1  is dwelling in the blood vessel. Yet further, as puncture of the indwelling needle for extracorporeal circulation  1  into a blood vessel is completed with only one puncture operation, it is preferable, as the number of occasions when a patient feels pain is fewer than that in a case where two indwelling needles are punctured into a blood vessel (specifically, a case where an indwelling needle for introducing blood into the blood circuit  4  and an indwelling needle for returning blood from the blood circuit  4  are separately punctured). 
         [0054]    The outer needle  3  is made by attaching the outer needle tip end portion  14  to the tip end portion of the longitudinal tube-like outer needle main body  13 . This makes it easier to manufacture the outer needle tip end portion  14 , using a harder material than the outer needle main body  13 , which makes it easier to manufacture an outer needle  3  that can facilitate puncture. Moreover, when the outer needle tip end portion  14  is made of plastic, inconvenience that the inner wall of a blood vessel is damaged is unlikely to be caused even when a patient moves his/her body while the indwelling needle for extracorporeal circulation  1  is indwelling and the outer needle tip end portion  14  resultantly abuts on the inner wall of the blood vessel. 
         [0055]    When the indwelling needle for extracorporeal circulation  1  is punctured into a blood vessel, the blood vessel communicates with one end portion of the blood circuit  4  via the outer needle  3  and the outer needle connection portion  15 , and also with the other end portion of the blood circuit  4  via the inner needle  2  and the inner needle connection portion  7 . Thereafter, a blood pump (not shown) connected midway in the blood circuit  4  is driven to cause the blood to circulate between the blood vessel and the blood circuit  4  via the indwelling needle for extracorporeal circulation  1 . Specifically, blood in the blood vessel is introduced through the tip end opening  2   b  of the inner needle  2  to flow through the inner space  2   a,  the base end opening  2   c,  and the inner needle communicating space  8  into the other end portion of the blood circuit  4 . Then, blood having flowed through the blood circuit  4  and discharged from one end portion of the blood circuit  4  now flows through the branched communicating space  22   a  and the outer circumferential space  16  to be discharged through the hole  17  of the outer needle  3  to be returned into the blood vessel. 
         [0056]    Alternatively, blood in a blood vessel is introduced through the hole  17  of the outer needle  3  to flow through the outer circumferential space  16  and the branched communicating space  22   a  into one end portion of the blood circuit  4 . Then, blood having flowed through the blood circuit  4  and discharged from the other end portion of the blood circuit  4  now flows through the inner needle communicating space  8 , the base end opening  2   c,  and the inner space  2   a  to be discharged through the tip end opening  2   b  of the inner needle  2  to be returned back into the blood vessel. When the blood flows as described above; that is, when the hole  17  is an inlet through which to introduce blood from the blood vessel, and the outer needle tip end portion  14  and the puncture portion  2   d  are outlets through which to return the blood having circulated in the blood circuit  4  to the blood vessel, it is possible to avoid inconvenience that blood is poured from the hole  17  even when the indwelling needle for extracorporeal circulation  1  indwelling in a blood vessel is erroneously removed partially from the blood vessel and the holes  17  are thereby exposed to the outside. Also, it is possible to keep returning the blood from the blood circuit  4  to the blood vessel so long as the indwelling needle for extracorporeal circulation  1  remains punctured in the blood vessel. 
         [0057]    Further, as a blood vessel communicates with the blood circuit  4  via the indwelling needle for extracorporeal circulation  1 , it is possible to maintain continuous blood circulation irrespective of the direction of a blood flow. Therefore, it is possible to achieve superior efficiency in extracorporeal circulation, compared to an intermittent operation in which blood is alternately introduced and returned, using an indwelling needle having branched channels connected to a single needle. With the above, it is possible to avoid prolonging of a blood extracorporeal circulation period (for example, a dialysis time), and thus to lessen excessive burden imposed on a patient subjected to blood extracorporeal circulation. 
         [0058]    Further, as the outer diameter of the inner needle  2  is set smaller than the inner diameter of the outer needle  3  to define a cylindrical outer circumferential space  16  between the outer circumferential surface of the inner needle  2  and the inner circumferential surface of the outer needle  3 , it is possible to form the outer circumferential space  16  by means of a simple structure. Further, it is possible to ensure a large cross section of the outer circumferential space  16 , and to achieve a structure for facilitating blood circulation without backset. 
         [0059]    Note that although a structure for facilitating an operation for moving the inner needle  2  is not provided in the above-described first embodiment, the present invention is not limited to the above description. For example, a second embodiment shown in  FIG. 4  is basically similar to the first embodiment, but different in that a slide mechanism for guiding the inner needle connection portion  7  in movement is provided. 
         [0060]    Specifically, as shown in  FIG. 4 , the inner needle connection portion  7  in the second embodiment has an inner needle movement operation unit  31  projecting outward from the outer circumferential portion of the inner needle connection portion  7 . The inner needle movement operation unit  31  includes a cylindrical engaged member  31   a  projecting from the outer circumferential surface of the inner needle connection portion  7 , and a disk-like movement operation piece  31   b  attached to the projecting end portion of the engaged member  31   a  and positioned outside the connection portion main body  21  of the outer needle connection portion  15 . Further, a slit of a movement guide protion  32  is formed in the connection portion main body  21  of the outer needle connection portion  15  so as to extend along the movement direction of the inner needle  2  for engagement with the inner needle connection portion  7  via the engaged member  31   a.  The width size (the width size along the circumferential direction of the connection portion main body  21 ) W of the movement guide protion  32  is set slightly smaller than the diameter φd of the engaged member  31   a  (see  FIG. 4   a ). 
         [0061]    An engagement portion with which the engaged member  31   a  can be engaged is formed at each end of the movement guide protion  32 . In detail, at the end of the movement guide protion  32  on the outer needle  3  side (the left side in  FIG. 4   a ), a projecting engagement portion  34   a  is formed with which the engaged member  31   a  is engaged with the inner needle  2  having moved to the projecting position. Meanwhile, at the end of the movement guide protion  32  on the released end side (the right side in  FIG. 4   a ) of the connection portion main body  21 , a housing engagement portion  34   a  is formed with which the engaged member  31   a  is engaged with the inner needle  2  having moved to the housed position. Each of the projecting engagement portion  34   a  and the housing engagement portion  34   b  is defined by a hole having a diameter that is wider than the width size W of the movement guide protion  32  and allows stable holding of the engaged member  31   a  when engaged. Further, the slit edge of the movement guide protion  32  positioned between the projecting engagement portion  34   a  and the housing engagement portion  34   b  (a slit edge extending along the movement direction of the inner needle  2 ) is defined as an engagement guide protion  35  where the engaged member  31   a  can slide so that the engaged member  31   a  can be guided in the movement direction of the inner needle  2  along the engagement guide protion  35 . 
         [0062]    On the connection portion main body  21  of the outer needle connection portion  15 , an entry notch slit  36  is formed on an extension line of the movement guide protion  32  on the housing engagement portion  34   b  side (the right side in  FIG. 4   a ). The entry notch slit  36  has a width smaller than the width size W of the movement guide protion  32  and the diameter φd of the engaged member  31   a,  and is released at the end of the connection portion main body  21  so that the engaged member  31   a  passes along the entry notch slit  36  to reach the movement guide protion  32  when the inner needle  2  is assembled into the outer needle  3 . 
         [0063]    According to the indwelling needle for extracorporeal circulation  1  having the movement guide protion  32  and the inner needle movement operation unit  31  having the above-described structure, the engaged member  31   a  is kept engaged with the housing engagement portion  34   b,  as indicated by the long dashed double-short dashed line in  FIG. 4 , so that the inner needle  2  is held so as not to be displaced from the housed position until immediately before puncture into a blood vessel. With the above, it is possible to achieve proper positioning of the inner needle  2  in the housed position, and thus to avoid inconvenience that the inner needle  2  unintentionally moves to the projecting position and the puncture portion  2   d  accordingly projects from the outer needle  3 , and resultantly, that the puncture portion  2   d  of the inner needle  2  having moved to the projecting position pricks and injures a person involved in operation. In puncturing into a blood vessel, the movement operation piece  31   b  of the inner needle movement operation unit  31  is pressed by a finger or the like to be slid from the housing engagement portion  34   b  side to the projecting engagement portion  34   a  side. With the above, the engaged member  31   a  is released from the housing engagement portion  34   b,  and the movement guide protion  32  (specifically, the engagement guide protion  35 ) guides the engaged member  31   a  and the inner needle connection portion  7  along the movement direction of the inner needle  2 . Therefore, it is possible to smoothly move the inner needle  2 , and thus to promptly execute an indwelling preparation operation for the indwelling needle for extracorporeal circulation  1 . Further, as it is possible to move the inner needle  2  by operating the inner needle movement operation unit  31 , it is possible to more readily move the inner needle  2 . 
         [0064]    When the inner needle movement operation unit  31  is sufficiently slid, the engaged member  31   a  is engaged with the projecting engagement portion  34   a,  as indicated by the solid line in  FIG. 4 , whereby the inner needle  2  is stably held so as not to be displaced from the projecting position. With the above, it is possible to achieve proper positioning of the inner needle  2  in the projecting position. After the inner needle  2  is positioned in the projecting position, the indwelling needle for extracorporeal circulation  1  is then punctured into a blood vessel. In the above, as the inner needle  2  is held at the projecting position by the engaged member  31   a  and the projecting engagement portion  34   a,  it is possible to avoid inconvenience that the inner needle  2  unintentionally moves from the projecting position to the housed position; in other words, inconvenience that the puncture portion  2   d  is pressed back into the outer needle  3  to disenable further puncture into a blood vessel even when the inner needle  2  is resisted by skin covering the blood vessel when puncturing. 
         [0065]    When the indwelling needle for extracorporeal circulation  1  is punctured and inserted into a blood vessel until the hole  17  on the outer needle  3  enters the blood vessel, the movement operation piece  31   b  of the inner needle movement operation unit  31  is pressed by a finger or the like to be slid from the projecting engagement portion  34   a  side to the housing engagement portion  34   b  side. With the above, the engaged member  31   a  is released from the projecting engagement portion  34   a,  and the movement guide protion  32  (specifically, the engagement guide protion  35 ) guides the engaged member  31   a  and the inner needle connection portion  7  along the movement direction of the inner needle  2 . Therefore, it is possible to smoothly move the inner needle  2  even after the indwelling needle for extracorporeal circulation  1  is punctured into a blood vessel, and thus to promptly execute an indwelling preparation operation for the indwelling needle for extracorporeal circulation  1 . Moreover, as it is possible to move the inner needle  2  by operating the inner needle movement operation unit  31 , it is possible to more readily move the inner needle  2  after puncture into a blood vessel. 
         [0066]    When the inner needle movement operation unit  31  is sufficiently slid, the engaged member  31   a  is engaged with the housing engagement portion  34   b,  as indicated by the long dashed double-short dashed line in  FIG. 4 , whereby the inner needle  2  is held so as not to be displaced from the housed position. With the above, it is possible to achieve proper positioning of the inner needle  2  in the housed position. Thus, it is possible to promptly execute an operation for moving the inner needle  2  from the projecting position to the housed position after puncture into a blood vessel, and to efficiently execute an indwelling preparation operation for the indwelling needle for extracorporeal circulation  1 . Further, it is possible to avoid unintentional displacement of the inner needle  2  once positioned. With the above, it is possible to avoid inconvenience that the puncture portion  2   d  projects from the outer needle tip end portion  14  while the outer needle  3  is indwelling in a blood vessel, and resultantly, that the projecting puncture portion  2   d  damages the inside wall of the blood vessel. 
         [0067]    In the second embodiment, there may be provided an urging member  38  for urging the inner needle connection portion  7  in a direction from the projecting position to the housed position. For example, in a modified example of the second embodiment shown in  FIG. 5 , an urging member  38  made of a coil spring is provided between the outer needle connection portion  15  and the inner needle connection portion  7 , and a tapered connection portion between the inner needle  2  and the inner needle connection portion  7  is positioned inside the urging member  38 . Then, one end portion of the urging member  38  is engaged with the seal member  23 , and the other with the inner needle connection portion  7 , whereby the inner needle connection portion  7  is urged by the urging force of the urging member  38  from the projecting position to the housed position. With this urging member  38  provided, when the inner needle movement operation unit  31  is slid with the inner needle  2  held in the projecting position to thereby release engagement between the engaged member  31   a  and the projecting engagement portion  34   a,  the inner needle connection portion  7  is urged by the urging force of the urging member  38 , whereby the inner needle  2  moves from the projecting position to the housed position. Further, the engaged member  31   a  is caused to be engaged with the housing engagement portion  34   b  due to the moving force of the inner needle  2  whereby the inner needle  2  is held so as not to be displaced from the housed position. With the above, it is possible to move the inner needle  2  to the housed position with only a one-touch operation for releasing the engaged member  31   a  engaged with the projecting engagement portion  34   a.  Thus, it is possible to more promptly complete an indwelling preparation operation for the indwelling needle for extracorporeal circulation  1 . 
         [0068]    Note that the urging member in the present invention is not limited to an urging member made of a coil spring. That is, so long as it is possible to urge the inner needle connection portion  7  in a direction from the projecting position to the housed position, any urging member having any structure can be employed. For example, when a sleeve-like projection is formed as an urging member projecting from a rubber seal member  23  toward the inner needle connection portion  7  side, the projecting end portion of the sleeve projection is held abutting on the inner needle connection portion  7 , and the inner needle  2  is moved to the projecting position, the sleeve projection is compressed along the movement direction of the inner needle  2 . Then, when the engaged member  31   a  in the projecting position is released from the projecting engagement portion  34   a,  the inner needle connection portion  7  is urged to move to the housed position by a restoring force of the sleeve projection in a compressed state. 
         [0069]    In the second embodiment and the modified example thereof, when a projection is formed on the front surface (a position touched by a finger or the like in operation) of the movement operation piece  31   b  of the inner needle movement operation unit  31 , a finger can be readily hooked on the inner needle movement operation unit  31 . This is preferable, as operability in moving the inner needle  2  can be improved. Further, although the inner needle connection portion  7  has the engaged member  31   a  and the outer needle connection portion  15  has the engagement portion  34 , the present invention is not limited to this structure. That is, any structure in which one of the outer needle connection portion  15  and the inner needle connection portion  7  has an engaged member and the other has an engagement portion is applicable. That is, a structure, for example, in which the inner needle connection portion  7  has an engagement portion and the outer needle connection portion  15  has an engaged member is applicable. 
         [0070]    Further, the structure of the engaged member  31   a  and the engagement portion  34  is not limited to the structure described in the second embodiment and the modified example. For example, a nail-like engaged member may be provided to one end portion of a swingable plate, an engagement operation unit adapted to a swing operation by an operator may be provided to the other end, and an engagement portion may be formed as a recess with which the nail-like engaged member can be engaged. In order to release engagement between the engaged member and the engagement portion, the engagement operation unit may be operated to swing the plate to thereby release engagement between the engaged member and the engagement portion. In the above, provision of the urging member between the inner needle connection portion and the outer needle connection portion is preferable, as it is possible to move the inner needle  2  to the housed position with a one-touch operation relative to the engagement operation unit. 
         [0071]    In the second embodiment and the modified example thereof, although the movement guide protion  32  (the engagement guide protion  35 ) guides the inner needle connection portion  7  and the engaged member  31   a  along the movement direction of the inner needle  2 , the present invention is not limited to the above description. That is, any structure in which a movement guide protion guides the inner needle connection portion  7  and an engagement guide protion guides the engaged member  31   a  is applicable, and the movement guide protion and the engagement guide portion may be separately provided. For example, the housing space  21   d  of the outer needle connection portion  15  may be formed slightly larger than the inner needle connection portion  7  so that the inner needle connection portion  7  can slide on the inner circumferential surface of the connection portion main body  21  of the outer needle connection portion  15  along the movement direction of the inner needle  2 . That is, the inner circumferential surface of the connection portion main body  21  may function as the movement guide portion in the present invention. 
         [0072]    Note here that although a part of the inner needle movement operation unit  31  is used as the engaged member  31   a  in the second embodiment and the modified example thereof, the present invention is not limited to this structure. For example, an engaged member may be provided to the inner needle connection portion  7  separately from the inner needle movement operation unit  31 . Further, although an indwelling needle for extracorporeal circulation  1  having a structure for guiding the inner needle  2  in movement (the movement guide portion  32 ), a structure for holding the inner needle  2  in a certain position (the engaged member  31   a  and the engagement portion  34 ), and a structure for operating to move the inner needle  2  (the inner needle movement operation unit  31 ) is described as an example in the second embodiment and the modified example thereof, the present invention is not limited to the above description. The indwelling needle for extracorporeal circulation may have a structure having at least one of the movement guide portion, the engaged member and the engagement portion, and the inner needle movement operation unit. 
         [0073]    Further, although the outer needle tip end portion  14  is attached to the tip end portion of the longitudinal tube-like outer needle main body  13  to form the outer needle  3  in the respective embodiments described above, the present invention is not limited to the above description. For example, in a third embodiment shown in  FIG. 6 , an outer needle tip end portion  14 ′ may be formed by thinning the tip end portion of a tube-like outer needle main body  13 ′ so as to have a smaller diameter in formation of an outer needle  3 ′. An outer needle  3 ′ having the above-described reduced diameter structure does not require formation of the outer needle tip end portion  14 ′ separately from the outer needle main body  13 ′. This can reduce manufacturing cost. 
         [0074]    Although in the respective embodiments described above the outer diameter of the inner needle  2  is set smaller than the inner diameter of the outer needle  3 ,  3 ′ to thereby form a cylindrical outer circumferential space  16  between the outer circumferential surface of the inner needle  2  and the inner circumferential surface of the outer needle  3 ,  3 ′, the present invention is not limited to the above description. That is, any structure in which the outer circumferential space  16  where blood can flow in the present invention may be formed between the outer circumferential surface of the inner needle  2  and the inner circumferential surface of the outer needle  3 ,  3 ′, and between the inner circumferential surface of the insertion space  21   c  and the outer circumferential surface of the inner needle  2  is applicable. For example, a groove may be formed on the outer circumferential surface of the inner needle  2  or a flat surface may be formed (formed such that the inner needle  2  has a D-shaped cross section) so that the space between the outer circumferential surface of the inner needle  2  and the inner circumferential surface of the outer needle  3 ,  3 ′ and between the inner circumferential surface of the insertion space  21   c  and the outer circumferential surface of the inner needle  2  is defined as the outer circumferential space  16 . However, when the space is too small, blood likely stops flowing, and thrombus may be caused. In view of the above, it is preferable that the outer circumferential space  16  is formed to be cylindrical so that blood is not likely to stop flowing, as shown in the respective embodiments. 
         [0075]    Use of the indwelling needle for extracorporeal circulation according to the present invention is not limited to blood extracorporeal circulation in dialysis, mentioned as an example. That is, the present invention can be used in any situation for extracorporeal circulation of blood of a patient. For example, the present invention is applicable to apheresis treatment for separation to remove a specific component from blood, for example. Further, a projecting flat piece (a so-called “wing”) may be formed projecting from a lateral side of an indwelling needle for extracorporeal circulation to facilitate securing of the indwelling needle for extracorporeal circulation on a patient, by means of tape. 
         [0076]    It should be understood that the above-described embodiments are only examples in any sense, and not limiting. That is, the present invention is not limited to the above description, but is defined according to the claims attached, and includes any modifications equivalent thereto in meaning and scope. 
       REFERENCE SIGNS LIST 
       [0000]    
       
           1  indwelling needle for extracorporeal circulation 
           2  inner needle 
           2   a  inner space 
           2   b  tip end opening 
           2   c  base end opening 
           2   d  puncture portion 
           3 ,  3 ′ outer needle 
           4  blood circuit 
           4   a  lock ring 
           4   b  lock ring 
           7  inner needle connection portion 
           8  inner needle communicating space 
           9  inner needle side male thread 
           13 ,  13 ′ outer needle main body 
           14 ,  14 ′ outer needle tip end portion 
           14   a  penetrating space 
           14   b  joint portion 
           15  outer needle connection portion 
           16  outer circumferential space 
           16   a  tip end side part 
           16   b  base end side part 
           17  hole 
           21  connection portion main body 
           21   a  tip end portion 
           21   b  base end portion 
           21   c  insertion space 
           21   d  housing space 
           22  branched portion 
           22   a  branched communicating space 
           23  seal member 
           23   a  seal-penetrating hole 
           24  branch side male thread 
           31  inner needle movement operation unit 
           31   a  engaged member 
           31   b  movement operation piece 
           32  movement guide portion 
           34  engagement portion 
           34   a  projecting engagement portion 
           34   b  housed engagement portion 
           35  engagement guide portion 
           36  entry notch slit