Patent Publication Number: US-2021187245-A1

Title: Catheter assembly

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a bypass continuation of PCT Application No. PCT/JP2019/032403, filed on Aug. 20, 2019, which claims priority to Japanese Application No. 2018-170580, filed on Sep. 12, 2018. The contents of these applications are hereby incorporated by reference in their entireties. 
    
    
     BACKGROUND 
     The present disclosure relates to a catheter assembly configured to be punctured and be indwelled in a blood vessel when performing an infusion or the like to a patient, for example. 
     Conventionally, a catheter assembly used when performing an infusion or the like to a patient has been known. This kind of the catheter assembly includes a hollow catheter, a catheter hub fixed to a proximal end of the catheter, a hollow inner needle that is inserted into the catheter and has a sharp needle tip at a distal end, and a needle hub fixed to a proximal end of the inner needle (for example, see JP 2008-43445 A). When using a catheter assembly, a skin and a blood vessel of a living body are punctured with each distal end of the inner needle and the catheter, and then, the catheter is advanced with respect to the inner needle so that the catheter is inserted into the blood vessel by a predetermined length. 
     SUMMARY 
     In a conventional catheter assembly having an inner needle and a catheter, a catheter distal end is sometimes caught by a blood vessel back wall (a blood vessel wall opposing a puncture spot) when a puncture angle is large. As a result, the catheter is hardly inserted into a blood vessel or the blood vessel wall is damaged by the catheter distal end. 
     Certain embodiments of the present invention have been developed in consideration of such a problem, and an object thereof is to provide a catheter assembly capable of preventing a catheter distal end from being caught by a blood vessel back wall at the time of advancing a catheter to a blood vessel even when a puncture angle, which is the angle between a central axis of the blood vessel to be punctured and a central axis of an inner needle with which the puncture is performed, is large. 
     One aspect of the present invention is a catheter assembly including a catheter and an inner needle inserted through the catheter. The catheter has a catheter body and a flexible portion that is provided on a distal portion of the catheter body, includes a distal-most portion of the catheter, and is more flexible than the catheter body. The catheter body is made of a first material, and the flexible portion is made of a second material. A change in flexibility of the second material between 25° C. and 37° C. is smaller than a change in flexibility of the first material between 25° C. and 37° C. 
     According to the catheter assembly of the present invention, the flexible portion, which is more flexible than the catheter body, is provided at the distal portion of the catheter body, and thus, it is possible to prevent a distal end of the catheter from being caught by a blood vessel back wall even when a puncture angle is large. Accordingly, it is possible to prevent the catheter from being hardly inserted into a blood vessel or to prevent a blood vessel wall from being damaged by the catheter distal end. Because the change in flexibility of the second material between 25° C. and 37° C. forming the flexible portion is smaller than the change in flexibility of the first material between 25° C. and 37° C. forming the catheter body, the distal end of the catheter is soft, and thus, hardly damages the blood vessel, and the catheter body is hard, and thus, is easily inserted when a catheter is inserted into a living body. After the catheter be indwelled, the flexible portion constituting the distal end of the catheter is not such soft as compared with the time of insertion, and thus, the flexible portion is hardly crushed during blood suction. On the other hand, after the catheter be indwelled, the catheter body softens due to the body temperature as compared with the time of insertion and adapts to a shape of the blood vessel, and thus, the stimulation to the blood vessel is reduced. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a perspective view of a catheter assembly according to an embodiment of the present invention; 
         FIG. 2  is a cross-sectional view of a distal portion of the catheter assembly; 
         FIG. 3  is a cross-sectional view of a distal portion in another configuration of the catheter assembly; 
         FIG. 4  is a first explanatory view of a procedure using the catheter assembly; 
         FIG. 5  is a second explanatory view of the procedure using the catheter assembly; 
         FIG. 6  is a third explanatory view of the procedure using the catheter assembly; 
         FIG. 7  is a fourth explanatory view of the procedure using the catheter assembly; 
         FIG. 8  is a cross-sectional view of a distal portion of a catheter assembly having another configuration; 
         FIG. 9A  is an explanatory view of first action of the catheter assembly illustrated in  FIG. 8 ; and 
         FIG. 9B  is an explanatory view of second action of the catheter assembly illustrated in  FIG. 8 . 
     
    
    
     DETAILED DESCRIPTION 
     Hereinafter, embodiments of a catheter assembly according to the present invention will be described with reference to the accompanying drawings. 
     The catheter assembly  10  whose initial state is illustrated in  FIG. 1  is applied when performing an infusion, a blood transfusion, and the like to a patient (living body), and forms an introduction portion for a medicinal liquid or the like by being punctured into the patient&#39;s body to be indwelled. The catheter assembly  10  may be configured as a catheter having a longer length (for example, a central venous catheter, a PICC, a mid-line catheter, and the like) than a peripheral venous catheter. Incidentally, the catheter assembly  10  may be configured as the peripheral venous catheter. In addition, the catheter assembly  10  is not limited to the venous catheter, and may be configured as an arterial catheter such as a peripheral arterial catheter. 
     As illustrated in  FIG. 1 , the catheter assembly  10  includes a catheter  12 , a catheter hub  14  fixedly holding the catheter  12 , a hollow inner needle  16  removably inserted into the catheter  12 , a needle hub  18  fixedly holding the inner needle  16 , and a catheter operation member  20  mounted to the catheter hub  14 . The inner needle  16  may be a solid needle. 
     The catheter assembly  10  forms a multi-tube structure (multi-tube portion) in which the catheter  12  and the inner needle  16  are sequentially stacked in an initial state before use. 
     The catheter  12  is flexible and has a lumen  13  formed to penetrate therethrough. The lumen  13  is formed to have a diameter capable of accommodating the inner needle  16  and capable of causing a medicinal liquid, blood, or the like to flow. A distal end of the catheter  12  is reduced in diameter in order to decrease a puncture resistance, and an inner surface of the catheter  12  is in close contact with an outer surface of the inner needle  16  at such a reduced diameter portion in the initial state of the catheter assembly  10 . A length of the catheter  12  is not particularly limited but can be appropriately designed according to use and various conditions, and is set to, for example, about 14 to 500 mm, about 30 to 400 mm, or about 76 to 200 mm. 
     A proximal portion of the catheter  12  is fixed to a distal portion inside the catheter hub  14 . The catheter  12  and the catheter hub  14  form a catheter member  17 . 
     The catheter hub  14  is exposed on the patient&#39;s skin in a state in which the catheter  12  has been inserted into a blood vessel, and indwelled together with the catheter  12  by being pasted with a tape or the like. The catheter hub  14  is formed in a tubular shape tapered in a distal direction. 
     A constituent material of the catheter hub  14  is not particularly limited, but a thermoplastic resin, such as polypropylene, polycarbonate, polyamide, polysulfone, polyarylate, a methacrylate-butylene-styrene copolymer, and polyurethane may be preferably applied. 
     A hollow portion  15  that communicates with the lumen  13  of the catheter  12  and through which an infusion solution can flow is provided inside the catheter hub  14 . A hemostatic valve, a plug, or the like (not illustrated) may be accommodated inside the hollow portion  15  in order to prevent back-flow of blood at the time of puncture with the inner needle  16  and to allow infusion along with insertion of a connector of an infusion tube. 
     The inner needle  16  is configured as a hollow tube having rigidity that enables puncture of a skin of a living body, and is arranged to penetrate through the lumen  13  of the catheter  12  and the hollow portion  15  of the catheter hub  14 . The inner needle  16  is formed to have a total length longer than that of the catheter  12 , and a sharp needle tip  16   a  is provided at a distal end thereof. A lumen penetrating in an axial direction of the inner needle  16  is provided inside the inner needle  16 , and this lumen communicates with a distal opening of the inner needle  16 . 
     Examples of a constituent material of the inner needle  16  include a metal material such as stainless steel, aluminum or an aluminum alloy, and titanium or a titanium alloy, a hard resin, ceramics, and the like. 
     The needle hub  18  has a needle holding member  22  fixed to a proximal portion of the inner needle  16 , and a housing  24  to which the needle holding member  22  is fixed and that extends along the inner needle  16  and the catheter  12 . The catheter assembly  10  accommodates a part of the multi-tube portion, the catheter hub  14 , and the catheter operation member  20  in the housing  24  in the initial state. Resin materials forming the needle holding member  22  and the housing  24  are not particularly limited, but, for example, the materials exemplified for the catheter hub  14  can be appropriately selected. Incidentally, the needle holding member  22  and the housing  24  may be integrally formed. 
     When the needle hub  18  is moved to a proximal direction with respect to the catheter  12 , the inner needle  16  is also moved in the proximal direction with respect to the catheter  12  along with the movement of the needle hub  18  because the needle hub  18  holds the inner needle  16  at the needle holding member  22 . 
     The catheter operation member  20  is attached to the catheter hub  14 . Thus, when the catheter operation member  20  is advanced relative to the needle hub  18 , the catheter member  17  is advanced relative to the inner needle  16 . The catheter operation member  20  has a hub mounting portion  20   a  detachably mounted on the catheter hub  14 , and an operation plate portion  20   b  extending from the hub mounting portion  20   a  along the catheter  12  in the distal direction. Incidentally, the catheter operation member  20  is not necessarily provided in the catheter assembly  10 . 
     The catheter assembly  10  is provided with a support member  26  on the distal side of the housing  24  in order to support a lower side of the catheter  12  held by the catheter operation member  20 . The support member  26  is rotatably attached to an arrangement concave portion  24   a  provided at a distal portion of the housing  24 . A distal portion of the catheter operation member  20  and the support member  26  constitute a deflection suppressing mechanism  27 . 
     When the skin is punctured with the inner needle  16  and the catheter  12 , the distal portion of the catheter operation member  20  supports the catheter  12  from above and the support member  26  supports the catheter  12  from below, and thus, deflections of the catheter  12  and the inner needle  16  are suppressed. When the catheter operation member  20  is removed out of the housing  24 , the support member  26  is rotated toward an outer side of the housing  24  by being pushed by the hub mounting portion  20   a , and thus, the catheter hub  14  can be withdrawn from the housing  24  in the distal direction. Incidentally, the support member  26  is not necessarily provided. 
     As illustrated to  FIG. 2 , the catheter  12  has a close contact portion  30 , which is in close contact with an outer circumferential surface of the inner needle  16 , in at least a part of an inner circumferential surface. The close contact portion  30  is provided on the inner circumferential surface of a distal portion of the catheter  12 . A flow path for flashback confirmation (hereinafter, referred to as “flashback flow path  32 ”) is formed between the catheter  12  and the inner needle  16  on the proximal side of the close contact portion  30 . The flashback flow path  32  extends up to a proximal opening of the catheter  12 . 
     The catheter  12  has a catheter body  34  that constitutes a main portion of the catheter  12  and a flexible portion  38  provided at a distal portion of the catheter body  34 . Thus, the catheter  12  becomes more flexible toward the distal-most portion on the distal side. The flexible portion  38  is exposed from the housing  24  ( FIG. 1 ). 
     The catheter body  34  accounts for most of the whole length of the catheter  12 . Thus, the distal-most portion of the catheter body  34  is positioned near the distal-most end of the catheter  12 . The catheter  12  and the flexible portion  38  are made of a resin material having flexibility. A creep strain of the catheter body  34  is greater than a creep strain of the flexible portion  38 . 
     The catheter body  34  has: a straight portion  34   a  that has a constant outer diameter along the axial direction; a tapered portion  34   b  that extends from the straight portion  34   a  in the distal direction and has an outer diameter decreasing in the distal direction; and a distal constituting portion  34   c  that extends from the tapered portion  34   b  in the distal direction and constitutes a portion up to the distal-most portion of the catheter body  34 . An inner circumferential surface of the distal constituting portion  34   c  is in close contact with (fitted to) the inner needle  16  in a liquid-tight manner over the whole outer circumferential surface. 
     The flashback flow path  32  is formed between an inner circumferential surface of the catheter body  34  (specifically, the straight portion  34   a  and the tapered portion  34   b ) and the outer circumferential surface of the inner needle  16 . At least the catheter body  34  between the catheter body  34  and the flexible portion  38  has transparency such that a flashback can be confirmed. 
     The catheter  12  is supported by the support member  26  ( FIG. 1 ) at a spot of the catheter body  34  (the catheter body  34  is supported by the support member  26 ). As a result, it is possible to reliably support the catheter  12  and to reduce a sliding resistance at the time of advancing the catheter  12 . Moreover, the portion supported by the support member  26  ( FIG. 1 ) is located on the proximal side of an interface  42  between the catheter body  34  and the flexible portion  38 , and thus, it is possible to prevent peeling of the interface  42  caused by sliding of the catheter  12  with respect to the support member  26 . 
     It is preferably that the catheter body  34  be less likely to swell as compared with the flexible portion  38 . As a result, it is possible to set an axial distance between a most proximal position of a blade surface  16   b  of the inner needle  16  and a distal-most position of the catheter  12  to a desired size and to reduce a variation for each product during steam sterilization (autoclave sterilization) or ethylene oxide gas sterilization in a process of manufacturing the catheter assembly  10 . 
     The catheter body  34  is made of a first material. Examples of a first material include a fluorine-based resin such as polytetrafluoroethylene (PTFE), an ethylene-tetrafluoroethylene copolymer (ETFE), and a perfluoroalkoxy fluorine resin (PFA), an olefin-based resin such as polyethylene and polypropylene or a mixture thereof, polyurethane, polyester, polyamide, a polyether nylon resin, a mixture of the olefin-based resin and an ethylene-vinyl acetate copolymer, and the like. A durometer hardness of the catheter body  34  is, for example, less than D70. 
     The flexible portion  38  includes the distal-most portion of the catheter  12 . The flexible portion  38  is more flexible than the catheter body  34 . That is, an elastic modulus k 1  of the catheter body  34  and an elastic modulus k 2  of the flexible portion  38  have a relationship of k 1 &gt;k 2 . 
     The flexible portion  38  has a straight portion  38   a  that has a constant outer diameter along the axial direction, and a tapered portion  38   b  that extends from the straight portion  38   a  in the distal direction and has an outer diameter decreasing in the distal direction. An inner circumferential surface of the flexible portion  38  is in close contact with (fitted to) an outer circumferential surface of the inner needle  16  in a liquid-tight manner over the whole outer circumference. 
     It is preferable that at least the flexible portion  38  (among the catheter body  34  and the flexible portion  38 ) have an X-ray contrast property. As a result, for example, when the catheter  12  is broken in a blood vessel, it is possible to easily confirm a location of the catheter  12 , which has been broken and left in the blood vessel, by X-ray. A contrast layer in the case where the flexible portion  38  has the contrast property may be provided, for example, in any form of a stripe shape, an intermediate layer in the radial direction, or the whole layer. 
     The flexible portion  38  is made of a second material. Examples of a second material include various rubber materials such as natural rubber, butyl rubber, isoprene rubber, butadiene rubber, styrene-butadiene rubber, silicone rubber, various thermoplastic elastomers such as polyurethanes, polyesters, polyamides, olefins, and styrenes or a mixture thereof, and the like. 
     A change in flexibility of the second material (constituent material of the flexible portion  38 ) between 25° C. and 37° C. is smaller than a change in flexibility of the first material (constituent material of the catheter body  34 ) between 25° C. and 37° C. Each change in flexibility can be recognized as a change in elastic modulus. For example, when the elastic modulus of the first material at 25° C. and 37° C. are H 1   a  and H 1   b , respectively, a change (degree of change) in elastic modulus of the first material between 25° C. and 37° C. is H 1   a /H 1   b . When the elastic modulus of the second material at 25° C. and 37° C. are H 2   a  and H 2   b , respectively, a change (degree of change) of the elastic modulus of the second material between 25° C. and 37° C. is H 2   a /H 2   b . Therefore, H 2   a /H 2   b &lt;H 1   a /H 1   b  is established. 
     Here, 25° C. is a typical temperature of room temperature. Further, 37° C. is a typical temperature of human body temperature. Both the first material and the second material have elastic modulus at 37° C. lower than elastic modulus at 25° C. That is, after the catheter  12  remains indwelled, the catheter body  34  and the flexible portion  38  are warmed to soften due to the body temperature, and become more flexible as compared with the time of inserting the catheter  12  into human (and the time before insertion). The first material and the second material may be of the same type having different hardness from each other. For example, even if the first material and the second material are of the same type, the above-described changes in elastic modulus with the temperature can be made different depending on an average molecular weight, a functional group, an additive, and the like. 
     In the catheter  12 , a single catheter body region  40 A where only the catheter body  34  between the catheter body  34  and the flexible portion  38  exists, a single flexible portion region  40 B where only the flexible portion  38  between the catheter body  34  and the flexible portion  38  exists, and a mixed region  40 C where the catheter body  34  and the flexible portion  38  exist are arranged in the axial direction. In the catheter  12  illustrated in  FIG. 2 , the interface  42  between the catheter body  34  and the flexible portion  38  is formed in a tapered shape that is inclined at a substantially constant angle with respect to an axis of the catheter  12 . 
     The single catheter body region  40 A is a portion of the catheter body  34  present on the proximal side of a most proximal portion of the flexible portion  38 . 
     The single flexible portion region  40 B is a portion of the flexible portion  38  present on the distal side of the distal-most portion of the catheter body  34 . An axial length L 1  of the single flexible portion region  40 B is set to, for example, 0.3 to 5.0 mm, preferably 0.4 to 2.0 mm, and more preferably 0.5 to 0.9 mm. The hardness of the flexible portion (the single flexible portion region  40 B) is, for example, A80 to D67 and preferably D53 to D64 at 23° C. The flexible portion  38  in the illustrated example is joined to the catheter body  34 . Because the axial length L 1  and the hardness of the single flexible portion region  40 B are set within the above ranges, it is possible to prevent the distal end (the flexible portion  38 ) of the catheter  12  from being curled at the time of puncture. In addition, it is possible to preferably suppress catching by a blood vessel back wall  50   a  at the time of inserting the catheter  12 . Further, it is possible to suppress crushing of the distal end of the catheter  12  at the time of suctioning blood. 
     The mixed region  40 C is a portion in which the catheter body  34  and the flexible portion  38  are stacked in the radial direction. An axial length L 2  of the mixed region  40 C is set to, for example, 1 to 5 mm, and preferably 2 to 3 mm. 
     In the catheter  12  illustrated in  FIG. 2 , the interface  42  between the catheter body  34  and the flexible portion  38  is inclined in the distal direction so as to approach the axis (center) of the catheter  12 . Thus, the flexible portion  38  is present on the outer side of the catheter body  34  in the mixed region  40 C. 
     Instead of the above configuration having the interface  42 , the catheter  12  may be formed so as to become soft in the distal direction by changing each compounding amount of materials different in hardness in the axial direction. In this case, extrusion molding may be performed while changing each extrusion speed of different materials. Alternatively, a content of a plasticizer at the distal portion of the catheter  12  may be increased. In this case, the plasticizer may be applied to the distal portion of the catheter  12 . 
     In the inner needle  16 , a backcut portion  16   c , which is continuous with the needle tip  16   a  and is inclined in a reverse direction to the blade face  16   b  with respect to the axis of the inner needle  16 , is provided on the opposite side to a blade face  16   b.    
     The inner needle  16  is provided with an introduction path  44  that communicates with the flashback flow path  32  to introduce blood into the flashback flow path  32 . The introduction path  44  illustrated in  FIG. 2  is a side hole  44 A that penetrates through a wall portion of the inner needle  16  in the radial direction. As illustrated in  FIG. 3 , the introduction path  44  may be a groove portion  44 B extending in the axial direction on the outer circumferential surface of the inner needle  16 . 
     In the initial state of the catheter assembly  10  illustrated in  FIGS. 2 and 3 , a proximal end  44   a  of the introduction path  44  is provided on the proximal side of an axial center position Pc of the single flexible portion region  40 B. More specifically, at least the proximal end  44   a  of the introduction path  44  is provided on the proximal side of a distal-most portion of the single catheter body region  40 A. The whole side hole  44 A illustrated in  FIG. 2  is provided on the proximal side of the distal-most portion of the single catheter body region  40 A. Incidentally, a part of the side hole  44 A may be present on the distal side of the distal-most portion of the single catheter body region  40 A. 
     In  FIG. 2 , the whole side hole  44 A is provided on the proximal side of the mixed region  40 C. A part of the side hole  44 A may be present on the distal side of a proximal end of the mixed region  40 C. 
     Regarding a position of the introduction path  44  in relation to the close contact portion  30 , at least the proximal end  44   a  of the introduction path  44  (the side hole  44 A or the groove portion  44 B) is provided on the proximal side of the close contact portion  30  in the initial state of the catheter assembly  10  illustrated in  FIGS. 2 and 3 . The whole side hole  44 A illustrated in  FIG. 2  is provided on the proximal side of the close contact portion  30 . 
     Next, a procedure (method for inserting the catheter assembly  10 ) using the catheter assembly  10  configured as described above will be described. 
     A puncturing operation of puncturing a patient&#39;s skin with the catheter assembly  10  is performed in the use of the catheter assembly  10  illustrated in  FIG. 1 . Prior to this puncturing operation, a tourniquet  54  is wrapped around a central side (side closer to the heart) of a planned puncture site SP in a part of the human body as illustrated in  FIG. 4  (a tourniquet attachment step). At a spot wrapped with the tourniquet  54 , a blood vessel  50  (vein) is compressed so that the blood vessel  50  is narrowed or collapses. The part of the human body illustrated in  FIG. 4  is an arm  56  (specifically, forearm). In another aspect, the tourniquet  54  may be wrapped around an upper arm and the planned puncture site SP may be located on the upper arm on the peripheral side of the tourniquet  54 . In still another aspect, the planned puncture site SP may be located on a lower limb and the tourniquet  54  may be wrapped around the lower limb on the central side of the planned puncture site SP. 
     After wrapping the tourniquet  54  in this manner, the puncturing operation is performed. In the puncturing operation, a user (a doctor, a nurse, or the like) presses the distal portion of the catheter assembly  10  against the patient while gripping the housing  24  illustrated in  FIG. 1 , thereby puncturing a skin S toward a puncture target blood vessel  50 . As a result, the skin S is punctured with the distal portions of the inner needle  16  and the catheter  12  as illustrated in  FIG. 5  (a puncture step). 
     Next, the user operates the catheter operation member  20  in the distal direction to advance the catheter member  17  (the catheter  12  and the catheter hub  14 ) to the central side while fixing the position of the needle hub  18  (the housing  24 ) illustrated in  FIG. 1  (a catheter advance step). Then, the catheter  12  is inserted to a target position in the blood vessel. At that time, the flexible portion  38  of the catheter  12  is caused to pass through a portion  50   n , which becomes narrower as compared with the time when the tourniquet  54  is not wrapped or collapses due to the tourniquet  54  wrapped around a part of the human body, of the blood vessel  50  as illustrated in  FIG. 4  (a passage step). In  FIG. 4 , the catheter  12  is illustrated by an imaginary line. 
     Next, the user pulls the housing  24  in the proximal direction while holding the positions of the catheter operation member  20  and the catheter member  17  illustrated in  FIG. 1 . Accordingly, the catheter member  17  and the catheter operation member  20  completely come out of the housing  24 , and the inner needle  16  is removed from the catheter  12  in the proximal direction. 
     Next, the catheter operation member  20  is detached from the catheter hub  14 . Accordingly, the catheter member  17  is indwelled in the patient. Incidentally, the catheter operation member  20  may be kept attached to the catheter hub  14  depending on a preference of the user. 
     Next, the connector of the infusion tube (not illustrated) is connected to the proximal side (the proximal portion of the catheter hub  14 ) of the catheter member  17  from which the inner needle  16  has been removed, and the infusion solution (medicinal liquid) is administered from the infusion tube to the patient. 
     In this case, the catheter assembly  10  according to the present embodiment has the following effects. 
     According to the catheter assembly  10 , the flexible portion  38 , which is more flexible than the catheter body  34 , is provided at the distal portion of the catheter body  34  as illustrated in  FIG. 2 . Thus, it is possible to prevent the distal end of the catheter  12  from being caught by a blood vessel back wall  50   a , which is a blood vessel wall of the blood vessel  50  on the opposite side of a puncture spot at the time of advancing the catheter  12  to insert the catheter  12  into the blood vessel  50  after puncturing a skin S with the distal portion of the catheter assembly  10  even when a puncture angle, which is an angle between a central axis of the blood vessel  50  to be punctured and a central axis of the inner needle  16  with which the puncture is performed, is large as illustrated in  FIG. 6 . 
     That is, the flexible portion  38  is brought into contact with the blood vessel back wall  50   a  and is pressed by the blood vessel back wall  50   a  to be easily deformed at the time of advancing the catheter  12  as illustrated in  FIG. 6 , and thus, it is possible to prevent the distal end of catheter  12  from being caught by the blood vessel back wall  50   a . As a result, it is possible to prevent the catheter  12  from being hardly inserted into the blood vessel  50  or to prevent the blood vessel back wall  50   a  from being damaged by the distal end of the catheter  12 . 
     Because the change in flexibility of the second material between 25° C. and 37° C. forming the flexible portion  38  is smaller than the change in flexibility of the first material between 25° C. and 37° C. forming the catheter body  34 , the distal end of the catheter  12  is relatively soft, and thus, hardly damages the blood vessel  50 , and the catheter body  34  is relatively hard, and thus, is easily inserted when the catheter  12  is inserted into the living body. After the catheter  12  indwells, the flexible portion  38  constituting the distal end of the catheter  12  is not such soft as compared with the time of insertion, and thus, the flexible portion  38  is hardly crushed during blood suction. On the other hand, after the catheter  12  indwells, the catheter body  34  softens due to the human body temperature as compared with the time of insertion and adapts to a shape of the blood vessel  50  (which is not linear but has some curvature in general), and thus, the stimulation to the blood vessel  50  is reduced. Thus, it is possible to reduce the discomfort given to the patient while the catheter  12  indwells, the occurrence of phlebitis, and the occurrence of extravasation. 
     As illustrated in  FIG. 2 , the flashback flow path  32  is formed between the catheter  12  and the inner needle  16 , and the inner needle  16  is provided with the introduction path  44  that communicates with the flashback flow path  32  to introduce blood into the flashback flow path  32 . The proximal end  44   a  of the introduction path  44  is provided on the proximal side of the axial center position Pc of the portion of the flexible portion  38  present on the distal side of the distal-most portion of the catheter body  34 . In addition, the catheter  12  has the close contact portion  30  in which at least a part of the inner circumferential surface is in close contact with the outer circumferential surface of the inner needle  16 , and at least the proximal end  44   a  of the introduction path  44  is provided on the proximal side of the close contact portion  30 . 
     With the above configuration, it is possible to prevent the flexible portion  38  from being deformed to block the introduction path  44  at the time of puncture, and thus, it is possible to easily confirm the flashback of blood. 
     In the close contact portion  30 , both the flexible portion  38  and the catheter body  34  are in close contact with the inner needle  16 . With this configuration, an appropriate fitting force between the inner needle  16  and the catheter  12  can be obtained. With the appropriate fitting force, the flexible portion  38  is prevented from being curled, and the inner needle  16  can be easily removed from the catheter  12  at the time of puncturing the skin. 
     In the above-described method for inserting the catheter assembly  10 , the catheter  12  is advanced with the tourniquet  54  wrapped as illustrated by the imaginary line in  FIG. 4 , and thus, it is possible to prevent the catheter  12  from falling off due to vasoconstriction that occurs when the tourniquet  54  is removed. Because the flexible portion  38  is provided at the distal end of the catheter  12 , the flexible portion  38  is easily deformed and easily enters the narrowed portion  50   n  of the blood vessel  50  when the catheter  12  passes from a peripheral side A to a central side B through the blood vessel  50  (portion  50   n ) narrowed by the tourniquet  54  as illustrated in  FIG. 7 . As a result, the catheter  12  can easily pass through the portion  50   n  of the blood vessel  50  narrowed by the tourniquet  54 , and damage to the blood vessel  50  accompanying the passage of the catheter  12  can be suppressed. 
     From the above description, the following invention (method for inserting the catheter assembly) can be grasped. 
     A method for inserting a catheter assembly including: preparing a catheter assembly that includes a catheter and an inner needle inserted through the catheter, the catheter having a catheter body and a flexible portion that is provided on a distal portion of the catheter body, includes a distal-most portion of the catheter, and is more flexible than the catheter body; 
     wrapping a tourniquet around a part of a human body on a central side of a planned puncture site; 
     puncturing a blood vessel at the planned puncture site in the part of the human body with the inner needle of the catheter assembly; 
     advancing the catheter into the blood vessel; and 
     causing the flexible portion to pass through a portion, which becomes narrower as compared with a time when the tourniquet is not wrapped or collapses due to the tourniquet wrapped around the part of the human body, of the blood vessel. 
     In a catheter assembly  10   a  illustrated in  FIG. 8 , a catheter  12   a  is provided with a side hole  60  that is open in the close contact portion  30 . The catheter  12   a  is configured in the same manner as the catheter  12  ( FIG. 1  and the like) except that the side hole  60  is provided. A plurality of the side holes  60  are provided at intervals in the circumferential direction. The side hole  60  is provided on the distal side of the most proximal position of the close contact portion  30 . The side hole  60  penetrates from an inner circumferential surface to an outer circumferential surface of the catheter  12   a . The side hole  60  penetrates through both the catheter body  34  and the flexible portion  38 . 
     In another aspect, only the single side hole  60  may be provided in the circumferential direction. The plurality of side holes  60  may be provided at intervals in the axial direction of the catheter  12   a . The side hole  60  may penetrate through only one of the catheter body  34  and the flexible portion  38 . On the inner circumferential surface of the catheter  12   a , the side hole  60  may be provided to straddle both the catheter body  34  and the flexible portion  38 . The side hole  60  may be inclined with respect to the radial direction of the catheter  12   a . When the groove portion  44 B as illustrated in  FIG. 3  is adopted as the introduction path  44  in the catheter  12   a , it is preferable that the side hole  60  of the catheter  12   a  be displaced from the groove portion  44 B in the circumferential direction. 
     In the use of the catheter assembly  10   a  configured as described above, blood flows into the flashback flow path  32  via the lumen of the inner needle  16  and the introduction path  44  as the blood vessel  50  is punctured with the catheter assembly  10   a  as illustrated in  FIG. 9A . Although the catheter  12   a  is provided with the side hole  60 , and the side hole  60  is open in the close contact portion  30  and is not open in the flashback flow path  32 , and thus, the blood does not leak out of the catheter  12   a  from the flashback flow path  32  through the side hole  60 . 
     In addition, the catheter  12   a  is provided with the side hole  60  that is open in the mixed region  40 C in the catheter assembly  10   a  illustrated in  FIG. 8 . Because the mixed region  40 C includes the catheter body  34 , and thus, is relatively harder than the single flexible portion region  40 B. 
     With the above configuration, it is possible to suppress the deformation of the catheter  12   a  during suction and prevent the blockage of the catheter  12   a  as compared with the case where the side hole  60  is provided in the single flexible portion region  40 B. 
     When a liquid L, such as a contrast agent, is introduced into the blood vessel at high pressure into the catheter  12   a  after removing the inner needle  16  from the catheter  12   a  as illustrated in  FIG. 9B , the liquid L is ejected not only from a distal opening  12   op  of the catheter  12   a  but also from the side hole  60 . Thus, as the pressure of the ejection of the liquid L disperses, it is possible to prevent the high pressure from acting locally on the blood vessel  50  and reduce the influence on the blood vessel  50 . In addition, it is possible to prevent the position of the catheter  12   a  from being displaced due to the reaction of the ejection of the liquid L. 
     Incidentally, the following invention (catheter assembly) can be grasped in relation to the configuration illustrated in  FIG. 8 . 
     A catheter assembly including: 
     a catheter; and 
     an inner needle inserted through the catheter, 
     in which the catheter has a catheter body and a flexible portion which is provided on a distal portion of the catheter body, includes a distal-most portion of the catheter, and is more flexible than the catheter body, 
     the catheter has a close contact portion in which at least a part of an inner circumferential surface is in close contact with an outer circumferential surface of the inner needle, both the flexible portion and the catheter body being in close contact with the inner needle in the close contact portion, 
     the catheter is provided with a side hole that is open in the close contact portion, 
     a flow path for flashback confirmation is formed between the catheter and the inner needle, and 
     the inner needle is provided with an introduction path that communicates with the flow path and introduces blood into the flow path. 
     In the present embodiment, the physical properties of the first material forming the catheter body  34  and the second material forming the flexible portion  38  in the catheter assembly  10   a  illustrated in  FIG. 8  are not limited to the above-described combination. For example, the change in flexibility of the second material between 25° C. and 37° C. may be the same as or larger than the change in flexibility of the first material between 25° C. and 37° C. 
     The present invention is not limited to the above-described embodiment, and various modifications can be made without departing from a gist of the present invention.