the constitution of a catheter insertion device according to a preferred embodiment of the present invention will be described hereinunder with reference to fig5 thru fig8 . the catheter insertion device comprises an inner needle 1 having a beveled surface 1a at its distal end ; an inner needle hub 6 attached to the proximal end of the inner needle 1 ; an outer catheter 2 having a through hole for receiving the inner needle 1 , adapted to receive the inner needle 1 in such a way that its beveled point is slightly projected when the inner needle 1 is inserted from the beveled surface side , and further having a catheter tapered tip portion 2a with a tapering outside diameter at its end ; and a catheter hub 7 attached to the proximal end of the outer catheter 2 , having a flange 7a and adapted to detachably engage with the inner needle hub 6 . the inner needle 1 and the outer catheter 2 are made of either metal or plastics , and the same is the case with the inner needle hub 6 and the catheter hub 7 . the above - mentioned constitution is not particularly different from a conventional catheter insertion device . new constituent parts will be described hereinunder . as shown in fig6 and fig7 an inner needle tapered portion 1b of a truncated cone shape having a tapering angle θ of from 4 to 16 degrees is formed in the vicinity of the above - mentioned beveled surface 1a at the end of the inner needle 1 . the beveled surface 1a is formed by cutting the inner needle tapered portion 1b obliquely at a given angle so that the width of the beveled surface 1a is not more than 90 % of the inner needle outside diameter ( e . g ., 1 mmφ ), preferably not more than 80 % ( 0 . 8 mmφ ). the basis of numerically limiting the width of the beveled surface 1a so as to be not more than 90 %, preferably not more than 80 %, of the inner needle outside diameter is according to the following experimental data . table 1 was obtained by puncturing a butyl rubber sheet ( thickness : 0 . 7 mm ; assumed to be a blood vessel wall ) with a catheter insertion device ( inner needle outside diameter : 1 mmφ , outer catheter outside diameter : 1 . 4 mmφ ), at five positions and measuring the time needed for 10 cc of water to leak out when a water pressure of 100 cm h 2 o is applied . table 1______________________________________beveled surface width (%) 100 95 90 85 80 75 70 ( proportion to inner needleoutside diameter ) time ( minute ) 2 3 5 9 13 18 25______________________________________ on the other hand , when a metal pipe is employed as the outer catheter , as shown in fig8 it is proper that the tapering angle α of the tapered tip portion 2a thereof should be from 4 to 16 degrees in accordance with the tapering angle θ of the inner needle tapered portion 1b , while when a plastic pipe is employed , it is preferable to make the angle larger . the above - mentioned inner needle tapered portion 1b is formed by drawing the inner needle end by means of swaging or the like in order to make the beveled surface smaller than the inner needle outside diameter . the tapering angle , from 4 to 16 degrees , is calculated as a range within which the length from the beveled point to the rear end of the inner needle tapered portion can be held not more than 4 . 5 mm when the width of the beveled surface 1a is set so as to be not more than 90 %, preferably not more than 80 %, of the inner needle outside diameter as mentioned above . because as the degree of the enlargement of the incision formed in the blood vessel increases , the pain inflicted on the patient becomes larger , it is necessary to set the width a of the beveled surface 1a of the inner needle 1 so as to be not less than 40 %, preferably not less than 50 %, of the outside diameter of the outer catheter 2 in order to alleviate the pain . accordingly , it is desirable that the width of the beveled surface 1a is not more than 90 %, preferably not more than 80 %, of the inner needle outside diameter so that a hemostatic effect is shown , as well as not less than 40 %, preferably not less than 50 %, of the outside diameter of the outer catheter 2 in order to minimize the pain inflicted on the patient . accordingly , the thinner the wall thickness of the outer catheter 2 becomes , the smaller the width of the beveled surface 1a can be made . however , when using plastics , the wall thickness of the outer catheter 2 has to be not less than 0 . 2 mm in view of strength requirement . therefore , if the inner needle outside diameter is 1 mm , the outer catheter outside diameter is 1 . 4 mm , so that the width of the beveled surface 1a can be determined within an extremely small range : from 0 . 8 to 0 . 7 mm . thus , it is desirable that the tapering angle θ is from 4 to 16 degrees , preferably from 8 to 10 degrees , according to the present invention from the necessity of holding the width of the beveled surface 1a within from 0 . 8 to 0 . 7 mm as well as the length from the beveled point to the rear end of the inner needle tapered portion under 4 . 5 mm . in addition , the beveled surface 1a is formed into a two - staged taper as shown in fig6 and fig7 . this is , however , not exclusive . moreover , the inner needle hub 6 is shown as having an air relief passage 6a for communicating the inner passage at the rear of a liquid - tight air - permeable member 8 adapted to close the inner passage with the outside besides the rear end opening of the inner passage , in order to relieve the air in the inner needle passage flushed back when the rear end opening of the inner passage is closed with a finger in use . as shown in fig9 and fig1 , the present invention includes another preferred embodiment wherein the inner needle is formed into an odd - shaped cylinder having longitudinally cut halves , only one of which is tapered and has a slightly crushed shape , i . e ., one substantial half of the cross section of the cylinder is inwardly flattened and the flatness increases toward the beveled point ( the hatching portion in fig9 ) while the other substantial half of the cross section is semicircular , and the beveled surface 1a is formed by cutting the flattened half of the odd - shaped cylinder 1b larger than the half having a semicircular cross section . further , the tapering angle θ of the flattened half seen in the direction perpendicular to the paper surface is set so as to be from 4 to 16 degrees , preferably from 8 to 10 degrees . as shown in fig1 , the constitution of the present invention may be such that the inner needle has a smaller diameter tubular portion 1c slightly extending from the inner needle tapered portion 1b toward the beveled point and further having a beveled surface 1a formed by obliquely cutting the inner needle tapered portion 1b and the smaller diameter tubular portion 1c simultaneously . as shown in fig1 , the constitution of the present invention may be such that the inner needle has a smaller - diameter tubular portion 1c slightly extending from the inner needle tapered portion 1b toward the beveled point and further having a beveled surface 1a formed by obliquely cutting the smaller - diameter tubular portion 1c . as shown in fig1 , the constitution of the present invention may be such that a cap 9 having the liquid - tight air - permeable member 8 provided with the air relief passage and adapted to close the passage , is fitted into the inner needle hub 6 . as shown in fig1 , the constitution of the present invention may be such that a stylet 10 is provided in the passage in the inner needle 1 in order to prevent the blood vessel wall from being cut out by the beveled surface of the inner needle when it punctures the blood vessel wall in case the inner needle has a large outside diameter . as shown in fig1 , the constitution of the present invention may be such that a catheter hub 7 with no flange is provided at the rear end of the outer catheter . the catheter insertion device according to the present invention described above is an over - the - needle type catheter insertion device comprising the inner needle , the inner needle hub , the outer catheter and the catheter hub , wherein the inner needle has an inner needle tapered portion formed in the vicinity of the beveled surface . accordingly , it is easy to conduct hemostasis because the width of the incision formed in the blood vessel is smaller than the outside diameter of the inner needle and equal to the width of the beveled surface . in addition , because the catheter insertion device according to the present invention has the tapered portion , for enlarging the incision , integrally formed with the inner needle , there are only two peaks , b and d , in the penetration resistance as shown in fig1 , and the value of the peak b is almost equal to the peak b shown in fig4 . therefore , it is possible to minimize the pain inflicted on the patient , and the catheter insertion device readily punctures the blood vessel . further , there is no possiblity of such a failure in securing a passage communicating with a blood vessel as frequently invited by the catheter insertion device shown in fig3 because according to the present invention the length from the beveled point of the inner needle to the outer catheter can be made shorter than that of the catheter insertion device shown in fig3 owing to the elimination of the dilator . moreover , it is possible to make the production cost lower than that of the catheter insertion device shown in fig3 although the inner needle tapered portion is formed at the end of the inner needle by means of swaging or the like , because the catheter insertion device according to the present invention has no dilator . furthermore , as a form covering the present invention , when the width of the beveled surface is made not more than 90 % of the outside diameter of the inner needle , the incision formed in the blood vessel is smaller than the inner needle outside diameter , so that the blood vessel wall clamps the inner needle . therefore , less blood leaks out from the blood vessel incision when a guide wire is inserted therein in the case where the catheter insertion device is used as a needle for introducing an angiography catheter . as another form covering the present invention , when the width of the beveled surface is not less than 40 % of the outside diamter of the catheter , the enlargement of the incision formed in the blood vessel can be held within limits of a given proportion , so that the pain inflicted on the patient is prevented from becoming larger . as still another form covering the present invention , when the tapering angle of the inner needle tapered portion is set so as to be from 4 to 16 degrees , particularly from 8 to 10 degrees , it is easy to form a beveled surface effective in hemostasis while it is possible to obtain dimensions for a beveled point by which a blood vessel passage is readily secured in puncture . it is to be noted also that the present invention is carried out in a variety of forms . one such form is that the inner needle tapered portion is formed into a truncated cone , and the present invention includes such a form that the inner needle tapered portion is formed into an odd - shaped cylinder such as by slightly flattening one side of a truncated cone . moreover , the present invention does not exclude such a form that a smaller - diameter tubular portion is provided on the converging side of the inner needle tapered portion , and the beveled surface is provided extending over the inner needle tapered portion and the smaller - diameter tubular portion or only at the smaller - diameter tubular portion .
since a typical catheter insertion device is used for percutaneous insertion of a catheter into an artery or a vein located in a deep part of a tissue , it is necessary to secure a sufficient lumen for introducing the catheter while alleviating pain inflicted on the patient when the catheter insertion device punctures the artery or the vein . the catheter insertion device of the invention has a tapered portion formed in the vicinity of a beveled surface of an inner needle in order to realize both necessary functions . accordingly , it is possible to decrease the size of the incision in the tissue because it is formed by the beveled surface of the tapered needle point with a smaller diameter , and the desired objects can be accomplished by means of an elastic insertion of the catheter into the smaller incision and , at the same time , bleeding from the incision can be minimized .