Patent Publication Number: US-11638807-B2

Title: Low profile introducer apparatus

Description:
RELATED APPLICATION 
     The present application is a Continuation of U.S. application Ser. No. 15/720,172 filed on Sep. 29, 2017, which is a Continuation of U.S. application Ser. No. 14/815,365 filed on Jul. 31, 2015 (now U.S. Pat. No. 9,795,768), which is a Continuation of U.S. application Ser. No. 14/132,642 filed on Dec. 18, 2013 (now U.S. Pat. No. 9,114,234), which is a Continuation of U.S. application Ser. No. 13/424,938 filed on Mar. 20, 2012 (now U.S. Pat. No. 8,628,496), which is a Continuation of U.S. application Ser. No. 11/440,834 filed on May 25, 2006 (now U.S. Pat. No. 8,152,767), which claims priority to U.S. Provisional Application Serial No. 60/685,188 filed on May 27, 2005, the contents of which applications are herein incorporated by reference in their entirety. 
    
    
     BACKGROUND 
     1. Technical Field 
     The present invention relates to the field of introducer assemblies for providing percutaneous access to the vascular system. More specifically, the invention relates to a low profile apparatus suitable for introducing catheters and other interventional devices into the vascular system with a minimal amount of trauma to the patient. 
     2. Background Information 
     Many medical procedures require the percutaneous placement of an interventional medical device, such as a catheter, into an artery or vein. Such interventional devices may be used for, among other things, blood pressure monitoring, blood sampling, and the administration of fluids and medicaments to a patient. 
     Typically, such devices are introduced into the vascular system using the well-known Seldinger percutaneous entry technique. In the Seldinger technique, the physician makes an oblique entry into the artery or vein with a beveled needle. A wire guide is passed through the bore of the needle into the artery or vein. The needle is thereafter withdrawn, leaving the wire guide in place. The catheter or other interventional device is then passed over the wire guide, through the puncture, and into the artery or vein at the needle puncture site. Once the catheter is in place, the wire guide can be withdrawn. 
     One of the disadvantages of this procedure is that the initial needle stick must normally be made with a needle that is large enough to accept the wire guide through its central bore. Conventional wire guides often comprise a tightly wound helical stainless steel wire coil. In order to have sufficient rigidity to properly support and lead many standard catheters and other interventional devices in common use in modern medicine, such wire guides are typically constructed to have an outer diameter in the range of about 0.035 to 0.038 inch (0.89 or 0.97 mm). This diameter of wire guide will typically pass through an 18 gauge thinwall needle. An 18 gauge needle typically has a 0.050 inch (1.27 mm) outer diameter (O.D.) and a 0.042 inch (1.07 mm) inner diameter (I.D.). 
     The 18 gauge needle is the most common sized needle used for initial vascular access, and has become a standard needle for use with the Seldinger technique for percutaneous catheterization. However, the O.D. of an 18 gauge needle is just large enough to damage tissue or cause excessive bleeding if it does not enter the vessel correctly, or if it inadvertently penetrates an organ or other unintended body structure. As a result, it is desirable to utilize a smaller gauge needle, such as a 21 gauge thinwall needle, for initial entry. A 21 gauge thinwall needle typically has a 0.032 inch (0.81 mm) O.D. and a 0.022 inch (0.56 mm) I.D., or smaller. Needles of 21 gauge thinwall, or smaller, are considered small enough that they do not damage tissue or organs, or cause excessive bleeding if inserted off target. In addition, smaller gauge needles generally have correspondingly shorter bevels at the needle tip compared to the size of the bevel tip of an 18 gauge needle. Thus, it is much easier to get a short bevel into the lumen of a small vessel than the longer bevel of the 18 gauge needle. 
     Unfortunately, the bore of a needle of 21 gauge, or smaller, is not large enough to enable a standard 0.035 inch or 0.038 inch (0.89 mm or 0.97 mm) diameter wire guide to be passed therethrough. The largest wire guide that can be easily introduced into such small gauge needles is normally a wire of 0.018 inch (0.46 mm) O.D. However, many diagnostic and interventional devices need at least a 0.035 inch (0.89 mm), and more preferably a 0.038 inch (0.97 mm), diameter wire guide to provide sufficient support to enable the physician to optimally introduce and manipulate the device through the vasculature over the wire. Thus, unless a larger diameter wire guide is introduced into the vasculature, many such devices cannot be successfully introduced. 
     U.S. Pat. No. 4,650,472 describes an apparatus which enables a physician to introduce a medical device, such as a catheter, into the body of a patient by making the initial puncture with a small gauge needle, such as a 22 gauge (0.028 inch; 0.72 mm O.D.) needle, in place of the larger conventional 18 gauge needle. The &#39;472 patent is incorporated by reference herein. A 0.018 inch (0.46 mm) outer diameter wire guide is initially inserted through the bore of the small gauge (e.g. 22 gauge) needle. The needle is thereafter withdrawn, and a removable inner cannula, or dilator, is provided over the wire guide but inside an outer sleeve portion of the catheterization apparatus. This removable inner cannula has a tapered tip, and provides a transition between the large distal opening of the outer sleeve and the 0.018 inch wire guide. The inner cannula is generally about 0.038 inch (0.97 mm) O.D., and the outer sleeve is sized to fit over the inner cannula. 
     The outer sleeve and the inner cannula of the apparatus disclosed in the &#39;472 patent are normally inserted into the blood vessel in tandem. The diametrical transition of the leading end of this tandem is intended to minimize the trauma that may otherwise be caused by the insertion of a large diameter outer sleeve over a small diameter wire guide. Once the outer sleeve is properly positioned within the blood vessel, the inner cannula and the smaller wire guide can be withdrawn, leaving the outer sleeve in place. A larger (0.035 to 0.038 inch) (0.89 to 0.97 mm) wire guide can then be introduced through the outer sleeve and into the vessel. If desired, the outer sleeve can thereafter be removed from the patient, leaving the larger wire guide in the vessel ready to accept a catheter or other interventional device. The apparatus of the &#39;472 patent has been successfully used to percutaneously insert a medical device, such as a catheter, having a large outer diameter into a blood vessel when the initial insertion is made with an introducer needle and a wire guide which are much smaller in diameter than the distal opening of the catheter. 
     The apparatus of the &#39;472 patent thus enables the physician to introduce larger diagnostic and interventional devices into a vessel than would otherwise be possible in a procedure in which initial vessel entry has been made with a small gauge needle. When the apparatus is inserted into the vessel as described, however, the physician must exert sufficient force to overcome the resistance provided at the “bump” that is present at the transition between the distal end of the outer sleeve and the underlying portion of the inner cannula. If this force is not carefully controlled, the physician may inadvertently exert too great a force to overcome the bump, and thereby puncture the side of the vessel opposite the initial stick. Thus, although the device of the &#39;472 patent may be successfully used to introduce large devices when initial entry is made with a small gauge needle, it is nonetheless desired to further improve this device, by providing a design which reduces the amount of force required to insert the outer sleeve into the vessel, and thereby reduces the possibility of an inadvertent puncture of the opposing vessel wall. 
     BRIEF SUMMARY 
     The problems of the prior art are addressed by the apparatus and method of the present invention. 
     In one form thereof, the invention comprises an introducer apparatus comprising an outer sleeve and an inner cannula. The outer sleeve has a lumen extending longitudinally therethrough, and has a profile such that at least a portion of the outer sleeve tapers toward the outer sleeve distal end at an angle not exceeding about 2° relative to a longitudinal axis of the apparatus. The outer sleeve has a distal open end sized such that a first wire guide is receivable therethrough. The distal open end of the outer sleeve has a wall thickness not exceeding about 0.003 inch. The inner cannula has a lumen extending longitudinally therethrough, and is sized to be received within the lumen of the outer sleeve. The inner cannula has a portion that tapers toward the inner cannula distal end. The inner cannula distal open end is sized such that a second wire guide is receivable therethrough, and the first wire guide is not receivable therethrough. The tapered distal portion of the inner cannula extends distal to the distal open end of said outer sleeve, and has a profile such that a generally smooth diametrical transition is provided between the outer sleeve tapered portion and the inner cannula open end. 
     In another form thereof, the invention comprises a method of inserting a wire guide into a body vessel of a patient for use in introducing a medical interventional device thereover. An introducer system comprises an introducer needle having an inner bore that does not exceed about 0.018 inch (0.46 mm) in diameter; a first wire guide having an outer diameter not less than about 0.035 inch (0.89 mm); a second wire guide having an outer diameter not greater than about 0.018 inch (0.46 mm) and being receivable in a bore of the introducer needle; and an introducer apparatus comprising an outer sleeve and an inner cannula. The inner cannula is removably received in a lumen of the outer sleeve. The outer sleeve has a profile such that a distal portion of the sleeve tapers toward the sleeve distal end at an angle not exceeding about 2° with a longitudinal axis of the sleeve. The outer sleeve distal open end is sized such that the first wire guide is receivable therethrough. The inner cannula has a lumen extending therethrough, and has a distal portion that tapers toward the inner cannula distal end. The inner cannula distal open end is sized such that the second wire guide is receivable therethrough and the first wire guide is not receivable therethrough. The tapered distal portion of the inner cannula extends distal to the distal open end of the outer sleeve, and has a profile such that a generally smooth diametrical transition is provided between the outer sleeve tapered portion and the inner cannula open end. The needle is injected into the body vessel, and the second wire guide is inserted through the needle bore such that a distal end of the wire guide extends beyond the needle in the body vessel. The needle is withdrawn from the body vessel over the second wire guide, ant the introducer apparatus is thereafter introduced over the wire guide such that the respective distal ends of the outer sleeve and inner cannula are in the body vessel. The second wire guide is withdrawn from the introducer apparatus while maintaining the introducer apparatus in the body vessel. The inner cannula is separated from the outer sleeve, and removed from the vessel while maintaining the outer sleeve in the body vessel. The first wire guide is guided through the outer catheter such that a distal end of the first wire guide extends beyond the outer sleeve in the body vessel. The outer cannula may then be withdrawn over the first wire guide. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a side view of the distal end portion of a prior art introducer apparatus suitable for entry into the vascular system with a small gauge needle; 
         FIG.  2    is an enlarged sectional view of the outer sleeve of the apparatus of  FIG.  1   ; 
         FIG.  3    illustrates one embodiment of a low profile introducer apparatus of the present invention; 
         FIG.  4    illustrates a side view of the outer sleeve of the low profile introducer apparatus of  FIG.  3   ; 
         FIG.  5    illustrates an enlarged distal end portion of the outer sleeve shown in  FIG.  4   ; 
         FIG.  6    illustrates a side view of the inner cannula of the low profile introducer apparatus of  FIG.  3   ; 
         FIG.  7    is a side view of a small gauge needle suitable for use in connection with the low profile introducer apparatus of the present invention; 
         FIG.  8    is a graph illustrating the relationship between compressive extension and compressive load for specimens 1-15 of an embodiment of the inventive apparatus; 
         FIG.  9    is a graph illustrating the relationship between compressive extension and compressive load for specimens 16-30 of an embodiment of the inventive apparatus; 
         FIG.  10    is a graph illustrating of relationship between compressive extension and compressive load for specimens 1-15 of a prior art apparatus; and 
         FIG.  11    is a graph illustrating the relationship between compressive extension and compressive load for specimens 16-30 of the prior art apparatus. 
     
    
    
     DETAILED DESCRIPTION OF THE DRAWINGS AND THE PRESENTLY PREFERRED EMBODIMENTS 
     For the purposes of promoting an understanding of the principles of the invention, reference will now be made to the embodiments illustrated in the drawings, and specific language will be used to describe the same. It should nevertheless be understood that no limitation of the scope of the invention is thereby intended, such alterations and further modifications in the illustrated device, and such further applications of the principles of the invention as illustrated therein being contemplated as would normally occur to one skilled in the art to which the invention relates. 
     In the following discussion, the terms “proximal” and “distal” will be used to describe the opposing axial ends of the inventive apparatus, as well as the axial ends of various related components. The term “proximal” is used in its conventional sense to refer to the end of the apparatus (or component) that is closest to the operator during use of the collar. The term “distal” is used in its conventional sense to refer to the end of the apparatus (or component) that is initially inserted into the patient, or that is in closest proximity to the patient. 
       FIG.  1    is a side view of the distal end portion of a prior art introducer apparatus  100  for introducing a medical device into a body vessel when the initial stick is made with a small gauge needle. Introducer apparatuses of this type are further described in the incorporated-by-reference U.S. Pat. No. 4,650,472.  FIG.  1    illustrates a typical dimensional relationship between an outer sleeve  102 , inner cannula  110  and small diameter wire guide  120 . Outer sleeve  102  includes a distal portion  104  that tapers to outer sleeve distal end  106 . Inner cannula  110  also includes a distal portion  112  that tapers to inner cannula distal end  114 . In the example shown, wire guide  120  extends from inner cannula distal end  114  in the normal fashion. 
       FIG.  2    is an enlarged sectional view of outer sleeve  102  of prior art apparatus  100 . Generally, for an outer sleeve having a typical outer diameter of about 5 French and a length of about 10 cm or more, the length a of tapered portion  104  in this prior art apparatus is approximately 4(±1) mm. The thickness b of the wall of sleeve  102  at distal end  106  is about 0.004(±0.0005) inch [0.10(±0.013) mm]. Tapered area  104  extends at an angle of greater than about 3°, typically greater than 3.5° from a longitudinal axis. 
       FIG.  3    illustrates one embodiment of an introducer apparatus  10  of the present invention. Introducer apparatus  10  comprises an outer sleeve  12  and an inner cannula  30  that extends through a lumen  17  ( FIG.  5   ) in the outer sleeve. A small diameter wire guide  40  extends through a lumen (not shown) in inner cannula  30 . Outer sleeve  12  is further illustrated in  FIG.  4   , and inner cannula  30  is further illustrated in  FIG.  6   .  FIG.  5    is an enlarged view of the distal end portion of outer sleeve  12 . 
     Like the prior art structure shown in  FIGS.  1  and  2   , apparatus  10  may be used for introducing a medical device into a body vessel using a small gauge needle, e.g., a needle of 21 gauge or smaller. One example of a suitable small gauge needle  80  is shown in  FIG.  7   . Needle  80  is a conventional small gauge needle, and includes a stainless steel shaft  82  having a lancet beveled tip  84 , and a lumen  86  therethrough. A standard hub  88  may be attached at the proximal end of needle  80 . 
     Unlike the prior art structure, outer sleeve  12  of the present invention is dimensioned to provide a very gradual transition between the distal end of the outer sleeve and the inner cannula. This transition is much smoother, and occurs in a much more gradual manner over a greater tapered length  14  of the outer sleeve, when compared to the much more abrupt transition of the tapered portion  104  of the prior art device shown in  FIG.  1   . The smooth, gradual transition at the distal end of the inventive apparatus forms a very sleek profile that enables the apparatus to be smoothly inserted into, and passed through, the initial body opening and the underlying tissue. As a result, the patient experiences reduced trauma, both at the initial insertion point and as the apparatus is further inserted into a body vessel of the patient. 
     As best shown in  FIGS.  4  and  5   , outer sleeve  12  includes a main shaft portion  13 , having a distal portion  14  and a proximal portion  15 . Distal portion  14  tapers to outer sleeve distal end  16 . The proximal end of proximal portion  15  is received within a conventional hub  18 . As shown in  FIG.  6   , inner cannula  30  also includes a main shaft portion  33 , having a distal portion  34  and a proximal portion  35 . Distal portion  34  tapers to an inner cannula distal end  36 . The proximal end of proximal portion  35  is received within a conventional hub  38 . Respective hubs  18 ,  38  are sized and shaped for locking engagement when the introducer apparatus is fully assembled. Hubs  18 ,  38  may be of any conventional design that permits releasable engagement therebetween, the specific designs shown in the figures merely representing examples of suitable hubs. The specific design of the hubs is not germane to an understanding of the present invention, and therefore, no further description of the hubs is provided. 
     When introducer apparatus  10  is fully assembled as shown in  FIG.  3   , inner cannula  30  is received within lumen  17  of outer sleeve  12 , and distal end portion  34  of inner cannula  30  extends beyond distal portion  14  of the outer sleeve. Unlike the tapered portion  104  of the outer sleeve in prior art structure  100 , distal portion  14  of the outer sleeve of inventive apparatus  10  tapers in a much more gradual fashion to the distal end of the sleeve. Thus, the length c ( FIG.  4   ) of tapered portion  14  of the inventive sleeve is longer, and in some embodiments considerably longer, than length a ( FIG.  2   ) of the more abrupt tapered portion of a prior art device of the same outer diameter. This difference in length c when compared to length a illustrates the more gradual taper, or transition, from the outer sleeve to the inner cannula in the inventive device, when compared to the prior art structure. Preferably, the length c of the tapered portion of the inventive sleeve is between about 5 and 50 mm, more preferably between about 8 and 20 mm long. 
     As a result of the extended tapered length of the inventive design, the sleek profile of the inventive sleeve results in a wall thickness d of sleeve distal end  16  that is less, and in many cases considerably less, than the thickness of the wall at the distal end of the prior art design. Preferably, thickness d is between about 0.0005 and 0.003 inch [0.013 and 0.076 mm], more preferably between about 0.0005 and 0.0015 inch [0.013 and 0.38 mm], and most preferably, about 0.001 inch(±0.0005 inch) [0.025±0.013 mm]. The wall thickness of the prior art design is typically about 0.004 inch(±0.0005 inch) [0.10±0.013]. As a result, tapered distal end  14  of the inventive sleeve has a much more gradual taper than that of the prior art device, and tapers to a much narrower wall thickness at the distal end. Preferably, tapered area  14  extends at an angle not exceeding about 2° from the longitudinal axis, and preferably about 1-1.5°. 
     The comparative dimensions provided hereinabove are for outer sleeves of similar French sizes, and in the examples given, for a 5 French outer sleeve. In this event, length c of the inventive design is about 15 mm. This compares to length a in the prior art design of about 4 mm. For a smaller French size, such as 4 French, the length c will normally be correspondingly smaller, such as about 8 mm for the inventive design. For a larger French size, such as 6 French, the length c will normally be correspondingly larger, such as about 17 mm. For comparison, the length a of a prior art 4 French sleeve is typically about 2 mm, and the length a of a prior art 6 French sleeve is typically about 5 mm. In each case, the length of the tapered area of the prior art sleeve is significantly shorter than the length of the tapered portion of the inventive sleeve. 
     Those skilled in the art will appreciate that the inventive apparatus  10  can be formed to have any conventional size for its intended purposes. Preferably, the outer sleeve will generally have a diameter between about 2 and 10 French, more preferably between 4 and 6 French, and most preferably, about 5 French. However, the teachings of the present invention are also applicable to sleeves of even larger diameters, as long as the length of the sleeve can accommodate a taper as described. 
     The outer sleeve is preferably sized for insertion therein of inner cannulae of the type commonly used in such devices for catheterization with a small gauge needle. Thus, a conventional apparatus of the type known in the art can be utilized, with the exception of the outer sleeve, which will be dimensioned as disclosed herein. In addition to the other dimensions provided hereinabove, the lumen  15  of the outer sleeve may have a diameter similar to that of existing devices. A typical lumen diameter is about 0.04 inch (1 mm). The dimensions provided hereinabove are only examples of suitable dimensions for an outer sheath, and sheaths of other dimensions are also within the scope of the invention. 
     The sleek design of apparatus  10 , and more particularly, of outer sleeve  12 , enables the inventive apparatus to be introduced into a body vessel of a patient with a minimum of trauma. Certain tests were carried out to simulate the amount of force that a physician must exert during the insertion of the inventive introducer apparatus through the skin at a body opening. This force was compared to the amount of force that must be exerted while inserting a prior art introducer apparatus through a similar body opening. The prior art apparatus included a 5 French outer sleeve, a tapered distal sleeve portion having a length a of 4 mm and a wall thickness b at its distal end of about 0.004 inch. The tapered portion of the prior art apparatus tapered at an angle of about 3 degrees. For comparison, the inventive apparatus included a 5 French outer sleeve, a tapered distal portion having a length c of 15 mm and a wall thickness d at its distal end of about 0.001 inch. The tapered portion of the prior art apparatus tapered at an angle of about 1 degree. The inner cannulae used in each test were identical, having a diameter of 3 French and a length of about 120 mm. The length of the prior art sleeve was about 100 mm, and the length of the inventive sleeve was about 105 mm. 
     A sheet of 0.038 inch thick condensed silicone with a translucent color was provided to simulate the skin of a patient. Silicone sheets of this type are commercially available from, among others, AAA-Acme Rubber Company, of Tempe, Ariz., under the name Dura Silicone. In each case, the initial puncture through the silicone sheet was made with a 21 gauge needle. A 0.018 inch wire guide was inserted through the bore of the needle in conventional fashion. The needle was thereafter withdrawn over the wire guide, and the sleeve/cannula apparatus was inserted over the wire guide and through the silicone sheet. 
     Simulations were performed on thirty specimens of the inventive apparatus and thirty specimens of a prior art apparatus. The testing conditions were intended to be as close to identical on all specimens as possible. The tests were designed to simulate and record the maximum load (in lbf) that is exerted on the skin as the introducer apparatus initially enters the skin through the needle puncture, the compressive extension (in mm) at the maximum load encountered during insertion, and the compressive load (in lbf) at 47 mm (with the inventive apparatus) and 42 mm (with the prior art apparatus), respectively. The compressive extension at the maximum load recites the depth at which maximum force is exerted during insertion. The compressive loads at 47 and 42 mm represent readings taken past the taper and transition length. These readings indicate that the push force needed to traverse the transition between the inner cannula and the outer sleeve with the inventive design is less than the force needed to traverse the sleeve. On the other hand, with the prior art device, the push force at the point of transition considerably exceeds the force along the sleeve. 
     The results of the tests on the 30 specimens of the inventive apparatus are shown below in Table 1. 
     
       
         
           
               
               
               
               
               
             
               
                 TABLE 1 
               
               
                   
               
             
            
               
                   
                   
                 Compressive 
                   
                   
               
               
                   
                   
                 extension at 
               
               
                   
                 Maximum 
                 Maximum 
                 Compressive 
               
               
                 Specimen 
                 Load 
                 Comp. load 
                 load at 47 mm 
               
               
                 Label 
                 (lbf) 
                 (mm) 
                 (lbf) 
                 Comment 
               
               
                   
               
               
                 1 
                 0.31 
                 4.47458 
                 0.27933 
                 Pushed without incident 
               
               
                 2 
                 0.35 
                 4.18979 
                 0.32828 
                 Pushed without incident 
               
               
                 3 
                 0.32 
                 32.73474 
                 0.28809 
                 Pushed without incident 
               
               
                 4 
                 0.40 
                 36.24515 
                 0.26727 
                 Pushed without incident 
               
               
                 5 
                 0.39 
                 5.53499 
                 0.24153 
                 Pushed without incident 
               
               
                 6 
                 0.33 
                 5.00999 
                 0.23552 
                 Pushed without incident 
               
               
                 7 
                 0.36 
                 35.05036 
                 0.20435 
                 Pushed without incident 
               
               
                 8 
                 0.29 
                 4.70999 
                 0.23899 
                 Pushed without incident 
               
               
                 9 
                 0.28 
                 47.49513 
                 0.24798 
                 Pushed without incident 
               
               
                 10 
                 0.36 
                 5.23041 
                 0.23015 
                 Pushed without incident 
               
               
                 11 
                 0.35 
                 41.46015 
                 0.18996 
                 Pushed without incident 
               
               
                 12 
                 0.43 
                 22.76017 
                 0.25893 
                 Pushed without incident 
               
               
                 13 
                 0.37 
                 5.86520 
                 0.18430 
                 Pushed without incident 
               
               
                 14 
                 0.34 
                 4.84437 
                 0.26116 
                 Pushed without incident 
               
               
                 15 
                 0.29 
                 46.74514 
                 0.22182 
                 Pushed without incident 
               
               
                 16 
                 0.33 
                 34.20495 
                 0.24218 
                 Pushed without incident 
               
               
                 17 
                 0.35 
                 5.20999 
                 0.25428 
                 Pushed without incident 
               
               
                 18 
                 0.36 
                 5.63499 
                 0.21307 
                 Pushed without incident 
               
               
                 19 
                 0.36 
                 5.34978 
                 0.21285 
                 Pushed without incident 
               
               
                 20 
                 0.37 
                 47.17951 
                 0.18557 
                 Pushed without incident 
               
               
                 21 
                 0.36 
                 46.88972 
                 0.24057 
                 Pushed without incident 
               
               
                 22 
                 0.36 
                 5.47499 
                 0.22677 
                 Pushed without incident 
               
               
                 23 
                 0.38 
                 6.07978 
                 0.19394 
                 Pushed without incident 
               
               
                 24 
                 0.33 
                 5.61041 
                 0.18142 
                 Pushed without incident 
               
               
                 25 
                 0.28 
                 4.99520 
                 0.19651 
                 Pushed without incident 
               
               
                 26 
                 0.33 
                 41.46952 
                 0.19551 
                 Pushed without incident 
               
               
                 27 
                 0.39 
                 5.98520 
                 0.16382 
                 Pushed without incident 
               
               
                 28 
                 0.37 
                 36.46015 
                 0.15755 
                 Pushed without incident 
               
               
                 29 
                 0.38 
                 5.68999 
                 0.20767 
                 Pushed without incident 
               
               
                 30 
                 0.34 
                 40.59056 
                 0.17002 
                 Pushed without incident 
               
               
                 Mean 
                 0.35 
                 19.97250 
                 0.22398 
               
               
                 Standard 
                 0.03480 
                 17.70996 
                 0.03969 
               
               
                 Deviation 
               
               
                 Minimum 
                 0.28 
                 4.18979 
                 0.15755 
               
               
                 Maximum 
                 0.43 
                 47.49513 
                 0.32828 
               
               
                   
               
            
           
           
               
               
               
            
               
                   
                 Rate 1 
                 150.0 mm/min 
               
               
                   
                 Data capture 
                 Manual 
               
               
                   
                 Control mode 1 
                 Compressive extension 
               
               
                   
                 Start of test Temperature (deg C.) 
                 21.0 
               
               
                   
                 Start of Test Relative Humidity (%) 
                 37.0 
               
               
                   
                 End of test Temperature (deg C.) 
                 21.0 
               
               
                   
                 End of test Relative Humidity (%) 
                 29.0 
               
               
                   
                   
               
            
           
         
       
     
     The data of Table 1 is illustrated graphically in  FIG.  8    for specimens 1 to 15, and in  FIG.  9    for specimens 16 to 30 of the inventive apparatus. In the figures, the “zero point” (“0”) of the “compressive extension” and the “compressive load” represents the point where the inner cannula initially touches the sheet as it is urged forwardly for insertion. 
     The results of the tests on the 30 specimens of the conventional, prior art apparatus are shown below in Table 2. 
     
       
         
           
               
               
               
               
               
             
               
                 TABLE 2 
               
               
                   
               
             
            
               
                   
                   
                 Compressive 
                   
                   
               
               
                   
                   
                 extension at 
               
               
                   
                 Maximum 
                 Maximum 
                 Compressive 
               
               
                 Specimen 
                 Load 
                 Comp. load 
                 load at 42 mm 
               
               
                 Label 
                 (lbf) 
                 (mm) 
                 (lbf) 
                 Comment 
               
               
                   
               
               
                 1 
                 0.60 
                 11.28040 
                 0.17221 
                 Pushed without incident 
               
               
                 2 
                 0.62 
                 11.46957 
                 0.13470 
                 Pushed without incident 
               
               
                 3 
                 0.61 
                 9.84978 
                 0.21689 
                 Pushed without incident 
               
               
                 4 
                 0.61 
                 10.67436 
                 0.17909 
                 Pushed without incident 
               
               
                 5 
                 0.57 
                 9.78998 
                 0.24985 
                 Pushed without incident 
               
               
                 6 
                 0.61 
                 9.47436 
                 0.28167 
                 Pushed without incident 
               
               
                 7 
                 0.59 
                 10.46415 
                 0.21618 
                 Pushed without incident 
               
               
                 8 
                 0.59 
                 11.01998 
                 0.14473 
                 Pushed without incident 
               
               
                 9 
                 0.57 
                 9.48040 
                 0.28587 
                 Pushed without incident 
               
               
                 10 
                 0.63 
                 10.59957 
                 0.19785 
                 Pushed without incident 
               
               
                 11 
                 0.60 
                 10.93436 
                 0.15891 
                 Pushed without incident 
               
               
                 12 
                 0.62 
                 10.51498 
                 0.18479 
                 Pushed without incident 
               
               
                 13 
                 0.59 
                 10.62915 
                 0.18130 
                 Pushed without incident 
               
               
                 14 
                 0.61 
                 11.20019 
                 0.16731 
                 Pushed without incident 
               
               
                 15 
                 0.57 
                 10.39457 
                 0.18708 
                 Pushed without incident 
               
               
                 16 
                 0.67 
                 10.64936 
                 0.22800 
                 Pushed without incident 
               
               
                 17 
                 0.58 
                 9.64540 
                 0.28844 
                 Pushed without incident 
               
               
                 18 
                 0.57 
                 10.12457 
                 0.21000 
                 Pushed without incident 
               
               
                 19 
                 0.57 
                 9.97436 
                 0.21853 
                 Pushed without incident 
               
               
                 20 
                 0.63 
                 10.49519 
                 0.20705 
                 Pushed without incident 
               
               
                 21 
                 0.59 
                 10.71936 
                 0.17773 
                 Pushed without incident 
               
               
                 22 
                 0.61 
                 11.48415 
                 0.12394 
                 Pushed without incident 
               
               
                 23 
                 0.60 
                 9.99478 
                 0.23544 
                 Pushed without incident 
               
               
                 24 
                 0.60 
                 10.29978 
                 0.22631 
                 Pushed without incident 
               
               
                 25 
                 0.57 
                 10.59540 
                 0.21824 
                 Pushed without incident 
               
               
                 26 
                 0.57 
                 10.41957 
                 0.18823 
                 Pushed without incident 
               
               
                 27 
                 0.57 
                 11.18477 
                 0.09785 
                 Pushed without incident 
               
               
                 28 
                 0.53 
                 9.67999 
                 0.26979 
                 Pushed without incident 
               
               
                 29 
                 0.58 
                 10.18103 
                 0.26243 
                 Pushed without incident 
               
               
                 30 
                 0.62 
                 10.91498 
                 0.16288 
                 Pushed without incident 
               
               
                 Mean 
                 0.60 
                 10.47128 
                 0.20244 
               
               
                 Standard 
                 0.02679 
                 0.57158 
                 0.04818 
               
               
                 Deviation 
               
               
                 Minimum 
                 0.53 
                 9.47436 
                 0.09785 
               
               
                 Maximum 
                 0.67 
                 11.48415 
                 0.28844 
               
               
                   
               
            
           
           
               
               
               
            
               
                   
                 Rate 1 
                 150.0 mm/min 
               
               
                   
                 Data capture 
                 Manual 
               
               
                   
                 Control mode 1 
                 Compressive extension 
               
               
                   
                 Start of test Temperature (deg C.) 
                 21.0 
               
               
                   
                 Start of Test Relative Humidity (%) 
                 32.0 
               
               
                   
                 End of test Temperature (deg C.) 
                 21.0 
               
               
                   
                 End of test Relative Humidity (%) 
                 30.0 
               
               
                   
                   
               
            
           
         
       
     
     The data of Table 2 is illustrated graphically in  FIG.  10    for specimens 1 to 15, and in  FIG.  11    for specimens 16 to 30 of the prior art apparatus. 
     As demonstrated by the simulations, considerably more force is required to enter the skin and underlying tissue when utilizing the prior art apparatus than with the inventive apparatus. This is particularly true at the point where the distal end of the outer sleeve initially penetrates the skin. This is demonstrated in the Tables, and is graphically illustrated by the respective curves shown in  FIGS.  8 - 11   . The x-axis of the graphs represents the compressive extension, or in other words, the length of insertion (in mm) of the apparatus through the skin. The y-axis represents the compressive load, or in other words, the force (in lbf) that is exerted by the physician upon insertion of the apparatus through the skin. As shown in each of the graphs of  FIGS.  8 - 11   , the compressive load builds as the apparatus is advanced into the skin until the inner cannula has initially penetrated the skin. This is represented by the first peak in each of the figures. In both the prior art apparatus and the inventive apparatus (e.g., in each of the  FIGS.  8 - 11   ), the first peak indicates a maximum compressive load that is typically between about 0.30 and 0.40 lbf. 
     Upon insertion of the inner cannula through the skin an immediate decrease in force is observed once the initial penetration, or puncture, has been completed. As the apparatus is further inserted, the force once again builds, to represent the force required for the outer sleeve to penetrate the skin. As illustrated in  FIGS.  10  and  11    of this simulation, and as documented in Table 2, considerable force is required for the outer sleeve of the prior art apparatus to penetrate the skin. This is shown as the large (second) peak. As shown, a maximum compressive load of from about 0.53 to 0.63 lbf must typically be exerted when the outer sleeve of the prior art apparatus penetrates the skin. The mean value of maximum compressive load of all thirty prior art specimens is indicated as 0.60 lbf. 
     For comparison, as illustrated in  FIGS.  8  and  9   , and as documented in Table 1, a much smaller maximum compressive load is required when the outer sleeve of the inventive apparatus penetrates the skin. Once again, this is graphically shown by viewing the second peak in each of these figures. This peak illustrates that a compressive load of only about 0.20 to 0.30 lbf is typically required at the insertion point of the outer sleeve. The reduction in force required with the inventive apparatus when compared to the prior art apparatus is dramatically indicated by the absence of the large second peak in the inventive specimens ( FIGS.  8  and  9   ). This indicates a much smoother insertion when compared to the prior art apparatus. The mean value of the maximum compressive load of all thirty of the inventive specimens is indicated as 0.35 lbf. In most of the inventive specimens, the maximum compressive load does not even occur at this outer sleeve insertion point (second peak), but rather, occurs either during the initial puncture, or later during the insertion procedure as the tapered outer sleeve continues to be pushed through the skin. 
     The inventive apparatus comprising the outer sleeve and inner cannula can be provided as a combined apparatus, or as separate components. Similarly, the remaining components discussed herein, such as the wire guide(s) and the needle, can be provided with the outer sleeve and inner cannula as a kit, or as separate components. The individual components are well known, and with the exception of the dimensional differences of the outer sleeve as described, may be formed in conventional manner and of well known compositions. Although the outer sleeve and inner cannula can be formed of any materials suitable for their intended use, preferably they will be formed from a suitable polymer well known for such use, such as polyethylene. 
     It is therefore intended that the foregoing detailed description be regarded as illustrative rather than limiting, and that it be understood that it is the following claims, including all equivalents, that are intended to define the spirit and scope of this invention.