Abstract:
An infusion set for administration of fluid to a subcutaneous layer includes a cannula housing adapted for mounting onto a patient&#39;s skin and a needle housing for connection to the cannula housing. The needle housing has a pair of flexible sidewalls and a resilient band connected to the sidewalls. The resilient band is lockably engageable with the cannula housing to thereby secure the housings together, and is releasable from the cannula housing when the sidewalls are pressed toward each other to deform the resilient band. A hollow needle extends out of a main body of the needle housing for delivering fluid to the cannula from a fluid source. The walls of the needle housing extend beyond a distal end of the hollow needle to prevent needle contact with contaminated surfaces and inadvertent injury.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to medical devices, and more particularly to a low profile infusion set for intermittent or continuous subcutaneous administration of medication or other substances beneficial to health. 
     2. Description of the Related Art 
     Frequent or continuous subcutaneous injection of medication is often accomplished through the use of an infusion set or injection port which may remain in place for several days. In the case of frequent injections, this reduces the need to constantly puncture the skin and thereby reduce the chance of infection and the formation of scar tissue. For continuous subcutaneous delivery of medication such as commonly used with portable insulin pumps, an infusion set is often used to provide a method of temporarily detaching the pump and fluid line for activities such as dressing or bathing. It is also desirable in this instance to detach the fluid line from the pump as close to the injection site as possible leaving a relatively small component attached to body to minimize the interference during dressing, bathing or other activities. 
     While devices for this purpose have been proposed, these devices have limitations making them less than ideal in practice. By way of example, U.S. Pat. No. 4,755,173 issued to Konopka et al. on Jul. 5, 1988, discloses a soft cannula subcutaneous injection set that relies on a length of tubing with a separate fluid connector for detachment from the source of medication. No provision is provided for disconnecting the fluid tubing from the injection site. The tubing must either be secured to the body with additional adhesive tape or left to awkwardly hang from the injection site where it has a tendency to snag on clothing. 
     U.S. Pat. No. 5,545,143 issued to Fischell on Aug. 3, 1996, describes a device for the subcutaneous delivery of medication. This device includes a short tubular extension with a connector to the main body of the device which eliminates the tubing but makes the overall package long and somewhat bulky. 
     U.S. Pat. No. 5,522,803 issued to Teissen-Simony on Jun. 4, 1996, discloses an infusion set that overcomes some of the problems with the other devices but presents it&#39;s own disadvantages. Namely, the infusion needle is not covered for protection against accidental needle sticks or contamination. Also, the cannula housing and needle hub are difficult to align and connect without being directly viewed by the user. This is especially a problem for diabetics with impaired vision. In addition, the guide pins and locking pins of this patent form multiple sharp projecting points which are susceptible to bending or breakage or accidentally poking the user, especially when connecting to injection sites not in the user&#39;s direct line of sight. 
     U.S. Pat. No. 6,056,715 issued to Funderburk et al. on May 2, 2000, discloses an infusion set that is similar to U.S. Pat. No. 5,522,803 and has some of the same problems and disadvantages, particularly in respect to alignment and use of the latch arms and locking fingers which must bend and are susceptible to breaking. 
     SUMMARY OF THE INVENTION 
     According to one embodiment of the invention, an infusion set comprises a cannula housing adapted for mounting onto a person&#39;s skin and a needle housing for connection to the cannula housing. The cannula housing has a locking element positioned thereon. A cannula is connected to the cannula housing and extends therefrom. The needle housing has at least a first flexible sidewall and a resilient band connected to the sidewall for deformation upon deflection of the sidewall. The resilient band is lockably engageable with the locking element to thereby secure the housings together, and is releasable from the locking element upon deflection of the sidewall to thereby deform the resilient band out of locking engagement with the locking element. A hollow needle extends through the needle housing for delivering fluid to the cannula from a fluid source. 
     According to a further embodiment of the invention, an infusion set comprises a cannula housing adapted for mounting onto a patient&#39;s skin and a needle housing adapted for connection to the cannula housing. A cannula is connected to the cannula housing and extends therefrom. A hollow needle for delivering fluid to the cannula from a fluid source extends from a main body of the needle housing such that a distal end of the hollow needle is spaced from the main body. The needle housing further has first and second sidewalls and an upper wall that extends from the main body beyond the distal end of the hollow needle to thereby prevent inadvertent contact of the hollow needle with contaminated surfaces when the needle housing is separated from the cannula housing. 
     Other objects and advantages of the invention will become apparent upon review of the following detailed description and appended claims, with reference to the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The preferred embodiments of the present invention will hereinafter be described in conjunction with the appended drawings, wherein like designations denote like elements, and wherein: 
     FIG. 1 is a top plan view of the assembled infusion set according to the invention, with a flexible plastic tubing and luer coupling connected at opposite ends of the infusion set; 
     FIG. 2 is a side elevational view of the assembled infusion set in FIG. 1 showing the inserted cannula in a cross section of the skin; 
     FIG. 3 is a top plan view of the assembled infusion set absent a mounting pad; 
     FIG. 4 is rear elevational view of the assembled infusion set of FIG. 3, absent the luer coupling; 
     FIG. 5 is a cross sectional view of the assembled infusion set taken along line  5 — 5  of FIG. 3; 
     FIG. 6 is a top plan view of a cannula housing that forms part of the infusion set of FIG. 1; 
     FIG. 7 is a cross sectional view of the cannula housing taken along line  7 — 7  of FIG. 6; 
     FIG. 8 is a side elevational view of the cannula housing; 
     FIG. 9 is a cross sectional view of the cannula housing taken along line  9 — 9  of FIG. 8; 
     FIG. 10 is a rear elevational view of the cannula housing shown in FIG. 8 in the direction of arrow A; 
     FIG. 11 is a top plan view of a needle housing that forms part of the infusion set of FIG. 1; 
     FIG. 12 is a cross sectional view of the needle housing taken along line  12 — 12  of FIG. 11; 
     FIG. 13 is a side elevational view of the needle housing; 
     FIG. 14 is a front elevational view of the needle housing; 
     FIG. 15 is a bottom plan view of the needle housing; 
     FIG. 16 is a cross sectional view of the needle housing taken along line  16 — 16  of FIG. 13; 
     FIG. 17 is a top plan view of an insertion needle housing connected to the cannula housing; 
     FIG. 18 is a side elevational view of the insertion needle housing connected to the cannula housing; 
     FIGS. 19A and 19B are side elevational views of a cannula and ferrule associated with the cannula housing and their method of assembly according to a further embodiment of the invention; 
     FIG. 20 is a cross sectional view similar to FIG.  5  and illustrating a further embodiment of the invention for retaining the cannula and a septum associated with the cannula in the infusion set; 
     FIG. 21 is a top plan view of an insertion needle housing according to a further embodiment of the invention connected to the cannula housing; 
     FIG. 22 is a side elevational view of the insertion needle housing and cannula housing of FIG. 21; 
     FIGS. 23A and 23B and are side elevational views of a ferrule according to a further embodiment of the invention and the manner in which the cannula is joined to the ferrule; and 
     FIG. 24 is a cross sectional view similar to FIG.  20  and illustrating the cannula and ferrule of FIGS. 23A and 23B mounted in the infusion set; 
     FIG. 25 is a top plan view of the assembled infusion set similar to FIG.  1  and illustrating a further embodiment of the invention; 
     FIG. 26 is a top plan view of a needle housing that forms a part of the infusion set of FIG. 25; 
     FIG. 27 is a side elevational view of the needle housing; 
     FIG. 28 is a front elevational view of the needle housing; 
     FIG. 29 is a perspective view of an assembled infusion set; 
     FIG. 30 is a perspective view of the cannula housing with the needle housing removed; and 
     FIG. 31 is a prospective view of a needle housing of a different embodiment of the invention removed from the cannula housing. 
    
    
     It is noted that the drawings are intended to depict only typical embodiments of the invention, and therefore should not be considered as limiting the scope thereof. The invention will now be described with additional detail with particular reference to the drawings. 
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring now to the drawings, and to FIGS. 1 and 2 in particular, an infusion set  10  according to the invention includes a cannula housing  12  releasably connected to a needle housing  14 . The needle housing  14  may be released from the cannula housing  12 , as will be described in greater detail below, for activities such as bathing, dressing, or the like. A flexible cannula  16  is connected to the cannula housing  12 . The cannula  16  is adapted to extend through the epidermis layer  22  and dermis layer  24  at an acute angle with respect to the epidermis layer, with an outer free end  17  of the cannula located in the subcutaneous fat layer  26  between the dermis layer  24  and muscle layer  28  for delivering medication or the like to the subcutaneous layer  26 . A length of flexible tubing  18  with a fluid connector or Luer fitting  20  is connected to the needle housing  14 . The fluid connector  20  is adapted for connection to a source of medication, such as insulin, or other fluids associated with health care for delivery of the fluids to the subcutaneous layer  26  through the housings  12 ,  14  and the cannula  16 . 
     The particular configuration of the connected housings  12 ,  14  lends well to reducing the overall size of the infusion set  10  over prior art devices. By way of example, the dimensions may be approximately 16.5 mm wide by 20 mm long by 7 mm high. Cooperating connection members located in the housings (described in greater detail below) afford relatively easy connection and disconnection of the housings, despite the small overall size. It is to be understood that the overall size of the assembled housings may be larger or smaller than the stated dimensions. 
     A mounting pad  30  is connected to a bottom surface  32  (FIG. 3) of the cannula housing  12 . The mounting pad  30  preferably includes an adhesive layer (not shown) for attaching the infusion set  10  to the epidermis layer  22  of a person. The cannula  16  extends through an opening  34  in the mounting pad  30  when the outer free end  17  of the cannula is located in the subcutaneous layer  26 . 
     With reference now to FIGS. 6 through 10, the cannula housing  12  includes a main body portion  38  with series of collinear stepped bores  40 ,  42  and  44  of increasing diameter formed therein. The bore  40  is the smallest in diameter and extends from a forward end  46  of the cannula housing  12  to the bore  42 . The bore  42  in turn extends between the bores  40  and  44 . The bore  44  opens at a rearward end  48  of the cannula housing  12 . The bores may extend at an angle of about 0° (parallel to the bottom  32  surface) to about 30° with respect to the bottom surface  32 , and preferably extend at an angle of approximately 7°. The choice of angle is determined by these considerations. Smaller angles allow the overall height of the assembled infusion set to be minimized for a given bore size, but angling the bore with respect to the bottom  32  minimizes the bending of the cannula and allows the cannula to exit the cannula housing closer to the bottom surface, thereby minimizing the exposure of the cannula above the skin. The preferred angle of 7° provides a reasonable compromise of the desirable properties. Alignment grooves  45 ,  47  are formed on each side of the cannula housing  12 . The alignment grooves  45 ,  47  preferably extend at the same angle as the bore  40  with respect to the bottom surface  32 , for aligning the needle housing  14  with the cannula housing  12  during assembly. A small protrusion  49  and groove  51  are formed on the top surface of the main body to lock the housings  12 ,  14  together, as will be described in greater detail below. The cannula housing  12  may be injection molded from a plastic, such as polypropylene, polycarbonate, or polyurethane. 
     As shown in FIG. 5, a stepped ferrule  50  is located in the bores  42  and  44 . The cannula  16  is fixedly mounted to the ferrule  50  and extends through the bore  40  and outwardly from the forward end  46  a predetermined distance. Preferably, the cannula extends approximately 15 mm beyond the forward end  46  of the cannula housing  12 . This length may vary greatly depending on the type of application, the thickness of body layers, and the location of the infusion set when mounted. 
     A self-sealing elastomeric septum  52  is sandwiched between the ferrule  50  and a septum retainer  54  in the bore  44 . The septum  52  has a self-closing aperture  56  that is preferably collinear with a central axis of the bores  40 ,  42  and  44  to seal the mounted end of the cannula  16  against the ingress of contaminants and the egress of fluids. The septum retainer  54  also includes an aperture  58  in alignment with the aperture  56 . A hollow needle  60  extends through the apertures  58  and  56  during use for delivering medication or other substances to the cannula  16  from the fluid source. The septum retainer  54  includes a protrusion  62  that engages a resilient locking tab  66  within an opening  64  at the bottom of the cannula housing  12  to hold the retainer  54 , and thus the ferrule  50  and septum  52 , within the housing  12 . Alternatively, the septum retainer can be bonded, ultrasonically welded, or retained by a snap fit or heat staking in the housing  12 . 
     The ferrule  50  can be molded from a plastic material such as polypropylene or polycarbonate, or formed from a bio-compatible metal (e.g. American Society for Testing and Materials (ASTM) grade 304 stainless steel). The elastomer septum can be constructed of a medical grade silicone rubber. The cannula retainer can also be molded from a plastic material such as polypropylene or polycarbonate. 
     During assembly, the cannula  16 , ferrule  50 , septum  52 , and septum retainer  54  are inserted into the bore  44  of the cannula housing  12  with the distal end  17  of the cannula extending out of the forward end  46  of the housing. An inner connection end of the cannula is preferably connected to the ferrule, but may alternatively be directly connected to cannula housing  12 . 
     With particular reference now to FIGS. 11 through 16, the needle housing  14  includes a main body portion  70  with a pair of collinear stepped bores  72 ,  74  of increasing diameter formed therein. The bore  72  is the smallest in diameter and extends from a forward end  76  of the main body  70  to the bore  74 . The bore  74  in turn extends between the bore  72  and the rearward end  78  of the needle housing  14 . The bores  72 ,  74  may extend at an angle of about 0° (parallel to the bottom surface  32 ) to about 30° with respect to the bottom surface  32  of the cannula housing  12  when assembled, and preferably extend at an angle of approximately 7°. The needle  58  extends through the bore  72  with an outer end of the needle extending forwardly of the bore  72 . Likewise, the tubing  18  is positioned in the bore  74  and extends outwardly from the rearward end  78  of the needle housing  14 . An upper wall  88  is formed with the main body portion  70  and extends forwardly therefrom. Guide rails  80  and  82  protrude generally downwardly from opposite sides  84  and  86 , respectively, of the upper wall  88 . Each guide rail includes a relatively straight portion  90  that terminates in a semi-cylindrical portion  92 . The semi-cylindrical portions  92  are adapted to slidably engage the to alignment grooves  45 ,  47  of the cannula housing  12  during assembly for aligning the needle housing  14  with the cannula housing  12 . The needle housing is preferably molded of a flexible, resilient plastic material such as polypropylene, polycarbonate, or polyurethane. 
     In an alternative embodiment, the cross sectional shape of the guide rails and alignment grooves can be square, rectangular, triangular, rounded, or any other suitable shape. Clearance between the guide rails and alignment grooves is preferably on the order of about 0.05 mm to accurately locate the needle  58  with the septum  52  but still enable the needle housing  14  to slide freely on the cannula housing  12 . 
     Resilient sidewalls  94  and  96  are formed at opposite sides  98  and  100 , respectively, of the main body portion  70 . The resilient sidewalls  94  and  96  extend forwardly of the forward end  76  and generally parallel to the sides  84  and  86 , respectively, of the upper wall  88 . The forward ends of the sidewalls  94 ,  96  are joined together by a resilient, arcuate locking band  102 . The band  102  is curved generally upwardly and is adapted to seat within the groove  51  when the housings  12  and  14  are assembled to thereby lock the housings together. A slot  104  is located between the upper wall  88 , the resilient sidewalls  94 ,  96  and the resilient band  102 . The sidewalls  94  and  96  flex inwardly toward each other but are preferably relatively stiff in bending in all other planes. In order to reduce the overall length of the assembled housings, a notch  106  is formed in the upper wall  88  to provide clearance for the protrusion  49 . 
     The upper wall  88  has a sufficient length and the sidewalls  94 ,  96  and guide rails  80 ,  82  have a sufficient height to extend beyond the end of the needle  58 . In this manner, the needle  58  is well shielded to prevent contact with contaminated surfaces and accidental needle punctures when the needle housing  14  is disconnected from the cannula housing  12 . 
     With reference now to FIGS. 1,  3  and  5 , during connection of the needle housing  14  with the cannula housing  12 , the guide rails  80 ,  82  of the needle housing engage the alignment grooves  45 ,  47 , respectively, of the cannula housing to pre-align the needle  58  with the aperture  56  of the septum  52  before the septum is penetrated by the needle. As the needle housing slides onto the cannula housing, the resilient band  102  of the needle housing deflects upwardly over the protrusion  49  of the cannula housing, causing deflection of the sidewalls  94 ,  96  toward each other. Once the band  102  passes over the protrusion  49 , it snaps back to its undeflected position in the groove  51  to thereby lock the housings together. This also results in an audible click or snapping sound which reassures the user that a secure connection has been made. 
     In order to disconnect the needle housing  14  from the cannula housing  12 , the sidewalls  94 ,  96  are squeezed toward each other with finger pressure to thereby deflect the resilient band  102  above the protrusion  49  on the cannula housing. This allows the needle housing to slide freely off the cannula housing. 
     The protrusion  49  on the cannula housing  12  preferably has a smooth, rounded rear side  108  (FIG. 6) that blends with the top surface of the cannula housing and a relatively flat forward side  110  nearest the cannula  16 . When viewed from above, the base of the protrusion is semi-circular with the forward side adjacent the resilient band  102  to thereby hold the band in the groove  51 . The rounded shape of rear side  108  allows the band  102  to be pushed and flexed over the protrusion  49  without squeezing the sidewalls  94 ,  96  together. Depending on the amount of sidewall movement desired, the height of the protrusion  49  above the top surface of the cannula housing can be varied in order to vary the amount of band deflection. The height of the protrusion  49  may be approximately equal to the band thickness. In one exemplary embodiment, the band thickness and the protrusion height is about 0.75 mm to thereby securely lock the housings and permit easy release of the housings when desired. 
     While it is possible to use a single flexible sidewall connected through the resilient gee band to a fixed sidewall or other member, the dual flexible sidewalls  94 ,  96  provide a degree of safety against accidental release. Since both sidewalls  94 ,  96  must be simultaneously squeezed toward each other, the needle housing  14  will not be released if one sidewall is inadvertently pressed, since both sidewalls would deflect in the same direction and fail to deflect the resilient band  102 . 
     As shown in FIG. 11, disconnection of the needle housing  14  from the cannula housing  12  can be facilitated by arranging the forward ends of the flexible side members  94 ,  96  to be narrower in width (in the plane of the skin) than the than the rearward end  108  of the needle housing. This could be achieved in a number of ways such as making the overall shape of the housing tapered towards the resilient band  102  so that the user would grip the narrower end and pull towards the wider end of the needle housing. According to a preferred embodiment, curved finger recesses  110  are formed on the flexible members at the forward end of the needle housing adjacent the resilient band  102  to thereby provide a natural location for finger and thumb placement when disconnecting the needle housing. The grip may also be enhanced by providing small serrations  112  in the curved recesses. 
     Referring again to FIG. 5, while the cannula  16  can be molded as an integral part of the cannula housing, fabricating the cannula separate from the cannula housing is preferred since the material used for each component can be optimized. The cannula  16  is preferably a thin walled, bio-compatible tube constructed of Teflon, such as polytetrafluorethylene, or other suitable material. Where Teflon tubing is used, it may be necessary to pretreat the attachment end of the cannula prior to adhesively bonding the cannula to the cannula housing  12 . Alternatively, the cannula can be bonded to the ferrule  50 . Although the size of the cannula can vary, an outside diameter of approximately 0.6 mm is preferred. 
     With particular reference to FIGS. 19A,  19 B and  20 , a further embodiment for connecting the cannula  16  to the cannula housing  12  is shown, wherein like parts in the previous embodiment are represented by like numerals. In this embodiment, a ferrule  120  includes a barb  122  for receiving a heat-shrink tubing  126 , which is preferably constructed of Teflon. A removable metal mandrel  124  that is substantially equivalent in diameter to an insertion needle  130  (FIG. 17) is inserted through the ferrule  120  and heat-shrink tubing  126 . Heat is then applied to the tubing  126 , causing it to shrink and deform around the barb  122  of the ferrule and the mandrel  124 . Due to the relatively low coefficient of friction associated with the Teflon material, the mandrel  124  is easily removed in a direction denoted by arrow  128  in FIG.  19 B. In this manner, the heat-shrink tubing  126  forms the cannula  16 , which is tightly held on the ferrule  120 . The ferrule and attached cannula  16  can then be installed in the cannula housing  12  together with the septum  52  and septum retainer  54 . As shown in FIG. 20, the retainer  54  is cylindrical along a substantial portion of its length, and includes a frustro-conical end portion  132  that faces rearwardly with respect to the cannula housing  12 . The rearward end  48  of the cannula housing  12  is then deformed over the frustro-conical end portion  132 , such as by heat staking, in order to permanently mount the cannula, ferrule, septum, and septum retainer in the cannula housing. 
     Referring now to FIGS. 23A,  23 B and  24 , a further embodiment for connecting the cannula  16  to the cannula housing  12  is shown, wherein like parts in the previous embodiments are represented by like numerals. In this embodiment, a ferrule  140  is provided with a hollow shaft portion  142  and a hollow conical portion  144  connected to one end of the shaft portion. The inner diameter of the shaft portion is preferably slightly greater than the outer diameter of the insertion needle  130  (FIG. 17) so that the insertion needle is free to slide within the ferrule  140 . In order to install the cannula  16  on the ferrule  140 , an attachment end  146  of the cannula  16  is heated to soften the attachment end. The shaft portion  142  is then inserted into the attachment end  146 , thereby expanding the diameter of the attachment end and creating a tight seal between the cannula  16  and the ferrule  140 . As shown in FIG. 24, the septum  52  acts as a biasing member to press the expanded attachment end  146  against the opening of the bore  40  to thereby form a compression seal. 
     With reference now to FIGS. 17 and 18, an insertion needle housing  150  for use with the cannula housing  12  is illustrated. The insertion needle housing  15  generally resembles the needle housing  14 , with the exception that a handle  152  is formed at the rearward end  78  of the housing, and an insertion needle  130  is provided. The needles used in both the needle housing and insertion needle assembly are preferably  27  gauge stainless steel tubing (ASTM grade 304) beveled at one end to create a sharp angled edge. As shown, the handle is generally hour-glass in shape with a gripping surface  154  located between the rearward end  78  and an enlarged head  156 . The hourglass shape of the handle  152  improves the grip during installation of the cannula  16  in the skin and mounting of the cannula housing  12  on the skin. 
     When the insertion needle assembly is connected to the cannula housing assembly with the same guide rail, sidewall and band configuration as the needle housing  12 , the end of the insertion needle  130  extends beyond the outer free end of the cannula  16 , which may be about 2 or 3 mm. The handle  152  on the insertion needle housing  150  allows the combined assembly of the insertion needle housing  150  and cannula housing  12  to be grasped with one hand while pinching a fold of skin with the other hand. The combined assembly can then be pressed into the pinched skin until the needle  130  punctures the skin along with the cannula. The mounting pad  30  can then be attached to the surface of the skin. This may be accomplished by removing a protective backing layer (not shown) to expose an adhesive layer on a lower surface of the mounting pad. Once the cannula housing  12  and cannula  16  are properly mounted, the insertion needle housing  150  is removed by pinching the resilient sidewalls  94 ,  96  to release the band  102  from the groove  51  in the cannula housing  12 . The needle housing  14  can then be attached to the cannula housing  12  to begin delivery of the medication or other fluid. 
     With reference now to FIGS. 21 and 22, an insertion needle housing  160  according to a further embodiment of the invention for use with the cannula housing  12  is illustrated, wherein like parts in the previous embodiments are represented by like numerals. The insertion needle housing  160  is substantially similar to the insertion needle housing  150 , with the exception that a handle  162  has a different configuration than the handle  152 . As shown, the handle  162  is generally rectangular and includes first, second and third gripping surfaces  164 ,  166 , and  168 , respectively. The gripping surfaces are preferably curved generally inwardly to thereby prevent or reduce inadvertent slipping during mounting of the cannula housing  12  and cannula  16 . 
     With reference now to FIGS. 25,  26 ,  27  and  28 , an infusion set  180  according to a further embodiment of the invention is illustrated, wherein like parts in the previous embodiments are represented by like numerals. The insertion needle housing  182  is substantially similar to the insertion needle housing  14 , with the exception that the housing has only one resilient sidewall  183  formed at one side  184  of the main body portion  70 . Except for the use of only one resilient sidewall, the needle housing  182  is structurally the same as the needle housing  14 , or may, if desired, the needle housing  14  may have the structure of the other alternative embodiments described herein. The forward end of resilient sidewall  183  is joined to curved band  102  which is adapted to seat within a groove in the cannula housing  12 . The needle housing  182  is joined to the cannula housing  12 . During connection of the needle housing  180  with the cannula housing  12 , the guide rails  80 ,  82  of the needle housing engage the alignment grooves  45 ,  47 , respectively, of the cannula housing to pre-align a needle (not shown) with the aperture of the septum before the septum is penetrated by the needle. As the needle housing slides into the cannula housing, the resilient band  102  of the needle housing deflects upwardly over the protrusion  49  of the cannula housing, causing deflection of the single sidewall  183  laterally inward. Once the band  102  passes over the protrusion  49 , it snaps back to its undeflected position in the groove to thereby lock the housings together. This also results in an audible click or snapping sound which reassures the user that a secure connection has been made. 
     To disconnect the needle housing  180  from the cannula housing  12 , the one sidewall  183  is squeezed laterally inward with finger pressure to thereby deflect the resilient band  102  above the protrusion on the cannula housing. This allows the needle housing to slide freely off the cannula housing. 
     Finally, for ease of further understanding the invention, FIG. 29 is a perspective view  10  of the assembled infusion set illustrated in FIGS. 1 through 16. FIG. 30 is a perspective of the cannula housing with the needle housing removed to better show how the parts fit together. 
     FIG. 31 is a perspective view of the needle housing shown in FIGS. 20 and 21, again, to better show the operability of the device. 
     While the invention has been taught with specific reference to the above-described embodiments, those skilled in the art will recognize that changes can be made in form and detail without departing from the spirit and the scope of the invention. Thus, the described embodiments are to be considered in all respects only as illustrative and not restrictive. The scope of the invention is, therefore, indicated by the appended claims rather than by the foregoing description. All changes that come within the meaning and range of equivalency of the claims are to be embraced within their scope.