ENHANCED INJECTION SITE

Abstract: An improvement has been found to the construction of septums used in a variety of medical applications; for example,injection sites (10) typical in intravenous administration sets and blood collection sets and port closures or stoppers in medical containers. The improvement includes a core portion (22) of the septum (16) of sufficient thickness to improve resealability of the septum (16) resulting in an increase duration of the septum (16) without adversely affecting the forces required to insert and remove a needle through the septum (16).

Description: ENHANCED INJECTION SITE TECHNICAL FIELD This invention relates to an improved septum construction for use in injection sites and closures for a variety of medical applications. BACKGROUND OF THE INVENTION Septum materials of pierceable resilient and resealable compositions have been used for many years in medical applications. For example, such septu s are used in unitary, molded injection sites typical in Y- or T-type sites in intravenous administration sets or in blood collection sets. Septums are also utilized in port closures or stoppers for medical containers or flexible fluid bags. One typical structure of these septums includes a needle-receiving surface integral with a central or core portion, a tail portion and a skirt portion, both carried by the core. Prior to insertion into a tubular housing unit, the tail and skirt portions extend away from the core in opposite directions. As inserted into the housing, the tail is retained in the housing and the skirt is folded back to grippingly contact the outer surface of the housing. The tubular housing then carries the core in compression. Several considerations are given in the construction of such an injection site and stopper. Among these considerations, for example, is the need of the health care professional being able to insert and withdraw a standard hypodermic needle through the site or stopper with relative ease and security. In addition, the septum itself must remain in position within the site or stopper housing despite back pressures which may be created. These forces insertion, removal and push- off depend upon or relate to the compression achieved by the interface between the housing and the septum. The prior art addresses some of these considerations, in particular the insertion force, by suggesting the septum utilized should have reduced effective thickness of material through which the needle must be inserted. For example, U.S. Patent No. 2,372,182 provides a container stopper with a relatively thin centrally located portion which may be readily penetrated or pierced by a hypodermic needle. U.S. Patent 3,017,050 discloses a stopper for a blood sample collection apparatus having a reduced-thickness area created by a central void. The void reduces the effective thickness of rubber through which the needle must be inserted. Further, when a needle pierces the septum it passes through the core portion in order to access the fluid flow path, for example, of an I.V. tube in communication with an injection site housing. As the needle is inserted, it cuts a path through the core. When the needle is withdrawn, the path is generally resealed within the core portion in a reliable manner. Again, this ability to reseal is related to the compression forces exhibited by the site housing on the septum. However, after repeated insertions of a needle, sufficient numbers of paths have been created so that reliable resealability of the septum is questionable. For various reasons, the septum material of these injection sites has a limited life or duration. The duration of a septum can be measured in terms of the number of needle insertions which can be made into the septum before leaking of fluid out of the injection site occurs. Because of this limited duration of the septum material, I.V. administration sets are often recommended and typically used for a maximum of 24 to 48 hours. In addition, the medical community has had to cope with some leaking injection sites in I.V. administration sets and stoppers or closures on flexible medical containers. In accordance with this invention, an improvement to the septum construction has been discovered which has surprisingly resulted in significantly increasing the duration of the septum without adversely effecting the insertion, removal or push-off forces. SUMMARY OF THE INVENTION The septum construction of the subject invention includes a means for providing improved resealability of the septum and creating an increased duration of the septum, without adversely affecting the forces required to pierce and remove a needle through the septum. It has been learned that this means includes the core portion of the septum having a sufficient thickness. Previously, septums were produced with an outer diameter of the core in the approximate range of 1.6 to 1.7 times the core thickness. It has been learned that even a 20% increase in the thickness of the core results in a significant increase in the number of needle insertions before the septum is sufficiently "cored," thereby effecting the resealing integrity of the septum. Contrary to the prior art teachings, such an increase in the core thickness surprisingly does not adversely affect insertion, removal and push-off forces. While it is entirely possible to increase the core thickness 100% so that the core and tail portion of the septum are a solid, uniform section, the insertion and removal forces required for needle insertion through such a solid section may become unacceptable to some health care professionals. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view, partly broken away in vertical section, of a Y-type injection site of an I.V. administration set showing the improved septum design of this invention; FIG. 2 is a cross sectional view of a prior art molded septum before insertion into a tubular housing; FIG. 3 is a cross sectional view of the improved septum of this invention prior to insertion into a tubular housing; FIGS. 4-7 represent the coring effects of repetitive needle insertion and insertion, removal and push-off forces, and septum to shoulder gap manufacturing tolerances of three separate septum samples housed in Y-type injection sites of the general type described in this application. The control group indicated by "." in FIG. 4 or by "Control Group" in FIGS. 5-7, has septums with cores of a commercially available thickness. The second group of septums indicated by "+" in FIG. 4 or by "Variation I" in FIGS. 5-7, has septums with cores approximately 25% thicker than the Control Group. The third group of septums indicated by "*" in FIG. 4 or by "Variation II" in FIGS. 5-7, has septums with cores approximately 50% thicker than the Control Group. DETAILED DESCRIPTION OF THE INVENTION Referring to Figure 1 as an example, a unitary molded Y-type injection site 10 typical of an I.V. administration set, has a tubular housing 12 having at one end an opening 14 adaptable to receiving a septum 16 of the construction of the subject invention. The second end of housing 12 fits integrally with a primary I.V. line, not shown in the Figures, which continues to the distal end of the I.V. administration set. A side branch or arm 18 intercepts housing 12 below opening 14. Both housing 12 and side arm 18 have internal fluid flow paths which are in communication with the flow path of the primary I.V. line, permitting the flow of fluid through the I.V. administration set. Preferably made from a latex material, septum 16 is shown to comprise a central, needle- receiving surface 20 integral with a central or core portion 22 and spanning opening 14. The core 22 having a cylindrical shape, carries a tail portion 24 which extends in a direction away from core 22 and a skirt portion 26 extending in an opposite direction from core 22 relative to tail 24. To install septum 16 into the tubular housing 12, such as the Y-type injection site previously described, the tail 24 of the septum 16 is inserted through opening 14 and is retained in housing 12 by co pressive forces created by the interaction between housing 12 and both tail portion 24 and core 22. Once fully inserted, core 22 is positioned inside housing 12 so that needle-receiving surface 20 spans opening 14. The skirt portion 26 is then folded to grippingly surround the outside of housing 12. The housing 12 is designed to maintain septum 16 in a compressed state, thereby assisting in both the retention and resealability of septum 16, even after repeated insertions of a needle. To assist in achieving the necessary compression, the inner diameter of the housing 12 and the outer diameter of the core 22. re appropriately sized as one skilled in the art can appreciate, to achieve the compression state sought. Typically, currently available injection site products have a gap 28 of minimal size. The sizing of housing 12 and core 22 take into consideration the typical manufacturing tolerances of gap 28 which adversely effects the retention of the compressed state for resealability. To further assist in the retention of septum 16, shrink bands, not shown in the Figures, are often positioned circumferentially about folded skirt portion 26. In this manner shrink bands reside on the outside of the entire structure to serve as a compression member to the entire assembly. Shown in Figure 2, previous septums 16* were produced with cores 22' having an outer diameter of the core 1.5 times greater than the core thickness. By increasing the thickness of the core by preferably 20-50% without other dimensional changes, significant increases are observed in the number of needle insertions prior to fluid leakage occurrences. Preferably, the increase to the thickness results in a total core thickness ranging from approximately 0.14 to 0.18 inch where an outer diameter of the core is approximately 0.18 to 0.19 inch. In addition, the critical sizing of gap 28 has greater flexibility or higher tolerance, from a manufacturing perspective, since a greater length of the core 22 is in a compressed state. Figure 4 represents the percent of units which leak after repeated needle insertions, as observed in three different septum groups housed in Y-type injection sites of the general type described in this application. Repetitive insertion of a needle into a septum is known to cause physical damage to the septum. This damage, known in the medical community as coring or laceration, can result in subsequent leakage through the septum. The data represented in Figure 4 relates the number of needle insertions possible before each of the different septum groups is sufficiently cored so that resealing integrity is effected. From the Weibull plot of this data, a decrease in leaking units is observed as the core of the septum tested is increased in thickness, thereby indicating a longer duration of the septum with the increase thickness in the core. Figure 5 represents the same three septum groups with regard to the insertion force, as measured in pounds, required to insert a standard 18 gauge hypodermic needle into each of the septum groups. The data of this Figure represents the mean insertion force with a 90% confidence level. Despite the significant increases to the septum thickness, the increase in the insertion force remains minimal. Figure 6 represents data obtained on the same three septum groups with regard to the removal force, as measured in pounds, required to remove a standard 18 gauge hypodermic needle from each of the septum groups. The data of this Figure represents the mean removal force with a 90% confidence level. Similar to the results for insertion force, a significant increase in the septum thickness resulted in a minimal increase in removal force. Figure 7 represents the push-off force, with 90% confidence levels, which is required to physically remove the three different septums from the Y-type injection site housing of the general type described in this application. Measured in pounds, the data indicates that minimal reduction in push-off force is observed with an increase septum thickness. Concluding from this functional data, one skilled in the art can appreciate that the minimal performance differences between septum groups II and III indicates that a greater variation in gap sizing can be tolerated in the manufacturing environment. While specific embodiments have been illustrated and described, numerous modifications come to mind without significantly departing from the spirit of the invention, and the scope protection is only limited by the scope of the accompanying claims. For example, the housing of the septum need not be strictly tubular in shape provided that the septum is held by compression with an interface of the housing.

Claims: CLAIMS What we claim is: 1. A unitary, molded injection site having a generally tubular housing with outer and inner surfaces and one end defining an opening adaptable to receiving and retaining under compression a resealing, needle-pierceable, resilient septum comprising a central, needle-receiving surface spanning the opening; a core portion integral with the needle- receiving surface having a cylindrical shape for compressive retention in the housing and having a sufficient thickness to provide improved resealability of the septum, creating an increase duration of the septum without adversely effecting the force required to pierce and remove a needle through the septum; an annular tail portion carried by the core and extending in a direction away from the core for insertion into and compressive retention in the housing; an annular skirt portion carried by the core and extending in an opposite direction from the core relative to the tail portion prior to the insertion of the tail portion into the tubular housing, the skirt portion folding to surround and gripping contact the outer surface of the tubular housing. 2. The septum of claim 1 wherein an outer diameter of the core portion is no greater than 1.4 times the thickness of the core portion. 3. The septum of claim 1 wherein an outer diameter of the core portion is no less than 1.0 times thickness of the core portion. 4. The septum of claim 1 wherein an outer diameter of the core portion ranges from 1.0 to 1.4 times the thickness of the core portion. 5. The septum of claim 1 wherein the thickness of the core portion is at least 0.14 inch and the outer diameter of the core portion is at least 0.18 inch. 6. The septum of claim 1 wherein the thickness of the core portion is at least 0.14 to 0.18 inch and the outer diameter of the core portion is at least 0.188 inch. 7. A unitary, molded injection site having a generally tubular housing with outer and inner surfaces and one end defining an opening adaptable to receiving and retaining under compression a resealing, needle-pierceable, resilient septum having a core portion with a cylindrical shape for compressive retention in the housing comprising an outer diameter of the core portion ranging from approximately 1.0 to 1.4 times a thickness of the core portion. 8. The septum of claim 7 wherein the outer diameter of the core portion is approximately 1.4 times the thickness of the core portion. 9. The septum of claim 7 wherein the thickness of the core portion is at least 0.14 to 0.18 inch and the outer diameter of the core portion is at least 0.188 inch. 10. The septum of claim 7 wherein the core portion is of a sufficient thickness to provide improved resealability of the septum, creating an increase duration of the septum without adversely effecting the force required to pierce and remove a needle through the septum. 11. A unitary, molded injection site having a generally tubular housing with outer and inner surfaces and one end defining an opening adaptable to receiving and retaining under compression a resealing, needle-pierceable, resilient septum comprising a central, needle-receiving surface spanning the opening; a core portion integral with the needle- receiving surface having a cylindrical shape for compressive retention in the housing, the core portion including means for providing improved resealability of the septum and creating an increase duration of the septum without adversely effecting the force required to pierce and remove a needle through the septum; an annular tail portion carried by the core and extending in a direction away from the core for insertion into and compressive retention in the housing; an annular skirt portion carried by the core and extending in an opposite direction from the core relative to the tail portion prior to the insertion of the tail portion into the tubular housing, the skirt portion folding to surround and gripping contact the outer surface of the tubular housing. 12. The septum of claim 11 wherein the means comprises an outer diameter of the core portion no greater than about 1.4 times than a thickness of the core portion. 13. The septum of claim 11 wherein the means comprises an outer diameter of the core portion of no less than about 1.0 times a thickness of the core portion. 14. The septum of claim 11 wherein the means comprises an outer diameter of the core portion from about 1 to 1.4 times a thickness of the core portion. 15. The septum of claim 11 wherein the means comprises the core portion having a thickness of at least about 0.14 inch and an outer diameter at least about 0.18 inch. 16. The septum of claim 11 wherein the means comprises the core portion having a thickness from about 0.14 to about 0.18 inch and an outer diameter about 0.188 inch.

Inventors: LAL BIRENDRA K, RICHARDSON JAMES, LAL, BIRENDRA, K., RICHARDSON, JAMES
Applicants: BAXTER INT, BAXTER INTERNATIONAL INC.
Application year: 1992
Main classification: A61M5
IPC codes: A61J1, A61M39