Injection Site For A Flow Conduit

Abstract

An injection site for a fluid flow conduit which comprises a housing and an elastomeric wall maintained within the housing under compression, in which the wall defines a portion of the fluid flow conduit. When a needle penetrates the wall for injection purposes, and is later withdrawn, the compressive force provides a positive seal capable of preventing the leakage of fluid from the conduit, even when the fluid is under positive pressure.

Description

BACKGROUND OF THE INVENTION

Parenteral solution administration equipment and blood flow conduits for solution infusion, blood transfusion, or the conveyance of blood between a patient and an artificial kidney or blood oxygenator, generally require sites where an injection needle can be inserted into the conduit to withdraw samples or to administer medication or the like. When the injection needle is withdrawn it is important that there be no leakage of solution or blood through the needle puncture.

Problems can arise with leakage of blood and solution, particularly when the conduit is under elevated pressure, as in the case of certain blood oxygenation and artificial kidney blood conduits, and in the case of the pressurized administration of parenteral solution or blood to a patient. In this circumstance, the conventional infusion sites, which are commonly latex tubes or bulbs which fit over the respective ends of vinyl conduit tubing, have been known to pop off, causing blood or parenteral solution to spurt out. In the same circumstance, blood and parenteral solution may tend to leak out through the needle punctures of the injection site. Similarly, air may leak through a needle puncture into the blood or solution line if the line is under reduced pressure.

Injection sites in blood or parenteral solution conduits are generally made of natural latex, which has good self-sealing properties, and thus has tended to partially compensate for the disadvantages of the prior art injection sites. However, natural latex is a relatively thrombogenic material, and is undesirable for use in blood flow conduits.

In accordance with this invention, a new injection site is provided having reliable sealing of needle punctures through materials such as silicone rubber, rather than latex or other materials having more pronounced blood clotting tendencies or other biologic incompatibilities.

Furthermore, an improved and more reliable injection site which does not pop apart under internal pressure can be provided by this invention.

Basically, while the prior art latex injection sites have been stretched over vinyl conduits or the like, the needle puncture site used in this invention is not stretched, but is placed under compression in a housing and abutted in an end-to-end relationship with the remaining fluid flow conduit to provide a more reliable high pressure injection site. This injection site can have the added advantage of a smooth bore, free of discontinuities, which discontinuities tend to cause blood to clot, or cause accentuated hemolysis. Furthermore, because of the compressive action in the present invention, blood-compatible, elastomeric materials can be utilized as the needle puncture member, even though their self-sealing capabilities are not the equal of the less biologically compatible latex materials.

DESCRIPTION OF THE INVENTION

The injection site for a fluid flow conduit of this invention comprises a housing, and an elastomeric wall maintained within the housing under compression, the wall defining a portion of the fluid flow conduit. When a needle penetrates the elastomeric wall, for adding a medicament or withdrawing fluid sample, and then is withdrawn, the compression of the elastomeric wall provides a positive seal of the needle puncture.

The injection site can be designed to seal effectively against a wide range of pressures using a wide range of elastomeric materials, depending upon the degree of the compressive force on the elastomeric wall.

Preferably, the elastomeric wall is made of silicone rubber, or similar biocompatible, antithrombogenic, and elastomeric material which does not readily "creep" into permanent deformation under compression.

In the drawings:

FIG. 1 is an elevational view of a preferred embodiment of the fluid flow conduit of this invention.

FIG. 2 is a magnified elevational view of the conduit of FIG. 1 with portions broken away and shown in section.

FIG. 3 is a sectional view taken along line 3--3 of FIG. 2.

Referring to the drawings, fluid conduit 10 is shown. This conduit might be used as part of the system to connect a patient's artery to a blood oxygenator or artificial kidney, or it may also be used as a connection between the aforesaid oxygenator or kidney and a vein of a patient. Similarly, the blood flow conduit might be used as part of the blood flow path in an organ perfusion device, such as the VIACELL.sup.TM organ perfusion system sold by Travenol Laboratories, Inc. of Morton Grove, Ill.

Flow conduit 10 comprises elastomeric tubing 12, 14, which can optionally be terminated with flanges 15 to assist in connecting tubing 12, 14 in sealing, abutting, end-to-end relationship with similarly flanged tubing by means of couplers of the type shown in Argentine Pat. No. 188,952 or U.S. Pat. No. 3,456,965.

Lengths of tubing 12, 14 which are typically made of non-thrombogenic plasticized polyvinyl chloride, have ends 16, 18 conventionally secured by solvent or heat sealing within tubular housing 20, which is typically made of ABS plastic or another strong, generally rigid plastic.

Elastomeric tube 22 is positioned within the bore of housing 20. Tube 22 has an uncompressed outer diameter which is greater than the bore of housing 20, so that when tube 22 is positioned in the bore of housing 20, as shown in the drawings, it is under radial compression. For example, housing 20 may have an outer diameter of 0.375 inch and an inner diameter of 0.298 inch. Tube 22 may have, prior to compression within bore 20, an outer diameter of 0.330 inch and an inner diameter of 0.210 inch, resulting in an uncompressed wall thickness of 0.060 inch. When tube 22 is made of silicone rubber and housing 20 is a rigid material such as ABS plastic, the above specifically designed arrangement will prevent leakage from a needle puncture in the presence of fluid pressures inside conduit 10 of up to about 25 p.s.i.. Preferably, the uncompressed outer diameter of tube 22 should be at least 10 per cent greater than the inner diameter (bore diameter) of housing 20, which, of course, governs and is equal to the compressed outer diameter of tube 22.

The bore diameter of compressed tube 22 is equal to the bore diameters of tubing 12, 14, to provide a smooth fluid flow path free of discontinuities.

Tubular housing 20 and elastomeric tube 22 are typically of circular cross-section, but equivalent structural parts having oval or polygonal cross-sections are contemplated to be within the scope of the invention.

Port 24 in housing 20 provides needle access to tube 22. It is desirable that the dimension of port 24 which is transverse to tube 22 be no more than about 60 percent of the outer transverse dimension (outer diameter) of tube 22, so that the portion of the tube which is exposed by port 24 does not lose an excessive amount of compression by compressive relief provided by port 24. If housing 20 is made of polyethylene, vinyl plastic, or the like, port 24 can be omitted in those cases in which housing 20 is thin enough to permit the needle to penetrate directly through the housing wall, as well as the wall of tube 22.

As an added advantage, housing 20 can be fabricated to prevent injection needles from accidentally passing entirely through the injection site, as frequently happens with the present latex tube sites. This is achieved when port 24 is adjacent a solid, needle-stopping wall 25 on the opposite side of housing 20.

The injection site of this invention can be theoretically designed to prevent leakage from a hypodermic needle injection puncture in tube 22 over a wide range of fluid pressures within bore 21, utilizing a wide range of materials for constructing tube 22, including natural latex, if desired.

The capacity of the injection site of this invention to seal against pressurized fluid after puncture is largely dependent upon the degree of compression of tube 22. The minimum degree of compression needed to seal against any given pressure can be expressed as a minimum difference between the outer diameter of the uncompressed tube 22 and the inner diameter of housing 20 (such difference being defined as the variable D) which provides sealing of a needle puncture at a given internal pressure P within bore 21. This value of D at any given value of P can be approximated by solving the following equation:

D.congruent. bP/E.sub.1 (C.sup.2 + b.sup.2 /C.sup.2 - b.sup.2 + .mu..sub.1)+bP/E.sub.2 (b.sup.2 + a.sup.2 /b.sup.2 - a.sup.2 - .mu..sub.2)

in which a is the radius of the bore of tube 22, b is the radius of the bore of housing 20, and c is the outer diameter of housing 20 (as illustrated in FIG. 3). E.sub.1 is the modulus of elasticity of the material of housing 20, E.sub.2 is the modulus of elasticity of the material of tube 22, .mu..sub.1 is Poisson's ratio of the material of housing 20, and .mu..sub.2 is Poisson's ratio of the material of tube 22.

As stated above, this equation approximates the limiting pressures at which leakage just begins for a compressed tube and housing arrangement made of given materials and having specified dimensions and a specific degree of compression. At significantly lower pressures of P than that used in the equation, there shall be no leakage, either out of hypodermic needle puncture sites or along the surface defined between housing 20 and tube 22. The effect of port 24 is not included in the calculation; it would of course lower the limiting pressure at which leakage would just begin.

Further details on the above equation can be found in the book entitled "Mechanical Engineering Design," by J. E. Shigley, published by McGraw Hill Publishers, N.Y. (1963), pp. 563-565.

Thus, injection sites for fluid flow conduits can be provided in accordance with this invention to resist leakage in the presence of almost any maximum fluid pressure desired. Furthermore, blood contacting portions of the injection site can be made of anti-thrombogenic material to provide the most favorable possible environment for blood which is being passed extracorporeally.

The above has been offered for purposes of illustration only, and is not to be considered as limiting the invention, which is defined in the claims below.

Claims

That which is claimed is:

1. In a fluid flow conduit, an injection site which comprises a housing, and an elastomeric wall maintained under radial compression and enclosed within said housing, said wall along its entire length defining a portion of said fluid flow conduit, and said compression being sufficient to prevent leakage through said wall after said wall is punctured with a needle.

2. The injection site of claim 1 in which the natural, uncompressed dimensions of said wall are at least 10 per cent greater than the compressed dimensions of said wall as maintained in the housing.

3. The injection site of claim 1 in which said wall is made of silicone rubber.

4. In a fluid flow conduit, an injection site which comprises a housing having a bore therein, an elastomeric tube having uncompressed, outer, transverse dimensions greater than the transverse dimensions of said bore, said tube along its entire length defining a portion of said fluid flow conduit, said tube being positioned in said bore under radial compression, and a port in said housing exposing a portion of said compressed tube to the exterior of said housing for access by an injection needle.

5. The injection site of claim 4 in which the uncompressed, outer, transverse dimensions of said elastomeric tube are at least 10 per cent greater than the compressed outer, transverse dimensions of said tube as maintained in said housing.

6. The injection site of claim 4 in which the side of said housing opposite and adjacent said port defines a solid wall to prevent an injection needle in said port from passing completely through said housing.

7. The injection site of claim 5 in which said port has a dimension transverse to said elastomeric tube which is no more than about 60 percent of the outer transverse dimension of said tube compressed in said housing.

8. The injection site of claim 7 in which conduits having bores of identical diameter to the bore of the compressed elastomeric tube are carried in each end of the bore of the housing in abutting relation with the ends of said elastomeric tube, whereby a smooth flow path, free of discontinuities, is defined through said conduits and elastomeric tubes.

9. The injection site of claim 8 in which said elastomeric tube is made of silicone rubber.

10. The injection site of claim 8 in which the uncompressed, outer, transverse dimensions of said elastomeric tube are at least 10 per cent greater than the compressed, outer, transverse dimensions of said tube as maintained in said housing.

11. The injection site of claim 5 wherein said elastomeric tube is made of latex rubber.