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Description  |
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BACKGROUND OF THE INVENTION
The invention herein is directed to a self-sealing subcutaneous injection
site. The injection site provides a resealable puncture housing for
surgical implantation.
Implantable injection sites are used in patient treatment techniques
wherein it is desirable or necessary to administer or withdraw a fluid to
a site within a patient. Subcutaneous injection sites can be used in
combination with skin expanders or inflatable mammary prostheses. The use
of a subcutaneous injection site with such skin expanders and prostheses
provides a means for introducing additional inflationary fluid to either
the skin expander or mammary prosthesis which can be interconnected to the
subcutaneous injection site. The use of a subcutaneous injection site for
such medical devices provides an ambulatory condition to the patient as
the patient can continue about their normal function and call upon the
physician only at the time additional fluid needs to be administered or
withdrawn. The use of a subcutaneous injection site in association with a
skin expansion chamber is described in U.S. Pat. No. 4,217,889 to Radovan.
The subcutaneous injection site can also be used for the administration of
medication to a patient. For example, in many therapeutic procedures there
is a need to implant a drug delivery device. Such an implantable drug
delivery device provides a bolus or therapeutic dose of the drug contained
therein to a particular location within the patient's body. In order to
replenish the drug in the implanted device, a self-sealing subcutaneous
injection site can be provided in fluid communication with the drug
delivery device. In some instances, a self-sealing subcutaneous injection
site can itself be the drug delivery device. The self-sealing subcutaneous
injection site provides a means for administering additional medicament
into the device as the medicament can be injected using a syringe inserted
subcutaneously into the injection site without the need for a subsequent
surgical procedure.
Resealable puncture housing for surgical implantation are disclosed in U.S.
Pat. No. 3,310,051; U.S. Pat. No. 3,831,583; and U.S. Pat. 4,190,040. U.S.
Pat. No. 3,310,051 describes a silicone capsule for implantation beneath
the skin into which fluid can be injected or withdrawn by hypodermic
syringe. The puncturable capsule described therein works well when
connected to a ventricular catheter for removing or injecting fluid into a
patient's brain. However, if a high pressure is experienced by the fluid
within the capsule, then the housing for such capsule can leak at the
needle puncture sites, thereby causing the fluid within the capsule to
flow into the surrounding tissue.
U.S. Pat. No. 3,831,583 describes a plug-shaped capsule that contains a
silicone gel for resealing needle punctures of the surgically implanted
capsule. The shape and dimension of the plug-like sealant chamber on such
an implantable housing is not conveniently usable with the injection angle
commonly used for nurses and physicians. In many instances, it is
difficult to palpate and locate the particular plug-like chamber. To gain
control over subcutaneous injections, the hypodermic needle is frequently
placed at a widely angled position almost parallel to the skin. This gives
the operator better control of the injection point and puncture depth than
a position more perpendicular to the skin. Thus, the device of U.S. Pat.
3,831,583 is not ideally suitable for use.
The implantable resealable puncture housing disclosed in U.S. Pat. No.
4,190,040 was an improvement over the previous implantable resealable
puncture housings. The housing in this patent utilizes a laminated
structure wherein a silicone gel is sandwiched between two silicone
layers. Such a device did provide for a more varied angle of penetration
for a hypodermic needle being inserted into the chamber. However, the
housing is not ideally structured for repeated puncturing with hypodermic
needles as if a large number of punctures are desired, gel bleed from the
housing can occur. In such instances, it is undesirable to have silicone
gel flow into the surrounding tissue. In addition, such a device after
repeated puncturing does not provide for effective sealing, particularly
when the fluid in the chamber within the housing is under elevated
pressures such as pressures at or near the blood pressure levels of a
patient.
It would be desirable to provide a self-sealing subcutaneous injection site
which can be used in situations requiring repeated and periodic puncturing
while maintaining a self-sealing capability even under elevated pressures
within the chamber of the injection site.
SUMMARY OF THE INVENTION
The present invention overcomes the problems described above and provides a
self-sealing subcutaneous injection housing having a bottom wall and a
generally dome-shaped resilient wall which defines an interior chamber
within the housing. The dome-shaped wall of the housing has a durometer
and shape for providing compressive forces within the wall for sealing
punctures through the wall upon fluid pressurization within the chamber. A
conduit extends through the wall and interconnects with the chamber for
providing fluid flow into and out of the chamber. The conduit can provide
for interconnecting with a catheter or other suitable tubing.
More particularly, the self-sealing subcutaneous injection site herein
includes a housing having a bottom wall, which bottom wall can be of a
material that is impenetrable by the cannula of a hypodermic syringe. Such
a bottom wall prevents the insertion of a hypodermic syringe completely
through the injection site while introducing fluid to the injection site.
The housing further includes a generally dome-shaped resilient wall
defining an interior chamber. The interior chamber has a convex upper wall
formed by a portion of the dome-shaped wall of the housing. In addition to
the upper wall of the chamber being convex, the sidewall of the chamber
can be convex and formed by a portion of the dome-shaped wall of the
housing. The convex shape of the upper wall and sidewall of the chamber
provides compressive forces within the upper wall or sidewall for sealing
punctures through either the upper wall or sidewall upon fluid
pressurization within the chamber.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a cross-sectional side elevational view of a self-sealing
subcutaneous injection site;
FIG. 2 is a cross-sectional side elevational view of another embodiment of
a self-sealing subcutaneous injection site;
FIG. 3 is a side elevational view of the embodiment of the self-sealing
subcutaneous injection site shown in FIG. 1;
FIG. 4 is a top elevational view of the self-sealing subcutaneous injection
site embodiment shown in FIG. 1;
FIG. 5 is a side elevational view of the embodiment of the self-sealing
injection site shown in FIG. 1 and showing penetration by a needle
cannula;
FIG. 6 is a side elevational view of the embodiment shown in FIG. 5 with
the needle cannula withdrawn; and
FIG. 7 is a side cross-sectional elevational view of still another
embodiment of a self-sealing subcutaneous injection site.
DETAILED DESCRIPTION
The self-sealing subcutaneous injection site will be described with regard
to the accompanying drawings. In particular, FIG. 1 shows an embodiment of
a self-sealing subcutaneous injection site 10. For facilitating
description herein, the injection site will be referred to as the
injection site. The injection site 10 has a housing 12 which consists of
an elastomeric material which is biocompatible with the human physiognomy.
An acceptable material from which the housing can be constructed is
silicone elastomer. The housing includes a generally dome-shaped wall 16
and a bottom wall 14. The bottom wall can be constructed of a resilient
material such as silicone elastomer or can be constucted of a material
which is impenetrable to puncture by a needle cannula such as a
polyethylene, polycarbonate and the like. When the bottom wall 14 is
constructed of such an impenetrable material, it functions as a needle
guard preventing a needle cannula, which is inserted into the housing to
fill the chamber therein, from completely penetrating through the
injection site. The bottom wall and dome-shaped wall are sealed together.
The dome-shaped wall of the housing defines an inner chamber 18 having a
volume for receiving fluid to be introduced or withdrawn from a patient's
body following implantation of the injection site. The volume of the
chamber can vary depending upon the contemplated end use for the injection
site. With regard to FIGS. 1 and 3-6, the embodiment of the injection site
shown therein has an inner chamber 18 formed by chamber sidewall 20 and
chamber upper wall 22. Both the chamber sidewall 20 and chamber upper wall
22 are formed by at least a portion of the dome-shaped wall 16 of the
housing. In the embodiment shown therein, the chamber sidewall 20 is
generally a straight, vertically extending sidewall. As can be seen from
the top view shown in FIG. 6, the chamber sidewall 20 extends in a circle,
forming a generally cylindrical chamber 18. The chamber 18 can have
geometric configurations other than cylindrical.
The chamber upper wall 22 has a generally convex shape with the upper wall
convex in regard to the chamber 18. The outer surface of the dome-shaped
wall 16, at least at the upper surface generally designated as area
A.sub.1 in FIG. 1, has a generally or substantially flat surface 17. The
geometric shape of the dome-shaped wall in the area A.sub.1, including the
convex surface and chamber upper wall 22, combine with the durometer of
the resilient material to provide compressive forces within the
dome-shaped wall such that such forces can close a puncture extending
through the dome-shaped wall. The self-sealing capability of the injection
site herein is illustrated in FIGS. 5 and 6.
With regard to FIG. 5 and 6, the embodiment of the injection site shown in
FIG. 1 is illustrated in a side elevational view. FIG. 5 shows the
injection site being punctured with a needle cannula 32 which penetrates
the dome-shaped wall 16 and extends into the inner chamber 18. A syringe
(not shown) filled with a fluid to be introduced to the chamber can be
connected to the needle cannula. As the dome-shaped wall is constructed of
a resilient material, it can be punctured by the needle cannula. Using the
syringe, fluid is introduced to the inner chamber 18. As fluid is
introduced to the chamber, the fluid creates a pressure within the
chamber, which pressure is exerted against the walls of the inner chamber.
The pressure exerted against the chamber upper wall 22 forces the upper
wall outwardly. Upon withdrawal of the needle cannula 32, the puncture 34
is closed and effectively sealed against fluid flow by the elastomeric
properties of the material comprising the done-shaped wall 16 and the
compressive forces in the done-shaped wall as a result of its structure.
Such compressive forces are shown by the vectors 36 which arise as a
result of the fluid pressure exerted against the convex chamber upper wall
22 which causes the chamber upper wall to lose its convexity and thereby
exert a closing pressure against the puncture 34 effectively sealing the
puncture at especially its innermost portion near the chamber upper wall
22. That is, as the chamber is pressurized by the fluid the elastic
dome-shaped wall is compressed. This compression is greatest at the inside
surface such as the chamber upper wall 22. The compression and resulting
material deformation causes the puncture to be effectively sealed along
the chamber upper wall 22.
The embodiment shown in FIGS. 1 and 3-6 can be used in situations where
there is a strong likelihood that the chamber will be filled by
penetrating the dome-shaped wall of the injection site in the area
designated as a A.sub.1 on FIG. 1. Such an embodiment provides an
injection site which can be repeatedly punctured by a needle cannula while
introducing fluid into the inner chamber, but which retains such fluid and
greatly inhibits leaking of such fluid into the surrounding tissue. In
addition, such a device can be used for infusing fluids into pressurized
areas which may be experienced in the body such as in the circulatory
system.
In some instances, it is desirable to provide an injection site which can
be punctured with a needle cannula in areas other than along the upper
surface. For example, the embodiment shown in FIGS. 1 and 3-6 has a
generally vertically extending chamber sidewall 20. The sidewall and the
corresponding area are designated as A.sub.3 in FIG. 1 along with the
upper corner between the chamber sidewall and chamber upper wall in the
area generally designated as A.sub.2. During filling of the chamber 18 and
pressurization of the chamber, the chamber sidewall 20 and corner area
experience a tensioning and resulting wall strain. The material
deformation through such tensioning causes any puncture extending the
corresponding areas A.sub.2 and A.sub.3 to open along the inside surface
which may take the shape of a concave surface at such areas. Upon such an
occurrence, the surface adhesion of the elastomer along the puncture is
easily overcome and leakage of the fluid from the chamber can occur
through such puncture. The surfaces of the edge radius between the chamber
upper wall and chamber sidewall and the chamber sidewall surface in the
tangential (or horizontal) direction can be tensioned upon achieving high
pressures within the chamber. The edge radius region can go into tension
because of circumferential stresses and due to its concave surface. The
chamber sidewall surface can go into tension tangentially because of the
circumferential stress upon pressurization. These undesirable edge and
chamber sidewall deformations can be lessened by constructing the
embodiment shown in FIG. 2 or by providing a cuff of reinforcing material
such as Dacron, Nylon and the like extending around and imbedded in the
chamber sidewall as is shown in FIG. 7. The high modulus Dacron material
prevents significant hoop strain at pressures which can be realized in the
chamber.
With regard to FIG. 7, another embodiment of the self-sealing subcutaneous
injection site is illustrated. In the embodiment shown in FIG. 7, the
injection site has the structure substantially equivalent to that of the
embodiment shown in FIG. 1. Injection site 38 of FIG. 7 includes a housing
40 having a resilient dome-shaped wall 42. The upper outer surface 43 of
the dome-shaped wall is generally flat. The housing includes a bottom wall
44 which can be sealed to the dome-shaped wall to form with the
dome-shaped wall and interior chamber 46. The interior 46 has a convex
chamber upper wall 48 and a chamber sidewall 50. Imbedded within the
chamber sidewall is a reinforcing material such as a reinforcing mesh
which can be constructed of Dacron, Nylon and the like. The reinforcing
cuff 52 substantially prevents distortion of the sidewall, thereby
assisting the sidewall in closing or sealing any punctures which extend
therethrough. That is, the reinforcing cuff prevents distortion of the
sidewall due to increased pressures which can occur in the inner chamber
46. The injection site 38 also can include an outwardly extending flange
54. Also in the embodiment shown in FIG. 7, the injection site therein
includes a separate needle guard 56 which is constructed of a material
impermeable to puncture by a needle cannula. the needle guard 56 is
positioned along the bottom wall 44 within the interior chamber 46. The
needle guard can be supported and spaced from the bottom wall by legs 58.
In the embodiment shown in FIG. 2, elements that are the same as the
elements of the embodiment shown in FIG. 1 are shown using the same
numbers. The embodiment shown in FIG. 2 is identical to that of FIG. 1
with the exception that the chamber sidewall 21 has a convex configuration
as opposed to the generally straight-walled chamber sidewall 20 of the
embodiment in FIG. 1. Such a convex structure along the chamber sidewall
performs in much the same manner as above described with regard to the
convex chamber upper wall 22 in the first embodiment. That is, the
embodiment shown in FIG. 2 can be repeatedly punctured either through the
area shown as A.sub.1 or A.sub.3 in FIG. 2 and maintain its self-sealing
capability. The only area remaining on the injection site wherein the
greatest beneficial properties of the chamber wall structures is not
realized is in the area designated as A.sub.2. The likelihood of
puncturing such a small area with a needle cannula is reduced in view of
the much greater areas in the areas designated A.sub.1 and A.sub.3.
The embodiment shown in FIG. 2 as well as that in FIG. 1 can be used for
implanting in high pressure situations such as accessing arterial blood or
as an injection site for inflating skin expansion bladders. The embodiment
shown in FIG. 2 can provide for widely angled puncture positions for a
syringe needle cannula used to introduce fluid into the inner chamber 18.
Again with regard to both embodiments shown in the accompanying drawings,
the housing includes a conduit 24 which can be a cylindrical conduit
integrally formed with the dome-shaped wall 16. The conduit 24 provides a
fluid-flow passageway 26 for providing fluid flow to and from the chamber.
The fluid-flow passageway 26 can receive a tubing connector for connecting
the injection site to a catheter or other tubing so that fluid introduced
to the inner chamber can be delivered through such tubing to a site within
the patient.
The housing can include an outwardly extending flange 28. The housing can
also be constructed in any geometric configuration, but in the preferred
embodiment a circular configuration as is shown in FIG. 4 is utilized. As
can be seen in the drawings and especially in FIG. 4, the outwardly
extending flange 28 extends around the periphery of the injection site.
The flange can extend around only portions of the periphery of the
injection site. One purpose of the flange is to provide for attachment of
the injection site to a location within a patient. For example, the flange
includes suture sites 30 through which sutures can be taken to fix the
injection site subcutaneously within a patient. Other techniques for
fixing the injection site within the patient can be used such as using
surgical staples. The suture sites 30 can be apertures opening through the
outwardly extending flange or can merely be areas along the flange of
lesser thickness than the flange itself such that such suture sites can be
easily penetrated by a surgical needle while suturing.
As state above, various geometric shapes can be employed in constructing
the injection site herein as long as the inner chamber is constructed as
described, namely providing the chamber wall most likely to be punctured
with a convex structure. In the preferred embodiment, the injection site
has the outer configuration with a rather flat upper surface 17 on the
dome-shaped wall 16 as is shown in FIGS. 1 and 2. Such a configuration
provides, upon fluid pressurization of the chamber, a direction of
expansion for the convex chamber upper wall.
The size of the injection site can be modified according to the
requirements for the treatment technique to which the injection site is
being used. That is, the size can be varied to provide for palpation,
different needle sizes, number of injections and expected back pressures
in order to accomplish the desired resealing characteristics. In this
manner, the injection site can be modified to meet the demands for
placement into different body structures such as intrathecal, venous,
arterial, intramuscular, and the like.
Integral rigid connectors can be incorporated into the injection site by
fitting such connectors into the fluid passageway 26 to provide and
simplify attachment of catheters and tubing. The injection site or
portions thereof can be made radiopaque by incorporating materials having
a radiopacity during molding or manufacture of the injection site. By
using radiopaque materials, the position of the device can be verified
post-operatively.
The utility and beneficial properties of an injection site made in
conformity with the invention herein demonstrated in a series of tests
wherein injection sites were repeatedly punctured. The tests were designed
to determine the efficacy of injection sites and their ability to reseal
after repeated needle puncture and for their use against transient
pressures as high as 200 centimeters of water which is comparable to a
high arterial blood pressure.
The test technique was performed using each injection site dome
configuration by puncturing each injection site up to the indicated number
of punctures with a needle cannula that was either 19 gauge or 21 gauge as
indicated having a regular bevel. The punctures were randomly distributed
over the area of the injection site with the indicated areas being those
areas as shown and designated in FIGS. 1 and 2. The injection sites were
also tested for fluid leak rate from the inner chamber at a pressure of
200 centimeters of water. The injection site chambers were pressurized to
200 centimeters water pressure and the amount of extruded fluid was
determined by soaking up the beads of fluid with a tared piece of
absorbent paper toweling which was subsequently weighed to determine the
amount of fluid.
In the first series of tests, three injection sites were tested. The
injection sites tested basically had the structure as shown in FIG. 1 with
the following limitations. The injection site designated as "A" was
substantially identical to the embodiment shown in FIG. 1; the injection
site designated as "B" was substantially similar to the injection site
shown in FIG. 1 with the exception that the chamber sidewall was concave;
and the injection site identified as "C" was substantially the same in all
material aspects as the injection site shown in FIG. 2. The injection
sites were punctured in the following pattern of puncture distribution: 25
punctures in the top region generally designated area A.sub.1 of FIG.1; 10
punctures in the edge region generally designated area A.sub.2 ; and 200
punctures in the side region generally designated area A.sub.3. For the
punctures in the side region A.sub.3, the area punctured included the
one-half of the injection site opposite the fluid-flow passageway. That
is, the one-half of the injection site as if a diameter were drawn
separating the injection site along the line 38 as shown in FIG. 4. The
following results shown in Table 1 were obtained with the pressure
readings in centimeters of water:
TABLE I
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Injection 10 Area 50 Area
100 Area
50 Area
Site 25 Area A.sub.1
A.sub.2 A.sub.3
A.sub.3
A.sub.3
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A >1200 240 190 180 76
A >1200 320 325 270 128
B >1200 340 340 250 78
B >1200 240 180 140 56
C >1200 550 342 297 125
C >1200 440 320 245 138
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From the above data it can be readily seen that the three injection site
configurations provide injection sites which can be repeatedly punctured
through area A.sub.1 and maintain effective sealing even under high
pressures in the chambers of the respective injection sites. The injection
site C can be used when punctured repeatedly in area A.sub.3 and maintain
effective sealing.
When the above three configurations of injection sites were tested by
pressurizing the chambers up to 200 centimeters of water pressure, the
resultant leakage following the 235 punctures is as shown in the following
table:
TABLE II
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Injection Site Ml/Minute Ml/Hour
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A 0.076 4.56
A 0.013 0.78
B 0.028 1.70
B 0.049 2.94
C 0.038 2.28
C 0.020 1.2
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The average leak rate in milliliters per hour for the three injection sites
were A, 2.60; B, 2.32; and C, 1.74.
The following tests using the above described techniques were also
performed to determine leak pressures around and along various areas of an
injection site having the structure shown in the embodiment in FIG. 2. Six
different injection sites were tested. Punctures were made using either a
21 gauge or a 19 gauge hypodermic needle having a regular bevel. The goals
of the tests on such six injection sites were to determine the internal
pressure which would cause leakage of the hypodermic needle punctures in
specific areas on the injection site dome. The domes were repeatedly
punctured, and the resulting pressure required to form a fluid bead on the
surface of each injection site in centimeters of water recorded for the
number of punctures. In the first section of the following table, the
injection site was randomly punctured with 25 punctures in the area
A.sub.1, 10 punctures in the area A.sub.2, and values determined for 10,
25 and 100 punctures in the area A.sub.3. The second portion of the table
shows the results upon puncturing one quadrant of the injection site with
25 punctures in each of the areas A.sub.1 and A.sub.2. The third section
of the table provides the results of minimum leak pressures determined for
the injection site after all of the punctures were made. The leak
pressures were recorded for leaks only in the areas recently punctured.
TABLE III
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I. II.
All Quadrants 1 Quadrant III.
Top
Edge
Side Top
Edge
Top
Edge
Minimum
A.sub.1
A.sub.2
A.sub.3 A.sub.1
A.sub.2
A.sub.1
A.sub.2
Leak
Dome
Needle
25
10
10
25
100
25
25
25
25
Pressure
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1 21 g
N.L.
328
460
390
256
N.L.
368
443
214
152
2 21 g
N.L.
726
606
554
188
328
204
219
162
119
3 21 g
770
698
476
387
242
642
256
495
238
176
4 21 g
689
261
361
298
220
470
264
346
212
124
5 19 g
N.L.
681
608
605
448
428
416
336
304
183
6 19 g
983
943
950
708
422
406
378
346
312
168
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(N.L. = No Leak .ltoreq. 1400 cm H.sub.2 O)
As can be seen from the above table, the injection site structure performed
very well with pressures requiring greater than 200 centimeters of water
in order to form a bead on the surface of the injection site and 200
centimeters of water would be considered a high arterial blood pressure.
In the above description, a specific example has been used to describe the
injection site herein. However, it is understood by those skilled in the
art that certain modifications can be made to this example without
departing from the spirit and scope of the invention.
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