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Description  |
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This invention relates to a catheter. It relates more particularly to
improved means for connecting a flexible infusion catheter to a source of
infusate.
BACKGROUND OF THE INVENTION
The treatment of certain diseases of the human body often requires the
short-term or long-term infusion of drugs, blood products or nutritional
or other fluids into the patient's venous or arterial system or peritoneal
or epidural space. While such fluids can be administered extracorporeally
by transcutaneous injection, in some cases, as when a particular patient's
regime requires repeated access for drug infusion, or where infection is
of acute concern, it is desirable to provide the patient with a totally
implanted infusion system.
Such a system includes an injection portal which is an infusate chamber
implanted subcutaneously and placed on the chest wall or other convenient.
body location. The portal is fitted with a needle-penetrable septum which
is located directly under the skin by which drugs or other fluids may be
introduced into the portal by transcutaneous injection through the septum.
The portal has a fluid outlet tube or stem which is connected to one end
of a flexible catheter which leads to the infusion site which is usually a
blood vessel or particular body cavity, e.g., the peritoneal cavity. Since
the system is completely implanted, it reduces the risk of infectious
complications and allows drug infusion which is targeted to the specific
patient malady. Even though the delivery system may be implanted for a
long period, the patient remains ambulatory and can be treated on an
out-patient basis and the system does not interfere with the normal daily
activities of the patient.
A similar prosthesis can be used to draw blood from an artery or vein for
blood sampling purposes.
Since an implantable device of this type may remain in the patient's body
for many months, it is essential that the connection or attachment of the
catheter to the portal remain secure and fluid-tight during the entire
period of implantation. If the connection should fail or if there should
be an infusate leak at that location, the infusate dose required to treat
the patient which is injected into the portal will not be conducted to the
targeted infusion site in the patient's body. Rather, some or all of the
infusate will be dispensed at the site of the portal and could cause
complications at that body location. In this connection, it should be
appreciated that after a drug delivery system is implanted, the catheter
is subjected to various stresses and strains due to movements of the
patient's body, weight changes, etc. These are reflected in tensile and
twisting forces at the connection of the catheter to the portal outlet
which tend to upset the integrity of that union.
In an attempt to avoid this leakage problem and the attendant
complications, various steps have been taken to strengthen the connection
between the catheter and the portal. These include the providing of raised
circular rings or ribs on the portal outlet stem over which the catheter
wall is stretched. These lines of localized resilient engagement resist
sliding movements of the catheter from the portal stem. In some systems,
the connection is made somewhat more secure by providing a locking ring or
bushing which encircles the catheter and is releasably captured on the
catheter segment engaged on the portal stem by the raised ribs thereon.
We have found, however, that these prior catheter connections are not
entirely satisfactory. Sometimes the tensile forces exerted on the
catheter due to movements of the patient still suffice to separate the
catheter from the portal or to tear the catheter at that point of
connection because of a poor distribution of stresses on the catheter
wall. Certain prior systems are disadvantaged in that it is quite
difficult to connect the catheter to the portal outlet stem. This is
because that stem is often very small (e.g. 1 mm OD), and to make the
connection, the stem must be threaded into the end of the catheter lumen
which is itself equally small. Furthermore, when inserting the portal stem
into the catheter, if one is not quite careful, the catheter will be
punctured by the end of the stem which, being so small, constitutes a
sharp point. Certain prior systems are disadvantaged in that they have
loose parts that are hard to handle and can be lost. This is because the
system requires a separate lock that must be put on the catheter before
the connection to the stem is made. These lock parts are small and easy to
drop or lose.
In addition, it should be kept in mind that it may be necessary to
disconnect the catheter from an already implanted injection portal in the
event that the catheter has to be replaced for one reason or another. For
example, it sometimes happens that the catheter lumen becomes clogged by
clots or other debris. Therefore, it is desirable that any connection
between the catheter and the portal be separable from the portal with a
minimum amount of effort and finger manipulation by the surgeon who must
make that repair subcutaneously. The prior catheter connection or
attachment systems of which applicant is aware, do not facilitate such
ready connection and disconnection of the catheter to and from the portal.
SUMMARY OF THE INVENTION
Accordingly, the present invention aims to provide an improved catheter
attachment system.
Another object of the invention is to provide a catheter attachment system
which is very strong, yet which can be released quite easily if the need
should arise.
Another object of this invention is to provide a catheter connection system
which has no loose part that can be lost.
Another object of the invention is to provide a catheter connection which
is specially adapted for use in an implantable infusion system for joining
the catheter to an injection portal.
Yet another object of the invention is to provide an attachment system of
this type which minimizes localized stresses on the catheter in the region
of the attachment.
Other objects will, in part, be obvious and will, in part, appear
hereinafter.
The invention accordingly comprises the features of construction,
combination of elements and arrangement of parts which will be exemplified
in the following detailed description, and the scope of the invention will
be indicated in the claims.
The catheter attachment or connection system of interest here may be used
in any application where it is necessary to releasably connect the end of
a flexible resilient catheter or other tube to a stem, tube or rod by
inserting the stem, tube or rod into the end of the catheter. Since the
invention has particular application to the connection of a catheter to
the outlet stem of an implantable injection portal, we will describe the
invention in this context. It should be understood, however, that the
invention may be applied to other applications where similar flexible
tube-to-rigid tube connections are required.
Briefly, the present attachment system involves the coaction and
cooperation of a flexible resilient catheter, a relatively rigid stem or
tube onto which the catheter is slid to effect the connection and a
specially designed, locking retainer which encircles the stem and catheter
on the stem. The system provides strain relief to the catheter and
minimizes localized stresses on the catheter due to tensile and other
forces exerted on the catheter in use.
The stem component of the system is formed with an axially symmetric radial
enlargement. This enlargement takes the form of a three-dimensional bulb
located adjacent to the distal end of the stem. The distal end segment of
the stem beyond the enlargement has a diameter which is approximately the
same as the diameter of the lumen in the catheter being connected to the
stem with the enlargement being appreciably larger than that lumen.
When the catheter, which is the second component of the system, is slid
onto the stem, the elastic wall of the catheter stretches outward as
required to accommodate the larger diameter stem enlargement. Thus, when
the end segment of the catheter has received the full extent of the stem,
the catheter resiliently engages the outer surface of the stem and
conforms closely to the enlargement thereof.
The third component of my connection system, namely the retainer, is a
sleeve or ring which loosely encircles the proximal end segment of the
portal stem. The sleeve is free to move back and forth along the stem, but
it cannot come off the stem due to its engagement with a flange adjacent
to the proximal end of the stem. When the catheter is slid onto the stem
over the stem enlargement it is guided into the sleeve until the end of
the catheter butts against the stem flange. When that sleeve is slid
outward along the stem, the sleeve captures the catheter against the stem
enlargement.
As will be described shortly in greater detail, when the retainer component
of my connection system is seated on the portal stem so that it captures
the catheter thereon, there results a very secure connection of the
catheter to the stem. Even very strong pulling, twisting and bending
forces exerted on the catheter are unable to disconnect the catheter from
the stem or to break the fluid-tight integrity of that connection.
Actually, as we will see, such forces enhance that connection.
The catheter connection system described here is also quite easy and
inexpensive to manufacture, being composed of simple metal parts which can
be fabricated in quantity at minimum cost. Also, the connection is easy to
make and to release, even if that needs to be done in the case of an
injection portal already implanted in the body. In other words, the
present apparatus facilitates sliding a catheter onto the end of a portal
outlet stem and into the locking sleeve to secure the catheter to the stem
with no loose parts. Also, simple finger movements suffice to manipulate
the connector's locking ring to release the catheter from the stem.
Consequently, the present attachment system could be used conveniently
wherever it is necessary to releasably connect a flexible catheter or
other tube to a relatively rigid rod or stem.
BRIEF DESCRIPTION OF THE DRAWING
For a fuller understanding of the nature and objects of the invention,
reference should be had to the following detailed description taken in
connection with the accompanying drawing, in which:
FIG. 1 is an isometric view of an implantable injection portal
incorporating a catheter attachment system made in accordance with this
invention;
FIG. 2 is an exploded side elevational view on a much larger scale and with
parts broken away showing the catheter attachment system in its unlocked
position; and
FIG. 3 is a side elevational view showing the connection system in its
locked position.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring to FIG. 1 of the drawing, my catheter attachment system,
indicated generally at 10, is shown connecting the proximal end of a
catheter 12 to the tubular outlet stem 14 of an implantable injection
portal 16. The portal is made of a material such as titanium and in use it
is implanted at a convenient location in the body, such as on the chest
wall. This portal might be used, for example, to conduct infusate to a
vein leading to the heart. Usually, small eyes 16a are provided around the
base of the portal through which sutures may be passed to anchor the
portal to the chest wall. The portal also includes a septem 16b composed
of a suitable resilient, needle-penetrable material, such as silicone
rubber.
When the portal is implanted, the septum is situated directly under the
patient's skin so that infusate can be introduced into the portal by
transcutaneous injection through the septum. The infusate thereupon flows
through the portal outlet stem 14 to the catheter 12 whose distal end is
placed at a selected infusion site in the body, such as a blood vessel or
a body cavity such as the peritoneal cavity. Catheter 12 is made of a
flexible, resilient biocompatible material, such as silicone rubber. The
inside diameter of the catheter, which corresponds more or less to the
nominal outside diameter of portal stem 14, may vary depending upon the
particular application, from, say 0.5 to 3.0 mm. Likewise, the volume of
the portal 16 may vary from, say, 0.4 ml to 1.0 ml.
Referring now to FIGS. 1 and 2 of the drawing, connection system 10 is
composed of three distinct parts or components. These include the proximal
end segment 12a of the catheter, the portal outlet stem 14 and a special
locking retainer shown generally at 18. The tubular stem 14 is formed with
a radial enlargement 22 along its length. In the system embodiment
depicted herein, the enlargement 22 is located adjacent to the outer or
distal blunt end segment 14a of the stem 14 and it has the general form of
a barrel with two back-to-back frustoconical segments 22a and 22b. The
enlargement has a relatively large, rounded shoulder 22c midway along its
length, i.e. between segments 22a and 22b whose diameter is appreciably
larger than the inside diameter of catheter 12. The enlargement 22 tapers
from that shoulder to stem end segment 14a and to a longer stem segment
14b closer to the portal 16 housing. The inner end of stem segment 14b
leads to a much larger proximal stem segment 14c projecting from the wall
of the portal housing. For reasons to be described later, a radial flange
24 is provided at the boundary of stem segments 14b and 14c. The flange
has a radial outer or distal surface 24a and a beveled inner or proximal
surface 24b. The diameter of stem segment 14a may be somewhat smaller than
the inside diameter of the catheter to aid in initiating catheter
engagement, i.e. in aligning the proximal end 22a of the catheter with the
stem end segment 14a. The diameter of stem segment 14b is somewhat larger
than the diameter of the catheter so that a fluid tight seal is produced
between that segment and the catheter.
The shape of the enlargement 22 is such that the stem end segment 14a and
the frustonconical segment 22b of the enlargement 22 can be introduced
into the end of the catheter segment 12a for a distance corresponding to
about half the enlargement diameter without extending or stretching the
catheter wall. Further penetration of the stem 14 into the catheter
segment 12a results in the catheter wall stretching or deforming to
accommodate enlargement 22, particularly shoulder 22c. That is, the
catheter 12, which is typically silicone rubber, is very resilient. Thus,
when catheter segment 12a is engaged fully on stem 14 as shown in FIG. 3,
i.e. with the end of the catheter engaging flange 24, due to the
resiliency of the catheter material, the catheter segment assumes the
exact shape of outlet stem 14, including its enlargement 22 and stem
segments 14a and 14b.
As best seen in FIGS. 2 and 3, the locking retainer 18 is a generally
cylindrical sleeve-like member which is slidably engaged on the stem 14.
Retainer 18 is an easily fabricated, metal (e.g. titanium) or molded
plastic part. The inside diameter of the retainer is slightly larger than
that of stem flange 24 and its length is comparable to the combined
lengths of stem segments 14b and 14c. The inner or proximal end of the
retainer is necked down to form an inwardly extending circular flange or
rib 18a which overhangs stem flange 24 and is oriented at more or less the
same angle as the bevelled surface 24b of that flange.
The outer or distal end of retainer 18 has a reduced inner diameter that
creates a circular inner rib, flange or ledge 18b on the retainer. Also,
that end of the retainer is bevelled to provide a flared or bevelled
surface 18c which extends from the inner edge of ledge 18b toward the
outer wall of the retainer. As best seen in FIG. 2, the ledge 18b and
bevelled surface 18c together produce a structure at the distal end of the
retainer which, in crosssection, has the general shape of an annular barb
whose blunted nose 18d projects toward stem 14. When the retainer and stem
are coaxial, the flare angle of surface 18c, as measured from the stem 14
longitudinal axis or centerline, is appreciably greater than that of
enlargement segment 22a so that when catheter 12 is tensioned, nose 18d
will bite into the catheter wall creating strong retention forces. For
example, the former angle may be 45.degree. and the latter angle
20.degree..
Retainer 18 is slidable along stem 14, with the stem flange 24 providing a
bearing surface, between an unlocking position shown in FIG. 2 established
by the engagement of the retainer flange 18a against the portal housing,
wherein the retainer surface 18c and nose 18d are spaced appreciably from
enlargement segment 22a and a locking position shown in FIG. 3 wherein the
surface 18c and nose 18d are situated close to segment 22a, with the nose
lying about halfway along the length of that segment. The stem flange 24,
in addition to functioning as a stop for catheter 12 and as a bearing
surface for the retainer as described above, also prevents the retainer 18
from sliding off the stem 14 by engaging the retainer flange 18a. A pair
of diametrically opposite holes 26 are provided in the wall of retainer 18
to make it easier for the surgeon to see that the catheter is completely
in place and abutting flange 24 inside the locking retainer.
The connection of catheter 12 to stem 14 can be made quite easily with one
hand, even when the surgeon has no clear view of the connection site. To
effect the connection, the surgeon grasps the end of the catheter and,
feeling with his fingers, slides the catheter onto the end segment 14a of
portal stem 14. He then pushes the end of the catheter over the stem
enlargement 22 and into sleeve 18 until the catheter end is stopped by the
stem flange 24. He can verify that the catheter is seated properly by
observation through the retainer holes 26. The surgeon then pulls back
gently on locking retainer 18 until the retainer nose 18d engages against
and compresses the outer surface of catheter segment 12a as shown in FIG.
3. Most desirably, the inner diameter of retainer ledge or flange 18b, or
more particularly of its nose 18d should be less than the diameter of
enlargement shoulder 22c in which event, retainer flange 18a could be
dispensed with. However, this creates manufacturing difficulties. To avoid
these difficulties, the diameter of retainer nose 18 d is dimensioned to
be smaller than the diameter of stem enlargement 22 plus twice the wall
thickness of the catheter segment stretched over that segment 14b.
When the connection is made and locked as shown in FIG. 3, it is
practically impossible to pull catheter 12 from the portal stem 14. Any
pulling or twisting forces applied to the catheter only serve to tighten
the connection between the catheter and the stem. That is, when catheter
12 is pulled away from portal 16, it pulls retainer 18 along with it to a
locking position against enlargement segment 22a at a circular area of
contact C (FIG. 3). Increased tensile forces only serve to pull the
retainer more tightly against segment 22a at contact surface C.
Resultantly, the retainer surface 18c and nose 18d are moved closer to the
frustoconical segment 22a of enlargement 22 so that nose 18d clamps or
bites even more firmly into the stretched catheter wall thereby further
increasing the retention forces on the catheter. Accordingly, a
frustoconical catheter segment is sandwiched or compressed ever more
tightly between enlargement segment 22a and the retainer surface at
contact surface C, as clearly seen in FIG. 3.
That engaged and compressed segment of the catheter has a relatively large
area so that the stresses on the catheter due to such pulling and twisting
forces are distributed uniformly over that segment, thus avoiding
localized strains in the catheter wall that might tend to promote tears or
punctures in that wall. Consequently, there is very little likelihood of
the catheter pulling away from the portal outlet stem 14 or tearing due to
movements of the patient in which the prosthesis is implanted. Indeed, the
integrity of the connection system 10 should be maintained for the entire
period of implantation.
However, if it should become necessary to replace the catheter 12 for some
reason, the present system 10 facilitates that as well. To remove the
catheter, the surgeon simply holds the retainer 18 back or urges it toward
the portal housing while pulling the catheter from stem 14. Since the
retainer cannot move outward, it cannot clamp the catheter segment 12a to
enlargement 22, so the catheter will pull off readily, leaving the stem 14
ready for a new catheter. Indeed, the same locking retainer and portal
stem can be assembled and disassembled many times if need be.
It will be seen from the foregoing, then, that my catheter connection
system establishes a reliable, releasible, fluid-tight and easily made
joint or connection between the end of a catheter or other flexible tube
and a rigid tube, stem or other fluid pathway. The system's locking
retainer is easy to manipulate when connecting and disconnecting the
catheter from the tube or stem, even if the surgeon's view is obstructed.
Yet the components of the system are relatively easy and inexpensive to
make so that the providing of this secure connection does not materially
increase the overall cost of the injection portal or other prosthesis
incorporating the invention.
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