U.S. patent number 3,633,579 [Application Number 04/843,866] was granted by the patent office on 1972-01-11 for catheter placement device and method.
This patent grant is currently assigned to Sherwood Medical Industries Inc.. Invention is credited to Ralph D. Alley, David S. Sheridan.
United States Patent |
3,633,579 |
Alley , et al. |
January 11, 1972 |
CATHETER PLACEMENT DEVICE AND METHOD
Abstract
A medical device for use in intravenous or intraarterial
injections of fluids, in blood sampling, in diagnostic procedures
such as intravascular blood sampling including sampling in the
heart, and in intravascular pressure measurements using
transducers. The device incorporates a novel catheter means and
method for placing a flexible cannula in a vein or artery such that
the catheter means can be threaded through the cannula into the
vein or artery of a patient an appropriate distance. The catheter
can be secured in position relative to the cannula by means of a
self-contained locking arrangement carried by the catheter. In
preferred forms, the locking force against the catheter can be
distributed over an area to assure a good lock without restricting
the catheter and without the expense of providing close tolerance
in the locking system.
Inventors: |
Alley; Ralph D. (Loudonville,
NY), Sheridan; David S. (Argyle, WA) |
Assignee: |
Sherwood Medical Industries
Inc. (N/A)
|
Family
ID: |
27093648 |
Appl.
No.: |
04/843,866 |
Filed: |
March 13, 1969 |
Related U.S. Patent Documents
|
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
|
640889 |
May 24, 1967 |
|
|
|
|
Current U.S.
Class: |
604/508;
604/164.01 |
Current CPC
Class: |
A61M
25/0662 (20130101) |
Current International
Class: |
A61M
25/06 (20060101); A61m 005/00 (); A61m
025/00 () |
Field of
Search: |
;128/2.05,214.4,221,348,DIG.16 |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
Lancet-Oct. 1964-pp. 941-942..
|
Primary Examiner: Truluck; Dalton L.
Parent Case Text
RELATION TO COPENDING APPLICATION
This application is a continuation-in-part of our copending
application Ser. No. 640,889, filed May 24, 1967 and entitled
"Catheter Placement Device and Method," now abandoned.
Claims
We claim:
1. In a catheter placement device comprising a flexible plastic
cannula, an elongate catheter threaded into said cannula, said
cannula having a tapered distal end portion and a flared proximal
end portion and locking means comprising a ferrule slidably carried
on said catheter for locking said catheter relative to said cannula
when said catheter is in position in said cannula, said ferrule
having a tapered outer wall and a continuous inner wall, the distal
end of said ferrule engaging with the inner surface of the tapered
distal end portion of the cannula for creating the locking action
against the outer surface of said catheter.
2. A device as claimed in claim 1 wherein said catheter is made of
a plastic material and has an X-ray opaque line extending from the
distal end through at least a portion of said catheter.
3. A device as claimed in claim 1 wherein said catheter is made of
an X-ray opaque material.
4. A device as claimed in claim 1 wherein means are provided on the
proximal end of said catheter for attaching said catheter to
another instrument.
5. The device of claim 1 wherein at least the distal end portion of
said ferrule is flexible.
6. The device of claim 1 wherein said locking action comprises
means for distributing the force against the catheter over a
portion of the length of said catheter.
7. The device of claim 6 wherein the force spreading means
comprises a frustoconical end on said ferrule engaging said
catheter.
8. The device of claim 6 wherein the force spreading means
comprises slit means in the wall of said ferrule extending axially
from the catheter engaging end thereof.
9. In a catheter placement device comprising a flexible plastic
cannula, an elongate catheter threaded into said cannula, said
cannula having an enlarged proximal end portion with a tapered
inner wall surface therein, locking ferrule means slidably carried
on said catheter in a position proximally located with respect to
said enlarged end of said cannula, said ferrule having an outer
wall surface tapered downwardly toward the distal end thereof, said
distal end of said ferrule being wedged between the inner tapered
wall of said cannula and the outer surface of said catheter for
locking said catheter relative to said cannula.
10. A method of placing a catheter in a patient comprising the
steps of inserting a cannula shrouded needle into a body cavity of
a patient, withdrawing the needle from the cannula and leaving the
cannula in position in the patient, sliding a locking ferrule that
surrounds an elongate thin flexible catheter toward the proximal
end of said catheter so as to expose a length of catheter forward
of said ferrule, threading said catheter through said cannula into
position in said patient, and locking said catheter relative to
said cannula by wedging said ferrule between said cannula and the
outer surface of said catheter.
11. In a catheter placement device comprising a flexible plastic
cannula, an elongate catheter threaded into said cannula, said
cannula having an enlarged proximal end portion with a tapered
inner wall surface therein, and locking means comprising a ferrule
slidably carried on said catheter for locking said catheter
relative to said cannula when said catheter is in position in said
cannula, said ferrule having a tapered outer wall and a continuous
inner wall, the distal end of said ferrule being wedged between the
inner tapered wall of said cannula and the outer surface of said
catheter for locking said catheter relative to said cannula.
12. A method of placing and securing a catheter in a patient
comprising the steps of inserting a cannula shrouded needle into a
vein or artery of a patient, withdrawing the needle from the
cannula and leaving the cannula in position in the patient,
positioning a locking ferrule over the distal end of the catheter
with the locking end of said ferrule pointed toward said distal
end, sliding said ferrule toward the proximal end of said catheter,
threading the distal end of said catheter through said cannula into
position in said patient, and locking said catheter relative to
said cannula by wedging said distal end of said ferrule between
said cannula and the outer surface of said catheter.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to improvements in a catheter and method of
placing same, and more particularly to an intravenous catheter
placement unit and method.
2. Statement of the Prior Art
A few short years ago intravenous catheters were placed by a doctor
making a surgical incision or cutdown in the skin and vein so that
the distal end of a catheter could be inserted directly into the
vein and threaded a limited distance therein as desired. Recently,
needle and catheter devices have been marketed which made it
possible to place an intravenous catheter by using the needle
portion of the device to penetrate the intact skin for the
catheter. That is, during a medical procedure requiring the use of
an intravenous catheter having a fitting on the proximal end
thereof or having a funnel-shaped proximal end portion, difficulty
has been experienced in disposing of the cannulated needle after
the catheter has been placed. At least three methods have been
known to have been used heretofore. The first method incorporates
the use of a relatively large bore needle with a flexible catheter
passing through said bore. The needle with the distal end of the
catheter nested therein is first inserted into the vein of the
patient whereupon the catheter is threaded through the needle into
the vein an appropriate distance. The needle is then withdrawn from
the wound, leaving the catheter in place. The needle, due to the
fitting or funnel on the catheter, cannot be removed from the
catheter and because of its stiffness and its sharp point must now
be secured to the patient and to the catheter in such a way as to
prevent the needle from rupturing the catheter or from further
puncturing the arm of the patient. This last-mentioned procedure
wastes considerable length of catheter and requires an additional
encumbrance to the patient where the needle is taped down to
protect the catheter. Another disadvantage of this system lies in
the fact that once the needle is removed from the vein, it becomes
almost impossible to advance the catheter further.
Another disadvantage of this system is that the catheter has to be
threaded through the needle while the needle is in position in the
vein of the patient. During the medical procedures requiring the
use of intravenous catheters it is often necessary to manipulate
the catheter in and out of the vein to pass the distal end past an
obstruction in the vein. Using the needle as the guiding means for
the catheter into the vein, any backward movement on the catheter
causes the heel on the beveled needle to cut into the catheter and
has been known to completely sever the catheter so that the severed
portion will float freely in the vein of the patient creating
medical complications. In addition, if the patient should move or
flex the portion of the body where the needle has been inserted, it
could cause the needle to damage the inside wall of the vein or to
even puncture another opening in the vein.
In another prior method a needle is nested on the inside of a
flexible catheter with the point of the needle extending forwardly
of the catheter. The combined catheter and needle is inserted into
the patient and the needle is then removed from the inside of the
catheter so as to leave the catheter in place in the vein. A
connection is made to the proximal portion of the catheter so as to
extract blood or inject fluids into the bloodstream. Using this
system, if it is desired to place a long catheter in the vein of
the patient, it is necessary to have an equally long needle passing
up the inside thereof. It is obviously impractical to have needles
150 cm. long and even longer since they become excessively
flexible, difficult to manipulate, and since the needle cannot bend
around turns or the like in the vein, they cannot be placed beyond
the first turn.
A third prior method provides a cannulated needle about the outer
surface of the catheter, which needle is split longitudinally such
that when the needle is removed from the patient, the needle can be
peeled back, removed from the catheter and discarded. This has
eliminated the problem of protecting the catheter from the needle
once the needle is removed from the patient, but difficulty in
finding materials stiff enough for use as a needle and still
pliable enough to be removed from the catheter as intended has been
a problem. Secondly, once the needle is removed, no means for
changing position of the catheter is available.
SUMMARY OF THE INVENTION AND EXEMPLARY USES
The present invention, to the extent described in our
above-identified copending patent application and also described
herein, overcomes the disadvantages of the prior art and provides
for a flexible cannula having a needle or stylet through the center
bore thereof with the point extending beyond the exposed end of a
cannula. The combined cannula and needle is inserted through the
skin and into the vein of a patient. The needle is then withdrawn
and the cannula is permitted to maintain its position in through
the skin and into the vein of the patient. A long flexible catheter
of matching size or of a smaller diameter is then inserted into the
flexible cannula and is threaded through the cannula into the vein
of the patient an appropriate distance. A locking system is
provided for locking the catheter relative to the cannula in
position in the vein. Any one of the well-known medical fittings is
provided on the proximal end of the catheter which makes it
possible to connect the catheter to selected equipment for either
injecting fluids into or for removing fluids from the patient. The
catheter can be unlocked from the cannula and can then be either
inserted further, manipulated, or withdrawn in whole or in part
from the cannula. The cannula can remain in position in the patient
and when no catheter is in position therein, its proximal end is
capped or sealed.
With the cannula in place in the patient, the doctor is free to
employ any one of many different catheters or diagnostic devices.
For instance, by way of example but not limited thereto, long or
short length catheters can be interchanged, different diametered
catheters up to the limit of the inside diameter of the cannula can
be used, catheters with different radio opacities such as X-ray
opaque lines or completely X-ray opaque, can be employed, and
catheters of different tip configurations can be substituted. The
required catheter is selected and is threaded through the cannula
into the patient as soon as the cannula is uncapped. The locking
system is adapted to lock the catheter to the cannula at the
required point, said locking system also serving as a sealing means
for preventing blood from flowing between the catheter and
cannula.
Although the device of this invention has been found to function in
an excellent manner, in a further and preferred aspect of the
invention we have now further improved the locking system
especially where the locking system includes means resiliently
urging against the outer surface of the catheter. Using the further
improvement, the resilient force can be distributed or dissipated
over a larger area of the catheter outer surface so that tolerances
in manufacture of the locking system need not be close. Further,
the preferred locking system is easier and more surely moved to a
locking and sealing relationship with the catheter and minimizes
forces which might tend to slightly restrict the catheter.
While this invention is susceptible of embodiment in many different
forms, there is shown in the drawing and will be described in
detail a specific embodiment of the invention together with
modifications thereof with the understanding that the present
disclosure is to be considered as an exemplification of the
principles of the invention and is not intended to limit the
invention to the embodiment or modifications illustrated.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 shows a catheter placement device incorporating the
principles of our invention;
FIG. 2 shows a cannula and needle of our device in position in a
vein or artery of a patient;
FIG. 3 shows the cannula of FIG. 2 in position in the patient with
the needle removed;
FIG. 4 shows the cannula of FIG. 3 in position in the patient with
a portion of a catheter threaded through a ferrule and through the
cannula;
FIG. 5 shows the cannula and catheter in position with the ferrule
locking the catheter relative to the cannula;
FIG. 6 is a cross-sectional view taken along the lines 6--6 of FIG.
5;
FIG. 7 is a cross-sectional view taken along the lines 7--7 of FIG.
6;
FIG. 8 is a cross-sectional view taken along the lines 8--8 of FIG.
6;
FIG. 9 is an enlarged partial cross-sectional view similar to a
portion of FIG. 6 only employing a different diametered
catheter;
FIG. 10 is a cross section showing an improved locking system in
locking and sealing position;
FIG. 11 is a fragmentary view of a locking member of the system of
FIG. 10;
FIGS. 12 and 13 are fragmentary views of other forms of locking
members which may be used in the same general manner as the locking
member in FIGS. 10 and 11; and
FIG. 14 is a fragmentary view from the top of the locking member as
illustrated in FIG. 11.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
As shown in FIGS. 1 through 9, one embodiment of the invention is
illustrated in substantially full scale view except certain
cross-sectional views are enlarged to help illustrate the principle
of the invention.
The embodiment of the invention shown in FIG. 1 comprises a needle
10 and a cannula 12 combined as one unit 14. A catheter 16 and
locking member or ferrule 18 is combined as a second unit 20. The
needle 10 can either be in the form of a stylet or a hollow needle
with either a pencil point (not shown) on the end thereof or a
tapered point 22, as desired. The tapered point 22 of the stylet or
needle 10 extends from sharp point gradually sloping to a junction
with the opposite wall of the needle. The point of the needle in
the illustrated form extends beyond the forward portion of the
cannula 12. The proximal end 26 of the needle is connected with a
cylindrical connector member 28 which has a knurled portion 30 on
its outer surface for gripping purposes. In the illustrated form of
needle 10, it is hollow and will permit fluids to flow through the
bore therein.
The cannula 12 is formed of a plastic material that is flexible
enough to flex and bend into conforming shapes without too much
effort and is still stiff enough to adhere to the needle and be
pushed through an incision made by the needle point into the vein
of the patient. The material of the cannula should also be stiff
enough to withstand collapsing forces created by the skin and
tissues of the patient against the cannula when the needle is
removed and the cannula is in unsupported condition in the
patient.
The cannula 12 has an elongate portion 32 of uniform diameter
conforming to the outside diameter of the body of the needle. At
the distal end of the portion 32 a taper 34 is formed sloping
downward to a feather edge 36. An enlarged section 38 is integrally
formed on the proximal portion of the cannula and has an inner
surface 40 tapering gradually from the proximal end down to the
elongate portion 32. The cannula 12 encircles the needle 10 with
the proximal end abutting against the cylindrical connector member
28 of the needle and with the feather edge 36 positioned either in
alignment with the rear edge of the point bevel 22 or spaced in
close proximity therewith.
The unit 20 including the catheter 16 and locking member or ferrule
18 is supplied as a separate item from the needle and cannula unit
14 although they are part of the same set. The catheter 16 may be
of any desired length varying from 15 cm. to 150 cm. and may be
extruded from clear polypropylene or polyethylene material. The
distal end 42 of the catheter may be provided with a single opening
or may be a rounded blind end with plural openings 44 spaced down
either side thereof. The major portion of the catheter 16 is
composed of a substantially uniform-diametered body portion 45. An
X-ray opaque line 46 may be embedded in said body portion and may
run from the distal end 42 the full length of the catheter to the
proximal end 48 or the line 46 can terminate at some intermediate
point short of the proximal end. Spaced from the distal end portion
42 the body portion 45 of the catheter is gradually enlarged as at
50 and has an attaching means 52 carried on the proximal end 48
thereof. The attaching means 52 could be for use with a Luer lock
arrangement or any other appropriate attaching device. The
gradually tapering portion 50 of the catheter has an external
surface lying at a predetermined shallow angle relative to the axis
of the catheter for a purpose to be described hereinafter. The
catheter can be made of an X-ray opaque material such that it will
permit visual placement of the catheter under fluoroscope.
The locking member or ferrule 18 has a tapered body portion 54
extending from a wide mouthed proximal end 56 to a narrow-mouthed
distal end 58. The opening at the distal end 58 is of a size
approximating the outside diameter of the body portion 45 of the
catheter so as to permit sliding relationship with the elongate
body portion of said catheter. The outer sloping surface of the
ferrule 18 lies at an angle relative to the axis of the ferrule
which is slightly less than the angle of slope of the inside
surface 40 of the enlarged portion 38 of the cannula 12. The inner
surface of the ferrule 18 parallel to the axis of said ferrule has
an angle which is slightly larger than the angle of slope of the
exterior surface of the proximal end portion 50 of the
catheter.
The ferrule or locking member 18 should be made of a material such
as polyvinyl which is softer than the material of the catheter so
that when it is desired to lock the catheter relative to the
cannula, the locking member or ferrule 18 is moved along the
catheter until the distal end portion end portion 58 wedges between
the slope 40 in the cannula and the outer surface of the body
portion 45 of the catheter. The wedging action will cause the
distal end 58 of the ferrule to constrict and grip the outer
surface of the catheter to lock the catheter against axial movement
relative to the cannula. The gripping action will be such as not to
constrict the catheter or to reduce its internal diameter in the
vicinity of the locking contact. To release the lock between the
cannula and catheter, the ferrule is twisted and urged toward the
proximal end of the catheter until it releases the locking action
whereupon the ferrule can be moved along the length of the catheter
and the catheter can be moved in or out relative to the
cannula.
As shown in FIG. 2, a section of the anatomy of a patient is shown
cut away illustrating a portion of skin 60 with a vein below the
skin identified as 62. The needle and cannula unit 14 is assembled
on the hub of a syringe or other manipulating instrument such that
the needle is used to puncture the skin and one wall of the vein
for placing the cannula in the vein. Once the point 22 of the
needle 10 punctures the vein, blood will flow up the hollow portion
of the needle so that the person placing the cannula can tell that
the vein has been pierced. The needle 10 can now be removed from
the cannula 12 and the proximal portion 38 of the cannula can be
capped with an appropriate seal to prevent bleeding through the
cannula. After removing the cap, the distal end 42 of the catheter
16 can be inserted through the cannula and can be carefully
threaded into the vein of the patient. With very careful placement
techniques the distal end of a catheter can be threaded through the
vein and/or artery for a considerable distance, even all the way to
the heart under certain circumstances.
Once the distal end of the catheter is positioned where desired,
the locking member or ferrule 18 is slid along the body portion 45
of the catheter 16 until the distal end 56 of the ferrule 18 enters
the proximal opening in the rear of the cannula. The ferrule 18 is
forced into the sloping end of the cannula so that the distal end
portion of the ferrule wedges between the sloping wall 40 of the
cannula and the outer surface of the catheter. The pressure created
by the wall 40 of the cannula against the outer forward surface of
the distal end of the ferrule will cause the ferrule to grip the
outer surface of the catheter and lock the catheter relative to the
cannula. The gripping action is such as not to collapse the wall of
the catheter but merely grips against the outer surface of the
catheter without affecting the internal diameter of the catheter.
The proximal end portion 52 of the catheter is then connected with
the appropriate equipment for either injecting intravenous fluids
into the vein of the patient or for whatever purpose the catheter
has been placed.
FIGS. 6, 7, 8 and 9 illustrate the locking action created by the
ferrule on the outer surface of the catheter and on the inner
surface of the cannula. FIG. 6 illustrates a catheter with an
outside diameter substantially coinciding with the inside diameter
of the cannula while FIG. 9 shows a catheter with an outside
diameter considerably smaller than the inside diameter of the
cannula. The forward or distal end portion 58 of the ferrule 18
first engages with the sloping wall 40 of the cannula which causes
the circumference of the ferrule to constrict slightly against the
outer wall surface of the catheter. This provides the gripping
action between the ferrule and catheter for preventing the catheter
from moving in or out relative to the ferrule. Since the ferrule on
its outer surface of the distal end thereof is gripped against the
slope of the cannula, it likewise cannot move and therefore the
catheter is locked relative to the cannula. If it is decided that
the catheter should be moved over or inserted in a greater distance
in the vein, it is merely necessary to slightly twist and pull
rearward on the ferrule until it is unseated from the cannula
whereupon the catheter may be further slid or threaded through the
cannula into the vein of the patient an appropriate distance.
In FIG. 9 the catheter 16' has an outside diameter which is smaller
than the inside diameter of the cannula 12. The ferrule 18 has its
distal end opening of an inside diameter coinciding with the
outside diameter of the catheter 16'. The end 58 of the ferrule is
adapted to engage the inner surface of the cannula to constrict the
opening in the ferrule sufficient to grip and lock the catheter
relative to the cannula. It is recognized that blood can flow
between the catheter and the cannula but the ferrule will serve as
a plug to block any bleeding around the catheter beyond the distal
end of the ferrule. As a practical matter only a few drops of blood
would be permitted to seep between the catheter and ferrule.
The last enumerated feature, namely, the ability to use different
diametered catheters up to a maximum equal to the inside diameter
of the cannula lends considerable flexibility to the device.
Frequently, after the cannula of a certain size is set in place, it
is desired to insert different catheters for different purposes,
each catheter possibly being of a different diameter or different
characteristic, i.e., X-ray opaque, blunt or open-ended and the
like. The ability to use the same cannula for various diagnostic
and treatment devices while still being able to lock the catheter
in a desired position is an important and useful element of our
invention.
The herein disclosed catheter placement device makes it possible to
have the needle which is used to assist in the placement of the
cannula in the vein completely removed from the device so as not to
create the usual hazards incident to having the needle on the
catheter during use of the device. It is contemplated that a
packaging means will be provided with the catheter and ferrule unit
such that the catheter could be threaded through the cannula
directly from a sterile package without the doctor or technician
actually touching the outer surface of the catheter.
The method of placing the catheter becomes quite simple when the
technique has been mastered. That is, the needle and cannula unit
14 is removed from its sterile package and is inserted through the
skin and into the vein of a patient. Blood coming up the needle
will indicate when the needle and cannula are in proper position.
The needle is then removed from the cannula, plugged by plug 39, an
the cannula is taped to the skin of the patient. Immediately prior
to entry of the appropriate catheter into the cannula, the plug 39
is removed from the cannula, and placed on the proximal end of the
catheter. Now the catheter with the ferrule surrounding the body
thereof is then threaded carefully through the cannula until the
distal end of the catheter reaches the appropriate location in the
patient. The ferrule is then slid forward on the catheter and locks
the catheter relative to the cannula. The proximal end portion of
the catheter is then attached to the appropriate mechanism for
intravenous feeding or whatever other purpose the catheter has been
placed.
The device makes it possible to require only one vein puncture such
that the catheter or different catheters may be inserted through
the cannula as many times as is desired. Once the needle and
cannula have entered the lumen of a vein, the needle is removed and
the cannula taped in position for an indefinite period of time, for
instance, up to 3 weeks. The proximal end of the cannula may be
plugged when no catheter is in position so as to prevent bleeding
up the cannula. Since the cannula is of plastic material, it does
not present sharp edges in the lumen of the vein and therefore
there is no danger that movement of the patient in the vicinity of
the cannula will cause the cannula to puncture the walls of the
vein or the skin of the patient.
Turning now to FIGS. 10, 11 and 14, the locking system shown is
similar to that shown in FIG. 9 except that ferrule 18a has a
tapered distal end 58a. When the ferrule 18a is moved to locking
position tightly engaging the outer surface of catheter 16, the
force against the outer surface is distributed over larger
elliptical area rather than a smaller circular area and the inner
surface of the ferrule 18a near end 58a is permitted to flatten out
more between the cannula inner surface and the catheter outer
surface for better sealing at less close fitting tolerances. Also,
the pointed end pivoted by the taper assists in assembly of the
device and movement of the ferrule 18a to its locking and sealing
position. The wide area of contact produces a better lock without
crushing or constricting the catheter.
In FIG. 12, a slit 59 at ends 58b provides a similar function in
increasing the area of engagement, distributing force, decreasing
the closeness of tolerances required and providing a better and
more positive seal. More than one slit 59 may be employed so as to
provide a greater tolerance level between inside of the cannula and
the outside diameter of the catheter. In making the slits some
material is removed so that the diameter of the outer end 58b can
be reduced by pressing the slit or slits 59 closed. This permits
the greater tolerance between the cannula and the catheter and
distributes the contact surface therebetween over a wider area. In
addition the slit intersection with the end 58b provides
longitudinal edges 60, 61 which serve to grip the inner surface of
the cannula and the outer surface of the catheter in a more
positive manner. That is, as the ferrule is pushed into the cannula
for locking it is twisted relative thereto and as a result either
edge 60 or 61 will bite into the cannula and catheter to increase
the gripping and locking action.
In FIG. 13, end 58c of ferrule 18c is provided with a circular
bevel eliminating the outer square circular edge of ferrule 18 and,
in effect, defining an inwardly tapered frustoconical end 64. The
tapered end 64 has two lines or rings 65, 66 of contact which are
spaced axially apart by the amount of taper in the end 64. As the
ferrule is pushed into the cannula and twisted for locking
purposes, the ring 66 will apply force to the cannula and the ring
65 will apply force to the catheter. As the locking forces increase
the areas around the rings 66, 65 will assume some of the locking
forces to provide a more positive lock to the catheter relative to
the cannula. It will be apparent that end 58c permits easier
movement of ferrule 18c to locking position and that the end, being
progressively less thick, will deform over a larger area between
the outer surface of catheter 16 and the cannula 12 and provide a
more complete force distributing seal even when the parts are made
to wider manufacturing tolerances.
Other modifications, uses and advantages of this invention will be
evident to those skilled in the art.
* * * * *