Note: Descriptions are shown in the official language in which they were submitted.
This invention relates to a dual lumen cannula,
and more par-ticularly to such a cannula or insertion into
the subclavian vein of a patient to facilitate haemodialysis
treatments.
For regular haemodialysis, permanent vascular
access is normally provided by means of a surgically
constructed arterio-venous fistula, created if possible in
advance of need.
The conventional method of conducting haemodi.alysis
on a patient is to introduce into an arterialized vein,
normally a lower arm vein, one or two blood flow needles.
Blood is removed from the patient to an exterior haemodi-
alysis machine and then the treated blood is returned to
the patient at substantially the same location. At least
one puncture of the vein needs to be made for such catheter
:; insertion whenever the patient undergoes a haemodialysis
treatment. Commonly two separate needle devices are used,
. one for blood outflow and the other for blood return,
although there is a growing interest in dual lumen catheters
which have the advantage that they require only one vein
puncture. Examples of conventional co-axially arranged
metal cannulae for use in a limb of the patient are to be
found in U.S. patents 4,037,599 to Raulerson; 4,073,297 to
Kopp; 4,134,402 to Mahurkar; and 4,096,86~ to McLauc~hlin.
All of these examples of prior art show a rigid, metal
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needle-type cannulae for temporary use during the actual
haemodialysis or transfusion etc. These devices are removed
once the procedure is completed. None of the devices is
suitable for insertion into a subclavian vein.
Although the arterio-venous fistula is the
standard and accepted method for permanent vascular access,
some patients experience end stage renal failure without
warning, and established fistulae may fail unexpectedly.
With the growth of large programmes for long-term peritoneal
dialysis, an increasing number of patients must be transferred
at short notice to haemodialysis because of peritonitis.
Such patients do not usually have arterio-v nous fistulae
constructed in advance, since many of them will never need
them. Patients on long-term peritoneal dialysis may also
need short-term haemodialysis while they undergo abdominal
surgery. Transplant recipients whose arterio-venous fistulae
have thrombosed may develop acute renal failure. For all
these categories of patients, the silastic teflon shunt,
though immediately usable, wastes blood vessels and may
not be feasible in patients whose access sites have already
been used. Temporary peritoneal dialysis is not always a
suitable alternative.
There is thus a need for a simple, immediately
usable vascular access method which does not destroy blood
vessels, and does not limit the patient's mobility. Tempor-
ary vascular access for haemodialysis can be obtained with
a femoral cannula introduced by the Se]dinger technique,
normally lnserted in the femoral vein.
With such prlor art devices, tlle patient must be
prepared and the catheter applied carefully, by medically
trained personnel, prior to every haemodialysis use. E`or
patients with absence of renal function, this can be
several times per week. The preparation and application
is time-consuming and difficult to perform on an emergency
basis. The cannula cannot be left in situ after dialysis
if the patient is to remain mobile~ Moreover, repeated
insertions lead to the build-up of scar tissue at the
access sltes of the patient. Some means of readily usable,
semi~permanent vascular access would be preferable.
The present invention is intended to provide an
indwelling subclavian cannula which is particularly suitable
for temporary haemodialysis. When not in use, the cannula
remains in situ without unduly restricting the mobility or
activities of the patient. Accordingly the invention provides
a dual lumen cannula, having inner and outer lumens located
co-axially so that only one insertion into the vein of the
patient is required. Both of the lumens are elongated and
the inner lumen is more fle~ible than the outer lumen which
is pre-formed to have an arcuate curve reflecting the general
shape of the subclavian vein. Although the cannula is
inser-ted with -the inner lumen inside the outer lumen, the
inner lumen can be replaced without removing the outer lumen.
Also, when not in use, the inner lumen is removed and
heparinized physiological saline solution can be injected
periodically into the outer lumen. The facility to remove
the inner lumen limits the possibility of blood clotting when
the cannula is not in use.
The invention will be better understood with
reference to the following description taken in combination
with the drawings, in which:
Fig. 1 is a diagramatic representation of a preferred
embodiment of a dual lumen cannula according to the invention
positioned in the subclavian vein of a patient and shown in a
storage mode between haemodialysis treatments;
Fig. 2 is a side view of the preferred embodiment
of dual lumen cannula according to the invention;
Fig. 3 is a sectional end view on line 3 3 of Fig. 2;
and
Fig. 4 is a sectional side view to an enlarged scale
and showing the tip or leading end of the cannula.
Reference is first made to Fig. 1 which shows the
preferred embodiment of subclavian haemodialysis cannula of
the present invention in position on a patien-t in a mode between
haemodialysis treatments. The cannula is secured in position
by means of a conventional adhesive dressing 20 with the cannula
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positioned through the dressing. The cannula is shown
generally by the numeral 22 and consists of an end portion
24 coupled to an outer tube or lumen 26, and also having
an inner tube or lumen which is not shown in -this figure
but which wlll be described subsequently. The inner lumen
is positioned within ~he outer lumen 26 during haemodialysis
procedures.
ReEerence is next made to E~ig. 2 to more Eully
describe the dual lumen cannula according to the invention.
As seen in Fig~ 2 the outer lumen 26 is curved and
terminates at its distal end in a tapered portion 28 which
fits snugly about an outer end of an inner tube or lumen
30. As seen in Fig. 3, the inner lumen 30 fi-ts loosely
within the outer lumen 26 to permit f]ow hetween -the lumens
as will be descri~ed.
Returning to Fig. 2, the outer lumen 26 ends at
lts inner end in a bulbous portion 32 which receives one
end of the flexible tubular connector 34. This connec-tor
is retained on the lumen 26 by a band 36 which is shrunk on
the connector and combines with the bulbous portion 32 to
make a strong mechanical joint between the connector 34 and
the lumen 26.
At its other end, the connector 34 is designed
to receive a male end portion of a Y-fitting 38 having a
first branch 40 and a second branch 42. A flexible tube
44 is pushed on an end of the branch 40 and, at its o-ther
end, receives a first part 46 of a luer fitting which is
conventionally used in medical equipment associated with
a cannula of this type. The other branch 42 is associated
with a further flexible tube 48 and this receives a further
first part 50 of another luer connector. The lnner lumen
30 is positioned inside the outer lumen 36 and passes
through the connector 34, second branch ~2 of the Y-fitting
38, through the flexible tube 48, and through the first
part 50 of the luer connector. The inner luer has attached
to it a second part 52 of the luer connector and this can
be threadably engaged on the part 50 and includes a tubular
part 54 projecting outwardly for receiving tubing from a
haemodialysis machine or the like in conventional manner.
lS A similar fitting would be provided on the first part 46
o:E the luer connector on the branch 40 simply for the purpose
of connecting tubing. With this arrangement set up and
positioned on the patient as shown in Fig. 1, it will be
appreciated that blood can be withdrawn through the space
between the inner and outer cannulae and through the branch
40 of the Y-fitting to apparatus (not shown) for haemodi-
alysis trea-tment. The treated blood is then returned via
the lower connector part 52 and innerlumen 30. In order
to facilitate flow into and out of the lumens 26, 30
they are perforated as shown in Fig. 4 which is drawn to a
larger scale than FigO 2. It will be seen that the inner
lumen 30 projects beyond the outer lumen 26 and is perforated
by openings 56. Similarly, the outer lumen 26 is perforated
by openings 58 and the general arrangement of flow is
indicated by arrows. It should be noted that the distal
end of the inner lumen 30 is tapered inwardly and this is
done to cause the lumen to fit snugly about ~ guide wire
used for insertion as will be described.
The procedure for using the cannula will be
described with reference particularly to Figs. 1 and 2.
After first preparing the patient for the procedure, the
patient lies on his back with his face turned away from the
site. Taking the normal medical precautions, an incision
is made and a fine wire is inserted into the subclavian
vein using the Seldinger technique. The cannula can then
be inserted by sliding it over the wire with the wire
engaged inside the inner lumen 30. The tapered end of the
lumen facilitates entry as does the tapered end of the outer
lumen 26~ The cannula is gradually worked into the subclavian
vein and the residual shape of the outer lumen~ although
flexible for insertion, naturally takes up the shape of the
vein. The purpose of this shaping is twofold. Firstly
it permits the use of a relatively rigid outer lumen which
resists kinking significantly while nevertheless permitting
sufficient resilience for insertion. This resistance to
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d~''''' A , _ ,
kinking is of course very important and not readily achieved
withou-t this combina-tion of curvature and rigidity.
After insertion the equipment used for haemodi-
alysls is connected to the cannula using the usual precautions
to avoid embolus etc. Flow can then take place from the
patient to the equipment essentially by the outer lumen
and then returned within the inner lumen.
After treatment the inner lumen can be withdrawn,
and the branch 42 of the Y-fitting sealed both by a luer
cap placed on the first part 50 of the luer connector
and by a sliding clip of the type indicated by numeral 58
-; in FigO 2 and identified as 60 in Fig. 1. This double
closure is of course for safety reasons so that should the
luer connec-tor fail, the clip will continue to seal the
branch 42.
The branch ~0 is treated slightly differently.
The cap placed on the first part 46 of the luer connector
consists of a cap having a diaphragm which can be perforated
by a needle Eor injecting heparin containing physiological
saline solution. This i5 done to prevent clotting at the
end of the outer lumen while this lumen remains in place
within the vein. It will be appreciated that because the
inner lumen has been removed, there is no location whcre
blood could be trapped and where this blood would c:Lo-t~ All
of the inner part of the outer cannula 26 receives and is
.
z~ l
washed by the heparin containing liquid. Also, after
inserting the liquid, a further clip 58 can be placed on
the tube 4~ to seal the branch 40 of the Y-fitting. The
cap used to permit injection of the heparin liquid also
serves as a seal so that both branches are double sealed.
The next time the patient requires haemodialysis,
it is a simple matter to insert a new inner lumen and to
couple the structure to the necessary equipment. It will
be appreciated that the inner lumen used for the second
procedure need not have the tapered end to fit on the wire
since the inner lumen passes into the vein inside the
outer lumen which is already positioned in the vein. It
is therefore possible to use a somewhat similar structure
for the inner lumen for the seconcl and subsequent uses of
the cannula.
In the preferred embodiment the outer lumen 26
is of polytetrafluoroethylene having an internal diameter
.125 in. and an external diameter .155. The innex
lumen is made of polyethylene having an inner diameter 075
in. and an outer diameter of .092 in. The connector 34 and
tubes 44, 48 are of a medical grade silicone rubber and the
Y-connector is made of polypropylene. ~-
It will be appreciated that the dimensions used
for the tubing can vary within the limitations of providing
adequate flow and insertion into the subclavian vein. If
the structure is to be used elsewhere on a human, then
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sim.ilar ~rameters wlll have to be consiclered in relation
to the speci:fic use of the cannula.
The outer lumen 26 is preferably of a radio-
opaque material to permit X-ray. If the structure is
trans~arent to X-ray then some .identifiction band will have
to be applied -to the outer-lumen.
It is a signi.ficant feature of the present
invention that although two lumens are used, in the period
between treatments there is a minimized risk of blood clot~
ting and a simplified procedure in that heparin containing
physiological. saline solution need be inserted in one side
of the Y-fitting only. In previously suggested structures,
it was not possible to remove the inner cannula and it was
necessary to provide heparin in both the inner and outer
cannulae~ Further, without removal of -the inner cannula
it is not foreseen how it would be possible to avoid stagnant
blood appearing.somewhere between the two cannulae with
resulting risk of clotting. Also, because the present
structure has sufficien-t inherent rigidity, i-t is unnecessary
to use an obturator. ~reviously suggested structures have
required an obturator to ensure that the outer cannula does
not kink during insertion. It would be appreciated that
in materials of this type, once the tube has kinked, the
weakness resulting from the kinking causes it -to collap.se
very readily. Yet a fur-ther advantage of this structure is
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~.....
that it can be inserted over the wire used in the Seldinger
techinque taking advantage of -the weak but small outer end
of the inner lumen because this is supported on the wire
during insertion. There is therefore a progressive
enlargement during insertion, beginning with the wire,
followed by the inner lumen and then by -the outer lumen.
This is advantageous in stretching the tissue and providing
a clean insertion.
It will also be appreciated that because the
inner lumen has been removed, the sealing of the tube 48
is improved. It is undesirable to attempt to seal a tube
which contains a further tube. No device can ensure proper
sealing and yet, where a dual lumen is concerned, such
sealings have been attempted. With the present s-truc-ture
once the inner lumen has been removed, then adequate sealing
can be provided simply both at the tube 48 and at the outer
end of the first part 50 of the luer connector.
It will be appreciated that the invention can
take many forms within the scope of the accompanying claims
and that the embodiment described is a preferred embodiment
which is explarary of these variations.
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