Note: Descriptions are shown in the official language in which they were submitted.
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This invention relates to subcutaneous insertion of
catheters into veins such as the femoral or subclavian veins,
and more particularly to a dilator for following a guide wire to
form a tunnel for receiving the catheter.
The invention will be described with reference to the
procedure of inserting a catheter for use in hemodialysis by the
Seldinger technique, but it will be recognised that this
description is exemplary of procedures for other purposes and
that the dilator described here can be used in such other
procedures.
Since Dr. Seldinger introduced his technique in 1953,
it has become common practice to use guide wires when inserting
catheters into veins. In hemodialysis procedures, a hollow
needle is first used to create a small incision in a vein,
typically 4 French. This hollow needle allows blood flow to
show that the needle has been positioned in the vein. Next a
very flexible wire is pushed through the needle, into the vein,
and then moved for some distance down the vein to act as a guide
for subsequent engagement of a dilator and then a catheter.
With the wire in place, the needle is withdrawn leaving behind
tissue expanded to about 4 French and an opening in the vein of
about the same size. The eventual catheter to be placed is
typically 11 French so that dilation to 11 French (or close to
this size) must take place. As the dilator is pushed along the
wire, blood will flow through the dilator so there is further
blood loss as this takes place.
At this point it is worthwhile noting that this is a
subcutaneous procedure which means that the leading end of the
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dilator must first stretch the quite strong skin which requires
a significant force and then dilate the underlying tissue,
before stretching the vein. The forces required and the fact
that the surgeon is dealing with very flexible and resilient
material makes it difficult for the surgeon to sense the dilator
following the wire, especially if larger forces are required due
to the enlargement being done by a single dilator. The
procedure can be very traumatic for the patient if not done
properly.
10One approach to creating a tunnel is to slide a dilator
over the wire. However the difference between 4 French and 11
French makes it difficult to insert an 11 French dilator over
the wire for two reasons. Firstly the enlargement demands
significant force, and secondly this force reduces the surgeon's
tactile sensitivity so that when the catheter is inserted over
the wire it can be driven off track taking the wire with the
catheter into adjacent tissue. This can result in serious
~ trauma. This problem is emphasized by the fact that the tissue
tends to return to its original form after the needle is removed
so that the dilation required can possibly be from the wire size
to 11 French.
The tactile sensitivity can be improved by the use of a
series of dilators of increasing diameter. Such a procedure is
slow because each of the dilators must be engaged over the wire,
removed, and a new dilator put in place. Because the dilators
are forming a tunnel of increasing size, there will be a
significant loss of blood. Also, each of the dilators must be
handled very carefully because the leading ends enter the vein
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and if the dilator is pushed too far, it could damage the side
of the vein opposite the entry opening.
A second approach to dilation which has been used is to
insert the ultimate catheter directly over the wire. This is
5 not a desirable procedure because the design requirements of a
catheter used in this way for dilation are contrary to the
design requirements of a catheter which make it suitable to be
placed in a vein for the time needed for treatment. On the one
hand, the tip of the catheter designed for dilation must be
quite firm so that when it is pushed along the wire, the tip
will dilate the tissue without collapsing the tip. By contrast
a catheter designed for prolonged use in a vein should have a
very flexible tip so that any movement which causes contact
between the tip of the catheter and the vein will result in the
tip flexing to minimize the risk of deforming the vein.
A further approach to dilation has been to provide a
set of dilators which fit one over another. A first and smaller
dilator is entered over the wire and then this is followed by
one or more dilators which are slipped over one another and lead
forwardly to a predetermined location so that the resulting
combination of dilators represents generally the size OL the
catheter to be placed. While this combination of dilators has
some advantages, it must be remembered that the sizes are very
small. The dilator is expanding tissue generally from the size
of the needle which is typically 4 French up to about 10 or 11
French. There is very little room for wall thickness in these
sizes and consequently the dilators are not simple to hand]e and
the procedure of sliding one over another can be quite dangerous
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due to the fact that the first dilator is in place ln the vein
and can cause damage if oscillated sideways or pushed forwardly.
As a result of these difflculties t:here is a need for a
single dilator which will follow a wire and form a tunnel of a
shape and size which will permit insertion of a catheter
directly regardless of the fact that the catheter may have a
very flexible tip.
Accordingly, a dilator is provided, in accordance with
one aspect of the invention, for use with a guide wire to create
a subcutaneous tunnel into a vein for subsequent insertion of a
calheter over the wire and into the vein. The dilator has an
elongate main body with a first cross-section extending about a
longitudi.nal axis and a tip portion extending from the main body
longitudinally and terminating at a distal end of the dilator.
The main body extends from the tip portion to a proximal end of
the dilator, and the tip portion has a leading taper enlarging
from the distal end towards a second cross-section smaller than
the first cross-section. ~ tailing taper extends smoothly from
the main body and converges from the first cross-section to the
second cross-section, and an opening extends between the
proximal and distal ends of the dilator for receiving the guide
wire.
In accordance w;th another aspect of the invention, a
method of creating a subcutaneous tunnel for catherisation
procedures involving inserting a catheter into a vein is
provided.
The invention will be better understood with reference
to the drawings,in which:
Fig.l is a somewhat schematic isometric view of a
preferred embodiment of a dilator according to the invention
shown partly entered ;nto a subcut:aneous tunnel and following a
wire which has been engaged ;n a vein.
The accepted procedure for subcutaneous insertion of a
catheter involves engaging a needle into a vein 20 underlying
body tlssue 22 beneath t:he skin 24. Typically the needle
creates a tunnel 26 of about 4 French and of course once the
needle is removed this tunnel tends to collapse around a
Seldinger guide wire 28 left behind when the needle is
withdrawn. For the purposes of the illustration the tunnel 26
is shown as it would appear with the needle engaged.
A dilator 30 according to the invention consists of an
elongate main body 32 extending about a longitudinal axis from a
proximal end fitting 34 to a tip portion 36 at the distal end of
the dilator. This tip portion has a leading taper 38 spaced
from a trailing taper 40 which together combine to dilate the
tunnel. The tapers 38 and 40 are separated in this preferred
embodiment by a leading portion 42 which is of reduced cross
section compared with the main body 32. Typically the main body
is of 12 French and the portion 41 of 10 French and an opening
extends longitudinally through the dilator to contain the wire
28 as shown in broken outline.
The leading taper 38 fits snugly about the wire 28 and
when the dilator is fed along the wire, it initially makes
contact with the skin 24 and the taper dilates the skin and then
commences dilation of the tissue 22. This continues until the
trailing taper 40 meets the skin whereupon dilation of the skin
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to the full size of the body 32 takes place as the taper 38
continues to dilate the tissue. As the dilator progesses, the
taper 40 dilates tissue until the taper 38 has dilated the vein
and entered the vein, to dilate the vein to the size of the
leading portion 42. At this point the skin and some of the
tissue has been dilated to the full size of the dilator and a
portion of the tissue controlled by the length of the leading
portion 42, and the access opening in the vein has been dilated
to the size of the portion 42.
The result is that a subcutaneous tunnel is formed
capable of receiviny a catheter guided by the wire 28 and which
is itself used to dilate only a portion of the tissue and the
vein from about 10 French to 11 French. This permits the use of
a relatively soft tip catheter and yet permits the catheter to
complete the dilation to the size and shape of the catheter.
Consequently, if the catheter is not entirely round or the exact
shape of the dilator, the stretching will enable the catheter to
form an opening in the vein which tends to be self sealing. At
the same time the catheter is not required to dilate all of the
tunnel but only the very last part where it engages the vein.
The tissue also stretches around the catheter and this combined
with the veln helps to ensure sealing.
It should also be noted that the catheter insertion is
done using a single dilator which minimizes time, ensures a good
seal, and at the same time makes engagement simple because the
lead part is of a small cross section and this gets buried in
the tunnel and then leads the larger taper 40.
Variations can of course be made to the dilator. In
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particular the leading portion 42 can have any length consistent
with meeting the requirements of having the portion 40 engage
through the skin and into the tissue at the time the leading
taper 38 engages the vein. Also, portion 42 could itself be
S slightly tapered resulting in a gradual dilation from the
leading end of the dilator through to the main body 32.
Procedurally, the dilator helps to ensure a smooth
entry of the catheter with minimal trauma. The dilation can be
considered to be in three stages: firstly dilation of the
complete tunnel to the size of portion 42; secondly, and
contemparaneously with the latter part of the dilation to the
size of portion 42, dilation of skin and adjacent tissue to the
size of body 32; and lastly, dilation of the vein and adjacent
tissue to the size of the catheter by the catheter.
~11 of these variations are within the scope of the
invention as claimed.
