Note: Descriptions are shown in the official language in which they were submitted.
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MEDICAL TUBE ASSEMBLIES
Background of the Invention
This invention relates to medical tube assemblies.
Tracheostomy tubes are inserted through a surgically-made opening in the
throat so
that one end of the tube locates in the trachea and the other end projects
externally.
Ventilation gas can then be supplied to the patient's airways via the tube or
the patient can
breath normally through the tube.
Tracheostomy tubes are often used where prolonged ventilation is required. In
use,
however, the inside of the tube becomes coated with secretions, which can
reduce the flow
of gas along the tube and provide a site for bacteria to multiply. Periodic
removal and
replacement of the tube is relatively traumatic and uncomfortable for the
patient, and must
be carried out by surgical staff. It is, therefore, preferable to clean the
tube, either by using a
suction catheter inserted along the bore of the tube or, preferably, by using
an inner cannula.
Where an inner cannula is used, this is configured to form a close sliding fit
within the tube
extending along its entire length. The inner cannula remains in place during
normal
ventilation and, when secretions have built up, it is removed and replaced by
a new inner
cannula. This replacement procedure can be carried out regularly by nursing
staff so
provides an efficient and effective arrangement for maintaining effective
ventilation and
reducing the risk of respiratory infection. Examples of tracheostomy tube
assemblies with an
outer tube and an inner cannula are described in, for example, GB2056285,
US4315515,
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US4817598, US5119811, US518461 1, US5386826, US6019753, US61351 10, US4817598,
GB0800112.5, W094/0 1 1 5 6 and W004/101048.
There are, however, problems with inner cannulae. The cannulae do reduce the
cross-
sectional area of the effective passage through the tube so it is important
for the wall
thickness to be as small as possible and for the cannula to be a close sliding
fit within the
outer tube whilst allowing free insertion and removal. It is also important
that the inner
cannula does not buckle, or otherwise deform in a manner that would reduce gas
flow, when
inserted along the outer tube, which may not be smoothly curved. The inner
cannula should
extend along the entire length of the outer tube without projecting from its
end and should
preferably form an effective seal at the patient end to prevent seepage of
material between
the inner wall of the inner cannula and the outer wall of the inner cannula.
It has been found
that a most effective assembly can be provided if the patient end of the outer
tube is formed
with a shallow intumed lip, in the manner described in US4315515. The inner
cannula is
configured so that its patient end abuts the rear-facing surface of this lip.
In this way, the lip
prevents the inner cannula projecting beyond the outer tube and also helps
improve the seal
between the patient end of the inner cannula and outer tube. One problem,
however, with this
arrangement is that when the inner cannula has been removed and a suction
catheter or other
elongate device is inserted through the outer tube to extend beyond the
patient end of the
outer tube, there is a tendency for the tip of the catheter or device to catch
on the intumed lip
at the patient end of the tube.
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Brief Summary of the Invention
It is an object of the present invention to provide an alternative medical
tube
assembly.
According to one aspect of the present invention there is provided a medical
tube
assembly comprising an outer tube and an inner cannula that is insertable and
removable
from the outer tube, the outer tube having, in use, a curve or bend along a
part at least of its
length and an internally-projecting lip towards its patient end adapted to
limit insertion of the
inner cannula, the lip being provided with a recess located at the outside of
the curve of the
tube such that, when the inner cannula is not in place, an elongate device can
be inserted
along the outer tube and slide through the recess beyond the patient end of
the outer tube
without catching on the lip.
According to another aspect of the present invention there is provided a
medical tube
assembly comprising: an outer tube; an inner cannula and a suction catheter,
the inner
cannula being insertable and removable from the outer tube, the outer tube
having, in use, a
curve or bend along a part at least of its length, a patient end, a machine
end and an
internally-projecting lip towards its patient end adapted to limit insertion
of the inner
cannula, the lip being provided with a recess located at an outside of the
curve of the tube
such that, when the inner cannula is not in place, the suction catheter can be
inserted along
the outer tube and slide through the recess beyond the patient end of the
outer tube without
catching on the lip.
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According to a third aspect of the present invention there is provided a
tracheostomy
tube assembly comprising: an outer tracheostomy tube and an inner cannula, the
inner
cannula being insertable and removable from the outer tube, the outer tube
having, in use, a
curve or bend along a part at least of its length, a patient end, a machine
end and an
internally-projecting lip towards its patient end adapted to limit insertion
of the inner
cannula, the lip being provided with a recess located at an outside of the
curve of the tube
such that, when the inner cannula is not in place, an elongate device can be
inserted along
the outer tube and slide through the recess beyond the patient end of the
outer tube and into
the trachea without catching on the lip.
According to a fourth aspect of the present invention there is provided a
medical tube
adapted to receive an inner cannula within it, the tube having, in use, a
curve or bend along a
part at least of its length, a patient end, a machine end and an internally-
projecting lip
towards its patient end adapted to limit insertion of the inner cannula, the
lip being provided
with a recess located at an outside of the curve of the tube such that, an
elongate device can
be inserted along the outer tube and slide through the recess beyond the
patient end of the
outer tube without catching on the lip.
According to a fifth aspect of the present invention there is provided a
method of
using a tracheostomy tube assembly comprising the steps of: inserting in a
patient a
tracheostomy tube assembly of the kind comprising an outer tracheostomy tube
and an inner
cannula, the outer tube having a patient end, a machine end and an internally-
projecting lip
towards its patient end adapted to limit insertion of the inner cannula, the
lip being provided
with a recess located adjacent the posterior surface of the trachea; enabling
ventilation via
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the assembly; removing the inner cannula; inserting an elongate device along
the outer tube
to slide through the recess and extend beyond the patient end of the outer
tube and into the
trachea without catching on the lip; removing the elongate device; and
inserting a new inner
cannula.
The elongate device may be a suction catheter.
A tracheostomy tube assembly according to any one of the preceding claims will
now
be described, by way of example, with reference to the accompanying drawings.
Brief Description of the Drawings
Figure 1 shows the assembly schematically;
Figure 2 is a perspective view of the inner cannula;
Figure 3 is a cross-sectional side elevation view of the patient end of the
outer
tube to an enlarged scale;
Figure 4 is a perspective view of the patient end shown in Figure 3;
Figure 5 is a cut-away perspective view of the patient end shown in Figures 3
and 4; and
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Figure 6 is an end view of the patient end of the outer tube shown in Figures
3
to 5.
Detailed Description of the Preferred Embodiment
With reference first to Figure 1, the tracheostomy tube assembly comprises an
outer
tube 1 and an inner tube or cannula 3, which is removable from the outer tube
so that it can
be periodically replaced in the usual way.
The outer tube 1 has a shaft 10 with straight forward or patient end section
11 and
rear or machine end section 12 joined by a right-angle bend section 13.
Alternatively, the
outer tube could be smoothly curved along its entire length. In another
embodiment the tube
could have a natural straight shape and be highly flexible so that it could be
bent during use
to the shape of the anatomy. Such a flexible tube might be reinforced, such as
by a helical
wire reinforcement. The tube 1 typically has an external diameter of about
11.3mm and an
internal diameter of about 9.3mm. A sealing cuff 14 embraces the shaft 10
close to its patient
end 15; this can be inflated for sealing, or deflated for insertion and
removal, via an inflation
line 16 and a combined inflation indicator balloon and coupling 17. At its
rear end 18, the
outer tube 1 has a flange 19 to which a tape (not shown) can be attached for
securing the
assembly around the neck of the patient. A hub 20 projects from the machine
side of the
flange 19 by which gas connection can be made to the tube 1. In use, the tube
1 extends
through a tracheostomy with the patient end 15 of the tube 1 located in the
trachea. The cuff
14 is inflated to form a seal between the outside of the tube 1 and the
tracheal wall so that
gas flow is confined along the bore of the tube. The machine end 18 of the
tube 1 extends
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externally of the tracheostomy. The patient end 15 differs from conventional
tubes in a
manner that will be described in detail later.
With reference now also to Figure 2, the inner tube or cannula 3 comprises a
shaft 30
and a machine end fitting 31. The inner cannula 3 is about 194mm long and its
shaft 30 has
an internal diameter of about 8mm and an external diameter of about 9mm along
the major
part of its length. In use, the cannula 3 extends as a close sliding fit
within the bore of the
outer tube 1 with the patient end 32 of the cannula extending to the patient
end 15 of the
outer tube and with its end fitting 31 locating in the hub 20 of the outer
tube. The shaft 30 is
of ePTFE and is made by cutting from a length of extruded stock tubing. The
nature of the
shaf130 is that it can flex readily to conform to the shape of the outer tube
I without kinking
as it is inserted. The shaft material has a very low coefficient of friction
so that it can be
inserted readily into the outer tube 1 as a close sliding fit without
excessive axial
compression forces being produced of a kind that could cause the shaft 30 to
buckle. The
shaft 30 is attached to a machine end fitting 31 in the manner described in
detail in
GB0800112.5 the contents of which are incorporated herein by reference.
With reference now to Figures 3 to 6, the patient end 15 of the outer tube 1
will be
described in more detail. The patient end 15 of the outer tube 1 is moulded
with an inturned,
part-annular lip 40, similar to the annular lip shown US4315515. The purpose
of this lip 40
is to provide a rear-facing surface 41, which acts as a stop for the patient
end 32 of the inner
cannula 3 and thereby prevents it projecting from the patient end 15 of the
outer tube 1. The
lip 40 also helps, to some extent, to reduce seepage of material between the
outside of the
inner cannula 3 and the inside of the outer tube 1. The lip 40 does not form a
complete
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annulus but is interrupted by a recess, notch or gap 42. This notch 42 is
located on the
outside of the bend of the outer tube 1(that is, the outside of the bend of
the tube during use)
for a reason that will become apparent later. Typically, the width W of the
notch is about
5mm and the internal diameter D of the lip is about 7mm. The width of the
notch 42 is
selected to provide a sufficient gap to allow a suction catheter 50 or other
elongate device to
be slid along the outer tube 1, after removal of the inner cannula 3, and to
extend beyond the
patient end 15 of the outer tube without catching on the lip 40. It will be
appreciated, that,
when a suction catheter 50 or the like is inserted within a curved tube, it
will slide along the
inner surface of the outer tube on the outside of its curvature or bend. It is
for this reason that
the notch 42 is located on the outside of the curve, that is, adjacent the
posterior surface of
the trachea in use. Although the notch 42 does expose a part of the region
between the inner
cannula 3 and outer tube 1, the risk of seepage is outweighed by the fact that
the outer tube
can be used easily with a suction catheter or the like. After suctioning in
this way, a new
inner cannula can be inserted in the outer tube.
It will be appreciated that the invention is not confined to tracheostomy tube
assemblies but could be used in other tube assemblies of an outer and inner
tube where an
elongate device needs to be insertable freely beyond the patient end of the
outer tube. The
inner cannula could be of any different form.
