Tracheostomy tube with disposable inner cannula

A tracheostomy tube includes an outer cannula and a removable, disposable inner cannula. The inner cannula is provided with a tapered portion located just behind its distal tip which forms simultaneously an air tight seal with the outer cannula and a stop device for preventing the protrusion of the tip substantially beyond the end of the outer cannula. The stop device furthermore compensates for variations in the length of the inner cannula by controlling the position of the tip between a location flush with the end of the outer cannula and one just slightly beyond. A coupling connector is mounted on the proximal end of the inner cannula to provide easy, releasable attachment of the inner cannula to the outer cannula. The inner cannulae are inexpensively constructed from a soft, flexible polyvinyl chloride material and are dimensionally compatible with any particular outer cannula.

RELATED APPLICATION 
The present application is the parent application of a continuation in part 
application, Ser. No. 260,072, filed May 4, 1981. 
BACKGROUND OF THE INVENTION 
The present invention relates to tracheostomy tubes having an outer cannula 
and a removable inner cannula, and, in particular, to a tracheostomy tube 
having a disposable inner cannula. 
Tracheostomy tubes have been used for some time to provide a bypass supply 
of air or mixture of gases to a patient having an obstruction in the 
larynx or the pharynx areas of the throat. The distal end of the 
tracheostomy tube is inserted into the trachea through an incision in the 
patient's neck below the obstructed area. The proximal end of the tube 
remains outside the trachea in communication with ambient air to permit 
passage of such air into the trachea. This proximal end of the tube can 
also be attached to a respiratory device to assist the patient's breathing 
or to anesthesia equipment for passing anesthetic gas to the patient prior 
to surgery. 
While thus in place within the patient's trachea, a tracheostomy tube can 
sometimes become partially or completely obstructed by accumulations of 
mucus or completely obstructed by accumulations of mucus or phlegm. U.S. 
Pat. No. 3,693,624 to Shiley et al, assigned to Shiley, Inc., assignee of 
the present invention, discloses and claims a tracheostomy tube which 
allows such obstructions to be cleared without causing pain and irritation 
to the patient, this invention providing an outer cannula, which remains 
in place in the trachea, and a removable inner cannula, which serves as an 
inner lining of the outer cannula. Thus, to clear the passageway of the 
tracheostomy tube, the inner cannula can be removed, cleaned, and then 
replaced. 
An important feature of lined tracheostomy tubes, which insures adequate 
cleaning, is that the inner cannula runs the entire length of the outer 
cannula. For example, if the distal tip of the inner cannula were to 
terminate within the bore of the outer cannula, mucus could accumulate on 
and adhere to the unlined portion of the interior surface of the outer 
cannula, obstructing the air passage of the tube and requiring its 
complete removal for cleaning. At the same time, however, the inner 
cannula should not extend substantially beyond the outer cannula, since 
removal and insertion of a protruding inner cannula could cause abrasion 
of the trachea and damage to the delicate cilia along the inner tracheal 
wall. Thus, the overall length of such removable inner cannulae must be 
carefully controlled. 
It is also important in such two-part, lined tracheostomy tubes that an 
adequate air seal be maintained between the inner and outer cannulae so 
that respiration pressure from an artificial respiration machine is not 
lost by leakage. One prior method for producing such an air seal at the 
proximal end of a tracheostomy tube is disclosed in U.S. Pat. No. 
4,009,720 to Crandall, entitled "Wedge Seal for a Tracheotomy Tube" 
assigned to Shiley, Inc. 
SUMMARY OF THE INVENTION 
The tracheostomy tube of the present invention provides a disposable inner 
cannula, so that the time and expense associated with cleaning and 
sterilizing it can be eliminated. A significant feature of this invention 
is that each disposable inner cannula is dimensionally compatible with any 
particular outer cannula of the same type and size, while at the same time 
possessing the critical length and air seal characteristics mentioned 
above. Furthermore, the inner cannula is sufficiently inexpensive to 
manufacture to make disposability practical, and yet dimensional 
tolerances may be held sufficiently close to achieve interchangeability. 
In the present invention a tapered distal portion on the inner cannula 
provides both an air seal with the outer cannula and a stop device for 
preventing the substantial protrusion of the inner cannula beyond the 
distal end of the outer cannula. Thus, the stop device compensates for 
variations in length among the present inner cannulae and maintains their 
dimensional compatibility with the outer cannulae. 
The tapered surface on the inner cannula faces and is located just behind 
the extreme distal tip of the inner cannula. The angle of inclination of 
the tapered surface is such that its diameter, at least at one point, is 
greater than the inside diameter of the narrowed distal end of the outer 
cannula. Thus, pressing the inner cannula longitudinally into the bore of 
the outer cannula will result in a tight, wedged engagement between the 
two to form the air seal and stop devices. 
The stop device on the inner cannula is designed so that the inner cannula 
tip is flush with or extends only slightly beyond the end of the outer 
cannula. Thus, the position of the tip, regardless of the length of the 
inner cannula, is controlled or regulated to fall within this narrow 
range. In order to prevent irritation to the trachea, should it be 
contacted by the tip of the inner cannula, the tip is rounded. 
Furthermore, the inner cannula is constructed from a soft, biologically 
inactive polyvinyl chloride material, further protecting the patient's 
trachea. This material is also very flexible to permit the inner cannula 
of the present invention to bend within the outer cannula. 
The inner cannula is removably attached to the outer cannula by means of a 
coupling connector which advantageously snaps onto and off of the outer 
cannula with only minimal or essentially no longitudinal force, in order 
to prevent pain and discomfort to the patient. The coupling connector is 
mounted on the proximal end of the inner cannula and includes an integral 
male adaptor, which communicates with the bore of the inner cannula, for 
receiving respiratory or anesthesia equipment. The connector and male 
cannula are designed to allow an adequate degree of rotational freedom of 
the connector relative to the outer cannula so that normal movement of the 
patient relative to the respiratory or anesthesia equipment is tolerated 
without causing any painful movement of the outer cannula. Furthermore, 
the nature of the coupling connection between the outer and inner cannulae 
is such that it provides for a secure attachment while permitting some 
longitudinal movement or "give" of the inner cannula with respect to the 
outer cannula. 
Inner cannulae so constructed are completely interchangeable, and at the 
same time provide an air seal with the outer cannula without extending 
substantially beyond it. That is, each inner cannula possesses a certain 
minimum length which is sufficient to permit the tapered sealing surface 
at its distal end to engage the outer cannula (thereby forming the air 
seal and stop devices) and to permit the coupling connector on its 
proximal end to snap onto the outer cannula. The stop device then serves 
to compensate for variations in length by preventing protrusion of the tip 
substantially beyond the outer cannula. Being secured at each end, the 
inner cannula further compensates for variations in length by virtue of 
its own flexibility and the longitudinal give permitted by the coupling 
connector. These features enable the inner cannulae of the present 
invention to be both dimensionally compatible and efficiently operative 
with any particular outer cannula. 
Another important feature of the inner cannula of the present invention, 
which enhances its disposability, is the relative inexpense associated 
with the polymer materials and methods of manufacture from which it is 
constructed. For example, the inner cannulae can be quickly and easily 
produced in large quantities using an injection molding process. 
Alternatively, they can be extruded and then end-formed using a Radio 
Frequency (RF) di-electric heating process. Furthermore, dimensional 
tolerances are held close only in the distal area of the inner cannula to 
assure adequate sealing and stopping, since variations over its remaining 
length are offset as explained above. Additionally, due to their 
interchangeability, inner cannulae of the present invention need not be 
dimensionally customized to properly fit a particular outer cannula.

DETAILED DESCRIPTION OF THE INVENTION 
Referring initially to FIGS. 1 and 2, there is shown the tracheostomy tube 
10 of the present invention, including an outer cannula 12 and a removable 
inner cannula 14, shown partially removed in FIG. 2. The cylindrical, 
arcuate outer cannula 12 is comprised of a distal end 16 for insertion 
into the trachea of the patient through an opening in the neck and a 
proximal end 18 remaining outside the trachea. 
Shown attached to the tracheostomy tube 10 near its distal end 16 is an 
inflatable cuff 20 which, when inflated, provides an air tight seal 
between the tracheostomy tube 10 and the inner wall of the trachea. Such 
sealing cuffs are described in more detail and claimed in U.S. Pat. Nos. 
3,659,612, and 3,693,624, assigned to Shiley, Inc. The cuff 20 is inflated 
by means of a flexible inflation tube 22 which extends into the cuff 20 
from the proximal end 18 of the outer cannula 12. A swivel neck flange 24 
located near the proximal end 18 of the outer cannula 12 is used to secure 
the tracheostomy tube 10 to the neck of the patient. The neck flange 24 is 
journaled in a pair of recessed openings 26 (FIG. 2) in the outer cannula 
12 to permit a degree of rotational freedom of the flange 24 and the 
patient's neck with respect to the outer cannula 12, significantly 
decreasing the pain and discomfort that may be caused by the patient's 
normal bodily movements. 
The inner cannula 14 is inserted into the bore 26 of the outer cannula 12 
and secured in place by means of a coupling connector 28 mounted on its 
proximal end 30, as shown in FIG. 2. The connector 28, which will be 
described in more detail in connection with FIG. 4, is provided with a 
pair of resilient lever arms 32 which engage an annular retaining collar 
34 located on the proximal end 18 of the outer cannula 12. The proximal 
end of the coupling connector 28 is provided with an opening 36 for 
receiving anesthesia equipment or artificial respiratory equipment (not 
shown) to assist the patient's breathing. As clearly shown in FIG. 1, the 
inner cannula 14 runs the entire length of the outer cannula 12 so that 
its distal tip 38 is flush with or slightly beyond the tapered necked-down 
portion 40 of the distal end 16 of the outer cannula 12 and the connector 
28 is securely releasably attached to the proximal end 18 of the outer 
cannula 12. Formed in the inner cannula 14 is a passageway 37 which 
communicates with the opening 36 in the connector 28 to permit air to flow 
into the trachea. 
FIG. 3 is a partial sectional view taken through the distal end of the 
tracheostomy tube 10 of the present invention. Located just behind the tip 
38 of the inner cannula 14 is a raised annular section 42 comprised of, 
from front to rear, a tapered, forwardly facing sealing surface 44, a 
non-tapered surface 46, and a tapered rearwardly facing surface 48. The 
sealing surface 44 is frustro-conical in shape and engages the interior 
surface 50 of the necked-down portion 40 on the distal end 16 of the outer 
cannula 12 to form a tight air seal between the outer cannula 12 and inner 
cannula 14. This sealing surface 44 is sufficiently tapered so that at 
least one portion has an outer diameter which is greater than the inside 
diameter of the opening 52 of the outer cannula 12. Thus, only a slight 
axial force is required to wedge the sealing surface 44 of the inner 
cannula 14 into the opening 52 of the outer cannula 12 to form this air 
seal. Furthermore, it has been found that a sealing surface 44 having a 
slope A with respect to the horizontal of about 10-15 degrees is 
preferable, since within this range the inclination of the sealing surface 
44 is sufficient to form a wedge-like seal with the necked-down portion 40 
of the outer cannula 12, without creating an undesirably long sealing 
surface 44. 
As clearly illustrated in FIG. 3, the engagement between the inner cannula 
14 and the outer cannula 12 also serves as a stop device to prevent the 
tip 38 of the inner cannula 14 from extending substantially beyond the 
very end 54 of the outer cannula 12. Moreover, the sloping interior 
surface 50 of the necked-down portion 40 of the outer cannula 12 
cooperates to form this stop device since it presents a large, relatively 
rigid obstacle to the raised portion 42 on the inner cannula 14 which 
prohibits substantial protrusion of the tip 38. Furthermore, the location 
and length of the sealing surface 44 on the inner cannula 14 and the size 
of opening 52 on the outer cannula 12, which together form the air seal 
and stop devices of the present invention, are such that the tip 38 will 
be flush with the end 54 of the outer cannula if the interior surface 50 
contacts the sealing surface 44 near its lower edge. If, on the other 
hand, the interior surface 50 contacts the upper edge of the sealing 
surface 44, the tip 38 will extend only slightly, e.g. about 0.050 inches, 
beyond the end 54 of the outer cannula. Thus, the stop device of the 
present invention advantageously regulates the position of the tip 38 
within this narrow range, thereby compensating for variations in overall 
length among the present inner cannulae. 
This minimal amount of possible extension is not sufficient to cause injury 
to the patient's trachea. The trachea is further protected by the rounded 
shape of the tip 38 of the inner cannula 14 and by the soft, biologically 
compatable polymer material from which it is constructed. Moreover, the 
length of the inner cannula 14 is such that the tip 38 does not terminate 
within the opening 52 of the outer cannula 12. This construction ensures 
the proper elimination of obstructions in the passageway 37 of the 
tracheostomy tube 10 upon removal of the disposable inner cannula 14. In 
the unlikely event that the raised portion 42 on the inner cannula 14 is 
forced beyond the end 54 of the outer cannula 12, the rear tapered surface 
48 of the raised portion 42 facilitates removal of the inner cannula 14 
from the opening 52 in the outer cannula 12. 
As mentioned above, the inner cannula 14 of the present invention can be 
constructed from a soft, flexible, polymer material, preferably a 
non-toxic polyvinyl chloride having a Shore A hardness of about 85. 
However, any other soft, biologically safe, elastomeric material having a 
Shore A hardness of 90 or less is also suitable. Moreover, the inner 
cannula 14 can be inexpensively manufactured using plastic injection 
molding techniques or can be made in a two part process including an 
extrusion step followed by the di-electric end forming of the tip 38 and 
raised portion 42. 
As is well known, shrinkage is a common problem experienced in the molding 
and forming of plastics, making dimensional tolerances difficult to hold. 
In the present invention, however, dimensional tolerances advantageously 
need be held closely only at the distal end of the inner cannula 14, where 
the critical tip 38 and sealing surface 44 are located, rather than over 
the entire length of the inner cannula. Furthermore, any dimensional 
inaccuracies in this area and any variations in length over the remainder 
of the inner cannula 14 are offset by the tracheostomy tube 10 of the 
present invention, as described below in more detail. Furthermore, there 
is no customized, cutting to length of the inner cannula 14 with respect 
to a particular outer cannula 12, since inner cannulae of the present 
invention are interchangeable. Thus, the inner cannula 14 of the present 
invention can be inexpensively manufactured, making its disposability 
economically practical. 
Referring again to FIG. 3, either of the above-mentioned methods of 
manufacturing the inner cannula 14 produce a passageway 37 having a 
completely smooth interior surface 56. This feature reduces the frictional 
forces exerted on air and anesthetic gas delivered to the patient through 
the tracheostomy tube 10, thereby enhancing its efficiency. Additionally, 
this smooth inner surface 56 provides for an essentially frictionless flow 
of bodily secretions which may enter the inner cannula 14, thus reducing 
the amount of such secretions which adhere to it and obstruct its 
passageway 56. Thus, the present inner cannula 14, to a degree, is 
self-cleaning and must be replaced only infrequently. 
As shown in FIG. 3 the outer diameter of the inner cannula 14 at points 
proximal to the raised portion 42 is sufficiently less than the inner 
diameter of the outer cannula 12 at corresponding locations to form a gap 
or space 58 within the bore 26 of the outer cannula 12. This space 58 
permits the flexible inner cannula 14 to bend, if necessary, within the 
outer cannula 12, allowing tracheostomy tube 10 of the present invention 
to further compensate for variations in length of the inner cannula 14 and 
to provide for its interchangeability. 
FIG. 4 is a sectional view taken through the proximal end of the present 
tracheostomy tube 10, illustrating the outer cannula 12, the inner cannula 
14 removably installed within the bore 26 of the outer cannula 12, and the 
coupling connector 28 mounted on the proximal end 30 of the inner cannula 
14 for attaching it to the outer cannula 12. The connector 28 has a distal 
face 60 with an opening 62 to receive the inner cannula 14. The proximal 
face 64 of the connector 28 is provided with a large opening 36 adapted to 
receive a conduit (not shown) from respiratory or anesthesia equipment 
which fits over the proximal end of the connector 28. The connector 28 is 
preferably constructed from copolyester or polypropylene material and then 
bonded to the inner cannula 14 by a solvent or other suitable means. 
Furthermore, the connector 28 can be inexpensively manufactured using 
injection molding techniques. 
Integrally formed on opposite sides of the coupling connector 28 are a pair 
of lever arms 32 which are biased forwardly or toward one another by 
arcuate, resilient hinges 66. In their relaxed state, these hinges 66 
cause the lever arms 32 to assume the position shown in FIG. 4. The lever 
arms 32 have locking ends 68, which are separated by a distance D, and 
handle ends 70. Each locking end 68 engages the distal face 72 of the 
retaining collar 34, which is mounted on the extreme proximal end 18 of 
the outer cannula 12, to lock the connector 28 and inner cannula 14 
assembly in place. The handle end 70 provides a finger location for the 
manual manipulation of the lever arms 32. The retaining collar 34 is also 
characterized by a proximal face 74, which is parallel with the distal 
face 60 of the connector 28, and by a tapered peripheral surface 76 which 
facilitates attachment of the connector 28 to the outer cannula 12. 
In operation, the coupling connector 28 of the present invention permits 
the inner cannula 14 to be easily and securely attached to the outer 
cannula 12 in a single axial, non-rotational movement. The tip 38 of the 
inner cannula 14 is first inserted into the bore 26 of the outer cannula 
12 and advanced until the locking ends 68 of the lever arms 32 engage the 
tapered periphery 76 of the retaining collar 34. Only slight axial force 
is then necessary to cause the lever arms 32 to be flexed backward, 
gradually increasing the distance D between the locking ends 68 as they 
advance along the collar periphery 76. When the distance D is greater than 
the outside diameter of the collar 34, the hinges 66 snap the locking ends 
68 toward one another in locking engagement with the distal face 72 of the 
retaining collar 34. 
As shown in FIG. 4, the connector/inner cannula assembly is locked to the 
outer cannula since the distance D between locking ends 68 of the lever 
arms 32, in their relaxed state, is less than the greatest outside 
diameter of the retaining collar 34. Attachment of the connector 28 to the 
outer cannula 12 is facilitated by the rounded leading edges 78 and 
including forward surface 80 on the locking ends 68 of the lever arms 32. 
This forward surface 80, which is inclined at approximately the same angle 
as the tapered periphery 76 of the retaining collar 34, reduces the amount 
of axial force necessary to cause the locking ends 68 to separate as they 
are advanced along the collar periphery 76. 
Alternatively, the connector 28 can be attached to the outer cannula 12 
with virtually no axial forces being exerted on the tracheostomy tube 10. 
In this method, the inner cannula 14 is inserted into the outer cannula 12 
and advanced, as before, until the locking ends 68 of the lever arms 32 
are positioned close to the tapered periphery 76 of the retaining collar 
34. The locking ends 68 are then manually spread apart by exerting an 
inward force from the fingers on the handle ends 70 of the lever arms 32 
until the locking ends 68 are separated by a distance D greater than the 
diameter of the collar 34. The connector 28 is then advanced slightly and 
the handle ends 70 released, permitting the hinges 66 to bias the locking 
ends 68 together in locking engagement with the distal face 72 of the 
retaining collar 34. The connector 28 of the present invention is unlocked 
and the inner cannula 14 removed from the outer cannula 12 by reversing 
these simple steps. 
In utilizing this manual method for locking or unlocking the connector 28, 
the hinges 66 are protected from damage due to backwards hyperextension by 
ribs 71 (also shown in FIG. 1) located on the back side of the handle ends 
70 of the lever arms 32. These ribs 71 contact stop blocks 73 to prevent 
the lever arms 32 from bending too far backwards during attachment or 
removal of the connector 28. 
Thus, inner cannula 14 of the present invention is easily attached to and 
removed from the outer cannula 12 with exertion of little or no 
longitudinal force, thereby preventing pain and discomfort to the patient. 
Furthermore, once attached to the outer cannula 12, the coupling connector 
28 of the present invention permits a degree of rotational freedom of the 
inner cannula 14 with respect to the outer cannula 12 so that the normal 
movement of the patient relative to a respiratory or anesthesia conduit 
attached over the opening 36 in the proximal end 64 of the connector 28 
will also not cause pain or discomfort. This rotational freedom is derived 
from the flexibility of the inner cannula 14 which, even though 
substantially fixed with respect to the outer cannula 12 at its distal 
end, absorbs the torsional forces exerted upon it by the rotation of the 
connector 28 at its proximal end 30. This rotational freedom is limited, 
however, by a pair of spaced tabs 82 (shown in FIGS. 1 and 2) which 
protect the inflation tube 22 from damage by contact with either of the 
lever arms 32. 
A significant feature of the coupling connector 28 of the present 
invention, which promotes the interchangeability and disposability of the 
inner cannula 14, is that it serves to securely attach the inner cannula 
14 to the outer cannula 12 while providing for a small gap 82 between the 
distal face 60 of the connector 28 and the proximal face 74 of the 
retaining collar 34. This gap 82 permits a degree of axial movement of the 
inner cannula 14 with respect to the outer cannula 12 in order to 
compensate for variations in the length among inner cannulae of the 
present invention, due for example to shrinkage during manufacture. 
Another important feature in this regard is the flexibility of the inner 
cannula 14 which permits it to bend within the gap 58 (shown in FIGS. 3 
and 4) between the inner cannula 14 and the outer cannula 12. 
Thus, the inner cannula 14 of the present invention need only possess a 
certain minimum length sufficient to permit some portion of its sealing 
surface 44 to wedge against the interior surface 50 of the necked down 
portion 40 of the outer cannula 12, thereby forming the air seal shown in 
FIG. 3, and to permit the locking ends 68 of the lever arms 32 to engage 
the distal face 72 of the retaining collar 34, as shown in FIG. 4. Beyond 
this minimum length, variations in length are offset by the axial give in 
the coupling connector 28 and by the bending flexibility of the inner 
cannula 14 itself. Furthermore, the tip 38 of the inner cannula 14 is 
prevented from extending substantially beyond the end 54 of the outer 
cannula 12, as explained above, further compensating for lengthwise 
variations. 
This ability of the present tracheostomy tube to compensate for dimensional 
differences among inner cannulae provides for the interchangeability and 
disposability of the inner cannula 14 of the present invention. 
Furthermore, as described above, these inner cannulae are sufficiently 
economical in terms of material and manufacturing cost to make their 
disposability practical, thus avoiding the problems and cost of 
sterilization.