GB2531902A

GB2531902A - Tracheal tube assemblies and inner cannulae

Info

Publication number: GB2531902A
Application number: GB1515801.7A
Authority: GB
Inventors: John Woosnam Christopher
Original assignee: Smiths Medical International Ltd
Current assignee: Smiths Medical International Ltd
Priority date: 2014-10-01
Filing date: 2015-09-07
Publication date: 2016-05-04
Also published as: GB201515801D0; GB201417326D0

Abstract

An inner cannula 20 for a tracheostomy tube 1 has two regions 30, 31 of circumferential corrugations 126 extending along only the outside of the cannula. The two corrugated regions 30 and 31 are separated by two uncorrugated regions 32 and 33. Towards the patient end 120 of the cannula 20 the peripheral extent of the corrugations 30, 31 gradually increases and the extent of the uncorrugated regions 32, 33 decreases, so that the patient end 121 is more flexible than the machine end 120.

Description

TRACHEAL TUBE ASSEMBLIES AND INNER CANNULAE

This invention relates to tracheal tube assemblies and inner cannulae.

Tracheostomy tube assemblies commonly include an outer tube and an inner tube or cannula that is a removable fit within the outer tube. The inner cannula can be removed and replaced periodically to ensure that the passage through the assembly does not become blocked by secretions. This avoids the need to remove the outer tube frequently.

The inner cannula presents various problems because it must be thin walled and a close fit within the outer tube so as to provide a large bore and thereby limit the resistance to flow of gas along the assembly. Where the outer tube is not of a constant radius along its entire length the inner eannula must be sufficiently flexible in order to be able to be inserted and removed without kinking. It can be advantageous for the inner cannula to be stiffer in some regions than in other regions along its length.

W094/01156 and W02004/101048 describe inner cannulae made of PTFE. EP1938857 describes an arrangement of tracheostomy tubes and inner cannulae where the hubs of the inner cannulae of different sizes are shaped differently so that they will only fit in the appropriate tracheostomy tube. EP2224985 describes an arrangement for attaching a hub to the shaft of an inner cannula. GB2056285 describes an inner cannula having a wall with annular corrugations and a longitudinal groove or other reinforcement member traversing at least some of the corrugations. US4817598 describes a smooth-walled inner cannula having a ring-pull formation at its rear, machine end. US5119811 describes an inner cannula with a flared patient end and formed of two layers of different materials. US5386826 describes an inner cannula with an outer helical filament or layer of low friction material. US5983895 describes an inner cannula with straight sections at opposite ends joined by an intermediate curved section. US6019753 describes an inner cannula with two elongate regions of different flexibility so that the cannula has a plane of preferential bending. US6019753 describes an inner cannula having a shaft formed with slots to make it more flexible, the slots being covered by an outer thin sheath. US6135110 describes a curved inner cannula that is retained with the outer tube by means of a rotatable spring fitting.

It is an object of the present invention to provide an alternative tracheal tube assembly and inner cannula According to one aspect of the present invention there is provided an inner cannula for a tracheal tube, the cannula having a wall provided with circumferential corrugations along at least a part of its length, the peripheral extent of the corrugations in a first region at a first location along the cannula being different from the peripheral extent of the corrugations in a second region at a second location along the cannula such that the flexibility of the cannula in the first region is different from that in the second region.

The cannula preferably has two zones of corrugations extending along the cannula separated along at least a part of their length by two zones that are uncorrugated, the ratio of the sum of the peripheral width of the corrugated zones to the uncorrugated zones being different in the first region from that in the second region.

According to another aspect of the present invention there is provided an inner cannula for a tracheal tube, the cannula having at least one zone of circumferential corrugations extending along a part at least of its length and at least one zone that is not corrugated extending alongside at least a part of the length of the corrugated zone, the ratio of the width of the cannula that is corrugated to the width that is uncorrugated being different at different locations along the cannula such that the flexibility of the cannula in one location is different from That at a different location.

The flexibility of the cannula preferably varies continuously along the corrugated part of the cannula. The inner cannula is preferably more flexible in a region towards its patient end than in a region towards its machine end. The corrugations may be provided on the external surface only of the cannula, the inner surface of the cannula being smooth.

According to a further aspect of the present invention there is provided a tracheal tube assembly including an outer tracheal tube and an inner cannula according to the above one or other aspect of the present invention inserted within the outer tracheal tube.

According to a fourth aspect of the present invention there is provided a tracheal tube assembly including an outer tracheal tube and an inner cannula that is inserted in and is removable from the machine end of the tracheal tube, the inner cannula having a wall provided with circumferential corrugations along at least a part of its length, the peripheral extent of the corrugations in a first region at a first location along the cannula being different from the peripheral extent of the corrugations in a second region at a second location along the cannula such that the flexibility of the cannula in the first region is different from that in the second region.

A tracheostomy tube assembly including an inner cannula, according to the present invention, will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a side elevation view of a tracheostomy tube assembly including an inner cannula; Figure 2 is a perspective view of the inner cannula from its machine end; Figure 3 is an enlarged plan view of the inner cannula; Figure 4 is an enlarged side elevation view of the inner cannula; Figure 5 is a further enlarged plan view of the region V of Figure 4; and Figure 6 is a further enlarged cross-sectional view of the region VI of Figure 4 With reference first to Figure 1, the tracheostomy tube assembly comprises an outer tracheostomy tube 1 and a removable inner cannula 20 inserted within the outer tube. The outer tube I has a shaft 10 with a straight forward section 11, a straight rear section 12 and a curved intermediate section 13 linking the forward and rear sections. An inflatable sealing cuff 14 embraces the forward section 11 close to the patient end 5 of the tube, the cuff being inflated via an inflation lumen 16 and a combined connector and inflation indicator 17. At its rear, machine end 6 the outer tube 1 has a hub 18 and flange 19 to which a retaining tape (not shown) can be fastened for securing the tube with the patient's neck. The inside of the hub 18 is formed with keying flats (not shown), of the kind described in EP1938857, adapted to prevent full insertion of an inner cannula of the wrong size. The outer tube 1 could have an internal diameter between about 6mm and 10mm, and its length could be between 60rnm and 200mm.

With reference now also to Figures 2 to 6, the inner cannula 20 is moulded from a plastics material such as by blow moulding or injection moulding. The main part of the length of the cannula 20 is provided by a shaft 21 of circular section. Typically the shaft 21 has an external diameter of about 8.6mm and a length of 125mm. The cannula 20 is completed at the rear, machine end 120 of the shaft 21 by a separate or integral hub portion 22 moulded as one piece with the shaft. The hub portion 22 has a smooth external surface, the portion 23 at its forward end being shaped to fit into a 15mm connector. The hub portion 22 may have a keying portion with flats of the kind described in EP1938857 adapted to fit with corresponding formations in the hub 18 of the outer tube 1. At its rear end the hub 22 has a ring-pull formation 24 of the kind described in 0E4817598, which facilitates removal of the inner cannula 20 from the outer tube 1 after use.

The shaft 21 has a smooth inner surface 25 and is partially corrugated with corrugations 126 on its external surface 26. The corrugations 126 typically have a V-shape profile but could have alternative profiles, such as of sine wave shape. The corrugations could be annular, forming a complete circle, or could be formed by adjacent turns of a helical form (the term "circumferential" is intended to include a helical locus as well as annular formations). The outer diameter of the shaft 21 (that is, measured across the peaks of the corrugations 126) is selected to be the same as the internal diameter of the outer tube 1 so that the inner cannula 20 is a close sliding fit within the outer tube. The wall thickness of the shaft 211s between 0.25mm and 1mm.

More particularly, the shaft 21 is corrugated along a region 27 extending along the major part of its length apart from a short region 28 at its patient end 121 and a longer region 29 at its machine end. The corrugated region 27 is divided into two longitudinally-extending corrugated zones 30 and 31 located diametrically opposite one another around the shaft and separated from one another by two respective uncorrugated zones 32 and 33. The width of the corrugated zones 30 and 31 tapers along the length of the corrugated region 27, the zones being relatively wide at their patient ends and relatively narrow at their machine ends. In this way, the peripheral extent of the corrugations 126 varies along the corrugated region 27 from a maximum towards the patient end to a minimum towards the machine end. Accordingly, the flexibility of the cannula 20 varies gradually or continuously from a maximum towards its patient end to a minimum towards its machine end. This enables the patient end of the inner cannula 20 to flex readily as it is inserted along the curved intermediate section 13 of the outer tube 1 whilst the machine end of the inner cannula is stiffer to enable a higher pushing force to be applied during insertion without the risk of buckling.

The two uncorrugated zones 32 and 33 are stiffer than the corrugated zones 30 and 31 so they give the cannula 20 a preferential plane of flexing along the axis of the cannula and orthogonal to the plane of Figure 3 and in the plane of Figure 4 as indicated by the arrow "F". The preferential plane of flexing of the cannula is aligned with the plane of curvature of the tracheostomy tube 1 so that it can readily bend to follow the shape of the different sections 12, 13 and 11 during insertion into the outer tube 1 without buckling or kinking.

It is not essential to have two corrugated zones since the cannula could have one, three or more zones. The number of zones could vary along the length of the cannula. For example, the cannula could be corrugated around its entire circumference towards the patient end and then divide into two or more zones rearwardly of the patient end to give a greater proportion of the cannula that was uncorrugated. The zone or zones need not vary in width gradually as described above but could vary by one or more step changes in width. The corrugated region could extend along the entire length of the shaft or only in one or more localised regions along the shaft.

The cannula described above has corrugations of constant pitch and height along the corrugated zones but the pitch and height could vary in different parts of the corrugated zones.

The smooth inner surface of the shaft 21 allows for smooth, non-turbulent flow of gas along the assembly. It also allows devices, such as endoscopes, probes, suction catheters or the like to be inserted freely along the cannula without the risk of catching, as might be the case with a cannula having a corrugated inner surface. The corrugated external surface of the inner cannula 20 helps enhance the radial rigidity of the cannula and reduce the risk of kinking and buckling whilst still ensuring that the inner cannula can bend freely during insertion in and withdrawal from the outer tube 1. The corrugations 126 form a close fit within the outer tube 1 but the reduced area of the corrugated zones compared with conventional corrugated cannulae that are corrugated around their entire circumference along their length reduces the friction for insertion and removal.

Although the inner cannula 20 is described as being an integral, one-piece moulding with the tip portion 26 and the hub portion 30, it could, instead, be formed of separate components. For example, the corrugated shaft could be extruded and the hub and tip portions subsequently attached with the shaft by overmoulding.

Claims

CLAIMS1. An inner cannula for a tracheal tube, the cannula having a wall provided with circumferential corrugations along at least a part of its length, wherein the peripheral extent of the corrugations in a first region at a first location along the cannula is different from the peripheral extent of the corrugations in a second region at a second location along the cannula such that the flexibility of the cannula in the first region is different from that in the second region.
2. An inner cannula according to Claim 1, wherein the cannula has two zones of corrugations extending along the cannula separated along at least a part of their length by two zones that are uncorrugated, and wherein the ratio of the sum of the peripheral width of the corrugated zones to the uncorrugated zones is different in the first region from that in the second region.
3. An inner cannula for a tracheal tube, wherein the cannula has at least one zone of circumferential corrugations extending along a part at least of its length and at least one zone that is not corrugated extending alongside at least a part of the length of the corrugated zone, wherein the ratio of the width of the cannula that is corrugated to the width that is uncorrugated is different at different locations along the cannula such that the flexibility of the cannula in one location is different from that at a different location.
4. An inner cannula according to any one of the preceding claims, wherein the flexibility of the cannula varies continuously along the corrugated part of the cannula.
5. An inner cannula according to any one of the preceding claims, wherein the inner cannula is more flexible in a region towards its patient end than in a region towards its machine end.
6. An inner cannula according to any one of the preceding claims, wherein the corrugations are provided on the external surface only of the cannula, and wherein the inner surface of the cannula is smooth.
7. An inner cannula substantially as hereinbefore described with reference to the accompanying drawings.
8. A tracheal tube assembly including an outer tracheal tube and an inner cannula according to any one of the preceding claims inserted within the outer tracheal tube.
9. A tracheal tube assembly including an outer tracheal tube and an inner cannula that is inserted in and is removable from the machine end of the tracheal tube, the inner cannula having a wall provided with circumferential corrugations along at least a part of its length, wherein the peripheral extent of the corrugations in a first region at a first location along the cannula is different from the peripheral extent of the corrugations in a second region at a second location along the cannula such that the flexibility of the cannula in the first region is different from that in the second region.
10. A tracheal tube assembly substantially as hereinbefore described with reference to the accompanying drawings.
11. Any novel and inventive feature or combination of features as hereinbefore described.