WO2019069040A1

WO2019069040A1 - Tubes and their manufacture

Info

Publication number: WO2019069040A1
Application number: PCT/GB2018/000115
Authority: WO
Inventors: Timothy Bateman; Stephen James Field
Original assignee: Smiths Medical International Limited
Priority date: 2017-10-07
Filing date: 2018-08-21
Publication date: 2019-04-11
Also published as: GB201716488D0

Abstract

An inner cannula (3) of a tracheostomy tube (1) has a wall (33, 133) mainly of ePTFE and a reinforcing rib (34, 134) extending along the length of its shaft (30). The rib (34, 134) is of a thermoplastic and is mechanically retained with the wall (33, 133) by flow of the ePTFE around the rib or through recesses (140) in the rib.

Description

TUBES AND THEIR MANUFACTURE

This invention relates to inner tubes or cannulae of the kind for insertion within an outer tube, the inner tube having a shaft formed mainly by a tubular wall of a first plastics material and one or more elongate strengthening members extending axially along the shaft.

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 tube can be removed and replaced periodically to ensure that the passage through the assembly does not become blocked by secretions. This avoids the need frequently to remove the outer tube.

The inner tube presents various problems because it must be thin walled and a close fit within the outer tube so as to limit the resistance to flow of gas along the assembly. It must, however, also be sufficiently stiff to be inserted in the outer tube without buckling or kinking. A particularly suitable material for the inner cannula is PTFE or expanded PTFE (ePTFE). The use of such a material in an inner cannula is described in WO94/01156 and in WO2004/101048. The Flextratube sold by Tyco Healthcare is made of ePTFE. US8419075 describes an inner cannula of ePTFE attached with a hub at one end by an overmoulding technique. Whilst such a material has various advantages it also has a problem of poor axial stability in that it can be compressed axially by a relatively small axial force. This is a problem because, if the inner cannula cannot be freely inserted in the outer tube, such as because of a deposit or other obstruction on the inside of the outer tube, the inner cannula could be partly compressed and restrict gas flow along the assembly. It is difficult to strengthen an inner cannula of ePTFE because this material does not bond well to other materials.

It is an object of the present invention to provide an alternative tube and a method of its manufacture.

According to one aspect of the present invention there is provided an inner tube of the above-specified kind, characterised in that the or each strengthening member is of a second plastics material different from the first and is mechanically attached with the wall by flow of one material in or around the other material.

The or each strengthening member may be encased around its girth within the material of the wall and may have an oval section. Alternatively, the or each strengmening member has a plurality of recesses and the wall material may be attached with the or each strengthening member by portions of wall material flowed into the recesses. The wall material flowed into the recesses may be flowed through the recesses and integrally linked with wall material at opposite ends of the recesses. The or each strengthening member may take the form of an elongate strip having an elongate channel along opposite edges and separated from one another by a central portion. The recesses may be formed through the central portion such that wall material in the two channels is integrally linked through the recesses. The recesses may be formed through the inner and outer plates on opposite sides of the central portion so that the wall material flows level with the inner and outer surfaces of the elongate strip. Alternatively, the tubular wall may be provided by a preformed sheet member having two rows of recesses along opposite edges and rolled into a tubular shape with its edges joined together by a reinforcing rib the material of which is flowed into the recesses. One of the first or second materials may form the major part of the shaft of the inner tube and be of ePTFE.

According to another aspect of the present invention there is provided a method of making an inner tube or cannula for insertion into an outer tube including the steps of forming a first component of a first material providing a part of the shaft of the inner tube, forming a second component of a second material different from the first material providing a different part of the shaft, characterised in that the second material is flowed in or around the first component such that the two components are mechanically attached with one another, and that the first and second components extend axially of the inner tube or cannula along the length of the shaft.

The method may include a subsequent step of attaching a machine end fitting to one end of the shaft. According to a further aspect of the present invention there is provided a tube or cannula made by a method according to the above other aspect of the present invention.

According to yet another aspect of the present invention there is provided a tracheostomy tube assembly comprising an outer tube and an inner tube according to the above one or further aspect of the present invention.

A tracheostomy assembly with an inner cannula and its method of manufacture according to the present invention, will now be described, by way of example, with reference to the accompanying drawings, in which:

Figure 1 shows the assembly schematically;

Figure 2 is a plan view of the inner cannula;

Figure 3 is a transverse cross-sectional side elevation view of the inner cannula to an enlarged scale;

Figure 4 is a further cross-sectional enlargement of a part of the wall of the inner cannula;

Figure 5 is a perspective view of a part of a second embodiment of the inner cannula;

Figure 6 is a perspective view of a third embodiment of the inner

cannula; and

Figures 7A to 7D show successive steps in the manufacture of a fourth

embodiment of the inner cannula.

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 is entirely conventional having a shaft 10 with straight forward or patient end section 11 and rear or machine end section 12 joined with the patient end section by a curved section 13. Alternative outer tubes could be smoothly curved along their entire length or could be highly flexible and reinforced with a natural straight shape. A sealing cuff 14 embraces the shaft 10 close to its patient end 15. The cuff 14 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 surgically-made tracheostomy opening in the neck, 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 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 externally of the tracheostomy.

With reference now also to Figures 2 to 4, the inner tube or cannula 3 comprises a shaft 30 and a hub or machine end fitting 31. The inner cannula 3 is about 194mm long and its shaft 30 has an internal diameter of about 8mm with 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 substantially level with the patient end 15 of the outer tube and with its machine end fitting 31 locating in the hub 20 of the outer tube.

The shaft 30 comprises a wall 33 of ePTFE and a strengthening member in the form of a reinforcing rib or strip 34 extending longitudinally along it. The reinforcing rib 34 is of a material different from the wall 33 and, more particularly, is of a flexible or semi-rigid plastics material such as polyethylene, polypropylene, PVC, nylon, polyester, EVA or polyurethane and is stiffer than the ePTFE material of the wall. The reinforcing rib 34 has an oval cross section with a smooth, continuous surface that is not interrupted by any recesses. Ribs of different cross section could be used. The rib 34 is embedded within the thickness of the wall 33 so that it is covered along its length and around its girth with the material of the wall, so that no part of the rib is exposed. In this way, although the ePTFE material of the wall does not bond securely to the material of the rib, the rib is securely mechanically retained in the shaft 30 by being totally encased in the wall material. The rib 34 increases the axial stiffness of the shaft 30, reducing the risk that the shaft will be axially compressed by any axial force applied during normal use. The rib 34 still enables the shaft 30 to be bent although it gives the shaft a plane of preferential bending that includes the rib. The inner cannula 3 is completed by attaching the hub or machine end fitting 31, which may be carried out by any conventional technique, such as by an overmoulding technique. To insert the inner cannula 3 in the tube 1 the rib 34 is aligned with the outside of the curve of the tube so that the inner cannula can readily bend along the curve of the tube.

Figure 5 shows an alternative form of reinforcing rib or strip 134 also of a thermoplastic material but extruded with an I-shape or girder cross section with an outer and inner plate 135 and 136 separated by a central internal wall or portion 137 running along the length of the rib. This forms two elongate channels 138 and 139 extending along opposite edges of the strip 134 divided by the wall 137. The wall 137 is interrupted by multiple recesses, passages or holes 140 extending through the thickness of the wall and

communicating between the two channels 138 and 139 on opposite sides. The holes 140 are equally spaced along the strip 134 and have an oval shape with their major axis aligned longitudinally of the wall. In this arrangement the outer and inner surfaces 141 and 142 of the plates 135 and 136 are exposed on the outer and inner surfaces of the cannula 103 and are curved across their width with the same radius as the outer and inner surface of the cannula respectively. The strip 134 is pre-formed by extrusion and is then integrated into the extrusion of the ePTFE wall material so that the wall material can flow into the channels 138 and 139 and through the holes 140 to form, when solidified, a mechanical link between the wall 133 and the strip. Alternatively, the strip could be co-extruded at the same time as the wall material.

Figure 6 shows an arrangement similar to that of Figure 5 in that the cannula 203 has a reinforcing strip 234 with recesses or holes 240 into which material of the wall 233 is flowed but differs in that the material does not flow through the recesses to combine with material on the opposite side. In the arrangement of Figure 6 the channels 238 and 239 have a V-shape section and the recesses 240 are formed through an outer plate 235 and an inner plate 236 on opposite sides of the central portion 237. The material of the wall 233 flows into the channels 238 and 239 and into the recesses 240 to flow level with the inner and outer surfaces of the strip 234, thereby filling the recesses and forming a secure mechanical join between the two materials when solidified.

Figures 7 A to 7D show steps in a process to make an alternative cannula 303, which differs from those described above in that, instead of the ePTFE material being flowed into recesses in the thermoplastic reinforcing strip, the thermoplastic material forming the reinforcing rib 334 is flowed into recesses in a pre-formed ePTFE member 333. More particularly, Figure 7A shows a first step in the process of providing a flat, rectangular sheet 333 of ePTFE with a length equal to that of the shaft of the cannula 303 and a width slightly less than its circumference. The next step, as shown in Figure 7B is to punch or otherwise form two rows of recesses in the form of holes 340 through the sheet 333 along opposite edges along its length. The sheet 333 is then rolled about its length as shown in Figure 7C and fed into a machine 350 that adds the reinforcing rib 334. The rib 334 may be added in the machine 350 by over moulding, extrusion or any other method suitable for adding a thermoplastic rib. The material of the rib 334 overlaps the opposite edges of the sheet 333 on its inside and outside and flows through the holes 340 along opposite edges so that, when the rib material has solidified, the cannula 303 has a reinforcing rib with edges on its inner and outer surface that overlap the edges of the ePTFE sheet and that are interlocked with each other by the material flowed through the holes in the sheet.

Although the inner cannulae described above all have a single reinforcing rib it would be possible to provide more than one rib, such as two ribs spaced around the cannula by 180°. The ribs could be spaced on opposite sides of the inner cannula so that when the cannula is curved by being inserted in the outer tube the ribs lie along two parallel planes on opposite sides of and parallel to the plane of curvature of the outer tube. Where a preformed rib is used this could be formed with a curve along all or a part of its length so that the cannula is similarly curved. This could be used to give the inner cannula a curve that fully or partially matches the curve along the outer tube. The reinforcing rib could incorporate a malleable element within it, such as a wire or strip of aluminium, to enable the inner cannula to be bent by the user to the desired shape.

Claims

1. An inner tube or cannula (3) for insertion within an outer tube (1), the inner tube having a shaft (10) formed mainly by a tubular wall (33, 133, 233, 333) of a first plastics material and one or more elongate strengthening members (34, 134, 234, 334) extending axially along the shaft, characterised in that the or each strengtfiening member (34, 134, 234, 334) is of a second plastics material different from the first and is mechanically attached with the wall (33, 133, 233, 333) by flow of one material in or around the other material.

2. An inner tube or cannula according to Claim 1 , characterised in that the or each

strengthening member (34) is encased around its girth within the material of the wall (33).

3. An inner tube or cannula according to Claim 1 or 2, characterised in that the

strengthening member (34) has an oval section.

4. An inner tube or cannula according to Claim 1, characterised in that the or each

strengthening member (34, 134, 234, 334) has a plurality of recesses (140, 240, 340), and that the wall material (33, 133, 233, 334) is attached with the or each

strengthening member by portions of wall material flowed into the recesses.

5. An inner tube or cannula according to Claim 4, characterised in that the wall material (133) flowed into the recesses (140) is flowed through the recesses and integrally linked with wall material at opposite ends of the recesses.

6. An inner tube or cannula according to Claim 4 or 5, characterised in that the or each strengthening member takes the form of an elongate strip (134, 234) having an elongate channel (138, 139, 238, 239) along opposite edges and separated from one another by a central portion (137, 237).

7. An inner tube or cannula according to Claim 6, characterised in that the recesses (140) are formed through the central portion (133) such that wall material in the two channels (138, 139) is integrally linked through the recesses (140).

8. An inner tube or cannula according to Claim 6, characterised in that the recesses (240) are formed through the inner and outer plates (236, 235) on opposite sides of the central portion (237) so that the wall material flows level with the inner and outer surfaces of the elongate strip (234).

9. An inner tube or cannula according to Claim 1 , characterised in that the tubular wall is provided by a preformed sheet member (333) having two rows of recesses (340) along opposite edges and rolled into a tubular shape with its edges joined together by a reinforcing rib (334) the material of which is flowed into the recesses (340).

10. An inner tube or cannula according to any one of the preceding claims, characterised in that one of the first or second materials forms the major part of the shaft of the inner tube and is of ePTFE.

11. A method of making an inner tube or cannula (3) for insertion into an outer tube (1) including the steps of forming a first component (34, 134, 234, 333) of a first material providing a part of the shaft (30) of the inner tube, forming a second component (33, 133, 233, 334) of a second material different from the first material providing a different part of the shaft, characterised in that the second material is flowed in or around the first component such that the two components are mechanically attached with one another, and that the first and second components extend axially of the inner tube or cannula along the length of the shaft (30).

12. A method according to Claim 11 , characterised in that the method includes a

subsequent step of attaching a machine end fitting (31) to one end of the shaft (30).

13. A tube or cannula made by a method according to Claim 11 or 12. A tracheostomy tube assembly comprising an outer tube and an inner tube according to any one of Claims 1 to 10 or Claim 13.