Patent Description:
Tracheostomy tubes are used to enable ventilation or respiration of a patient. They are inserted into the trachea via a surgically formed opening in the neck so that one end of the tube locates in the trachea and the other end locates outside the patient adjacent the neck surface. Tracheostomy tubes are generally used for more long-term ventilation or where it is not possible to insert an airway through the mouth or nose. Various types of different tracheostomy tubes are presently available to suit different needs. One example of a tracheostomy tube having a rotatable coupling that is used to retain an inner cannula in place is described in <CIT>. The tube may be moulded of a soft material, such as a silicone plastics material, where there is a greater risk of trauma to the tracheal lining, such as in paediatric patients or patients with a damaged trachea. Typically, tubes are made by a one-shot moulding process where the shaft of the tube and the flange by which it is secured to the patient are moulded together an integral, one-piece component. The machine end coupling by which gas connection is made to the shaft is separately moulded from a different, harder material and subsequently attached to the machine end of the shaft and flange sub-assembly. The different properties of the materials from which the connector and shaft are made can make it difficult to ensure a secure, leak-proof connection of the coupling to the shaft. Also, the mould tooling required to mould the flange and shaft together is relatively large and expensive. Problems therefore exist in providing tracheostomy tubes with the desired properties that can be used safely and manufactured at low cost.

It is an object of the present invention to provide an alternative tracheostomy tube and a method of manufacturing such a tube.

According to one aspect of the present invention there is provided a tracheostomy tube of the above-specified kind, characterised in that the coupling is of a harder material than the shaft, that the rear, machine end of the shaft is attached with the coupling by material of the shaft flowed around a retaining formation at the patient end of the coupling to form a subassembly by mechanical interlocking of the shaft with the coupling, that the external surface at the rear end of the subassembly is formed with an abutment surface facing towards the forward, patient end of the tube, and that the flange has an attachment portion with an abutment surface facing rearwardly, the abutment surface on the flange abutting the abutment surface on the subassembly so as to prevent forward movement of the subassembly relative to the flange.

The retaining formation is preferably provided by a ring structure extending around the forward end of the coupling, the material of the shaft being flowed in and around the ring structure. The ring structure may include two discs spaced from one another along the length of the coupling. The two discs are preferably spaced from one another by an annular cavity, the forward disc being formed with a plurality of apertures opening through the disc into the cavity. The flange is preferably bonded with the abutment surface on the subassembly. The abutment surface at the rear end of the subassembly is preferably provided by ar_ externally enlarged boss formed with a locating lug arranged to locate in a notch formed in the flange. The shaft may be of a silicone material. The flange may be of a silicone material. The coupling may be of polysulphone.

According to another aspect of the present invention there is provided a method of manufacturing a tracheostomy tube including the steps of: moulding a coupling of relatively hard material and having a retaining formation around its forward, patient end; moulding a shaft of a softer material onto the coupling so that material at the rear, machine end of the shaft flows around the retaining formation to form a subassembly by mechanical interlocking of the shaft with the coupling, the external surface of the rear end of the subassembly being formed with an abutment surface facing forwardly; providing a flange having an attachment portion with an opening and an abutment surface around the opening facing rearwardly; threading the opening on the flange along the shaft from its patient end to its machine end until the abutment surface on the flange abuts the aburment surface on the subassembly; and bonding the flange to the shaft with the engagement of the abutment surfaces and preventing forward movement of the subassembly relative to the flange.

According to a further aspect of the present invention there is provided a tracheostomy tube made by a method according to the above other aspect of the present invention.

A tracheostomy tube 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:.

With reference first to <FIG> and <FIG>, the tube is formed of three components joined with one another, namely a shaft <NUM> providing a gas passage to the trachea, a connector or coupling <NUM> for enabling gas connection with the shaft, and a flange <NUM> for securing the tube with the patient's neck.

The shaft <NUM> is moulded of a silicone or other relatively soft plastics material with a circular cross-section and is curved along its length. The forward, patient end <NUM> of the shaft <NUM> is adapted for location in the patient's trachea. The rear, machine end <NUM> of the shaft is adapted to extend through the tracheostomy opening and to project from the surface of the neck. The machine end <NUM> is moulded with an externally enlarged boss <NUM> that will be described in detail later. The shaft <NUM> is shown without any sealing cuff but any conventional sealing cuff and inflation line could be provided. The shaft <NUM> could have alternative shapes and sections, and could be made of other materials.

With reference now also to <FIG>, the connector or coupling <NUM> is moulded of a relatively hard plastics material such as polysulphone and has a tubular shape with a generally circular section. The greater part of the length of the connector <NUM> is provided by an externally-tapered coupling portion <NUM> that forms a male mating surface adapted to fit within a cooperating female tapered coupling at the end of a breathing tube (not shown). Externally, at the patient end of the coupling portion <NUM>, the connector is formed with two flat faces <NUM> arranged parallel and diametrically opposite one another, facing outwardly of the coupling <NUM>. A circular flange <NUM> projects outwardly around the connector <NUM> on the patient side of the flat faces <NUM> and has a diameter slightly larger than that of the coupling portion <NUM>. A retaining formation including a ring structure <NUM> of the same diameter as the flange <NUM> but about twice its width is spaced a short distance forwardly of the flange to form an annular cavity <NUM> on the patient side of the flange. The ring structure <NUM> is divided into a forward and rearward disc <NUM> and <NUM> by two annular, part-circular slots <NUM> and <NUM> opening both externally of the ring structure and internally into an annular recess <NUM> extending around an inner tubular patient end portion <NUM> of the connector <NUM>. The discs <NUM> and <NUM> are supported on the tubular patient end portion <NUM> by a number of outwardly-extending struts <NUM> spaced around the connector <NUM>, which are separated from one another by a number of apertures <NUM> opening into the annular recess <NUM> and the annular cavity <NUM>. The purpose of these slots, apertures, recesses and cavities <NUM>, <NUM>, <NUM>, <NUM> and <NUM> is to form flow paths that enable plastics material from the rear end boss <NUM> of the shaft <NUM> to flow around the rear end retaining formation <NUM> of the connector <NUM> and form a secure mechanical interlocking of the shaft with the connector, despite the different properties of the materials of the shaft and connector. The combination of the shaft <NUM> with the connector <NUM> forms a subassembly <NUM>.

Forwardly of the rear end step <NUM> on the boss <NUM> of the shaft <NUM> is an intermediate annular step <NUM> the diameter of which is slightly less than the external diameter of the ring structure <NUM> so that a forwardly-facing, radial, annular abutment surface or wall <NUM> is formed between the two steps. The intermediate step <NUM> has a larger diameter than the outside of the main part of the shaft <NUM> so that a second, forward wall <NUM> is formed between this step and the rear end <NUM> of the shaft. The external surface of the rear end step <NUM> is also formed with two short location lugs <NUM> (only one visible in <FIG>) of generally rectangular shape that project radially outwardly diametrically opposite one another and aligned along an axis orthogonal to both the axis of the connector <NUM> and the plane of curvature of the shaft <NUM>.

The internal surface <NUM> of the connector <NUM> has a circular section the diameter of which is reduced slightly along a forward patient end portion <NUM>. The step <NUM> between the forward portion <NUM> and the rear part of the surface <NUM> is tapered to form a part-annular incline. The internal surface <NUM> of the connector is also interrupted by two parallel longitudinally extending flats <NUM> arranged parallel to one another. The flats <NUM> form keys to ensure that only an inner cannula (not shown) with a corresponding keyway on its machine end fitting can be fitted fully in the tracheostomy tube.

The third component of the tube is the flange <NUM>, shown most clearly in <FIG> and <FIG>. This is moulded from a soft, flexible plastics, such as silicone, and may be the same as the material of the shaft <NUM>. The flange <NUM> has a central collar <NUM> providing an attachment portion for attaching with the shaft <NUM>. Two arms <NUM> extend radially outwardly on opposite sides of the collar <NUM> and are terminated at their outer ends by enlarged lugs <NUM>. Each lug <NUM> has a slot <NUM> formed through its thickness to receive a neck strap (not shown) by which the tube is secured around the patient's neck. The patient end surface <NUM> of the collar <NUM> is level and continuous with the patient surface of the arms <NUM>. The length or thickness of the collar <NUM> is greater than the thickness of the flange <NUM> so that the rear, machine end <NUM> of the collar projects beyond the rear surface of the flange. The length of the collar <NUM> is selected to be equal to the length of the enlarged boss <NUM> at the rear end of the shaft <NUM>. The inside or opening <NUM>' of the collar <NUM> includes a rear, machine end portion <NUM> having a diameter equal to the external diameter of the rear end step <NUM> of the shaft and connector sub-assembly. The machine end internal portion <NUM> is interrupted by two location notches <NUM> of rectangular section located diametrically opposite one another along an axis parallel with the length of the two arms <NUM>. The notches <NUM> extend longitudinally of the length of the machine end portion <NUM>. The internal machine end portion <NUM> is divided from an internal patient end portion <NUM> by a rearwardly-facing annular abutment surface or wall <NUM> around the opening <NUM>'. The diameter of the internal patient end portion <NUM> of the flange <NUM> is equal to the external diameter of the intermediate annular step <NUM> on the shaft <NUM>. The internal dimensions and configuration of the collar <NUM> of the flange <NUM> and the external dimensions and configuration of the boss <NUM> on the shaft <NUM> are such that the boss fits snuggly within the collar with the forward-facing annular surface <NUM> on the boss abutting the rearward-facing annular surface <NUM> in the collar. The two lugs <NUM> at the rear end of the shaft <NUM> align with and locate in the two notches <NUM> in the collar <NUM> of the flange <NUM> so as to ensure that the arms <NUM> of the flange extend orthogonally to the plane of curvature of the shaft.

The tube is made by initially separately moulding the connector <NUM> and flange <NUM> as discrete components of different plastic compositions. The connector <NUM> is then placed in a mould tool having a cavity defining the shape of the shaft. Flowable plastics material is then injected into the cavity so that it flows along the part defining the shape of the shaft and also flows around the retaining ring structure <NUM> of the connector <NUM>. The material of the shaft <NUM> is softer and has a lower melt temperature than that of the connector <NUM>. When the shaft material has fully cured the sub-assembly of connector <NUM> and shaft <NUM> is removed from the mould tool as the subassembly <NUM>. The next step is to apply a bonding agent such as a solvent or adhesive to the inner surface of the collar <NUM> on the flange <NUM> and to the cuter surface of the boss <NUM> on the connector and shaft sub-assembly. The patent end <NUM> of the shaft <NUM> is then extended through the collar <NUM> of the flange <NUM> and the flange is threaded along the shaft until the boss <NUM> on the shaft enters the collar. At this stage the flange <NUM> is appropriately oriented so that the lugs <NUM> on the outside of the boss <NUM> align with the notches <NUM> in the collar <NUM>, thereby ensuring that the flange is appropriately oriented with respect to the plane of curvature of the shaft. After the bonding agent has fully cured the tube is ready for use or for any finishing operations.

The moulded connection between the shaft and the connector ensures an effective gas and liquid seal between these two components and also ensures an effective mechanical interlocking between the shaft and the connector. This prevents any risk these components could separate. The engaging surfaces <NUM> and <NUM> on the flange <NUM> and the boss <NUM> of the shaft <NUM> also ensure that, even if the bond between them should break down, there would be no risk that the subassembly <NUM> could separate from the flange and displace into the patient.

Claim 1:
A tracheostomy tube comprising a shaft (<NUM>) for providing a gas passage to the trachea, a coupling (<NUM>) for enabling gas connection with the shaft (<NUM>), and a flange (<NUM>) for securing the tube with a patient's neck, wherein the coupling (<NUM>) is of a harder material than the shaft (<NUM>), the rear, machine end (<NUM>) of the shaft (<NUM>) is attached with the coupling (<NUM>) by material of the shaft flowed around a retaining formation (<NUM>) at the patient end of the coupling (<NUM>) to form a subassembly (<NUM>) by mechanical interlocking of the shaft (<NUM>) with the coupling (<NUM>), the external surface at the rear end of the subassembly (<NUM>) is formed with an abutment surface (<NUM>) facing towards the forward, patient end (<NUM>) of the tube, and the flange (<NUM>) has an attachment portion (<NUM>) with an abutment surface (<NUM>) facing rearwardly, the abutment surface (<NUM>) on the flange (<NUM>) abutting the abutment surface (<NUM>) on the subassembly (<NUM>) so as to prevent forward movement of the subassembly (<NUM>) relative to the flange (<NUM>).