Patent Publication Number: US-2023141119-A1

Title: Tracheostomy tubes and their manufacture

Description:
This invention relates to tracheostomy tubes of the kind comprising a shaft for providing a gas passage to the trachea, a coupling for enabling gas connection with the shaft, and a flange for securing the tube with a patient&#39;s neck. 
     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. 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 an 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 abutment 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: 
         FIG.  1    is a perspective view of the rube from its forward, patient end; 
         FIG.  2    is a perspective view of the tube from its rear, machine end; 
         FIG.  3    is a perspective view of a sub-assembly of a shaft and connector at a preliminary stage of manufacture; 
         FIG.  4    is a cut-away view along the axis of the sub-assembly shown in  FIG.  3   ; 
         FIG.  5    is an enlarged perspective view of the connector before moulding with the shaft; 
         FIG.  6    is cut-away view along the axis of the connector shown in  FIG.  5   ; 
         FIG.  7    is a perspective view of the flange before assembly; and 
         FIG.  8    is a cut-away view of the tube from its rear, machine end. 
     
    
    
     With reference first to  FIGS.  1  and  2   , the tube is formed of three components joined with one another, namely a shaft  1  providing a gas passage to the trachea, a connector or coupling  2  for enabling gas connection with the shaft, and a flange  5  for securing the tube with the patient&#39;s neck. 
     The shaft  1  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  10  of the shaft  1  is adapted for location in the patient&#39;s trachea. The rear, machine end  11  of the shaft is adapted to extend through the tracheostomy opening and to project from the surface of the neck. The machine end  11  is moulded with an externally enlarged boss  12  that will be described in detail later. The shaft  1  is shown without any sealing cuff but any conventional sealing cuff and inflation line could be provided. The shaft  1  could have alternative shapes and sections, and could be made of other materials. 
     With reference now also to  FIGS.  3  to  8   , the connector or coupling  2  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  2  is provided by an externally-tapered coupling portion  20  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  20 , the connector is formed with two flat faces  21  arranged parallel and diametrically opposite one another, facing outwardly of the coupling  2 . A circular flange  22  projects outwardly around the connector  2  on the patient side of the flat faces  21  and has a diameter slightly larger than that of the coupling portion  20 . A retaining formation including a ring structure  23  of the same diameter as the flange  22  but about twice its width is spaced a short distance forwardly of the flange to form an annular cavity  24  on the patient side of the flange. The ring structure  23  is divided into a forward and rearward disc  25  and  26  by two annular, part-circular slots  27  and  28  opening both externally of the ring structure and internally into an annular recess  29  extending around an inner tubular patient end portion  30  of the connector  2 . The discs  25  and  26  are supported on the tubular patient end portion  30  by a number of outwardly-extending struts  31  spaced around the connector  2 , which are separated from one another by a number of apertures  32  opening into the annular recess  29  and the annular cavity  24 . The purpose of these slots, apertures, recesses and cavities  27 ,  28 ,  29 ,  24  and  32  is to form flow paths that enable plastics material from the rear end boss  12  of the shaft  1  to flow around the rear end retaining formation  23  of the connector  2  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  1  with the connector  2  forms a subassembly  7 . 
     Forwardly of the rear end step  13  on the boss  12  of the shaft  1  is an intermediate annular step  14  the diameter of which is slightly less than the external diameter of the ring structure  23  so that a forwardly-facing, radial, annular abutment surface or wall  15  is formed between the two steps. The intermediate step  14  has a larger diameter than the outside of the main part of the shaft  1  so that a second, forward wall  16  is formed between this step and the rear end  11  of the shaft. The external surface of the rear end step  13  is also formed with two short location lugs  18  (only one visible in  FIG.  3   ) 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  2  and the plane of curvature of the shaft  1 . 
     The internal surface  35  of the connector  2  has a circular section the diameter of which is reduced slightly along a forward patient end portion  37 . The step  38  between the forward portion  37  and the rear part of the surface  35  is tapered to form a part-annular incline. The internal surface  35  of the connector is also interrupted by two parallel longitudinally extending flats  36  arranged parallel to one another. The flats  36  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  5 , shown most clearly in  FIGS.  1  and  7   . This is moulded from a soft, flexible plastics, such as silicone, and may be the same as the material of the shaft  1 . The flange  5  has a central collar  50  providing an attachment portion for attaching with the shaft  1 . Two arms  51  extend radially outwardly on opposite sides of the collar  50  and are terminated at their outer ends by enlarged lugs  52 . Each lug  52  has a slot  53  formed through its thickness to receive a neck strap (not shown) by which the tube is secured around the patient&#39;s neck. The patient end surface  54  of the collar  50  is level and continuous with the patient surface of the arms  51 . The length or thickness of the collar  50  is greater than the thickness of the flange  5  so that the rear, machine end  55  of the collar projects beyond the rear surface of the flange. The length of the collar  50  is selected to be equal to the length of the enlarged boss  12  at the rear end of the shaft  1 . The inside or opening  50 ′ of the collar  50  includes a rear, machine end portion  56  having a diameter equal to the external diameter of the rear end step  13  of the shaft and connector sub-assembly. The machine end internal portion  56  is interrupted by two location notches  57  of rectangular section located diametrically opposite one another along an axis parallel with the length of the two arms  51 . The notches  57  extend longitudinally of the length of the machine end portion  56 . The internal machine end portion  56  is divided from an internal patient end portion  58  by a rearwardly-facing annular abutment surface or wall  59  around the opening  50 ′. The diameter of the internal patient end portion  58  of the flange  5  is equal to the external diameter of the intermediate annular step  14  on the shaft  1 . The internal dimensions and configuration of the collar  50  of the flange  5  and the external dimensions and configuration of the boss  12  on the shaft  1  are such that the boss fits snuggly within the collar with the forward-facing annular surface  15  on the boss abutting the rearward-facing annular surface  59  in the collar. The two lugs  18  at the rear end of the shaft  1  align with and locate in the two notches  57  in the collar  50  of the flange  5  so as to ensure that the arms  51  of the flange extend orthogonally to the plane of curvature of the shaft. 
     The tube is made by initially separately moulding the connector  2  and flange  5  as discrete components of different plastic compositions. The connector  2  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  23  of the connector  2 . The material of the shaft  1  is softer and has a lower melt temperature than that of the connector  2 . When the shaft material has fully cured the sub-assembly of connector  2  and shaft  1  is removed from the mould tool as the subassembly  7 . The next step is to apply a bonding agent such as a solvent or adhesive to the inner surface of the collar  50  on the flange  5  and to the cuter surface of the boss  12  on the connector and shaft sub-assembly. The patent end  10  of the shaft  1  is then extended through the collar  50  of the flange  5  and the flange is threaded along the shaft until the boss  12  on the shaft enters the collar. At tits stage the flange  5  is appropriately oriented so that the lugs  18  on the outside of the boss  12  align with the notches  57  in the collar  50 , 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  59  and  15  on the flange  5  and the boss  12  of the shaft  1  also ensure that, even if the bond between them should break down, there would be no risk that the subassembly  7  could separate from the flange and displace into the patient 
     The tube also has various manufacturing advantages. Tracheostomy tubes are provided in a range of different sizes for patients of different builds and anatomies, but the flange usually has the same size across the entire range from neonatal, paediatric to adult patients. By forming the flange as a separate component, it is possible for the same flange to be used across the entire range of sizes, thereby enabling more effective inventory management. Also, forming the flange separately from the shaft means that they could be made of different materials with different properties. The lug and notch features on the flange and the boss of the shaft ensure that the flange can only be mounted on the tube at the correct orientation, thereby preventing incorrect assembly and possible waste. One conventional manufacturing technique involves moulding the shaft and flange together as a single component. The problem with this is that the flange and shaft extend in different planes leading to large and expensive mould tools. By forming the flange separately from the shaft smaller and lower cost mould tools can be used, thereby enabling the cost of manufacture to be minimized.