Abstract:
An inflation indicator balloon for a cuffed tracheal tube is moulded directly onto an and of an inflation line. The inflation line is slipped on one end of a core pin and a parison is injection moulded in a first cavity with one end of the parison on top of the inflation line. The parison is then blow moulded to the desired shape of the inflation balloon in a second cavity. The balloon and line are removed from the core pin and a valve is inserted in the end oposite the inflation line.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    This invention relates to inflation indicators and their manufacture.  
           [0002]    Cuffed medical tubes, such as tracheal tubes, are provided with some form of inflation indicator so that a clinician can determine whether the cuff is inflated or deflated when the tube is located in the body. The inflation indicator may be a flat balloon joined at one end with a small bore inflation line and at the other end with a connector and valve by which a syringe or similar device is connected to the inflation line. When the cuff of the tube is inflated, pressure is communicated to the inflation indicator, which is inflated to a more circular section. Conventionally, the indicator balloon is blow moulded and subsequently assembled onto and attached to the inflation line, the valve/connector and to its dust cap. Blow moulding a shape of this kind tends to lead to a relatively large amount of waste material and the assembly operations also add to the cost of the final product. It can also be a problem joining the balloon to the inflation line without leaking because the flat shape of the balloon does not lend itself to forming an effective seal around the cylindrical surface of the inflation line. Examples of inflation indicators are described in, for example, U.S. Pat. Nos. 3,810,474, 4,018,231, 4,130,617, 4,178,939, GB 2164565, GB 2174303 and GB 2213592.  
         BRIEF SUMMARY OF THE INVENTION  
         [0003]    It is an object of the present invention to provide an alternative inflation indicator and method of manufacture.  
           [0004]    According to one aspect of the present invention there is provided an inflation indicator for a cuffed medico-surgical tube, the indicator including an inflatable balloon attached at one end to an inflation line, the balloon being moulded to its final shape with the inflation line extending in the one end of the balloon so that the balloon is moulded onto the inflation line.  
           [0005]    The balloon may have an inflatable region that is generally flat and may include a valve assembly disposed in an opposite end of the inflatable balloon. The balloon preferably includes a dust cap moulded with it.  
           [0006]    According to another aspect of the present invention there is provided a method of manufacture of an inflation indicator comprising the steps of forming a parison of generally tubular shape about an end of an inflation line, then moulding the parison to the shape of an inflation balloon with the inflation line in situ such that the end of the inflation line is attached sealingly with one end of the balloon.  
           [0007]    The inflation line is preferably fitted on one end of a core pin and the parison is preferably moulded in a first cavity on the core pin about an end of the inflation line. The parison is preferably moulded on the core pin to the shape of the inflatable balloon in a second cavity. The parison may be formed by injection moulding and be moulded to the shape of the inflation balloon by blow moulding. The method may include the subsequent step of inserting a valve in the opposite end of the balloon. The parison may be moulded with an integral dust cap.  
           [0008]    According to a further aspect of the present invention there is provided an inflation indicator made by a method according to the above other aspect of the present invention.  
           [0009]    According to a fourth aspect of the invention, there is provided a cuffed medico-surgical tube including an inflation indicator according to the above one or further aspect of the present invention.  
           [0010]    A cuffed tracheostomy tube with an inflation indicator, and its method of manufacture, will now be described, by way of example, with reference to the accompanying drawings. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]    [0011]FIG. 1 is a side elevation view of the tube;  
         [0012]    [0012]FIG. 2 is an enlarged side elevation view of the inflation indicator;  
         [0013]    [0013]FIG. 3 is an enlarged sectional view along the line III-III of FIG. 2;  
         [0014]    [0014]FIG. 4 is an enlarged transverse sectional view along the line IV-IV of FIG. 2;  
         [0015]    [0015]FIG. 5 is a sectional side elevation view of a first station of the machine used to preform the inflation indicator;  
         [0016]    [0016]FIG. 6 is an enlarged sectional side elevation view of the pre-form produced by the machine shown in FIG. 5; and  
         [0017]    [0017]FIG. 7 is a sectional side elevation view of a second station of the machine used to form the inflation indicator. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0018]    With reference first to FIGS.  1  to  4 , the tracheostomy tube includes a curved, moulded shaft  1  of circular section with an inflatable cuff  2  surrounding the shaft close to the patient end  3 . The machine end  4  of the tube has an integrally moulded flange  5  and connector  6 . The cuff 2  is inflated and deflated by means of a small bore inflation line  10  secured in a channel  11  extending along the outside of the shaft  1  or via an extruded lumen within the wall of the tube. The patient end of the inflation line  10  extends within and opens into the interior of the cuff  2 . The machine end of the inflation line  10  is provided with an inflation indicator  12 .  
         [0019]    The inflation indicator  12  includes a moulded balloon  13  and a separate valve/connector assembly  14 . The balloon  13  includes an inflatable region  15 , a patient end portion  16  joined with the inflation line  10 , and a machine end portion  17  joined with the valve assembly  14 . The inflation balloon  13  is of PVC and is moulded in a two-stage process of injection and blow moulding, which will be described in greater detail later. The inflatable region  15  is of generally rectangular shape with tapered ends and is substantially flat (in its uninflated state), with a raised rib  18  extending longitudinally in the centre of each side to ensure a continuous gas path through the indicator, even when a negative pressure is applied (as described in greater detail in GB 2213592). The balloon  13  is about 50 mm long, with the inflatable region  15  being about 35 mm long and 20 mm wide. The wall thickness of the balloon  13  along the inflatable region  15  and the patient end  16  is about 0.5 mm, whereas at the machine end, the wall is about 2 mm thick. The balloon  13  is moulded with an integral dust cap  19  attached with the machine end of the indicator by a flexible web  20  about 25 mm long.  
         [0020]    The patient end portion  16  is in the form of a short collar of cylindrical shape, with an internal diameter of about 1.4 mm and an external diameter of 2.4 mm. The collar  16  is moulded about and bonded to the machine end of the inflation line  10 , as will be described in greater detail later. At its machine end  17 , the balloon  13  has a larger diameter sleeve  21 , with an internal diameter of about 7 mm. The valve-assembly  14  is conventional and is bonded into the sleeve  21 , the external end of the valve assembly having a female connector  22  shaped to allow the nose of a syringe to be inserted. The connector  22  is shaped to allow the nose of the syringe to contact and displace a valve element (not shown) from a valve seat within the assembly  14  so as to open a gas flow passage through the valve. At the same time, the nose of the syringe forms a seal with the connector  22 .  
         [0021]    With reference now to FIGS.  5  to  7 , the inflation indicator balloon  13  is made in two stages on a moulding machine  30  having a base assembly  31  and two different upper stations  32  and  33 . As shown in FIG. 5, the base assembly  31  comprises a base  34  and a vertically-extending, hollow and porous core pin  35 , the external shape of which defines the internal shape of a preform of the indicator. More particularly, the core pin  35  has a lower section  36  of cylindrical shape and diameter of 7 mm, an intermediate section  37 , which tapers at a shallow angle to a reduced diameter to a more steeply tapered shoulder  38 , which joins with a small diameter upper section  39 . The upper section  39  receives the machine end of the inflation line  10  pushed onto the core pin  35  by a distance of about 4 mm. The first upper station  32  is an injection moulding station and has two mould parts  41  and  42  that are slidable down and outwardly along angled pins  43  and  44  extending parallel to respective heel blocks  45  and  46 . The mould parts  41  and  42  have respective opposed, vertical faces  47  and  48  shaped with recesses or cavities  49  and  50  to define a cavity for the external shape of the balloon preform  60  (FIG. 6). More particularly, the cavities  49  and  50  conform substantially to the profile of the core pin  35  except that the spacing between the recesses and the core pin allows for a thicker layer of material along the intermediate section  37  than along the shoulder  38  and upper section  39 . The lower surface  51  of one of the mould parts  41  is formed with a recess and the base  34  is formed with a projection (neither shown) which together define the dust cap  19  and web  20  of the balloon  13 .  
         [0022]    In operation, the upper station  32  is lowered about the base assembly  31  and the two mould parts  41  and  42  are closed around the core pin  35  with the inflation line  10  in place. Molten PVC is then injected into the cavity between the mould parts  41  and  42  and the core pin  35 . The upper station  32  is then lifted and the mould parts  41  and  42  are separated, leaving a preform or parison  60  of the kind shown in FIG. 6 on the base assembly  31 , with an integral, moulded dust cap.  
         [0023]    The base assembly  31  is then moved on to the second, blow station  33  (FIG. 7), which also has two mould parts  61  and  62  with recesses or cavities  63  and  64  in their respective opposed vertical faces  65  and  66 . These cavities  63  and  64  are shaped with the external profile of the final shape of the balloon  13 , that is, they define the generally flat shape of the indicator balloon.  
         [0024]    The blow station  33  is lowered and the mould parts  61  and  62  are closed about the core pin  35  and preform  60 . The mould parts  61  and  62  are heated and pressure is applied via the core pin  35  to the inside of the preform  60  so that this is blown outwardly to fill the shape of the cavities  63  and  64 . The upper station  33  is then raised and the mould parts  61  and  62  are separated allowing the balloon  13  in its final form to be removed from the core pin  35 . The indicator  12  is completed by inserting the valve assembly  14  into the sleeve  21  and bonding this in position such as by welding or adhesive. It may be necessary in some cases for the blow moulding stage to be carried out in two parts. The parison is first blow moulded to an intermediate shape at a first blow station and is then moved to a second blow station where it is blow moulded to its final shape. This helps ensure a more constant wall thickness over the indicator balloon.  
         [0025]    It can be seen that, because the patient end of the balloon is moulded about the inflation line, there can be a perfect seal with the inflation line, which cannot always be guaranteed when previous assembly techniques are used. The manufacturing method described enables the number of manual assembly operations required to be greatly reduced. Assembly is also reduced because the dust cap can be moulded integrally with the balloon, rather than being made separately and subsequently assembled. The amount of waste material produced by the injection blow moulding technique described can be less than previous blow moulding techniques. The two stage process of injection moulding and blow moulding also enables more accurate control of wall thickness of the final product.