This invention relates a method of making a sealing cuff for a medico-surgical tube in which a tubular member is provided and then expanded along at least a part of its length to form an enlarged, central inflatable portion and two opposite end attachment portions.

Tracheal tubes are used to supply ventilation and anaesthetic gases to a patient, such as during surgery. The tracheal tube may be inserted via the mouth or nose, in the case of an endotracheal tube, or may be inserted via a surgically-made tracheostomy opening in the neck, in the case of a tracheostomy tube. Most, but not all, tracheal tubes have some form of a seal on their outside which forms a seal between the outside of the tube and the inside of the trachea so that gas flow is confined to the bore of the tube and cannot flow around the outside of the tube, between the tube and the trachea.

The most common form of seal is provided by an inflatable cuff that is inflated and deflated via a small bore lumen extending rearwardly along the tube and connected towards its rear end to an inflation line terminated by an inflation indicator, valve and connector. These inflatable cuffs may be of the high-volume/low-pressure kind where the cuff is formed of a flexible material moulded with a natural annular or doughnut shape that is inflated without stretching by relatively low-pressure gas supplied via the inflation line.

Alternatively, the cuff may be of the low- volume/high-pressure kind where the cuff is of an elastic material that lies close to the tube shaft when uninflated but is inflated and stretched to a larger diameter by relatively high pressure gas supplied via the inflation line. Various problems exist with both forms of cuff. One concern arises from the secretions that collect above the cuff during use. It is desirable to minimise the leakage of these secretions between the outside of the cuff and the trachea since secretions that flow into the respiratory passages can lead to infection, such as VAP (ventilator-associated pneumonia). Leakage of secretions passed the inflated cuff can be reduced by making the wall of the cuff thin so that it can conform more readily to the anatomy of the tracheal wall. Ideally, the entire inflatable wall of the cuff should have a constant thickness to ensure the most effective seal. A common way to make these sealing cuffs is initially to extrude a tube of constant wall thickness along its length. Subsequently, the tube is expanded midway along its length, such as by gas pressure, in a blow moulding process. This leads to a Ihinning of the wall in the expanded section that is proportional to its diameter. Consequently, opposite ends of the inflated region of the cuff are thicker, and hence stiffer than the central part of the inflated region. These variations in wall thickness over the surface of the cuff can lead to uneven contact with the tracheal wall.

It is an object of the present invention to provide an alternative tracheal tube and cuff, and an alternative method of manufacturing a cuff.

According to one aspect of the present invention there is provided a method of the above-specified kind, characterised in that the tubular member is configured with a wall thickness before expansion that varies along at least that part that is to be expanded, with the central part being thicker midway along its length than in end regions adjacent the central part, such that, when expanded, the inflatable portion has a wall thickness that is more constant along its length than would be the case if the tubular portion before expansion had a constant wall thickness along its length.

The tubular member is preferably expanded by a blow moulding technique. The tubular member is preferably made by an injection moulding technique. The tubular member before expansion preferably has opposite end regions of a first wall thickness, a central region between the two end regions of a second wall thickness greater that the first wall thickness and two intermediate regions between the central region and opposite end regions, the intermediate regions varying in thickness along their length between that of the central region and that of the respective end region. The tubular member may be of a crystalline or semi-crystalline plastics.

According to another aspect of the present invention there is provided a cuff made by a method according to the above one aspect of the present invention.

According to a further aspect of the present invention there is provided a method of making a medico-surgical tube, characterised in that the method includes the steps of providing a tube with an inflation lumen extending along its length and opening on the outside of the tube towards its patient end, and attaching a cuff made by a method according to the above one aspect of the present invention to the outside of the tube with the inflatable portion located over the opening.

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

According to a fifth aspect of the present invention there is provided a sealing cuff for a medico-surgical tube, characterised in that the sealing cuff is made from a tubular member formed initially with a wall thickness that varies along at least a part of its length with a central part being thicker midway along its length than in end regions adjacent the central part, that the tubular member is radially expanded at least along the central part to form an inflatable portion of the cuff with a wall thickness that is more constant along its length than would be the case if the tubular portion before expansion had a constant wall thickness along its length.

According to a sixth aspect of the present invention there is provided a medico- surgical tube including an inflation lumen extending along its length and opening on an outside of the tube towards its patient end and a sealing cuff according to the above other or fifth aspect of the present invention attached at opposite ends to the outside of the tube and extending over the opening from the inflation lumen.

The medico-surgical tube may be a tracheal tube, such as a tracheostomy or endotracheal tube.

According to a seventh aspect of the present invention there is provided a tubular member for use in a method according to the above one or further aspect of the present invention.

A tracheostomy tube and a method of making a cuff for the tube, 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 the tube;

Figure 2 A is a sectional side elevation view of a conventional cuff;

Figure 2B is a side elevation view of the conventional cuff of Figure 2 A in a deflated state on a tube shaft;

Figure 3 is a sectional side elevation view of a cuff of the present invention at a preliminary stage;

Figure 4 is a sectional side elevation view showing a subsequent stage in the manufacturing process; and

Figure 5 is a sectional side elevation view of a cuff according to the present invention.

The tracheostomy tube includes a tubular shaft 1 having a bore 2 extending along its length. The tube is formed with a relatively straight patient end portion 3 and a relatively straight machine end portion 4 linked by a curved intermediate portion 5 so that the patient and machine ends 6 and 7 are angled at about 100° to one another. The shaft 1 is extruded or moulded from a plastics material such as PVC. Towards its patient end 6 the tube has sealing means provided by an inflatable cuff 10 embracing the shaft 1. The cuff 10 is of the high- volume/low-pressure kind so that it has a relatively floppy shape when deflated but, when inflated, it fills out at low pressure to a diameter matching the internal diameter of the trachea. The cuff 10 is attached to the shaft 1 by two collars or attachment portions 8 and 9 at opposite ends. The cuff 10 extends over an opening 11 on the outer surface of the shaft 1 into an inflation lumen 12 extending along the shaft within its wall thickness. The inflation lumen 12 is connected towards the rear end of the tube with a small-bore inflation line 13 that is terminated by a combined inflation indicator or pilot balloon, valve and connector 14. At its machine end 7 the tube has a flange 20, to which a neck strap (not shown) is attached, and a standard 15mm female coupling 21.

As so far described, the tube is conventional.

Conventional cuffs for tracheal tubes are usually made by an in-line extrusion blow moulding process. This involves extrusion of a parison of cylindrical shape and subsequent blowing with gas pressure to expand the central region outwardly to form the inflatable portion of the cuff. The parison is extruded with a constant wall thickness along its length. The blowing process expands the central region, thereby making the wall thinner in this region. The shoulder regions, because they are not expanded to the same extent, are thicker than the main body of the cuff. This is illustrated in Figure 2A, which shows the opposite end, attachment regions or collars 31 and 32 being relatively thick, the central, cylindrical main body portion 33 being thin and of a relatively constant thickness, and the sloping shoulder regions 34 and 35 between the collars and the main body portion being thicker than the main body portion and varying in thickness along their length, being thickest adjacent the collars where expansion is least. The shoulder regions 34 and 35 should, however, preferably be relatively thin and of the same thickness as the main body portion 33 so that they can flex freely without applying pressure to the opposite ends of the main body portion. The stiffness of these shoulder regions 34 and 35 also results in unwanted thickened regions 36 and 37 when the cuff is deflated, as shown in Figure 2B. This bunching produces an interruption of the smooth surface of the tube and a localised increase in its bulk, which can cause an obstruction to insertion through a tracheostomy. This increased external bulk is also a disadvantage when the cuff is deflated in the trachea to enable the patient to speak since the extra bulk interrupts air flow over the outside of the tube making it more difficult for the patient to speak clearly. In the present invention, instead of extruding a parison with a constant wall thickness, a preform is formed with a tailored, variable wall thickness along its length that is chosen to reduce the variation in wall thickness in the expanded section of the final cuff. Figure 3 shows an example of a preform 40 with a wall thickness that varies along its length. In particular, the preform 40 has two opposite end regions 41 and 42 with a wall thickness of di _, a central region 43 with a wall thickness of d ₂ and two intermediate, sloping regions 44 and 45 between the central region and respective end regions where the wall thickness varies along their length between of di and d ₂ . The preform 40 is preferably made by injection moulding but could be made by other techniques. The preform is preferably of a crystalline or semi-crystalline plastics such as polyamide, polyester, polyethylene or TPE so that it strain hardens as it expands. Other materials such as PVC, polyurethane or thermoplastic elastomer could be used. Instead of injection moulding the preform it could be made by an extrusion process where the wall thickness is varied by altering the line speed or die gap, although such a process is more difficult to control. The preform could be moulded with strengthening formations such as ribs or other surface features.

The preform 40 shown in Figure 3 is heated, such as using infra-red or direct heating, and is then placed in a cavity 50 of a blow moulding tool 51, as shown in Figure 4. The dimensions of the cavity 50 define the desired external dimensions of the finished cuff 10 so allow a space around the preform 40 for expansion. The preform 40 is clamped at one end and connected to a source 52 of pressurized gas at its opposite end, which applies pressure within the preform causing it to expand radially where it is unconstrained. When the preform 40 has fully expanded and cooled it is removed from the mould tool 51. The finished cuff 10 is shown in Figure 5 after trimming off short portions at opposite ends distorted by the blow moulding process. The cuff 10 differs from previous cuffs in that at least the entire expansible or inflatable region has a constant, or near constant, wall thickness. In particular, the central, cylindrical, main body portion 55 has the same wall thickness as the sloping shoulder regions 56 and 57, which is achieved by profiling the wall thickness along the corresponding regions of the preform 40 so that the thickness is greater along the main body portion than along what will become the shoulder regions. In this way, the inflatable portion 55, 56 and 57 of the finished cuff 10 has a wall thickness that is more constant than would be the case if the preform 40, before expansion, had a wall thickness that was constant along its length.

In the arrangement shown in Figure 4 there is a close fit of the ends of the parison in the mould cavity so that there is zero or negligible blow expansion of these regions. It would, however, be possible to arrange for the end, collar regions to be expanded to the desired diameter by the blow moulding process simply by providing space between the outside of the parison and the mould cavity in these regions, with the cavity in these regions defining the desired finished external diameter of the collars. In such an arrangement the collar regions of the parison would be formed with an original external diameter less than that of the desired final diameter.

The cuff of the present invention can enable a more even distribution of pressure along the entire area of contact with the trachea. Also, when deflated, the shoulder regions, being thinner and more flexible, lie closer to the tube shaft causing less obstruction on the outside of the tube.

The cuff need not be of the same shape as described with a central region of cylindrical shape but could have other conventional shapes, such as with a rounded or with a tapered profile. Cuffs according to the present invention could be used on other medico- surgical tubes, not just on tracheal tubes.