ASSEMBLY

This invention relates to cuff inflation indicators of the kind for a tube with a sealing cuff, the indicator including an inflation line arranged to communicate at one end with the interior of the sealing cuff and at its opposite end to extend through an opening of a flexible enclosure that is inflated by pressure from the sealing cuff via the inflation line.

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 a cuff that is inflated and deflated via a small bore lumen extending 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 plastics material moulded with a natural annular or doughnut shape. Such cuffs are inflated without stretching, to contact the wall of the trachea, 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. The sealing cuff may alternatively be inflated by a liquid, such as saline, especially when it is of the low-volume/high pressure kind of cuff.

The inflation line usually connects with some form of inflation indicator or cuff pressure indicator externally of the patient, towards the machine end of the inflation line. The purpose of the inflation indicator is to show the clinician whether the sealing cuff is correctly inflated. Most commonly this inflation indicator is in the form of a small flexible pilot balloon connected with the inflation line by some form of bond between the outside of the inflation line within an opening at one end of the balloon. Conventionally the inflation line is an extruded tube having a constant diameter internally and externally. This is cut to length and then dipped into a solvent before it is inserted into the patient end of the pilot balloon. The joint between the outside of the inflation line and the pilot balloon relies on the interference between the two parts and the solvent to create a good joint. The balloon is inflated by fluid from the cuff via the inflation line. If the balloon is not fully inflated it indicates that the cuff pressure may be too low. It is important that the connection between the inflation line and the balloon is secure and does not leak. Forming such a secure connection presents difficulties because of the relatively small diameter of the inflation line and the thin material from which the balloon is made. This leads to relatively high assembly and quality verification costs. Inflation indicator balloons can take various different forms, such as being of circular section and curved along its length, or of a relatively flat profile when deflated, or of a corrugated shape. In all cases, however, the same problem exists of making a secure seal between the outside of a small diameter inflation line and an opening into the indicator.

It is important that the inflation indicator functions reliably because if the pressure in the cuff should fall it could prevent proper ventilation of the patient and lead to suffocation. Incomplete inflation of the cuff could allow secretions that collect above the cuff to leak between the cuff and the trachea and enter the bronchial passages. This could contribute to ventilator-associated pneumonia (VAP). The cuff may lose pressure over time as gas permeates gradually through the wall of the cuff from the higher pressure in the cuff to the lower ambient pressure outside the cuff,

A hard, over-inflated inflation indicator could indicate an excessive cuff pressure. This can be caused by anaesthetic gases or water vapour permeating into the cuff through its wall.

It is an object of the present invention to provide an alternative cuff inflation indicator, an alternative cuffed tube including a cuff inflation indicator and a method of assembly of such an indicator. According to one aspect of the present invention there is provided a cuff inflation indicator of the above-specified kind, characterised in that the inflation line is tapered outwardly along a section towards its opposite end within the enclosure to an outer diameter greater than the internal diameter of the opening, and that the outer, tapered surface of the inflation line is bonded to the enclosure where it extends through the opening.

According to another aspect of the present invention there is provided a cuffed medical tube including a tube shaft having an inflatable sealing cuff towards its patient end and an inflation line communicating with the interior of the sealing cuff, characterised in that the tube has a cuff inflation indicator according to the above one aspect of the present invention connected at the machine end of the inflation line.

The tube may be a tracheostomy tube.

According to a further aspect of the present invention there is provided a method of assembling a cuff inflation indicator enclosure on an inflation line including the steps of providing an inflation line having an outwardly tapered section towards one end, extending the inflation line through an opening into the enclosure to bring its tapered section into contact with an end of the opening within the enclosure, and bonding the outside of the inflation line in the region of the tapered section with the opening to provide a secure connection of the inflation line with the enclosure.

The tapered section of the inflation line may be formed by inserting a heated tapered mandrel into one end of an inflation line of constant diameter so that both the internal and external surfaces of the inflation line are given a tapered shape. Alternatively, the tapered section may be provided by adding material to the outside of an inflation line of constant diameter to form a tapered section with increased wall thickness. The tapered section of the inflation line may be coated with a bonding liquid before being brought into to contact with an end of the opening. The tapered section of the inflation line may be displaced from a position where the tapered section is located within the enclosure and is spaced from the opening to a position where a part at least of the tapered section extends within the opening. According to a fourth aspect of the present invention there is provided a method of assembling a cuff inflation indicator enclosure on an inflation line including the steps of providing an inflation line, extending the inflation line through an opening into the enclosure so that the machine end of the inflation line is spaced on the machine side of the opening, the machine end of the inflation line being coated with a bonding liquid, displacing the inflation line relative to the opening of the enclosure so that the machine end of the inflation line moves into the opening and the bonding liquid forms a bond between the outside of the inflation line in the region of its machine end with the opening to provide a secure connection of the inflation line with the enclosure.

According to a fifth aspect of the present invention there is provided an assembly of an inflation line and cuff inflation indicator enclosure assembled by a method according to the above further or fourth aspect of the present invention.

According to a sixth aspect of the present invention there is provided a cuffed tracheal tube including a sealing cuff and an assembly of an inflation line and cuff inflation indicator enclosure according to the above fifth aspect of the present invention connected with the sealing cuff.

According to a seventh aspect of the present invention there is provided a cuffed tracheostomy tube having an inflation line joined at its machine end to a cuff inflation indicator, characterised in that the machine end of the inflation indicator is threaded through an opening of the inflation indicator, that the machine end of the inflation line is tapered outwardly using a heated mandrel, that the outside tapered region of the inflation line is coated with a bonding liquid, and that the inflation line is pulled to draw the coated tapered region into the opening to wedge it in position where it bonds with the inflation indicator.

A cuffed tracheostomy tube with an inflation line and cuff pressure indicator, and a method of assembling an inflation line and cuff pressure indicator 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; and

Figures 2 and 3 show successive stages in forming the tapered section on the inflation line;

Figure 4 is a cross-sectional side elevation of the machine end of the inflation line after forming the tapered section;

Figure 5 is a cross-sectional side elevation showing the inflation line being assembled with the pilot balloon; and

Figures 6 and 7 are cross-sectional side elevations of the machine end of two alternative inflation lines.

The tracheostomy tube 1 has a patient end 10 adapted to locate wilMn the trachea and a machine end 11 adapted to locate outside the patient adjacent the neck surface. The tube 1 has a tubular shaft 12 of circular section with a bore 13 extending along its length. The shaft

12 has a substantially straight patient end portion 14 and machine end portion 15 joined by a curved central portion 16 so that opposite ends of the shaft are inclined at about 100° to one another. The shaft 12 is extruded or moulded from a plastics material such as PVC.

The tube could be of various different shapes and sizes and need not be for use in the trachea but could be adapted for use in other body cavities.

Towards its patient end 10 the tube 1 has sealing means provided by an inflatable cuff 20 embracing the shaft 12. The cuff 20 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 20 is attached to the shaft 1 by two collar portions 21 and 22 at opposite ends. The cuff 20 extends over an opening 23 on the outer surface of the shaft 12 into an inflation lumen 24 extending along the shaft within its wall thickness. The inflation lumen 24 is connected towards the rear, machine end 11 of the tube with a small-bore inflation line 26 terminated by an inflation indicator 27 with a valved connector 28. The inflation indicator 27 takes the form of a flexible pilot balloon or other flexible enclosure. In the present example the pilot balloon 27 has a generally flat, rectangular shape with the connector 28 at its machine end and a tapering tail 29 at its patient end. The machine end 30 of the inflation line 26 is sealed and bonded into the tail 29 of the balloon 27. It can be seen that when the sealing cuff 20 on the tube 1 is inflated the fluid pressure in the cuff will communicate via the inflation line 26 to the pilot balloon 27 thereby also inflating this from its normal flat shape to a more rounded shape. Similarly, if the cuff pressure should fall, the pilot balloon 27 would deflate to a flatter state, thereby providing a warning indication to the clinician.

Alternative sealing cuffs could be used, such as elastic, small- volume, high pressure cuffs and these could be attached to the shaft in different manners. The cuff could be inflated with a gas such as air or a liquid such as saline.

With reference now to Figures 2 to 5, the machine end 30 of the inflation line 26 is modified before assembly with the pilot balloon 27 so that it has an end section 31 that tapers or flares along its length to a larger diameter towards the machine end of the inflation line. Typically the outer diameter at the machine end tip of the flared section 31 is about 40% greater than the diameter along the main part of the inflation line 26 and the length of the flared section is about three times the outer diameter of the main part of the inflation line 26. These dimensions can vary according to nature of the inflation indicator, the material of the inflation line and other factors.

The flared section 31 of the inflation line 26 is formed in the manner shown in Figures 2 and 3. The inflation line 26 is initially extruded (not shown) from a thermoplastics material such as PVC with a constant outer and inner diameter and a circular cross section, and is then cut to the appropriate length. As shown in Figure 2, the machine end of the line 26 (which may be warmed to soften the plastics) is then brought up to the end of a heated mandrel 40. The mandrel 40 has a tapering outer surface 41 set back a short distance from a lead nose 42 having an outer diameter slightly smaller than the internal diameter of the inflation line 26. The lead nose 42 of the mandrel 40 is inserted into the machine end 30 of the inflation line 26 and then the flared section 41 is pushed into the inflation line to expand it outwardly slightly to the desired tapering shape as shown in Figures 3 and 4. The mandrel 40 is then removed from the inflation line 26.

As shown in Figure 5, to assemble the inflation line with the pilot balloon 27 the patient end of the inflation line 26 is threaded through the machine end 28 of the pilot balloon (before assembly of the valve in the connector) and the line is pulled through until the flared section 31 projects a short distance beyond the machine end of the balloon. The flared section 31 of the inflation line 26 and a short length beyond the flare is then dipped in (or otherwise coated with) a suitable bonding liquid such as a solvent, such as THF, IPA or similar, or an adhesive. It will be appreciated that the solvent coating could take place at any stage. The inflation line 26 is then pulled further so that the flared, coated section 31 enters the inside of the pilot balloon 27 and then the flared section contacts and wedges itself into the narrower opening of the patient end tail 29 of the pilot balloon, as shown in Figure 5. Some of the solvent transfers from the inflation line 26 to coat the inside of the tail 29 and some is wiped along the outside of the inflation line towards its machine end. This produces a secure bond after curing. The patient end of the inflation line 26 can then be joined to the inflation lumen 24 extending along the tube shaft 12 using any conventional technique. It will be appreciated that various alternative manufacturing sequences are possible. For example, the patient end of the inflation line 26 could be attached to the inflation lumen 24 with the machine end of the line extending through and beyond the pilot balloon 27 and before the inflation line is flared. The inflation line would then be flared, coated in solvent and pulled into the pilot balloon. Different materials could be used for the inflation line and balloon, such as including silicone.

The flared section 31 of the inflation line 26 has several advantages. It avoids the need to control the tolerances of the outer diameter of the inflation line and the internal diameter of the opening in the pilot balloon as closely as with a normal, unflared line since the cone shape of the flared section provides a wider tolerance range and ensures an optimal fit at a point along the increasing outer diameter of the flare. Also, the flare increases the surface contact area between the outside of the inflation line 26 and the opening into the pilot balloon 27. Furthermore, because the end of the inflation line is larger than the opening in the pilot balloon, it creates a wedge that helps strengthen the bond. Moreover, the assembly process also helps ensure that the solvent or adhesive reaches the internal surfaces of the pilot balloon tail. In conventional methods of joining the inflation line to the pilot balloon the end of the line is coated with solvent and is pushed into the patient end opening of the balloon from outside. This results in some of the solvent being wiped rearwardly along the outside of the inflation line and forming a wave of solvent on the outside of the inflation line adjacent the outer end of the pilot balloon opening. This does not contribute significantly to the strength of the connection between the inflation line and the balloon. By contrast, in the arrangement of the present invention the solvent wiped along the inflation line as it is pulled through the patient end opening of the pilot balloon remains inside the balloon. When the solvent wiped rearwardly has cured it forms an annular protrusion around the inflation line and within the balloon that resists being pulled out of the patient end opening of the balloon. This helps increase the strength of the attachment to the inflation line with the balloon.

The method of pulling the inflation line out from inside the pilot balloon also has advantages with conventional inflation lines that have a constant diameter along their entire length and are not flared. By wiping the solvent, adhesive or the like to the machine end of the inflation line inside the balloon the joint is strengthened even without the taper formation.

The pilot balloon need not have the flat shape described above but could have any of the other shapes of conventional pilot balloons, such as a circular section or an accordion or circumferentially pleated shape.

It is not essential that the tapered section of the inflation line be at the very end of the line. Instead, the inflation line 126 could have a section 132 of constant, increased diameter extending from the wide end of the flared section 131 as shown in Figure 6. This enlarged section 132 would project into the inflatable part of the pilot balloon and could help prevent the pilot balloon folding across its width. Instead of using a solvent or adhesive to bond the balloon with the inflation line it could be attached in other ways such as by welding or by moulding the balloon about a flared end of the inflation line.

The tapered section need not be formed by expanding the inflation line but could be formed by moulding or otherwise adding material to the outside of the inflation line 226 so that its wall thickness is increased to form the externally-tapered section 232, as shown in Figure 7. In this arrangement the internal diameter of the inflation line 226 is constant along its length, even along the tapered section 231.