Cuffed medical tubes

A cuffed silicone tracheostomy tube has two tapered recesses (17) and (18) on its outer surface in which opposite ends (7) and (8) of a resilient cuff 6 are bonded using an adhesive or solvent. Two shallow ribs (22) and (23) extend around the tube on the inner edge of each recess (17) and (18), projecting outwardly to prevent the adhesive or solvent spreading onto the inflatable portion (10) of the cuff (6). The cuff (6) has several shallow ribs (9) extending around the cuff and spaced along its inflatable portion (10) to promote even inflation.

This invention relates to cuffed medical tubes of the kind having a tubular shaft and an inflatable sealing cuff extending coaxially along a part of the shaft, the opposite ends of the cuff being attached with the shaft by an adhesive or solvent in respective annular attachment regions of the shaft.

The invention is more particularly, but not exclusively, concerned with cuffed tracheal tubes.

It is common practice for tracheal tubes to have an inflatable sealing cuff towards their patient, distal end. The cuff is deflated so that it lies close to the wall of the tube during insertion and is then inflated via an inflation line so that the cuff expands and contacts the wall of the trachea to provide a seal with patient tissue. In this way, passage of gas along the trachea is confined to flow along the bore of the tube.

The cuffs are of tubular shape extending coaxially along the tube and are attached at opposite ends, or collars, to the outside wall of the tracheal tube shaft. The attachment is typically achieved by means of a solvent or adhesive applied between the collar and the wall of the shaft, or by thermal bonding. These methods of attachment work well with tubes made of PVC and some other plastics but there can be difficulties with cuffs made of silicone or other highly elastic material where these are arranged to be a tight fit on the shaft when deflated. In such cuffs there is a tendency for the cuff-bonding adhesive to seep from the cuff region towards the region that is intended to be inflatable. This can lead to a poorly-defined attachment border and an irregular shape when inflated. Also, the longer cure time of some adhesives may make it more difficult to form a good join.

It is an object of the present invention to provide an alternative cuffed medical tube and a method of manufacture of a cuffed medical tube.

According to one aspect of the present invention there is provided a cuffed medical tube of the above-specified kind, characterised in that each attachment region has a raised annular rib projecting above the surface of the shaft at inner ends of the respective regions to restrict flow of adhesive or solvent beyond the attachment regions and onto the inflatable portion of the cuff.

The attachment region towards the patient end preferably includes a recess in which an end of the cuff is attached and preferably, both attachment regions include a recess in which a respective end of the cuff is attached. The or each recess preferably slopes to provide a frusto-conical surface that is deeper towards the or each end of the cuff. Preferably, both recesses slope to provide frusto-conical surfaces, the recesses inclining in opposite senses. The depth of the or each recess at one end is preferably substantially the same as the thickness of the cuff such that there is a substantially stepless transition between the surface of the shaft and the surface of the cuff. The cuff is preferably of a resilient material and is arranged so that its inflatable portion closely embraces the shaft when deflated. The shaft and cuff are preferably of a silicone material. The cuff may have a plurality of shallow annular ribs on its inner surface spaced from one another along the inflatable portion.

According to another aspect of the present invention there is provided a method of manufacture of a cuffed medical tube including the steps of providing a tubular shaft having two annular attachment regions spaced from one another along the shaft and bounded by respective annular ribs projecting above the surface of the shaft at the ends of the regions closer to one another, providing an inflatable sealing cuff that is a close fit on the shaft at least at opposite ends of the cuff, applying an adhesive or solvent to the attachment regions, and applying the cuff to the shaft such that opposite ends of the cuff locate on the attachment regions and are bonded thereto by the adhesive or solvent to leave an inflatable region of the cuff between the bonded ends.

According to a further aspect of the present invention there is provided a cuffed medical tube having a tubular shaft and an inflatable sealing cuff extending coaxially along a part of the shaft and attached with the shaft at opposite ends, the cuff being of a resilient material and closely embracing the shaft along its entire length when deflated, characterised in that the cuff has a plurality of annular ribs spaced from one another along the length of the cuff on the inner surface of its inflatable portion and adapted to promote even inflation of the cuff.

The tube comprises a curved tubular shaft1with a flange2, close to the machine end3, by which the tube is retained in position in a tracheostomy. A cylindrical coupling4is attached with the shaft1and projects from the machine side of the flange2. Close to its opposite, patient end5, a tubular sealing cuff6is attached at opposite end collars7and8with the outer surface of the shaft1. The cuff6, shaft1and flange2are all moulded of a relatively soft silicone material. In its natural, deflated state the cuff6is substantially cylindrical, lying close to the surface of the shaft1. The cuff6has several shallow, internal annular ribs9spaced from one another along its central inflatable portion10, the purpose of which will be explained later. A small bore inflation line11extends along the tube bonded into a moulded channel12along the shaft1. The inflation line11extends along one side of the shaft1, that is, displaced by 90° from the plane of curvature of the shaft. The inflation line11extends beneath the machine end collar7of the cuff6; its machine end13is terminated beneath the inflatable portion10, being retained between two shallow wedge-shape projections14(FIG. 2). These projections14act as an anti-occlusion feature to prevent the cuff6valving closed the end13of the inflation line11and also protect the cuff from damage by the end of the inflation line.

The two collars7and8of the cuff6are secured with the outer surface of the shaft1in respective attachment regions17and18(FIGS. 2 and 3). These regions17and18are provided by shallow annular recess19and20in the surface of the shaft1. The recesses19and20each slope to form frusto-conical surfaces, being deeper at their outer ends and being level with the shaft surface at their inner ends, as shown most clearly inFIG. 3. In this way, it can be seen that the ends of the collars7and8on the cuff6locate at the deeper end of the recesses19and20respectively. The depth of the recesses19and20at their deeper ends is about 0.38 mm, which is substantially the same as the thickness of the cuff material allowing for a thickness of adhesive used to bond the cuff collars7and8to the shaft1. In this way, there is a stepless transition between the surface of the shaft1and the surface of the cuff6at both ends.

The shaft1has a further surface feature in the form of two shallow annular ribs22and23located at the inner end of each recess19and20, that is, at the ends of the recesses closer to one another. The ribs22and23project by about 0.2 mm above the surface of the shaft1and serve as dams to restrict flow of adhesive or solvent out of the recesses19and20and inwardly of the cuff6.

The tube is manufactured by moulding the shaft1and flange2from silicone as a single piece about the coupling4, which is of a harder material. An adhesive is applied to the inflation line channel12and the inflation line11is threaded through a hole26in the flange2and then laid into the channel so that its patient end13locates between the two wedge-shape projections14. Adhesive is then applied around the two recesses19and20and the cuff6is loaded onto the shaft1so that its end collars7and8locate in the recesses. It will be appreciated that the adhesive or solvent could be applied to the inner surface of the collars7and8instead of directly to the recesses19and20. The shape and resilient nature of the cuff6are such that the cuff closely and tightly embraces the surface of the shaft1along its entire length when deflated. Without the ribs22and23there would be a tendency for adhesive in the recesses19and20to wick between the inside surface of the cuff6and the shaft surface and flow outside the recesses. This would lead to an uneven boundary of the bonded regions, which in turn would lead to a distorted shape of the inflatable portion10when inflated. The problem is made worse because of the relatively long cure times of adhesives used with silicone, which makes it more difficult to attach one collar at a time to the shaft. The frusto-conical shape to the recesses19and20, however, ensures that there is a smooth, stepless transition between the outside surface of the shaft1and the cuff6where they meet and also ensures that the cuff can lie in intimate contact with the surface of the recesses along a greater part of their length than would be the case with a recess of cylindrical shape. The taper in the recesses19and20also helps make the external surface of the tube smoother in the region of the ribs22and23. The smooth surface presented in the transition regions at opposite ends of the cuff6facilitates atraumatic insertion and removal through a tracheostomy opening. This is more important at the patient end of the cuff6, for insertion, than at the machine end of the cuff, so it would be possible to use a conventional join at the machine end if desired although preferably, both ends are attached in the same manner.

To inflate the cuff6, air is supplied via the inflation line11, such as by a syringe (not shown) so that it flows out at its machine end13into the potential space between the cuff6and the outside of the shaft1. The ribs9around the inside of the cuff6channel the air to flow initially around the tube in an annular channel defined between adjacent ribs on either side of the machine end13of the inflation line1. As pressure increases, these ribs9lift away from the surface of the shaft1to allow air to flow into the adjacent channels and so on. This ensures that the cuff6inflates symmetrically.

The invention could be used with other cuffed medical tubes and is not confined to tracheal tubes. The tubes could be reinforced with a helical reinforcement member, such as a wire. Although the invention has particular advantages with silicone tubes, it could be used with tubes of various different plastics. The ribs on the inside of the cuff may be used without the ribs on the shaft or the ribs on the shaft may be used without the ribs on the cuff.