Medico-surgical tubes

Abstract

A tracheostomy tube (1) has a curved shaft (10) with an inflatable silicone sealing cuff (20) attached to the patient end of the shaft by two spaced collars (22) and (23). The shaft is formed with two annular steps (26) and (27) against which outer ends of the collars are abutted. The forward step (27) at the patient end of the shaft is arranged orthogonally to the shaft axis. The rear step (26) is inclined at an angle α to the orthogonal arranged such that the length d1 of the inflatable part (21) of the cuff (20) along the inside of the curve of the shaft is more nearly equal to the length d2 along the outside of the curve than would be the case if the rear collar (22) were arranged orthogonally to the shaft axis.

Description

[0001] MEDICO-SURGICAL TUBES

[0002] This invention relates to medico-surgical tubes of the kind having a shaft extending between a forward, patient end and a rear, machine end of the tube and being curved along a part at least of its length, the tube including an inflatable cuff adapted to contact the wall of a body cavity, and the cuff comprising a flexible sleeve joined with the shaft at opposite ends by respective collars attached with the outside of the shaft so that the cuff extends along a curved part of the shaft along at least a part of its length.

[0003] The invention is more particularly, but not exclusively, concerned with tracheostomy tubes with an inflatable sealing cuff towards their patient end.

[0004] Airway tubes are often provided with a sealing cuff close to their patient end, which is used to seal the outside of a tube with the trachea so that gas is confined to flow along the bore of the tube. It is important that the seal provided by this cuff be effective but does not damage patient tissue. A poor seal can allow secretions to leak past the cuff and pass down into the lower parts of the respiratory system. It is thought that such secretions entering the lungs may give rise to ventilator-associated pneumonia. The seal provided by the cuff is also important in ensuring that there is no leakage of gas since this could reduce the effectiveness of the ventilation and lead to escape of anaesthesia gases to atmosphere.

[0005] Many different forms of cuff have been proposed in an attempt to improve the seal or interface of a tracheal tube with the trachea. Various different shapes of cuff and surface formations have been proposed, together with modifications in cuff material, coatings, or thickness in an attempt to increase the effectiveness of the seal. The most common form of cuff takes the form of a tubular sleeve embracing the shaft of the tube towards its patient end and positioned centrally over the opening of an inflation line extending rearwardly along the shaft. The sleeve has collar regions at opposite ends that are bonded to the outside of the shaft using an adhesive, glue, solvent, or other bonding substance to prevent the escape of inflation fluid. Inflatable sealing cuffs are usually one of two different types. They can be of a high-volume / low-pressure kind where the cuff is moulded of a non-elastic material with a relatively floppy shape when uninflated and is inflated at low pressure to a more rounded doughnut shape. Alternatively, the cuff can be of a low-volume / high-pressure kind moulded of a relatively elastic material, such as silicone, that lies tight against the shaft when uninflated. Such a cuff is inflated elastically to the desired sealing shape by a relatively high- pressure gas or liquid. These elastic sealing cuffs have an advantage that they can have a low profile when inserting the tube, which is a particular advantage with tracheostomy tubes inserted through a surgical opening. Also, when the cuff is deflated in the trachea, such as when weaning the patient off a ventilator, or to enable speech, the cuff presents a very low profile that allows for a laminar flow of air over its surface and a reduced work of breathing. One problem, however, with elastic cuffs such as of silicone is that they can suffer from asymmetric inflation in that the side of the cuff on the outside of the curve of the tube can inflate to a different extent from that side of the cuff on the inside of the curve. Uniform cuff inflation is important because it helps centre the tube in the trachea and reduces the risk that the patient end tip of the tube will contact the anterior or posterior wall of the trachea. This could lead to irritation of the trachea or, if unaddressed for prolonged periods can cause further complications.

[0006] It is an object of the present invention to provide an alternative cuffed tube.

[0007] According to the present invention there is provided a medico-surgical tube of the above-specified kind, characterised in that the collar at one end at least of the cuff is attached with the shaft at an angle inclined away from the orthogonal to the axis of the shaft such that the distance between the inner ends of the two collars along the inside of the curve of the shaft is more nearly equal to the distance around the outside of the curve compared with an arrangement where both collars are attached orthogonally to the shaft.

[0008] The shaft preferably has an annular formation on its outer surface inclined at an angle away from the orthogonal to the axis of the shaft, the collar of the cuff at the one end being positioned against the formation. The shaft may have a forward annular formation towards its patient end and a rear annular formation rearwardly of the forward formation, the forward formation being arranged orthogonal to the axis, and the rear formation being inclined at an angle away from the orthogonal to the axis. The or each formation is preferably a step against which the outer end of the or each collar is abutted. The cuff is preferably of an elastic material and may be of a silicone material. The shaft of the tube may be curved along its entire length. The tube may be a tracheostomy tube.

[0009] A conventional tracheostomy tube and a tracheostomy tube according to the present invention, will now be described, by way of example, with reference to the accompanying drawings, in which:

[0010] Figure 1 is a side elevation view of a conventional tracheostomy tube;

[0011] Figure 2 is a side elevation view of a tracheostomy tube according to the present invention; and

[0012] Figure 3 is an enlarged side elevation of a part of the shaft of the tracheostomy tube shown in Figure 2 with the cuff omitted for clarity.

[0013] With reference first to Figure 1, the tube 1 is of conventional form, having a moulded shaft 10 of silicone, which is curved along its entire length, and has a forward, patient, or distal end 11 adapted, during use, for location in the trachea. The shaft 10 has a rear, machine, or proximal end 12 adapted to project outwardly of the tracheostomy stoma. The tube 1 has a neck flange at the machine end 12, which is omitted from the drawing for clarity. The machine end 12 of the shaft 10 is joined with a 15mm tapered male connector 16, which projects axially outwardly. An inflation line 17 extends along a channel 17’ in the side of the shaft 10 to an opening 18 at one end towards the patient end 11 of the shaft. The machine end of the inflation line 17 extends outwardly of the shaft and is terminated at its rear or machine end by a conventional combined inflation indicator and valved connector 19. The tube 1 supports an inflatable sealing cuff 20 close to its patient end. The cuff 20 is of an elastic material such as silicone and has a central inflatable region 21 positioned over the opening 18 of the inflation line 17. When deflated, this central region 21 lies flat, tight against the outer surface of the underlying part of the shaft 10. The cuff 20 also has two opposite end collars 22 and 23 by which it is secured with the outside of the shaft 10. Towards its patient end 11 the outer surface of the shaft 12 is formed with two annular attachment regions or necks 24 and 25 to which the collars 22 and 23 of the cuff 20 are attached. The attachment regions 24 and 25 taper inwardly slightly to form a shallow step 26 and 27 at their outer ends. The two steps 26 and 27 provide annular formations On the outside of the shaft 10 that help locate the ends of the collars 22 and 23 to ensure accurate positioning of the cuff 20 while it is being assembled on the shaft. The height of the steps 26 and 27 is selected to ensure a smooth, stepless transition between the outside of the shaft 10 and the outer surface of the collars 22 and 23. The inner end of each region 24 and 25 is bounded by a shallow outwardly-projecting rib or glue dam 28 and 29, which serve to restrict the flow of bonding substance away from the attachment regions 24 and 25. This prevents the bonding substance leaking into the region between the two ribs 24 and 25 over which the inflatable portion 21 of the cuff 20 extends. These positioning or attachment features, namely the attachment regions 24 and 25, steps 26 and 27, and the ribs 28 and 29 are all formed orthogonally, that is, at right angles to the axis “A” of the shaft 10.

[0014] It can be seen that, in this conventional arrangement, the curve of the shaft 10 results in the distance di between the two ribs 28 and 29 along the inside of the curve of the shaft being less than the distance di along the outside of the curve. This causes a corresponding difference in the length of the inflatable portion 21 of the cuff 20 along the inner and outer curve of the shaft 12. When an elastic cuff, such as of silicone, is assembled on the shaft it closely embraces the shaft and will be stretched more on the outside of the curve than on the inside as the ends of the collars are brought into abutment with the respective positioning steps. This uneven stretching can lead to uneven inflation around the cuff 20.

[0015] With reference now to Figures 2 and 3, there is shown a modified tube 101 according to the present invention. Features of this tube 101 similar to those in the conventional tube 1 are given the same numeral with the addition of 100. The tube 101 is similar to the tube 1 in Figure 1 in having the same shape shaft 110. The outer surface of the shaft 110, along the region where the lower, patient end collar 123 of the cuff 120 is attached to the shaft is the same as in the conventional tube 1, with the surface features, namely the attachment neck portion 125, the step 127, and the rib 129 are all formed orthogonally, that is, at right angles to the axis “A” of the shaft 112. The tube 101, however, differs along the region where the upper, machine end collar 124 of the cuff 120 is attached with the shaft 110. Along this region the attachment neck portion 124, the step 126 and the rib 128 are each inclined at an angle a away from the orthogonal to the shaft axis A, as shown most clearly in Figure 3. The optimal angle a depends on the curvature of the shaft but in the example shown in Figures 2 and 3 is approximately 25°. The angle a is chosen such that the distance di between the inner ends of the two collars 22 and 23 along the inner side of the curve of the shaft 110 (and hence the length of the inflatable portion 121 of the cuff 120) is equal to the distance d2 along the outer side of the curve. Elastic cuffs, such as of silicone, closely embrace the shaft when they are slid along the shaft during assembly. By arranging the distance between the two collars to be the same on the inner and outer sides of the curve of the shaft there is less risk that one side of the cuff will be stretched more than the other side.

[0016] The arrangement described above achieves an equal distance between the two collars by angling only the upper, machine end attachment formations away from the orthogonal. It will be appreciated that the same effect could be achieved instead by angling the lower, patient end attachment formations, or by angling both the upper and lower attachment formations to a lesser extent. Although the use of the positioning steps described above is helpful in assembling the cuff on the shaft, to ensure the desired mounting angle, these steps are not essential. Instead, the cuff could be assembled using an appropriately configured jig, or just by using a guide marking printed on the shaft at the desired angle. The benefit of the arrangement described above is more with elastic, low-volume / high-pressure cuffs than with high-volume / low-pressure cuffs but some benefit of more even inflation might also be achieved with such high-volume cuffs. The arrangement is particularly useful in tracheostomy tubes but might also have benefit in other medico-surgical tubes with an inflatable cuff on a curved part of the tube.

Claims

CLAIMS1. A medico-surgical tube (1) having a shaft (10) extending between a forward, patient end (11) and a rear, machine end (12) of the tube and being curved along a part at least of its length, the tube including an inflatable cuff (20) adapted to contact the wall of a body cavity, and the cuff comprising a flexible sleeve (20) joined with the shaft at opposite ends by respective collars (22 and 23) attached with the outside of the shaft (10) so that the cuff extends along a curved part of the shaft along at least a part of its length, characterised in that the collar (22) at one end at least of the cuff (20) is attached with the shaft (10) at an angle (a) inclined away from the orthogonal to the axis of the shaft such that the distance (di) between the inner ends of the two collars (22 and 23) along the inside of the curve of the shaft is more nearly equal to the distance (di) around the outside of the curve compared with an arrangement where both collars are attached orthogonally to the shaft.

2. A tube according to Claim 1 , characterised in that the shaft (10) has an annular formation (26) on its outer surface inclined at an angle away from the orthogonal to the axis of the shaft, and that the collar (22) of the cuff (20) at the one end is positioned against the formation (26).

3. A tube according to Claim 2, characterised in that the shaft (10) has a forward annular formation (27) towards its patient end (11) and a rear annular formation (26) rearwardly of the forward formation, that the forward formation (27) is arranged orthogonal to the axis, and that the rear formation (26) is inclined at an angle (a) away from the orthogonal to the axis.

4. A tube according to Claim 2 or 3, characterised in that the or each formation is a step (26, 27) against which the outer end of the or each collar (22, 23) is abutted.

5. A tube according to any one of the preceding claims, characterised in that the cuff (20) is of an elastic material.

6. A tube according to any one of the preceding claims, characterised in that the cuff (20) is of a silicone material.

7. A tube according to any one of the preceding claims, characterised in that the shaft (10) of the tube is curved along its entire length.

8. A tube according to any one of the preceding claims, characterised in that the tube is a tracheostomy tube (1).

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