TRACHEAL TUBE

Abstract: There is disclosed a double-walled tracheal tube (10, 20) which is intended for child or adult use, and which comprises a tubular outer portion (11, 21), and an inner tubular portion in the form of a lining (12, 22) which is removably mounted therein to permit withdrawal of the inner tubular portion when a build-up of secretion thereon has occurred, in which the inner tubular portion is arranged within the outer portion in such a way as to promote substantially laminar gas flow through the tracheal tube or thereby to promote substantially turbulence free gas flow in either direction and minimise the lifting-off of droplets of secretions on the internal wall of the tube.

Description: TRACHEAL TUBE This invention relates to a tracheal tube for use in the mechanical ventilation of a patient. It is a matter of common experience that tracheal tubes used with mechanically ventilated patients build-up a film of respiratory secretions and bacteria - known as a biofilm, on their internal surfaces,, and this has to be removed periodically. Investigations have been carried out into the formation of biofilm in tracheal tubes, its bacterial content and its interaction with ventilator gas flow. Bacteria contaminating the inner surface of tracheal tubes have been shown to come from an endogenous source. Detachment of fluid droplets from aqueous biofilm has been shown to occur during the inspiratory phase of mechanical ventilation. Following contamination of the tracheal tube biofilm with the patient's own gastro-intestinal flora, entrainment of bacteria in the inspiratory gas flow provides a mechanism for the initial and repeated colonisation of the lungs. Pneumonia is an important cause of morbidity and mortality in Intensive Care Units, and ventilator- associated pneumonia is preceeded by bacterial colonisat-ion of the ventilated lung. It is therefore important to prevent excessive build¬ up,of secretions on the internal surface of a tracheal tube, by removing the material periodically, but this must be carried out in such a way as to minimise the risk of droplets of material being carried over into the lungs. Also, the build-up of secretions causes an obstruction to gas flow which must be removed before it becomes excessive which would otherwise give risk to blocking of the tube occuring. When blocked tracheal tubes require replacing, this can be a hazardous procedure in some patients. It is therefore essential that the deposited secretions should be removed before excessive build-up occurs, which can otherwise take place quite rapidly during prolonged mechanical ventilation. However, existing techniques are not entirely satisfactory, such as the insertion of a suction head to draw off the liquid film, since this inevitably liberates droplets which fall downwardly into the lungs. There is therefore a clear need, as yet unfulfilled, to provide a means whereby the film of secretions can be removed with reasonable reliability and quickly and easily, but without prolonged interruption of oxygen supplied to the patient, or liberation of bacteria into the lung. It is known to provide a tracheal tube for use with newly born babies, to remove initial secretions, and this tracheal tube has a removable core tube which is used a single time and then removed and discarded, and is therefore not intended for re-insertion into the tracheal tube. According to the invention there is provided a double- walled tracheal tube intended for child or adult use, and comprising a tubular outer portion, and an inner tubular portion in the form of a lining which is removably mounted therein to permit withdrawal of the inner tubular portion when a build-up of secretion thereon has occured, and in which the inner tubular portion is arranged within the outer portion in such a way as to promote substantially laminar gas flow through the tube. It has been appreciated in certain medical circles that turbulent gas flow through tracheal tubes is undesirable, since this will tend to lift-off droplets of secretions on the internal wall of the tube, and therefore the invention provides a significant improvement in tracheal tubes, and especially double-walled tubes, by arranging the removable inner lining in such a way as to promote substantially turbulence free gas flow in either direction along the tube i.e. inspiratory gas flow and exhaling gas flow. Preferably, the tracheal end of the lining i.e. the end inside the trachea and remote from the mouth end of the tracheal tube, is arranged to form a gas type seal with the adjacent end of the outer tubular portion. By this means, the risks of turbulent airflow generation at the tracheal end may be reduced, at least during exhaling gas flow. To further minimise the risks of turbulent gas flow being generated, it is preferred that the tracheal end of the lining defines a smooth transition from the inner surface of the lining to the adjacent inner surface of the outer portion. This may be achieved, in one embodiment, by aerodynamic shaping of the tracheal end of the lining. In another embodiment, the tracheal end of the lining may be arranged to engage against a shoulder or abutment face of a curved lip at the tracheal end of the outer tubular portion. In this way, the inner lining can form a smooth prolongation of this lip, whereby laminar flow of gas in either direction is encouraged. The engagement between the tracheal end of the lining and the lip may be of any suitable form, including a releasable snap-fit engagement which also provides a substantially gas-tight seal. However, this engagement is capable of being uncoupled, by withdrawal of the inner lining from the mouth end of the tracheal tube. The mouth end of the tracheal tube may be provided with a flange or lip to prevent accidental passage into the patient, and which is joined to the mouth end of the outer tubular portion. The adjacent end of the inner lining may be fixed to this flange in any convenient manner, , which of course is the end which is attached to a ventilator circuit . To improve the sealing between the outer wall of the outer tubular portion of the tracheal tube and the trachea, an inflatable cuff may be provided as a component part of the outer tubular portion, located near to the tracheal end thereof, and which can be inflated upon location in a desired position, in order as far as possible to prevent aspiration of extraneous material into the lung. Two embodiments of double-walled tracheal tube according to the invention will now be described in detail, by way of example only, with reference to the accompanying drawings in which: Figure 1 is a diagramatic i llustraction in longitudinal section of a first embodiment of double-walled tracheal tube according to the invention; Figure 2 is a detail view of the fixed upper end of the tracheal tube shown in Figure 1; Figure 3 is a detail view showing the tracheal end of the tracheal tube shown in Figure 1; and. Figure 4 is a diagramatic illustration in longitudinal section of a second embodiment of double-walled tracheal tube according to the invention. As will become apparent from the subsequent detailed description of the two preferred embodiments of the invention, there is disclosed herein a double-walled tracheal tube which comprises a tubular outer portion and a tubular lining replaceably mounted in the outer portion so that it can be removed entirely from the outer portion when secretions or biofilm build-up on its inner wall to a certain extent, so that the lining can be cleaned and then re-used. A sterilised replacement lining will normally be made available for introduction into the outer portion after removal of the contaminated lining which will be cleaned and sterilised for subsequent use. During prolonged mechanical ventilation of patients, a film of respiratory secretions are built-up on the inner wall of the lining, and it is important to remove the lining before these build-up to such an extent as to cause an obstruction to gas flow, or even give rise to risk of complete blockage. This build-up also should not be allowed to take place to such an extent that droplets of the film can be liable to fall under gravity into the lungs, or to be conveyed along the tube into the lungs by the inspiratory gas flow. In order to minise the risk of droplets of biofilm being conveyed along the tube by the inspiratory gas flow, the tubular lining is arranged within the tubular outer portion in such a way that it imparts substantially turbulence free and laminar gas flow to the gas passing along it in either direction. The means whereby the tubular lining can be suitably arranged to achieve this effect will be described in more detail below with reference to the two preferred embodiments of the invention. Referring now to Figures 1 to 3 of the drawings, the first embodiment of double-walled tracheal tube according to the invention is designated generally by reference 10 and comprises a tubular outer portion 11 and a tubular lining 12 replaceably mounted therein. The lining 12 closely fits within the tubular outer portion 11. and is fixed in position at the upper fixed end 13 by a peg or similar mechanism (not shown) to fix the lining in position and prevent accidental passage into the trachea. In order to prevent accidental removal, the upper end of the lining 12 is therefore contained within a usual tracheal tube connector 13, as shown in Figures 1 and 2. In order to prevent movement of the replaceable lining 12 within the outer portion 11, by passage of expired gases between the outer wall of the lining 12 and the inner wall of the tubular outer portion 11, the lower tracheal end 14 of the lining 12 is aerodynamically shaped and also forms a gas-tight seal with the lower end of the tubular portion 11, as shown to an enlarged scale in Figure 3. The tubular lining 12 is therefore able to generate substantially turbulence free and laminar gas flow to both inspiratory gas. and also expired gas, which thereby minimises the risk of droplets of biofilm being carried into the lungs. As can be seen from Figure 3, the tracheal end of the lining 12 is smoothly curved to form a smooth transition with the adjoining inner wall surface 11a of the tubular outer portion 11. An inflatable cuff 15 is provided as a component part of the outer portion 11, and located near the tracheal end, and can be inflated to provide a gas seal within the trachea, with a view to prevent as far as possible aspiration of extraneous material into the lungs. The embodiment of Figures 1 to 3 therefore provides a double-walled tracheal tube having the following features: a tubular lining that allows frequent removal of biofilm without necessitating replacement of the entire tracheal tube; a construction of tracheal tube which is resistant to collapse, whether constructed of plastics, ceramic, metal or other non-collapsable material; a curved lining structure which may be provided in a range of sizes to closely fit inside a tracheal tube of any internal diameter, covering its entire internal surface, and without projection beyond the lower end of the tracheal tube: a lower end structure which is constructed to resist folding or buckling, and forms a gas-tight seal with the tracheal tube, providing minimum interference with gas flow; and, an upper end assembly which can be fixed to prevent accidental passage into the trachea or unintended removal from the tracheal tube, causing minimum interference with gas flow and no additional circuit dead space, and constructed in such a way as to cause no impediment to the connection of the tracheal tube to other parts of the ventilator circuit. Referring now to Figure 4, there is shown a second embodiment of double-walled tracheal tube according to the invention, and which is designated generally by reference 20. This comprises a tubular outer portion 21 and a replaceable tubular inner lining 22 which is a close substantially gas-tight fit within outer portion or sleeve 21. The sleeve 21 has the inflatable cuff 15 to provide a gas seal within the trachea, and also has a lip 23 arranged to prevent accidental passage into the patient, and to provide for fixation to an adjacent flange 24 provided at the upper end of the inner lining 22 and to other external structures. Also, in this embodiment, the tubular lining 22 has a forward projection in the form of a short wider section 25 which is shaped to provide a connection with ventilator tubing or other ventilator circuit devices (not shown) . This embodiment also has an arrangement of the tubular lining which is such as to impart substantially turbulence free and laminar gas flow through the tracheal tube in either direction, while also being mounted in such a way as to be capable of easy replacement. To provide a gas-tight seal between the inner lining and the outer sleeve, as well as streamline gas flow, the lower tracheal end 26 of the lining 22 has a smooth connection with an inturned lip 27 at the lower end of the outer sleeve 21. The connection between end 26 and lip 27 forms a substantially uninterrupted and smooth continuing surface, thereby promoting turbulence free and laminar gas flow. Also, by virtue of the gas tight seal provided therebetween, this prevents passage of expired gases and respiratory secretions between both components. The embodiment of Figure 4 therefore provides a double-walled tracheal tube with the following features: a removable core to allow removal of secretions adhering to the inner surface of the tube, without necessitating removal of the entire device; a structure which is resistant to collapse or kinking, including during removal and placement of the core; a lower end structure which can resist folding or buckling, and to prevent the inner and outer components from separation by secretions or expired gases; and. in which the upper end of both the inner and outer components is constructed to prevent accidental passage into the trachea, to allow for fixation of both parts to each other and to a third structure, and to provide the upper section of the inner lining or core with a push pit into the outer sleeve and into adjacent ventilator circuit devices.

Claims: CLA I MS 1. A double-walled tracheal tube intended for child or adult use, and comprising a tubular outer portion, and an inner tubular portion in the form of a lining which is removably mounted therein to permit withdrawal of the inner tubular portion when a build-up of secretion thereon has occured, and in which the inner tubular portion is arranged within the outer portion in such a way as to promoted substantially laminar gas flow through the tube. 2. A tracheal tube according to Claim 1, in which the tracheal end of the lining forms a gas type seal with the adjacent end of the outer tubular portion. 3. A tracheal tube according to Claim 2, in which the tracheal end of the lining forms a smooth transition from the inner surface of the lining to the adjacent inner surface of the outer tubular portion. 4. A tracheal tube according to Claim 2 or 3, in which the tracheal end of the outer tubular portion has an inturned lip, and the tracheal end of the lining is engageable with said lip so as to form a smooth prolongation of the lip. 5. A tracheal tube according to Claim 4, in which the lip is a curved lip. 6. A tracheal tube according to Claim 4 or 5, in which the tracheal end of the lining and the lip have a releasable snap-fit type of interengagement which can form a substantially gas-tight seal against the gas flow between the outer surface of the lining and the inner surface of the outer tubular portion. 7. A tracheal tube according to any one of Claims 1 to 6. in which a flange is joined to the mouth end of the outer tubular portion to prevent accidental passage of the tracheal tube into the patient. 8. A tracheal tube according to Claim 7, in which the mouth end of the lining is fixed to said flange. 9. A tracheal tube according to any one of Claims 1 to 8, in which an inflatable cuff is provided on the outer tubular portion, at or near to the tracheal end thereof, and which is inflatable in order to provide resistance to aspiration of extraneous material into the lung of the patient.

Inventors: INGLIS TIMOTHY, MILLAR MICHAEL, INGLIS, TIMOTHY, MILLAR, MICHAEL
Applicants: UNIV LEEDS IND SERVICE LTD, UNIVERSITY OF LEEDS INDUSTRIAL SERVICES LIMITED
Application year: 1989
Main classification: A61M16
IPC codes: A61M16