IMPROVEMENTS IN AND RELATING TO CATHETERS

Abstract: A catheter tube of the type having a sleeve provided therearound adjacent the end which is inserted into a body channel, the ends of sleeve being secured to the tube and the sleeve being inflatable is described. The sleeve is either formed from gas impermeable material or is at least partly coasted with such material to prevent passage of gas into and/or out of the space between the sleeve and the tube. A rise in the pressure exerted on the body channel by the sleeve and consequent tissue damage or a pressure drop and consequent danger of slippage or loss of gas, if the catheter is being employed to supply gas to a patient, can therefore be prevented.

Description: IMPROVEMENTS IN AND RELATING TO CATHETERS This invention relates to catheters that is, it relates to tubes which are inserted through channels of the body for example the throat, and serve to admit or remove gasses or liquids therefrom. One known form of catheter is provided near the end which is to be inserted with a sleeve, the ends of which are secured to the tube. The interior of this so-called ■■ balloon" is connected to a source of air or liquid so that it can be inflated when the tube has been correctly positioned. The balloon then acts as a cushion to protect the internal tissues from traumatic damage and to hold the tube in place. This type of catheter is employed for, amongst other things, removal of urine from a body or as an artificial airway. In the former case the catheter is termed a "urinary catheter" whilst in the latter it is known as an "endotracheal tube" or a "tracheostomy tube" depending on whether it is inserted via the nasal passage or down the throat or via slit cut into the trachea. When the catheter is employed as an artificial airway the balloon further serves to provide a gas seal and thereby facilitates respiration by the ventilator attached to the tube since all the induced gasses will reach the patient's lungs. It has been found that there is a tendency for the pressure in the balloons or sleeves to change while the tube is in place. The change in pressure in the balloon is due firstly to osmosis, that is, diffusion through the permeable balloon material of, firstly, gasses in particular anaesthetic gasses, for example nitrous oxide and oxygen into the balloon and secondly, and to a much lesser degree, the inflating liquid or gas out of the balloon to try to equalise the partial pressures. Secondly, pressure changes occur when the temperature changes. These pressure changes are undesirable since if the pressure in the balloon rises above the peristaltic blood pressure, necrosis of the tissues around the balloon may occur with consequent damage to the patient. This can be very serious and it has been reported that most major tracheal complications result from excessive pressure exerted by the sleeve. If the pressure drops too much, the balloon may no longer either securely hold the tube in place or, where it is used to provide an artificial airway, effect a gas seal which may allow induced gases to escape before entering the lungs. A solution to this problem is to provide a pressure gauge in the connection between the balloon and the source of air or liquid. This is constantly monitored, normally by the anaesthetist or a nurse, and the pressure in the balloon maintained at a constant level by forcing more gas or liquid into the balloon or allowing gas or liquid to come out of the balloon. This arrangement increases both the amount of equipment required and the number of monitors which have to be watched. Alternatively a pressure balancing device which absorbs or delivers pressure by reference to an elastic reservoir of known characteristics may be employed. This adds to the amount and complexity of equipment required and consequently to the cost. Moreover, although this type of device is said to be self-regulating, it has been found to require monitoring for complete safety. A catheter in accordance with the invention comprises a length of tubing having a sleeve provided therearound adjacent the end which is to be inserted through a body channel, the ends of the sleeve being secured to the tube and the interior of the sleeve being connected to a source of gas or liquid whereby it may be inflated when the tube is correctly positioned in the body channel, wherein the nature of the material of the sleeve is such that, or is so treated that, passage of gas through at least part of the sleeve is prevented in at least one direction. Preferably the sleeve is coated with a gas impermeable material on at least part of its outer surface to prevent ingress of gasses. Suitably the half of the sleeve which is closest to the inserted end of the tube is coated on its outer surface. It is this region, where diffusion is most likely since it will normally be surrounded by gasses, in * articular anaesthetic gasses. The whole of the outer surface of the sleeve may be coated which will prevent any diffusion of gas which escapes towards the insertion end around the exterior of the sleeve. Suitably the inside of the tube in the region of the sleeve may also be coated with a gas impermeable material. This will substantially prevent diffusion of gasses passed down the tube into the sleeve. The sleeve can be coated on the inner surface with gas impermeable material. This will prevent any gas from inside the sleeve permeating through the sleeve and will also substantially reduce the amount of anaesthetic gas which can pass into the space between the sleeve and the tube. The sleeve may be coated inside and outside with gas impermeable material or it may be formed from a gas impermeable material, suitably polyvinyl acetal. All these arrangements prevent undesirable pressure, and consequent volume, changes of the sleeve and therefore enables the catheter to be used without damage to the internal tissues of the patient and without risk of leakage of gas past the sleeve when the catheter is employed as an artificial airway. Furthermore the pressure in the sleeve does not have to be monitored and adjusted constantly which reduces the work load on nurses or anaesthetist and simplifies procedure. Nor is any complicated, and therefore expensive, automatic pressure regulating device required. The coating may also be liquid impermeable. This is particularly suitable when the inserted end of the catheter will be surrounded by liquid or when liquid is employed to inflate the balloon. Suitably the sleeve is formed by dip coating and then secured in place onto the tube. The impermeable coating(s) can therefore be ■ readily provided during the dip coating process. The impermeable coating(s) may be alternatively provided as a laminate or by a blow moulding or by spraying or by co-extrusion with the sleeve. Suitably, the coating may comprise either polyvinylidene chloride or polyethylene terephthlate or polyvinyl alcohol. Preferably the tube has a loose-fitting cover over its mouth and means to remove the cover once the tube has been correctly inserted. The cover is conveniently arranged in its operative position to extend from the mouth of the tube over the sleeve. The cover serves to prevent ingress of saliva and mucus into the tube and protects the balloon during insertion. The invention will now be further described by way of example with reference to the accompanying drawings in which:- Figure 1 is a longitudinal section through a catheter in accordance with the invention and Figure 2 is a similar view to Figure 1 with the sleeve inflated. The catheter shown in the Figures is an endotracheal tube which comprises a length of flexible tubing 2 the inserted end 4 of which is cut obliquely to form a mouth and has rounded edges 6. Near the end 4 of the tube 2 a sleeve 8 is provided around the tube, the ends 7 of the sleeve 8 being secured to the tube 2. Gas or liquid is supplied to the space 9 between the sleeve 8 and the tube 2 to inflate the sleeve 8 (see Figure 2) from an external pump 10 via capillary tube 12 and an outlet 14 in the tube 2. A pressure measuring device (not shown) is provided in the pump or capillary tube which indicates the pressure achieved in the sleeve. The endotracheal tube is shown in Figure 1 ready for insertion. A loose fitting cover 16 formed from a soft flexible material covers the mouth 4 of the tube 2 and the sleeve 8. A tube 18, one end of which is securely attached to the inside of the cover 16 extends through tube 2, the other end 24 protruding from the insertion end 22 of the tube 2 a sufficient distance to allow it to be firmly gripped. The tube 2 is inserted into the nose or trachea and correctly positioned. Mucus or other matter which might otherwise block the mouth of the tube as it is inserted is retained on the outer surface of the cover 16. The sleeve 8 is inflated by pumping its pump 10 until the correct pressure is achieved as determined by the pressure measuring device. The cover 16 is then removed by pulling protruding end 24 of tube 18 which turns the cover 16 inside out so that any retained mucus or the like is inside the inverted cover and does not come into contact with the inner surface of the tube 2. Consequently a clear pathway to the patient's lungs is provided. When the tube 2 is in position, as shown in Figure 2 the inserted portion tends to be surrounded by anaesthetizing gasses. The material from which the sleeve of balloon 8 is formed in known tubes is permeable and the gas tends to osmate into the space 9 between the sleeve 8 and the tube 2 to equalise the partial pressures. The pressure inside the sleeve therefore rises and if greater than the peristaltic pressure can cause necrosis of the tissues adjacent the sleeve with consequent discomfort to he patient. This is prevented from occurring in the tube shown in the drawings by providing a gas impermeable coating 26 on the outer surface of the sleeve 8. The coating 26 prevents osmosis of the anaesthetizing gasses through the sleeve but still allows at least some passage of gas in the other direction which means that if, per chance, excess gas is inadvertently passed down capillary tube 12 while the tube 2 is in position this can escape. Alternatively the sleeve could be coated on its inner surface 28 with a gas impermeable material. This would reduce the amount of anaesthetizing gasses which could pass into the space 9 from outside the sleeve and prevent passage of gas out of the space 9. The sleeve 8 can also be coated on both its inner and outer surfaces to prevent passage of gas in either direction. The interior of the tube 2 in the region of the sleeve 8 can also be provided with a gas impermeable coating 30. This prevents gasses being passed down the tube into the patient from passing into the space 9 and raising the pressure therein. Suitably coating materials include polyvinylidene chloride, polyethylene terephthlate or polyvinyl alcohol, all of which have good barrier properties. The sleeve is preferably formed by a dip coating process and the impermeable layer can be applied as part of the process. Alternatively the barrier layer can be applied as a laminate, by a blow moulding process, by spraying or by co-extrusion with the sleeve. The sleeve may in another embodiment be formed from an impermeable material in which case no coating process is enquired. However the material used must not be too hard or damage to the patient could still occur. Although described specifically in relation to an endotracheal tube, it will be appreciated that the invention is equally applicable to any other type of catheter where a balloon is provided, for example, a urinary catheter or a tracheostomy tube.

Claims: CLAIMS ; 1. A catheter comprising a length of tubing having a sleeve provided therearound adjacent the end which is to be inserted through a body channel, the ends of the sleeve being secured to the tube and the interior of the sleeve being connected to a source of gas or liquid whereby it may be inflated when the tube is correctly positioned in the body channel, wherein the nature of the material of the sleeve is such that, or is so treated that, passage of gas through at least part of the sleeve is prevented in at least one direction. 2. A catheter as claimed in claim 1 wherein the sleeve is formed from a gas impermeable material. 3. A catheter as claimed in claim 2 wherein the gas impermeable material from which the sleeve is formed is polyvinyl acetal. 4. A catheter as claimed in claim 1 wherein the sleeve is coated with a gas impermeable material on at •least part of its outer surface. 5. A catheter as claimed in claim 4 wherein the coating is provided on the half of the sleeve which is closest to the end of the tube which will be inserted into the body channel. 6. A catheter as claimed in claim 4 wherein the coating is provided on the whole of the sleeve outer surface. 7. A catheter as claimed in any one of claims 1 or 4 to 6 wherein the inner surface of the sleeve is coated with a gas impermeabXe material. 8. A catheter as claimed in any preceding claim wherein the interior surface of the tube in the region of the sleeve is coated with a gas impermeable material. 9. A catheter as claimed in any one of claims 4 to 8 wherein the coating material is also liquid impermeable. 10. A catheter as claimed in any one of claims 4 to 9 wherein the coating is provided by dip coating, lamination, spraying, blow moulding or co-extrusion. 11. A catheter as claimed in any one of claims 4 to 10 wherein the coating comprises either polyvinylidene chloride or polyethylene terephthlate or polyvinyl alcohol.

Inventors: PERRY COLIN EDWARD, PERRY, COLIN, EDWARD
Applicants: WARNE SURGICAL PRODUCTS LTD, WARNE SURGICAL PRODUCTS LIMITED
Application year: 1989
Main classification: A61M25
IPC codes: A61L29, A61M25