GB2378904A

GB2378904A - Rebreathing bag with filter and fresh air inlet

Info

Publication number: GB2378904A
Application number: GB0214958A
Authority: GB
Inventors: David Robert Grice
Original assignee: Intersurgical Ltd
Current assignee: Intersurgical Ltd
Priority date: 2001-07-10
Filing date: 2002-06-28
Publication date: 2003-02-26
Anticipated expiration: 2022-06-28
Also published as: GB0116785D0; GB0214958D0; GB2378904B

Abstract

A device (1) is disclosed for use in rebreathing. The device (1) comprises an enclosed bag (2) which is impermeable to moisture. The bag (2) is filled with a mouthpiece (9) adapted to be held between a user's lips and the mouthpiece (9) is in fluid communication with the interior of the bag (2). A filter (6) is interposed between the mouthpiece (9) and the bag (2) and there is provided a fresh air inlet (7) between the mouthpiece (9) and the filter (6).

Description

Title-Medical Device This invention relates to a medical device, and in particular to a device for use in the treatment or prevention of alkalosis resulting from hyperventilation.

The respiratory system ventilates the lungs, extracting oxygen gas from the atmosphere and transferring it to the bloodstream for use in the body via the lungs.

This process also facilitates the excretion of carbon dioxide (CO2) and water vapour and maintains the normal acid/base balance of the blood. The respiratory centres in the brain (Medulla Oblongata) control the respiratory movements by reacting to variations in the CO2 content of the blood. A high level of CO2 stimulates respiration, increasing the breathing rate and thus ridding the body of waste products.

Hyperventilation (breathing at an abnormally high rate) results in an increased loss of CO2, which leads to alkalosis-an increase in blood alkalinity producing symptoms such as anxiety,"pins and needles"and fainting. The traditional method of treatment for hyperventilation is to make the patient breathe into a paper bag. The bag traps the exhaled air (high in CO2) and forces the patient to inhale the same CO2-rich air once more from the bag. This gradually brings the blood CO2 levels back to normal and is known as rebreathing.

The paper bag has long been used for rebreathing with hyperventilating patients but its use suffers from a number of disadvantages. Water vapour is exhaled as well as CO2 during respiration and paper bags will absorb this moisture and become weakened. This may lead to tearing and leaks in the bag, greatly reducing its efficiency. Also, paper bags are often not easy to obtain in an emergency, especially as they have been largely replaced by plastic bags in recent years. It is also necessary from time to time to remove the paper bag from the patient's mouth to allow the patient to breathe fresh air, since otherwise the patient may inhale insufficient oxygen. Another disadvantage of the use of a

paper bag is that it is relatively difficult to hold the paper bag to the patient's mouth in such a manner as to create a good seal around the mouth. Considerable pressure may need to be used and this can lead to a perception by the patient that the airways are being blocked, which may exacerbate rather than alleviate the patient's sense of anxiety etc. Furthermore, and particularly importantly, small fragments of debris may also be present in paper bags and may be inhaled, which could cause serious infection of the airways and lungs.

There has now been devised an improved form of device which overcomes or substantially mitigates the above-mentioned and/or other disadvantages of the use of paper bags in the treatment of hyperventilation and the associated alkalosis.

According to the invention, there is provided a device for use in rebreathing, said device comprising an enclosed bag which is impermeable to moisture, the bag being fitted with a mouthpiece adapted to be held between a user's lips, the mouthpiece being in fluid communication with the interior of the bag, and wherein a filter is interposed between said mouthpiece and said bag and wherein there is provided a fresh air inlet between said mouthpiece and said filter.

The device according to the invention is advantageous for numerous reasons. It is light and readily portable, eg by paramedical staff, and may therefore form part of the standard equipment of such personnel, being then readily available in the event that it is needed. The bag, being impermeable to moisture, is not liable to damage or leakage which might otherwise impair its function. The filter interposed between the mouthpiece and the bag prevents the inhalation of any particulate matter that may be contained within the bag. The fact that the mouthpiece fits easily in the user's mouth means that an effective seal between the mouth and the mouthpiece is easily formed, without the need for pressure to be applied to the user's face. This is far less physically imposing than the application of a paper bag or facemask and as such reduces the feelings of stress and anxiety that a patient may otherwise experience. The presence of the air inlet facilitates the

entrainment of fresh air with the"rebreathed"air, thereby ensuring that the patient receives sufficient oxygen while at the same time inhaling an increased concentration of carbon dioxide.

The bag may be formed of any suitable material, that is to say any material which is impermeable to moisture and maintains its integrity in use, and which is flexible enough to expand and contract as the user exhales into, and inhales from, the bag. The bag is most preferably formed of a synthetic plastics material. One suitable material is polyvinylchloride (PVC). Most preferably, the bag is formed by welding or otherwise joining together two sheets of such material.

The material used for the bag may be elastic so that the bag expands and contracts as the patient breathes, but is more preferably substantially inelastic, the bag simply expanding to a predetermined volume when the patient exhales into it, and collapsing when the patient inhales. If the patient exhales a volume of air greater than the capacity of the fully expanded bag then the additional exhaled air may escape via the air inlet. Likewise when the patient inhales, air is entrained in the inhaled airstream via the air inlet, and if the volume inhaled exceeds the initial volume of air in the bag the additional air is inhaled entirely via the air inlet.

The volume of the bag is preferably less than the normal inspiratory and expiratory volume of a patient, so that the air inhaled is made up partly of rebreathed air and partly of fresh air (containing normal concentrations of oxygen and carbon dioxide) introduced via the air inlet. Typically, the bag will have a volume of greater than 0. 5 litre and less than 2 litres, eg about 1 litre.

The filter may be of any material effective to permit flow of air at sufficient flow rates in both directions but to prevent passage of particulate or discrete matter from the bag. One suitable form of filter is a glass microfibre filter.

The filter is most preferably housed in a filter unit. Such a unit is preferably

interposed in a breathing tube connecting the mouthpiece to the bag and is most preferably of enlarged diameter relative to the breathing tube. In a particularly preferred embodiment, the filter unit comprises a pair of cooperating elements which together define a filter housing and which captivate between them the filter The air inlet is preferably a simple port, which is formed most conveniently in the filter unit, on the same side of the filter as the mouthpiece. The port most preferably has a cross-sectional area of approximately 6mm2 to 20mm2. When the port is circular in cross-section, its diameter is most preferably of the order of 3mm to 5mm.

The components making up the filter unit, the breathing tube and the mouthpiece are most preferably formed in suitably rigid plastics material, normally by injection moulding. One suitable material for such components is polypropylene.

A currently preferred embodiment of the invention will now be described in greater detail, by way of illustration only, with reference to the accompanying drawings, in which Figure 1 is a plan view of a rebreathing device according to the invention ; and Figure 2 is an exploded perspective view of the device of Figure 1.

Referring first to Figure 1, a rebreathing device according to the invention is generally designated 1 and comprises a generally rectangular bag 2 of flexible PVC material. The bag 2 is formed from two sheets of PVC material that are sealed together around the periphery of the bag 2, save for a neck portion 2a that is bonded by means of adhesive tape 3 to a tube 4. The bag 2 has a volume of 1 litre.

The tube 4 is formed integrally with one half 5a of a filter housing 5, that half 5a

cooperating with a second filter housing half 5b to form an assembly with the general form of a shallow cylinder. The juxtaposed circular edges of the filter housing halves 5a, 5b are formed with mating formations which cause the two halves 5a, 5b to engage with a snap fit. The two ends of the filter housing 5 are slightly domed in shape and are formed internally with integral ribs 5c (visible in Figure 2 on the internal surface of the first filter housing half 5a) that increase the rigidity of the filter housing 5.

A disc 6 of glass microfibre filter material is interposed between the two filter housing halves 5a, 5b during assembly, in such a way that the disc 6 is captivated between the two halves 5a, 5b in the completed filter housing 5 and spans the centre of the filter housing 5.

The second filter housing half 5b is formed with an extension tube 8 that is coaxial with the tube 4. The extension tube 8 actually comprises a pair of concentric inner and outer tubes 8a, 8b (see Figure 2), between which the end of a mouthpiece 9 can be inserted with an interference fit. The tip 9a of the mouthpiece 9 is flattened so as to fit easily and comfortably between a user's lips.

The second filter housing half 5b is also formed with an integral air inlet port 7 in the form of a small diameter tube disposed parallel to the extension tube 8.

The mouthpiece 9 and the two filter housing halves 5a, 5b are both formed by injection moulding of polypropylene.

In the embodiment described, the internal diameter of the tube 4 is approximately 15mm, that of the inner extension tube 8a is approximately 12mm and the diameter of the filter housing 5 (ie of the disc 8) is approximately 60mm. The diameter of the air inlet port 7 is approximately 4mm.

In use, a patient suffering from the effects of hyperventilation is given the device 1

and inserts the flattened tip 9a of the mouthpiece 9 in his or her mouth. The patient is then instructed to breathe normally through the mouthpiece 9.

Exhalation causes the bag 2 to expand to its maximum capacity. Further exhaled air is vented via the air inlet port 7. As the patient then inhales, the air contained within the bag 2 is then inhaled once again. The bag 2 collapses completely and fresh air from the external atmosphere is entrained into the inhaled airstream via the air inlet port 7, so providing that the inhaled air is a mixture of"rebreathed"air (enriched with carbon dioxide) and fresh air.

Claims

Claims 1. A device for use in rebreathing, said device comprising an enclosed bag which is impermeable to moisture, the bag being fitted with a mouthpiece adapted to be held between a user's lips, the mouthpiece being in fluid communication with the interior of the bag, and wherein a filter is interposed between said mouthpiece and said bag and wherein there is provided a fresh air inlet between said mouthpiece and said filter.
2. A device as claimed in Claim 1, wherein the bag is formed of a synthetic plastics material.
3. A device as claimed in Claim 1, wherein the bag is formed of polyvinylchloride.
4. A device as claimed in any preceding claim, wherein the bag is formed by welding or otherwise joining together two sheets of material.
5. A device as claimed in any preceding claim, wherein the material used for the bag is substantially inelastic.
6. A device as claimed in any preceding claim, wherein the volume of the bag is between 0.5 and 2 litres.
7. A device as claimed in any preceding claim, wherein the volume of the bag is less than the normal inspiratory and expiratory volume of a patient.
8. A device as claimed in any preceding claim, wherein the filter is a glass microfibre filter.
9. A device as claimed in any preceding claim, wherein the filter is housed in a

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filter unit, the filter unit being interposed in a breathing tube connecting the mouthpiece to the bag.
10. A device as claimed in Claim 9, wherein the filter unit is of enlarged diameter relative to the breathing tube.
11. A device as claimed in Claim 10, wherein the filter unit comprises a pair of cooperating elements which together define a filter housing and which captivate between them the filter.
12. A device as claimed in any one of Claims 9 to 11, wherein the air inlet is a port formed in the filter unit on the same side of the filter as the mouthpiece.
13. A device as claimed in Claim 12, wherein the port has a cross-sectional area of from 6mm2 to 20mm2.
14 A device as claimed in any preceding claim, wherein the filter unit, the breathing tube and the mouthpiece are formed in rigid plastics material.
15. A device as claimed in Claim 14, wherein said rigid plastics material is polypropylene.

16 A device substantially as hereinbefore described and illustrated in the accompanying Figures.