A GAS-DISPENSING DEVICE

Abstract: A gas-dispensing device (2) for dispensing a gas into breathing gas, comprising a membrane (6) through which the gas can diffuse into the breating gas, is described. The gas-dispensing device (2) is simple and reliable because it contains a self-contained chamber (4) in which the gas is held at a predefined overpressure, and the membrane (6) is arranged to form a part of the chamber's (4) wall.

Description: Description A gas-dispensing device The present invention relates to a gas-dispensing device according to the preamble to claim 1. The present invention also relates to a breathing apparatus according to the preamble to claim 7. In conjunction with respiratory care (with a respirator, ventilator, anaesthetic machine or other breathing machine) , the physician may sometimes wish to supplement the breathing gas with a medical gas. NO is an example of a medical gas, but there are other gases with a therapeutic or other effect (e.g. anaesthetic, analgesic). One way to dispense a gas is to utilise a membrane permeable to the gas. The rate of diffusion then governs the amount dispensed. Connecting a gas source containing the gas to be dispensed into the flow of breathing gas in a breathing apparatus via a membrane is previously known. One disadvantage of this system is that the gas source may be bulky. Patient transport then becomes more difficult, or dispensing may need to be interrupted during transport. The gas source can also require more rigorous safety precautions to ensure that the gas source does not leak. This is the case for e.g. NO and anaesthetic gases. In addition, the gas- dispensing system must be equipped to prevent overdosing, even if the membrane or some other component (e.g. a pressure regulator) should fail. Another disadvantage of the prior art is that special monitoring equipment, or special pressures combined with fixed valves etc., are required if a specific total amount (a given amount of gas) is to be dispensed. One objective of the present invention is to achieve a gas- dispensing device that eliminates, at least in part, the problems associated with gas-dispensing devices according to the prior art. Another objective is to achieve a breathing apparatus, which allows the dispensing of a gas into breathing gas in a simple and uncomplicated fashion that is still safe and accurate. The objective of the gas-dispensing device is achieved according to the invention when the gas-dispensing device is devised as is evident from the characterising part of claim 1. Advantageous refinements and embodiments are evident from the dependent claims of claim 1. Instead of a procedure in which a source of gas is connected to a dosing means, a self-contained chamber is charged with a specific amount of gas to be dispensed. This is accomplished by filling the chamber with gas at a specific overpressure and close it. The chamber also contains a membrane through which the gas diffuses. When the chamber is placed in the flow paths of a breathing apparatus (or when at least the membrane is placed in contact with the flow paths) , the enclosed gas is continuously dispensed. Since the diffusion is mainly ruled by the partial pressure difference on both sides of the membrane, the overpressure need not be specifically large. Gas dispensing can be suitably regulated by covering the membrane with a covering means (preventing leakage before use) that can be removed to differing extents. This expose the membrane to varying degrees, and the amount dispensed can thereby be varied. The total amount dispensed can never exceed the amount held in the chamber. Pressure in the gas-dispensing device drops as gas diffuses out, thereby causing a drop in the amount dispensed. The rate of decline is virtually linear. This could be an advantage in some situations. Some gases need to be dispensed in large quantities initially but in gradually declining amounts thereafter until no more gas is dispensed. This kind of control was previously hard to achieve and demanded constant resetting of valves or other control components. With the gas-dispensing device according to the invention, dispensing gas in declining amounts is automatic. When dispensing needs to be more uniform over a longer period of time, an increasingly large area of the membrane can be uncovered at certain intervals. A large exposed area leads to large diffusion that compensates for drops in pressure. However, this does give rise to some variation in the amount of gas being dispensed. A more uniform dispensing of gas is provided when the chamber contains a donor substance for the gas. The donor substance could be a liquid (e.g. anaesthetic liquid) or a solid (e.g. an NO donor material) . As long as there is a donor substance present (or as long the donor substance provides the gas), a partial pressure will be sustained. In order to achieve completely uniform gas dispensing, it would be advantageous if the gas-dispensing device comprised a pressure device that maintains pressure inside the chamber. One such pressure device could be e.g. a spring-loaded piston that compresses the gas. This could also be done when there is a donor substance present in the chamber. Pressure in the dosage container can be measured with a pressure gauge. The pressure gauge can advantageously be battery-powered. It would be advantageous during long periods of gas dispensing if the gas-dispensing device were equipped with a refill means, particularly when the gas-dispensing device is incorporated into or a fixed part of the breathing apparatus. The refill means could be adapted for refill of gas and/or donor substance. The second objective is achieved according to the invention when the breathing apparatus is devised as is evident from the characterising part of claim 7. Depending on the application, having a separate gas- dispensing device placed in the flow paths may sometimes be unsuitable. The breathing apparatus could then be suitably devised so the gas-dispensing device is a fixed, integral part of the breathing apparatus. Integrating the gas-dispensing device with a tracheal tube or inspiratory line would then be particularly advantageous. The gas-dispensing device and the breathing apparatus according to the invention are described below, referring to the figures, in greater detail. FIG. 1 shows a first embodiment of a gas-dispensing device according to the invention, FIG. 2 shows a second embodiment of a gas-dispensing device according to the invention, FIG. 3 shows a third embodiment of a gas-dispensing device according to the invention, FIG. 4 shows a breathing apparatus according to the invention with indications showing where a gas-dispensing device according to the invention could be located or incorporated. FIG. 1 shows a first embodiment of a gas-dispensing device 2 according to the invention. The gas-dispensing device 2 has a closed chamber 4 holding a gas, at a predefined overpressure, to be dispensed. A membrane 6 is arranged at one end of the chamber 4. The membrane 6 can occupy a smaller or larger part of the chamber 4. Gas inside the chamber 4 diffuses out into atmosphere when the membrane 6 is uncovered. When the gas- dispensing device 2 is placed in the flow paths of a breathing apparatus, the gas can be dispensed into a breathing gas. A covering means covers the membrane 6 before the membrane is put into use. This prevents leakage of gas before dispensing is to take place. The figure shows how the covering means can consist of different segments 8A-C removed, one at a time (one segment has already been removed to show the membrane) , from the chamber 4. The magnitude of the dispensed dose can be selected by exposing the membrane to differing degrees. For example, exposure of a small area of the membrane 6 can be selected for neonates, a somewhat larger area for infants etc. up to the largest area for adults. Pressure (the partial pressure of the gas) in the gas- dispensing device 2 drops as the gas diffuses out through the membrane 6. This leads, in turn, to a drop in the amount of gas dispensed. This is an advantage with some gases, since it leads to gentler tapering off of medication. However, more uniform dispensing is desirable with other gases. One way to maintain the amount of gas dispensed is to increase the area of exposed membrane 6 by removing more segments 8A-C. FIG. 2 shows a second embodiment of a gas-dispensing device 10. The gas-dispensing device 10 can be connected to a system of tubing on a breathing apparatus via a first connection end 12A and a second connection end 12B. Breathing gas can flow e.g. as designated by the arrow 14. The gas to be dispensed is in a chamber 16 and is dispensed into the flow of breathing gas 14 via a membrane 18. A small piston 20 is arranged to compress the gas so as to keep gas dispensing as constant as possible over time. In this instance, the piston 20 is driven by a spring 22. Relatively constant gas dispensing can be achieved, as long as any gas is left in the chamber 16, by the choice of dimensions for the chamber 16 and the piston 20 and the type of spring 22. FIG. 3 shows a third embodiment of the gas-dispensing device according to the invention, in the form of a tracheal tube 24 in this instance. The tracheal tube 24 has an end 26 devised for insertion into a patient's airways. Gas in a chamber 28 is dispensed via a membrane 30 into the breathing gas flowing through the tracheal tube 24. The partial pressure of the gas is maintained for a prolonged time by providing the chamber 28 with a donor substance 29 for the gas. The donor substance could be a liquid or a solid. As long as the donor substance can provide the gas, an essentially constant dosing of the gas is maintained. The chamber can be refilled with fresh gas and/or donor substance via a refill nipple 32 when necessary. FIG. 4 shows one embodiment of a breathing apparatus, in the form of a ventilator 34, according to the invention. The ventilator 34 can be connected to a patient 36 in order to supply her/him with breathing gas. The breathing gas can consist of one or more gas components. The figure depicts the ventilator 34 with a first gas inlet 38A and a second gas inlet 38B to illustrate this. The gases are mixed in the correct proportions and quantities in a gas regulator 40. The breathing gas then flows through an inspiratory channel 42 to an inspiratory line 44. The inspiratory line 44 is connected to a 3-way connector 46. The 3-way connector 46 is connected to a tracheal tube 48 and to an expiratory line 50. The expiratory line 50 carries breathing gas from the patient, via an expiratory valve 52, to atmosphere or an evacuation (not shown). A control unit 54 controls the ventilator. Other common components in the ventilator 34, such as pressure and flow gauges, are not shown in the figure because they are prior art. A plurality of examples of where the gas-dispensing device can be placed or made an integral part of the ventilator 34 is shown for the ventilator 34. Here, a first gas-dispensing device 56A is shown in the inspiratory channel 42, a second gas-dispensing device 56B is shown connected to the inspiratory line 44, a third gas- dispensing device 56C is shown connected to the inspiratory line 44 and a fourth gas-dispensing device 56D is shown connected to a tracheal tube 48. The second and fourth gas- dispensing devices 56B, 56D can consist of the gas-dispensing devices shown in FIG. 2 and FIG. 3 respectively. Combinations of the depicted embodiments are fully feasible. Thus, all the gas-dispensing devices can be equipped with one or more segments according to FIG. 1, a piston and spring according to FIG. 2, donor substance and a refill nipple according to FIG. 3. In a similar fashion, the gas-dispensing device according to the invention can be used with respirators, anaesthetic machines, subacute devices (e.g. for home nursing) etc.

Claims: Claims 1. A gas-dispensing device (2; 10; 24; 56A-D) , for dispensing a gas into a breathing gas, comprising a membrane (6; 18; 30) through which the gas can diffuse into the breathing gas, characterised in that the gas- dispensing device (2; 10; 24; 56A-D) comprises a self- contained chamber (4; 16; 28) in which the gas is held at a predefined overpressure, and the membrane (6; 18; 30) is arranged to form a part of the chamber's (4; 16; 28) wall. 2. A gas-dispensing device according to claim 1, characterised in that the gas-dispensing device (2) also comprises a covering means (8A-C) for the membrane (6), dispensing of the gas only being possible after removal of the covering means (8A-C) . 3. A gas-dispensing device according to claim 2, characterised in that the covering means (8A-C) is segmented, whereby a varying area of the membrane (6) can be exposed in order to establish a given amount to be dispensed. 4. A gas-dispensing device according to any of the above claims, characterised in that the chamber is adapted to contain a donor substance that evaporates the gas. 5. A gas-dispensing device according to any of the above claims, characterised in that the gas-dispensing device (10) comprises a pressure device (20, 22) for maintaining pressure in the chamber (16) during dispensing. 6. A gas-dispensing device according to any of the above claims, characterised in that the gas-dispensing device (24) comprises a refill means (32). 7. A breathing apparatus (34) for supplying breathing gas to a patient (36), characterised in that the breathing apparatus (34) comprises a gas-dispensing device (2; 10; 24; 56A-D) according to any of claims 1-6. 8. A breathing apparatus according to claim 7, characterised in that the gas-dispensing device (56B) is incorporated into an inspiratory passage, preferably an inspiratory line (44), in the breathing apparatus. 9. A breathing apparatus according to claim 7, characterised in that the gas-dispensing device (56D) is incorporated into a patient connector, preferably a tracheal tube (48), in the breathing apparatus (34).

Inventors: PSAROS GEORGIOS, PSAROS, GEORGIOS
Applicants: PSAROS GEORGIOS, SIEMENS ELEMA AB, PSAROS, GEORGIOS, SIEMENS-ELEMA AB
Application year: 2001
Main classification: A61M16
IPC codes: A61M15, A61M16