Abstract:
A breathing tube for conducting a gas mixture in a ventilation system is provided, the tube including a tube portion; a coupler connectable to the tube portion; a connecting piece connectable to the coupler and which is attachable to a tube or a machine; wherein a filter element for filtering the gas mixture is arranged between the coupler and the connecting piece. 
     The coupler includes a first integral electrical heating device which surrounds the filter element and which is adapted to heat the filter element effectively.

Description:
FIELD OF INVENTION 
       [0001]    The present invention pertains to a breathing tube for conducting a gas mixture in a respirator for ventilating patients and to a breathing tube system. 
       BACKGROUND OF THE INVENTION 
       [0002]    When patients are being ventilated mechanically on an intensive-care ward, for example, the patient to be ventilated is connected pneumatically to the ventilator by means of a breathing tube system. Because the breathing gas which is supplied to the patient must be adjusted with respect to temperature and humidity to the physiological needs of the patient, a respiratory humidifier is arranged in the inhalation or inspiration tube to warm and humidify the breathing gas. The respiratory humidifier comprises a liquid container filled with distilled water in the usual manner; the inhalation gas is conducted through this container, and its moisture content is thus increased. 
         [0003]    To prevent moisture from condensing inside the breathing tube system, the inhalation tube and the expiration or exhalation tube are usually provided with electrical tube heaters, which warm the inhalation and exhalation gas flowing through them during operation. A loop of heating wire, for example, is used, which is integrated into the interior of the inhalation or exhalation tube, or the inhalation or exhalation tube is wrapped in each case with a coil of heating wire. 
         [0004]    Breathing tube systems of this type are known from, for example, DE 10 2008 039 137 B3, DE 10 2007 003 455 A1, and DE 44 41 380 A1. 
         [0005]    In the exhalation part of the breathing tube system, it is possible, especially in the case of patients with infectious diseases, to install filters to prevent the exhalation gas from carrying pathogens into the environment, which could result in additional patients or medical staff becoming infected. A filter of this type must be designed so that no condensate can form in it, because this would clog the filter and thus impair the filtering function. In the worst case, the ventilation function can also become defective, which can lead to negative results for the patient. Normally, the formation of condensate in the filter is prevented by means of additional heating devices and/or by means of water traps, as disclosed, for example, in U.S. Pat. No. 4,727,871. The general use of filter elements in ventilators is disclosed, for example, in U.S. Pat. No. 3,556,097. 
         [0006]    GB 1 294 307 A describes a heatable anesthesia filter, which is used on the inhalation side of a respirator. A sleeve, in which a heater is integrated, is placed over a hermetically sealed container which contains a filter. The container is connected to the inhalation tubes by means of connecting pieces, one arranged at the beginning and the other at the end of the container. 
         [0007]    The disadvantage of the above-mentioned breathing tube systems according to the prior art is that the heating of filters requires additional components such as cables, connectors, etc., which, because of the large number of cables and tubes to be connected, can lead to a loss of time and to the possible confusion of the operators. It can also be bothersome in the patient environment and can be susceptible to damage. The alternative use of unheated filters carries with it the danger of clogging attributable to the formation of condensate as previously described. 
       SUMMARY OF THE INVENTION 
       [0008]    It is therefore the object of the present invention to provide a breathing tube which makes it possible to filter the exhalation gas effectively, reliably and permanently, avoids the formation of water condensate in the filter, and minimizes the number of additional elements such as tubes, electrical lines, and their connections, etc. 
         [0009]    This object is achieved by the present invention. Advantageous elaborations and embodiments are the subjects of the subclaims. 
         [0010]    According to the invention, a breathing tube for conducting a gas mixture in a ventilation system is provided with a tube portion; a coupler connectable to the tube portion; a connecting piece connectable to the coupler and which is attachable to a tube or a machine, wherein a filter element for filtering the gas mixture is arranged between the coupler and the connecting piece. The coupler includes a first integral electrical heating device which surrounds the filter element and is adapted to heat the filter element effectively. As a result of the transfer of heat by convection or conduction from the coupler to the filter element, it is ensured that, when the gas mixture is being filtered, no condensate which could clog the filter element or the filter will form. In addition, the ventilation tube is simple and space-saving in design, and performs its task without any additional elements besides the connecting piece. 
         [0011]    It is especially advantageous for the filter element and the connecting piece to form a single integral unit. As a result, the ventilation tube is simplified even more, because fewer components are needed. 
         [0012]    The tube portion, the coupler, and the connecting piece preferably have a circular cross-section. This allows the use of standard commercial cylindrical filter elements. Handling is also simplified as are assembly and possible disassembly of the individual elements. 
         [0013]    It is also advantageous to form the connection between the coupler and the connecting piece in detachable fashion as a screw-in or plug-in connection or as a bayonet mount. These types of connections are easy to attach and release, which facilitates handling, and their use is not unusual in the clinical field. 
         [0014]    In order to be able to use the breathing tube in current ventilators already present in hospitals, it is advantageous for the tube to be configured as a medical-grade single-use/disposable article. 
         [0015]    The tube portion preferably includes a second electrical heating device which is connectable to the first electrical heating device. It is also advantageous for at least certain parts of the first and/or the second electrical heating device to be configured as heating coils. Here the second electrical heating device is preferably integrated into the walls of the tube portion. A heating coil represents a simple design and ensures effective heating of the ventilation tube and thus effective transfer of heat to the gas mixture in the ventilation tube. The first and second electrical heating devices can be connected to each other by means of simple plug-in connectors, which are sturdy and inexpensive. 
         [0016]    It is also advantageous for the tube portion and the coupler to be configured as a single, integral unit. This, too, results in an especially simple design, producible, for example, by means of coextrusion of the components. The fewer the number of elements of the ventilation tube or of the entire breathing tube system, the less effort is required of the operators for assembly, etc. 
         [0017]    The way in which the coupler and filter element are arranged guarantees maximum heat transfer from the first electrical heating device to the filter element. The heat transfer occurs here by convection, for example, or also by conduction. It must be kept in mind that the filter function of the filter element may not be impaired; that is, the gas mixture must be able to flow through the filter at the desired rate so as not to interfere with the ventilating function. 
         [0018]    The filter element is preferably cylindrically shaped, wherein the distance between the outer lateral surface of the filter and the inner lateral surface of the coupler is from approximately 0.1 mm to approximately 8 mm. These types of cylindrical filters are industrially produced and commercially obtainable. An example of the principle of a design of a filter of this type without a heater is shown in FIGS. 11-13 of U.S. Pat. No. 3,356,097. Here, a ring-shaped filter is arranged axially inside a housing, and the breathing gas flows from the outer lateral surface of the ring through the filter material to the inner lateral surface and from there through the outlet opening of the housing. It is obvious, however, that various other designs of filter elements with connecting pieces and couplers can also be used in the present invention. For example, an essentially spherical filter element is conceivable, which would comprise a hollow space into which the gas mixture would flow from the outer surface into the filter material. 
         [0019]    It is also advantageous for the breathing tube to include a sensor for detecting parameters of the connection between the coupler and the connecting piece. Thus it is possible, by way of the user interface of a respiratory humidifier, for example, or the interface on the ventilator, to activate a display which confirms that the coupler and the connecting piece have been properly connected. Thus, the function of the filter element can be monitored more effectively, and an incorrect attachment and other malfunctions can be detected more quickly. 
         [0020]    It is especially advantageous for the connecting piece to include its own electrical heating device which is electrically connectable to the heating device of the coupler. As a result, the heat output for the filter element can be increased, wherein the electrical connection between the coupler and the connecting piece can be established easily, for example, by way of the elements used to attach them. Thus, the above-mentioned function of a sensor can also be realized, in which, for example, the presence of an effective electrical connection between the coupler and the connecting piece confirms that the connection has been properly established. Alternatively, the heating device of the connecting piece and possibly that of the coupler can also be supplied by way of a connecting element which is connected directly to the connecting piece. 
         [0021]    Also according to the invention is a breathing tube system with an inhalation tube and an exhalation tube which is formed as a ventilation tube as described above. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0022]    The invention is explained below on the basis of exemplary embodiments with reference to the attached figures, in which: 
           [0023]      FIG. 1  is a schematic diagram of a preferred embodiment of the breathing tube system of the present invention; and 
           [0024]      FIG. 2  is a perspective diagram of a preferred embodiment of the ventilation tube according to the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0025]      FIG. 1  shows a perspective diagram of the inventive breathing tube system. A ventilator (not shown in  FIG. 1 ) is connected to a first inhalation tube  3  by a first connecting element. First inhalation tube  3  and a second inhalation tube  5  are connected to a liquid container  11  of a respiratory humidifier (not shown in  FIG. 1 ) by appropriate connecting pieces  7  and  9 , respectively. The free end of second inhalation tube  5  can be connected to a Y-piece (not shown) which establishes the connection to the patient by way of a mouthpiece. First and second inhalation tubes  3  and  5  are both equipped with electrical tube heaters in the form of heating coils integrated into the tube walls. In  FIG. 1 , only the pneumatic connections between first and second inhalation tubes  3  and  5  and the liquid container  11  via connecting pieces  7  and  9 , respectively, are shown; the electrical connection of all of the electrical lines passing through the tubes is accomplished by contact elements which are integrated into connecting pieces  7  and  9  and which establish the electrical connection by contacting corresponding opposing contact elements on the housing of the breathing air humidifier. An exhalation tube  13  can be connected to the ventilator by means of a connecting piece  15 . The other end of exhalation tube  13  is connected during operation to the Y-piece near the patient. 
         [0026]    In the embodiment shown here, exhalation tube  13  embodies the breathing tube according to the invention and comprises a tube portion  17  which is provided with an electrical heating device configured as a heating coil integrated into the tube wall. Between connecting piece  15  and tube portion  17 , exhalation tube  13  includes a coupler  19  with a filter element  20 , wherein coupler  19  is permanently connected to tube portion  17  but detachably connected to connecting piece  15 . The details of the exhalation tube will now be described with reference to  FIG. 2 . 
         [0027]    In the embodiment shown in  FIG. 2 , a connecting element  21  is arranged between the connecting piece  2  of first inhalation tube  3  and coupler  19  of exhalation tube  13  to establish the electrical connection. In addition to the pneumatic opening, connecting piece  2  of first inhalation tube  3  includes a sleeve element into which a corresponding plug element at the end of connecting element  21  is permanently plugged. In the same way, coupler  19  of exhalation tube  13  also comprises a sleeve element, into which the corresponding plug element of connecting element  21  is permanently plugged. The term “permanently” in this context is to be understood as meaning that operators cannot disconnect the electrical connections between connecting element  21  and connecting piece  2  or coupler  19  by a reasonable amount of effort. 
         [0028]    Because the diagram in  FIG. 1  pertains to the elements which form, as usual, the medical-grade single-use/disposable articles representing the necessary replaceable accessories for the function of a respiratory humidifier together with the breathing tube system, other elements such as the Y-piece or the housing of the respiratory humidifier have been omitted. 
         [0029]    The material of the tubes, that is, of first inhalation tube  3 , second inhalation tube  5 , and exhalation tube  13 , is of a suitable plastic material such as polyethylene or polypropylene. Other suitable materials may also be used. The tubes are extruded or coextruded by known technology. The inside diameter of the tubes is usually about 19 mm or about 22 mm in the case of a ventilation system for adults, but it would also be possible to use smaller diameters such as 12 mm or 15 mm in the case of ventilation systems intended, for example, for pediatric or infant-care wards. The connecting pieces, which form the transition between the tubes and the corresponding machines or the Y-piece, are also extruded of plastic material. Because strict requirements are imposed on materials in the medical field, these materials must meet the requirements of ISO standard 5367-2000. As previously mentioned, the breathing tube system according to the invention is configured either as a medical-grade, single-use/disposable article or alternatively as a reusable medical article, which can be restored to a usable state by washing and autoclaving. All components of the breathing tube system must also be configured so that they contain no harmful substances and can withstand a cold disinfectant such as CIDEX, Sekusept, Korsolex, etc. 
         [0030]      FIG. 2  shows in perspective view the details of exhalation tube  13  of the preferred embodiment of the breathing tube of the present invention. Tube portion  17  includes an electrical heating device configured as a heating coil  18 , which is integrated into the tube wall. Cylindrical coupler  19  is connected to tube portion  17 , wherein the heating coil  18  is electrically connected to the electrical heating device which is integrated into the coupler  19  but which is not visible from the outside. When heating coil  18  of tube portion  17  is carrying heating current, the current also flows through the heating device of coupler  19 . Alternatively, it is also conceivable that the heating device of coupler  19  could have its own separate electrical connection and be controlled by way of connecting element  21 , which is mounted laterally on coupler  19  by way of a sleeve element. In the embodiment shown in  FIG. 2 , coupler  19  includes a flange  22  which has a plurality of locking elements  23  on its inside surface. Coupler  19  includes a cylindrical hollow space to receive the filter element  20 . 
         [0031]    Connecting piece  15  has the shape of a cylinder on the coupler side with essentially the same cross-sectional dimension as coupler  19  and is thus connectable to coupler  19 . On the lateral surface of connecting piece  15 , locking elements  25  in the form of external projections are arranged, which are adapted to engage with the locking elements  23  of coupler  19  in the manner of a bayonet mount. Alternatively, it would also be possible to use some other type of detachable attachment mechanism such as a screw joint, a magnetic closure, a plug-in connection, or other type of connection familiar to the person skilled in the art. 
         [0032]    Proceeding from the part with the larger cross-section, i.e., at the end facing away from connection to coupler  19 , connecting piece  15  tapers down in a funnel-like manner to a cylindrical section  27  of smaller cross-section which is adapted to be attached to the appropriately configured opposing piece of a ventilator. Connecting piece  15  also comprises a hollow cylindrical space, in which filter element  20  is accommodated. To hold filter element  20  firmly in position inside the hollow space, retaining elements can be provided, but they may not completely prevent the flow of the gas mixture during operation, that is, during the time that connecting piece  15  and coupler  19  are properly connected to each other. In other words, the installation of filter element  20  between coupler  19  and connecting piece  15  must ensure both sufficient heat transfer from the heating device of coupler  19  and sufficient gas mixture flow through the ventilation tube. 
         [0033]    For this reason, various configurations within coupler  19  and connecting piece  15  are also possible which deviate from the embodiment shown in  FIG. 2  but which still fulfill the function described above. 
         [0034]    It is also conceivable that connecting piece  15  could be provided with its own heating device capable of heating filter element  20 . This can be achieved, for example, by integrating an electrical heating coil into the lateral surface of connecting piece  15 , which coil, in the embodiment illustrated here, can be electrically connected to the heating device in the coupler via the elements of the bayonet mount. As a result, an electrical connection is established between the heating device of coupler  19  and the heating device of connecting piece  15 . Other types of heating devices are also possible. 
         [0035]    It is possible, furthermore, to mount connecting element  21  on connecting piece  15  instead of on coupler  19 . The two heating devices can then be supplied with current via the alternative of connecting element  21 . 
         [0036]    With the subject matter of the present invention, a breathing tube has been provided which makes it possible to filter the exhalation gas effectively, reliably and permanently, avoids the formation of condensate in the filter, and minimizes the number of additional elements such as tubes, electrical lines, and their connections, etc.