Patent Publication Number: US-2007113854-A1

Title: Injection control for non-invented mask

Description:
CROSS REFERENCE TO PRIORITY APPLICATION  
      This application claims the benefit of U.S. Provisional Application No. 60/528,716, filed Dec. 12, 2003, incorporated by reference in its entirety. 
    
    
     BACKGROUND OF THE INVENTION  
      This invention relates to the field of masks, in particular, this invention relates to the field of reducing risk of cross-infection during the administration of non-invasive positive pressure ventilation (NIPPV) therapy or continuous positive airway pressure (CPAP) therapy. Of course, the disclosure may also have application to ventilators in general.  
       FIG. 1  illustrates a prior art mask assembly  10  including a mask shell  12  including an inlet  14  and at least one strap connection point  18  which provides a point of attachment for headgear (not shown). A facial interface in the form of face contacting cushion  16  is attached to the shell to thereby define an interior chamber into which pressurized breathable gas is introduced via the inlet  14 . The shell  12  includes at least one aperture, which in this case is covered with an elastomeric insert  20  including a plurality of vent openings  22 . Although the mask assembly  10  is shown to be a nasal mask, it could also be a full face mask. The nasal mask of  FIG. 1  is fully described in U.S. Pat. No. 6,561,190, assigned to ResMed Limited and incorporated herein by reference in its entirety.  
      The administration of positive airway pressure therapy requires that exhaled air is adequately exhausted from the mask to prevent rebreathing of expired CO 2  by the patient.  
      When using bi-level or CPAP devices, exhaled air is exhausted from the mask via one or more vents that are built into the mask or attached proximally to the mask, as shown in  FIG. 1 . During therapy, fresh air from the device flushes out exhaled air through the vents. The exhaled gases, including aerosols, are exhausted from the mask vents under pressure into the surrounding atmosphere. For highly infectious respiratory diseases, there may be potential to increase the risk of cross-infection from the patient to healthcare workers or to other patients. Accordingly, it may be desirable to create a mask that eliminates or at least reduces the risk of cross-infection due to unfiltered venting during positive pressure therapy.  
     BRIEF SUMMARY OF THE INVENTION  
      According to one aspect of the invention, a mask is provided with a filter or other device which filters gas exhausted by a patient. In one preferred form, the mask is a non-vented mask.  
      It is another aspect of the invention to provide a nasal or full face mask with a filter assembly suitable to reduce the risk of cross-infection during positive airway pressure therapy.  
      In accordance with an embodiment of the invention, a mask assembly is provided with a mask shell having an inlet and a cushion provided to the mask shell. A source of pressurized breathable gas is provided to the interior of the mask shell, for delivery to the airways of the patient. A filter assembly is provided in communication with the shell to filter gas exhaled by the patient. The filter assembly may be connected directly to the mask shell, so as to communicate the interior of the mask shell to the atmosphere via a filter, or the filter assembly may be connected to a joint, e.g., an elbow or a T, that is provided to the inlet of the mask shell. The filter assembly may be provided at one or more ends of the joint, e.g., at the inlet and outlet ends of a T-joint.  
      In still another aspect, there is provided a patient interface configured for connection to a patient in use, the patient interface being in communication with a source of gas pressurized above atmospheric pressure, and a filter assembly configured to receive gas exhaled by the patient in use, whereby the exhaled gas is vented to atmosphere following passage through said filter assembly.  
      These and other aspects of the invention will be described in or apparent from the following description of preferred embodiments. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      Preferred embodiments will be described with reference to the following drawings, in which like reference numbers indicate like parts and wherein:  
       FIG. 1  illustrates a prior art mask assembly;  
       FIG. 2  illustrates a first embodiment of a mask assembly according to the present invention;  
       FIG. 3  illustrates a top view of the filter assembly shown in  FIG. 2 ;  
       FIG. 4  illustrates the mask assembly of  FIG. 2  in use;  
       FIG. 5  illustrates a second embodiment of the present invention;  
       FIG. 6  illustrates a third embodiment of the present invention;  
       FIG. 7  illustrates a fourth embodiment of the present invention;  
       FIG. 8  illustrates a fifth embodiment according to the present invention;  
       FIG. 9  illustrates a sixth embodiment according to the present invention;  
       FIG. 10  illustrates a seventh embodiment according to the present invention; and  
       FIG. 11  illustrates an eighth embodiment according to the present invention.  
    
    
     DETAILED DESCRIPTION OF ILLUSTRATED EMBODIMENTS  
      Preferred embodiments of the invention will be described in relation to  FIGS. 2 through 11  in which like reference numbers indicate like parts.  
       FIG. 2  is a schematic view of a mask assembly  30  according to a first embodiment of the present invention. The mask assembly  30  includes a mask shell  32  having a face contacting portion in the form of a cushion  34 , and an inlet  36 . The mask shell and cushion are commercially available in various sizes from ResMed Limited. Of course, these and other commercially available components described herein are only examples. Other masks, shells and cushions are also available from ResMed Limited and other OEMs.  
      A T-shaped connection joint  38  includes an inlet  40  which is provided with a source of pressurized breathable gas via air delivery tube  42 . The joint  38  includes a conduit  44  through which breathable gas is supplied to the patient and through which exhaled air (including CO 2 ) is exhausted. The joint  38  includes an outlet conduit  46  that is connected to a filter assembly  48 . The filter assembly  48  includes an inlet  50 , a central chamber  52  and an outlet  54 . Preferably, the filter assembly  48  is hydrophobic such as is commercially available from Pall, Part No. BB50T. The outlet  54  is connected to a calibration cap  56  which is currently available from ResMed Limited, Part No. 16934. Also, the joint  38  is commercially available from Intersurgical, Part No. 1980.  
      As shown in  FIG. 2 , air is directed through a filter  58  of the filter assembly  48 , and then passes through one or more orifices in the calibration cap  56  to atmosphere.  
       FIG. 3  is a top view of the filter assembly  48  without the calibration cap  56 . The filter assembly includes a filter  58  which is placed within main chamber  52  of the filter assembly.  
       FIG. 4  illustrates mask assembly  30  in use on a patient P. In  FIGS. 1-3 , each of the conduit portions are preferably connected using male and female connections, e.g., having a standard diameter of 22 or 15 mm. It should be noted that these dimensions are merely illustrative of this embodiment, and that other orientations, connections and dimensions are within the scope of the present invention.  
       FIG. 5  illustrates a second embodiment of the present invention which differs from the embodiment of  FIG. 2  in regard to the vent assembly  48 . In  FIG. 5 , the vent assembly  48  is commercially available from Pall, Part No. BB25A. Vent assembly  48  includes a plug  60  and a vent port  62  which in this embodiment is preferably uncapped. In  FIG. 5 , the T-shaped joint  38  also has a slightly different configuration in that the outlet  46  is a female part rather than a male part.  
       FIG. 6  illustrates a third embodiment of the present invention which has another configuration. In particular, the mask assembly includes an elbow joint  38  rather than a T-shaped joint which is available from Intersurgical, Part No. 1992. The elbow joint  38  is connected to filter assembly  48  which is similar to that shown in  FIG. 2 . The filter assembly  48  in turn is connected to an in-line vent  65  commercially available from ResMed Limited, Part No. 17921. As indicated by the arrows A in  FIG. 6 , exhaust is achieved via in-line vent  64 . In other words, gas or CO 2  gas exhaled by the patient passes through the elbow joint  38  and filter assembly  48  and is then exhausted via in-line vent  64  following filtering in the filter assembly  48 .  
       FIG. 7  illustrates a fourth embodiment of the present invention which is similar to that shown in  FIG. 6 . The main difference in the embodiment of  FIG. 7  is that the filter assembly  48  is similar to that shown in  FIG. 5  where the filter air is exhausted through the vent port  62  rather than through the in-line vent  64  shown in  FIG. 6 . The filter assembly  48  and the air delivery tube  42  are connected via a straight connector  66 , available from Intersurgical, Part No. 1960.  
       FIGS. 8-11  illustrate further assemblies according to the present invention, including, e.g. filter assemblies that are not commercially available or “off-the-shelf”. These embodiments include modified components (e.g., housings, vents, etc.) or operating characteristics (vent flow, etc.) that may have some benefit for the environment and application of NIPPV or CPAP. Of course, modifications to other components, such as the mask, can also be made to optimize performance.  
       FIG. 8  illustrates a fifth embodiment of the present invention which is similar to the embodiment of  FIG. 7 . The main difference is that the filter assembly  48  includes two male ends such that the filter assembly  48  can connect directly to the air delivery tube  42  without the use of the straight connector  66  shown in  FIG. 7 .  
       FIG. 9  illustrates a sixth embodiment of the present invention in which the mask shell  32  is provided with or connected to a filter assembly  48 . Communication between the interior chamber of the mask assembly and the filter assembly  48  would require modification of the shell, for example, an aperture can be provided in the shell. In an alternative, the filter assembly could be configured to communicate with the mask shell interior via a pre-existing aperture found in vented masks available, e.g., from ResMed Limited. For example, the inlet side of the filter assembly may be configured to mate with a vent aperture as shown in Prior Art  FIG. 1  (removal of the vent  20  would reveal the aperture).  
       FIG. 10  shows a seventh embodiment of the present invention which is similar to that shown in  FIG. 9 . The main difference is that the filter assembly in  FIG. 10  has a reduced profile such that it reduces possible interference with patient vision and it has less possibility of interfering with movement of the patient&#39;s head.  
       FIG. 11  illustrates an eighth embodiment of the present invention which is similar to that shown in  FIG. 5 . The main difference is that the vent assembly  48  in  FIG. 11  has a low profile which is achieved, for example, by eliminating or reducing the height of the outlet tube  54  shown in  FIG. 5 .  
      In deciding which embodiment to use, several factors should be taken into consideration. For example, any filter used should have negligible, if any, effect on the air flow. This is less of a factor if it is only the vent flow that is being filtered. Moreover, the filter impedance should be predictable and relatively constant. Further, any potential possibility of CO 2  rebreathing should be eliminated or at least minimized to acceptable levels. Inclusion of the filter assembly should also have little or no adverse impact upon breath triggering sensitivity. Further, ultimate venting of the filtered air should be provided such that it does not produce an undesirable level of noise.  
      The filter should preferably have a viral efficiency of greater than 99.999%. For the embodiments of  FIGS. 6-8 , e.g., where the filter is between the source of pressurized gas and the patient, the impedance of the filter preferably should be as low as possible, and it should not exceed 2.0 cm H 2 O at 60 1/min. flow. The flow impedance requirements can be slightly relaxed for other embodiments where only the vent flow is being filtered, e.g., see  FIGS. 2, 5  and  9 - 11 . The filter should have a resistance to blockage tested for a minimum of 24 hours continuous use without the filter impedance exceeding the requirements mentioned above. Of course, these values may change depending on application. The preferred filter is suitable for exhaled gas, that is it maintains efficiency in humid gases. One suitable example is a mechanical hydrophobic filter.  
      In general, full face mask systems used with positive airway pressure devices usually have a built in anti-asphyxia valve. Therefore, if the device stops delivering pressure, the anti-asphyxia valve allows the patient to breath room air rather than rebreathing exhaled air. The embodiments described above do not include an anti-asphyxia valve although they could be modified to include such. For example, the filter cap and/or the vent itself could include an anti-asphyxia valve. If an anti-asphyxia valve is not included, the mask system should preferably be used only in a controlled environment and strictly supervised.  
      While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not to be limited to the disclosed embodiment, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the present invention. For example, while the embodiments of  FIGS. 2-11  illustrate a fill face mask with a frontal inlet aperture, the filter assembly could be used in conjunction with a nasal or mouth only mask, nasal prongs, nasal pillows, nasal cannulae or a mask with an “over the head” type inlet as shown in  FIG. 1 , all of which are generally referenced to herein as a mask or mask assembly.