Abstract:
A moisture sump integrated into a carbon dioxide absorber canister provides a collection reservoir for condensate from a patient ventilator system when the carbon dioxide absorber canister is attached to the ventilator system. The volume of the moisture sump is appropriately sized so that the time interval required to collect a maximum amount of condensate interval is not more than the life expectancy of the carbon dioxide absorbing material contained within the canister. The moisture sump allows condensate management of difficult to drain areas such as the inlet to the expiratory check valve of a ventilator system. The removal of the carbon dioxide absorber canister by a patient attendee to replace the carbon dioxide absorbing material ensures that the condensate collected by the integral moisture sump is eliminated from the patient ventilator system.

Description:
FIELD OF THE INVENTION 
     This invention relates to patient ventilator systems in which breathing gas is circulated through a carbon dioxide absorber canister, and more particularly, to an improved carbon dioxide absorber canister having an integral moisture sump. 
     BACKGROUND OF THE INVENTION 
     In ventilator systems designed to provide respiratory gases to patients, condensation of water vapor commonly occurs in breathing circuit components due to the high humidity of patients&#39; expired gases. Breathing circuits of the re-circulatory type include a carbon dioxide absorbing canister. Condensate is especially troublesome in carbon dioxide absorbing canisters and associated tubing and valves and may interfere with proper operation of the canisters and breathing circuit. When a patient requires prolonged use of a ventilator system, substantial condensate can accumulate, requiring medical personnel attending the patient to periodically rid the ventilator system of the excessive moisture. 
     Prior art ventilator systems have utilized various sumps to trap and remove condensate. The carbon dioxide absorbing canister itself has often been relied on as a common sump although the canister&#39;s primary function is removing carbon dioxide from the patient&#39;s expired breathing gases. 
     However, there exist areas in the breathing circuit that are difficult to drain to the carbon dioxide absorber canister. For example, the canister inlet structure, located upstream of the canister itself, including the expiratory check valve of the breathing system, is inherently difficult to maintain free of excessive condensate. In prior systems, the periodic actuation of a valve by a patient attendee was necessary for removal of condensate in this area. 
     Alternatively, separate stand-alone sumps have been employed specifically to drain the moisture from problematic areas. These sumps allowed the patient&#39;s attendees to view the collected moisture through a window or a transparent container so that the attendee could empty the collected moisture before the sump overflowed into the breathing circuit. 
     In practice, both the valve actuation mechanisms and the stand alone sump arrangements require extensive vigilance on the part of the patient&#39;s attendees. This demand on the attendees only adds to the already numerous ventilator servicing requirements which include removing and replacing spent carbon dioxide absorbing materials from the canister, ensuring proper composition of ventilator gases, maintaining desired gas volumes and pressures in the breathing circuit, and maintaining optimum humidity in inspiratory breathing gases. These varied tasks create multiple opportunities for operating errors to occur. 
     Therefore, an approach that avoids the above-described condensate-related problems and reduces condensate buildup problems in hard to drain breathing circuit areas, while simultaneously lowering the demands on the patient attendees, is highly desirable. 
     SUMMARY OF THE INVENTION 
     This invention is a carbon dioxide absorber canister with an integral moisture sump. The moisture sump collects condensate from areas of a breathing circuit that are difficult to drain to a common sump, such as the carbon dioxide absorber canister itself. The moisture sump found in the present invention may be integrally formed into the structure of the carbon dioxide absorber canister, the canister including a hollow container adapted to contain a carbon dioxide absorbing material. 
     The moisture sump includes a reservoir chamber for accepting collected condensate. The reservoir chamber may be arcuately-shaped with an upwardly facing entrance formed by surrounding walls. The entrance to the reservoir chamber offers a sealing surface for pneumatically sealing with the breathing circuit. This pneumatic seal is arranged so that the seal is accomplished by attachment of the carbon dioxide absorber canister to the patient ventilator system and is broken when the canister is subsequently removed from the system. 
     The moisture sump is adapted to collect condensate from breathing circuit areas proximate the inlet and outlet ports of the canister. Such areas include the inlet structures and outlet structures located in the patient ventilator system, specifically, the expiratory check valve and the inspiratory check valve. As noted above, the expiratory check valve is known to be a particularly troublesome area from which to drain condensed moisture. 
     The moisture sump&#39;s reservoir chamber may have a volume sized to accommodate the maximum amount of condensate collected in a given time interval, such as the life expectancy of the carbon dioxide absorbing material contained within the hollow container of the canister. Therefore, the patient&#39;s attendees are not required to monitor the moisture buildup in the moisture sump independently of other tasks. Removal of the carbon dioxide absorber canister from the breathing circuit automatically ensures that the condensed moisture contained in the integral sump is also removed. 
    
    
     Further advantages of a carbon dioxide absorber canister with an integral moisture sump of the present invention will be evident from the following detailed description and accompanying drawings. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the drawings: 
     FIG. 1 is an overview of a ventilator breathing circuit showing elements of the circuit as distinct functional blocks. 
     FIG. 2 is a perspective view of a patient ventilator system including one embodiment of the carbon dioxide absorber canister with moisture sump according to the invention. 
     FIG. 3 is an exploded perspective view of the canister and associated valve structure depicted in FIG.  2 . 
     FIG. 4 is a cross-sectional view of the canister and associated valve structure shown in FIG. 2 taken generally along the line  4 — 4  of FIG.  2 . 
     FIG. 5 is an alternate embodiment of the carbon dioxide absorber canister and moisture sump shown in a cross-sectional view similar to FIG.  4 . 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Like numerals are used to refer to like elements throughout the figures and the following description. 
     FIG. 1 is an overview of a patient ventilator breathing circuit  10  showing elements of the circuit as distinct functional blocks. Exhaled breathing gases initially travel from the patient through a flow sensor  12 . Flow sensor  12  provides output information to a patient attendee regarding flow characteristics of the exhaled gases. Expired breathing gases then flow to an expiration valve structure  16 . In expiration valve structure  16 , moisture is separated from the expired breathing gases and drains into moisture well or condensate sump  14 . The breathing gases then pass through the expiratory check valve  17  contained in the structure  16  associated with a CO 2  absorber (canister)  18 . Mechanical ventilator, or manually operated flexible bag,  20  is connected to the flow path for the breathing gases downstream of the expiratory check valve  17  to drive the re-circulating breathing gases through CO 2  absorber  18 . Within CO 2  absorber  18 , CO 2  gas is removed by contact with a CO 2  removing material, such as soda lime. 
     In FIG. 1, the functional blocks representing condensate well  14  and carbon dioxide absorber  18  are interconnected to graphically represent the integral design of these components found in the present invention. Also, and as shown in diagrammatic form in FIG. 1, moisture (water) carried by the breathing gases is removed from the gases before the gases pass through the expiratory check valve  17 , thereby avoiding an excessive build up of moisture that could interfere with the operation of the valve  17 . Further, removing moisture from the breathing gases upstream of the expiratory check valve  17  is advantageous in limiting or precluding moisture from entering ventilator/bag  20 . 
     After the CO 2  content of the expiratory gas is reduced in canister  18 , the expiratory gas exits CO 2  absorber  18  and fresh anesthesia gases, block  22 , are added if necessary. The gases flow through an inspiratory check valve  23  located within an inspiratory valve structure  24  before being returned to the patient. Between the inspiratory check valve  24  and the patient, a pressure sensor  26 , oxygen sensor  28 , flow sensor  30 , and other apparatus may be present. 
     FIG. 2 depicts a patient ventilator apparatus  32  including a CO 2  absorber canister  18  with an integral moisture sump  14  according to the present invention. FIG. 3 shows an exploded perspective view of the apparatus of FIG.  2 . FIG. 4 shows a cross-sectional view of the canister  18  with sump  14  of FIGS. 2 and 3. 
     Referring to FIGS. 2 and 3, a patient ventilator apparatus  32  includes a flow sensor module  36  partially enclosing a ventilator.  20 , an expiratory valve structure  16  and an inspiratory valve structure  24 . Expiratory valve structure  16  includes an expiratory valve inlet  34  seen protruding from ventilator housing  36  in FIG.  2 . Expiratory valve inlet  34  communicates with the expiratory valve body  38  located within flow sensor module  36 . Expiratory valve body  38  communicates with an expiratory valve outlet  40  located on the underside of the ventilator apparatus  32 . 
     FIG. 4 illustrates that between inlet  34  and outlet  40 , expiratory valve body  38  contains valve disk  41  mounted on valve seat  43  to control the passage of gas through the valve body  38 . The expiratory valve structure  16  communicates with ventilator  20  through ventilator port  94 . Ventilator port  94  is located downstream of the point in expiratory valve body  38 , at which moisture is removed from the expiration gases. Condensed moisture reaching ventilator  20  is thus largely reduced. 
     As seen in FIGS. 2-4, expiratory valve body  38  includes an expiratory valve drain  42  adapted to collect and route condensed moisture away from the expiratory valve body  38 . Condensate in the breathing circuit enters expiratory valve body  38  through valve inlet  34  and, unable to follow the upwardly leading path of the breathing gases shown by arrow a in FIG. 4, will drain to a lower portion  78  of the expiratory valve body  38 . Condensate collected at the lower portion  78  then enters valve drain  42  and travels downward to reservoir chamber  80  of moisture sump  14 . Reservoir chamber  80  is formed by sump wall  82  which extends from an upper entrance  84  downward to transition into a bottom  86 . Lower portion  48  of drain tube  42  forms a pneumatic seal with reservoir chamber  80  through O-ring  46 . 
     The preferred embodiment of the invention utilizes an arcuately-shaped reservoir chamber  80  formed by sump wall  82  which is integral with container wall  88  as shown in FIGS. 2-4. However, reservoir chamber  80  and container chamber  90  are physically isolated from each other, as shown in FIG.  4 . Container body  44  and sump  14  are preferably molded as a single unit. Suitable materials may include polysulfones with polyphenyl sulfone being preferred since these materials can withstand autoclaving. Polypropylene would also be a suitable material for canister construction. 
     Expiratory valve outlet  40  forms a pneumatic seal with a canister inlet port  52  located on a top  54  of hollow container body  44 . Expiratory gases exiting valve outlet  40  are conveyed in the direction of arrow b to container body  44  where they interact with a CO 2  absorbing material contained therein. The CO 2  absorbing material may be any material suitable for removing CO 2  from breathing gas. Soda lime is the preferred material. 
     As shown in FIG. 4, the breathing gases exit hollow container body  44  in the direction of arrow c through a canister outlet port  56  located on top  54  of container body  44 . An inspiratory valve inlet  58  forms a pneumatic seal with the canister outlet port  56  and carries the breathing gases upward to the inspiratory valve body  60  (arrow d). Inspiratory valve body  60  is equipped with a gas flow controlling valve disk  61  and seat  63 , and an inspiratory valve outlet  62  which is in communication with subsequent elements of the breathing circuit. A fresh breathing gas port  64  communicates with inspiratory valve body  60  so that fresh breathing gases may be introduced into the breathing circuit if so desired by patient attendees. 
     Canister  18  with integral sump  14  is secured to the expiratory valve outlet  40 , expiratory valve moisture drain  42 , and inspiratory valve inlet  58  through latches  66  located on top  54  of the hollow container body  44  which opposingly engage fixed latch receiving members  68  and movable-type latch receiving members  70 . Movable type latch receiving members  70  are located on a latch actuator mechanism  72  which includes a latch actuator  74 . The latch actuator  74  may be operated by a patient attendee to disengage the movable members  70  from the latches  66  to break the pneumatic seals between valves  16 ,  24 , drain  42  and the carbon dioxide absorber canister  18  and moisture sump  14 . 
     Following replacement of the CO 2  absorbing material and emptying of the moisture sump  14 , the canister  18  with sump  14  may be reinstalled via the latching mechanism  72  to reestablish the pneumatic seals and consequently direct the expiratory gases of the breathing circuit past the moisture sump  14  and through container body  44 . 
     As noted above, the container body  44  is adapted to contain an amount of CO 2  absorbing material, suitable for removing CO 2  from a given volume of breathing gases. The volume of the reservoir chamber  80  of sump  14  is appropriately sized to accommodate the maximum amount of condensate produced from the given volume. Therefore, a patient attendee need not be burdened with checking and removing/replacing a moisture sump separate from removing and replacing a CO 2  absorber canister. 
     The integrated moisture sump  14  acts as a trap for condensed moisture formed before expired gases reach canister  18 . The invention ensures that not only the expiratory valve  16  remains free of condensed moisture but that excessive moisture does not build up in the container chamber  90  of the canister  18 . This improvement allows for less erratic response of the expiratory valve  16  as well as increased life and efficiency of the CO 2  absorbing material. 
     FIG. 5 depicts an alternative embodiment of the invention. FIGS. 1-4 show a single sump  14  on canister  18 . In the embodiment shown in FIG. 5, a second moisture sump  92  provided on canister  18  to collect condensed moisture from an inspiratory valve drain (not shown) is alternately provided. The second moisture sump  92  shown in this embodiment resembles the first moisture sump  14  and appropriate modifications are made to canister  18  and valve structures  16  and  24 . 
     Various alternatives and embodiments are contemplated as being within the scope of the following claims particularly pointing out and distinctly claiming the subject matter regarded as the invention.