Abstract:
An orientation independent, disposable, flexible exudate management canister that is capable of conforming to curved surfaces, for collecting exudate fluids from a wound as part of a negative pressure wound therapy system. The canister may be used with existing Negative Pressure Wound Therapy (NPWT) suction pumps and wound dressings, or with the suction pump and wound dressing described in this embodiment to make a complete NPWT system.

Description:
CROSS-REFERENCED TO RELATED APPLICATIONS 
       [0001]    Provisional application No. 61/755,534, filed on 23 Jan. 2013. 
     
    
     FEDERALLY SPONSORED RESEARCH 
       [0002]    Not applicable 
       SEQUENCE LISTING 
       [0003]    Not applicable 
       FIELD OF THE INVENTION 
       [0004]    This invention relates to systems for treating wounds by the application of negative pressure, and to devices for use in such systems. 
       BACKGROUND 
       [0005]    It is well known that wounds can be treated by applying suction to the wounds under an airtight wound cover to aspirate wound exudate and other liquids from the wound, lowering the bacterial bio-burden and promoting wound healing. 
         [0006]    There are numerous system available, with varying features, based around creating a vacuum with a vacuum source, applying the vacuum to a wound site, applying a wound cover to seal the wound, providing a wound filler in the wound to prevent the wound cover being drawn into the wound, drawing the exudate from the wound under vacuum and storing the wound exudate in some kind of wound exudate canister. The vacuum source, exudate storage canister and wound cover are normally connected together with flexible tubing, but some components may be connected directly to others. U.S. Pat. No. 5,645,081 Argenta et al, describes the use of negative pressure wound therapy and proposes the use of open celled wound fillers. U.S. Pat. No. 7,216,651 Argenta et al, describes the use of a source of vacuum coupled to a vessel to contain the exudate flow which is in turn connected to a wound dressing. 
         [0007]    Wounds with a large exudate flow (for example greater than 50 cc/day) often require a large vacuum source, usually an electrically driven pump and a high volume exudate canister, usually made from a rigid material. These systems are not easily portable and usually require the patient to remain in a fixed place during treatment. U.S. Pat. No. 7,857,806 Karpowski et al, describes a typical negative pressure wound therapy system comprising of an electrically driven pump and controller, rigid exudate canister and wound dressing for use in a medical facility. 
         [0008]    Wounds with a small exudate flow (for example less than 50 cc/day) do not need a large vacuum pump or a large exudate canister, and so are suitable for treatment with a smaller, lighter and portable system. Many such portable negative pressure wound therapy systems exist on the market and are often used for patients who are in a homecare environment. These systems primarily fall into one of two categories, those that pull the wound exudate into an absorbent dressing and those that pull the exudate into a rigid canister attached to the pump. 
         [0009]    Portable systems that use an absorbent dressing to contain the exudate have the disadvantage of making a bulky dressing at the wound site, increasing the risk of applying unwanted pressure to the wound, hold the exudate near to the wound which increases the risk of infection, prevents easy examination of the wound and the entire wound dressing needs to be changed when full of exudate, which can unnecessarily disturb the wound bed. U.S. Pat. No. 7,779,625 Joshi et al, describes such a system comprising of a small portable pump which pulls the exudate into a dressing which has an exudate storage system in the dressing. 
         [0010]    Portable systems that use a rigid canister attached to the pump have the disadvantage of a bulky canister to be carried around that is the same size full or empty, and are orientation dependent to allow the exudate to fall into the canister, risking tips and spills in a portable product, and hold the exudate close to the pump. As the pump must be monitored frequently for correct operation and alarm activation, having the exudate canister attached to the pump risks embarrassment and loss of dignity to the user if wound exudate is then seen by others nearby. U.S. Pat. No. 8,257,328 Augustine et al, describes such a system and discusses the use of a ball float valve in the canister to prevent leakage from moving or tipping. 
         [0011]    It would be advantageous to have a portable negative pressure wound system that has an exudate collection system that is orientation independent, flexible and could conform to curved body parts for easy carrying and is independent from the wound interface for easy changing without disturbing the wound bed. Such a system could hold the exudate away for the wound site to lower the risk of infection and could hold the exudate away from the pump so that the pump could be discretely worn by the user, without the risk of other people seeing the exudate. It would be further advantageous to hold the exudate without risk of leakage when the patient is moving about, and is as small and discreet as possible to maintain the patient&#39;s dignity. 
         [0012]    U.S. Pat. No. 8,034,038 Biggie et al, describes the use of a portable negative pressure wound therapy system with a flexible disposable canister, filled with a superabsorbent polymer. However this invention is orientation dependent, hanging the canister from the pump body and requires an approximate vertical orientation of the canister to work as it has lower, middle and upper segments. The device described in this patent also requires a supporting structure inside the exudate collection bag to keep the flexible walls of the bag from collapsing in under the forces of the vacuum, increasing the empty size of the canister and limiting its ability to conform to curved surfaces, such as a patient limb. 
         [0013]    This invention described here relates to the use of a flexible exudate collection canister as part of a portable Negative Pressure Wound Therapy (NPWT) system to overcome the disadvantages discussed above. The flexible exudate collection canister is made from flexible materials so that it can form itself to the shape of the human body and be worn discretely by a patient who is mobile and active in their daily lives. It has an exudate handling core made from a highly fluid absorbent material covered with an impermeable flexible outer cover, an air distribution layer, a first inlet for connecting it to the wound interface, a second inlet for connecting it to a pump and a hydrophobic membrane covering the input between the canister and the suction pump to prevent fluid from leaving the canister and moving towards the pump. The flexible exudate canister is separate from the wound dressing and the suction pump, and is connected to them via flexible plastic tubing. This allows the canister to be mounted discretely on the user at an optimum position and changed when full without disturbing the wound dressing. The canister does not need any internal support structure to stop its walls collapsing under the forces of the vacuum, so it can be manufactured as thin as the wall and fluid core will allow, and expand in thickness as it absorbs exudate until it reaches its fluid capacity. The flexible nature, orientation independence, ability to be mounted on a patient limb away from the pump, thin size and ease of changing without disturbing the wound be give this invention an advantage over the current devices. 
       SUMMARY 
       [0014]    This invention relates to the use of a flexible exudate collection canister as part of a portable Negative Pressure Wound Therapy (NPWT) system. The flexible exudate collection canister is made from flexible materials so that it can form itself to the shape of the human body and be worn discretely by a patient who is mobile and active in their daily lives. It has an exudate handling core made from a highly fluid absorbent material covered with an impermeable flexible outer cover, an air distribution layer, a first inlet for connecting it to the wound interface, a second inlet for connecting it to a pump and a hydrophobic membrane covering the input between the canister and the suction pump to prevent fluid from leaving the canister and moving towards the pump. The flexible exudate canister is separate from the wound dressing and the suction pump, and is connected to them via flexible plastic tubing. This allows the canister to be mounted discretely on the user at an optimum position and changed when full without disturbing the wound dressing. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]      FIG. 1  is a block diagram illustrating the components of a preferred embodiment of the negative pressure wound therapy system, showing the flexible exudate canister in relation to other components in the system. 
           [0016]      FIG. 2  is a block diagram illustrating the components of a preferred embodiment of the suction pump. 
           [0017]      FIG. 3  illustrates an exploded perspective view of a preferred embodiment of the flexible exudate canister. 
           [0018]      FIG. 4  illustrates a partial exploded perspective view of a preferred embodiment of the flexible exudate canister showing the hydrophobic filter membrane and conduit connections. 
           [0019]      FIG. 5  is a side cutaway view of a preferred embodiment of the wound dressing and wound interface. 
       
    
    
     DETAILED DESCRIPTION 
       [0020]    It will be readily understood that the components of the embodiment as generally described and illustrated in the Figures herein could be arranged and designed in a wide variety of different sizes, shapes and combinations. The following detailed description is not intended to limit the scope of the present disclosure, but merely representative of the preferred embodiment. The present invention may be embodied in other specific forms without departing from its spirit or essential characteristics. One skilled in the art will recognize that the invention can be practiced without one or more specific features, and that the features are not limited by their shape, size of combination. This invention relates to the use of an orientation independent, flexible exudate canister for use in a negative pressure wound therapy system, and as such may be used with other wound vacuum pumps or wound interfaces and wound dressings than that which is described here, but the detail has been limited in the description of those items to avoid obscuring aspects of the invention. 
         [0021]    The proposed invention shown in  FIG. 1  as a block diagram consists of an orientation independent, flexible exudate canister  20  with an input  21  to a suction pump  10  and an input  22  to a wound dressing  30 . The flexible exudate canister  20  is connected by a flexible tube  40  to a portable suction pump  10  that will provide a source of vacuum to the canister  20 . The flexible exudate canister  20  is connected to the wound dressing  30  by a second flexible tube  50 . The wound dressing  30  consists of a wound interface connection  31  for the flexible tube  50  to a commercially available wound dressing  30 . This allows the flexible exudate canister  20  to be positioned on a user&#39;s body away from the wound site in a place that is not loaded by the weight of the patient in everyday life, and allows the flexible exudate canister  20  to be changed when full without disturbing the wound bed. 
         [0022]      FIG. 2  shows the components of a portable suction pump suitable for use in this system. The portable suction pump is a pump specially designed for negative pressure wound therapy use and provides a vacuum at the required therapeutic level. This level is often either −80 mmHg or −125 mmHg, but other vacuum levels can be used depending on the clinical need. The pump may be a battery operated electrical pump, or use a mechanical means to generate the required vacuum levels. The pump  10  is controlled via a microcontroller  14  mounted on a PCB  12  which provides an interface between the power source  11  and the compressor  13 . The vacuum levels are monitored by a pressure transducer  17  on the PCB  12 , and the compressor  13  is switched on or off by the PCB  12  to control the level of vacuum required. A switch  18  on the PCB  12  turns the pump on and off, and LEDs  15  and a buzzer  16  provide feedback on the status of the pump to the user. A one way valve  19  between the compressor  13  and the outlet  101  ensures that leakage of vacuum through the compressor valves is kept to a minimum. When the pump  10  is switched on, the compressor  13  is turned on until a preset level of vacuum is reached, a typical value for use in negative pressure wound therapy is −80 mmHg, and then the compressor  13  is switched off. If the pressure falls below a preset value, due to leaks in the pneumatic system of from exudate being pulled out of the wound, the compressor  13  will turn back on until the desired level of vacuum is reached, as read by the pressure transducer  17 . A connection  101  from the pump  10  allows a flexible tube to be connected between the compressor in the pump and the flexible exudate canister. 
         [0023]    The power source  11  may be a battery power source (for example 2 AA lithium batteries), a capacitor power source, or any other kind of portable electrical power. 
         [0024]      FIG. 3  shows a preferred embodiment of the flexible exudate canister  20 . The flexible exudate canister  20  stores the wound exudate that is pulled from the wound by the suction pump. In this figure an exploded perspective view of the flexible exudate canister is shown. The flexible exudate canister  20  is made from a top sheet of thin flexible plastic  21  and a bottom sheet of this thin flexible plastic  22 , which may be connected together around their perimeter  27  to make a canister. Typically the material would be PVC or Polyurethane which is high frequency welded around the perimeter, but the material may be any flexible plastic material and the connection method may be any suitable method such as high frequency welding, ultrasonic welding, heat sealing, laser welding, adhesive connections etc. 
         [0025]    Sandwiched between the  2  layers of plastic sheeting is a super absorbent polymer in a cellular absorbent matrix  23 , the type of which is commonly used in disposable diapers and female hygiene products. This material holds the exudate fluid in its polymer matrix as a gel, preventing spillage and leakage under pressure. The material consists of two sheets an open-cell porous fabric, which may be an air-laid cellulose material, with the super absorbent polymer crystals sandwiched in between them to form a thin sheet. The open-cell porous fabric acts as a wicking agent, drawing the exudate fluid away from the canister sides and into the superabsorbent polymer crystals. The exudate forms a gel with the superabsorbent polymer, expanding in size as it does so. 
         [0026]    The super absorbent polymer matrix  23  must have an affinity and molecular bonding for the exudate fluid that is higher than the vacuum applied to the canister, or the flexible sheets  21  and  22  will squeeze the exudate fluid back out of the absorbent matrix. The capacity of the flexible exudate canister will depend on the amount of super absorbent polymer used, and this must be selected depending on the factors of the absorbency per unit area, and the area of the superabsorbent matrix to ensure that the flexible exudate canister will absorb the required volume or weight of exudate. When the superabsorbent polymer matrix  23  has absorbed its designated amount of exudate, any extra exudate sucked into the canister will appear as a liquid on the inner surfaces of the canister and be drawn to the input  25  from the canister to the suction pump. A hydrophobic filter membrane  26  is positioned over the input  25  to stop any fluid from exiting the bag and being drawn into the suction pump. 
         [0027]    An air distribution channel structure  24  is placed over the superabsorbent polymer matrix  23  to ensure that the flow of air or exudate fluid from the exudate input  28  to the vacuum input  25  over the superabsorbent polymer matrix  23  is not blocked by the top and bottom layers of plastic sheet  27  and  28  being forced together by the vacuum inside them. This air distribution channel  24  is flexible and can be a woven or knotted nylon mesh material 
         [0028]    The outer layer of the bottom thin plastic sheet  22  that forms the flexible exudate canister may be covered with a skin contact adhesive to allow the flexible exudate canister to be suck onto a patient limb as a way of carrying the canister near to the wound site. 
         [0029]      FIG. 4  shows a partial exploded perspective view of a preferred embodiment of the flexible exudate canister  20 . In this view the thin plastic base sheet  201 , superabsorbent polymer matrix  202  and air distribution layer  203  are all shown in their normal unexploded state, in contact with each other. The first input to the canister  211  is the connection between the suction pump and the canister. This can be a grommet  207  and flexible tube  208  fastened to the top plastic sheet  204 , over a hole  211  to allow vacuum access to the inside of the canister. This grommet  207  may typically be PU material high frequency welded to the top sheet  204 , but other materials and joining methods such as ultrasonic welding, heat sealing, laser welding or an adhesive connection. Another embodiment is to fasten the tube  208  directly into the canister using a high frequency tube welded joint between the canister outer sheets  204  and the tube  208 . Other joining methods could be ultrasonic welding, heat sealing, laser welding, or an adhesive connection. 
         [0030]    The second input  212  to the canister the connection between the wound dressing and the canister. This can be a grommet  209  and flexible tube  210  fastened to the top plastic sheet  204 , over a hole  212  to allow exudate fluid access to the inside of the canister. The flexible tube  208  and flexible tube  210  should be of different diameters to prevent misconnection in use. This grommet  209  may typically be PU material high frequency welded to the top sheet  204 , but other materials and joining methods such as ultrasonic welding, heat sealing, laser welding or an adhesive connection. Other methods may be to fasten the tube  210  directly into the canister using a high frequency tube welded joint between the canister outer sheets  204  and the tube  210 . Other joining methods could be ultrasonic welding, heat sealing, laser welding, or an adhesive connection. 
         [0031]    A hydrophobic filter membrane  205  is connected on the inside of the top sheet  204 , covering the input hole  211 . This allows the passage of air into the pump, but not fluid. The filter membrane is attached around its periphery to the top sheet of the canister  204  by high frequency welding, ultrasonic welding, heat sealing, laser welding, or an adhesive connection. The filter membrane is alternatively be attached around its periphery to the bottom of the grommet  207  by high frequency welding, ultrasonic welding, heat sealing, laser welding, or an adhesive connection. In order to ensure there is a sufficient air flow across the filter at all times, an air distribution layer  206  is placed between the top sheet  204  or the grommet body  207  and the filter membrane  205 . This material may be the same as used in the canister on the superabsorbent polymer  203  or the air distribution layer may be an air channel shape molded into the face of the grommet that touches the filter disk. 
         [0032]      FIG. 5  is a side cutaway view of a preferred embodiment of the wound dressing and wound interface. The wound interface consists of a grommet  31  connected to a flexible tube  50 . The grommet  31  may be a polyurethane or similar plastic molded part, with a large flat flange base. The base is covered by a pressure sensitive adhesive with a peel back adhesive backing paper. The grommet has an internal conduit connecting the flat flange to the grommet inlet. The grommet inlet is connected to the flexible tube  50  that comes from the exudate input port of the flexible canister. The connection between the flexible tube and the grommet may be fastened using high frequency welding, ultrasonic welding, heat sealing, laser welding, or an adhesive connection or it may be a mechanical push on connector interface such as a bayonet or barbed connector. The wound interface would normally be provided sterile, in a sterile packing. 
         [0033]    The wound dressing has a flexible membrane  32 , e.g. a polymeric or elastomeric film, which includes a bio-compatible adhesive on all or part of one side. A preferred embodiment would be to use a standard commercially available transparent film occlusive dressing with a hypoallergenic adhesive (eg Polyskin II from Covidien or Tagerderm from 3M). This would be trimmed to size to suit the particular wound and a small hole cut into it to allow a fluid connection  31  between the wound and the wound interface. The wound interface grommet  31  would have the pressure sensitive adhesive backing removed from the flange and the flange stuck onto the occlusive dressing film  32  such that the connecting hole in the grommet  31  marries up with the hole cut into the occlusive dressing  32  to provide a fluid path. The void in the wound  60  is filled by using a commercially available wound filler  33  (such as Kerlix gauze from Covidien). The wound cover would then have its pressure sensitive backing removed, and the wound cover sealed around the edges of the wound  34  to form an airtight seal.