Patent Publication Number: US-2021162107-A1

Title: Npwt system with selectively controllable airflow

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of priority to U.S. Provisional Application No. 62/657,342, filed on Apr. 13, 2018, which is incorporated herein by reference in its entirety. 
    
    
     BACKGROUND 
     The present disclosure relates generally to wound therapy systems and devices, and more particularly to a drape for use with a negative pressure wound therapy device that provide selectively controllable airflow therethrough. 
     Negative pressure wound therapy (NPWT) is a type of wound therapy that involves applying negative pressure (relative to atmospheric pressure) to a wound site to promote wound healing. Some NPWT systems include a drape substantially sealed over a wound site and a pump which operates to maintain the wound site at negative pressure and remove wound exudate from the wound site via a tube coupled to the drape. However, wound exudate and other debris can create blockages that restrict fluid from being pulled through the tube, leading to fluid buildup. In some scenarios, improved air flow through the wound site may minimize the possibility of blockages in the connector tube and enhance removal of wound exudate. 
     SUMMARY 
     One implementation of the present disclosure relates to an assembly. The assembly includes a drape substantially sealable over a wound bed and a trackpad configured to couple a tube to the drape and allow the tube to provide suction to the wound bed. The assembly also includes a vent opening in the drape, a filter coupled to the drape and communicating with the vent opening, a cover coupled to the drape and movable between a first position to cover the vent opening and filter and a second position to uncover the vent opening and the filter, and a fluid indicator coupled to the drape and operable to provide a visual indication that fluid build-up is present in the wound bed. 
     In some embodiments, the cover includes a peelable polymer cover. In some embodiments, the peelable polymer cover includes a pressure-sensitive adhesive layer positioned at a bottom surface of the peelable polymer cover. The pressure-sensitive adhesive layer includes one or more of polyacrylate, polymethacrylate, polyurethane, hydrogel, natural rubber, synthetic rubber, styrene block copolymer, polyvinyl ether, polyolefin, hydrocolloid, silicon or silicone based material, styrene butadiene, polyisoprene, polychlorprene, polybutadiene, polychlorosulphonated polyethylene, rosin tackifier, coumarone resin, or coumarone indene resin. In some embodiments, the peelable polymer cover is shaped as one or more of a circle, a triangle, a square, a rectangle, a pentagon, a hexagon, a heptagon, or other polygonal shape. In some embodiments, the peelable polymer cover has an abstract, non-polygonal, or otherwise irregular shape. 
     In some embodiments, the vent opening includes a plurality of vent openings and the cover comprises a plurality of peelable polymer covers. In some embodiments, the plurality of vent openings and the plurality of peelable polymer covers are disposed in a pattern on the drape to provide a selectively customizable air flow profile beneath the drape. In some embodiments, the vent has a surface area within a range between approximately 0.001 square centimeters and approximately 40 square centimeters, preferably in the range of 0.01 to 1 square centimeter. 
     In some embodiments, the filter prevents the passage of microbes through the vent opening, prevents backflow through the vent, and allows the flow of air through the vent opening when the cover is in the second position. In some embodiments, the filter is hydrophobic. The filter includes pores with average diameter in a range between approximately 0.1 micron and approximately 0.4 micron and is fabricated from one or more of polyether sulfone, cellulose acetate, cellulose nitrate, nylon, polypropylene, or polytetrafluoroethylene. 
     In some embodiments, the fluid indicator includes a top layer and a bottom layer. The bottom layer includes a substrate coated with a water-soluble biocompatible colorant (e.g., dye, ink, pigment). The top layer is substantially unpigmented and is configured to allow capillary action from the bottom layer. The capillary action draws the colorant to the top layer when the bottom layer contacts fluid. In some embodiments, the substrate includes one or more of a polymer, a textile, or cellulose. The top layer includes one or more of an absorptive textile or paper. The top layer has a thickness and absorptivity tuned such that a change in color of the top layer corresponds to a predetermined amount of fluid buildup in the wound bed. 
     In some embodiments, the fluid indicator is also operable to indicate at least one of a pH, a presence of microbes, a presence of matrix metalloproteinases, or a presence of other proteases. In some embodiments, the cover includes the fluid indicator. 
     In some embodiments, the assembly also includes a plurality of additional vent openings interspersed on the drape and a plurality of additional filters. Each additional filter is coupled to the drape and is communicating with one of the plurality of additional vent openings. The assembly also includes a plurality of additional covers, each additional cover positioned at a corresponding filter of the plurality of additional filters and movable between a closed position to seal the corresponding filter and an open position to unseal the corresponding filter. 
     In some embodiments, the drape includes perforations that allow for customization of the drape in a plurality of possible shapes. The vent opening and the plurality of additional vent openings are positioned on the drape to provide at least one vent opening for each of the plurality of possible shapes. 
     In some embodiments, the cover includes a film having perforations or fenestrations that allow air flow to the filter when the cover is in the first position. In some embodiments, the cover includes a valve, for example a one-way valve. In some embodiments, the cover is further moveable to a range of intermediate positions between the first position and the second position. The range of intermediate positions corresponds to a range of air flow rates through the filter. 
     Another implementation of the present disclosure is a wound dressing assembly. The wound dressing assembly includes a drape configured to cover and seal around a perimeter of a wound bed and a track pad disposed on the drape. The track pad is configured to couple to a tube operable to provide suction to the wound bed. The wound dressing assembly also includes at least one vent opening in the drape and a cover coupled to the drape. The cover is incrementally movable between a sealed position and an unsealed position to permit a selectively controllable amount of an airflow through the vent opening to the track pad. The wound dressing assembly also includes an indicator coupled to an underside of the drape and operable to provide a visual indication that a fluid build-up is present in the wound bed. 
     In some embodiments, the wound dressing assembly also includes a filter coupled to the drape proximate the vent opening and configured to filter the airflow. In some embodiments, the filter includes a hydrophobic membrane filter. In some embodiments, the fluid indicator is disposed on the drape distal from the track pad and configured to provide a fluid indication proximate an edge of the wound bed. 
     In some embodiments, the at least one vent opening includes a pattern of perforations or fenestrations, and the cover comprises one or more peelable sheets that are controllably removable in one or more segments to create a desired airflow. 
     In some embodiments, the indicator is further operable to detect at least one or more of a pH, a presence of microbes, a presence of MMPs and/or other proteases. In some embodiments, the indicator can convey presence of or can vary in colorimetric visualization to provide a threshold indication. 
     Another implementation of the present disclosure is a wound dressing assembly. The wound dressing assembly includes a drape configured to cover and seal around a perimeter of a wound bed and a track pad disposed on the drape. The track pad is configured to couple to a tube operable to provide suction to the wound bed. A fluid indicator is coupled to an underside of the drape and operable to provide a visual indication that fluid build-up is present in the wound bed. A vent assembly is attachable to the drape and operable to provide an airflow through the drape to the wound bed. The vent assembly includes a flange defining a vent opening, a peelable cover disposed on the flange and incrementally movable between a sealed position and an unsealed position, and an adhesive layer disposed on the flange for attachment to the drape. In some embodiments, the flange includes a projection configured to pierce the drape when the flange is attached to the drape. 
     Another implementation of the present disclosure is a negative pressure wound therapy system. The negative pressure wound therapy system includes a tube, a pump configured to provide a negative pressure to the tube, and a dressing. The dressing includes a drape substantially sealable over a wound bed, a track pad configured to couple a tube to the drape and allow the tube to provide suction to the wound bed, a vent opening in the drape, a filter coupled to the drape and communicating with the vent opening, a cover movable between a first position to seal the filter and a second position to unseal the filter, and a fluid indicator coupled to the drape and operable to provide an indication that fluid build-up is present in the wound bed. Moving the cover to the second position provides airflow through the vent opening, the wound bed, and the tube, and moving the cover to the first position allows the negative pressure to be substantially maintained in the wound bed. In some embodiments, the cover is further moveable along a range of intermediate positions to adjust a rate of airflow permitted through the vent opening. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a front view of a negative pressure wound therapy system, according to an exemplary embodiment. 
         FIG. 2  is a cross-sectional view of a wound dressing assembly for use with the negative pressure wound therapy system of  FIG. 1  with a cover in a first position, according to an exemplary embodiment. 
         FIG. 3A  is a cross-sectional view of the wound dressing assembly of  FIG. 2  with the cover in a second position, according to an exemplary embodiment 
         FIG. 3B  is a cross-sectional view of the wound dressing assembly of  FIG. 2  with the cover in an intermediate position, according to an exemplary embodiment. 
         FIGS. 4A-D  are top views of various arrangements of the elements of the wound dressing assembly of  FIG. 2 , according to exemplary embodiments. 
     
    
    
     DETAILED DESCRIPTION 
     Referring to  FIG. 1 , a negative pressure wound therapy (NPWT) system  100  is shown, according to an exemplary embodiment. NPWT system  100  includes a therapy device  102  fluidly connected via a tube  104  to a drape  106  substantially sealed over a wound bed  108 . Wound bed  108  is a typically a tissue wound on a patient, for example a trauma wound, a chronic wound, a third-degree burn, etc. A wound insert  110 , for example a foam dressing configured for use with the NPWT system  100 , may be positioned in a volume  112  between the wound bed  108  and the drape  106 . 
     Therapy device  102  is configured to provide negative pressure wound therapy by reducing the pressure at wound bed  108 . More particularly, therapy device  102  includes a pump (not shown) that can draw a negative pressure (relative to atmospheric pressure) at wound bed  108  by removing wound exudate, air, and other fluids or debris from wound site  108  via tube  104 . More particularly, the pump operates to provide a negative pressure to the tube, which causes air and/or fluid to be sucked through the tube and deposited in a canister  114 . Wound exudate may include fluid that filters from a patient&#39;s circulatory system into lesions or areas of inflammation. For example, wound exudate may include water and dissolved solutes such as blood, plasma proteins, white blood cells, platelets, and red blood cells. Removing fluid from the wound bed  108  helps to minimize fluid pooling in the wound bed  108  and prevent complications associated with maceration in order to promote wound healing. Negative pressure at the wound bed  108  may also increase blood flow to the wound bed, reduce infection risks, and provide other benefits to the patient. 
     Drape  106  is substantially sealed over the wound bed  106 , such that little to no air leaks through or past the drape  106  and into the wound bed  108 . Drape  106  thereby facilitates the maintenance of negative pressure in the volume  112  between the drape  106  and the wound bed  108  created by the pump via tube  104 . In some cases, however, the seal between the drape  106  and the wound bed  108  is sufficient to create the risk of fluid blockages in the tube  104 . For example, the pump may cause a cross-section of the tube  104  to be filled with a fluid. In such a case, a seal is created where the fluid meets the tube  104 , such that as the fluid is pulled towards the pump, the pressure drops in the volume  112 . At some point, the pressure in the volume  112  becomes equal to or lower than the pressure exerted by the pump, such that the pump no longer pulls the fluid towards the therapy unit  102 , creating a blockage. The tube  104  and a trackpad  116  that couples the tube  104  to the drape  106  may include features intended to reduce the risk of such blockages. Another possible solution to fluid blockage in the tube  104  is to provide some amount of air flow to the wound bed  108  that can serve to fill in behind a potential blockage to prevent the pressure in the volume  112  from dropping to or below the pressure exerted by the pump. As described in detail with respect to  FIGS. 2-4 , the wound dressing assembly described herein is configured to combat fluid blockages and buildup by providing an indication of the presence of fluid buildup in the wound bed  108  and selectively providing microbe-free airflow to the wound bed  108  to facilitate the flow of fluid through the tube  104 . 
     Referring now to  FIG. 2 , a cross-sectional view of a wound dressing assembly  200  with a cover  206  in a closed position is shown, according to an exemplary embodiment. The wound dressing assembly  200  includes a drape  106 , a trackpad  114 , a vent opening  202 , a filter  204 , a cover  206 , and an indicator  208 . 
     The drape  106  is configured to cover and seal around a perimeter of the wound bed  118 . The drape has an inner surface  210  adjacent the volume  112  and an outer surface  212  facing the patient&#39;s external environment (e.g., the air surrounding the patient). 
     The trackpad  114  is configured to couple the tube  104  to the drape  106  and allow the tube  104  to provide suction to the wound bed  108  (i.e., to the volume  112 ). In some embodiments, the trackpad  114  is integrated into the drape  106 . In some embodiments, the trackpad  114  adheres to the outer surface  212  of the drape  106  to align the tube  104  with a hole through the drape  106 . 
     The vent opening  202  extends through the drape  106 . According to various embodiments, the vent has a surface area within a range between approximately 0.001 cm 2  and approximately 40 cm 2 . A preferable surface area of the vent opening  202  may be within a range of approximately between 0.01 cm 2  and 1 cm 2 . Smaller or larger surface areas are also possible. The vent opening  202  may be any suitable shape, including a rectangle, circle, ellipse, slit, pentagon, octagon, irregular polygon, etc. While the wound dressing assembly  200  of  FIG. 2  shows a single vent opening  202 , any number of vent openings  202  may be included in a variety of arrangements, as discussed in detail with reference to  FIGS. 4A-D . 
     The filter  204  is coupled to the drape  106  and is communicable with the vent opening  202 . As shown in  FIG. 2 , the filter  204  fills the vent opening  202 , for example aligned with the inner surface  210  and the outer surface  212  of the drape  106 . The filter  204  allows the flow of air through the vent opening  202  into the volume  112 , for example as illustrated in  FIGS. 3A-B , while preventing the passage of microbes or other contaminants through the vent opening  202  and is intended to prevent backflow of air and/or fluid out of the volume  112  through the vent opening  202 . Accordingly, the filter is a hydrophobic membrane that includes pores with an average diameter in a range between approximately 0.1 micron and approximately 0.4 micron, preferably between 0.20 and 0.22 micron. The filter may be fabricated from one or more of polyether sulfone, cellulose acetate, cellulose nitrate, nylon, polypropylene, or polytetrafluoroethylene. In an embodiment where the wound dressing assembly  200  includes a plurality of vent openings  202 , the wound dressing assembly  200  may also include multiple filters  204 , each filter  204  corresponding to one of the vent openings  202 . 
     The cover  206  is positioned proximate the vent opening  202  and the filter  204 . More particularly, the cover is coupled to the drape and moveable between a first position (shown in  FIG. 2 ) to cover the vent opening  202  and the filter  204  and a second position (shown in  FIG. 3A ) to uncover the vent opening  202  and the filter  204 . In some embodiments, the cover  206  is also moveable through a range of intermediate positions between the first and second positions, for example as shown in  FIG. 3B , to adjust a rate of airflow through the filter  204  and the vent opening  202 . 
     In the embodiments shown in  FIGS. 2-4 , the cover  206  is a peelable polymer cover manufactured from one or more of polyurethane, polyamide, polypropylene, polyethylene, polyvinyl chloride, ethylene vinyl acetate copolymers, polyvinyl alcohol, or polyether block amide polymers. The cover  206  may be any suitable shape, including a circle, triangle, square, rectangle, pentagon, hexagon, or heptagon, or some combination thereof. In other embodiments, the cover  206  may include, or may be, a valve articulable between an open and closed position. 
     The cover  206  of  FIGS. 2-3D  is also shown to include a pressure-sensitive adhesive layer  220  positioned at a bottom surface  222  of the cover  206  that is configured to removably couple the cover  206  to the outer surface  212  of the drape  106  around the vent opening  202 . The pressure-sensitive adhesive layer  220  can be pressed against the outer surface  212  to couple the cover  206  to the drape  106 , and peeled away from the drape  106  to remove the cover  206  or a portion of the cover  206  from the drape  106 . The cover  206  can thereby be repeatedly coupled to and decoupled from the drape  106 . In various embodiments, the pressure sensitive adhesive layer  220  is manufactured from one or more of polyacrylate, polymethacrylate, polyurethane, hydrogel, natural rubber, synthetic rubber, styrene block copolymer, polyvinyl ether, polyolefin, hydrocolloid, silicon or silicone based material, styrene butadiene, polyisoprene, polychlorprene, polybutadiene, polychlorosulphonated polyethylene, rosin tackifier, coumarone resin, or coumarone indene resin. 
     When the adhesive layer  220  adheres the cover  206  to the drape  106  around the vent opening  202  as shown in  FIG. 2 , the cover  206  substantially seals the vent  202  and the filter  204 . A remaining leak rate through the cover  206  (i.e., through the vent opening  202  into the volume  212  when the cover  206  is not in the first position) may vary within a range of between approximately 0.01 and 2 liters per minute, preferably in the range of approximately 0.05 to 0.5 liters per minute. In some cases, the cover  206  includes a film that has perforations or fenestrations that allow air flow to the filter  204  and vent opening  206  when the cover  206  is in the first position (i.e., when the cover is vent opening  206  is ‘closed’). 
     Referring further to  FIGS. 2-4D , the indicator  208  is coupled to the drape at a strategically advantageous location and is operable to provide a visual indication that fluid build-up is present in the wound bed  108 . In some cases, the indicator  208  is additionally or alternatively operable to indicate one or more of a pH, a presence of microbes, a presence of matrix metalloproteinases, or a presence of other proteases. 
     The indicator  208  includes a top layer  230  and a bottom layer  232 . The bottom layer  232  includes a substrate coated with a water-soluble biocompatible colorant (e.g., dye, ink, pigment, etc. with a color of blue, red, green, etc.). The substrate of the bottom layer  232  includes one or more of a polymer, a textile, or cellulose. The top layer  230  is substantially unpigmented and is configured to allow capillary action from the bottom layer. The bottom layer  232  and the top layer  230  are arranged such that when the bottom layer  232  contacts fluid, capillary action draws the colorant to the top layer and causes the top layer to turn the color of the colorant. Accordingly, the top layer  230  is manufactured from one or more of an absorptive textile or paper, with a thickness and absorptivity tuned (e.g. by tailoring the amount of capillary action) such that a change in color of the top layer corresponds to a predetermined amount of fluid buildup in the wound bed. For example, in some cases 0.2 mL of fluid will not turn the top layer  230  the color of the colorant (e.g., blue), but 2 mL of fluid will turn the top layer  230  the color of the colorant. In some embodiments, the top layer  230  is configured to return to an unpigmented appearance after fluid build-up in the wound bed  108  is reduced. The indicator  208  may be configured to show a dichotomous indication of fluid buildup (i.e., fluid or no fluid), or may provide a colorimetric visualization that shows a range fluid levels and may provide a threshold indication. 
     As shown in  FIG. 2 , the indicator  208  is coupled to the inner surface  210  of the drape  106 . The drape  106  is transparent or translucent such that the color of the top layer  230  of the indicator  208  can be seen through the drape  106 . In other embodiments, the indicator  208  extends through the drape  106 , such that the top layer  230  is aligned with or protrudes from the outer surface  212  of the drape  106 . In some embodiments, the indicator  208  is included with the cover  206  (e.g., coupled to the cover  206 , integrated into the cover  206 ). 
     The indicator thereby communicates (e.g. by changing color, etc.) to a patient or caregiver that additional airflow is needed to the wound bed  108  to facilitate the removal of fluid via tube  104  to reduce the level of fluid build-up. That is, a change in color of the top layer  230  to the colorant color indicates that a blockage is likely present in the tube  104 , which is preventing removal of fluid from the wound bed  108 . In response to a change in color of the top layer  230 , then, a patient or caregiver may move the cover  206  from the first position (as shown in  FIG. 2 ) to the second position (shown in  FIG. 3A  and described in detail below) to provide airflow that facilitates the elimination of the blockage. 
     Referring now to  FIG. 3 , a cross-sectional view of the wound dressing assembly  200  with the cover  206  in a second position is shown, according to an exemplary embodiment. To transition the cover  206  from the first position shown in  FIG. 1 , where the adhesive layer  200  substantially seals the cover  206  around the vent opening  202 , to the second position shown in  FIG. 2 , the cover  206  is peeled away from drape  106 . The cover  206  may include a tab, grip, flap, etc. to help a patient or caregiver grab the cover  206  and peel the cover  206  away (e.g., pull, un-adhere, decouple) from the drape  106 . In some embodiments the cover  206  is securely coupled to the drape  106  at an edge or corner of the cover  206  to allow the cover  206  to be peeled away from the drape  106  as shown in  FIG. 2  without completely separating from the drape  106 . In other embodiments, the cover  206  is configured to be completely removable from and replaceable on the drape  106 . 
     When the cover  206  is in the second position of  FIG. 3A , the vent opening  202  and the filter  204  are uncovered and unsealed. The cover  206  can be selectively moved from the first position to the second position to permit airflow through the vent opening  202  and the filter  204 , and replaced in the first position from the second position to substantially prevent airflow through the vent opening  202  to facilitate the maintenance of negative pressure in the volume  112 . 
       FIG. 3A  includes flow arrows that illustrate a flow path  300  of airflow through the vent opening  202  and filter  204 , across the wound bed  108 , and into the tube  104 . As air flows through the vent opening  202 , the filter  204  filters the air to prevent microbes, moisture, and/or particulates from reaching the wound bed  108 . As the filtered air flows across the wound bed  108 , fluid and other debris from the wound bed  108  is picked up with it, flowing towards the tube  104 . The air and fluid flow is then directed out of the volume  112  through the trackpad  114  and the tube  104  to the therapy unit  104  (shown in  FIG. 1 ). Positioning the cover  206  in the second position thereby facilitates airflow that facilitates movement of fluid from the wound bed  108  towards the tube  104 . Furthermore, when the cover  206  is in the second position, the volume  112  is open to a source of air at atmospheric pressure, which substantially prevents the pressure in the volume  112  from dropping to or below the negative pressure created by the pump. Placing the cover  206  in the second position may thereby release a fluid blockage in the tube  104  and/or reduce the risk of future fluid blockages. 
     A possible scenario may be as follows. A fluid blockage in the tube  104  leads to fluid buildup in the volume  112  (i.e., because the fluid is blocked from removal via tube  104 ). The top layer  230  of the indicator  208  changes color in response to the fluid buildup, and is noticed by a patient or caregiver. The patient or caregiver then peels the cover  206  from the first position of  FIG. 2  to the second position of  FIG. 3A , allowing airflow through the vent opening  202  and the filter  204  into the volume  112 . Because the volume  112  and the tube  104  are at negative pressure relative to the atmospheric pressure of the outside air, the outside air is pulled through the filter and towards the tube  104 , releasing the fluid blockage in the tube  104 . The built-up fluid can then also be drawn through the tube  104 . At some point, the fluid build-up has been sufficiently reduced, and the cover  206  can be replaced to allow the pump and tube  104  to reestablish a negative pressure in the volume  112 . 
     In some cases, an intermediate level of airflow may be preferable, for example to provide a continuous, consistent, and/or limited air flow.  FIG. 3B  shows the wound dressing assembly  102  with the cover  206  in an intermediate position, according to an exemplary embodiment. In the intermediate position, the cover  206  covers a portion of the vent opening  202  and the filter  204 , while uncovering the remainder of the vent opening  202  and the filter  204 . As shown in  FIG. 3B , a first portion  350  of the adhesive layer  220  is adhered to the drape  106 , blocking airflow to a portion of the vent opening  202  and the filter  204 . A second portion  352  of the adhesive layer  220  is peeled away from the drape  106 , allowing airflow through the vent opening  202  and filter  204  as indicated by flow path  354 . 
     By changing the relative sizes of the first portion  350  and the second portion  352  (i.e., adhering more or less of the adhesive layer  220  to the drape  106 ), the cover is incrementally moveable from the first (sealed) position to the second (unsealed) position to permit a selectively controllable or tunable amount of airflow through the vent opening  202  into the volume  102  and to the trackpad  144  and tube  104 . For example, an amount of airflow may be chosen that optimally minimizes the risk of fluid blockages and buildup while also allowing a negative pressure to be maintained in the volume  112 . Advantageously, the cover  206  is repeatedly moveable through the range of positions corresponding to a range of airflow rates, such that airflow can be repeatedly tuned, or adjusted, for example on a set schedule, in response to an indication of the indicator  208 , to adjust to changing wound conditions as healing occurs, to experiment to find an ideal airflow rate for a particular wound and patient, and to allow the wound assembly  106  to be used with a variety of wounds types, wound sizes, and patients. For example, the cover  206  is repositionable to reseal the vent opening  202  after the fluid buildup or liquid pooling has been substantially eliminated by the increased airflow. As discussed with reference to  FIGS. 4A-D , similar advantages are achievable using multiple covers  206 . 
     Referring now to  FIGS. 4A-D , top views of a variety of possible arrangements of the elements of the wound dressing assembly  200  are shown, according to exemplary embodiments. In general, the present disclosure contemplates any arrangement of one or more trackpads  114 , one or more vent openings  202 , one or more filters  204 , one or more covers  206 , and/or one or more fluid indicators  208  on drapes  106  of various shapes and sizes.  FIGS. 4A-D  illustrate several such arrangements. 
       FIG. 4A  shows the indicator  208  strategically disposed on the drape  106  at a location distal from the track pad  114 . In other words, the indicator  208  is separated from the track pad  114  by a large proportion of distance on the drape  106 . The indicator  208  is positioned and configured to provide a fluid indication proximate an edge of the wound bed  108 . The trackpad  114  is positioned across the wound bed  108  (e.g., along an opposite edge, near an opposing corner), such that the fluid indication provided by the indicator  208  corresponds to fluid buildup in an area of the wound bed  108  far from the trackpad  114 . The cover  206  is located near the indicator  208 , and covers a vent opening  202  and a filter  204 . The cover  206  may be peeled away from the drape  106  to provide airflow to the wound bed  108  proximate the indicator  208 . 
     In  FIG. 4B , the cover  206  is shown according to another embodiment as a cover strip  410 . The cover strip  410  may cover a series of vent openings  202 , a single vent opening  202  that extends under the strip of covers  410 , or a vent opening  202  made up of a pattern of perforations or fenestrations disposed under the strip of covers  410 . The cover strip  410  is shown by way of example to include multiple peelable sheets  412  that are controllably removable in one or more segments to create a desired airflow, in combination with the nature of openings disposed therebeneath (e.g. series of openings, an elongated opening, a plurality of perforations or fenestrations, etc.). The peelable sheets  412  are separated by perforations, such that each peelable sheet  412  is independently movable from a sealed position to an unsealed position to provide airflow to a vent opening  202  or a segment of a vent opening  202  disposed under that peelable sheet  412 . Airflow direction and rates can thus be selectively tuned and customized, e.g. in response to an indication of the presence or absence of fluid in the wound bed from indicator  208 , by unsealing various combinations of the peelable sheets  412  that make up cover strip  410 . 
     In  FIG. 4C , the trackpad  114  is shown by way of example to be centrally located on the drape  106 . Multiple vent openings  202  are each covered by a cover  206 . As shown, four vent openings  202 , each with a corresponding filter  204 , are covered by four peelable polymer covers  206 . The vent openings  202  and the covers  206  are disposed in a pattern on the drape  106  to provide a selectively customizable air flow profile beneath the drape  106  (i.e., in volume  206 ). That is, each of the multiple covers  206  can be moved between a closed position to seal the corresponding vent opening  202  and filter  204 , an open position to unseal the corresponding vent opening  202  and filter  204 , and a range of intermediate positions in between. Multiple indicators  208  are provided to deliver indications of fluid buildup under various locations of the drape  106 , which may be useful in selectively tuning the location nand amount of airflow using selected locations and positions (e.g. open, closed, intermediate open, etc.) of the multiple covers  206 . 
     In  FIG. 4D , the drape  106  is shown by way of example to include dashed lines (or in some embodiments, perforations  440 ). Perforations  440  are intended to allow for customization of the drape in multiple possible shapes and/or sizes, shown as a rectangle  442 , a square  444 , and an oval  446 . Several vent openings  202  and covers  206 , and indicators  208  are positioned on the drape  106  to provide at least one vent opening for each of the possible shapes  442 - 444 . Thus, the drape  106  of  FIG. 4D  provides customizability of drape size and shape as well as airflow. For example, the drape may be separated or cut along any of the dashed lines or perforations for adaptation to a shape of a particular wound bed. 
     Other possible implementations of the wound dressing assembly  200  are possible. For example, in some embodiments a vent assembly is attachable to the drape  106  to selectively position the vent assembly. In such embodiments, the vent assembly includes a flange defining a vent opening, a peelable cover disposed on the flange and incrementally moveable between a sealed position and an unsealed position, and an adhesive layer disposed on the flange for attachment to the drape. The flange may include a projection configured to pierce the drape when the flange is attached to the drape, creating an opening through the drape. One or more of such vent assemblies can be positioned by a user anywhere on the drape  106  to provide the desired selectable airflow. An indicator may be included with the drape  106  as described above, included with the vent assembly, or independently positionable on the drape  106 . 
     According to any exemplary embodiment, a wound dressing for a NPWT system is provided that permits a selectively tunable flow of filtered air through and beneath a drape, in response to an indication of the presence or absence of a fluid buildup in the wound bed. The dressing typically includes a drape, a tube and track pad integrated with the drape and communicating with a negative pressure source, a vent opening (or pattern of vent openings of various shapes and/or sizes) and having a hydrophobic filter disposed in airflow communication therewith, and a fluid indicator coupled to the drape at strategic locations intended to permit a caregiver to assess the location and amount of fluid buildup occurring within the wound bed. The features of the wound dressing permit a controlled airflow through and beneath the drape, in coordination with the capacity of the negative pressure therapy device and the rate (or rate of change of) fluid build-up in the wound bed. A method of selectively tuning an airflow in a negative pressure wound dressing is also disclosed. The method includes at least the steps of observing via one or more indicators the presence or absence of a fluid buildup condition with a wound bed, and establishing a controlled airflow through a drape of the dressing in response to the observation. A method of making a selectively tunable, negative pressure wound therapy dressing is also disclosed. The method includes the steps of providing a drape, coupling one or more fluid indicators to the drape, and providing one or more vent openings that are selectively and/or incrementally openable to establish an airflow in response to an indication from the indicators representative of a fluid buildup. All such variations are intended to be within the scope of this disclosure. 
     Other arrangements and combinations of the elements described herein and shown in the Figures are also contemplated by the present disclosure. The construction and arrangement of the systems and apparatuses as shown in the various exemplary embodiments are illustrative only. Although only a few embodiments have been described in detail in this disclosure, many modifications are possible (e.g., variations in sizes, dimensions, structures, shapes and proportions of the various elements, values of parameters, mounting arrangements, use of materials, colors, orientations, etc.). For example, the position of elements can be reversed or otherwise varied and the nature or number of discrete elements or positions can be altered or varied. Accordingly, all such modifications are intended to be included within the scope of the present disclosure. Other substitutions, modifications, changes, and omissions can be made in the design, operating conditions and arrangement of the exemplary embodiments without departing from the scope of the present disclosure.