Patent Publication Number: US-2013231621-A1

Title: Secondary wound dressings for securing primary dressings and managing fluid from wounds, and methods of using same

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation-in-part under 35 U.S.C. §120 of U.S. patent application Ser. No. 12/788,077, filed May 26, 2010 and entitled “Deformable and Conformable Wound Protecting Apparatus and its Method of application,” which is a continuation of U.S. patent application Ser. No. 11/107,452, filed Apr. 16, 2005 and entitled “Deformable and Conformable Wound Protecting Apparatus and its Method of application,” the entire contents of both of which are incorporated by reference herein. 
     This application is also a continuation-in-part under 35 U.S.C. §120 of U.S. patent application Ser. No. 12/416,826, filed Apr. 1, 2009 and entitled “Systems and Methods for Wound Protection and Exudate Management,” the entire contents of which are incorporated by reference herein. 
    
    
     FIELD OF THE INVENTION 
     This application relates to secondary wound dressings for securing primary dressings, and methods of using same. 
     BACKGROUND OF THE INVENTION 
     Wounds occur when the integrity of any tissue is compromised, affecting one or more layers of skin. Wounds may be caused by an act, surgical procedure, an infectious disease or an underlying condition. Acute wounds may be caused by an initiating event, such as a accident-related injury, surgical procedure or by operation of an infectious disease, and generally take the form of punctures, abrasions, cuts, lacerations, or burns. Chronic wounds are wounds that generally do not heal in orderly stages or in a predictable amount of time, the way many other wounds do; for example, chronic wounds typically do not heal within three months. Chronic wounds may, for example, be due to one or more of ischemia of the vessels supplying the tissue, venous hypertension or compromise of the immune response, such as observed, for example, with venous ulcers, diabetic ulcers and pressure ulcers. Depending on etiology, such as diabetes, venous insufficiency, or cardiovascular failures, acute wounds may become recalcitrant and even chronic. 
     Injurious contacts with foreign objects may be caused from various sources, ranging from brushing of clothing or bed sheets to fresh, uncovered wounds to adherence of wound dressing to the wound. The latter issue, referred to here as the sticking issue, leads to deleterious consequences for the patient. This problem is particularly exacerbated when wounds are left unattended for a substantial period. It is reported that in certain circumstances patients are administered morphine to withstand the pain caused form dressing removal, especially with wounds having a large surface area. Equally important, tearing of skin graft, newly formed cells or scab adhered to dressing disrupts the healing process. 
     The introduction of bacteria from external sources into the wound typically causes inflammation that activates the patient&#39;s immune response, in turn causing white blood cells, including neutrophil granulocytes, to migrate towards the source of inflammation. While they fight pathogens, such neutrophils also release inflammatory cytokines and enzymes that damage cells. In particular, the neutrophils produce an enzyme called myeloperoxidase that in turn is metabolized to produce reactive oxygen species that kill bacteria. Collaterally, such enzymes and reactive oxygen species damage cells in the margin surrounding the wound, referred to as the “periwound region,” thereby inhibiting cell proliferation and wound closure by damaging DNA, lipids, proteins, the extracellular matrix and cytokines that facilitate healing. Because neutrophils remain in chronic wounds for longer than in acute wounds, they contribute to higher levels of inflammation. Moreover, the persisting inflammatory phase in chronic wounds contributes to exudate (fluid that flows from the wound) with high concentrations of matrix metalloproteases (MMPs). Excess MMPs results in degradation of extracellular matrix protein. In addition to damaging the wound, exudate damages the periwound tissue exposed to it as well. In particular, exudate that flows out of the wound and onto periwound region may damage the fragile skin, which is already compromised due to the patients underlying etiology, such as diabetes. Such damage may degrade the periwound skin and cause its breakdown and turn it into a wound. Thus, exudate flow onto the periwound region may cause many complications, including the potential for increasing the size of the wound and prolonging its healing. Such damage to the skin in the periwound region (periwound skin) may make the skin more susceptible to tearing and resultant intense pain as dressings or devices adhered to them are removed. Other complications may include, for example, infection of the periwound region and intense itching. 
     Patients suffering from chronic wounds frequently report experiencing severe and persistent pain associated with such wounds, which may arise from necrosis of and/or nerve damage of the skin and underlying tissue. Treatment for such pain often consists of low dose analgesics, while topical antibiotics and/or debridement, which seeks to remove necrotic tissue from the wound, may be used to control the bacterial load at the wound site. 
     Conventional wound treatment also typically involves covering the wound with a primary dressing to prevent further contamination and infection, to retain moisture, and to absorb exudate. By “primary dressing” it is meant a dressing used to cover the wound, without any intervening dressing between the wound and the primary dressing. While exudate contains biochemical compounds that benefit wound healing as noted above, its excessive amount in wound or its presence in the periwound region facilitates degradation of tissue, and the exudate additionally serves as a growth medium for bacteria. The consistency of exudate varies, depending on the type of wound and the stage of healing. For example, exudate may be watery, extremely viscous, or somewhere in between. Moreover, the sizes of wounds can vary greatly, as can their care. 
     Although a wide variety of primary dressings have been developed, few previously-known wound treatment systems properly manage exudate, e.g., by removing a sufficient amount of exudate from the wound site, while protecting the periwound region from damaging contact with the exudate. Moreover, conventional systems typically do not address the pain created by the wound treatment system, particularly where the wound treatment system continuously contacts the wound. For example, gauze, which is applied directly onto a wound, is capable of absorbing only a limited amount of exudate, and readily transports excess exudate onto the periwound region, causing maceration and damage. Moreover, the gauze typically is in direct contact with the wound and adheres to it, so that normal motion of the patient results in rubbing, itching and discomfort. In addition, removal of the gauze at periodic intervals is painful and frequently disrupts any healing that may have occurred. 
     Some previously-known approaches to wound treatment attempt to reduce adhesion between the wound and the primary dressing by applying additional substances. For example, the wound and dressing may be soaked in saline water to loosen adherence and/or soften any scabs that formed, thus facilitating removal of the dressing. Or, for example, antibiotic ointments such as polymyxin B sulfate or bacitracin can be applied to reduce sticking. However, such methods are not always satisfactory because soaking a particular wound in water or applying ointments may not be practicable or recommended. 
     Some previously-known primary dressings are promoted as being “non-stick” or “non-adherent,” such as TELFA™ and XEROFORM™, and other brands that may be composed of materials such as hydrocolloids, alginates, and hydrofilms. Regardless of the level of adherence of such dressings to the wound, continuous contact between the primary dressing and wound disturbs the fragile wound matrix, and may undermine the growth of blood vessels and epithelial cells in the wound bed. Such disturbance often occurs when the dressing is removed, or simply as a result of the contact between the bandaged area and the patient&#39;s environment. Pain is often concomitant with such disturbances. In addition, previously-known “non-stick” dressings usually do not absorb sufficient amounts of exudate, and thus require frequent monitoring and changing. These drawbacks add to the cost of use and limit the applicability of such previously-known wound treatment systems. 
     Previously-known primary dressings commonly have only a limited ability to manage wound exudate. As noted above, prolonged exposure of otherwise healthy skin to exudate may cause degradation of the periwound region. The moisture of the exudate may cause maceration, which is a softening of the skin that compromises its integrity and makes the skin in the periwound region vulnerable to physical insult and infection. 
     Some previously-known primary dressings attempt to manage exudate to address the foregoing issues, but provide either limited benefit and/or at a much higher perceived cost. For example, a foam dressing such as ALLEVYN® (marketed by Smith &amp; Nephew, Largo, Fla., USA) is designed to absorb large amounts of exudate. However, use of this product is restricted to highly exuding wounds, because its highly absorptive properties can result in desiccation of wounds that are not highly exuding, thereby impeding healing. In addition, because foam used in that product cannot be conformed to the size and shape of the wound, the dressing typically overlaps with the periwound region. Consequently, exudate absorbed by the foam is transported throughout the foam and onto the periwound region, where prolonged exposure leads to maceration and degradation of the periwound region. Other previously-known dressings, such as ACQUACEL® hydrofiber dressing (available from ConvaTec, Inc., Princeton, N.J., USA) contact the wound bed, and are intended to absorb exudate and transfer and sequester the exudate in a layer disposed atop the wound. This and similar previously-known dressings do not entirely contain or absorb exudate. Moreover, like foam and other previously-known dressings, hydrofiber dressings essentially plug the wound surface, and create an osmotic environment in which the fluidic osmotic pressure within the wound bed approximates that of the surrounding tissue. Consequently, exudate is not sufficiently drawn from the wound, and its buildup in the wound may adversely affect the wound and periwound region. Furthermore, ALLEVYN®, ACQUACEL®, and similar previously-known primary dressings do not provide an adequate moisture vapor transfer rate (MVTR) away from the wound environment, thus creating the potential for an over-hydrated environment that hinders wound healing. 
     Other previously-known wound treatment systems, such as the V.A.C.® system, available from Kinetic Concepts, Inc. (San Antonio, Tex., USA), employ a mechanically operated contact-based dressing that continuously vacuums exudate from the wound bed. It and other dressings incorporating the concept of Negative Pressure Wound Therapy have proven particularly useful in healing large wounds, such as surgical wounds. However, such systems are costly, difficult to apply and time consuming. In addition, because such systems require insertion of a sponge (for the V.A.C.® system) or gauze (as commercialized by other wound care companies) directly into the wound bed, they likely cause considerable pain and discomfort for the patient, and may not be appropriate for many types of wounds. 
     Several previously-known primary dressings also have been developed that are promoted as “non-contact” dressings, which seek to prevent adhesion of the wound tissue to dressing, or to facilitate certain treatments that by their nature cannot contact the wound, e.g., thermal therapy. Such dressings are commonly formed as an inverted cup or a raised bandage that covers the wound without contacting it. Such previously-known primary dressings, however, also have failed to adequately heal wounds and protect the periwound region. Such non-contact dressings are provided in pre-formed shapes and sizes, and have limited deformability, thus limiting their ability to prevent exposure of the periwound skin to exudate. Additionally, the limited deformability of such previously-known dressings makes application of such dressings difficult or impossible to wounds on small surfaces or in areas with complex topology, such as the ankle or foot. Previously-known non-contact primary dressings also do not allow the pressure applied to the periwound region to be readily managed, and may result in the formation of pressure rings around the wound, thereby inducing ischemia in the wound and surrounding tissue. Finally, such previously-known primary dressings do not provide any mechanism to stimulate the flow of exudate, nor do they sequester exudate away from the wound in any appreciable volume. Such previously-known primary dressings also trap humidity over the wound and periwound region, leading to maceration, periwound degradation and impeded healing. 
     In some circumstances, secondary dressings are used to secure primary dressings over a wound. However, it may not always be practicable or safe to secure a primary dressing using a previously-known secondary dressing, such as an ACE™ elastic bandage (3M). For example, using such a bandage to secure a primary dressing over an upper body wound may involve wrapping the bandage around the entire torso, which may undesirably compress internal organs, may be uncomfortable, and also may be inconvenient to place and remove on a frequent basis. Other body parts over which it may be difficult to secure primary dressings include joints that undergo a relatively large range of motion during normal use. 
     SUMMARY OF THE INVENTION 
     The present invention provides secondary wound dressings for securing primary dressings and managing fluid from wounds, and methods of using same. The secondary dressings include a fabric layer that is larger than the primary dressing, and a biocompatible adhesive layer disposed along the periphery of the fabric layer. The biocompatible adhesive layer may be secured to the skin about the primary dressing, which brings the fabric layer into contact with the primary dressing. The height difference between the primary dressing and the skin imposes a tension on the fabric, which causes the fabric to apply pressure to the primary dressing. The magnitude of the pressure can be selected appropriately based on the type of wound and the type of primary dressing. Such a feature is particularly useful when the primary dressing is to be secured onto a part of the body where previously-known types of secondary dressings cannot be placed conveniently or safely, such as on the upper body, or on a joint. The secondary dressings also are highly breathable, allowing fluid from the wound that may be absorbed by the primary dressing to evaporate into the air. 
     In some embodiments, the secondary dressings of the present invention may be used in conjunction with primary dressings that manage exudate and cushion wounds from external pressure sources. The primary and secondary dressings may be used individually, or in conjunction with one another, for a wide range of chronic and/or acute wounds, including venous ulcers, pressure ulcers, and surgical wounds. In addition, dressings constructed in accordance with the present invention may be advantageously used for surgical wounds to protect the incision site, particularly for surgical areas where skin is most vulnerable, such as split-thickness graft sites and cosmetic surgeries, as well as for regions of the skin that are compromised but not necessarily wounded. 
     Primary and/or secondary dressings constructed in accordance with the present invention also may advantageously be used to treat acute wounds and to protect the wound from further trauma, such as occurs in industrial accidents and in the battle field settings. In particular, dressings in accordance with the present invention may be applied to reduce contact pressure on the wound bed. In a battlefield setting, for example, this aspect of the invention may be particularly valuable, since a bandaged wound may still have debris or shrapnel in it, and the primary and/or secondary dressings can be applied to prevent such contaminants from being pushed further into the wound during evacuation of the wounded subject. 
     According to one aspect of the present invention, an apparatus for protecting a region of compromised skin includes a primary dressing configured for application over the region of compromised skin, the primary dressing including fluid-absorbing material; and a secondary dressing configured for application over the primary dressing. The secondary dressing is configured to apply pressure to the primary dressing so as to maintain the primary dressing in place over the region of compromised skin and so as to promote the flow of fluid from the region of compromised skin into the fluid-absorbing material, and is further configured to allow moisture in the fluid to evaporate from the fluid-absorbing material. 
     In some embodiments, the secondary dressing includes a fabric layer and a biocompatible adhesive layer, the adhesive layer disposed along a periphery of the fabric layer and configured to secure the fabric layer over the primary dressing. The secondary dressing may further include a foam layer disposed between the fabric layer and the biocompatible adhesive layer, the foam layer having an aperture therein, the aperture being larger than the primary dressing. The fabric layer may include a woven fabric or a nonwoven fabric. In some embodiments, the fabric layer has a machine direction and a cross direction, and wherein an elasticity of the fabric layer is different in the machine direction than an elasticity of the fabric layer in the cross direction. The pressure applied by the secondary dressing on the primary dressing may be based on an orientation of the machine and cross directions of the fabric layer. 
     In some embodiments, the primary dressing includes a strip of the exudate-absorbing material, the strip having first and second ends, a lower surface, an upper surface, and a length, the upper and lower surfaces being parallel to one another along the length. The strip may be adapted to flex along its length to circumscribe the region of compromised skin. The primary dressing may further include an adhesive disposed on the lower surface of the strip, the adhesive securing the strip adjacent the region of compromised skin. 
     In some embodiments, the primary dressing further includes a support cushion configured to surround the region of compromised skin and the exudate-absorbing material. The primary dressing may further include a biocompatible adhesive configured to secure the support cushion around region of compromised skin and the exudate-absorbing material. 
     The primary dressing may further include a reservoir configured to be suspended over and in engagement with the exudate-absorbing material so that the material transfers exudate from the region of compromised skin to the reservoir. The primary dressing may further include a cover configured to be positioned over the reservoir, the secondary dressing being in contact with the cover. 
     The secondary dressing may have a moisture vapor transfer rate (MVTR) that is greater than an MVTR of the primary dressing. 
     Under another aspect of the present invention, a dressing for protecting a region of compromised skin includes a fabric layer sized to cover the region of compromised skin; a foam layer secured to the fabric layer and having an aperture defined therein, the aperture being sized to cover the region of compromised skin; and a biocompatible adhesive layer disposed on the foam layer. 
     In some embodiments, the foam layer extends to a periphery of the fabric layer. The foam layer may be hydrophobic. The foam layer optionally includes slits for breathability. The foam layer optionally includes perforations enabling adjustability of the dressing&#39;s size and/or the tension that the foam layer applies to the fabric layer. 
     The fabric layer may include a woven fabric or a nonwoven fabric. The fabric layer may have a machine direction and a cross direction, and an elasticity of the fabric layer may be different in the machine direction than an elasticity of the fabric layer in the cross direction. 
     Under another aspect of the present invention, a method for protecting a region of compromised skin includes applying a primary dressing over a region of compromised skin, the primary dressing including fluid-absorbing material; applying a secondary dressing over the primary dressing, the secondary dressing configured to apply pressure to the primary dressing so as to maintain the primary dressing in place over the region of compromised skin and so as to promote the flow of fluid from the region of compromised skin into the fluid-absorbing material, the secondary dressing further configured to allow moisture in the fluid to evaporate from the fluid-absorbing material. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS. 1A and 1B  and are an exploded view and a cross-sectional view, respectively, of an exemplary primary dressing, while  FIG. 1C  is a partial sectional view illustrating transfer of exudate from the wound to the reservoir via the wicking strip of the primary dressing of  FIGS. 1A and 1B . 
         FIG. 2  illustrates steps in accordance with one method of managing exudate with a primary dressing. 
         FIG. 3  illustrates a perspective view of an illustrative application of a primary dressing of  FIGS. 1A-1C  to a patient. 
         FIG. 4  schematically illustrates a plan view of one preferred embodiment of a support cushion and wicking strip suitable for use in a primary dressing. 
         FIGS. 5A-5C  illustrate alternative embodiments of a wicking strip suitable for use in a primary dressing. 
         FIGS. 6A-6B  illustrate further alternative embodiments of a wicking strip suitable for use in a primary dressing. 
         FIG. 7  schematically illustrates a plan view of a reservoir, cover, and optional vent according to some embodiments of a primary dressing. 
         FIG. 8  is a plan view of an alternative embodiment of a support cushion and wicking strip suitable for use in a primary dressing. 
         FIG. 9  is a plan view of another alternative embodiment of a support cushion and wicking strip suitable for use in a primary dressing. 
         FIG. 10  is a perspective view of an embodiment of a primary dressing that includes a lavage system, in which the wicking strip has been omitted for improved clarity. 
         FIG. 11  is a perspective view of an embodiment of a primary dressing that includes a manually-operated bellows for applying a negative pressure within the dressing. 
         FIGS. 12A and 12B  respectively are an exploded view, and a partial sectional view, of another embodiment of a primary dressing. 
         FIGS. 13A and 13B  respectively are a plan view, and a perspective view, of an alternative embodiment of a cover and reservoir suitable for use in a primary dressing. 
         FIG. 14  schematically illustrates a plan view of a kit containing a primary dressing. 
         FIGS. 15A-15B  respectively illustrate plan and cross-sectional views of a secondary dressing, according to some embodiments of the present invention. 
         FIG. 15C  illustrates the use of the secondary dressing of  FIGS. 15A-15B  with the primary dressing of  FIGS. 1A-1C , according to some embodiments of the present invention. 
         FIG. 16  illustrates steps in accordance with one method of securing a primary dressing and managing fluid from a wound with a secondary dressing. 
         FIG. 17  is a plan view of an alternative secondary dressing, according to some embodiments of the present invention. 
         FIG. 18  is a cross-sectional view of another alternative secondary dressing, according to some embodiments of the present invention. 
         FIG. 19  is a cross-sectional view of another alternative secondary dressing, according to some embodiments of the present invention. 
         FIGS. 20A-20B  respectively illustrate plan and cross-sectional views of yet another alternative secondary dressing, according to some embodiments of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention provides secondary wound dressings for protecting and promoting wound healing by securing primary dressings over a wound, and managing fluids that may be released by the wound. In some embodiments, the secondary wound dressings include a fabric layer, a foam surround, and a biocompatible adhesive layer. The fabric layer includes a lightweight material that, in some embodiments, has a moisture vapor transmission rate (MVTR) that is at least as great as the MVTR of the primary dressing over which it is applied. As such, the fabric layer allows for the ready evaporation of any fluids from the wound that may have been captured by the primary dressing, as described in greater detail below. The foam surround includes upper and lower surfaces and a central aperture that is at least as large as the primary dressing. The upper surface of the foam surround is suitably secured to the fabric layer, and the biocompatible adhesive layer is disposed on the lower surface of the foam surround. During use, the central aperture of the foam surround is approximately centered over the primary dressing, which has already been placed over the wound. The foam surround is then secured around the primary dressing by pressing the biocompatible adhesive layer against the patient&#39;s epidermis around the primary dressing, which brings the fabric layer into contact with the primary dressing. When the secondary dressing is secured to the patient&#39;s epidermis via the biocompatible adhesive layer, the height difference between the primary dressing and the foam surround applies tension to the fabric, which in turn applies a gentle compressive force to the primary dressing. The magnitude of this compressive force may be adjusted by preselecting the elasticity of the fabric layer, as described in greater detail below. As such, the secondary dressing allows primary dressings readily to be secured with a desired pressure over any desired body part, including the upper body, where previously-known secondary dressings typically cannot be used safely or conveniently. 
     In some embodiments, the primary wound dressing is selected to allow the wound to remain moist, while at the same time may transfer excess fluid, such as exudate, away from the wound and periwound region to a separately located reservoir that is elevated above the wound. In this manner, neither the wound nor the periwound region come into prolonged contact with excess fluid, such as exudate, and thus both may be protected from maceration or bacterial action that degrades tissue and skin. The secondary dressing may facilitate the evaporation of fluid from the reservoir, further reducing the risk of maceration. Such an arrangement may further promote wound healing by reducing the disruption of the wound bed (and pain) caused by periodic replacement of previously-known primary dressings, such as gauze, which adhere to the wound bed. Both the primary and secondary dressings also may allow the flow of exudate from the wound to be managed by manipulating the amount and profile of pressure applied to the periwound skin, which also is expected to enhance the rate of healing of the wound. 
     First, exemplary embodiments of primary dressings that may be used with the secondary dressings will be described, as well as a method of applying and using the primary dressings. Further details on the individual components employed in the primary dressings, and alternative embodiments and methods, will then be described. Then, exemplary embodiments of secondary dressings will be described, as well as a method of applying and using the secondary dressings with a variety of primary dressings, including the primary dressings described herein. Alternative embodiments of secondary dressings will then be described. 
     Overview of Illustrative Primary Dressing 
       FIGS. 1A and 1B  illustrate an exemplary embodiment of a primary wound dressing  10  that may be used in conjunction with the secondary wound dressings described in greater detail below. In this exemplary embodiment, primary dressing  10  comprises three discrete components that are assembled and applied by the patient, nurse, clinician or other caregiver over wound W on patient&#39;s epidermis E. In particular, primary dressing  10  includes support cushion  20 , wicking strip  30 , and reservoir  40 , preferably pre-attached to cover  50 . Preferably, components  20 ,  30 ,  40  and  50  of dressing  10  are sized for use with one another and are enclosed in a sterile package with suitable instructions to enable the patient or caregiver to quickly and accurately apply the dressing. Alternatively, because for some embodiments certain components of primary dressing  10 , such as wicking strip  30  and/or reservoir  40 , may be replaced on a frequent basis than other portions of the primary, such components may be individually packaged. 
     Support cushion  20  preferably comprises a closed-cell polyolefin foam and is designed to surround wound W and periwound region P, i.e., the region of epidermis E extending from the wound margin, to protect the wound and elevate reservoir  40  and cover  50  above the wound bed. In the illustrated embodiment, support cushion  20  has a stepped profile, including sidewall  21  and flange  22 . The upper surface of flange  22  forms ledge  23  that supports reservoir  40 , as depicted in  FIG. 1B . Lower surface  24  of support cushion  20  includes layer  25  of biocompatible adhesive, which preferably is hydrophobic and breathable, and inhibits exudate from leaking onto periwound region P. Upper surface  26  of support cushion includes layer  27  of adhesive or a portion of a reusable fastening system, e.g., the pile of a hook and pile fastening system, such as Velcro. Use of a non-permanent adhesive for layer  27  permits the cover to be removed to periodically replace wicking strip  30  and/or reservoir  40 , as described below. In addition, support cushion  20  preferably includes slits or perforations  28  that extend through the heights of sidewall  21  and flange  22  to facilitate moisture vapor transfer, e.g., the escape of perspiration from beneath support cushion  20 , when the cushion is fastened by adhesive layer  25  to epidermis E. Support cushion  20  includes opening  29  that exposes a portion of the periwound region P extending away from the margin of wound W, to permit placement of wicking strip  30 , as depicted in  FIG. 1B . 
     Wicking strip  30 , which preferably comprises an open-cell polyurethane foam, overlays periwound region P between the margin of wound W and flange  22  of support cushion  20 . In the embodiment of  FIGS. 1A-1B , wicking strip  30  is depicted as a curved strip of foam, although it takes other forms as described herein for alternative embodiments. Wicking strip  30  preferably includes layer  31  of biocompatible adhesive, which preferably is hydrophobic and breathable, and inhibits contact between exudate and the periwound region P, on lower surface  32 . During application, wicking strip  30  may be rolled to a tighter spiral than depicted in  FIG. 1A , such that it fits snugly within opening  29  of support cushion  20  and the innermost edge of the wicking strip overlaps the margin of the wound by 1-2 mm. Note, however, that wicking strip  30  need not necessarily overlap the margin of the wound. For example, the inner edge of wicking strip  30  may be substantially even with the margin of the wound, or the inner edge of wicking strip may be spaced apart from the margin of the wound, e.g., 1-2 mm away from the margin of the wound, leaving a small region of the periwound skin uncovered by the wicking strip. For the embodiment of  FIG. 1A , wicking strip  30  may be cut with a scissor to ensure that the foam is not overly compressed when adhered to the periwound region by layer  31 . In a preferred embodiment, establishing snug contact between the outermost edge of wicking strip  30  and the inner-facing surface of flange  22  ensures that exudate does not leak onto an exposed portion of the periwound region between wicking strip  30  and support cushion  20 . Alternatively, outer-facing surface  32  of wicking strip  30  may employ a hydrophobic film or coating that prevents exudate from seeping into the periwound region. 
     Still referring to  FIGS. 1A-1B , reservoir  40  preferably comprises a sandwich of different density open cell polyurethane foams  41  and  42  joined to mesh  43 , in which the foams  41  and  42  are selected to absorb exudate from wicking strip  30  and to sequester the exudate away from the wound bed. In the embodiment depicted in  FIGS. 1A-1B , reservoir  40  is fastened to the underside of cover  50 , and is sized so that the outer edges of the reservoir are supported on ledge  23  of support cushion  20 , while the more central regions of the reservoir engage the upper surface of wicking strip  30 . Preferably, reservoir  40  fits within sidewall  21  of support cushion  20 , so that exudate drawn into the reservoir from wicking strip  30  cannot seep out of the lateral face of the reservoir. As shown in  FIG. 1B , flange  22  suspends reservoir  40  over wound W, thus inhibiting contact between reservoir  40  and wound W and limiting the extent to which force applied to cover  50  and reservoir  40  is transmitted to wicking strip  30 . Wicking strip  30  may additionally support reservoir  40  over wound W. Optionally, a layer of adhesive may be disposed on the lower surface of the reservoir  40  that engages ledge  23  of the support cushion to removably secure those components together. Reservoir  40  preferably includes one or more vents  44  that assist in modulating the humidity within the dressing through cover  50 . 
     Cover  50 , preferably a breathable material, overlays reservoir  40 . Layer  51  of adhesive preferably is used to removably secure reservoir  40  to cover  50 . Alternatively, reservoir  40  may be removably fastened to cover  50  using a removable fastening system, such as hook and pile arrangement. In addition, layer  27  of adhesive, or a removable fastening system, is used to secure cover  50  to the upper surface of sidewall  21  of support cushion  20 , so that cover  50  and/or reservoir  40  may be periodically removed from dressing  10  to inspect the wound, to apply topical medications or other substances to the wound, e.g., moisturizing ointments, growth factors, nutrients, and/or antibiotics, or to replace wicking strip  30  or reservoir  40 . In other embodiments, cover  50  and/or reservoir  40  are left in place over the wound while dressing  10  is applied to the patient. 
     As described in greater detail below, the components of primary dressing  10  may each be provided with one or more non-stick liners to facilitate handling of the different components of the system, e.g., while placing support cushion  20  on epidermis E. The liners may be removed as appropriate to expose the adhesive layers and secure components to epidermis E or to each other. 
     Referring now to  FIGS. 1B and 1C , during use of primary dressing  10 , exudate EX flows out of wound W at a flow rate that depends on many factors, including the pressure with which wicking strip  30  is pressed against the periwound region, the lateral profile of wicking strip  30  (described in greater detail below with reference to  FIGS. 5A-5C ), the characteristics of wound W, and the consistency of the exudate. As exudate EX is released from the wound, some of the exudate pools on top of wound W. As discussed above, such accumulation of excess exudate with high concentrations of MMPs leads to degradation of extracellular matrix protein both in the wound and on periwound skin. However, excess exudate may flow from the wound, or gravity and/or patient movement may displace exudate from the wound bed so that it contacts and is absorbed by wicking strip  30 . 
     As depicted in  FIG. 1C  (from which cover  50  has been omitted for clarity), wicking strip  30  transports exudate EX laterally (in the plane of epidermis E) and then vertically (perpendicular to the plane of epidermis E) to reservoir  40 . Specifically, the exudate travels along a gradient from relatively wet regions to relative dry regions of the wicking strip via capillary action. Exudate transported laterally may eventually reach the inner surface of flange  22  of support cushion  20 . Because support cushion  20  is formed of a hydrophobic material, it inhibits further lateral transport of the exudate. Instead, exudate preferably is transported vertically from wicking strip  30  and into reservoir  40 , which sequesters exudate away from the wound. In accordance with one aspect of the invention, reservoir  40  preferably has a large absorptive surface area and the capacity to hold large amounts of exudate, e.g., sufficient capacity so that reservoir  40  need only be replaced once every few days (for example, every 7-10 days). Reservoir  40  is also breathable, so that it releases water in the exudate in the form of vapor V into the atmosphere via breathable cover  50 . Additionally, ledge  23 , upon which reservoir  40  rests, and sidewall  21 , adjacent to reservoir  40 , are hydrophobic and cannot transfer exudate from reservoir  40  onto the periwound region. Further, adhesive layers  25  and  31  are hydrophobic and further inhibit contact between exudate and the periwound region P. Accordingly, multiple features of dressing  10  are configured to inhibit prolonged contact between the exudate and periwound region, and thus to inhibit maceration or other degradation of the periwound region, as observed with previously-known dressings. 
     Multiple features of primary dressing  10  both enhance the healing of wound W and protect periwound region P from maceration and degradation. Among other things, although reservoir  40  is arranged to protect the wound from the environment and absorb exudate, it is suspended over and thus is not in continuous contact with the wound. This feature may both reduce any pain experienced by the patient and promote healing. For example, initially placing reservoir  40  (and the other components of primary dressing  10 ) does not require touching the wound bed itself, resulting in significantly less pain than, for example, than the V.A.C.® or systems similar to it described above that rely on inserting a sponge or gauze directly into the wound. Wicking strip  30  and/or reservoir  40  also may readily be removed without disrupting re-epithelialization of the wound. Moreover, because reservoir  40  sequesters the exudate, when reservoir  40  is removed to observe the wound, exudate does not flow onto the adhesive used to secure cover  50  to support cushion  20 . This arrangement allows wicking strip  30  and/or reservoir  40  to be replaced and for cover  50  to be re-secured to support cushion  20 , without having to replace the entire dressing. By contrast, removing previously known dressings (which contact the wound) often disrupts re-epithelialization and allow exudate to flow onto the adhesive, requiring the entire dressing to be discarded and a new one applied. 
     It is noted that although reservoir  40  is designed to be suspended over, rather than in contact with the wound, occasions may arise where the reservoir will contact the wound. For example, if sufficient pressure is applied directly onto cover  50  and reservoir  40 , the reservoir may deflect sufficiently to contact the wound for as long as that pressure is applied. Such temporary contact is not believed to significantly impede the healing of the wound, and the durometer and resiliency of support cushion  20  preferably is selected to provide adequate support for cover  50  and reservoir  40  in the expected range of applications. 
     Primary dressing  10  also encourages the flow of exudate from the wound, and thus reduces the bacterial load of the exudate in contact with the wound bed. Without wishing to be limited by theory, the inventors believe that the flow of exudate from the wound may stimulate healing. First, primary dressing  10  encourages exudate flow by continuously wicking exudate out of the wound, thereby providing a lower osmotic pressure at the wound than in the surrounding tissue. This osmotic pressure differential encourages exudate to flow from the surrounding tissue into the wound to attempt to equalize the osmotic pressure. In contrast, conventional dressings that directly contact the wound typically do not generate an osmotic pressure differential. In addition, because primary dressing  10  absorbs exudate from the wound and promotes replenishment of exudate, the bacterial load of the exudate in contact with the wound bed remains relatively low. Primary dressing  10  also is configured to allow a variety of different types of pressure to be applied to the periwound region, depending on the type of wound, as described in greater detail below with respect to  FIGS. 5A-5C . 
     Additionally, primary dressing  10  is well-suited for use in treating pressure sores that may be acquired by patients whose skin may be damaged by, for example, continuously lying in bed without sufficient movement. Such pressure sores may occur where skin is thin, has reduced integrity, and/or where bone and skin are close together, without sufficient intervening muscle or fat. Support cushion  20  rests on regions of epidermis E that surround the wound, thus protecting the wound from the type of pressure that initially caused the wound. Support cushion  20  may be formed of a supple, easily bendable material that does not create a pressure ring around the wound. In some embodiments, support cushion  20  is formed of a polyolefin that distributes pressure, inhibiting that pressure from concentrating in one region. 
     Overview of Method of Using Primary Dressing 
       FIG. 2  illustrates steps in a method  60  of using primary dressing  10  for managing exudate from a wound, according to some embodiments of the invention. Typically, the method is implemented by a physician, nurse, or other caregiver. However, the method is relatively simple to employ, and the patient himself may apply primary dressing  10 . 
     First, at step  61 , the caregiver obtains support cushion  20 , wicking strip  30 , reservoir  40 , and cover  50 , e.g., a kit as described below with respect to  FIG. 7 . Next, in step  62 , support cushion  20  is applied to the epidermis of a patient, so that the support cushion surrounds the wound and periwound region. For example, a non-stick liner covering lower surface  24  of support cushion  20  may be removed to expose the adhesive on its lower surface. The support cushion then is roughly centered around the wound, and pressed onto the patient&#39;s epidermis using gentle manual pressure. A non-stick liner covering layer  27  on the upper surface of support cushion  20  may be left in place until a later step, described below. 
     At step  63 , wicking strip  30  is applied within the periwound region between the margin of the wound and support cushion  20 . For example, wicking strip  30  will include a non-stick liner covering layer  31 , and this liner will be removed to expose the adhesive. A first end of wicking strip  30  then is applied and adhered to a first portion of the periwound region, e.g., just overlapping the margin of the wound. The free end of the wicking strip then is spiraled around the wound, with subsequent portions of wicking strip  30  adhered to adjacent portions of the periwound region, for example, as illustrated in  FIG. 4 , until the entirety of the periwound region exposed within opening  29  of the support cushion is filled. Preferably, wicking strip  30  fills substantially the entire periwound region between the wound and support cushion  20 , to prevent seepage of exudate from the outermost lateral face of the wicking strip. In some circumstances, the wound may be sufficiently large that the entire wicking strip  30  is not needed to fill the periwound region between the wound and support cushion  20 , in which case wicking strip  30  may be cut to the appropriate length. The wound may have a relatively irregular shape, and simply spiraling wicking strip  30  around the wound will adequately fill the entire periwound region. Alternatively, wicking strip  30  may be cut into multiple pieces of appropriate lengths, which are individually adhered to the periwound region as appropriate. 
     At step  64 , reservoir  40  and cover  50  (which is preferably pre-adhered to reservoir  40 ) then are applied over wicking strip  30 . For example, the non-stick liner may be removed from layer  27  disposed on the upper surface of side wall  21 , and reservoir  40  inserted into support cushion  20  so that the exposed adhesive on support cushion  20  adheres to cover  50 , as illustrated in  FIG. 1B . 
     At step  65 , compression wrap  70  optionally is wrapped over primary dressing  10  to apply a desired pressure onto the dressing and wound, e.g., as illustrated in  FIG. 3 . For example, as discussed above, the amount of applied pressure may affect the flow of exudate and the rate of healing of the wound, so the physician may elect to compress primary dressing  10 . The appropriate amount of pressure and wrap type may differ from wound to wound, and may be selected based on the physician&#39;s knowledge and experience with particular wound types. Elastic compression wraps such as PROFORE® (Smith &amp; Nephew, Largo, Fla., USA) may suitably be used. 
     For example, if using an elastic compression wrap to compress primary dressing  10  against a venous leg ulcer, the wrap may be stretched beyond a specified proportion of its native length, and then secured in that stretched configuration. The physician optionally may apply other wraps on dressing  10 , such as gauze or Unna Boot or both. Such intervening layers of material also may be applied with compression, as appropriate. 
     Some wound sites located on broad surfaces, such as the torso, may not easily be wrapped with a compression wrap. In such circumstances, or in any other appropriate circumstance, a secondary dressing provided by the present invention may be used in place of the elastic compression wrap to secure and/or compress the primary dressing, as described in greater detail below. Alternatively, or additionally, the differential heights between the support cushion, reservoir and wicking strip of primary dressing  10  may be adjusted to provide sufficient pressure to stimulate the flow of exudate. For example, as described herein after with respect to the embodiment of  FIGS. 5A to 5C , a wicking strip having a variable height may be employed with the dressing of the present invention. Depending upon how the wicking strip is applied surrounding the wound, the dressing and compression wrap, if present, may be adjusted to provider either greater or lesser pressure on the tissue surrounding the wound, or to provide a uniform pressure at the wound site in view of complex limb topology. 
     Optionally, a medication or other substance may be applied to the wound or periwound region during any appropriate step in method  60 . For example, the wound and periwound region may be cleaned, dried, and/or debrided or moisturized before applying support cushion  20  to the epidermis. Or, for example, a wound dressing such as PROMOGRAN PRISMA™ collagen and silver dressing (available from Systagenix Wound Management, London, UK), or Dermagraft® (available from Advanced BioHealing, La Jolla, Calif., USA), or Apligraf® (available from Organogenesis, Inc., Canton, Mass., USA), and other similar collagen or biological dressings, may be applied to the wound after applying wicking strip  30 , but before applying reservoir  40  and cover  50 . Other substances may be used, such as time-release topical medicines. 
     Further details of the construction of the individual components of primary dressing  10 , and alternative embodiments, are now provided. 
     Support Cushion  20   
     Referring to  FIG. 4 , support cushion  20  and wicking strip  30  of primary dressing  10  are further described. Support cushion  20  includes sidewall  21  and flange  22 , which forms ledge  23 . Each of sidewall  21  and flange  22  includes plurality of slits  28  that enhances its breathability and flexibility. In particular, slits  28  may be arranged in radial or circumferential directions, or with another preferred orientation to improve conformability of the support cushion to the anatomy of a specific limb. Support cushion  20  preferably is secured to patient&#39;s epidermis using a biocompatible adhesive layer, which is preferably hydrophobic but breathable, and additionally or alternatively may be secured using a compression wrap, gauze, ACE™ bandage, or Unna boot that overlays the dressing, or a secondary dressing of the present invention, such as illustrated in  FIGS. 15A-20 . 
     In some embodiments, support cushion  20  is of unitary construction, with sidewall  21  and flange  22  being formed from different portions of the same piece of material. Alternatively, sidewall  21  and flange  22  may be individually constructed and then heat-fused or adhesively bonded together, thus allowing the materials, thicknesses, and other characteristics of sidewall  21  and flange  22  to be selected and tailored for specific applications. For example, it may be preferable to form sidewall  21  using a relatively thick layer of a large-cell hydrophobic material and flange  22  using a relatively thin layer of a small-cell hydrophobic material. Such a combination of materials and thicknesses imparts support cushion  20  with sufficient flexibility to be conformable to substantially any body part, e.g., an arm, leg, neck, or torso, while maintaining a sufficient level of hydrophobicity to prevent exudate from leaking onto the periwound region. Examples of suitable hydrophobic materials for use in support cushion  20  include polyolefin, foams, and silicone-based materials, in open cell or closed cell forms. Any suitable adhesive or bonding procedure can be used to adhere sidewall  21  to flange  22 . 
     As mentioned above, slits  28  may enhance the flexibility and breathability of support cushion  20 , e.g., to allow support cushion  20  to more readily conform to various body parts and to allow humidity in the regions of the epidermis underlying support cushion  20  to escape, thus reducing maceration. Slits  28  may be simple “cuts” that extend through support cushion  20 , e.g., through sidewall  21  and flange  22 , without removing material. Alternatively, slits  28  may be apertures formed by removing material from sidewall  21  and/or flange  22 . Slits  28  may be formed in any appropriate size, shape, density, or pattern. For example, slits  28  may extend in a single direction, as illustrated in  FIG. 4 , may extend radially (perpendicular to curvature of support cushion  20 ), may extend parallel to the curvature of support cushion  20 , or may extend at an angle relative to the curvature of support cushion  20 . Some slits  28  may extend at different angles than other slits  28 . 
     Alternatively, support cushion  20  of the present invention may include a spacer fabric, such as the polyester/nylon spacer fabric designated style DNB69, available from Apex Mills, Inward, N.Y., USA. Such materials are hydrophobic, but include an open weave that is highly breathable, thereby permitting moisture to readily evaporate from the patient&#39;s skin during prolonged use, while preventing maceration. 
     In the embodiment illustrated in  FIG. 4 , support cushion  20  is pre-formed in a generally oval shape, and is suitable for use with wounds up to a fixed size, e.g., up to 30 mm in length. However, support cushion  20  also may be formed in any other appropriate shape and size and may be provided having a range of size of openings  29  in flange  22 . For example, support cushion  20  may be pre-formed in a generally circular, rectangular, triangular, or other polyhedral shape, optionally having rounded corners, or may even be pre-formed in an irregular shape. Alternatively, support cushion  20  may be formed as a strip that may be applied around the wound and periwound region. The strip may be of predetermined length, or may even be provided on a roll and cut to a desired length. In such embodiments, it may be convenient to apply support cushion  20  to the epidermis after wicking strip  30  is applied around the wound. 
     To accommodate such free-form embodiments of the support cushion, it may be desirable for reservoir  40  and cover  50  to have a basket-like configuration, such as described in detail below with respect to  FIGS. 13A-13B . 
     In still other embodiments (not illustrated), support cushion  20  may be an annular structure filled with a fluid, e.g., air or water, a gel, an expanded plastic, or fibers. Such structure may be formed of molded plastic, welded polymer, or a laminate. 
     Note that ledge  23  need not necessarily be included in all embodiments of support cushion  20 . For example, in embodiments omitting ledge  23 , the lower surface of reservoir  40  directly contacts the upper surface of wicking strip  30 , which suspends reservoir  40  over wound W. 
     Wicking Strip  30   
     In the embodiment illustrated in  FIG. 4 , wicking strip  30  of primary dressing  10  is an elongated strip of hydrophilic material spiraled around wound W in the space between the wound and the inner surface of flange  22 . Preferably, wicking strip  30  is sufficiently flexible that it may be applied in any desired pattern to the epidermis, e.g., that it may be packed so as to fill substantially the entire space between the wound and the innermost surface of defining opening  29  of support cushion  20 . One example of a suitable hydrophilic, flexible material for use in wicking strip  30  is an open-cell foam such as hydrophilic polyurethane. Alternatively, wicking strip  30  may include any suitable absorbent structure, e.g., a woven fabric, a nonwoven fabric, a hydrogel (which may include modified starch), or a pouch filled with a polymeric absorbent material. Layer  31  of biocompatible adhesive is disposed on the lower surface of wicking strip  30 , and may be hydrophobic so as to inhibit contact between exudate absorbed by wicking strip  30  and the periwound region P. 
     In the embodiment of  FIGS. 1A-1B , wicking strip  30  is depicted as having the same height as flange  22  of support cushion  20 . However, wicking strip  30  may actually have a different height than flange  22 , but reservoir  40  may compress the two components to the same height during use. For example, wicking strip  30  may be thicker or thinner (taller or shorter, respectively) than flange  22 , and may have a different compliance. In one embodiment, wicking strip  30  is thicker than flange  22 , but is more easily compressed, allowing both components to be compressed to the same thickness by reservoir  40  during use. 
     Likewise, wicking strip  30  may have a variable width along its length, as depicted in  FIG. 1A . In other embodiments, such as that depicted in  FIG. 4 , the width of wicking strip  30  is essentially constant along its length. Referring to  FIG. 5A , an embodiment of a wicking strip is depicted wherein a first end of wicking strip  30 ′ has a first height h 1 , and a second end a second height h 2 , wherein h 1  is less than h 2 . As illustrated in  FIG. 5B , the asymmetrical-height wicking strip  30 ′ may be applied to the periwound region with the first, shorter end adjacent to the wound and the second, taller end furthest from the wound. When reservoir  40  is compressed onto wicking strip  30 ′ in this arrangement, wicking strip  30 ′ will apply a lower pressure adjacent to the wound, due to the smaller amount of material being compressed, and a higher pressure further from the wound, due to the greater amount of material being compressed in that region. While compressed, wicking strip  30 ′ may appear to have the same height along its length, even though its thickness varies in its native (non-compressed) state. Alternatively, as illustrated in  FIG. 5C , wicking strip  30 ′ may be applied to the periwound region with the second, taller end adjacent the wound and the first, shorter end furthest from the wound. When reservoir  40  is compressed onto wicking strip  30 ′ in this arrangement, wicking strip  30 ′ will apply a higher pressure adjacent the wound, due to the greater amount of material being compressed, and a lower pressure further from the wound, due to the smaller amount of material being compressed. The arrangement of such an asymmetrical wicking strip  30 ′ may be selected based on the type of wound being treated. For example, pressure wounds may benefit from a lower pressure being applied near the wound, whereas venous leg ulcers may benefit from a higher pressure being applied near the wound. Other types of wounds may benefit from different pressure gradients being applied. In many embodiments, wicking strip  30  is composed of a supple material that, when pressure is applied to it, does not create a potentially harmful pressure ring around the wound. 
     As illustrated in FIGS.  4  and  5 A- 5 C, the wicking strip may have a relatively even width along its length. However, the wicking strip of the present invention also may be provided in a variety of other shapes and sizes, depending on the intended application.  FIG. 6A  illustrates an embodiment in which wicking strip  30 ″ is additionally provided with relaxation cuts  33  that enhance its lateral flexibility, thereby facilitating lateral bending without buckling or crimping. Non-stick liner  34  is attached to layer  25  of adhesive, and may include tabs  35  that facilitate application of the wicking strip. 
       FIG. 6B  illustrates an embodiment in which wicking strip  30 ″′ is pre-formed in a bowed or arcuate shape, optionally including wider thicker portion  36 , which may facilitate application of the wicking strip around the wound by reducing the lateral bending required to surround the wound. The degree to which wicking strip  30 ′″ is bowed may vary, depending on the size of the wound with which it is intended to be used, and the compliance of the material. For example, wicking strip  30 ′″ may be highly bowed, e.g., formed to be a spiral in its native configuration (before adhesion to the epidermis).  FIG. 6B  also illustrates tabs  35 , which are part of or attached to non-stick liner  34  and may facilitate removal of the liner, which may optionally be included in any embodiment of wicking strip  30 . 
     In still other embodiments (not illustrated), the wicking strip is pre-formed into an annular form. If the inner boundary of such an annular form does not come sufficiently close to the border of the wound to protect the periwound region, then additional pieces of wicking strip may be applied in the gap between the annular form and the margin of the wound. 
     Reservoir  40   
     As illustrated in  FIGS. 1A-1B , reservoir  40  of primary dressing  10  may include multiple layers bonded together or alternatively may be formed of a single, hydrophilic layer. In the embodiment of  FIG. 1 , reservoir  40  includes upper layer  41 , lower layer  42  and intervening layer  43 . Lower layer  42  engages the upper surfaces of wicking strip  30 , and transfers exudate through intervening layer  43 , and into upper layer  41 . Although reservoir  40  is composed of breathable material that allows for the transfer of moisture vapor as needed, reservoir  40  optionally may contain vent  44  that extends through the reservoir to provide a less impeded route for moisture vapor transfer. 
     Referring again to  FIG. 1B , both upper layer  41  and lower layer  42  are hydrophilic. However, layers  41  and  42  may have the same or different hydrophilicities, mechanical properties, transfer rates for exudate, and capacities for absorbing exudate. In some embodiments, layers  41  and  42  are formed from hydrophilic polyurethane foams, e.g., commercially purchased polyurethane foams from Rynel, Inc. (Wicasset, Me., USA). The foam from which lower layer  42  is fabricated has a higher hydrophilicity than that of upper layer  41 , allowing it to rapidly transfer exudate into upper layer  41 . The polyurethane foams may be coated or interlaced with any suitable antibacterial or antimicrobial agents (e.g., silver) to combat or prevent infection. 
     Intervening layer  43  enhances the strength and stiffness of reservoir  40 , making it more difficult to inadvertently deflect reservoir  40  downward to contact the wound. Intervening layer  43  may be, for example, a substantially non-stretchable mesh or scrim, such as a metallic, nylon, or polyester-based mesh. 
     In some embodiments, layers  41 ,  42 , and  43  are co-selected to enable reservoir  40  to form a dome-like shape as it absorbs exudate and swells, while still maintaining contact with ledge  23  and sidewall  21  of support cushion  20 . For example, intervening layer  43  may be formed to have a larger diameter than the diameter defined by the sidewall  21  of support cushion  20 . As reservoir  40  absorbs exudate and swells, this difference in diameter allows intervening layer  43  to buckle upward. 
     Cover  50   
     Referring now to  FIGS. 1B and 7 , cover  50  of primary dressing  10  is described having pre-fastened reservoir  40  with vent  44 . Cover  50  may be adhered to upper layer  41  with a layer of adhesive, or otherwise attached to upper layer  41  before or after reservoir  40  is placed over the wound. During use, cover  50  is adhered to sidewall  21  using layer  27  of adhesive, which urges reservoir  40  against wicking strip  30 . In some embodiments, cover  50  extends beyond the lateral dimensions of support cushion  20 , so that when primary dressing  10  is applied to a patient, cover  50  drapes over support cushion  20  and covers layer  27  of adhesive. Such draping protects the edges of support cushion  20  from lifting, and additionally provides a smooth, comfortable surface over which clothing and bed linens may slide freely. In other embodiments, layer  27  may comprise a removable fastener, such as a hook and pile arrangement that enables the cover to be periodically removed to inspect the wound, apply medicaments, or to replace the wicking strip or reservoir. 
     Cover  50  is made of a soft, occlusive material that provides an antibacterial barrier between the wound and the environment, and also allows humidity to escape from reservoir  40  and vent  44 . One example of a suitable material for cover  50  is Intelicoat  2327 , available from Intelicoat Technologies (South Hadley, Mass., USA). The material may be coated or intercalated with any suitable antibacterial or antimicrobial agent to combat or prevent infection. 
     Additional Alternative Embodiments of Primary Dressing  10   
     Referring now to  FIGS. 8 and 9 , additional embodiments of support cushions and wicking strips suitable for use in primary dressings are described, which may simplify the construction and application of the primary dressings. In  FIG. 8 , support cushion  70  comprises sidewall  71  of uniform height defining opening  72  and wicking strip  80  disposed within opening  72 . The upper surface of wicking strip  80  visible in  FIG. 8  is recessed below the top of sidewall  71  of support cushion  70  to accept reservoir  40  and cover  50  as described with respect to preceding embodiments. Preferably, the height of wicking strip  80  is in a range of 40-60% of the height of sidewall  71 . In this embodiment, wicking strip  80  is pre-adhered to support cushion  70  so that the lower surfaces of support cushion  70  and wicking strip  80  are flush, and includes opening  81  that may be used to visually position the unit over a wound. Wicking strip  80  includes spiral perforation  82  that extends through the height of the wicking strip, so that the perforation forms spiraled inner portion  83  of the wicking strip. The innermost end of the spiraled portion terminates at pull tab  84 . 
     Support cushion  70  and wicking strip  80  preferably include a layer of adhesive on the lower surface, similar to layer  25  in the embodiment of  FIG. 1B , which is covered by non-stick liner having removal tab  85 . Support cushion  70  also includes layer  27  of adhesive or other suitable fastening means on its upper surface, and may include a plurality of slits  28 , as described for preceding embodiments, to improve breathability and conformability of the support cushion. Reservoir  40  and cover  50 , as described for preceding embodiments, may be employed, so that the reservoir fits snugly within the recess above wicking strip  80 . 
     In the embodiment of the invention depicted in  FIG. 8 , spiraled portion  83  of wicking strip  80  is configured to be removed, using pull tab  84 , to unwind the wicking strip to just expose the margin of the wound. The length of the spiraled portion  83  that is unwound to expose the margin of the wound then is cut off with a scissor and discarded. In this manner, the wicking strip may be easily positioned at the preferred location at the margin of the wound, with the remainder of wicking strip  80  covering the periwound region, thereby reducing the time required to apply the inventive dressing. Once the support cushion and wicking strip are positioned, and the appropriate length of spiraled portion  83  removed to expose the margin of the wound, the reservoir and cover then is fastened atop support cushion  70  and wicking strip  80  so that the reservoir is engaged with the upper surface of wicking strip  80 . 
     In the embodiment of  FIG. 9 , support cushion  90  is configured similar to support cushion  70  of  FIG. 8 , and includes sidewall  91  of uniform height that defines opening  92 . Wicking strip  100  is disposed within opening  92  so that its upper surface is recessed below the top of sidewall  91  to accept reservoir  40  and cover  50  as described with respect to preceding embodiments. Preferably, the height of wicking strip  100  is in a range of 40-60% of the height of sidewall  91  and is pre-adhered to support cushion  90  so that the lower surfaces of support cushion  90  and wicking strip  100  are flush. Wicking strip  100  includes opening  101  that may be used to visually position the unit over a wound, plurality of circular perforations  102  and illustratively, four radially-directed perforations  103  that divide the wicking strip into quadrants. Pull tabs  104  are connected to the innermost ring of the wicking strip in each quadrant. Perforations  102  and  103  extend through the height of the wicking strip, so that the perforations form arcs of predetermined length  105  that may be individually removed using pull tabs  104 . 
     Support cushion  90  and wicking strip  100  preferably include a layer of adhesive on the lower surface, similar to layer  25  in the embodiment of  FIG. 18 , which is covered by non-stick liner having removal tab  106 . Support cushion  90  also includes a layer of adhesive or other suitable fastening means on its upper surface, and may include a plurality of slits, as described for preceding embodiments, to improve breathability and conformability of the support cushion. Reservoir  40  and cover  50 , as described for preceding embodiments, may be employed. 
     In the embodiment of the invention depicted in  FIG. 9 , arcs  105  of wicking strip  100  are configured to be removed, using pull tabs  104 , to remove the portion of the wicking strip up to the margin of the wound. Thus, the patient or caregiver would first remove the non-stick liner from the support cushion and wicking strip, and align it centered on the wound using opening  101 . The patient or caregiver then would remove a selected, and perhaps unequal, number of arcs  105  from each quadrant using pull tabs to best approximate, or slightly overlap, the margin of the wound. The removed arcs  105  of wicking strip  105  then may be discarded. Once the support cushion and wicking strip are so applied, a reservoir and cover, as described for preceding embodiments, is fastened atop support cushion  90  and wicking strip  100  so that the reservoir is engaged with the upper surface of the wicking strip. 
     It should be understood that the dressing of  FIG. 9  advantageously permits an uneven number of selected arcs  105  of the wicking strip to be removed from each quadrant, thereby enabling the patient or caregiver to best approximate irregularities in the margin of the wound. This in turn provides a high degree of protection of the periwound region, without the need to custom fit the entire length of the wicking strip to cover the periwound region between the support cushion and the margin of the wound, for example, as described with respect to  FIG. 4 . In addition, it should be understood that while the wicking strip  100  of the embodiment of  FIG. 9  includes four radially-directed perforations, a greater or lesser number of such perforations may be provided, and that sectors defined by such perforations need not encompass equal areas. 
     Referring now to  FIG. 10 , a further alternative embodiment of a primary dressing  110  is described which provides the ability to periodically apply medications or to lavage wound W in epidermis E without disassembling dressing  110 . Primary dressing  110  includes support cushion  111 , a wicking strip as described with respect to preceding embodiments (omitted for clarity in  FIG. 10 ), reservoir  112  and cover  113 . The support cushion, wicking strip, reservoir and cover are constructed substantially as described for preceding embodiments. Primary dressing  110  differs from preceding embodiments in that support cushion  111  includes flexible tube  114  that may be permanently or removably inserted through the sidewall of the support cushion to deliver fluids, such as topical antibiotics or washing fluids through the sidewall to wound W, without needing to remove the reservoir and cover. Syringe  115  may be selectively coupled to the distal end of tube  114  to inject fluids into primary dressing  110 . 
     In addition, because the primary dressing, when assembled and applied to a patient, provides an essentially closed system (other than by permitting excess humidity to dissipate through the breathable cover), it is also possible to employ the primary dressing to in negative pressure wound therapy. For example, rather than using syringe  115  in the embodiment of  FIG. 10  to inject fluids into the dressing, by pulling the piston of an empty syringe, the syringe could be used to create a negative pressure environment in the wound environment. Optionally, the syringe may include a check valve to assist with maintaining the negative pressure environment. Alternatively, instead of the syringe  115 , tube  114  instead may be connected to a conventional squeeze ball/valve arrangement or low-pressure vacuum pump to partially evacuate the dressing. In this manner, the patient or caregiver may periodically reduce the pressure within the compartment formed by primary dressing  110  to promote exudate flow, and speed the healing process. 
     With respect to  FIG. 11 , an alternative design of a primary dressing is described. Dressing  120  includes support cushion  121 , a wicking strip as described with respect to preceding embodiments (again omitted for clarity), reservoir  122  and cover  123 . The support cushion, wicking strip, reservoir and cover are constructed substantially as described for preceding embodiments. Dressing  120  differs from preceding embodiments in that cover  123  includes bellows  124  that communicates with the vent that passes through the reservoir (see vent  44  in  FIG. 1B ). Bellows  124  preferably comprises a light-weight plastic or synthetic rubber and includes one-way valve  125 , so that depressing bellows  124  induces a negative pressure within dressing  120 . As for previously-described embodiments, cover  123  preferably comprises a breathable material that permits excess humidity to be released from within dressing, but is sufficiently air-tight to retain a negative pressure induced within the dressing by bellows  124  for an appropriate amount of time, e.g., 5-10 minutes, to stimulate exudate flow. In this manner, the patient or caregiver may periodically reduce the pressure within the compartment formed by dressing  120  by depressing bellows  124 , thereby speeding the healing process with reduced or no pain or discomfort to the patient. 
     Referring now to  FIGS. 12A and 12B , a further alternative embodiment of a primary wound dressing is described. As for the embodiment of  FIG. 1 , dressing  130  includes three discrete components that are assembled and applied over wound W on patient&#39;s epidermis E. In particular, dressing  130  includes support cushion  131 , wicking strip  132 , and reservoir  133 , which may be pre-attached to cover  134 . Preferably, components  131 - 134  are sized for use with one another and are enclosed in a sterile package with suitable instructions to enable the patient or caregiver to quickly and accurately apply the dressing. 
     Support cushion  131  preferably comprises a closed-cell polyolefin foam and is designed to surround wound W and periwound region P, i.e., the region of epidermis extending from the wound margin, to protect the wound and elevate reservoir  133  and cover  134  above the wound bed. In the embodiment of  FIGS. 12A-12B , support cushion  131  has a uniform height, so that reservoir  133  is supported directly by the upper surface of support cushion  131 , as depicted in  FIG. 12B . As for preceding embodiments, the lower surface of support cushion  131  includes a layer  25  of biocompatible adhesive, which preferably is hydrophobic and breathable, and inhibits contact between exudate and the periwound region P. Support cushion  131  preferably includes slits or perforations  135  that extend through the height of the support cushion to facilitate the escape of perspiration from beneath the support cushion when the cushion is fastened to epidermis E. Support cushion  131  includes opening  136  that exposes a portion of the periwound region extending away from the margin of wound W, to permit placement of wicking strip  132 , as depicted in  FIG. 12B . As noted above, support cushion  131  may comprise a breathable open weave spacer fabric instead of a closed-cell polyolefin foam. 
     Wicking strip  132 , which preferably comprises an open-cell polyurethane foam, overlays periwound region P between the margin of wound W and opening  136  of support cushion  131 . In the embodiment of  FIGS. 12A-12B , wicking strip  132  is depicted as a curved strip of foam, although it may take other forms as described with respect to  FIGS. 5A-6B . Wicking strip  132  preferably includes a layer  31  of biocompatible adhesive, which preferably is hydrophobic and breathable, on its lower surface to adhere to the patient&#39;s epidermis and to inhibit contact between exudate absorbed by the wicking strip and the periwound region P. During application, wicking strip  132  fits within opening  136  of support cushion  131 , so that the innermost edge of the wicking strip preferably overlaps the margin of the wound by 1-2 mm. For the embodiment of  FIG. 12A , wicking strip  132  may be cut with a scissor to ensure that the foam is not overly compressed when adhered to the periwound region. 
     Still referring to  FIGS. 12A-12B , reservoir  133  preferably comprises a sandwich of different density open cell polyurethane foams, as described with respect to the embodiment of  FIGS. 1A-1C , and comprises one or more foams selected to absorb exudate from wicking strip  132  and to sequester the exudate away from the wound bed. Reservoir  133  may be fastened to the underside of cover  134 , and may include a layer of adhesive along the perimeter of its lower surface to adhere to the upper surface of support cushion  131 . Reservoir  133  includes a hydrophobic gasket  137  disposed on its lateral face, as depicted in  FIG. 12B , so that exudate drawn into the reservoir from wicking strip  132  cannot seep out of the lateral face of the reservoir. Gasket  137  may comprise a hydrophobic film applied to the exterior lateral surface of reservoir  133 . Alternatively, gasket  137  may comprise a closed cell hydrophobic foam adhered to the perimeter of reservoir  132 , which is capable of supporting a compressive load (like the material of support cushion  131 ). Reservoir  133  is sized so that its outer edges are supported on the upper surface of the innermost portions of support cushion  131  and wicking strip  132 . Reservoir  133  preferably includes one or more vents  138  that assist in modulating the humidity within the dressing through cover  134 . 
     Cover  134  is preferably a breathable material and overlays reservoir  133 , and includes a layer of adhesive along the circumference of its lower surface that may be used to removably secure reservoir  133  in engagement with epidermis E and to adhere cover  133  to epidermis E. In accordance with one aspect of the present invention, cover  134  includes plurality of holes  139  that permit the reservoir and cover to be correctly aligned with the wicking strip and support cushion during application. In particular, holes  139  permit the caregiver to sight through the holes during application of the cover and reservoir to confirm proper positioning of the cover and reservoir relative to support cushion  131 . 
     As illustrated in  FIG. 12B  (from which cover  134  has been omitted for clarity), during use of dressing  130 , exudate EX flows out of wound W at a flow rate that depends on many factors, including the pressure with which wicking strip  132  is pressed against the periwound region, the lateral profile of the wicking strip as described above with reference to  FIGS. 5A-5C , the characteristics of wound W, and the consistency of the exudate. As exudate EX is released from the wound, it contacts and is absorbed by wicking strip  132 . Wicking strip  132  transports exudate EX laterally (in the plane of epidermis E) and then vertically (perpendicular to the plane of epidermis E) to reservoir  133 . Exudate transported laterally may eventually reach support cushion  131 , which is formed of a hydrophobic material, and inhibits further lateral transport of the exudate. Instead, exudate EX is transported vertically from wicking strip  132  and into reservoir  133 , which sequesters exudate away from the wound. Reservoir  133  preferably has a large absorptive surface area and the capacity to hold large amounts of exudate, e.g., sufficient capacity so that reservoir  133  need only be replaced once every few days. Additionally, gasket  137  inhibits leakage of exudate onto periwound region P. Because reservoir  133  is constructed of a breathable material, the water in the exudate absorbed by reservoir  133  is released in the form of vapor V into the atmosphere via breathable cover  134 . 
     Referring now to  FIGS. 13A and 13B , an alternative embodiment of a reservoir and cover suitable for use with a primary dressing is disclosed. In the embodiment of  FIGS. 1A-1C , sidewall  21  provides structural support for the reservoir against compressive loads applied to the dressing, while gasket  137  of reservoir  133  provides a similar function in the embodiment of  FIGS. 12A-12B . As described earlier, however, it may be desirable, with an irregularly shaped wound, to custom-fit a support cushion using a strip. A problem with this approach, however, is that if the reservoir is cut to the overall shape of the wicking strip and support cushion, the gasket or hydrophobic film at the edge of the reservoir may be removed, and exudate may leak from the exposed edge of the reservoir. One solution is to drape the cover over the sides of the cut reservoir, having this approach does not provide mechanical support to reservoir to resist compressive loads. 
     One solution to the foregoing concern is construction for the reservoir and cover depicted in  FIGS. 13A and 13B . In this embodiment, cover  140  includes rigid inverted basket  141  joined along its lower edge to elastomeric adhesive bandage  142 . Reservoir  150 , which may be similar in construction to reservoir  133  of  FIG. 12 , and includes gasket  137 , is disposed within basket  141 . Basket  141  is formed from plurality of radial struts  143 , circumferential struts  144  and vertical struts  145 . Struts  143 ,  144  and  145  preferably are formed from a tough, resilient plastic, such as polyurethane, and protect reservoir  150  from compressive loads. 
     Advantageously, cover  140  and reservoir  150  are preformed in specific sizes, e.g., small, medium and large diameters. During application of the inventive dressing to an irregularly shaped wound, the wicking strip and support cushion may be custom-fit from strip-shaped support cushion and wicking strips by wrapping the support cushion and wicking strip around the wound. A suitably sized cover  140  and reservoir  150  may then be selected from the preformed sizes such, when applied, that the outer edge of the reservoir sits atop at least the innermost rings (or spirals) of the support cushion. For example, if the wound is relatively small, the reservoir may extend to the outermost ring of the support cushion. On the other hand, if the wound is large, the reservoir may sit atop the innermost ring of the support cushion. Since for this embodiment it is not necessary to cut the outer edge of the reservoir, the gasket remains intact and prevents diffusion of exudate through the lateral edges of the reservoir. In addition, the basket provides mechanical support and protection for the reservoir against compressive loads, thus preventing exudate absorbed into the reservoir from being inadvertently released into the wound bed. 
     Primary Dressing Kits 
     The components of a primary dressing suitable for use with the secondary dressing described herein, illustratively primary dressing  10  of  FIGS. 1A-1C , may be provided to patients or caregivers as a kit  160 , illustrated in  FIG. 14 . Kit  160  includes a cardboard or other sturdy, disposable backing  161  upon which support cushion  20 , wicking strip  30 , reservoir  40 , and cover  50  are removably mounted. Examples of alternative disposables backing  161  are dark, colored or translucent trays of materials such as polystyrenes (for example available from Sealed Air Corp., Elmwood Park, N.J., USA; or Perfecseal®, a BEMIS Co., Oshkosh, Wis., USA). Kit  160  may also include additional components, e.g., extra wicking strips  30 , or different sizes and shapes of support cushion  20 , to be able to accommodate different sizes and shapes of wounds. In an alternative embodiment, the components of primary dressing  10  are instead provided in one or more compartments of a tray. 
     In the illustrated embodiment, foldable tabs  162  cut from backing  161  and/or pieces of excess material adhered to backing  161  may be used to secure the components of dressing  10  to hacking  161  until they are needed. For example, the hole in support cushion  20  may be formed by cutting piece  163  from a layer of flange material, and then adhering that piece  163  to backing  161 . Because piece  163  snugly fits into the hole of support cushion  20 , the friction between piece  163  and support cushion  20  serves to removably retain support cushion  20  on backing  161  without the need for additional adhesive or tabs, until removed by the patient or caregiver. Similarly, reservoir  40  may be cut from the center of a larger piece  164  that is subsequently adhered to backing  161 . Friction between reservoir  40  and piece  164  retains reservoir  40  frictionally engaged on backing  161  without the need for additional adhesive or tabs, until removed for use. Alternatively, tabs  162  may be used to secure all of the components onto backing  161 . 
     Instructions for use  165  for applying the different components of dressing  10  to a patient may be printed on backing  161 , e.g., instructions for implementing the method described with respect to  FIG. 2 . The instructions may be sterilized so that they may be safely used in a sterilized field, such as an operating room. The adhesive layers on the different components are covered with non-stick, removable liners that may be color coded to guide the patient or caregiver in determining the order in which to apply the components of primary dressing  10 . Such non-stick liners may facilitate handling of the different components of primary dressing  10 , e.g., while placing support cushion  20  on the patient&#39;s epidermis. 
     Kit  160  preferably further includes a pouch (not shown) in which backing  161  and dressing  10  are sealed until needed. Preferably, the pouch is transparent on at least its upper surface, allowing backing  161  and the other components to be viewed. Additionally, instructions for use  165  may be located on backing  161  so as to make possible reading of the instructions before opening the pouch. The pouch also may be constructed to aid retention of the components of primary dressing  10  on backing  161 . Kit  160  preferably is sterilizable, e.g., may be sterilized after assembly, such that the contents of the pouch remain sterile until it is opened, e.g., immediately before the dressing is applied to a patient. The pouch preferably comprises a material that retains its integrity during conventional sterilizing procedures, e.g., exposure to gamma radiation, to an electron beam, or to ethylene oxide gas. 
     It is envisioned that a typical wound care treatment environment, such as a hospital, wound care outpatient clinic or doctor&#39;s office, may stock an inventory of kits  160  designed for use with different sizes or shapes of wounds. For example, a plurality of kits  160  may be manufactured having support cushion  20 , wicking strip  30 , reservoir  40 , and cover  50  in a variety of sizes and shapes, according to different wound sizes and shapes with which they may be suitable for use. Alternatively, or in addition, individual components of the dressing, such as the wicking strips and reservoirs, may be individually packaged, for example to permit periodic replacement of the wicking strip or reservoir with greater frequency than the dressing as a whole. As a still further alternative, as described above, the wicking strip and support cushion may be individually packaged in a roll form or fait folded configuration, so that the dressing may be applied in a custom-fit manner, while cover and reservoir combinations, such as described above with respect to  FIG. 13 , may be made available in discrete sizes, so that the dressing may be applied to a wide range of wound topologies. 
     Secondary Dressings 
     As noted above, the secondary dressings of the present invention may be used to comfortably secure a primary dressing over a wound, thus inhibiting slippage of the primary dressing while at the same time applying a desired amount of compression to the primary dressing. Such a feature is particularly useful when the primary dressing is to be secured onto a part of the body where previously-known types of secondary dressings cannot readily be placed. For example, the primary dressing may be placed over a sacral ulcer, or over a wound from chest surgery. It may not be practicable or safe to secure a primary dressing in such a position using a previously-known secondary dressing, such as an ACE™ elastic bandage (3M). For example, using such a bandage to secure a primary dressing over a sacral, abdominal, hip, ischial, back, breast, buttock, or chest wound typically would require wrapping the bandage around the entire torso, which may undesirably compress internal organs, may be uncomfortable, and also may be inconvenient to place and remove on a frequent basis. Additionally, depending on the location of the primary dressing, the bandage may apply either too little or too much pressure to the primary dressing or may shift too readily with motion, which may fail to properly secure the primary dressing and/or may worsen the wound. For example, applying too much pressure to a dressing applied over a pressure wound may aggravate the wound. Other body parts over which it may be difficult to secure dressings include knee, shoulder (scapula), elbow, and ankle, because of their relatively large range of motion during normal use. By comparison, the secondary dressings of the present invention may readily secure a primary dressing over any desired body part, including those enumerated above, and may apply an appropriate amount of pressure to the primary dressing without compressing other portions of the body. Additionally, the inventive secondary dressings may allow for stretching if swelling (edema) develops at the wound site. 
       FIGS. 15A-15B  respectively illustrate plan and cross-sectional views of a secondary dressing  200  constructed in accordance with some embodiments of the present invention. Dressing  200  includes fabric layer  210 , foam surround  220  (not visible in  FIG. 15A ) secured to fabric layer  210 , and biocompatible adhesive layer  230  disposed on foam surround  220 . Removable liner  240  (not shown in  FIG. 15A ) optionally protects biocompatible adhesive layer  230  until secondary dressing  200  is ready for use, at which point the liner may be removed to expose adhesive layer  230  for securement to the patient&#39;s epidermis. As can best be seen in  FIG. 15B , fabric layer  210  is secured to foam surround  220  via adhesive layer  223 , which may be substantially the same as biocompatible adhesive layer  230 . However, any suitable means for securing fabric layer to foam surround  220  may be used. In one example, adhesive layer  223  is a thin (e.g., 1/32″) layer of foam adhesive. 
       FIG. 15C  schematically illustrates a cross-section of secondary dressing  200  applied over primary dressing  10  described above with reference to  FIGS. 1A-1C . Biocompatible adhesive  230  is secured to the patient&#39;s epidermis E, while fabric layer  210  is disposed over cover  50  of primary dressing  10 . Fabric layer  210  can be seen to conform to dressing  10 , and to provide a smoothly varying profile between the outer edges of dressing  10  and epidermis E, enabling bed sheets, clothing, or other dressings to slide relatively easily over secondary dressing  200 . Additionally, the height differential between cover  50  and foam surround  220  imposes tension T on fabric layer  210 , gently compressing dressing  10  against epidermis E. In some embodiments, the magnitude of tension T may be adjusted by selecting the elasticity of fabric layer  210  in one or both lateral dimensions, as described in greater detail below. In general, the greater the elasticity of fabric layer  210 , the lower the tension T that secondary dressing  200  will apply to the primary dressing. Tension T, coupled with the smooth profile provided by fabric layer  210 , help to secure primary dressing  10  to the epidermis and reduce the risk that dressing  10  will slip from its initial position because of interactions with bed sheets, clothing, other dressings, or the like. 
     As  FIG. 15C  illustrates, fabric layer  210  has larger dimensions than the primary dressing with which it is to be used, e.g., primary dressing  10  described above with reference to  FIGS. 1A-1C . Foam surround  220  extends to the periphery  213  of fabric layer  210 , and also has defined therein a central aperture  250  (best seen in  FIGS. 15A-1513 ) with larger dimensions than the primary dressing. Alternatively, as described below with reference to  FIG. 20 , the periphery  213  of fabric layer  210  may extend beyond foam surround  220 , e.g., by at least half an inch in each direction. In general, the respective sizes and shapes of fabric layer  210  and aperture  250  may be appropriately selected for use with primary dressings of any desired size or shape. For example, fabric layer  210  may have a width between 2 inches and 20 inches in one or both lateral dimensions, e.g., between 4 and 18 inches, or between 6 and 16 inches, or between 8 and 14 inches. Aperture  250  may, for example, have a width between 1 inch and 18 inches in one or both lateral dimensions, or between 2 and 16 inches, or between 4 and 14 inches, or between 6 and 12 inches. Additionally, fabric layer  210  and aperture  250  are preferably sized relative to each other such that the portion of foam surround  220  and adhesive  230  disposed thereon has sufficient surface are to adequately secure the primary dressing in place. In various embodiments, one or both of fabric layer  210  and central aperture may be square, rectangular, triangular, polygonal, round, oval, curved, or irregularly shaped, optionally with rounded corners, e.g., as illustrated in  FIG. 15A . In one preferred embodiment, fabric layer  210  is approximately 8 inches square, and aperture  250  has a diameter of 6 inches. 
       FIG. 16  illustrates steps in an exemplary method  1600  of using a secondary dressing, e.g., secondary dressing  200  illustrated in  FIGS. 15A-15C , with a primary dressing. First, at step  1610 , a caregiver obtains and applies a primary dressing over a wound. For example, in embodiments where the primary dressing is dressing  10  described above with reference to  FIGS. 1A-1C , the caregiver may implement the steps of method  60  illustrated in  FIG. 2 . However, it should be understood that the secondary dressing  200  can be used with any suitable primary dressing. Examples of suitable primary dressings with which secondary dressing  200  may be used include primary dressings for chronic wounds and primary dressings for acute (e.g., incisional) wounds. For example, secondary dressing  200  may suitably be applied over a hydrocolloid dressing, a foam dressing, an ABD (abdominal) pad dressing, sutures, staples, an adhesive (e.g., steri strips), a gauze pad, a nonwoven pad, a surgipad and/or a skin glue. In one specific embodiment, the primary dressing is a dressing described in copending U.S. patent application Ser. No. 12/504,590, filed Jul. 16, 2009 and entitled “Systems and Methods for Protecting Incisions,” the entire contents of which are incorporated by reference herein. 
     Then, at step  1620 , the caregiver obtains secondary dressing  200 , and confirms that secondary dressing  200  is appropriately sized for use with the primary dressing, for example by approximately positioning dressing  200  over the primary dressing and confirming that all dimensions of aperture  250  are larger than the primary dressing. Then, at step  1630 , the caregiver applies secondary dressing  200 . For example, the caregiver may remove removable liner  240  from biocompatible adhesive  230  and apply the adhesive to the patient&#39;s epidermis such that aperture  250  is approximately centered on the primary dressing. This step secures foam surround  220  about the primary dressing, disposes fabric layer  210  over the top surface of the primary dressing, and applies tension on fabric layer  210  that secures the primary dressing against the patient&#39;s epidermis. Optionally, the caregiver may adjust the tension that the secondary dressing applies to the primary dressing (step  1640 ). For example, the caregiver may select the orientation of the fabric of the secondary dressing and/or may apply tension to the patient&#39;s epidermis while applying the secondary dressing, so as to further adjust the tension on fabric layer. 
     It should be noted that in some circumstances, the primary dressing may include features that remain outside of secondary dressing  200 . For example, as described above with reference to  FIG. 10 , the primary dressing may include tubing connected to a syringe or other reservoir that may be used to introduce material to the wound and periwound region and/or to remove material from the wound and periwound region. Such tubing, for example, may be passed under foam surround  220 , enabling a caregiver to access the reservoir and thus introduce and/or remove material from the wound and periwound region via the tubing without the need to remove the secondary or primary dressings. 
     The secondary dressing can alternatively be applied directly over a region of compromised skin, e.g., over a wound, diseased skin (such as skin affected by shingles), or otherwise unhealthy skin, without the use of a primary dressing. In such embodiments, secondary dressing  200  is preferably sized and configured such that aperture  250  is larger than the affected region of skin, so as to avoid contact between adhesive  230  and the affected region of skin. Moreover, the inventive secondary dressing can be applied over more than one other dressing, e.g., can be applied over other secondary dressings, or even over tertiary dressings, to secure such dressings in place. 
     Further details of the components of secondary dressing  200 , and some alternative embodiments, will now be described. 
     Referring again to  FIGS. 15A-15C , fabric layer  210  preferably is breathable, with an MVTR that is at least as great as an MVTR of the primary dressing with which it is to be used. As such, when applied over the primary dressing, fabric layer  210  does not significantly slow the evaporation of vapor out of the primary dressing. Such a feature may be particularly useful in embodiments where secondary dressing  200  is used in combination with primary dressing  10  described above. As noted above, primary dressing  10  is designed to facilitate the transfer of a fluid away from a wound bed and periwound region and into a reservoir. The fluid may evaporate from the reservoir and through secondary dressing  200 , inhibiting maceration while keeping the wound sufficiently moist. Fabric layer  210  may include any suitable breathable fabric, such as a woven fabric or non-woven fabric, which may be synthetic, natural, or a mixture of synthetic and natural fibers. For example, in one embodiment, fabric layer  210  is an open weave polyester mesh. Optionally, fabric layer  210  is impregnated with a therapeutic composition, such as any suitable antibacterial or antimicrobial agents (e.g., silver), that inhibits bacterial growth or performs another suitable therapeutic function. 
     In some embodiments, fabric layer  210  may have different elasticities in each of its two lateral dimensions, which may enable the caregiver to better adjust the tension T that fabric layer  210  applies to the primary dressing. For example, as illustrated in  FIG. 17 , fabric layer  210 ′ may have a greater amount of stretch or elasticity in the machine (M) direction as compared to the cross (C) direction. The M and C directions of fabric layer  210 ′ may be suitably oriented relative to foam surround  220  during the manufacturing process. Removable liner may have a plurality of asymmetrically configured tabs designed to facilitate the caregiver&#39;s recognition of the more elastic direction of the fabric, and/or fabric layer  210 ′ may include markers indicating the more elastic direction of the fabric. Either or both of these features may assist the caregiver in determining how to orient secondary dressing  200  relative to the primary dressing. For example, if the caregiver applies the dressing of  FIG. 17  beginning from left to right (parallel to the machine direction), then fabric layer  210 ′ will stretch by a relatively large amount as it is brought to overlay the primary dressing, resulting in less compression of the primary dressing. By contrast, if the caregiver instead applies the dressing from top to bottom (perpendicular to the machine direction), then fabric layer  210 ′ will stretch by a relatively small amount as it is brought to overlay the primary dressing, resulting in more compression of the primary dressing. The caregiver may orient the M and C directions of the fabric at any desired angle relative to the primary dressing, so as to select a particular magnitude of tension on the fabric that is appropriate to the primary dressing and the wound. 
     Referring back to  FIGS. 15A-15B , foam surround  220  may include a relatively thin layer (e.g., less 0.25″) of any suitable foam, for example, a closed-cell polyolefin foam. As for the support cushion described further above with respect to  FIGS. 1A-1C , foam surround  220  optionally may have a plurality of slits or apertures defined therein to enhance the breathability of foam surround  220 . Foam surround  220  may in some embodiments be replaced by a polyurethane layer. Alternatively, as illustrated in  FIG. 18 , a single adhesive layer  270  may be used in place of adhesive layer  223 , foam surround  220 , and biocompatible adhesive layer  230 . Adhesive layer  270  may be a relatively thick layer of adhesive that has substantially the same lateral profile as foam surround  220 . Optionally, adhesive layer  270  may be reinforced with a woven fabric or a nonwoven fabric. Adhesive layer  270  may be provided already applied to fabric layer  210 , and have removable liner  271  disposed thereon to protect layer  270  until ready for use. In an alternative embodiment (not illustrated), adhesive layer  270  may be provided separately from fabric layer  210 , and have removable liners disposed on both of the major surfaces of layer  270 . During use, a first removable liner may be removed to expose a first major surface of layer  270 , which surface may then be applied to the patient&#39;s epidermis. The second removable liner may then be removed to expose the other major surface of layer  270 , to which fabric layer  210  may then be applied. 
     As noted above with reference to  FIGS. 15A-15C , fabric layer  210  provides a relatively smooth profile over which other fabrics may readily glide, reducing the probability that those other fabrics may cause the primary dressing to slip from its desired position on the epidermis. As illustrated in  FIG. 19 , the profile of secondary dressing  200 ′ may further be smoothed by tapering the height profile of foam surround  220 ′, as well as adhesive layers  223 ′,  230 ′. 
     In another illustrative embodiment, as illustrated in  FIGS. 20A-20B , dressing  200 ″ includes alternative fabric layer  210 ″ having an extended periphery  213 ″ configured to extend beyond the perimeter of foam surround  220 ″, e.g., by half an inch in each direction. Such a feature is useful because it inhibits the edge of secondary dressing from lifting, and provides a smooth, comfortable surface over which clothing and bed linens may slide freely. Additionally, the extended periphery of fabric layer  210 ″ may inhibit any residual adhesive at the edge of foam surround  220 ″ from contacting clothing or bed linens. Alternative dressing  200 ″ also includes modified foam surround  220 ″ having a plurality of perforations  280  defined therein, e.g., four perforations  280  on the diagonals of foam surround  220 ″ and configured to separate foam surround  220 ″ into four portions of approximately equal size. Perforations  280  provide dressing  200 ″ with enhanced control over the tension applied to fabric layer  210 ″. Specifically, perforations  280  allow each portion of foam surround  220 ″ to be pulled independently, so as to adjust the tension on fabric layer  210 ″. Additionally, perforations  280  provide enhanced versatility in the size of secondary dressing  200 ″ and its use over primary dressings of different sizes, as well as enhanced positioning on different parts of the body, because each portion of foam surround  220 ″ may be separated from the others and moved independently to an appropriate location. It should be understood that not all embodiments of dressing  200 ″ need include both perforations  280  and an extended fabric periphery  213 ″; for example, a dressing may have only perforations  280  and no extended periphery  213 ″, or may have only extended periphery  213 ″ but no perforations  280 . 
     While various illustrative embodiments of the invention are described above, it will be apparent to one skilled in the art that various changes and modifications may be made therein without departing from the invention. The appended claims are intended to cover all such changes and modifications that fall within the true spirit and scope of the invention.