Vented wound dressing

Abstract: A wound dressing (10) comprising a base sheet having an opening (16) for placement over the wound; a vent sheet (20) providing controlled leakage of fluid along a path from the wound through the opening of the base sheet (14); and a chamber containing a fabric reservoir (44) for receiving and retaining the wound fluid, the walls defining the chamber being constructed so as to provide a complete barrier to bacteria and other external contaminants while at the same time permitting egress of air from the voids or interstices of the fabric reservoir, so as to optimize the wicking and amount of wound fluid which can be retained in the volume provided by the fabric reservoir.

Description: The present invention relates to a wound dressing comprising a primary dressing comprising a base sheet for contacting the skin having at least one opening for placement over a wound, and vent means for providing controlled leakage of wound fluid. EP-A-0 392 640, a document citable under Art 54 (3) EPC, is directed to the task of providing an improved wound dressing of simplified construction which maintains a moist environment and prevents scab formation while at the same time obviating the problems which can occur when the wound exudate builds up a pressure bubble beneath the dressing. Such problems include the tendency of the pressure bubble of wound exudate to undermine the adhesive seal to the skin, the resulting increased possibility of contamination of the wound, and the messiness inherent in the escape of wound exudate from the dressing. In accordance with the invention described and claimed therein, the task is solved in an elegant manner by providing a dressing comprising a base sheet having an opening for placement over the wound; means for securing the base sheet to the skin; and vent means for providing controlled leakage of wound fluid along a path from the wound through the opening of the base sheet. In a preferred embodiment, the vent means comprises a vent sheet secured to the base sheet over the opening and having a raised portion defining at least one channel extending from the opening to an edge of the vent sheet, the channel communicating with at least one opening permitting the fluid to be vented to the outer surface of the dressing. The opening(s) for venting the fluid may be provided by permitting at least one and preferably two opposed edges of the vent sheet to be free of attachment to the base sheet. Various embodiments of the vented sheet dressings are described and illustrated in the accompanying drawings. In the embodiments such as are illustrated in Figs. 16 and 17, the wound fluid leaks from the channel through the unsealed edges to the outside of the dressing where it comes in contact with the outside air as well as bacteria or other external contaminants which may be present. In other embodiments such as are illustrated in Figs. 1-3, an absorbent layer such as a gauze sponge for receiving and retaining the wound fluid may be located over the back surface of the base sheet and over the vent sheet. As disclosed, a back film of a bacteria impervious material may be secured to the back surface of the absorbent layer. In still another embodiment, as shown in Figs. 6 and 7, a fabric layer impregnated with an antimicrobial agent is secured around its periphery to the back surface of the base sheet. A fluid-impervious cover sheet is secured to the front surface of the fabric layer, i.e. between the fabric layer and the base sheet. The cover sheet is free of attachment to the base sheet and serves as a vent through which fluid can leak and be wicked to the fabric layer. In summary, EP-A-0 392 640 discloses embodiments wherein the wound fluid is present on the outer surface of the dressing. While fully satisfying the objectives of the application in obviating the problems which can occur when wound fluid builds up in and on the wound, it nevertheless is not fully satisfactory in all aspects desired for a wound dressing. Specifically, wound exudate is exposed to the environment as well as to contact with any objects which may be present. Moreover, the outer surface is exposed to bacteria as well as other external contaminants including food or liquid which may be spilled by the patent on the wound, which contaminants can adversely affect the healing process. In other embodiments, e.g. that shown in Figs. 1-3, a bacteria-impervious material is disposed over the reservoir for retaining the wound fluid. While such embodiments will serve to prevent ingress into the dressing of external contaminants, they do present one significant problem, namely the ability for the fabric reservoir to reach its optimum potential for receiving wound fluids. In order to approximate optimum efficiency of receiving and retaining wound fluids, it is necessary to provide means for removal or displacement of air entrained in the interstices or voids of the fabric reservoir. In other words, it is axiomatic that for one fluid (e.g. wound exudate) to be able to diffuse or wick to a given volume of space, any fluid (e.g. air) initially present in this volume of space must first be permitted to be displaced. EP-A-0 099 748 discloses a moisture vapour transmitting would dressing, comprising a conformable backing layer having an adhesive layer on one of its surfaces, and an adsorbent pad on the adhesive side of the backing layer. The adhesive pad comprises an absorbent layer of an open cell foam of a hydrophilic polymer and a conformable wound facing layer of an elastomer net. The dressing described does not comprise a releasably attached secondary dressing. GB-A-2,175,208 describes a wound dressing comprising a base sheet, an absorbent pad and a chamber to receive the pad. The chamber is heat-sealed or otherwise unreleasably attached to the back surface of the base sheet. In the base sheet an opening is provided so that wound fluid can be absorbed by the pad. EP-A-0 002 509 describes a wound dressing system comprising two adhesive parts to surround a wound, a perforated foil or net to cover the wound, and a convex shaped absorption pad to cover the adhesive parts and the foil or net. The absorption pad is adhered to the skin using adhesive strips. The primary task of this invention is to provide an improved vented dressing of the type described in EP-A-0 392 640 having a fabric reservoir for wound fluid disposed over the vent sheet, the fabric reservoir having means protecting it from external contaminants, including bacteria, while at the same time permitting entrained air to be removed so as to optimize the efficiency of the reservoir and, in turn, to minimize the number of dressing changes which may be required. BRIEF DESCRIPTION OF THE INVENTION In accordance with this invention the task is solved by employing the teachings of EP-A-0 441 417, which document was filed on the same date as the application covering the present invention, to provide a vented dressing wherein the fabric reservoir for wound exudate is contained within a chamber, the walls of which provide an effective barrier to bacteria and other external contaminants, at least a portion of a wall of the chamber being air permeable so as to permit egress of air from within the voids in the fabric reservoir. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is an exploded top plan view of the novel wound dressing of this invention; Fig. 2 is a sectional view taken substantially as indicated along the line 2-2 of Fig 1 with the thicknesses exaggerated for purposes of illustration. DETAILED DESCRIPTION OF THE INVENTION As heretofore mentioned, the present invention is directed to certain improvements over the vented dressings described and claimed in EP-A-0 392 640, the essence of the invention being providing a fabric reservoir for receiving and retaining wound fluids vented through the dressing, the fabric reservoir being contained within a chamber which is free from external contaminants while, at the same time, permitting displacement of air entrained within the reservoir so as to optimize the ability of the reservoir to receive the wound fluids diffusing thereto. The novel chamber containing the fabric reservoir is an adaptation of and borrows from the invention described and claimed in the simultaneously filed EP-A-0 441 417. More in particular, the present invention relates to a wound dressing as described in claim 1. The nature and objects of the invention may best be understood from the following detailed description taken in conjunction with the accompanying drawings. As shown in the Figs. 1 and 2, the novel wound dressing 10 of this invention consists essentially of a vented dressing component 12 adapted for placement on the wound; and a cover component 34 adapted to receive and to retain wound exudate diffusing from dressing component 12. Component 12 corresponds essentially to the illustrative embodiment shown in Figs. 16 and 17 of the aforementioned EP-A-0 392 640. Component 12 is illustrated to have a base sheet 14 having an opening 16 extending therethrough. The base sheet has a layer of adhesive 18 on the front surface thereof for securing the dressing 10 to the skin of the patient with the opening 16 over the wound (not shown). The dressing component 12 also has a vent or cover sheet 20 covering the opening 16. The vent sheet 20 has a pair of side edges 22a and 22b and a pair of end edges 24a and 24b connecting the side edges 22a and 22b. While the shape of the vent sheet is not critical and may vary, it preferably is of a generally rectangular configuration. The dressing component 12 has a pair of sealing lines 26 and 28 on either side of opening 16 and extending between the end edges 24a and 24b sealing the cover sheet 20 to the base sheet 14. Sealing lines 26 and 28 may be provided by heat sealing or by means of a suitable adhesive, e.g. a per se known heat or pressure-sensitive adhesive. The vent sheet 20 has an upraised portion or fold 30 located between the sealing lines 26 and 28 defining a channel 32 extending between opening 16 and the end edges 24a and 24b. In use, when excess pressure builds up due to the presence of wound fluids in the wound, the wound fluid will leak from channel 32 through the unsealed end edges 24a and 24b to the outside or back of base sheet 16, rather than undermining the adhesive layer 18 of the base sheet securing the dressing on the wound. In accordance with the present invention, the dressing component 12 is provided with a cover component 34 including a fabric reservoir adapted to receive and retain wound fluids which have leaked through channel 32 to the back surface of base sheet 14 of wound dressing component 12. Cover component 34 is essentially the same as the dressing described and claimed in the simultaneously filed EP-A-0 441 417, adapted for placement directly on the wound, except that in the modification of this invention, it will be appreciated that the adhesive layer of the wound dressing of the aforementioned copending application to adhere the dressing to the skin is not necessary in the practice of the present invention. As shown, the cover component 34 is of generally the same configuration as dressing component 12. The cover component 34 has a bottom sheet or film 36 which is shown to have a plurality of perforations 38 permitting passage of wound fluid through bottom sheet 36. Sheet 36 and base sheet 14 of dressing component 12 are sealed around their common periphery, to provide a barrier against ingress of bacteria or other external contaminants, as well as to preclude lateral escape of wound fluid through the edges of the dressing. Sheets 36 and 14 are releasably secured around their common periphery by means of a suitable pressure-sensitive adhesive. In this embodiment, when the reservoir is filled, the cover component may then be removed and replaced with another without removing the dressing component on the wound, thereby obviating the trauma associated with dressing removal which can adversely affect the healing process. An outer liquid- and bacteria-impermeable cover sheet 40 is sealed in liquid- and bacteria-tight relationship around its periphery to the periphery of perforated sheet 36 to define a chamber 42 in which is disposed a fabric reservoir 44 for receiving and retaining wound fluids diffusing from the upper surface of sheet 14 through the perforations 38 in sheet 36. As illustrated, the outer cover sheet 40 has one or more openings or windows 40a to permit egress of air from the interstices or voids in fabric reservoir 44. Each window or opening 40a is covered by an air-permeable bacterial barrier sheet material 46 of slightly larger dimensions than the dimensions of opening 40a. As shown, bacterial barrier sheet material 16 is sealed around its periphery to the edges of sheet 40 around opening 40a so as to prevent ingress of bacteria around the edges of the opening into chamber 42. The particular materials employed for preparing the various components of the dressing may be selected from those heretofore known in the art for providing their respective functions. Since such materials are well known and their selection will be a matter of choice within the expected judgment of the skilled worker in the light of the foregoing description, their selection per se accordingly comprises no part of this invention. However, by way of illustration, base sheet 14, which may be on the order of 2.54-3.81 µm (1-1.5 mils) thick, may be constructed of a suitable, preferably moisture vapor permeable flexible polymeric material such as polyurethane, SARAN (trademark of Dow Chemical Company), a cellulose ester, etc. Adhesive coating 18 may be any of the so-called medical grade adhesive heretofore employed for application to the skin. Such known adhesives include the rubber-based, acrylic, vinyl ether and hydrocolloid pressure-sensitive adhesives. To provide a suitable bacterial barrier, they must be applied as a continuous layer around at least the entire periphery of the base sheet. Vent sheet 20, which may be on the order of 2.54 µm (one mil) thick, may also comprise a flexible polymeric material such as those heretofore mentioned for the base sheet. The bottom sheet 36 of cover component 34 (Figs. 1 and 2) may comprise any of the per se known perforated flexible films and may also be on the order of 2.54 µm (one mil) thick. As examples of such films, mention may be made of polyurethane, cellulose acetate, cellulose triacetate, etc. While for purposes of illustration film or sheet 36 has been shown to be perforated, it will be appreciated that where found desirable or expedient to do so, suitable porous materials such as cellulose esters, vinyl polymers and the like may be employed in lieu thereof, including porous sheet materials which have been chemically treated or coated to make them more suitable for use in the contemplated wound dressings. Since the desired degree of porosity or permeability to wound exudate will vary according to such factors as the nature of the intended wound to be covered, the anticipated amount of exudate and/or the frequency of dressing changes contemplated, it is not susceptible to precise quantification. In any event, the selection of the particular permeability to wound exudate for a given dressing will be a matter of choice of design within the judgement of the skilled worker in the light of this description. The opening 16 (Fig. 1) has been shown for purposes of illustration as being generally circular. However, the openings in the base sheet may be elongated or of any other suitable shape, as is shown and disclosed in the parent application. Moreover, as disclosed therein, a plurality of openings in the base sheet may be provided in lieu of a single opening. In any case, as will be appreciated, the opening or openings must be sufficient to permit passage therethrough into the dressing of excess wound fluid so as to inhibit pressure build-up and the heretofore discussed problems resulting therefrom. Fabric reservoir 44 may comprise any of the fabric materials heretofore employed for wound dressings to retain exudate, e.g. cotton, gauze sponges, absorbent pads such as those customarily used for abdominal surgery, and the like. If desired, they may additionally contain an antimicrobial agent such as chlorhexidine, although the use of such a reagent is not considered necessary. Water-impermeable sheet 40 should of course also be impermeable to bacteria as well. It may, for example, be on the order of 1.27 to 2.54 µm (0.5 to 1.0 mil) thick and comprise a suitable polymeric material such as polyurethane, "Saran" (trademark of Dow Chemical), a polyolefin such as polyethylene or polypropylene, a polyester such as polyethylene terephthalate, etc. In any event, sheet 40 must be imperforate as well as being flexible and conformable. Bacterial barrier 46 may comprise any of the per se known bacterial barrier air filters such as NUCLEOPORE, MILLIPORE, GELLMAN, etc. As will be understood, in practice excess wound fluid or exudate will pass through the opening(s) in the base sheet covering the wound, leak through the vent sheet and then be wicked or diffuse into the fabric reservoir contained in an external contaminant-free environment which in turn prevents migration of bacteria and/or other contaminants down through the dressing to the wound. The air-permeable bacterial barrier covering the dressing permits egress of air from the voids or interstices of the reservoir while at the same time maintaining the external contaminant-free integrity of the drawing. It is to be expressly understood that the wound dressings shown in the illustrative drawings are capable of various modifications without departing from the scope of the invention herein contemplated. For example, since the known bacterial barrier sheet 46 is relatively expensive, the cover for the dressing has been shown to consist essentially of a conventional impermeable sheet material provided with an opening or window which is covered by the relatively more expensive bacterial barrier sheet. However, it is contemplated that the cover may instead comprise a single air-permeable, bacteria-and liquid-impermeable sheet material. Alternatively, the external sheet 44 may of course be provided with a plurality of windows covered in turn by a corresponding plurality of bacterial barrier sheets. Other changes will be readily suggested in the light of the foregoing description. By way of recapitulation, it will be seen that the present invention provides a vented wound dressing of the type described in EP-A-0 392 640, the dressing having a fabric reservoir for receiving and retaining wound fluids, the reservoir being encased within outer walls which provide an effective barrier to external contaminants while at the same time permitting egress of air from within the interstices or voids of the fabric reservoir in order to optimize the amount of wound fluid which can be wicked into the fabric reservoir. This optimizing of wicking in turn minimizes the frequency of dressing changes which may be required. An important feature of the present invention is the ability to replace the cover component and wound fluid reservoir without removing the base sheet covering the wound, which removal may cause injury to the healing skin and thereby impair the healing process. Since it is not possible to ascertain whether the bacterial barrier precludes the presence of any bacteria within the reservoir so that it can be said to be totally bacteria-free, as used herein and in the appended claims, the term "effective barrier" is used, denoting a barrier which effectively precludes ingress of bacteria from the ambient atmosphere to said reservoir, whereby the reservoir and the chamber in which it is contained can be reasonably regarded as being safe from the danger of infection induced by the presence of bacteria entering the dressing from the ambient atmosphere. Since certain changes may be made without departing from the scope of the invention herein contemplated, all matter contained in the foregoing description and drawing shall be taken as being illustrative and not in a limiting sense.

Claims: A wound dressing (10) comprising a primary dressing (12) comprising a base sheet (14) for contacting the skin, said base sheet having at least one opening (16) adapted for placement over a wound, and vent means (20) for providing controlled leakage of wound fluid along a path from said wound through said opening(s) (16) of said base sheet (14), characterized in that the primary dressing (12) has releasably secured thereto a secondary dressing (34) having outer wall members (40, 46) defining a chamber (42) into which said wound fluid leaking through said vent means (20) can wick or diffuse, which chamber (42) contains a fabric reservoir (44) having voids or interstices adapted for receiving and retaining said wound fluid diffusing thereto, the outer wall members (40, 46) defining said chamber (42) providing an effective barrier against ingress of bacteria and other external contaminants, at least a portion of the outer wall members (46) of said chamber (42) being both a bacterial barrier and air permeable, the air permeability of said at least portion (46) being sufficient to permit egress of air from said voids or interstices within said reservoir (44) to optimize the amount of fluids the reservoir (44) can receive and retain, wherein the primary dressing (12) and the secondary dressing (34) are releasably sealed around their common periphery, to provide a barrier against ingress of bacteria or other external contaminants as well as to preclude lateral escape of wound fluid through the edges of the dressing (10). A wound dressing (10) as defined in claim 1 wherein said vent means (20) comprises a vent sheet (20) secured to said base sheet (14) over said opening (16). A wound dressing (10) as defined in claim 2 wherein said vent sheet (20) has a raised portion (30) defining at least one channel extending from the opening to an edge (24a, 24b) of said vent sheet (20). A wound dressing (10) as defined in claim 2 wherein said vent sheet (20) has a pair of opposed side edges (22a, 22b) and a pair of opposed end edges (24a, 24b) connecting said side edges (22a, 22b), said vent sheet (20) being secured to the inner surface of said base sheet (12) at a location adjacent at least one of said edges (22a, 22b), with the other of said edges (24a, 24b) being free of attachment to the base sheet (14), whereby to permit leakage of wound fluid diffusing through said opening(s) (16) through said unattached edges (24a, 24b). A wound dressing (10) as defined in claim 4 wherein said vent sheet (20) is secured to the inner surface of said base sheet (14) at a location adjacent each of said end edges (24a, 24b). A wound dressing (10) as defined in claim 1 wherein each said opening in said base sheet (14) is generally circular. A wound dressing (10) as defined in claim 1 wherein said base sheet (14) contains a single said opening (16), said vent sheet (20) has a pair of side edges (22a, 22b) and a pair of end edges (24a, 24b) connecting said side edges (22a, 22b), and said opening (16) is generally located between said edges (22a, 22b, 24a, 24b) of said vent sheet (20). A wound dressing (10) as defined in claim 1 wherein said base sheet (14) has an adhesive layer (18) on the outer surface thereof for securing the base sheet (14) to the skin (S). A wound dressing (10) as defined in claim 1 wherein said outer wall member (40, 46) comprises a liquid-impermeable first sheet material (40) having at least one opening or window (40a) through which air can pass, each said opening or window (40a) being covered by a second sheet material (46) of slightly larger dimensions than the dimensions of said window or opening (40a) it covers, each said second sheet material (46) being sealed to said first sheet material (40) to provide an effective bacterial barrier around the periphery of each said opening or window (40a), each said second sheet material (46) comprising an air-permeable bacterial barrier. A wound dressing (10) as defined in claim 1 wherein said chamber (42) has a bottom wall member (36) permeable to wound fluids, said bottom wall member (36) and said base sheet (14) being sealed together around their common periphery. A wound dressing (10) as defined in claim 11 wherein said bottom wall member (36) comprises a substantially liquid-impermeable sheet material (36), said sheet material having a plurality of perforations (38) permitting passage of said wound fluid therethrough to within said chamber (42).

Inventors: GILMAN THOMAS, GILMAN, THOMAS
Applicants: KENDALL & CO, THE KENDALL COMPANY
Application year: 1991
Main classification: A61F13
IPC codes: A61F13