Novel absorbent pad for wound treatment

Abstract: Novel wound dressing (10) having a sealed absorbent fabric design and structure wherein an absorbent fabric providing a reservoir (20) for retaining wound exudate is contained between a bottom liquid-permeable sheet material (12) permitting the wicking or diffusion of wound exudate and an outer cover characterized as being a bacterial barrier, at least a portion (18) of the outer cover also being air-permeable for permitting egress of air from the interstices or voids in the fabric reservoir to the ambient atmosphere.

Description: This invention relates to novel wound dressings and, more particularly, to wound dressings such as those applied after surgery for the wicking and reservoir or retention of wound fluid. The prior art is replete with references to various types of wound dressings from the simplest of absorbent pads to the more sophisticated designs additionally providing a barrier to external contaminants. As an illustration of the latter, mention may be made of those described and claimed in U.S. Patent No. 4,499,896 which may additionally include an absorbent pad. GB-A-2,175,208 describes a wound dressing having adhesive on a front surface of a flexible base sheet. The dressing further comprises an absorbent pad and a flexible film completely covering said pad. This flexible film is said to be highly permeable to water vapor and oxygen. The task of the present invention, simply stated, is to provide a new and improved absorbent fabric structure for wound treatment which not only provides a complete barrier to bacteria and other external contaminants but also optimizes the wicking and amount of wound fluid which can be retained in the volume provided by the absorbent fabric, thereby minimizing the frequency of dressing changes required in the wound treatment procedure. BRIEF DESCRIPTION OF THE INVENTION In accordance with the present invention, this task is solved in an efficient, cost-effective and elegant manner by providing a sealed absorbent fabric design and structure wherein the absorbent fabric providing a reservoir for retaining wound exudate is contained between a thin bottom liquid-permeable film or sheet material permitting the wicking or diffusion of exudate from the wound to the absorbent fabric fluid reservoir contained therein; and an outer cover characterized as being a bacterial barrier, at least a portion of the outer cover also being air-permeable for egress of air from the interstices or voids in the fabric reservoir to the ambient atmosphere. In accordance with this invention, the novel sealed absorbent fabric structure of this invention is designed and adapted for placement directly on the wound. EP-A-0 441 418. filed concurrently describes and claims a modification thereof wherein the sealed fabric structure is employed for use in combination with a dressing of the type described in EP-A-0 392 640, which is a document citable under Art 54(3) EPC. BRIEF DESCRIPTION OF THE DRAWING Fig. 1 is a top plan view of the novel sealed fabric wound dressing of this invention; Fig. 2 is a bottom plan view of the dressing of Fig. 1; and Fig. 3 is a sectional view taken substantially as indicated along the line 3-3 of Fig. 1 with the thicknesses exaggerated for purposes of illustration. DETAILED DESCRIPTION OF THE INVENTION The desirability of removing exudate from the healing wound surface is of course well documented. Apart from the messiness of the exudate escaping from the confines of the dressing or diffusing laterally to cause the adhesive retaining the dressing to lose its aggressiveness for holding the dressing in place, the presence of the exudate on the wound is conducive to bacterial infection. For these primary reasons, it is well known to provide various reservoirs including plain gauze sponges, absorbent pads, hydrogel or other hydrocolloid materials and the like to retain wound exudate. It is also known in the art to provide a bacterial barrier cover for the dressing. As heretofore alluded to, U.S. Patent No. 4,499,896 describes an embodiment of a dressing wherein an absorbent fabric reservoir for retaining wound fluid is provided with a cover that is a barrier to bacteria and/or other external contaminants. However, the patented dressing contains no means for removal of air entrained within the interstices or voids of the fabric reservoir. Since removal or displacement of this entrained air is necessary to free these interstices to act as a sponge for retention of wound fluid diffusing thereto, it follows that the capacity of the patented dressing for receiving wound exudate is appreciably less than its potential. A primary task of this invention accordingly may be said to be to improve over the teachings of U.S. patent No. 4,499,896 and provide a wound dressing having an absorbent pad or fabric reservoir for receiving and retaining wound exudate, which dressing provides a complete barrier to bacteria and/or other external contaminants while at the same time optimizing the ability of the fabric reservoir to wick, i.e. receive wound fluid. This task is accomplished by providing the barrier with means permitting egress of air entrained in the fabric reservoir to the atmosphere, which entrained air will prevent optimum wicking of the wound fluid. In other words, it is axiomatic that for one fluid to be able to diffuse or wick to a given volume of space, any fluid (e.g. air) initially present therein must first be permitted to be displaced. More in particular, the invention relates to a wound dressing as described in claim 1. The nature and objects of the invention may best be understood by reference to the accompanying illustrative drawing taken in conjunction with the following detailed description. As shown therein, the novel dressing 10 of this invention comprises a bottom thin sheet or film 12 adapted for Placement on the skin over the wound (not shown). Film 12 is shown to have a plurality of perforations 14 permitting passage of the wound fluid therethrough to a porous fabric reservoir 20. Reservoir 20 is shown to be covered with a liquid-and bacteria-impermeable sheet 16. Sheet 16 and film 12 are sealed in liquid-and bacteria-tight relationship around their common periphery so that exudate cannot escape through the edges of the dressing, nor can any external contaminants, including bacteria, enter into the dressing and then pass through the porous film 12 to the underlying wound. As shown, the outer cover is provided with one or more windows or openings 16a to permit egress of air from the interstices of reservoir 20. Each such window or opening is shown to be covered by an air-permeable bacterial barrier sheet material 18 of slightly larger dimensions than the dimensions of opening 16a. As illustrated, sheet 18 is sealed around its periphery to the edges of sheet 16 around opening 16a so as to prevent ingress of bacteria around the edges of the opening. In order to secure the dressing to the skin, and to maintain the barrier function of the dressing against bacteria and other external contaminants, pressure-sensitive adhesive coating 22 is provided around the entire periphery of film 12. It will be appreciated that the adhesive coating 22 may and typically will be initially covered with a suitable release sheet or sheets to prevent premature contact of the adhesive prior to application of the dressing. Most preferably, the release sheet will be impermeable to bacteria to provide the additional function of maintaining the contaminant-free environment of the dressing during its shelf life and prior to application over a wound. 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 judgement 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 further illustration, film or sheet 12 may comprise any of the known perforated films adapted for placement on a wound surface and may 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 12 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 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 applying to the wound. 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. As will be appreciated, the particular material selected for film 12 should be "wound friendly", i.e. a material that is innocuous with respect to the healing wound and easily removable with minimal damage or insult to the healing skin. Water-impermeable sheet 16 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 16 must be imperforate as well as being flexible and conformable. Bacterial barrier 18 may comprise any of the per se known bacterial barrier air filters such as NUCLEOPORE, MILLIPORE, GELLMAN, etc. Reservoir 20 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 additional contain an antimicrobial agent such as chlorhexidine, although the use of such a reagent is not considered necessary. The adhesive employed around the periphery of bottom sheet 12 may be any of the known so-called medical grade adhesives heretofore employed for application to the skin. Such known adhesives include the rubber-based, acrylic, vinyl ether and hydrocolloid pressure-sensitive adhesives. It will of course be understood that in order to provide the bacterial barrier critical to the practice of this invention, the selected adhesive must be applied as a continuous layer around the periphery of the bottom sheet. As the particular materials selected per se comprise no part of this invention, in like manner it is not material to the practice of this invention how sheet 16 is secured in the described manner to sheet 18 and/or film 12. They may, for example, be secured in bacteria-tight relationship by heat sealing or by means of a suitable heat-or pressure-sensitive adhesive. It is to be expressly understood that the wound dressing shown in the illustrative drawing is capable of various modifications without departing from the scope of the invention herein contemplated. For example, since the bacterial barrier sheets are 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. Embodiments are also contemplated wherein the dressing does not have a perforate bottom sheet and, in lieu thereof, the absorbent pad is attached to the outer cover, e.g. by spot sealing. In such embodiments, the bottom sheet is not needed and the adhesive coating for securing the bandage and will instead be situated around the periphery of the cover sheet. 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 wound 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. 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) including a reservoir (20) for receiving and retaining wound fluids, which dressing (10) comprises: (a) a bottom sheet material (12) permeable to wound fluids adapted for placement on the skin over a wound; (b) an outer cover (16) being a bacterial barrier; the outer cover (16) and bottom sheet material (12) being sealed together around their common periphery in spaced relationship to define a chamber therebetween for receiving wound fluids diffusing through said bottom sheet material (12), wherein the seal provides a barrier against the ingress into said chamber of bacteria or other external contaminants; and (c) a fabric material disposed within said chamber, said fabric material having voids or interstices whereby to provide said reservoir (20) for receiving and retaining wound fluids, characterized in that said bottom sheet material (12) has a continuous, imperforate layer of a pressure-sensitive adhesive (22) around the entire periphery to permit securing of said bottom sheet material (12) to the skin surrounding the wound in an effectively bacteria-tight relationship, that, at least a portion of said cover (16) is air permeable, and that the air permeability of said cover (16) is sufficient to permit egress of air from said voids or interstices in said reservoir (20) to optimize the amount of fluids said reservoir (20) can receive by diffusion through said bottom sheet material (12). Wound dressing (10) according to claim 1, wherein said cover (16) comprises a liquid-impermeable first sheet material having at least one window (16a) through which air can pass, each said window (16a) being covered by a second sheet material (18) of slightly larger dimensions than said window (16a), said first sheet material (16) and each said second sheet material (18) being sealed to provide a bacterial barrier around the periphery of each said window (16a), each said second sheet material (18) comprising an air-permeable bacterial barrier. Wound dressing (10) according to claim 1 or claim 2, wherein said bottom sheet material (12) comprises a substantially liquid-impermeable material, said sheet material (12) having a plurality of perforations (14) permitting passage of wound fluid therethrough. Wound dressing (10) according to anyone of the preceding claims, wherein the fabric material reservoir (20) is in the form of a pad or sponge. Wound dressing (10) according to anyone of the preceding claims, including a release sheet covering said adhesive layer (22) and the bottom surface of said bottom sheet material (12).

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