[0028] The present invention lends itself to use in conjunction with surgical techniques that require repeated access to the abdominal cavity after surgery therein. The present invention is directed toward providing a removable and beneficial dressing that facilitates both healing of the wound and its final closure. Reference is made to U.S. patent application Ser. No. 08/951,832 and also to U.S. Ser. No. 09/078,223 and GB Patent No. 2307180 (WO 94/20041 and WO 97/18007), for a description of a negative pressure system suitable for implementing the vacuum required for use of the dressing structures, and treatment method, described herein. The disclosure of these documents is incorporated herein by reference. Negative pressure is defined herein as a vacuum of less than 1 atmosphere of pressure. Controlling the negative pressure and collecting and disposing of exuded fluids are also described in the above cited references. The manner of using such systems in conjunction with the dressing structure described herein will become apparent to those of ordinary skill in the art.

[0029] Reference is made to FIG. 1 for a description of a first embodiment of the present invention wherein a single lower layer of foam is utilized in the wound contact layer of the dressing. Both FIG. 1 and FIG. 2 are partially exploded views of the dressing of the present invention. During use, the layers of foam and the intervening sheets of elastomeric material would be in close and sometimes sealed contact with each other.

[0030] The complete wound dressing 10 shown in FIG. 1 comprises upper foam layer 12 and lower foam layer 36 . Lower foam layer 36 is enveloped within two sheets of elastomeric material 38 such as are used for the membranes of surgical drapes. The elastomeric sheets 38 may preferably be constructed from polyurethane film, which provides both the necessary strength and resiliency needed for placement in direct contact with the wound. Another suitable material is polytetrafluoroethylene (PTFE). Elastomeric sheets 38 are sealed on their periphery, e.g. by welding or adhesive, in a manner that surrounds the lower layer of foam 36 . Elastomeric sheets 38 resist the formation of wound adhesions and are therefore appropriate for placement in direct contact with the tissue surfaces within the wound and around the wound periphery.

[0031] Placing such non-porous film material in contact with the wound opening, rather than open cell foam or a mesh material greatly reduces the occurrence of adhesions that, over time would make removal of the dressing difficult or dangerous. The pliable and flexible lower layer envelope is easily inserted over and/or into the wound. The lower layer envelope may, as desired, be placed either over the wound wherein the edges of the layer are in contact with the skin surrounding the wound or preferably into the wound leaving the upper surface of the upper surface of the lower layer envelope exposed above the wound.

[0032] The overall dressing 10 has a generally flat profile as shown in cross section in FIG. 2 and FIG. 3 . The shape of the dressing can vary significantly depending on the size and shape of the wound to which it is to be applied. A rectangular or square shape having dimensions on the order of 8 inches by 8 inches up to as much as 18 inches by 18 inches might be appropriate for use in conjunction with the abdominal wounds described above. Other dimensions and shapes, such as circular, oval or even oblong may be suitable for other types of wounds. Typical dimensions for thicknesses and for planar dimensions of oval or elliptical foam slabs are given above. This basic structure may be easily implemented with any of these, or even other, shapes and sizes.

[0033] Elastomeric sheets 38 are provided with a plurality of holes 32 and 34 in the upper and lower walls 28 and 30 of the envelope they define. These holes may be of the order of 3 mm (⅛ inch) to 6 mm (¼ inch) in length, diameter or maximum dimension and may be dispersed across the surface of the defined envelope on 25 to 75 mm (1 inch to 3 inch) centres. Preferably, the holes are slit- or slot-shaped. The positions of the holes may be associated with holes positioned into and through lower foam layer 36 as described in more detail below. Where holes are provided in the foam, they may be of different sizes and shapes.

[0034] Lower foam layer 36 is preferably constructed from polyurethane having a high degree of reticulation and good permeability under suction. Foams having at least 90% and preferably 95% of interconnecting cells are preferred. Preferably, the foams have from 20 to 60 pores per inch Preferably, the polyurethane foams are prepared by reacting a hydrophilic polyether polyol with a tolylene diisocyanate in the presence of water. Carbon dioxide is liberated in the reaction which provides a gaseous blowing agent. Pore size can be controlled by temperature and stirring. Reticulation is enhanced by maintaining the foam in the chamber in which the foam is initially formed and causing the blowing agent to expand further and rupturing cell walls.

[0035] As indicated above, lower foam layer 36 is punctuated by a plurality of holes that pass entirely though the layer from its upper to lower surface. As will be seen from their placement with respect to holes 32 and 34 in the elastomeric envelope, the holes in the lower foam layer 36 are provided to form “sinks” into which the exuded fluids from the wound may be drawn. Holes 34 in the lower surface of the elastomeric envelope 38 may be positioned directly over the holes in the foam layer 36 .

[0036] Holes 32 in the upper surface 28 of the elastomeric envelope 38 are preferably positioned so that they are not aligned with the holes in the foam layer 36 and the holes in the lower surface 30 of the envelope 38 . In this manner, fluids are withdrawn (by appropriate negative pressure) from the wound into the holes 34 positioned in the lower surface 30 of the envelope 38 and into the “sink” holes in the lower foam layer 36 . The fluids are then drawn into the cells of the lower foam layer 36 where they are dispersed before again being drawn through holes in the elastomeric envelope 38 , this time in the upper surface 28 of the envelope 38 . Placement of the lower foam layer/envelope onto or into the wound therefore requires proper orientation of the holes as shown.

[0037] A problem encountered in the prior art has been the deterioration of flow caused by the clogging of the medium through which the exuded fluids, and the accompanying debris, must flow. Such flows are drawn towards the source of the negative pressure thus becoming clogged most quickly along the direct path towards the vacuum source, in this case the suction tube. The present invention disperses the vacuum so as to de-localize the flow. The layers of foam and the spaced holes in the elastomeric sheets provide this dispersion. Even without an interleaved layer of foam, the off set holes accomplish this purpose. The dark arrows in both FIG. 1 and FIG. 2 show the flow of exuded fluid through the dressing.

[0038] Upper foam layer 12 provides the initial mechanism for dispersing the vacuum that draws the fluids up from the wound. In the presently preferred embodiment as shown in FIG. 1 , upper foam layer 12 is a coarser polyester-based or polyurethane foam having greater rigidity than the lower layer of polyurethane foam. For example, the lower layer of foam 36 may have about 1.5 to 2 times the pores per inch of the coarser foam layer. Typically, the coarse layer of foam may have 20 to 30 pores per inch. Upper foam layer 12 should be somewhat less pliable so as to hold its shape under the influence of even relatively strong negative pressure. Upper foam layer 12 is placed in direct contact with the upper surface 28 of the elastomeric envelope 38 containing lower foam layer 6 . Covering upper foam layer 12 and the balance of the dressing is elastomeric drape 14 , which in the preferred embodiment is made of the same type of polyurethane film, as is elastomeric envelope 38 .

[0039] Drape 14 is a single sheet, cut large enough to fully cover upper foam layer 12 and an additional area of skin surrounding the wound site. A pressure sensitive adhesive, such as a permanently tacky acrylic adhesive, is coated on at least the periphery of drape 14 for creating an airtight seal against the skin, effectively closing the dressing and the wound beneath it.

[0040] Connector 16 is positioned over a hole cut in drape 14 and is fixed thereto by sealing patch 22 . Sealing patch 22 , which is circular in the preferred embodiment, adheres to a bottom flange portion 20 of connector 16 as well as drape 14 . In this manner, a negative pressure is drawn in upper foam layer 12 when an appropriate suction line is attached to tube connector 18 positioned on connector 16 . Flange portion 20 may have a lower surface shaped with channels to direct flow of fluid from the porous pad to the tubular portion 18 of the connector. A suitable suction head connector is shown in GB 2329127 and in U.S. Pat. NO.6,216,701 (WO 99/13793).

[0041] Another embodiment of the present invention is depicted in FIG. 3 . In this embodiment, the principles of operation are identical, but the dressing is comprised of but a single foam layer, the foam layer within the non-porous film is dispensed with. The foam utilized is black coloured open cell polyurethane currently commercialised in assignee's V.A.C. product.

[0042] Referring to FIG. 3, a flexible sheet 38 of semi-stiff plastics material, e.g. formed from plasticised pvc is placed in contact with the wound so that the trimmed edges line the walls of the wound. The sheet is formed with holes 34 which are preferably slits or narrow slots. A reticulated plastics foam is placed on top of the sheet 38 . A suction head connector 16 is placed with its flange portion 20 in contact with the top surface of the foam pad and a surgical drape 14 is placed over the foam and the sheet 38 to seal the dressing in the wound.

[0043] Instead of providing a separate sealing patch 22 to seal the connector to the dressing, the patch may be part of the surgical drape, as described and illustrated in GB 2,329,127 and U.S. Pat. No. 6,216,701.

[0044] The dressing structure of the present invention could be applied in a number of circumstances in association with a variety of different wound types. In the case of an open abdominal wound as might result from surgery, the lower foam layer contained within the elastomeric envelope would be positioned within the wound with the periphery possibly extending under the fascia and peritoneum of the abdominal wall. The upper foam layer could then be cut to a size appropriate for positioning on the exposed upper surface of the lower layer envelope. The drape with the appropriately positioned spigot may then be placed over the upper foam layer and the wound as a whole, extending two or more inches over the skin surrounding the wound, and adhesively holding the dressing in place. Application of a suction line as described above draws the entire dressing onto the wound and serves to initiate the flow of effluent through the dressing.

[0045] The thickness of the upper and lower foam layers is determined in part by the desire to have a flat profile to the dressing when it is in place. The more rigid upper layer of foam may, in the preferred embodiment, have a thickness on the order of 25 to 75 mm (1 inch to −3 inches) uncompressed. Its rigidity should limit compression to 80%-90% under the negative pressures normally associated with wound suction and the like. The more pliable lower foam layer, where employed, should have a thickness on the order of 5 to 15 mm, e.g. 5 to 10 mm (about ¼ to ¾ inch) so as to be capable of being easily inserted into the wound.

[0046] The structure of the present invention may likewise be utilized on the surface of the skin when the open wound is not associated with an internal cavity or the like. In such a case the periphery of the elastomeric lower envelope may contact the skin surrounding the wound. This is appropriate as long as the periphery of the drape covering the upper foam layer extends suitably beyond the lower envelope to adhere to the skin and seal the dressing. It therefore becomes apparent that the lower elastomeric envelope may be pre-made in a variety of shapes and sizes while the upper foam layer and the drape may be cut, at the time the dressing is placed on the wound, to the appropriate size and configuration.

[0047] FIG. 2 discloses an alternate preferred embodiment of the present invention wherein the single lower layer of foam shown in FIG. 1 is replaced with a double layer of foam. In this embodiment, elastomeric envelope 38 encloses a first lower foam layer 40 and a second lower foam layer 42 . The advantage realized by this arrangement lies in the offset positioning of the holes interspersed in both foam layers. Holes 34 punctuating the lower wall 30 of elastomeric envelope 38 remain positioned in line with the “sink” holes positioned in the second (bottom) layer of foam 42 . Holes 32 punctuating the upper wall 28 of elastomeric envelope 38 are, as described above, offset from alignment with holes 34 in the lower surface of the envelope, but are aligned with the “sink” holes positioned in the first (top) layer of foam 40 . Under this structure further dispersion of the flow of fluid occurs thus decreasing the localization of clogging debris and prolonging the effective life of the dressing. The remaining components, applications, and methods of use of the dressing are as described above in conjunction with FIG. 1 .

[0048] The present invention has been described in conjunction with certain preferred embodiments. Alternative embodiments and further applications of the invention will be anticipated by those skilled in the art without departure from the basic concepts and principles of the invention. Certain materials have been descried as suitable for the specific layers of foam and film although a variety of similar materials would be equally suitable. Certain geometries and dimensions have been described as appropriate under various conditions and with various applications of the dressing, especially in conjunction with open and re-enterable abdominal wounds. These geometries and dimensions are not intended as limiting but are described as representative of the various shapes and sizes possible using the fundamental layered structure of the dressing. The scope of the invention is therefore not limited by the foregoing description but is best defined by the specific claims that follow.