Patent Description:
Use of an oxygen chemical scavenger to produce negative pressure relative to atmosphere in a fixed volume system is considerably less expensive, requires no power supply, and is silent in operation. However, an oxygen chemical scavenger naturally produces a negative pressure of <NUM>-160mmHg, or internal pressure of <NUM>-600mmHg (depending on relative humidity, RH) by removal of the oxygen that constitutes <NUM>% of dry air.

<CIT> discloses a wound covering assembly with of wound covering membrane and a removable layer. The wound covering membrane can allow liquid or air to pass through the wound covering membrane from a wound site covered by the wound covering membrane to ambient and vice versa. The removable layer covers a portion of the wound covering membrane and is removable from the wound covering membrane when the wound covering membrane is affixed to skin around the wound site. The removable layer is configured and connected with the wound covering membrane such that air and liquid are inhibited from passing through the wound covering membrane and the removable layer when the wound covering membrane is affixed to skin surrounding the wound site and the removable layer is connected with the wound covering membrane. The wound covering assembly can be used with a pump assembly to provide negative pressure to the wound site. The pump assembly disclosed in <CIT> comprises a pump and a pump drape. The pump drape connects with the pump. The pump drape is configured to inhibit passage of air and liquid through the pump drape. The pump drape is also configured to affix this to the wound covering membrane or human skin and to cover the at least opening after the removable layer has been removed from the wound covering membrane.

According to an aspect, a negative pressure tissue treatment system comprises a drape formed of a flexible material capable of maintaining a negative pressure underneath the drape upon application of a vacuum. A gasket material is secured on a skin-facing surface of the drape. The gasket material together with the drape define an enclosed volume beneath the drape and surrounded by the gasket material when the drape is affixed to skin around a tissue site. A reactor housing defines a closed chamber in fluid communication with the enclosed volume. A reactor is positioned in the closed chamber and is configured to consume oxygen. The closed chamber and the enclosed volume define a system volume. The drape and the reactor housing are configured such that the system volume reduces from an initial system volume toward a reduced system volume that is between about <NUM>% and about <NUM>% of the initial system volume as a result of the reactor consuming oxygen from the system volume.

The invention is not limited in its application to the details of construction and arrangement of components provided in the following description or illustrated in the attached drawings. The invention is capable of other embodiments and being practiced in various manners. Moreover, the use of "including," "comprising," or "having" and variations thereof is meant to encompass the items listed thereafter and equivalents thereof as well as additional items. The present disclosure generally relates to negative pressure-type wound systems, but the system described herein need not always be used with wound therapy and can be used in other applications.

For <NUM>% RH at room temperature, water vapor pressure is about 9mmHg. For dry air, removal of <NUM>% oxygen will produce a negative pressure of 158mmHg (760mmHg - 9mmHg = <NUM> mmHg). While this is still regarded as within the therapeutic range, lower negative pressures relative to atmosphere are often preferred as more comfortable for the patient and less likely to cause tissue stress when applied and removed.

It is recognized that a dressing sealed to patient skin will likely contain a higher water vapor pressure than those discussed below, since local atmospheric RH will vary, the skin will have a near-constant water vapor pressure and the temperature within the system will be somewhat closer to body temperature. These variables will have only a minor effect on the quantitative calculations below.

Allowing the NPWT system volume to decrease controllably under negative pressure can produce a controlled negative pressure less than the "natural" <NUM>-160mmHg (internal pressure <NUM> ± 5mmHg). As shown in the calculations below, a volume reduction of <NUM>%-<NUM>% will produce a negative pressure of about 120mmHg, and a volume reduction of about <NUM>% will produce a negative pressure of about 80mmHg. <MAT> where P1 = 605mmHg (155mmHg negative pressure).

With reference to <FIG> and <FIG>, a negative pressure tissue treatment system <NUM> includes a drape <NUM>, a gasket material <NUM>, a reactor housing <NUM>, a reactor <NUM>, and fluid connections <NUM> (depicted schematically). The negative pressure tissue treatment system <NUM> can include further components that will be described in more detail below. The drape <NUM> is made of a flexible material capable of maintaining a negative pressure underneath the drape <NUM> upon application of a vacuum. The gasket material <NUM> is positioned underneath the drape <NUM> when the drape <NUM> is affixed to skin S and defines an enclosed volume <NUM> beneath the drape <NUM> and surrounded by the gasket material <NUM> when the drape <NUM> is affixed to skin S around a wound, surgical incision, or other tissue site (hereinafter simply referred to as a "tissue site") so as to maintain a negative pressure environment beneath the drape <NUM> and around the tissue site for extended periods of time, and also allows easier handling for placement of the dressing onto the skin. The reactor housing <NUM> defines a closed chamber <NUM> in fluid communication with the enclosed volume <NUM> via the fluid connections <NUM>. The reactor <NUM> is positioned in the closed chamber <NUM> and is configured to consume oxygen. The closed chamber <NUM>, the enclosed volume <NUM> and the fluid connections <NUM> define a system volume, i.e., a volume of air from which the reactor <NUM> consumes oxygen. The drape <NUM>, the reactor housing <NUM> and/or the fluid connections <NUM> is/are configured such that the system volume reduces from an initial system volume toward a reduced system volume that is between about <NUM>% and about <NUM>% of the initial system volume as a result of the reactor <NUM> consuming oxygen from the system volume.

The drape <NUM> can be a thin film capable of maintaining a negative pressure underneath the drape <NUM> upon application of a vacuum. The thin film from which the drape <NUM> is made can be substantially impermeable to liquids but somewhat permeable to water vapor, while still being capable of maintaining negative pressure underneath the drape <NUM>. For example, the thin film material from which the drape <NUM> is made may be constructed of polyurethane or other semi-permeable material such as that sold under the Tegaderm® brand or <NUM> TPU tape available from <NUM>. Similar films are also available from other manufacturers. Even though the film from which the drape <NUM> is made may have a water vapor transmission rate of about <NUM>/m<NUM>/day or more, these films are still capable of maintaining negative pressure underneath the drape <NUM> when an appropriate seal is made around the periphery of a tissue site. The drape <NUM> can be made from other flexible materials capable of maintaining a negative pressure underneath the drape <NUM> upon application of a vacuum, such as silicone, rubber and the like.

When the drape <NUM> is made from a thin film, the drape <NUM> can be cast onto a casting sheet <NUM>, which can be made from paper, as part of a dressing <NUM>. When the dressing <NUM> is assembled, the casting sheet <NUM> can be kiss cut to provide a casting sheet opening <NUM>. The drape <NUM> can be made from a transparent material such the gasket material <NUM> can be visible within a "window" defined by the casting sheet opening <NUM> in the casting sheet <NUM>.

A pressure-sensitive acrylic-based adhesive <NUM> can be applied on a skin-facing surface <NUM> of the drape <NUM>. Other types of adhesives could be applied to the drape <NUM>, however, a pressure-sensitive acrylic-based adhesive is known to provide strong initial tack that can last for a relatively long time, for example a few days, when in contact with the skin. The pressure-sensitive acrylic-based adhesive <NUM> can be applied over an entirety of the skin-facing surface <NUM> of the drape <NUM>, which can also be useful to retain other components of the dressing <NUM> during assembly.

The drape <NUM> can also include an opening <NUM>, which can allow for the connection of a vacuum source <NUM> to the dressing <NUM>. The opening <NUM> can be cut through the casting sheet <NUM> (prior to removal of the portion of the casting sheet <NUM> which forms the casting sheet opening <NUM>) and the drape <NUM> within an area surrounded by the gasket material <NUM>. A fitting <NUM> (schematically depicted in <FIG>) can be placed over the opening <NUM> and connect to a vacuum source <NUM>, which includes the reactor <NUM>, via a hose <NUM> (also schematically depicted in <FIG>), which along with the fitting <NUM> can be a component of the fluid connection <NUM>. An air-permeable/liquid-impermeable filter <NUM> can be provided covering the opening <NUM> in the drape <NUM>. As shown in <FIG> and <FIG>, the air-permeable/liquid-impermeable filter <NUM> is positioned against the skin-facing surface of the drape <NUM>; however, the air-permeable/liquid-impermeable filter <NUM> can be provided on an outer surface of the drape <NUM>.

The gasket material <NUM> can be a silicone gel that is applied on a silicone gel backing film <NUM>. When used for negative pressure wound therapy applications, it is desirable that the gasket material <NUM> have the following functional characteristics: (<NUM>) the material from which the gasket material <NUM> is made is extremely biocompatible, i.e., able to be worn for durations measured in days and weeks, with no discernible effects to the skin on which it resides, (<NUM>) the material should have mild adhesive properties, relative to skin, so that the material does not become unsealed as the wearer performs activities of daily living, and (<NUM>) the material should be flexible and conformable to adjust to the movements of the patient, while maintaining a "vacuum" seal at all times. Of the available biomedical materials, silicone gel is identified as a gasket candidate, such as the gel available from Polymer Science, Inc. as part number PS-<NUM>. Other materials, such as hydrogel, could function as a sealing gasket but are not as biocompatible as silicone gel.

The vacuum source <NUM> includes the reactor <NUM>, which is a chemical oxygen scavenger that removes oxygen from the air within the enclosed volume <NUM> so as to reduce the gas pressure within the enclosed volume by approximately <NUM>%, unless there is a change in volume in the system volume. Since the vacuum source <NUM> in this embodiment includes the reactor <NUM>, which is a chemical oxygen scavenger, any leakage around the enclosed volume <NUM> is important to prevent. The ingress of outside oxygen, which could use up the reactor <NUM> in the vacuum source <NUM>, should be prevented from penetrating either through the drape <NUM> or the gasket material <NUM> or between the gasket material <NUM> and the skin S.

In <FIG>, the reactor <NUM> is positioned in the closed chamber <NUM>. The reactor <NUM> is in fluid communication via the fluid connection <NUM> and the opening <NUM> with the enclosed volume <NUM> beneath the drape <NUM> and surrounded by the gasket material <NUM> when the dressing <NUM> is affixed to skin S around the tissue site. The closed chamber <NUM>, which is defined by the reactor housing <NUM>, and/or the enclosed volume <NUM> typically does not communicate with ambient unless there is a leak in the negative pressure tissue treatment system <NUM>. This is in contrast to known negative pressure systems which employ a mechanical pump that draws air from an enclosed volume through the mechanical pump into ambient. Leakage in these mechanical pump systems is not as critical since the mechanical pump typically can overcome the effect of a relatively small flow of air entering the enclosed volume by way of leakage in the system. In contrast, too much leakage when using the reactor <NUM> may result in the reactor <NUM> being consumed and no longer able to scavenge oxygen.

The drape <NUM>, the reactor housing <NUM> and/or the fluid connection <NUM> is/are configured such that the system volume reduces from an initial system volume toward a reduced system volume that is between about <NUM>% and about <NUM>% of the initial system volume as a result of the reactor <NUM> consuming oxygen from the system volume. <FIG> depicts the drape <NUM> being drawn toward the skin S as a result of the reactor <NUM> consuming oxygen from the system volume, which reduces the volume of the enclosed volume <NUM>. Since the drape <NUM> is not a rigid housing placed over the tissue site, the initial volume of the enclosed volume <NUM>, i.e., prior to the reactor <NUM> consuming oxygen from the system volume, can reduce the system volume from the relatively larger initial system volume to the reduced system volume. In addition to or alternatively, the reactor housing <NUM> and/or the fluid connection <NUM> can reduce in volume as a result of the reactor <NUM> consuming oxygen from the system volume. <FIG> depicts the reactor housing <NUM> having side walls that draw in as a result of the reactor <NUM> consuming oxygen from the system volume and the fitting <NUM> including an elastic or resilient element (such as a dome-shaped element) <NUM> that draws in as a result of the reactor <NUM> consuming oxygen from the system volume. Each of these components, e.g., the drape <NUM>, the reactor housing <NUM> and the fluid connection <NUM> can be configured such that the system volume reduces from an initial system volume toward a reduced system volume that is between about <NUM>% and about <NUM>% of the initial system volume as a result of the reactor <NUM> consuming oxygen from the system volume.

If desired, the dressing <NUM> can include an island of absorbent material <NUM> useful to absorb exudate from a wound. The island of absorbent material <NUM> can be applied onto the skin-facing surface <NUM> of the drape <NUM> and affix to the drape <NUM> via the pressure-sensitive acrylic-based adhesive <NUM>. The island of absorbent material <NUM> has a smaller area than the drape <NUM> so as to leave a margin of adhesive-coated drape around the island of absorbent material <NUM>. The absorbent material from which the island of absorbent material <NUM> is made can be a super absorbent polyester. Examples of such absorbent materials include a hydroactive wound pad available under the trademark Vilmed®. A silicone coating <NUM> can be provided on a skin-contacting side of the island of absorbent material <NUM>, if desired, which is very compatible with skin and other tissue. As mentioned above, the drape <NUM> can be made from a transparent material such that the island of absorbent material <NUM> is visible when applying the dressing <NUM>. As is evident in the embodiment depicted in <FIG>, the casting sheet <NUM> is kiss cut around the area of the gasket material <NUM> so as to allow for the person placing the dressing <NUM> onto the tissue site to see both the gasket material <NUM> and the island of absorbent material <NUM> during placement of the dressing <NUM>.

With reference back to <FIG>, the island of absorbent material <NUM> can be spaced from the gasket material <NUM> at a predetermined distance, which can be a function of the system volume, so as to allow the drape <NUM> to be drawn toward the skin S between the island of absorbent material <NUM> and the gasket material <NUM> as oxygen is being removed from the system volume. The spacing between the island of absorbent material <NUM> and the gasket material <NUM> can be configured such that the system volume reduces from an initial system volume toward a reduced system volume that is between about <NUM>% and about <NUM>% of the initial system volume as a result of the reactor <NUM> consuming oxygen from the system volume based on the flexibility of the drape <NUM> and/or the compressibility of the absorbent material from which the island of absorbent material <NUM> is made.

Where the island of absorbent material <NUM> is compressible, its use to reduce the system volume and lower the negative pressure also mitigates some of the effect of absorbed exudate from a wound or incision. In a rigid system, e.g., one in which the drape is made from a rigid material, absorption of exudate will displace air volume, causing the net pressure to increase (and the negative pressure to decrease). If volume reduction is controlled by the net pressure on the system, lowering the air volume due to exudate will also increase the system volume due to the increased air pressure. Thus, the net loss of negative pressure will be less than that of a rigid volume system.

The reactor housing <NUM> can be configured such that its side walls, or another resilient or flexible component on the reactor housing <NUM>, draws in as a result of the reactor <NUM> consuming oxygen from the system volume. The side walls or other resilient or flexible component on the reactor housing <NUM> can be configured such that the system volume reduces from an initial system volume toward a reduced system volume that is between about <NUM>% and about <NUM>% of the initial system volume as a result of the reactor <NUM> consuming oxygen from the system volume. The degree to which the side walls or other resilient or flexible component on the reactor housing <NUM> draws in or compresses so as to reduce the volume of the closed chamber <NUM> can be a function of the system volume so that the system volume reduces from the initial system volume toward a reduced system volume that is between about <NUM>% and about <NUM>% of the initial system volume as a result of the reactor <NUM> consuming oxygen from the system volume.

Similarly, the elastic or resilient element <NUM> on the fitting <NUM> can also be configured to draw in as a result of the reactor <NUM> consuming oxygen from the system volume. The degree to which the elastic or resilient element <NUM> draws in or collapses so as to reduce the volume of the fluid connection <NUM> can be a function of the system volume so that the system volume reduces from the initial system volume toward a reduced system volume that is between about <NUM>% and about <NUM>% of the initial system volume as a result of the reactor <NUM> consuming oxygen from the system volume.

Each of the drape <NUM>, the reactor housing <NUM> and the fluid connection <NUM> can be configured such that the system volume reduces from an initial system volume toward a reduced system volume that is between about <NUM>% and about <NUM>% of the initial system volume as a result of the reactor <NUM> consuming oxygen from the system volume. In other words, the drape <NUM>, the reactor housing <NUM> and the fluid connection <NUM> can all collapse to result in a reduction of system volume, or only one or two of the drape <NUM>, the reactor housing <NUM> and the fluid connection <NUM> can collapse.

In addition, the drape <NUM> can be configured to collapse even further so that the reduced system volume approaches zero ml or cc. This can be beneficial in situations where negative pressure with respect to atmosphere need not be in the therapeutic range discussed above, but limiting the oxygen around the wound is desirable. For example, the reactor <NUM> can be placed in the enclosed volume <NUM> or in a chamber (similar to the closed chamber <NUM>) having little or no volume. As the drape <NUM> collapses toward the skin S as a result of oxygen being removed from the enclosed volume <NUM>, the enclosed volume <NUM> would reduce from an initial volume toward a reduced volume. As such, the pressure in the enclosed volume <NUM> would rise toward atmospheric pressure, but oxygen would be removed from the enclosed volume <NUM> and thus around the tissue site surrounded by the gasket material <NUM>.

Claim 1:
A negative pressure tissue treatment system comprising:
a drape (<NUM>) formed of a flexible material capable of maintaining a negative pressure underneath the drape (<NUM>) upon application of a vacuum;
a gasket material (<NUM>) secured on a skin-facing surface of the drape (<NUM>), the gasket material (<NUM>) together with the drape (<NUM>) defining an enclosed volume (<NUM>) beneath the drape (<NUM>) and surrounded by the gasket material (<NUM>) when the drape (<NUM>) is affixed to skin around a tissue site;
a reactor housing (<NUM>) defining a closed chamber (<NUM>) in fluid communication with the enclosed volume (<NUM>);
a reactor (<NUM>) positioned in the closed chamber (<NUM>) and configured to consume oxygen,
wherein the closed chamber (<NUM>) and the enclosed volume (<NUM>) define a system volume,
characterized in that the drape (<NUM>) and the reactor housing (<NUM>) are configured such that the system volume reduces from an initial system volume toward a reduced system volume that is between about <NUM>% and about <NUM>% of the initial system volume as a result of the reactor consuming oxygen from the system volume, and
the closed chamber (<NUM>) is remote from the enclosed volume (<NUM>), the enclosed volume (<NUM>) is in fluid communication with the closed chamber (<NUM>) via a fluid connection (<NUM>) including a hose (<NUM>), and the fluid connection (<NUM>) further defines the system volume.