the composite wound dressing of the present disclosure promotes healing of a wound via the use of a vacuum reservoir . the vacuum reservoir subjects the wound to vacuum or subatmospheric pressure to effectively draw wound fluid including liquid exudates from the wound bed without the continuous use of a vacuum source or pump . hence , vacuum pressure can be applied once or in varying intervals depending on the nature and severity of the wound until the composite wound dressing is saturated with exudate or the wound is healed . if the wound dressing is saturated with exudate and the wound is not healed , certain and / or all layers of the composite wound dressing can be replaced and the process of applying subatmospheric pressure can be repeated . referring now to fig1 - 3 , the composite wound dressing 100 in accordance with a preferred embodiment of the present disclosure is illustrated in the form of an article with multiple layers arranged in juxtaposed or superposed relation . the multiple layers include , but , are not limited to a lower or base layer 102 , an absorbent / packing layer 104 , an adherent layer 106 , and a top layer 108 which includes and / or defines the internal vacuum reservoir 110 . the base layer 102 is in direct contact with the wound bed “ w ”. the base layer 102 is typically porous allowing passage of subatmospheric pressure to the wound bed . in one preferred embodiment , the base layer includes a “ non - adherent ” material . “ non - adherent ” as used herein refers to a material that does not adhere to tissues in and around the wound bed . “ porous ” as used herein refers to a material which contains numerous small perforations or pores which allow wound fluids of all kinds to pass through the material to the dressing layers above . the passage of wound fluid through the porous material may be unidirectional such that wound exudate does not flow back to the wound bed . this direction flow feature could be in the form of directional apertures imparted into the material layer , a lamination of materials of different absorption to the base layer 102 or specific material selection that encourages directional flow . exemplary materials used as the base layer 102 include a contact layer sold under the trademark xeroflow ® by kendall corp ., a division of tycohealthcare . in the alternative , the base layer 102 may include an adherent material . in addition , agents such as hydrogels and medicaments could be bonded or coated to the base layer 102 to reduce bioburden in the wound , promote healing and reduce pain associated with dressing changes or removal . medicaments include , for example , antimicrobial agents , growth factors , antibiotics , analgesics , debridement agents and the like . furthermore , when an analgesic is used , the analgesic could include a mechanism that would allow the release of that agent prior to dressing removal or change . exemplary triggers of a release mechanism could be temperature change . the layer proximal to the base layer 102 or composite structures making the base layer 102 is the absorbent / packing layer 104 . the absorbent / packing layer 104 of the wound dressing 100 is intended to absorb and capture wound fluid and exudates . exemplary absorbent materials include foams , nonwoven composite fabrics , hydrogels , cellulosic fabrics , super absorbent polymers , and combinations thereof . typically , the absorbent / packing layer 104 can absorb up to about 100 cubic centimeters ( cc ) or more of wound fluid . preferably , the absorbent material includes the antimicrobial dressing sold under the trademark kerlix ® by kendall corp ., a division of tycohealthcare . in one preferred embodiment , the absorbent / packing layer 104 could be preformed or shaped to conform to varying shapes of the wound bed . those skilled in the art will recognize that the absorbent / packing layer 104 can be formed in any suitable shape . absorbent / packing layer 104 may include multiple layers . the only requirement as to shape is that the absorbent / packing layer 104 is suitable to treat a particular shape of the wound . additionally , the absorbent / packing layer 104 could be treated with medicaments . medicaments include , for example , an anti - infective agent such as an antiseptic or other suitable antimicrobial or combination of antimicrobials , polyhexamethylene biguanide ( hereinafter , “ phmb ”), antibiotics , analgesics , healing factors such as vitamins , growth factors , nutrients and the like , as well as a flushing agent such as isotonic saline solution . with continued reference to fig1 - 3 , the adherent layer 106 at least encompasses the perimeter of the wound dressing 100 to surround the wound bed to provide a seal around the perimeter of the wound bed “ w ”. for instance , the sealing mechanism may be any adhesive bonded to a layer that surrounds the wound bed “ w ” or an adhesive applied directly to the skin . the adhesive must provide acceptable adhesion to the tissue “ t ” surrounding the wound bed “ w ” skin , e . g ., the periwound area , and be acceptable for use on skin without contact deterioration ( for example , the adhesive should preferably be non - irritating and non - sensitizing .) the adhesive may be semi - permeable to permit the contacted skin to transmit moisture or may be impermeable . additionally , the adhesive could be activated or de - activated by an external stimulus such as heat or a given fluid solution or chemical reaction . adhesives include , for example , the dressing sold under the trademark ultec ® hydrocolloid dressing by kendall corp ., a division of tycohealthcare . the adherent layer 106 may also be in the form of an entire layer proximal to the absorbent / packing layer 104 or preferably is annular or “ donut shaped ” as shown . preferably , the adherent layer 106 is not bonded to the absorbent / packing layer 104 to allow for easy replacement of the absorbent / packing layer 104 . in a preferred embodiment , the adherent layer 106 is at least bonded to the periphery of the base layer 102 . in turn , the peripheral portion 108 a of the top layer 108 may be bonded to the adherent layer 106 to provide a seal around the perimeter of the wound . alternatively , the adherent layer 106 may be positioned on the peripheral portion 108 a of the top layer 108 and secured to the tissue “ t ” about the wound bed “ w ”, and not bonded to the base layer 102 . as a further alternative , the peripheral portion 108 a of the top layer 108 may include an adhesive surface . it is anticipated that removable contact liners may also be used to protect the adhesive surface of the adherent layer 106 prior to use . the top or upper layer 108 typically seals the top of the wound dressing 100 and helps maintain the appropriate vacuum level within the wound dressing 100 . in one preferred embodiment , the top layer 108 includes the flexible transparent dressing manufactured under the trademark polyskin ® ii by kendall corp ., a division of tycohealthcare . polyskin ® ii is a transparent , semi - permeable material which permits moisture and oxygen exchange with the wound site , and provides a barrier to microbes and fluid containment . in the alternative , the top layer 110 may be impermeable . as a further alternative , the top layer 108 may include a resilient , e . g ., elastomeric , material in the shape , e . g ., of a dome . the top layer 108 defines a sealed or enclosed vacuum reservoir 110 . the vacuum reservoir 110 is preferably maintained at an appropriate vacuum level for a predetermined period of time sufficient to initiate or complete healing of the wound bed “ w ”, i . e ., to draw wound fluid and exudate away from the wound bed “ w ” while subjecting the wound to subatmospheric pressure . the vacuum may be re - applied as needed to maintain a therapeutic effect . the vacuum may be continuous or intermittent as desired . as best seen in fig1 , the vacuum reservoir 110 is defined within the dome of the top layer 108 . as shown in fig2 , once vacuum is applied , the dome of the top layer 108 is drawn downwardly toward the absorbent / packing layer 104 with the vacuum or subatmospheric reservoir 110 created beneath the top layer 108 . typically , the top layer 108 includes a vacuum port or connector 114 in fluid communication with the vacuum reservoir 110 . preferably , the vacuum port 114 includes a one - way valve ( shown schematically as reference numeral 116 ) which provides unidirectional flow of suction and may provide a means for allowing connection of the composite wound dressing 100 to the vacuum source 112 . the one way valve 116 may be incorporated within the vacuum port 114 or , alternatively , be “ in line ” with the vacuum source 112 . a flexible tubing 118 is connected to the vacuum port 114 and the vacuum source 112 . the tubing 118 provides suction to the wound from the vacuum source 112 and enables the wound fluid to be transferred from the wound dressing 100 . the tubing 118 may be fabricated from pvc , silicone based material or other flexible materials ( polymers ). the tubing 118 may optionally include a connection to a collection canister 120 for wound drainage and debris . hence , the vacuum source 112 can draw wound fluid through the composite wound dressing 100 and tubing 118 into the canister 120 . in a preferred embodiment of the present disclosure , the canister 120 is portable so that the patient will have the freedom to move about rather than being confined to a fixed location . the canister 120 may also house an absorbent material to absorb wound fluid and exudate . the vacuum source 112 may apply vacuum to the wound by means such as a manual pump as disclosed in commonly assigned u . s . pat . no . 5 , 549 , 584 to gross , the entire contents of which are hereby incorporated herein by reference . in the alternative , the vacuum source 112 may include an automated pump . typically , the vacuum level is in a range between about 20 mmhg to about 500 mmhg , more preferably , about 40 mmhg and about 125 mmhg . the automated pump may be a wall suction apparatus such as those available in an acute or sub - acute care facility . the automated pump may be in the form of a portable pump . the portable pump may include a small or miniature pump that maintains or draws adequate and therapeutic vacuum levels . in a preferred embodiment , the pump is a portable , lightweight , battery operated , suction pump which attaches to the distal end of the tubing . typically , the vacuum source 112 has regulation means to apply the optimal vacuum pressure for healing the wound . furthermore , the vacuum source 112 would preferably contain a mechanism to detect a leak in the system if the optimal vacuum pressure is not achieved . preferably , the vacuum source 112 would also contain an indicator ( not shown ) to indicate when the optimal vacuum pressure is achieved . in the alternative , a hand pump in the form of a squeeze bulb or a foot pump may serve as the vacuum source 112 . preferably , a pump is used as the vacuum source 112 . typical pumps include diaphragm or voice coil activated styles that can deliver variable vacuum up to 50 cc / minute . with reference now to fig1 - 4 , the top layer 108 may include an access door 122 to provide access to the interior of the wound dressing 100 and / or the wound bed “ w ”. the door 122 could be a flap integrally formed with the top layer 108 or a separate component connected to the top layer 108 via a hinge or the like . the door 122 is preferably resealable to maintain the integrity of the vacuum reservoir 110 and provide a seal relative to the top layer 108 . one suitable means for releasably sealing the door 122 includes a snap fit arrangement , tongue and groove arrangement , “ zip lock ®” arrangement , adhesives , velcro ®, etc . the door 122 preferably provides access to the wound bed “ w ” to enable the clinician to monitor the status of the wound , change the absorbent / packing layer 104 , or apply additional medical treatment to the wound such as antimicrobial agents , growth factors , debriders , or other wound healing agents as needed . once the desired procedure is completed , the door 122 would be resealed relative to the top layer 108 to maintain the integrity of the vacuum reservoir 110 . fig4 illustrates the removal of the absorbent / packing layer 104 through the door 122 when the door 122 is in an open position . as discussed , a new absorbent / packing layer 104 subsequently may be introduced through the door 122 to absorb the exudates from the wound bed “ w ”. with reference now to fig3 and 5 , in conjunction with fig1 - 2 , the wound dressing 100 may include a visual indicator device 124 mounted to the top layer 108 to provide a visual indication of vacuum pressure within the wound dressing 100 . the visual indicator device 124 may include at least one electronic position indicator for detecting the relative position of the top layer 108 and the wound bed , and , thus the state of the vacuum within the wound dressing 100 . in accordance with this embodiment , the top layer 108 may have a resilient characteristic either through the material of construction of the top layer 108 or through reinforcement ( e . g ., elastomeric ) members incorporated in the top layer 108 . in one embodiment depicted in fig6 , the visual indicator device 124 includes at least one , preferably , three position - sensitive switches 126 a - 126 c , and a self - powered electronic signaling module 128 . the module 128 may include an electronic signaling module circuit board 130 , a battery power source 132 , at least one transducer including three light emitting diodes ( led ) 134 a - c and / or a loudspeaker 136 electrically connected 138 to the circuit board 130 . the leds 134 a - c are color coded red , yellow and green respectively . the position - sensitive switches 126 a - 126 c each may be a pressure sensor which electrically bridges contacts 140 a , 140 b of the visual indicator device 124 . in the embodiment shown , three position switches 126 a - c are mounted to top layer 108 . the switches 126 a - c include switch plates or contact arms arranged as a series of decreasing diameter annular coaxial elements . alternatively , the switches may be linear in configuration depending downwardly from the top layer 108 . the switch plate or contact arm of switches 126 a - c are of predetermined length extending downwardly from the top layer 108 within the vacuum reservoir 110 . ( fig4 and 5 ) the contact arm of outer switch 126 a of the pressure indicator 124 has the greatest length . the contact arm of the middle switch 126 b has a length less than the length of the contact arm of the outer ring 126 a . the contact arm of the inner switch 126 c has the smallest length . the contacts 140 a of switches 126 a - c are integrated within the contact arms . contacts 140 b of the switches 126 a - c may be disposed on the top surface of the absorbent / packing layer 104 or integrated within the absorbent / packing layer 104 in general longitudinal alignment with their respective contact arms . alternatively , the position sensor may be a magnetic proximity sensor . the self - powered electronic signaling module 130 may be any conventional modules adapted to emit light and / or audible sound etc . upon closing of the switch . when the top layer 108 is drawn down by vacuum pressure within the vacuum reservoir 110 toward its vacuum state of fig2 , inner switch 126 c is in contact with a respective coupler or contact 140 b disposed within the absorbent / packing layer 104 thereby energizing the visual indicator device 124 to illuminate the green led 134 c within the pressure indicator device mounted to the top layer 108 . the green light of the leds 134 c indicates a full vacuum condition of the vacuum reservoir 110 . as appreciated , switches 126 a , 126 b may also be in contact with their respective couplers in this vacuum condition of top layer 108 . however , it is envisioned that circuit board 130 will incorporate circuitry to override the electrical contact of these two switches when switch 126 c is in contact with its respective coupler . as vacuum pressure decreases and the dome of the top layer 108 begins to assume its normal condition of fig1 , through , e . g ., the resilient characteristic of the top layer 108 discussed hereinabove , the inner switch 126 c loses contact with the absorbent / packing layer 104 while the middle switch 126 b maintains / establishes electrical contact with its associated contact 140 b . the electrical connection of the middle switch 126 b results in illumination of the yellow led 134 b . the yellow led 134 b represents a partial vacuum or marginal vacuum condition of the vacuum reservoir 110 . as the vacuum pressure further decreases and the top layer 108 moves towards its fully expanded or normal condition of fig1 , the outer switch 126 a is the remaining switch in contact with its associated contact 140 b within the absorbent / packing layer 104 . in this condition , the red led 134 a is energized and visible to the clinician essentially providing a warning that the vacuum within the vacuum reservoir has dissipated or is nearly dissipated ( i . e ., subatmospheric pressure is close to or no longer present ). consequently , the vacuum source 112 may be actuated either manually or automatically to reestablish the vacuum state within the vacuum reservoir 110 . further vacuum loss will result in the remaining switch 126 c losing its contact where no lights are visible to the patient . it is also envisioned that the circuit board 130 could be devoid of the aforementioned override circuitry . as a result , in the full vacuum condition of dressing 100 , each of the green , yellow and red leds 134 a - 134 c would be illuminated while in the partial vacuum state , the yellow and red leds 134 a , 134 b would be illuminated and in the warning state , the red led 134 a would be illuminated . it is further envisioned that the loudspeaker 136 could emit an audible alarm when any of the aforementioned vacuum states are realized . fig7 illustrates an alternate embodiment of the visual pressure indicator 124 . in accordance with this embodiment , the visual pressure indicator 124 is mounted to the absorbent / packing layer 104 or positioned on the absorbent / packing layer 104 in juxtaposed relation . the top layer 108 is preferably transparent to permit viewing of the pressure indicator 124 through the top layer 108 and into the vacuum reservoir 110 . the positioning of the visual pressure indicator 124 is reversed or arranged on its back in a manner where the respective switches 126 a - c extend upwardly toward top layer 108 . the respective coupler or contacts 140 b are incorporated within the top layer 108 . in the full vacuum state or condition of fig2 , the contact 140 b of the top layer 108 is in contact with the switch 126 c thereby energizing the led 134 c to display the green color to the clinician . during healing , as the vacuum reservoir begins to lose its vacuum , the top layer 108 moves towards its open condition of fig1 , the inner switch 126 c loses its contact with its respective coupler 140 b of the top layer 108 resulting in electrical contact with the yellow led 134 b indicating a partial vacuum condition of the vacuum reservoir 110 . continued loss of vacuum within the vacuum reservoir 110 causes the electrical contact of the coupler 140 b with the outer switch 126 c . this contact of the led 134 c with the outer switch 126 c is indicated by the presence of its red color and may correspond to a loss or near loss of vacuum within the vacuum reservoir 110 thus prompting the clinician to activate the vacuum source 112 or pursue other clinical measures . fig8 illustrates another embodiment where the leds 134 a - 134 c are supplemented with additional visual indicia . the visual indicia may include various symbols which correspond to the state of the vacuum within the vacuum reservoir 110 . when a desired level of vacuum is reached , the “ smiley ” symbol 152 would illuminate indicating an adequate vacuum state . a partial vacuum state would result in the illumination of the “ caution triangle ” symbol 154 . a loss or near loss of vacuum would result in the illumination of the “ octagon ” symbol ( no vacuum ) 156 . one skilled in the art will readily appreciate the design of electronic circuitry to achieve this objective . fig9 - 11 illustrate an alternate embodiment of the present disclosure . in accordance with this embodiment , the visual indicator device 124 may include a series of rings 200 , 202 , 204 disposed on the underside of the top layer 108 , e . g ., printed on the top layer 108 , and arranged in concentric relation as shown . the rings include outer ring 200 , middle ring 202 and inner ring 204 and are color coded red , yellow and green , respectively . each colored ring 200 , 202 , 204 is positioned to contact the absorbent / packing layer 104 depending on the state or condition of the vacuum within the vacuum reservoir 110 . under full vacuum depicted in fig1 , all the rings 200 , 202 , 204 would contact absorbent / packing layer 104 and thus be activated and visible through the top of the wound dressing . as the vacuum within the reservoir dissipates or is reduced , the top layer 110 pulls away from the absorbent / packing layer 104 . in one embodiment with an elastomeric dome , the inner ring 204 first loses contact followed by the middle and outer rings , 202 , 200 , respectively , as the vacuum is reduced . as each colored ring 200 , 202 , 204 loses contact with absorbent / packing layer 104 , the respective ring becomes less visible or not visible from above the wound dressing 100 thus indicating to the clinician the condition of the vacuum within the vacuum reservoir . the rings 200 , 202 , 204 may incorporate electronic switches to be activated in the manner discussed hereinabove in connection with the embodiment of fig1 - 6 . alternatively , each ring 200 , 202 , 204 may incorporate an analytical test strip device which , e . g ., may detect the presence of a predetermined analyte in the exudates contained in the absorbent / packing layer 104 . upon contact with the predetermined analyte , the test strip device of each ring 200 , 202 , 204 assumes a color such as red , yellow or green . when a respective ring 200 , 202 , 204 loses contact with the predetermined analyte , the color of the respective ring may fade or assume a neutral color . one exampled of a color coded test strip device suitable for use with the present disclosure is disclosed in u . s . pat . no . 7 , 049 , 130 to carroll et al ., issued may 23 , 2006 , the entire contents of which are incorporated herein by reference . one skilled in the art may determine the parameters and characteristics of a test strip device to perform the objectives discussed hereinabove . in addition , the door 122 of the embodiment of fig9 - 11 is adapted to pivot along hinge 208 to provide access to the vacuum reservoir 110 . the opening of the door 122 is disposed adjacent the periphery of the wound dressing 102 and thus provides a relatively large access opening upon pivoting or opening the door 122 along the hinge 208 . this facilitates removal and replacement of absorbent / packing layer 104 . it is further contemplated that the wound dressing apparatus may incorporate external means or applications to stimulate tissue growth and / or healing . for example , an ultrasonic transducer may be incorporated into the wound dressing apparatus to impart mechanical energy for the treatment of the tissue such as , for instance , directing thermal or vibratory energy on the wound area to stimulate healing and / or further encouraging exudates removal by vacuum and / or introducing various drugs into the human body through the skin . other sensor types are also contemplated for incorporation into the wound dressing apparatus including oxygen , chemical , microbial and / or temperature sensors . the detection of oxygen adjacent the wound area would assist the clinician in determining the status of wound healing . the presence of an elevated temperature may be indicative of an infection . while the disclosure has been illustrated and described , it is not intended to be limited to the details shown , since various modifications and substitutions can be made without departing in any way from the spirit of the present disclosure . for example , it is envisioned the subject matter of the commonly assigned u . s . patent application ser . no . 11 / 517 , 210 , filed on sep . 6 , 2006 , and which claims priority to u . s . provisional application ser . no . 60 / 714 , 812 , filed on sep . 6 , 2005 , and the subject matter of the commonly assigned u . s . patent application ser . no . 11 / 516 , 216 , filed on sep . 6 , 2006 , and which claims priority to provisional application no . 60 / 714 , 912 , filed on sep . 7 , 2005 , ( the entire contents of each application being incorporated herein ) may be incorporated into the present disclosure . as such , further modifications and equivalents of the invention herein disclosed can occur to persons skilled in the art using no more than routine experimentation , and all such modifications and equivalents are believed to be within the spirit and scope of the disclosure as defined by the following claims .
a wound dressing apparatus includes a wound dressing member dimensioned for positioning relative to a wound bed . the wound dressing member including an internal vacuum reservoir and has a port in communication with the vacuum reservoir for applying subatmospheric pressure to the vacuum reservoir to facilitate removal of fluid from the wound bed . the wound dressing member includes a visual pressure indicator associated therewith for indicating a level of pressure within the vacuum reservoir . the visual pressure indicator includes color indicia having a plurality of colors corresponding to a condition of the pressure within the vacuum reservoir . the wound dressing member includes a lower absorbent member positionable adjacent the wound bed and an upper member which at least partially defines the vacuum reservoir . at least one of the top member and the lower absorbent member has the visual pressure indicator mounted thereto .