Subatmospheric pressure dressing (SPD) is a United States Food and Drug Administration (FDA) approved, non-experimental device and treatment method for healing of open wounds, that has been commercially available in the United States since 1995. The device is manufactured by Kinetic Concepts, Inc., San Antonio, TX, and is marketed under the brand name VAC(TM) (vacuum assisted closure). It is currently being used in a number of medical centers in the United States. It has had the most dramatic impact on wound healing of any development in the past several decades.
The VACTM system employs a medical grade, reticulated, polyurethane ether foam dressing, with 400 to 600 um size pores that maximize tissue growth. Embedded in the foam is a non-collapsible evacuation tube that is connected to a bedside vacuum unit, which creates a specified subatmospheric pressure over the wound. Side ports in the evacuation tube allow communication to its lumen, while the open cell nature of the foam ensures equal distribution of any applied (subatmospheric) pressure to every surface of the wound in contact with the foam.
The SPD sterile foam dressing is trimmed at the bedside in a clean fashion to the appropriate size for each individual wound. The foam dressing is placed into the wound, allowing the evacuation tube to exit parallel to the skin surface. For very large wounds, multiple foam dressings are placed in contact with one another. Provided the foam dressings are in contact with one another, subatmospheric pressure transmitted to one foam is equally transmitted to all contiguous foam dressings. The surface of the wound containing the foam dressing is covered with an adhesive drape (Ioban(TM)), that extends 5 cm beyond the margins of the wound, onto adjacent intact skin, to create an airtight seal. The open wound is thus encased in a controlled, closed environment. The evacuation tube is located to avoid bony prominences and other stress intolerant tissues, so it does not become a source of pressure on adjoining tissues. The proximal end of the evacuation tube leads to a remote collection canister, into which the effluent from the wound is drawn when subatmospheric pressure is applied. Sensing devices are incorporated into the VACTM System collection canister, so that warnings are sounded when the canister is filled, to avoid uncontrolled, excessively rapid fluid egress. The magnitude of the subatmospheric pressure applied, and whether the vacuum application is continuous or intermittent is adjustable [Argenta, et al. 1997].
Russian medical literature describes the use of a "vacuum" version of SPD to heal wounds as early as 1966 [Mirazimov, et al. 1966]. German surgeons published reports of their use of SPD therapy on wounds in 1993 [Fleischmann, et al. 1993]. In the United States, a plastic surgeon began placing patents on his version of SPD in the early 1990s [Zamierowski 1990]. At approximately the same time, Argenta and Morykwas, of the Bowman Gray Medical Center Department of Plastic Surgery began work on the current commercially available version known as Vacuum Assisted Closure? (VAC?). Kinetic Concepts, San Antonio, TX, the manufacturer obtained FDA approval for the VAC? and has marketed it since 1995. The Argenta-Morykwas team published their landmark articles on SPD in 1997 [Argenta, et al. 1997; Morykwas, et al. 1997]. Their animal and human studies showed SPD to be effective in reducing edema, increasing local blood flow, decreasing bacterial wound count, promoting granulation tissue formation, and closing most varieties of open wounds. In applications to date, no serious complications have been reported that are attributable to SPD.
A review of the pathophysiology of subacute and chronic wounds helps explain how SPD treatment works in enhancing wound healing. Edema, infection, and poor blood flow are conditions that impair wound healing. Landis showed that edema detrimentally increases interstitial pressures and venous congestion and decreases capillary flow [Aston 1997]. Also, by mechanisms not completely understood, edema of chronic wounds has been shown to inhibit the cells crucial to wound healing [Falanga, et al. 1994]. SPD treatment reduces edema, increases local blood flow, and decreases bacterial wound count to a greater degree than WTMD. These vulnerary effects, in turn, stimulate wound healing and granulation tissue formation necessary for regenerative skin coverage and wound repair.
To date SPD treatment of amputation wounds has been limited. This application, however, especially in treatment of traumatic amputation wounds, such as those incurred from land mines where immediate closure is contraindicated because of wound contamination from (blast) injury, offers special promise. In the 1960's and early 1970's, progress in improving amputation wound healing was made with introduction of enhanced surgical procedures, including osseous beveling, myodesis, neurovasculature ligation, musculocutaneous flap rotation, incorporation of Penrose drains, etc.; and with development of immediate post-operative prosthetic fitting (IPOP) techniques and rigorous rehabilitative care programs [Weiss 1966, 1970; Schrock, et al. 1968; Burgess, et al. 1969]. Enhanced results were reported under the comprehensive and closely coordinated rehabilitative and prosthetics care programs developed at the respective institutions [Burgess, et al. 1968; Goldbranson, et al. 1967; Mooney, et al. 1971; Wu and Krick 1987]. However, at other centers without closely managed, comprehensive surgical and rehabilitative care programs, only moderate, or no, improvement in outcome was obtained [Cohen, et al. 1974; Imparato 1974; Kane and Pollak 1980]. Because of this, and the extra expense and effort entailed in IPOP treatment and rehabilitative care, soft dressing treatments of amputation wounds, with delay of residual limb prosthetic fitting and patient rehabilitation until completion of healing, has remained the most common practice. For complex, open amputation wounds this is almost invariably true. However, no controlled, comparative studies, stratified by wound type and complication, have been performed to date to establish treatment efficacies, or general indications and contraindications . There is no evidence to date showing improved outcomes with either IPOP treatment and immediate post-surgical rehabilitative care, or with saline WTMD treatment and post-healing rehabilitative care. Research in amputation wound healing conducted more recently has been principally directed toward predicting the most distal level at which a limb will heal following amputation, and thus obviate the need for revision or more proximal reamputation [Ray, et al. 1997; Malanin, et al. 1998; Padberg, et al. 1996; Mears, et al. 1996; Boyko, et al. 1996; Bunt and Holloway 1996; Wutschert and Bounameaux 1997; Holloway, et al. 1976 ]. This is because below-knee amputees' (BKA's) residual limbs are biomechanically more functional, stable, and strength and energy efficient than are more proximally amputated limbs. As such, BKA's evidence a much higher rehabilitation success rate than AKA's [Rutherford 1995]. Thus, it is desirable to salvage BKA limbs whenever possible. SPD treatment can substantially contribute toward achievement of this goal.
A research study currently underway at the New York University School of Medicine and the Department of Veterans Affairs New York Harbor Health Care System is comparing the efficacy of SPD treatment versus conventional WTMD treatment in a controlled investigation of patients with complicated and open BKA wounds (the group that evidences the highest rate of wound complication and limb salvage failure). This study includes: quantitative measurement of wound geometry (volume, surface area, and depth) versus treatment time, control for patient vascularity, smoking, history of diabetes, state of health and nutrition, plus measurement of changes in cellular and molecular determinants of healing, e.g., growth factor expression, matrix metalloproteinase production and activation, and the ability of the wound effluent to stimulate cell division and collagen gel contraction. A future study comparing SPD and IPOP treatment is also planned to establish the relative performance and efficacy, and indications and contra-indications for each of the three regimens in treating cases of trauma, vascular and other systemic disease, and cancer. Preliminary results to date indicate SPD to be the treatment of choice in traumatic cases. Results of the NYUSM/VA NYHHCCS research will more precisely define the role of SPD, as well as that of the other traditional methods, in treating amputation wounds of specific etiologies.

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