User:BexarTech/Negative pressure wound therapy draft

Negative pressure wound therapy (NPWT), also known as topical negative pressure, sub-atmospheric pressure dressings or vacuum sealing technique, is a therapeutic technique used to promote healing in acute or chronic wounds and enhance healing of first and second degree burns. NPWT involves the controlled application of sub-atmospheric pressure to the local wound environment, using a sealed wound dressing connected to a vacuum pump. The use of NPWT in wound management increased dramatically over the 1990s and 2000s and a large number of studies have been published examining NPWT, in particular Kinetic Concepts Inc.'s Vacuum Assisted Closure Therapy. Reviews of published studies have evaluated the effectiveness of NPWT compared to other treatments. A review published in 2007 called for more research, stating there was a lack of evidence for significant increase in chronic wound healing, while a 2010 review found sufficient evidence that NPWT accelerates healing in chronic leg wounds.

Overview
In NPWT a wound is sealed to promote wound healing using sub-atmospheric pressure applied through a specialized dressing. The continued application of pressure draws out edema from the wound, increases blood flow to the area, and is thought to accelerate contraction of the wound and promote wound healing. The vacuum may be applied continuously or intermittently, depending on the type of wound being treated and the clinical objectives. Typically, the dressing is changed two to three times per week. The dressings used for NPWT include open-cell foam dressings and gauze, sealed with an occlusive dressing intended to contain the sub-atmospheric pressure at the wound site. Where NPWT devices allow delivery of fluids, such as saline or antibiotics, to irrigate the wound, intermittent removal of used fluid supports the cleaning and drainage of the wound bed.

NPWT may be used for treatment of a range of wounds. A consensus document produced in 2008, drawing on the clinical research evidence and the best practice opinions of 26 international wound care experts, outlined recommendations for the use of NPWT (in particular, Kinetic Concepts Inc.'s Vacuum Assisted Closure Therapy) in diabetic foot ulcers, complex leg ulcers, pressure ulcers, dehisced sternal wounds, open abdominal wounds and traumatic wounds. In addition to these uses, NPWT is used in reconstructive surgery and an article in the Nursing Times states that NPWT can be used to treat "almost any type of wound", provided that it is possible to obtain and maintain a seal; such wound types include: burns, skin grafts, rotational/free flaps, and postoperative mediastinitis.

In 1995, Kinetic Concepts Inc. (KCI) Vacuum Assisted Closure (V.A.C.) Therapy System was the first NPWT product cleared by the US Food and Drug Administration (FDA), specifically for the treatment of acute/traumatic wounds, dehiscent wounds, flaps and grafts, pressure ulcers and chronic wounds. Following increased use of the technique by hospitals in the US, the NPWT procedure was approved for reimbursement by the Centers for Medicare and Medicaid Services in 2001.

Technique
General technique for NPWT is as follows: a dressing is fitted to the contours of a wound and sealed with a transparent film. A drainage tube is connected to the dressing through an opening of the transparent film. The drainage tube is also connected to a vacuum source, turning an open wound into a controlled, closed wound while removing excess fluid from the wound bed to enhance circulation and remove wound fluids. This creates a moist healing environment and reduces edema. The technique is usually used with chronic wounds or wounds that are expected to present difficulties while healing (such as those associated with diabetes).

Commercial NPWT products are generally divided into three categories based the type of dressing used over the wound surface: open-cell foam, gauze or honeycombed textiles with a dimpled wound contact surface.

Foam
The use of foam dressings is most common with the V.A.C. Therapy System. In 1997, Morykwas & Argenta described an approach using a sealed polyurethane foam dressing. Foam dressings are used to fill open cavity wounds and can be cut to size to fit wounds. The foam dressing is applied, filling the wound and then a film drape is applied over the top to create a seal around the dressing. A vacuum tube is connected through an opening in the film drape to a canister on the side of a vacuum pump. With V.A.C. Therapy the action of negative pressure on the wound bed has been shown to lead to microdeformations of the wound surface, which act to stimulate perfusion and granulation tissue formation. Silver-impregnated foam dressings have been developed that are used to provide a barrier to bacterial penetration. The V.A.C. system has unique technology in its tubing and pump that monitors the pressure at the wound bed and automatically adjusts to ensure the set pressure is actually being delivered to the wound bed. With this technology the pressure at the wound bed is maintained at prescribed levels.

Gauze
Using gauze for NPWT is a technique where the materials used are standard medical supplies such as open weave cotton gauze, transparent film, a flat drain and tubing that connects to a vacuum pump. The flat drain is sandwiched in gauze and this is then placed onto the wound. A film drape is used to cover the wound and create a complete seal, and then the drain is connected to the pump via the tubing.

BioDome
In addition to the use of foam and gauze, there is a third type of dressing which uses Bio-Dome Technology. The dressing is made up of layers of non-woven polyester, joined by a silicone elastomer, and has a non-adherent wound contact surface. The surface in contact with the wound bed features many Bio-Domes, small semi-rigid dome structures. The dressing is placed onto the wound and covered with a film drape, then a pad with a tube is placed over an opening cut into the film drape. A low level of suction is provided by a vacuum pump attached to the tube. The domes in the dressing are intended to allow the dressing to be in contact with the wound surface while also providing voids to allow for tissue growth.

Negative pressure and dressing use
With all three techniques, once the dressing is sealed the vacuum pump can be set to deliver continuous or intermittent pressures, with levels of pressure depending on the device used. With V.A.C. Therapy the normal therapeutic level is -125mmHg which can be reduced if the wound is particularly painful. A lower pressure of -75mmHg is used with Bio-Dome Technology. For intermittent regimes, the vacuum will follow a set cycle. The NPWT device may be used for set period of hours each day (such as 6 to 8 hours for the Versatile 1 system) or kept in use a minimum of 22 hours a day. For patients with multiple wounds or extremely large wounds, more than one NPWT device can be used. There are different safety features and recommended applications for each negative pressure wound therapy device.

The dressing type used depends on the type of wound, clinical objectives and patient. For pain sensitive patients with shallow or irregular wounds, wounds with undermining or explored tracts or tunnels, gauze may be used, while foam may be cut easily to fit a patient’s wound that has a regular contour and perform better when aggressive granulation formation and wound contraction is the desired goal. In a study on pigs, gauze was found to effect less tissue ingrowth than foam. According to a study from Journal of Wounds 2007, while foam allows easy removal of exudate and infectious material, this is absorbed by gauze, which keeps in contact with the wound bed. The study added that there is scientific evidence that microstrain (which leads to granulation and contraction of the wound) occurs in NPWT using V.A.C. Therapy with open-cell foam dressings, however there was no evidence to support this when gauze is used. A Massachusetts Institute of Technology study in 2004 particularly identified microstrain, leading to promotion of granulation tissue formation, as a unique mechanism of action in V.A.C. Therapy. One NPWT device manufacturer has claimed that NPWT using gauze has the same benefits as foam in reducing wound dimension, exudate, and improving granulation tissue. However, only V.A.C. Therapy has the following labeled mechanisms of action: promotion of granulation tissue formation; exudate and infectious material removal; edema reduction; and stimulation of perfusion.

Studies
Hundreds of reports have been published in peer-reviewed journals on the effectiveness of use of NPWT, with the majority of studies providing information on NPWT with V.A.C. Therapy. The V.A.C. system in particular is supported by 22 randomized and controlled clinical trials,. The Blume et al 2008 randomized controlled clinical trial of 342 patients with diabetic foot wounds, published in Diabetes Care, showed that healing effectiveness and time to healing were "significantly better" where wounds were treated with NPWT, than where they were treated with standard moist wound therapy. Blume stated that the time to "all healing end points was significantly shorter in the V.A.C. group" than in the moist wound group. An earlier randomized clinical trial undertaken by Armstrong et al in 2005, published in the Lancet, studied the outcomes of treatment for 162 patients with diabetic foot amputation wounds in a 16 week trial and found that compared with the control group (39% of patients healed), more patients were healed using NPWT (56% of patients healed). The study also concluded NPWT is a "safe and effective treatment" and compared with standard care, NPWT had "faster healing rates" and its use could lead to fewer re-amputations. In a randomized clinical trial of 60 hospitalized patients with chronic ulcers, Vuerstaek at al in 2006, found that the median time to complete healing was reduced significantly (from 45 days in the control group to 29 days in the V.A.C. Therapy group). The treatment of 34 patients with fasciotomy wounds using NPWT was addressed by a randomized clinical trial in 2006, where Yang et al found that the average time to definitive closure of wounds reduced from 16.1 days (in the control group) to 6.7 days (in the V.A.C. Therapy group). These studies report that their results are statistically significant.

Reviews evaluating the studies undertaken have acknowledged the evidence for NPWT as an effective wound treatment, however call for further study due to weaknesses in methodology. A Cochrane Review stated that, based on seven studies conducted on NPWT, there is "no valid or reliable evidence that topical negative pressure increases chronic wound healing." The review concluded that although there was evidence for a "beneficial effect" from NPWT, "more, better quality research" was needed. A later independent review of studies, in 2010, identified 17 random clinical trials, five of which had not been included in previous reviews, and evaluated their outcomes. The review concluded that although further studies are needed for other types of wound, "there is now sufficient evidence to show the NPWT is safe, and will accelerate healing" in chronic leg wounds associated with diabetes. Evidence for accelerated healing of other wounds was considered "encouraging" and it was noted that there was no increase in significant complications with use of NPWT compared with other techniques.

Cost effectiveness
The cost effectiveness of NPWT has been addressed in a number of studies, as the cost of the treatment is not insignificant. Studies consider length of stay in hospital, the number of surgeries required and re-admissions, all of which indicate whether NPWT is cost-effective. The Vuerstaek et al 2006 study of V.A.C. Therapy used to heal leg ulcers found that length of stay in hospital was significantly reduced with V.A.C. Therapy compared with standard care. A 2005 retrospective study of over 2,300 patients by Schwien et al observed that patients with pressure ulcers treated with V.A.C. Therapy were hospitalized less, had fewer hospitalizations due to wound problems and also fewer hospital visits for emergency care related to their wounds. Compared with other forms of treatment, for V.A.C. Therapy patients there was a cost saving of $4, 209. A study addressing resource utilization, procedures, and direct costs was carried out by Apelqvist et al in 2008, which found that the average total cost to achieve healing for 162 patients with diabetic foot ulcers was $25,954 for patients treated with NPWT compared with $38,806 for patients in the control group. In terms of effect on number of surgeries required, a 2007 retrospective by Siegel et al found that in treatment of wound complications following surgery for 22 patients with soft tissue sarcoma there was a statistically significant reduction in number of surgeries required and more patients healed without need for soft tissue transposition. Catarino et al's 2000 study highlighted a reduction in treatment failures (which could lead to further surgery) when using V.A.C. Therapy for poststernotomy mediastinitis in the place of other treatments, and was cited by an article in Nursing Times as being indicative of cost effectiveness.

Military and home use
The use of NPWT was adopted by the US military in the mid-2000s, beginning with use of the technique in military hospitals, drawing from medical personnel's prior experience. A study by Leininger et al in 2006 found that for 77 patients treated with NPWT in US military hospitals the wound infection rate was reduced from approximately 80% (based on anecdotal reporting) to 0%. The use of NPWT during aeromedical transport was approved by the military in 2006, following the flight certification of the V.A.C. Freedom portable device. The following year, NPWT began to be used on the front lines in combat zones for wounded military patients.

In addition to use by the military and in hospitals, NPWT has been used by patients at home since the early 2000s. KCI launched the first NPWT device specifically designed for home use in the late 2000s. In the US, as part of the FDA's 2010 Medical Device Home-Use Initiative, companies producing NPWT devices were asked to state on their product labeling that the device is not intended for home use if the device had not been specifically approved for that use. The FDA stated that it intends to produce guidelines for safer home use of the devices. NPWT device developers, such as KCI, stated that they support the initiative.