Negative pressure wound therapy options promote patient care
The literature supports use of the modality, but it also suggests standard protocols may need to be reconsidered.
By: Michael S. Miller, DO, Rhonda Brown, LPN, and Cheryl McDaniel, LPN
Negative pressure wound therapy (NPWT) is a topical treatment intended to promote healing in acute and chronic wounds. It involves the application of negative pressure (suction) to the wound bed. There are two main NPWT equipment systems commonly used in the U.S., one called the VAC (vacuum-assisted closure), offered by Kinetic Concepts (San Antonio), and the other called the Versatile 1 (V1) wound vacuum system by Blue Sky Medical (La Costa, CA).
NPWT consists of a nonadherent, porous wound dressing, a drainage tube placed adjacent to or inserted in the dressing, an occlusive transparent film sealing the wound and the drainage tube, and a connection to a vacuum source, which supplies the negative pressure. The concept is to turn an open wound into a controlled, closed wound while removing excess fluid from the wound bed, thus enhancing circulation and disposal of cellular waste from the lymphatic system.1
This technique is usually considered for chronic wounds (those that fail to progress through the normal phases of healing-inflammation, proliferation, maturation-and thus do not heal), acute wounds (wounds that are expected to heal and demonstrate evidence of progression through the phases of healing), and difficult wounds (wounds with such associated factors as diabetes, arterial insufficiency, and venous insufficiency). Common applications for NPWT appear in Table 1.1
In 1995 the Food and Drug Administration was presented with and first approved negative pressure equipment that was subsequently marketed as the VAC, by Kinetic Concepts.
How does NPWT work?
The Starling-Landis equation illustrates how suction helps heal a wound. This equation defines the filtration pressure, Jv, out of the blood and into the surrounding tissues as well as JL, the filtration pressure out of the tissues and into the lymphatic system.
In an acute wound or burn, the Starling forces are altered, creating a large increase in Jv, which then exceeds the JL. This disequilibrium causes rapid edema in the wound. NPWT creates a compression force that is directed against the Jv, changing the balance between the Jv and the JL, thus improving the equilibrium between fluid leakage and fluid reabsorption. Simultaneously, the NPWT suction drains out the accumulated edema in the wound. The combination of improved filtration equilibrium plus the removal of edema contributes to more rapid healing (Figure 1).
Benefits of NPWT
The use of negative pressure to promote healing of open wounds has considerable evidence in the literature to support its efficacy. The effects of NPWT are thought to promote wound healing through several actions including the removal of exudate from the wound to help establish fluid balance,2 provision of a moist wound environment,3 removal of slough,3 a potential decrease in a wound's bacterial burden,4 a reduction in edema, an increase in blood flow to the wound,3-6 an increase in growth factors, and the promotion of white cells and fibroblasts within the wound.7 Negative pressure brings tissue together, encouraging the tissues to stick together through natural tissue adherence, which increases healing.
Philbeck and Whittington found that "healing time can be as high as 61% faster and 38% less costly with combination treatment utilizing a controlled suction drain system."8
Literature review
The effect of exposing wounds to subatmospheric pressure has been studied in a variety of settings for at least 50 years.1 Between 1970 and 1997, numerous articles appeared in the Russian literature exploring the use of negative pressure for managing suppurative wounds.9-12
In the 1980s Katherine Jeter, RN, explored a combination of products to deliver negative pressure therapy to the wound bed. Together with Mark Chariker, MD, she designed a clinical study and in 1985 they published their findings, that "their closed suction wound drainage system revolutionized the management of enterocutaneous fistulae complicating ventral abdominal wounds."14
In the Russian medical literature, Kostiuchenok et al4 in 1986 discussed the failure of surgical debridement alone to significantly reduce the microbe count in the tissue of purulent wounds. The authors concluded that negative pressure treatment of purulent wounds in combination with surgical debridement significantly reduced the bacterial burden within the wound and resulted in improved wound healing.
Usupov and Yepifanov15 in April of 1987 published their findings regarding the effects of wound drainage after surgical intervention. Until this time there had been no uniform opinions on when to use vacuum therapy, what the duration of the therapy should be, or what amount of negative pressure would be most beneficial. Treating wounds created in adult rabbits, the authors concluded that to avoid tissue damage, pressures in active drainage systems should not exceed -80 mm Hg and that lower pressures were less likely to demonstrate postoperative hemorrhage.
In 1991, Davydov et al authored a review article discussing the different modalities used to treat purulent wounds after aggressive debridement.12 Therapies included fluid pulse jets, enzymatic debridement, laser and ultrasound necrolysis, and forced suction. With the exception of suction therapy, the authors felt that these various modalities were not "universal enough to affect all elements of the biological system of healing during the inflammatory phase." This retrospective review included 744 subjects with purulent wounds. Vacuum therapy after surgical debridement was utilized in 406 subjects while 338 subjects received surgical debridement alone. After evaluating multiple serological, bacterial, and tissue/cellular effects of the vacuum therapy, the authors found that "a pronounced immunocorrecting effect"12 was observed. Consistent with this finding were the reduced number of infectious wound complications, fewer repeat surgeries, reduced purulence-related fevers, and decreased sepsis over traditional sharp debridement alone.
In 1997 Morykwas and Argenta, of Wake Forest University, published three landmark articles regarding their experience with vacuum-assisted wound closure.5,6,16 They described a system in which "subatmospheric pressure" was applied through a closed system to an open wound for 48-hour periods.5,6 Subatmospheric pressure was directed at the surface of the wound in either a constant or an intermittent mode, based on the clinical experience of the physician, through an interface between the wound surface and a polyurethane sponge, which allowed for distribution of the negative pressure. The VAC device is based largely on the 1997 findings of Morykwas and Argenta.
A VAC consensus group was formed in 2003 in Canada. They agreed that the VAC is a commonly used adjunctive treatment in the management of acute and chronic wounds. Their consensus paper contains a literature review, recommendations for specific chronic wounds, and survey results from the group based solely on the VAC product.17
Room for more
In our recent review article,13 we identified literature that predates the VAC research by more than 10 years. Based on this information, we found several areas of confounding results between current commonly accepted practices with the VAC product and the literature. One such area is the optimal pressure level. While experience-based protocols and the common VAC settings are typically around 125 mm Hg of negative pressure,5 early Russian literature15 and a recent article18 suggest pressures around -75 to -80 mm Hg may reduce tissue damage and pain, both of which can occur when using the current product and practice parameters. These lower pressures are supported by the V1 NPWT product.
Another discrepancy involves the duration of treatment. The conventional VAC source of NPWT requires continuous use for 24 to 48 hours until a dressing change. The V1 follows conclusions offered in the Russian literature and can be effectively used for six to eight hours a day.
At present, there are unanswered questions and further research is needed to define the most efficacious parameters for pressure intensity, duration of treatment, interval between treatments, and the mode and timing of application in order to provide the most efficient form of therapy.
With much yet to learn about optimal mechanisms and protocols, researchers are increasing their study of NPWT, as evidenced by a growing number of published articles on this subject.19 However, researchers are limiting their study to a single NPWT product and practice parameters. Approximately 42 articles on the subject of NPWT were published in 2003.19 Most of these articles explored NPWT with different types of wounds, and all of the researchers used the VAC device and VAC protocols to perform negative pressure therapy. With the rediscovery of the earlier literature and the confounding results between that early literature and commonly accepted VAC practices, it is quite likely that researchers will investigate NPWT administered through a variety of pressure devices and with varying protocols. The likely result will be more effective therapy for a greater variety of wounds.
Case review of a spider bite patient The patient was a 57-year-old woman who developed severe pain in her right calf while walking outdoors in a wooded area in which brown recluse spiders were endemic. She had no previous history of lower extremity problems.
The patient was treated at the local hospital without success. The hospital treatment plan included oral antibiotics, an Ace wrap, and ice for the progression of the pain, swelling, and ecchymosis. When this failed to bring about any improvement, she underwent surgical debridement. After this treatment failed, the patient received a strong recommendation for below knee amputation to prevent spreading. See Figure 2 for the initial presentation of the wound.
About a week after surgical debridement, on April 23, 2004, the patient came to our facility, the Wound Healing Center in Terre Haute, IN. The wound contained edema and was covered with thick fibrous exudates and had necrotic skin edges. NPWT was administered to the patient using the new Versatile 1 device.
We selected the Chariker-Jeter technique for administering negative pressure.14 The technique uses materials found in supply departments of most facilities: open weave cotton gauze, a flat Jackson-Pratt drain, transparent film, and a connecting tube.
The wound was covered with a clear, semipermeable dressing (Tegaderm), which was cut to fit the dimensions of the wound, thus protecting the adjacent skin. A gauze sandwich was made around the flat, silicone Jackson-Pratt drain. The entire drain sandwich was placed on the wound and covered with another piece of Tegaderm to create a complete seal. The drain was connected to tubing, which was then connected to the V1.
Using the parameters indicated from the early Russian literature, The V1 was set at 80 mm Hg of negative pressure in constant mode. At home, the patient used NPWT for six to eight hours in every 24-hour period. Therapy was usually administered during night hours when the patient was sleeping. This facilitates normal activities of daily living and is a unique feature of the V1. In contrast, the conventional NPWT product (VAC) requires constant use, 24 hours a day. The patient was instructed to change dressings three times per week.
Under this treatment plan, the patient underwent NPWT for approximately 19 weeks, until healing plateaued and therapy was discontinued (Figure 3). When a healthy bed of granulation tissue was identified, the vacuum therapy ended and the patient applied calcium alginate with a composite dressing on an every-other-day schedule to promote epithelialization. Complete healing occurred three weeks later and the dressings were discontinued. The patient experienced a full recovery. The wound dimensions appear in Table 2.
Michael S. Miller, DO, CWS (certified wound specialist), is medical director of the Wound Healing Center in Terra Haute, IN. Rhonda Brown, LPN, and Cheryl McDaniel, LPN, are on staff at the Wound Healing Center.
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