Emerging Concepts With VAC Therapy
Vacuum Assisted Closure (VAC, KCI) may be the most impressive device for the foot since AO fixation revolutionized elective foot surgery. For large or difficult wounds, VAC therapy can rapidly improve granulation tissue and speed up coverage of exposed tendon and bones. Indeed, this often occurs in days to weeks rather than months. Most clinicians are convinced at the bedside when they see dramatic changes in the characteristics of a wound such as size, depth and exposed structures. There is a growing body of evidence that supports the clinical observations and animal research that have been the mainstay of evidence on VAC therapy since the Food And Drug Administration (FDA) approved the device in 1995. While the study on the use of VAC therapy for open amputations was a milestone, other randomized clinical studies, which should be published in the not too distant future, may help us understand more about VAC therapy applications and economic advantages of this type of advanced wound care technology.1 Animal studies have demonstrated that VAC therapy can significantly reduce the bacterial load in contaminated wounds, increase blood flow, improve granulation tissue and spur flap survival. Morykwas and colleagues compared wounds in a Chester pig model treated with and without VAC therapy.2,3 Negative pressure wound therapy increased granulation tissue threefold. Due to the dramatic increase in granulation tissue, structures such as bone, tendon and exposed hardware that are usually difficult to cover can be bridged with VAC therapy.1 The tissue coverage can be dramatic. Armstrong’s study demonstrated a significant improvement in granulation tissue in the VAC therapy treatment group, faster healing rates and a higher proportion of healed wounds.1 Patients reached a level of 76 to 100 percent granulation tissue coverage of the wound bed twice as fast with VAC therapy. Additionally, 56 percent of open amputations treated with VAC therapy healed completely in 16 weeks compared to 39 percent in the control arm. The rate of complete healing in wounds that average 20 cm2 was as good as Dermagraft (Advanced BioHealing) and Apligraf’s (Organogenesis) healing in wounds that were 2 to 3 cm2.4 That represents about a tenfold difference in wound size with the same healing rate. Can VAC Therapy Lead To Reduced Bioburden In The Wound? Morykwas also identified a significant reduction in quantitative bacterial cultures with VAC therapy.2,3 By the fifth day, quantitative cultures decreased to less than 105 organisms per gram in the wounds treated with VAC therapy and during the same time period, quantitative cultures increased in control wounds.2 In the randomized clinical study by Armstrong in 2005, there was not a significant difference in wound infections in 163 patients with diabetes treated with VAC therapy for open foot amputations compared to standard therapy.1 It seems logical that an active drainage system under pressure would reduce edema and facilitate the removal of infectious materials from the wound bed. Infection was not a primary endpoint of the study and the study did not require routine qualitative or quantitative cultures. Accordingly, it was difficult to evaluate if there was a measurable difference in bioburden or if different diagnostic criteria across study sites may have played a role. There may have been a bias to treat patients with antibiotics if they had periwound redness and maceration. One often sees these conditions with the use of VAC therapy. When it comes to high-risk patients, the rule of thumb is to err on the side of more aggressive treatment. In clinical practice, this probably means using antibiotics to treat a wound that one suspects of being infected. In the Lancet randomized clinical trial, there was not a significant difference in serious adverse events in VAC therapy and standard therapy groups (including infection). However, there was a trend toward more patients requiring a second amputation in the standard therapy group.1 Using VAC Therapy With STSGs And Bioengineered Tissue Researchers have demonstrated that negative pressure wound therapy (NPWT) improves graft take and decreases the failure rate with split thickness skin grafts (STSGs).3,5-7 Study authors have also advocated the use of NPWT to improve bioengineered tissue products as well.8 Scherer reported that VAC therapy patients required fewer repeat grafts versus standard therapy with a bolster dressing (3 percent vs. 19 percent).5 Likewise, Llanos reported no split thickness skin graft loss in the NPWT group, whereas there was 4.5 cm STSG loss among control patients.6 This translated into significantly shorter hospital stays and significant cost savings. For grafts or bioengineered tissue applications, a lower setting is usually used (<100 mmHg). We often use VAC therapy in combination with bioengineered tissue products or xenograft products such as OrthoADAPT (Pegasus Biologics) or GraftJacket (Wright Medical). In addition, we often incorporate silver impregnated dressings with this therapy to further reduce the bacterial load of the wound bed. A Guide To ‘Bridging’ Wounds With VAC Therapy The foot is a challenging area to heal wounds to begin with due to the difficulty in offloading. Add to that the many curved and recessed surfaces, and applying any dressing can be a challenge, especially when dressings require a tight seal. Wounds on the bottom of the foot seem to be the most challenging when using VAC therapy but creative techniques to “bridge wounds” on the bottom of the foot can be helpful. We are treating smaller wounds and wounds on the sole of the foot more often than we did in the past. Indeed, “bridging techniques” have expanded the application of VAC therapy to wounds we would not considered in the past. “Bridging a wound” is a simple technique that allows one to place the TRAC Pad on a non-weightbearing surface (top of the foot). The ability to bridge wounds on the sole of the foot allows patients to offload the ulcer in a removable cast boot and facilitates ambulation to perform activities of daily living. The following example illustrates the “bridging technique.” To bridge a wound, one would perform thorough surgical debridement in order to remove non-viable and infected tissue. The photo on page 85 shows a deep deficit in a 45-year-old male with diabetes and neuropathy as the result of a neglected ulcer that developed a deep abscess four days after debridement. Prepare the periwound skin. Cut the reticulated foam to fit the wound and then cover it with the adhesive drape. Cut an aperture in the drape to expose the central aspect of the foam. Then extend a second piece of adhesive drape from the ulcer site medially to the top of the foot to protect the skin from the foam. Cut a separate piece of foam (the bridge) and place it from the ulcer aperture to the top of the foot. Then seal it with another piece of drape. Cut a second aperture over the dorsum of the foot, exposing a section of the foam bridge. Proceed to apply the TRAC Pad (KCI). Then connect and activate VAC therapy. The foam bridging allows the subatmospheric pressure to extend or flow from the ulcer to the top of the foot. Addressing The Issue Of Periwound Tissue Maceration There are a number of techniques to reduce the frequency and severity of periwound tissue maceration. Maceration is not a reason to give up on VAC therapy. One has to be creative in options to eliminate or reduce maceration. One of the simplest approaches is to have the patient keep the involved extremity elevated as much as possible. In patients with difficult wounds, we often use continuous rather than intermittent negative pressure therapy so there is less opportunity for fluid to pool at the periphery of the wound. In addition, one can protect the skin with betadine, a tincture of benzoin or other skin prep agents. Physicians can protect the periwound skin with different barriers such as Duoderm (Convatec), Tegapore (3M) or other occlusive dressings. Severe maceration sometimes requires the patient to discontinue VAC therapy for a day or two in order to allow the tissue to dry out. Once the skin has normalized, then one can restart VAC therapy. Attention to skin preparation and protection will allow patients to have uninterrupted VAC therapy. In Conclusion No single technology is a panacea for all wounds but VAC therapy clearly adds a powerful and exciting tool to our wound care armamentarium. Keep in mind, though, that VAC therapy cannot restore perfusion to an ischemic foot or improve the wound bed when there is necrotic tissue present. Physicians have to use the product as part of a comprehensive treatment plan to optimize perfusion, remove devitalized tissue and eliminate infection. Whether one uses VAC therapy alone or in conjunction with other topical technologies such as bioengineered tissue or skin grafts, the modality makes it more gratifying to care for our patients. Dr. Lavery is a Professor in the Department of Surgery at Texas A&M Health Science Center College of Medicine. Dr. Murdoch is an Assistant Professor with the Department of Surgery at Scott and White Hospital, Texas A&M University College of Medicine in Temple, Texas.
References 1. Armstrong DG, Lavery LA: Negative pressure wound therapy after partial diabetic foot amputation: a multicentre, randomised controlled trial. Lancet, 12;366:1704-10, 2005. 2. Morykwas MJ, Argenta LC, Shelton, Brown EI Vacuum assisted closure: a new method for wound closure and treatment: animal studies and basic foundation. Annals Plastic Surgery 38: 553-602, 1997. 3. Morykaws MJ, Faler BJ, Pearce DJ, Argenta LC. Effects of varying levels of subatmospheric pressure on the rate of granulation tissue formation in experimental wounds in swine. Annals Plastic Surgery 47:547-551, 2001. 4. Defranzo AJ, Argenta LC, Marks MW: the use of vacuum-assisted closure therapy for the treatment of lower extremity wounds with exposed bone. Plastic and Reconstructive Surgery 108: 1184-1191, 2001. 5. Scherer LA, Shiver S, Chang M, Meredith, JW, Owings JT. The vacuum assisted closure device: a method of securing skin grafts and improving graft survival. Arch Surg 137(8):930-3, discussion 933-4, Aug 2002. 6. Llanos S, Damilla S, Barraza C, Armijo E, Pineros JL, Quintas M, Searle S, Calderon W. Effectiveness of negative pressure closure in the integration of split thickness skin grafts: a randomized, double-masked controlled trial: Ann Surg 244(5):700-5, 2006. 7. Moisidis E, Heath T, Boorer C, Ho K, Deva AK. A prospective, blinded, randomized, controlled trial of topical negative pressure use in skin grafting. Plast Reconstr Surg 114(4):917-22, Sept. 2004. 8. Espensen EH, Nixon BP, Lavery LA, Armstrong DG. Use of subatmospheric (VAC) therapy to improve bioengineered tissue grafting in diabetic foot wounds. J Am Podiatr Med Assoc 92(7):395-7, July-Aug 2002. 9. Gupta S: Differentiating negative pressure wound therapy devices: an illustrative case series. Wounds suppl 19: 1-9, 2007.