Cath Lab Digest

Yes. Lee C. Rogers, DPM cites the evidence from negative pressure wound therapy (NPWT) trials and says the characteristics of NPWT foam facilitate the development of granulation tissue and improved healing in diabetic foot ulcers.

   There is no question that negative pressure wound therapy (NPWT) is a valuable modality in facilitating wound closure. In particular, the use of foam dressings with NPWT has demonstrated success in reducing wound surface size and accelerating the formation of granulation tissue.

   The foam most commonly used in NPWT is the Vacuum-Assisted Closure (VAC) Granufoam (Kinetic Concepts, Inc.). This is an open-cell polyurethane foam. Its defining properties are cell (pore) size, contractility and non-absorbency. Each of these properties influences the wound bed.

   Researchers have shown that the cell size of VAC therapy foam produces tangential strain, which causes microdeformation of the cells in the wound bed and stimulates proliferation.¹ This micro-strain results in undulations in the surface of the wound and leads to robust formation of granular tissue. In regard to the use of VAC therapy foam, researchers have shown, in vitro, fibroblast migration as well as increased proliferation through mitosis.

   In many cases, one can see budding of vascular tissue in the wound bed after using the foam under negative pressure. The open cell foam allows uniform application of negative pressure to the wound bed.

   One of the benefits of an open-cell foam is its ability to contract under negative pressure. In a paper submitted for publication, Rogers and colleagues performed an evaluation comparing the surface area of gauze and foam under negative pressure at -125 mmHg.² The foam reduced to 40 percent of its original area whereas the gauze decreased to only 88 percent of its original size. Wound contraction is an important principle in healing and foam is far superior at achieving this effect in comparison to gauze.³

   A foam is technically non-absorbent whereas a sponge (gauze) is absorbent. The foam allows the wound exudate to pass through into the negative pressure canister. Gauze sponges absorb some of this exudate and keep it in contact with the wound bed during use. Not only can the amount of fluid produced by a wound be an impediment to healing but the inflammatory factors in that fluid also impair healing. Pro-inflammatory cytokines and matrix metalloproteinases (MMPs) are present in high concentrations in chronic wound fluid.^4,5 Furthermore, these proteinases destroy growth factors.⁶

What The Studies Reveal About NPWT And Foam

   Most notably, in all of the randomized controlled trials comparing NPWT with the standard of care in diabetic foot ulcers, physicians used VAC Granufoam under negative pressure.^7,8,9 Study authors have found that wounds healed faster in the NPWT foam groups. There have been no randomized controlled trials evaluating the use of gauze with negative pressure and no comparison trials of gauze versus foam.

   McCallon and colleagues studied 10 patients with non-healing, postoperative diabetic foot ulcerations. These patients were randomized into either a VAC therapy group or a control saline gauze group. The study found that patients in the NPWT group achieved satisfactory healing in 22.8 (+/- 17.4) days in comparison to 42.8 (+/- 32.5) days in the control group.

   In addition, Blume and co-workers studied 342 patients with diabetic foot ulcers.⁹ They found that patients undergoing NPWT had fewer home care therapy days and significantly fewer secondary amputations in comparison to those treated with advanced moist wound therapy.⁹