A Guide To Current And Emerging NPWT Modalities

Adam Isaac, DPM, and David G. Armstrong, DPM, PhD, MD

   While the VAC Instill Therapy Unit is more accessible than the SVED system in most clinical settings, its “hold” cycle — during which fluid infuses into the foam and NPWT pauses — may result in maceration and a loss of seal.14 Recent modifications to the updated KCI instillation system may have improved the seal.

   Researchers have studied fluids such as Dakin’s solution (sodium hypochlorite), insulin, doxycycline, Dilantin (phenytoin), diluted Betadine, lactoferrin and biguanide antiseptics for their potential application to fluid instillation NPWT.14-16 The instillation of Dakin’s solution may prevent wound maceration and colonization, and researchers have shown that insulin-like growth factor increases the rate of wound healing.14,16 Furthermore, doxycycline is antimicrobial and is a competitive inhibitor of MMPs as well as tissue necrosis factor-a.15 This tetracycline antibiotic may also reduce inflammation in the wound by decreasing nitric oxide synthesis.15

What You Should Know About NPWT And Tension Stress

Another way in which NPWT works to improve wound healing can be explained by the law of tension stress. As the clinician applies NPWT, the wound bed experiences a negative, deforming force, which stretches individual cells and results in increased cell proliferation and angiogenesis.10,17

   In 2004, Saxena and colleagues reported that finite element modeling of VAC therapy was able to produce strains consistent with the levels needed for promoting cellular proliferation in vitro.17 Researchers have investigated the notion that micromechanical forces are able to induce cell proliferation and division with respect to the use of tissue expanders for reconstructive plastic surgery, and distraction osteogenesis for bone lengthening.10,17,18

Expanding The Use Of NPWT Beyond DFUs: What The Literature Reveals

More recently, the use of NPWT has expanded beyond the treatment of diabetic foot ulcers. Negative pressure wound therapy improves the take of split-thickness skin grafts by acting as a bolster and preventing an accumulation of fluid beneath the graft site.10 In 2004, Moisidis and co-workers found that the take for split-thickness skin grafts subjected to NPWT was qualitatively improved in 50 percent of the cases they studied.19

   Researchers have also studied the benefits of NPWT with respect to the healing of wounds secondary to traumatic, open fractures. In 2009, Stannard and colleagues reported on the results of a prospective, randomized study in which 58 patients with 62 open fractures received either standard wet-to-dry dressings or NPWT.20 The authors found that the group treated with NPWT was one-fifth as likely to develop an infection as the control group, suggesting that NPWT may be an effective adjunct in the treatment of severe, open fractures.

   Another trend that has been gaining popularity in recent years is the use of NPWT over closed incision sites. As previously discussed, NPWT reportedly increases local tissue perfusion, reduces edema, increases the rate of granulation tissue formation and promotes cellular proliferation through micromechanical forces. When one applies NPWT over a clean, closed incision, the modality acts to protect the wound bed and creates a splinting effect on the surrounding soft tissue.21 Furthermore, this eliminates the need for frequent dressing changes on high-risk incision sites and authors have shown that the incidences of dehiscence and infection are lower.22,23

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