A Guide To Current And Emerging NPWT Modalities

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

   In 2005, Armstrong and Lavery reported on the results of a multicenter, randomized clinical trial comparing the proportion and rate of wound healing in 162 patients with diabetic wounds secondary to partial foot amputation and evidence of adequate perfusion.8 The patients were randomly assigned to two groups, one of which received NPWT while the other group had standard moist wound therapy. The study, which took place over a period of 16 weeks in 18 study sites, found that treatment with NPWT resulted in a higher number of healed wounds (56 percent versus 39 percent) as well as a faster rate of wound healing. Furthermore, the group receiving NPWT demonstrated an increase in the rate of granulation tissue formation as well as a potential trend toward a reduced risk of re-amputation.

   Blume and colleagues reported similar results in an even larger study published in 2008.9 Over a period of 16 weeks, the authors demonstrated that a greater proportion of diabetic foot ulcers achieved complete closure with NPWT (43.2 percent versus 28.9 percent) and that patients receiving NPWT required fewer amputations.

Weighing The Pros And Cons Of NPWT

While there are several factors that may explain the success of NPWT, there is no consensus regarding the dominant mechanism. Rather, the combination of a moist wound healing environment, active removal of exudate and infectious materials, maintenance of adequate wound temperature, and physical stimulation of cells created by NPWT along with increased tissue perfusion all contribute to improved wound healing.10 When a wound bed is moist, this maintains the lateral voltage gradient and there is a greater potential for wound healing.10

   Furthermore, researchers have shown that wounds with excessive exudate contain an increased number of matrix metalloproteinases (MMPs), which degrade the adhesion proteins necessary for wound repair while an increase in interstitial pressure may occlude the surrounding microvasculature and lymphatics, thus depriving the tissue of vital nutrients and oxygen.10,11

   For some time, it has been widely accepted that infection may be detrimental to wound healing. In their study, Morykwas and co-workers were able to demonstrate a significant reduction in the number of organisms between days four (108) and five (105) in wounds receiving treatment with NPWT.6 However, Weed and colleagues, in a retrospective review of 25 patients, actually found an increase in the bacterial bioburden of 43 percent of wounds treated with NPWT over an average of 12.8 weeks.12

   While quantitative bacteriology may not be the ideal method to measure a patient’s response to colonization, it is worth noting and discussing. Future works might delve deeper into both the specific microbiome and virulence factors secreted by that microbiome.

   Besides the potential for wound colonization during prolonged periods of NPWT, there may be maceration of the wound, which could necessitate the temporary or permanent discontinuation of NPWT. In a 2002 case report, Chester and Waters reported that the closed, air-free environment created by NPWT led to a progressively worsening anaerobic wound infection in a 76-year-old man who developed sepsis following a groin wound dehiscence while undergoing treatment with NPWT.13

   Although similar cases in the literature are unreported, it serves as a stark reminder that clinicians must carefully monitor all patients receiving NPWT for systemic changes as well as changes to the overall presentation of the wound.

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