Negative Pressure Wound Therapy Remains Important Strategy for Wound Healing

Care of the lower extremity is important for individuals with diabetes to avoid amputation. Over the years, advanced wound care modalities have emerged as critical tools in limb salvage, including negative pressure wound therapy, which has become an important vertical strategy for wound healing, according to a report.

Negative pressure wound therapy (NPWT) involves the application of local subatmospheric pressure to a wound or defect through an open-celled foam or gauze that is connected to a pump.

“[NPWT] has been shown to decrease wound margins and promote granulation tissue formation and perfusion. It also serves to maintain a moist wound-healing environment,” the researchers wrote in the report. “When a wound bed is moist, the lateral voltage gradient is maintained and a greater potential exists for wound healing. Mechanical stimulation of a wound by NPWT contributes to improved wound healing through macrostrain and microstrain properties.”

Vacuum-assisted closure device

Several devices exist that allow a safe and effective delivery of NPWT, according to the researchers. The most widely used system is the vacuum-assisted closure device (V.A.C. Therapy) which consists of reticulated, open-cell foam covered with a semipermeable adhesive drape and is connected to a negative pressure therapy unit through evacuation tubing. One of the most widely used systems, there are several proprietary types of foams used with NPWT, including the V.A.C. GranuFoam, V.A.C. GranuFoam Silver and V.A.C. WhiteFoam.

Previous studies have shown when applying V.A.C. Therapy to the healthy, intact forearm skin of patients, there was a significant increase in cutaneous blood flow at a negative pressure of 300 mm Hg and no decrease in the baseline blood flow at negative pressures approaching 500 mm Hg. While these high levels of pressure have been used experimentally in healthy patients, they have not been adopted in people with chronic wounds. These patients generally receive pressures from 75 mm Hg to 125 mm Hg.

Use of NPWT for wound healing compared with standard moist wound therapy showed a higher number of healed wounds and faster healing rates, as well as an increase in the rate of granulation tissue formation and a reduced risk of amputation. A greater number of diabetic foot ulcers also closed completely with NPWT compared with advanced moist wound therapy.

Fluid instillation therapy

NPWT also can be used in wound healing and limb salvage through fluid instillation therapy. The use of the V.A.C. Ulta NPWT System in conjunction with V.A.C. VeraFlo Therapy delivers and removes fluids across a wound site while maintaining NPWT. According to researchers, the addition of fluids to a wound undergoing NPWT may also be helpful when the wound in contaminated or infected. In a study published in 2011, results showed use of V.A.C. VeraFlo Therapy increased wound fill by 43% over 7 days compared with standard NPWT.

Researchers have also reported and investigated the use of fluids such as Dakin solution, insulin, doxycycline, biguanide antiseptics and several others with NPWT. The combination of V.A.C. VeraFlo Therapy with polyhexamethylene biguanide reduced Pseudomonas aeruginosa bioburden in biofilm by 99.8%, according to study results.

“The instillation of Dakin’s solution prevents maceration and bacterial colonization within the wound, and the addition of insulin-like growth factor has been shown to increase rates of wound healing,” the researchers wrote. “Furthermore, doxycycline, which is more commonly used for its antimicrobial properties, serves as a competitive inhibitor of matrix metallo-proteinases, and tissue necrosis factor-alpha. It may also help reduce inflammation in the wound through decreasing nitric oxide synthesis.”


Smart negative pressure wound care system

The Smart Negative Pressure (SNaP) Wound Care System is a non-electrically powered ultra-portable device that uses specialized springs to deliver NPWT. Disposable and quiet, the SNaP Wound Care System is designed for smaller wounds and available for off-the-shelf use, eliminating the need for costly rental agreements that are common with NPWT devices.

Consisting of a cartridge, which doubles as a storage canister and can deliver negative pressures of 75 mm Hg, 100 mm Hg and 125 mm Hg, a hydrocolloid dressing layer with integrated nozzle and tubing and a foam interface, the SNaP device may be worn around a patient’s leg and hidden beneath clothing.

In a study comparing the SNaP Wound Care System and V.A.C. Therapy, 115 patients with noninfected, nonischemic, nonplantar lower extremity diabetic and venous wounds were treated during 16 weeks. Overall, SNaP-treated patients demonstrated noninferiority in percent decrease in wound area at 4 weeks, 8 weeks, 12 weeks and 16 weeks compared with V.A.C.-treated patients. While complete wound closure was not significantly different when using the SNaP Wound Care System compared with V.A.C. Therapy, the application time for SNaP was significantly shorter and patients reported improved activities in daily living as well as less interruption in sleep.

Future of wound care

According to the researchers, the uses of NPWT extend beyond the treatment of diabetic foot and venous leg ulcers. NPWT can serve as a bolster dressing after the application of split-thickness skin grafts by preventing the accumulation of fluid beneath the graft site. It also improves outcomes in the management of traumatic open fractures and can be applied over a clean closed incision as protection to the wound bed.

The researchers said the future of wound care and limb salvage will rely not only on NPWT, but also the “organization and integration of care, with an emphasis placed on identifying key points in healing and warning signs for recurrence.” For example, wound measurement has been found to correlate with wound healing, but the assessment of wound size may be overlooked because of limited resources in most clinical settings. Furthermore, the complex geometry of certain wounds makes them difficult to measure. However, many of these issues have been addressed by advances in intelligent topographic recognition technology and improvements in metric reconstruction, the researchers said.

The role of proteases in wound diagnostics could also pave the way for improved outcomes in wound care. Although clinical signs do not always correlate with the presence of high protease activity, a registry focused on markers of protease activity could be useful in predicting wound healing and a point-of-care protease test could help guide clinicians to select the most appropriate treatment for a difficult-to-treat wound. — by Casey Tingle

For more information:
Isaac AL. Med Clin N Am. 2013;97:899-909.

Disclosure: Issac had no relevant financial disclosures. Armstrong received research support from KCI and Spiracur and serves on the scientific advisory board of Spiracur.

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