Temple University School of Podiatric Medicine Journal Review Club
Editor's note: This post is part of the Temple University School of Podiatric Medicine (TUSPM) journal review club blog series. In each blog post, a TUSPM student will review a journal article relevant to wound management and related topics and provide their evaluation of the clinical research therein.

Article Title: Influence of Negative-Pressure Wound Therapy on Tissue Oxygenation in Diabetic Feet
Authors: Jung, Jae-A; Yoo, Ki-Hyun; Han, Seung-Kyu; Lee, Ye-Na; Jeong, Seong-Ho; Dhong, Eun-Sang; Kim, Woo-Kyung
Journal: Adv Skin Wound Care 2016;29(8):364–70
Reviewed by: Kyle Miller, Class of 2020, Temple University School of Podiatric Medicine

Introduction

Diabetic foot ulcers do not always respond well to conventional wound healing methods for a multitude of reasons. Fibroblasts in people with diabetes have decreased migration and proliferation potential as a result of increased metalloproteinase levels in the wound bed of diabetic foot ulcers. These patients are also prone to bacterial infection within the wound because of the immunocompromised status of a patient with diabetes. Negative pressure wound therapy (NPWT) can mediate these issues. The precise mechanism of action of NPWT is not clearly defined, but some possibilities have been conceptually determined. NPWT stimulates cell activity and migration, decreases bioburden in the wound by removing fluid, and reduces edema. However, the authors theorized that the increased pressure induced by NPWT on the skin could cause decreased tissue oxygenation in the wound bed.

Methods

A total of 21 patients with diabetes with an average age of 55.7 years were included in the study. Inclusion criteria required history of diabetes mellitus for longer than 5 years; type 1 or 2 diabetes was not defined. Any patient with cellulitis, wound infection, or a vascular intervention that had been performed less than three months earlier was excluded from the study. Evaluation of tissue perfusion was determined by transcutaneous partial oxygen pressures (TcPO2). The sensor was placed on the dorsum of the foot at the first intermetatarsal space of an unwounded patient with diabetes. Readings were performed by a single expert. A foam dressing was used with a central cutout for the sensor before the NPWT device was applied at a pressure of −125mmHg. The TcPO2 was measured before, during, and after NPWT application. Each measure was taken once a steady-state value had been found.

Results

The authors found that there was a significant drop in TcPO2 in the diabetic foot when NPWT was applied. The mean TcPO2 value before application of NPWT was 44.6mmHg; during therapy it dropped to 6.0mm Hg, and after therapy it rebounded to 40.3mmHg. This finding represents an 84% reduction in TcPO2 values once NPWT was applied, whereas in a healthy patient’s feet, only a 13.5% decrease was found.

Discussion

There are a number of reasons that a person with diabetes would experience a greater decrease in TcPO2. Glycosylated end products in walls of blood vessels cause increased thickness and decreased permeability of capillaries. Non-enzymatic glycosylation of red blood cells stiffens these cells and makes it more difficult for them to pass through capillaries. In addition, arteriovenous shunts are more common in persons with diabetes, thereby leading to decreased blood flow through the capillaries.

The study itself had systemic errors throughout that the authors noted. The study was performed in a matter of hours, a time frame that did not allow for any long-term TcPO2 collection data. It was performed over healthy skin, so results may differ over a wound bed. Finally, the foam cutout where the sensor sat likely did not eliminate the increased pressure on the sensor. For this reason, quantitative conclusions cannot be drawn from this study. What can be concluded, however, is that NPWT does in fact decrease tissue perfusion more in patients with diabetes than in patients without diabetes. This finding supports those of other recent studies.

Conclusion

NPWT still has a place in healing of diabetic foot ulcers because hypoperfusion can be beneficial by inducing neovascularization. The authors do not apply NPWT in patients with TcPO2 values less than 40mm Hg. In their experience, this can commonly lead to wound margin necrosis or can agitate the wound condition because of the already poor perfusion to the wound. To minimize compression on the skin and thus the negative effect on tissue perfusion, the authors suggest using a gauze filler over a foam dressing while also using lower and intermittent negative pressures throughout.

About the Author
Kyle Miller is a third-year student at Temple University School of Podiatric Medicine (TUSPM). He graduated from University of Colorado- Boulder in 2016 with a Bachelor of Arts in Biochemistry. Upon starting school at TUSPM, he has become involved with a multitude of clubs and currently holds officer positions in the American Public Health Association Club and Journal Club. Kyle is interested in reconstructive surgery, limb salvage and diabetic wound care.

Dr. James McGuire is the director of the Leonard S. Abrams Center for Advanced Wound Healing and an associate professor of the Department of Podiatric Medicine and Orthopedics at the Temple University School of Podiatric Medicine in Philadelphia.