Mechanical Negative Pressure Wound Therapy: Real-World Effectiveness in Challenging Patient Presentations

When used for wound management, negative pressure wound therapy (NPWT) delivers subatmospheric pressure at the wound site, exerting multiple beneficial effects. The field of mechanobiology, an emerging combination of physics, engineering, and biology, has shown that mechanical or physical forces (eg, negative pressure as seen in V.A.C. Therapy; 3M Health Care) can induce microstrain. The associated cellular deformation that occurs contributes to biological responses, including cellular division and keratinocyte migration.¹ For example, fibroblasts are important cells in the healing process; they synthesize and remodel collagen, tumor necrosis factor alpha, matrix metalloproteinases, and growth factors. Fibroblasts are also known to respond to mechanical cues such as tension, compression, and shear.² The microstrain exerted during NPWT is thought to contribute to the expedited healing observed. Macrostrain also occurs during the delivery of properly applied NPWT, whereby the dressing supports the wound edges and aids in wound contraction. An additional mechanism of action of NPWT is the assistance it provides with drainage management by removing and containing drainage away from the wound bed. Wound drainage can contain high levels of inflammatory cytokines and bacteria that potentiate the inflammatory cycle, contributing to stagnation and delayed wound healing. Another benefit associated with the use of NPWT is the improved perfusion that results from the removal of subcutaneous and interstitial edema. Compared with standard wound dressings, NPWT is associated with improved granulation tissue, decreased time to healing, and reduced overall cost of treatment.³

Mechanical NPWT (mNPWT) delivers positive wound outcomes using similar mechanisms of action.^4,5 Unlike traditional NPWT (tNPWT), however, mNPWT is disposable, lightweight, ultraportable, and quiet, and it does not require electrical power to provide subatmospheric pressure at the wound site.

The 3 complex patient cases reported herein describe the routine use of mNPWT (SNAP Therapy System; 3M Health Care) between December 18, 2020, and June 7, 2021, at a community hospital-based outpatient wound center within an academic health system. All patients received local standard of care, including bedside surgical debridement, soap and water cleansing of the wound and extremity, hypochlorous acid 5-minute soak prior to dressing application, nonsting skin barrier periwound protection, smoking cessation and nutrition counseling, and chronic disease management. For each case, -125 mm Hg negative pressure level canisters were used. No dressing interface was used between the foam and the wound.

Case 1
A 66-year-old female presented to the outpatient wound center with a left foot surgical dehiscence following left first metatarsophalangeal joint arthrodesis with hardware placement, second digit hammer toe repair with proximal interphalangeal joint arthrodesis, flexor extensor tendon transfer, and second metatarsophalangeal joint contracture release that occurred 5 months prior to presentation at the wound clinic (Figure 1). Pertinent past medical history included prediabetes, fibromyalgia, hypothyroidism, methotrexate therapy for large granular lymphocytic leukemia, vitamin D deficiency, and rheumatoid arthritis. The wound had completely granulated and was nearly epithelialized when the patient’s clinical course was complicated by COVID-19 infection, wound decline, and osteomyelitis. In addition to antibiotic treatment for osteomyelitis, the patient was returned to the operating room for hardware explantation and a single application of a dermal repair scaffold, which remained in place for 2 weeks. At presentation to the wound clinic, the wound measured 3.0 × 0.9 × 0.1 cm (surface area, 2.7 cm²). The patient underwent a total of 17 mNPWT dressing changes over 13 weeks. Time to healing, defined as presentation to the wound clinic to documented wound closure, was 19 weeks, 1 day (134 days). Mechanical NPWT was selected for the wound due to minimal depth, lack of undermining, moderate exudate, and wound size and placement fitting comfortably beneath the mNPWT dressing. The periwound skin, including the skin bridge between ulcers, was protected using an ostomy ring to prevent the foam dressing from contacting and irritating the periwound.

Case 2
A 66-year-old female presented to the outpatient wound center with bilateral venous leg ulcers of the lateral calves that had been open for 6 months but had opened intermittently for several years (Figure 2). Pertinent past medical history included a peptic ulcer provoked by ibuprofen intake related to wound pain prior to presentation, venous insufficiency, renal insufficiency, venous stasis dermatitis, recurrent cellulitis, family history of thrombi contributing to mortality, and vitamin D deficiency. The patient’s right leg epithelialized following treatment with a microfiber pad between surgical debridements, gentian violet, methylene blue foam, and 2-layer compression system in addition to standard of care. However, the left leg ulcer remained stalled. At presentation to the wound clinic, the left leg wound measured 19.1 × 16.5 × 0.1 cm (surface area, 315.15 cm²). Venous duplex ultrasound indicated left common femoral, superficial femoral, popliteal, and superficial saphenous veins with partially occlusive thrombi, which did not resolve following chronic anticoagulation with apixaban. Hypercoagulability panels were negative. Sclerotherapy of the left leg was performed. Per an interventional radiology consultation, the patient was not a candidate for additional intervention. The use of advanced therapies, including noncontact, low-frequency ultrasound as well as cellular tissue products, was initially delayed and eventually intermittent due to sporadic and challenging insurance coverage. The patient underwent a total of 11 mNPWT applications over 4 weeks. The portability of the product allowed her to continue to work during use. The wound improved from 25% granulation tissue and 75% yellow fibrin to nearly 100% granulation tissue; however, mNPWT was discontinued due to dermatitis. At the time of this writing, the patient continued to receive treatment in the outpatient wound clinic. Her wound was selected for mNPWT due to the need for frequent activity at work, minimal depth, lack of undermining, moderate exudate, periwound inflammation, and the need for granulation tissue formation.

Case 3
A 57-year-old male presented to the outpatient wound center with a right medial ankle ulcer that had been open intermittently for 8 months following an open tibiofibular fracture sustained during a fall from a roof while intoxicated (Figure 3). He underwent open reduction and internal fixation with hardware placement; the hardware was removed before the patient presented to the wound clinic. Pertinent past medical history included active alcohol and tobacco misuse, peripheral arterial disease, alcohol-induced polyneuropathy, atrial fibrillation, and venous insufficiency. At presentation to the wound clinic, the wound measured 1.4 x 0.8 x 0.7 cm (surface area, 1.12 cm²). An out-of-state hospitalization for atrial fibrillation complicated the clinical course because gauze was applied beneath a foam bordered dressing without skin protectant and remained in place for an unknown period of time, with associated wound decline and dimension enlargement. The patient underwent a total of 16 mNPWT applications over 11 weeks. Successful use of mNPWT was facilitated by drape breaks or periods without application of the device to allow resolution of dermatitis flair-ups using silicone bordered foam dressing to maintain a moist wound environment. The portability of the product allowed him to continue to perform manual labor during use. Mechanical NPWT was discontinued 4 weeks prior to epithelialization due to periwound dermatitis with drainage and pruritus. Time to healing, defined as presentation to the wound clinic to documented wound closure, was 18 weeks, 2 days (128 days). The wound was selected for mNPWT due to the need for frequent activity at work, minimal depth, lack of undermining, exudate, stabilization and protection of the site from repeated trauma, and the need for granulation tissue formation.

Comparative effectiveness research has found tNPWT and mNPWT to have similar wound healing and adverse event outcomes.^3,6 Therefore, considerations for patient selection for mNPWT vs tNPWT are in alignment with the 2021 International Consensus Panel Recommendations for the Optimization of Traditional and Single-Use Negative Pressure Wound Therapy in the Treatment of Acute and Chronic Wounds,⁷ including therapeutic goals, wound-related factors, patient satisfaction, quality of life, care setting, economic-related factors, and product design. Patient presentation factors include mobility, dexterity, psychosocial constraints, insurance or financial status, and wound variables that may add preference for one NPWT system. Mechanical NPWT is especially convenient in the ambulatory setting, where device portability is an important consideration. Wounds with excessive drainage, significant depth or undermining, or in difficult locations still benefit from tNPWT or NPWT with instillation and dwell time. Dermatitis was observed in 2 of the cases reported in this study, which is a known complication of tNPWT.⁸

It is also important to consider other NPWT quality-of-life measures. Compared with tNPWT, mNPWT is associated with increased comfort as well as decreased noise, effect on social interactions, and sleep disruption.³ Quality of life is improved with mNPWT compared with tNPWT because the mNPWT device weighs less than 3 ounces,⁹ does not need to be plugged in to charge, is typically silent, and patients do not need to carry additional baggage. With mNPWT, the lightweight device is strapped near the wound site, thereby limiting excessive tubing and eliminating electrical cords. This can decrease the risk of falls and associated injuries. Some patients returning to their job, especially to work with physical requirements, request mNPWT to increase mobility.

Limitations to this case series include its retrospective case compendium design as opposed to a clinical research study or randomized controlled trial. As such, quantitative data on quality of life using a validated tool was not collected. Instead, the patient’s quality of life had improved, which was ascertained based on a faster return to work and the ability to ambulate safely.

From the cases reported herein, it can be inferred that mNPWT is a convenient therapeutic option in the wound clinician’s armamentarium that appears to deliver healing outcomes comparable to those of tNPWT but with additional improved wound-related quality of life. The cases described herein reveal the real-world effectiveness of mNPWT in the setting of challenging patient presentations and wounds that have stalled. The cases outline common endpoints for advanced therapy usage outside of wound closure, such as granulation tissue formation and quality of life.

Author: Laura Swoboda, DNP, APNP, FNP-BC, FNP-C, CWOCN-AP

Affiliation: Froedtert & the Medical College of Wisconsin Community Hospital Division, Menomonee Falls, WI

Disclosure: The author discloses no financial or other conflicts of interest.

Correspondence: Laura Swoboda, DNP, APNP, FNP-BC, FNP-C, CWOCN-AP, Froedtert & the Medical College of Wisconsin Community Hospital Division, Outpatient Care Center, N180 W8085 Town Hall Road, Menomonee Falls, WI 53051; laura.swoboda@froedtert.com