Negative pressure wound therapy (NPWT) is a useful management tool in the treatment of traumatic wounds and high-risk incisions after surgery. Since its development nearly 2 decades ago, uses and indications of NPWT have expanded, allowing its use in a variety of clinical scenarios. In addition to providing a brief summary on its mechanism of action, this article provides a focused, algorithmic approach on the use of NPWT by reviewing the available data, the appropriate clinical scenarios and indications, and the specific strategies that can be used to maximize outcomes.
Key points
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Negative pressure wound therapy (NPWT) is ideal for soft tissue defects that can heal through secondary intention or require skin grafting.
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NPWT prevents desiccation, reduces edema, limits hematoma, and facilitates wound drainage.
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NPWT is an effective way to downscale the complexity of soft tissue reconstruction.
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NPWT can decreases the risk of wound complication when applied to high-risk incisions after fracture surgery.
Introduction
Since its inception more than 20 years ago, negative pressure wound therapy (NPWT) has had a major impact in the management of orthopedic injuries. NPWT has been widely adopted for use in a variety of clinical scenarios, and has had reported success in the setting of high-energy trauma, open fractures, infections, and excessive soft tissue damage. However, although its success has led to widespread use in orthopedic trauma, a deeper understanding of its mechanism of action, along with the ideal clinical scenarios for use, is required. This article reviews the nuances of NPWT application, including its mechanism of action, clinical indications, and specific strategies used in order to achieve desired clinical outcomes.
Introduction
Since its inception more than 20 years ago, negative pressure wound therapy (NPWT) has had a major impact in the management of orthopedic injuries. NPWT has been widely adopted for use in a variety of clinical scenarios, and has had reported success in the setting of high-energy trauma, open fractures, infections, and excessive soft tissue damage. However, although its success has led to widespread use in orthopedic trauma, a deeper understanding of its mechanism of action, along with the ideal clinical scenarios for use, is required. This article reviews the nuances of NPWT application, including its mechanism of action, clinical indications, and specific strategies used in order to achieve desired clinical outcomes.
What is it?
To administer NPWT, there are 3 main components that create a subatmospheric pressure environment: a porous dressing sealed via an occlusive adhesive, a vacuum device, and a connector that allows communication ( Fig. 1 ). In orthopedic trauma, the dressing of choice is a dry, black, hydrophobic, reticulated polyurethane-ether foam with a pore size of 400 to 600 μm (KCI, San Antonio, TX). A polyvinyl alcohol (PVA) foam is also available (KCI, San Antonio, TX). It differs from the large-pore foam because it has a smaller pore size (60–270 μm) and comes premoistened with sterile water. The hydrophilic nature and smaller pore size of the PVA foam offers a less-adherent application and has significantly less granulation and perfusion than the large-pore dressing. Thus, for most of the clinical scenarios in orthopedic trauma, the large-pore foam is preferred. Placed on the area of interest, the wound and sponge dressing are sealed off with a plastic adhesive and occlusive dressing, and communicate with the vacuum device via a connector creating a localized negative pressure environment.
How does it work?
NPWT allows improved wound management and healing via 2 main mechanisms. Following initial injury, a substantial inflammatory response is generated from damaged tissue, initiating a vicious cycle of increasing interstitial edema and pressure, leading to cell death and necrosis secondary to lack of nutrient inflow combined with a congested outflow of cellular waste (see Fig. 1 ). With the use of NPWT, a subatmospheric environment is created, acting at the level of the interstitium to eliminate unwanted edema, inflammatory mediators, and bacteria (see Fig. 1 ). This environment creates more favorable healing conditions by removing the volume that obstructs inflow and outflow, allowing greater nutrient and oxygen inflow as well as venous drainage.
In addition, NPWT promotes mitogenesis and granulation tissue formation via increased cellular substrate recruitment. Dynamic tissue formation is facilitated by the mechanical strain placed on the tissue by the negative pressure environment. The strain created by the vacuum allows microdeformation and stretch at the cellular level, allowing cellular chemotaxis, angiogenesis, and new tissue formation via the recruitment of growth factors (ie, vascular endothelial growth factor [VEGF], Fibroblastic Growth Factor [FGF]-2). Labler and colleagues analyzed wound fluid from NPWT dressings and noted significantly higher levels of interleukin-8 and VEGF compared with fluid analyzed from a standard dressing. Furthermore, histologic analysis noted significantly higher levels of angiogenesis and granulation tissue formation.
The effect of the subatmospheric environment is also evident at the genetic transcriptional level. Chen and colleagues measured the presence of proto-oncogenes during NPWT in a pig model. The negative pressure environments produced significantly higher levels of C-MYC, C-JUN, and BCL-2, corresponding with proportional increases in the cells required for granulation tissue formation. These cellular-level changes serve as the basis for the clinical advantages seen with NPWT.
Indications
In addressing purely soft tissue traumatic wounds, the best-supported indication for NPWT is to provide temporary wound cover following thorough debridement when definitive closure is not possible, such as in cases of significant wound contamination, need for subsequent debridement, significant edema, or in a patient who is critically ill. This form of therapy can be quickly applied and accomplishes the goals of prevention of desiccation, minimizing microbial contamination, reduction of edema, and facilitation of wound drainage. Because it is changed less frequently than wet-to-dry dressings and subsequently provides less discomfort for the patient, NPWT is less labor intensive for hospital staff. With regard to indications for its use, NPWT has been particularly successful in the treatment of fasciotomy incisions because delayed primary closure allows for edema to subside and compartment pressures to normalize. For similar reasons, NPWT has also been shown to be more effective when applied over surgical wounds or incisions at fracture sites known to have a high incidence of wound complications compared with dry dressings ( Fig. 2 ). Several randomized trials in the orthopedic literature support these findings, particularly in high-risk closed extremity and acetabular fractures. In a randomized trial of 263 patients, Stannard and colleagues showed a decreased risk of deep infection and dehiscence in high-risk lower extremity fractures using continuous negative pressure at 125 mm Hg for 2 to 3 days. Animal models have reproduced these findings, showing a mechanism of action through edema reduction, accelerated wound healing, decreased lateral tension on wound edges, and reduction in hematoma or seroma.
This therapy has also proved to be a superior means to preserve skin grafts, improve skin graft incorporation, and reepithelialize the donor site. When applied directly over a newly applied skin graft, Llanos and colleagues showed in a randomized trial of 60 subjects that the median rate of skin graft loss and the median hospital stay were significantly reduced compared with a control group.
NPWT has also been successful as a means to downscale the complexity of soft tissue reconstruction ( Fig. 3 ). Parrett and colleagues showed a decrease in the number of free flaps needed when NPWT was used in reconstruction with no difference in infection, nonunion, amputation, or reoperation rates between groups. In progressing a complex wound to a smaller and simpler state, clinicians may avoid morbidity for patients and also reduce cost of care. Although first performing an aggressive debridement of all nonviable soft tissue is advised, NPWT can be a useful tool to promote granulation tissue growth during a state of wound bed unsuitability. Exposed bone, tendon, and orthopedic implants can preclude definitive wound closure. NPWT may enhance tissue granulation over these substrates to allow staged closure. However, care must be taken to protect any exposed blood vessels or nerves and not place the dressing within too close proximity ( Fig. 4 ).
