Introduction

The concept of treating wounds with negative or subatmospheric pressure was first described by Fleishmann ( Tables 1–6 ). At that time, the wound treatment modality consisted of applying a negative pressure wound dressing consisting of a semiocclusive dressing and a suction device over an open fracture. Negative pressure wound therapy (NPWT) on open fractures resulted in improved granulation tissue formation. Fleishmann and colleagues subsequent work described the usefulness in traumatic, acute, and chronic wounds.

Argenta and Morykwas and Morykwas and colleagues reported findings from animal as well as human clinical trials showing the usefulness of NPWT on 300 acute, subacute, and chronic wounds, including a 4-fold increase in blood flow levels when 125 mm Hg subatmospheric pressure was applied. A significantly increased rate of granulation tissue formation ( P ≤.05) was reported with continuous (63.3% ± 26.1%) and intermittent (103% ± 35.3%) application of NPWT and tissue bacterial counts were also significantly decreased ( P ≤.05) after 4 days of application.

Since that time, NPWT has overwhelmed the wound-healing world. The use of subatmospheric pressure on wounds has increased exponentially, as has the number of capable devices available. NPWT can be and has been applied to nearly every region of the body: scalp, face, trunk, and extremities. Certain types of wounds such as open sternal wounds and diabetic foot ulcers have occurred frequently enough for them to provide a large body of evidence. This evidence varies in quality from observational case reports and series to randomized controlled trials (RCTs).

We have developed an algorithm after careful evaluation and analysis of the scientific literature supporting the use of these devices.

Mechanism of action of negative pressure wound healing

Since antiquity, wound dressings have been used to facilitate and accelerate wound healing. Two concepts that are critical to dressing selection are:

• 1.
  

  Occlusion

  
  
• 2.
  

  Absorption.

Wounds treated with occlusive dressings have been shown to re-epithelialize more quickly than wounds left exposed and allowed to dry. Excessive exudates tend to macerate the skin around wound edges and also encourage bacterial overgrowth, resulting in impaired wound healing, hence the need for absorptive dressings. NPWT fulfills both these basic tenets and provides additional benefits to the healing wound.

NPWT derives its beneficial effects on wound healing from multiple interactions, with changes effected both on a microscopic as well as a macroscopic level.

Mechanism of action of negative pressure wound healing

Since antiquity, wound dressings have been used to facilitate and accelerate wound healing. Two concepts that are critical to dressing selection are:

• 1.
  

  Occlusion

  
  
• 2.
  

  Absorption.

Wounds treated with occlusive dressings have been shown to re-epithelialize more quickly than wounds left exposed and allowed to dry. Excessive exudates tend to macerate the skin around wound edges and also encourage bacterial overgrowth, resulting in impaired wound healing, hence the need for absorptive dressings. NPWT fulfills both these basic tenets and provides additional benefits to the healing wound.

NPWT derives its beneficial effects on wound healing from multiple interactions, with changes effected both on a microscopic as well as a macroscopic level.

NPWT algorithm

NPWT has become a mainstay of treatment of acute and chronic wounds. The evidence for use of NPWT is variable. Most clinicians have developed a personal algorithm for application of NPWT, and there have been attempts at creating a consensus statement or guidelines for use of NPWT.

Paramount to use of NPWT are:

• 1.
  

  Primary wound assessment

  
  
• 2.
  

  Wound bed preparation

  
  
• 3.
  

  Optimization of patient comorbidities.

After control of these issues, we assess each wound individually. We base our decision to use NPWT on the wound characteristics, including:

• •
  

  Presence of necrotic tissue

  
  
• •
  

  Presence of infected tissue

  
  
• •
  

  What is exposed in the wound bed.

Other wounds such as sternal osteomyelitis have been well studied and these are considered separately. Chronic wounds have been well studied in regard to particular comorbidities such as venous stasis ulcers and diabetic foot ulcers. The use of NPWT is controversial for some uses, such as over flaps, and is well documented for others, such as skin grafts.

Technical aspects of application of NPWT have been studied, but no consensus is clear. Technical modifications include the choice of material under a semiocclusive dressing, the type of semiocclusive dressing, a wound/NPWT device interface, the negative pressure, and the type of pressure (continuous or intermittent). Each of these modifications and evidence for it is reviewed.

Wound assessment and preparation

The benefits of NPWT are based on certain principles that are relevant to wound care and healing in general. Local infection, hypoxia, trauma, foreign bodies, or systemic problems such as diabetes mellitus, malnutrition, or immunodeficiency are most frequently responsible for delay in wound healing and in the formation of chronic wounds. The addition of NPWT does not ameliorate these deleterious effects.

For NPWT to be beneficial in healing wounds, several conditions must be fulfilled:

• •
  

  Paramount to wound healing, regardless of device or dressing choice, is the need for accurate diagnosis. Wound care practitioners must make an accurate diagnosis to provide adequate treatment of underlying medical and wound conditions such as diabetes, peripheral vascular disease, or malignancy.

  
  
• •
  

  Wounds should generally be clean of debris and necrotic tissue. Debridement removes devitalized tissue, which can be a source of endotoxins that inhibit fibroblast and keratinocyte migration into the wound.

  
  
• •
  

  Wounds should have an adequate vascular supply. Angioplasty or arterial bypass grafting may be necessary to ensure adequate oxygenation.

  
  
• •
  

  Compressive garments may improve venous stasis or insufficiency.

  
  
• •
  

  Better glycemic control should be instituted. Glycosylation in diabetes mellitus impairs neutrophil and macrophage phagocytosis of bacteria, prolonging the inflammatory phase of wound healing.

  
  
• •
  

  Infection should be controlled either with systemic antibiotics or local debridement or drainage. Cellulitis prolongs the inflammatory phase by maintaining high levels of proinflammatory cytokines and tissue proteases, which degrade granulation tissue and tissue growth factors, and by delaying collagen deposition.

  
  
• •
  

  Optimization of patient comorbidities and the wound bed are essential.

Contraindications to NPWT

There are specific contraindications to NPWT. Kinetic Concepts (San Antonio, TX, USA) has listed the following contraindications for its NPWT vacuum-assisted closure (VAC) product :

These contraindications are specifically for the VAC, but they can be generalized to all NPWT devices.

Before initiation of NPWT, the wound must be adequately debrided of necrotic tissue. Evidence of wound infection should be treated before initiation of NPWT.

The use of NPWT in areas with exposed vital organs is contraindicated. Several case reports indicate the development of hemorrhage, anastomotic breakdown, and enteric.

NPWT should be used cautiously when:

• •
  

  There is active bleeding

  
  
• •
  

  The patient is on anticoagulants

  
  
• •
  

  There is difficult wound hemostasis

  
  
• •
  

  Placing the dressing beside blood vessels.

Some of these adverse effects may be mitigated by the addition of a wound contact layer, but this is anecdotal.

The presence of inadequately debrided wounds, as stated, prevents the formation of granulation tissue. The presence of untreated osteomyelitis or grossly contaminated tissue within the vicinity of the wound may lead to abscess formation. The presence of necrotic tissue with eschar, in addition to increasing the infection burden, also inhibits the establishment of effective vacuum across the wound and hence is contraindicated.

The presence of malignancy in the wound is also a contraindication for negative pressure therapy because it may, theoretically, lead to cellular proliferation of malignant cells.

NPWT use is contraindicated on fragile skin resulting from age, chronic steroid use, or collagen vascular disorders. The repeated trauma of dressing changes can inflict severe injury to fragile skin, resulting in the development of more chronic wounds.