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Negative Pressure Wound Therapy

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Negative pressure wound therapy (NPWT) is increasingly being used to treat difficult to heal wounds. NPWT is a therapeutic technique that applies vacuum suction to promote healing in acute or chronic wounds. NPWT involves intermittent or continuous application of sub-atmospheric pressure directly to the localized wound.

What is NPWT?

NPWT is a topical treatment used to promote healing of both chronic and acute wounds by applying sub-atmospheric pressure to the wound bed. In most instances the wound is first debrided. It is then cleaned with a wound wash and then filled with a disposable dressing material. An ideal wound dressing for use in negative-pressure would have the following properties: non-adherent; antimicrobial; non-cytogenic and porous. Negative pressure is generated by a pump that is attached to a drainage tube. In use, negative pressure typically ranges from a low of -60mmHg to a high of -150mmHg. An evacuation tube is connected to a disposable canister that is attached to the pump. The canister collects exudate (fluid) from the wound over the course of the healing process. Proximal to the wound, the evacuation tube connects to a drainage tube that terminates through a variety of drainage devices, depending on the nature of the wound. These drainage devices include a dome-like device (dome or REVA) which is a fixed over and external to the wound and a variety of drains that are inserted directly to the wound bed, including flat drains, channel drains and Jackson Pratt-style drains and the REVA. To maintain constant or controlled intermittent pressure, the wound and suction tubing proximal to the wound is covered by a semipermeable film or drape or in some cases a transparent adhesive film dressing.

Mechanism of Action

Negative pressure accelerates wound healing by initiating a cascade of localized of responses. NPWT creates a moist healing environment, drains exudate within the wound site, reduces tissue edema and the pain associates with swelling, contracts the margin of the wound, mechanically stimulates, alters the blood flow and stimulates angiogenesis and the formation of granulation tissue.

Mechanical Effects
A fundamental effect of NPWT is the deformation of the peri-wound as the wound contracts. This is referred to as macrodeformation. The contraction affects the cytoskeleton through shearing forces applied to the wound edges, which leads to granulation tissue formation. The contraction and reduction of the wound size is related to the speed and the quality of wound healing.
Blood Flow Effects
The localized improvement in blood flow which is thought to improve the wound healing process may be as a result of dilating the vascular bed. Increased blood flow may provide improved oxygenation and nutrient support to the localized area. In addition to nutrient support, the increase in blood flow may help to remove waste products.
Granulation Tissue Formation
Negative pressure applied to the wound accelerates the formation of granulation tissue, which results in faster healing. The degree and the characteristics of the type of granulation have been demonstrated to be dependent on the type of wound dressing being used as a contact layer.

When is NPWT Indicated

NPWT should be considered when the wound:

  • Is not progressing with an expected healing trajectory, based clinical exam and established standards
  • Produces excessive exudate
  • Is in a difficult position to achieve a proper seal and fit for a dressing application
  • Requires a reduction in the size to achieve surgical closure

Frequently Asked Questions

What are the short-term goals for NPWT treatment?

  • Management of exudate
  • Management of odor
  • Reduction in pain
  • Prevention of infection

What are the long-term goals for NPWT treatment?

  • Reduction in the size of the wound area
  • 90% wound closure
  • Reduction in the volume of wound exudate

When should NPWT be discontinued?

  • When sufficient and uniform granulation tissue has redeveloped in the absence of infection
  • The patient is not tolerating negative pressure well
  • When wound volume reduction is less than expected based on the type of wound and established clinical protocols
  • There is excessive bleeding or when the patient complains of extreme pain
  • There is evidence of localized or widespread infection

What are some of the contraindications for NPWT?

  • Untreated osteomyelitis
  • Proliferation of malignant cells
  • Non-enteric and unexplored fistulae
  • Exposed vasculature, nerves, anastomic sites or organs
  • Presence of necrotic tissue with eschar present or thick slough in the wound bed, which may require debridement prior to initiation of NPWT

How frequently must the dressing systems be changed when using NPWT?

The frequency of dressing changes depends on many factors including the characteristics of the wound and the type of dressing system being used. If an infection is present, it is highly recommended that daily dressing changes be performed. In some cases these types of wounds may require dressing changes on a more frequent basis depending on established clinical protocols and local practices. Heavily exudating wounds may also require more frequent dressing changes. Foam based dressings must be changed every two to three days or more frequently to avoid tissue ingrowth. Tissue ingrowth is an unwanted consequence of negative pressure when used in conjunction with foam without a contact layer. Tissue ingrowth causes pain and bleeding when the foam is removed, causes damage to newly formed tissue and may leave foreign bodies that could cause infections or impede the normal healing process. In contrast, Cutimed Sorbact may be used as a wound filler with less frequent dressing changes without the deleterious effects of ingrowth. In addition, Cutimed Sorbact has sustained antimicrobial activity.

Benefits IHT NPWT Systems

Control of Exudate
Negative pressure protects the peri-wound surface.
Reduction in the Number of Dressing Changes
This decreases cost, nursing time and creates less disturbance to the wound bed. Fewer dressing changes, while maintaining the integrity of a sealed environment, further decreases the likelihood of wound contamination and infection due to repeated exposure.
Rapid Wound Granulation
Negative pressure stimulates granulation and epithelialisation, resulting in new and healthy tissue growth. The intermittent and continuous positive pressure causes contraction at the margins of the wound, encouraging more rapid wound closure.
Reduced Pain at Dressing Changes
Cutimed Sorbact has been demonstrate to decrease pain on dressing changes, primarily due to less tissue ingrowth that is typically seen with porous foam materials. In one study, 80% of patients indicated that the using the IHT NPWT System was pain free.
Reduces Odor
Improved management of exudate in combination with frequent irrigation of the wound bed with PhaseOne to neutralize toxins and the use of Cutimed Sorbact to sequester pathogens without releasing harmful toxins reduces odor and improves the quality of life for patients with chronic and acute wounds.