Basics of Negative Pressure Wound Therapy

Question 1

What is Negative Pressure Wound Therapy (NPWT)?

Answer 1

NPWT is a device or wound care apparatus that applies vacuum to a wound surface. It includes a wound-interface
material, an adhesive film or drape, and tubing connected to a vacuum source.

Question 2

When was NPWT first introduced?

Answer 2

Closed suction drainage has been a long recognized principle of surgery that predates NPWT. However, Morykwas
and Argenta first introduced the concept of NPWT in the early 1990s.

Question 3

What are the indications of NPWT?

Answer 3

NPWT is indicated in acute, chronic, traumatic, and dehisced wounds; partial-thickness burns; diabetic, pressure,
and venous ulcers; flaps and grafts.

Question 4

What are contraindications to NPWT?

Answer 4

NPWT is contraindicated in wounds with exposed vasculature, nerves, anastomotic sites and solid organs, malignancy in the wound, untreated osteomyelitis, necrotic tissue present in the wound, and nonenteric or unexplored fistulas.

Question 5

What is the basic principle of NPWT?

Answer 5

The exact mechanism of action of NPWT is multifactorial and includes accelerated wound healing by increasing granulation tissue formation, removal of wound fluid, maintenance of moist wound environment, and contracting the wound edges together.

Question 6

What factors do NPWT effect to increase blood flow in the wound?

Answer 6

Blood flow is dependent on the pressure applied, distance from the edge, and the tissue type. Blood flow decreases at the wound edge, but immediately increases with vacuum release suggesting that intermittent NPWT may further increase blood flow.

Question 7

How does NPWT effect wet or draining wounds?

Answer 7

In patients with large open wounds, serous fluid may accumulate in the wound bed and be efficiently removed by NPWT leading to accelerated wound healing.

Question 8

What effect does NPWT have on skin surrounding the wound?

Answer 8

In wounds where the surrounding skin is deformable, such as the abdomen or thigh, it is commonly observed that
the wound shrinks considerably when using an NPWT device.

Question 9

How does NPWT maintain wound homeostasis?

Answer 9

Covering the wound with a semiocclusive dressing and using foam with insulation qualities minimize evaporation,
desiccation, and heat loss.

Question 10

What complications can occur from NPWT?

Answer 10

Bleeding and infection have been reported by the FDA in a small number of patients. In addition, retained foam dressing pieces have also been reported.

Question 11

Can NPWT be used in patients on anticoagulants or platelet aggregation inhibitors?

Answer 11

Extreme caution should be used with patients at high risk of bleeding and hemorrhage, on anticoagulants or
platelet aggregation inhibitors.

Question 12

How is NPWT applied to wounds?

Answer 12

An interface material is fitted to the size of the wound and placed on or into the wound bed. The adhesive dressing is placed over the wound. Tubing is connected to the wound through a hole in the adhesive drape and connected to a collection canister and a vacuum source.

Question 13

What is used for the wound-interface material?

Answer 13

Many materials can be used including open pore foam, gauze, polyvinyl alcohol sponges, and corrugated polymers.
Open pore sponges are most commonly used.

Question 14

How does the wound-interface material act on the wound?

Answer 14

The interface material distributes the vacuum throughout the wound and allows for fluid removal. In addition, the
wound-interface material causes microdeformations at the wound surface and draws the surrounding skin together.

Question 15

Can the wound-interface material be hemostatic on the wound?

Answer 15

The wound-interface materials used in NPWT are not hemostatic and should not be applied to wounds that are bleeding or have a potential to bleed.

Question 16

Does the wound-interface material have antibacterial properties?

Answer 16

The commonly used wound-interface materials are inert substances that have no inherent antibacterial properties and should not be applied to grossly infected wounds. There is a silver-impregnated foam that can be used with certain NPWT devices and there are also antibacterial gauze products that can be used with the device.

Question 17

What happens to the wound if there is no adequate seal to maintain continuous suction on the wound bed?

Answer 17

There must be an adequate seal to maintain the vacuum or air will leak into the wound causing desiccation.

Question 18

What pressure is commonly used for NPWT?

Answer 18

There are no established guidelines on the amount of pressure applied in NPWT. Applying a pressure of 125 mm
Hg is most commonly used, but pressures between 60 and 150 mm Hg have also been applied.

Question 19

What waveforms are commonly used?

Answer 19

The original work by Morykwas and Argenta showed increased granulation tissue formation with cycling waveforms; however, varying the level of suction can cause pain and may not be well tolerated by patients. Instead, continuous suction is most commonly used.

Question 20

When is a wound ready for NPWT?

Answer 20

Wounds may be ready for NPWT after complete debridement of infected and necrotic tissue.

Question 21

Does NPWT debride wounds?

Answer 21

NPWT does not debride or remove devitalized tissue in wounds but rather aids to accelerate wound healing.

Question 22

How often does the wound-interface material need to be changed?

Answer 22

There are no specific recommendations for changing the wound-interface material. In heavily colonized wounds, the dressing should be changed every 12 to 24 hours, for several days to make sure the wound is clean. Afterwards, the dressings are generally changed every 2 to 3 days.

Question 23

When changing the NPWT dressing, what should be assessed?

Answer 23

The wound should be assessed for infection, odor, and need for further debridement. In addition, the wound bed should be assessed frequently for duskiness, bruising, and bleeding. The surrounding skin integrity should be monitored for skin breakdown from the adhesive drape and rash secondary to contact dermatitis or fungal infection. Devitalized tissue should be removed as indicated with each dressing change. If the wound is malodorous, the treatment should be stopped for 24 to 48 hours and replaced with saline dressings until the odor has subsided. Then NPWT treatment can be resumed.

Question 24

How long can NPWT be used on a wound?

Answer 24

Prolonged use of NPWT beyond 3 months may not be of benefit unless the wound surface area continues to significantly decrease.

Question 25

When should NPWT be discontinued?

Answer 25

NPWT should be discontinued if the patient does not tolerate dressing changes or if the wound needs to be frequently assessed for infection. If the wound bed is dusky, bruised, or bleeding, the wound becomes grossly infected, or there is persistent devitalized tissue present, the therapy should be discontinued. The therapy should also be immediately stopped if blood or purulent exudate is noted in the suction canister.

Question 26

Can NPWT be used in dirty or grossly contaminated wounds?

Answer 26

NPWT devices should be used with extreme caution in infected wounds. Some clinicians use NPWT devices on infected wounds, and if used, the device should be changed every 12 to 24 hours to avoid worsening infection or sepsis.

Question 27

Can NPWT be applied to diabetic wounds?

Answer 27

NPWT has been used as a wound healing therapy after debridement of diabetic foot ulcers. Most of the few randomized diabetic foot ulcer trials compare NPWT to hydrogel, alginate, or gauze—all indicating better wound healing with NPWT.

Question 28

How does NPWT prepare a wound for surgical closure?

Answer 28

NPWT prepares the wound bed for surgical closure with skin grafts or tissue substitutes by increasing granulation
tissue formation, decreasing the surface area, and possibly increasing blood flow to the wound bed.

Question 29

What effect does NPWT have on lower extremity wounds?

Answer 29

NPWT can be used in patients with lower extremity stasis ulcers. In studies of patients with lower extremity ulcers, there was a trend toward less secondary amputations with NPWT applied to the wounds compared to nontreated controls. Patients with lower extremity traumatic injuries, specifically tibia-fibula fractures, treated with NPWT were less likely to require free flap closure of their wounds and were more likely to be closed primarily or with simple skin grafts.

Question 30

How is NPWT used in the treatment of an open abdomen?

Answer 30

When the abdominal fascia is left open after a laparotomy, NPWT can be applied in the wound to control infection, manage exudate, and reduce visceral edema. Any exposed viscera should be covered with a nonadherent dressing prior to placement of the NPWT wound-interface material.

Question 31

How can NPWT be applied to enterocutaneous fistulae?

Answer 31

The fistula can be isolated and controlled from the surrounding tissues by placing wound-interface material over the fistula. The effluent can be controlled, while the surrounding tissues are protected, the tissues can granulate and the wound can contract around the fistula. Additional therapy must be directed at the underlining cause and control of the fistula.

Question 32

Can NPWT prevent burn wound progression?

Answer 32

Early work by Morykwas showed that NPWT prevents tissue injury progression in swine after partial-thickness burns. There have been several small studies since, but no robust clinical trial has been performed to assess the theoretical edema reduction, improved tissue perfusion, or less scarring with NPWT.

Question 33

Can NPWT be used in chest wall wounds following median sternotomies?

Answer 33

NPWT allows for wound drainage, chest wall stabilization, and isolation of the chest cavity to prevent contamination, maintenance of a moist environment, granulation stimulation, and increased blood flow to the tissues. After NPWT is used for several days in a deep sternal wound, definitive closure is usually performed with soft tissue flaps.

Question 34

How is NPWT used as a bolster for skin grafts?

Answer 34

The use of NPWT as a bolster for skin grafts has been shown to increase graft take compared with foam bolsters without vacuum. NPWT is generally used for 48 to 72 hours and then removed. A nonadherent material should be applied between the skin graft and wound-interface material.

Question 35

How is NPWT used to treat lower extremity compartment syndrome?

Answer 35

NPWT can be applied to open fasciotomy wounds, which decreases the edema and promotes granulation tissue formation allowing these wounds to either completely close in an accelerated manner or contract enough to accept a skin graft.

Question 36

What role does NPWT have in controlling lymphatic injuries?

Answer 36

NPWT is effective in controlling lymphocele or lymphatic fistula with complete resolution of the drainage in a
mean of 1 to 2 weeks.