Negative Pressure Wound Therapy

Introduction

Management of difficult acute and chronic wounds poses a significant challenge to the patient and the caregiver. The application of negative pressure wound therapy (NPWT) has proven to ease some of this burden by promoting a favorable wound-healing environment, decreasing the need for frequent dressing changes, improving patient comfort, and reducing associated costs. In NPWT, a pliable foam dressing is cut to shape, placed into a wound, and covered with an occlusive dressing. Controlled sub-atmospheric pressure is then applied to the wound by evacuating air and liquids from the foam dressing. The most commonly used device for applying NPWT is the wound VAC®.

Mechanism

Initial research on pigs demonstrated the superiority of NPWT when compared with moist saline dressings. Although few randomized controlled trials exist in humans, one review suggests that NPWT improves granulation, augments wound contraction, and reduces the need for systemic antibiotics. Several mechanisms may be responsible for these observations. NPWT has been shown to improve local tissue perfusion and reduce the bacterial load on wounds. NPWT may also improve granulation tissue formation by reducing proteolytic enzymes found in wound exudates, by promoting a moist wound, and by applying shear forces that induce cellular hyperplasia.

Indications

Since NPWT has become commercially available, the list of indications has continued to grow (Table 5.1). NPWT is indicated for almost any open wound where surgical closure is not feasible or desirable. While it may be used as a sole treatment toward achieving wound closure, NPWT is often used as a bridge toward definitive surgical management. Much of its utility is in creating favorable conditions for subsequent wound reconstruction.

With the success seen in treating a variety of wounds, many authors have tried to extend the application to improve graft take and flap survival. When flaps are used to cover wounds, some studies suggest that additional use of the NPWT may promote improved flap survival and overall wound healing. In several case series, skin graft take was shown to be 90% or greater when the VAC was employed in lieu of a traditional bolster dressing. Recipient sites with irregular contours, susceptibility to shear forces, and excess drainage were thought to be particularly amenable to VAC dressings. Nevertheless, these results have yet to be confirmed in randomized control trials.

Practical Plastic Surgery, edited by Zol B. Kryger and Mark Sisco. ©2007 Landes Bioscience.

Table 5.1. Indications and contraindications for use of NPWT

	Indication							Notes
	Chronic open wounds
	Diabetic ulcer
	Pressure sore							Debridement must be performed prior to application
								of NPWT
	Traumatic wounds
	Extirpative defects							Brachytherapy and external-beam irradiation can be
								performed through the dressing
	Spinal and orthopedic							Dressing can be placed directly over hardware
	wounds							after debridement has been performed
	Sternotomy defects
	Open abdomen							Excellent for the temporary management of bowel
								edema and gross peritoneal contamination
	Burns							May be applied over allograft of skin substitute
	Skin graft bolster							NPWT improves graft take by limiting shear forces
								and evacuating fluid collections

Contraindications
Malignancy in the wound

Untreated underlying osteomyelitis Nonenteric or unexplored fistulas Undebrided necrotic tissue Untreated active soft tissue infection Exposed internal organs Exposed blood vessels or vascular prosthetic grafts Coagulopathic patients (relative)
Technique

Application of NPWT can be performed by anyone with the appropriate training, provided that the wound is hospitable. Prior to application, the wound should be debrided of any necrotic or fibrinous debris and adequate hemostasis achieved. The surrounding skin is then cleansed and dried. The sponge is cut to be slightly smaller than the volume of the wound. The adhesive dressing is then applied over the sponge such that there is at least a 6 cm overlap on adjacent skin; it is imperative that a hermetic seal be achieved. Once the adhesive dressing has been applied, it is pierced and the adhesive suction tube is applied over this opening. The device is then turned on and continuous suction is applied. When placed properly, the dressing will create a closed suction environment. Depending on the nature of the wound, the NPWT dressing can be changed every 48 to 72 hours. The dressing should be taken down sooner should the patient show signs of infection or if the seal on the dressing becomes compromised.

The VAC® device comes with two types of foam available for use. The original foam is black, and it is made of polyurethane. It is hydrophobic which enhances exudate removal. It has reticulated pores and is considered to be the most effective at stimulating granulation tissue while aiding in wound contraction. The second, newer available foam is white. It is a denser foam with a higher tensile strength. It is hydrophilic and possesses overall nonadherent properties. The white foam does not require the use of a nonadherent layer. It is generally recommended for situations in which slower growth of granulation tissue into the foam is desired or when the patient cannot tolerate the black foam due to pain. Due to the fact that it has a higher density than the black foam, higher pressures must be utilized in order to provide adequate negative pressure distribution throughout the wound. Newer foams are constantly emerging, such as silver-impregnated foams.

Pearls and Pitfalls

• Though the NPWT dressing is applied less frequently than the comparable saline dressings, some patients find it painful and require appropriate premedication with analgesics.
• The skin surrounding the wound should be completely dry prior to placement of the adhesive. Shaving of hair and application of Benzoin^TM may facilitate adhesion.
• The foam should be cut down to the proper size so that it fits within the borders of the wound, otherwise it will compress the surrounding healthy skin.
• After placing the dressing and applying the vacuum, ensure an adequate seal by clamping the tubing leading to the dressing and then disconnecting the tubing from the machine. If the seal is adequate, the sponge should slowly return to its original shape.
• If poor hemostasis is presumed or if the wound is particularly “weepy”, close monitoring of the patient’s hemodynamic and fluid status is warranted.
• The foam should not encroach on normal surrounding skin. However, two separate wounds can be hooked up to a single suction tubing by bridging the two sponges with a thin piece of foam that traverses the normal interfering skin.
• A useful trick for dressing change analgesia is to clamp the tubing and inject 1% lidocaine with epinephrine (10-30 ml) into the tubing distal to the clamp. The vacuum will suck the local anesthetic into the wound.

Suggested Reading

1. Argenta LC, Morykwas MJ. Vacuum-assisted closure: A new method for wound control and treatment: Clinical experience. Ann Plast Surg 1997; 38:563.
2. Morykwas MJ, Faler BJ, Pearce DJ, Argenta LC. Effects of varying levels of subatmospheric pressure on the rate of granulation tissue formation in experimental wounds in swine. Ann Plast Surg 2001; 47(5):547-51.
3. Evans DL, Land LL. Topical negative pressure for treating chronic wounds: A systematic review. Br J Plast Surg 2001; 54:238.