Negative Pressure Wound Therapy: What You Should Know

Negative pressure wound therapy (NPWT) can change the course of healing. This approach helps reduce instances of infection and helps difficult wounds heal more smoothly.

NWPT is an approved, effective treatment for both acute and chronic wounds. This procedure promotes tissue granulation and healing, but like any treatment, there are elements to consider, including appropriate dressings, condition of the wound, and medications.

To better understand NWPT as well as the most appropriate uses, we spoke with Karen Shum, DPM, Director of the Limb Preservation Center at Torrance Memorial Medical Center, a Cedars Sinai Affiliate located in Torrance, California.

Defining negative pressure wound therapy

NWPT uses a closed system that applies sub-atmospheric pressure and vacuum suction to promote healing, said Shum.

This process creates granulation tissue by increasing local tissue perfusion, which aids in faster wound healing than conventional wound dressings, she said.

“It is the act of suctioning that brings blood to the surface of the tissue,” said Shum. “This helps to stimulate wound healing and granulation tissue formation.”

NPWT also involves the application of porous foam dressings. “Applying the negative pressure from the device through the foam dressings helps transport fluid and exudate out of the wound bed via porous foam cells, also known as porous foam channels,” she said. “These channels form with the act of suctioning.”

Shum added that the exudate and fluid flows from the wound through the channels in the foam to a cannister. “This removal of interstitial fluid helps to increase tissue perfusion and reduce interstitial edema,” she said.

Wound types treated with NPWT

Different wounds benefit from different treatments. And with negative pressure wound therapy, specific wounds can heal faster and more effectively. The types of wounds in which NPWT can treat are:

• Skin grafts
• Skin flaps
• Surgical wounds
• Deep wounds

When utilizing negative pressure wound therapy over a skin graft, the foam conforms to the wound bed evenly over the skin graft. “This results in improved skin graft adherence and prevents shear forces and disruption of the graft,” Shum said.

And according to Shum, this method also helps remove drainage which reduces hematomas and seromas (both which contribute to skin graft and skin flap failure).

She added that using NPWT along an incision site reduces swelling, minimizes tension on sutures or staples (reducing the risk of wound dehiscence), and lowers the risk of infections.

When using NPWT over deep wounds with a muscle or tendon or bone exposed, Shum said she also uses it in conjunction with an allograft or xenograft to help with granulation and healing.

In her practice, Shum uses NPWT primarily for patients with diabetic foot ulcers (DFUs). “The accelerated healing it provides is akin to limb preservation,” she said.

Necessary supplies for treatment

From dressings to irrigation, NPWT requires certain supplies to achieve the best outcome. The supplies needed are:

• Wound vac (a battery-powered machine)
• A canister to collect drainage
• Foam (polyurethane foam dressing)
• Scissors (to cut the foam dressing to the correct shape and size needed)
• Gloves

Dressings

According to Shum, the dressings used when administering NPWT depend on the wound type, as there are different types of foam. The types of foam include:

• Black: Black foam has polyurethane foam cells.
• Silver: This foam contains silver which has antimicrobial action.
• White: White-colored foam is used to prevent desiccation of tissue structures like exposed tendon or bone. White foam can protect these tissue structures and prevent them from drying out.
• Non-adhering: Use non-adherent dressings first with skin grafts of flaps, prior to placing the foam. The foam should not come in direct contact with the wound.
• Intermitted irrigation: Intermittent irrigation infuses fluid into the wound to remove bacterial bioburden. It needs to stay in the wound for several minutes. Then, instill the appropriate foam with the irrigation and suction the fluid back out. There is a separate cassette attached to the machine with fluid hooked up to instill the foam with this irrigation.

Medications and cleansing solutions

Normal saline is sometimes used to irrigate wounds receiving NPWT. Other times, the instillation fluid used to reduce bacterial bioburden is a non-cytotoxic antimicrobial wound cleanser. If the patient experiences pain with dressing changes, a topical lidocaine is also used to reduce their pain with foam dressing changes.

Treatment duration and frequency

The duration and frequency of NPWT can vary, depending on the indication for use and what you want to achieve, said Shum.

For skin grafts, flaps, and incision sites, this procedure can be done between one to two weeks. If using as an incisional wound vac, there are no dressing changes while it’s left in place for during one- to two-week period.

When using NPWT for creating granulation tissue for filling in a wound defect, treatment is usually longer than the standard one to two weeks. Typically, foam dressing changes need to occur two to three times a week if the goal is granulation tissue formation.

In addition to the treatment above, Shum suggests taking the following steps:

• Make sure to assess the wound bed at each visit to ensure the wound is free of infection.
• Evaluate the peri wound to check that it is intact and not macerated.
• Assess for the need for debridement, as some wounds may need to be debrided at subsequent visits.
• Ensure the healing process is progressing as planned.

Benefits and potential contraindications

When used for exposed deep tissue structures, NPWT reduces the risk of infection and loss of tissue structures. And for patients overall, there is a decrease in dressing changes which in some cases may result in less pain for the patients.

NPWT also has its challenges. Shum said do not use NPWT in ischemic wounds (wounds with poor vascularity); over vital organ structures, vessels, nerves, implants; or in the presence of an acutely infected wound or wounds with necrotic tissue. Lastly, avoid NPWT in malignant wounds.

Negative pressure wound therapy is a treatment modality that all wound care specialists should be adept at using, said Shum. “It’s proven to reduce healing time, reduce discomfort, reduce costs, and improve patient outcomes.”