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Applying suction to wounds may speed the formation of granulation tissue, decrease the amount of localized edema, increase blood flow, and accelerate healing. In a prospective study conducted by investigators at the Bowman Gray School of Medicine in Winston-Salem, NC, nearly all of the 300 wounds they treated with a new device called the Vacuum Assisted Closure System (VAC) responded well. About 75% showed "significant improvement."
The VAC (Kinetic Concepts, San Antonio, TX) incorporates a vacuum pump connected by tubing to an open-cell foam dressing in the wound. The pump creates a negative pressure of 125 mm/Hg below ambient pressure within and around the sealed dressing.
The suction deforms cells along the wound margins and induces them to multiply, says Louis C. Argenta, professor and chairman of the Department of Plastic and Reconstructive Surgery at Bowman Gray. In addition, the force of the suction removes fluid from the area immediately adjacent to the wound, enabling blood flow to increase. The collection of interstitial fluid compromises the microvasculature and lymphatic system and impedes the delivery of oxygen and nutrients as well as the egress of inhibitory factors and toxins.1 Exudate volumes of up to 1,000 ml of fluid per day were safely removed from large ulcers without any significant hemodynamic or biochemical imbalances. In addition, decreased bacterial colonization was reported in wounds treated by vacuum-assisted closure compared with those treated conventionally.
"We were looking for a way to treat open wounds and get around the system of just using dressing changes and packing," says Argenta. "A very large number of our patients couldn’t be transferred home or to a nursing home because they required dressing changes that were either too much for family members to handle, because they presented insurance problems, or because they required specialized nursing care."
Gradually, Argenta and his colleagues conceived of a system that would pull wound margins together with a minimal amount of pain and discomfort, nursing time, and long-term care. "Sutures just pull together a couple of cells on the edge of a wound," he says. "We came up with the idea of putting a vacuum in the wound and creating a controlled seal, then using a vacuum applied equally to every cell in that wound to draw them centripedally into the middle of the defect."
At first, he adds, it took a while to convince his colleagues that the technique wasn’t quackery.
Linda Dickerson, RN, BSN, CETN, an ET nurse at Emory University Hospital in Atlanta, knows the VAC is no fraud. She used it on a paraplegic male patient with five stage 4 pressure ulcers. None had responded well to prior treatment, and the ulcers were even getting larger. "We saw very good results in managing the wounds [with the VAC]. The wounds contracted, blood supply increased, and odor of the drainage decreased," she says. "Even though the wounds were large and deep, there was significant granulation." She kept photographic records of the wounds’ progress.
The VAC was discontinued when muscle/skin flap surgery was ordered, which was only partially successful. "I think if we had continued to to use the VAC to control fluid accumulation after the surgery, the procedure would have been more successful," she says.
In the Bowman Gray study, all wounds were treated until they were completely closed, covered with a split thickness skin graft, or until a flap was rotated into the healthy, granulating wound bed. This is the classification of the 300 wounds Argenta and his colleagues studied:
• 175 chronic wounds that had been opened and showed no progress toward healing for a minimum of one week. Most had been opened for far longer. These included pressure ulcers, long-term dehisced wounds, venous stasis ulcers, radiation ulcers, and diabetic ulcers. All but four chronic wounds responded well to VAC treatment.
• 94 subacute wounds that had been open for less than seven days. Those responded more rapidly and uniformly than chronic wounds.
• 31 acute contaminated wounds and traumatic injuries, such as gunshot wounds, eviscerations, tissue avulsions, and hematomas. Acute soft-tissue wounds developed granulation tissue extremely rapidly and healed more quickly than chronic or subacute wounds.
The VAC system is composed of several components:
• medical-grade reticulated polyurethane ether foam dressing whose pores range from 400 to 600 microns in diameter;
• a noncollapsible evacuation tube that is embedded in the foam;
• an effluent collection canister that is hooked to the proximal end of the tubing;
• a vacuum pump adjacent to the collection canister.
The unit is about the size of a lunch box, weighs under nine pounds, and runs from standard electrical outlets. A portable battery-powered unit weighing about 14 pounds is also available from the manufacturer, which plans to introduce a lighter and smaller model (about the size of a portable cassette player) next year. The system rents for $75 to $80 a day, according to Kinetic Concepts.
Dressings are trimmed to the appropriate size at bedside and placed in the wound. The evacuation tube is attached to the VAC, and the distal end is positioned so it exits parallel to the skin’s surface. The surface of the wound is then covered with an adhesive tape, which extends 5 cm beyond the wound margins. This ensures that an airtight seal is created. When applied, the suction collapses the foam dressing, and because the foam is open-celled, the suction is distributed equally throughout the dressing.
Argenta emphasizes that wounds should be carefully debrided before the use of the VAC, because nonviable tissue "becomes a focus for bacterial proliferation and a source of lytic enzymes, bacterial toxins, and other factors that impede wound healing. All nonviable tissue is debrided in the operating room, in the clinic, or at the bedside."1
At first, Argenta used continuous suction, but he subsequently observed better results when suction was applied in cycles of five minutes on and two minutes off. The pulsating effect, he explains, dramatically increases blood flow, which leads to decreased bacterial load in the wounds.
Dressings are changed every 48 hours and can be done at the bedside as a clean, but not necessarily sterile, procedure. Dressings for massive wounds should be done in the operating room or other room equipped for patent sedation. Patients are allowed to shower and bathe during dressing changes and can disconnect themselves from the vacuum pump as desired. Long vacuum tubes permit patients a degree of mobility when connected to the VAC unit. According to Argenta, outpatient nurses and often patients and family members can be trained to change the dressings at home.
Based on his research and clinical observations, Argenta concluded that several interrelated factors are the basis for the success of vacuum-assisted closure:
• the removal of excess interstitial fluid;
• the increase in vascularity and associated decrease of bacterial colonization;
• response of tissues around the wound to mechanical forces.
He also notes that the study revealed 34 independent variables that influence wound healing, highlighting the need for further investigation. A randomized prospective study is planned.
Argenta stresses that vacuum-assisted closure is an adjunctive treatment not meant to replace surgery. It’s well-suited for patients who are too sick for surgery, and it can be used to take care of surgical complications such as wound dehiscence. Argenta is trying the system out on burn patients, and he says the military is considering the VAC for treating battlefield wounds.