Negative Pressure Wound Therapy for Amputations and Decubitus Heel Ulcerations
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Start with the working definition of negative pressure wound therapy or V.A.C. therapy. Negative pressure wound therapy is the controlled application of subatmospheric pressure to a wound using an electric pump. Subatmospheric pressure is applied intermittently or continuously through a specialized wound dressing, which includes an open cell foam dressing. The dressing is sealed with an occlusive bandage to contain the subatmospheric pressure at the wound site. Drainage from the wound is collected in a sterile canister.
There are several devices that can be used for negative pressure wound therapy. In the upper right hand corner is the classic V.A.C. unit which is often the unit that is first utilized in the hospital. There is also the V.A.C. ATS on the top left, the V.A.C. Freedom on the lower left, and the V.A.C. instill system on the lower right.
There are several therapeutic benefits or advantages to using V.A.C. therapy or negative pressure wound therapy. This type of therapy helps to uniformly draw wounds closed. In addition, it helps to remove interstitial fluid from the wound bed and decreases local edema. It helps to remove infectious materials and it protects and insulates the wound from bacterial pathogens. Negative pressure wound therapy also assists in covering exposed structures with granulation tissue and thereby helps to maintain their viability.
The V.A.C. can be used in a number of complex wounds such as chronic ulcers; compromised flaps and grafts; acute or traumatic wounds; wounds with exposed tendon, bone, or hardware; decubitus ulcerations; and open amputations.
Often the objective when using V.A.C. therapy is to cover vital structures and improve the granulation tissue in the wound bed, so it can be grafted or so a delayed primary closure can be performed. In most cases, this is not a therapy that is used until the wound heals by secondary intention.
Contraindications to V.A.C. therapy include untreated bone infection, malignancy in the wound, exposed blood vessels or organs, the presence of fistulas, and necrotic or devitalized tissue within the wound.
You should also consider taking additional precautions in patients that have the potential for bleeding problems. This is especially true for patients that have had aggressive surgical debridement or open amputation. Often, these patients will have active bleeding or you will have directly observed difficulty with wound hemostasis while you are in the operating theatre. In these patients, I generally will wait to apply the V.A.C. for 24 or 48 hours after surgery to make sure that they have adequate hemostasis. You may also want to be cautious in patients that are receiving anticoagulation therapy or in patients that have weakened, irradiated, or sutured blood vessels.
When the foam dressing will be applied in close proximity to blood vessels or organs, you may want to consider using a protective barrier between the area of concern and the open cell foam. You should also take extra precautions when there is a potential for bone fragments or sharp edges after resecting the bone or when using the V.A.C. with open fractures and when there is a potential for fistulas. Just as in all wound therapies, universal precautions should be rigorously utilized.
The foundation for clinical trials with negative pressure wound therapy started with evidence from animal studies. This is one of the classic V.A.C. studies using a pig model. These studies have demonstrated a decrease in bacterial load, an increase in granulation tissue formation, and an increase in local perfusion when negative pressure wound therapy is utilized.
This is from a study that was published in Annals of plastic surgery in 1997. This graph shows the percent increase in granulation tissue formation of acute wounds with V.A.C. therapy compared to wet-to-moist saline gauze therapy. With both continuous and intermittent negative pressure wound application, there was a significant increase in the rate of granulation tissue formation in this animal model. With continuous negative pressure wound therapy, there was a 63.3% increase in granulation tissue compared to wet-to-moist saline dressings. With intermittent application of negative pressure wound therapy, there was a 103.4% increase in granulation tissue formation.
In the same study, the bacterial load was evaluated in animals that received wet-to-moist saline dressings and negative pressure wound therapy. The control therapy is represented by the green line and V.A.C. therapy is represented by the blue line in the graft. Clinical infection or bacterial load of ten to the fifth organisms is represented by the red line. In this study, by the fourth day, there was a significant reduction in bacterial clearance in wounds treated with V.A.C. therapy compared to saline moistened gauze.
The next part of this study evaluated the effect of intermittent negative pressure wound therapy on perfusion. To measure local tissue perfusion, a laser Doppler needle Flow probe was placed into the subcutaneous tissue at the edge of the wound. The flow measurements increased over time compared to baseline. The V.A.C. was applied cyclically. It was on for 5 minutes and off for 2 minutes at 125 mmHg. Flow measurements returned to baseline values during the off cycle.
Animal worked with negative pressure therapy has demonstrated significant improvement in bacterial clearance, blood flow, and the rate of granulation tissue formation compared to standard therapy with saline wet-to-moist gauze dressings.
There are a growing number of clinical trials to help us understand the implications of negative pressure wound therapy. With the next series of slides, I would like to focus on the results from clinical studies. Joseph reported the results of a randomized clinical study in 24 patients with 36 wounds of mixed etiologies. Joseph compared negative pressure wound therapy again to saline wet-to-moist dressings as the standard therapy. All patients were followed to healing or amputation. In addition, wounds were biopsied at 3 and 6 weeks to evaluate histology.
Joseph observed that wounds treated with negative pressure wound therapy showed a significant reduction in wound volume compared to standard therapy. Negative pressure wound therapy also had a protective effect when there was exposed tendon or bone. In addition, negative pressure wound therapy had a significantly more granulation tissue in the wound bed compared to patients who received saline dressing therapy.
In this graph, wounds treated with negative pressure wound therapy are represented by the red line and wounds treated with wet-to-moist saline dressings are represented by the blue line. Joseph showed significantly faster wound closure rates in this study. The volume of the wounds decreased by 78% in patients that received negative pressure wound therapy compared to 30% in patients that received the controlled therapy.
There is also a significant difference in other wound parameters. This graph shows that there was a 66% change in wound depth in patients that received negative pressure wound therapy compared to a 20% change in patients that received controlled therapy. Joseph also showed significant difference in width and length of the wounds in patients treated with negative pressure wound therapy.
In 2000, McCallon reported the results of a small randomized clinical trial in diabetics with nonhealing foot wounds. Negative pressure wound therapy was again compared to saline moistened gauze. V.A.C. subjects healed in about half the time that it took controls to heal. In addition, V.A.C. patients showed an average reduction in surface area of 28.4% compared to a 9.5% average increase in patients that received saline gauze therapy.
The next study is a retrospective cohort of 31 diabetics with foot amputations that were treated with negative pressure wound therapy. This paper was published by David Armstrong in 2002. The V.A.C. was used in those cases to prepare the wound bed for additional therapy such as delayed primary closure or split thickness skin grafts. These were relatively large wounds with an average area of 28 cm2. The wounds had been treated for an average of 25 weeks prior to initiating negative pressure wound therapy. The descriptive results reported by Armstrong include time to closure, proportion of wounds that healed at the initial amputation level, and complications or adverse events.
This graph shows the time distribution that the V.A.C. was used in this cohort of patients. On average, the V.A.C. was used for 4.7 weeks. As you can see, many of the patients had V.A.C. therapy for a much shorter period of time. The mode was 2 weeks.
In this cohort of patients, negative pressure wound therapy was successful in limb salvage in the majority of patients. Ninety point three percent of patients healed their wounds at the primary amputation level in an average of 8 weeks. In this cohort, often multiple additional therapies were combined with negative pressure wound therapy. These included application of bioengineered tissue, split thickness skin grafts, and delayed primary closures. Only 3 patients required a proximal amputation. The most common adverse event was periwound maceration. This was observed in 19% of the study subjects. Two patients experienced infection, one patient had cellulitis, and one patient had a deep space infection. The photo on the right shows one of the patients that developed soft tissue infection. This was successfully treated with a short course of oral antibiotics.
The final study I will discuss was recently published in the Lancet. This was a large multicenter randomized clinical trial that evaluated negative pressure wound therapy and compared it to standard moist wound healing therapies as described in WOCN guidelines. The patient population included persons with diabetes with open foot amputations. This study is unique in that it allowed the treating clinician to use a variety of wound care products within the WOCN guidelines. In addition, wound therapy could be changed based on changes in the wound or the wound characteristics. This was also the first randomized clinical trial to evaluate healing in open foot amputations. This was a 16-week long study.
In this study, the primary inclusion criteria included the presence of a foot wound in a person with diabetes that was due to a partial foot amputation. These patients had to have evidence of adequate perfusion to their foot determined by ankle brachial indices, toe pressures, or transcutaneous oxygen measurements. In addition, they had to be at least 18 years of age and have evidence of adequate nutrition. Exclusion criteria included patients that had Charcot arthropathy; wounds from electrical, chemical, or radiation burns; or venous insufficiency. Patients were also excluded if their hemoglobin A1c was greater than 12%. If they had received growth factors, dermal substitutes, or other wound therapies that would be confounding within 30 days of screening or if they had received negative pressure wound therapy within 30 days of screening.
This slide shows the flowchart for this study. We will take a couple of seconds and walk through enrollment and randomization.
Hundred sixty two patients met the inclusion and exclusion criteria and were randomized into the study.
Subsequently, 85 patients were randomized in the control arm and 77 were randomized into the negative pressure wound therapy arm.
A similar proportion of patients in both treatment arms withdrew from the study prior to the last active phase treatment visit without closure of their wound. Twenty two point four percent of controls and twenty four point seven percent of negative pressure wound therapy subjects withdrew before the end of the 16-week active treatment phase without having complete wound closure.
During this 16-week active treatment phase of the study, 55.9% of patients randomized to receive V.A.C. therapy had complete wound closure. Forty point three percent of these patients healed without surgical closure. Fifteen point six percent healed with surgical closure.
Overall, a smaller proportion of wounds healed that were treated in the control arm. Nine point four percent of wounds healed with the surgical intervention while twenty nine point four percent healed by secondary intention in this treatment group.
During the 16-week active treatment period, a significantly higher proportion of open amputations healed in the group that received negative pressure wound therapy. Fifty five point nine percent of patients treated with the V.A.C. healed compared to thirty eight point eight percent of patients treated in the control group. The majority of patients in both treatment arms healed their wounds by secondary intention. Only 15.6% of V.A.C. patients and 9.4% of patients treated with standard therapy healed with surgical intervention.
This graph shows the Kaplan-Meier survival analysis for this study. V.A.C. patients are represented by the blue line while controls are represented by the red line. This graph shows significantly faster healing in subjects that were treated with V.A.C. therapy.
This graph shows re-amputations in both treatment arms. There was a strong trend that fewer subjects treated with negative pressure wound therapy required an additional amputation. This trend was not statistically significant. It had a P value of 6%. Ten point six percent of patients in the control arm required a second amputation. Nine patients had an additional amputation at the level of the foot and five required more proximal amputation consisting of either a below or above knee amputation. Among V.A.C. patients, only 2.6% required a second amputation. All of these were foot level amputations. None were below the knee or above the knee amputations. The relative risk ratio from this data indicated that negative pressure wound therapy patients were only one-fourth as likely to require a second amputation compared to control subjects.
This table compares new granulation tissue formation in a high-risk subset of the study population. In this subanalysis, we evaluated patients that presented with 0 to 10% granulation tissue within their wound at the beginning of the study. This graph shows that patients treated with negative pressure wound therapy responded significantly faster and had a more robust granulation tissue response. The median time to reach 76 to 100% granulation tissue was 42 days in patients that received negative pressure wound therapy and 84 days in the control group.
The results of this large randomized clinical study suggest the treatment with negative pressure wound therapy delivered through the V.A.C. therapy system yields a high proportion of healed wounds, a faster time to wound closure, a rapid and robust granulation tissue response, and a strong trend towards the reduction in the risk of a second amputation compared to standard wound therapy. This study is also important because it is the first randomized clinical study that evaluates healing in open amputations and certainly the first study that evaluates a therapy such as negative pressure wound therapy in this high-risk population.
I believe the results of a Lancet study are even more impressive when you compare them to previous studies of wound healing modalities for diabetic foot ulcerations. The population evaluated in the Lancet project with negative pressure wound therapy were patients that had wounds that were much larger and more complex than previous randomized clinical trials. For the most part, these other studies systematically eliminated wounds that penetrated to the tendon or bones. Traditionally, these are wounds that have a much higher complication rate and slower healing parameters. Previous studies primarily included superficial neuropathic foot wounds that were 7 to 8 times smaller than the negative pressure wound study we just discussed. These other studies had less severe more superficial wounds. It is surprising because they had very similar results with approximately 50% wound healing in 12 to 20 weeks.
We will finish this presentation with the discussion of 2 cases. The first case involves a 74-year-old gentleman who was well known to me. He has a past medical history that was significant for diabetes for 17 years, hypertension, and heart disease. This gentleman was referred to me by a local PA for debridement of a recalcitrant callus on the sole of his foot. This gentleman had a history of multiple digit and ray amputations. Each episode in the past required a protracted period of treatment of 8 to 14 months. For each of these previous wounds, he had multiple therapies including hyperbaric oxygen therapy, growth factors, IV antibiotics, and bioengineered tissue.
This gentleman presented with a full thickness ulceration under the fourth metatarsophalangeal joint. The bone of the fourth metatarsal head was exposed. It was friable with a small amount of purulence from the wound bed. As you can see from the slide on the bottom left hand corner, the plain film radiographs show erosions and fragmentation of both the proximal phalanx and the metatarsal head. This gentleman had excellent perfusion to his foot and dense sensory loss. In addition, you can appreciate the severe and rigid structural deformities of his digits.
The slide to the upper right shows the patientâs wound 3 days after initiation of negative pressure wound therapy. As you can see, the resected portion of the distal metatarsal shaft is completely covered with granulation tissue. The bed of the wound has beefy red granulation tissue throughout and there are no signs of infection. If you then direct your attention to the screen on the bottom left, this is the slide of a gentleman approximately 10 days after his discharge from the hospital. You can see that the wound is beginning to close. There is some characteristic maceration of the tissue which is one of the most common adverse events in patients receiving V.A.C. therapy. For this gentleman, periodically he would have macerated tissue and we would stop his therapy for a day and then initiate it again.
The slide on the upper right is a picture of this patient approximately 2-1/2 weeks after his discharge from the hospital. Again, you can note that the wound bed is beefy red and granular. The wound is more superficial. Again, he has some maceration of the tissue at the periphery of the wound. The wound on the bottom left is now completely epithelialized, the wound is closed, there is no drainage, and V.A.C. therapy had been stopped approximately 5 days prior to this photo being taken.
The next case is a 64-year-old gentleman who worked for the local power company. He had a history of diabetes for 13 years and undiagnosed sensory neuropathy. While he was assisting on a service call over the weekend, he developed a full thickness burn on the plantar aspect of his heel simply from standing on asphalt in South Texas in the middle of the summer for a prolonged period of time. This gentleman had excellent perfusion to his foot. His ABI to the effected foot was 0.93. His vibration perception threshold with the biothesiometer was 38 volts bilaterally and he missed 6/10 sites on both feet with a 10 g Semmes-Weinstein monofilament. Prior to initiating V.A.C. therapy, this gentleman had aggressive surgical debridement of the eschar from his wound. It was treated with silver dressings and bioengineered tissue. This gentleman had a significant amount of drainage from his wound.
As you can see, he presents with a large ulceration on the plantar aspect of his foot. This is immediately following the first week of negative pressure wound therapy. The wound essentially covers the entire plantar aspect of his foot. The next slide shows reduction of his wound. You can see the pattern within the granulation tissue from the foam dressing, and again, this gentleman has a small amount of periwound maceration from application of the wound V.A.C.
This is a photo of this gentleman approximately 3 weeks after initiating V.A.C. therapy. As you can see, the wound is significantly smaller than the previous photo. Again, a photo 2 weeks later, you can continue to see the pattern of the foam dressing within the wound bed and he continues to have a small amount of maceration at the periphery of the wound. And, this third picture shows the wound the day that we stopped V.A.C. therapy. This is a very superficial wound, and although it is not completely epithelialized, this heals within the next 10 days with local wound care.
In summary, negative pressure wound therapy provides noninvasive active therapy using controlled localized subatmospheric pressure. The FDA has cleared and approved this product to promote wound healing. It assists in the formation of granulation tissue. It is indicated for a wide variety of wounds including pressure ulcers, chronic wounds, acute and traumatic wounds, compromised grafts and flaps as well as open _______.
Negative pressure wound therapy is a useful adjunctive method for large decubitus wounds, especially if they have a lot of exudate or drainage from the wound bed. I particularly like this application to cover exposed bone or tendon and to prevent them from desiccating or becoming infected. This is a product whose primary application is often to prepare the wound bed for subsequent procedures such as grafting or delayed primary closure, and there now exists strong evidence of the effectiveness of negative pressure wound therapy to treat open amputations in patients with diabetes.
|Goals and Objectives|
After participating in this activity, the viewer should be better able to:
1. Define negative pressure wound therapy.
2. Review VAC applications.
3. State the VAC outcomes from the literature.
Estimated time to complete this activity is 45 minutes.
Physicians, diabetes educators, and other health care professionals who treat patients with diabetes.
Complete the 4 steps to earn CE/CME credit:
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