From The British Journal of Diabetes and Vascular Disease
Negative Pressure Wound Therapy
Michael Kirby
Posted: 02/06/2008; British Journal of Diabetes and Vascular Disease. 2007;7(5):230-234. © 2007 Sherborne Gibbs Ltd.
Abstract and Introduction
Abstract
Diabetic foot disease is a major global burden. Foot ulcers frequently develop complications and become chronic, representing a considerable challenge as these are typically very difficult to treat. New therapies are needed to address these wounds and there is an increasing focus on negative pressure wound therapy (NPWT). This technique has been shown to accelerate wound healing and although its costs are significant, there is also evidence to show that it compares favourably with more conventional alternatives. However, most studies to date have been small, and larger trials are needed before NPWT becomes more routine. In the meantime, the procedure may be most suitable for large, chronic, heavily exuding wounds that do not respond to established therapies.
Introduction
NPWT also known as TNP has emerged as a non-pharmacological treatment for acute and chronic wounds, including pressure ulcers, diabetic wounds, abdominal wounds, and trauma wounds. It is primarily used for more complex chronic wounds.
Chronic, non-healing open wounds remain an ongoing challenge. Inadequate treatment for foot ulcers results in avoidable complications and unnecessarily extended healing times. The lifetime risk of a person with diabetes developing a foot ulcer is as high as 25%[1] - and foot ulcers are the leading cause of hospitalisation of patients with diabetes. In the US approximately 16% of all hospital admissions and 23% of total hospital days are attributed to diabetic foot complications.[2]
New Approaches to Treatment
New treatments for diabetic foot ulcers continue to be introduced; in addition to NPWT, other recent developments include bone-marrow-derived stem cells, bioengineered skin equivalents and growth-factor therapy.[3] NPWT, however, is one area of therapy that is attracting an increasing amount of interest.
Negative Pressure Wound Therapy
It has been suggested that NPWT is best suited for the management of large, Stage III and Stage IV ulcers with inadequate or poor granulation tissue and heavy exudate (figures 1 and 2).[4] Generally, NPWT can be considered in a chronic wound if the wound size decreases by less than 30% after four weeks following debridement or if excessive exudate cannot be managed effectively with daily dressing changes.[4]
Figure 1. DFU on the plantar surface of a right midfoot
Figure 2. A healed DFU on the plantar surface of a right midfoot, post VAC therapy
NPWT delivers intermittent or continuous subatmospheric pressure to a wound at 50-175 mmHg (expert opinion is that the optimal setting is 125 mmHg).[5] The therapy is based on the idea of turning an open wound into a controlled, closed wound while removing excess fluid from the wound bed, thus enhancing circulation and disposal of cellular waste from the lymphatic system.[4] The system consists of a nonadherent, porous wound dressing (such as foam), a draining tube placed in the dressing (or adjacent to it), a transparent film to seal the wound and drainage tube that is connected to a vacuum source for negative pressure. A computerised therapy unit applies the pressure while drawing exudate away from the wound, into a sealed canister. The system is usually applied to an open wound for periods of 48 hours (figure 3).
Figure 3. How VAC works
These systems have now been commercially available for over a decade. Kinetic Concepts Incorporated's VAC Therapy system was launched in the UK in 1995, followed by the more recent introduction of the Versatile 1 Wound Vacuum System, from BlueSky Medical Group, in 2006. Nearly all trial and clinical data to date focuses on the former, as the newer system has yet to be more fully investigated.
The concept of exposing wounds to subatmospheric pressure, however, is not new: it has been studied for the last 50 years.[4] Closed wound suction drainage has been used since the early 1950s and in 1976 Fox and Golden reported that continuous suction, negative pressure drains serve as an excellent ‘atmospheric bandage' in subcutaneous surgical procedures while helping to expedite wound healing.[6] During 1980s and early 1990s a number of articles investigating the use of negative pressure for treating wounds were published in Russian literature.
Evidence on NPWT
The main reported mechanisms of action for NPWT are the provision of a moist wound healing environment, removal of fluids and infectious materials, assisted profusion, decreased bacterial colonisation and enhanced formation of granulation tissue.[7] Reported benefits of NPWT include rapid cell division, increase in local blood flow, reduction in bacteria levels and removal of harmful proteases.[8]
Clinical evidence supporting NPWT has largely been based on case studies and small cohort studies, and the majority of studies on the effect of NPWT have looked at wound reduction or other clinical measures of healing. Joseph et al. (2000) compared the VAC system with standard saline WM dressings among 24 patients with chronic, non-healing wounds in a prospective randomised trial.[9] The patients had previously failed multiple medical and surgical wound treatments. Histologically, the VAC wounds showed angiogenesis and healthy tissue growth (64% saw granulation tissue formation), whereas in the WM group, 81% displayed inflammation and fibrosis.
While most studies have looked at various types of wounds, one small study (ten patients) specifically focused on postoperative diabetic foot wounds. It found that among patients receiving VAC therapy, definitive closure was achieved by delayed primary closure in four out of five subjects.[2] This compares with two out of five patients in the saline-moistened gauze therapy group.
More recently a larger multi-centre randomised intentionto-treat trial, involving 162 patients, looked at whether NPWT improves the proportion and rate of wound healing after partial foot amputation in patients with diabetes.[10] NPWT was delivered through the VAC Therapy System, while control patients received standard moist wound care according to consensus guidelines. More patients in the VAC group achieved complete closure during the 16-week assessment (56% compared with 39% in the control group). The study also found that among patients who presented with 0-15% granulation at baseline, the time to reach 76-100% granulation time was faster in the VAC group than in the control group (median 42 days versus median 84 days).
Cost-Effectiveness
In the UK, the estimated annual cost of disease-related foot complications in 2001 was £252 million, out of the estimated £3 billion national health service expenditure that was attributable to diabetes in 2001.[11] Patients with recurrent ulcers run up the highest costs for inpatient care, social services and home care. Patients who undergo amputation have annual high costs for social services and home care.
Clearly, improving the management of the diabetic foot wound may result in longer-term cost savings, and this is where new therapies, such as NPWT may have a role. However, the costs of undergoing the therapies must first be taken into account and NPWT is certainly more expensive, given the cost of the machine itself, disposable dressings, canisters, drainage tubes and adhesive drapes.
Due to this significant difference, questions will immediately be raised about incurring the cost of NPWT when far more economical options are available. Thus, the potential benefits of NPWT can only be viewed in a longer-term analysis. Despite the initial higher costs, Philbeck et al. demonstrated that NPWT is nevertheless cost effective in use.[12] Based on an analysis of healing rates, they calculated that the average 22.2 cm2 wound in their study would take 247 days to heal and cost $23,465 (£11,629.31)* with traditional therapy. Using negative pressure wound therapy, the wound would heal in 97 days and cost $14,546 (£7,208.89)*.
In June 2006, the Drug Tariff listing of VAC GranuFoam disposable dressings reduced the cost of these dressings from approximately £25 per dressing, to the price of a prescription for multiple dressings (of the same size).
NPWT usually requires less frequent dressing changes than conventional therapy. In the partial foot amputation study, for instance, patients in the control group had their dressings changed daily, rather than every 48 hours as recommended with NPWT. This is an advantage for many patients and it also saves nursing staff time.
A Dutch study involving 54 patients compared the costs of NPWT with conventional (moist gauze) therapy in the management of full-thickness wounds that required surgical closure[13] ( Table 1 ).
Table 1. Summary of Results Adapted From Moues et al[13]*
Using NPWT in Practice
When weighing up the decision of whether to use NPWT in certain situations, the drawbacks of the therapy must be considered. The need for trained healthcare professionals must be taken into account: failure of NPWT is often due to inadequate staff education and skill.[4] Healthcare professionals must also have the appropriate tools to apply and remove the NPWT device.
Patients may experience discomfort or pain when the foam dressing is changed; the pressure may be titrated accordingly but if the pain persists or worsens therapy should be stopped and the wound examined.[14] Topical skin problems may arise during use of NPWT, and these include an overgrowth of yeast or Candida infection, skin stripping and subepidermal granulation.[4] Pain may be associated with subatmospheric therapy, but it can be difficult to differentiate this pain from that associated with the wound itself.
Foam removal frequently results in trauma to the wound, in the form of minor capillary and granulation tissue disruption (similar to the trauma from saline gauze removal). If the foam dressing is left for more than 48 hours, excessive ingrowth of granulation tissue into the foam dressing could occur. Similarly, if the evacuation tube is positioned directly over the bone, this can lead to erosion of adjacent tissue. A contraindication to this therapy is exposed bone. Achieving and maintaining a vacuum seal can be difficult at times, especially when treating wounds around, or in contact with, the toes.[2]
It is recommended that if no positive effect can be seen after seven to eight days, the indication of NPWT should be reevaluated. Treatment should be stopped if there is frank pus in the dressing or canister or if there is excessive bleeding under the dressing.[14]
However, when NPWT is successfully used, expedited wound closure results in shorter hospitalisations, reduced costs and reduced risks of infection. Complications such as infection typically prolong hospitalisation, requiring subsequent procedures for patients. Treatment with NPWT, however, allows these patients to be discharged from hospital and treated at home, where they can maintain greater mobility with improved quality of life. Within home healthcare settings, NPWT may help to improve patient care and decrease costs associated with numbers of visits.
NPWT can also help to keep patients from returning to hospital, as its role has been evaluated for its impact on hospital readmissions. In a retrospective analysis of NPWT in open foot wounds with significant tissue defects, Page et al. found that the risk of complications, subsequent foot surgeries, and hospital readmissions (secondary outcomes) were all reduced by 70% or more for the patients treated with NPWT, compared with patients treated with standard WM salinesoaked gauze dressings.[15] Length of stay during readmissions tended to be shorter; rates of wound cavity filling and wound healing (primary outcomes) tended to be greater with NPWT, although the differences were not statistically significant.
Conclusion
All people with diabetes are at risk of developing foot ulcers, and despite measures to prevent complications a number of diabetic wounds become chronic and non-healing (potentially leading to amputation). More effective methods of wound healing are needed to address these problematic and difficultto-treat wounds.
NPWT represents one such method. Although the concept of using subatmospheric pressure to treat wounds is not new, the currently available systems are still novel, and more large prospective controlled trials are needed to continue to assess their effectiveness and use.
There are now over 325 publications on VAC Therapy, including 15 randomised clinical trials. To date, the system has been shown to have a number of important advantages: it appears to be safe and it results in faster wound healing than conventional methods - thus proving cost effective, despite much greater material costs.
Based on current available clinical and anecdotal evidence, diabetic foot ulcer wounds most suitable for NPWT are those that are complex with poor healing responses and higher rates of complications.
Sidebar: Key Messages
Foot ulcers remain the leading cause of hospitalisation in patients with diabetes. Treatment for complex and chronic wounds is still sub-optimal
Negative pressure wound therapy (NPWT) represents a new non-pharmacological wound therapy. It appears to be safe and findings thus far look promising as its faster wound healing than conventional therapy
Currently clinicians may want to consider NPWT for difficult-to-treat foot ulcers where more traditional therapies are insufficient
There is nevertheless a need for larger randomised trials on effectiveness and cost-effectiveness of NPWT. Costs for NPWT are significantly greater than traditional therapy, although evidence suggests it is nevertheless cost-effective due to shorter healing times
References
Singh N, Armstrong DG, Lipsky BA. Preventing Foot Ulcers in Patients With Diabetes. JAMA 2005;293:217-28.
McCallon SK, Knight CA, Valiulus JP et al. Vacuum-assisted closure versus saline-moistened gauze in the healing of postoperative diabetic foot wounds. Ostomy Wound Manage 2000;46(8):28-34.
Cavanagh P, Lipsky BA, Bradbury AW, Botek G. Treatment for diabetic foot ulcers. Lancet 2005;366:1725-35.
Fleck CA, Frizzell LD. When negative is positive: a review of negative pressure wound therapy. Wound Care 2004;3(4):20-5.
Sibbald RG, Mahoney J; V.A.C. Therapy Canadian Consensus Group. A consensus report on the use of vacuum-assisted closure in chronic, difficult-to-heal wounds. Ostomy Wound Manage 2003;49 (11):52-66.
Fox JW, Golden GT. The use of drains in subcutaneous surgical procedures. Am J Surg 1976;132:673-4.
Gupta S, Baharestani M, Baranoski S et al. Guidelines for managing pressure ulcers with negative pressure wound therapy. Adv Skin Wound Care 2004;17(suppl 2):S1-S16.
Mendez-Eastman S. Guidelines for using negative pressure wound therapy. Advances in Skin & Wound Care 2001;14:314-25.
Joseph E, Hamori CA, Bergman S, et al. A prospective randomised trial of vacuum-assisted closure versus standard therapy of chronic nonhealing wounds. Wounds 2000;12(3):60-7.
Armstrong DG, Lavery LA; Diabetic Foot Study Consortium. Negative pressure wound therapy after partial diabetic foot amputation: a multicentre, randomised controlled trial. Lancet 2005;366: 1704-10.
Boulton AJ, Vileikyte L, Ragnarson-Tennvall G et al. The global burden of diabetic foot disease. Lancet 2005;366:1719-24.
Philbeck TE, Whittington KT, Millsap MH et al. The clinical and cost effectiveness of externally applied negative pressure wound therapy in the treatment of wounds in home healthcare Medicare patients. Ostomy Wound Manage 1999;45(11):41-50.
Moues CM, van-den-Bemd GCM, Meerding-WJ et al. An economic evaluation of the use of TNP on full-thickness wounds. J Wound Care 2005;14:224-7.
Banwell PE, Teot L. Topical negative pressure (TNP): the evolution of a novel wound therapy. J Wound Care 2003;12(1):22-8.
Page JC, Newswander B, Schwenke DC et al. Retrospective analysis of negative pressure wound therapy in open foot wounds with significant soft tissue defects. Adv Skin Wound Care 2004; 17:354-64.
Authors and Disclosures
Michael Kirby, Professor, University of Hertfordshire, Clinical Trials Co-ordinating Centre, Hatfield, Hertfordshire
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