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IN their discussion of evidence-based practice, Clark and Price1 review the value of randomized controlled trials (RCTs) in determining best clinical evidence and acknowledge that ‘not all research questions can neatly be answered using the randomised controlled trial’. The following recent articles demonstrate the expanding body of V.A.C.® Therapy™ evidence that provides a clinical panorama through RCTs as well as other types of studies.

V.A.C.® Therapy™ reached an important milestone with the publication of the results of a large multicenter randomized controlled trial (RCT) in the 12 November 2005 issue of The Lancet. The findings in this study validate the earlier small RCTs that reported positive results for V.A.C.® Therapy™ in both chronic and acute wounds.

Armstrong and Lavery2 investigated V.A.C.® Therapy™’s effectiveness in treating partial foot amputation wounds in patients with diabetes. Such patients often suffer from comorbidities that can result in delayed healing of these complex wounds. In this RCT 162 patients with amputations up to the transmetatarsal level of the foot were randomly assigned to receive either V.A.C.® Therapy™ (n = 77) or standard moist wound care (hydrocolloids, alginates, foams or hydrogels) according to consensus guidelines (n = 85). Wounds were treated until closure or the completion of the 112-day active treatment phase. Complete wound closure was defined as 100% re-epithelialization without drainage.

Patients treated with V.A.C.® Therapy™ achieved favorable outcomes with respect to wound closure, granulation tissue formation, and rate of secondary amputation. The most common adverse event was wound infection, and in both treatment groups the number and severity of adverse events were similar. The authors conclude, ‘… our results indicate that NPWT as delivered through the V.A.C.® Therapy™ System™ seems to be a safe and effective treatment for complex diabetic foot wounds.’

Further elucidation of V.A.C.® Therapy™ System™ mechanisms of action corroborates the importance of the material at the wound surface interface in the delivery of therapeutic outcomes. Newer evidence about the foam-tissue interface confirms the adage that “Foam Matters.” Saxena (2004)3 and Greene (2006)4 report on complementary studies that aid in a better understanding of the way in which the structure of the foam dressing under negative pressure helps to promote wound healing. Jones (2005)5 studies the effect of different interface materials on the amount of pressure actually transmitted to the wound surface.

Microdeformational Wound Therapy (MDWT)

Saxena and colleagues2 use computer modeling and clinical experience to validate the crucial role of the V.A.C.® Therapy™ foam in creating the mechanical microstrain that helps to stimulate cell proliferation and granulation tissue formation. The authors propose that the application of mechanical forces to the wound surface through interaction with the foam dressing under pressure may be the most significant mechanism of action for V.A.C.® Therapy™. They created a finite element computer model of a wound and simulated V.A.C.® Therapy™ application. They then compared the deformations described in this model with histologic sections of wounds treated with V.A.C.® Therapy™. They found that, ‘Importantly, the deformation predicted by the model also was similar in morphology to the surface undulations observed in histologic cross-sections of the wounds’.

Microvessel Density and Matrix Metalloproteinases

Greene et al.3 report additional clinical data that support the findings of the Saxena study. Over a two-week period the authors studied tissue taken from three debilitated patients whose chronic wounds were debrided prior to application of V.A.C.® Therapy™. The authors compared samples of tissue that had been in contact with the foam dressing to samples of tissue that had been in contact only with the adhesive drape (and presumably some of the negative pressure). They found that wound tissue in contact with the V.A.C.® Therapy™ foam had greater microvessel density after both weeks one and two, compared to baseline and wound areas without foam contact. Greene and colleagues also studied the levels of matrix metalloproteinases (MMPs) in tissue that was in contact with the foam dressing and tissue that was not. Elevated levels of MMP-2 and MMP-9 and their complexes are associated with non-healing wounds. In tissue with foam contact, Greene and colleagues reported 39% and 15% reductions in MMP-2 active, at one and two weeks respectively. For MMP-2 latent, the reductions at one and two weeks were 51% and 52%, respectively. MMP-9 activity was reduced by 30% and 32% at one and two weeks respectively, and MMP-9/NGAL activity decreased by 54% and 76%, respectively.

While this study by Greene et al. is limited by sample size and heterogeneity of the wounds, it supports the previous work done by Saxena and colleagues and provides direction for possible future research clarifying the role of the V.A.C.® Therapy™ foam dressing in the generation of granulation tissue.

Intervening layers impact microstrain

Materials intervening between the foam and tissue can impede the delivery of subatmospheric pressure and potentially the amount of therapy-specific microstrain. In an RCT of 40 healthy volunteers, Jones and colleagues5 evaluate the influence that different types of interposed dressings may have on the transmission of negative pressure to the wound interface during V.A.C.® Therapy™. Subjects were randomly assigned to one of four groups: group I, V.A.C.® Therapy™ foam dressing alone; group II, petroleum jelly (Vaseline)-impregnated gauze (Jelonet®) interposed dressing and V.A.C.® Therapy™ foam; group III, nonadherent silicone dressing (Mepitel®) interposed dressing and V.A.C.® Therapy™ foam; and group IV, mylar perforated polyester film dressing (Telfa Clear®) interposed dressing and V.A.C.® Therapy™ foam. The foam dressing was applied to the medial calf of each subject and pressure sensors placed between the skin surface and the interposed dressing were used to ascertain wound surface pressure throughout the experiment. According to the authors, in group I (V.A.C.® Therapy™ foam only) the pressure readings at the skin surface remained very close to the target pressures on the V.A.C.® Therapy™ unit throughout the treatment. The results in group IV (Telfa Clear® and
V.A.C.® Therapy™ foam) most closely approximated those found in group I. In group III (Mepitel® and V.A.C.® Therapy™ foam) in 30% of the subjects, there was a progressive pressure drop of up to 16.7 mm Hg over time.

Finally, in group II (Jelonet® and V.A.C.® Therapy™ foam), changes in wound surface pressure were not recognized by the machine or corrected rapidly, resulting in recorded skin surface pressures that dropped progressively up to 41.8 mm Hg from the target pressure at the machine. The authors conclude that while interposed dressings may have a protective effect on the wound surface, they may also interfere with the effects of V.A.C.® Therapy™ and clinicians need to take that possibility into consideration. Home care settings benefit from the use of V.A.C.® Therapy™ after patient discharge
The impact of health economics and the focus on clinically cost effective care are global healthcare concerns. Aging populations equate to more patients, who demand the best care – which puts greater demands on already stressed budgets. Increasing the number of patients treated at home requires effective use of staff and resources to be cost-effective. In a comparative retrospective study in the U.S. home care setting6, patients with pressure ulcers treated with V.A.C.® Therapy™ had reduced rates of hospitalisation and emergency care when compared to other
wound care and treatment. Outcome Concept Systems (OCS), a leading benchmarking company in Seattle, Washington, tracked the progression of Stage III and Stage IV pressure ulcers in a sampling of 60 patients on V.A.C.®
Therapy and compared it to a case-matched group of 2,288 patients treated with other wound therapies in the home
care setting. The incidence of hospitalisation was lower in the VAC Therapy treated group (35%) than in the comparison group (48%). In addition, the authors found that 14% of study patients who were not treated with V.A.C® Therapy were hospitalized due to wound infection or deteriorating wound status; in the V.A.C.® Therapy™ group 5% of patients were hospitalized for wound-related problems. No patient on V.A.C.® Therapy™ required emergency
care for wound-related problems; however, 189 patients (8%) needed emergency care for wound problems in the comparison group. Based on these findings the authors concluded that V.A.C.® Therapy™ could potentially help home health agencies to improve patient care and to decrease unexpected health costs. The authors recommended
further research with a large national sample to validate these findings and study other quality outcomes.

References:
1. Clark M, Price PE. Evidence-based practice: Sound
in theory, weaker in practice? ETRS Bulletin. 2005;
12 (1–2). Accessed online at <http://www.etrs.org/
bulletins.html> on 26 April 2006.
2. Armstrong D, Lavery L. Negative pressure wound
therapy after partial diabetic foot amputation: a
multicentre, randomised controlled trial. Lancet.
12 Nov. 2005; 366(9498): 1704–10.
3. Saxena V, Hwang C-W, Huang S, Eichbaum Q,
Ingber D, Orgill DP. Vacuum-assisted closure:
microdeformations of wounds and cell proliferation.
Plastic and Reconstructive Surgery. Oct 2004;
114(5): 1086–1096; discussion 1097–8.
4. Greene AK, Puder M, Roy R, Arsenault D, Kwei S,
Moses MA, Orgill DP. Microdeformational Wound
Therapy: Effects on Angiogenesis and Matrix
Metalloproteinases in Chronic Wounds of 3 Debilitated
Patients. Annals of Plastic Surgery. Apr. 2006;
56(4): 418–422.
5. Jones SM, Banwell PE, Shakespeare PG. Interface
dressings influence the delivery of topical negativepressure
therapy. Plastic and Reconstructive Surgery.
15 Sept. 2005; 116(4): 1023–8.
6. Schwien T, Gilbert J, Lang C. Pressure ulcer prevalence
and the role of negative pressure wound
therapy in home health quality outcomes. Ostomy/
Wound Management. Sept 2005; 51(9): 47–60.