Topical negative pressure (TNP): the evolution of a novel wound therapy

TOPICAL NEGATIVE PRESSURE THERAPY

Topical negative pressure (TNP): t'he evolution of a novel wound therapy Paul BanweH

Department of Plastic Surgery, Radcliffe Infirmary, Oxford Luc Teot

Surgery and Burn Unit, LaPeyronie Teaching Hospital, Montpellier, France Key words: Topical negative therapy, wound therapy

In 2002 the European Tissue Repair Society (ETRS) held a focused meeting in Nice on the status of new technologies in tissue repair at the beginning of the 21st century. This paper was a Introduction Topical negative pressure is a novel non-pharmacological therapy that is now being adopted as a standard of care in wound care management programmes. This review assesses where and how it can be best used. The cornerstone of wound-care algorithms in surgical practice has been the reconstructive ladder. Wounds may be allowed to heal by granulation tissue or covered with skin grafts, or even local or distant tissues, using pedicled flaps or microvascular free tissue transfer. However, incorporation of topical negative pressure therapy (TNP) into wound management programmes has now enhanced this philosophy (Figure 1). This therapy has extended the indications for simpler surgical techniques in elderly and neurologically-deficient patients and has made it easier to manage complex trauma. An expanding evidence base suggests it should become a mandatory part of the armamentarium of surgeons, nurses and all clinicians involved in wound care

contribution to that meeting. The Journal of Tissue Viability would like to thank the ETRS for their approval to reproduce this material from the ETRS Bulletin Volume 12, 2005. a variety of changes in the wound, pOSitively influencing the healing process" Using suction drainage to treat wounds is not new"", and a variety of systems and designs have been used B.". Despite a controversial editorial explaining otherwise"', application of a suction force across the wound using a dressing interface is a patented concept commercially known as vacuum-assisted closure (VAC) (KCI, Witney, Oxon, UK). Generic terms to describe the therapy and avoid commercial bias have been suggested. They include: • Topical negative pressure (TNP)' • Sub-atmospheric pressure J5 • Sub-atmospheric pressure dressings (SPD)'6 • Vacuum sealing technique (VST)3 • Sealed surface wound suction (SSS)" This review charts some of the latest experimental and clinical evidence for using TNP and highlights some of the applied technologies for the future.

History and development

Experimental evidence

TN P therapy has emerged as a powerful, non­ pharmacological tool that can manipulate the wound­ healing environment using physical forces. Following Argenta and Morykwas'" pioneering work and that of Fleischmann', clinicians and researchers have embraced the technique worldwide. TNP involves applying a suction force or vacuum across a sealed wound, using a reticulated foam interface. Both the suction effect and the mechanical forces generated at the interface of the foam and wound lead to

Morykwas and Argenta in I997 were the first to investigate systematically the component parts of TNP's postulated multimodality mechanism of action". Since then the improved outcome param ters observed clinically in a variety of wounds have acted as a catalyst for the development of comprehensive research programmes around the world, involving collaboration between vascular biologists, molecular biologists, microcirculatory experts, engineers and biochemists. At present, postulated contributing factors include an increase in dermal perfusion, stimulation of granulation tissue formation, decrease in interstitial fluid accumulation (oedema

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FIGURE 1 TOPICAL NEGATIVE PRESSURE IN WOUND MANAGEMENT PROGRAMMES

reduction), decrease in bacterial colonisation, control of wound exudate and reverse tissue expansion effect. There is also evidence for a significant role in tissue salvage. Figure 2 illustrates TNP's mechanism of action.

Enhanced dennal perfusion The effect of TNP on the vascular biology of wounds is complex and not fully ~nderstood. Initially, the effect on wound perfusion was thought to be the principal result of the therapy. Using needle probe laser Doppler f1owmetry, sub-atmospheric pressures of 125mmHg resulted in a four-fold increase in blood flow in an excisional porcine wound model (n= 10 wounds)'. Simple volunteer studies have demonstrated an immediate increase in blood flow in uninjured forearms using a transcutaneous ultrasonic Doppler flow velocity meter"·,· and laser Doppler imagin '. TNP was also used to treat 32 burns in a deep dermal burn wound model. Despite a delay in treatment of six hours, it still resulted in a statistically significant increase in dermal blood flow in burns treated for 72 hours". Using a polyurethane foam interface dressing, the changes in blood flow appeared to be pressure-dependent': increasing pressure to 400mmHg across the wounds actually decreased blood flow in excisional wounds. However, increasing the pressures in a clinical scenario does not necessarily have a deleterious effect on wound outcome as many units in continental Europe'·22 usc high pressures effectively with a polyvinylalcohol foam. This implies that the interface foam dressing may actually be critical in the transmission of pressure. Of note, early work suggested that a continuous suction regimen led to an eventual decline in blood flow back to baseline readings after 5-7 minutes. However, unpublished data from Evison et al (2002) suggested that

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even continuous suction may lead to a cyclical pattern of blood flow. Further work is required to investigate this. These direct effects on the dermal vasculature are thought to be mediated by influencing vasomotor tone and vasoactive mediators. However, the indirect effects of mechanical forces exerted on the extracellular matrix will inevitably affect the microvasculature contained within it. Mechanical stress, therefore, may be the principal effector (personal communication, P. Shakespeare).

Mechanical stress This has a variety of effects on cellular activity and migration. Indeed, during a keynote lecture at the European Tissue Engineering Society Meeting in Germany, in 2001, Professor Michael Morykwas emphasised that 'the balance between internal cytoskeletal forces and extracellular matrix forces is critical for control of cell shape, migration, differentiation and tissue patterning'. While the importance of physical forces in the mechanism of TNP is still hypothetical, there is good evidence that mechanical stress does modulate hard and soft tissue repair and angiogenesis,·-2It. This has been confirmed by early work in the US, which suggests a signiflcant effect of mechanical stress (from TNP) on a variety of upstream pathways involved in wound healing'''. Granulation tissue fonnation In an excisional full-thickness wound model, alginate impressions were taken daily follOWing treatment with TNP'. Volume displacement of these casts demonstrated that TNP-treated wounds increased granulation tissue formation compared with the controls by 63.3 per cent and 103.4 per cent (continuous and intermittE'nt suction respectively). However, it was not known what effect contraction played in these dorsal midline wounds. Another group recE'ntly studied the skin-excised rabbit ear wound model and, using a lens micrometer,

FIGURE 2 TOPICAL NEGATIVE PRESSURE MECHANISM OF ACTION

RrUII' !Qn In .,,~·ntJ.

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TOPICAL NEGATIVE PRESSURE THERAPY

demonstrated a significant increase in granulation tissue formation'''. Joseph et aI" studied granulation tissue formation and commented on new vessel growth and fibroblast morphology, which together with macrophages form the dominant constituents of granulation tissue. However, no attempt to quantify this was made. A number of groups around the world are now investigating the quantitative effect of granulation tissue formation following application of suction.

Reverse tissue expansion Use of foam dressings and TNP in open wounds, such as abdominal dehiscence, demonstrates the powerful effect of skin stretching or reverse tissue expansion of this therapy. In a closed system, the contraction (shrinkage) of the foam dressing exerts a centripetal effect on the wound edges. There are many similarities between this phenomenon and tissue expansion, which uses silicone balloons to stretch skin for recontructive purposes. Likewise, a number of studies are investigating mitotic rates and angiogenesis in TNP-treated tissue Bacterial colonisation Experimental wounds in swine inoculated with a human isolate of Staphyloccocus aureus and a swine isolate of Staphyloccocus epidermidis were treated with either TNP or controlled moist saline dressings (n=5). Daily biopsies were taken for two weeks. Incubatl'd agar plate analysis revealed a reduction from I08 to I05 or Janisms between days four and five in TNP­ treated wounds compared with a mean of II days in the control wounds'. Others have also documented this effect.'·'·2l.1>-J'. Large controlled trials currently under way should confirm these findings in a variety of wounds. Oedema reduction and interstitial fluid Despite dramatic reduction in oedema formation following treatment with TNP - for example, in bums ­ and the removal of often large amounts of exudate, there is no quantitative evidence to support a reduction in interstitial wound t1uid. Measurement of oedema is notoriously difficult, althoug-h high-resolution ultrasound scanners (Longport, US) are being used in a trial to evaluate changes in skin thickness following TNP (personal communication, T. Adams). Control of exudate Exudate management remains a priority in order to minimise labour-intensive, repeated dressing changes which expose practitioners to hazardous, infected material. One of the advantages of TNP therapy is that it utilises a closed system, which adheres to optimal

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practice guidelines and universal precautions. Furthermore, overall nursing time is significantly reduced as fewer dressing changes are required, especially in chronic wounds. Currently, TNP has a built-in odour control system, although anti-odour factors or antimicrobials (such as silver preparations) could be potentially integrated into th foam. Elevated levels of proteolytic enzymes have been demonstrated in chronic wound t1uids and burns""')'. These may contribute to a non-healing wound environment due to continued matrix degradation;. High levels of proteolytic enzymes, cytokines and acute­ phase proteins have been reported in suction-treated wound t1uid and serum)' "'.

Salvage of tissue In reconstructive surgery, burns or following trauma, salvaging tissue may have significant implications for patient outcome. Studies have indicated a potential role for TNP therapy in this respect. Using a random-pattern t1ap experimental model in swine, 20 t1aps were assigned to a variety of treatment groups including: • TNP pre- and post-surgery • TNP pre-surgery • TNP post-surgery • No treatment (controls). The survival of pre- and post-treated skin t1aps was significantly greater than that of the controls (p
Wound-healing research One of the novel sequelae of vacuum therapy is the ability to collect acute and chronic wound t1uid in a reliable, controlled fashion. Simple adaptation of the system with integration of sputum pots allows investigators to quantitate the volume of exudate as well as to collect aliquots - anyone of two or more samples - for biochemical analysis (Figure 3). A number of wound-healing laboratories now use the VAC system to collect wound t1uid for wound-healing research, although one group recently devised a novel version called The Stoke Mandeville Device (personal communication, Adams).

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Clinical studies and evidence Trauma Trauma cases can be considered as the best responders to TNP"'. Exposed noble structures like bones, tendons and neurovascular bundles are rapidly surrounded and covered by healthy granulation tissue. Patients who are otherwise young and healthy mount a prolific angiogenic response to TNP. Until recently, most authorities would have considered that soft tissue cover within 72 hours was mandatory in grade III or IV open fractures. Hence, as part of the reconstructive ladder (Figure 1), flaps ­ muscular, fascial, cutaneous, or compound - have been recommended to prevent bone infection. In certain cases, TNP can now be considered an alternative for preventing infection during the first weeks. Hovvever, early and radical debridement of all devitalised tissue, wound lavage, control of permeability of the vascular axes of the involved member, and a perfect immobilisation of the limb are required. These rules must be kept in mind when using TNP. • Open tibial fractures - TNP treatment can have spectacular results, especially in chronically opened tibial fractures. Covering the tibial bone extremities (inner and outer parts of the cortex) and filling the defect with granulation tissue usually takes from two \veeks for small defects to 7-9 weeks for large defects. If healing is not observed, a simple split-skin graft can close the defect. Bone grafting may be performed months later if necessary. With TNP, during the acute

TABLE 1

PRIMARY INDICATIONS FOR TOPICAL

NEGATIVE PRESSURE THERAPY

Traumatic wounds - Upper/lower limb trauma

- Burns

Infected wounds

Sternal dehiscence

Abdominal dehiscence

Skin graft fixation

Wound bed preparation

Pressure ulcers

- Sacral

- Trochanteric

- Ischial

Leg ulcers - Venous

- Diabetic

stage of an open fracture, after vascular evaluation and complete removal of necrotic tissue, oedema is reduced, and granulation tissue fills the different sinuses of these multidirectional heterogeneous wounds. Exposed corticospongious bone can progressively be covered by granulation tissue within a mean of 2-4 weeks, especially when the skin defect is

FIGURE 3 COLLECTION SYSTEM FOR WOUND HEALING RESEARCH USING TOPICAL NEGATIVE PRESSURE AND A SPUTUM TRAP

\

V""m

d"",o,

on burn wound

Sputum pol

Ice

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~

--Wound exudate

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TOPICAL NEGATIVE PRESSURE THERAPY

FIGURE 4

A NEW VAC ATS SYSTEM

small and located in an area where approximation of the skin edges is less important. In other areas, such as the anterior aspect of the leg, the exposed cortical bone can be difficult to cover completely. If the exposed bone surface is limited, drilling into the cortical bone can help stimulate formation of granulation tissue under TNP. • Large skin/muscle loss - This can be successfully treated using TNpJ.' H,. After complete excision of the non-viable tissues, application of TNP for 2-3 weeks can prevent local infection and, by retracting the edges and producing granulation tissue, transform difficult­ to-manage situations into simple exposed granulation tissue, which can easily be covered with a simple skin graft. This advantage is important in aged or debilitated patients, in whom amputation rates can be reduced. Tissue loss in the foot, simple exposure of tendons or transfixiant loss of substance in gunshot wounds are also good candidates for TNP. Degloving injuries may also be salvaged·\·'··17-"'. Promotion of granulation tissue may be more limited or even absent when a large joint is opened. At present, this may be considered a relative contraindication for TNP due to permanent synovial fluid leakage and difficulty in correctly draining the closed space of the joint. In distal wounds of the extremities, a flap sometimes leads to an impaired outcome due to excessive volume, poor lymphatic drainage, imperfect colour-matching or chronic instability of the skin over the deep structures. Using TNP as an alternative solution in our recon-structive ladder algorithm (Figu re 1) can often lead to a better result in terms of function as well as aesthetics '6 by stimulating granulation tissue formation followed by a skin graft.

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Pressure ulcers In aged patients, nutritional deficits and polypathology often preclude reconstructive surgery'''. Patients with neurologic deficiencies are at risk due to the absence of neurotrophic factors and an increased propensity to infection. Surgery must therefore be reserved to selected situations. In these situations the quality of granulation tissue is uncertain and TNP can be considered a new tool to promote healing" ". Reduced dressing changes (twice a week) also optimise patient care by reducing 'hands­ on' nursing time while actively treating the wound'. The amount of pressure applied on these pressure ulcers can be important. This paper's authors recommend between lSO-17SmmHg. The only limitation is the risk of pain. In such cases pressure should be titrated accordingly. In patients with paraplegia, some authors consider that TNP, applied for a short periods, can be used as a wound-bed preparation tool before definitive surgical closure'". • Grade II, III and IV sacral pressure ulcers - These create major skin defects whose tendency to enlarge is due to the mechanical forces e;xerted on the edges by the large muscles and the convex shape of the sacrum, often exposing the sacral bone. Shear forces often lead to the development of a large undermined area with a narrow skin orifice and a cavity extending laterally. Surgical excision of the skin to ensure complete exposure of the wound is necessary before applying TNP. This promotes a circumferential stimulation of the granulation tissue. In very large sacral ulcers, extending close to the anal or genital areas, faecal diversion must also be discussed. Generally, the adhesive films covering the foam can prevent faecal contamination, but local handling difficulties can make it difficult to obtain an effective seal. • Trochanteric pressure ulcers - Permanent movements of the femoral upper extremity create shear forces, leading to a cavity progressing in depth. The undermined area is often larger than the skin defect, and the foam must fill the cavity completely. A combination of polyvinylalcohol foam in the deep cavity and polyurethane foam across the wound could be used, for example. TNP can facilitate granulation tissue follOWing a large surgical excision of the skin covering the undermined area, except when the capsule of the hip joint is open. • Ischial pressure ulcers - These usually form deep sharp wounds, often exposing infected ischial bone. The foam, which can also be polyvinylalcohol, must be cut long and narrow in order to fill the cavity. Complete closure can reasonably be expected if the ischial bone infection has been controlled. • Heel pressure ulcers - Here the skin tends to retract and coverage of the defect is limited. TNP aids coverage of exposed calcaneum with granulation tissue,

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but time taken to achieve complete epithelialisation is often prolonged. Increasing experience suggests TNP may significantly modulate the local wound-healing environment in some subgroups of wounds that are difficult to manage, such as diabetic wounds. Publications have demonstrated beneficial effects and a large randomised controlled trial is under way"""". Leg ulcers • Venous leg ulcers - In large fibrous venous leg ulcers, circumferentially extending around the leg, TNP can help the progression of gnlOulation tissue, but the results can vary over time. Using alternatively continuous and intermittent mode can help. TNP can be used after pinched skin grafts to secure the contact between the graft and the granulation tissue. [n these cases care must be taken with the level of suction to prevent physical damage on the freshly applied skin graft"'. • Mixed-origin and arterial ulcers - [n mixed-origin ulcers the progression of the granulation tissue is often slow due to the vascular deficiency inherent in this wound. [n arterial ulcers the absence of revascularisation prevents healing even after a long period of TNP. Moreover, the foam may create a local necrosis on the skin edges. However, TNP can be used as a waiting or holding procedure before a definitive revascularisation surgical procedure. Other situations • Post-sternotomy infections - Cardiac revascular­ isation is one of the commonest elective procedures performed worldwide but postoperative complications are associated with significant morbidity and mortality, particularly wound infections. These may be superficial or deep. The former respond extremely well to TNP"', which may also be beneficial for deeper wounds, although adequate debridement before definitive flap closure is essential for optimum results. In significant wound infections, maintaining adequate sternal bone stabilisation is problematic as the two parts of the severed sternum may negatively influence respiratory movements, impairing the artificial ventilation. However, a major benefit of TNP is that the crinkled foam acts as a splint and limits the abnormal movements of the thorax";; • Dehisced abdominal wounds - TNP has emerged as an invaluable tool to augment the management of patients with a dehisced abdominal wound. Multiple publications now support its use to bide time, improve the wound bed and facilitate closure of the abdomen" 73. Broadly speaking these wounds may be classified as type [ (superficial), type II (deep) or type III (complex) for the purposes ofTNP treatment. Type I wounds may be closed in a delayed primary fashion within ten days; use of foam alone without an interposed dressing is acceptable. [n type II (exposed bowel, omentum or VOL 16 NO.1 FEBRUARY 2006

BOX 1 SUMMARY OF MAIN POINTS Topical negative pressure therapy applies a suction force across the wound using a foam dressing interface between the wound and! the vacuum device. Studies have proposed several ways for how topical negative pressure works. Suggestions include that it enhances dermal perfusion, stimulates granulation tissue formation, reduces oedema, decreases bacteria, salvages tissue and has a reverse tissue expansion effect. Mechanical stress is also said to playa part. This paper reviews the relevant papers Trauma cases respond best to topical negative pressure, with rapid formation of granulation tissue. Bones. tendons and neurovascular bundles may be covered. Topical negative pressure may be used as a primary treatment or as an adjunct to surgery when treating pressure ulcers and leg ulcers. Topical negative pressure should not be used if it causes excessive pain, psychological intolerance or if there has been no healing response after two successive dressings. Similarly, it is contraindicated if frank pus appears on the dressing or cannister and if there is excessive bleeding under the dressing.

mesh) and type III (presence of fistulae) wounds, caution should be exercised in regards to the dressing technique, and an interposed dressing is recommended. Large trials are evaluating the benefits of TNP in this important area. • Skin graft fixation - Fixation of skin grafts by conventional means is less than ideal, especially in contoured areas where graft take can be suboptimal. The ideal method to maintain skin grafts over a suitable wound bed involves firm fixation, prevention of shearing forces, adaptation to convex and concave surfaces, evacuation of sub-graft haematoma and seroma, and minimisation of infection. Splintage with foam dressings and TN P fulfils these criteria and various studies now support take rates of >90 per cent, even in difficult contoured areas"'"". Extended uses Exposed vascular graft can successfully be covered by the granulation tissue after two weeks' application of TNP. An interface dressing is recommended. Reported uses ofTNP therapy include: • Oral and maxillofacial surgery"

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FIGURE 5 THE TRAC SYSTEM ALLOWS FEEDBACK FROM THE WOUND SURFACE

outcomes, Syringing saline alone or in combination with a local anaesthetic preparation down the drainage tube half an hour before removal of the foam dressing may also facilitate pain-free dressing changes. Psychological intolerance Some patients are unahle to cope with being attached to mains-operated vacuum pumps. However, ambulatory devices (Figure 4) or machines with batteries now avoid this complication hl .

No healing response at two successive dressings If after 7-8 days of treatment no positive effect can be seen or if the local situation deteriorates, indication of TNP must he re-evaluated, Pressure-relieving systems, nutrition and anti-infectious general therapies must be rechecked,

• • • • • • •

For spinal exposed hardware'· Necrotising fasciitis 70 Gynaecological prohlems'· Burns"" Insect bites" Reducing donor site: morbidity"" Extravasation injury".

Contradindications to TNP TNP cannot be applied on sloughy, infected or necrotic tissue. The wound bed must be prepared, either using surgical dehridement or by a progressive local treatment eliminating dead tissues. As mentioned above, the presence of an open joint should also be viewed cautiously. In all other cases, clinical judgement must be used when applying TNP. In the presence of hlood dyscrasias (abnormal clotting), fistulae, open body cavities or in patients following oncological resections, TNP is not necessarily contraindicated. Research shows that it has been used to treat fistulae very effectively"o.7173,

When to stop TNP Excessive pain Patients may experience discomfort when the foam dressing is changed"'. If pain occurs, the pressure may be titrated accordingly. If it persists or worsens, therapy should be stopped and the wound examined to exclude a serious cause. During the treatment of acute traumatic wounds, the pores of the foam may adhere strongly to the newly developed granulation tissue. The use of non-adhesive porous interface dressings is recommended at this stage, although it is not known what effect interface dressings have on treatment

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Frank pus in dressing/cannister This is an absolute indication to stop treatment. Excessive bleedinglhaematoma under dressing This warrants cessation of treatment and wound inspection.

The future This review has highlighted the expanding clinical indications and experimental evidence for using TNP in wound care (Table]). However, parallel to clinicians' innovation, we have also seen an evolution in the design of available products from an engineering perspective. In an age of advancing computer technology, we now have more powerful vacuum pumps with the finesse to tailor treatment. The development of the 'high-tech' TRAC system enables constant feedback at the foam/wound inter-face and allows monitoring of the local wound environment (Figure 5). At present this measures pressure only, but has the capacity to incorporate other wound diagnostic and therapeutic features in the future. Thus the concepts of tailored, interactive therapy in wound care are borne together with the possibility of distance control and telcmedicine via integrated modems. Combination therapies are also being tria lied and researchers have integrated a variety of treatments including the use of tissue engineering and skin substitutes, larval therapy, compression therapy and the installation of drugs'". While the principles of treatment of TNP still hold true to DeBakey's ideals of being 'simpler, safer and shorter"''', the nuances of this powerful, non­ pharmacological therapy have now evolved, setting the standards for wound care for the future.

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experience. Ann Plast Surg 1997; 38(6),563-76. 2. Morykwas, MJ, Argenta LC, Shelton-Brown EI, McGuirt W. Vacuum-assisted closure: a new method fur wound control and treatment: animal studies and basic foundation. Ann Plast Surg ] 997; 38(6), 553-62. 3. Fleischmann W, Be -ker U, Bischoff M, HOE'kstra H. Vacuum sealing: indication, technique and results EurJ Orthop Surg & Trauma 1995; 5, 37-40. 4. Banwell PE. Topical ne.gative pressure in wound care. ] Wound Care 1999; 8(2), 79-84. 5. r\ilorykwas MJ, Argenta Le. Nonsurgical modalities to enhance healing and care. of suft tissue wounds. ] Southern Orth Assoc 1997; 6(4),279-88. 6. fox JW IV, Golden GT. The use of drains in subcutaneous surgical procedures. Am ] Surg 1976; ]32(5),673-4. 7. ray MF Drainage systems: their role in wound healing. AORNJ 1987; 46(3), 442-55. 8. Brock WB, Barker DE, Burns RP. Temporary closure of open abdominal wounds: the vacuum pack. Am Surg ]995; 61(1), 30-5. 9. Shaer WD. Inexpensive vacuum-assisted closure employing a conventional disposable closed-suction drainage system. Plast Recunstr Surg 2001; 107(1),292-3. 10.Nakayama Y, lino T, Soeda S. A new method for the dressing offrec skin grafts. Plast Reconstr Surg 1990; 86(6),1216-19 I] .Masters 1. Reliable, inexpensive and simple suction dressings. BrJ Plast Surg ]998; 51(3), 267. 12.strove.r AE, Thorpe R. Suction dressings: a new surgical dressing technique. ] R Coll Surg Edin 1997; 42, 119-21. 13.Banwell PE, Withey S, Holten IW. The use of negative pressure to promote healing. Br ] Plast Surg ] 998; 511, 79. 14.Greer SE. Whither subatmospheric pressure therapy) Ann Plast Surg 2000; 453, 332-4; Discussion 335-6. ] 5.IVlorykwas MJ, David LR, Schneider AM et al. Use of subatmospheric pressure to prevent progression of partial­ thickne . burns in a s''''ine model. ] Bum Care Rehabil1999; 201, ]5-21. 16.Greer SE, Duthie E, Cartolano B et al. Techniques for applying subatmospheric pressure dresSing to wounds in difficult regions of anatomy. ] Wound Ostomy Continence Nul's] 999; 265, 250-3. 17.Banwell E. 'Vacuum therapy. Advances in Wound Care for th New Millennium.' 1st European Topical Negative Pressure Symposium, Salisbury, December 2001. 18.skagen K, Henriksen O. Changes in subcutaneous blood flow during locally applied negative pressure to the skin. Acta Physiol Sealld 1983; 117(3),41 1-4. ]9.rentem PH, Matthews JA. The duration of the incr·ase in arterial inHow during exposure of the forearm to subatmospheric pressure. ] Physiol Lond 1970; 2102, 65P­ 66P. 20.Banwell PE, Jones S, Evison D et al. Topical negative pressure modulates dermal micruvascular blood flow dynamics and temperature profiles at the wound-dressing interface. ] Wound Care 2002; (submitted). 2] .Banwcll PE, Morykwas MJ, Jennings DA et al. Dermal microvascular blood flow in experimental partial thickness burns, the effect of topical sub-atmospheric pressure. ] Bum Care Rehabil 2000; 21, s 161 22.Mullner T, Mrkonjic L, Kwasny 0, Vecsei V. The use of negative pressure to promote the healing of tissue defects: a clinical trial using the vacuum sealing technique. BrJ Plast Surg ]997; 50, ]94-9. 23.Urschd JD, Scott PG, Williams HTG. The effect of mechanical stress on soft and hard tissue repair: a review. Br ] Plast Surg 1988; 41,182-6. 24.Ryan TJ, Barnhill RL. Physical factors and angiogenesis in development of the vascular system. Ciba Foundation Symposium 100. London: Pitman Books, 1983. 25.lchioka S, Shibata M, Kosaki K et al. Effects of shear stress

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on wound-healing angiogen sis in the rabbit ear chamher. ] Surg Res 1997; 721, 29-35. 26.Cherry GW, Austad E, Pasyk K et al. Increas d survival and vascularity of random-pattern skin flaps elevated in controlled, expanded skin. Plast Reconstr Surg 1983; 72, 680­ 7.

27.0Ienius M, Dalsgaard CJ, Wickman M. Mitotic activity in expanded human skin. Plast Recollstr SIng 1993; 91, 213-6. 28.Sumpio BE, Banes AJ, Levin LG et al. Mechanical stress stimulates aortic endothelial cells to proliferate. ] Vase Surg ] 987; 6; 252-6. 29.Morykwas M1. 'Topical Negative Pressure Therapy: Experimental evidence.' 2nd European Vacuum Therapy Symposium, Salisbury, UK, June 2002. 30.Fabian TS, Kaufman HJ, Lett ED et al. The evaluation of subatmospheric pressure and hyperharic oxygen in ischemic full-thickness wound healing. Am Surg 2000; 6612, 1136­ 43. 31.Joseph E. et al. A prospective randomized controlled trial of vacuum-assisted closure versus standard therapy of chroniC non-healing wounds. Wounds 2000; 12(3),60-7. 32. www.vacuumtherapy.co.uk 33. Fleischmann W, Lang E, Russ M. Treatment of infection by vacuum sealing. Unfall.chintrg 1997; 1004,301-4. 34.Giovannini UM, Demaria R, Teot L. Benefits of negative pressure therapy in infected surgical wounds after cardiovascular surgery. Wounds 2001; 132,82-7. 35.0bdeijn MC, de Lange MY, Lichtendahl DH, de Boer, W1. Vacuum-assisted closure in the treatment of poststernotomy mediastinitis. Ann Thome Surg 1999; 686, 2358-60. 36.Wysocki AB, Staiano-Coico L, Grinnell F. Wound fluid from chronic leg ulcers contains elevated levels of metalloproteinasC's MMP-2 and MMP-9. ] Invest Dermatol 1993; 101,64-8. 37.Yager DR, Nwomeh Be. The proteolytic environment of chronic wounds. Wound Repair ReKeH 1999; 76, 433-41. 38.Banwell PE. Novel perspectives in wound carC': topical negative pressure therapy. ETRS Bulletin 2002; 92, 49-50. 39.Buttenschoen K, Fleischmann W, Haupt U, Kinzl L, Buttenschocn De. The influence of vacuum assisted closure on inflammatory tissue reactions in the postoperative course of ankle fractures. Foot & Ankle Surg ZOO I; 7, 165-73. 40.Gustafsson R, Johnsson P, Algotsson Let al. Vacuum assisted closure therapy guid -d by C-reactive protein level in patients with deep sternal wound infection. ] Thorac Cardiovasc Surg 2002; 1235, 895-900. 4 I .Morykwas MJ, Fal,'r BJ, Pearc DJ, Argenta Le. Effects of varying levels of sub-atmospheric pressure on the rate of granulation tissue formation in experimental wounds in swine. AmI Plast SlIrg 2001; 475,547-51. 42.Banwell PE, Morykwas MJ, Jennings DA et al. Application of topical sub-atmospheric pressure modulates inflammatory cell extravasation in experimental partial thickness injury. Wound Rep Regen 1999; 74, A287. 43.Banwell PE 'The Role of TNP in Burns.' 2nd European Vacuum Therapy Symposium, Salisbury, UK, June 2002. 44.Meara JG, Guo L, Smith JD ct al. Vacuum-assisted closure in the treatment of degloving injuries. Ann Plast Surg 1999; 426,589-94. 45.Mooney JF III, Argenta LC, Marks MW et a!. Treatment of soft tissue defects in pediatric patients using the VAC system. Clin Ortho1' 2000; 376, 26-31. 46.DeFranzo AJ, Argenta LC, Marks MW et al. The use of vacuum-assisted closure therapy for the treatment of lower­ extremity wounds with exposed bone. Plast Reconstr Surg 2001; 1085, 1184-91. 47.DeFran7.0 AJ, Marks MW, Argenta LC, Genecov DG. Vacuum-assisted closure for the treatment of deglOVing injuries. Plast Reconstr SurK 1999; 1047, 2]45-48. 48.Josty IC, Ramaswamy R, [,aing JH. Vacuum assisted closure:

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an alternative strategy in the management of degloving injuries of the foot. Br Plast Surg 2001; 544, 363-5. 49.Banwell PE, Evison 0, 'vVhitworth IH. Vacuum therapy in degloving injuries of the foot: technical refinements. Br] Plast Surg 2002; 553, 264-6. 50.Deva AK, Siu C, Nettle WJ. Vacuum-assisted closure of a sacral pressure sore. ] Wound Care 1997; 67, 311-2. 51.Azad S, Nishikawa H. Topical negative pressure may help chronic wound healing. BM] 2002; 3247(345),1100. 52. Baynham SA, Kohlman P, Katncr HP. Treating stage IV pressure ulcers with negative pressure therapy: a case report. Ostomy Wound Maru:zge 1999; 454,28-35. 53. Philbeck TE Jr, Whittington KT, Milsap MH et a1 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; 4511, 41-50. 54.Schwarzl F, Moshammer H, Haas F. Treatment of pressure ulcers with VAC Acta Chir Austriaca, Supple-mentum 1998; 150, 8-9 55.Ford CN, Reinhard ER, Yeh 0 et a1 Interim analysis of a prospective, randomized trial of vacuum-assisted closure versus the health point system in the management of pressure ulcers. Ann Plast Surg 2002; 491, 55-61; Discussion

6\ 56.Coggrave M et al. Topical negative pressure for pressure ulcer management. Br] Nurs 2002; 116 Suppl, S29-36. 57. 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; 468, 28-34. 58 Clare MP, Fit<.gibbons TC, McMullen ST et al. Experience with the vacuum assisted closure negative pressure technique in the treatment of non-healing diabetic and dysvascular wounds. Foot Ankle Int 2002; 2310, 896-90 I. 59.Espensen EH, Nixon BP, Lavery LA, Armstrong DC. Use of subatmospheric VAC therapy to improve bioengineered tissue grafting in diabetic foot wounds. ] Am Pod Med Assoc 2002; 927, 395-7. 60.Armstrong DG, Lavery LA, Abu-Rumman Pet al. Outcomes of subatmospheric pressure dressing therapy on wounds of the diabetic foot. Ostomy Wound Manage 2002; 484, 64-8 61.Sposato G, Molea G, DiCaprio G et al. Ambulant vacuum­ assisted closure of skin graft dressing in the' low,'r limb using a portable VAC device. Br] Plast Surg 2001; 543, 235-7. 62.Giovannini UM, Demaria RG, Otman S et al. Treatment of poststernotomy wounds with negative pressure. Plast Reeonstr Surg 2002; 1095, 1747. 63.Tang AT, Okri SK, Haw MP. Vacuum-assisted closure to tn'at deep sternal wound infection following cardiac surgery. ] lMmnd Care 2000; 95, 229-30. 64 Harlan JW. Treatment of open sternal wounds with the vacuum-assisted closure system: a safe, reliable method. Plast Reconstr Surg 2002; 1092, 710-12. 65.0bdeijn MC, de Lange MY, Lichtendahl DH, de Boer WJ. Vacuum-assisted closure in the treatment of poststernotomy mediastinitis. Ann Thome Surg 1999; 686, 2358-60. 66.Hersh RE, Jack JM, Dahman MI et a1. The vacuum assisted closure device as a bridge to sternal wound closure. Ann Plast Surg 2001; 463, 250-4. 67.Giovannini UM, Teot L. Aspirative hydrocellular dressing in thoracic and vascular surgery. Ann Plast Surg, in press. 68.Garner GB, Ware ON, Cocanour CS et al. Vacuum-assisted wound closure provides early fascial reapproximation in trauma patients with open abdomens. Am ] Surg 2001; 182(6), 630-38. 69. Erdmann 0, Drye C, Heller L et al. Abdominal wall defect and enterocutaneous fistula treatment with the Vacuum­

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Assisted Closure (VAC) system. Plast Reeonstr Surg 2001; 1087,2066-8. 70. Bonnamy C, Hamel F, Leporrier J et al. Use of the vacuum­ assisted closure system for the treatment of perineal gangrene involving the abdominal wall. Ann Chir 2000; 125(10),982-4. 71.Alvarez AA, Maxwell GL, Rodriguez GC Vacuum-assisted closure for cutaneous gastro-intestinal fistula management. Gyneeol Oneol 200 I; 803, 413-6. 72.Kercher KW, Sing RF, Matthews BD, Heniford BT. Successful salvage of infected PTFE mesh after ventral hernia repair. Ostomy Wound Manage 2002; 4810, 40-5. 73.Cro C, George KJ, Donnelly Jet at. Vacuum assisted closure in the management of entero-cutaneous fistulae. Postgrad Med J 2002; 78(920), 364-5 74.Schneider AM, Morykwas MJ, Argenta LC A new and reliable method of securing skin grafts to the difficult recipient site. Plast RecollStr Surg 1998; 1024, I 195-8. 75. Blac:kburn JH, Boemi L, Hall 'vVW eet a1. Negative-pressure dressings as a bolster for skin grafts. Ann Plast Surg 1998; 405,453-7. 76. Banwell PE. Skin graft fixation. Br J Oral Maxillo Surg 1998; 36(6),480-81. 77.Banwell PE, Gillespie PH, Inglefield C, Holten rw. Use of topical negative pressure and foam dressings for skin graft fixation. Wound Rep Regen 1999; 74, A247. 78.Blackburn JH II, Boemi L, Hall WW et al. Negative-pressure dressings as a bolster for skin grafts. Ann Plast Surg 1998; 405,453-7. 79.Scherer LA, Shiver S, Chang M et al. The vacuum assisted closure device: a method of securing skin grafts and improving graft survival. Areh Surg 2002; 1378, 930-3; Discussion 933-4. 80.Chang KP, Tsai CC, Lin TJvl et al. An alternative dressing for skin graft immobilisation: negative pressure dressing. Burns 2001; 278, 839-42 81.Avery C, Pereira J, Moody A, Whitworth l. Clinical experience with the negative pressure wound dressing. Br] Orl Maxilla Surg 2000; 384, 343-5 82.Yuan-Innes MJ, Temple Ct, Lacey MS. Vacuum-assisted wound closure: a new approach to spinal wounds exposed hardware. Spine 2001; 1(263), 130-3. 83.Argenta PA, Rahaman J, Gretz HF III et at. Vacuum-assisted closure in the treatment of complex gynecologic wound failures. Obstet Gyneeol 2002; 993, 497-501. 84.Banwell PE, Herrick SE, Roberts AHN, McGrouther DA. Active Treatment of the Acute Burn Wound with Foam Suction Dressings: Early clinical experience. In: Proceedings from the 12th Congress of the International Confederation of Plastic, Reconstructive and Aesthetic Surgery IPRAS, San Francisco, 27 June-2 July, 1999. 85. von Gossler eM, Horch RE. Rapid aggressive soft-tissue necrosis after beetle bite can be treated by radical necrectomy and vacuum suction-assisted closure. ] Cutan Med Surg 2000; 44, 2 r 9-22. 86.Greer SE, Longaker MT, Margiotta M et al. The use of subatmospheric pressure dressing for the coverage of radial forearm free flap donor-site exposed tendon complications. Ann Plast Surg 1999; 435,551-4. 87.Morykwas MJ, Kennedy A, Argenta JP, Argenta LC Use of subatmospheric pressure to prevent doxorubicin extravasation ulcers in a swine model.] Surg Oneol 1999; 72, 14-7. 88. Krasner DL. Managing wound pain in patients with vacuum­ assisted closure devices. Ostomy Vllound Manage 2002; 485, 38-43. 89.Fleischmann W, Russ M, Westhauser A, Stampehl M. Vacuum sealing as a drug release system for controlled local drug administration in wound infection, Unja/lehirurg 1998; 101,649-54

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