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Novel Perspectives in Wound Care: Topical
Negative Pressure Therapy
Paul Banwell FRCS, Department of Plastic and Reconstructive Surgery
The Radcliffe Infirmary, Oxford, UK E-mail: pbanwell@aol.com
 Paul
Banwell FRCS
Over recent years we have seen and adopted a variety of
strategies to help manipulate the wound healing process. In particular,
the role of 'high-technology' treatment modalities such as impregnated
dressings, anti-scar therapies, growth factors and genetically-engineered
constructs have served as a focus for some exciting research and clinical
innovation.
In contrast to these 'high-tech' therapies, another method to manipulate
the wound healing process has also been trialled over recent years: topical
negative pressure (TNP) therapy. This is a powerful, non-pharmacological
therapeutic tool that has now been shown to modulate the wound environment
in a number of ways. The principle of the therapy revolves around the
application of a suction force across the surface of the wound in a controlled
manner utilising a reticulated, foam dressing interface within an enclosed
environment. This has a multitude of effects including changes in wound
perfusion, tissue fluid dynamics, cellular changes, mechanical sequelae
and bacterial clearance rates.
Initial scepticism of such a simple idea (using physical forces) has been
replaced by an emerging enthusiasm resulting from the many potential applications
of this therapy in clinical practice. Indeed, a large body of evidence
in the literature now supports its use in a variety of indications although
we still await the important results of large on-going clinical trials.
History and Development
Suction drainage is fundamental to surgical practice and is used with
the aim of minimising post-operative collection formation and wound healing
problems. However, the use of a suction force across the surface of the
wound is a novel application of existing practice. This technique has
been developed and popularised world-wide by Professor Louis Argenta and
Professor Michael Morykwas from the USA, and by Dr Wim Fleischmann from
Germany; they have since been responsible for continued innovation and
advanced usage in a variety of settings thus gaining a formidable following
in both the research and surgical communities.
Many different terms have been used to describe the principle of the technique
including vacuum therapy (VT), topical negative pressure (TNP), sub-atmospheric
pressure dressings (SPD) vacuum-pack technique, sealed surface wound suction
(SSS) and vacuum sealing technique (VST). The commercially-patented term
used for this treatment modality is Vacuum-Assisted Closure™ (VAC).
Research
The pioneering studies published and presented by Argenta and Morykwas
from the early 1990s has spawned a huge interest in a number of laboratories
and units world-wide leading to the establishment of comprehensive research
programmes and clinical trials.
Over twenty multi-centre clinical trials, many random-ised, are currently
underway investigating the role of TNP in chronic wounds, abdominal dehiscence,
sternal wound infection, skin graft take, lower limb trauma, diabetic
foot problems and pressure sores amongst others. Other studies are focussing
on its use in a community setting, its role in telemedicine as well as
others confirming cost-effectiveness. Perhaps of even greater interest
is the study of dermal perfusion, vacuumed wound fluid and the effect
of mechanical forces generated at the foam-wound interface. Already a
number of groups have defined the effect of TNP on secondary messenger
pathways, oncogenic expression (c-myc, c-ras), transcription factors (p53,
hif), acute phase proteins (CRP), cytokines (IL-6, IL-8, TNF), growth
factors (VEGF, TGF-b, FGF, PDGF), proteases and their inhibitors (metalloproteases,
neutrophil elastase, cathepsin G, myeloperoxidase, proteinase-3, TIMPs,
alpha-1 protease inhibitor) and collagen deposition. There is also some
evidence that TNP may also modulate the inflammatory response secondary
to differential effects on cellular extravasation.
However, despite these encouraging results, there are still many unanswered
questions. One of the postulated mechanisms of action is a demonstrable
effect on bacterial colonisation rates. Whether this is due to a concomitant
increase in blood flow or secondary to a mechanical debridement effect
of the dressing change is unknown. Further work is required to confirm
this finding as well as delineate its mechanism. The contraction of the
foam dressing ,on application of suction, also exerts a skin stretching
effect on open wounds; this 'reverse tissue expansion' has been utilised
by general surgeons when dealing with dehisced abdominal wounds, aiding
the closure of such wounds in an accelerated fashion. However, this may
be seen as very subjective and published studies are therefore urgently
required to quantitate this phenomenon. Perhaps most importantly is the
quantification of the rate of granulation tissue occurring in TNP-treated
patients compared to controls; a well designed experimental model is urgently
required as the early results have not been corroborated.
The effect of TNP on dermal perfusion was thought to have been the principal
mechanism of action of this therapy. However, whilst several studies have
shown significant increases in blood flow in both clinical and experimental
models, this may well be secondary to mechanical, defor-mational changes
on the matrix and the vasculature residing within this. Indeed, Professor
Michael Morykwas and colleagues have an extensive research programme investigating
the effect of VAC mechanical loading on secondary messengers and other
downstream pathways.
One interesting spin-off from research into this area is the ability to
reliably collect aliquots of wound fluid using the VAC device. A number
of groups now use this method to collect acute and chronic wound fluid
for their studies. This idea has been taken even further and an annotated
device (Stoke Mandeville device) has been devised to facilitate wound
investigation over very limited areas undergoing treatment.
Clinical Applications
Topical negative pressure therapy has already had an impact on many different
clinical specialties including plastic surgery, general surgery, gynaecological
surgery, vascular surgery, trauma and orthopaedics, paediatric surgery,
spinal injuries, dermatology and tissue viability. Broadly speaking, the
therapy may be arbitrarily divided for use in four areas: acute wounds
and trauma, chronic wounds, as an adjunct for surgery and finally as a
salvage manoeuvre in difficult wounds. Originally, treatment with TNP
was reserved only as a last resort in wounds non-responsive to 'traditional'
dressings although over time we have seen an evolution of this philosophy
and TNP now forms an integral part in our algorithm of wound care.
Much akin to the the laparoscopic revolution of the early 1980s where
there was an intense desire to perform every surgical operation endoscopically,
we have seen a proliferation of described uses for TNP in the literature:
leg ulcer treatment, pressure sores, spina bifida, exposed metalwork in
lower limb trauma, infected wounds, exposed bone and tendon, necrotising
fasciitis, radiation ulcers, diabetic foot ulcers, aversion of free flaps,
extravasation injury, lymphocutaneous fistulae, enterocutaneous fistulae,
gunshot wounds, snake and spider bites, burns, frostbite injury, osteomyelitis,
abdominal dehiscence and degloving injuries. In particular, the use of
TNP as an adjunct to surgery has had important ramifications in that it
has re-defined the usual algorithm used (re-constructive ladder) to determine
wound closure. Furthermore, at the recent ETRS Focus Group Meeting on
wound bed preparation held in Oxford, an important role for TNP in this
area was discussed.
Education
Over recent years there have been a number of independent and commercially-sponsored
meetings featuring topical negative pressure as a concept. Indeed, some
interesting discussions were held on the topic at the combined WHS/ETRS
Meeting in Baltimore earlier this year. The inaugural European Vacuum
Therapy Symposium organised by the Odstock Centre for Burns and Reconstructive
Surgery in Salisbury, UK was extremely well received and attended and
more meetings around the globe have been planned (a report on the 2nd
European Symposium will follow in a future edition of this Bulletin).
To satisfy the demand for education via the World Wide Web, a new, independent
web-site,
http://www.vacuumtherapy.co.uk
has also been set up by some interested clinicians to act as a forum for
discussion on all aspects of the therapy.
Future
Further developments have already occurred in the design of the vacuum
pump system and a new commercially-available pump is currently in use.
So-called 'TRAC technology' allows the ability to continually monitor
the wound environment and paves the way for interactive treatment. Furthermore,
in-built modems in such machines may also allow distance control with
tailored patient-specific and wound-specific therapy.
Lastly, another direction using a combination approach has also been utilised.
Dr Fleischmann in Germany has been developing so-called instillation therapy
whereby antibiotics (and possibly other therapeutic agents) may be delivered
to the wound in combination with suction.
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