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Physicians and healers have been sucking poisons and toxins (for example, snake bite venom) from wounds for about 2,500 years . Cupping, a procedure thought to stimulate blood flow, has also been used for many centuries. In effect therefore, negative pressure wound therapy (NPWT), also known as topical negative pressure (TNP) and vacuum assisted closure (VAC), is not new. The first mention of a ‘vacuum’ wound treatment appeared in the Russian literature in the 1980’s . Further developments finally led to the Vacuum Assisted Closure (VAC™) , the forerunner of most modern systems.
The mode of action in open wounds
A closed drainage system applies controlled suction (negative pressure) to the wound bed. The wound bed is covered firstly with a wound contact layer (WCL), then a wound filler. As the pre-determined negative pressure is applied, the filler compresses into the surface of the wound, reducing microvascular blood flow at the wound bed and contraction at the wound margins (macro-deformation). Negative pressure is often applied at -125mmHg, although pressure may be tailored to the patient’s risk of ischaemia and pain tolerance .
Fillers include open-pore polyurethane foam or saline-moistened gauze – the choice depends upon the wound, the system used, and patient preference. Gauze is more conformable (good for large and/or irregular wounds) , is thought to minimise scarring . and produces thinner, dense granulation tissue . Foam filler produces thick, hypertrophic granulation tissue (Borgquist et al, 2009), and if used without a WCL, can facilitate in-growth of granulation tissue, causing pain and/or bleeding upon removal, disruption of the wound bed tissue, and potentially acting as a focus for infection .
Effectiveness of NPWT
There is a plethora of studies indicating the clinical effectiveness and financial/patient benefits of NPWT in both dehisced wounds (abdomen, sternum) and chronic wounds such as pressure ulcers and leg ulcers. These include meta-analyses , systematic reviews , literature critiques  and evidence based recommendations .
- Rapid wound healing , through exudate management, reduction of oedema , and direct stimulation of granulation tissue 
- Fewer dressing changes, therefore less clinician time required , leading to reduced wound management costs and length of stay 
- Improvement in patient quality of life (QoL) 
Incisional NPWT (iNPWT)
Single-use products for reducing closed incision complications in high risk patients have been developed over the past decade. This has been in response to the increasing incidence and cost of treating incisional complications (SSCs) such as surgical site infection (SSI) and dehiscence, which increase length of stay and costs, may require repeat surgeries, and poor patient outcomes, particularly as infection can present several days post-discharge and can affect long-term survival . Tanner et al’s study  identified a higher SSI percentage that that reported in the literature (27% incidence, vs. 19.4%), most of which manifested post-discharge. SCC’s present a large financial burden and may devastate (or even kill) the patient, so along with assessing risk factors, prevention strategies must be considered.
Incisional NPWT is emerging as a possible prophylactic measure against SSCs. Studies both published and currently being undertaken demonstrate decreased SSI, wound dehiscence and better scar quality in:
- Breast surgery 
- Cardiothoracic surgery 
- Trauma [20,21]
- Orthopaedic surgery 
- Abdominal surgery [7, 23]
- Diabetic foot wounds 
On-going iNPWT studies have also been presented at a recent expert meeting .
The cost-effectiveness of iNPWT has been demonstrated . In an earlier study, Stannard et al  estimated that the application of INPWT costs less than $500 for the mean 2.5 days of therapy, making it a cost-effective intervention due to shortened hospital stay and prevention of postoperative surgical site infection.
To date, many of the studies have centred on patients with high risk factors for SSC – those who are obese, use steroids, have had previous radiation exposure (or awaiting radiotherapy), or who smoke. Other risk factors include the actual procedure and use of implants. Further studies are needed to explore any clinical and/or cost benefits in low-risk patients undergoing high-risk procedures.
iNPWT mode of action
How exactly iNPWT works is not entirely clear; Stannard et al  suggests that the reduction in haematoma and seroma, accelerated wound healing, increased removal of oedema and splinting of the incisional area, appear contribute to its effectiveness, but further studies are required to ascertain the exact mechanisms of action.
While further studies are required to determine iNPWTs exact mechanism of action, early indications are that it is a useful prophylactic tool for the prevention of surgical site complications.
If you would like to comment on any of the issues raised by this article, particularly from your own experience or insight, Healthcare-Arena would welcome your views.
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