Robin Paul Martin

Negative‐pressure wound therapy using gauze or open‐cell polyurethane foam: Similar early effects on pressure transduction and tissue contraction in an experimental porcine wound model

Negative‐pressure wound therapy (NPWT), also known as topical negative‐pressure therapy, is widely used to manage wounds and accelerate healing. NPWT has so far been delivered mainly via open‐cell polyurethane foam, but increasing interest has been directed toward delivering NPWT via gauze. In the present study, the early effects of NPWT on pressure transduction and wound contraction were examined in wounds filled with either polyurethane foam or gauze. An experimental setup of a porcine wound model was used, in which the animals were anesthetized for 12–14 hours. Negative pressures between −50 and −175 mmHg were applied in −25 mmHg increments. Wound bed pressure was measured using a saline filled catheter sutured to the bottom of the wound. The contraction of the wound edges was also determined. The recordings were performed upon reaching steady state, which typically occurred within 1 minute. For both fillers, wound bed negative pressure increased linearly with delivered vacuum with little deviation from set pressure (correlation coefficient 0.99 in both cases). Similar tissue contraction was observed when using foam and gauze. The most prominent contraction was observed in the range of 0 to −50 mmHg with greater vacuum only producing minor further movement of the wound edge. In conclusion, the present experimental study shows that gauze and foam are equally effective at delivering negative pressure and creating mechanical deformation of the wound.

Wound edge microvascular blood flow: effects of negative pressure wound therapy using gauze or polyurethane foam.

The aim of this study was to examine the effects of negative pressure wound therapy (NPWT) on wound edge microvascular blood flow, comparing different wound fillers. Wounds were created on the backs of 7 pigs. NPWT was applied, using either foam or gauze, at −50,−75, −100, −125, −150, or −175 mm Hg. Microvascular blood flow was measured in muscle tissue, subcutaneous tissue, and in the wound bed, at 0.5, 1, and 2.5 cm from the wound edge, using laser Doppler velocimetry. Similar patterns of blood flow response were observed when using foam or gauze. At 2.5 cm from the wound edge there was an increase in microvascular blood flow, while blood flow was decreased closer (0.5 cm) to the wound edge. The blood flow effects were similar at the different levels of negative pressure in muscle tissue, subcutaneous tissue, and in the wound bed. Altered microvascular blood flow to the wound edge may be one of the mechanisms by which NPWT facilitates healing.

Simplified negative pressure wound therapy: clinical evaluation of an ultraportable, no-canister system

The aim of this study was to evaluate a prototype negative pressure wound therapy (NPWT) system that has been developed to simplify NPWT for wounds at the lower end of the acuity scale. The new device has a single preset pressure of −80 mmHg, is single use and operates without an exudate canister. The disposable NPWT system (PICO™) was tested in a prospective, non‐comparative, multicentre clinical trial to assess device functionality and clinical acceptance. Twenty patients were recruited for a maximum treatment period of 14 days. The NPWT devices were fitted with data log chips to enable longitudinal assessment of negative pressure and leak rates during therapy. Sixteen (80%) patients had closed surgical wounds, two (10%) patients had traumatic wounds and two (10%) patients received meshed split thickness skin grafts. The mean study duration was 10·7 days (range: 5–14 days) and the mean dressing wear time per individual patient was 4·6 days (range: 2–11). Fifty‐five percent of wounds had closed by the end of the 14‐day study or earlier, with a further 40% of wounds progressing to closure. Real‐time pressure monitoring showed continuous delivery of NPWT. Three cases are discussed representing different wound locations and different patient factors that can increase the risk of post‐surgical complications. Clinical studies of the disposable NPWT system confirmed the ability of the simplified single‐use device to function consistently over the expected wear time. The anticipated reduced costs, ease of use and increased mobility of patients using this system may enable NPWT benefits to be available to a greater proportion of patients.

Non-invasive assessment of negative pressure wound therapy using high frequency diagnostic ultrasound: oedema reduction and new tissue accumulation.

Tissue oedema plays an important role in the pathology of chronic and traumatic wounds. Negative pressure wound therapy (NPWT) is thought to contribute to active oedema reduction, yet few studies have showed this effect. In this study, high frequency diagnostic ultrasound at 20 MHz with an axial resolution of 60 µm was used to assess the effect of NPWT at – 80 mmHg on pressure ulcers and the surrounding tissue. Wounds were monitored in four patients over a 3‐month period during which changes in oedema and wound bed thickness (granulation tissue) were measured non‐invasively. The results showed a rapid reduction of periwound tissue oedema in all patients with levels falling by a mean of 43% after 4 days of therapy. A 20% increase in the thickness of the wound bed was observed after 7 days due to new granulation tissue formation. Ultrasound scans through the in situ gauze NPWT filler also revealed the existence of macrodeformation in the tissue produced by the negative pressure. These preliminary studies suggest that non‐invasive assessment using high frequency diagnostic ultrasound could be a valuable tool in clinical studies of NPWT.