Biological effects of a disposable, canisterless negative pressure wound therapy system

Abstract

Objective: Recent developments of negative pressure wound therapy (NPWT) systems have focused on making pumps smaller, lighter, and more portable. The recently introduced PICO system manages wound fluid through a highly breathable film within the dressing, thereby negating the need for a canister, which allows greater mobility and patient concordance. The aim of this study is to compare the biological effects of this system compared to a traditional NPWT system.

Methods: Laboratory tests were carried out to demonstrate the fluid handling properties of the PICO™ system. Porcine full thickness defect wounds and sutured incisional wounds were used to compare the biological effects. Wounds were treated with PICO dressings or traditional NPWT dressings and connected to either a PICO device or a traditional NPWT device.

Results: The PICO dressing manages exudate predominantly through evaporative loss (up to 85% of all fluid entering the dressing). Both traditional NPWT and the PICO system maintained therapeutic levels of negative pressure in all wounds. Both NPWT systems produced similar effects on wound edge contraction and microvascular blood flow in defect wounds. No significant changes in blood flow or wound contraction were noted in incision wounds for any NPWT combinations tested.

Conclusions: The disposable, canisterless PICO NPWT system functions in the same manner as the traditional NPWT systems with regard to fluid handling, pressure transmission to the wound bed, tissue contraction, and changes in blood flow.

Keywords: Blood flow; NPWT; dressing; vacuum; wound.

Figure 1

The structure and working principles of the PICO™ dressing. The PICO system simplifies NPWT by replacing the exudate canister with an absorbent dressing that has a high evaporative loss. The top panel illustrates wound exudate removal through the dressing. The PICO dressing is absorbent and is composed of 4 layers, as follows. The wound contact layer is a perforated flexible silicone adhesive layer, bonded to a lower airlock layer and an upper fluid absorption layer that delivers negative pressure, removes wound exudate, and aids evaporation of fluid through the high moisture vapor transmission rate upper film layer. The bottom panel is a scanning electron micrograph cross-section through a PICO dressing showing the 3 lower layers.

Figure 2

Fluid handling properties of the PICO™ system. Fluid was pumped into an in vitro wound model covered with a PICO dressing at low exudate rate of 7.5 mL/24 h for 7 days (bottom panel) and high exudate rate 70 of mL/24 h for 45 hours (top panel). Continuous weight measurements were taken to establish how much fluid was retained in the dressing and how much fluid was lost to transpiration. A background air leak at a rate of 10 mL/min was introduced to reflect possible clinical conditions of use. Results are shown as means values of 3 experiments.

Figure 3

Photos of the treated wounds. Both incision and defect wounds were studied. In defect wounds, the wound cavity was either filled with polyurethane foam or gauze or left empty. The sutured incision wounds were either covered with a small piece of foam or gauze or left bare. Both wound types were then covered with either a 15 × 20 cm² PICO™ dressing or a standard NPWT adhesive drape and wound drain. The NPWT dressings were connected either directly to a PICO prototype pump or a traditional NPWT pump set to deliver a negative pressure of −80 mm Hg. See “Methods” for details.

Figure 4

Pressure distribution, studied in vivo. Wounds were treated with different device, dressing and filler combinations set to provide NPWT at −80 mm Hg. The horizontal line (—) indicates the −80 mm Hg set point of the NPWT pumps. The arrow indicates the combination that represents the PICO™ system with no filler. The pressure was measured in the wound bed of defect wounds (top panel) or on top of the suture line of incisional wounds (bottom panel). Results are shown as means ± SEM of 8 experiments.

Figure 5

Wound contraction. Wounds were treated with different device, dressing, and filler combinations set to provide NPWT at −80 mmHg. For defect wounds, the vertical and horizontal diameters of the wound, and for incisional wounds, distance between previously defined landmarks from the wound edge, were measured before and after the application of negative pressure and the mean value of the percent change was calculated. The arrow indicates the combination that represents the PICO™ system with no filler. Results are shown as means ± SEM of 8 experiments.

Figure 6

Wound edge microvascular blood flow. Wounds were treated with different device, dressing, and filler combinations set to provide NPWT at −80 mm Hg. Microvascular blood flow in the wound edge was measured using laser Doppler velocimetry before and after application of NPWT. In defect wounds, the probes were placed 0.5 cm and 2.5 cm from the wound edge. In incision wounds, the probes were placed at a depth of 0.5 cm and 2.5 cm from the skin surface, close to the incision edge. Microvascular blood flow is expressed as percentage change relative to baseline values. The arrow indicates the combination that represents the PICO™ system with no filler. Results are shown as means ± SEM of 8 experiments.