Comparison of the Effects of Different Negative Pressure Wound Therapy Modes-Continuous, Noncontinuous, and With Instillation-on Porcine Excisional Wounds

Abstract

Objective: Negative pressure wound therapy (NPWT) can be delivered in continuous or noncontinuous modes, while NPWT with instillation (NPWTi) couples NPWT with automated delivery and removal of topical wound treatment solutions and suspensions. This porcine study compared granulation response of NPWTi (instillation foam dressing with saline) to NPWT (standard foam dressing) in continuous and noncontinuous modes.

Methods: Full-thickness dorsal excisional wounds in pigs were treated with continuous NPWT, intermittent NPWT, dynamic (controlled variable) NPWT, and NPWTi with saline (n = 10 per group). Wound dimensions were determined from 3D images collected on days 0, 2, 5, and 7. On day 7, animals were euthanized and specimens were harvested for histopathological review.

Results: Average granulation thickness was not statistically different among continuous (3.29 ± 0.33 mm), intermittent (3.03 ± 0.47 mm), and dynamic (3.40 ± 0.34 mm) NPWT wounds at day 7. Average granulation thickness of NPWTi wounds (4.75 ± 0.54 mm), however, was statistically greater (P < .05) by 44%, 57%, and 40%, respectively, than that of wounds treated with continuous, intermittent, and dynamic NPWT. Analysis of 3D images revealed a greater reduction in wound area and perimeter in NPWTi wounds compared to all NPWT wounds (P < .05). In addition, the average wound fill rate for NPWTi wounds was faster than that for continuous (40%; P < .05), intermittent (25%; P > .05), and dynamic (65%; P < .05) NPWT wounds.

Conclusions: Although not confirmed in humans, these porcine data suggest that NPWTi with saline may stimulate a faster rate of wound granulation than NPWT in continuous and noncontinuous modes.

Keywords: dynamic NPWT; negative pressure wound therapy with instillation; preclinical model; variable NPWT; wound cleansing.

Figure 1

Schematics of negative pressure profiles evaluated in this study: (a) continuous NPWT at −125 mm Hg; (b) intermittent NPWT with cycles of 5 minutes at −125 mm Hg followed by 2 minutes of 0 mm Hg; (c) dynamic NPWT with a 3-minute rise to −125 mm Hg followed by a 3-minute fall to −25 mm Hg; and (d) NPWTi with each cycle consisting of a short instillation phase, following by a 5-minute soak phase, followed by a 2.5-h negative pressure phase.

Figure 2

Progression of a single representative wound at (a) day 0 creation, (b) day 2 dressing change, (c) day 5 dressing change, and (d) day 7 termination. Note the paucity of granulation tissue at day 2, suggesting the wound has not fully left the inflammatory phase of healing. However, the wound enters the granulation phase of healing by day 5, and a robust granulation layer is present by day 7. (Wound shown was treated with continuous NPWT, scale bar = 2 cm.)

Figure 3

Representative photomicrograph of a wound treated with continuous NPWT. The top image shows the histological section stained with hematoxylin and eosin. The bottom image shows the same section with the bottom (black tracing) and top (green tracing) of the granulation tissue marked. The vertical blue lines are the incremental granulation tissue thickness measurements, spaced every 2 mm. These increments are averaged to determine the average granulation tissue thickness for this wound. (Scale bar = 5 mm)

Figure 4

Average granulation tissue thickness measured in histology specimens at day 7. Data are shown as mean ± standard error of the mean. (n = 10 wounds per group; *P < .05 for NPWTi compared to all NPWT groups)

Figure 5

Changes in wound perimeter (top) and surface area (bottom) calculated from 3D wound reconstructions. Data are shown as mean ± standard error of the mean. (n = 10 wounds per group, *P < .05 for NPWTi compared to all NPWT groups.)

Figure 6

The rate of change of wound volume, calculated as percent fill per day. Data are shown as mean ± standard error of the mean. (n = 10 wounds per group, *P < .05 for NPWTi compared to continuous NPWT and dynamic NPWT.)