Evaluation of closed incision negative pressure therapy systems on the closure of incisional space model.

OBJECTIVE: The objective of this study was to compare the ability of foam dressing-based and non-foam-based closed incision negative pressure therapy (ciNPT) systems to close isolated incisional deficits in a tissue model. METHODS: Similarly sized foam-based and non-foam-based absorbent ciNPT dressings were applied to ~36cm long, ~3mm and ~6mm wide simulated incisions in gel sheets covered with drape (n=6 dressings/group/experimental condition spread over three respective therapy units). Changes in incision widths were measured directly or with overlying solid gel sheeting (to mimic tissue resistance), at five equally spaced locations before, immediately upon and one hour after initiating negative pressure using associated therapy units. RESULTS: Foam-based ciNPT closed simulated incisions more often than non-foam-based ciNPT in all tested conditions (p<0.05). While foam-based ciNPT almost completely closed the ~3mm wide incisional spaces, unlike non-foam-based ciNPT, the biggest differences between the two groups were observed with the ~6mm incisional width, which allowed maximal inward-stretching of the appositional faces without complete closure. The additional gel layer blunted closure in both groups, but much more with non-foam-based ciNPT. There was minimal impact of negative pressure duration on these results. CONCLUSION: Foam-based ciNPT closed incisional widths in simulated tissue significantly more compared with non-foam-based ciNPT. Different ciNPT systems should not be considered necessarily equivalent in performance.

Evaluation of the use of recombinant human basic fibroblast growth factor in combination with negative pressure wound therapy with instillation and dwell time in porcine full-thickness wound model.

NPWT with instillation and dwell time (NPWTi-d), which combines NPWT with wound irrigation, has been clinically applied as a more effective treatment than conventional NPWT. Commercially available recombinant human basic fibroblast growth factor (rh-bFGF) has been demonstrated to be beneficial for use over the wound beds. The objective of this study was to evaluate the effectiveness of combined treatment with NPWTi-d and rh-bFGF. Six pigs received 12 full-thickness excisional skin wounds and were treated with six different treatment groups for each pair. The treatment regimens were composed NPWTi-d, NPWT, or advanced wound care with or without rh-bFGF. On day 6, the minimum granulation tissue thickness and blood vessel number of the group of combined treatment with NPWTi-d and rh-bFGF spray were significantly greater than that of the control group. Combined treatment with NPWTi-d and rh-bFGF spray reads to good granulation tissue formation and vascularization for accelerating wound healing.

Healed porcine incisions previously treated with a surgical incision management system: mechanical, histomorphometric, and gene expression properties.

BACKGROUND: Computer and bench models have shown previously that surgical incision management with negative pressure (SIM) immediately decreases lateral tissue tension and increases incisional apposition. Better apposition is known to improve healing. Thus, SIM was hypothesized to improve the quality of incisional healing. This study evaluated the impact that 5 days of SIM had on mechanical properties and associated changes in the histology/histomorphometry and gene expression of healed porcine incisions. METHODS: One incision in each of the 4 pairs of contralateral, sutured, full-thickness incisions in each of 6 Yucatan swine were treated with either SIM (Prevena™ Incision Management System; n = 24 incisions/treatment group) or standard of care (SOC; sterile absorbent abdominal pads; n = 24/group) for 5 days, after which both groups received SOC for an additional 5 days. Biopsies for gene-expression analyses were collected on days 5 (n = 6 pairs/group), 20 (n = 6 pairs/group), and 40 (n = 12 pairs/group). On day 40, the animals were killed, after which healed incisions were harvested for mechanical testing (n = 12/group) and histologic/histomorphometric evaluation (n = 12/group). RESULTS: Compared with SOC-treated incisions, SIM-treated incisions had significantly improved (p < 0.05) mechanical properties (strain energy density, peak strain) and a narrower scar/healed area in the deep dermis on day 40. Differences in gene expression between SOC- and SIM-treated specimens were observed primarily on day 5. The SIM-treated specimens had significantly fewer genes, which were differentially expressed and showed reduced upregulation of genes associated with inflammation, hypoxia, retardation of reepithelialization, impaired wound healing, and scarring. CONCLUSION: Early application of SIM improved the quality of healed porcine incisions in terms of mechanical, histomorphometric, and gene-expression properties. NO LEVEL ASSIGNED: This journal requires that authors assign a level of evidence to each submission to which Evidence-Based Medicine rankings are applicable. This excludes Review Articles, Book Reviews, and manuscripts that concern Basic Science, Animal Studies, Cadaver Studies, and Experimental Studies. For a full description of these Evidence-Based Medicine ratings, please refer to the Table of Contents or the online Instructions to Authors www.springer.com/00266 .

Comparison of tissue damage, cleansing and cross-contamination potential during wound cleansing via two methods: lavage and negative pressure wound therapy with instillation.

The use of lavage was compared to negative pressure wound therapy (NPWT) with instillation (NPWTi) to assess extent of soft tissue damage, debris removal and environmental cross-contamination susceptibility in three distinct models. Scanning electron microscopy in an ex vivo model showed increased visible tissue trauma from lavage treatment at low and high pressures versus NPWTi, with the degree of trauma relative to the pressure of the irrigant. These results were corroborated in granulating full-thickness excisional swine wounds coated with dextran solution to simulate wound debris. Both low-pressure lavage and NPWTi demonstrated effective cleansing in this model, reducing debris by >90%. However, using three-dimensional photography to evaluate tissue damage by measuring immediate tissue swelling (changes in wound volume and depth) showed significantly greater (P < 0.05) swelling in low-pressure lavage-treated wounds compared with NPWTi-treated wounds. Lastly, bench top wound models were inoculated with fluorescent bacterial particles to assess environmental cross-contamination potential and collected at measured distances after treatment with low-pressure lavage and NPWTi. No evidence of cross-contamination was found with NPWTi, whereas one-half of the particles became 'aerosolised' during low-pressure lavage (P < 0.05). Collectively, these studies demonstrate the effective wound cleansing capabilities of NPWTi without the tissue damage and environmental contamination associated with lavage.

Burst strength testing of porcine intestinal anastomoses following negative pressure therapy.

The effect of negative pressure therapy (NPT; The ABThera™ Open Abdomen Negative Pressure Therapy System, KCI USA, Inc., San Antonio, TX) on the integrity of small intestinal anastomoses was evaluated using in situ burst strength testing in a domestic pig model. In each of 3 swine, 8 anastomoses were created, 4 using sutures and 4 using staples. After 24 hours of continuous NPT, each anastomosis was subjected to burst strength testing in situ. Mean ratios of burst strength of sutured anastomoses to baseline intraluminal pressure were 9.0 to 10.9. Stapled anastomoses had significantly lower burst strength than sutured anastomoses, but mean values were still at least 4.6 times greater than baseline. No differences were seen between anastomoses that were located in close proximity with treatment and those remotely placed or when measured with negative pressure on or off at burst assessment. NPT had no acute adverse effect on intestinal anastomoses in swine.

Evaluation of closed incision management with negative pressure wound therapy (CIM): hematoma/seroma and involvement of the lymphatic system.

The objective of this porcine study was to evaluate the effect of closed incision management with negative pressure wound therapy (CIM) on hematoma/seroma formation, fluid removal into the CIM canister, and involvement of the lymphatic system. In each swine (n = 8), two sets of ventral contralateral subcutaneous dead spaces with overlying sutured incisions were created. Stable isotope-labeled nanospheres were introduced into each subcutaneous dead space. Each contralateral incision was assigned to CIM (continuous -125 mmHg negative pressure) and control (semipermeable film dressing), respectively. Following 4 days of therapy, hematoma/seroma was weighed, total fluid volume in canisters was measured, five pre-identified lymph nodes were harvested, and five key organs were biopsied. There was 25 ± 8 g (standard error [SE]) (63%) less hematoma/seroma in CIM sites compared to control sites (p = 0.002), without any fluid collection in the CIM canister. In lymph nodes, there were ∼60 µg (∼50%) more 30- and 50-nm nanospheres from CIM sites than from control sites (p = 0.04 and 0.05, respectively). There was significantly greater nanosphere incidence from CIM sites than from control sites in lungs, liver, and spleen (p < 0.05); no nanospheres were detected in kidney biopsies. Thus, in this porcine model, application of CIM significantly decreased hematoma/seroma levels without fluid collection in the canister, which may be explained by increased lymph clearance.

Cardiopulmonary effects of continuous negative pressure wound therapy in swine.

BACKGROUND: Negative pressure wound therapy (NPWT) has been used for complex sternotomy wounds. Some reports describe foam placement below the posterior sternal table. We compared the hemodynamic and pulmonary effects of foam location during NPWT after median sternotomy. METHODS: Swine were randomized into four groups (n = 6 per group). A polyurethane open cell foam dressing was placed either within or below the sternal table. In one-half, a silicone mesh barrier was placed between the heart and the foam. The NPWT was applied at -125 mm Hg and then released to ambient pressure. This cycle was repeated two more times, and the foam was removed. Heart rate, mean arterial pressure, cardiac output, mixed venous oxygenation, central venous pressure, and pulmonary artery wedge pressure were measured. Peak inspiratory pressure, mean airway pressure, work of breathing, and intrathoracic pressure measurements were recorded. RESULTS: Intersternal placement of foam did not affect hemodynamic parameters. Substernal placement resulted in depression of hemodynamic variables which improved when negative pressure was applied. Pulmonary mechanics were not affected by foam location. CONCLUSIONS: Initial placement of the foam dressing below the posterior sternal table caused reversible depression of cardiac function which appears to be consistent with direct cardiac compression. NPWT therapy had no clinically significant impact on pulmonary parameters. The use of a protective barrier does not alter hemodynamic or pulmonary parameters but continues to be recommended when NPWT is used for sternotomy wounds.

V.A.C. Therapy normalizes vascular response of injured tissue in full-thickness wounds in rabbits.

V.A.C. Therapy applied to a cutaneous wound was hypothesized to alter vascular regulation in underlying tissue. Two full-thickness wounds were created on the dorsum of 7 New Zealand albino rabbits. One site was treated with V.A.C. Therapy; the other, with saline-moistened gauze. Local perfusion levels in the muscle were measured using laser Doppler flowmetry. Using vena caval occlusion, blood pressure was decreased progressively from baseline under vasonormal conditions and during systemic infusion of a vasodilator and a vasoconstrictor. The pressure-flow relationships for the carotid and V.A.C. Therapy-treated wound sites showed 3 distinct curves, with vasodilator curves shifted upwards and vasoconstrictor curves downwards relative to vasonormal curves (P < 0.05). By contrast, vasodilator curves in the saline-gauze treated sites were indistinguishable from vasonormal curves. Thus, in a rabbit model, application of V.A.C. Therapy to cutaneous wounds normalized the vascular response to vasoactive drugs in a manner similar to undisturbed carotid circulation.

Effect of Vacuum Assisted Closure Therapy on early systemic cytokine levels in a swine model.

Vacuum Assisted Closure (V.A.C.) Therapy has previously been shown to facilitate healing of wounds. However, the physiological mechanism(s) of this treatment modality and its systemic effects require further investigations. The goal of this porcine study was to investigate the effect of V.A.C. Therapy on the systemic distribution of the inflammatory cytokines interleukin (IL)-6, IL-8, IL-10, and transforming growth factor-beta1. Twelve pigs were each given one full-thickness excisional wound, using electrocautery. Six of the pigs were treated with V.A.C. Therapy and six with saline-moistened gauze. Serum samples were collected immediately after wound creation, and hourly for 4 hours. Samples were analyzed using commercially available enzyme-linked immunosorbent assay kits. During the initial 4 hours of treatment, V.A.C. Therapy resulted in earlier and greater peaking of IL-10 and maintenance of IL-6 levels compared with saline-moistened gauze controls, which showed decreased IL-6 values over the first hour (both at p<0.05). No other treatment-based differences were detected.