Clinical Experience With the Use of Negative Pressure Wound Therapy Combined With a Silver-impregnated Dressing in Mixed Wounds: A Retrospective Study of 50 Cases

Introduction. Although negative pressure wound therapy (NPWT) has been used for more than 20 years, as far as the authors are aware, there is little research aimed at the evaluation of the combination of NPWT with a silver-impregnated dressing. Objective. The aim of this study was to examine the effect, efficacy, and safety of NPWT in conjunction with a silver-impregnated dressing. Materials and Methods. The authors used a retrospective study of 54 acute and chronic wounds treated in 50 patients over a 2-year period. Demographic data, wound characterizations, wound cultures before and after NPWT, the duration of NPWT and number of sponge changes for each patient, the types of surgical procedures used for wound closure following NPWT, and the healing time and length of hospital stays were recorded. Results. In 26 wounds, deep structures (ie, bones and tendons) were exposed. The mean NPWT duration was 9.2 days. Mean healing time was 16 days. There was a statistically significant decrease in the pathogenic microbial strains after NPWT treatment combined with the silver-impregnated dressing (paired t test; P = 0.0038). The shift from complicated to easier surgical wound-closure procedures was observed. Discussion. According to all results obtained, described, and discussed, the authors consider the use of a nonadherent silver-impregnated dressing in conjunction with NPWT to be beneficial and efficacious. No adverse events or reactions related to the silver-impregnated contact layer used during NPWT have been observed in the patients, which confirmed the safety of this method. 

The management of wounds with problematic healing (eg, massive infection or extensive tissue loss with/without exposure of deep structures such as muscles, tendons, or bones), where conservative and conventional surgical treatment methods are insufficiently effective, attracts considerable attention of many clinicians. Advanced wound care treatment methods are necessary to achieve healing of these problematic wounds. Negative pressure wound therapy (NPWT), introduced by Morykwas,¹ offers treatment options for the management of problematic wounds. This nonpharmacological treatment method utilizes physical principles (subatmospheric pressure) for wound environment manipulation to enhance natural wound healing processes, leading to accelerated wound healing. To date, NPWT has proven its versatility in the management of both acute and chronic wounds in a wide range of indications: open fractures²; extensive tissue loss, severe wound infections, destructive burn injuries,³ and frostbite; enhancement of skin graft and skin substitute take^4,5; salvage of compromised flaps⁶; wounds with massive edema and/or venostasis; trophic ulcers (ie, venostatic, arterial, neuropathic, diabetic,⁷ and postirradiation); pressure ulcers⁸; and sternal or abdominal dehiscences.^9,10 Nevertheless, it must be emphasized that NPWT cannot replace surgical debridement, which should always be performed before applying topical negative pressure. However, the indication and contraindication criteria for NPWT usage should be considered and strictly followed as with any other treatment method. In NPWT, several mechanisms act in concert and exert beneficial effects: stimulation of blood flow, angiogenesis, and granulation formation; derivation of soluble wound healing inhibitor substances from the wound area; mechanical forces pulling the wound edges together; reduction of tissue edema; and reduction of bacterial contamination.The latter is considered to be one of the key factors in wound healing. To stimulate wound healing, according to the literature,^11,12 the authors attempted to enhance this antibacterial effect by using a silver-impregnated dressing in conjunction with NPWT. To prove the antimicrobial activity and clinical effectiveness of this combination are not the same, different types of wounds were included, which also gives more insight into the management of problematic wounds. The authors describe their experience with NPWT combined with a silver-impregnated dressing for the treatment of 54 wounds in 50 patients over a 2-year period. 

Inclusion criteria
All patients with nonhealing or any type of problematic wounds hospitalized at the Department of Burns and Reconstructive Surgery, Comenius University and University Hospital Ružinov, Bratislava, Slovak Republic, who have been treated using NPWT from September 2011 to December 2013 were eligible for inclusion in this retrospective study. This study was approved by the Ethics Committee of the University Hospital Ružinov.

Negative pressure wound therapy treatment system
The NPWT treatment system is a closed, airtight system consisting of a sterile hypoallergic polyurethane foam connected to the source of subatmospheric pressure by the tube which, in addition to negative pressure distribution, also serves for derivation of wound exudates to a container attached to the device. Patients included in this study were treated using the Vivano negative pressure therapy system (PAUL HARTMANN AG, Heidenheim, Germany), which consists of the VivanoTec negative pressure unit and VivanoMed wound-dressing kit (PAUL HARTMANN AG, Heidenheim, Germany). The fine-pored, flexible polyurethane sterile foam (ie, sponge) dressing can be trimmed and shaped to ensure contact with all wound surfaces for equal distribution of subatmospheric pressure. The sponge placed on the wound surface is sealed using an adhesive drape (Hydrofilm, HARTMANN USA, Inc, Rock Hill, SC). After the creation of a small hole through the drape in the center of the sponge surface, the silicone adhesive port is attached. The opposite end of the tube is connected to the negative pressure unit with a detachable collection container (300 mL or 800 mL).The pressure unit is a subatmospheric pressure device equipped with a touch screen to adjust the intensity, duration, and frequency (ie, continuous or intermittent) of the subatmospheric pressure to the wound surface. In the authors’ department, particular preference has been given to intermittent negative pressure. During treatment, there is a continual change between 2 negative pressure values at specified intervals: negative pressure of 125 mm Hg for 5 minutes followed by negative pressure of 20 mm Hg for 2 minutes. Intermittent negative pressure increases blood flow to the wound tissue more effectively and the proliferation of granulation tissue is higher over continuous negative pressure.^1,13

Polyurethane foam as a wound contact layer can lead to granulation tissue ingrowth, with possible damage to the underlying tissues and increased bleeding and pain¹⁴ caused by necessary sponge change or removal. Additionally, applying the foam directly on the exposed deep structures (ie, bones, tendons, and nerves) is not recommended. Because of these reasons, and with the intention to enhance bacterial contamination reduction, the authors decided to use a nonadherent wound contact layer with antimicrobial properties. In this study, NPWT treatment was combined with a polyamide tulle dressing chemically coated with metallic silver and impregnated with nonpetroleum triglyceride based ointment (Atrauman Ag, PAUL HARTMANN Ltd, Heywood/Lancashire, UK). On contact with wound exudate, the silver ions responsible for antimicrobial properties are activated. All products indicated for the treatment of the patients in this study were purchased by the authors’ hospital, and the treatment effect was retrospectively evaluated.

Treatment details
Each patient was examined thoroughly regarding history, associated illnesses, medications, nutritional status, vascular system with regard to wound-area perfusion, and compensation of diabetes, if present. Wound swabs were taken for bacterial wound culture. Wound examination was always performed together with wound assessment. Prior to the admission of each patient to the hospital, each wound was examined by a specialist from the authors’ department, including a search for wound-edge undermining or wound fistulas. When indicated, ultrasound examination, fistulography and/or bone x-ray examinations were also performed. The treatment plan usually consisted of 3 phases.

First, the preparatory phase included the previously mentioned examinations as well as laboratory findings and auxiliary examinations. A detailed wound assessment and decision on whether to use NPWT treatment was also made during this phase. Regular dressing changes with topical antimicrobial treatment of heavily contaminated, mainly chronic wounds were then performed to reduce the bacterial load. 

Surgical debridement of the wound with subsequent application of the NPWT system comprised the second phase of the treatment plan. The surgical intervention started with wound exploration followed by thorough debridement with the removal of all devitalized and necrotic tissues. Meticulous hemostasis of bleeding points was of utmost importance. The silver-impregnated, nonadherent mesh was applied to the wound followed by foam application, sealed with adhesive drapes, and connected to the negative pressure unit. When the authors treated 2 independent wounds that were both suitable for NPWT treatment (eg, on the same leg laterally and medially), the foams covering the wounds were connected using this process when 2 independent wounds (eg, located on the same extremity) were both suitable for NPWT.  The foam was connected using an “overbridging“ foam and sealed with adhesive drapes together to create a single-closed system; thereafter, it was connected to a single negative pressure unit. Immediately after the NPWT system application, the treatment was initiated by the application of a continuous negative pressure of 125 mm Hg. After 2-4 hours, it was changed to an intermittent negative pressure of 125 mm Hg for 5 minutes, alternating with a negative pressure of 20 mm Hg for 2 minutes. Depending on the wound characteristics and amount of exudate, the first sponge change and wound exploration was done after 3-5 days. The wound was debrided repeatedly, where relevant, before every NPWT system reapplication. The main goals of NPWT treatment should include the achievement of a clean wound surface with a sufficient amount and quality of granulation tissue, decreased bacterial contamination, reduced edema, and the feasibility of conservative or surgical wound closure.

In the third phase, once an acceptable wound condition was achieved either surgical wound closure was performed (foam removal was performed in the operating room) or the wound was considered to have sufficient capacity to heal using conservative treatment methods. 

Evaluation criteria
Information obtained for the evaluation criteria included the following: demographic data; the time interval between wound development and NPWT initiation; wound characterization (ie, wound etiology, localization, diameter, wound bed, wound margins, and periwound area characterizations); wound cultures before and after NPWT; duration of NPWT and the number of sponge changes for each patient; wound appearance after NPWT; types of surgical wound closures following NPWT; healing time calculated from the end date of NPWT to the date of achieving a healed wound after the wound closure; and length of hospital stay. Data are presented as the means ± standard deviation (SD). A value of P < 0.05 was considered statistically significant.

Demographic data
Between September 2011 and December 2013 at the Department of Burns and Reconstructive Surgery, Comenius University and University Hospital Ružinov, Bratislava, Slovak Republic, 50 patients with 54 wounds were treated and included in this retrospective study. Of the 50 patients, 35 (70%) were male and 15 (30%) female (Table 1). The patients with both acute and chronic wounds were included, and the time interval between wound development and NPWT varied from 14 to 600 days with a mean time interval of 71.6 ± 97.3 days (95% confidence interval of the SD: 81.27–121.24). 

Figure 1. Wound etiology of 50 patients

Wound characterization
The wound etiology was considerably heterogenous, mostly represented by posttraumatic and diabetic defects (Figure 1). The majority of wounds were lower extremity, with nearly equal distribution on the leg and foot, followed by other less frequent wound locations (Figure 2).  Among the 50 patients in the present study, 3 with wounds after fasciotomies had 2 wounds located on the lateral and medial sides of their lower legs, and 1 patient with inveterate burns had 2 independent wounds located on each leg; hence,there were 54 wounds in 50 patients. The average wound size was 97.2 cm² (range, 1 cm²–375 cm²). Despite some wounds having a small surface area, they were usually complicated with extensive wound-edge undermining and affected deep structures which were exposed following necrectomy. In addition to wound size, the wound bed, edges, and periwound areas were included in the wound assessment (Table 2). 

Figure 2. Localization of 54 wounds in 50 patients.

Wound cultures
Wound swabs were taken before and after NPWT. The authors compared the wound culture results obtained from swab cultivations before and after NPWT to assess the efficacy of the treatment. Figure 3 shows the comparison of main pathogenic microbial strains from wound cultures before and after NPWT, where reduction of pathogenic microbial strains after NPWT was observed. To compare the values obtained that were related to each other (before and after NPWT) a paired t test was performed. A statistically significant reduction of pathogenic microbial strains were observed after NPWT (P = 0.0038). 

. 
Figure 3. Bacteriology before and after negative pressurewound therapy (NPWT) treatment. Statistically significantreduction of pathogenic microbial strains in wound culturesafter NPWT confirmed by pairedttest (P= 0.0038 < 0.05).

Negative pressure wound therapy treatment
In 50 patients with 54 wounds, the mean NPWT duration was 9.2 ± 7.2 days (range, 5–36 days).For all 54 wounds in this study, the mean number of foam changes was 1 per wound. In 16 patients with 17 wounds, where NPWT was repeated, the mean number of foam changes was 2.4 ± 1.94 (range, 1–7). A low average number of foam changes and a relatively short NPWT duration in all patients can be explained by meticulous initial wound decontamination followed by thorough wound debridement performed before NPWT application, and by the performance of the surgical wound closure as soon as the wound surface and conditions allowed for this procedure.

Wound closure
An appropriate type of surgical wound closure was chosen with regard to clinical conditions, wound appearance after NPWT, and wound localization. Table 3 provides an overview of the treatment methods chosen for wound closure. In 34 of 54 wounds, the preferred method was a split-thickness skin graft (STSG), selected in cases where the wound bed was well prepared for graft take. Split-thickness skin grafts were meshed to achieve greater drainage of wound fluid and to obtain better graft adherence to the wound surface, thus enhancing skin graft take. This method could be used in many of the cases where deep structures were exposed. For example, bones or tendons that were overgrown by healthy granulation tissue that was stimulated by the beneficial effects of NPWT. Closure of the wounds with remaining deep structures exposed even after NPWT required the use of  healthy tissue from the wound-adjacent areas. The following surgical methods were used: direct suture after wound edge mobilization and adjacent fasciocutaneous, muscle, or musculocutaneous flaps or their combinations. These methods were performed much more easily and with considerably greater safety because of decreased tissue edema and increased tissue perfusion after NPWT. Three muscle flaps in combination with fasciocutaneous flaps and 1 musculocutaneous flap were used in the wound closure of 2 ischial and 2 sacral pressure ulcers, respectively. Conservative treatment was chosen 3 times in patients with chronic foot defects with a small remaining wound surface (maximum 2 cm x 2 cm). 

Wound-healing time and mean hospital stay
The wound-healing time was defined as the time interval between foam removal (end of NPWT) and complete wound closure. The mean wound-healing time for 53 of 54 healed wounds was 16 ± 7.53 days (range, 7–50). One patient with diabetes acutely admitted with phlegmon in the heel region displayed no progress following initial debridement and NPWT. A second surgical intervention due to progression of infection to the plantar space showed plantar aponeurosis involvement after evacuation of an extensive plantar abscess. After repeated necrectomy and NPWT application, again no healing progress was observed, which led to the suspicion of a compromised blood supply to the affected area. Lower leg arterial sonography showed multiple segmental obstructions of the main supplying arteries, which required correction by percutaneous transluminal angioplasty and stenting of the affected vessels, performed at the National Institute of Cardiovascular Diseases, Bratislava, Slovak Republic. Following intravascular intervention, the patient was transferred back to the authors’ department, where repeated debridements and NPWT, including 7 foam changes, were performed until complete wound closure was finally achieved. The mean hospital stay for the 50 patients in the study was 28 ± 20.8 days (range, 10–138 days). The hospitalization time of patients with more than 1 wound, particularly those with multiple pressure ulcers, was related not only to the wounds with NPWT treatment but to the treatment of all other wounds for which NPWT was not used. Therefore, the mean length of hospital stay did not fully reflect NPWT efficacy. For this reason, the wound-healing time was considered to be more suitable. (Figure 4)

As the results have shown, the majority of the patients included in this study had wounds that were contaminated, undermined, had exposed deep structures, and that had irregular surfaces and wound edges. The majority of patients with this type of wound had been transferred to the authors’ facility following the failure of conventional wound treatment methods, both conservative and surgical. Although the wound etiology and duration (acute and chronic wounds) were variable, the beneficial effects of NPWT observed were similar to those described in the literature.¹ After thorough surgical debridement and NPWT application, wound fluids were derived, blood flow and angiogenesis were supported, tissue edema was reduced, and granulation tissue growth was induced. 

In addition to the clinical assessment of the wounds, wound culture results are equally important regarding the treatment options and outcomes of patients; although it should not be the sole criterion in the decision process. Reduction of bacterial contamination is frequently attributed to the effects of NPWT. Although some studies have shown a significant decrease in the bacterial load of Staphylococcus aureus and S. epidermidis,¹ in others,^15,16 NPWT was more effective in the clearance of Pseudomonas aeruginosa and nonfermentative gram-negative rods, with no significant difference in S. aureus clearance. The wound culture results of this study showed a statistically significant decrease in all pathogenic microbial strains after NPWT treatment. Because a significant reduction in bacterial rebound when using NPWT in combination with topical silver dressing was previously reported,^11,17 the results obtained in this study can be attributed not only to meticulous debridement and the effect of NPWT, but also to the antimicrobial activity of the silver-impregnated dressing used as the wound contact layer in all patients. In the authors’ experience, the use of a nonadherent dressing as a wound contact layer in combination with NPWT appeared to have further advantages. First, foam removal was far easier, with less bleeding, less or minimal pain, and less damage to the underlying granulation tissue. Second, in wounds with irregular edges, the foam could be placed on the wound without any concern that it would exceed the edges of the wound already covered by the dressing, thus avoiding maceration of healthy skin. For all the above-mentioned reasons, the authors consider the use of a nonadherent, silver-impregnated dressing in conjunction with NPWT to be an advancement in wound treatment. No adverse events or reactions related to the silver-impregnated contact layer used during NPWT were observed in the patients, which confirmed the safety of this method.

On completion of NPWT treatment, after foam and nonadherent dressing removal, the dead spaces and skin underminings were reduced or even obliterated, and former wound-surface irregularities were filled with healthy granulation tissue which, in many cases, overgrew the exposed deep structures (ie, bones and tendons); this facilitated the use of simpler surgical techniques of wound closure, as can be seen in Table 3.  This shift from complicated to easier surgical wound closure procedures was observed in the current study in accordance with findings of other studies in the literature.¹⁸ Some patients with chronic wounds with multiple comorbidities could benefit from a less-invasive operative procedure (eg, the use of split-thickness skin graft instead of a flap) and a shorter operation time. 

In 6 cases, direct suturing of the wound could be performed after NPWT, resulting from a contraction effect of NPWT on the wound, which pulls the edges together.¹⁹ In 2 of these patients with wounds on the heel and knee, respectively, sutured under slight tension, NPWT was placed directly on the sutured wound to enhance the beneficial effect of increased capillary perfusion around wounds induced by negative pressure.

Six patients in the current study were referred to the authors’ facility with wounds that had resulted from open fractures of the lower extremity stabilized with external fixation. Following debridement and foam application, it was technically demanding to achieve an airtight seal of the spaces around some of the Steinmann pins using adhesive drapes in the treated area. The authors suggest using silicone adhesive strips approximately 5 cm–7 cm long, 3 mm–4 mm wide, and 2 mm–3 mm thick, then wrapping them around the Steinmann pins wherever there is contact between the pins and adhesive drapes to seal any air leaks after connection to the negative pressure source. Further investigations need to be performed to solve this problem. 

To obtain the best possible results, in accordance with the authors’ experience, the NPWT-treatment method should be:

• Individual. Each patient must be treated as unique. All comorbidities and medications must also be taken into consideration. The whole patient and not the wound alone should be treated (ie, holistic approach²⁰).
• Selective. Negative pressure wound therapy represents a method of choice for the treatment of only indicated wounds. The contraindications are listed in Table 4.²¹ Additionally, patient risk factors/characteristics must be considered before NPWT use, for example, patients at high risk for bleeding or hemorrhage, on anticoagulants or platelet aggregation inhibitors, with friable or infected vessels, or other contraindications.²¹
• Complementary. Negative pressure wound therapy as a complementary method is an integral part of wound treatment in indicated cases. The position of NPWT in the wound-healing process should be somewhere in the middle, between the initial surgical debridement and the surgical or conservative wound closure at the end. 

 Negative pressure wound therapy treatment represents a valuable adjunct in accelerating the healing of deep defects or problem wounds in indicated cases and in the preparation of wounds for successful wound closure, preferably (but not exclusively) using split-skin grafting and/or other surgical or nonsurgical methods. The combination of NPWT with a silver-impregnated dressing has been shown to be beneficial. The results of this study showed a reduced mean wound healing time and reduced length of hospital stay. 

In NPWT treatment, several mechanisms of actions and factors act in concert and exert several beneficial effects. Negative pressure wound therapy offers new options in treating problem wounds in indicated cases. It can provide a good alternative in cases where classical wound-treatment methods have been ineffective as a preparation for final surgical wound closure. Nevertheless, initial decontamination and meticulous surgical debridement of the wound prior to the use of NPWT treatment is of paramount importance.

Affiliations: Department of Burns and Reconstructive Surgery, Comenius University and University Hospital Ruzinov, Bratislava, Slovak Republic

Correspondence:
Peter Bukovcan, MD, PhD
Department of Burns and Reconstructive Surgery
Comenius University and 
University Hospital Ružinov
Bratislava, Slovak Republic
bukovcanmed@gmail.com 

Disclosure: The authors disclose no financial or other conflicts of interest.