Using Medical Silicone to Ensure an Airtight Negative Pressure Wound Therapy Dressing Seal in Challenging Wounds: A Case Series

Negative pressure wound therapy (NPWT) has been used for a broad range of indications and wound types. However, it can be difficult to maintain an airtight dressing seal when the wound is located in an anatomically challenging area or environment. To address this problem, medical silicone, used to create intraoral vacuum dressings, was used in five patients (one woman, four men, age range 57 to 66 years) to seal leaking NPWT dressings (four polyurethane dressings and one polyurethane silver foam dressing).   The wounds were located in the head and neck, abdominal, lower extremity, and anogenital areas. Initial wound sizes ranged from 2.5 cm^² to 700 cm^², and periwound areas were characterized by irregular surfaces (scars, skin folds, or curved surfaces), humid milieu, or mobile structures. In all five patients, negative pressure was set at -125 mm Hg constant suction, and the silicone was able to seal the leaking dressings. Wound size reductions from 2.5 cm^² to 13.5 cm^² were observed during 9 to 64 days (range) of NPWT treatment. In these patients, medical silicone was found to be a suitable material to facilitate airtight sealing of the dressings used with NPWT.

Negative pressure wound therapy (NPWT) is a method to facilitate wound healing. NPWT uses a vacuum system consisting of a therapy unit that creates a subatmospheric pressure, which is transferred via tubes to a foam dressing placed directly on the wound.

Originally, NPWT was used for complicated chronic wounds. As described in literature reviews,^1-3 the clinical indications for NPWT have been widely discussed. Review articles,^4,5 clinical trials,^6-8 and case series^9,10 have shown NPWT to be effective in the treatment of diabetic wounds, pressure ulcers, and burns, as well as a preparatory method for skin grafts and flap surgery.

Important effects of applying subatmospheric pressure to wounds described in animal experiments,^11,12in vitro studies,¹³ case series,^14-16 and randomized controlled trials^17,18 include decrease in wound edema, promotion of granulation tissue formation, decrease of wound size due to mechanical creep of the wound edges, increased perfusion of the wound and the surrounding area, and reduction of bacterial load.

NPWT can be used for various anatomical regions, but problems maintaining an airtight seal with the NPWT system can occur in regions with irregular surfaces (such as skin folds, scars, or curved surfaces), a humid milieu, or mobile structures. To address these challenges, approaches have included pretreating the wound’s surrounding areas with dermal-adhesion agents, such as Compound Benzoine Tincture (3M Health Care, Inc, Neuss, Germany) or Skin-Prep (Smith & Nephew, Inc, Hamburg, Germany), to improve the adherence of the occlusive drape of the vacuum system.¹⁹ In a retrospective study, Andrews et al²⁰ presented 12 patients who had undergone NPWT of complicated head and neck wounds. The authors maintained the airtight seal of the NPWT dressings using a combination of occlusive drape, Skin Prep, benzoine, and Tegaderm (3M Health Care, Inc, St. Paul, MN) on the surrounding skin. To protect the surrounding wound area and to prevent leakage of dressings under high-humidity conditions, Jerome’s²¹ guidelines and recommendations for use of NPWT include placing a hydrocolloid dressing around the wound. Bookout et al’s²² case series reports use of stoma paste to fill in crevices to achieve an airtight closure.

Silicone. Medical silicones have widespread applications in healthcare. Due to its excellent biocompatibility and biodurability,^23,24 silicone can be used for intracorporeal and extracorporeal medical equipment such as joint implants, aesthetic implants, medical tubes or membranes, prosthetics, facial prostheses (epitheses), or dental impression materials.²⁵ Its use also has been described for creating an intraoral vacuum dressing in a case of an extended keratocyst of the mandible.²⁶ To enable intraoral NPWT, the authors applied silicone impression material, which is mainly used in dentistry and epithetics.

As manufacturer data show, silicone impression material combines the advantages of high biocompatibility and the possibility of application as a low-viscosity malleable silicone, its rapid setting comparable to an elastic material. Additionally, the authors` practical experiences in using the silicone impression material revealed easy, rapid, and painless removal from skin.

The material is dispensed in an automix cartridge delivery system, and manufacturer-provided, single-use tips aid in application.

Silicone impression materials mainly consist of vinyl polysiloxane and are commercially available in different viscosities, hardnesses, and setting times. The viscosity of silicones can be light, regular, or heavy. Degree of hardness is characterized by shore hardness A, which is between 20 and 80 Shore. Higher values of Shore hardness A characterize higher values of hardness of the elastomer and vice versa. The silicones are available as slow, regular, or fast-setting. Silicone should not be used in case of hypersensitivity against vinyl polysiloxanes. Per manufacturer instructions, contact with the eyes, uncontrollable application in body cavities, or use on open wounds must be avoided. The silicone (VPS Hydro, Light Body, Fast Set [Henry Schein, Inc., Melville, NY] used to achieve an airtight seal with NPWT (V.A.C. Therapy System (KCI, Inc., Wiesbaden, Germany with either polyurethane or polyurethane silver foam) has a Shore hardness A of 45±2 Shore.

The purpose of this case study was to describe the use of this silicone to achieve an airtight seal for NPWT in five patients.

Patients. Efforts to achieve an airtight NPWT seal using materials such as paste or hydrocolloid dressings had been unsuccessful in five patients (one woman, four men) with challenging wounds. Clinicians decided to try medical silicone to create the necessary seal. The patients were treated at the University Hospital Leipzig, Germany, between May 2010 and March 2012.

Procedure. The skin surrounding the wound was shaved thoroughly. Afterward, the wound, including the surrounding area, was disinfected with an aqueous wound antiseptic (Octenisept. Schülke & Mayr, Inc, Norderstedt, Germany). The skin then was degreased using Compound Benzoine Tincture (3M Health Care, Inc, St. Paul, MN) and dried carefully. The foam dressing was cut into the correct shape to cover the wound but not overlap the surrounding skin and placed directly onto the wound, followed by a layer of adhesive drape. A small part of the drape covering the foam was removed to provide an area to place the pad, including the tube. The pad then was fixed by another layer of adhesive drape.

The system was assessed visually for air leakage. Obvious leaks were sealed with the silicone material, which was directly applied under the drape using the cartridge delivery system and single-use tips. After visual inspection, the vacuum pump was switched on and an audible check by an unaided ear was performed. If leaks were detected, the pump was switched off, areas of leakage identified, and the silicone seal reapplied. The amount of silicone needed for sealing a vacuum dressing depends on the size of the wound and the leaks — usually, approximately 2–20 mL per dressing. The silicone always was allowed to set completely (1 minute) before the pump was switched on again. If the silicone is not completely set, it can be sucked into the foam, compromising its use.

The silicone material was easily removed at dressing changes by pulling it off and then reapplied as described for each new NPWT dressing. Negative pressure was set at -125 mm Hg constant suction. Dressings were changed every 2–3 days.

The method described was used with all five patients presented. In one patient, silicone sealing was combined with Nu-Derm hydrocolloid dressings (Johnsen & Johnsen, Inc, Neuss, Germany).

Head and neck.
Case study 1. On September 1, 2010, 60-year-old Ms. A was admitted to the hospital with a suspected squamous cell carcinoma (SCC) of the right tonsil, cheek, and upper and lower jaw (see Table 1). Her medical history revealed long-time alcohol and nicotine abuse. Examination, imaging, and histological confirmation of the diagnosis were performed. After resection of the tumor, the defect was reconstructed on October 27, 2010, using a latissimus dorsi myocutaneous flap and a fibula osteomuscular flap. Following the surgical procedure, radiochemotherapy was initiated, which was discontinued prematurely at the patient’s request. During the postoperative course, a dehiscence of 2.5 cm^² appeared at the graft edges in the infra-auricular region. On November 16, 2010, NPWT with -125 mm Hg constant suction was applied. Airtightness of the NPWT dressing was compromised by an uneven and mobile surface formed by the earlobe and scarred contractions of the right lateral neck. Complete sealing of all leaks and maintenance of this sealing until the next dressing change was achieved using the silicone material (see Figure 1). After 17 days of NPWT, the dressing was removed. A residual wound of 0.5 cm^² with granulation tissue formation was closed by sutures and treated with panthenol ointment. After 7 days, wound healing was completed and sutures were removed.

Case study 2. On June 23, 2010, 60-year-old Mr. B was hospitalized because of extensive skin necrosis of the left extraoral submandibular region. Resection of a SCC of the left cheek and subsequent radiochemotherapy had been performed approximately 2 years prior. After this surgical procedure, the defect was reconstructed using a temporalis myofascial flap, a local pediculated pectoralis major myocutaneous flap, and an autologous iliac crest bone graft. Previous follow-up appointments had revealed necrosis ensuing from the graft edges. After necrectomy and wound debridement were performed, NPWT with -125 mm Hg constant suction was applied on June 24, 2010. The scars, earlobe, facial hair, mouth angle, and its humid milieu hampered maintenance of an airtight NPWT dressing. Detected leaks were sealed by silicone (see Figure 2). Initial wound size of 7 cm^² was reduced to 4 cm^² after 12 days of NPWT. On day 22 of NPWT, the wound size was 2 cm^². During every dressing change, wound size was reduced step-by-step with sutures, so high skin tension and risk of dehiscence could be avoided. The dressing was removed August 6, 2010. A superficial residual defect of 1.5 cm^² remained, which was treated with panthenol ointment in outpatient care and healed by secondary wound closure.

Abdomen.
Case study 3. On December 22, 2011, 66-year-old Mr. C was referred to the interdisciplinary operative acute care unit because of postoperative medical conditions and a complicated clinical course after left hemicolectomy, perforated sigmadiverticulitis, and peritonitis. Mr. C’s history revealed multiple allergies to antibiotics. On admission, he suffered sepsis syndrome, peritonitis, and fistulae of the bile duct and small bowel. On December 24, 2011, revision surgery with lavage of the abdomen, adhesiolysis and partial resection of bowel, occlusion of bowel fistulae, and bile-duct stent implantation were performed. Intravenous antibiotic therapy was initiated. Postoperative wound healing proceeded in a complicate^². For further treatment, nonsurgical therapy included NPWT at -125 mm Hg constant suction. Proximity to the colostomy with its humid milieu and the operation scar hampered airtight sealing of the NPWT dressing. Silicone and hydrocolloid strips were provided to maintain vacuum function (see Figure 3). After 9 days of NPWT, stable wound conditions with granulation tissue formation were achieved, and wound size decreased to 110 cm^². The patient was discharged to an abdominal surgery facility for further surgical treatment, with NPWT dressing in situ.

Lower extremity.
Case study 4. On November 20, 2011, Mr. D, a 57-year-old with rheumatism, was admitted to the orthopedic clinic with a pressure ulcer on the left heel and a wound dehiscence and necrosis of the left lower ankle joint. He had undergone an arthrodesis of the left rear foot with autologous bone interposition graft 3 months prior. Additionally, he was prescribed immunosuppressive drug therapy. After surgical debridement, a latissimus dorsi myocutaneous flap was transplanted on December 20, 2011 to reconstruct the defect in the region of the ankle joint. A necrosis occurred at the lateral graft edge on postop day 16. After necrectomy under local anesthesia, NPWT at -125 mm Hg constant suction was initiated. Simultaneous NPWT of the heel pressure ulcer and the graft was performed with one foam piece covering both wounds (GranuFoam Silver, KCI, Inc, Wiesbaden, Germany). A layer of adhesive drape was applied on the skin between both wounds to protect it from maceration (not shown in Figure 4). The curved surface and the operation scars caused the occlusive dressing to leak. Silicone was applied to maintain an airtight seal (see Figure 4). In addition to the NPWT, an antibiogram was performed for appropriate intravenous antibiotic therapy. The initial overall wound size of 14 cm^² was reduced to 7 cm^² after 11 days of NPWT. On February 3, 2012, the wound measured 3 cm^². During each dressing change, wound size was reduced step-by-step with few sutures, and healing proceeded in an uncomplicated manner; NPWT was suspended after 9 weeks. On March 20, 2012, Mr. D was released from the hospital.

Anogenital region.
Case study 5. Mr. E is a 64-year-old obese man suffering Fournier gangrene with pararectal and retroperitoneal abscesses and necrotizing fasciitis of the pelvic region and both thighs. He was admitted to the interdisciplinary operative acute care unit on November 23, 2011. His medical history included nicotine use and diabetes mellitus. On the day of admission, extensive necrectomy and surgical lancing of abscesses were performed under general anesthesia. Intravenous antibiotic therapy was initiated. After open wound treatment during the first postoperative days, NPWT was applied to the abdominal wall, genitals, and both thighs on January 26, 2012. NPWT application posed a challenge for the medical team because of numerous body folds and crevices (intergluteal fold, gluteal fold, inguinal folds), the body orifices (anus, external urethral orifice) with their humid milieu, the extensive wound size of approximately 700 cm^², and curved wound surfaces. Sealing was achieved using dental silicone to level the complex surface (see Figure 5). At each dressing change, wound size reduction of approximately 10 cm^² was achieved by successive suturing of the wound edges. After 12 days of NPWT at -125 mm Hg constant suction, the wound measured approximately 650 cm² and Mr. E was referred to a highly specialized wound care unit in stable medical condition with a NPWT dressing in situ.

Since the advent of NPWT as a potential wound management system, the range of indications in which it has been used has increased. Different wound locations and surface characteristics often require special techniques and aids, as well as an experienced user, for proper application of the NPWT.²⁷ In this context, maintaining an airtight seal in order to enable the NPWT dressing to function poses a common problem. The airtight seal is essential for NPWT functionality. Additionally, dressing leakage increases the risk of bacterial penetration, which can cause new infections.

In the cases described, silicone was used to seal NPWT dressings in wounds with challenging shapes, locations, and surroundings to facilitate use of NPWT. None of the silicone-sealed NPWT dressings failed to perform as designed until the next dressing change or caused dermal irritations of the skin.

Silicone is suitable for sealing because of its special features: biological compatibility and biodurability^23,24 that prevent skin irritations; simple and precise application using the cartridge delivery system with single-use tips and rapid setting, which enables economical utilization; and rapid and painless application and removal to improve patient comfort. No special skills are required from the user. In the authors’ experience, the technique of silicone sealing can be extended to all NPWT dressings using adhesive drape, irrespective of whether they work with gauze or foam. A small amount of silicone is needed for sealing one dressing, and the opened cartridge delivery system can be stored at 73˚ F for approximately 3 years as defined by the manufacturer.

Despite the advantages of silicone sealing, the costs for this product may be higher in comparison to other adjuvants such as stoma paste or hydrocolloid dressings. Thus, its use should be limited to the sealing of NPWT dressings covering complex wound areas with challenging conditions.

In addition, some cases have been reported of allergic contact dermatitis of the surrounding skin in patients with colostomy caused by components of the stoma paste or its removal wipes.²⁸ Craig²⁹ has described high biocompatibility of silicone impression material; his in vitro study has shown silicone material does not induce fibroblast response in cell culture. Thus, because of its high biocompatibility and its ability to remove the material without any adjuvants, medical silicone could be used with NPWT in patients who are allergic to a variety of dressings or who exhibit clinical signs of dermatitis.

The application by cartridge delivery system allows precise placement of the silicone, even directly under the affixed adhesive drape, so silicone also can be used as a repair material to save costs and efforts to apply a new dressing if leakage of a time-consuming and complex NPWT dressing occurs before regular dressing change.

When using silicone to seal vacuum dressings, several steps were identified that produced optimal conditions for adhesion of the occlusive dressing to the skin and prevented leakage of the NPWT system under complicated conditions:
    1) shaving and disinfecting the skin surrounding the wound;
    2) degreasing the skin using dermal-adhesion agents and careful drying;
    3) applying the NPWT system according to the manufacturer’s instructions; and
    4) visually and audibly inspecting the setup to identify leaks. After these four steps, silicone sealing can be performed as described.

In the authors’ experience, the use of light-body silicones with Shore hardness A 45±10 Shore and a short setting time of 1–2 minutes can be recommended for the sealing of NPWT dressings. In cases of extremely uneven or mobile structures surrounding the wound, the application of a silicone with lower viscosity and shore hardness can be considered.

The patients presented in this study had wounds surrounded by complicated surfaces (such as scars, skin folds, or curved surfaces), a humid milieu, or mobile structures. In these situations, medical silicone and its combined use with other adjuvants, such as dermal-adhesion agents and hydrocolloid dressings, maintained airtightness of the NPWT dressings. Medical silicone seems to be a useful aid in NPWT.

Maintaining an airtight seal when using NPWT in wounds surrounded by irregular surfaces sometimes poses a problem. Silicone is commonly used for intracorporeal and extracorporeal medical equipment. The authors present and describe their experience using silicone as an innovative material to obtain and maintain an airtight seal of NPWT dressings for wounds located in regions with special conditions. Silicone sealing combined with other products such as dermal-adhesion agents or hydrocolloid dressings were used in five patients and found to be an effective method of achieving good outcomes using NPWT.

Dr. N. Hendricks is a dentist, Department of Paediatric and Preventive Dentistry; Dr. J. Hendricks is and oral and maxillofacial surgeon, Department of Oral and Maxillofacial Surgery, Facial Plastic Surgery; Ms. Hoffmann is a wound care nurse, Department of Surgical Medicine, Wound, Ostomy and Kinesiatrics Management; Prof. Dr. Hemprich and Dr. Halama are oral and maxillofacial surgeons, Department of Oral and Maxillofacial Surgery, Facial Plastic Surgery, University Hospital Leipzig, Leipzig, Germany.

Please address correspondence to: Dirk Halama, DMD, MD, Department of Oral and Maxillofacial Surgery, Facial Plastic Surgery, University Hospital Leipzig, Liebigstrasse 10-14 Leipzig, Sachshen 04103, Germany; email: dirk.halama@medizin.uni-leipzig.de.