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NPWT and Pediatrics Part 2: Devices, Mechanism of Action, and Recommendations

Children With Wounds: Asking the Right Questions

NPWT and Pediatrics Part 2: Devices, Mechanism of Action, and Recommendations

Introduction

The pediatric community has been using negative pressure wound therapy (NPWT) successfully for various wounds, yet pediatric and neonatal guidelines for NPWT use do not exist. Evidence comes from case reports, series, and retrospective reviews. Questions arise about devices, settings, type of negative pressure therapy (NPT), tolerability, and efficacy. Before I touch on these topics, let’s review why NPWT can be useful.

Wound healing progresses through four physiologic interconnected phases, starting with hemostasis, inflammation, proliferation, and remodeling. Each phase has its key players. Platelets, growth factors, and cytokines are essential for immediate fibrin plug generation and bleeding control. Concomitantly they are signaling to neutrophils, monocytes, and macrophages to start the inflammatory phase with the area “cleaning,” cell apoptosis, and further cytokine and growth factors release. Growth factors prepare the wound bed for fibroblasts collagen production, angiogenesis, and extracellular matrix deposition leading to granulation and eventually epithelialization. We know that all wounds heal via these stages, whether acute, surgically closed or stagnant, chronic, or dehisced. The TIME acronym offers guidance on approaching wound healing, starting with tissue, infection or inflammation control, moisture balance, and edge viability. When I think about negative pressure therapy, I can see its usefulness in each of the TIME components as well as wound healing stages.  

NPWT Devices

Traditional negative pressure technology involves the use of a medical grade foam that is attached to a non-collapsible evacuation tube attached to a vacuum source. The foam can be reticulated polyurethane black ether foam (Granufoam, 3M + KCI), foam impregnated with silver, dense hydrophilic white foam, or perforated foam. The packing may not be a foam but an antimicrobial packing product. The reticulated foam dressing serves both to absorb wound exudate and to distribute evenly the negative pressure over the entire wound. An adhesive drape consisting of a transparent film is placed over the foam dressing and the tube, extending 3 to 5 cm beyond the edges of the wound, and is affixed to intact periwound skin, creating an airtight compartment over the wound bed. A perforated contact layer or petrolatum-impregnated gauze can be used as contact layers in more shallow wounds such as chest wounds. Antimicrobial medical honey, collagen dermal templates, hydrolyzed collagen powder/gel, amniotic-based products, or bilayer cellular dressings can be packed into the wound before closure. The evacuation tube is connected to a collection vessel, which is connected to an adjustable vacuum pump. The pump creates a negative pressure that pulls effluent from the wound into a collection vessel. Typically, the vacuum pump can be programmed to provide various amounts of negative pressure on an intermittent or continuous basis depending on the wound type.

Traditional NPWT is indicated for a variety of wounds, especially wounds with significant tissue defects, edema, and exudate production. The advantages of a traditional unit include adjustable pressure, ability to instill antimicrobial and cleansing agents, and intermittent mode, which in some studies has shown increased efficacy due to intermittent hyperemia around wound edges. There are some disadvantages to these units: in-hospital inpatient use leading to longer hospital stay, bulky equipment limiting mobility, limited parent–child interactions due to cumbersome equipment, painful removal and initiation of certain models, and difficulty in obtaining outpatient reimbursement.

Portable NPWT single-use devices have changed the way we manage vacuum-assisted closure (VAC), from lack of internal fillers to canister-less equipment allowing freedom of movement, earlier discharge home, and shorter hospital stays. These units work in part by exudate absorption but mostly evaporation; thus, they should be prescribed for mild to moderately exudative wounds (between 300 and 500 mL). The adhesive materials are often atraumatic (silicon) while the inside absorptive layers are often made up of special technology. 

Last month we talked about the PICO (Smith and Nephew Healthcare, Watford, UK) negative pressure system, with its special configuration of an internal absorptive pad. Outer high moisture vapor transmission rate film allows a high rate of evaporation, while the middle absorbent layer absorbs exudate and supports evaporation (20% absorption/80% evaporation); the inner airlock layer allows even distribution of negative pressure across the dressing. Different models can function continuously between 1 and 2 weeks, transmitting 80 mm Hg continuously. This is the most common portable single-use NPWT model we use in my hospitals. The wounds vary from acute trauma, dehisced surgical wounds, pressure injuries, severe extravasations, and wounds related to malignancies to high-risk wounds benefiting from incision support.

Other companies have modified their internal materials to include an absorptive gelling internal layer, such as the Avelle NPWT system by ConvaTec (Deeside, UK). On contact with exudate, the hydrofiber technology gel locks bacteria and exudate, contours to the wound shape to minimize dead space, and provides a soft interphase for the outer wound layer. The middle layer has special fenestrations, designed to augment evaporation, covered by the foam designed to distribute the negative pressure, and finally film that is also breathable, silicone made and continuing into the perforated border that is atraumatic upon removal. The post entry is soft, the connecting tubing is flat, and the working time is up to a month of continuous use and up to 80 mm Hg negative pressure.

These devices combine traditional mechanisms of action of VAC with evaporative capability.

Proposed Mechanisms of Action

Pressure gradient stimulates the movement of exudate and cells from the surrounding tissue to the wound bed to the absorptive layer of the device. We know that inflammatory cytokines exist in every wound bed. Certain ones are beneficial to granulation tissue formation, whereas others can be toxic, especially in excessive quantities. Removing excessive proteases, oxygen radicals, and cytokines maybe beneficial in reducing inflammation. In addition, inflammatory cytokines induce dermal/subcutaneous layer edema, causing decreased oxygenation and poor healing. Studies have suggested that NPT may pull this extra fluid, decrease edema, and increase oxygen and nutrients delivery to new extracellular matrix.1,2 

Mechanical deformation of the edges leading to macrostrain may pull an increased number of keratinocytes over the wound bed and support wound edges approximation. Computer models have demonstrated that pressures used in NPT are enough to deform cells by 20%, a change known to induce cell proliferation in vitro. This microstrain likely upregulates cell mitosis, cell proliferation, and angiogenesis3-5 via increased production of growth factors, upregulating extracellular matrix production.

Increased perfusion is another mechanism likely related to NPT success. Studies have demonstrated increased blood flow to the wound margins, especially for the first few minutes after continuous NPT initiation and even more so with intermittent pressure.6 Increased nutrients, growth factors, and oxygen delivery while removing waste would support the finding of increased granulation tissue development with NPWT. Microscopic evaluation of NPT-affected tissue has demonstrated increased vascular diameter as well as increased blood flow velocity and volume, leading to increased angiogenesis.7 

Finally, NPWT is an occlusive, absorptive, and protective dressing facilitating stable temperature, moist healing environment (especially with certain fillers), and continuous protection against outside elements without frequent dressing changes. NPT—similar to other surgical devices such as staples, sutures, and glues—can reduce lateral tension, minimize edge gaping, and approximate the edges closer. Closed-incision NPWT works specifically by this mode, providing preventive care, minimizing risk of surgical site infection, dehiscence, seroma or hematoma formation, or local skin ischemia and necrosis.

Efficacy and Clinical Outcomes

PWT has been used for a broad range of pediatric wounds. Overall, the results show that this therapy is efficacious and improves clinical outcomes, with very few side effects.8 Baharestani9 published a review of 24 pediatric wounds, of which 22 reached full closure with traditional VAC. Patients varied from newborns to adolescents and had dehisced sternal and abdominal wounds, pressure injuries, compartment syndrome, exposed bones/hardware, necrotizing fasciitis, and degloving injuries. The pressure settings varied from 50, 75, 100, and 125 mm Hg, with the youngest patients and those with sternal wounds receiving the lowest settings. She cautions about the potential for fistula development while using NPWT on abdominal wounds.

Another large pediatric review of traditional NPWT was published by McCord and colleagues.10 A total of 68 patients with 82 wounds were described. These patients varied from 7 days to 18 years old. The wounds included pressure injuries, extremity wounds, dehisced surgical wounds, open sternal wounds, and abdominal wall defects. In their series 93% of wounds decreased in volume while no major complications were identified. Minor complications were related to periwound dermatitis, bleeding from sponge removal, and pain with dressing changes. They also recommend lower pressures in young children and those with exposed viscera, in the range of 50 to 75 mm Hg, and noted that results were comparable to children receiving higher pressures. They highlighted safety and efficacy of NPWT in neonates with large abdominal wall defects, such as gastroschisis (extruded viscera), ruptured omphalocele, and large open abdomen. 

Multiple papers highlight the efficacy of NPT in dehisced sternal wounds. Agarwal et al11 reviewed 103 patients with open sternal wounds, including children from 3 months to 14 years. All tolerated NPT well, 68% were closed with the therapy, and the remaining progressed to decreased size and eventually closure by secondary intention. 

Wong and colleagues12 described use of NPT in pediatric oncology patients. A total of 66 patients (ranging from 10 month to 23 years of age) with 74 wounds had a 70% closure rate and great tolerance. Wounds varied from dehiscence, trauma, postsurgical, infections, pressure injuries, cutaneous cancer manifestations, extravasations, and vascular wounds. All wounds were related to various malignancies. The pressures applied during the continuous traditional NPWT varied between 75 and 125 mm Hg, and 3 different foams were utilized. 

Many papers have described the efficacy of portable single-use NPWT in pediatrics. Personally, I have published our experience with dehisced sternal wounds and sNPWT.13 I have used this modality on pressure injuries, extravasation injuries, open abdominal wall defects, dehisced wounds, oncologic wounds, and traumas. Lower pressure (80 mm Hg) is sufficient in my experience in older children and not too high even in the smallest of neonates. Neonates as young as 25 weeks’ gestational age are able to tolerate portable sNPWT. No perturbations in blood pressure, urine output, or electrolytes signifying hemodynamic instability were observed in any of my neonatal cases. The following are a few examples. All photos provided are with the consent of the patients’ parents.

Case Reports

Case 1. A 2-week-old neonate with failure to thrive due to congenital intestinal obstruction and repair was receiving total parenteral nutrition (TPN) and sustained severe extravasation. Sharp debridement was augmented with a few days of collagenase and eschar cross-hatching. Once the wound bed was prepared, sNPWT was applied. The wound healed completely (Figure 1).

Case 2. Sternal wound dehiscence after the first stage repair in a neonate born with hypoplastic left heart. The wound was infected and underwent gentle mechanical debridement before sNPWT placement (Figure 2).

Case 3. A neonate with a dehisced sternal wound for which dialkylcarbamoyl chloride (DACC)-coated ribbon (Cutimed Sorbact, BSN Medical, Charlotte, NC) was utilized as a packing antimicrobial element under sNPWT (Figure 3).

Case 4 is an example of a 28-week gestational age, 1-week-old neonate with intestinal obstruction requiring ostomy and mucous fistula creation. His abdominal incision dehisced. The smallest portable sNPWT was placed. Continuous 80 mm Hg pressure was tolerated without any hemodynamic instability (Figure 4).

Case 5 is an example of a neonate with dehisced myelomeningocele repair (severe form of spina bifida, characterized by a cleft in the vertebral column, with a corresponding defect in the skin, leading to exposed meninges and spinal cord). This case shows the use of sNPWT hydrofiber technology to enhance closure and eliminate periwound seroma. The infant had an 8-cm incision. On postoperative day 3, two (2) areas of dehiscence were noted in the lumbar and mid-thoracic area. Wound culture results were negative. The patient had significant bowel incontinence. Keeping the incision clean was challenging. A portable sNPWT unit (Avelle, ConvaTec) was placed on the infant. A hydrocolloid ridge was constructed in the bottom of the dressing, serving as partial barrier for stool contamination. After 10 days the wound was closed in both locations (Figure 5).

General Recommendations About Neonatal and Pediatric NPWT Application

Both traditional and single-use portable NPWT units are safe to use in pediatric patients. Consider delivering lower pressure (60–80 mm Hg) via traditional units in neonates and young children because the threshold for circulatory instability can vary. Portable sNPWT units deliver 80 mm Hg, which seems effective and safe from personal experience.

Intermittent NPWT causes more pain and may not be the optimal choice in pediatrics; if used, pain consideration is paramount.

Consider discontinuing pressure application 15 to 20 minutes before dressing removal; it decreases pain upon removal.

Always apply silicon-based dressing remover to the edges of the dressing/drape. It releases the adhesive bond between epidermis and dressing, minimizing epidermal stripping and pain.

Apply a non-alcohol liquid barrier to periwound skin before applying the dressing/drape.

Consider premedication with analgesics before therapy initiation and dressing changes, especially in young children and adolescents. If they remember a painful experience, the next change will be more challenging. If available, Child Life Services can be a great asset because distraction can be the key to a less painful or anxious experience.

Neonates often tolerate dressing changes with sugar water (oral sucrose solution), swaddling, and positioning; a low threshold for analgesic medication is important. 

If traditional units are used, granulation tissue ingrowth into foam and bleeding should be minimized. I find those issues less with white foam compared with black, but I also like placing a contact layer on the wound bed first as well as on top of the foam.

Combining NPWT with various products can have a positive synergistic effect. Medical grade honey can provide some antimicrobial, pro-granulation, and debriding effects. Soft, DACC-coated ribbon can provide an antimicrobial hydrophobic surface and a filler. Collagen dermal template or hydrolyzed collagen work really well with NPWT, as well as amniotic membrane/umbilical cord–based products. ν

Affiliation

Dr. Boyar is Director of Neonatal Wound Services,  Cohen Children’s Medical Center of New York, New Hyde Park; and Assistant Professor of Pediatrics, Zucker School of Medicine, Hofstra/Northwell, Hempstead, NY. This article was not subject to the Wound Management & Prevention peer-review process.