NPWT has been used to treat wounds in numerous different anatomical locations, with different levels of complexity and varying pathologies. The following section will review the evidence available on the application of NPWT in different wounds.
Basic applications of NPWT: At its most basic application, NPWT has been used in the management of open wounds, where the foam is directly applied to the wound bed. Common targets are poorly healing ulcers such as those caused by diabetes, venous or arterial pathologies and pressure necrosis.
More specifically, NPWT has been found to promote wound area reduction, wound bed granulation and clearance of microbial infection in diabetic foot ulcers. NPWT has been associated with a higher rate of limb salvage. Furthermore, treatment of diabetic, arterial and venous ulcers in high-risk patients using NPWT results in a higher rate of successful closure, with the greatest difference seen in venous ulcers. When NPWT is applied earlier on in the treatment these wounds display faster healing times. In nonoperative treatment of scleroderma ulcers, NPWT has been found to prevent digit amputation. In the treatment of pressure ulcers, NPWT has been shown to reduce the surface area, volume and depth of wounds, to enhance granulation and to decrease the likelihood of hospitalisation[39,49,50]. Vowden K NPWT may also be effective in treating nonhealing deep-pressure ulcers covered by soft-necrotic tissue which require rapid formation of granulation tissue. It is important to be noted that NPWT needs to be used concurrently with disease specific treatment, for example medical treatment for vasculitis and pyoderma gangrenosum.
In the treatment of surgical wounds, NPWT often acts as the pre-treatment before a skin flap or graft, or before secondary closure with NPWT. More specifically, in the excision of melanoma, NPWT enhances both functional (improves vascularity) and cosmetic (scar reduction) outcomes, whereas in the postoperative treatment of lymphangioma in children it is believed to decrease the risk of recurrence and infection.
Skin graft and dermal scaffold recipient site preparation: NPWT is often used to prepare a recipient site for skin grafts and dermal scaffolds. Large wounds, where granulation tissue spans the entire wound, can be rapidly closed with autologous skin grafting. One prospective RCT investigated the efficacy of NPWT prior to skin grafting in patients with acute traumatic wounds. NPWT improved total successful graft uptake, decreased regrafting, and required shorter lengths of hospital stay.
Dermal scaffolds are often used in wounds where tendon or bone is exposed to induce vascularization of the wound bed in preparation for skin grafting[56,57]. Concurrent treatment with NPWT and dermal scaffolds (Matriderm, Dr Suwelack Skin and Health Care AG, Billerbeck, Germany) enhances the contact between the wound surface and the scaffold and is believed to result in scars with higher elasticity and more natural skin pigmentation, and a decreased occurrence of postoperative wound contamination one year post-operatively.
Combination therapy: Various bioactive factors have been incorporated in NPWT to enhance efficacy.
Silver has been used in various wound dressings and has proven useful in burn care. In NPWT therapy, silver was added to the coating of the PU foam in order to decrease the bacterial load in the wound. In a goat model of complex infected orthopedic wounds, silver dressings placed beneath the negative pressure dressings resulted in a decrease in the bacterial load, most notably in the numbers of S. aureus. The MDWT foam can be modified to contain silver in order to act as an antimicrobial agent, as has been used in wound bed preparation for substantial split-thickness skin grafts (STSGs) to treat recalcitrant venous stasis ulcers. However, silver-infused dressings are not always indicated.
A combined treatment of NPWT, platelet-rich plasma (PRP), STSGs and bilayered acellular matrix grafting was found to completely heal a large necrotizing fasciitis wound in a patient with diabetes. Furthermore, one study used a combination therapy of PRP and NPWT on patients with sternal osteomyelitis and sinus tract after thoracotomy. The treatment regimen was PRP gel on the day of surgery followed by continuous NPWT for 20 d. This combination therapy was found to shorten the sinus tract sealing time, wound healing time, and length of hospital stay. Secondary repair surgery was also avoided.
Instillation therapy is the injection of fluid, such as normal saline, into the wound through a port on the NPWT connecting tube to enhance wound healing (Figure 7). This technique has been successfully applied in massive venous stasis wounds to reduce bacterial concentrations in the wound prior to STSG. A single-delivery-instillation system, whereby a series of intermittent cycles of MDWT was followed by a single injection of dilute sodium hypochlorate solution, appeared to create good wound bed preparation.
Figure 7 Instillation vacuum-assisted closure.
Fluid, such as normal saline, is instilled into the wound through a port on the connecting tube to enhance wound healing. Reproduced from, Huang C, Leavitt T, Bayer LR, Orgill DP. Effect of negative pressure wound therapy on wound healing. Curr Probl Surg 2014; 51: 301-331. Copyright 2016 by Elsevier.
In continuous-instillation MDWT a second port is connected to the continuous-drip system, which can allow continuous instillation of a fluid, for example insulin, to decrease the time required for wound healing. In full-thickness excisional wounds in a porcine model, NPWT with simultaneous irrigation with polyhexanide biguanide (PHMB) or saline showed improved wound healing with either irrigation solution when compared with NPWT alone. Other factors which can be instilled are dilute Betadine, doxycycline, phenytoin and lactoferrin. Further research is needed to investigate the efficacy of this concept. Instillation MDWT has been recommended in patients with multiple comorbidities with difficult wounds, although without high level of evidence to support these recommendations.
Further examples of adjuvants include platelet gel, activated protein C, arginine-rich dietary supplements, and Manuka and Leptospermum honeys. Platelet gel, added to the wound bed following initial NPWT, has been used in the treatment of a nonhealing ileocutaneous fistula leading to complete wound healing. In orthopedic wounds, activated protein C, an anticoagulant, was injected into the wound bed resulting in a decrease in the area and depth of the wound and an increase in granulation tissue formation. Studies on the use of arginine-rich dietary supplements, which are believed to enhance local circulation at the wound bed, have shown that treatment with the supplements results in complete healing of infection-induced wound dehiscence with only one month of treatment and no recurrence at the 6-mo follow-up. Leptospermum and Manuka honeys have been used in the treatment of a nonhealing postsurgical wound and an abdominal phlegmonous lesion, respectively[73,74].
NPWT in burns: NPWT has been found to preserve perfusion in acute partial-thickness hand burns. It has also been used as a dressing over a dermal substitute in burn wounds, where it was believed to have no effect on graft adherence, but did improve long-term scar elasticity. When NPWT was used with porcine acellular dermal matrix (ADM) dressing as combination therapy in deep burn wounds it was found to decrease wound exudate and bacterial load and promote wound healing. NPWT has also been used in a patient with major third and fourth-degree high voltage electrical burns to enhance granulation tissue formation in preparation for skin grafting. Through the use of NPWT, major chronic soft tissue defects in the right leg were covered and amputation was avoided.
Treatment of deep infected wounds: The efficacy of NPWT in deep wounds has been studied using soft tissue blast injuries in porcine models. In these models, NPWT was found to decrease bacterial load, inhibit infection-induced tissue necrosis, and induce early initiation of granulation tissue formation. Research on humans has shown that NPWT is effective in controlling infection, specifically in thoracic and abdominal wounds.
NPWT in open fractures: NPWT has also been used in the treatment of open wounds with exposed bone or joints, where it is believed to keep the wound moist, warm and sterile by preventing external contamination. The rate of wound healing in open fractures has also been shown to be expedited with NPWT. Furthermore, the rate of deep infection in open tibial fractures is believed to be lower in NPWT treated wounds than in conventional treatment. Treatment with NPWT in an open left knee-joint wound, induced formation of granulated wound bed which fully covered the exposed bones and joint. NPWT is especially important in cases where free-flap transfer is contraindicated[82,83]. NPWT in Gustilo grade IIIB open tibial fracture treatment helps reduce the size of the flap required but can also eliminate the need for a flap transfer all together. However, it should be noted that treatment with duration longer than 7 d was associated with higher likelihood of infection and amputation. NPWT in patients with grade III open fractures significantly reduced bacterial load at the wound site, as well as decreasing the risk of recurrent infection.
Deep sternal wound infection: Use of NPWT as the first line of therapy in deep sternal wound infections (DSWI) has been shown to decrease rates of early reinfections, as well as reducing numbers of late chronic sternal infections and mortality. The length of hospital stay is also shortened by 1 wk. In methicillin-resistant DSWIs following cardiovascular surgery, MDWT has been shown to decrease length of hospital stay, healing time, and infection recurrence.
NPWT is believed to have the ability to stabilize the thoracic cage, improving hemodynamics and pulmonary status. NPWT in conjunction with a tissue flap can provide adequate control of infection preventing sepsis and hemodynamic instability. In the presence of poststernotomy osteomyelitis, adequate debridement and antibiotic therapy is still necessary with the use of NPWT[90,91].
NPWT as an augmented surgical drain: NPWT enables improved drainage of the fluid which builds up in anatomical cavities or abscesses in deep wound infections. For example, application of NPWT in the treatment of a deep neck abscess reduced the need for open thoracotomy by preventing accumulation of purulent material. Concurrent open window thoracotomy and NPWT was found to eradicate local infection and hence control sepsis in postoperative or recurrent pleural empyema. In complex chest wall wounds NPWT inhibited empyema recurrence and enhanced lung expansion. A modified NPWT therapy has been used to treat deep cavitary defects, such as those caused by blast injuries or high-velocity projectiles. By connecting a superficial foam dressing to the surgical drain, deep cavitary defects can be converted into superficial ones. This modified therapy can apply suction deep in the wound cavity and result in a decrease in the dead space, reduced edema and lower risk of infection. In comparison to traditional VAC therapy, draining is enhanced, and the risk of deeper cavities closing off is minimized. VAC therapy has been successfully used in cases of Hidradenitis suppurativa where immediate primary closure was not possible secondary to the large size of the defect. An internal VAC was found to accelerate delayed closure and reduce the rate of recurrence in hidradenitis excisions.
NPWT as biologic sampling device: NPWT is increasingly being used as a biologic sampling device, where mediastinal fluid is collected from the wound and cultured for microorganisms. In one study, NPWT was found to increase the rate of detection of microorganisms and was recommended as a replacement to traditional biologic sampling devices. On the other hand, microbiology of NPWT specimens in patients with prosthetic vascular graft infections was found to have limited diagnostic value, with anaerobe species being the most poorly identified in NPWT foam samples. Additional studies are, however, required before general conclusions on the efficacy of NPWT as a sampling device can be drawn.
Intra-abdominal NPWT: A further potential target for NPWT are deep intra-abdominal wound infections.
Specifically, in a case of acute necrotizing pancreatitis, placement of NPWT foam dressing in the opening created during lesser sac marsupialization in classical laparotomy was found to accelerate wound closure, hence improving patient outcome. In addition, examination of wound secretions improved, abdominal compartment syndrome was prevented and care was overall simplified. NPWT has also been successfully used endoscopically in the treatment of rectal wall anastomotic disruptions.
NPWT and gynecological laparotomy: NPWT has also been used as a prophylactic measure in laparotomy wounds in patients with gynecologic malignancies. The rate of wound complications was similar in patients who received traditional treatment and those receiving prophylactic NPWT dressing, despite those receiving NPWT having significantly higher BMIs.
NPWT and soft-tissue sarcomas: NPWT has been shown to be safe and effective as an adjunct to wound closure in cases of wide tumor resection for soft-tissue sarcomas. Continuous suction, with pressures from -200 to -300 mmHg, was applied on the soft-tissue defects as preparation for wound closure. This treatment was found to decrease wound complications, such as post-operative infection and recurrence, while also reducing edema, draining exudate, and promoting granulation tissue formation.
NPWT and congenital deformities: NPWT holds potential for the treatment of congenital deformities such as giant omphalocele or complex gastroschisis. However the efficacy for this has yet to be established and the treatment is not approved by the Food and Drug Administration (FDA). In pediatric patients, the granulation tissue response is often much more robust than in adults, often leading to more frequent dressing changes to avoid ingrowth into the interface material.
NPWT and digestive surgery: Most recently, there have been suggestions of using NPWT in digestive surgery, however this use is yet to be established. One previous pilot study investigated NPWT use following ileocecal resection in Crohn’s disease and found that NPWT shortened length of hospital stay by 70%-80%. It is important to note that one major concern of NPWT use in digestive surgery is the development of enteric fistulas due to negative pressure. Prophylactic NPWT at the ostomy closure wound in patients with ulcerative colitis was found to be safe with no enterocutaneous fistula formation or postoperative bleeding. However, in this particular study, no effect on the duration of wound healing was observed and the prophylactic efficacy of NPWT could not be proven. Further studies are needed to prove the efficacy of NPWT in digestive surgery.