INTRODUCTION — Negative pressure wound therapy (NPWT), also called vacuum-assisted wound closure, refers to wound dressing systems that continuously or intermittently apply subatmospheric pressure to the system, which provides a positive pressure to the surface of a wound. NPWT has become a popular treatment modality for the management of many acute and chronic wounds .
Subatmospheric pressure has multiple beneficial effects on wound healing in animal models. However, clinical evidence of its superiority over conventional wound dressing techniques for all wound types has not been proven. The available randomized trials have significant heterogeneity in the nature of wounds treated and in primary and secondary endpoints, making rigorous comparisons difficult and limiting the ability to generalize their results.
The general mechanism of action of NPWT, its clinical uses and contraindications, placement and management of the device, and efficacy in specific clinical applications will be reviewed here.
DEVICE AND PLACEMENT — Commercially available systems for negative pressure wound therapy (NPWT) include the vacuum-assisted closure (VAC therapy) device and the Chariker-Jeter wound sealing kit. VAC therapy is the most widely studied system in randomized trials.
NPWT systems consist of an open-pore polyurethane ether foam sponge, semiocclusive adhesive cover, fluid collection system, and suction pump . The following steps are involved in placing the device (figure 1):
●The foam sponge is trimmed to fit the size of the open wound and placed into the wound, taking care that the foam does not extend beyond the margin of the wound.
●The foam is then secured beneath an adhesive sheet. A hole is cut in the adhesive and a suction port (more than one may be used) with tubing placed; the tubing extends to a disposable collection canister.
●A portable pump is connected to the suction tubing. The pump applies -50 to -175 mmHg of continuous or intermittent suction, which reduces the volume of the foam by up to 80 percent . The porous nature of the polyurethane foam evenly distributes subatmospheric pressure throughout the foam, resulting in a positive pressure to the surface of the wound [4,5], and it also provides a conduit for fluid removal from the wound surface to the collection system. (See 'Mechanism of action' below.)
When fragile structures are present within the wound, they should be protected with an interposition layer placed beneath the foam. The interposition layer should slide easily over the tissue. Examples of materials used as interposition layers include mesh (eg, Vicryl) or petrolatum gauze . Denser foams (eg, white) may also be used for this purpose.
Dressing changes — The dressing and tubing are typically changed every 48 to 120 hours (two to five days) depending upon the clinical situation. The device is turned off and the semiocclusive dressing is removed. The sponge is carefully removed. If it is adherent to the underlying granulation tissue, the sponge can be soaked with saline and allowed to sit for a few minutes before removal. If pain is excessive during sponge removal, the sponge can be soaked with topical Xylocaine without epinephrine, prior to its removal either directly or via the suction tubing (suction off) . Pain is controlled more effectively when analgesia is administered prior to the dressing change.
Wounds treated with NPWT may become malodorous, and infection may be suspected; however, bacterial counts typically remain low . Hydrotherapy at the time of dressing changes, or the placement of a silver-containing interposition layer (table 1), can help reduce contamination and odor and may reduce healing time . Alternatively, NPWT can be withheld for a day or two. (See "Basic principles of wound management", section on 'Antiseptics and antimicrobial agents'.)
Pain management — Most patients do not complain of significant pain with NPWT between dressing changes. However, NPWT is most often painful when applied circumferentially or on intermittent cycle with high intensity, or if applied under excessive stretch. Pressures may be adjusted (ie, less negative would cause less force on the wound). Appropriate pain medication should be given as the need arises (eg, acetaminophen with codeine).
Patient training and counseling — The patient should receive training on how to use the device and be comfortable managing the device at home. Patients should be monitored frequently in an appropriate care setting by a trained practitioner. Leak or blockage in the system are most common; bleeding is potentially the most significant complication. The patient should be informed of the potential complications associated with the device, and of the necessity to seek medical assistance immediately if bleeding is observed. (See 'Complications' below.)
MECHANISM OF ACTION — Negative pressure wound therapy (NPWT) accelerates wound healing. Normal wound healing progresses through the following phases: hemostasis, inflammation, proliferation, and remodeling.
Both systemic and local wound factors can contribute to delayed wound healing. Systemic factors (eg, poor nutrition, wound ischemia) should be identified and corrected to the extent that is possible. (See "Management of chronic limb-threatening ischemia" and "Overview of lower extremity chronic venous disease" and "Overview of perioperative nutrition support", section on 'Nutritional assessment in the surgical patient' and "Clinical assessment and monitoring of nutrition support in adult surgical patients", section on 'Initial assessment of nutritional status'.)
Local wound factors that interfere with normal healing include desiccation, tissue edema, excessive exudate, poor tissue apposition (eg, grafts and flaps), and wound infection. Stagnant fluid is associated with cytogenetic factors that impede wound healing [7-13].
Animal studies have shown that subatmospheric pressure improves the local wound environment through both direct and indirect effects; these effects accelerate healing and reduce the time to wound closure [14-18].
Direct effects — The semipermeable dressing of the negative pressure system maintains a moist and warm environment that is stable and more conducive to wound healing. The closed system generates a pressure gradient between the wound and suction canister that promotes fluid transport, first from the wound bed, and then from the interstitial space, reducing wound edema. Fluid is removed through the application of pressure, similar to the manner in which compression stockings support fluid removal in venous stasis disease.
The open porous structure of the foam distributes subatmospheric pressure throughout the foam, resulting in a positive pressure to the wound surface . The actual pressure applied varies but is usually in the region of 5 to 10 mmHg. The exact pressure experienced depends upon the negative pressure delivered, the nature of the wound, and its application (whether circumferential, a cavity, or a surface). Clinical judgment should therefore dictate the pressure settings applied, as certain patients' circulation may be impaired.
The foam also contracts, drawing the edges of the wound together, firmly bolstering any skin grafts or flaps that are present [2,19]. The degree of tissue deformation depends upon the stiffness of the tissue; scar tissue has less mobility and will have less of a response. Tissue deformation is an important stimulus for tissue remodeling mediated at the cellular level [19,20].
Indirect effects — NPWT is associated with a variety of indirect effects that promote wound healing . These include:
●Alterations in blood flow – The increased wound surface pressure alters the blood flow [4,15,21,22]. It was initially suggested that NPWT increases perfusion in the wound, thus stimulating healing. However, thermography and other studies have shown that due to the positive pressure applied to the wound surface, perfusion is actually reduced, at least transiently [5,23-27]. This initial relative ischemia stimulates the release of growth factors and other vasoactive agents, resulting in increased granulation routinely seen clinically, which is more prominent with the use of intermittent or variable NPWT settings, compared with the continuous setting. Excessive pressures applied to the system (more than -175 mmHg) will decrease blood flow .
●Diminished inflammatory response – Reductions in systemic (eg, interleukins, monocytes) and local mediators of inflammation have been demonstrated in experimental models . In humans, decreased matrix metalloproteinase activity has been documented in patients treated with NPWT .
●Altered bacterial burden – A reduction in bacterial burden was noted during the first clinical experiments evaluating NPWT, but the results were variable in later studies [15,30,31]. In a randomized trial, for example, both increasing and decreasing bacterial loads were seen depending upon the initial culture result .
●Changes in wound biochemistry – Mechanical deformation alters the local environment through the process of mechanotransduction (conversion of mechanical stimulus into chemical activity). In vitro, stretch increases human fibroblast growth and migration . In an animal wound closure model, the rate of wound closure was significantly higher in the NPWT group compared with controls that used gauze-only dressings at day 7 (54 versus 43 percent) .
INDICATIONS — The application of negative pressure to assist in wound healing was first described in the management of soft tissue injury in association with open fracture . The demonstration of beneficial effects in animal models spurred the development of the negative pressure wound systems that are widely available [15,34].
Negative pressure wound therapy (NPWT, also called vacuum-assisted wound closure) has been applied to a wide range of clinical situations, including the open abdomen, following surgical debridement of acute or chronic wounds (eg, orthopedic, necrotizing infection, pressure ulcer), diabetic foot ulcers, and reconstructive surgery (eg, burns, skin graft, muscle flap) [1,35]. It has also been used in an effort to prevent surgical wound infection (ie, prophylactic) and as a means of instillation therapy.
Advantages — Compared with traditional wound care modalities, NPWT offers several clinical advantages compared to usual care.
●Traditional therapy of complicated or dirty wounds usually consists of moist dressings that are changed up to three times daily. If too much time elapses between dressing changes, the gauze may become painfully adherent, and its removal may debride desirable granulation tissue as well as devitalized tissue. Much of the pain associated with wound care occurs during dressing changes. In contrast, NPWT dressings are changed less frequently (eg, two to five days), and anticipated pain can be managed preemptively. (See 'Device and placement' above and 'Dressing changes' above.)
●Compared with other forms of wound dressing, NPWT is easier to tailor and maintain in position. Almost every configuration of wound, including circumferential extremity wounds (ie, degloving injuries) and wounds located in proximity to orthopedic fixation frames, can be managed with relative ease [36-38]. As a result, NPWT may allow less complex modes of reconstructive surgery.
●Accelerated wound healing with NPWT significantly reduces the time to wound closure in diabetic patients, returning these patients to baseline more quickly and improving quality of life . (See 'Chronic wounds' below.)
Disadvantages — From the patient's perspective, the main disadvantage of NPWT is the need to carry the portable pump.
NPWT systems are more expensive than traditional wound dressings. However, the overall cost of wound care depends upon the frequency of dressing changes, need for skilled nursing care, and duration of treatment. Significant clinical reductions in time to wound closure would be needed to offset the increased cost of the device and special supplies for NPWT to be cost effective, but data are limited.
Contraindications — NPWT should not be used when any of the following are present :
●Exposed vital structures – NPWT, in the presence of exposed organs, blood vessels, or vascular grafts, increases the risk for tissue erosion, which can lead to enteric fistula or hemorrhage [17,41]. NPWT is generally avoided until an intervening granulation layer or tissue flap or graft provides coverage. Although some clinicians report success using barrier dressings, caution is advised when implementing this practice. (See 'Device and placement' above and 'Complications' below.)
●Presence of malignant tissue – As with normal tissues, growth of malignant tissue is promoted in the presence of subatmospheric pressure. Malignant tissue is also more friable and prone to bleeding [2,17]. (See 'Bleeding' below.)
Relative contraindications include the following:
●Ischemic wounds – Although not absolutely contraindicated, no benefit has been demonstrated with the use of NPWT in patients with ischemic wounds . The application of negative pressure to these wounds would be expected to worsen tissue ischemia, in keeping with the biomechanism of this device. (See 'Chronic wounds' below.)
●Ongoing infection or devitalized tissue – Adequate debridement of devitalized tissue and treatment of infection should generally be undertaken prior to using NPWT . However, instillation therapy has allowed the use of NPWT in the presence of infection, or to augment the surgical management of infection. (See 'Indications' above and "Acute cellulitis and erysipelas in adults: Treatment" and "Necrotizing soft tissue infections".)
●Fragile skin – Caution should be used when using NPWT in patients with fragile skin due to age, chronic corticosteroid use, or collagen vascular disorder. Shearing forces at the wound margin can lead to skin avulsion and necrosis. NPWT may nevertheless offer considerable benefits in at-risk patients if the perimeter of the wound is adequately protected.
●Adhesive allergy – NPWT requires an adequate seal to maintain the applied suction. The adhesive cover typically overlaps the skin 4 to 5 cm with a significant amount of adhesive in contact with the patient's skin. Sensitive patients can develop shearing of the skin and bullae formation.
Overall efficacy — Multiple systematic reviews have sought to evaluate the efficacy of negative pressure wound therapy (NPWT), but none have reached definitive conclusions [3,35,42-49]. The most rigorous of these reviews identified eight randomized trials that met three inclusion criteria: randomized, chronic wound, and specific endpoints . NPWT was used to treat diabetic ulcers, pressure (decubitus) ulcers, or chronic lower extremity ulcers. The primary endpoints were one of the following:
●Time to complete healing
●Days to reach 50 percent of initial wound volume
●Percent reduction in wound surface area
●Percent decrease in wound length, width, depth, or volume
●Days until ready for surgery
Because only one study was available for each endpoint, comparisons could not be made. Even if a meta-analysis were able to be performed, there would still be the question of whether chronic (or acute) wounds of differing mechanisms in different patient populations should be compared to each other.
Another approach evaluates the available data (observational and randomized trials) for a specific clinical situation such as wounds from acute injury (eg, trauma, burns, surgical debridement) [35,45,46,50], wounds in diabetic patients (eg, ulcers, postoperative wounds) [43,48], open abdomen , and open sternum (eg, following debridement) . Available trials are presented for these individual clinical situations.
Acute wounds — Acute wounds are often traumatic but can also be due to surgical debridement of infected or necrotic tissue. Management of necrotizing soft tissue infection requires extensive and repeated surgical debridement. The debrided regions often present a wound dressing challenge due to anatomic location (eg, Fournier's gangrene), the size of the tissue defect, or the patient's body habitus. (See "Necrotizing soft tissue infections", section on 'Surgical debridement'.)
The open wound that results is often substantial. For most patients, the question is generally when, not if, their wounds will heal. The time interval required until either secondary closure can be performed or healing by secondary intention occurs is variable and depends upon the size of the defect and the patient's overall clinical status (eg, other injuries, nutrition, comorbidities).
NPWT dressings can be applied immediately following operative debridement, which simplifies postoperative wound care. The ability of the foam and adhesive dressing to conform to almost any wound contour, shape, or size contributes to the success of NPWT, as detailed in case reports, in these complex wounds [51-54]. NPWT can also be used in conjunction with skin grafts or flaps, which are frequently needed to cover tissue defects.
NPWT has been used instead of traditional bolstering methods to provide skin graft fixation [35,55,56]. The NPWT dressing ultimately distributes a positive pressure uniformly over the surface of the fresh graft, immobilizing the graft with less chance of shearing . Improved qualitative skin graft take and quantitative improvements in skin graft success (eg, reduced number of repeat grafts) have been described in observational studies [58-61] and two randomized trials [62,63]. In one of the trials, 60 patients were randomly assigned to conventional bolster dressing or NPWT following split-thickness skin graft . NPWT was associated with significant reduction in the loss of graft area (0 versus 4.5 cm in the control group) and the median duration of hospitalization (13.5 versus 17 days). (See "Skin autografting", section on 'Graft immobilization'.)
For acute open wounds, NPWT is associated with a reduced time to wound closure [30,31]. As an example, one trial randomly assigned 54 patients with open wounds to receive either NPWT or moist saline dressings . The NPWT group had healthier-appearing wounds and significantly faster reduction of the wound surface area (3.8 versus 1.7 percent per day).
NPWT has also been used to manage acute wounds resulting from lower extremity fasciotomy, degloving injury, open amputation, and complex traumatic wounds with exposed tendon, bone, or orthopedic hardware. These wounds are typically large and difficult to dress. Systematic reviews have not identified any randomized trials; however, the available observational studies suggest that NPWT is safe and with an efficacy comparable to standard dressings [46,64]. The primary clinical advantage of NPWT in the trauma population is its ease of application, decreased number of dressing changes, and reduction in the complexity of subsequent reconstructive procedures [34,58,59,65-69].
NPWT may have a particular role in the treatment of burn wounds. Impairment of blood flow in the zone of stasis may lead to burn wound progression (ie, partial-thickness burn becomes full-thickness burn). In animal models, subatmospheric pressure increases burn wound perfusion and limits this progression  (see 'Mechanism of action' above). Anecdotal case reports and small case series have reported NPWT in the treatment of acute burn wounds [45,71,72]. Two studies have looked at bilateral hand burns as a model: one hand is treated with conventional dressings and the other with NPWT [71,72]. A significant clinical advantage of the NPWT group was the ability to position the hand without the need for additional splinting. These preliminary studies have demonstrated the safety and feasibility of NPWT in burn patients.
Chronic wounds — NPWT may improve the healing of some types of chronic wounds/ulceration, such as diabetic foot ulcers, pressure ulcers, and open abdomen, provided that the wounds are well vascularized [37,46,73,74]. (See "Overview of treatment of chronic wounds", section on 'Negative pressure wound therapy'.)
Patients with extremity wounds and inadequate peripheral pulses should undergo noninvasive vascular testing to confirm adequate perfusion prior to instituting NPWT, especially patients with diabetes or other risk factors for peripheral artery disease. (See "Noninvasive diagnosis of upper and lower extremity arterial disease".)
Venous stasis ulcers are uncommonly confused with other types of chronic ulcers. These ulcers are associated with significant wound edema and exudate, and while they are managed with local wound care and compression therapy, NPWT may be useful for initial management of wound exudate and for wound bed preparation for skin grafting or use of skin substitutes. (See "Skin substitutes" and "Skin autografting" and "Medical management of lower extremity chronic venous disease", section on 'Ulcer care'.)
Post-sternotomy mediastinitis is an uncommon but devastating complication of cardiac surgery with high morbidity and with mortality . Management consists of aggressive debridement, antibiotics, and wound care, which may include the use of NPWT to manage the open wound or for instillation therapy while awaiting sternal closure. The use of NPWT in this population is discussed in detail elsewhere. (See "Surgical management of sternal wound complications", section on 'Negative pressure wound therapy'.)
Prophylactic use — Evidence suggests that there may be a role for prophylactic NPWT. Numerous small trials have been performed in a variety of surgeries and have suggested that rates of surgical site infection (SSI) for some incision types may be lower if NPWT is used on overlying closed incisions, rather than conventional wound dressings. The mechanism of incisional NPWT may involve bolstering, stabilization of the wound, or reduced shear across the incision and any combination of these. In a meta-analysis of 31 trials, prophylactic NPWT reduced SSI compared with standard dressings (8.8 versus 13.0 percent; relative risk [RR] 0.66, 95% CI 0.55-0.80) . Among the studies evaluating other outcomes, the rate of deep SSI, hematoma, seroma, blisters, wound dehiscence, pain, reoperation, and death was similar between the groups. Overall, NPWT was not cost effective. Before any recommendation can be made regarding the use of prophylactic NPWT, larger randomized trials with longer follow-up are needed to assess benefits in specific wound types and patient populations and cost effectiveness.
●Abdominal and pelvic surgery – NPWT for closed abdominal incisions may reduce SSI compared with standard therapy, particularly among those at risk for wound complications. The risk of SSI depends upon a number of factors, including the urgency of the procedure. (See "Overview of the evaluation and management of surgical site infection", section on 'Incidence and risk factors'.)
The role for prophylactic NPWT following emergency surgery was evaluated in a meta-analysis that included seven studies (two trials, six observational studies) . The rate of surgical site infection (superficial/deep) was lower for prophylactic NPWT compared with standard dressings alone (13.6 versus 25.1 percent; odds ratio [OR] 0.43, 95% CI 0.30-0.62) as was the rate of overall wound complications (15.9 versus 30.4 percent; OR 0.41, 95% CI 0.28-0.59). Abdominal and pelvic incision closure is discussed more fully in separate topic reviews. Cost effectiveness was not evaluated in this study. (See "Clinical features, diagnosis, and prevention of incisional hernias", section on 'Prevention' and "Principles of abdominal wall closure", section on 'Negative pressure dressings' and "Cesarean birth: Overview of issues for patients with obesity", section on 'Negative pressure wound therapy'.)
●Vascular surgery – Prophylactic NPWT has been used following abdominal aortic surgery (open and endovascular) and following lower extremity revascularization [75,77-87]. In a meta-analysis of seven trials, NPWT applied to closed groin wounds (open/endovascular aortic repair, lower extremity bypass) significantly reduced the risk of SSI (odds ratio [OR] 0.35, 95% CI 0.24-0.50) . Among trials that reported complications, there were no significant differences, but the numbers of events were small. In the Cochrane meta-analysis described above , prophylactic NPWT significantly reduced the incidence of SSI associated with lower extremity bypass surgery (RR 0.46, 95% CI 0.32-0.66). Longer follow-up is needed to evaluate other outcomes (eg, graft complications) and to determine cost effectiveness in this clinical setting. (See "Overview of lower extremity peripheral artery disease".)
●Orthopedic surgery – Prophylactic NPWT has been tried following elective hip or knee arthroplasty, spine surgery, amputation, and fracture fixation [66,75,88-94]. In the Cochrane meta-analysis described above, SSI was similar for prophylactic NPWT compared with standard dressings for arthroplasty (RR 0.69, 95% CI 0.32-1.49) and lower extremity traumatic injury (RR 1.15, 95% CI 0.61-2.20). In the largest of the included trials (1548 patients), the rate of deep surgical infection was similar at 30 and 90 days for NPWT compared with standard wound dressings (30 days: 5.8 and 6.7 percent, respectively; 90 days: 11.4 and 13.2 percent, respectively) . Other wound complications were not affected by NPWT. Most patients (81 percent) were treated for closed fracture. In an earlier trial that included 249 patients with 263 fractures that were deemed high-risk (calcaneus, tibial pilon, tibial plateau), the incidence of infection was overall reduced in the NPWT group (18.8 versus 9.9 percent) . The differences in rates of SSI between studies may reflect differing fracture sites/types or may reflect other factors (eg, type of NPWT dressing, antimicrobial usage).
COMPLICATIONS — NPWT is generally safe and well tolerated. Complications can include bleeding, infection, pain, organ damage, and possibly death . Such complications are most likely to occur when NPWT is applied to patients whose wounds have devitalized tissue or exposed vital structures (eg, organs, blood vessels, vascular grafts). (See 'Contraindications' above.)
Bleeding — Bleeding is the most serious complication of NPWT and can occur in hospitals, long-term care facilities, and at home . Minor bleeding during dressing changes due to granulation tissue at the base of the wound is common and is best managed with firm pressure to the wound surface. Severe hemorrhage can occur during removal of foam that has become adherent to the granulation tissue below, especially in patients who are anticoagulated, or in patients with exposed vessels or vascular grafts. In patients with severe bleeding, direct pressure should be applied and emergency services contacted. Surgery may be needed to control bleeding.
Infection — Infection related to the use of NPWT is often due to prior wound infection that was inadequately controlled prior to initiating NPWT. When infection is suspected (eg, fever, erythema, cellulitis), the NPWT dressing in discontinued, the wound irrigated and debrided, wound cultures obtained, and empiric antibiotics initiated. (See "Acute cellulitis and erysipelas in adults: Treatment".)
Enterocutaneous fistula — Scattered case reports suggest that NPWT may expedite control and closure of postoperative enterocutaneous fistula. However, NPWT is also more likely to cause enteric fistula formation [96-100]. (See "Management of the open abdomen in adults" and "Enterocutaneous and enteroatmospheric fistulas".)
SUMMARY AND RECOMMENDATIONS
●Negative pressure wound therapy (NPWT), also called vacuum-assisted closure, is an adjunctive therapy used in the management of open wounds that applies subatmospheric pressure to the wound surface. The wound care system consists of an open-cell foam dressing, semiocclusive adhesive cover, fluid collection system, and suction pump. (See 'Introduction' above and 'Device and placement' above.)
●NPWT exerts its effect through direct and indirect effects of subatmospheric pressure. These effects include stabilization of the wound environment, increased blood flow, and deformation of the wound. Deformation is a powerful stimulus for cellular processes that stimulate granulation tissue and accelerate wound healing. (See 'Mechanism of action' above.)
●NPWT has several advantages over traditional wound management, including simplification of wound care (primarily through a reduced number of dressing changes and ease of tailoring the dressing), accelerated wound healing, and reduction in the complexity of subsequent reconstructive procedures. (See 'Clinical applications' above.)
●NPWT has been used in the treatment of acute and chronic wounds. High-quality data supporting the use of NPWT are available only for the management of diabetic foot wounds. NWPT used prophylactically may reduce the incidence of superficial surgical site infection; however, it is has not been shown to be cost effective. (See 'Clinical applications' above and "Overview of treatment of chronic wounds", section on 'Negative pressure wound therapy' and "Management of diabetic foot ulcers" and 'Prophylactic use' above.)
●NPWT should not be directly used on exposed vital structures (organs, blood vessels, or vascular grafts) or on malignant tissues. Perfusion to the wound should be adequate, as NPWT can cause or worsen tissue ischemia in accordance with its mechanism of action. Devitalized tissues should be debrided and infection should generally be controlled prior to undertaking NPWT; however, instillation therapy has allowed the use NPWT in the presence of infection, or to augment the surgical management of infection. Other relative contraindications include skin or tissue fragility, and adhesive allergy. (See 'Contraindications' above.)