Commentary by Phyllis A. Bonham
The presentation of these cases has provided relevant and useful information about the successful use of NPWT with Versatile 1 system in 3 patients with complex wounds. The discussion serves to highlight several important questions related to NPWT, including (1) Is there an ideal method of delivering NPWT? (2) Is NPWT effective in the presence of necrotic tissue? (3) Is there a benefit of using NPWT in conjunction with other adjunctive therapies? and (4) How do costs, complications such as pain, and wound healing outcomes compare among different NPWT modalities?
Negative Pressure Wound Therapy
The practice of using suction to prevent accumulation of hematoma and serotoma and to drain toxic substances has a long history in wound management.1 The intentional delivery of pressure below atmospheric pressure to promote wound healing is known by several names, which are used interchangeably in the literature. They include NPWT, topical negative pressure, vacuum-assisted closure (VAC), subatmospheric pressure therapy, vacuum sealing, sealed surface wound suction, and closed suction.1-3 NPWT has been recommended for (a) chronic wounds that fail to progress toward healing (less than 30% decrease in 4 weeks) despite proper attention to systemic and local host factors and wound bed preparation, (b) adjunctive treatment to surgery to prepare the wound bed for split-thickness skin grafts or flaps, and (c) wounds with excessive drainage that cannot be managed effectively with conventional dressing methods.4
Methods and Mechanisms
NPWT is believed to promote wound healing by several mechanisms. Based on 4 animal studies (pig model), Morykwas and associates5 determined that subatmospheric pressure (-125 mmHg) increased blood flow levels fourfold and increased granulation tissue with both continuous (63% +/- 26.1%) and intermittent therapy (103% +/- 35.3%). Treatment also decreased bacterial counts after 4 days and significantly increased flap survival by 21% when compared to controls. In contrast, pressures of -400 mmHg lessened blood flow. Wackenfors and associates6 also confirmed that VAC at -50 to -200 mmHg increased microvascular blood flow to inguinal wounds in pigs. The researchers observed that the magnitude of blood flow created by NPWT depended on the tissue involved and that soft tissue is more vulnerable to hypoperfusion from high levels of negative pressure as compared to stiffer muscular tissue. Based on these observations, they concluded that low negative pressure levels may be beneficial in soft tissue to minimize ischemic effects.
Do Wounds Heal Faster With NPWT?
Empirical support for NPWT is based primarily on case reports in which treatment was typically instituted after a variety of conventional dressings or measures failed. Although the number of anecdotal reports about the successful use of NPWT continues to proliferate, a paucity of controlled trials needed to establish its efficacy compared to other treatment options exists. Also, few data are available about alternative forms of NPWT and evidence is lacking about the effect of NPWT on cost, quality of life, and pain or comfort.7
The question of whether wounds heal faster treated with NPWT compared to traditional dressings has not been conclusively determined. According to 3 systematic reviews of NPWT using the VAC system, data from 2 small randomized controlled trials provide weak evidence that NPWT may be superior to moist saline dressings in chronic human wounds. Nevertheless, insufficient evidence exists to determine whether NPWT is superior to other advanced dressings in promoting wound healing.4,7,8 Four other studies compared NPWT using the VAC system to wound therapy with antimicrobial dressings,9 enzymatic dressings,10 saline dressings,11 or dressings moistened with Ringer's solution.12 None found statistically significant differences in the healing rates of wounds treated with NPWT when compared to traditional dressings. Therefore, it remains unclear whether NPWT is clearly superior to other wound treatments. Several additional questions remain about the role of NPWT. What is the optimum treatment regimen, type dressing, and duration of therapy? Is there an optimal level of negative pressure? Is continuous or intermittent negative pressure ideal? Are there specific indications and contraindications for selecting one version of NPWT over another? Is NPWT a first-line therapy?1,7 Elucidation of these questions is urgently needed to determine the optimal role for NPWT in the management of complex acute and chronic wounds.
Alternative Forms of NPWT
Negative pressure therapy with the VAC system has been used extensively since the 1990s, and much of the current published literature has focused primarily on this device. However, alternative systems are available for NPWT. Several Russian investigators described the use of vacuum therapy using funnel or chamber type devices that applied -0.8 to -1.0 atmospheres of negative pressure to the wound with treatments ranging from 5-20 minutes to 2-3 hours twice daily for 1-6 days. Usopov and Yepifanov13 applied negative pressure to wounds in a rabbit model and reported that pressures of -120 to -125 mmHg caused hemorrhage of coagulated vessels and recommended that subatmospheric pressure should not exceed -80 mmHg. Davydov and associates14,15 used vacuum suction applied with a chamber to deliver pressures of -0.1 to -0.15 atm for 1 hour per day for 6 days on purulent wounds and reported that the vacuum therapy in combination with aggressive debridement shortened the purulent inflammatory process and decreased local bacterial counts when compared to debridement alone. In general, the treatments described in those studies from Russia were of shorter duration and used lower levels of negative pressure than typically used in current NPWT regimens.
Closed Suction
The use of NPWT or "closed suction" is not new to the field of wound care. Many WOC/ET nurses have used closed suction since the 1980s after the techniques were outlined by Chariker and associates,2 who used suction along with various dressings or pouches to manage high-output enterocutaneous fistulae, and Wooding-Scott and colleagues,3 who managed excessively large exudative wounds with suction. Both methods used a suction catheter that was placed on the wound bed and connected to low levels of continuous suction (60-80 mmHg). Each recommends covering the wound with an adhesive semipermeable thin-film drape to provide an airtight seal. Additionally, Chariker and colleagues used damp saline gauze to obliterate the dead space in the wound, which they believed contributed to the success of the suction. The dressings were changed every 3-5 days and, in some instances, 7 days. These authors listed several benefits of their suction technique, including patient comfort, skin protection, ability to quantify output, low cost, and infrequent dressing changes, which saved staff's time.
Tachi and associates16 described yet another method of applying topical negative pressure using a drainage pouch without a dressing to treat undermined stage 3 and 4 pressure ulcers in a group of 9 subjects. They applied a 1-piece drainable ostomy pouch, cut to fit around the wound, and inserted a chest tube (18 F) into the bottom drain and connected it to a portable suction machine set to maintain -80 mmHg continuous negative pressure. The system was changed every 3-7 days. In all cases, the size of the ulcers deceased and 4 ulcers healed completely after 3-20 weeks without any reported complications. The authors concluded that NPWT without a dressing was cost effective, easy to perform, and saved time for dressing changes, although they did not report specific time or cost data.
Treatment for Recalcitrant Wounds
It must be emphasized that NPWT is an adjunctive treatment and not a replacement for proper wound care or surgical procedures.17 Recalcitrant wound healing can be the result of multiple factors, including misdiagnosis or inappropriate wound care. Accurate assessment of etiology and determination of underlying systemic conditions must be considered to guide treatment options. For example, a specific problem for the patients in cases 1 and 2 was lower extremity arterial disease (LEAD). Assessment of perfusion status is critical for all individuals with lower extremity wounds because therapy depends on the vascular supply. National clinical practice guidelines recommend that patients with lower extremity wounds have noninvasive tests, such as ankle brachial index (ABI) or toe brachial index (TBI) to rule out arterial disease.18,19 These tests can be performed easily at the bedside or in an office or clinic to evaluate the potential for wound healing. Also, in cases with an amputation, noninvasive testing is warranted to assess the perfusion status in the remaining limb because LEAD may occur bilaterally.
It is important to evaluate tissue perfusion before debridement of lower extremity wounds and to continue monitoring even after revascularization because restenosis occurs in a high number of cases.18,20 If lower extremity arterial flow is inadequate, maintenance of dry stable eschars is recommended and patients should be referred for additional vascular/surgical evaluation. Furthermore, if wounds do not heal in a timely fashion, evaluation of tissue perfusion by transcutaneous oxygen measurement (TCOM) can be obtained to help determine if patients are appropriate candidates for adjunctive treatments, such as hyperbaric oxygen therapy (HBOT).18,19
Principles of good wound management that must be routinely addressed include identification and elimination or treatment of causative factors, debridement of necrotic tissue, treatment of underlying infection, absorption of excess exudate, filling dead space, insulating the wound, protecting the periwound skin, maintaining a moist wound environment, and opening closed wound edges. Use of the current best evidence when making clinical decisions is vital for successful outcomes. To assist clinicians in managing complex wounds, systematic reviews and evidence-based guidelines can be obtained from the Cochrane Library (http://www.cochrane.org/), National Guidelines Clearing House (http://www.guidelines.gov/), and the Wound, Ostomy, and Continence Nurses Society (http://www.wocn.org/).
Nutrition
Each of the 3 patients in this discussion was at risk for malnutrition. Thorough nutritional evaluation and appropriate referrals are warranted for all patients with wounds to ensure that nutrition and protein stores are adequate for healing. Regular monitoring of laboratory values, weights, and intake/output are necessary to ensure that nutritional intake matches needs. For malnourished patients with wounds, if compatible with overall goals of care, a diet that provides 30-35 calories/kg/day and 1.25-1.5 g of protein/kg/day, along with a daily high-potency multivitamin is warranted.21
Preparation of the Wound Bed
The presence of necrosis and infection were complications in each of these cases. Most authors have reported that wounds must be free of necrotic devitalized tissue, which impedes granulation and healing, before initiating adjunctive therapy such as NPWT.4,17,22-24 There are a few anecdotal case reports where topical enzymatic debriding agents were used in conjunction with NPWT, but no studies exist that demonstrate any proven benefit with such a practice.23,25,26 Research is needed to evaluate the healing rates and cost effectiveness of using NPWT in necrotic wounds to determine if using topical enzymatic agents with NPWT provides any benefit that justifies the additional cost.
Infection Control
As illustrated by these 3 cases, NPWT alone cannot be relied on to treat wound infection or osteomyelitis. Rather, it comprises adjunctive care in patients with infected wounds of the foot and necrotizing fasciitis.1 Based on findings from the early VAC animal studies in which bacteria levels were more than 105 before institution of NPWT but decreased by day 4-5 of therapy and remained less than 105 during the remaining 2 weeks of the trials,5 it has been believed that NPWT decreases bacterial levels in wounds. Davydov and colleagues15 indicated that their vacuum therapy treatment on purulent soft tissue wounds in conjunction with surgical incision decreased the bacterial counts to 10 per cm2 by day 5, compared to 104 per cm2 in patients treated with only traditional incision/drainage. Also, Tachi and colleagues16 reported reductions in bacterial levels after 3 weeks of NPWT (N = 9) in which the total number of organisms per wound decreased in 6 of 8 wounds and Staphylococcus aureus was eradicated in 5 of 7 wounds.
However, the issue of whether NPWT enhances bacterial clearance has been questioned by Weed and associates,27 who recently conducted a retrospective study (N = 26) using the VAC system and found that 43% of the wounds had an increase in bacterial burden during the therapy, 35% showed no significant change after NPWT, and only 22% of the wounds had a decrease in bacterial colony counts. In that study, NPWT was placed immediately after surgical debridement (n = 14) or onto wounds with healthy appearing tissue (n = 12), so it was expected that the bacterial burden would decrease. The researchers suggested that the frequency of dressing changes may have affected bacterial levels, because in most clinical settings, dressings are changed every 2-3 days or 3 times per week, compared to the original animal studies where dressings were changed every 24 hours. These findings led Weed's group to pose the following questions: (1) Does the frequency of dressing changes affect the bacterial count enough to affect wound healing? (2) Is there a role for topical antimicrobials, such as silver dressings, along with NPWT to control bacterial loads? and (3) Are frequent dressing changes advantageous when compared to biweekly changes in wounds that are heavily colonized or infected?
Management of Comorbid Factors and Complications
Management of systemic conditions must be addressed along with local wound complications to achieve successful outcomes. The care of these 3 patients was particularly complicated by several comorbid conditions: diabetes/neuropathy (Case 2); arterial insufficiency (Cases 1 and 2); cellulitis, osteomyelitis, and MRSA (Case 2); and necrotizing fasciitis (Case 3).
For patients with diabetes and wounds, adequate glycemic control (HbA1c < 7.0%) and nutrition are essential.19 Nutritional support with >= 2000 calories per day for 11 days preoperatively and postoperatively aids healing in patients with amputations.18,19 Also, supplementation with L-Arginine has improved wound tensile strength in animal studies, increased pain-free walking and vasodilation of the femoral artery in patients with LEAD, and improved blood flow in patients with diabetes and neuropathy.18,19
Ischemia
Atherosclerosis is generally bilateral in patients with diabetes, and vascular screening of the remaining limb is essential. Subsequent amputation of a remaining limb occurs within 2-5 years in 50-84% of patients with diabetes, and the 5-year survival rate is less than 50%.19 Therefore, based on these grim data, key elements to include in the care of patients with diabetes and neuropathy (Case 2) are assessment of lower extremity arterial perfusion with an ABI and screening for loss of protective sensation with a monofilament (10 g, 5.07 log) or tuning fork.19 ABI less than .9 indicates LEAD, and a toe pressure less than 30 mmHg indicates significant LEAD and is predictive of failure to heal.18,19 If the ABI is more than 1.3, which may occur in patients with diabetes or renal failure resulting from calcified arteries, a TBI is indicated, and less than .6 indicates ischemia.18,19 Also, it is vital to educate patients and families about proper foot care and footwear and ensure that pressure relief is provided for heels, limbs, and other areas at risk for pressure necrosis.
During healing, the patient in Case 2 used a pillow to keep pressure off the heel while in bed, which is an inexpensive and readily available method to float heels, protect bony prominences, and position patients. Several products are commercially available that provide heel protection by suspending the heel. Patients with wounds, amputations, or high-risk foot conditions must also be referred and evaluated for appropriate assistive devices, specialized footwear or orthotics after healing for proper offloading and pressure redistribution because patients who wear their own shoes have an 83% recurrence of wounds compared to 26% recurrence in individuals wearing specialty fitted shoes.19,21
Osteomyelitis
As occurred with the patient in Case 2, osteomyelitis is present in a substantial portion of infections in patients with diabetes and the risk of amputation is higher in patients with diabetes than in those without the disease. Early and aggressive identification and treatment of infection and osteomyelitis are critical for patients with diabetes. Magnetic resonance imaging (MRI) is considered the most accurate noninvasive method to diagnose osteomyelitis in patients with diabetes and foot wounds.28 Standard treatment of osteomyelitis involves surgical resection of all infected bone and antibiotics. Recently, conservative surgery (foot sparing) and long-term systemic antibiotic therapy with a combination of IV and oral antibiotics or long-term high-dose oral therapy have proven effective alternatives to amputation in some patients.29
Pain Management
A common theme in these 3 cases was the concern over trauma, bleeding, and pain associated with NPWT. There have been no scientific investigations of pain levels associated with NPWT, and it is unknown whether one method of NPWT is more painful than another or how the use of gauze, sponge, or omitting dressings affects pain. It has been reported that patients experience pain during NPWT (ie, VAC) dressing changes or when the pump is started and bleeding occurs from granulation tissue growth into the pores of the foam dressing that generally stops easily with direct pressure.17,30,31 Whelan and associates17 reported that although NPWT can be uncomfortable for some, the discomfort usually resolves quickly and pain with NPWT is comparable to that during most other types of dressing changes.
There are additional concerns when using NPWT in wounds with exposed bones, organs, or tendons, such as the patient (Case 2) with exposed tendons. When NPWT is used over tendons or viscera, application of a protective layer of nonadherent material between the wound surface and the dressing is recommended.1,32 In each of the cases presented in this article, Aquaphor was used as a protective interface between the wound and the gauze dressing and was effective to minimize trauma, bleeding, and pain.
Eliminate or Control Source of the Pain
Assessment of patients for wound or treatment-related pain is an essential part of wound management. In 2001, the Joint Commission of Accreditation of Health Care Organizations (JCAHO) mandated that pain not be ignored.33 Healthcare providers are urged to consider pain as the fifth vital sign and to use valid and reliable pain assessment tools.34 Several pain assessment tools are available to measure pain, such as the Visual Analog Scale, Numeric Pain Intensity Scale, or FACES Pain Rating Scale.34
Several strategies can be employed to minimize trauma, bleeding, and pain associated with difficult or painful NPWT dressing changes. Reducing levels of suction in 25 mmHg increments down to a minimum of 75 mmHg may decrease discomfort associated with NPWT or changing to intermittent mode.22 Other interventions have also been recommended to protect the wound bed, including (1) application of a nonadherent porous interface dressing, such as Adaptic (Johnson & Johnson Wound Care, New Brunswick, NJ) or nonadherent silicone dressing, such as Mepitel or Mepilex (Molnlycke Health Care, Newtown, Pa); (2) coating the wound base with hydrogel; (3) lining the wound with the white polyvinyl alcohol sponge (VAC); and (4) changing dressings more frequently to prevent dressing from drying out and minimize tissue growth into the sponge.22,34
Other measures to prevent trauma, bleeding, and pain associated with NPWT include saturating the dressing by instilling 10-30 mL saline through the suction tubing or directly into the dressing 15-30 minutes before the change to moisten and loosen the dressing. A 1% lidocaine solution (without epinephrine) may be instilled directly into the dressing or via the tubing for 15-20 minutes before changes. Alternatively, a Eutectic Mixture of Local Anesthetics (EMLA cream) (Astra Zeneca, Wayne, Pa) may be applied topically for 30-60 minutes under occlusion before debridement or dressing changes. Finally, the patient may be premedicated with sedatives, opioid analgesics, or combination agents 30-50 minutes before dressing changes.22,34,35
Clinicians are cautioned about possible systemic absorption of lidocaine from large wounds that might cause untoward side effects.34 According to a recent systematic review by Evans and Gray,35 the strongest evidence for topical anesthesia to reduce pain associated with dressing changes or debridement is for EMLA cream, and there is insufficient evidence about the effectiveness of other measures, such as 5% lidocaine gel, lidocaine patches, and lidocaine-soaked gauze.
Periwound Skin Protection
Protection of the periwound skin is important with NPWT to prevent irritation and maceration from wound drainage, discomfort and skin stripping from removal of the drape, or reaction to the drape adhesive. Various skin sealants or barriers are commercially available in multiple formulations (sprays, wafers, pastes, and powders) that can be used alone or in combination to protect the periwound skin and prevent injury. Special attention should be paid to placement of the suction tube and protection of the skin from pressure of the overlying tube. Care is needed to ensure that the exit position of the suction drain or tube avoids bony prominences or weight-bearing surfaces. Also, proper pressure relief devices or support surfaces must be considered if sites of the wound or dressing are on weight-bearing surfaces and subject to pressure. In the 3 cases presented in this article, the clinician specifically reported that a skin sealant was used on the periwound skin and a hydrocolloid applied to protect the skin from the suction tubing.
Safety Concerns
Safety, as well as efficacy, is a concern with NPWT. Some authors have discussed issues about alternate forms of NPWT, including concerns about wound contamination from backflow in low-volume suction systems, the safety and efficacy of standard wall suction devices for NPWT, precision of suction controls in wall suction devices, potential of cross-contamination when using wall suction units, and use of devices that lack alarms to alert to backflow or other malfunctions.22,23 Clinicians must be vigilant to complications that may occur if NPWT equipment is not functioning properly and future investigation is needed to determine what safety features or practices are required to insure that proper protections are in place for safe delivery with NPWT equipment or devices.
Cost Effectiveness
Often, advanced wound therapies are considered more costly than conventional therapies, such as moist gauze dressings. However, additional factors that reflect the total expenses for care must be included in cost analysis that addresses healing rates, outcomes, caregiver time, length of treatment, and duration of hospitalization. Schimp31 recently reported that the cost of NPWT using the VAC system was $150 per day but provided no control comparisons of cost. Moues and associates36 reported significantly higher mean material expenses for full-thickness wounds (N = 54) treated with NPWT using the VAC compared with moist gauze dressings, but the costs were offset by significantly lower nursing expenses and shortened hospital stays for the NPWT group, which lowered overall hospital costs. They concluded that no significant differences in the total costs per patient between the two therapies exist but that benefits, such as fewer dressing changes, may provide a rationale for selecting one method vs another. More studies are needed to directly compare costs and outcomes among alternate modalities of NPWT.
Combination Therapy
If wounds are not progressing toward in healing in 2-4 weeks, an adjustment in the care plan is warranted, along with consideration of additional or alternative adjunctive therapies.8 When managing patients with complex wounds, it is important to determine if combining NPWT with other adjunctive therapies offers any additional benefits. For example, the patients in these cases may have benefited from HBOT in conjunction with NPWT.26 HBOT has been approved for patients with diabetes and Wagner Grade 3 or higher lower extremity wounds that have not responded to standard treatment and also for treatment of necrotizing soft tissue infections.37 Patients can be assessed with TCOM to evaluate for periwound hypoxia. TCOM measures of less than 40 mmHg that rise to more than 100 mmHg when the patient is breathing 100% oxygen at 1 ATA, indicates that HBOT may be beneficial.37 Other interventions that have been associated with enhanced healing in neuropathic wounds include recombinant platelet-derived growth factor, collagen and oxidized regenerated cellulose dressings, and tissue-engineered skin substitutes or human fibroblast-derived dermal substitutes.19,38
Antimicrobial Treatment
Each of these 3 patients had complications from infection. Although topical antimicrobials alone are not recommended to treat advancing cellulitis, osteomyelitis, or infected ischemic ulcers, antimicrobial dressings, such as silver or cadexomer iodine, may have a role in conjunction with systemic antimicrobials and other therapies.19 Silver has been used in conjunction with NPWT,39 and both silver and cadexomer iodine dressings are effective against MRSA, which was a specific problem for the patient in Case 2.24,38
Wound Instillation
For painful or infected wounds, there is a recent advance in negative pressure therapy that instills topical products to the wound bed along with NPWT (VAC Instill).26 Typical instillation solutions include normal saline, antibiotics, antifungals, and local anesthetics to decrease bacterial burden and decrease pain. From a small case series of 5 patients with infected, painful, and contaminated wounds, NPWT and instillation of antibiotics (1 g vancomycin in 250 mL normal saline) and/or topical anesthetics (25 mL 1% lidocaine in 500 mL normal saline or 25 mL 2% lidocaine in 500 mL normal saline) every 3 hours reduced both bacterial burden and pain.26
Ultrasound
Ultrasound is another emerging modality that might complement NPWT. Low-frequency ultrasonic energy is applied directly onto the wound surface; it debrides surface tissue and may help decrease bacterial burden.40 Ultrasound can be delivered at the bedside without topical anesthesia, and anecdotal case studies indicate that it provides painless debridement. Results of in vitro studies and limited case reports offer promising results for this therapy, but further research is needed to validate these initial findings.40
Conclusions
These case discussions provide an informative overview of a clinician's use of an alternative form of NPWT using the V1 wound vacuum system in the management of complex and challenging wounds in 3 patients. The discussion also highlights that there are multiple unresolved questions about NPWT, which accentuates the need for continued research in this area, including larger randomized controlled studies in humans to compare NPWT to traditional and novel adjunctive therapies for recalcitrant wounds.
References