A Review of Negative Pressure Wound Therapy

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A Review of Negative Pressure Wound Therapy

Postby patoco » Sat Jan 06, 2007 2:53 am

When Negative is Positive: A Review of Negative Pressure Wound Therapy

- Cynthia A. Fleck, RN, BSN, ET, WOCN, CWS, DAPWCA, and Lisa D. Frizzell, RN, BSN, ET, CWOCN

A 47-year-old man with diabetes mellitus presented with a severe leg injury with exposed muscle and tendon. The wound measured 34cm x 11cm x 2.2cm (see Figure 1). To prevent amputation, the wound, ostomy, and continence nurse urged the surgeon to postpone surgical removal and try negative pressure wound therapy (NPWT) to save the limb. Consent was obtained and negative pressure therapy began at 125mmHg. Five days later, at the second dressing change, the wound measured 34cm x 9.5cm x 1.5cm (see Figure 2). At day 11, the wound had granulated and contracted to the point that the patient was taken to surgery for graft placement with a flap placed over the tendons near the distal end. Negative pressure therapy was reapplied over the graft for four days, and the patient was discharged to home two days later with an intact and functional leg.

This is a perfect example of an appropriate use of negative pressure wound therapy (NPWT). Is it the universal remedy for hard-to-heal wounds? Is it a new treatment? Read on to learn more about this popular adjunctive wound management tool.

History and Evidence

The effect of exposing wounds to subatmospheric pressure has been studied in a variety of settings for the last 50 or so years. Although drains within a body cavity have been used for centuries, it was not until the first half of the 19th century that their use became routine. Suction drainage has been used since 1947 whenever a postoperative accumulation of blood, bile, or exudate was anticipated.1 With the introduction of closed wound suction drainage in 1952, prophylactic drainage appeared to greatly enhance wound healing, minimize postoperative complications, and reduce the duration of hospitalization following surgery.1 Subsequently, reports in the literature have confirmed the efficacy of wound drainage for a variety of uses including an accumulation of fluid or cellular debris. In 1978, Fox and Golden described continuous suction, negative pressure drains as excellent “atmospheric bandages” that help to expedite wound healing.1 Montgomery, Everett, and Betancourt explained similar systems in the mid-1980s.2–4

In the early 1980s, the principle of applying constant suction to promote healing gained renewed interest with surgeons and product manufacturers.5 The trend toward early patient discharge and quicker rehabilitation routines has increased the need for controlled systems to accelerate healing, eliminate dead space, promote soft tissue approximation, and minimize the risk of infection. A key factor in facilitating the process of wound healing in general is the ability to contain, control, and remove excess fluid, air, or material that may disrupt the normal healing process. Chariker, Jeter, and colleagues depicted the use of a closed suction wound drainage system for effective management of incisional and cutaneous fistulae in 1989.6.

In 1991, Nakayama and Soeda7 described using adhesive drapes and a disposable suction drain to create a “vacuum package” over free skin grafts on hands. Brock, et al.,8 studied a technique to provide temporary closure of abdominal surgical wounds when conditions of the abdominal wall or peritoneal cavity prevented immediate closure or when early re-exploration was planned. Their technique described a “three-layered, sutureless, occlusive dressing that is stabilized by a continuous vacuum seal.” The first layer was a polyethylene sheet, the second a moist sterile surgical towel, and the third a polyester sheet backed with an acrylic adhesive. Between the second and third layers, silicone drains were placed to 100–150mmHg continuous negative pressure.

Blackburn, et al.,9 studied using negative pressure dressings as bolsters for skin graft sites. He described how these dressings addressed multiple factors that have typically been the cause of skin graft failure (hematoma, seroma, infection, movement, poor graft bed, pressure necrosis, bridging across crevices, and technical error). In this report, he described the technique of applying a nonadherent gauze to the site, bolstered with sterile open-cell foam and covered to create a sterile isolated system.

The presence of bacteria in a wound will inevitably delay the healing process. In Moscow, Kostiuchenok, et al.,10 found that vacuum treatment of a purulent wound after surgical debridement significantly reduced the microbe count in the wound tissues. Similar findings were published by Morykwas,et al.,11 in 1997 where it was reported that tissue bacterial counts decreased significantly after four days with negative therapy. This study also looked at determining the optimal level of negative pressure. Circular defects (2.5cm) were produced on the backs of pigs. The wounds were then dressed with open cell polyurethane-ether foam. Laser Doppler technique was used to evaluate blood flow, and the authors’ results indicated that an increase in blood of four times above the baseline occurred with negative pressure values of 125mmHg. When values reached 400mmHg, blood flow was shown to be inhibited.

What is it? How Does it Work?

Despite recent press, marketing efforts, and commercialization of a “kit” in the last decade, this adjunctive treatment is anything but new. The theories that we know as modern day NPWT were arranged as a convenient kit of equipment and supplies, presented to the Food and Drug Administration (FDA), and approved as a device in 1995. Its positive effects, however, have been utilized long before it was commercially available.

NPWT applies subatmospheric pressure or negative force to the wound bed by means of a suction unit, dressing, a noncollapsible, fenestrated evacuation tube, and a transparent semi-occlusive, vapor-permeable outer dressing or “drape” and is connected to a collection container. The concept is to turn an open wound into a controlled, closed wound while removing excess fluid from the wound bed, thus enhancing circulation and disposal of cellular waste from the lymphatic system. It is considered for complex and difficult-to-manage wounds.

It is hypothesized that NPWT works clinically by removing excessive interstitial edema, thereby decompressing the small vessels and restoring local blood flow, removing chronic wound fluid that contains matrix metalloproteinases (MMPs) that can inhibit wound healing, and stimulating proliferation of fibroblasts and endothelial cells and vascular smooth muscle by mechanically deforming the cells.

The clinical benefits include increasing local blood flow, decreasing bacterial colonization, facilitating the ability to measure and assess wound fluid, and increasing the rate of granulation tissue creation, contraction, and epithelialization. The wound is additionally uniformly drawn closed by applying controlled, localized negative pressure. NPWT supports granulation tissue formation through the promotion of wound healing.12

Clinical Indications: Who, What, Where, and When

A thorough assessment should be performed on every patient considered for NPWT. Generally, NPWT can be considered in a chronic wound if the wound size decreases by less than 30 percent after four weeks following debridement or if excessive exudate cannot be managed effectively with daily dressing changes. Areas of contemplation include the patient’s ability to heal, nutritional assessment together with albumin/pre-albumin levels, diabetes control, and systemic steroid, immunosuppressant, or anticoagulant use. These factors all impact the healing process. Patient compliance with dressing changes and follow-up care are important to determine prior to dressing application. Patients with a history of noncompliance with other dressing regimes should be monitored closely. If the wound is on a bony prominence, appropriate pressure relieving and/or offloading measures should be initiated.

NPWT, when ordered by the surgeon or physician medically directing the patient’s wound care regime, is deemed appropriate for the following conditions :

• Acute wounds
• Partial- and full-thickness burns
• Surgically created wounds and surgical dehiscence—Patients with other medical problems, i.e., diabetes, coronary artery disease, and renal disease, may be more susceptible to wound dehiscence and delayed wound healing. NPWT may provide increased wound stability.
• Neuropathic (diabetic) ulcers
• Venous or arterial insufficiency ulcers unresponsive to standard therapy
• Traumatic wounds (i.e., flap or meshed graft)
• Pressure ulcers (stage 3 and stage 4).
Contraindications for NPWT include (see Table 2):
• Necrotic tissue with eschar present if debridement has not been attempted
• Malignant or neoplastic diseases in the wound margin
• Untreated osteomyelitis—The patient should be on antibiotics to address the underlying infection
• Presence of a fistula to an organ or body cavity within the cavity of the wound
• NPWT dressings should not be applied directly over exposed blood vessels or organs.

NPWT can be utilized in a variety of care settings and applied by any trained, licensed healthcare professional. The key word here is trained. Failure of NPWT is often due to inadequate staff education and skill, particularly in smaller chronic care facilities. Work directly with your manufacturers and distributors to make sure that your staff is adequately trained, periodically inserviced, and has the necessary tools to apply and remove the NPWT device safely and effectively.

Dressing changes should occur routinely every 72 to 120 hours depending on the dressing type, amount of drainage, and physician’s order. In acute care, dressings are typically changed on Monday, Wednesday, and Friday. If the wound is infected, however, dressing change frequency should be increased to every 12 to 24 hours to assess any changes in wound status. NPWT should not be off for more than two hours during a 24-hour period as maceration of the periwound skin can occur. For the home care patient, always provide an alternative dressing in case the dressing becomes dislodged or there is a disruption in electrical power. Dressings over meshed grafts are usually placed in the operating room, typically left for three to four days, then therapy discontinued before the patient is discharged home.

Preparing the Wound Bed

Wounds treated with NPWT should be debrided, cleaned, and prepared as with any wound.13 At Baptist Hospital in Nashville, Tennessee, clinicians often confer with physical therapists, who, upon physician order, perform wound irrigations at the bedside utilizing a pulsed lavage system. This thoroughly cleans the wound at an appropriate pressure with each dressing change before the new dressing is applied. If there is not a large amount of necrotic tissue present or if gentle cleansing is indicated (pain in or around the wound; clean, granulating wound bed), a noncytotoxic commercially prepared wound cleanser can be applied.

Before placing the dressing, the periwound skin should be carefully dried and prepared by using a skin prep or by cutting a thin hydrocolloid wafer to the exact shape of the wound. The actual NPWT packing dressing should be cut to fit the size and shape of the wound bed, including tunnels and any undermining. Often, more than one piece is necessary. A knowledgeable colleague offers the suggestion to actually write the number of dressings used on the transparent outer dressing. She has seen wounds that have healed with dressings left in them and then the wounds have to be re-opened and the dressings surgically removed. She has therefore made the “dressing count” in NPWT a part of her facility’s policy.

An example of what a proper NPWT dressing looks like when the pressure has been activated is analogous to a dried up, wrinkled prune or raisin (See Figure 4. Note the furrowed transparent drape. This particular dressing employed the use of a foam dressing.)


Depending on the device used, therapeutic negative pressure recommended levels vary. A vacuum is simply an empty space from which matter or air has been removed. The degree to which that air is removed and how effectively the space is isolated from outside factors determines the amount of suction that is created. Suction is the resulting force created by vacuum pressure. In the clinical setting, suction force is measured in millimeters of mercury or mmHg, centimeters of water, or pounds per square inch (psi).

According to expert opinion, the optimal setting for NPWT is 125mmHg.14 For example, pressure ulcer therapy target pressure is recommended at 125mmHg, and target pressure for a meshed graft is 75 to 125mmHg. Pressures should be continually evaluated based on changes in wound status. Patients on anticoagulants, the elderly, or emaciated patients should be started at a lower setting (75 to 100mmHg) then adjusted up as tolerated. There is also an option of continuous versus intermittent therapy. Continuous therapy is indicated if there is significant discomfort during the intermittent therapy mode, if there are tunnels or undermined areas, if there are high levels of wound exudate beyond the first 48 hours, or if it is a difficult site to maintain a seal, e.g., perirectal area, fingers, or toes. Intermittent therapy (five minutes on/two minutes off) has been shown to increase granulation tissue formation.

Sizes, Shapes, Types, and Configurations

All suction systems used in the clinical setting have similar components and mechanisms to provide a vacuum. The components include a suction drainage device, extension tubing connecting the drain to an inlet port on the collection unit, a vessel that provides the source of vacuum, an occlusive or semi-occlusive dressing or drape, and an exit port through which air is expressed. The factors that vary among products are drain design, the power source used to create suction, the dressings, and the method used to control and contain wound fluid.

To facilitate the flow of drainage and offer the earlier mentioned benefits of NPWT, these systems rely on some form of vacuum pressure to create suction force. The power that creates a vacuum may be a manually activated drum or a power-driven pump. Pumping devices may be stationary (e.g., a wall regulator connected to a central vacuum system), a line-powered pump (e.g., connected to a standard 120 volt AC outlet), or a portable device. All pumps are designed to facilitate wound drainage by creating a vacuum. There are currently several sizes and special versions of NPWT from which to choose. For instance, some offer a long-life battery to enable the patient to be mobile; others are small enough to be portable without difficulty. Some of the newer systems present a filter system that helps minimize wound odor, and others have intuitive touch screens with on-screen user guides to make use easy.

Different systems utilize various dressings in the wound bed. V.A.C.® (Vacuum Assisted Closure™) Therapy™ from Kinetic Concepts, Inc. (KCI, San Antonio, Texas), for instance, uses two kinds of foam. The white foam is a polyvinyl alcohol (PVA) that is hydrophilic (water attracting), holding moisture in an open pore structure, which allows exudate to be removed through it. It has a higher tensile strength, which makes it difficult to tear or rip when pressure is applied. It is premoistened with sterile normal saline, which helps make it less adherent. It is recommended for use in tunnels and shallow undermining, painful wounds, shallow wounds, and areas with exposed tendons and bones. The black foam is a polyurethane (PU) foam that is hydrophobic (water repelling). It doesn’t hold moisture and also has open cell foam, which allows exudate to be removed through it. It is less dense than the white foam and is reticulated, meaning the pores communicate with one another, allowing for increased pressure across the wound bed.

Other systems, such as wound drainage systems (Chariker-Jeter® Wound Drainage Kit, Wooding-Scott® Drainage/Irrigation Kit, and Kremlin™ Wound Drainage Kit) from BlueSky Medical (La Costa, California), suggest the use of drainage kits that utilize impregnated gauze. The key to all these commercially prepared systems is convenience.

Handling Skin Problems

Typical skin problems that can arise during use of NPWT include an overgrowth of yeast or Candida infection, skin stripping, and subepidermal granulation.

• A Candida infection most often occurs in areas where it is dark and moist, such as in skin folds, and often manifests as a result of placing multiple transparent drapes over the sponge dressing causing a decrease in moisture vapor permeability. This can be remedied by using a two-percent miconazole powder or antimicrobial silver gel or powder and/or taking a short break from NPWT.

• Skin stripping can occur when the NPWT drape is removed. Suggestions include preparing the periwound skin prior to application with a skin prep barrier and removing the drape with care, just as you would any transparent dressing.

• Subdermal granulation can happen when the sponge dressing overlaps and contacts the periwound skin. This can be avoided again by applying a proper skin barrier and placing the sponge dressing within the wound cavity, not touching the skin.

Tricky Situations and Challenges

How do you handle more than one wound with only one pump? Bridging and Y-connecting are the answers. Bridging can be accomplished with multiple wounds of similar pathology in close proximity to one another. You simply place the transparent dressing or drape on the intact skin between wounds and place a strip of foam from one wound bed to the other over the draped skin. As long as all pieces of foam are touching each other, you can place the tubing in a central location and use one pump to distribute pressure throughout all the wounds. Y-connecting allows you to treat multiple, noninfected wounds that are a larger distance apart by using a connector that can support two separate tubing connections. Therapy in either situation is evenly distributed across the wounds yet controlled by one pump.

How about dealing with foul odor? First off, identify and treat the odor’s cause. If the wound is infected, a topical antimicrobial, such as an ionic silver powder (Arglaes Powder™, Medline Industries, Inc., Mundelein, Illinois) or amorphous hydrogel (SilvaSorb™ Gel, AcryMed, Inc., Portland, Oregon), after thorough debridement may be the ticket. Changing the dressing more often may be helpful too. Other options include adding a gel pack or povidone iodine in the canister to help with odor and changing the canister when it is 2/3 full.7

Billing and Reimbursement

Current Procedural Terminology (CPT) codes. Although there is no specific CPT code for NPWT, in 2001, the American Medical Association (AMA) provided CPT codes for Active Wound Care Management. These codes were established to provide nonphysician practitioners (e.g., nurses, physician assistants, physical therapists, occupational therapists) specific codes for wound care activities they perform. The definition of these codes includes the topical application of dressings. The two codes and their definitions are:

• 97601—Removal of devitalized tissue from wound; selective debridement without anesthesia (e.g., high-pressure water jet, sharp selective debridement with scissors, scalpel, and tweezers) including topical application(s), wound assessment, and instruction(s) for ongoing care per session
• 97602—Nonselective debridement without anesthesia (e.g., wet-to-moist dressings, enzymatic abrasion) including topical application(s), wound assessment, and instruction(s) for ongoing care per session.
A hospital or acute care facility can include charges for the daily pump rental and dressings and canisters on its bill. The charge is established in the hospital charge description master with an association to the following UB92 revenue codes:
• Daily pump rental—UB92 code 270 (medical surgical supplies)
• Dressings and canisters—UB92 code 272 (sterile medical surgical supplies).

Inpatient settings.

Acute care hospitals, skilled nursing facilities (SNFs), rehabilitation hospitals, and long-term acute care hospitals (LTACs) are required by Medicare regulations to provide all services to inpatients, whether directly or through contracts with third-party providers. In essence, a patient should not receive a bill for any facility services from any facility other than the one in which he or she was hospitalized. This provision excludes the professional services of physicians that are billed to Medicare Part B.

Medicare reimburses facilities for inpatient care based on prospectively determined rates. Each type of facility (acute care, skilled nursing, and rehabilitation) has a different prospective payment through Medicare for the covered services provided to patients.

Nursing homes. Medicare doesn’t provide coverage for services provided in nursing home facilities. Coverage guidelines exclude this setting from being considered the patient’s “home,” as nursing services are provided.

Home care. Medicare reimbursement for services rendered to homebound patients has also undergone a transformation to a prospective payment system. As of October 1, 2000, the nursing services provided by a home health agency (HHA) and reimbursed by Medicare Part A are subject to the Home Health Prospective Payment System.

Under the system, a HHA is responsible for providing all covered home health services during a patient’s 60-day episode of care. Items falling into the following categories are reimbursed separately from the Prospective Payment System (PPS) episode of care: durable medical equipment (DME), orthotics and prosthetics, oxygen, and parenteral nutrition. DME, as well as the other items mentioned, are segregated into a separate payment category, as they fall into a benefit category reimbursed under Medicare Part B.

NPWT dressings and canisters necessary to the NPWT’s operation are generally supplied directly to the patient in his or her home. The HHA provides the skilled nursing care ordered by the physician. Dressing changes performed by the HHA nurses are reimbursed under the HHA PPS. The NPWT manufacturer or distributor then submits claims for the NPWT unit, dressings, and canisters directly to the Medicare Part B DMERC. The DMERC adjudicates claims and remits payment for 80 percent of the allowable to the manufacturer or distributor of the product. The patient or his or her supplemental insurer is responsible for the 20 percent coinsurance.

Secrets from the Experts

The more experience a clinician has with NPWT the more skillful he or she becomes with it. We learn little tips and tricks that make things go more smoothly for us and for our patients. We spoke with some of the experts and this is what they shared:

• In order to decrease bioburden and pain, reduce hypergranulation, as well as increase outcomes and decrease the number of days of NPWT use, many authorities recommend using an ionic silver gel or powder, such as SilvaSorb Gel and Arglaes Powder (Medline Industries, Inc., Mundelein, Illinois) beneath the dressing.15

• For those difficult locations, how do you achieve a good seal? Many experts have had success using stomahesive paste6 and Strip Paste from Coloplast Corp. (Marietta, Georgia) in particular due to its easy moldability and its ability to conform well to creases and skin folds.

• All the clinical specialists that we interviewed used a skin prep or barrier wipe with a special affinity for 3M™ Cavilon™ No Sting Barrier Film (3M Health Care, St. Paul, Minnesota). This is used under the drape after wound cleansing.

• Use of contact layers, such as petrolatum gauze or soft silicone, can help lessen pain at the wound bed.

• Using normal saline (10–30cc) to saturate the foam prior to removal (15 to 30 minutes) helps diminish pain and assists in taking the dressing out.

• Turning off the pump 5 to 10 minutes before beginning to remove the dressing is helpful in decreasing pain too.

• Consider premedicating the client 30 to 40 minutes prior to dressing change if pain is an issue.16

Future Options?

NPWT is a unique system that promotes wound healing with a variety of acute, traumatic, and chronic wounds and is available in all care settings. Are you considering adding this select therapy to your treatment cache? Are you looking for an innovative addition to this already utilized therapy? As treatment moves into the 21st Century, refinements in technology, variations on the original design, novel dressings, additives, kits, and new inventions will come to the forefront, challenging the industry to offer better outcomes and more cost-effective care. Be on the look out for these cutting-edge enhancements, new companies, and equipment to answer your taxing wound care dilemmas.

Helpful Websites

http://wocn.org/literature—Wound, Ostomy, and Continence Nurses Society literature on NPWT
http://www.blueskymedical.com—BlueSky Medical
485256959006EC27D?OpenDocument—Medicare B coverage criteria

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