There are many treatment options available for abdominal wounds. This commentary will focus on the use of Negative Pressure Wound Therapy (NPWT) for abdominal wounds in response to the article "Negative Pressure Therapy for Laparotomy Wounds-A Word of Caution" by Andrabi and Ahmad in this month's JWOCN. Negative pressure wound therapy, if used appropriately, has been shown to be beneficial in promoting healing wounds.1,2 The benefits of NPWT therapy over usual dressings are: (1) removal of exudate and bacteria, (2) diminished interstitial pressure, (3) increased blood flow and mitotic activity, and (4) preservation of a moist wound healing environment.2,3

When choosing a treatment for abdominal wounds, the clinician should be prepared to answer multiple pertinent questions (Box 1). A comprehensive assessment of the patient is completed. Past medical and surgical history may reveal conditions that impede healing such as diabetes mellitus or anemia. The patient's history may identify medications that hinder wound healing such as steroids, immunosuppressants, and chemotherapy agents. When NPWT is considered, the administration of anticoagulants such as warfarin (Coumadin) and heparin must be carefully considered because they may increase the risk of bleeding. Wound homeostasis is imperative and frequent monitoring of activated partial-thromboplastin time (PTT), and/or prothrombin time (PT), with international ratio (INR) levels is necessary. The assessment also incorporates the patient's nutritional status since poor nutritional intake will decrease healing. The intake of protein is especially important for promoting wound healing.4 Although NPWT has been shown to promote wound closure, it cannot compensate for poor protein levels.2 Therefore, consultation with a dietician and adequate nutritional intake are essential aspects of this comprehensive assessment.

Box 1. Essential Questions When Managing an Open Abdominal Wound

Careful inspection of the wound is also completed prior to application of NPWT. Different techniques may be used to protect the underlying tissue and exposed bowel when Vacuum Assisted Closure (VAC) (KCI Inc., San Antonio, TX) is used to deliver NPWT. For example, when the wound involves subcutaneous tissue and muscle GranuFoam (Black) (KCI, Inc., San Antonio, TX) is cut to fit the wound bed. Based on the patient's pain level a layer of nonadherent dressing can be placed on the wound bed prior to sponge placement. An alternative sponge, VersaFoam (KCI, Inc., San Antonio, TX), is nonadherent and can be used in place of the nonadherent dressing. I have found that application of GranuFoam and a layer of nonabsorbant dressing decreases pain and discomfort during dressing changes (Figures 1 and 2).

FIGURE 2. Abdominal wound with use of GranuFoam and nonadherent dressing.

FIGURE 1. Abdominal wound being treated with GranuFoam. Please note sutures are from a biopsy.

The type of dressing applied over a mesh graft depends on how much bowel and mesh are exposed in the wound base. The abdominal wound dressing can be used with meshed graft covering the bowel (Figure 3). GranuFoam with a nonadherent dressing can also be used in abdominal wounds covered with meshed grafts (Figure 4). Other types of mesh may be used to cover the bowel and GranuFoam may be placed over these without difficulty (Figure 5).

FIGURE 5. Permacol (Tissue Science Laboratories, Andover, MA) in abdominal wound prior to VAC therapy with GranuFoam.

FIGURE 4. Abdominal wound with Vicryl mesh prior to VAC therapy with GranuFoam and nonadherent dressing.

FIGURE 3. Vicryl (J&J, Division of Ethicon, Cincinnati, OH) mesh in an abdominal wound prior to VAC therapy with abdominal wound dressing.

Exposed bowel may be managed with the abdominal wound dressing, which has a fenestrated nonadherent layer with GranuFoam in the center. It is applied directly over the bowel and tucked into the gutter surrounding the bowel. The GranuFoam is placed over the fenestrated nonadherent layer, which fills the remaining defect (Figure 6).

FIGURE 6. Exposed bowel prior to VAC therapy with abdominal wound dressing.

Continuous negative pressure is recommended for the first 48 hours of therapy, followed by intermittent negative pressure.5 Intermittent negative pressure is believed to increase granulation tissue formation.6 However, it may not be appropriate for wounds that are painful or produce copious amounts of drainage. Continuous suction will eliminate the pain felt by the patient when the negative pressure is cycled through the off to on phase. Leaking will occur with a highly exudating wound from under the VAC drape requiring unnecessary dressing changes. Once the patient reports virtually no pain with the dressing change and a dramatic reduction in drainage is noted, then intermittent negative pressure may be applied. Other considerations for the use of continuous negative pressure are: (1) presence of sinus tracts and undermined areas, (2) use of VersaFoam, (3) problems with maintaining the seal, (4) NPWT over meshed grafts, (5) use with previously described abdominal wound dressing, and (6) surgical flap sites.5

The magnitude of negative pressure applied to a wound varies based on the amount of drainage and type of foam used. The standard negative pressure with applied with VAC and a GranuFoam sponge is 125 mm Hg, but this value may be increased depending on the volume of drainage.5 The optimal magnitude of negative pressure varies by manufacturer, but the need for increased pressure when using VAC is justified when leakage of fluid from under the drape occurs. In this scenario, the negative pressure can be increased to 150 mm Hg-200 mm Hg as needed. Pressure should be decreased to 125 mm Hg once the drainage has decreased. Negative pressure with the use of the white, nonadherent foam (VersaFoam) is also begun at 125 mm Hg, but I have found that 150 mm Hg is used in most cases owing to the density of the foam. Negative pressure over suture lines, some types of mesh, and flaps should be set at 75 to 125 mm Hg with a nonadherent layer prior to foam placement.5 The addition of nonadherent dressing under the foam decreases the amount of negative pressure to the tissue. Evaluation of the tissue response is necessary with each dressing change. Morykwas and Argenta6 reported that increased negative pressure does not increase the rate of granulation tissue development.

It is recommended that the suction tubing be placed over omentum.5 In cases where the omentum or other muscles cannot be used to cover the bowel, other techniques may be used to protect the gut. For example, the abdominal wound dressing or 2 to 3 layers of a nonadherent dressing may be placed under the sponge. This creates a situation to protect the bowel from GranuFoam. Negative pressure is equal throughout the entire foam dressing for all methods of dressing applications. Another technique can be used in wounds whose length or width is smaller then the Trac pad (KCI, Inc., San Antonio, TX) or tubing. In this case, a layer of the VAC drape can be applied to the adjacent skin with a layer of the GranuFoam extending past the wound edge. The Trac pad or tubing is applied to this area to protect the periwound. The Trac pad or tubing can be placed at the distal or lateral end of the wound, which allows for increased mobility for the patient. I found no previous cases reporting that use of NPWT and placement of the Trac pad or tubing caused bowel necrosis or thinning of the bowel wall.

NPWT therapy can be used as a bridge especially in patients who are too unstable for wound closure in the operating room. Dressing removal may be painful, but prior to dressing removal the patient can receive pain medication, a topical anesthetic agent, or antianxiety medication to reduce the pain and anxiety associated with dressing changes.

Conclusion

Abdominal wounds can be treated with NPWT after a comprehensive assessment of the patient and wound. VAC has been used with abdominal wounds that contain exposed bowel, fascia, muscle, subcutaneous tissue, flaps, fistulas, and mesh. Clinicians are cautioned to adhere closely to clinical guidelines that are provided by the manufacturers of NPWT products.

References