Combination of Subatmospheric Pressure Dressing and Gravity Feed Antibiotic Instillation in the Treatment of Post-Surgical Dia

Disclosure: Dr. Bernstein has received speaker honoraria from the company that manufactures the products discussed in this article. A new negative pressure wound therapy (NPWT) device with solution instillation capability (V.A.C.® Instill™, KCI, San Antonio, Tex) is now available to the surgeon treating chronic and acute wounds. One of the most challenging wounds encountered by the wound specialist is the post-surgical diabetic foot wound. The mainstays of successful diabetic foot surgery include radical debridement and lavage of all devitalized tissue with preservation of viable structures, insurance of adequate blood supply, use of tissue transfers when necessary, protection of tissues from post-surgical shear and pressure, and antibiosis through the use of topical, oral, and parenteral antibiotics. Past attempts at delivery of high doses of antibiotics directly to the post-surgical field have been simple antibiotic solution-soaked dressings, antibiotic-impregnated cement beads and spacers, antibiotic-laced bone allografts and collagen sponges,¹ Kritter-type catheters with passive egress, and closed-suction irrigation techniques. These historical methods will be reviewed and contrasted with NPWT with instillation followed by 5 surgical case studies. Antibiotic-Laced Beads Antibiotic beads have been a mainstay in the senior authors’ practice for dead-space management following osteomyelitis resection. The use of this modality is well documented.^2–12 However, several limitations have been noted. The antibiotic cannot be changed based on sensitivity testing and must be heat stable, as the curing process of the beads is an exothermic process. The manufacturing of beads increases operating room time and can necessitate return trips to the operating room for bead exchange if either sensitivity testing or the need for long-term elution warrants fresh bead implantation. Proper elution from the beads necessitates either primary wound closure over the beads or coverage with an impermeable film dressing to create a “bead pouch.” The beads must typically be resected at a later date, particularly if they remain in a weightbearing area. Resection can be complicated by failure of the wire that is used to percutaneously remove the beads, bleeding, and generalized wound trauma after excision, sinus tract formation at the site of wire egress, and a possible second trip to the operative theater to remove bead chains that have ruptured off of the wire or fibrosed into the healing tissues. There also can be variability of antibiotic elution from the construct. Lastly, resistance and subsequent colonization of the bead surface has been noted by the authors in the past. A newer attempt at limiting some of these difficulties is the use of calcium sulfate as the bead medium, which allows slow resorption of the beads themselves. However, a significant increase in drainage occurs during this process, which can complicate the wound healing process. Instillation and Closed Suction Irrigation Various attempts at the instillation of antibiotic solution into a wound have been made with either passive egress through the suture line or active suction via an exterior pump.^13–19 Experience of the primary author with these devices has shown multiple limitations. Typically, these have included entry or exit site pressure damage, excoriations, and wound maceration. With the modified Kritter-type instillation technique, this maceration can be significant. Even with the addition of an exterior pump to create a closed suction irrigation technique, difficulties in ensuring adequate suction due to general mechanical insufficiencies created a significant burden on hospital staff. Fabrication of the device was time consuming. Secondary infections due to the uncontrolled drainage hindered the therapeutic success. Even when suction is applied successfully, the mechanics of the implanted catheter limit any local negative pressure effects to the immediate vicinity of the tube and result in incomplete treatment of the overall dead space. Lastly, uniform distribution of antibiotic solution throughout the wound is difficult to ensure via a simple catheter. Pockets of incomplete suction distribution and subsequent undrained areas are likely. Generally, as a prerequisite for use, both antibiotic beads and Kritter-type instillation techniques depend on the ability to primarily close over the device. Negative Pressure Wound Therapy Negative pressure dressings are now widely accepted in the treatment of chronic and acute wounds, including fistulas, traumatic wounds, dehisced wounds, flaps and grafts, pressure ulcers, diabetic foot ulcers, post-operative wounds, chronic wounds in patients who are poor surgical candidates, partial-thickness burns, and exposed hardware.^20–38 The ability of these negative pressure dressings to maintain a controlled, moist environment over large cavitating wounds has allowed for optimal radical debridement to normal tissue planes in the authors’ practice rather than the suboptimal conservative debridements performed in the past. The devices work through application of a disposable, open-cell foam dressing to the wound base, which is covered with an impermeable film drape. An evacuation tube embedded in the foam dressing is connected through an adjustable vacuum pump to remove effluent to a remote collection container. Microprocessor controls can be programmed for varying pressures and cycles of constant and intermittent suction. As subatmospheric pressure is applied to the dressing, the foam collapses, which results in multiple benefits including: • Increased local blood flow via enhancement of capillary flow • Increased angiogenesis with profuse granulation formation • Increased number of active fibroblasts and macrophages • Enhanced epithelial cell migration • Decreased bioburden, bacterial toxins, and subsequent cessation/delay of healing and decreased tensile strength of wound • Decreased harmful, chronic wound fluid and byproducts and subsequent senescent cells and tissue damage • Decompressed excess interstitial fluid with subsequent decreased periwound induration, inelasticity, and microvascular occlusion • Reduced number of dressing changes and subsequent decreased damage to delicate new tissue, pain, desiccation, and exposure to nosocomial infection • Provision of a moist, normothermic wound environment that allows more efficient epithelialization, growth factor synthesis and availability, and overall wound healing potential • Provision of mechanical approximation of wound edges as the open-cell foam collapses • Promotion of viscoelastic flow and distraction histiogenesis due to tissue stretch and stimulation of cytoskeleton with subsequent enhanced mitosis • Decreased shear forces of graft during inosculation via uniform wound bed immobilization under the collapsed foam • Increased graft take secondary to enhanced nutritional fluids being drawn through graft prior to capillary ingrowth with maintenance of intimate contact of graft to wound bed • Decreased seroma/hematoma of grafts and flaps • Limitation of zone of injury after acute orthopedic trauma.³² Relative and absolute contraindications and precautions include malignancy in the wound margins, untreated osteomyelitis or necrotic wound eschar, fistulas to organs or cavities, exposed blood vessels and nerve, exposed organs, exposed bone spicules, severe peripheral vascular disease, dry wounds, active bleeding, anticoagulants and difficult hemostasis, and proximity to sutured or irradiated vessels or organs. Complications are rare but can include infection, desiccation, pain, erosions, odor, tissue ingrowth, maceration, and bullae. Combination of Negative Pressure Wound Therapy with Solution Instillation Negative pressure wound therapy with instillation is a new device available in the acute care setting. A review of the new device with case studies was published by Wolvos in 2004.³⁶ He discussed the indications for choosing the NPWT with instillation platform rather than traditional NPWT platforms in order to address the need for concomitant pain control and to treat grossly contaminated and infected wounds. This device was developed from the platform of the V.A.C.®ATS (KCI, San Antonio, Tex) with the addition of a second ingress tube that allows gravity feed of solutions into the foam. The device has an incorporated intravenous pole that accommodates standard intravenous fluid bags. In addition to clinical benefits of the platform’s negative pressure management, NPWT with instillation allows automatic delivery and removal of topical solutions to the wound site. The same programmable microprocessor that controls the amount and cycles of negative pressure also can be adjusted to allow for varying lengths of solution infusion and dwell times into the foam. A mechanical clamp closes and opens the intravenous tubing. The solution is gravity fed. Accordingly, the intravenous bag must be at or slightly above the level of the wound. The unit can be programmed to apply negative pressure continuously for up to 12 hours. In addition, the clinician can choose an instillation time from 1 second to 2 minutes and solution dwell time from 1 second to 1 hour. The device functions as a standard V.A.C.®ATS unit for the remainder of the treatment period with continuous negative pressure. A range of topical solutions has been proposed, including cleansers, antibiotics, antifungals, antiseptics, and anesthetics. Negative pressure wound therapy with instillation is intended for use with aqueous solutions in a physiologic pH range defined as 6.0–7.4. Physician discretion is advised when using NPWT with instillation on wounds requiring continuous NPWT, such as wounds with fresh flaps and grafts. It should be noted that NPWT with instillation is not approved for use outside of a hospital. (continued in Part 2)