Examining The Role Of NPWT In Limb Salvage
Diabetic foot ulcerations are a significant public health concern and cause an increasingly heavy demand on our healthcare systems. Diabetic foot infections cause more than 300,000 admissions to hospitals each year, leading to approximately 92,000 amputations.1 The resulting wounds require intensive local wound care and are slow to heal, resulting in prolonged disability and hospitalization.
The hospitalizations required for effective treatment of diabetic foot ulcerations have become very costly to the healthcare system. When it comes to providing appropriate treatment and wound care products to these patients, there seems to be a constant battle between physicians and healthcare systems.
Research has shown that using negative pressure wound therapy (NPWT) decreases bacterial colonization and interstitial edema, and increases capillary blood flow with an overall increase in granulation tissue to diabetic foot wounds.2 In addition, NPWT reduces wound surface area by the traction force of negative pressure, which increases mitosis of tissue around the wound.3,4
With negative pressure wound therapy introduced to the healthcare plan of many patients with diabetic foot ulcerations, both the overall cost to the healthcare system and the morbidity of patients have decreased. While the initial cost of NPWT is frontloaded, researchers have shown that this therapy can decrease the time to healing and decrease hospitalizations for the treatment of diabetic foot ulcerations.
Assessing The Research On NPWT
Flack and colleagues designed a Markov model to estimate the cost per amputation avoided and the cost per quality-adjusted life year of vacuum assisted closure (VAC) therapy in comparison with both traditional and advanced dressings.5 With this model simulating 1,000 patients over one year, the researchers focused on uninfected ulcers, infected ulcers, infected ulcers post-amputation as well as healed ulcerations, healed post-amputation ulcers, amputation and death. The study included males and females ages 50 to 65 with type 1 or type 2 diabetes mellitus, and only assessed direct costs to the patients.
This study found improved healing rates with VAC therapy (61 percent versus 59 percent) and an overall lower cost of care ($52,830 versus $61,757) in comparison to more traditional wet to dry dressings and advanced skin substitute dressings.5
Philbeck and colleagues examined the cost effectiveness of VAC therapy in the home care of Medicare patients.6 This retrospective study compared the costs of stage III and stage IV pressure ulcers treated with NPWT to those of patients who historically received conventional wound care. Patients with 566 pressure ulcers treated with NWPT closed at an average rate of 0.23 cm2 per day in comparison to 0.090 cm2 for the historical control. Using these healing rates, researchers found NPWT-treated wounds were 38 percent less costly to treat than those receiving conventional treatment.
A pilot study by McCallon and colleagues examined the outcomes in the treatment of postoperative diabetic foot ulcerations.7 Wounds treated with NPWT achieved closure three weeks sooner than those treated with normal saline moist-to-moist dressings twice daily. Wounds treated with conventional dressings exhibited an increase in surface area of 9.5 percent whereas wounds treated with NPWT decreased by 28.4 percent.
Armstrong and co-workers retrospectively evaluated the outcomes of 31 patients with large diabetic foot wounds before and after NPWT.8 The mean duration of wounds before NPWT was 25.4 weeks. Ninety percent of wounds healed without the need for further bony resection in an average of 8.1 weeks.
A Closer Look At The GranuFoam Silver Dressing
Out of the commercially available NPWT systems, the Info VAC (KCI) has the most historical use and the most research behind it. The KCI dressings available for diabetic foot ulcerations include the GranuFoam, GranuFoam Silver, WhiteFoam and the recently introduced GranuFoam Bridge system. Each of these dressings has an open-cell, polyurethane reticulated foam structure and a pore dimension of approximately 400 to 600 microns.9
With the GranuFoam Silver dressing, the reticulated polyurethane foam has micro-bonded with metallic silver via a metallization process. Exposure of the dressing to wound fluid results in oxidation of metallic silver to ionic silver. This allows the continuous, sustained release of silver ions for antimicrobial activity. Ionic silver binds to and damages microbial cell walls at multiple sites. Ionic silver has various mechanisms of action. This multi-pronged attack of silver makes it difficult for microorganisms to develop defense mechanisms.10,11
The concentration of silver ions released impacts antimicrobial efficacy. Having too high a concentration could lead to tissue toxicity.12 An in vitro silver elution study showed the VAC GranuFoam Silver dressing provided sustained release of ionic silver up to 72 hours. The approximate concentration of silver in the extract solution at 72 hours for the VAC GranuFoam Silver dressing was not statistically different from Aquacel Ag (ConvaTec) dressing and the Acticoat 7 Day (Smith and Nephew) dressing under identical experimental conditions.9
Another study looked at the aforementioned dressings over an eight-day span with researchers taking 3 mm punch biopsies and measuring the ionic silver tissue levels. At the end point, the average value was 315 mg Ag+/g of tissue and the average value for the VAC GranuFoam plus Acticoat dressing was 151 mg Ag+/g of tissue.9
Previous research indicates that the ability of the silver-containing dressing to conform to the contours of the wound is important to reduce the non-contact area where bacteria may proliferate.13 The compressible foam under negative pressure allows the VAC GranuFoam Silver dressing to obtain complete contact to the surface of the wound bed.
Although in vitro data has shown the VAC GranuFoam Silver dressing has lower elution concentrations than adjunctive silver dressings like Acticoat, animal tests performed under negative pressure conditions revealed that the VAC GranuFoam Silver dressing results in having twice as much silver available at the wound site.9
What Preliminary Findings From One Retrospective Review Reveal
Commercially available NPWT systems were not available on the inpatient formulary at Georgetown University Hospital until June 2008. On a trial basis, physicians employed five InfoVAC NPWT systems for inpatients undergoing limb salvage surgical care. A retrospective review examined the effect on length of stay for this patient group in comparison to a historical control group of similar patients.
Using retrospective discharge data at Georgetown University Hospital, researchers compared the length of stay for patients receiving InfoVAC therapy to patients admitted to the same inpatient service before VAC therapy was available. All patients receiving InfoVAC therapy at Georgetown University Hospital were included in the study and were admitted from June 2008 through January 2009. The study included consecutive patients who did not receive VAC therapy, who were identified from service admissions February 2008 through May 2008.
Researchers utilized the InfoVAC system for the lower extremity wounds of 89 patients during 93 different admissions. The average length of stay for the InfoVAC patients was 10.83 days. In the control group of 78 patients who did not receive InfoVAC therapy, the average length of stay was 13.88 days. The patients receiving InfoVAC therapy had an average length of stay that was 3.05 days fewer than those patients who did not receive InfoVAC.
In Conclusion
Performing diabetic limb salvage inpatient surgery in a setting of increased financial accountability requires diligent use of resources.
The preliminary evidence of the KCI InfoVAC system trial at Georgetown University Hospital has shown that one can achieve a decreased length of stay in this patient population through the incorporation of commercially available NPWT into the treatment algorithm. There is an abundance of clinical data that confirms the improved wound healing associated with the use of NPWT systems.14 This retrospective utilization review now provides evidence for improved fiscal accountability for the hospital and care provider as well.
Dr. Keplinger is a third-year resident within the Inova Fairfax Hospital Podiatric Residency Program in Falls Church, Va.
Dr. Steinberg is an Assistant Professor in the Department of Plastic Surgery at the Georgetown University School of Medicine in Washington, D.C. Dr. Steinberg is a Fellow of the American College of Foot and Ankle Surgeons.
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References:
1. Eginton MT, Brown KR, Seabrook, GR, Towne JB. A prospective randomized evaluation of negative-pressure wound dressings for diabetic foot wounds. Ann Vasc Surg 2003; 17(6):645-649 2. Argenta LC, Morykwas MJ. Vacuum-assisted closure: a new method for wound control and treatment: clinical experiences. Ann Plast Surg 1997; 38(6):563-576. 3. DeFranzo AJ, Marks MW, Argenta LC, Genecov DG. Vacuum-assisted closure for the treatment of degloving injuries. Plast Reconstr Surg 1999; 104(7):2145-2148. 4. Kirby JP, Fantus RJ, Ward S, et al. Novel uses of a negative pressure wound care system. J Trauma 2002; 53(1):117-121. 5. Flack S, et al. An economic evaluation of VAC therapy compared with wound dressings in the treatment of diabetic foot ulcers. J Wound Care 2008; 17(2):71-8. 6. Phillbeck TE Jr., Whittington KT, Millsap MH, et al. The clinical and cost effectiveness of externally applied negative pressure wound therapy in the treatment of wounds in home healthcare Medicare patients. Ostomy Wound Manage 1999; 45(11):45-50. 7. McCallon SK, Knight CA, Valiulus JP, et al. Vacuum-assisted closure versus saline-moistened gauze in the healing of post-op diabetc foot wounds. Ostomy Wound Manage 2000; 46(8):28-34. 8. Armstrong DG, Lavery LA, Abu-Rumman P, et al. Outcomes of subatmospheric pressure dressing therapy on wounds of the diabetic foot. Ostomy Wound Manage 2002; 48(4):64-68. 9. Ambrosio A, et al. V.A.C. GranuFoam Silver Dressing – a new antimicrobial silver foam dressing specifically engineered for the use with V.A.C. Therapy. Kinetic Concepts, Inc (KCI). San Antonio, 1996, pp.1-15. 10. Fridkin SK, Gaynes RP. Antimicrobial resistance in intensive care units. Clin Chest Med 1999;20(2):303-315. 11. Ovington LG. The truth about silver. Ostomy Wound Manage 2004;50(9A Suppl):1S-10S. 12. Faust RA. Toxicity summary for silver. Report prepared for the Oak Ridge Reservation Environmental Restoration Program, December 1992. 13. Jones S, Bowler PG, Walker M. Antimicrobial activity of silver-containing dressings is influenced by dressing comfortably with a wound surface. Wounds 2005;17(9):263-270. 14. Page JC, Newstander B, Schwenke DC, et al. Retrospective analysis of negative pressure wound therapy in open foot wounds with significant soft tissue defects. Advances Skin Wound Care 2004; 17(7):354-364.
