Examining The Role Of NPWT In Limb Salvage
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.