Is Foam More Effective Than Gauze With Negative Pressure Wound Therapy?

Yes. Lee C. Rogers, DPM cites the evidence from negative pressure wound therapy (NPWT) trials and says the characteristics of NPWT foam facilitate the development of granulation tissue and improved healing in diabetic foot ulcers.

   There is no question that negative pressure wound therapy (NPWT) is a valuable modality in facilitating wound closure. In particular, the use of foam dressings with NPWT has demonstrated success in reducing wound surface size and accelerating the formation of granulation tissue.

   The foam most commonly used in NPWT is the Vacuum-Assisted Closure (VAC) Granufoam (Kinetic Concepts, Inc.). This is an open-cell polyurethane foam. Its defining properties are cell (pore) size, contractility and non-absorbency. Each of these properties influences the wound bed.

   Researchers have shown that the cell size of VAC therapy foam produces tangential strain, which causes microdeformation of the cells in the wound bed and stimulates proliferation.1 This micro-strain results in undulations in the surface of the wound and leads to robust formation of granular tissue. In regard to the use of VAC therapy foam, researchers have shown, in vitro, fibroblast migration as well as increased proliferation through mitosis.

   In many cases, one can see budding of vascular tissue in the wound bed after using the foam under negative pressure. The open cell foam allows uniform application of negative pressure to the wound bed.

   One of the benefits of an open-cell foam is its ability to contract under negative pressure. In a paper submitted for publication, Rogers and colleagues performed an evaluation comparing the surface area of gauze and foam under negative pressure at -125 mmHg.2 The foam reduced to 40 percent of its original area whereas the gauze decreased to only 88 percent of its original size. Wound contraction is an important principle in healing and foam is far superior at achieving this effect in comparison to gauze.3

   A foam is technically non-absorbent whereas a sponge (gauze) is absorbent. The foam allows the wound exudate to pass through into the negative pressure canister. Gauze sponges absorb some of this exudate and keep it in contact with the wound bed during use. Not only can the amount of fluid produced by a wound be an impediment to healing but the inflammatory factors in that fluid also impair healing. Pro-inflammatory cytokines and matrix metalloproteinases (MMPs) are present in high concentrations in chronic wound fluid.4,5 Furthermore, these proteinases destroy growth factors.6

What The Studies Reveal About NPWT And Foam

   Most notably, in all of the randomized controlled trials comparing NPWT with the standard of care in diabetic foot ulcers, physicians used VAC Granufoam under negative pressure.7,8,9 Study authors have found that wounds healed faster in the NPWT foam groups. There have been no randomized controlled trials evaluating the use of gauze with negative pressure and no comparison trials of gauze versus foam.

   McCallon and colleagues studied 10 patients with non-healing, postoperative diabetic foot ulcerations. These patients were randomized into either a VAC therapy group or a control saline gauze group. The study found that patients in the NPWT group achieved satisfactory healing in 22.8 (+/- 17.4) days in comparison to 42.8 (+/- 32.5) days in the control group.

   In addition, Blume and co-workers studied 342 patients with diabetic foot ulcers.9 They found that patients undergoing NPWT had fewer home care therapy days and significantly fewer secondary amputations in comparison to those treated with advanced moist wound therapy.9

   Armstrong and Lavery studied 162 patients who had partial foot amputation wounds up to the transmetatarsal level and evidence of adequate perfusion. Patients received either VAC therapy or standard moist wound care.10 The study found that NPWT with foam accelerated the formation of granulation tissue and also limited secondary amputations.

   Two trials involving patients with pressure ulcers compared NPWT with foam with other therapies. Both showed better healing in the NPWT foam groups.11,12 In particular, Ford and co-authors studied 22 patients with 35 full-thickness decubitus ulcers. Patients received either VAC therapy with foam or the Healthpoint system of wound gel products. The mean percent reduction in ulcer volume at six weeks was 51.8 percent in the NPWT group in comparison to 42.1 percent in the wound gel group.11

   There have been no randomized controlled trials in foot wounds using gauze under NPWT. Therefore, the use of gauze under NPWT for DFUs is still experimental and unpredictable. To my knowledge, no trials are currently underway that compare foam to gauze under negative pressure.

Case Study: When A Patient Presents With A Malodorous, Fibrotic Ulcer

   A 62-year-old Caucasian male with type 2 diabetes and lymphedema presented with a dorsal foot ulceration of one month in duration. The foot ulcer was malodorous and thoroughly fibrotic. Physicians performed aggressive debridement with the Versajet hydroscalpel (Smith & Nephew). The tibialis anterior tendon became exposed. Debridement and parenteral antibiotics were able to control the infection.

   The physician applied VAC Granufoam intraoperatively in a hospital setting. After two VAC therapy dressing changes in six days, the wound was clean, granular and level with the surrounding skin. The patient underwent a split thickness skin graft which came from the ipsilateral thigh. The physician secured the graft in place on the ulcer with skin staples.
   The podiatrist used VAC Granufoam as a bolster dressing and also employed a non-adherent dressing between the foam and skin graft. The most important considerations in postoperative graft treatment are prevention of hematoma and seroma, and limiting graft shearing. Negative pressure wound therapy achieves these goals. One would use NPWT for three to five days continuously over the graft and subsequently discontinue its use. The interstices filled in and complete healing occurred in three weeks.

In Conclusion

   Researchers have shown that the use of foam under NPWT speeds wound closure, enhances granulation tissue formation and limits secondary amputations. Therefore, I recommend the use of foam with negative pressure wound therapy for diabetic foot ulcers whenever possible.

Dr. Rogers is the Director of the Amputation Prevention Center at Broadlawns Medical Center in Des Moines, Iowa. He directs research at the center and has been an investigator on over 20 clinical trials.

References

1. Saxena V, Hwang CW, Huang S. Vacuum-assisted closure: microdeformations of wounds and cell proliferation. Plast Reconstr Surg 2004;114:1086-96.
2. Rogers LC, Bevilacqua NJ, Armstrong DG. Contraction properties of 3 biomaterials with negative pressure wound therapy. Submitted for publication 2009.
3. Gross J, Farinelli W, Sadow P, et al. On the mechanism of skin wound “contraction”: a granulation tissue “knockout” with a normal phenotype. Proc Natl Acad Sci USA 1995;92:5982-6.
4. Tarnuzzer RW, Schultz GS. Biochemical analysis of acute and chronic wound environments. Wound Repair Regen 1996;4:321-5.
5. Weckroth M, Vaheri A, Lauharanta J, et al. Matrix metalloproteinases, gelatinise and collagenase, in chronic leg ulcers. J Invest Dermatol 1996;106:1119-24.
6. Wlaschek M, Peus D, Achterberg V, et al. Protease inhibitors protect growth factor activity in chronic wounds. Br J Dermatol 1997;137(4):646.
7. Eginton MR, Brown KR, Seabrook GR, et al. A prospective randomized evaluation of negative-pressure wound dressings for diabetic foot wounds. Ann Vasc Surg 2003;17(6):645-9.
8. McCallon SK, Knight CA, Valiulus JP, et al. Vacuum-assisted closure versus saline-moistened gauze in the healing of postoperative diabetic foot wounds. Ostomy Wound Mange 2000;46:28-34.
9. Blume PA, Walters J, Payne W, et al. Comparison of negative pressure wound therapy using vacuum-assisted closure with advanced moist wound therapy. Diabetes Care 2008;31:631-6.
10. Armstrong DG, Lavery LA, Diabetic foot study consortium. Negative pressure wound therapy after partial diabetic foot amputation: a multicentre, randomised controlled trial. Lancet 2005;366:1704-10.
11. Ford CN, Reinhard ER, Yeh D, et al. Interim analysis of a prospective, randomized trial of vacuum-assisted closure versus the Healthpoint system in management of pressure ulcers. Ann Plast Surg 2002;49:55-61.
12. Wild T, Stremitzer S, Budzanowski A, et al. Definition of efficacy in vacuum therapy – a randomised controlled trial comparing with V.A.C. therapy. Int Wound J 2008;5:641-7.

Editor’s note: For related articles, see “Expert Pointers On Negative Pressure Wound Therapy” in the July 2007 issue of Podiatry Today, “How To Use VAC Therapy On Chronic Wounds” in the July 2002 issue or “Combining VAC Therapy With Advanced Modalities: Can It Expedite Healing?” in the September 2005 issue.

For other related articles, please visit the archives at www.podiatrytoday.com

No. Michael Miller, DO says gauze is more cost-effective and has significantly fewer associated complications than foam with NPWT.

   The goal of negative pressure wound therapy (NPWT) is to apply a stimulus in the form of negative pressure to a wound to promote healing. In simplest terms, the foam, gauze or other porous, non-adherent wound contact layer acts as a conduit from the suction generating device to the surface of the wound.

   The question is not whether foam and/or gauze can act in this manner and promote a healing effect. Rather, the question is, what are the comparative benefits and detriments to each?

   I will not belabor the multiple effects of a negative pressure stimulus on a wound since there are numerous articles identifying the attributes (both actual and theorized) that contribute to wound healing on both the microscopic and macroscopic levels. Studies published on the effects of all negative pressure conduits have various merits and weaknesses. However, the drawback is there still remains a paucity of evidence conclusively demonstrating the definitive superiority of porous, non-adherent wound contact media (the most recognized of which is gauze) over foam or vice-versa.

   When one replaces the hype, marketing and profit motive with simple science such as Boyle’s law, Charles’ Laws and Poiseuille’s equation, then the question of whether foam or gauze is more effective as a conduit becomes a moot point since they act in accordance with these laws of physics. The real question then becomes an elegantly simple one. Does the use of foam provide definitively superior healing effects and results over gauze when comparing both as conduits for negative pressure?

Foam Or Gauze: Which Has More Associated Complications?

   One of the most prevalent concerns for ethical healthcare providers involves the risks and complications of a given therapy. Regardless of the perceived or actual benefits, the potential for and actual occurrence of complications must be an ongoing consideration for all treatments including conduits for negative pressure. If one considers the benefits, one must also consider the detrimental effects.

   A search of the Manufacturer and User Facility Device Experience (MAUDE) database using the search terms “VAC” and “Granufoam” identified 24 reports of complications from the period of January 8, 2009 to March 24, 2009. The MAUDE data represents reports of adverse events involving medical devices identified to the FDA. These adverse events included surgical procedures for retained foam, bleeding, death and other complications. Extrapolating these reported complications to a one-year time period, there would be 96 reported complications, the majority of which would be related directly to the foam.

   Even if one considers the significant, worldwide number of patients in whom foam is used, this number of problems referable to a simple conduit (especially after 12 years of commercial utilization) demonstrates that there are clear reasons to be concerned regarding foam’s “effect.”

   In contrast, using the search terms “gauze” and “AMD”, there were less than 10 reports of complications from 1992 through March 24, 2009. Note that these reports were identified in MAUDE because the words “gauze” and “AMD” were in the text of the report although they were not related to the reported complication. Clearly, a less desirable effect is the numerous and ongoing identification and reporting of complications referable to the use of foam with negative pressure, an effect not identified with gauze.

What About Cost-Effectiveness?

   In today’s economic climate, costs are a significant consideration. A recent report by the Office of the Inspector General found it is highly likely that reimbursement for the NPWT pumps themselves will be subject to competitive bidding (and hence mitigate the differences in costs).1

   The document clearly identified that not only was there insufficient evidence to support the superiority of one system and conduit over any other, but that the reimbursement related to NPWT systems and conduits were excessive and were highly likely to be dramatically reduced in the immediate future.

   Looking specifically at the costs of the conduits provides clear and stark differences. The total cost of a “kit” consisting of a single piece of AMD gauze ($.04) and a silicone drain ($3.25) is in stark contrast to the cost of a small piece of black, sterile, PVC foam at about $30. Figures are based on available research from numerous sources including materials management departments at several Indiana hospitals, long-term care facilities and competing NPWT durable medical equipment suppliers, and are subject to variations.

   Note that the costs for the foam products are based on numerous factors including the quantity purchased, size of the foam and extras (such as the addition of silver, the connecting piece from the foam to the pump, the “buying power” of the respective organization, etc.).

   Even in the best of circumstances and with respect to innumerable factors, there are significant differences between a gauze/drain kit at $3.29 and best conceivable pricing for a foam-based NPWT conduit. Clearly, the dramatic cost differentials between these two conduits suggest that yet another effect needs to undergo stringent evaluation when it comes to perceived and actual value. To warrant the considerable cost differential, the use of foam would have to be unquestionably superior in a plethora of comparisons including pain, time to healing, the effect on infection and ease of use.

Assessing Recent Data That Compares NPWT Modalities

   What does the data show regarding the true superiority of one system over another? The Agency for Healthcare Research and Quality recently published a technology assessment report for NPWT devices.2 The committee developed four key questions to guide the evaluation.

    1. Does any single NPWT system have a significant therapeutic distinction in terms of wound healing outcomes in comparison to any other NPWT system for the treatment of acute or chronic wounds?
   2. Does any component of a NPWT system have a significant therapeutic distinction in terms of wound healing outcomes compared to any other similar component of a NPWT system for the treatment of acute or chronic wounds?
   3. What are the reported occurrences of pain, bleeding, infection, other complications and mortality for NPWT systems?
   4. Do patients being treated with one NPWT system have a significant therapeutic distinction in terms of less pain, bleeding, infection, other complications or mortality in comparison to other NPWT systems?

   This voluminous document concluded (based on the aforementioned search strategies and the materials provided by interested parties) that no studies directly comparing one NPWT system to another addressed questions 1, 2 or 4. Regarding the third question, the document noted insufficient literature/published data to identify the propensity of occurrence in one system over another.

   The authors were not able to identify a significant therapeutic distinction of one NPWT system or component over another through the use of head-to-head comparisons.2

What A Recent Study Reveals About Gauze

   In actuality, the questions of a more or less “effective” treatment are too nondescript to allow for any single answer. Studies published or presented thus far to date in the literature have had the taint of commercial sponsorship in the paper or, in some other way, a financially beneficial position.

   However, a recently completed randomized, controlled trial compared the foam-based VAC therapy system to wall suction applied to sealed gauze dressings, a method called G-SUC, in the inpatient setting of a university hospital. Researchers acknowledged that VAC therapy is expensive and difficult to use (and frequently fails) in wounds with excess fluid drainage, and in wounds near body orifices.3 Researchers initially used G-SUC clinically in the hospital for the management of infected wounds and when patients had an inability to maintain a dressing seal with the VAC therapy system (due to excess drainage or wound location). The authors reported that G-SUC was “effective without any specific negative side effects.”3

   The study concluded that G-SUC provides an alternative negative pressure wound therapy that is at least as effective as VAC therapy with respect to wound volume and surface area. The authors also concluded that G-SUC offers significant cost savings to the hospital, saves time on each dressing application by the wound therapist and is also less painful during dressing changes than VAC therapy.3

   This study closed in March 2008 with expected publication in the very near future. As of this date, the authors have not yet confirmed specifics regarding publication. This is the first study to provide head to head comparison on the more salient points of contention between foam and gauze as NPWT conduits.

Dr. Miller is a physician specializing in wound care in Indiana. He is the Chairman of Mobility Solutions, which helped develop and currently markets several new NPWT dressing products. Dr. Miller has written numerous articles and book chapters on NPWT, and other wound-related topics. One can reach him at www.doc@docmillers.com.

References

1. Department of Health and Human Services Office of the Inspector General. Comparison of prices for negative pressure wound therapy pumps. March 2009. Accessed at www.oig.hhs.gov.
2. Sullivan N, Snyder DL, Tipton K, et al. Negative pressure wound therapy. Technology assessment. June 2009. Rockville, MD: Agency for Healthcare Research and Quality. https://www.ahrq.gov/clinic/ta/negpresswtd/
3. Gottlieb L. A prospective randomized control trial comparing two methods of negative pressure wound therapy: gauze suction versus vacuum assisted closure device. Abstract presented at the American Association of Plastic Surgeons, 2009. In press, 2009.