Dear Editor:
In reference to the article by Parsons et al published in the August 2005 issue of WOUNDS [Parsons D, Bowler PG, Myles V, Jones S. Silver antimicrobial dressings in wound management: a comparison of antibacterial, physical, and chemical characteristics. WOUNDS. 2005;17(8):222–232.], we have come upon several shortcomings of the tests and misleading conclusions. We point out 3 as follows:
1. The measurement of antibacterial activity was conducted in different ways with 2-fold amount of fluid and a total of 33% surplus of bacteria for the 2 foam dressings compared with the other dressings. Nevertheless, the results are compared and discussed and conclusions made without acknowledgement of the dissimilar test setup.
2. The absorption tests were carried out for 20 seconds, which is inappropriate for most dressings on the market. When the absorption capacity of foam A (Contreet® Foam, Coloplast, Humlebaek, Denmark) was tested for 30 minutes according to “EN 13726-1:2002—section 3.2 free swelling capacity” and under compression equal to 40 mmHg, absorption of 73.2 g/100 cm2 was observed for zero pressure and 70.2 g/100 cm2 with 40 mmHg compression. When comparing these data with the 20 seconds absorption data from the article, the results without compression were almost equal, while the absorption with 40 mmHg compression was extremely dissimilar (more than 2-fold difference). This indicates that 20 seconds is indeed not enough to allow foam A to achieve maximum absorption under compression. Furthermore, the authors interpret the percentage difference between absorption with and without 40 mmHg compression for 20 seconds as a dressing’s capability of retaining fluid under pressure, which, as the example above emphasizes, is clearly misleading.
3. The silver release measurements were carried out in deionized water, which is an inappropriate medium, especially for dressings that release silver ions by ion exchange.
In all tests, nonwoven A (AQUACEL® Ag, ConvaTec, Skillman, NJ, USA) comes out the best. It is not evident from the results that this would be the case had the authors used comparable methods for all dressings and more standardized and clinically relevant test methods. Based on these examples, we request that the authors substantiate the methods applied and conclusions drawn or, if not able to do so, publish an erratum and refrain from citing these conclusions in future publications.
Maibritt B. Andersen, MSc, PhD
Mogens Dolmer, MSc
Medical Outcomes Department/Research &
Development
Coloplast A/S
Humlebaek, Denmark
Dear Editor:
We would like to thank Dr. Andersen and Mr. Dolmer for the issues they raise and we welcome the opportunity to respond to them. Rather than simply focus on silver, the aim of our article was to broaden the scope of the debate to encompass all aspects of an antimicrobial dressing. The application of a range of tests attempted to illustrate many different and important features and to demonstrate that not all dressings perform in the same way. Because of this, we hoped to show that looking at only a single feature or test may not necessarily lead to the selection of the most appropriate dressing. It proved impossible to perform all potential tests on all available dressings; therefore, a variety of popular types were chosen so that similarities and differences could be highlighted.
With respect to antibacterial activity, Dr. Andersen and Mr. Dolmer are correct to point out that the 2 foam dressings (foam A, Contreet® Foam, and foam B, PolyMem® Silver) received a higher volume of challenge solution and a greater number of bacteria. In this respect, the test conditions were not entirely equivalent; this fact is clearly referenced in the text and in the figure legends. The difference in method was necessary to compensate for the higher free swell absorption of the foam dressings and to allow sampling of free fluid without undue agitation of the samples. Viewing this from a user perspective, a key selling feature of foams is their perceived high absorbency. If this is true, a greater volume of bacterial challenge may be an appropriate representation of such dressings in use.
To investigate fluid handling properties, we used a method based on British Pharmacopoeia 1993 Appendix XX T (water-retention capacity). When no pressure was applied, there appeared to be little difference in results for foam A between this test and EN 13726:2002 (66.8 g versus 72.3 g/100 cm2). However, the correspondents highlighted a significant difference when testing dressings under applied pressure. This difference is likely to be due to the stage in the test at which pressure is applied. EN 13726:2002 requires the application of pressure after 30 minutes of pressure-free absorption, whereas the method described in this article applies the pressure before any contact with fluid. It is clear that different properties are being measured in each test. Therefore, it is unsurprising that differences are observed. Although neither test truly reflects all possible clinical situations, the 50% reduction in absorption capacity for foam A that we have reported could be interpreted as being indicative of a lower absorption capacity under a compressive secondary dressing. We hope this is a clearer and more accurate interpretation of the results with respect to foam dressings.
Some authors promote the use of water as a test medium.1 However, we are trying to highlight the unsuitability of using silver release into water as a means of predicting antimicrobial activity. Therefore, we are in full agreement with Dr. Andersen and Mr. Dolmer; if dissolution rate is to be used in product promotion, then it should be into a relevant test solution. Furthermore, it is essential that only ionic silver and not other forms of silver be measured.
In preparing this article, we have tried to be as objective as possible in our selection of tests and the interpretation of results. Where practical, we have supplied descriptions of the methods used so that they are open to question and review. However, because nonwoven A (AQUACEL® Ag) was specifically engineered to combine excellent dressing characteristics with an appropriate level of antimicrobial activity, we were unsurprised by its overall favorable performance.
David Parsons, PhD
Philip G Bowler, MPhil
Viv Myles, MSc
Samantha Jones, BSc
ConvaTec Wound Therapeutics™ Global
Development Centre
Deeside, Flintshire, United Kingdom
Reference
1. Brett DW. A discussion of silver as an antimicrobial agent: alleviating the confusion. Ostomy Wound Manage. 2006;52(1):34–41.
Dear Editor:
Dear Editor:
In the December 2005 issue of WOUNDS, Frye and Luterman published an article on hypertrophic scar formation and its relation to 2 different treatment regimes [Frye KE, Luterman A. Decreased incidence of hypertrophic burn scar formation with the use of collagenase, an enzymatic debriding agent. WOUNDS. 2005;17(12):332–336.].
The authors state that better cosmetic outcomes and fewer problems with hypertrophic scars may be attributed to the use of collagenase.
Indeed, it is commonly accepted that rapid debridement allows for faster reepithelization and, consequently, may be linked to fewer problems with hypertrophy. However, a wet-to-dry dressing regime, which was the comparator against which collagenase was tested, may be detrimental to wound healing itself, since it will not prevent a wound from desiccation. Furthermore, wet-to-dry dressings may stick to the wound bed as well, causing trauma upon removal and, consequently, possible secondary deepening of the wound. Thus, a dressing regime that is less detrimental than wet-to-dry dressings, even without the benefit of enzymatic debridement, would probably have led to faster healing anyway and, consequently, to fewer hypertrophic scars.
The authors also state that during the last stages of wound management barrier dressings were used. Assuming that the term barrier dressing refers to semi-occlusive or semi-permeable materials, these materials per se are known to contribute to faster wound healing. Therefore, the timing (post-burn day) of application of these dressings may contribute to overall better results as well. Unfortunately, the authors do not mention this timing issue in the article nor do they indicate the criteria for changing to barrier dressings. The authors also do not define barrier dressings or indicate which ones were used.
The article would have been more complete—and the conclusions more solid—had these aspects been taken into account.
Michel H.E. Hermans, MD
Hermans Consulting Inc.
Newtown, PA
United States
Dear Editor:
The comments in the letter to the editor regarding our article on hypertrophic scar and the use of collagenase raise some legitimate issues. The study reported in the article was a retrospective review. The ideal method of study would have obviously been a prospective, randomized trial in which collagenase was compared to a simple petroleum-based ointment lacking any enzymatic or antimicrobial agents. To perform such a study would require a prolonged period of time and require that a large number of patients would not benefit from collagenase.
The term barrier dressing refers to semi-permeable materials. The most common barrier dressings used at our institution have historically been either xenograft or Biobrane® (UDL Laboratories, Inc., Rockford, Ill, USA). The indications for barrier dressings consist of a dermis free of necrotic tissue and free of bacterial growth. These indications were used for the wet-to-dry group as well as the collagenase group.
Karen E. Frye, MD, FACS
University of South Alabama
Mobile, AL
United States
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