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Odour Absorbing Dressings
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advice to correspondents.
We read with interest the article 'Odour-absorbing dressings: A comparative laboratory study' by Thomas et al (World Wide Wounds, March 1998) and wish to make a few comments.
First, we would like to clarify the actual function of the product tested. It is our belief that these dressings have been designed as odour adsorbing rather than absorbing products. The activated charcoal component within each of these products acts like a filter allowing odour molecules, among others, to accumulate on its surface within the numerous micropores that make up increased surface area. The charcoal cannot absorb material directly into its structure, merely bind it by weak electrical forces to the surface.
Second, the author proposes this method as an objective way for comparing the performance of odour absorbing dressings under simulated conditions of use with a volatile amine test solution. It is our belief that this stated method is fundamentally flawed and does not simulate in use conditions. Potential deficiencies in the method have already been outlined by the author focusing on representative exudate flow rates and choice of diethylamine.
We agree with the author's critique but feel that his arguments in support of existing methodology are difficult to fully justify. A lower flow rate is likely to exhibit different flow and distribution characteristics increasing the ability of activated charcoal to deal with odour molecules. The presence of diethylamine only indicates a static system representing the presence of odour like molecules, but fails to allow provision for the source of the odour. Failure to combat the source of the odour by limiting bacterial growth would eventually result in an increase in odour production during routine use.
Third, we would like to point out that simulated conditions of use were not followed in this study as the dressings tested were evaluated in isolation and not as part of the recommended treatment regime. Inclusion of a single component product not designed to handle exudate with an all-in-one format provides an unequal baseline for comparison. If a single component product were tested in conjunction with an absorbent, as often recommended in the manufacturer's instructions, any differences between the products would be less marked. Using the author's own data for Actisorb Plus and Release, the combined effect would be 13.4ml compared to 9.5ml (volume of test solution applied to dressings to produce 10ppm diethylamine in test chamber) for Actisorb Plus alone. This result compares with 12.7ml - 17.1ml for other dressings tested. Limited sample size and variability within the data does not allow meaningful conclusions to be drawn about the differences between these products.
In addition we must question the overall sensitivity of this particular approach in using a single end point to accurately assess a multifaceted problem. Addition of further absorbent layers or secondary dressings would also be expected to increase the effectiveness of these products based on this test. Therefore this method would appear not to simulate conditions found in-vivo where several dressing layers can be applied and variation in treatment depends on level of wound exudate.
Finally, we would agree with the author's comment regarding testing product impairment following saturation with wound fluid. We believe that this should be tested in conjunction with the treatment's ability to channel wound fluid away from the activated charcoal component as well as effectively deal with the underlying cause of the odour (i.e. antimicrobial activity). Odour detection and assessment is highly subjective although this approach would appear to provide a more appropriate simulation of conditions in use.
Lead Author, Dr Steve Thomas, replies:
The comments made by Warrick and Wiggans further highlight the problems of testing dressings designed to contain wound odour. Since the original study was published we have undertaken additional work using different test conditions. Instead of applying the test solution at 30 ml/hour, we used a flow rate of 1 ml/hour although we had to increase the concentration of the diethylamine in the test solution from 2% to 10% in order to obtain an adequate concentration of the diamine in the air in the test chamber.
The results of this second study were comparable with those of the initial work in that Carboflex, Carbonet and Lyofoam C produced mean values ranging from 0.83 - 0.89 ml whilst the Actisorb Plus result was 0.53 (+/- 0.08) ml. Release gave a mean result of 0.16(+/-0.01) ml which was only marginally better than the blank value of 0.11 (+/-0.03) that was recorded in the absence of any dressing.
Whilst it is true that Actisorb Plus would normally be used as part of a dressing system, it is marketed as a primary dressing and as such, the manufacturers recommend that it be placed in intimate contact with the wound surface. From the results of our work, it is my belief that once a charcoal dressing becomes wet and strike through occurs, even over a single small area, the ability of the dressing to adsorb odour molecules is seriously impaired.
It is proposed that an absorbent layer interposed between the wound and the charcoal component will act as a spreader layer retarding strike through and maximising the area of charcoal exposed to the volatile molecules responsible for the odour. It is unlikely that the application of an absorbent layer to the outer surface of a charcoal dressing will be as effective in this regard although this could easily be tested in the laboratory.
It is true that this study did not take into account the antimicrobial
activity claimed for the silver present in Actisorb Plus. Whilst it is
accepted that this may help to prevent the growth of bacteria on the dressing
itself, the evidence for a more widespread antimicrobial effect within the
wound itself is less convincing. This is clearly an area where further work
could usefully be undertaken.
Dr. Stephen Thomas's article on Hydrocolloids is a great informative piece on the different properties of the hydrocolloid dressings.
Unfortunately in almost 13 years of attempts to use them in clinical practice, I have been very disappointed in the clinical performance of this type of dressing in necrotic or sloughy types of wounds.
Clinically when I do have successful response, it is very slow, measured in months as opposed to days or weeks. As such I have found that the times that I use hydrocolloids now is as a secondary dressing only. For example in an ischemic necrotic wound I will use papain urea based enzymatic ointment as the primary material followed by a hydrocolloid as the secondary dressing. I can eliminate most necrotic materials in about a week this way changed every 3 days. I have been treating these types of cases this way for about a year now and only have about 12 or so that I have tried it on. my results have been favorable.
All 12 cases have had the necrosis eliminated and then I must change the material as I do not feel enzymatic agents should be used on healthy granulating tissue. As we are aware there are several types of enzymatic agents that are out there.
Could Dr. Thomas possibly consider the a laboratory comparison of enzymatic agents. Here in the states we have the following agents available to us
My thoughts are based only on my clinical results; as such I think that the following would be a viable experiment. Take a sheet of pig skin and char it to create a burn surface equivalent to a 3rd degree burn. Use a control of petrolatum ointment applied to the charred skin. Apply an equal weighted amount of the six enzyme agents spread evenly to the surface area say 6cm x 6 cm to the charred pig skin and cover in a petrie dish at room temperature.
Review the area for amount of necrotic material that responds to each of the enzyme systems measured by the controlled weight of the pig skin remaining after 6, 12, 18, 24, 36, 48, 72, 96 hours. The next phase would be to do the same base experiment only with no charring to the pig skin as a basic model and see what the results are.
This whole experiment could be repeated with both a thin and thick hydrocolloid as a secondary dressing. I would be very interested to see the results of this type of experiment. Furthermore I think that this type of experiment could then lead to a clinical comparison in patients to determine an inexpensive way to treat this difficult problem such as the necrotic heel that you had in one of the articles in this journal.
Thank you for your consideration.
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