Porcine xenografts vs. (cryopreserved) allografts in the management of partial thickness burns: Is there a clinical difference?☆
Introduction
Biological dressings, xenografts as well as allografts, have been used for the management of burns for long while, with the first documented application going back several centuries [1]. Porcine skin is available as preserved skin (particularly with glutaraldehyde [2]), and as decellularised matrices [3] while it has also been combined with silver in an attempt to lower colonisation levels [4]. Skin allografts are available in different forms as well, with glycerol immersion and cryonic techniques most commonly used for preservation.
Both allografts and xenografts are used as dressings for partial thickness burns, as a temporary dressing in excised, non-grafted burns 5, 6 and as dressings for chronic lesions and non-thermal skin loss injuries 7, 8, 9, 10, 11, 12, 13. Allografts are also used as cover dressings in excised and grafted full thickness burns [14] while xenografts are sometimes used on skin graft donor sites [15].
All biologic dressings are known to provide a series of properties that are beneficial for the patient and the wound [16]. When applied to partial-thickness wounds, all seem to increase the speed of healing when compared with traditional dressings 17, 18, 19.
Xenografts and (particularly) cryopreserved allografts (CPA) also have distinct differences and both types of biological dressings have strong advocates, predominantly with regard to viability and its (perceived) role in supporting wound healing, and the (potential for) disease transfer (Table 1).
A literature search was undertaken, aimed at analysing whether these differences are relevant for the clinic with regard to the management of partial thickness burns. Other aspects that might play a role in deciding on a certain type of graft, such as availability and pricing, also were investigated.
Section snippets
Search methods and search results
The databases of Pubmed, Medline, Google and the search engine of the Endnote X5 programme (Thompson Reuters, Carlsbad, CA, USA) were searched, focussing primarily on partial thickness burns, porcine skin, porcine derived matrix, preservation methods, as well as on related topics such as bacteriology (including disease transfer), cost, and outcomes, particularly healing, pain and long term results.
Articles on dressings made of the submucosa of the porcine small intestine were excluded (since it
Preservation methods, risks of disease transfer
Porcine skin is most commonly preserved with glutaraldehyde: its protein crosslinking properties have a biocidal and preservative effect on tissues, making xenografts more durable and safe [21] while killing the cells in the graft. (The lack of) viability does not seem to have a clinical impact: in a test with a rat recipient wound model, viable (fresh) vs. preserved porcine skin did not show any difference in clinical performance [22]. A study on clinical performance of allografts, preserved
Availability and costs
Skin allograft availability is limited by the number of donors, which is restricted [39] and unpredictable over time as well [40]. Cadaver skin also requires a designated and expensive infrastructure which has to include harvesting teams which have to be available at odd times, extensive culturing facilities, and a skin bank for preservation and storage. These are among the reasons why many regions in the world do have limited or no immediate access to cadaver skin [41]. Financial, cultural and
Clinical studies (Table 3)
Relatively few studies on clinical results of porcine skin in burn care have been published and in only two studies xenografts are compared directly to allografts, although healing (reepithelialisation) was not a study objective for either study 44, 45. Two xenograft studies were published in Chinese medical journals, with only the abstracts in English 46, 47.
Bacterial clearing of granulating wounds was shown to be similar for allografts and xenografts in a study with 16 patients [44]. In a
Discussion
All biological dressings share a number of properties: they protect the wound from fluid, protein and heat loss and from physical trauma, while providing pain relief and relatively fast (compared to more conventional materials) healing and reepithelialisation. Long term results (with regard to scarring and scar quality) are better than with conventional materials as well, among other reasons because these materials increase wound healing [57]. Both xenograft and cadaver skin have strong
Limitations
Given the long history of using allograft and xenografts in burn care, the number of (comparative) clinical trials is surprisingly small and for the two studies with the largest number of patients treated with porcine xenografts only an abstract is available in English. The lack of standardisation in trials with (biological) dressings is a major limitation of this, and any, literature review [61]. In the articles on porcine materials referenced here many crucial aspects, such as depth of a
Conclusion
In spite of the strong beliefs and perceptions amongst clinicians, no evidence was found showing that xenograft, their derivatives, or allografts perform better clinically in the management of partial thickness burns. All these materials provide rapid reepithelialisation, pain relief, protection of the wound and, generally, good long term results.
Therefore, clinical outcomes being equal, the decision of choosing one type of biological dressing over another has to be based on other aspects, such
Conflict of interest
The author, Michel Hermans, is a paid consultant for Mölnlycke Health Care, Gothenburg, Sweden.
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This study was supported by Mölnlycke Health Care, Gothenburg, Sweden.