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By Liza G. Ovington
Wound and Continence Management
Home Health Care Division, Southeast Florida
Columbia Healthcare Corp.
Ft. Lauderdale, FL
In the February issue, we discussed foam dressings and extolled their virtues as a highly absorbent material for moderately to heavily draining wounds. Today’s column will cover another category of highly absorbent dressings, the alginates. The alginates have an unusual origin as well as unique behaviors in use. This is one category of dressing that may be somewhat tricky to use appropriately without adequate knowledge of how it is designed to perform.
Alginates are fiber products derived from brown seaweed. Alginates in powder form have long been used in the food industry as thickening agents. If you have eaten ice cream, you have probably consumed alginate. The alginate used in wound dressings is calcium alginate (the calcium salt of alginic acid), which has been spun into a fiber. The alginate fibers are then prepared either as a compressed nonwoven sheet or as a staple fiber or rope.
Alginates excel at fluid absorption and are useful in the management of highly exudative wounds. As the alginate fiber absorbs excess fluid from a wound, it gels. The gel that is formed then keeps the wound moist. Here’s how it works:
Calcium alginate is a solid. When it contacts any solution containing sodium (such as wound drainage), the calcium exchanges for sodium and results in sodium alginate. Sodium alginate is a gel.
The various alginates are relatively similar in their absorptive behavior, but they can differ in the nature of the gel that is formed. Some alginates gel to such an extent that they cannot be lifted out in one piece and must be irrigated out of the wound bed with saline. Other alginates gel and yet retain enough structural integrity that they can be lifted out of the wound bed. The difference has no effect on wound healing but can be a matter of clinician preference.
All of the alginates require a secondary dressing for attachment. The choice of the secondary dressing is an important one.
The primary advantage of the alginates is their high absorbent capacity and rate of absorbency. Use of alginates in highly exudative wounds may decrease the number of dressing changes required. There is evidence of a bacteriostatic effect of the alginates as well as of a mild hemostatic effect, perhaps because of the released calcium. There also have been anecdotal reports of wound malodor reduction associated with alginate use.
Care must be taken not to use an alginate product on a wound with only a little drainage. Alginates were designed for use on wounds with moderate to high amounts of drainage and may actually dry out a wound with lower amounts of drainage.
Choice of the secondary dressing used for attachment is important in terms of maintaining the gelled state of the alginate. If an alginate gels and the gel then dries out, the resulting dried material can be quite difficult to remove from the wound bed. A covering layer of petrolatum gauze can help maintain the gelled alginate, or a film or foam dressing may be used to cover the alginate.
Two alginates on the market are not in the traditional compressed fiber configuration. One brand of alginate is freeze-dried rather than fibrous (Seasorb/Coloplast-Sween). It has the usual high absorbent capacity but claims an advantage over other brands due to its lack of fibers, which if left in the wound bed may elicit a foreign body response. The other nonfibrous alginate is a foamed version (Polymem Alginate Dressing/Ferris).
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