Alginate dressings in surgery and wound management--Part 1

Large quantities of alginate dressings are used each year to treat exuding wounds, such as leg ulcers, pressure sores and infected surgical wounds. Originally these dressings were a loose fleece formed primarily from fibres of calcium alginate. More recently they have been developed so that the fibres have been entangled to form a product with more cohesive structure, which increases the fabric's strength when it is soaked with exudate or blood. Some products also contain a significant proportion of sodium alginate to improve the gelling properties of the dressing in use. Other dressings have been produced from freeze-dried alginate. Once in contact with an exuding wound, an ion-exchange reaction takes place between the calcium ions in the dressing and sodium ions in serum or wound fluid. When a significant proportion of the calcium ions on the fibre have been replaced by sodium, the fibre swells and partially dissolves forming a gel-like mass. The degree of swelling is determined principally by the chemical composition of the alginate, which depends on its botanical source. Although it is recognised that the differences between the various brands of dressings may influence their handling characteristics--particularly when wet--it is generally assumed that these differences are of limited relevance to the dressing's performance clinically or at a cellular level. There is some evidence to suggest, however, that these assumptions may be wrong and that alginates may influence wound healing in a number of ways not yet fully understood. This three-part review of the literature encompasses the history, origin, structure, chemistry and clinical applications of alginates and alginate dressings. This review reveals that, despite their widespread use, alginates have been the subject of very few well-controlled clinical studies. There is fairly convincing evidence, however, that they do offer advantages over more traditional dressings for at least some clinical indications. It has also become obvious that there is a general lack of understanding about the importance of secondary dressing systems that must be used in with alginate dressings. Careful examination of the design and outcomes of the published studies suggests that the choice of both the primary alginate dressing and the secondary dressing can play a major role in determining treatment outcomes.