Despite appearances, hydrocolloid performance can vary greatly

Best used with light to moderate exudate

Although the different kinds of hydrocolloid dressings are all similar in appearance, their performance varies considerably when it comes to properties such as absorbency, ability to handle fluids, and conformability, according to researchers.

At the Surgical Materials Testing Laboratory (SMTL), an independent research organization located in South Wales, UK, investigators compared the properties and performance of 12 hydrocolloid dressings in the laboratory.

According to the investigators, the majority of hydrocolloid dressings look much the same, so users often assume that their performance characteristics will be similar.1 SMTL's research results proved otherwise when key properties of several hydrocolloid dressings from a variety of manufacturers were examined. All of the dressings were manufactured in Europe, but similar, and sometimes identical, products are available in the United States. The European products studied were: Tegasorb Thin and Tegasorb (3M Health Care); Cutinova Hydro (Beiersdorf AG); Askina Biofilm Transparent and Askina Transorbent (Braun); Comfeel Plus Plaque Biseautees, Comfeel Plus Transparenter, and Comfeel Plus Flexibler (Coloplast); Varihesive and Granuflex (ConvaTec); Hydrocoll (Hartmann); and Algoplaque (Laboratories Urgo).

The researchers compared the dressings in the categories of thickness, fluid handling properties, moisture vapor permeability, conformability, acidity/alkalinity of extract, and fluid retention/gel cohesion.

Thickness ranged from 0.37 mm (Comfeel Plus Transparenter) to 2.78 mm (Askina Transorbent). When the researchers quantitatively measured fluid handling - considered to be one of the most important measurements of dressing performance - after 24, 48, and 96 hours, capacity was defined as the sum of the weight of the test solution retained from each dressing, and the weight of fluid lost by transmission through the dressing as moisture vapor.

Actual weight absorbed after 24 hours ranged from 0.24 gm for the Askina Biofilm Transparent (which was not the thinnest of the dressings) to 5.62 gm for the Hydrocoll (which was not the thickest). The same two products accounted for the low and high points for fluid handling capacity, which factors in the weight of the dressing: 0.51 gm for the Askina Biofilm Transparent and 6.12 for the Hydrocoll. Other top performers after 24 hours were Tegasorb (5.01 gm), Askina Transorbent (4.16), and Comfeel Plus Flexibler (4.10 gm).

After 48 hours, dressings with the highest test results for fluid handling were Tegasorb and Hydrocoll (both 7.52 gm), Comfeel Plus Flexibler (5.66 gm), and Cutinova Hydro (4.80 gm). (For a complete listing of results, see chart, above.)

According to study author Stephen Thomas, MD, director of the SMTL, measured values for the total fluid handling capacity ranged from < 1 gm/10 cm2 to 6 gm/10 cm2 in 24 hours, increasing to 11 gm/10 cm2 after 96 hours. These figures fall into context when compared with results from studies measuring exudate production from leg ulcers, which averaged about 5 gm/10 cm2 after 24 hours with a range of 4 to 12 gm/10 cm2 for 24 hours.2 Thomas says such values agree with those obtained by other researchers who have measured evaporative water loss from burns and reported values on the order of 5 gm/10 cm2/24 hours.3

"This clearly suggests that if fluid absorption and transmission by hydrocolloid dressings were the only mechanism involved in the control of exudate, many of the products examined in this study might be expected to perform poorly in the treatment of exuding wounds," says Thomas. "It has been demonstrated, however, that if a hydrocolloid dressing applied to a leg ulcer forms a secure waterproof seal onto the surrounding skin, it will actually reduce the amount of exudate produced by the wound by up to 50%. It is believed that the chamber formed beneath the dressing becomes filled with exudate under pressure. As this pressure increases and approaches that within the capillaries, the loss of further fluid is inhibited. This effect will occur, however, if the dressing forms an adequate seal over the wound. Once this seal is broken, the mechanism fails."1 This may explain, Thomas continues, why some products that reduce exudate formation by creating a tight seal perform poorly in laboratory studies but satisfactorily in clinical use.

Dressing classification system proposed

The study results, says Thomas, demonstrate the marked difference in performance among hydrocolloid dressings, with considerable variation in their ability to absorb test solution and transmit moisture vapor that may have significant clinical implications. He suggests the introduction of a classification system or grading system for hydrocolloid dressings based upon their ability to cope with fluid production. Such a system would provide users with information that would facilitate the selection process. "It is proposed that the methods used in the present study could form a basis of such a battery of tests," says Thomas.

Hydrocolloid dressings are those that contain gel-forming agents, such as sodium carboxymethylcellulose and gelatin. Often, these chemicals are combined with elastomers and adhesives and applied to a carrier, which typically consists of a sheet of polyurethane foam or film. The result is an absorbent, self-adhesive, waterproof dressing.

When intact, most hydrocolloid sheet dressings are impermeable to water vapor, but become progressively more permeable as the dressing contents gel. Gelling is instigated by the presence of wound exudate. The properties of the gel differ depending on the formulation of the hydrocolloid dressing. The increasing amount of permeability allows water to travel through the dressing and evaporate, therefore enhancing the ability of the dressing to cope with additional exudate.

Hydrocolloid dressings are used to manage leg ulcers, burns, donor sites, and pressure sores. Thomas notes that, with a few exceptions, the dressings' relatively limited fluid handling properties limit use to wounds with light to moderate amounts of exudate. Alginate and polyurethane dressings are often chosen for heavily exuding wounds.

References

1. Thomas S, Loveless P. A comparative study of the properties of twelve hydrocolloid dressings. World Wide Wounds; July 1997.

2. Thomas S, Fear M, Humphreys J, et al. The effect of dressings on the production of exudate from venous leg ulcers. Wounds 1996; 8:145-150.

3. Lamke LO, Nilsson GE, Reichner HL. The evaporative water loss from burns and water vapour permeability of grafts and artificial membranes used in the treatment of burns. Burns 1977; 3:159-165.