Exudate-handling mechanisms of two foam-film dressings

To investigate the fluid-handling mechanisms of film-backed foam dressings.

The fluid-handling properties of two dressings (ActivHeal Foam Island, Advanced Medical Solutions, and Allevyn Adhesive, Smith & Nephew) were compared using a standard laboratory technique, which provided comparative data on the dressings' absorbency and moisture vapour transmission. Movement of exudate through one of the dressings was also investigated in vivo using ultrasound. The fluid-handling data obtained in the laboratory were compared with exudate rates for various wound types reported in the literature to predict wear times for above products.

Absorbencies of the two dressings were broadly comparable. After 24 hours, under the test conditions, ActivHeal retained a mean of 3.44 g (SD 0.04) of the test solution and Allevyn Adhesive 4.32 g (SD 0.04), but a major difference was detected in the permeability of the two products: 12.35 g (SD 0.42) of the test solution evaporated through the back of Allevyn over 24 hours compared with 1.67 g (SD 0.11) through ActivHeal (p<0.0001). The results of the preliminary ultrasound study suggest that, in the clinical situation, exudate migrates away from the wound surface and accumulates beneath the outer film.

The difference in fluid-handling properties of the two dressings was due to the presence in one of an 'intelligent' polyurethane film component, the permeability of which varied in response to the presence of liquid. The data suggested that the film's permeability was such that the product might be expected to cope with even the most heavily exuding wounds for an extended period, but this performance would be influenced in vivo by factors such as the size of the dressing relative to the wound, and local environmental conditions, which would affect moisture vapour transmission. The somewhat unexpected finding that fluid tended to accumulate beneath the outer film during clinical use suggested the possibility of an 'osmotic pump' effect.