Foam dressings were introduced about 25 years ago. They are usually made of polyurethane, although a silicone foam was also developed, and provide a soft, absorbent dressing for granulating wounds of varying aetiologies and sizes. They are also gas-permeable, provide thermal insulation and help to maintain a moist wound environment (Thomas, 1993). Unlike gauze, foam dressings do not shed fibres or particles, and depending on their formulation they can be used on lightly, moderately or heavily exudating wounds.
Polyurethane foams
Polyurethane foams are available in a number of different forms and a variety of shapes and sizes, with or without adhesive borders (Morgan, 1999).
Foam sheets
These are made up of open-cell hydrophilic polyurethane foam sheets. They are permeable to gas and water vapour, while their outer surfaces remain hydrophobic (Dale, 1997). Depending on the
nature and condition of the wound and the amount of exudate, they may need to be changed anything from twice a day to once a week.
- Practice point
The way in which foam sheets absorb blood or exudate varies according to their formulation. One particular product draws fluid up into a heat-treated surface and then spreads it laterally across the face of the dressing. This means that, to prevent maceration or leakage, the dressing must overlap the wound bed by at least 2-3cm (Thomas, 1996).
Some foam sheets were originally recommended for the management of light exudate only, but a more absorbent version has since been produced that is suitable for moderately to heavily exudating wounds (Banks et al, 1997).
Film-backed foam dressings
These have three constituents: a low-adherent polyurethane net that comes into contact with the wound and is designed to prevent or reduce adhesion, a central layer of hydrophilic polyurethane foam, and a polyurethane film backing that blocks the passage of exudate (Dale, 1997).
They are highly absorbent, can often be left on the wound for several days and can be used on heavily exuding wounds without fear of maceration (Thomas, 1996).
Polyurethane membranes
These consist of a thin microporous sheet of polyurethane foam that has been coated with a hydrophilic adhesive and bonded to a polyurethane film backing. They are highly permeable to moisture vapour and their permeability adapts according to the amount of exudate produced.
However, they have limited absorbency and are therefore suitable only for lightly exuding wounds.
These dressings should be changed when the exudate is visible within 1cm of the edge of the dressing or after five to seven days, depending on the type of wound.
Foam dressings have many different compositions and structures so they can be used on a variety of wounds, including leg ulcers, traumatic wounds, minor burns, donor sites, malignant wounds and cavity wounds. They are not suitable for dry necrotic wounds but can be used in conjunction with a debriding agent. For example, with a hydrogel to promote autolysis (Thomas, 1993).
