The dressing is freely permeable to moisture vapour and gases but resists the penetration of liquids due to the hydrophobic nature of the unmodified back. When placed in contact with blood or exudate, the fluid is slowly drawn up into the wound contact layer and transferred laterally across the face of the dressing. The aqueous component then evaporates into the large cells at the back of the dressing from where it is lost to the environment as water vapour. As this process continues, the cells in the facing layer become filled with cellular debris and solid material and the dressing itself becomes progressively more occlusive. The dressing, which was originally sold for the treatment of burns, is able to absorb large volumes of fluid, some of which is lost by evaporation through the film on the back of the dressing.
Some chronic wounds produce an unpleasant odour as a result of bacterial contamination.
This treatment should only be carried out under medical su- pervision. One group of wounds that are often particularly difficult to heal are sinuses and other lesions which have a narrow open- ing leading to a flask shaped cavity under the skin. In these situations some form of packing is often inserted to ensure that the entrance does not close over before the main body of the wound is healed. Ribbon gauze packs are most commonly used, but a number of the new dressing materials can also be of value. If the wound is moist, it may be packed with alginate ribbon using a suitable probe, but care should be taken to ensure that it is not packed in too tightly.