<p>The appts. includes a porous pad which is permeable to fluids for introduction onto a wound. A dressing covers the wound and provides an air-tight seal around the wound. A drainage tube connects the pad to a suction pump so that negative pressure can be applied to the wound to draw fluids from the wound. The tube is connected to the pump via a canister for collecting fluids sucked from the wound. At least one filter is interposed between the canister and the pump. The filter is located in the canister which is removably attached to a housing for the pump. The canister is removably received in a recess in the housing. A detector determines when the canister is full of fluid by sensing change of capacitance as the canister fills up. The pad is a polymer foam with interconnecting cells.</p>
