Wound dressings provide a tenacious occlusive seal against the skin of a wearer, even in the presence of excessive blood or heavy perspiration. The preferred embodiment uses a hydrogel island providing superior hydrophilic gel adhesion. The product performs under extreme temperatures (i.e., 32-140° F.), and may be used to hold other dressings in place. Different “vented” embodiments are disclosed. A preferred structure includes a cover layer peripherally bonded to backing and hydrogel layers having a central aperture therethrough. The cover layer may have one or more holes, passages, tunnels or pockets to release pressure from a wound through the central aperture to the ambient environment. Layers that come in contact with blood products are preferably anti-thrombogenic to reduce or eliminate thrombi, or clotting that might interfere or obstruct venting. In particular, blood-contacting cover and cover/backing layers may use a thermoplastic polyurethane (TPU) film, more particularly a polyether TPU film.
