Which stage of a pressure ulcer is defined by complete tissue loss with the ulcer base covered by slough or eschar?

The stage of a pressure ulcer that is defined by complete tissue loss with the ulcer base covered by slough or eschar is indeed classified as unstageable. This designation is used when there is an inability to assess the depth of the ulcer due to the presence of necrotic tissue, such as eschar or slough, obscuring the wound bed. Since the underlying structures and the extent of the injury cannot be visualized, it is impossible to accurately determine the stage of the ulcer.

In terms of the other stages: Stage 2 involves partial thickness loss of skin, which would not meet the criteria for complete tissue loss. Stage 3 involves full thickness loss of tissue but does not include slough or eschar obstructing the view, allowing for assessment of the depth. Stage 4 represents full thickness tissue loss with exposure of muscle, bone, or supporting structures, but does not involve coverage that prevents assessment. Thus, the defining characteristic of unstageable ulcers relates directly to the presence of slough or eschar that precludes complete evaluation.