What clinical appearance indicates critical limb ischaemia between 12 to 24 hours?

The clinical appearance characterized by fixed mottling is indicative of critical limb ischemia, particularly within the time frame of 12 to 24 hours. This condition arises when there is an inadequate blood supply to the limb, leading to tissue ischemia. Mottling refers to a pattern of discoloration that develops when the skin is no longer receiving adequate perfusion, resulting from a combination of venous stasis and inadequate arterial flow. In the context of critical limb ischemia, the fixed nature of the mottling suggests that the condition has progressed and tissue viability is being significantly compromised.

The other appearances listed would not align with the signs of critical limb ischemia during that time period. A bright red limb with normal sensation indicates a well-perfused limb, which contradicts the definition of ischemia. A swollen and warm extremity may suggest inflammation or an acute process, which is not necessarily indicative of fixed ischemia. Lastly, necrotic black tissue would typically be associated with end-stage complications of limb ischemia, occurring after a longer duration than specified in the 12 to 24-hour timeframe. Consequently, fixed mottling serves as a crucial clinical indicator of disseminated ischemia during critical stages of limb vascular compromise.