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

The clinical appearance of fixed mottling is indicative of critical limb ischaemia between 12 to 24 hours. This finding occurs due to a significant decrease in blood flow to the limb, leading to tissue ischemia and subsequent changes in color as blood supply diminishes. Mottling reflects the development of tissue damage, where areas of the skin become pale and discolored while others may take on a reddish or purplish hue due to underlying vascular compromise.

This presentation suggests that the limb is not receiving adequate perfusion, resulting in the subtle but significant alterations in skin coloration. The "fixed" aspect implies that this mottled appearance does not fluctuate or improve, indicating that the ischemia is severe and potentially irreversible if not addressed promptly.

Other appearances, such as a bright red limb with normal sensation, would typically suggest adequate blood flow and are not consistent with critical limb ischaemia. A swollen and warm extremity might indicate inflammation or infection rather than ischaemia. Necrotic black tissue signifies advanced tissue death, which would usually occur after a longer duration of critical ischaemia, rather than within the 12 to 24-hour timeframe in question.