Acute Limb Ischaemia

Acute Limb Ischaemia

Acute limb ischaemia (ALI) is a time‑critical vascular emergency caused by a sudden reduction in arterial perfusion to a limb that threatens tissue viability. It carries substantial risks of limb loss, systemic complications (reperfusion injury, acute kidney injury, metabolic disturbance) and increased mortality.

Rapid recognition, immediate anticoagulation, early vascular specialist involvement and timely revascularisation are the priorities.

Definitions and scope

• ALI: a sudden decrease in limb perfusion that has the potential to produce a threat to limb viability, typically evolving over hours to days.
• Distinguish ALI from chronic limb‑threatening ischaemia (CLTI): CLTI progresses gradually, often with collateralisation and chronic signs such as skin changes and ulceration.
• NICE guidance for peripheral arterial disease provides authoritative background on PAD and CLTI but does not provide a dedicated guideline for acute ischaemia (NICE CG147).
• For ED operational detail, combine NICE background with RCEM and local vascular network protocols (RCEM pre‑alert guidance).

Pathophysiology - embolus vs in situ thrombosis ALI results from abrupt interruption of arterial inflow by either:

• Embolus - a clot or debris that travels from a proximal source (most commonly cardiac: atrial fibrillation, left ventricular thrombus, recent myocardial infarction or valvular disease). Embolic events tend to be sudden in previously well limbs and commonly lodge at bifurcations. On imaging an embolus may show a concave border (the “meniscus...