3.3 Acute Limb Ischaemia – Peripheral Artery Thrombosis

📄 Definition

Acute limb ischaemia (ALI) is a sudden reduction in arterial blood flow to a limb, typically occurring over hours to days, threatening tissue viability and requiring urgent intervention.

⚠️ Causes

🧠 Mnemonic: SAD TOES

  • Stroke of embolus (e.g. AF, left ventricular thrombus)

  • Atherosclerotic plaque rupture and thrombosis

  • Dissecting aortic aneurysm (rare)

  • Trauma (arterial injury or occlusion)

  • Operative complications (e.g. graft occlusion)

  • External compression (e.g. compartment syndrome)

  • Spontaneous arterial thrombosis in PAD

6 Ps – Classic Features

  • Pain (sudden, severe, distal)

  • Pallor

  • Pulselessness

  • Perishing cold (coldness)

  • Paraesthesia

  • Paralysis (late sign – poor prognostic factor)

🔺 Sensory loss and paralysis indicate imminent limb loss.

🩺 Clinical Assessment

  • Capillary refill – delayed

  • Temperature – compare limbs

  • Pulse exam – femoral, popliteal, posterior tibial, dorsalis pedis

  • Buerger’s Test – limb elevation worsens pallor

🧪 Investigations – 

🥇 First-Line (Initial Bedside & Emergency)

  • ECG – Look for AF (most common embolic source)

  • Doppler Ultrasound (Handheld) – Pulse presence/absence

  • ABPI – May be unreliable in ALI, but attempted

  • Bloods: FBC, U&Es, Clotting, Glucose, Lactate, CRP/ESR

  • Neurovascular Examination – Document baseline function

🥈 Second-Line (Confirmatory Imaging)

  • CT Angiography (CTA) – Gold standard for vessel occlusion

  • Duplex Ultrasound (DUS) – If CTA unavailable or contrast contraindicated

  • MRI Angiography – Less used due to accessibility

🥉 Tertiary / Monitoring

  • Troponin – Rule out MI in context

  • Echo – Check for thrombus or valvular embolic source

  • Thrombophilia screen – In younger or recurrent cases

🚨 Severity – Rutherford Classification

  • Viable – No immediate threat

  • Threatened – Urgent intervention needed

  • Irreversible – Limb non-viable, risk of sepsis

Management

🧠Mnemonic: ACT FAST

  • Anticoagulate (IV heparin)

  • Confirm diagnosis (CTA)

  • Team referral (Vascular surgery)

  • Fasciotomy (if compartment syndrome risk)

  • Angioplasty/thrombectomy/embolectomy

  • Supportive: analgesia, fluids, monitor vitals

  • Thrombolysis – Consider if no contraindications

📆 Follow up

  • Long-term antiplatelet (e.g. clopidogrel)

  • Treat underlying cause (e.g. AF with DOAC)

  • Smoking cessation, exercise, statin, BP control

  • Duplex surveillance if stented or revascularised

🔎 Key PARA Exam Traps

💡When answering a question on a cold, pulseless leg, follow this logic:

  1. First Step: Handheld Doppler (to confirm absence of flow).

  2. Immediate Treatment: IV Unfractionated Heparin bolus (to stop the clot from growing).

  3. Gold Standard Image: CT Angiography (to find the blockage).

  4. The “Trap”: If the leg is paralysed and rigid (Rutherford III), the answer is Amputation, not revascularization (due to the risk of death from reperfusion injury).

🔺Last updated in line with:

  • NICE NG106 (2026 Update): Focusing on standardized pathways for Acute Limb Ischaemia (ALI) and the integration of Handheld Doppler assessment in primary care.

  • Vascular Society of Great Britain and Ireland (2025): New standards for the “Time to Reperfusion” for Rutherford IIb (Immediately Threatened) limbs.

  • NICE TA (Technology Appraisals) 2024/25: Regarding the use of mechanical thrombectomy devices in peripheral arterial occlusion.

  • PARA/MLA-aligned: Fully reviewed February 2026 for the UK Medical Licensing Assessment and Physician Associate Registration Assessment.

🔒 PASSMAP Assurance: All content is peer-reviewed, NICE-compliant, and optimized for the 2026 UK clinical examination cycle.

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Educational platform. Not medical advice.

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