Cardiovascular · Topic 41 of 48

Acute Limb Ischemia

Cardiovascular · peripheral vascular emergency

Acute Limb Ischemia

A sudden arterial occlusion that threatens the limb. Heparin now, grade it by sensation and strength, and revascularize within hours.

Key numbers

Sudden loss of limb perfusion, under 2 weeks< 2 weeks

IV heparin bolus at diagnosisUFH 70–100 U/kg IV

Threatened limb: revascularize emergently, within hoursmuscle tolerates 4–6 h

Post-reperfusion compartment syndrome: fasciotomy> 30 mmHg

01 · Look forSix P's of an ischemic limb

The six P's are pain, pallor, pulselessness, poikilothermia (cold limb), paresthesias and paralysis; pain out of proportion to the examination comes first, and sensory loss or weakness means the limb is threatened.

02 · GiveIV heparin bolus at diagnosis

Give an IV unfractionated heparin bolus (about 70–100 units/kg) as soon as acute limb ischemia is diagnosed, unless contraindicated, to stop clot propagation; use argatroban if the patient has HIT.

03 · DoThreatened limb: revascularize emergently, within hours

Skeletal muscle tolerates ischemia for only about 4–6 hours: a marginally threatened limb (IIa) is salvageable with prompt revascularization, and an immediately threatened limb (IIb) needs immediate revascularization.

What it is

Core idea

Sudden loss of limb perfusion, under 2 weeks must knowAcute limb ischemia is a sudden fall in arterial perfusion that threatens limb viability, present under 2 weeks — from embolus, thrombosis of a plaque, graft or stent, aortic dissection or trauma.

Presentation

What you'll see

Occlusion lies just below last palpable pulseThe occlusion is usually at the arterial bifurcation just distal to the last palpable pulse (palpable femoral pulse means a common femoral bifurcation block); check pedal arterial and venous Doppler signals.

Diagnosis & monitoring

Work-up

Rutherford grade: sensation, strength, Doppler must knowRutherford I: viable, no sensory or motor loss, audible arterial Doppler. IIa: marginally threatened, minimal (toe) numbness. IIb: immediately threatened — sensory loss beyond the toes, rest pain, mild–moderate weakness, inaudible arterial Doppler.

Do right now

In this order

First moves

IV heparin bolus at diagnosisUFH 70–100 U/kg IV

→

Rutherford grade: sensation, strength, Doppler

→

Threatened limb: revascularize emergently, within hoursmuscle tolerates 4–6 h

Why each step

IV heparin bolus at diagnosisGive an IV unfractionated heparin bolus (about 70–100 units/kg) as soon as acute limb ischemia is diagnosed, unless contraindicated, to stop clot propagation; use argatroban if the patient has HIT.

Rutherford grade: sensation, strength, DopplerRutherford I: viable, no sensory or motor loss, audible arterial Doppler. IIa: marginally threatened, minimal (toe) numbness. IIb: immediately threatened — sensory loss beyond the toes, rest pain, mild–moderate weakness, inaudible arterial Doppler.

Threatened limb: revascularize emergently, within hoursSkeletal muscle tolerates ischemia for only about 4–6 hours: a marginally threatened limb (IIa) is salvageable with prompt revascularization, and an immediately threatened limb (IIb) needs immediate revascularization.

Management

Orders

Rutherford III: primary amputation, not revascularizationRutherford III is irreversible ischemia — profound anesthesia, paralysis or rigor, and no arterial or venous Doppler signal; amputate as the index procedure, because revascularizing nonviable tissue is harmful (fatal reperfusion injury).

IIb limb: do not delay for CTImage viable or marginally threatened limbs (I, IIa) with duplex ultrasound or CTA to plan treatment; an immediately threatened limb (IIb) goes straight to angiography or the operating room.

Catheter-directed lysis for viable, recent occlusionsCatheter-directed thrombolysis suits a salvageable limb with occlusion under 2 weeks old; it is too slow for IIb, where surgical or percutaneous mechanical thrombectomy is used. Systemic thrombolysis is not recommended.

Continue heparin and find the embolic sourceAfter revascularization continue heparin, get an ECG and echocardiogram to look for atrial fibrillation or cardiac thrombus, and give long-term anticoagulation when the cause is embolic.

Red flags & don'ts

Avoid harm

No lysis with bleeding, ICH or compartment syndrome avoidAbsolute contraindications to catheter-directed thrombolysis: active bleeding, intracranial hemorrhage, established or developing compartment syndrome, and ischemia severe enough to need immediate surgery.

Reperfusion: hyperkalemia, acidosis, myoglobinuric AKI complicationAfter revascularization, washout from necrotic muscle causes hyperkalemia, metabolic acidosis, myoglobinuria with AKI and arrhythmias; monitor potassium, CK, lactate, blood gases and urine output closely.

Post-reperfusion compartment syndrome: fasciotomy complicationReperfusion edema can cause compartment syndrome, most often in the anterior leg compartment (foot drop, pain on passive stretch); compartment pressure above 30 mmHg confirms it — perform fasciotomy promptly.

Embolus or thrombosis?

Commonly confused

Onset	Sudden and severe; often timed to the minute
History	Atrial fibrillation, prior embolism, known embolic source
Collaterals	None, so ischemia is profound
Other leg	Normal contralateral pulses

Commonly confused

Tell apart

Mimics: dissection, phlegmasia, shock, vasopressorsConditions that mimic or cause secondary limb ischemia include aortic dissection involving the iliac arteries, phlegmasia cerulea dolens (massive DVT), compartment syndrome, low-flow shock and vasopressor use.

More detail

Reference

Show 5 reference facts

Foot drop from peroneal nerve ischemia is often the first motor sign and marks an urgent limb; muscles may become tender after 6–8 hours.

Early on the limb is marble white from arterial spasm, then mottled with cyanosis that still blanches on pressure; irreversible purpura and contracture appear as ischemia becomes irreversible.

Despite early revascularization, 30-day amputation and mortality rates are each about 10–15%, reflecting the cardiovascular comorbidity of these patients.

Causes in series: arterial embolism about 30–46%, native arterial thrombosis 24–40%, and graft or stent thrombosis 10–20%; popliteal aneurysm thrombosis and trauma are about 5% each.

Cholesterol (atheroembolic) showers after catheterization or aortic instrumentation cause painful blue toes and ulceration rather than a large-artery occlusion.

Pearl

The clock is nerve and muscle: once sensation and strength start to go, the limb has hours — heparinize and get the vascular team, not another scan.

Sources · Merck Manual Professional — Acute Limb Ischemia · Revascularization for Acute Limb Ischemia. Ann Vasc Dis 2026 (PMC13212160) · Acute Limb Ischemia: An Update on Diagnosis and Management. J Clin Med 2019;8:1215 (PMC6723825) · ACC — Peripheral Matters | PAD: Putting the 2024 Guideline Into Practice · Gornik HL et al. 2024 ACC/AHA/Multisociety Guideline for the Management of Lower Extremity Peripheral Artery Disease. Circulation 2024;149:e1313–e1410 · Starter sheet built from the verified AGACNP fact map (facts reviewed 2026-10-15).