Limb Ischemia

Acute limb ischemia is a limb- and life-threatening arterial occlusion in which bedside vascular exam matters more than waiting on labs. Absent Doppler flow, evolving sensory or motor deficits, and fixed mottling signal a threatened extremity that may need immediate revascularization without imaging delay.

Acute Limb Ischemia Recognition

• Arterial flow cessation: Acute limb ischemia is sudden loss of perfusion distal to an occlusion, most often arterial thrombosis in patients with known peripheral arterial disease.
• High-stakes outcomes: This is uncommon at roughly 14 to 26 cases per 100,000 yearly, but mortality reaches 9% to 25% and 30-day amputation rates run 10% to 30%.
• Six Ps progression: Pain is the earliest and most common symptom, while pulselessness and paralysis are later findings that push concern toward irreversible ischemia.
• Mottling prognosis clue: Early pallor can progress to mottling, and fixed mottling is a red flag for irreversible ischemia with poor limb salvage potential.
• Chronic PAD pattern: Patients with baseline claudication may still have acute occlusion, but the pain is typically more sudden, more severe, and no longer resolves like prior episodes. We get into the bedside distinctions in the episode.

Bedside Evaluation And Initial Management

• Doppler over palpation: Palpation alone is inadequate; distal pulses should be checked with Doppler, and an absent arterial signal means the limb is immediately at risk.
• Rutherford severity staging: The Rutherford system uses sensation, motor function, and Doppler findings to separate viable, threatened, and unsalvageable limbs and guide urgency.
• ABI severity marker: If Doppler flow is present, the ankle-brachial index helps grade ischemia, and an ABI below 0.40 indicates severe occlusion.
• CTA first-line imaging: CT angiography is the preferred imaging test, with over 99% sensitivity and 97% specificity, but severe presentations should not wait for scanning.
• Immediate antithrombotic therapy: With reasonable suspicion for acute occlusion, start unfractionated heparin at 80 U/kg bolus then 18 U/kg/hr infusion, plus aspirin and analgesia.
• Revascularization urgency: Category IIB ischemia means the limb is salvageable only with immediate revascularization, while category III with paralysis and profound sensory loss is often unsalvageable. We walk through the no-delay cases in the chapter.

Etiologies And Upper Extremity Cases

• Thrombosis dominant cause: Arterial thrombosis causes about 80% of acute limb ischemia in patients with peripheral arterial disease, making atherosclerotic disease the usual substrate.
• Important alternative causes: Embolism, dissection, trauma, thrombosed popliteal aneurysm, and occluded bypass grafts can all present with the same ischemic syndrome.
• Embolic CTA pattern: A relatively clean vessel with abrupt occlusion and no distal flow suggests embolism, whereas a tapered cutoff with diffuse atherosclerosis favors thrombosis.
• Upper limb ischemia: Upper extremity cases account for about 17% of presentations and are more often cardioembolic, usually involving the axillary or brachial arteries.

References:

1. Arnold J, Koyfman A, Long B. High risk and low prevalence diseases: Acute limb ischemia. Am J Emerg Med. 2023;74:152-158. PMID: 37844359