What is acute limb ischemia (ALI)?

From the Guidelines

Acute limb ischemia (ALI) is a medical emergency that requires immediate attention, and the most recent guidelines from 2024 recommend prompt recognition and treatment to prevent limb loss and mortality. According to the 2024 ACC/AHA/AACVPR/APMA/ABC/SCAI/SVM/SVN/SVS/SIR/VESS guideline for the management of lower extremity peripheral artery disease 1, ALI is one of the most treatable and potentially devastating presentations of PAD. The guideline defines ALI as a sudden decrease in limb perfusion that threatens tissue viability, typically developing within 14 days of symptom onset.

Causes and Presentation

ALI most commonly results from arterial embolism (30-40% of cases), thrombosis of pre-existing atherosclerotic lesions (40-50%), or arterial trauma. Patients typically present with the "6 Ps": pain, pallor, pulselessness, paresthesia, paralysis, and poikilothermia (coldness). The 2018 ESC guidelines on the diagnosis and treatment of peripheral arterial diseases 1 also emphasize the importance of prompt recognition and treatment of ALI, and provide a classification system for ALI based on the severity of symptoms and the presence of neurological deficits.

Diagnosis and Initial Management

Diagnosis relies on clinical examination and confirmation with imaging studies like duplex ultrasound, CT angiography, or conventional angiography. Initial management includes anticoagulation with intravenous unfractionated heparin (typically 80 units/kg bolus followed by 18 units/kg/hour infusion, adjusted to maintain aPTT at 1.5-2.5 times normal) 1. The 2006 ACC/AHA practice guidelines for the management of patients with peripheral arterial disease 1 also recommend anticoagulation with unfractionated heparin as initial management for ALI.

Definitive Treatment

Definitive treatment depends on severity and cause but may include catheter-directed thrombolysis using tissue plasminogen activator (tPA), surgical thromboembolectomy, bypass grafting, or endovascular interventions like angioplasty and stenting. The 2018 ESC guidelines 1 recommend endovascular therapy as the initial treatment of choice, especially in patients with severe co-morbidities, if the degree of severity allows time for revascularization. Fasciotomy may be necessary if compartment syndrome develops after revascularization.

Long-term Management

Long-term management includes antiplatelet therapy (aspirin 81-325 mg daily), statins, risk factor modification, and treatment of underlying conditions like atrial fibrillation (often with anticoagulants). Prompt recognition and treatment are essential, as delayed intervention beyond 6-8 hours significantly increases the risk of limb loss and mortality, with overall amputation rates of 10-15% and mortality rates of 15-20% within 30 days.

Some key points to consider in the management of ALI include:

• Prompt recognition and treatment are essential to prevent limb loss and mortality
• Anticoagulation with unfractionated heparin is recommended as initial management
• Endovascular therapy is the initial treatment of choice, especially in patients with severe co-morbidities
• Fasciotomy may be necessary if compartment syndrome develops after revascularization
• Long-term management includes antiplatelet therapy, statins, risk factor modification, and treatment of underlying conditions.

From the Research

Definition and Causes of Acute Limb Ischemia

• Acute limb ischemia occurs when there is an abrupt interruption of blood flow to an extremity, usually due to embolic or thrombotic vascular occlusion 2.
• The causes of acute limb ischemia include thrombosis of a limb artery or bypass graft, embolism from the heart or a diseased artery, dissection, and trauma 3.
• The etiology is broadly divided into embolism and thrombosis with various comorbidities 4.

Symptoms and Diagnosis of Acute Limb Ischemia

• The symptoms of acute limb ischemia are abrupt, with pain, numbness, and coldness of the lower limb, and paresthesia, contracture, and irreversible purpura will appear with the exacerbation of ischemia 4.
• A suspicion of acute ischemia based on history and physical examination warrants heparin administration and vascular surgery consultation 5.
• Classification of severity of acute limb ischemia is based on clinical variables 5.
• Assessment determines whether the limb is viable or irreversibly damaged 3.

Treatment and Management of Acute Limb Ischemia

• Prompt diagnosis and revascularization by means of catheter-based thrombolysis or thrombectomy and by surgery reduce the risk of limb loss and mortality 3.
• The decision for endovascular thrombolysis or standard surgery depends on etiology, duration, and location of vascular occlusion 5.
• Alternative imaging modalities include ultrasound, contrast-enhanced computed tomographic angiography, and magnetic resonance angiography 2.
• Amputation is performed in patients with irreversible damage 3.
• Acute limb ischemia can be treated by means of open surgical revascularization, endovascular, or hybrid approach with rapid systemic administration of heparin 4.

Prognosis and Outcomes of Acute Limb Ischemia

• Despite urgent revascularization, amputation rate is 10%-15% in patients during hospitalization, mostly above the knee, and mortality within 1 year is 10%-15% due to coexisting conditions 3.
• Limb amputation should be done without hesitation when the limb is diagnosed as irreversible 4.
• The best patient outcome requires tailoring the treatment to the individual patient 6.