10th March 2024

Acute Limb Ischaemia

Acute limb ischaemia is a life-limb-threatening condition caused by a rapid or sudden decrease in limb perfusion, endangering tissue viability. Two possible events are implicated in the cause. Arterial thrombosis originating from a pre-damaged atherosclerotic site represents 85% of causes, and non-atherosclerotic peripheral embolism accounts for 10-15%. The incidence is approximately 1.5 cases per 10,000 persons per year. The most common aetiologies are:

• Native arterial thrombosis: atherosclerotic plaque, aneurysm, dissection, hypercoagulability. 
• Injury: iatrogenic or traumatic
• Thrombosis following intervention
• Embolism: arterial or paradoxical
• Peripheral vasoconstriction/ vasospasm 

Most patients with acute limb ischaemia will have a background of peripheral artery disease (PAD) and will experience intermittent claudication caused by a mismatch between active muscle demand and blood supply; and atypical lower extremity pain. A threatened limb is referred to those patients whose arterial blood flow is insufficient to meet the demand of resting muscle or tissue. 

Clinical presentation

Presentation may be acute or acute-on-chronic limb ischaemia, depending on the onset, location and the possible collateral vessels available. 

Acute-on-chronic limb ischaemia is common in patients with background of peripheral artery occlusive disease or previous revascularisation. Symptoms will have an increasing course and are similar to those of PAD. Acute limb ischemia, on the other hand, will present with rapidly evolving symptoms which can be remembered as the six Ps:

• Pain
• Pallor 
• Poikilothermia (inability to maintain a constant core temperature) 
• Pulseless 
• Paraesthesia 
• Paralysis

Diagnosis

Diagnosis can be made using clinical categories or with the use of ankle-brachial pressure index (see Table 3). After categorising based on cause and severity, consideration can be made whether to proceed with additional investigations. The clinical categories used are: 

• Viable or marginally threatened: no sensory loss or muscle weakness, and both arterial and venous Doppler signals are audible.
• Immediately threatened: Sensory loss involves more than the toes; rest pain and mild-to-moderate muscle weakness are present. Arterial Doppler signals are usually inaudible, and venous Doppler signals are audible.
• Irreversibly ischemic: profound sensory loss and muscle weakness (paralysis and possible rigor). Arterial and venous Doppler signals are inaudible. 

CT angiography or catheter-based arteriography are the investigations of choice, the second one providing a therapeutic option. 

Table 3. Ankle-Brachial Pressure Index interpretation. 

Management

The success of treatment depends on several factors, including the aetiology, location, duration of symptoms, availability of autologous vein for bypass grafting and suitability of the patient for surgery or intervention. The management of acute limb ischaemia is done by catheter-directed thrombolysis (with or without endovascular intervention) or surgical revascularisation.