Peripheral arterial disease is a term used to describe a narrowing or occlusion of the peripheral arteries, affecting the blood supply to the lower limbs.

Acute limb ischaemia is a sudden decrease in limb perfusion that threatens limb viability. In acute limb ischaemia, decreased perfusion and symptoms and signs develop over less than 2 weeks.

Causes

Peripheral arterial disease of the lower limbs is most commonly caused by atherosclerosis which narrows the affected arteries. This limits blood flow to the affected limb.

Acute limb ischaemia is caused by a sudden reduction in arterial perfusion of the limb, most commonly due to thrombosis within a diseased artery when an atherosclerotic plaque ruptures (80–85%). Less common causes include cardiac embolisation (AF, post-MI, prosthetic valves, atrial myxoma, vegetations, and rheumatic heart disease), aortic dissection or embolisation; graft thrombosis; thrombosis of a popliteal aneurysm; trauma; hypercoagulable states; or iatrogenic complications of vascular interventions.

Risk factors

• Risk factors for peripheral arterial disease are typical of those predisposing to other cardiovascular diseases, with smoking and diabetes mellitus being the strongest.
• Other risk factors for peripheral arterial disease include:
  • Advanced age.
  • Hypertension.
  • Hypercholesterolaemia.
  • Known atherosclerotic disease elsewhere (for example coronary, carotid, abdominal aorta).
  • Chronic kidney disease.
  • High serum homocysteine.
• Not all people with acute limb ischaemia have risk factors.

Clinical features

Typical features of acute limb ischaemia include (not all need to be present for diagnosis):

• Pain — constantly present and persistent.
• Pulseless.
• Pallor (or cyanosis or mottling).
• Power loss or paralysis.
• Paraesthesia or reduced sensation or numbness.
• Perishing with cold.

If there is ischaemia due to an embolus:

• Onset is acute.
• The limb appears white (because there is no collateral circulation).
• Vascular examination in the other leg is usually normal.

If there is ischaemia due to thrombosis:

• Onset is more gradual.
• The leg may not be white and symptoms may be less severe (due to collateral circulation, which is often well-developed in people with chronic peripheral vascular disease).
• Presentation is usually with worsening claudication and rest pain. Pulses in the other leg may also be absent.

Differential diagnosis

Acute limb ischaemia is a commonly missed diagnosis as it is often not considered. Conditions that can mimic arterial occlusion include:

• Chronic peripheral neuropathy — pulses are present, unless there is also chronic arterial occlusive disease or vasospasm, and skin temperature is normal (unlike in acute limb ischaemia).
• Acute compressive peripheral neuropathy (compartment syndrome) — tense muscle compartments (not present in acute limb ischaemia).
• Acute deep vein thrombosis — pulses are usually palpable (unless chronic arterial occlusive disease, vasospasm, or significant oedema is also present), and oedema does not usually occur with acute limb ischaemia.
• Low cardiac output in conjunction with chronic lower extremity peripheral arterial disease.

Management

• If acute limb ischaemia is suspected, arrange emergency assessment by a vascular specialist. Acute limb ischaemia is a surgical emergency. Complete arterial occlusion will lead to irreversible tissue damage within 6 hours. Early senior surgical support is vital.
• Give appropriate pain relief (usually IV opioid).
• Correct hypovolaemia and other causes of low- flow states.
• Management will depend on the type of occlusion (thrombosis or embolus), location, duration of ischaemia, neurological deficit, comorbidities, type of conduit (artery or graft), the risks of treatment, and the viability of the limb. Suspected cases should be initially investigated with beside Doppler ultrasound scan (both limbs), followed by considering a CT angiography.
• Interventions include:
  • Endovascular therapies, for example:
    • Percutaneous catheter-directed thrombolytic therapy.
    • Percutaneous mechanical thrombus extraction.
  • Surgical interventions, for example:
    • Surgical thromboembolectomy.
    • Endarterectomy.
    • Bypass surgery.
    • Amputation if the limb is unsalvageable.

Complications

Complications of acute limb ischaemia include:

• Muscle necrosis and subsequent amputation.
• Compartment syndrome — reperfusion of ischaemic muscles can cause oedema and increased compartmental pressure.
• Reperfusion injury — products of cell death (for example potassium, phosphate and myoglobin) are released when blood flow to the ischaemic limb is restored. This can result in acidosis, hyperkalaemia, rhabdomyolysis, cardiac dysrhythmia, acute kidney injury, multiorgan failure, and disseminated intravascular coagulation.