Acute limb ischaemia

Acute limb ischaemia refers to a sudden decrease in blood supply resulting in ischaemic injury to the lower limbs.

Peripheral artery disease (PAD) is characterised by the presence of narrowing’s or occlusion of peripheral arteries leading to compromise of blood supply to the lower limbs.

As with many areas of medicine terminology can be confusing. In this note we follow terminology referred to in the 2017 ESC guidance on peripheral arterial diseases. Peripheral arterial diseases refers to ‘all arterial disease other than coronary arteries and the aorta’. Peripheral artery disease refers to what may also be termed lower extremity artery disease (LEAD). 

It can be categorised as acute or chronic depending on the presentation:

• Acute limb ischaemia: refers to a sudden decrease in blood supply resulting in ischaemic injury. Typically the features are said to develop in less than 2 weeks.
• Chronic limb ischaemia: refers to chronic narrowing of peripheral arteries resulting in intermittent claudication, rest pain and may threaten limb viability. 

Acute limb ischaemia is caused by sudden decrease in perfusion to the lower limb.

Embolisation is commonly implicated. This refers to a solid deposit (typically thrombus) travelling from its source (typically central) and lodging in a distal vessel. This often occurs from a cardiac source of thrombus (e.g. secondary to AF, MI) or one associated with a proximal aneurysm (e.g. AAA, popliteal). 

Thrombosis and plaque rupture occurs when the cap of a thrombus ruptures exposing a rough and thrombogenic surface resulting in further relatively rapid thrombus progression.

Anything that causes sudden occlusion or narrowing can be implicated:

• Progressive thrombosis, plaque rupture
• Embolism
• Trauma
• Compartment syndrome
• Aortic dissection
• Popliteal aneurysm thrombosis
• Iatrogenic (complication of surgery)
• Phlegmasia cerulea dolen (look it up, its interesting!)

Smoking and diabetes are the two most significant risk factors for developing PAD.

• Smoking
• Diabetes
• Age
• Hypertension
• Hyperlipidaemia
• Obesity

Classically the 6 P’s are used to describe the features of acute limb ischaemia.

In embolic disease, onset is sudden and the limb is more likely to be ‘white’ with a complete lack of peripheral blood flow beyond the point where the embolism settled. There is no time for collaterals to have developed.

Where ischaemia occurs due to thrombosis, onset may be more gradual and collateral supply may have developed. They often present with acute worsening of underlying vascular disease.

The six P’s of acute limb ischaemia are:

• Pain
• Pulseless 
• Pallor
• Paralysis
• Paraesthesia
• Perishingly cold

Most texts refer to pallor as a pale or white appearence. This will however appear differently depending on the patients skin tone. It is important to note overall black individuals appear to be at an increased risk of limb ischaemia. Changes may be subtle or less apparent and as such a higher index of suspicion should be held.

The Rutherford classification can be used to grade and guide management in acute limb ischaemia.

Investigations can be non-invasive (e.g. US, CT) or invasive (e.g. DSA).

Duplex ultrasound: A non-invasive technique that allows visualisation of the arteries and assessment of stenosis.

CT angiogram: A non-invasive technique that uses IV contrast to allow visualisation of the arteries and any narrowing/occlusion.

Digital subtraction angiography: An invasive technique that utilises catheter guided contrast injection combined with fluoroscopy and digital subtraction to isolate the vessels.

The rate of amputation is linked to ‘time to reperfusion’, as such prompt recognition and management is key.

A variety of treatment modalities are available and choice should be guided by experienced specialists. Choice depends on presentation, with the presence of neurological deficit of particular importance.

Management is complex, here an outline of possible management options are shown. They are adapted from ESC Guidelines on the Diagnosis and Treatment of Peripheral Arterial Diseases, 2017.

Initial management

Once recognised, if not at a specialist centre, you must lease with and discuss transfer to your local vascular centre. 

Initial management typically consists of analgesia and heparin. Heparin is an anticoagulant that potentiates the action of antithrombin III. 

Rutherford I

There may be time to arrange imaging work-up. Revascularisation may be attempted with catheter-directed thrombolysis, embolectomy or bypass. If an underlying vascular lesion is present endovascular therapy or surgery should be attempted.

Patients will need ongoing medical therapy, psychological care, rehabilitation and surgical follow-up.

Rutherford II

Urgent revascularisation is indicated, typically with a embolectomy or bypass. If an underlying vascular lesion is present endovascular therapy or surgery should be attempted. 

Patients will need ongoing medical therapy, psychological care, rehabilitation and surgical follow-up.

Rutherford III

Irreversible damage with dead, non-viable tissue mandates amputation of affected areas.

Patients will need ongoing medical therapy, psychological care, rehabilitation and surgical follow-up.