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Limb Embolism And Ischaemia

See related article peripheral vascular disease

Acute ischaemia is most often due to acute thrombotic occlusion of a previously partially occluded, thrombosed arterial segment or due to embolus. Without surgical revascularisation, complete acute ischaemia leads to extensive tissue necrosis within six hours. The effects of sudden arterial occlusion depends on the state of collateral supply. The collateral supply in the leg is usually inadequate unless there has been pre-existing occlusive disease. Subclavian artery has many collateral vessels so that occlusion of a major artery does not necessarily make a limb non-viable.

Epidemiology
Incidence Acute leg ischaemia occurs in 1 in 12,000 patients per year.

Risk Factors

• Embolism: left atrium in patients in atrial fibrillation, mural thrombus after myocardial infarction, prosthetic and abnormal heart valves, aneurysm (aorta, femoral, or popliteal) proximal atheromatous stenosis, tumour, or foreign body.
• Thrombosis.
• Other causes include trauma, dissecting aneurysm and Raynaud's Syndrome.
• Compartment syndrome may lead to acute ischaemia. It occurs when perfusion pressure falls below tissue pressure in a closed anatomical space. Causes include orthopaedic (tibial or forearm fractures), vascular (haemorrhage, Phlegmasia caerulea dolens), soft-tissue injury (prolonged limb compression, crush injury, burns).
• Most cases of leg ischaemia result from the presence of thrombus at sites of atherosclerotic narrowing. Can be acute, resulting from emboli from rupture of proximal atherosclerotic plaque or thrombus. Chronic ischaemia in the legs usually results from gradual extension of thrombus with development of collateral vessels. Less common causes include Phlegmasia cerulea dolens (massive thrombosis in the major veins of the limbs causing gross swelling that obstructs arterial flow), congenital causes of early-onset leg ischaemia (e.g. aortic hypoplasia).
• Causes of ischaemia of the arm: most often embolism from the heart but also be due to damage to the subclavian artery or thoracic outlet syndrome.

Presentation

• History and examination should identify the severity of ischaemia and whether it is likely to be embolic or thrombotic. Important features to differentiate include rapidity of onset of symptoms, features of pre-existing chronic arterial disease, potential source of embolus and, in lower limb ischaemia, the state of foot pulses in the contralateral leg.
• The affected part becomes pale, pulseless, painful, paralysed, paraesthetic and 'perishing with cold' ('the 6 Ps').
• The onset of fixed mottling of the skin implies irreversible changes.
• The limb may be red when dependent, leading to a misdiagnosis of inflammation, e.g. gout or cellulitis.

Investigations

• If diagnosis is in doubt, perform urgent arteriography.
• Identify source of embolus: ECG, echocardiogram; ultrasound aorta, popliteal and femoral arteries. Blood tests for full blood count, ESR, glucose, lipids and thrombophilia screen.

Management

• This is an emergency and may require urgent open surgery or angioplasty. Objective sensory loss requires urgent treatment. Immediately heparinise (may double limb-salvage rate) and provide analgesia.
• Ischaemia following trauma and acute thrombosis may require urgent reconstruction.
• The limb must be checked for evidence of compartment syndrome and if necessary a fasciotomy should be performed.
• If the occlusion is embolic, the options are surgical embolectomy (Fogarty catheter) or local intra-arterial thrombolysis.
• If embolectomy with a Fogarty catheter fails, an on-table angiogram is performed and bypass graft or intraoperative thrombolysis considered. Routine intraoperative angiography for arterial thromboembolectomy has been shown to be beneficial³.
• After successful embolectomy, anticoagulation with heparin to prevent recurrence.
• Intra-arterial thrombolysis⁴:
  • Heparin infusion is combined with the thrombolytic agent.
  • Thrombolysis can be accelerated by using pulse spray through a multiple side-hole catheter, aspiration thrombectomy (debulking thrombus aspiration) and by using a high dose over a shorter time.
  • Complications of thrombolysis are haemorrhage, pericatheter thrombosis, haemorrhagic stroke and distal embolization.
  • The contraindications are critical ischaemia with neurological deficit, irreversible ischaemic changes.
  • Recombant tissue plasminogen activator (the preferred agent): up to 60-90% of thromboses will show clinically useful lysis. However, there is a high rate of reocclusion.
  • Following successful lysis, correction of the underlying problem, possibly including angioplasty or operation, may be required.
• Thrombotic disease: intra-arterial thrombolysis, angioplasty or bypass surgery. If due to thrombosis of an arterial graft, initially attempt thrombolysis.
• If limb is irreversibly ischaemic, amputation will be required.

Other management

• Reduction in the rate of deterioration includes regular exercise, smoking cessation, treating hypertension and hyperlipidaemia, improving diabetes control.
• Management of associated and underlying problems: treat anaemia or polycythaemia, cardiac disease.
• Low dose aspirin or clopidogrel. Warfarin if otherwise indicated.
• ACE inhibitors have been shown to reduce morbidity and mortality due to cardiovascular disease in patients with peripheral vascular disease by 25%.
• Statin to reduce total and LDL-cholesterol.

Complications

• Reperfusion injury may cause more damage than the initial ischaemia:
  • neutrophils migrate into the reperfused tissue causing injury.
  • limb swelling due to increased capillary permeability may cause a compartment syndrome.
  • leakage from damaged cells may cause acidosis and hyperkalaemia (leading to cardiac arrhythmias) and myoglobinaemia (leading to acute tubular necrosis).
• Chronic pain syndromes: acute complete ischaemia can lead to peripheral nerve injury.

Prognosis The mortality associated with acute ischaemia remains high as thrombosis or embolism is not infrequently a pre-terminal event in patients dying from other causes such as heart failure.

Prevention Long-term anticoagulation for potential causes of thromboembolism.

References Used

1. Callum K, Bradbury A; Acute limb ischaemia; British Medical Journal 18 March 2000; 320; 764-7
2. Acute limb ischaemia; Surgical Tutor (2004)
3. Ebner H, Zaraca F, Randone B.; The role of intraoperative angiography in arterial thromboembolectomy for non-traumatic acute upper limb ischaemia. Chir Ital. 2004 May-Jun;56(3):345-50.
4. Kessel DO, Berridge DC, Robertson I.; Infusion techniques for peripheral arterial thrombolysis. Cochrane Database Syst Rev. 2004(1):CD000985.

Acknowledgements EMIS is grateful to Dr Colin Tidy for authoring this article. The final copy has passed peer review of the independent Mentor GP authoring team. ©EMIS 2004.

Last issued 15 Aug 2005