- 5000 patients present annually with acute limb ischaemia. There is a 20% mortality rate, with 40% suffering limb loss.
- Complete arterial occlusion will lead to irreversible tissue damage within 6 hours of onset.
The differential diagnosis for the sudden onset of limb pain includes:
- Acute deep venous thrombosis +/- venous gangrene
- Spinal cord compression/infarct
60% are due to thrombotic occlusion of a previously stenosed artery. Conditions which may predispose to or cause this include:
- Acute plaque rupture
- Pump failure
- Unusual posture/activity
- Aneurysm - thrombosis particularly occurs in popliteal aneurysms
30% are due to embolisation. Possible sources of emboli include:
- >80% arise from the left atrial appendage due to atrial fibrillation
- Left ventricle e.g. post-MI
- Heart valves
- Prosthetic bypass grafts
- Aneurysmal disease
- Paradoxical embolus
- Atrial myxoma
- Arterial dissection (commonly aortic)
- External compression e.g. cervical rib, popliteal entrapment
Look for the 6 P’s of acute ischaemia:
- Perishingly cold
The latter two features are late signs which are key to diagnosing complete ischaemia. The affected limb whitens and acquires a mottled appearance, followed by hardening of the muscles and skin blistering. Eventually gangrene develops.
Assessment: Identifying the Cause
Certain features within the history and examination findings can help to determine the most likely cause. The key features of acute ischaemia due to thrombosis and embolism are compared in the table below.
Some features of the history may help to identify the cause of ischaemia. Some factors implicating the different aetiologies include:
- Previous chronic ischaemia – claudication, rest pain
- Vascular isease in the other leg
- Known aneurysmal disease
- Vascular risk factors
2. Embolic risk:
- Known atrial fibrillation
- Valve disease
- Previous myocardial infarction
- DVT - ‘paradoxical embolus’
- Atrial myxoma
- Subacute bacterial endocarditis
3. Pain of dissection - characteristically tearing pain radiating to the back
4. History of trauma/vascular intervention
- The 6 P's (pain, pallor, pulseless, perishingly cold, paraesthesia, paralysis)
- Atrial fibrillation
- Valve disease
Assessing Severity: Is the Limb Threatened?
The acutely ischaemic limb always represents an emergency. Prompt treatment can save a newly ischaemic or threatened limb. However, after a critical period of ischaemic time has elapsed, the limb becomes unsalvagable, with amputation the only treatment option. The table below highlights the clinical features that indicate the severity of ischaemic damage, and therefore guide treatment options.
- Adopt an ABCDE approach.
- Discuss immediately with seniors and vascular surgeons.
- If there are no contraindications, give an IV bolus of heparin to limit propagation of the thrombus and protect collateral circulation.
If an embolus is suspected:
- Give intravenous heparin
- Rapid resuscitation to best medical condition, including intravenous fluids. Consider catheterisation, aiming for a good urine output
- Urgent surgery is needed — embolectomy (with Fogarty balloon, by aspiration, or surgically, together with histology and culture) or bypass.
If thrombosis is suspected:
- Optimise patient to best medical condition.
- Give intravenous heparin.
- Perform arteriogram before theatre: angioplasty, thrombolysis or bypass surgery may be required.
Irreversible damage: Amputation remains the only treatment option.
- After revascularisation, patients can suffer reperfusion injury.
- Oxygen free radicals, neutrophil activation and increased endothelial permeability can cause limb swelling.
- Increased pressure within the osteofascial compartments can compromise first venous drainage, then arterial supply, resulting in compartment syndrome, with death of muscle and other tissues.
- If untreated, this can lead to systemic upset or shock, with myoglobinuria inducing acute tubular necrosis and renal failure, acidosis and hyperkalaemia.
- Untreated patients develop irreversible muscle loss, contractures, and can suffer from chronic pain/reflex sympathetic dystrophy.
- Prompt fasciotomy is needed to prevent these complications.
Images in this article have been taken from Ken Callum, Andrew Bradbury 'ABC of arterial and venous disease: Acute limb ischaemia', BMJ 2000, 320 : 74
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