ABC of arterial and venous disease Acute limb ischaemia

Ken Callum, Andrew Bradbury

Limb ischaemia is classified on the basis of onset and severity. Complete acute ischaemia will lead to extensive tissue necrosis within six hours unless the limb is surgically revascularised. Incomplete acute ischaemia can usually be treated medically in the first instance. Patients with irreversible ischaemia require urgent amputation unless it is too extensive or the patient too ill to survive.

Clinical features

Apart from paralysis (inability to wiggle toes or fingers) and anaesthesia (loss of light touch over the dorsum of the foot or hand), the symptoms and signs of acute ischaemia are non-specific or inconsistently related to its completeness. Pain on squeezing the calf indicates muscle infarction and impending irreversible ischaemia.

Acute arterial occlusion is associated with intense spasm in the distal arterial tree, and initially the limb will appear "marble" white. Over the next few hours, the spasm relaxes and the skin fills with deoxygenated blood leading to mottling that is light blue or purple, has a fine reticular pattern, and blanches on pressure. At this stage the limb is still salvageable. However, as ischaemia progresses, stagnant blood coagulates leading to mottling that is darker in colour, coarser in pattern, and does not blanch. Finally, large patches of fixed staining progress to blistering and liquefaction. Attempts to revascularise such a limb are futile and will lead to life threatening reperfusion injury. In cases of real doubt the muscle can be examined at surgery through a small fasciotomy incision. It is usually obvious when the muscle is dead.

Aetiology

Acute limb ischaemia is most commonly caused by acute thrombotic occlusion of a pre-existing stenotic arterial segment (60% of cases) or by embolus (30%). Distinguishing these two conditions is important because treatment and prognosis are different. Other causes are trauma, iatrogenic injury, popliteal aneurysm, and aortic dissection.

More than 80% of peripheral emboli arise from the left atrial appendage in association with atrial fibrillation. They may also arise from the left ventricle, heart valves, prosthetic bypass grafts, aneurysmal disease, paradoxical embolism, and atrial myxoma (rare). In 15% of cases the source of embolus is obscure. Thrombosis in situ may arise from acute plaque rupture, hypovolaemia, or pump failure (see below).

Management

Classification of limb ischaemia Terminology

Definition or comment

Onset: Acute

Acute on chronic Chronic

Severity (acute, acute on chronic): Incomplete Complete Irreversible

Ischaemia < 14 days Worsening symptoms and signs (< 14 days) Ischaemia stable for >14 days

Limb not threatened Limb threatened Limb non-viable

Symptoms and signs of acute limb ischaemia Symptoms or signs Comment

Pain Occasionally absent in complete ischaemia

Pallor Also present in chronic ischaemia

Pulseless Also present in chronic ischaemia

Perishing cold Unreliable as ischaemic limb takes on ambient temperature

Paraesthesia* Leading to anaesthesia (unable to feel touch on foot or hand) Paralysis* Unable to wiggle toes or fingers

*Anaesthesia and paralysis are the key to diagnosing complete ischaemia that requires emergency surgical treatment

Marble Leg Acute Limb Ischemia
Marble white foot (left of picture) in patient with acute ischaemia

Differentiation of embolus and acute arterial thrombosis (thrombosis in situ)

Clinical features Embolus Thrombosis

General measures

When a patient is suspected to have an acutely ischaemic limb the case must be discussed immediately with a vascular surgeon. A few hours can make the difference between death or amputation and complete recovery of limb function. If there are no contraindications (acute aortic dissection or multiple trauma, particularly serious head injury) give an intravenous bolus of heparin to limit propagation of thrombus and protect the collateral circulation.

Differentiation of embolus and acute arterial thrombosis (thrombosis in situ)

Clinical features Embolus Thrombosis

Severity

Complete (no

Incomplete

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