Acute limb ischaemia

The features of the acutely ischaemic limb are conveniently known as the 6 Ps (Table 3.33). Of these, loss of motor (ability to wiggle the toes/fingers) and/or sensory function (light touch over the forcfoot/dorsuin of the hand) are the most important and indicate nerve ischaemia. Once these features are present the limb will become irreversibly damaged unless the circulation is restored within a few hours. Calf muscle tenderness is another grave sign indicating impending muscle infarction.

The common causes of acute limb ischaemia are embolus (usually cardiac in origin) or thrombotic occlusion of a narrowed atherosclerotic arterial segment (Table 3.34).

Acute arterial occlusion is associated with intense spasm in the arterial tree distal lo the blockage and the limb will appear 'marble white'. Over the next few hours, the spasm relaxes and the skin fills with deoxygenaled blood leading to mottling which is light hlue or purple, has a fine reticular pattern and blanches on pressure. As ischaemia progresses, blood coalescing in the skin produces a coarser pattern which is dark purple, almost black, and does not blanch. The final stage is large patches of fixed staining leading on to blistering and liquefaction. Fixed mottling of an anaesthetic, paralysed limb, in association with muscle rigidity and

TABLE 3.32 The clinical features of arterial, neurogenic and venous claudication

Arterial

Neurogenic

Venous

Pathology

Stenosis or occlusion ol major lower limb arteries

Lumbar nerve root or cauda equina compression (spinal stenosis)

Obstruction to the venous outflow of the leg due to iliofemoral venous occlusion

Site of pain

Muscles, usually the calf but may Involve thigh and buttock

Ill-defined. Whole leg. May be associated with numbness and tingling

Whole leg. 'Bursting' In nature

Laterality

Unilateral if femoropopliteal. and bilateral il aortoiliac disease

Often bilateral

Nearly always unilateral

Onset

Gradual after walking the 'claudication distance'

Often immediate upon walking or even standing up

Gradual, often from the moment walking commences

Relieving features

On cessation ol walking, Ihe pain disappears completely in 1-2 minutes

Eased by bending forwards and stopping walking. May have to sit down to obtain M relief

Usually necessary to elevate leg to relieve discomfort

Colour

Normal or pale

Normal

Cyanosed, Often visible varicose veins

Temperature

Normal or cool

Normal

Normal or Increased

Oedema

Absent

Absent

Always present

Pulses

Reduced or absent

Normal

Present but may be difficult to feel owing to oedema

Straight leg raising

Normal

May be limited

Normal

TABLE 3.33 Signs of acute limb isctiaemia

TABLE 3.33 Signs of acute limb isctiaemia

Soft signs Pulseless Pallor

Perishing cold

Hard signs (indicating a threatened limb)

Paraesthesla

Paralysis

Pain on squeezing muscles

TABLE 3.34 Acute limb ischaemia - embolus vs thrombosis in situ

Embolus

Thrombosis

Onset and severity

Owing lo lack of preexisting collaterals the onset is acute (seconds or minutes) and the ischaemia profound

Owing to pre-existing collaterals, onset is more Insidious (hours or days) and ischaemia less severe

Embolic source

Present! usually AF)

Absent

Previous claudication

Absent

Present

Pulses in contralateral leg

Present

Often absent

Diagnosis

Clinical

Angiography

Treatmenl

Embolectomy and anticoagulation

Medical, bypass surgery, thrombolysis

CASE HISTORY

This patient was admitted with an acutely painful right hand. On examination, Ihe patient was in atrial fibrillation, the hand was pale and the fingers mottled (Fig. 3.41). Right arm pulses were absent. Arteriography showed occlusion of the right axillary artery consistent with embolus (Fig. 3.42). The patient was heparinised, underwent successful brachial embolectomy under local anaesthetic and was then commenced on warfarin.

Learning points

• Acute embolism is the commonest cause of acute arm ischaemla.

• To avoid amputation, time Is critical; all patients with a suspected acutely Ischaemic limb should be considered for vascular surgery Immediately.

turgor, indicates irreversible isctiaemia and amputation is the only option.

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