Case 27.2 – Lower Limb Arterial Disease

Clinical features of an ischaemic limb:

• pulseless
• pain
• pallor
• 'perishing' cold
• paralysis
• paraesthesia.

Faced with the acutely ischaemic limb, the following questions must be addressed: Is the limb salvageable? Is the limb threatened?

The non-viable limb:

Features that indicate the limb is no longer salvageable include:

• fixed staining of tissues
• lack of blanching on pressure
• anaesthesia with rigid muscles-rigor mortis.

The threatened limb:

Features of an ischaemic limb that is likely, in the absence of revascularisation, to become non-viable include:

• loss of sensation
• loss of active movement
• pain on passive movement and when the calf muscles are squeezed.

When these features are present, there is a maximum of 6 hours in which to re-establish normal flow to avoid irreversible nerve and muscle injury.

Intermittent claudication (IC):

IC is pain felt in the legs on walking due to arterial insufficiency. It is the most common symptom of peripheral arterial disease. The pain typically occurs in the calf secondary to femoropopliteal disease but may be felt in the thigh and/or buttock if proximal (aorto-iliac) obstruction to blood flow is present. Patients describe a tightness or 'cramp-like' pain which develops after a relatively constant distance, which is shorter if walking uphill. The pain disappears completely within a few minutes of rest but recurs on walking. The claudication distance is how far patients say they can walk before pain starts.

Neurogenic claudication:

This is leg pain on walking due to neurological and musculoskeletal disorders of the lumbar spine.

Venous claudication:

This is pain due to venous outflow obstruction from the leg following extensive deep vein thrombosis.

Neurogenic and venous claudication is much less common than arterial claudication, and can be distinguished on history and examination:

	Arterial	Neurogenic	Venous
Pathology	Stenosis or occlusion of 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 buttocks	Ill-defined. Whole leg. May be associated with numbness and tingling	Whole leg. 'Bursting' in nature
Laterality	Unilateral if femoropopliteal, and bilateral if aorto-iliac disease	Often bilateral	Nearly always unilateral
Onset	Gradual after walking the 'claudication distance'	Often immediate on walking or standing up	Gradual, from the moment walking starts
Relieving features	On stopping walking, the pain disappears completely in 1-2 minutes	Bending forwards and stopping walking. May sit down for full relief	Leg elevation
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

Pathophysiology of Claudication Pain:

Arterial insufficiency causes ischaemic muscle pain on walking: At rest, the blood requirement is met by the collateral circulation through the profunda femoris system which joins the popliteal artery below the blockage usually just above the knee. However, exercise produces a demand which cannot be met, and the calf muscles become ischaemic. Because the thigh muscles still have a normal blood supply, the pain is usually felt only in the calf. If stenosis is more proximal (aorto-iliac), then pain is felt in the whole leg and even the buttock if the blood flow to the internal iliac artery is compromised.

Vascular anatomy of the lower limb:

The vascular anatomy includes the aorta bifurcating into the common iliac arteries, which divide into internal and external iliac arteries. The external iliac becomes the common femoral artery, which bifurcates into the superficial femoral artery and profunda femoris. The superficial femoral artery continues as the popliteal artery, which then divides into the anterior tibial, posterior tibial, and peroneal arteries supplying the lower leg and foot.

Common sites of atherosclerotic thrombosis:

The most common site for atherosclerotic narrowing/occlusion are the superficial femoral artery, aorto-iliac and femoropopliteal segments.

Sites for lodgement of emboli:

Emboli, usually are of cardiac origin (80%); they also can originate from proximal atheroma, tumor, or foreign objects. Emboli tend to lodge at artery bifurcations or in areas where vessels abruptly narrow. The femoral artery bifurcation is the most common site (43%), followed by the iliac arteries (18%), the aorta (15%), and the popliteal arteries (15%).

Ankle:brachial pressure index:

The severity of ischaemia can be estimated by determining the ratio between the ankle and brachial blood pressures. The latter is recorded in the normal way, the former using a cuff and a hand-held Doppler device.

Interpretation:

• Normal: should be at least 1 (the pressure at the ankle at least as high as that in the arm)
• Intermittent Claudication: usually 0.5-0.9
• Chronic limb ischaemia: usually less than 0.5

Critical Limb Ischaemia (CLI):

Critical Limb Ischaemia (CLI) is usually caused by multiple lesions affecting different arterial segments. These patients have tissue loss (ulceration or gangrene), with or without rest pain, and, by definition, have an ankle blood pressure of less than 50 mmHg. Without revascularization, such patients will usually lose their limb-and often their life-in a matter of weeks or months.

Subcritical limb ischaemia (SCLI) describes patients who have night and/or rest pain, but not tissue loss. They are in an intermediate group between IC and CLI, and share features of both. A proportion of these patients may respond to BMT, thereby obviating the need for arterial reconstruction to save the limb.

Severe limb ischaemia (SLI) describes all patients with chronic limb ischaemia that is more severe than IC: that is, CLI and SCLI.

Medical therapy:

• Immediate, absolute and permanent cessation from smoking
• Control of hypertension
• Control of hypercholesterolaemia. It is increasingly apparent that, whatever a patient's baseline cholesterol, if there is any manifestation of atherosclerosis, then that level of cholesterol is too high for the individual patient and should be lowered. While dietary advice is important, virtually all patients will require drug therapy, usually with statins, to obtain the necessary fall in total cholesterol. There is increasing evidence that statins, as well as having cholesterol-lowering properties, also stabilize atheromatous plaques and prevent the development and progression of aneurysmal disease through as yet incompletely understood anti-inflammatory mechanisms.
• Prescription of an antiplatelet agent. This is normally aspirin (100 mg daily), but in the significant proportion of patients who state they are unable to tolerate this, clopidogrel (75 mg daily) is an equally effective alternative.
• Regular exercise (if possible).
• Control of obesity. (improving blood pressure, cholesterol and exercise tolerance)
• Active treatment of patients with diabetes, including foot care

Active intervention, by either endovascular or open surgery, should not normally be considered until the patient has been compliant with BMT for at least 6 months.

Surgical management:

Endovascular management:

Percutaneous transluminal (balloon) angioplasty (PTA) has been used successfully in the iliac, femoral, popliteal and tibial arteries. PTA is performed under local anaesthesia. The lesion is identified on duplex ultrasound or arteriography and crossed with a wire. A balloon catheter is introduced over the wire and the balloon inflated. This ruptures the atheromatous plaque, thereby enlarging the lumen. In suprainguinal (aorto-iliac) occlusions and complex disease, metal stents may be deployed across the lesion to improve patency and reduce distal embolic complications.

In Intermittent claudication:

PTA is relatively expensive, associated with a 1-2% morbidity rate, and there is possible lack of durability in femoro-popliteal segment. However, such patients tend to be younger with shorter walking distances and bilateral symptoms, and may not achieve satisfactory improvement with BMT alone. The long-term patency of PTA and stenting is optimal in high-flow, large-calibre vessels, leading to durable benefit in most patients.

In Critical limb ischaemia:

PTA may be safer, cheaper and quicker, may require less hospitalization, and it can be repeated. Even if unsuccessful, it may not prejudice the chances of subsequently performing a successful arterial bypass. However, many patients tend to have complex multilevel disease and are unsuitable for conventional PTA.

Arterial reconstruction:

In Intermittent claudication, most surgeons are reluctant to perform infra-inguinal bypass surgery because the risk of limb loss is very low with medical therapy, surgery is associated with significant mortality and morbidity (exceeding 5% for infra-inguinal bypass and 10% for aorto-bifemoral bypass), and when the graft occludes, the patient is usually returned to a worse level of ischaemia than before the operation.

Procedures of arterial reconstruction:

Endarterectomy: This involves the direct removal of atherosclerotic plaque and thrombus. With the advent of prosthetic large-calibre grafts and successful endovascular treatment, endarterectomy is relatively uncommon except at the carotid bifurcation.

Bypass grafting: For a surgical bypass operation to be successful in the long term, three conditions must be fulfilled:

• There must be high-flow, high-pressure blood entering the graft (inflow).
• The conduit must be suitable.
• The blood must have somewhere to go when it leaves the graft (outflow).

Two main types of conduit are available:

• autogenous material, most commonly the ipsilateral long saphenous vein
• prosthetic material (polytetrafluoroethylene or Dacron).

The main advantage of vein is that it is lined by endothelium that is actively antithrombotic and profibrinolytic, and more resistant to infection.

Extra-anatomic bypass: Where anatomic bypass is not possible or desirable, a so-called extra-anatomic bypass can be inserted. For example, if only one iliac artery is blocked, a femoro-femoral crossover graft can be performed.

Complications of arterial reconstruction:

In the early post-operative period (30 days), vascular patients are susceptible to all the general complications of major surgery. As such patients are usually elderly and unfit with widespread vascular disease, the morbidity of vascular surgery is considerably higher than for most other types of major surgery.

In the longer term, the major complications are graft occlusion and infection. Once a prosthetic graft is infected, it must be removed to rid the patient of sepsis and/or to prevent anastomosis breakdown and potential life-threatening haemorrhage.