Critical limb ischaemia (CLI)

Overview:

• Defined as ‘rest pain which requires strong (opiate) analgesia for a period of 2 weeks or more, and tissue loss, in association with an ABPI of <50mmHg’
• The inference is that, without intervention, a patient with CLI will come to major amputation within weeks or months

Symptoms:

Rest pain is indicative of severe ischaemia, usually felt in the forefoot and, typically, the pain is worse at night and disturbs sleep. The reasons for this are:

• Metabolic rate in the foot is increased under the warm bedclothes
• Cardiac output and BP fall during sleep
• The beneficial effect of gravity on pedal BP is lost

For these reasons, relief at night is often sought by hanging the leg over the side of the bed or walking about on a cold floor

Signs:

• In addition to the findings of arterial insufficiency, there may be evidence of multilevel disease
• Constant pain in the foot with single level arterial disease is uncommon and should lead to a search for other causes
• Ischaemic tissue is extremely sensitive to injury; even minor wounds fail to heal and ulceration follows
• Minor damage quickly leads to infection and bacterial toxins destroy yet more tissue
• Frank gangrene then ensues and can spread extremely rapidly, especially in diabetics

Medical management:

In contrast to a presentation with claudication, rest pain is a warning that tissue loss is imminent. In the great majority, CLI does not improve without surgical intervention but medical therapies have important roles:

• Assessment and treatment of heart failure, intercurrent infection and anaemia
• Control of diabetes
• Antibiotic therapy for local infection
• Pain relief
• Use of anticoagulants and, occasionally, prostacyclin-based drugs when tissue loss is minimal

All of these measures can ensure that an optimum condition is achieved before surgical intervention is performed

Balloon angioplasty:

• In patients with early rest pain and/or minimal tissue loss (subcritical ischaemia), PTA may tip the balance just enough to salvage the limb when surgical reconstruction is not feasible
• However, some believe that all patients with CLI should in the first instance be managed with PTA and that operation should be reserved for those who do not respond

Amputation:

• This is a last resort
• Primary amputation can be the best option in the elderly frail patient with extensive tissue loss, but mortality is inevitably high

Surgery:

Bypass surgery and, to a far lesser extent, local endarterectomy are the mainstays of treatment, although the frequently present multisystem medical and vascular problems dictate a mortality for limb salvage surgery of up to 10%

Aortoiliac disease:

• In CLI, this is usually associated with infra-inguinal disease
• In younger, fitter patients who are considered unsuitable for PTA, the standard operation is aortobifemoral bypass graft
• In those not fit for aortic surgery, an extra-anatomical bypass may be suitable. For example, if there is an iliac occlusion on one side and a relatively disease-free vessel on the other, a femorofemoral crossover graft is possible

Femorodistal bypass:

• This refers to an arterial reconstruction below the inguinal ligament in which common femoral or superficial femoral arteries are the site of proximal anastomosis and the popliteal or tibial vessels are the site of distal anastomosis

The requirements for a successful distal bypass are:

• Good inflow
• A reliable conduit
• Good outflow

Management of thrombosis in a graft:

The options are:

• If the leg is viable then it may be sensible to do nothing and wait for collaterals to develop
• Thrombolysis – if successful, the underlying lesion which caused the graft to block can then be identified and corrected by either surgery or PTA
• Thrombectomy – mechanical removal of thrombosis, followed by an operative angiogram to identify the underlying lesion and surgical correction
• Construction of a new graft