What is critical limb ischaemia? 

Critical limb ischaemia, now increasingly referred to in clinical practice as Chronic Limb-Threatening Ischaemia (CLTI), is the advanced and most severe stage of Peripheral Vascular Disease (PVD). It occurs when the blood supply to a limb is so severely restricted that it can no longer meet the basic metabolic needs of the tissues even at rest. This leads to chronic pain, non-healing sores, and eventually tissue death or gangrene. In the UK, this condition is treated as a high-priority vascular situation because, without urgent revascularisation, there is a significant risk of major limb amputation. 

Unlike standard claudication, where pain only occurs during exercise, CLTI is defined by its persistence during periods of inactivity. It represents a systemic failure of the circulatory system to provide oxygen to the most distal parts of the body, usually the toes and feet. In 2026, the focus of UK vascular services is on rapid identification and ‘limb salvage’ through a combination of surgery, minimally invasive procedures, and intensive medication. This article explores the diagnostic signs, the physiological causes, and the urgent treatment pathways used to manage this condition. 

What We will cover in this Article 

• The clinical transition from stable PVD to CLTI. 

• Identifying ischaemic rest pain and its relief through gravity. 

• The appearance of arterial ulcers and dry gangrene. 

• Diagnostic tests including Ankle Brachial Pressure Index (ABPI). 

• Urgent revascularisation options such as bypass and stenting. 

• Differentiation between chronic and acute limb ischaemia. 

• Holistic management of cardiovascular risk factors. 

Defining the symptoms of CLTI 

The most distinctive symptom of CLTI is ischaemic rest pain. This is a severe, burning, or aching pain that usually starts in the toes or the forefoot. Because the blood flow is so poor, gravity is often needed to help pull blood into the foot. Patients frequently report that their pain is worst at night when they are lying flat in bed and is only relieved by hanging their leg over the edge of the mattress or getting up to walk. 

Clinical Signs of Tissue Loss 

Arterial Ulcers 

These are typically small, deep, and ‘punched out’ in appearance. They usually occur on the toes, heels, or bony parts of the foot. Unlike venous ulcers, they often have very little bleeding and can be extremely painful. 

Gangrene and Necrosis 

When blood flow is completely absent, the skin and underlying tissues begin to die. This can manifest as dry gangrene, where the skin becomes black, shrivelled, and hard, or wet gangrene if an infection is present. 

Causes and biological triggers 

The primary cause of CLTI is widespread atherosclerosis, where fatty plaques have narrowed multiple segments of the arteries. While the body often tries to grow collateral vessels (natural bypasses) to compensate for these blockages, CLTI occurs when the rate of disease progression outpaces the growth of these new pathways. 

The trigger for the transition from stable disease to CLTI can be a sudden worsening of a blockage or an increased demand for blood that the body cannot meet, such as during a foot infection or after a minor injury. In patients with diabetes, this is particularly dangerous because nerve damage (neuropathy) may mask the initial pain, allowing the ischaemia to reach a critical state before it is noticed. 

Differentiation: Chronic vs Acute Ischaemia 

It is important to differentiate between CLTI and Acute Limb Ischaemia (ALI). While both involve a lack of blood flow, the timeline and causes are different. CLTI develops over weeks or months, whereas ALI is a sudden, minute-to-minute emergency often caused by a blood clot. 

Feature	Chronic Limb-Threatening Ischaemia	Acute Limb Ischaemia
Onset	Gradual (more than 2 weeks)	Sudden (minutes to hours)
Main Cause	Progressive atherosclerosis	Embolism or sudden thrombosis
Pain Level	Persistent rest pain	Sudden, excruciating pain
Temperature	Often cool or cold	Perishingly cold
Emergency Sign	Non-healing ulcers/gangrene	The 6 Ps (e.g., Paralysis, Pallor)

Urgent treatment and revascularisation 

In 2026, the clinical goal for anyone diagnosed with CLTI in the UK is revascularisation. This means restoring the blood supply as quickly as possible to save the tissue. All patients with suspected CLTI are referred for urgent assessment by a vascular multidisciplinary team. 

Revascularisation Strategies 

Balloon Angioplasty and Stenting 

This minimally invasive ‘keyhole’ approach uses a balloon to stretch the artery and a stent to hold it open. It is often the first choice for patients who are too frail for major surgery. 

Vascular Bypass Surgery 

If the blockages are too long or complex for a stent, surgeons use a vein or a synthetic graft to create a new route for the blood to travel around the obstructed area. 

Best Medical Therapy 

Alongside procedures, patients are started on high-dose statins and antiplatelet medications like clopidogrel. These drugs do not fix the immediate blockage but are essential for preventing heart attacks and ensuring any new graft or stent stays open. 

To Summarise 

Critical limb ischaemia is the end-stage of peripheral arterial disease and represents a direct threat to the limb. Characterised by rest pain, ulcers, and gangrene, it requires immediate clinical intervention to restore blood flow. Whether through bypass surgery or angioplasty, the objective is to relieve pain and prevent amputation. Understanding these symptoms and seeking help early is the most effective way to protect your long-term mobility. If you experience severe, sudden, or worsening symptoms, especially a cold, pale, or numb foot, call 999 immediately. 

Authority Snapshot 

This article was written by Dr. Rebecca Fernandez, a UK-trained physician with an MBBS and experience in general surgery, cardiology, internal medicine, gynecology, intensive care, and emergency medicine. Dr. Fernandez has managed critically ill patients and has extensive experience in the clinical assessment and treatment planning for vascular emergencies. This guide follows the standards for the management of peripheral arterial disease and was reviewed by Doctor Stefan to ensure it meets the MyPatientAdvice 2026 framework.