ConditionHeart & circulation
Acute Limb Ischemia
Acute limb ischemia is a sudden drop in blood flow to an arm or leg, usually from a blood clot that blocks an artery. Without blood the limb's muscles and nerves start dying within about 6 hours. The warning signs are the "6 P's": pain, pallor (pale skin), pulselessness, poikilothermia (a cold limb), paresthesia (pins and needles or numbness) and paralysis. It is a vascular emergency: call 911 or your local emergency number. Fast treatment with blood thinners and clot removal can save the limb.
Also called: ALI, acute arterial occlusion, acute leg ischemia, arterial embolism of the limb
At a glance
- What it is
- Sudden loss of blood flow to a limb, threatening its survival.
- Warning signs
- Pain, pallor, pulselessness, cold limb, numbness, paralysis (the 6 P's).
- Main causes
- A clot from the heart (often in atrial fibrillation) or a clot forming on a narrowed artery.
- Time window
- Muscle and nerve damage begins within about 4 to 6 hours.
- Treatment
- Heparin, then surgical clot removal, clot-dissolving drugs or bypass.
When to get help
Call 911 or go to the ER
- A suddenly painful, cold, pale or bluish arm or leg
- Sudden numbness, tingling or weakness in one limb, especially with a cold, pale foot or hand
- A limb that becomes painful and pale after a heart attack, heart procedure or with atrial fibrillation
- Sudden worsening of leg pain at rest in someone with peripheral artery disease or a leg bypass
See a doctor within a day or two
- Leg pain at rest that wakes you at night, eased by hanging the leg over the bed
- A foot sore or black toe that is not healing in someone with poor circulation
Book a routine appointment
- Calf pain when walking that eases with rest (claudication)
What happens in acute limb ischemia
Arteries carry oxygen-rich blood to the limbs. When one is suddenly blocked, the tissues beyond it have no reserve supply. Nerves are most sensitive and stop working first, causing numbness, then muscles start to die. After about 6 hours, damage may be irreversible, and when blood flow returns, swollen muscles can cause compartment syndrome and release toxins into the bloodstream.
Legs are affected far more often than arms.
The 6 P's of acute limb ischemia
| P | What it means | Significance |
|---|---|---|
| Pain | Sudden, severe, constant pain, worse with movement | Usually the first symptom |
| Pallor | Pale, white or mottled skin | Poor blood flow |
| Pulselessness | No pulse felt at the foot or wrist | Confirms an arterial block |
| Poikilothermia | Limb cold to touch compared with the other side | Poor blood flow |
| Paresthesia | Pins and needles or numbness | Nerve damage starting; urgent |
| Paralysis | Weakness or inability to move toes or fingers | Advanced; limb at immediate risk |
Loss of sensation and muscle weakness mean the limb is "threatened" and needs restoration of blood flow within hours.
Causes
Embolism
A clot forms elsewhere, often in the heart, and travels to lodge in a limb artery. Sources include:
- atrial fibrillation, the most common
- a recent heart attack with a clot in the heart chamber
- heart valve disease or artificial valves
- an aneurysm in the aorta or behind the knee
Embolic ischemia starts very suddenly in a previously healthy limb.
Thrombosis
A clot forms on an artery already narrowed by atherosclerosis, in people with peripheral artery disease. Because small bypass vessels may have developed, symptoms can be slightly less abrupt. Blocked leg bypass grafts and stents also cause thrombosis.
Other causes
- injury to an artery from trauma, fractures or medical procedures
- aortic dissection
- clotting disorders, cancer, and severe dehydration
- a popliteal aneurysm that clots
Diagnosis
Diagnosis is made at the bedside: examination of pulses, skin color, temperature, sensation and movement, and a handheld Doppler to listen for blood flow. Treatment should not be delayed for extensive testing in a threatened limb. Imaging may include:
- CT angiography to show where the blockage is
- Duplex ultrasound
- Catheter angiography, which can be combined with treatment
- ECG and echocardiogram to find a heart source
Treatment
- Immediate heparin through a vein to stop the clot spreading.
- Restoring blood flow: - Surgical embolectomy: a balloon catheter pulls out the clot through a small incision in the groin or arm. - Catheter-directed thrombolysis: a clot-dissolving drug delivered through a catheter, for limbs that are not immediately threatened. - Mechanical thrombectomy: devices that break up and suck out the clot. - Bypass surgery or stenting for underlying narrowed arteries.
- Fasciotomy: cutting the tight tissue around muscles to relieve or prevent compartment syndrome after blood flow returns.
- Amputation if the limb cannot be saved.
Afterward, long-term anticoagulation is usually needed for embolism from atrial fibrillation, along with treatment of atherosclerosis risk factors.
Complications
- compartment syndrome and muscle breakdown (rhabdomyolysis) after reperfusion
- kidney injury from muscle breakdown products
- high potassium and dangerous heart rhythms
- permanent nerve damage, weakness or foot drop
- limb loss
Outlook
Acute limb ischemia carries a significant risk of amputation and death, especially in older people with heart disease. Outcomes are best when blood flow is restored within 6 hours. Treating atrial fibrillation with anticoagulation and controlling smoking, blood pressure, cholesterol and diabetes reduce the risk of recurrence.
Frequently asked questions
What are the 6 P's of acute limb ischemia?
They are pain, pallor, pulselessness, poikilothermia (coldness), paresthesia (numbness or tingling) and paralysis. Numbness and weakness are the most worrying, as they show nerves and muscles are being damaged and the limb needs blood flow restored urgently.
How long can a limb survive without blood flow?
Damage to nerves and muscles begins within a few hours. After about 6 hours, there is a high risk of permanent damage, although it varies with how complete the blockage is and whether small bypass vessels exist. Treatment should be as fast as possible.
What is the most common cause of acute limb ischemia?
The most common causes are a clot traveling from the heart, usually in atrial fibrillation, and a clot forming on an artery already narrowed by peripheral artery disease. Bypass graft blockage and trauma are other important causes.
What is the difference between acute limb ischemia and DVT?
Acute limb ischemia is a blocked artery, causing a pale, cold, pulseless and numb limb. Deep vein thrombosis is a clot in a vein, causing a warm, swollen, red or bluish leg with normal pulses. Both need urgent medical care.
Sources
This guide was written from current patient and clinical guidance, including:
- Society for Vascular Surgery: Reporting standards for acute limb ischemia
- American Heart Association/American College of Cardiology: Guideline for the management of lower extremity peripheral artery disease
- European Society for Vascular Surgery: Clinical practice guidelines on the management of acute limb ischaemia
- MedlinePlus: Arterial embolism
- NHS: Peripheral arterial disease