Acute limb ischemia

Acute limb ischemia (ALI) is a vascular emergency caused by the sudden loss of arterial perfusion, most commonly due to arterial thrombosis and cardiac emboli. The typical signs and symptoms of ALI are referred to as the “6 Ps”: pain, pallor, pulselessness, paralysis, paresthesia, and poikilothermia of the limb distal to the site of vascular occlusion. Prompt diagnosis based on physical examination and bedside Doppler studies is crucial to prevent loss of the limb. Imaging studies (e.g., CTA) may be obtained but should not delay urgent restoration of perfusion. Systemic anticoagulation with heparin is recommended for most patients. Definitive treatment depends on clinical presentation and limb viability. Options include endovascular or surgical revascularization for viable or threatened limbs and amputation for nonviable limbs.

• A sudden decrease in arterial blood supply to an extremity resulting in symptoms or signs of ischemia for < 2 weeks duration; can threaten limb viability ^[1]
• See “Critical limb ischemia” for symptom duration ≥ 2 weeks. ^[2]

Lower extremity ALI accounts for 80% of cases and is usually caused by arterial thrombosis. Upper extremity ALI is usually caused by an arterial embolism. ^[3][4][5]

Arterial thrombosis

• Atherosclerosis
• Trauma (e.g., blunt or penetrating extremity trauma, posterior knee dislocation, iatrogenic trauma during arterial catheterization)
• Stent or graft thrombosis
• Aneurysmal thrombosis (most commonly in popliteal artery aneurysms) ^[5]
• Vasculitis, thrombophilia, hypercoagulable states (e.g., antiphospholipid syndrome, which is rare)

Arterial embolism

Emboli most commonly occlude small vessels (e.g., digital arteries) or large vessels at bifurcations (e.g., the popliteal bifurcation).

• Cardiac emboli
  • Atrial fibrillation (most common) ^[4]
  • Myocardial infarction
  • Infective endocarditis
  • Cardiac myxoma
• Cholesterol embolism (e.g., blue toe syndrome)
• Paradoxical embolism via a patent foramen ovale

Nonthromboembolic causes

• Aortic dissection or large artery dissection
• Arterial vasoconstriction
  • Vasoactive medications (e.g., norepinephrine)
  • Raynaud phenomenon
• Shock (e.g., septic shock) ^[6]
• Vascular compression (e.g., crush injury, compartment syndrome, thoracic outlet syndrome, popliteal entrapment syndrome)
• AV access steal syndrome
• Phlegmasia cerulea dolens

The 6 Ps of ALI describe the signs and symptoms of complete arterial occlusion, although they are rarely all present simultaneously. ^[6]

• Pain
• Pallor
• Pulselessness
• Paralysis
• Paresthesia
• Poikilothermia

Severe pain in ALI indicates that limb viability is at risk. Pain may be absent after prolonged complete occlusion. ^[5][7]

Arterial embolus pain is typically sudden and severe, whereas arterial thrombus pain usually develops slowly and can be preceded by claudication. ^[6]

Management of ALI is time-sensitive and based on the Rutherford classification, which can be rapidly determined from the physical examination and handheld Doppler findings.

• Perform a neurovascular examination of the affected limb.
• Assess distal arterial pulses and venous flow with a handheld Doppler. ^[7]
• Consult a vascular surgeon immediately if ALI is suspected.
• Identify and treat nonthromboembolic causes of ALI if present, e.g., acute compartment syndrome or aortic dissection.
• Obtain blood for laboratory studies and preoperative diagnostics.
• Begin unfractionated heparin for thromboembolic ALI as soon as possible unless contraindicated (see “Treatment of ALI” for details).
• Initiate urgent supportive care, e.g., manage acute pain, address acid-base disturbances, and replete electrolytes.
• Consider imaging studies (e.g., CTA) only if they do not delay treatment.
• Admit the patient and expedite revascularization based on the Rutherford classification of ALI (see “Definitive management” in “Treatment of ALI” for details).

ALI is a vascular emergency: Consult a specialist early and do not delay treatment for diagnostic imaging. ^[2][6]

Prioritize revascularization over diagnostic evaluation if limb viability is clearly at risk.

Bedside testing

• Handheld Doppler device: : best initial test for detecting blood flow ^[8]
  • Select a frequency of 5–10 MHz.
  • Apply a large amount of acoustic or water-soluble gel to the skin over the artery.
  • Align the probe with the axis of the artery.
  • Angle the probe at 45° to the skin.
  • Fan and/or sweep the probe to locate the strongest signal.
  • Compare the signal to that of the contralateral limb.
• Ankle-brachial index
  • Indication: ALI suspected despite audible Doppler signal
  • Interpretation
    • < 0.9: peripheral arterial disease
    • < 0.4: severe peripheral artery disease ^[9]

A diminished or absent handheld Doppler signal in the affected limb suggests reduced blood flow.

Imaging ^[6]

Optimal timing and type of vascular imaging depend on ALI severity, resource availability, treatment urgency, and specialist preference. Check local protocols for individual guidance.

• CTA: (most common initial study): identifies the site of occlusion, vascular anatomy, and surgical targets
• Digital subtraction angiogram: facilitates immediate therapeutic intervention, e.g., catheter-directed thrombolysis
• Duplex ultrasound: identifies site of occlusion and graft patency
• MR angiography: similar indication as CTA Long examination time limits usefulness.

Do not delay surgical consultation and treatment to obtain imaging if limb viability is threatened.

Laboratory studies ^[4]

• CBC and coagulation studies: for management of systemic anticoagulation
• CMP: to identify renal insufficiency and electrolyte abnormalities, e.g., secondary to ischemic rhabdomyolysis
• Blood gas analysis: to identify metabolic acidosis
• Serum lactate: may be elevated ^[6]
• Blood compatibility testing: for potential perioperative blood transfusion
• CPK and/or serum myoglobin: to identify significant muscle injury and/or risk for acute kidney injury
• Preoperative testing for high-risk surgery: to identify coexisting diseases that affect perioperative management, e.g. LFTs for liver failure

Do not use biomarkers of perfusion (e.g., CK, lactate, myoglobin) to guide decisions about revascularization. ^[6]

Supportive testing

• EKG: detects arrhythmias, e.g., undiagnosed atrial fibrillation
• Echocardiography: identifies a cardiac source for emboli, e.g., infective endocarditis

See “Initial management of ALI” for a prioritized sequence of simultaneous evaluation and urgent treatment measures for acute presentations.

Intravenous systemic anticoagulation ^[2][6]

• Begin as soon as possible in consultation with a vascular surgeon.
• Heparin weight-based protocol is recommended.
• Evaluate the risk-benefit ratio in patients with contraindications to anticoagulation.

Systemic thrombolytic therapy is not generally recommended for ALI. ^[6]

Initial supportive care

• Parenteral analgesics for acute pain management
• Electrolyte replacement
• Management of acute kidney injury (if required)
• Acute management of underlying conditions as needed, e.g.:
  • Management of trauma, e.g., penetrating extremity trauma, blunt extremity trauma
  • Management of rapid Afib
  • Management of acute coronary syndrome
  • Treatment of infective endocarditis
  • See “Etiology” for other conditions.

Definitive management ^[2]

• Viable, nonthreatened limb (Rutherford stage I, Rutherford stage IIa)
  • Urgent angiography (or other imaging) to localize the occlusion
  • Revascularization procedure within 6–24 hours
• Threatened limb: (Rutherford stage IIb): urgent revascularization procedure within 6 hours
• Nonviable limb: (Rutherford stage III): amputation

Endovascular and surgical revascularization have similar short- and long-term outcomes; the technique is chosen based on local resources, specialist preference, and patient-related factors. ^[10]

Endovascular revascularization ^[2][6]

• Indications: Rutherford stage I, Rutherford stage IIa, and Rutherford stage IIb ^[4][11]
• Techniques
  • Catheter-directed thrombolysis
  • Percutaneous mechanical thrombectomy
  • Percutaneous thromboaspiration

Surgical revascularization ^[2][6]

• Indications
  • Suspected graft infection
  • Absolute contraindication to thrombolysis
  • Consider for Rutherford stage IIb and embolic ALI. ^[4][11]
• Techniques
  • Balloon thrombectomy
  • Bypass surgery
  • Graft revision
• Adjunct procedures
  • Endarterectomy
  • Fasciotomy (for compartment syndrome) ^[2]
  • Endovascular stenting and/or surgical repair of dissecting aneurysm

• Perform a neurovascular examination of the affected limb.
• Assess distal circulation with a handheld Doppler.
• Consult a vascular surgeon as soon as ALI is suspected.
• Assess severity using the Rutherford classification of ALI.
• Identify and treat acute compartment syndrome and/or aortic dissection if present.
• Obtain blood for laboratory studies, e.g., CBC, BMP, and coagulation studies.
• Obtain preoperative diagnostics.
• Initiate unfractionated heparin unless there are contraindications to anticoagulation (in consultation with the vascular surgeon).
• Consider imaging studies (e.g., CTA) in consultation with the vascular surgeon.
• Correct any acid-base disturbances.
• Replete electrolytes.
• Manage acute pain with parenteral analgesics.
• Begin acute management of urgent underlying conditions, e.g., trauma, Afib, or acute coronary syndrome.
• Admit the patient and expedite definitive management.

Leriche syndrome (aortoiliac occlusive disease) ^[12]

Occlusion at the level of the aortic bifurcation or bilateral occlusion of the iliac arteries that usually presents with:

• Pain in both legs and the buttocks
• Bilaterally absent femoral, popliteal, and ankle pulses
• Erectile dysfunction
• Shock

Hair tourniquet syndrome ^[13]

• Definition: : a condition in which a hair or thread becomes wound around an appendage tightly, putting the appendage at risk of ischemic damage
• Epidemiology: usually affects infants
• Pathophysiology: hairs or threads inside socks or under bed sheets can become spontaneously tied round a toe and tighten with the child's movement → venous and lymphatic return is impaired → further obstruction may cause arterial occlusion and ischemic injury
• Clinical features: painful, swollen, reddened appendage with a deep groove proximal to it, in which the constricting fiber may be visible
• Treatment: prompt removal of the constricting hair or fiber, either by means of a hair-dissolving product or a scalpel

Drug-induced vasoconstriction ^[14]

• Definition: peripheral ischemia due to prolonged treatment with vasopressors (e.g., norepinephrine)
• Pathophysiology: prolonged alpha receptor agonism → vasospasm of distal arterioles and their branches → ischemia and consequent necrosis of most distal extremities
• Clinical features: symmetrical cyanosis, coldness, and necrosis of fingers and/or toes

• Permanent nerve damage: sensory loss, muscle weakness, paralysis
• Loss of limb due to irreversible ischemia
• Reperfusion injury (postischemic syndrome)

We list the most important complications. The selection is not exhaustive.