Acute Arterial Occlusion

Sudden loss of arterial flow to a limb (within 14 days), producing acute limb ischaemia. Incidence is about 1 to 2 per 10,000 persons per year. It is a vascular emergency, and delay of more than 6 hours in an immediately threatened limb sharply reduces salvage.

• Causes: in situ thrombosis on atherosclerotic stenosis (about 40 to 60%), embolism (about 20 to 30%), thrombosis of a bypass graft or stent (about 10 to 20%), thrombosed popliteal or femoral aneurysm, aortic or peripheral dissection, trauma, popliteal entrapment, low flow states with hypercoagulability (cancer, antiphospholipid syndrome, heparin induced thrombocytopenia, myeloproliferative neoplasms), and drug related vasospasm (ergotamine, vasopressors).
• Outcome: 30-day amputation about 10 to 30% and mortality about 10 to 20%. Patients with chronic arterial disease have collaterals, so the onset may be less dramatic than in embolism, but the limb is often more difficult to salvage because of the underlying disease.
• Reperfusion injury causes hyperkalaemia, rhabdomyolysis, compartment syndrome and acute kidney injury.

• Pain, pallor, pulselessness, coldness, paraesthesia and weakness; severity depends on collaterals. A history of claudication or rest pain, absent pulses in the contralateral leg, or a previous bypass suggests thrombosis in situ. A history of atrial fibrillation, recent infarction or valve disease suggests embolism.
• Signs: mottled, cool, pale or cyanotic limb, loss of capillary refill, sensory loss, weakness, muscle tenderness or tense compartments, absent arterial Doppler signal.
• Differential diagnosis: arterial embolism, aortic dissection, phlegmasia cerulea dolens, cardiogenic or septic shock with peripheral hypoperfusion, spinal cord infarction or compression, acute nerve injury, severe cellulitis, and acute compartment syndrome.
• Complications: irreversible limb ischaemia and amputation, compartment syndrome, reperfusion injury, acute kidney injury, myocardial infarction, stroke, recurrent thrombosis, and death.

• Examine pulses, Doppler signals, sensation and motor function, and grade the limb:
  • Viable: no sensory loss or weakness, audible arterial Doppler signal.
  • Marginally threatened: minimal sensory loss of the toes or none, no weakness, inaudible arterial signal.
  • Immediately threatened: sensory loss beyond the toes with rest pain, mild or moderate weakness, inaudible arterial signal.
  • Irreversible: profound anaesthesia, paralysis, rigor, absent arterial and venous signals.
• CT angiography or duplex ultrasonography to define the level, inflow, outflow and cause (do not delay surgery for an immediately threatened limb); digital subtraction angiography at the time of intervention.
• Blood tests: creatine kinase, potassium, creatinine, lactate, troponin, glucose, full blood count and platelets (heparin induced thrombocytopenia), coagulation, group and crossmatch; ECG, echocardiography and rhythm monitoring; thrombophilia and antiphospholipid antibodies in patients under 50 or without atherosclerosis.

• Immediate treatment:
  • Unfractionated heparin 80 units/kg IV bolus then 18 units/kg/h, aPTT 1.5 to 2.5 times control.
  • Morphine 2 to 5 mg IV for pain, oxygen, IV fluids, correction of hyperkalaemia and acidosis, and protection of the limb (neutral position, no heat or ice).
  • Aspirin 300 mg once then 75 to 100 mg daily, and atorvastatin 80 mg daily once the patient can swallow.
• Revascularisation by category:
  • Viable: urgent imaging and revascularisation within 6 to 24 hours.
  • Marginally threatened: urgent revascularisation within 6 to 24 hours.
  • Immediately threatened: emergency revascularisation within 6 hours (embolectomy, open surgery or fast endovascular treatment).
  • Irreversible: primary amputation after resuscitation.
• Techniques:
  • Catheter directed thrombolysis: alteplase 0.5 to 1 mg/h (maximum total about 40 mg) with a multi-side-hole catheter, checking fibrinogen every 4 to 6 hours (stop at less than 1 g/L), repeat angiography at 12 to 24 hours. Suitable for viable or marginally threatened limbs, graft thrombosis, and distal thrombus.
  • Percutaneous aspiration or mechanical thrombectomy with or without short duration thrombolysis.
  • Surgical thrombectomy or embolectomy (balloon catheter), thrombo endarterectomy with patch angioplasty, and bypass (femoropopliteal or femorotibial with saphenous vein where possible).
  • Treat the culprit lesion after clearing thrombus (angioplasty with or without stenting, or bypass), because the underlying stenosis causes recurrence.
  • Graft thrombosis: thrombolysis or thrombectomy, then revision of the anastomotic or inflow and outflow stenosis.
  • Popliteal aneurysm: thrombolysis to restore run off, then exclusion with bypass.
  • Contraindications to thrombolysis: active bleeding, stroke or neurosurgery within 3 months, intracranial tumour, major surgery or trauma within 3 weeks, severe uncontrolled hypertension (greater than 180/110 mmHg), and an immediately threatened limb that needs rapid reperfusion.
• Fasciotomy: four compartment fasciotomy of the calf when ischaemia has lasted more than 4 to 6 hours, when compartments are tense, when deficit develops after reperfusion, or when creatine kinase rises steeply.
• Reperfusion injury:
  • 0.9% saline to keep urine output at more than 1 mL/kg/h (200 to 300 mL/h with significant rhabdomyolysis); check potassium, creatine kinase and creatinine every 4 to 6 hours.
  • Hyperkalaemia (potassium greater than 6.5 mmol/L or ECG change): calcium gluconate 10% 10 to 20 mL IV over 10 minutes, soluble insulin 10 units with 25 g glucose IV, salbutamol 10 to 20 mg nebulised; dialysis for refractory hyperkalaemia, acidosis or oliguria.
• Prevention of recurrence:
  • Antiplatelet: aspirin 75 to 100 mg daily or clopidogrel 75 mg daily; after revascularisation consider aspirin 100 mg daily with rivaroxaban 2.5 mg twice daily in patients with low bleeding risk.
  • Atorvastatin 40 to 80 mg daily; blood pressure target less than 140/90 mmHg (less than 130/80 mmHg in diabetes); glycaemic control; smoking cessation with nicotine patches (21 mg/24 h for more than 10 cigarettes a day) or varenicline 0.5 mg daily titrated to 1 mg twice daily.
  • Cardiac source: apixaban 5 mg twice daily (2.5 mg twice daily if two of age 80 or more, weight 60 kg or less, creatinine 133 micromol/L or more) or warfarin to INR 2.0 to 3.0.
  • Hypercoagulable states: warfarin to INR 2.0 to 3.0; antiphospholipid syndrome needs warfarin rather than a direct oral anticoagulant; heparin induced thrombocytopenia needs argatroban 2 micrograms/kg/min IV.
  • Cancer: enoxaparin 1 mg/kg twice daily for at least 6 months.
• Special groups:
  • Pregnancy: enoxaparin 1 mg/kg twice daily or unfractionated heparin; surgery preferred over thrombolysis.
  • Diabetes and renal failure: higher amputation risk, limit contrast and treat infection promptly.
  • Elderly and frail: consider primary amputation when ischaemia is irreversible or the patient is unfit for revascularisation.
  • Intravenous drug users: look for local injection injury and infection.
• Red flags: limb ischaemia lasting more than 6 hours, paralysis, tense compartments, dark urine, potassium greater than 6.5 mmol/L, falling platelets on heparin.
• Follow up: review at 1 week, 1 month and 3 months with ankle pressure and duplex ultrasonography; graft surveillance at 1, 3, 6 and 12 months; vascular risk factor clinic; imaging for any new symptom.