PassFinals
Vascular Surgery

Acute Limb Ischaemia

Sudden arterial occlusion cuts limb perfusion faster than collaterals can compensate, so nerve and then muscle fail within hours and the limb is lost unless flow is restored.

In a nutshell

Acute limb ischaemia (ALI) is sudden arterial occlusion threatening the limb, by convention with symptoms for under two weeks. Refer to vascular surgery immediately, give unfractionated heparin 5000 units IV then 18 units/kg/hour, and aim to restore flow within 6 hours.

Classic presentation

A woman in her seventies in atrial fibrillation develops a sudden painful, white, cold, pulseless leg, numb above the toes, with weak dorsiflexion.

Key points

  • The venous Doppler signal separates a salvageable limb from a dead one: audible in Rutherford IIb, inaudible in III.
  • Heparin itself causes hyperkalaemia by suppressing aldosterone, and heparin-induced thrombocytopenia shows as a 30% fall in platelet count.
  • Protamine sulfate reverses unfractionated heparin. It only partly reverses low molecular weight heparins, which is one reason unfractionated heparin is used here.
  • Check the platelet count before starting heparin, and repeat it regularly if treatment continues beyond 4 days.
  • The European Society for Vascular Surgery (ESVS) advises against continuous systemic heparin during catheter-directed thrombolysis: it increased major bleeding without benefit.
  • Ankle brachial pressure index (ABPI) is the highest ankle systolic pressure divided by the highest brachial pressure; no ankle signal means no ABPI.
  • Examine both legs. Bilateral findings or absent femoral pulses point to an aortic cause rather than a single embolus.
  • Supplemental oxygen is recommended while the patient waits for revascularisation, alongside heparin and analgesia.

First-line investigation

Bedside examination of both limbs with a handheld Doppler: sensation, power, and arterial and venous signals, which together give the Rutherford grade.

Management

Call vascular surgery, heparinise, treat the pain

  • Call the on-call vascular surgeon before any imaging. Acute limb ischaemia is one of four emergency pathways every UK vascular network must have.7,2
  • Unfractionated heparin: 5000 units IV loading dose, or 75 units/kg, then 18 units/kg/hour by continuous infusion, titrated against the activated partial thromboplastin time (APTT).6,1
  • Laboratory monitoring is essential, preferably daily. Check the platelet count before starting and regularly if heparin continues beyond 4 days.6
  • Heparin is contraindicated after major trauma, in recent cerebral haemorrhage, peptic ulcer and previous heparin-induced thrombocytopenia; if that is suspected, use danaparoid instead.6
  • Morphine 5 mg by slow IV injection, titrated to pain; use a reduced dose in frail or elderly patients. Give supplemental oxygen.8,1
  • Keep the limb below heart level by lowering the foot end of the bed. Do not elevate an ischaemic limb.1

Grade the limb: the Rutherford classification

  • The Rutherford classification grades the threat to the limb from sensation, power and Doppler signals. It decides who goes straight to theatre.1,3
  • I, viable: no sensory loss, no weakness, arterial and venous Doppler signals both audible. No immediate threat to the limb.1
  • IIa, marginally threatened: sensory loss confined to the toes, no weakness, arterial signal inaudible, venous signal audible. Salvageable if treated promptly.1
  • IIb, immediately threatened: sensory loss beyond the toes with mild or moderate weakness, arterial signal inaudible, venous signal audible. Salvageable only if revascularised now.1
  • III, irreversible: profound anaesthesia, paralysis, sometimes rigor; arterial and venous signals both inaudible. Major tissue loss and permanent nerve damage are inevitable.1

Restore flow, or amputate

  • Start treatment as soon as possible, ideally within 6 hours. Rutherford IIb or worse goes for urgent revascularisation.3
  • Embolus in a normal artery: embolectomy. Thrombosis on disease, a graft or a stent: treat the lesion too, by thrombolysis, endovascular, open or hybrid surgery.1
  • Catheter-directed thrombolysis is an alternative to surgery in IIa, and may be considered in IIb if started promptly, often with aspiration or thrombectomy.1
  • Rutherford III: primary amputation is recommended. Revascularising dead muscle can kill the patient. The decision is a senior multidisciplinary one.1

Reperfusion injury: potassium, kidneys, compartments

  • Cardiac monitoring after reperfusion. Recheck potassium, bicarbonate, creatine kinase, renal function and urine output; dark urine suggests myoglobinuria.1,4
  • Potassium 6.5 mmol/L or more with ECG changes, or any hyperkalaemic ECG change at a lower level: calcium gluconate 10%, 30 mL IV over 10 minutes.4
  • Potassium 6.0 mmol/L or more: 10 units soluble insulin in 50 mL of glucose 50% IV over 5 to 15 minutes, into a large vein.4
  • If pre-treatment glucose is below 7.0 mmol/L, follow with 10% glucose 50 mL/hour IV for 5 hours. Recheck potassium at 1, 2, 4, 6 and 24 hours.4
  • Compartment syndrome: pain out of proportion, pain on passive stretch, tense compartments. Assess hourly and re-evaluate 30 minutes after releasing circumferential dressings.5
  • Inconclusive signs: measure compartment pressure. A gap below 30 mmHg from the diastolic pressure indicates increased risk; above 40 mmHg absolute, consider decompression. A consultant decides.5
  • Diagnosis means immediate decompression: two-incision, four-compartment fasciotomy in the lower limb. Discuss with plastic surgery within 24 hours and re-explore within 72.5

Find the cause, prevent the next event

  • Hunt the embolic source: ECG and ambulatory rhythm monitoring for atrial fibrillation, echocardiography, and imaging of the aorta.1,2
  • Secondary prevention: clopidogrel 75 mg once daily, or aspirin 75 mg once daily if not tolerated, plus atorvastatin 80 mg once daily.2
  • Patients already on an anticoagulant gain nothing from an added antiplatelet. Smoking, blood pressure, diabetes and weight are managed as in any peripheral arterial disease.2
  • Give written information and a 24-hour telephone number, and safety-net for recurrent pain, pallor, coldness or numbness in either leg.2

Exam traps

  • All six Ps together are rare. A warm limb or one palpable pulse does not exclude ALI if sensation or power is failing.
  • CT angiography (CTA) plans the operation; it does not justify delay in Rutherford IIb. Image only when it will not hold up treatment.
  • Creatine kinase and myoglobin on admission must not be used to choose between revascularisation and primary amputation.
  • Rutherford IIa has an inaudible arterial signal too. Numbness confined to the toes with normal power is what makes it IIa rather than IIb.
  • A normal ECG does not exclude dangerous reperfusion hyperkalaemia; treat potassium of 6.5 mmol/L or more whatever the trace shows.
  • Compartment syndrome is diagnosed on pain out of proportion and pain on passive stretch, not on the pulse. Assess hourly.
  • Successful revascularisation is not the end of the emergency: hyperkalaemia, acute kidney injury and compartment syndrome follow it.
  • Atrial fibrillation points to embolism, but thrombosis on existing arterial disease, a graft or a stent is increasingly common and the two coexist.

Illustrations

Progression of six PsThe six Ps of acute limb ischaemia in order of increasing threat: pain, pallor, pulselessness, poikilothermia, paraesthesia and paralysis, with later sensory and motor signs highlighted as more advanced ischaemia.PassFinals · original
Distal cyanosis from acute limb ischaemiaMarked unilateral plantar cyanosis caused by acute arterial thrombosis, contrasted with the normally perfused opposite foot.James Heilman, MD, Wikimedia Commons · CC-BY-SA-3.0
Fasciotomy after acute limb ischaemiaLower-limb fasciotomy wound with skin graft following revascularisation for limb ischaemia.Sarte at English Wikipedia (Original text: Sarte), Wikimedia Commons · CC-BY-SA-3.0

Key sources

  1. European Society for Vascular Surgery (ESVS) 2020 Clinical Practice Guidelines on the Management of Acute Limb Ischaemia (Bjorck M et al, European Journal of Vascular and Endovascular Surgery 2020;59:173-218. Table 2 (clinical categories according to Rutherford), section 1.3 (primary amputation in class III), section 1.5 (incidence, and the rise in native artery thrombosis), section 2.1 (six Ps; cardiac examination), section 2.3 (creatine kinase and myoglobin), section 3.1 (initial unfractionated heparin and analgesia) and Recommendations 1, 4, 5, 6, 8, 9, 10, 24, 25 and 29)Published 1 Feb 2020
  2. Vascular Society of Great Britain and Ireland: A Best Practice Clinical Care Pathway for Peripheral Arterial Disease (March 2022. Page 3: acute limb ischaemia, of less than two weeks' duration, requires immediate referral to vascular surgery. Page 8: written information with a 24/7 telephone number for advice. Page 11: cardiovascular risk factor modification, including clopidogrel 75 mg once daily, aspirin 75 mg once daily as second line, and high-intensity statin treatment such as atorvastatin 80 mg once daily)Published 1 Mar 2022
  3. Royal College of Anaesthetists: Raising the Standard, quality improvement compendium, chapter 14.9 Acute Limb Ischaemia (Section 14.9, Background and Suggested data to collect: treatment instigated as soon as possible, ideally within 6 hours; Rutherford IIb or higher requires urgent revascularisation; intravenous heparin and adequate analgesia while awaiting revascularisation)
  4. UK Kidney Association, Clinical Practice Guideline: Treatment of Acute Hyperkalaemia in Adults (Final version October 2023. Severity bands (mild 5.5 to 5.9, moderate 6.0 to 6.4, severe 6.5 mmol/L or more); guidelines 16.3.1 to 16.3.3 (insulin-glucose and the 10% glucose cover); guidelines 16.2a and 16.2b (calcium is indicated in the presence of ECG changes) with Appendix 3A (calcium gluconate 10%, 30 mL over 10 minutes))Published 19 Dec 2023
  5. British Orthopaedic Association Standard for Trauma (BOASt): Diagnosis and Management of Compartment Syndrome of the Extremities (Last updated July 2025. Standards 5, 7, 8, 9, 10 and 11 and footnote ***: hourly assessment; re-evaluation within 30 minutes of releasing circumferential dressings; compartment pressure measurement; a difference of less than 30 mmHg between diastolic and compartment pressure; an absolute pressure greater than 40 mmHg; immediate decompression; two-incision four-compartment lower limb fasciotomy; plastic surgery discussion within 24 hours and re-exploration within 72 hours)Published 1 Jul 2025
  6. BNF: Heparin (Indications and dose, treatment of acute peripheral arterial occlusion: loading dose 5000 units, alternatively 75 units/kg, then 18 units/kg/hour by continuous intravenous infusion, laboratory monitoring essential, preferably daily. Also contra-indications, platelet count monitoring beyond 4 days, heparin-induced thrombocytopenia, hyperkalaemia and protamine sulfate reversal)
  7. Vascular Society of Great Britain and Ireland: Provision of Services for People with Vascular Disease 2021 (Recommendations 7.36 (acute limb ischaemia is one of four emergency vascular network pathways), 7.41 (a single point of contact for time-critical referrals) and 7.43 (rapid transfer to the network arterial centre))Published 1 Dec 2021
  8. BNF: Morphine (Indications and dose, acute pain, adult, by slow intravenous injection: initially 5 mg every 4 hours, reduced dose in frail and elderly patients, adjusted according to response)

This page is exam revision material, not medical advice, and must not be used for patient care. Always check drug doses against the BNF and current guidance. Full disclaimer.