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Limb Ischaemia/Arterial Insufficiency

1. ACUTE LIMB ISCHAEMIA

  • Sudden interruption or cessation of blood flow in a major artery supplying the limb
  • The blood supply becomes inadequate to meet basal metabolic requirements

Etiology

  • Embolisation – emboli from a thrombus travels distally to occlude the artery. Can be due to
    • Atrial fibrillation
    • Mural thrombus after recent myocardial infarction
    • Abdominal aortic aneurysm (AAA)
    • Prosthetic heart valves
  • Thrombus in situ – from thrombus formation on atherosclerotic plaque, frequently occurs in the setting of peripheral artery disease (PAD)
  • Trauma, compartment syndrome

Classification

Fontaine Classification – solely based on symptoms

  • Stage 1 – no clinical symptoms
  • Stage 2 – intermittent claudication
    • 2a – well compensated; able to walk >200 meters
    • 2b – poorly compensated; only able to walk <200 meters
  • Stage 3 – pain at rest
  • Stage 4 – gangrene, ischaemic ulcer

Rutherford Classification – based on symptoms and diagnostic results

  • Stage I (viable) – no pain, no neurological deficit, Doppler shows audible signal, venous flow present
  • Stage IIa (marginally threatened) – no pain, numbness, no audible Doppler signal, venous flow present
  • Stage IIb (immediately threatened) – persistent pain, sensory and motor loss, no Doppler signal, venous flow present
  • Stage III (irreversible) – paralysis and anaesthesia, no venous flow

Clinical features

  • Six Ps
    • Pain
    • Pallor
    • Pulselessness
    • Paraesthesia
    • Perishingly cold
    • Paralysis
  • Irreversible neuromuscular damage is more likely >6 hours after symptom onset
  • Differentiating between thrombus vs embolus
    • Embolus – contralateral pulse is palpable; sudden onset of symptoms
    • Thrombus – contralateral pulse is not palpable; less sudden onset

Investigations

  • Bloods – FBC, PT/APTT, ABGs, LDH
  • Doppler US
  • Ankle-brachial pressure index (ABPI) –
    • ABPI = Pleg / Parm
      • 1 is normal (>1.2 could mean abnormal vessel hardening i.e. calcification)
      • <0.9 means ischaemia is present
      • <0.3 means severe ischaemia with gangrene
    • Pleg – systolic BP in leg (dorsalis pedis artery/posterior tibial artery)
    • Parm – systolic BP in arm (brachial artery)
  • CT angiography  

Treatment

  • Considered a surgical emergency – irreversible tissue damage occurs within 6 hours

Initial management

  • Correct fluid and electrolyte imbalance
  • High-flow oxygen and heparin bolus IVV
  • Analgesia – opioids and COX2 inhibitors

Embolic etiology

  • Balloon catheter embolectomy
  • Endovascular procedures
  • Arterial bypass/reconstruction
  • Amputation

Thrombotic etiology

  • Thrombolytics – streptokinase, urokinase, rTPA
  • Arterial bypass/reconstruction
  • Endovascular – angioplasty, stents
  • Catheter thrombectomy
  • Amputation

2. CHRONIC LIMB ISCHAEMIA

  • Peripheral arterial disease that results in symptomatic reduced blood supply to the limbs

Etiology

  • Atherosclerosis – most common in the lower limbs
  • Risk factors – smoking, diabetes mellitus, hypertension, hyperlipidemia, family history, obesity

Clinical features

  • Progression of symptoms – asymptomatic → intermittent claudication → ischaemic rest pain → ulceration and gangrene
  • Rest pain is exacerbated when limb is elevated and relieved by sitting or standing

Critical limb ischaemia

  • Advanced form of chronic limb ischaemia
  • Defined as
    • Ischaemic rest pain for >2 weeks, requiring opiate analgesia
    • Presence of ischaemic lesions or gangrene
    • ABPI <0.5

Investigations

  • Buerger’s test – patient lies supine and raises legs until they go pale; then lowers them until the colour returns
    • Buerger’s angle – the angle at which the limb goes pale – angle <20o indicates severe ischaemia
  • ABPI – see above
  • Dopple US
  • CT angiography

Treatment

  • Management of cardiovascular risk – lifestyle modifications, statins, anti-platelets (clopidogrel)
  • Surgery
    • Angioplasty
    • Bypass grafting
    • Amputations
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