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Acute limb ischaemia

Definition: Acute limb ischaemia (ALI) is a rapid decrease in limb perfusion, often due to an arterial occlusion, which threatens limb viability. It requires urgent diagnosis and treatment to prevent limb loss.

Etiology:

  • Thrombosis: In situ thrombosis often occurs in a limb with pre-existing peripheral arterial disease.
  • Embolism: A common cause, usually from cardiac sources like atrial fibrillation or post-myocardial infarction.
  • Trauma: Direct trauma to the vessels or compartment syndrome can also lead to ischaemia.

Clinical Presentation (The ‘6 Ps’):

  • Pain: Sudden onset, severe and persistent limb pain.
  • Pallor: The affected limb appears pale.
  • Pulselessness: Absent or reduced pulses distal to the occlusion.
  • Paraesthesia: Tingling or ‘pins and needles’ sensation due to nerve ischemia.
  • Paralysis: Muscle weakness or paralysis indicates advanced ischaemia.
  • Poikilothermia: The limb feels cooler on palpation due to the lack of blood flow.

Diagnosis:

  • Clinical Assessment: Immediate assessment of the ‘6 Ps’ is crucial.
  • Doppler Ultrasound: To assess blood flow and differentiate between arterial and venous issues.
  • CT Angiography/MRA: Provides detailed images of the vasculature and location of occlusion.
  • Blood tests: May include full blood count, coagulation profile, and lactate levels (indicates tissue ischemia).

Management:

  • Resuscitation: Address Airway, Breathing, Circulation. Start IV fluids, pain management, and anticoagulation (usually heparin).
  • Revascularisation: Urgent surgical or endovascular intervention is typically required.
    • Catheter-directed thrombolysis: Administering thrombolytics directly to the clot.
    • Surgical Embolectomy: Removal of the embolus if thrombolysis is contraindicated or unsuccessful.
    • Bypass Surgery: Creating a new route for blood flow around the blocked artery.
  • Amputation: As a last resort if revascularisation fails or the limb is non-viable.

Complications:

  • Compartment syndrome: Increased pressure within muscle compartments leading to further ischemia.
  • Rhabdomyolysis: Muscle breakdown releasing myoglobin, which can cause kidney damage.
  • Reperfusion injury: Can occur after blood flow is restored, leading to tissue damage.

Prognosis:

  • The prognosis depends on the speed of diagnosis and revascularisation. Early treatment can lead to good outcomes.
  • Delayed treatment can result in permanent disability or amputation.

Prevention:

  • Managing risk factors such as atrial fibrillation, monitoring for heart diseases, and managing peripheral arterial disease can help prevent ALI.

Conclusion: ALI is a vascular emergency that requires a high index of suspicion and prompt intervention to salvage the affected limb. It encompasses a broad differential diagnosis and necessitates a structured approach to management, with the aim of rapid revascularisation to restore perfusion and prevent irreversible damage.

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