Acute ischaemic limb

Limb ischaemia is classified based on its onset and severity:

• Complete acute ischaemia leads to tissue necrosis within six hours unless revascularisation occurs.
• Incomplete acute ischaemia may be managed medically.
• Irreversible ischaemia necessitates urgent amputation unless contraindicated due to extent or patient status.

Pathophysiology

Complete acute ischaemia will lead to tissue necrosis within six hours unless the limb is revascularised.

• Acute ischaemia: < 14 days duration
• Acute on chronic: worsened symptoms within 14 days
• Chronic: stable symptoms > 14 days

Severity classifications:

• Incomplete: limb not threatened
• Complete: limb threatened
• Irreversible: limb non-viable

Causes

1. Thrombosis (60%): Acute thrombotic occlusion of stenotic arteries
2. Embolism (30%): Commonly cardiac (AF), atheromatous artery, or aneurysm
3. Dissection: Peripheral vessel or aorta
4. Trauma: Blunt or penetrating
5. Other causes: Masses causing arterial compression, vasculitis, vessel spasm

Complications

• Rhabdomyolysis: Hyperkalemia, myoglobinuria, renal failure
• Infection: Gangrene, septicaemia

Clinical Assessment

History

• Cardiac history (e.g., AF)
• Peripheral vascular disease risk factors
• Previous graft surgery
• Onset timing

Examination

• “5 Ps” of ischaemia:
  • Pulselessness
  • Pain
  • Paraesthesia/paralysis
  • Pallor
  • Perishing cold
• Pulse: Check for AF
• Aneurysm evidence (as an embolic source e.g AAA, popliteal aneurysm)
• Trauma assessment – Any evidence of trauma to a vessel.
• Bilateral lower limb ischaemia:
  • Saddle embolus (may present with femoral pulses, pallor to waist, paraplegia)
  • Aortic dissection

Patients with acute embolic occlusion of the aortic bifurcation, (ie an aortic saddle embolus) may still have femoral pulses but appear marble white or mottled to the waist.

They may also present with paraplegia due to ischaemia of the cauda equina, which can be irreversible. Immediate bilateral embolectomy restores lower limb perfusion, but many patients subsequently die from reperfusion injury, (ie rhabdomyolysis

Clinical Progression

Acute arterial occlusion is associated with intense spasm in the distal arterial tree, and initially the limb will appear “marble” white.

Over the next few hours, the spasm relaxes and the skin fills with deoxygenated blood leading to mottling that is light blue or purple, has a fine reticular pattern, and blanches on pressure. At this stage the limb is still salvageable.

Finally, large patches of fixed staining progress to blistering and liquefaction. Attempts to revascularise such a limb are futile and may lead to life threatening reperfusion injury

1. Marble white limb
2. Mottled (blanching): limb salvageable
3. Mottled (non-blanching): coagulated blood
4. Fixed staining, blistering: irreversible

Investigations

Bloods (as indicated):

• FBE
• U&Es/glucose (check potassium)
• CK/myoglobin
• Coagulation screen

ECG:

• Check for AF

Imaging:

• Doppler ultrasound: Bedside confirmation of no flow
• CT angiogram: Preferred for suspected dissection/saddle embolism
• MRA: If contraindications to CT contrast. Very sensitive and specific investigation for the visualization of the blood vessels, however it is rarely required in the acute setting
• Arteriography: Gold standard but rarely needed acutely

Management

1. Resuscitation:
   • IV access and fluids
2. Analgesia:
   • Narcotic analgesia for severe pain
3. Rhabdomyolysis management:
   • Anticipate hyperkalemia, renal failure
4. Vascular consultation:
   • Urgent referral
5. Heparinisation:
   • Prevent clot propagation
6. Revascularisation:
   • IV thrombolysis
   • Embolectomy
   • Bypass surgery

If ischaemia is complete, the patient must be taken directly to the operating theatre because angiography will introduce delay, thrombolysis is not an option, and lack of collateral flow will prevent visualisation of the distal vasculature.

If ischaemia is incomplete the patient should have preoperative imaging since simple embolectomy or thrombectomy is unlikely to be successful, thrombolysis may be an option, and the surgeon requires a “road map” for distal bypass.

Strategy based on severity:

• Complete ischaemia: Direct to OR, no time for imaging
• Incomplete ischaemia: Pre-op imaging for planning

7. Amputation:
   • Required for necrotic/gangrenous limbs
8. Antibiotics:
   • If infected necrosis present

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References

Publications

• Callum K, Bradbury A. ABC of arterial and venous disease: Acute limb ischaemia. BMJ. 2000 Mar 18;320(7237):764-7. 
  

FOAMed

• Rippey J. Ultrasound Case 057. LITFL