Vascular: Acute Limb Ischaemia

Question 1

What is acute limb ischaemia? Name 3 reasons it can occur.

Answer 1

Sudden decreased in limb perfusion due to occlusion of arterial supply, that threatens the viability of the limb - can lea to ischaemia within hrs.

Causes:

1. THROMBOSIS (60%) - rupture of arterial atheromatous plaque causing thrombus formation on plaque’s cap. Can be acute or acute-on-chronic (background of peripheral artery disease) presentation.
2. EMBOLISATION (30%) - thrombus from proximal source travels distally to occlude artery, e.g. from AF, post-MI mural thrombus, prosthetic/damaged heart valve, aneurysm (aorta, femoral, popliteal), etc.
3. TRAUMA (10%) - inc. compartment syndrome

Question 2

Describe the common presentation of ALI.

Answer 2

Sudden onset of 6 Ps:

• pain
• pallor
• pulselessness
• paraesthesia
• perishingly cold
• paralysis

Question 3

How will appearance of the limb change over 12hrs? When do changes become irreversible?

Answer 3

0-6hrs:

• pallor (marble white)
• reversible

6-12hrs:

• mottled appearance (due to capillary pooling), blanches on digital pressure
• partly reversible

> 12hrs:

• fixed staining: mottled areas coalesce and no longer blanch to pressure
• irreversible

Question 4

Which investigations would you perform on someone with suspected ALI?

Answer 4

1. Bloods
   - FBC: ischaemia is aggravate by anaemia
   - ESR: inflammatory disease, e.g. giant cell arteritis, other CT disorders
   - UandEs: risk of hyperkalaemia
   - glucose: diabetes
   - lactate/venous blood gas: assess level of ischaemia
   - clotting: thrombophilia screen if <50yrs without known risk factors
   - group and save, and cross-match
2. Bedside tests
   - Doppler USS: both limbs (initial investigation)
   - ECG: identify source of embolus, e.g. MI, AF
   - Echocardiogram, aortic, popliteal and femoral artery USS: identify source of embolus
3. Imaging:
   - CT angiography: if limb considered salvageable, can provide more information regarding anatomical location of occlusion and can help decide operative approach

Question 5

When is a limb considered irreversibly damaged (Rutherford classification)?

Answer 5

Category III:

• profound sensory loss
• paralysis
• inaudible arterial and venous doppler

Prognosis: major tissue loss, permanent nerve damage inevitable

Question 6

How would you initially manage a Pt with ALI

Answer 6

ABCDE

1. IV access and fluids
2. Analgesia: morphine
3. High-flow O2
4. Immediate HEPARINISATION (may double limb salvage rate): UFH bolus dose then heparin infusion
5. Check limb for compartment syndrome and if necessary, perform fasciotomy.

Question 7

How would you definitively manage a Pt with Rutherford I or IIa ALI (no/minimal sensory loss, no motor deficit, audible venous doppler)?

Answer 7

Conservative: prolonged course of heparin

Question 8

How would you definitively manage a Pt with Rutherford IIb or III ALI (sensory loss, motor deficit, inaudible arterial doppler)?

Answer 8

If embolic occlusion:

• surgical embolectomy with Fogarty balloon catheter
• local intra-arterial thrombolysis
• bypass surgery

If thrombotic occlusion:

• local intra-arterial thrombolysis
• angioplasty
• bypass surgery

If irreversible limb ischaemia: urgent amputation

Question 9

What would you prescribe a Pt with hyperkalaemia?

Answer 9

Ca2+ gluconate + insulin/dextrose infusion or salbutamol nebulisers

Question 10

Name 3 possible complications of ALI.

Answer 10

1. ISCHAEMIA-REPERFUSION SYNDROME: sudden increase in capillary permeability can result in COMPARTMENT SYNDROME or release of substances from damaged muscle cells such as:
   - K+ ions… HYPERKALAEMIA
   - H+ ions… ACIDOSIS
   - myoglobin… significant AKI (ATN)
2. CHRONIC PAIN SYNDROME: peripheral nerve injury due to ischaemia
3. EXTENSIVE TISSUE NECROSIS

Question 11

What is the mortality rate of ALI?

Answer 11

20%