46. Limb ischaemia and acute arterial insufficiency

1. Definition

• Peripheral arterial disease (PAD) → narrowing or occlusion of the arteries of the limbs, mostly by atherosclerosis
• Chronic limb ischaemia → slow loss of perfusion, from claudication to rest pain and tissue loss
• Chronic limb-threatening ischaemia (CLTI) → rest pain, ulcer or gangrene for > 2 weeks with proven arterial insufficiency (formerly "critical limb ischaemia")
• Acute limb ischaemia (ALI) → sudden fall in limb perfusion that threatens viability; symptoms < 2 weeks

2. Epidemiology

• PAD → about 20% of people over 60 years; many have no symptoms
• Intermittent claudication → 4% of people over 55; mostly men
• Claudication course → one-third improve, one-third stay the same, one-third get worse; only about 2% need amputation
• ALI → about 1 in 6,000 a year; death about 20%, limb loss up to 40%
• 40% of PAD patients have coronary or cerebral disease → most die of myocardial infarction or stroke

3. Aetiology and risk factors

Chronic

• Atherosclerosis → most cases
• Risk factors:
  • Smoking → the strongest
  • Diabetes mellitus
  • Hypertension, hyperlipidaemia
  • Age, male sex, family history
  • Chronic kidney disease
• Rare → Buerger's disease, vasculitis (Takayasu's), popliteal entrapment, cystic adventitial disease

Acute

• Thrombosis in situ (about 60%) → on an atherosclerotic plaque; dehydration, low blood pressure, cancer, polycythaemia, thrombophilia; bypass graft or stent thrombosis
• Embolism (about 30%):
  • Heart in 80% → atrial fibrillation (left atrial appendage), mural thrombus after MI, valve disease, endocarditis
  • Aneurysms (aorta, popliteal) → 10%
  • Paradoxical embolus → patent foramen ovale
• Others → trauma, iatrogenic (catheters), aortic dissection, thrombosed popliteal aneurysm, intra-arterial drug injection

4. Pathogenesis

Chronic

1. Plaque narrows the artery
2. Flow at rest is enough; exercise needs more → muscle ischaemia → claudication
3. Collaterals develop over time
4. More narrowing → flow is too low at rest → rest pain (worse at night, relieved by hanging the leg down)
5. Tissue loss → ulcers, gangrene

Acute

• No time for collaterals → severe ischaemia
• Tolerance → nerves and muscle are most sensitive; irreversible muscle damage after about 6 h
• Emboli lodge at bifurcations → common femoral (most common), popliteal, brachial, aortic bifurcation ("saddle embolus")
• Reperfusion injury → potassium, myoglobin, acid and free radicals enter the circulation → hyperkalaemia, acidosis, renal failure, arrhythmia; muscle swelling → compartment syndrome

5. Classification

Chronic: Fontaine

• I → no symptoms
• IIa → mild claudication (> 200 m); IIb → moderate to severe claudication (< 200 m)
• III → ischaemic rest pain
• IV → ulcer or gangrene

Chronic: Rutherford categories

• 0 none; 1–3 mild, moderate, severe claudication; 4 rest pain; 5 minor tissue loss; 6 major tissue loss
• WIfI (wound, ischaemia, foot infection) → staging of limb threat in CLTI

Acute: Rutherford

• I Viable → no sensory loss, no weakness; arterial Doppler audible
• IIa Marginally threatened → minimal sensory loss (toes); salvageable if treated promptly
• IIb Immediately threatened → sensory loss beyond toes, rest pain, mild to moderate weakness; needs revascularisation now
• III Irreversible → anaesthetic, paralysed, rigid muscles, fixed mottling; no arterial or venous Doppler signal

6. Clinical picture

Symptoms

• Intermittent claudication → cramping muscle pain on walking, relieved by rest within minutes; same distance each time
  • Calf → femoropopliteal disease
  • Buttock and thigh → aortoiliac disease; with impotence → Leriche syndrome
• Rest pain → burning pain in the forefoot at night; patient sleeps in a chair or with the leg over the bed
• Ulcers, gangrene of toes
• ALI → the six Ps:
  1. Pain
  2. Pallor
  3. Pulselessness
  4. Paraesthesia
  5. Paralysis
  6. Perishingly cold

Signs

• Absent or weak pulses; bruits over iliac and femoral arteries
• Cold, pale, hairless, shiny skin; thick nails
• Buerger's test → leg pales when raised (angle < 20° severe); rubor on hanging down
• Slow capillary refill
• Ischaemic ulcers → toes, heel, pressure points; punched out, painful
• ALI → compare with the other leg:
  • Embolus → sudden onset, a source (AF), normal pulses in the other leg
  • Thrombosis → past claudication, slower onset, weak pulses in both legs
• Late ALI → fixed mottling, muscle tenderness, woody rigid muscles

7. Diagnosis

Bedside

• Ankle-brachial pressure index (ABPI) → ankle systolic ÷ brachial systolic:
  • 0.9–1.3 → normal
  • 0.5–0.9 → claudication
  • < 0.5 → CLTI; ankle pressure < 50 mmHg
  • > 1.3 → calcified, incompressible vessels (diabetes, kidney disease) → use toe pressures
• Fall in ABPI after exercise → confirms claudication
• Handheld Doppler signals (ALI grading)

Imaging

• Duplex ultrasound → first imaging; site and length of stenosis
• CT angiography → plan for revascularisation; acute cases when the limb allows the delay
• MR angiography → kidney impairment
• Digital subtraction angiography → at the time of endovascular treatment
• ALI source → ECG (AF), echocardiography, CT for aneurysm

Laboratory

• FBC, U&E, glucose and HbA1c, lipids, clotting
• ALI → creatine kinase, potassium, lactate, group and save, troponin

8. Differential diagnosis

• Claudication versus spinal stenosis (neurogenic claudication: relieved by bending forward, not standing still)
• Hip or knee osteoarthritis
• Sciatica, nerve root pain
• Venous claudication (after iliofemoral DVT)
• Popliteal artery entrapment (young athletes)
• ALI versus DVT with phlegmasia, spinal cord compression, low-output shock

9. Treatment

Conservative: chronic

• Best medical therapy for all:
  • Stop smoking
  • Antiplatelet → clopidogrel or aspirin; low-dose rivaroxaban + aspirin in selected patients
  • High-intensity statin
  • Control blood pressure and diabetes
• Supervised exercise → 2 h a week for 3 months; first-line for claudication
• Naftidrofuryl if exercise does not help
• Foot care

Surgical: chronic

• Claudication → intervene only for severe lifestyle limits after exercise therapy
• CLTI → revascularise whenever possible
• Endovascular → angioplasty ± stent:
  • Aortoiliac → > 90% success
  • Short femoropopliteal lesions
  • First choice in high-risk patients
• Open surgery:
  • Aortobifemoral bypass → aortoiliac disease; 5-year patency > 90%
  • Femorofemoral crossover or axillobifemoral → unilateral disease or unfit
  • Common femoral endarterectomy with patch
  • Femoropopliteal and femorodistal bypass → long occlusions; autologous great saphenous vein is the best conduit (BEST-CLI)
• Amputation → unreconstructable CLTI, non-viable limb, uncontrolled sepsis

Surgical: acute limb ischaemia

1. Oxygen, IV access, fluids, analgesia (opiate)
2. Bloods, ECG; call senior help
3. Heparin 5,000 IU IV bolus, then infusion (unless contraindicated)
4. Grade by Rutherford → decides the timing
5. I and IIa → imaging (CT angiography), then:
   • Catheter-directed thrombolysis (tPA) → thrombosis, graft occlusion; takes hours; bleeding and stroke risk
   • Angioplasty or bypass for the underlying lesion
6. IIb → surgery at once:
   • Embolectomy with a Fogarty balloon catheter through a groin (common femoral) or brachial arteriotomy
   • Success → fresh clot out, good back-bleeding and inflow; on-table angiogram
   • Thrombosis on plaque → bypass, endarterectomy or stent
   • Fasciotomy of all four calf compartments if ischaemia > 4–6 h or swelling
7. III → primary amputation or palliation; revascularisation can kill through reperfusion
8. After an embolus → lifelong anticoagulation and treat the source

10. Complications

• Reperfusion syndrome → hyperkalaemia, acidosis, myoglobinuria, acute kidney injury, arrhythmia
• Compartment syndrome → anterior compartment most often
• Re-occlusion, graft thrombosis
• Bleeding → thrombolysis, anticoagulation; stroke
• Limb loss, death (MI)
• Chronic → ulcers, gangrene, infection, amputation
• Graft → infection, false aneurysm, intimal hyperplasia