Acute Limb Ischemia
Surgical emergency. “Time is tissue.” The 6 P’s: Pain, Pallor, Pulselessness, Poikilothermia, Paresthesia, Paralysis. Start heparin IMMEDIATELY, call vascular surgery.
Overview
6 P’s
- Pain, sudden, severe
- Pallor
- Pulselessness
- Poikilothermia (cold)
- Paresthesia
- Paralysis (late = bad)
Rutherford Classification
| Category | Status | Sensory | Motor |
|---|---|---|---|
| I | Viable | None | None |
| IIa | Marginally threatened | Minimal | None |
| IIb | Immediately threatened | Rest pain | Mild-moderate |
| III | Irreversible → amputation | Anesthetic | Paralysis |
SURGICAL EMERGENCY. Start heparin IMMEDIATELY. Do NOT wait for imaging to anticoagulate.
Embolism vs Thrombosis
| Feature | Embolism | Thrombosis (in-situ) |
|---|---|---|
| Onset | Sudden, dramatic (“bolt from the blue”) | More insidious (hours–days) |
| History | AF, recent MI, valvular disease, endocarditis | Known PAD, prior bypass/stent, claudication |
| Contralateral leg | Normal pulses | Often diminished pulses (bilateral PAD) |
| Location | Bifurcations (femoral, popliteal, aortic saddle) | At site of prior stenosis/graft |
| Collaterals | Absent (no time to develop) | Present (chronic disease) |
| Treatment | Embolectomy (Fogarty catheter) | Thrombolysis, angioplasty, or bypass |
Clinical Pearl: Embolic ALI → look for AF on ECG (most common source). Always check both legs, normal contralateral pulses suggest embolism; diminished bilateral pulses suggest thrombosis on PAD.
Time-to-Intervention Urgency
| Rutherford Class | Time Window | Intervention |
|---|---|---|
| I, Viable | Not immediately threatened | Heparin + elective angiography within hours |
| IIa, Marginally threatened | Hours (urgent) | Catheter-directed thrombolysis (tPA 0.5–1 mg/hr × 12–24h) |
| IIb, Immediately threatened | Minutes to hours (emergent) | Surgical embolectomy or bypass, NO time for thrombolysis |
| III, Irreversible | Too late for salvage | Amputation ± palliative care. Revascularization risks fatal reperfusion injury |
Key Distinction: Rutherford IIa = thrombolysis OK (sensory loss only). Rutherford IIb = motor deficit present = go directly to OR for embolectomy/bypass. Do NOT waste time with catheter-directed thrombolysis.
Workup
Workup
- ABI, CTA (if stable). Labs: CBC, BMP (K+), lactate, CK, coags
- ECG for AF (common embolic source)
- Do NOT delay heparin for imaging
Management
Management
| Step | Action |
|---|---|
| 1 | Heparin 80u/kg bolus → 18u/kg/hr IMMEDIATELY |
| 2 | Vascular surgery consult STAT |
| 3 | Catheter-directed thrombolysis, embolectomy, or bypass |
| 4 | Post-reperfusion: watch compartment syndrome → fasciotomy |
Reperfusion Injury: After revascularization, watch for the “deadly triad”, hyperkalemia (cardiac arrest risk), rhabdomyolysis (CK >10,000, AKI), and metabolic acidosis. Aggressive IVF, monitor K+ q2h, consider empiric calcium gluconate and sodium bicarbonate.
Medications
Medications
| Drug | Dose | Notes |
|---|---|---|
| Heparin UFH | 80u/kg bolus, 18u/kg/hr | aPTT 60–80s. Prevents clot propagation |
| tPA (catheter-directed) | 0.5–1mg/hr intra-arterial | Rutherford I–IIa. Takes 12–24h |
On Rounds
Most common cause of ALI?
Embolism (AF most common source) and in-situ thrombosis (on atherosclerotic disease). Embolic = sudden, no prior claudication. Thrombotic = PAD history, more insidious.
What is the first medication to give in suspected ALI, and why?
Unfractionated heparin (UFH) 80 u/kg bolus → 18 u/kg/hr infusion. Prevents clot propagation distally and proximally while definitive intervention is arranged. Start BEFORE imaging, “time is tissue.”
How do you distinguish Rutherford IIa from IIb, and why does it matter?
IIa = sensory loss only, no motor deficit → catheter-directed thrombolysis is an option. IIb = motor deficit present (cannot wiggle toes) → must go directly to surgical embolectomy or bypass. Thrombolysis takes 12–24h and is too slow for IIb.
Name 3 clinical features that distinguish embolic from thrombotic ALI.
Embolic: (1) sudden onset with no prior claudication, (2) normal contralateral pulses, (3) known AF or recent MI. Thrombotic: (1) history of PAD/claudication, (2) diminished bilateral pulses, (3) prior bypass graft or stent.
What is the “deadly triad” of reperfusion injury after revascularization?
Hyperkalemia (can cause fatal arrhythmia), rhabdomyolysis (CK >10,000, myoglobinuric AKI), and metabolic acidosis (lactic acid washout from ischemic tissue). Treat with aggressive IVF, calcium gluconate, bicarbonate, and monitor K+ q2h.
When should you suspect compartment syndrome post-revascularization, and what is the treatment?
Suspect when there is tense swelling, pain out of proportion, and pain with passive stretch of compartment muscles. Compartment pressure >30 mmHg (or within 30 mmHg of diastolic BP) is diagnostic. Treatment is four-compartment fasciotomy of the affected leg.
Why is Rutherford III considered irreversible, and what is the danger of attempting revascularization?
Rutherford III = anesthetic limb with paralysis, rigor, and mottling. Muscle is already necrotic. Revascularization at this stage causes massive reperfusion injury, washout of potassium, myoglobin, and lactate can cause cardiac arrest, DIC, and multi-organ failure. Primary amputation is indicated.
A patient has ALI and you find AF on ECG. After acute management, what long-term anticoagulation is needed?
AF-related arterial embolism requires lifelong anticoagulation. After acute heparin therapy and intervention, transition to a DOAC (apixaban, rivaroxaban) or warfarin (INR 2–3). Also consider rate vs rhythm control for the AF and evaluate for LA thrombus with TEE. RE-LY, 2009; ARISTOTLE, 2011
Clinical Examples
📋 Case 1, Embolic ALI from Atrial Fibrillation
Patient: 72F with known AF (not on anticoagulation, “refused warfarin”), presents with sudden onset left leg pain, pallor, and coldness 3 hours ago. No prior claudication.
Exam: Left leg pale, cool, no popliteal or pedal pulses. Sensation diminished over foot. Can still weakly dorsiflex toes. Right leg warm with normal pulses.
Classification: Rutherford IIa (sensory loss, minimal motor). Normal contralateral pulses + AF + sudden onset = embolic etiology.
Management:
- Heparin 80 u/kg bolus → 18 u/kg/hr started immediately in ED
- CTA confirms occlusion at left common femoral artery bifurcation (classic embolic location)
- Vascular surgery performs Fogarty balloon embolectomy under local anesthesia
- Completion angiogram shows restored flow. Pedal pulses return
- Post-op: monitor for compartment syndrome, K+ q2h, CK trending
- Long-term: Started apixaban 5 mg BID for AF (CHA₂DS₂-VASc = 4). Cardiology follow-up
Key lesson: Embolic ALI from AF is preventable with anticoagulation. Fogarty embolectomy is first-line for embolic ALI.
📋 Case 2, Thrombotic ALI in Peripheral Arterial Disease
Patient: 65M with history of PAD (prior right SFA stent 2 years ago), DM2, smoking. Presents with 18 hours of worsening right foot pain and numbness. Reports baseline 1-block claudication.
Exam: Right foot mottled, cool. No pedal pulses. Cannot dorsiflex toes (motor deficit). Left leg has diminished but palpable dorsalis pedis pulse.
Classification: Rutherford IIb (motor deficit). Bilateral diminished pulses + PAD history + gradual onset = thrombotic etiology (likely in-stent thrombosis).
Management:
- Heparin bolus + infusion started immediately
- Rutherford IIb with motor deficit → NO thrombolysis (too slow). Taken to OR emergently
- Intra-op: thrombosed SFA stent with propagation into popliteal. Surgical thrombectomy + fem-pop bypass with reversed saphenous vein graft
- Post-op: pedal pulses restored. CK peaked at 8,200. K+ 5.8 → treated with calcium gluconate + insulin/dextrose
- Monitored for compartment syndrome, pressures remained <25 mmHg, no fasciotomy needed
- Long-term: Dual antiplatelet (ASA + clopidogrel), statin, smoking cessation, DM optimization
Key lesson: Rutherford IIb (motor deficit) = go to OR, not cath lab. Thrombotic ALI in PAD often needs bypass rather than simple embolectomy.
📋 Case 3, Reperfusion Injury After Revascularization
Patient: 58M s/p emergent embolectomy for Rutherford IIb ALI (6-hour ischemia time). Pulses restored in OR. Four hours post-op, develops tense calf swelling, escalating pain, and oliguria.
Labs: K+ 6.4, CK 45,000, Cr 2.8 (baseline 1.0), pH 7.22, lactate 8.5, urine dark brown (myoglobinuria).
Diagnosis: Reperfusion injury with rhabdomyolysis, hyperkalemia, and metabolic acidosis. Tense calf = compartment syndrome.
Management:
- Hyperkalemia: Calcium gluconate 1g IV (cardiac membrane stabilization), insulin 10 units + D50, kayexalate. Continuous telemetry for peaked T-waves
- Rhabdomyolysis: Aggressive IVF (target UOP 200–300 mL/hr), sodium bicarbonate drip to alkalinize urine (target urine pH >6.5)
- Compartment syndrome: Compartment pressures 42 mmHg → emergent four-compartment fasciotomy
- ICU admission: Continuous renal replacement therapy (CRRT) initiated for refractory hyperkalemia and acidosis. CK trended downward over 5 days
- Fasciotomy wounds closed with split-thickness skin graft at day 7
Key lesson: Reperfusion injury is the “second hit” after revascularization. Longer ischemia time = higher risk. Anticipate hyperK, rhabdo, and compartment syndrome. ICU monitoring is mandatory.
Monitoring
| Parameter | Frequency |
|---|---|
| Pulse checks | q1h |
| Compartment pressures | Post-reperfusion. >30mmHg → fasciotomy |
| K+, CK, Cr | q4–6h post-reperfusion |
| aPTT | q6h |
Summary
Summary
Recognize It
Surgical emergency: time is tissue. The 6 P's: pain, pallor, pulselessness, poikilothermia, paresthesia, paralysis. Paresthesia and paralysis are the late two and mark a limb that is already threatened, so do not wait for them to appear.
First Move
Start heparin immediately and call vascular surgery. Do not wait for imaging to anticoagulate: heparin limits clot propagation while the plan is arranged, and the delay to imaging is where limbs are lost.
Rutherford Class Decides the Treatment
I viable (no sensory or motor loss) → heparin, angiography within hours. IIa marginally threatened (sensory loss only) → catheter-directed thrombolysis is acceptable. IIb immediately threatened (motor deficit) → straight to the operating room. III (anesthetic, paralyzed) → irreversible, amputation.
The Class That Catches People
IIa versus IIb is the whole decision. Any motor deficit makes it IIb, and thrombolysis takes hours the limb does not have. Do not spend that time on a lytic catheter: embolectomy or bypass now.
Embolism or Thrombosis
Embolism: sudden onset, a source such as AF or recent MI, normal pulses in the other leg, no collaterals, lodges at bifurcations → Fogarty embolectomy. In-situ thrombosis: more insidious over hours to days, known PAD or prior bypass, diminished pulses bilaterally, collaterals present → thrombolysis, angioplasty or bypass.
Always Examine Both Legs
The contralateral leg is the single most useful physical finding. Normal pulses on the other side point to embolism; diminished pulses on both point to thrombosis on background PAD, and the two have different operations.
Reperfusion Is Its Own Emergency
After revascularization watch the deadly triad: hyperkalemia (risk of cardiac arrest), rhabdomyolysis with CK above 10,000 and AKI, and metabolic acidosis. Aggressive IV fluids, potassium every 2 h, and monitor for compartment syndrome, which may need fasciotomy.
Find the Source
ECG for atrial fibrillation, which is the commonest embolic source, plus echo for thrombus or endocarditis. Long-term anticoagulation for embolic disease, and secondary prevention for atherosclerosis if it was in-situ thrombosis.
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