emDOCs Podcast – Episode 141: Acute Limb Ischemia

How does acute limb ischemia occur?

• Acute limb ischemia is cessation of blood flow distal to the occlusion site.
• The most common cause is arterial thrombosis. In patients with known peripheral arterial disease (PAD), this accounts for about 80% of cases.
  • Other causes of limb ischemia:
    • Embolism from the heart or proximal artery
    • Dissection
    • Thrombosis of a popliteal aneurysm or cyst
    • Trauma
    • Occlusion of a previous bypass graft
• All etiologies result in the same problem:
  • Sudden cessation in blood flow, nutrients, and oxygen delivery to the tissues of the affected area (muscles, nerves, skin).
  • Lack of perfusion leads to ischemia and an anaerobic state, accumulation of lactate, and finally necrosis with the release of cellular contents.

How common is limb ischemia?

• Limb ischemia is uncommon.  Approximately 14-26 cases per 100,000/year.
• Over 80% of cases involve the lower limb.
• Cases of limb ischemia due to an embolism have decreased due to:
  • Reduce rates of cardiac valve disease from rheumatic fever.
  • Improved anticoagulation and management of atrial fibrillation.
• Even with this decrease, there has not been a change in mortality or amputation-free survival rates after hospital discharge.
• Amputation rate is 10-30%.
• Limb ischemia carries a mortality rate of around 10-25%.
• Major risk factors: known PAD, heart disease, atrial fibrillation, aneurysms, HTN, HLD, DM, tobacco use, chronic inflammation (ESRD, HIV, SLE).

What signs and symptoms should make us think about limb ischemia?

• Presentation depends on several factors:
  • When the occlusion occurs
  • Where it occurs in the vessel
  • Presence of underlying vascular pathology
  • Presence of collateral vessels
• The classic “six P’s” of limb ischemia:
  • Pain
    • This is the earliest and most common symptom.
    • The pain will be distal to the site of occlusion.
    • Increases in severity as ischemia worsens.
    • May eventually go away due to ischemia of sensory nerves.
  • Paresthesias
    • Common early in the disease course.
    • As ischemia progresses, sensation will decrease.
  • Pallor
    • An early sign of ischemia due to vascular obstruction and vasospasm.
    • As the ischemia worsens, skin mottling will start to occur.
    • Skin will initially blanch but will become fixed in the later stages of ischemia.
    • Mottling is a poor prognostic sign that suggests irreversible ischemia.
  • Poikilothermia
    • Inappropriate temperature regulation; the ischemic limb will feel cool compared to the contralateral side.
    • Later finding associated with poorer outcomes.
  • Pulselessness
    • Late finding associated with irreversible ischemia and poor prognosis.
  • Paralysis
    • Weakness occurs later in the disease and progresses to complete paralysis of the affected limb.
    • Associated with irreversible ischemia and worse prognosis.

Evaluation of patients with known chronic PAD:

• Chronic PAD will present differently because of collateral vessel formation over time.
• Patients have chronic pain with exertion.
• If the patient experiences an acute occlusion, the symptoms may start similar to a previous episode of claudication, but will usually be more sudden, severe, and will not resolve like their typical chronic pain.
• Patients with collateral flow from chronic PAD may develop symptoms of acute occlusion over a longer time period of hours or even days.

Key components of a vascular evaluation:

• Look for risk factors such as past episodes of claudication, known PAD, or AFib.
• Ask about the chronology of symptom onset, the location/severity of the pain, and if the pain has worsened over time.
  • Duration of symptoms and the presence of motor weakness or sensory changes play an important role in determining the urgency of intervention.
• Physical exam:
  • Color
  • Pulses
  • Sensation
  • Motor
  • Temperature
  • Capillary refill
  • Comparison of the contralateral limb.
• Palpating distal pulses is not sufficient.  Use Doppler to evaluate for pulses distal to the occlusion (may use US).
  • If there is no Doppler signal, that can confirm occlusion and severe ischemia.
  • If able to detect a Doppler signal, that means blood flow is present; calculate an ABI.
• Calculating the ABI:
  • Place the patient in the supine position.
  • Measure the systolic blood pressure (SBP) from both brachial arteries using the blood pressure cuff and Doppler over the antecubital fossa.
  • Measure the SBP in the dorsalis pedis (DP) and posterior tibialis (PT) arteries with the blood pressure cuff placed just proximal to the malleoli with the Doppler over the artery.
  • Calculate ABI by dividing the highest ankle SBP (DP versus PT) by the highest brachial SBP.

Rutherford system:

• Classification system for limb ischemia that incorporates sensation, motor, and Doppler exam.
• An important tool that helps determine the next steps for testing and treatment based on the patient’s category:
  • Category I: no sensory loss or muscle weakness; arterial and venous flow is present on Doppler. The limb is viable and not immediately threatened.
  • Category II: sensory changes and potentially altered arterial Doppler signal, but it’s broken further into IIA and IIB.
  • Category IIA: limb with minimal sensory loss and no weakness, indicating that the limb is salvageable if treated promptly.
  • Category IIB: limb with increasing sensory loss and mild to moderate weakness; no arterial Doppler present. The limb is salvageable only with immediate revascularization.
  • Category III: irreversible ischemic damage that is unsalvageable. It’s characterized by severe sensory loss and motor weakness. No sensation plus paralysis. Absent venous and arterial Doppler.
• Society guidelines:
  • The 2016 American Heart Association/American College of Cardiology:
    • Imaging is not required for any patient presenting with signs and symptoms consistent with acute limb ischemia.
    • Recommends urgent revascularization for Category I.
    • Recommends emergent revascularization for Category IIA/IIB.
  • The 2007 Trans-Atlantic Inter-Society Consensus for the Management of Peripheral Arterial Disease:
    • Recommends imaging for patients with Category I and Category IIA.
    • Recommends emergent revascularization without the need for imaging for Category IIB.
  • The 2017 European Society of Cardiology:
    • Recommends imaging for patients with Category I.
    • Recommends urgent revascularization for Category IIA and IIB.
    • States that imaging should not delay revascularization.
  • All three recommend amputation for Category III.

Labs/Imaging:

• Labs:
  • No lab test can definitely rule in or exclude limb ischemia.
  • While there may be an elevated WBC, lactate, and CK, waiting on lab results can be a pitfall that delays definitive management.
• Imaging:
  • CTA first-line modality. Widely available, rapid, and provides a more complete picture of the arterial vasculature of the affected limb.
  • CTA is over 99% sensitive and 97% specific.
    • Arterial thrombosis on a CTA will demonstrate a vessel with a sharp or tapered cutoff with diffuse atherosclerosis.
    • If the vessel appears relatively clean with a sudden occlusion and no distal flow, that indicates arterial embolism.
  • If CTA is unavailable, duplex arterial US is a viable alternative for evaluating an acute arterial occlusion.
    • Duplex US is capable of identifying arterial occlusion due to thrombosis and embolism, as well as thrombosed arterial aneurysms.
    • The exam is US technician-dependent and does not provide as thorough an evaluation as a CTA.

Management:

• Consult vascular surgery at the first sign of concern for acute limb ischemia.
• Medical management:
  • Start an unfractionated heparin bolus and infusion if there is a reasonable suspicion of occlusion before imaging.
    • 80 U/kg bolus followed by an 18 U/kg/hr infusion.
    • Titrate to maintain an activated partial thromboplastin time of 2-2.5X baseline.
  • Give aspirin.
  • Provide IV fluids as needed to correct hypovolemia and improve perfusion.
  • Patients are usually in significant pain; provide adequate analgesia.
• Surgical management:
  • Vascular surgery has three primary reperfusion techniques:
    • Catheter-directed thrombolysis
    • Endovascular clot aspiration/fragmentation/fibrinolysis
    • Operative revascularization
  • Several techniques may be performed together or in conjunction with other treatments.
  • There is no one revascularization technique that is superior to others; treatment options are often patient-specific.
  • For patients with prolonged ischemia who have no sensation and/or complete paralysis (Category III), amputation is often the only viable option.
  • 10-30% of patients with acute limb ischemia will require amputation either at the time of presentation or within one year.

Upper Limb Ischemia:

• Acute upper limb ischemia is less common (less than 17% of cases of limb ischemia).
• Typically due to a cardiac embolism rather than a thrombosis.
• The most common sites of occlusion include the axillary and brachial arteries.
• Presentation, evaluation, and treatment are the same as lower extremity occlusions.

Summary:

• Acute limb ischemia is a sudden decrease in limb perfusion.
• Acute pain is the most common presenting symptom, and paresthesias may also occur in the early stages of the disease. Skin changes, weakness, and temperature changes typically occur later in the disease.
• Assess distal pulses with Doppler ultrasound in the affected limb; palpation alone is inadequate. Absent Doppler arterial signal indicates that the affected limb’s survival is at risk.
• CTA is the first-line imaging modality, but consult the vascular specialist first if concerned about limb ischemia.
• Anticoagulate, administer analgesics, and give fluids if they’re hypovolemic.

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