Acute limb ischemia: Clinical sciences

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Introduction 0:00–1:24

Limb ischemia is the acute reduction of blood flow to an extremity, resulting in decreased oxygen delivery. The acute reduction of blood flow most commonly occurs from a thromboembolism, which is when a clot travels from a different area of the body and occludes the blood flow in the limb.
It can also occur when a diseased vessel is narrowed by atherosclerotic plaque, resulting in slower blood flow, stasis, and clot development.
Regardless of the cause, ischemia can quickly lead to tissue necrosis if it’s left untreated, and can become a medical emergency, as skeletal muscle can only tolerate ischemia for 4 to 6 hours before dying.
Depending on the patency of the blood flow, ischemia can range from mild to severe. Now, limb ischemia is categorized by the Rutherford classification system.
A Rutherford class I limb is viable and not immediately threatened, whereas a Rutherford class IIa limb is marginally threatened but salvageable if promptly treated.
A Rutherford class IIb limb is immediately threatened but salvageable with immediate revascularization. Finally, a Rutherford class III limb is where major tissue loss or permanent nerve damage is inevitable, and the limb is irreversibly damaged.
Alright, when a patient presents with a chief concern suggesting limb ischemia, your first step is to perform an ABCDE assessment to determine if the patient is unstable or stable.

Unstable patient 1:24–5:29

If the patient is unstable, stabilize their airway, breathing and circulation. Obtain two large bore intravenous lines and start IV fluid resuscitation.
Continuously monitor their vital signs including blood pressure and heart rate; and, if needed, don’t forget to provide supplemental oxygen.
Next, assess for red flag symptoms like profound sensory loss and paralysis, which indicate severe ischemic injury of the affected limb, along with sensory and motor nerve damage.
Typically, most patients experience a progression of symptoms starting with worsening pain followed by pulselessness and pallor, resulting in paresthesia and paralysis towards the end.
Additionally, you can expect to see a limb that’s cool to touch, sometimes with frank necrosis or gangrene, which can trigger a systemic inflammatory response that can lead to sepsis.
Here’s a high-yield fact! You can remember the presentation of acute limb ischemia with the 6 Ps for pain, pulselessness, poikilothermia, pallor, paresthesias, and paralysis.
Now, if these are your findings, your next step is to perform an arterial and venous Doppler to assess the blood flow. If no Doppler signals are found, there’s likely no blood flow in the limb.
This represents a non-viable or Rutherford class III limb. The treatment includes obtaining an emergent surgical consult for amputation of the limb in addition to supportive therapy with IV fluid resuscitation and empiric antibiotics.
Here’s a clinical pearl! There’s a difference between a Doppler signal and an ultrasound doppler exam.
A doppler signal is an auditory sound reflecting blood flow within an artery. You can classify the result based on what you hear which can be monophasic, biphasic, or triphasic sounds.
An ultrasound Doppler, on the other hand, provides images of soft tissue and vasculature and is often used to rule out DVT.
Now, there are three types of signals you might find on a Doppler exam. The first is a triphasic doppler signal, which is typically heard in healthy arteries.
The triphasic signal is made up of three different sounds; a systolic velocity peak indicating forward flow, a reflux phase where there is a reversal of flow, followed by a smaller late diastolic velocity peak representing the second forward flow.
The second type of signal you might hear is a biphasic doppler signal. This is where two sounds are heard; a systolic peak followed by a diastolic peak reflective of the forward flow followed by a reverse flow component.
Biphasic signals are often found in minimally diseased vessels. The third type, a monophasic doppler signal, is abnormal and indicates a diseased vessel.
Only one sound is heard which is forward flow without a reverse flow component. When performing a vascular exam, remember to assess different areas of the limb.
For example, if the lower extremity is involved, start distally by evaluating the dorsalis pedis and posterior tibial arteries first.
Then, move up to the popliteal and femoral arteries. Compare the signals of each site to identify the location of the vascular occlusion.
Understanding the vascular anatomy can help you plan appropriate intervention, which may include thrombolytic therapy, revascularization, and even amputation.
Additionally, labs like CBC and lactate can help you assess the patient’s systemic response to the ischemic limb. The severity of ischemia is reflected in leukocytosis and an elevated lactate.
Now that unstable patients are taken care of, let’s shift our attention to stable patients. For stable patients, your first step is to obtain a focused history and physical examination.

Stable patient 5:29–6:44

On history, patients usually report acute extremity pain, absent or decreased mobility of the extremity, and in some cases, paresthesias and a prior history of claudication.
Additionally, patients might have risk factors that affect blood vessels like hypertension, smoking, and hyperlipidemia; as well as risk factors for embolization like a history of myocardial infarction, atrial fibrillation, or valvular lesions.
Keep in mind that atrial fibrillation is the most common cause of embolic limb ischemia as small thrombi formed in the heart can embolize and occlude smaller arteries of distal limbs.
Now, on exam, you can expect to find absent or diminished pulses, pallor or cyanosis, cool extremities, prolonged capillary refill, and possibly sensory or motor deficits.
With these findings, you should suspect acute limb ischemia. Next, perform a vascular exam with an arterial and venous Doppler to help you determine the Rutherford criteria.
Okay, let’s start with Rutherford Class I, which is the mildest form. On history, patients often report mild to moderate pain of the extremity.

Viable, non-threatened limb 6:44–9:14

Physical exam usually shows no sensory loss or muscle weakness. In patients with underlying peripheral artery disease, you might see signs of chronic arterial insufficiency, like loss of hair and thickened nails.
Now, on Doppler, you can expect audible arterial and venous signals. In this case, you’re dealing with a viable and non-threatened limb, also known as Rutherford class I.
In terms of management, start with an IV heparin infusion to prevent worsening of the arterial occlusion. Then, order a computed tomography angiography, or CTA; or an arteriogram of the affected limb to visualize the occlusion and identify the level of the arterial disease.
The CTA should show the aorta all the way down to the distal limb to assess for aortoiliac disease in addition to the distal occlusion.
Patent vessels look like a continuous flow contrast, whereas an occlusion looks like a sudden stop of contrast within a vessel.
Sometimes, you might see tapering off of contrast which represents a diseased vessel with stenosis or luminal narrowing.
In some cases, you might also see smaller collateral circulation around the site of occlusion, which is the body’s response to decreasing blood flow by providing alternative routes for blood to flow.
Extensive collateral circulation is an indication of chronic disease, while an abrupt cessation of flow supports the diagnosis of acute limb ischemia.
Now, if the CTA shows no arterial occlusion or stenosis, consider an alternative diagnosis such as musculoskeletal causes of acute limb pain.
On the other hand, if the CTA reveals arterial occlusion or stenosis, diagnose acute limb ischemia. Treatment involves urgent surgical consultation for revascularization to reestablish adequate blood flow, to minimize the ischemic damage to the limb.
Generally speaking, there are two methods of revascularization. The first is a thrombectomy, where the occluding thrombus is removed mechanically via minimally invasive or open surgical techniques, or broken up with medication to restore the blood flow.
The second method is a bypass, which is a surgical procedure where a new path of blood flow is created using a graft to bypass the occlusion.
Alright, let’s move on to marginally threatened limb or Rutherford class IIa. These patients typically report severe pain, and on exam, show mild sensory loss with no muscle weakness.

Marginally threatened limb 9:14–10:39

On Doppler, arterial signals may or may not be audible, but venous signals will be audible. You can assess for the venous signal by holding the probe over the vein and applying compression distally.
If you hear a reversed blood flow signal, you have an audible venous signal. With these findings, diagnose a marginally threatened limb, also known as Rutherford class IIa.
Next, initiate an IV heparin infusion and order a CTA to confirm the diagnosis and assess vascular anatomy for surgical planning.
You can expect the CTA to show acute arterial occlusion of contrast to the major vasculature of the affected limb, often with evidence of chronic vascular disease.
If IV contrast is contraindicated due to concomitant renal insufficiency, ultrasound can be used to visualize the occlusion and evaluate the affected vasculature, where you can see loss of flow in the artery and loss of the associated Doppler waveform.
For treatment, consult the surgical team urgently to evaluate for revascularization, usually within 6 to 24 hours. Finally, let’s talk about an immediately threatened limb or Rutherford class IIb.

Immediately threatened limb 10:39–11:47

On history, patients will report severe pain, and show significant sensory loss beyond the distal digits with mild to moderate muscle weakness on exam.
You can expect to find the 6 Ps, so pain, pulselessness, poikilothermia, pallor, paresthesias, and paralysis; and symptoms are often more severe and progressive when compared to a marginally threatened limb.
On Doppler, there will be no audible arterial signals, indicating there’s no arterial flow to the distal limb; but audible venous signals will be present.
This confirms the diagnosis of immediately threatened limb or Rutherford Class IIb. In this case, start an IV heparin infusion immediately and obtain a CTA of the extremity for surgical planning.
That’s because an arterial occlusion causing an immediately threatened limb is a surgical emergency requiring revascularization usually within 6 hours.
So, make sure to consult the surgical team right away for immediate revascularization. Alright, as a quick recap… Acute limb ischemia is the sudden reduction of blood flow to an extremity categorized by the Rutherford staging system.

Review 11:47–12:36

Class I represents a viable, non-threatened limb; Class IIa is a marginally threatened limb; Class