Acute limb ischemia: Clinical sciences

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.

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. 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.