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The World Health Organization lists cardiovascular disease as a leading cause of mortality worldwide, and in America alone, stroke was the fifth leading cause of all deaths in 2019. Plaque build-up in the carotid arteries restricts normal blood flow, often resulting in transient ischemic attacks (TIA). This condition, called carotid artery stenosis, can be diagnosed through multiple TIAs in symptomatic cases or through tests such as ultrasound, computed tomography angiography (CTA), cerebral angiography, and magnetic resonance angiography in asymptomatic patients.
Carotid endarterectomy (CEA) is a procedure that focuses on removing plaque blockage in the carotid arteries. Generally, this surgery is recommended only for moderate to severe carotid stenosis in symptomatic patients and severe carotid stenosis in asymptomatic patients. CEA involves placing a cross-clamp on all three carotid artery branches (external, common, internal) before removing the plaque build-up in the opened artery.
Most of the risk associated with CEA comes from ischemic risk during the procedure.
Cross-clamp placement restricts blood flow through the carotid arteries to the brain on the ipsilateral side of the procedure. Typically, patients with good collateral circulation in the circle of Willis can maintain an adequate level of perfusion through the contralateral carotid arteries. However, 20 to 50% of patients have poor collateral circulation, and there is a risk of cerebral ischemia potentially causing an intraoperative stroke.
Intraoperative neurophysiological monitoring (IONM) can minimize these risks by continuously providing valuable information about the cerebral perfusion level. IONM modalities, somatosensory evoked potentials (SSEPs), and electroencephalography (EEG) can indirectly measure cerebral perfusion. Any changes in these real-time recordings, often in the form of decreased waveform complexity or complete signal loss, reflect critical decreases in perfusion. This allows the surgeon to determine which surgical manipulation may place stress on neural structures and the appropriate intervention to minimize any irreversible damage resulting in a postoperative deficit.
Often, the intervention for cross-clamp-induced changes is the placement of an intraluminal shunt within the dissected carotid artery to reroute blood flow around the surgical site. However, shunt placement in all patient cases, routine shunting, is highly discouraged as it can increase the risk of dislodging microemboli, causing a postoperative stroke. Therefore, shunt placement is recommended only when necessary, with selective shunt placement determined by criteria of SSEP and EEG changes after preliminary cross-clamping tests to assess the patient’s degree of collateral circulation, making IONM an essential part of CEA.
Outside of selective shunt placement, SSEP and EEG should also be run continuously throughout the surgery to detect ischemic changes caused by other surgical maneuvers. Microemboli can also be dislodged during the reperfusion of the carotid arteries after the clamp is removed, causing an intraoperative or postoperative stroke. Other neuromonitoring modalities such as transcranial Doppler (TCD) can also be added for better visualization and quantification of emboli in the arteries.
Multiple scientific studies and reviews have also found that multimodality IONM using both SSEP and EEG has yielded the highest specificity and sensitivity in predicting postoperative deficits, supporting those changes in these recordings reflect stress on neural structures. IONM’s utility in monitoring cerebral perfusion levels, a critical aspect of the procedure, is why IONM is considered the standard of care for CEA.
