SSEP and EEG Changes During Carotid Endarterectomy with Shunting
July 07, 2024
Carotid endarterectomy aims to reduce a patient’s risk of stroke by removing atherosclerotic plaque from the carotid artery. When combined with the real-time data afforded by intraoperative neurophysiological monitoring (IONM), surgeons can better prevent potential neurological deficits, detect and respond to issues like insufficient cerebral perfusion, and ultimately provide better patient outcomes.
In the case of a 73-year-old female patient, somatosensory evoked potential (SSEP) and electroencephalogram (EEG) IONM modalities played significant roles during her carotid endarterectomy by alerting the surgeon to the need to shunt.
The patient presented with multiple symptoms of distress: disorientation regarding person, place, time, and situation, and abnormal speech. The patient was diagnosed with carotid stenosis and had a medical history that included cardiac procedures and coronary artery bypass graft surgery. Given her condition, she was scheduled for a carotid endarterectomy to mitigate the risk of stroke.
Neurophysiological Monitoring During Surgery
To ensure the patient's safety during surgery, a comprehensive monitoring protocol was employed, including SSEP and EEG modalities. Small needle electrodes were placed in the patient's wrists and ankles to stimulate nerve responses, while additional electrodes were positioned on the scalp to record these responses. Electrodes were also placed on the head to monitor brain activity. All electrodes were connected to amplifiers for accurate readings, and the setup was completed post-sedation.
Throughout the procedure, the surgical team continuously monitored the patient's nerve and brain activity using these tools. Key observations included:
- Right Median SSEP: Following the placement of the clamp, there was a significant decrease in the right median SSEP, which persisted despite rising blood pressure. This SSEP returned to baseline after the shunt was placed but decreased again upon shunt removal. The SSEP only resolved after the clamp was removed, with bilateral upper SSEPs returning to baseline by the end of the surgery.
- Bilateral Lower SSEP: These remained stable and reproducible at baseline throughout the procedure.
- EEG: The EEG was symmetric and continuous at baseline. However, after the clamp was applied, the left-side EEG decreased and slowed. This returned to baseline once the shunt was in place.
After the procedure, the upper and lower SSEPs were within acceptable limits relative to their baselines, considering the anesthetic effects. The EEG showed no significant abnormal activity, and the TOF ratio was 1/4.
The Importance of Neurophysiological Monitoring in Surgery
Without real-time SSEP and EEG monitoring, the important signals indicating poor blood flow to the brain may have been missed. Failure to notice and respond to large declines in SSEP amplitudes, like those that occurred during this procedure, could have led to this severely distressed patient suffering significant brain damage or a stroke.
However, the real-time IONM data helped improve the surgeon's awareness and allowed them to recognize these alterations and respond accordingly by shunting. Each piece was critical in assuring patient safety and optimizing the success of the carotid endarterectomy procedure.
Intraoperative neurophysiological monitoring is an essential component of modern surgical procedures, particularly those with high risks. By providing real-time data, SSEP and EEG monitoring enable surgeons to make informed decisions that can prevent severe postoperative complications and offer better patient care and outcomes.
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