HYPOTHESIS - EEG and SSEP used concurrently would be equally sensitive and timely in predicting the need for intraoperative shunt placement during CEA

Methods:

We studied 34 patients and performed selective shunting. Using the standard 10-20 system, baseline digital EEGs were performed pre-operatively, and continuous monitoring was used in the operating room. SSEPs were likewise recorded, by stimulating bilateral median and posterior tibial nerves.

Intraoperative Monitoring During CEA Christopher Loftus M.D, DHC (Hon.), FACS Zakaria Hakma, MDDepartment of Neurosurgery, Temple University School of Medicine, Philadelphia, USA

Predictive value of EEG/SSEP

• EEG predicted 9/34 times and missed 1/34

• SSEP predicted 5/34 times and missed 5/24.

ResultsIn 24/34 (70%) patients, there was no change in either EEG or SSEPs. There were concurrent changes in 4/34. There were only EEG changes in 5/34 (15%). In one case (3%), SSEPs alone predicted the need for shunting. All patients with significant, enduring changes in either EEG or SSEPs (9/34) underwent shunt placement. There were no postoperative strokes. EEG predicted ischemia 9/34 times, including one patient with transient changes not requiring a shunt (3%). SSEPs predicted ischemia which required shunting 5/34 times; SSEPs missed ischemia in 5 patients, but one of those patients did not need a shunt.

no CHanges

EEG alone

Both

SSEP alone

Conclusions:• Clearly these two techniques are not completely overlapping

• Combining EEG and SSEP during CEA adds a safety factor (burst suppression), and slightly increases the rate of ischemia detection.

• We are not prepared to use SSEP alone to detect cross-clamp ischemia in our patients for two reasons

– Signal averaging time

– Potential insensitivity

Discussion:

We shunt for any monitoring change, and were curious if the addition of SSEP would augment EEG in detecting clamp ischemia, and if there were cases where SSEP alone would change with normal EEG, since SSEP is less affected by anesthesia and medication.

In our 24 CEA patients, EEG and SSEP correlated in 28/34 (82%). Addition of SSEP identified one false negative in the EEG group; in this case the SSEP changes happened much earlier than EEG (possibly secondary to residual anesthetics) and the shunt was placed based on the SSEP changes; later during the case (shunt removal) EEG and SSEP changes did correlate.In 33/34 cases EEG was sufficient to predict shunt need.