In this case, the EEG monitoring takes place for a longer Duration of time
The CPT code for the EEG for an extended period of time is 95812 and 95813. The Code 95812 covers duration of 41-60 minutes and the code 95813 covers the duration of more than an hour. On an average, the duration of the carotid endarterectomy is more than an hour. So, the most appropriate code for this EEG is 95813.