Carotid endarterectomy (CEA) is one of the modalities to treat carotid artery disease. One of the perioperative complications of this surgery includes stroke, a condition that occurs when the blood supply to part of your brain is interrupted or reduced. To prevent cerebral ischemia during carotid endarterectomy several methods have been employed in clinical practice, such as awake neurocognitive assessment, electroencephalography, evoked potentials, transcranial Doppler, carotid stump pressure, and near infrared spectroscopy (Regional Oximetry).

Meta-analysis published by Nwachuku EL and colleagues suggests that intraoperative somatosensory evoked potential (SSEP) is a highly specific test in predicting neurological outcome following CEA. Sridharan and colleagues advise multimodality in intraoperative monitoring, with simultaneous use of EEG and SSEP which will improve the diagnostic accuracy. Use of regional oximetry as a continuous, real time and non-invasive monitoring, during CEA is controversial, with pros and cons studies that do not contribute to a clear picture of its application in everyday clinical practice.

Masimo's O3 Regional Oximetry is new monitoring approved in 2020 by FDA for monitoring somatic tissue oxygenation saturation in all patient populations and for monitoring relative changes in haemoglobin, oxyhaemoglobin, and deoxyhaemoglobin in adult brains. This monitoring can help clinicians to monitor cerebral oxygenation in situations in which pulse oximetry alone may not be fully indicative of the oxygen in the brain. One such example is carotid endarterectomy (CEA).

Masimo's O3 regional oximetry is integrated part of the SedLine® Brain Function Monitoring (Masimo, Irvine, California, USA, 1989) on the Root® Patient Monitoring Platform. Sensors are equipped within Masimo Open Connect (MOC-9) modules which are applied to the patient's forehead and connected to the Masimo Root® patient monitoring and connectivity platform.

Masimo's O3 Regional Oximetry provides regional or tissue haemoglobin oxygen saturation and unlike peripheral pulse oximetry, which reflects the body's general arterial blood oxygenation, O3 provides information about the local tissue's haemoglobin oxygen saturation, both in cerebral and somatic applications. This information provides additional insight that may help inform clinicians of changes in cerebral or somatic tissue oxygen levels.

Regional Oximetry is already part of the standard monitoring used during CEA in Cleveland Clinic Abu Dhabi, together with electroencephalography and the somatosensory evoked potentials.

Using new Masimo's O3 regional oximetry monitoring (same sensor, only the module is new with new parameters) we will have additional parameters that have not been analysed before:

• Δbase
• ΔSpO2
• ΔcHbi
• Δ HHbi
• ΔO2Hbi

With this in mind, the authors would like to analyse the correlation between new Masimo's O3 regional oximetry parameters, EEG and SSEP in CEA.

Inclusion Criteria:

1. Subjects older than 18 years of age
2. Subjects undergoing carotid endarterectomy.
3. American Society of Anaesthesiologists Classification (ASA) score I to III.

Exclusion Criteria:

1. American Society of Anaesthesiologists Classification (ASA) score IV and V.
2. Subject has skin abnormalities affecting the sensor placement
3. Emergency cases
4. Cognitive/Mentally impaired or unable to provide consent
5. Pregnant subject

This is prospective observational pilot study and only 10 subjects will be recruited after application of the below inclusion/exclusion criteria. Subjects will be included only if they sign informed consent for study. The anticipated duration of subject's participation in this study will not exceed duration of surgery.