Optical monitoring of cerebral blood flow and metabolism during carotid endarterectomy

Carotid endarterectomy (CEA) is a surgical operation to eliminate plaque in the carotid bifurcation where patients are at risk of embolic stroke. CEA requires cross-clamping of carotid arteries (common, internal, and external) to halt the blood flow in the surgical area, causing a hemodynamic challenge to the surgical hemisphere and the risk of embolus. Therefore, cerebral hemodynamics or electrophysiology is intraoperatively monitored via different modalities, including near-infrared spectroscopy (NIRS), electroencephalogram (EEG), somatosensory evoked potentials, carotid stump pressure, and transcranial Doppler ultrasound. Although EEG is a commonly used and reliable monitoring technique for CEA, it is a surrogate measure of cerebral blood flow (CBF). Further, different anesthetic regimens could suppress its waveforms, making it difficult to rely on to ensure adequate CBF. Furthermore, there has been no gold standard for monitoring CBF during CEA. Therefore, we aimed to investigate changes in CBF index (CBFi) and cerebral metabolism via combined diffuse correlation spectroscopy (DCS) and NIRS system in patients who underwent CEA. We compared changes in EEG power spectra with cerebral hemodynamics on twenty-three CEA patients by quantifying a well-known EEG spectral method, desynchronization function. We also assessed different induction anesthesia on desynchronization functions to indicate electrophysiological and neurovascular changes with respect to clamping. Finally, we evaluated variability within CBFi and EEG power spectra by quantifying the coefficient of variation to capture hemispheric differences. A combined DCS-NIRS system can deliver complementary cerebral hemodynamic assessment to electrophysiology during CEA. Furthermore, intraoperative monitoring of clamp-induced cerebral hypoperfusion with a combined DCS-NIRS system would help make acute management changes in inpatient care (e.g., arterial shunting). Assessing the electrophysiological and neurovascular status of the brain can avert undesirable events such as hypoperfusion and hypoxia, prevent cerebral ischemia and allow determining personalized perfusion strategies.