Cerebral Neuromonitoring During Cardiac Surgery: A Critical Appraisal With an Emphasis on Near-Infrared Spectroscopy

Neurological complications of cardiac surgery have a large effect on patient outcomes. In this review, the value of several modes of central nervous system monitoring for improving perioperative care is critiqued. The electroencephalogram (EEG) has been used as a means for detecting brain ischemia. Even though EEG changes are specific for ischemia, the reliability is tempered by many confounding factors. The effectiveness of the processed EEG for ensuring amnesia during surgery is controversial, but it may have value for optimizing anesthetic dose and thus reducing the risk for delirium. Transcranial Doppler may be beneficial in confirming flow to both cerebral hemispheres during antegrade cerebral perfusion such as during aortic arch surgery and in detecting cerebral emboli. Transcranial Doppler can be used for monitoring cerebral autoregulation, allowing for individualization of blood pressure targets during surgery. Measures of adequacy of cerebral oxygen balance include jugular bulb venous oxygen saturation and near-infrared spectroscopy monitoring. Both monitors have limitations that reduce the sensitivity for detecting brain ischemia. Because near-infrared spectroscopy-measured regional cerebral oxygen saturation does not distinguish arterial from venous blood, these measurements reflect the adequacy of oxygen delivery versus demand. Over short periods, filtered regional cerebral oxygen saturation data may provide a clinically feasible method of monitoring cerebral autoregulation that overcomes many limitations of transcranial Doppler. Ongoing studies have demonstrated that the latter methodology for determining perioperative blood pressure targets has large potential for reducing organ injury from cardiac surgery.