Neuromonitoring During Cardiac Surgery

Neurological complications of cardiac surgery have a large impact on patient morbidity and mortality. Clinicians have relied on several modes of monitoring of the central nervous system as a means for reducing the risk of these complications including the electroencephalogram. While electroencephalogram changes are specific for cerebral ischemia, the reliability is tempered by many confounding factors. The effectiveness of the processed electroencephalogram for ensuring amnesia during surgery is controversial but it may have value for minimizing anesthetic dose as a strategy to reduce the frequency of postoperative delirium. Somatosensory and motor evoked potential provide critical information about the continuity of the central nervous system particularly of value for surgery where spinal cord blood supply is compromised. Transcranial Doppler (TCD) can be used for confirming cerebral blood flow during aortic arch surgery and in detecting cerebral emboli. Measuring the sufficiency of cerebral oxygen supply versus metabolic demand can be monitored with jugular bulb venous oxygen saturation or near infrared spectroscopy (NIRS) monitoring. The latter is achieved using sensors placed on the forehead and, is thus, technically easier than the former. There is growing evidence for the use of cerebral autoregulation monitoring to individualize blood pressure during and after surgery. This can be performed using TCD but this method is technically challenging. The results of laboratory and clinical studies suggests that NIRS measured regional cerebral oxygen saturation can provide an acceptable surrogate of cerebral blood flow for autoregulation monitoring. A growing body of evidence using NIRS-based autoregulation monitoring supports its further development and clinical implementation as an approach for ensuring organ perfusion during cardiac surgery.