Near-infrared spectroscopy in adult cardiac surgery: between conflicting results and unexpected uses

Neurological complications after cardiac surgery, ranging from permanent stroke to transient dysfunction, represent a key issue in the management of geriatric patients. Many patients aged 70 or more have history of neurological dysfunctions, which increases the risk of complications and sequelae. Severe neurologic diseases, such as strokes, occur in up to 6% of patients undergoing cardiac surgery. Therefore, in the setting of fragile patients, prevention is more important than treatment. There are several intraoperative mechanisms of neurological injury, such as embolism, inflammation, intraoperative anemia, carotid or intracranial artery disease, but hypoperfusion appears to be the final common pathway of cerebral damage. Many systems to monitor cerebral oximetry and allow physicians to restore an adequate cerebral perfusion have been developed over the years. Among these, near-infrared spectroscopy (NIRS) has been extensively investigated and currently represents the non-invasive real-time tool to monitor the oxygen content of cerebral tissue during adult cardiac surgery. However, its effectiveness is highly debated, since current studies lead to controversial results. The existing literature raises four major questions:  1. Why current studies about NIRS are contradictory? 2. Can NIRS be useful to monitor brain damage? 3. Can NIRS be useful to monitor other damages? 4. Can NIRS be useful in the outpatient clinic?