[Near Infrared Spectroscopy for cerebral monitoring during cardiovascular surgery]

Near-infrared spectroscopy (NIRS) is an optical imaging technique for medical applications, able to monitor the variation of hemoglobin saturation into the tissues. The NIR photon passes through the biological tissue following a path similar to a more or less complex split. The NIR absorption of photons is proportional to the concentration of chromophores (pigments that absorb the light in the spectral region of interest). NIRS probes are used as the light source on the same side of the source receiver, being this last able to capture the photons after their journey into the tissues. The NIRS methodology may be applied as an imaging technique for various organs. In this review the authors describe the use of NIRS for the continuous monitoring of regional cerebral oxygen saturation in the course of cardiovascular surgical procedures. Thanks to the NIRS technique, changes in cerebral oximetry can be monitored continuously during cardiovascular surgery. A desaturation greater than 20% of baseline or an rSO2 absolute value less than 50%, are associated with a reduction of the cortical somatosensory evoked potentials and an increase of neurological damage and / or cognitive impairment. During carotid surgery, reduction and / or asymmetries of rSO2 value are encountered in the course of intraoperative clamping causing cerebral hypoperfusion. Instead, rSO2 increase may predict hyperperfusion syndrome after carotid stenting or endarterectomy. Cerebral hyperperfusion syndrome is rare, but often fatal once it has established. The NIRS may represent an added value in those patients. The NIRS is also applied during surgery performed with cardiopulmonary bypass, including aortic arch surgery with cardiocirculatory arrest. Continuous monitoring of any changes in cerebral rSO2 allows a rapid treatment in the aim to improve the psycho-neurological outcome of patients undergoing this type of surgery.