Peri-operative Monitoring of Cerebral Oxygenation and the Onset of Delirium in Patients Undergoing Cardiac Surgery

Near infrared spectroscopy (NIRS) is a non-invasive technique that uses near infrared light between 700 and 1100nm which penetrates several centimeters through skin and bone structures. Light is absorbed by chromophores. There are multiple chromophores which can be detected in the NIR spectrum such as water, lipids, melanin, myoglobin, oxygenated hemoglobin and deoxygenated hemoglobin. Each chromophore has a specific absorption spectrum. By using different wavelengths, it is possible to differentiate chromophores. The difference between oxygenated hemoglobin and deoxygenated hemoglobin can be calculated using the modified Beer-Lambert law, resulting in a numeric value which is a representation of the regional cerebral oxygen saturation.