Non-invasive monitoring of human cerebral oxygen saturation by near infrared spectroscopy: instrumentation, calibration and application in cardiopulmonary bypass.

Cerebral oxygenation especially regional cerebral oxygen saturation (rSO<inf>2</inf>) needs to be monitored to avoid irreversible damages induced by hypoxia. Based on steady-state spatially resolved spectroscopy (SRS), rSO<inf>2</inf>was obtained by the NIRS oximeter developed by our group. The oximeter was calibrated by blood gas analyzer using the liquid tissue model made up by our group. The results indicate that the correlation between rSO<inf>2</inf>and the real oxygen saturation of the model is excellent (R>0.99), and the influences by the background absorption and overlaying tissues are little. The rSO<inf>2</inf>of 14 patients were monitored during cardiopulmonary bypass (CPB) non-invasively by our oximeter. The results indicate that first, NIRS is almost the only available method to monitor rSO<inf>2</inf>non-invasively during CPB; second, rSO<inf>2</inf>is negatively correlated with body temperature and positively with blood perfusion rate, so it reflects the balance between cerebral oxygen supply and consumption; third, the low perfusion rate stage and the rewarming stage are relatively critical because rSO<inf>2</inf>decreases significantly and may be relatively low.