Monitoring Cerebral Oxygen Saturation Using Near Infrared Spectroscopy during Cardiopulmonary Bypass: Comparing with Monitoring Mixed Venous Oxygen Saturation

Cerebral oxygenation can be monitored non-invasively by near infrared spectroscopy (NIRS), which is significantly important for clinical cerebral protection against hypoxia. Our group developed an NIRS oximeter, by which regional cerebral oxygen saturation (rSO₂) can be monitored non-invasively, continuously and in real time. Using it, we monitored cerebral rSO₂ of three children during cardiac surgery all with cardiopulmonary bypass (CPB). The mixed venous oxygen saturation of the vena cava (SvO₂) at the entrance of the artificial CPB pump was also measured at the same time by another monitor. The results indicated that there was statistical correlation between cerebral rSO₂ and mixed SvO₂ (R=0.547, 0.465 and 0.695 respectively, and p all less than 0.01). But all the above R was not high, because cerebral rSO₂ was mainly reflected by cerebral venous oxygen saturation, which was generally not consistent with the SvO₂. During CPB, when the perfusion rate or the body temperature was changed, the changes of the mixed SvO₂ were delayed for several minutes compared with the corresponding changes of cerebral rSO₂. This was because cerebral venous blood flew relatively low, and it might take a period that the venous blood flew from the brain into the vena cava. Therefore, the mixed SvO₂ cannot trace the changes of cerebral oxygenation in real time during CPB, and monitoring cerebral rSO₂ using NIRS is of greatly advantages than the mixed SvO₂.