Background: The aim of the study is to detect the regional cerebral oxygen saturation by the help of near infrared spectroscopy (NIRS) monitorization and to diagnose the hypoxemic or hyperoxemic episodes for the assessment of the effects of hypoxia episodes on cerebral perfusion during cardiopulmonary bypass (CPB) as early as possible. Methods: The study had been performed in Acibadem Kadiköy Hospital during February 2011 and June 2011. Seventy patients who were admitted with coronary heart disease (CHD) and scheduled for coronary artery bypass graft (CABG) surgery were included in the study. The patients were divided into two equal groups. Thirty five percent of the 35 patients (n=12) were female in group 1, 50% of 50 patients (n=18) were female in group 2. The mean age was 60±10 years and 57±11 years in group 1 and group 2, respectively. Group 1 consisted of 35 patients with adjusted inspired oxygen fraction (FiO2) at 0.35-0.45 during CABG. Group 2 consisted of 35 patients with adjusted FiO2 a t 0.40-0.50 during surgery. In addition to the standard monitorization, cerebral cortical oxygen saturation of all patients was monitored by NIRS. The measurements were done five times during the course of CABG. Results: In group 1, hypoxia was detected in five patients (14%) in at least one of the five measurement periods. In these patients, FiO2 value increased accompanied by increased ScO2. In group 2, hyperoxemia was observed in at least one of the measurement periods in 15 (42.8%) patients. Hypoxia was not observed in any of the patients in group 2. Conclusion: It is possible to detect hypoxic periods and to adjust FiO2 accordingly by means of noninvasive cerebral cortical oxygen saturation measurement in nonpulsatile flow of CPB.