Objective:To explore the cerebral protection of carbon dioxide (CO2) field flooding on open heart surgery with extracorporeal circulation(ECC). Methods:From Jun 2012 to Mar 2013,97 patients undergoing open heart surgery with ECC were randomly divided into either CO2 insufflation(group Ⅰ,n = 50)or unprotected controls(group Ⅱ,n = 47). Blood samples were collected from the internal jugular vein at 5 min after anesthesia(T0),5 min(T1),1 h(T2),4 h(T3)and 24 h(T4)after release of the aortic cross-clamp,and the plasma concentrations of S-100β and neuronspecific enolase(NSE)were measured. The mini-mental state examination (MMSE)was performed to assess cognitive function before and 7 days after the operation. It was considered to be postoperative cognitive dysfunction (POCD)when the score decreased ≥ 1 standard deviation. Results:The plasma concentrations of S-100β at T1-T3 and NSE at T1-T4 in group I were higher than those at T0(P < 0.05). The plasma concentrations of S-100β and NSE at T1-T4 in group II were higher than those at T0(P < 0.05). Compared with group II,the concentrations of S-100β at T1-T4 and NSE at T2-T4 in Group Ⅰ were significantly decreased(P < 0.05). MMSE after surgery could not be performed in two patients of each group for reduced physical or mental status on the 7th postoperative day,respectively. The postoperative MMSE scores were significantly reduced in both groups compared with preoperative MMSE scores(P < 0.05),and the score in group Ⅱ was lower than that in group I(P < 0.05). Sixteen patients suffered POCD in group Ⅰ,and 25 cases in group Ⅱ,and the differences were significant(P < 0.05). Conclusion:It is very important to apply CO2 field flooding during open heart surgery,which can reduce the increasing extent of plasma S100β and NSE concentrations,and improve early postoperative cognitive function and cerebral protection.