Abstract: Objective To investigate the effect of dexmedetomidine on regional cerebral oxygen saturation (rSO2) during cardiopulmonary bypass (CPB) and postoperative cognitive dysfunction (POCD) in patients undergoing heart valve replacement. 
Methods A total of 80 patients undergoing elective heart valve replacement were selected and randomly divided into the control group and the observation group, with 40 cases in each group. In observation group, 0.5 μg/kg dexmedetomidine was injected intravenously before induction of anesthesia, and then maintained at a dose of 0.5 μg·kg-1·h-1 until the end of the operation, and the control group was intravenously infused with normal saline. Both groups of patients received intravenous midazolam, sufentanil, etomidate, and rocuronium bromide for induction of anesthesia, and intravenous infusion of propofol and rocuronium bromide, and intermittent infusion of sufentanil to maintain anesthesia. The rSO2, partial pressure of carbon dioxide (PCO2), hematocrit (HCT), hemoglobin (Hb), mean arterial pressure (MAP), tumor necrosis factor-α (TNF-α), and interleukin-6 (IL-6) levels on the left and right sides at each time period of before operation (T0), before induction (T1), after induction and before the initiation of CPB (T2), from the initiation of CPB to the end of cooling (T3), and from the end of CPB cooling to the initiation of rewarming (T4), from the initiation of CPB rewarming to shutdown (T5), and at 30 min after shutdown (T6) were compared between two groups. The cognitive function of the patients was assessed before and at 7 d after the operation, and the incidence of POCD was recorded. 
Results There were significant differences in PCO2, HCT, Hb and MAP between two groups at different time points (P＜0.05), but there was no significant difference in inter-group comparison and interaction between groups and time points (P＞0.05). The difference of interaction between groups, time points and time points between groups were statistically significant with respect to left rSO2, right rSO2, serum TNF-α and IL-6 (P＜0.05). The scores of mini-mental state examination (MMSE) in both groups decreased after operation, which were higher in the observation group than in the control group (P＜0.05). The postoperative incidence of POCD in the observation group was 2.50%, which was lower than 17.50% in the control group (χ2=5.000, P=0.025). 
Conclusion Pre-filling dexmedetomidine during heart valve replacement and maintaining the administration until the end of the operation can effectively increase the patient′s rSO2, the reduce the levels of TNF-α and IL-6 and the levels of inflammatory indicators. Therefore, it can effectively improve the balance of cerebral oxygen supply and demand during CPB, and reduce the incidence of POCD.

Key words: heart valve plasty, cognitive, dexmedetomidine