Abstract: Objective To explore the effect of cerebral oxygen saturation on postoperative cognitive dysfunction and inflammation in elderly patients undergoing hip surgery during perioperative anesthesia. 
Methods A total of 120 elderly patients undergoing hip arthroplasty were collected, and the decrease in regional saturation of cerebral oxygen (rScO2) during perioperative anesthesia was set to be greater than 20% before surgery as cerebral hypoxia. According to the intraoperative rScO2, the patients were divided into hypoxia group (n=57) and non-hypoxia group (n=63). The preoperative and postoperative cognitive levels of patients were assessed using the Mini-Mental State Examination (MMSE) and the Montreal Cognitive Assessment (MoCA)Scale score. Statistical analysis of the correlation of rScO2with MMSE and MoCA was performed. ELISA was used to detect neuron specific enolase (NSE), S100-β protein, tumor necrosis factor α (TNF-α), and interleukin-6 (IL-6) levels in the plasma of patients before and after surgery. The number of white blood cells (WBCs) and neutrophils in peripheral blood of the patients was measured. 
Results The rScO2 in the non-hypoxia group and the hypoxia group firstly decreased and then increased with the increase of time, and there were significant differences in interaction between groups, time points, and time points between groups (P＜0.05). There were no significant differences in MMSE, MoCA scores, plasma NSE, S100-β, TNF-α, IL-6 levels, peripheral blood WBC and neutrophil counts between the two groups before surgery (P＞0.05). The scores of MMSE and MoCA in the hypoxia group were significantly lower than those in the non-hypoxia group (P＜0.05). Spearman correlation analysis showed that rScO2 level during anesthesia was positively correlated with MMSE and MoCA scores. The levels of plasma NSE, S100-β, TNF-α, IL-6 as well as peripheral blood WBC and neutrophil counts in the hypoxia group were significantly higher than those in the non-hypoxia group (P＜0.05). 
Conclusion Insufficient cerebral oxygen saturation during perioperative anesthesia can promote postoperative cognitive dysfunction and immune dysfunction in elderly patients undergoing hip surgery. This study provides a reference for the control of cerebral oxygen saturation during perioperative anesthesia in elderly patients undergoing hip surgery. 

Key words: oxygen saturation, perioperative anesthesia, elderly