Abstract: Objective To explore the changes of nonlinear dynamic parameters of electroencephalogram (EEG) before and after operation in the elderly patients undergoing elective general anesthesia, and to investigate its role in the study of memory capacity. Methods The elderly patients undergoing elective non-cardiac surgery under general anesthesia were randomly divided into group with anesthesia depth monitoring (group A) and group without anesthesia depth monitoring (group N). The EEG signals of the two groups of patients before and after operation in rest state and memory task state were collected, and the nonlinear analysis index including correlation dimension and approximate entropy of the two groups of patients were compared and analyzed. The memory and execution screening scale (MES) was used to evaluate the memory ability of patients before and after operation. Results One day before operation, there was no significant difference in correlation dimension and approximate entropy between the two groups in rest state and memory task state (P>0.05); On the first day after surgery, the correlation dimension and approximate entropy decreased in both groups in both states, but the indexes in group A were higher than those in group N, and the difference was statistically significant (P<0.05). There was no significant difference in MES score between the two groups 1 day before operation (P>0.05). On the first day after operation, the MES score in both groups decreased (P<0.05), but the score of group A was higher than that of group N (P<0.05). Conclusions For elderly patients, there may be a decrease in EEG nonlinear analysis index and short-term memory ability after general anesthesia surgery, especially in patients without intraoperative anesthesia depth monitoring.

Key words: memory, electroencephalogram, nonlinear analysis, aged