Abstract: Objective To explore the relationship between post-operative cognitive dysfunction (POCD) and the dose of general anesthetic propofol in the elderly. Methods 96 patients undergoing thoracic operation were selected and randomly assigned to high bispectral index (BIS) value (HIBIS 50~60, low dose of propofol) and low BIS value (LOBIS 30~40, high dose of propofol). Remifentanyl was infused in both group with the dose of 0.2 μg/kg &#8901; min. The dose of propofol was adjusted with target-controlled infuse (TCI) according to the different ranges of BIS value in different groups. The mean arterial pressure was maintained in a certain level. The dose of propofol was recorded during the operation. Cognitive function was assessed by 12 neurophysiological tests recommended by International Study of Post Operative Cognitive Dysfunction (ISPOCD) on the day before operation and the 7th day after operation. And the D-value of the tests before and after the operation was calculated. Results 47 cases in the HIBIS group and 45 cases in the LOBIS group were included in the end. The incidences of POCD were 6.3%(3 cases) and 2.2%(1 case) respectively in HIBIS group and LOBIS group according to Mini-Mental State Examination (MMSE) score, and 12.8% (6 cases) and 6.7% (3 cases) according to combination judgment, but there was no significantly difference (P>0.05). The post-operative scores were significantly lower than pre-operative scores (P<0.01) on Hopkins Verbal Learning Test-Revised (HVLT-R) in HIBIS group. and HVLT-R dealyed Recall Test, Hvlt- r Recognition Discrimination Index and Verbal Fluency Test in both groups (P<0.01), including verbal and words. The D-values of 4 neurophysiological tests were higher in the HIBIS group than in the LOBIS group. The dose of propofol was significantly lower in the HIBIS group than in the LOBIS group (P<0.01). Conclusion As the same level of analgisia and hemodynamics, the more the dose of propofol is, the better the post-operative function is in the elderly.

Key words: post-operative cognitive dysfunction, propofol, dose, elderly