Abstract: To investigate the influence of inhaled anesthesia on bispectral index (BIS) of elderly patients with cognitive decline at loss of consciousness and regain of consciousness, and on deepening of sedation. Methods: The patients aged more than 65 years undergoing elective operations from January 2012 to September 2012 were recruited, then 60 cognitive intact patients and 60 cognitive decline patients were screened by mini-mental state examinations. Inhaled anesthesia was administered using sevoflurane. BIS’s of the two groups at loss of consciousness and regain of consciousness, and during endtidal concentration of sevoflurane (C_ETSev) changing from 0.7% to 2.8% were recorded. The data were compared with independent-samples t test and repeated-measures general linear model of ANOVA. Results: In the study, 117 patients finshed the investigation, The BIS’s of the cognitive decline group at loss of consciousness were significantly higher than those of the cognitive intact group (P<0.01). There were no significant differences at regain of consciousness between the two groups (P>0.05). The BIS’s of the cognitive decline group during C_ETSev changing from 0.7% to 2.8% were significantly lower than those of the cognitive intact group (P<0.05). The BIS’s of the cognitive decline group at C_ETSev 0.7%, 1.05%, 1.4% and 1.75% were significantly lower than those of the cognitive intact group (P<0.05), but there were no significant differences at C_ETSev 2.1%, 2.45% and 2.8% between the two groups (P>0.05). Conclusion: During inhaled anesthesia, the BIS of the elderly patients with cognitive decline at loss of consciousness is higher than that of the patients with cognitive intact, The BIS of elderly patients with cognitive decline on deepening of anesthesia is lower than that of the patients with cognitive intact, especially during light anesthesia, and its mechanisms may attribute to cognitive decline related neurodegeneration and neurotransmitter system dysfunction.

Key words: Anesthesia, inhalation, Cognition disorders, Aged