Objective: One-lung ventilation（OLV） is considered to be one of the risk factors for postoperative cognitive dysfunction（POCD）. However

it is unknown whether there is time effect between OLV and POCD. Therefore

this study aims to explore the correlation between duration of OLV and POCD in elderly patients undergoing a thoracic surgery. Methods: A total of 198 elderly patients who were scheduled to undergo a thoracic surgery in the Affiliated Traditional Chinese Medicine Hospital of Southwest Medical University from October 2018 to October2019 were selected. According to the intraoperative duration of OLV

the patients were divided into four groups:group A1（duration of OLV ≤ 1 h）

group A2（1 h < duration of OLV ≤ 2 h）

group A3（2 h < duration of OLV ≤ 3 h）

and group A4（duration of OLV > 3 h）. At 1 day before surgery and 7 days after surgery

the cognitive function of all the patients was assessed using cognitive assessment tools including Mini-Mental State Examination（MMSE）

Digit Span and Symbol Test（DSST）

Trail Making Test A（TMTA）

vocabulary fluency test（VFT）

and word recognition test（WRT）. The Z score was calculated to assess the incidence of POCD in each group

and indices of significant differences were analyzed to evaluate their correlation with the duration of OLV. Results: A total of 164 patients（37 in group A1

51 in group A2

53 in group A3

and 23 in group A4） completed the study. There were no significant differences in preoperative general information and cognitive function between the four groups（P > 0.05）. At 7 days after surgery

POCD occurred in 51 patients（31.10%）

including 4（10.81%） in group A1

11（21.57%） in group A2

23（43.40%） in group A3

and 13（56.52%） in group A4. There were significant differences in the incidence of POCD between the four groups（P < 0.05）. The incidence of POCD in groups A3 and A4 was significantly higher than that in groups A1 and A2（P < 0.05）. In addition

at 7 days after surgery

groups A3 and A4 had significantly reduced MMSE

DSST

and VFT scores

as compared with groups A1 and A2（P < 0.05）. An analysis of Pearson correlation between the above four indices and the duration of OLT indicated that MMSE and VFT scores were negatively correlated with the duration of OLV（P < 0.05）. Conclusion: Intraoperative OLV is a risk factor for POCD in patients undergoing a thoracic surgery; the longer the duration of OLV

the higher the incidence of POCD.