Background
 Postoperative delirium (POD) is an adverse complication that often occurs in patients undergoing vascular surgery. Endovascular repair of aortic aneurysm (EVAR) decreased the incidence of POD compared to open aortic aneurysm repair. Patients undergoing EVAR also exposed hypothermia during EVAR procedure because it is difficult to prevent heat loss from the body surface. We retrospectively investigated the risk factors of POD after EVAR to prove our hypothesis, the hypothermia during the surgery caused POD in patients undergoing EVAR.

Method
 After approval of Institutional Ethics committee, we conducted a retrospective review of all patients who underwent EVAR at our hospital from July 2015 to July 2017. Body temperatures (after anaesthesia induction, lowest, emergence from anaesthesia) and established risk factors were enrolled in multivariate logistic regression models. The POD was diagnosed using the Confusion Assessment Method for the ICU.

Results
 One hundred forty-one patients were enrolled. POD was present in 43 (30.5%) patients. Multivariate logistic regression identified two risk factors for POD: body temperature after induction of general anaesthesia (odds ration (OR)=0.261, 95% confidence interval (CI)=0.100-0.684) and pre-existing psychiatric disease (OR=11.627, 95%CI=1.171-115.438).

Discussion
 Our results showed that hypothermia at the end of general anaesthesia induction was associated to the POD. Twenty-four patients showed hypothermia (body temperature <36℃) at that time point. However, the lowest temperature during the anaesthesia or the body temperature at the emergence from general anaesthesia was not the risk factor for the POD in our result. Even though we did not measure the body temperature before the induction of general anaesthesia, the rapid dropping of the body temperature in the beginning of general anaesthesia seemed to be the risk factor for the POD. As our investigation is retrospective, the POD may be under-diagnosed in the ICU.

Conclusion
 The hypothermia during general anaesthesia was associated with postoperative delirium in patients who had undergone endovascular repair of aortic aneurysm. Prospective study should be conducted to show the efficacy of intraoperative body temperature maintenance to prevent POD.

03 / Hypothermia during general anaesthesia was associated with the postoperative delirium after endovascular repair of aortic aneurysm