Table 1.

Inclusion and exclusion criteria for patients in this study

Inclusion criteria	Exclusion criteria
•Patients scheduled to undergo elective gastrointestinal tumor resection via laparotomy with expected duration >2 h	•With cognitive impairment characterized by MMSE <24
•ASA class 2 and 3	•History of dementia
•Ages ≥60 years	•Chronic lung disease
•Informed consent to participate in the study signed by patients	•Allergy against one of the drugs administered during the study
	•BMI >24.5 kg/m2
	•Any disease of the central nervous system
	•History of surgery within 6 weeks
	•Mechanical ventilation within 1 month
	•Low patient compliance
	•Inability to read, or serious hearing or vision loss
	•Poor comprehension of the Chinese language
	•Recent cerebrovascular accident (<6 months)

ASA, American Society of Anesthesiologists; MMSE, Mini-Mental State Examination; BMI, Body Mass Index.