The goal of this clinical trial is to compare the permeability of blood-brain barrier between the intravenous anesthesia group and the inhalation gas anesthesia group in the elderly patients undergoing surgery. The main questions it aims to answer are:

• [Is the permeability of blood-brain barrier between the intravenous anesthesia group and the inhalation gas anesthesia group in the elderly patients different?]

• [Is the incidence of postoperative cognitive dysfunction between the intravenous anesthesia group and the inhalation gas anesthesia group different?] Participants will be anesthetized with different categories of anesthetics.

  • Intravenous anesthetics
  • Inhalation gas anesthetics

This clinical trial targets patients aged 60 years or older with American Society of Anesthesiologists physical status (ASA) 1 to 3 who undergo surgery under general anesthesia at our hospital. Before entering the operating room, patients are randomly assigned to the intravenous anesthesia group and the inhalation gas anesthesia group. The intravenous anesthesia group uses propofol for anesthesia, and the inhalation gas anesthesia group uses sevoflurane. A 3 mL blood sample is collected four times: before surgery, at the end of surgery, 4 hours after surgery, and 1st day after surgery. All blood samples will be immediately transferred to the department of Laboratory medicine and stored at -80 degree. Pre-scheduled tests to determine the brain-blood barrier permeability and inflammatory cytokines will be conducted after the recruitment of all samples. In addition, for patients scheduled to be transferred to the intensive care unit (ICU) after surgery among the study subjects, a 3 mL of cerebrospinal fluid sample is collected two times: before surgery, and at the end of surgery. The same preservation protocol will be applied to the cerebrospinal fluid samples. All study subjects will be monitored for postoperative delirium daily for up to 7 days after surgery or until discharge. Cognitive function is assessed using telephone version of the Montreal Cognitive Assessment (T-MOCA) before surgery and 3 months after surgery.

Inclusion Criteria:

• age equal to or older than 60
• american Society of Anesthesiologists (ASA) grade I to III
• general anesthesia longer than 2 hours

Exclusion Criteria:

• history of dementia
• history of schizophrenia, epilepsy, or Parkinson's disease
• history of stroke or craniectomy
• patient denial

Individual participant data that underlies the results of this study will be made available upon reasonable request, after deidentification (text, tables, figures, and appendices).

Beginning 3 months and ending 5 years following article publication

Data will be available to researchers who provide a methodologically sound proposal to the corresponding author of the article. To gain access, data requestors will need to sign a data access agreement.

This study is a double-blinded randomized controlled trial. The group assignment is conducted by the pre-generated random number table. The participant, investigator and the outcome assessor are blinded to the group assignment.