The aim of this study is to conduct a prospective, single-center randomized controlled study to investigate the changes of plasma NFL concentration in patients undergoing laparoscopic surgery with mild hypercapnia, and further explore its impact on the central nervous system.

Plasma NFL concentrations were measured preoperatively and 1 day postoperatively.

Secondary endpoints:CAM (Confusion Assessment Method) is conducted to check the subjects' baseline cognitive function preoperative day and 1 day postoperatively to assess whether delirium occurs.

Inclusion Criteria:

• age over 60 years
• duration of pneumoperitoneum greater than 60 minutes
• American Society of Anesthesiology (ASA) status Ⅱ-Ⅲ
• undergoing laparoscopic surgery under general anesthesia with endotracheal intubation

Exclusion Criteria:

• history of mental or neurological disorders
• preoperative use of antipsychotic drugs
• American Society of Anesthesiology (ASA) status Ⅳ
• severe abnormalities in heart, lung, liver, kidney, and coagulation function
• Intracranial space-occupying lesions or major cerebrovascular diseases (such as carotid atherosclerosis and cerebral aneurysm)
• Severe hypertension or hypotension
• Severe metabolic acidosis or hypercapnic respiratory failure before surgery

Single