ICU delirium are assessed by clinical nurses twice every day. Delirious patients are matched with patients according to their disease, gender and age range(±3 years). Stool samples for gene sequencing are collected. Gut barrier function are studied with several serum biomarkers (endotoxin, etc.). Ecological analyses, regression models and mediation equation will be performed.

ICU delirium are assessed by clinical nurses twice every day using Confusion Assessment Method for the ICU (CAM-ICU). Delirious patients are matched with patients according to their disease, gender and age range(±3 years). Stool samples for gene sequencing are collected within 24 hours after surgeries. Gut barrier function are studied with several serum biomarkers (endotoxin, etc.). Ecological analyses, regression models and mediation equation will be performed.

Inclusion Criteria:

• to have had heart valve surgery or coronary artery bypass grafting (CABG)
• to have no planned transfer to another ward or hospital within 24 hours after surgery
• to have no preoperative cognitive impairment and can speak and read Chinese
• more than 18 years old

Exclusion Criteria:

• to have a hearing or visual impairment that could impact delirium assessment
• to have a history of alcohol or drug abuse
• to have a preoperative intestinal irritation syndrome or history of gastrointestinal disease
• to have received antibiotics or probiotics within 28 days before admission
• to have a life expectancy less than 24 hours
• to have an experience of ICU hospitalization, mechanical ventilation in the past 30 days
• to have a cardiac surgery or hypoxic brain injury in the past 3 months.

Patients after cardiac surgery and admitted to CSICU are recruited.