This is a prospective cohort study aiming to construct a prediction model for postoperative cognitive dysfunction (POCD) in elderly cardiac patients. We plan to enroll elderly patients aged ≥65 years undergoing cardiac surgery. Peripheral blood samples and functional magnetic resonance imaging (fMRI) data will be collected at baseline and key time points post-surgery. The primary objectives are to identify novel peripheral blood protein biomarkers for POCD, explore the correlation between fMRI characteristics and POCD, and establish a reliable early prediction model to improve perioperative management and reduce the incidence of POCD in elderly cardiac surgical patients.

Inclusion Criteria:

• Subjects aged ≥65 years, with no gender restriction. Patients meet the indications for cardiac surgery (cardiac surgery with cardiopulmonary bypass).

Normal liver and renal function during the screening period. No evidence of active infection during the screening period. Able to cooperate in answering questions related to the MMSE and MoCA cognitive scales during the screening period.

Have signed the informed consent form.

Exclusion Criteria:

• The investigator considers that the subject has conditions that may interfere with the study results.

Subjects with evidence of active liver disease (liver function test results: ALT or AST ≥ 2 times the upper limit of normal [ULN]) or chronic active hepatitis B or C within 1 month.

Active systemic infection requiring antibacterial drugs within 1 week before surgery.

Preoperative low MMSE score (illiterate: <17 points; primary school education: <20 points; middle school education or above: <24 points).

Patients with one or more of the following diseases:

Classified as obese (body mass index ≥ 30 kg/m²); Uncontrolled hypertension (defined as systolic blood pressure ≥ 180 mmHg or diastolic blood pressure ≥ 100 mmHg); History of organ transplantation, including corneal transplantation; Any clinically significant uncontrolled respiratory disease, including but not limited to chronic obstructive pulmonary disease, asthma, bronchiectasis, or pleural effusion; Previously diagnosed or suspected demyelinating diseases, including multiple sclerosis, Guillain-Barré syndrome, etc.; Use of any glucocorticoids or immunosuppressive agents; Any disease that significantly affects the nervous system. Participation in other clinical trials.

This is a prospective cohort study enrolling elderly patients aged ≥65 years, regardless of gender, who are scheduled for elective cardiac surgery with cardiopulmonary bypass. Eligible subjects must have normal liver and renal function, no evidence of active infection during screening, and be able to cooperate with MMSE and MoCA cognitive assessments. Patients with conditions that may interfere with study results, active liver disease, preoperative severe cognitive impairment, uncontrolled comorbidities, organ transplantation history, demyelinating diseases, or participation in other clinical trials will be excluded. All participants provide written informed consent.