90 consecutive patients scheduled for mitral valve replacement or aortic valve replacement under moderate hypothermic CPB gave written informed consent and were enrolled in this study.

In the operating room, patients received routine monitoring. Systemic arterial blood pressure was measured via radial artery catheterization. After induction of anesthesia, a central venous catheter was inserted for monitoring central venous pressure (CVP) and fluid management. Baseline readings of hemodynamics were taken every 5 to 10 min after radial artery cannulation was completed.

Induction of anesthesia was performed with target-controlled infusion of propofol. All patients received an infused scheme of several steps that started from a target plasma concentration (Cp) of 0.5 mg/mL that was increased stepwise by 0.5 mg/mL until the patient fell asleep and maintain BIS at 40-60. The interval between each step was 3 min. After loss of consciousness, cisatracurium (0.2 mg/kg) and fentanyl (10-15 mg/kg) were infused in all groups. The trachea was intubated and the lungs were ventilated with oxygenenriched air (fraction of inspired oxygen 0.6) to an end-tidal carbon dioxide partial pressure of 35 to 45 mmHg. The propofol target Cp was adjusted according to BIS. Intermittent IV boluses of fentanyl (10-15 mg/kg) were administered according to blood pressure and heart rate (HR) at the following time points: before the skin incision, before the onset of CPB, and after separation from CPB, for a total dose of 40 to 50 mg/kg. All patients received infusion of cisatracurium at 0.1 mg/kg/h throughout the surgery.

Surgery was conducted on all patients via a standard median sternotomy approach. Porcine heparin was administered at a dose of 300 IU/kg and supplemented when required to maintain an activated coagulation time of at least 480 s during CPB. Heparin was neutralized with 1 mg of protamine/100 IU of heparin administered after separation from CPB. Body temperature was cooled to 30℃-32℃ on CPB (moderate hypothermia). All patients were treated with an intermittent antegrade infusion of cooled high-potassium blood cardioplegia during continuous aortic cross-clamping (ACC) using a nonpulsatile flow rate of 1.8 to 2.8 L/min/m2 and a membrane oxygenator to keep the mixed venous saturation at more than 75% during CPB. Phenylephrine (bolus, 20-100 mg) or epinephrine (0.1 mg/kg/min) or both were used to restore systemic vascular resistance, and MAP was maintained at a target range of 60 to 80 mmHg. Patients were warmed to a bladder temperature of 36.5℃ before separation from CPB, with the highest temperature not exceeding 37℃. Blood remaining in the CPB circuit and from the surgical field was collected in a cell-saving device. After centrifuging and washing, it was infused to the patient within 4 hours after CPB. Hematocrit was maintained at more than 25%, with the addition of blood as necessary. Insulin therapy was initiated during the surgery to treat serum blood glucose levels higher than 150 mg/dL. Hemodynamic (pre- or post-CPB) management aimed to keep MAP at 60 to 100 mmHg. Hypertension was treated with an additional bolus dose of fentanyl (0.2-0.3 mg) or with nitroglycerin (0.1-0.5 mg/kg/min or with both). Hypotension was treated with fluid intake (including crystalloids, colloids, and blood products) or vasoactive drug administration (phenylephrine IV, 20-100 mg or concomitant use of epinephrine, o 0.1 mg/min). The vasoactive drug dosage, fluid intake, and output (urine and blood loss) were recorded when the surgery was finished.

As the surgeons began to close the skin, a 0.08 mg/kg bolus dose of midazolam was given intravenously and the infusion of propofol was stopped. After the surgery, all patients were admitted to the surgical intensive care unit (ICU). The patients were extubated when they were able to sustain adequate spontaneous respiration and required minimal oxygen support, as reflected by normal arterial blood gas levels. The patients then were discharged from the ICU when they were hemodynamically stable with blood gas variables within the normal range and when they did not need inotropic or oxygen support. The tracheal extubation time and the length of the ICU stay were recorded. For all patients, hemodynamic measurements were made and recorded at the following times: Before induction of anesthesia, before skin incision, after sternotomy, at the cessation of CPB (CPB-cessation), and at 1 (Post-CPB 1 h), 2 (Post-CPB 2 h), and 4 (Post-CPB 4 h) hours after CPB. At pre-incision, CPB-cessation, Post-CPB 2 h, and PostCPB 4 h, the radial arterial blood was sampled for blood gas analysis, as well as blood glucose and lactic acid analyses. Before induction of anesthesia, at the end of the operation, 7 days after the operation, peripheral venous blood was sampled to measure IL-1B, IL-18 and NLRP3 inflammatory protein expression in peripheral blood monocytes.

Neuropsychological tests were administrated one day before surgery and seven days after surgery for all patients in a quiet place of the general wards. Neuropsychological tests included seven tests with nine subscales. Specific tests used were as follows: MMSE, Trail Making (A/B), Stroop Color- Word, Rey Auditory Verbal Learning Test, WAIS Digit Symbol Substitution Test, WAIS Digit Span, Verbal fluency test. Two psychologists carried out these tests. During the study phase, testing was performed and scored in a standardized manner in order to minimize inter-examiner difference. Repeat assessments for each patient were conducted by the same examiner. Parallel forms of tests were used in a randomized manner in sequential testing in order to minimize practice effect. Performance on each test was compared with cognitive test data of control subjects. A low test score was defined when the score was ≥ 2 SD lower than control subjects. For tests in which a higher score indicates decrement in performance, a score ≥ 2 SD higher than control subjects was considered as "low test score." Patients were defined as having preoperative cognitive impairment if they had low test scores on two or more tests.

For patients, preoperative scores were compared with postoperative test results, subtracted the average practice effect from these changes, and then divided the result by the control-subject SD to obtain a Z score for each test. The test results were adjusted so that a positive Z score indicated deterioration from the baseline test. The Z scores of all tests in an individual patient were then summarized and divided by the SD for this sum of Z scores in the control subjects, creating a combined Z score. A patient was defined as having POCD when two Z scores in individual tests or the combined Z score were 1.96 or more.

Statistical analysis A continuous outcome was expressed as the mean ± SE, while a categorical outcome was expressed as percentages or frequencies. Differences in continuous and categorical outcomes were tested using the one-way analysis of variance and Chi square analysis, respectively. The unpaired Student t test, paired T test, analysis of variance and Pearson correlation analysis were performed on normally distributed data. Case-control differences in nominal data were evaluated with the Chi square test. Multivariate Cox regression analysis was done for predictors of adverse events. The NLRP3 level, IL-1B, IL-18 and neurobehavioral scores were compared using ROC curves. Kaplan-Meier curves were used for correlation with POCD. All statistical analyses were performed with SPSS 21.0 (IBM Inc.) and P \< 0.05 was considered signifcant.