The Perioperative Risks of Adverse Events After Cardiac Surgery: a Retrospective Study

Cardiac surgeries under cardiopulmonary bypass (CPB) are a major treatment for heart valve disease and coronary artery disease, and over 1-1.25 million such procedures are performed annually worldwide. These procedures are associated with mortality rates of 0.9-4.0% and morbidity rates up to 45.9%.The analysis of perioperative risk factors for these adverse events can provide beneficial help for improving the prognosis of patients undergoing cardiac surgery.Patients undergoing cardiac surgery under CPB at West China Hospital of Sichuan University between January 1, 2011 and June 30, 2017 and the Second Affiliated Hospital in the School of Medicine of Zhejiang University between September 1, 2013 and June 30, 2017 will be enrolled,and demographic data, preoperative and intraoperative data, and postoperative adverse events were collected.Independent perioperative risk factors of death, organ injury and other adverse events in cardiac surgery patients under CPB were studied by univariate and multivariate Logistic regression analysis to provide evidence for prevention and intervention in clinic.

1. Anesthesia management The standard procedures of anesthesia and CPB in the two institutions were applied as described (49, 50). Briefly, anesthesia was induced with midazolam, sufentanil, muscle relaxant and/or etomidate, and maintained by continuous remifentanil infusion and sevoflurane inhalation, combined with intermittent muscle relaxant and sufentanil intravenous injection.
2. CPB management CPB involved a roll pump, a membrane oxygenator, a filter and connecting tubes and was primed with colloid solution of 1000 mL and 500 ml crystalline liquid. During CPB, blood flow was at 2.0-2.4 L/m2/min to maintain mean arterial pressure at 50-80 mmHg. Cold 4:1 blood cardioplegia was used for heart arrest. During CPB, nasopharyngeal temperature was maintained at 32-340C during these procedures and moderate hemodilution was used. All patients received an initial heparin dose of 375 U/kg to achieve systemic anticoagulation, and additional heparin was intermittently injected to maintain activated clotting time longer than 480 s during CPB. After weaning from CPB, heparin was neutralized with protamine in a 1:1 ratio based on the initial heparin dose.
3. Data Collection Form (DCF) In order to minimize the role of potential confounders on adverse outcomes, we will do a systematic search for "risk factor, predictor, adverse outcome, mortality, morbidity, complications, and cardiac surgery" using EMBASE, Cochrane and PubMed databases from Jan 1, 2000 to Dec 31, 2015. All the perioperative potential risk factors mentioned in these studies will be on the DCF.
4. Data collection All variables in the DCF will be retrieved from the Hospital Electronic Medical Record System and medical records. If information on a certain variable cannot be acquired, it will be recorded as ☒. For example, there may be no record of the hemoglobin level on the fifth day after surgery, so we will write ☒ in brackets on the fifth day hemoglobin value.

   After the data collection is finished, the investigators will sign their names on the first page of the DCF.
5. Data Checking Two supervisors will check data promptly. If data are doubted, they will send their questions to the first investigator. According to the Schedule of Events, an "X" will be recorded after the data are confirmed to be correct. Once the whole DCF is completed, the supervisors sign their names and send the DCF to the statisticians.
6. Data Input Data will be input by one statistician using EpiDate3.0 (Odense, Denmark, http://www.epidata.dk/), and another independent statistician will confirm this procedure. Then the CRFs will be stored sequentially.
7. Quality control and quality assurance Diagnosis must be performed strictly according to pre-established definitions. All data in the DCF will be inspected promptly and correctly in order to guarantee reliability. All procedures in this study will be performed by two independent researchers.
8. Statistical analysis Data analysis will be carried out by experienced biostatisticians.Categorical variables are expressed as frequencies (percentages), and compared between patient groups using the chi-squared or Fisher's exact tests. Shapiro-Wilk tests are used to determine the distribution of continuous variables. Normally distributed data are reported as mean ± standard deviation (SD), and compared between groups using one-way ANOVA test. Skewed data are expressed as median \[interquartile range (IQR)\] and compared between groups using Wilcoxon rank sum tests. The incidence of complications between groups will be performed with the chi-squared test or Fisher's exact tests. Logistic regression analysis will be performed to evaluate risk factors for complications.

Eligibility Criteria:
Inclusion Criteria:

1. Age ≥ 18 years
2. Valve replacement or/and coronary artery bypass graft surgery under CPB

Exclusion Criteria:

1. Combined surgery involving ascending aortic replacement surgery or cardiac tumor resection
2. Emergency surgery (defined as surgery performed before the end of the same workday as admission);
3. Died on the operating table, or could not be weaned off CPB;
4. Medical data missing