All children from age 0 to18 years who underwent surgery for CHD at our pediatric cardiac center between April 1, 2011, and September 30, 2019, were included. Only the first operation of the index admission was included. Patients who underwent isolated patent ductus ligation were excluded, as the length of stay and mortality in those patients were dependent on other factors not related to the cardiac pathology. We have also excluded patients with significant prematurity (< 28 weeks of gestation) and extreme small weight. Those patients may indeed be at higher risk due to technical and technological limitations of the current state of surgical and technological methods and tools.
The data was harvested from our prospective electronic database. The primary outcome of interest was operative mortality defined as death in the index admission at any time. The secondary outcomes were prolonged hospital stay more than 14 days and length of stay in hospital. Age and weight at the time of operation were the main predictors of interest. Other variables included to account for heterogeneity were gender, preoperative hospital stay, redo operation, cardio-pulmonary bypass (CPB) time, aortic cross-clamp time, deep hypothermic circulatory arrest (DHCA) time, and the Risk Adjustment in Congenital Cardiac Surgery (RACHS) classification, version 1 [6]. Prematurity, birth weight, and the presence of extra-cardiac or chromosomal anomalies were not included as these variables were not reliably recorded in the prospective database. In patients who underwent surgery without CPB, CPB time was recorded as zero. Similarly, if the patient did not require aortic clamping or DHCA, the respective time variable was recorded as zero.
The surgical methods may vary as two surgeons contributed to the data; however, 98% of the operations were performed by a single surgeon (the author). In general, patients who required CPB were placed on bypass by aortic and bicaval or atrial cannulation as needed. Before June 2015, cold intermittent antegrade blood cardioplegia was used, and cold antegrade DelNido cardioplegia was used thereafter [7]. If DHCA was needed, it was established at 18°. Antegrade cerebral perfusion was applied at 30 ml/kg/min. Delayed sternal closure was used as needed.
All patients after September 2016 were cared for in a dedicated pediatric cardiac intensive care unit. Before that date, patients were cared for in a general pediatric intensive care unit.
Statistical analysis
The data which was imported from the prospective electronic database into the R statistical system with the following packages was used for analysis: rms, Hmisc, and survival [8,9,10,11]. Categorical variables were described as frequency and percent. Continuous variables were described as median and upper and lower quartiles. For descriptive purposes, the data was divided into neonates, defined as age less than 28 days, and post-neonatal children age 29 days to 18 years. For statistical modeling, age was used as a continuous variable and the neonatal status was included as a separate variable as appropriate. The normality and linearity of continuous variables were tested, and the appropriate transformation was used. A restricted cubic spline function was used where non-linear association was identified. For the primary outcome of in-hospital mortality, logistic linear regression was used. For the postoperative length of stay, the analysis was restricted to survivors and a generalized linear regression model with Poisson distribution was used due to the skewed nature of the length of stay (Fig. 1). This model was used to graphically study the association between length of stay and the predictive variables. For ease of interpretation and clinical relevance, prolonged hospital stay was defined as a total postoperative length of stay of greater than 14 days. A logistic regression model was used to study factors associated with a prolonged hospital stay. A p value of 0.05 was accepted as significant.
The study was approved by the local Hospital board of research ethics.
