In pediatric cardiac surgery, transfusion requirements are associated with age, development status, pathology, type of surgical intervention and extracorporeal bypass. In adult cardiac surgery, reinterventions (redo)are clearly linked to higher transfusion rates. The investigators want to study if this association is also true in pediatric cardiac surgery.

Whereas in adult cardiac surgery, redo-interventions are clearly linked to a higher transfusion rate, this is not really known in paediatric cardiac surgery. In this retrospective study, the investigators will analyse our database for paediatric cardiac surgery patients aged 0-16 years and operated between 2002 and 2017. Patients with a single cardiac surgery will be compared to patients with a second cardiac operation under extracorporeal bypass. The investigators will test the variables for normal distribution using a Shapiro-Wilk test. Non normal distributed variables will be compared by a non-parametric test (Mann Whitney U), frequency analysis will be done by a Chi-Square test. A univariate analysis will determine predicting factors for transfusion. Factors with a P value < 0.1 will be analysed by a multivariate analysis to determine independent factors for transfusion. Odds with 95% confidence intervals will be calculated. A P value < 0.05 will be considered statistically significant.

Inclusion Criteria:

• Patients between 0 and 16 years
• Cardiac surgery with cardiopulmonary bypass

Exclusion Criteria:

• Jehova's witness

All patients between 0 and 16 years undergoing cardiac surgery with cardiopulmonary bypass in our institution. We will exclude Jehovah's witness patient as they refuse a transfusion.