The aim of this study will be to evaluate vancomycin and cefoxitin blood levels during elective cardiopulmonary bypass (CPB) surgery in four pre-determined pediatric strata: neonates, infants, children weighting less than 40 kg and children weighting more than 40 kg.

Few data are available in current literature about pharmacokinetics (PK) of antibiotics administered as surgical prophylaxis to children scheduled for cardiac surgery with CPB. In particular, vancomycin PK during CPB has been studied only in small case series, whereas no specific study has been conducted, so far, in the specific setting of children receiving cefoxitin during CPB.

CPB affects patients' volemia and drugs PK is eventually altered. On the other side during and after surgery for heart defects, many risk factors may decrease renal and hepatic clearance, including altered renal perfusion, use of vasoactive agents, and use of concomitant nephrotoxic medications.

Primary Objective of the study will be:

• To study the pharmacokinetic profile of vancomycin and cefoxitin administered, as antibiotic prophylaxis to children undergoing elective CPB.

Secondary Objectives will be:

• To evaluate if a significant difference in blood levels will occur in the four predetermined patients' categories.
• To evaluate the role of hemodilution during CPB on studied antibiotics' serum concentration
• To verify the incidence of post-operative infections in the studied population with particular attention to sensitive bacteria
• To evaluate the impact of ultrafiltration in studied antibiotics' clearance
• To evaluate safety of the administered antibiotics This is a prospective monocentric, open label, not controlled clinical trial.

Inclusion Criteria:

1. Elective cardiac surgery schedule with the planned application of CPB
2. Parents of neonates, or their legal representative, able to consent and comply with protocol requirements.

Exclusion Criteria:

1. Urgent or emergent surgery
2. Antibiotic therapy (any) administered before surgery
3. Patients receiving, before surgery, any other ofr of extracorporeal treatment (i.e extracorporeal membrane oxygenation, continuous renal replacement therapy)
4. Previous renal or hepatic dysfunction requiring need for antibiotic posology modification.
5. Surgery requiring antibiotic prophylaxis with different drug combinations (i.e vancomycin and gentamycin)
6. extremely low birth weight neonates.

Children undergoing cardiac surgery requiring cardiopulmonary bypass and antibiotic prophylaxis with vancomycin and cefoxitin