Rationale: During cardiac surgery, neonates are at high risk of cerebral damage: 36-78% will have new cerebral lesions after surgery. Adequate cerebral perfusion (CBF) is mandatory to prevent postoperative brain damage and neurobehavioral outcomes. For CBF, the systemic blood pressure should be managed above the brain's critical closing pressure (CrCP), and preferably above the lower limit of autoregulation (LLA), if intact.

Objective: The investigators aim to study the patient specific threshold for arterial blood pressure to maintain adequate cerebral perfusion (CBFV) in the perioperative setting and the association between perioperative abnormalities with postoperative brain damage and neurobehavioral outcomes.

Study design: In a prospective observational cohort study bilateral cerebral blood flow velocity (CBFV) measurements are performed with transcranial doppler (TCD), together with invasive arterial blood pressure (iABP) measurements in the perioperative period.

Study population: Neonates (semi-) electively scheduled for major cardiac- and non cardiac surgery.

Main study parameters/endpoints: Main study endpoint is the Critical Closing Pressure (CrCP) within and between subjects. Furthermore, we evaluate the association with new white matter injury (WMI) on the postoperative MRI.

Nature and extent of the burden and risks associated with participation, benefit and group relatedness: Anticipated risks caused by TCD monitoring in neonates are considered negligible when monitoring is executed according to the BMUS guidelines and ALARA principle. Each time energy is converted from one form to another, part of it is inevitably converted to heat. Theoretically, if at all, the maximum temperature rise will happen at the skin- temporal bone side, where the monitoring probes are placed. A maximal thermal index (TI) of 0.7 is allowed, this corresponds with 0.7 o C temperature rise.

Patients might not benefit from participation in this study as the TCD measurements are only visible and available to the TCD operator, and we do not yet know how the results could possibly influence the procedure. However, in the unlikely situation where cerebral perfusion is severely compromised for a longer period of time or in case of occurrence of large air emboli, improper cannulation or cross clamping the cardiac team will be notified. Therefore, a neonate might benefit from participation.

Inclusion Criteria:

• Term infant aged < 42 days / Preterm born > 32 weeks and with a corrected age < 42 days
• (Semi-) elective cardiac of major non-cardiac surgery
• Routine placement of an arterial cannula for invasive blood pressure monitoring.

Exclusion Criteria:

• Grade III-IV intracranial hemorrhage.
• Emergency surgery or semi-elective surgery performed out of hours.
• Informed consent from the parents is not obtained.

Eligible patients are term infants within 42 days (6 weeks) after birth, or infants prematurely born (with a gestational age >32 weeks) at a corrected age of <42 days, who are scheduled for cardiac or non-cardiac surgery.