During mechanical ventilation (MV) hypoxemic or hyperoxemic events should be carefully monitored and a quick response should be provided by the caregiver at the bedside. Pediatric mechanical ventilation consensus conference (PEMVECC) guidelines suggest to measure SpO2 in all ventilated children and furthermore to measure partial arterial oxygen pressure (PaO2) in moderate-to-severe disease. There were no predefined upper and lower limits for oxygenation in pediatric guidelines, however, Pediatric acute lung injury consensus conference PALICC guidelines proposed SpO2 between 92 - 97% when positive end-expiratory pressure (PEEP) is smaller than 10 cm H2O and SpO2 of 88 - 92% when PEEP is bigger or equal to 10 cm H2O. [1] For healthy lung, PEMVECC proposed the SpO2>95% when breathing a FiO2 of 21%.[2] As a rule of thumb, the minimum fraction of inspired O2 (FiO2) to reach these targets should be used. A recent Meta-analyze showed that automated FiO2 adjustment provides a significant improvement of time in target saturations, reduces periods of hyperoxia, and severe hypoxia in preterm infants on positive pressure respiratory support. [3] This study aims to compare the closed-loop FiO2 controller with conventional control of FiO2 during mechanical ventilation of pediatric patients

The study has a crossover design. Patients will start in standard ASV 1.1 settings, then attending physician will assess the ventilation parameters according to study protocol and will note them in the case report form as he starts the data recording with MemoryBox (MB)in the mixed mode. Afterwards, the clinician will start the first phase by either keeping the patient in ASV 1.1 without any closed-loop controllers activated or switching to ASV 1.1 with only FiO2 controller activated according to the randomization. After 2.5 hours of recording in the first phase, the clinician will switch the patient to the second phase regarding randomization order. If the patient was ventilated without FiO2 controller activated in the first phase, the controller will be activated in the second phase. The patient will stay in the second phase for 2.5 hours as well. The first 0.5 hours of the first phase will be considered as run-in phase and the first 0.5 hours of the second phase will be considered as wash-out phase. Therefore the first 0.5 hours of each phase will be excluded from data analysis due to cross-over study design.

Inclusion Criteria:

• Pediatric patients between 1 months and 18 years
• Patients above 7kg of IBW
• Informed consent was signed by next of kin
• Requiring FiO2 ≥ 25% to keep SpO2 in the target ranges defined by the clinician

Exclusion Criteria:

• Candidate for extubation in the next 5 hours.
• Patient included in another interventional study in the last 30 days
• Hemodynamically instable patients (defined as a need for continuous infusion of epinephrine or norepinephrine > 1 mg/h)
• Patients with congenital or acquired hemoglobinopathies effecting SpO2 measurement
• Patient included in another interventional research study under consent
• Patient already enrolled in the present study in a previous episode of acute respiratory failure