Comparison of Gas Exchange Between Two Invasive Mechanical Ventilation Modes in Children

Inclusion Criteria: * Informed consent provided by the participant or the participant's parents or legal guardians. In case of an emergency situation, a physician who is independent of the research project must be consulted prior to inclusion in order to safeguard the interests of the test subject. * Admission to PICU at the University Children's Hospital Zurich * Need for mechanical ventilation for \>60 min during PICU hospitalization. Need for mechanical ventilation will be based on clinical decision of the treating physician. * Need for an arterial line during PICU hospitalization. Need for an arterial line will be based on clinical decision of the treating physician. * Age \<18 years * Weight \>2 Kg Exclusion Criteria: * Substantial air leaks around the endotracheal tube (\>30%) * Cyanotic shunt lesions * Intracranial hypertension (i.e. traumatic brain injury or patients admitted after neurosurgery) * Pulmonary hypertension under treatment (i.e sildenafil or inhaled nitric oxide) * Time from start of invasive mechanical ventilation until time of screening is \> 24 hours * Previous enrolment in the study in the past 30 days * Inability of the parents or legal guardians to understand the study due to linguistic or cognitive reasons