Although there is a widespread use of HighFlow therapy around the world, there is still uncertainty about the most appropriate initial HighFlow level after nasal continuous positive airway pressure therapy. Higher levels might produce excessive and harmful intra-alveolar pressures exceeding those reached during nasal continuous positive airway pressure therapy. Low levels may not generate sufficient distending pressures, which may result in a loss of functional residual capacity and an increased risk of respiratory failure. Therefore, the aim of this study is to assess the effect of different HighFlow levels on the functional residual capacity and to compare these findings to the functional residual capacity during nasal continuous positive airway pressure therapy.

Inclusion Criteria:

• Written Informed Consent by one or both parents or legal guardians as documented by signature
• 30 - 35 weeks postmenstrual age
• Respiratory support with nCPAP PEEP 5mbar and FiO2 < 0.30
• > 72 hours old

Exclusion Criteria:

• Inability of the parents to understand the study concept or procedures due to cognitive or linguistic reasons
• Congenital malformations adversely affecting lung aeration or pulmonary perfusion (e.g. congenital heart or lung defects)