The study is a two-armed randomized cross-over comparison of leakage with nasal prongs and nasal mask interface in newborn infants treated with CPAP, born after 28 weeks of gestational age. For infants with an interface leakage, the trial also includes an observational part evaluating simple measures to reduce leakage.

The study will be carried out in the Karolinska University Hospital Stockholm and in the Östersund Hospital.

The study will recruit a total of 50 infants receiving CPAP for respiratory support at the Karolinska University Hospital and the Östersund Hospital. The infant should be stable and not in major respiratory distress. Consent from the parents will be obtained before enrolment.

The included infants should have stable spontaneous breathing and be older than 28 weeks (corrected age) at the time of enrolment. The reason for respiratory failure and CPAP treatment is not relevant for study purposes. If an infant cannot participate in the study at a given time, he or she can be enrolled later. A child can only participate once.

The primary outcome is leakage. This is recorded using equipment for measuring air flow during CPAP treatment. Measurement of leakage is first performed for one interface and then the next (cross-over). The interface order is randomized. The leakage will be measured after a few minutes of stabilization (part 1). If there is leakage, a few simple measures to reduce the leakage will be evaluated (part 2). The second part will approximately add 10-20 minutes and includes simple measures such as adjusting the nasal mask, closing the mouth, changing the position or changing the size of nasal mask/prongs. Part 1 and part 2 are then repeated for the next interface. If the child shows signs of distress or agitation the measurement will be paused or stopped.

Part 1: The CPAP system with the randomized interface (nasal mask or nasal prongs) is applied and adjusted by experienced NICU staff. The staff is blinded for the outcome variable, leakage. The choice of size and other adjustments are guided by clinical experience and not by protocol. The NICU staff is not allowed to participate in the explorative part where measures to reduce leakage are evaluated. This precaution is to avoid staff learning what adjustments affect leakage and influence care of infants enrolled at a later stage.

Part 2: In this part the investigators can evaluate the effect of simple measures to minimize the leakage. The level of leakage is displayed on a screen. Examples of measures are; closing the mouth of the infant, adjusting straps, adjusting position and changing the size of the interface. Not every child will undergo all measures to reduce leakage, since the aim of this explorative part is to explore ways to reduce leakage.

It is estimated that these tests and measures will take 15-60 minutes per child. No other measurements or follow-up is planned. No blood samples will be collected or analysed.

The study will collect information on the infant and the birth. This includes birth weight, gestational age at birth, gender, previous respiratory support and medical history.

The main outcome variable is absolute leakage (via mouth or via CPAP interface). Other collected variables are oxygen saturation, respiratory rate, inspired oxygen concentration, apneas, heart rate, if the infant is awake/asleep or in distress. Safety variables include skin irritation or damage of the nose caused by the interface, instability or deterioration of respiration or circulation, problems with the equipment or other adverse events. The investigation can be stopped immediately in the case of distress or instability. The study is, as far as the investigators know, the first one of its kind. The air flow meters do not affect the CPAP system and use a technique that measures the total leakage in L/min. These improvements have been emphasized in previous studies. The study follows GCP (good clinical practice) standards and The Helsinki declaration.

Inclusion Criteria:

• Gestational age over 28 weeks (corrected age) at the time of inclusion
• Patient receiving respiratory support with CPAP

Exclusion Criteria:

• Airway, pulmonary, cardiac or gastro-intestinal malformations
• Neuromuscular disease
• Circulatory unstable patient
• FiO2 higher than 0.5
• Nasal damage or major skin irritation.
• Extubation less than 24 h before investigation
• Surgery less than 5 days before investigation