Current evidence suggests that noninvasive positive pressure ventilation (NIPPV) is more effective than continuous positive airway pressure (CPAP) in preventing respiratory failure in preterm infants with respiratory distress syndrome (RDS), both as initial and post-extubation support. NIPPV may be delivered in synchronized (sNIPPV) or non-synchronized (nsNIPPV) modes, with sNIPPV offering clear benefits by coordinating support with the infant's own breathing. Recent studies indicate sNIPPV is superior to nsNIPPV in preventing respiratory failure, though the intrapulmonary mechanisms behind this advantage remain unclear. To address this, the present study uses Electrical Impedance Tomography (EIT) to evaluate how lung volume changes during different types of breaths and ventilator inflations - spontaneous breaths, synchronized inflations, non-synchronized inflations, and backup inflations - in preterm infants receiving sNIPPV.

Hypothesis:

Synchronized inflations during NIPPV will increase tidal volumes (VT) and lung aeration when compared with non-synchronized inflations. Pressure peaks delivered during expiration (non-synchronized inflations), between spontaneous breaths (backup inflations), or during periods of apnea (backup inflations) will not increase relative VT.

Primary objective:

The primary objective is to assess lung volume changes between spontaneous breaths and synchronized inflations, non-synchronized inflations, and backup inflations using EIT.

Secondary objectives:

The secondary objectives are to assess regional differences in aeration and ventilation among spontaneous breaths, synchronized inflations, non-synchronized inflations, and backup inflations using EIT.

Primary endpoint:

Difference in relative Vt (rel. Delta-Z) between spontaneous breaths and synchronized inflations.

Study procedures:

Study procedures include attaching an EIT belt and a pulse oximeter sensor during the final nursing care session before the study begins. Synchronized NIPPV is provided by EVEneo ventilators, and synchronization will be achieved through an abdominal capsule (Graseby).

1. Sixty minutes after the beginning of the EIT recording , the noninvasve ventilation mode will be switched to CPAP for 2 minutes. This 2-minute period will be the baseline period during which spontaneous breathing will be assessed.
2. The NIV mode will then be switched back to sNIPPV. Ventilator settings will be maintained at the same levels used before the start of the study, and adjustments will not be permitted.
3. Prior to the next nursing care session, a second 2-minute nCPAP period will be introduced and serve as the baseline (together with the 1st CPAP period) .
4. The EIT recording and SpO2/HR measurements will continue until the next nursing care round, at which point the EIT belt and SpO2 sensor will be removed.

Inclusion Criteria:

• Written informed consent by one or both parents or legal guardians
• Gestational age at birth < 30 0/7 weeks
• Infants on sNIPPV respiratory support
• Below 4 weeks chronological age

Exclusion Criteria:

• Severe congenital malformation adversely affecting lung aeration or perfusion (e.g., congenital heart defects)
• Too ill/unstable in the opinion of the treating physician.

This study will take place at the Department of Neonatology of the University Hospital Zurich. Preterm infants on a synchronized mode of non-invasive positive pressure ventilation will be screened for eligibility and parents will be approached by the treating physician or a clinician-researcher who is authorized to access the patient's clinical data.