High Frequency Oscillatory Ventilation Combined With Intermittent Sigh Breaths: Effects on Lung Volume Monitored by Electric Tomography Impedance.

Background Ventilator induced lung injury (VILI) remains a problem in neonatology. High frequency oscillatory ventilation (HFOV) provides effective gas exchange with minimal pressure fluctuation around a continuous distending pressure and therefore small tidal volume. Animal studies showed that recruitment and maintenance of functional residual capacity (FRC) during HFOV ("open lung concept") could reduce lung injury. "Open lung HFOV" is achieved by delivering a moderate high mean airway pressure (MAP) using oxygenation as a guide of lung recruitment. Some neonatologists suggest combining HFOV with recurrent sigh-breaths (HFOV-sigh) delivered as modified conventional ventilator-breaths at a rate of 3/min. The clinical observation is that HFOV-sigh leads to more stable oxygenation, quicker weaning and shorter ventilation. This may be related to improved lung recruitment. Electric Impedance Tomography (EIT) enables measurement and mapping of regional ventilation distribution and end-expiratory lung volume (EELV). EIT generates cross-sectional images of the subject based on measurement of surface electrical potentials resulting from an excitation with small electrical currents and has been shown to be a valid and safe tool in neonates. Purpose, aims: * To compare HFOV-sigh with HFOV-only and determine if there is a difference in global and regional EELV (primary endpoints) and spatial distribution of ventilation measured by EIT * To provide information on feasibility and treatment effect of HFOV-sigh to assist planning larger studies. We hypothesize that EELV during HFOV-sigh is higher, and that regional ventilation distribution is more homogenous. Methods: Infants at 24-36 weeks corrected gestational age already on HFOV are eligible. Patients will be randomly assigned to HFOV-sigh (3 breaths/min) followed by HFOV-only or vice versa for 4 alternating 1-hours periods (2-treatment, double crossover design, each patient being its own control). During HFOV-sigh set-p