Phase two: in-vivo study
This prospective observational study took place between January 2021 and January 2022 in the neonatal intensive care unit (NICU) of the Centre Hospitalier Intercommunal de Creteil. We included ELBW born ≤ 28 weeks of gestational age with a body weight of less than 1500 g at the time of the study and requiring mechanical ventilation. Patients were included in the analysis when a recording of humidity was possible in both IPPV and HFOV during their ventilatory support course. The choice of ventilatory mode and ventilatory settings were left to the clinician’s expertise and were not modified due to the study. Parents were informed of the study and stated that they did not object. The institutional ethics committee approved the study on December 1, 2020. The number of subjects to include could not be predicted because the difference of inspired airway humidity between the two ventilatory modes has never been described. Thus, the study duration was set at one year.
The standard Y-piece was replaced by a sterilized Y-piece equipped with a hygrometer during nursing care to record the humidity and temperature. This recording lasted for two hours for each patient and each ventilatory mode. The Y-piece with the hygrometer was removed the next time a nurse attended the baby. Ventilator settings, heater-humidifier device information (chamber inlet and outlet temperature and flow rate), ambient temperature, and barometric pressure were all collected during the 2-hour recording. After a stabilization period, any intervention (such as opening the incubator or changing ventilatory settings) during the 2-hour recording period was recorded. Only MR-B was used as a heater humidifier to adhere to the airway humidification protocol in the NICU.