Temperature and Humidity During Different Neonatal Respiratory Support Modes: An In‐Vitro Performance of Four Heated Humidifiers

Background: Adequate heating and humidification of inspired gas are crucial in preterm infants requiring respiratory support. Our objective was to compare the temperature (T) and absolute humidity (AH) achieved with different neonatal heated humidifiers commonly used during different respiratory support modes and respiratory settings. Methods: Four neonatal heated humidifiers were tested at different gas flow rates and during conventional and high-frequency oscillatory ventilation at clinically relevant settings. The patient was simulated using a neonatal test lung placed in a neonatal incubator warmed at 37°C. Temperature and relative humidity were measured using a thermohygrometer placed proximal to the test lung and used to calculate AH. Results: Measured temperature and humidity varied among heated humidifiers and respiratory support settings. The bias flow was the primary determinant of the measured temperature and humidity: temperature and AH significantly increased with flow. When the flow through the chamber was below 5 L/min the MR950 produced T < 36.7°C and AH < 37 g/m3 proximal to the patient. The Hydraltis 9500neo with chamber and proximal temperature set to 38°C and 40°C and the MR850 produced AH > 44 g/m3 in most conditions. Conclusion: The temperature and humidity proximal to the patients' airways might vary considerably based on the heated humidifiers and the flow through the chamber. Further clinical studies are needed to evaluate the effect of such variability on the patients.