A humidifier in the invasive mode during noninvasive respiratory support could increase condensation and thereby impair airway patency

Aim: Humidifying noninvasively ventilated preterm infants is critical to prevent dehydration of respiratory mucosa, but over-humidification can result in impaired airway patency and lung mechanics. This neonatal bench study investigated the humidity delivered using invasive and noninvasive humidification modes during nasal continuous positive airway pressure. Methods: The study was conducted at the neonatal intensive care unit of Emma Children's Hospital, the Netherlands, in March 2014. A mannequin was connected to a CareFusion Infant Flow SiPAP system, combined with a Fisher & Paykel MR850 humidifier and a Carefusion Infant Flow LP Generator. We measured the temperature, relative humidity and absolute humidity at the humidification chamber's expiratory port and at the patient's mask. Results: The absolute humidity at the mask was 35–40 mg H2O/L at 38–39°C (relative humidity 74–80%) for the invasive mode of the humidifier and 23–27 mg H2O/L at 34–35°C (relative humidity 63–70%) for the noninvasive mode. The absolute humidities exceeded the recommended values for the invasive mode of the humidifier, but not the noninvasive mode, and could be associated with increased condensation. Conclusion: The absolute humidity delivered by the humidifier in invasive mode could be associated with increased condensation, which has been associated with airway impairment.