Mechanisms of nasal high flow therapy in newborns

摘要

In newborns, it is unclear how nasal high flow (NHF) generates positive airway pressure. In addition, the reported benefits of NHF such as reduction in work of breathing may be independent of airway pressure. The authors hypothesized that during NHF the area of leak and the flow determine airway pressure and that NHF can reduce the required minute ventilation to maintain gas exchange. In response to NHF, pressure was measured in the upper airways of 9 newborns and ventilation was measured in another group of 17 newborns. In a bench model, airway pressures were measured during NHF with different prong sizes. nare sizes, and flows. The airway pressures during 8 L/min NHF were greater when a larger cannula versus a smaller cannula was used (P < 0.05). NHF reduced minute ventilation in 16 of 17 neonates, with a mean decrease of 24% from a baseline of 0.66 L/min (SD 0.21)(P < 0.001), and was unrelated to changes in airway pressure; arterial oxygen saturation by pulse oximetry (Sp(o2)) and tissue CO2 were unchanged. In the bench model, the airway plessure remained <2 cmH(2)O when <50% of the "nare" was occluded by the prongs. As the leak area decreased, because of a smaller nare or a larger cannula, the airway pressure increased exponentially and was dependent on flow. In newborns NI IF using room air substantially reduced minute ventilation without affecting gas exchange irrespective of a decrease or an increase of respiratory rate. NHF generates low positive airway pressure that exponentially increases with flow and occlusion of the nares.