Abstract
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 () and tissue CO2 were unchanged. In the bench model, the airway pressure remained <2 cmH2O 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 NHF 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.NEW & NOTEWORTHY In healthy newborns, nasal high flow (NHF) with room air reduced minute ventilation by one-fourth without affecting gas exchange but, in contrast to adults, produced variable response in respiratory rate during sleep. During NHF, pressure in the upper airways did not exceed 2 cmH2O at 8 L/min (3.4 L·min−1·kg−1) and was unaffected by opening of the mouth. NHF can generate higher pressure with larger prongs that decrease the leak around the cannula or by increasing the flow rate.
Highlights
Nasal high flow (NHF) provides respiratory support for spontaneously breathing patients across all ages
The results indicate that the change in the respiratory rate during NHF in neonates should be considered with caution; an increase in the respiratory rate may still be associated with a reduction in the required minute ventilation
The present findings address concerns raised by initial studies regarding the potential for a high level of positive airway pressure generated by delivering gas via nasal cannula [16]
Summary
Nasal high flow (NHF) provides respiratory support for spontaneously breathing patients across all ages. It is used in newborns because of its ease of use and ability to accommodate feeding and contact with parents [4, 8]. Some studies have found continuous positive airway pressure (CPAP) to be superior to NHF in neonates of low birth weight [17, 24, 29]. NHF is a flow-controlled therapy, and the positive airway pressures that are generated remain unclear. During NHF, the nasal prongs do not occlude the nares; determining the airway pressures is difficult. The available data are conflicting [12, 15, 16, 30, 32, 33, 36], and it is important to define how airway pressures are generated during NHF
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Schedule a callMore From: Journal of applied physiology (Bethesda, Md. : 1985)
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