ObjectiveTo compare the resistance of interfaces used for the delivery of nasal continuous positive airway pressure (CPAP) in neonates, as measured by the generated system pressure at fixed gas flows, in an in vitro setting.DesignGas flows of 6, 8 and 10 L/min were passed through three sizes of each of a selection of available neonatal nasal CPAP interfaces (Hudson prong, RAM Cannula, Fisher & Paykel prong, Infant Flow prong, Fisher & Paykel mask, Infant Flow mask). The expiratory limb was occluded and pressure differential measured using a calibrated pressure transducer.ResultsVariation in resistance, assessed by mean pressure differential, was seen between CPAP interfaces. Binasal prong interfaces typically had greater resistance at the smallest assessed sizes, and with higher gas flows. However, Infant Flow prongs produced low pressures (<1.5 cmH2O) at all sizes and gas flows. RAM Cannula had a high resistance, producing a pressure >4.5 cmH2O at all sizes and gas flows. Both nasal mask interfaces had low resistance at all assessed sizes and gas flows, with recorded pressure <1 cmH2O in all cases.ConclusionsThere is considerable variation in measured resistance of available CPAP interfaces at gas flows commonly applied in clinical neonatal care. Use of interfaces with high resistance may result in a greater drop in delivered airway pressure in comparison to set circuit pressure, which may have implications for clinical efficacy. Device manufacturers and clinicians should consider CPAP interface resistance prior to introduction into routine clinical care.