%0 Journal Article %A Zheyi Liew %A Alan C Fenton %A Sundeep Harigopal %A Saikiran Gopalakaje %A Malcolm Brodlie %A Christopher J O’Brien %T Physiological effects of high-flow nasal cannula therapy in preterm infants %D 2020 %R 10.1136/archdischild-2018-316773 %J Archives of Disease in Childhood - Fetal and Neonatal Edition %P 87-93 %V 105 %N 1 %X Objective High-flow nasal cannula (HFNC) therapy is increasingly used in preterm infants despite a paucity of physiological studies. We aimed to investigate the effects of HFNC on respiratory physiology.Study design A prospective randomised crossover study was performed enrolling clinically stable preterm infants receiving either HFNC or nasal continuous positive airway pressure (nCPAP). Infants in three current weight groups were studied: <1000 g, 1000–1500 g and >1500 g. Infants were randomised to either first receive HFNC flows 8–2 L/min and then nCPAP 6 cm H2O or nCPAP first and then HFNC flows 8–2 L/min. Nasopharyngeal end-expiratory airway pressure (pEEP), tidal volume, dead space washout by nasopharyngeal end-expiratory CO2 (pEECO2), oxygen saturation and vital signs were measured.Results A total of 44 preterm infants, birth weights 500–1900 g, were studied. Increasing flows from 2 to 8 L/min significantly increased pEEP (mean 2.3–6.1 cm H2O) and reduced pEECO2 (mean 2.3%–0.9%). Tidal volume and transcutaneous CO2 were unchanged. Significant differences were seen between pEEP generated in open and closed mouth states across all HFNC flows (difference 0.6–2.3 cm H2O). Infants weighing <1000 g received higher pEEP at the same HFNC flow than infants weighing >1000 g. Variability of pEEP generated at HFNC flows of 6–8 L/min was greater than nCPAP (2.4–13.5 vs 3.5–9.9 cm H2O).Conclusions HFNC therapy produces clinically significant pEEP with large variability at higher flow rates. Highest pressures were observed in infants weighing <1000 g. Flow, weight and mouth position are all important determinants of pressures generated. Reductions in pEECO2 support HFNC’s role in dead space washout. %U https://fn.bmj.com/content/fetalneonatal/105/1/87.full.pdf