NHF will be applied at 8 L/min using the AIRVO 2 through smaller and larger Optiflow nasal cannula. The study will have a randomized crossover design. The larger or smaller cannula size will be applied as the first intervention during each experiment. During each experiment, if the larger cannula is applied first, then the smaller cannula will be applied second and if the smaller cannula is applied first, then the larger cannula will be applied second. Each experiment will last for 1.5 hour.~During baseline, supplemental oxygen will be added during NHF therapy to keep SpO2 in normal ranges (90%-94%). When the SpO2 has stabilized then the level of supplemental oxygen will be set for the entire experiment unless there is a significant change in SpO2 as determined by the attending consultant.~There will be three consecutive 30-min periods of recording during each experiment and each experiment will last approximately 1.5 hour.~Ventilation will be assessed by Respiratory Inductance Plethysmography (Respitrace) and transcutaneous carbon dioxide and oxygen.~Recordings will be made using ADInstruments Powerlab and Labchart software with video recording of the patient.~Routine measurement of heart rate, respiratory rate and oxygen saturations will be performed as per standard neonatal practice.~The researcher is an experienced neonatal consultant who will be directly observing the baby throughout the study.
Treatment with nasal high flow therapy (NHF) is an increasingly popular method of respiratory support in newborns.~Safe and effective use of NHF requires selection of an appropriate nasal prong-to-nares ratio because leak can influence the delivered pressure.~To the best of our knowledge, this is the first study to investigate the effect of using different NHF cannula size on peripheral oxygen saturation in newborns with respiratory distress.