Lung Volume Changes in Stable Preterm Infants Weaned From Nasal CPAP to High Flow

BackgroundWeaning preterm infants off nasal CPAP (nCPAP) using nasal high-flow therapy has gained popularity. The effects of such a weaning strategy on lung volumes are unclear.Research QuestionHow does the transition from nCPAP to high flow and varying flow levels affect lung volumes in stable preterm infants?Study Design and MethodsThis was a prospective cohort study in infants 30 to 35 weeks' postmenstrual age. After a baseline period on nCPAP 5 cm H2O, infants were switched to high flow 8 L/min for 30 minutes. The flow level was reduced by 2 L/min every 30 minutes to a minimum of 2 L/min and subsequently increased to the initial level of 8 L/min, followed by another nCPAP period. Using electrical impedance tomography, end-expiratory lung impedance as a proxy for end-expiratory lung volume (EELV) and cardiorespiratory parameters were recorded at each flow level and compared with baseline.ResultsOverall, 8,438 breaths from 19 infants were analyzed. EELV changed significantly during the study (P = .002), which was mainly attributable to a loss of EELV when high flow was reduced to 6 and 4 L/min and reescalated to 4, 6, and 8 L/min. Apart from a reduction in minute ventilation (P = .004), no other significant changes were found in electrical impedance tomography ventilation parameters. Alterations in lung volume were accompanied by an increase in heart rate (P = .02) and a decrease in Spo2/Fio2 ratio (P < .001).InterpretationThe transition from nCPAP to high flow is likely to result in a reduced EELV, accompanied by physiological responses in heart rate and oxygenation. Despite a stepwise escalation to preweaning flow levels, only partial recovery of lung volume losses is achievable with high flow.Clinical Trial RegistrationClinicalTrials.gov; No.: NCT05237622; URL: www.clinicaltrials.gov