Regional ventilation characteristics during non-invasive respiratory support in preterm infants

Objective: To determine the regional ventilation characteristics during non-invasive ventilation in stable preterm infants. The secondary aims were to explore the relationship between indicators of ventilation homogeneity and other clinical measures of respiratory status. Design: Prospective observational study. Setting: Two tertiary neonatal intensive care units. Patients: Forty stable preterm infants born <30 weeks gestation receiving either CPAP (n=32) or nHF(n=8) if <36 weeks corrected gestation, and extubated for at least 24 hours at time of study. Interventions: Continuous electrical impedance tomography imaging of regional ventilation during 60-minutes of quiet breathing on clinician-determined non-invasive settings. Main outcome measures: Gravity-dependent and right-left centre of ventilation (CoV), percentage of whole lung tidal volume by lung region, and percentage of lung unventilated were determined for 120 artefact-free breaths/infant (4770 breaths included). Oxygen saturation, heart and respiratory rates were also measured. Results: Ventilation was greater in the right lung (mean (SD) CoVRL 69.1 (14.9)%) and the gravity non-dependent lung; ideal-actual CoV 1.4 (4.5). The central third of the lung received the most tidal volume, followed by the non-dependent and dependent regions (p<0.0001 repeated measure ANOVA). Ventilation inhomogeneity was associated with worse SpO2/FiO2, (p=0.031, r2 0.12; linear regression). In those infants that later developed bronchopulmonary dysplasia (n=25) SpO2/FiO2 was worse and non-dependent ventilation inhomogeneity greater than in those that did not (both p<0.05; t test Welch correction). Conclusions: There is high breath-by-breath variability in regional ventilation patterns during NIV in preterm infants. Ventilation favoured the gravity non-dependent lung, with ventilation inhomogeneity associated with worse oxygenation.