Lung liquid clearance in preterm lambs assessed by magnetic resonance imaging.

Background: Postnatal adaptation requires liquid clearance and lung aeration. However, their relative contribution to the expansion of functional residual capacity (FRC) has not been fully investigated. We studied evolution of lung liquid removal and lung aeration after birth in preterm lambs.

Methods: Lung liquid content and lung volume were assessed at birth and every 30 min over 2 h using magnetic resonance imaging (MRI) in three groups of lambs delivered by cesarean: preterm, late preterm, and late preterm with antenatal steroids. Lung function and mechanics of the respiratory system were also measured.

Results: Lung liquid content increased by approximately 30% in the preterm group (P < 0.05), whereas it did not change significantly in the late preterm lambs. Antenatal steroids induced a 50% drop in the lung liquid content (P < 0.05). Total lung volume increased in all groups (P < 0.05) but was higher in the late preterm + steroids group relative to other groups (P < 0.05). Compliance and resistances of the respiratory system were significantly correlated with lung liquid content (P < 0.05).

Conclusion: FRC expansion results mainly from an increase in lung volume rather than a decrease in lung liquid in preterm and late preterm lambs. Antenatal steroids promote FRC expansion through increases in lung volume and liquid clearance.