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Sustained inflation at birth did not protect preterm fetal sheep from lung injury.

Sustained lung inflations (SI) at birth may recruit functional residual capacity (FRC). Clinically, SI increase oxygenation and decrease need for intubation in preterm infants. We tested whether a SI to recruit FRC would decrease lung injury from subsequent ventilation of fetal, preterm lambs. The preterm fetus (128±1 day gestation) was exteriorized from the uterus, a tracheostomy was performed, and fetal lung fluid was removed. While maintaining placental circulation, fetuses were randomized to one of four 15-min interventions: 1) positive end-expiratory pressure (PEEP) 8 cmH2O (n=4), 2) 20 s SI to 50 cmH2O then PEEP 8 cmH2O (n=10), 3) mechanical ventilation at tidal volume (VT) 7 ml/kg (n=13), or 4) 20 s SI then ventilation at VT 7 ml/kg (n=13). Lambs were ventilated with 95% N2/5% CO2 and PEEP 8 cmH2O. Volume recruitment was measured during SI, and fetal tissues were collected after an additional 30 min on placental support. SI achieved a mean FRC recruitment of 15 ml/kg (range 8-27). Fifty percent of final FRC was achieved by 2 s, 65% by 5 s, and 90% by 15 s, demonstrating prolonged SI times are needed to recruit FRC. SI alone released acute-phase proteins into the fetal lung fluid and increased mRNA expression of proinflammatory cytokines and acute-phase response genes in the lung. Mechanical ventilation further increased all markers of lung injury. SI before ventilation, regardless of the volume of FRC recruited, did not alter the acute-phase and proinflammatory responses to mechanical ventilation at birth.