Airway liquid modulates the level of supplemental oxygen required by preterm lambs at birth.

Although supplemental oxygen is necessary to support preterm infants at birth, it is unclear what fraction of inspired oxygen ([Formula: see text]) should be used. We hypothesized that the presence of liquid in the distal gas exchange regions of the lung will impede oxygen exchange and so the [Formula: see text] levels required during lung aeration will rapidly decrease. Using standardized ventilator settings, we examined the effects of high, mid, and low [Formula: see text] on oxygenation during and after lung aeration. Preterm lambs (126/147 days) were intubated and instrumented with catheters and oxygen probes in the carotid artery (CA), femoral artery (FA), and brain tissue and flow probes around the CA (CBF) and pulmonary artery (PBF). Ventilation commenced immediately following cord clamping, with an [Formula: see text] of either 0.3, 0.6, or 1.0. After lung aeration (10 min of ventilation), [Formula: see text] was reduced to 0.21 and subsequently increased to 1.0. During ventilation with an [Formula: see text] of 1.0, the rate of increase in arterial partial pressure of oxygen ([Formula: see text]) levels in the CA was markedly lower during lung aeration (16.9 ± 1.8 mmHg/min) than following lung aeration (67.7 ± 6.7 mmHg/min). During lung aeration, [Formula: see text] in the CA, FA, and brain was greatest in 1.0 [Formula: see text] group and lowest in the 0.3 [Formula: see text] group, commencing from ∼2 min after ventilation onset. Although PBF and blood pressures were similar, CBF was substantially higher in [Formula: see text] 0.3 group (P < 0.001) and was inversely correlated with CA and brain tissue Po2 as well as cerebral oxygen saturation. The degree of lung aeration determines how [Formula: see text] influences oxygenation in preterm lambs, with high [Formula: see text] having a greater effect on oxygenation following lung aeration.NEW & NOTEWORTHY This study shows that circulating oxygen levels during the cardiopulmonary transition depend on both the level of inspired oxygen provided and the degree of lung aeration. Since aeration of the lung is hampered in preterm infants, which limits the surface area available for gas exchange, high inspired oxygen concentrations may be required to increase the partial pressure gradient for oxygen diffusion. Carotid blood flow is very sensitive to oxygenation levels in preterm lambs.