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

While supplemental oxygen is necessary to support preterm infants at birth, it is unclear what fraction of inspired oxygen (FiO2) should be used. We hypothesised that the presence of liquid in the distal gas exchange regions of the lung will impede oxygen exchange and so the FiO2 levels required during lung aeration will rapidly decrease. Using standardized ventilator settings, we examined the effects of high, mid and low FiO2 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 FiO2 of either 0.3, 0.6 or 1.0. After lung aeration (10 minutes of ventilation), FiO2 was reduced to 0.21 and subsequently increased to 1.0. During ventilation with an FiO2 of 1.0, the rate of increase in PaO2 levels in the CA was markedly lower during lung aeration (16.9±1.8mmHg/min) than following lung aeration (67.7±6.7mmHg/min). During lung aeration, PaO2 in the CA, FA and brain were greatest in 1.0 FiO2-group and lowest in 0.3 FiO2-group, commencing from ~2min after ventilation onset. While PBF and blood pressures were similar, CBF was substantially higher in FiO2 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 FiO2 influences oxygenation in preterm lambs, with high FiO2 having a greater effect on oxygenation following lung aeration.