PC1041: The Hemodynamic Benefits of Brief 100% Oxygen Use During Preterm Resuscitation with an Intact Umbilical Cord Using Asphyxiated and Non-asphyxiated Surfactant Deficient Ovine Model

Background: The use of 100% supplemental O2 is not recommended in the resuscitation of preterm neonates due to the risk of systemic oxygen toxicity. A recent meta-analysis suggests that more than 50% of preterm infants are born with a heart rate < 100 bpm. Not achieving an HR of ≥100bpm and saturation (SpO2) of ≥80% by 5 min places a preterm infant at a higher risk of morbidity/mortality. Ventilation with an intact cord improves hemodynamic transition in a preterm neonate. In an asphyxiated preterm neonate, the use of 100% O2 with an intact cord could improve alveolar oxygenation with less systemic toxicity due to buffering by umbilical venous return. Our objectives are to study the effect of initiating positive pressure ventilation (PPV) with 100% O2 with and without an intact umbilical cord in asphyxiated and non-asphyxiated preterm lambs.

Methods: Preterm lambs (125-127d gestation) were randomized into 4 groups: a) AXDCC - asphyxiated (to HR < 100 bpm) and ventilated with an intact cord,
b) AXECC – asphyxiated, early cord clamping and PPV, c) NoAXDCC - non-asphyxiated delayed cord clamping, d) NoAXECC - non-asphyxiated, early cord clamping. The cord clamping is delayed in all DCC groups for 5 min. The primary outcome is the incidence of HR of ≥100 bpm and SpO2 of ≥80% by 5 min. The secondary outcomes were measures of gas exchange, hemodynamics, and oxidative stress (oxidized to reduced glutathione ratio in the blood). In all the groups PPV was initiated with 100% O2 for 2 min and titrated proportional to the difference in observed and targeted SpO2 every min.

Results: Asphyxia led to lower PaO2, SpO2, HR and higher PaCO2 at the initiation of PPV. The primary outcome was achieved in 4/7 (AXECC), 6/7 (AXDCC), 5/6 (NoAXECC) & 7/7 (NoAXDCC). By 5 min, the preductal SpO2 was higher in DCC groups despite lower O2 exposure compared to other groups (Fig 1B & Fig 1C). Intact cord resuscitation led to lower PaCO2 in asphyxiated lambs along with higher peak pulmonary and carotid flow (Fig 2). At 5 min, there was no significant difference in oxidized to reduced glutathione ratio between groups (Fig 2D).

Conclusion: In both asphyxiated and non-asphyxiated preterm lambs, initial use of 100% with an intact cord improved hemodynamic and respiratory transition by increasing peak pulmonary blood flow, with lower oxygen exposure, improved ventilation without any change in oxidative stress markers.