478 - Optimal FiO2 and PaO2 to Achieve Normoxemia and Pulmonary Vascular Transition in an Ovine Model of Term Neonates with Meconium Aspiration and Birth Asphyxia

Publication Number: 1458.478

Sylvia Bowditch, University of California Davis Children's Hospital, Sacramento, CA, United States; Evan M. Giusto, UC Davis Health, Sacramento, CA, United States; Antoine Koehl, University of California, Davis, School of Medicine, Sacramento, CA, United States; Deepika Sankaran, University of California Davis Children's Hospital, Sacramento, CA, United States; Michelle J. Lim, University of California, Davis, School of Medicine, Sacramento, CA, United States; Rebecca Valdez, University of California Davis Children's Hospital, Sacramento, CA, United States; Amy Lesneski, UC Davis, Davis, CA, United States; Victoria Hammitt, UC Davis Stem Cell Research, Davis, CA, United States; Payam Vali, University of California, Davis, School of Medicine, sacramento, CA, United States; Evan Maher, University of California, Davis, School of Medicine, Woodland, CA, United States; Jocelyn Livezey, University of California, Davis, School of Medicine, Davis, CA, United States; Morgan Hardie, University of California, Davis, School of Medicine, Philadelphia, PA, United States; Luna Khanal, University of California Davis Children's Hospital, Sacramento, CA, United States; Michele Persiani, University of California, Davis, School of Medicine, Sacramento, CA, United States; Paulina Hume, University of California Davis Children's Hospital, Sacramento, CA, United States; Xiaohan Li, University of California, Davis, School of Medicine, Davis, CA, United States; Thomas Simas, University of California, Davis, School of Medicine, Davis, CA, United States; Satyan Lakshminrusimha, UC Davis, Sacramento, CA, United States

Background: The current Neonatal Resuscitation Program (NRP) guidelines recommend an initial fraction of inspired oxygen (FiO2) of 0.21 in term infants. Compared to healthy newborns, neonates with meconium aspiration syndrome (MAS) and birth asphyxia with resultant hypoxic ischemic encephalopathy (HIE) are at high risk for developing pulmonary hypertension with high pulmonary vascular resistance (PVR). It is not known if starting with an FiO2 of 0.21 and titrating to goal preductal saturation reduces PVR in a model of MAS+HIE with parenchymal lung disease and acidosis.

Objective: We sought to compare FiO2, PVR, and preductal PaO2 between term lambs with meconium aspiration and birth asphyxia (MAS + HIE group) to non-asphyxiated term lambs without parenchymal lung disease (control group) for the first 60 minutes.

Design/Methods: Time-dated ewes were anesthetized and their fetuses instrumented. For the MAS + HIE cohort, fetal lambs were administered meconium endotracheally and asphyxia as induced via umbilical cord occlusion. The control cohort was simply delivered. Both groups were resuscitated via NRP guidelines with initial FiO2 of 0.21. If oxygen saturation (SpO2) was different from target, we changed FiO2 by 0.1 if preductal SpO2 was < 10% off target and by 0.2 if preductal SpO2 was ≥ 10% off target every 60 seconds.

Results: We studied 19 lambs with MAS + HIE and 6 controls. There was no difference in weight or gestational age between groups. Fetal PaO2 and PVR values were similar (p = 0.08 and p = 0.55, respectively). All of the control lambs achieved goal saturation with 0.21 FiO2. Rapid titration of FiO2 in the first 10 minutes after birth to variable degree (0.21 to 1.0) was needed in lambs with MAS + HIE (Figure 1). Both groups showed a decrease in their PVR over time, and the MAS + HIE lambs were able to drop their PVR further than the control group (Figure 2). PaO2 values did not significantly differ between the two groups at any time points (Figure 3).

Conclusion(s): For lambs in the MAS + HIE group, rapid titration to a higher FiO2 achieved similar preductal PaO2 values and pulmonary vascular transition as the control group. A preductal PaO2 value of approximately 45 - 75 mmHg in the MAS + HIE cohort seemed to be the optimal range to maintain saturations and decrease PVR. These findings reassure us that current NRP recommendations of optimal lung ventilation and starting FiO2 of 0.21 and rapid titration to target SpO2 every 60 seconds achieves effective pulmonary vascular transition in acidotic lambs with perinatal asphyxia and MAS.

Figure 1
Fraction of inspired oxygen over time

Figure 2
Pulmonary vascular resistance over time

Figure 3
Partial pressure of oxygen in arterial blood over time