Abstract 14220: Establishing Dosing Parameters for the Use of Maternal Hyperoxygenation to Affect Fetal Cardiovascular Physiology

Introduction: Maternal hyperoxygenation (MH) has been used to aid in the prognosis of fetal abnormalities. No data exist on the dose-response relationship or washout time of short-term MH administration related to fetal cardiovascular effects.

Hypothesis: There may be a dose-response to MH with effect on pulmonary vascular resistance as measured by pulmonary artery pulsatility index (PAPI) and combined cardiac output (CCO).

Aims: The aims of this study were: to determine the appropriate MH dose to obtain a physiologic response (i.e. decrease in PAPI), to evaluate the change in CCO, and to identify the washout period.

Methods: Expectant mothers with normal fetal echocardiograms were prospectively recruited from 3/2019 to 6/2023. A research echocardiogram with MH was performed after 31 weeks gestation. Fetal cardiac abnormalities and other comorbidities were excluded. Patients were randomly assigned to either; 2 liters (L) nasal cannula (NC), 4L NC or 8L facemask, all at 100% Fi0 ₂ . Measurements of PAPI and CCO were performed at baseline, at 1 minute (min) and at 5 min intervals to 20 mins. The same time points were repeated off oxygen. Differences in PAPI were compared between doses and between time points using a mixed effects model.

Results: We recruited 29 patients at a mean gestational age of 32.9 (± 0.9 weeks). On oxygen, there was a statistically significant decrease in the PAPI at 8L (-0.18 per min, 95% CI -0.32, -0.05), with the largest decrease occurring between baseline and 5 mins, and PAPI stabilizing after 10 mins (figure). During the washout period, starting at 1 min off oxygen, PAPI values normalized, with no statistically significant changes with 2L, 4L or 8L compared to baseline. No effect on CCO was seen from MH administration.

Conclusions: An oxygen dose of 8L is needed for an appropriate PAPI response, with the largest effect occurring before 10 mins. After oxygen is removed, PAPI values normalize by one min. Changes in CCO were not seen with MH in this normal population.