Background: Limited left atrial egress due to a restrictive/intact atrial septum (RIAS) can lead to abnormal pulmonary vascular development, severe cyanosis at birth, and is a risk factor for survival in HLHS. Maternal hyperoxygenation (MH) can lead to observable fetal pulmonary vasodilation in the third trimester of pregnancy and may offer a means for testing the fetal pulmonary vasculature.
Objective: To determine the utility of MH in assessing pulmonary vasoreactivity in the fetus with HLHS.
Methods: Doppler derived pulsatility index (PI), a measure of vascular resistance, was evaluated in the distal branch pulmonary artery (PA) of fetuses with HLHS before, during, and after MH with 20 minutes of 60% oxygen. 68 studies were performed; 56 had open atrial septum and 12 had RIAS, of which 7 required urgent intervention at birth due to severe cyanosis.
Results: MH resulted in a significant decrease in PA-PI in comparison to room air (RA) in open septum, but not in RIAS fetuses (see table). Absence of pulmonary vasoreactivity at > 30 wks gestation defined as PA-PI change of < 10% with MH was highly predictive of severe cyanosis, discriminating within the RIAS group for those who required urgent intervention at birth. There was no significant change in umbilical or middle cerebral artery PI with MH and no ductal constriction.
Conclusions: MH is safe and useful in evaluating fetal HLHS and should be incorporated into routine prenatal assessment of this anomaly.