Acute maternal hyperoxygenation to predict hypoxia and need for emergency intervention in fetuses with transposition of the great arteries: a pilot study.

Background: Newborns with transposition of the great arteries (TGA) are at risk of severe hypoxia from inadequate atrial mixing, closure of the arterial duct and/or pulmonary hypertension (PPHN). Acute maternal hyperoxygenation (AMH) might assist in identifying at-risk fetuses. We report pulmonary vasoreactivity to AMH in TGA fetuses and its relationship to early postnatal hypoxia and requirement for emergency balloon atrial septostomy (e-BAS).

Methods: Standard fetal echocardiographic (FE) assessment of the foramen ovale (FO): total septal length and morphology of flap valve of FO were used to predict need for e-BAS. Following prospective recruitment, additional assessments were performed in fetuses with TGA at baseline and repeated after 10minutes of 10L/min of 100% oxygen delivered via non-rebreather mask to the pregnant mother. Analysis included measurement of atrial septal excursion, branch pulmonary artery pulsatility index (PA-PI), middle cerebral artery (MCA) PI and cardiac output. Delivery and newborn status were reviewed. Hypoxia was defined as preductal oxygen saturations <75% and e-BAS when undertaken within two hours of birth. Area under receiver operating characteristics curves (AUROC) were calculated.

Results: 30 cases underwent FE at 34.6weeks' gestation (IQR: 34.6-35.6). All 7 predicted to require e-BAS based on standard FE were correctly identified prenatally. 3/30 were hypoxic without FO restriction and treated with nitric oxide (PPHN). Change in PA-PI < 15% was associated with PPHN (p=0.001), but not with e-BAS. The MCA-PI response to AMH varied according to newborn condition, a mean reduction occurred in the non-hypoxic newborns (-7.8 ± 18.3, p=0.05). Increase in MCA-PI Z score AUROC 0.837 (95% CI: 0.663-1.00, p=0.01); reduction in right ventricular cardiac output 0.811 (95% CI: 0.623-0.998, p=0.04), reduction in combined cardiac output (0.851 (95% CI: 0.699-1.0, p=0.01)) were moderately associated with e-BAS. Changes in atrial septal excursion and FO flow direction with AMH did not correlate with newborn condition.

Conclusions: PA-PI change < 15% to AMH was associated with postnatal hypoxia due to PPHN. Increase in right and combined cardiac output and reduced MCA resistance with AMH are seen in those who do not require e-BAS.