1168: Fetal tolerance of maternal resuscitative endovascular balloon occlusion of the aorta in a sheep model

Abstract

Hemorrhage is the leading cause of maternal mortality. Resuscitative endovascular balloon occlusion of the aorta (REBOA) is an emerging therapy to decrease post-partum hemorrhage but creates profound ischemia to the placenta preventing its use before delivery. Employing partial REBOA (pREBOA) prior to delivery may improve maternal outcomes by decreasing placental perfusion and hemorrhage while still providing a small amount of distal perfusion to the placenta. Yet, this is only a viable strategy if the attenuated blood flow is tolerated by the fetus. Our objective was to evaluate how progressive levels of pREBOA effect the fetus. A REBOA catheter was placed in the distal aorta of 3 gravid ewes at term. Carotid arterial access and an oximeter were placed on the fetuses. The balloon was gradually inflated in 10min increments of attenuated distal mean arterial pressure at the placenta (pMAP) by 5-10mmHg. Fetal arterial blood gases, oxygen saturation and hemodynamic parameters of heart rate (HR) and mean arterial pressure (MAP) were obtained at baseline and each pREBOA inflation increment. Maternal baseline pMAP was 60.3 ±15.0mmHg. Fetal SaO2 declines first appeared at a pMAP of 40mmHg (59.0 ±12.1 vs 37.6 ±14.8%, p=0.0009) and correlated with decreases in fetal SaO2 as the aorta was progressively occluded with pREBOA (R=0.80, p< 0.0001, Fig. 1). Fetal MAP declines began at a pMAP of 35mmHg (51.3 ±5.8 vs 56.1 ±10.1mmHg, p=0.04), as did pH (7.20 ±0.08 vs 7.17 ±0.07, p=0.01). Fetal lactate increases were not seen until the pMAP reached 30mmHg (2.0 ±0.5 vs 2.4 ±0.4mmol/L, p=0.02). Fetal HR did not significantly differ from baseline at any pMAP, including the lowest of 25mmHg (159.7 ±19.1 vs 183.0 ±26.9bpm, p=0.56). All fetuses survived the progressively increasing pREBOA. Physiologic changes in the fetus first appear at a pMAP of 40mmHg. The fetus tolerates attenuation of placental MAP with partial REBOA to a high level before delivery, raising the possibility of employing pREBOA to limit maternal hemorrhage earlier in the perinatal period without injuring the fetus.