592: Autonomic and cerebral response to umbilical cord occlusions with worsening acidosis in the fetal sheep

Abstract

Labor is a situation at risk of fetal hypoxia due to uterine contractions and/or compression of the umbilical. It could lead to fetal brain injury and hypoxic-ischemic encephalopathy (HIE). The autonomic nervous system (ANS) is a key mediator of fetal homeostasis, and its activity can be measured with heart rate variability (HRV) analysis. The objective of this experimental study in a fetal sheep model, was to evaluate HRV variation and cerebral injury. Repeated 1-minute umbilical cord occlusions (UCO) were performed at a mild (phase A, 1UCO/5mn)), moderate (phase B, 1 UCO/3mn), and severe (phase C, 1UCO/2mn) period until arterial pH reached 6.90. Hemodynamic, blood gas analysis, S100B and Troponin T assessment, and HRVwere recorded at specific time points. S100B is a protein linked with cerebral injury. ANS activity was evaluated though a new index developed by our team, the Fetal Stress Index (FSI), which was correlated in previous studies with parasympathetic activity and acidosis. Ten experiments were performed. UCOs resulted in progressive severe fetal acidosis with pH dropping to 6.99 0.13. FSI increased with acidosis: 57.7 8.6 during phase A vs 71.9 11.4 during phase C (p=0.032). Fetal S100B also increased throughout UCO series with a rise of 7% 4 during phase A compared to initial value, and 24% 8 during phase C (p< 0.001). FSI was correlated with pH (r=-0.529, p=0.003) and fetal S100B variation (r=0.583, p= 0.002). The main objective of fetal monitoring during labor is to prevent HIE. In this study, we observed that HRV analysis could predict cerebral injury and be a future marker of fetal well-being during labor.