Fetal hemodynamic parameters and blood samples

The FHR, MAP, and IAP (IntelliVue MX700; Philips, Eindhoven, Netherlands) were continuously monitored and recorded using a data acquisition board (Physiotrace©; Estaris Monitoring, Lille, France) during the study period [14]. MAP refers to the amniotic cavity pressure (MAP = observed MAP—observed IAP). We defined the percentage changes in FHR and MAP from baseline were calculated as (time point value—baseline value) × 100 / baseline value and were described as “change in FHR” and “change in MAP”, respectively. The baseline is the value obtained just before the occlusion. FHR, MAP, change in FHR, and change in MAP during UCO were recorded with a resolution of 1 second. Moreover, we defined six time points, averaged over 10 seconds, to compare change in FHR and change in MAP to baseline: just before UCO (baseline); then at 10, 30, 60, 120, and 300 seconds after starting UCO. To consider the intra-individual variability in the hemodynamic response to UCO, we averaged the values of the 3 UCOs to account for intraindividual variability in the hemodynamic response to UCO. In the case of outliers due to technical problems, these values were not taken into account during the analysis. Blood gases (pH, PaCO₂, PaO₂) and plasma lactate concentrations were measured from blood samples taken from the ascending aorta at baseline before drug infusion and then adjusted to the ewe’s physiological temperature of 39°C (i-Stat Handheld©; Abbott Laboratories, Washington, DC, USA). In addition, blood gas analyses and measurement of plasma lactate concentration were performed at the end of the three UCOs.