The effects of partial amniotic carbon dioxide insufflation in an ovine model.

Abstract

We aim to assess the effect of partial amniotic carbon dioxide insufflation (PACI) at increasing pressures on fetal acid-base, fetal-placental perfusion, and fetal membrane morphology in an ovine model. Pregnant ewes and fetuses were instrumented under isoflurane anesthesia at 105days gestation (term 145days) to monitor utero-placental blood flow, fetal and maternal blood pressure, heart rate, and blood gas status. One group (n=6) was exposed to PACI (unheated dry CO2 ), involving 10mmHg stepwise increases in insufflation pressure (5 to 25mmHg), for 80minutes followed by 20minutes of desufflation. Un-insufflated controls (n=5) were monitored for 100minutes. At postmortem, fetal membranes were collected for histological analysis. PACI at 25mmHg caused severe fetal hypercapnia (PaCO2 =143±5 vs 54±5mmHg, P<0.001), acidosis (pH=6.85±0.02 vs 7.25±0.02, P<0.001), hypoxia (SaO2 =31±4% vs 57±4%, P=0.01), and reduced uterine artery flow (50±15 vs 196±13mL/min/kg, P=0.005) compared with controls. These effects were greater at higher PACI pressures. PACI resulted in leukocyte infiltration in the amnion (1.77×10-5 ±0.61×10-5 vs 0.38×10-5 ±0.19×10-5 cells/μm2 , P=0.04) and chorionic membranes (2.94×10-5 ±0.67×10-5 vs 0.84×10-5 ±0.42×10-5 cells/μm2 , P=0.01). Higher PACI pressures results in larger disturbances in fetal acid-base, uterine blood flow, and fetal membrane inflammation in sheep. Differences between human and sheep utero-placental structure should be considered.