Deceleration area and capacity during labour-like umbilical cord occlusions identify evolving hypotension: a controlled study in fetal sheep.

Abstract

Cardiotocography is widely used to assess fetal well-being during labour. The positive predictive value of current clinical algorithms to identify hypoxia-ischaemia is poor. In experimental studies, fetal hypotension is the strongest predictor of hypoxic-ischaemic injury. Cohort studies suggest that deceleration area and deceleration capacity of the fetal heart rate trace correlate with fetal acidaemia, but it is not known whether they are indices of fetal arterial hypotension. Prospective, controlled study. Laboratory. Near-term fetal sheep. One minute of complete umbilical cord occlusions (UCOs) every 5minutes (1:5min, n=6) or every 2.5minutes (1:2.5min, n=12) for 4hours or until fetal mean arterial blood pressure fell <20mmHg. Deceleration area and capacity during the UCO series were related to evolving hypotension. The 1:5min group developed only mild metabolic acidaemia, without hypotension. By contrast, 10/12 fetuses in the 1:2.5-min group progressively developed severe metabolic acidaemia and hypotension, reaching 16.8±0.9mmHg after 71.2±6.7 UCOs. Deceleration area and capacity remained unchanged throughout the UCO series in the 1:5-min group, but progressively increased in the 1:2.5-min group. The severity of hypotension was closely correlated with both deceleration area (P<0.001, R2 =0.66, n=18) and capacity (P<0.001, R2 =0.67, n=18). Deceleration area and capacity predicted development of hypotension at a median of 103 and 123minutes before the final occlusion, respectively. Both deceleration area and capacity were strongly associated with developing fetal hypotension, supporting their potential to improve identification of fetuses at risk of hypotension leading to hypoxic-ischaemic injury during labour. Deceleration area and capacity of fetal heart rate identify developing hypotension during labour-like hypoxia.